RU2390099C2 - Controlled optical add/drop multiplexer - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention is a method for a controlled selective adding/dropping a channel in a fibre-optic communication system with wavelength-division multiplexing of 2^N channels whose optical frequencies can be adjusted, but the spectral interval Δv between neighbouring channels is contestant, through controlled optical add/drop multiplexers (70, 80, 90), which include multi-stage structures of differently connected optical filters ({75-i}, {85-i}, {95-i}), having devices for controlled adjustment of their transfer constants. The optical filters used are asymmetrical single-stage (20), two-stage (40) and/or multi-stage (60) Mach-Zehnder interferometers.

EFFECT: adding/dropping a desired channel from an optical signal by controlling spectral characteristics of filter stages of the multiplexer.

22 cl, 12 dwg, 1 tbl

Description

Technical field

The invention relates to fiber-optic communication systems (hereinafter BOSS) with spectral multiplexing of channels, in particular to methods for controlled input / output of channels, to controlled and reconfigurable optical channel input / output multiplexers (hereinafter t-OADM and ROADM, respectively), and can be used both in dense spectral multiplexing systems (hereinafter referred to as DWDM) and moderate spectral multiplexing systems (hereinafter referred to as CWDM).

State of the art

Currently, to increase the throughput of trunk, city and local fiber-optic communication systems, technologies of spectral channel multiplexing are widely used. There are dense spectral multiplexing - DWDM and moderate spectral multiplexing - CWDM. At the same time, DWDM technologies are used mainly in long trunk lines, and CWDM technologies are used in urban and local communication systems.

DWDM technologies are characterized by extremely high bandwidth, but are very expensive. The standard for the grid of wavelengths, introduced by the International Telecommunication Committee (hereinafter referred to as the ITU Standard), provides for the spectral interval between channels 200, 100, 50 or 25 GHz (the interval in wavelengths of 1.6, 0.8, 0.4 and 0.2 nm, respectively); systems with even higher (12.5 GHz) channel multiplexing are already in use.

Compared to DWDM technologies, the number of channels in CWDM systems that can be passed through a single fiber is much smaller, and the ITU recommended spectral spacing between channels is 20 nm. The CWDM technique is much easier to use and cheaper.

At VOCS nodal points, optical input / output multiplexers (hereinafter OADM) are usually used for channel input / output. They allow you to remove one or more channels from the line and simultaneously enter a signal at the same wavelengths with new information. This allows you to significantly increase the efficiency of communication systems.

OADM with fixed channel frequencies allow you to enter / output only a limited number of channels. The systematically increasing bandwidth requirements of communication systems and the use of new approaches require greater flexibility for such devices.

The use of dynamically reconfigurable or controlled optical input-output multiplexers (respectively ROADM or t-OADM) removes these restrictions, allowing you to enter / output the required channels at any time; In addition, t-OADM can also be used in spectral multiplexing systems where the channel wavelengths themselves can be tuned. Thus, ROADM and POADM provide the possibility of operational control of VOSS traffic, increasing even more the throughput of the communication system.

Well-known to specialists in the field of optical systems, the ROADM design is a device consisting of discrete components and including a demultiplexer, optical switches and a multiplexer. A pair of demultiplexer-multiplexer can represent multi-stage structures on interference filters, devices on diffraction gratings or in planar design on the so-called ordered bundles (AWG). The optical switches used to input, output, and transmit channels are typically electromechanical microswitches.

However, such a device is expensive, especially if the number of channels in the communication system is large. It is characterized by large insertion loss and degradation of the quality of the optical signal. In addition, optical switches are not resistant enough to environmental influences such as temperature, vibration, and other factors.

The main functional element of t-OADM is a tunable optical filter - a selective device in which the center frequency (wavelength) of the spectral band can be dynamically tuned. Many tunable optical filters are known, but most of them, due to various reasons, are poorly adapted for use in t-OADM.

For example, a tunable acousto-optic filter has a strong polarization dependence, which creates many practical problems. The Bragg filter is tuned mechanically or using temperature, so the tuning speed is relatively low, about a millisecond. A tunable filter based on Fabry-Perot interferometers is also not very acceptable, since if it is tuned in a wide range, its spectral band is not narrow enough, but if the spectral band is narrow, then it can only be tuned in a limited range.

A tunable optical filter based on an asymmetric Mach-Zehnder interferometer (hereinafter referred to as a single-stage MZI) is characterized by low insertion optical losses and low polarization dependence. Equipped with an electro-optical phase shift device, it can provide the fastest possible adjustment.

Specialists in the field of fiber-optic communication systems are aware that a multistage structure based on single-stage MZIs, having the number of stages 8 or 9, is characterized by high selectivity and is sufficient to cover the full spectral band used in spectral multiplexing systems. Therefore, such a tunable filter of all of the above is most suitable for use in t-OADM and ROADM.

A tunable optical input / output multiplexer (US 6,795,654 B2) is known having an input port, an output port and an output port and including devices providing input of a signal containing several channels, a multi-stage structure of optical filters connected to the input port, each of which passes odd ones or even channels and reflects even and odd channels, respectively, a device that provides transmission of reflected channels to the output port and the channel passed through all filters (output channel ) to the output port. Moreover, the optical filter in each stage contains a Mach-Zehnder fiber interferometer having a phase shift element and a mirror for reflecting channels that are not transmitted by the Mach-Zehnder interferometer. Devices that allow transmission of reflected channels to the output port and input of a new channel to be added through the input port, as a result of which the newly introduced channel is passed to the output port, may contain circulators.

Using such a tunable multiplexer, a known method for selectively inputting and outputting a given channel (US 6,795,654 B2) is carried out, which consists in selectively transmitting even or odd channels and reflecting the odd or even channels, respectively, and this operation is repeated as many times as necessary to reflect all the channels, in addition to the set, the output of the set channel to the output port, combining the reflected channels in the output port, entering an additional channel through the input port and combining it with the channel E directed to the output port.

A diagram of one of the options for such a multiplexer — device 10 — is shown in FIG. The multiplexer 10 has an input port 11, an output port 12, an output port 13, an input port 14, and includes three single-stage MZIs: 15-1, 15-2, and 15-3, formed using three pairs of fiber optic splitters {16-1, 16-2}, {16-3, 16-4} and {16-5, 16-6} and, as the interference arms connecting their optical fibers {17-1, 17-2}, {17-3, 17 -4} and {17-5, 17-6}. The difference in the lengths of the shoulders in the three interferometers successively doubles in passing to the next interferometer.

Each of the three indicated single-stage MZIs 15-1, 15-2 and 15-3 selectively transmits odd or even channels and, using fiber-optic reflectors 15-1-1, 15-2-1 and 15-3-1, reflects and sends back even or odd channels respectively. Two circulators are used: circulator 18-1, connected to input 11 and output 12 ports, for inputting channels into the device and transmitting mirrored channels to output port 12, and circulator 18-2 for transmitting selected channels to output port 13 and input new channels through port 14 instead of the displayed channels.

The three-stage structure provides the output of one channel when 8 channels are input and the input of a new channel instead of the output. The controlled elements of the phase shift 15-1-2, 15-2-2 and 15-3-2, installed in one of the arms of each of the three interferometers 15-1, 15-2 and 15-3, respectively, are used for controlled tuning of the spectral characteristics these single-stage MZIs 15-1,15-2 and 15-3 and, thus, for input / output of any of the 8 channels.

According to the patent (US 6795654 B2), in other proposed variants, it is proposed that single-stage MZIs be performed using “discrete” elements: beam splitters, prism mirrors, polarizers, or advanced Layot filters. As an alternative to mirrors 15-1-1, 15-2-1 and 15-3-1 and circulators 18-1 and 18-2, you can also use an additional structure of optical filters on single-stage MZIs to pass channels to output port 12.

The known device discussed above allows you to enter and output any channel from eight channels on which the optical network operates. However, the known device has significant disadvantages.

Specialists in the field of optical communication systems are aware that the structure described above containing a large number of optical elements - single-stage MZIs in fiber or discrete versions, reflectors and circulators - is very cumbersome and cannot be reliable and stable in real conditions, since single-stage MZIs are very sensitive to environmental conditions, to temperature, vibration and other influences. Therefore, to implement devices for this purpose, a different approach is needed - an approach using integrated optical technologies.

It is also known that the spectral characteristics of single-stage MZIs do not have an ideal shape — nonplanar peaks and slowly falling edges of the spectral bands, which, when used in spectral densification systems with a high channel density, can cause channel overlap and poor channel isolation. In addition, single-stage MZIs introduce significant dispersion into the channels, which, at a high transmission rate, can lead to an increase in the pulse duration and thereby to a decrease in the throughput of the optical communication system.

It is known that two-stage asymmetric MZIs or multi-stage asymmetric MZIs (hereinafter referred to as two-stage and multi-stage MZIs) have significantly better spectral characteristics and lower dispersion, but these devices are not reversible and therefore cannot be used in the input / output multiplexer 10 described above.

To enable integrated-optical execution of a controlled optical input-output multiplexer, the number of optical elements used should be reduced and circulators and reflectors should be excluded, since they are incompatible with integrated-optical technology. Reducing the number of optical elements used is also advisable from the point of view of reducing the cost of the device.

Thus, the creation of a method of controlled input / output and a controlled optical input / output multiplexer, which is simpler in design and meets the existing requirements for channel isolation and introduced dispersion and is suitable for integrated optical performance, is an urgent problem. At the same time, it is desirable that the device has additional functionality, is as dynamic and flexible as possible, that is, it ensures the best balance between technical characteristics and cost in various applications.

Disclosure of invention

When creating the invention, the task was to create a method and device for input / output of the desired channel from the optical signal by selecting the channels of the optical signal by controlling the spectral characteristics of the filter stages of the multiplexer with the subsequent output of the desired channel, passing unwanted channels, inputting a new signal.

The problem was solved by the development according to the invention of a method of controlled, selective input / output of a channel in a fiber-optic communication system with spectral multiplexing of 2 ^N channels, the optical frequencies of which can be tuned, but the spectral interval Δν between adjacent channels is constant, in which:

(a) a multichannel optical signal is supplied from the optical network to an N-stage structure, in which each stage contains an optical filter having one input or two inputs and two outputs, configured to control the transmission coefficients and characterized in the nth stage, at n = 1, 2, ..., N, with a frequency interval Δν _n = 2 ^n-1 Δν between adjacent extrema in the dependences of the transmission coefficients on the frequency, and the optical filter in each stage, except the first, one input and one of the outputs is connected, respectively with alone of the outputs and one input of optical filter of the previous stage, with one optical filter of the first stage is input an input port of N-stage structure, and one of the outputs of optical filter of the last stage is an output port in N-stage structure;

(b) selecting a channel to be input / output;

(c) adjust the optical filter of each stage so that the transmission coefficient of the optical filter from input to output used in the optical filter connections described in a) has a maximum value at the frequency of the selected channel;

(d) pass a multi-channel optical signal through an N-stage structure and get the selected channel at the output of the last-stage optical filter, which is the output port in the N-stage structure;

(e) enter a new channel at the optical frequency of the output channel, combine the new channel and all channels except the output, and return the combined channels to the optical network.

Moreover, according to the invention, it is advisable that when using optical filters having two inputs, a new channel is introduced through the input port of an N-stage structure connected to the input of the last-stage optical filter not used in the optical filter connections described in a), of the channel and all channels except the withdrawn one, was carried out by connecting the output of the optical filter of each stage, except for the first one, which is not used in the connections of the optical filters described in a), with the optical input of the filter of the previous stage, not used in the optical filter connections described in a), and the combined channels were returned to the optical network through the output of the optical filter of the first stage, not used in the filter connections described in a).

In addition, according to the invention, it is advisable that when using optical filters having one input, the input of a new channel is carried out through one of the inputs of the optical adder having N + 1 inputs and one output, the combination of the new channel and all channels except the output is carried out by connecting the output of the optical filter of each stage, not used in the connections of the filters described in a), with one of the inputs of the specified adder, while through the output of the adder the combined channels were returned to the optical network.

The problem was also solved by the development of a controlled optical input / output multiplexer for a fiber-optic communication system with spectral multiplexing of 2 ^N channels, the optical frequencies of which can be tuned, but the spectral interval Δν between adjacent channels is constant, according to the invention, having one input port, one output port, one output port, one input and including port:

- N-step structure containing one optical filter in each stage, made with the possibility of controlled tuning of transmission coefficients, characterized in the n-th stage, with n = 1, 2, ..., N, the frequency interval Δν _n = 2 ^n-1 Δν between neighboring extrema in the dependences of transmission coefficients on frequency and having two inputs and two outputs;

- a controller for controlling the adjustment of transmission coefficients of these optical filters.

Moreover, according to the invention, it is advisable that the input / output multiplexer in the specified N-stage structure:

- the optical filter of each stage, except for the first, by one of the inputs and one of the outputs was connected respectively to one of the outputs and one of the inputs of the optical filter of the previous stage;

- the optical filter of the first stage by another input was connected to the input port;

- the optical filter of the first stage with the other one output was connected to the output port;

- the optical filter of the last stage with another output was connected to the output port;

- the optical filter of the last stage with another input was connected to the input port.

Moreover, according to the invention, it is advisable that in the input / output multiplexer, the optical filters of the steps of the N-step structure are single-stage and / or two-stage asymmetric Mach-Zehnder interferometers.

The problem was also solved by the development of a controlled optical input / output multiplexer for a fiber-optic communication system with spectral multiplexing of 2 ^N channels, the optical frequencies of which can be tuned, but the spectral interval Δν between adjacent channels is constant, according to the invention, having one input port, one output port, one output port, one input and including port:

- N-step structure containing one optical filter in each stage, made with the possibility of controlled tuning of transmission coefficients, characterized in the n-th stage, with n-1, 2, ..., N, the frequency interval Δν _n = 2 ^n-1 Δν between adjacent extrema in the dependences of the transmission coefficients on the frequency and having one input and two outputs;

- an optical adder having N + 1 inputs and one output connected to the output port;

- a controller for controlling the adjustment of transmission coefficients of these optical filters.

Moreover, according to the invention, it is advisable that in the input / output multiplexer in the specified N-step structure:

- the optical filter of each stage, except for the last stage, was connected by one of the outputs to the input of the optical filter of the next stage, and by the other output connected to one of the inputs of the optical adder;

- the optical filter of the first stage is connected to the input port by its input;

- the optical filter of the last stage with one output connected to another input of the optical adder, and the other output connected to the output port;

- the optical adder is connected to the input port by another input.

Moreover, according to the invention, it is advisable that the optical filters of the N-step structure are multistage asymmetric Mach-Zehnder interferometers.

The problem was also solved by the development of a controlled optical input / output multiplexer for a fiber-optic communication system with spectral multiplexing of 2 ^N channels, the optical frequencies of which can be tuned, but the spectral interval Δν between adjacent channels is constant, according to the invention, having one input port, one output port, one output port, one input and including port:

- interconnected first and second multi-stage structures containing in each of their stages one optical filter configured to manage their transmission coefficients in a controlled manner, while the first structure has N ₁ steps, the second structure has N ₂ steps and N ₁ + N ₂ = N;

- an optical adder having N ₁ + 1 inputs and one output;

- a controller for controlling the adjustment of the spectral characteristics of the optical filters of the first and second multistage structures.

Moreover, according to the invention, it is advisable that in the input / output multiplexer:

- the optical filter in the first multi-stage structure had one input and two outputs and was characterized in the n _1-st stage with n ₁ = 1, 2, ..., N ₁ frequency interval Δν _n1 = 2 ^n1-1 Δν between adjacent extrema in the dependences of the transmission coefficients on frequency;

- the optical filter in the second multi-stage structure had two inputs and two outputs and was characterized in the n _2nd stage with n ₂ = 1, 2, ..., N _{2 in the} frequency interval Δν _n2 = 2 ^{n2 + N1-1} Δν between adjacent extrema in the dependencies transmission coefficients from frequency.

Moreover, according to the invention, it is advisable that in the input / output multiplexer:

- in the first multi-stage structure, the optical filter of each stage, except for the last, was connected by one output to the input of the optical filter of the next stage, and the other output was connected to one of the inputs of the optical adder;

- in the first multi-stage structure, the optical filter of the last stage with one output was connected to one of the inputs of the optical adder, and the other output was connected to one of the inputs of the optical filter of the first stage of the second multi-stage structure;

- in the second multi-stage structure, the optical filter of each stage, except for the first, was connected to one of the outputs and one of the inputs of the previous stage optical filter by one of the inputs and one of the outputs;

- in the second multi-stage structure, the optical filter of the first stage of the structure with a different output was connected to another input of the optical adder;

- in the first multi-stage structure, the optical filter of the first stage by another input was connected to the input port;

- in the second multi-stage structure, the optical filter of the last stage with one of the outputs was connected to the output port;

- in the second multi-stage structure, the optical filter of the last stage with another input was connected to the input port;

- the optical adder output was connected to the output port.

Moreover, according to the invention, it is advisable that in the input / output multiplexer the optical filters of the first multi-stage structure are multistage asymmetric Mach-Zehnder interferometers, and the optical filters of the second multi-stage structure are single-stage and / or two-stage asymmetric Mach-Zehnder interferometers.

Moreover, according to the invention, it is advisable that the optical filters contain electro-optical or thermo-optical phase shift devices to control the adjustment of transmission coefficients.

Moreover, according to the invention, it is advisable that the input / output multiplexers were made by integrated-optical technology on a single chip.

In addition, according to the invention, it is advisable that the input port, output port, output port and input port in the input / output multiplexers are made using optical fibers.

Thus, the problem of creating a controlled optical input-output multiplexer (t-OADM) discussed above is solved by the present invention, which uses a multi-stage structure of optical filters. As optical filters, single-stage, two-stage, and multi-stage MZIs containing phase shift devices and having one or two input ports and at least two output ports can be used.

In the method of controlled selective input / output of one channel from a multi-channel optical signal according to the present invention and in all versions of the controlled optical input / output multiplexer according to the present invention, the optical filter of each stage, except for the first stage filter, is connected to one of the inputs and one of the outputs with one from the outputs and one of the outputs of the previous stage optical filter.

When a multi-channel optical signal is transmitted through the entire multi-stage structure, each filter divides the channels into two groups: one containing odd ones; the other is even channels, while one of the groups contains a channel to be input / output. The spectral characteristics of optical filters are adjusted in such a way that the selected channel is always in the group sent to the next stage; as a result, only one channel comes to the output of the last stage filter - a selectable input / output channel. All other channels, together with the newly introduced channel, are combined and routed to the output port.

In one embodiment of the t-OADM according to the present invention, in which optical filters having two inputs and two outputs can be used, combining a new channel and all channels except the output one is carried out by connecting another output of the optical filter of each stage except the first stage, with another, previously not used input of the optical filter of the previous stage, and the return of the combined channels to the optical network is carried out through the previously unused other output of the optical filter of the first stage.

In another embodiment of the t-OADM according to the present invention, which uses optical filters having one input and two outputs, the input channel and the transmitted channels are combined using an optical adder, the inputs of which are connected to the second outputs of all filters, as well as to the input port.

In the third embodiment of the controlled optical input / output multiplexer according to the invention, optical filters having one input and two outputs and optical filters having two inputs and two outputs can be used together, and the multiplexer is made of two multi-stage structures, one of which corresponds to the first option t-OADM, and the second - the second option t-OADM. The combination of the skipped channels in each of the two structures is carried out similarly to the combination used in the first two versions of the device, and the introduction of a new channel - as in the first embodiment.

Moreover, according to the invention, single-stage and / or two-stage asymmetric Mach-Zehnder interferometers are used as optical filters having two inputs and two outputs, multi-stage asymmetric Mach-Zehnder interferometers are used as optical filters having one input and two outputs, and for To control the adjustment of transmission coefficients, optical filters contain electro-optical or thermo-optical phase shift devices.

In addition, it is essential that, according to the invention, the proposed multiplexers are made by integrated-optical technology on a single chip.

A brief description of the drawings.

The invention is further explained by the description of examples of the method of controlled selective channel I / O in a fiber-optic communication system with spectral multiplexing of 2 ^N channels, the optical frequencies of which can be tuned, but the spectral interval Δν between adjacent channels is constant according to the invention, using controlled optical I / O multiplexers according to the invention, and the accompanying drawings, which show:

Figure 1 is a diagram of a known controlled optical input / output multiplexer;

Figure 2a is a diagram of a known single-stage Mach-Zehnder interferometer;

Fig.2b - conditional image of a single-stage MZI shown in Fig.2A;

Figure 3 - dependence of the transmission coefficients on the optical frequency for a single-stage MZI shown in Fig.2A;

Figa is a diagram of a well-known two-stage MZI;

Fig.4b is a conditional image of a two-stage MZI shown in Fig.4a;

Figure 5 - dependence of the transmission coefficients on the optical frequency for the two-stage MZI shown in Figa;

Figa is a diagram of a well-known multi-stage filter, including three two-stage MZI;

Fig.6b is a conditional image of a multistage filter shown in Fig.6A;

7 is a diagram of a controlled optical input / output multiplexer according to the invention, containing single-stage MZIs, with illustration of operation when an optical signal containing 8 CWDM channels is applied to the input port;

Fig. 8 is a diagram of a controllable input / output multiplexer according to the invention containing multi-stage MZIs, with illustration of operation when an optical signal containing 64 DWDM channels is supplied to the input port;

Fig.9 is a diagram of a controlled input / output multiplexer according to the invention, containing single-stage, two-stage and multi-stage MZIs, with an illustration of the operation when an optical signal containing 64 DWDM channels is input.

Best Mode for Carrying Out the Invention

According to the invention, the main element of a controlled input / output multiplexer is the well-known asymmetric Mach-Zehnder interferometer or, as they have agreed to call it, a single-stage MZI (M. Born, E. Wolf. "The Optic Base", Pergamon Press, Oxford) , Fifth Oxford, Fifth Edition, 1975, pp. 312-316; M. Born and E. Wolf. Fundamentals of Optics. Per. Edited by G.P. Motulevich. M., Nauka, 1970, pp. 342-346) .

The single-stage MZI is an interferometer with two single-mode arms and a pair of splitters at both ends. The term "asymmetric" means that the lengths of the shoulders of the IMC are obviously unequal. Differences in the length, temperature, or other parameters of the arms of the interferometer cause a phase shift for the waves propagating along the arms, which manifests itself upon interference of the output waves.

Embodiments of a single-stage MZI using fiber-optic splitters, beam splitters, prism mirrors, polarizers, and other elements are considered above when describing the well-known. managed optical input / output multiplexer (US 6,795,654 B2).

On figa shows a schematic representation of a waveguide version of a single-stage MZI 20, its conditional image for the purposes of describing the present invention is shown in figa. The device 20 is placed on one substrate 21, where a single-stage MZI 22 is formed by splitters 23 and 24 and two arms 22-1 and 22-2 formed by waveguides of unequal length 1 ₁ and 1 _2, respectively. The coupling coefficients k ₁ and k ₂ , respectively, of the splitters 23 and 24, are equal and divide the optical power in a ratio of 50/50. The one-stage MZI 22 has conclusions on the one hand, a and b, and conclusions on the other hand, c and d.

In this case, a single-stage MZI 22 contains a phase shift device 25 in the arm 22-2, which introduces an additional phase shift φ into the phase of the traveling wave and is a controllable element used to adjust the spectral characteristics of the MZI.

The magnitude of the phase shift φ is controlled by the thermo-optical or electro-optical effect by changing the magnitude of the electric current or voltage. Accordingly, the phase shift device 25 can be manufactured using a thermo-optical material, such as silicone, or an electro-optical material, such as lithium niobate (LiNbO3) or gallium arsenide. Such phase shift devices are known in the spectral densification technique as a tool for tuning the spectral characteristics of optical filters based on the IMC, and are also used in other devices - modulators and switches.

When radiation of unit power is input through the first input a, the light intensity at the two outputs c and d can be expressed using the transmission coefficients K _ac (ν, φ) and K _ad (ν, φ):

where D = 2πnΔLν / c is the phase delay due to different optical lengths of the shoulders 22-1 and 22-2; ΔL = 1 ₁ -1 ₂ ; n is the refractive index of the material; ν is the optical frequency and c is the speed of light in the void.

When excited through the second input b, the light intensity at the same outputs c and d can be represented using the transmission coefficients K _bc (ν, φ) and K _bd (ν, φ):

The transmission coefficients (1) ÷ (4) considered on a frequency range ν (or wavelengths λ) become the spectral characteristics of a single-stage MZI. As can be seen, the indicated spectral characteristics (1) ÷ (4) are periodic functions of the light frequency ν and wavelength λ and the difference of the arm lengths ΔL, refractive index n, and phase shift φ.

The following properties are essential for the performance of a single-stage MZI:

- the distances between adjacent extrema Δν and Δλ in the spectral characteristics (1) ÷ (4) in units of optical frequency and in units of wavelengths are respectively equal to:

- transmission coefficients (1) ÷ (4), corresponding to the transition of optical radiation from one of the inputs, a or b, to the first c and second d outputs, differ in phase by π;

- transmission coefficients when changing two indices do not change, that is

K _ad (ν, φ) = K _bc (ν, φ) and K _ac (ν, φ) = K _bd (ν, φ);

- changing the magnitude of the phase shift φ, you can change the spectral characteristics (1) ÷ (4), shifting them along the axis of frequencies (or wavelengths); this leads, in particular, when changing the phase shift by δφ = ± π, to the inversion of the signals at the outputs;

- transmission coefficients do not change when the direction of signal transmission changes, that is, a single-stage MZI is a reversible device.

In turn, from these properties it follows that when a single-stage MZI receives an optical signal containing several channels whose frequencies (or wavelengths) coincide with the position of the extrema in the dependences of the transmission coefficients on the frequency (or wavelength), the signals are divided into two groups that are output to different outputs. One group contains odd channels, the other group contains even channels, and in both groups the spectral interval between channels becomes twice as large as at the input of a single-stage MZI. When the same optical signal arrives at another input, the even and odd channels at the outputs change places.

Since a single-stage MZI is a reversible device, then in another situation, when odd channels are fed to one input and even channels are fed to the other input, then both groups of channels are combined into one optical stream with a denser channel arrangement.

Devices that perform the function of dividing channels into odd and even channels and the inverse function of combining odd and even channels into one stream are called interleaves in foreign literature; in the domestic literature there is no term for devices of a similar purpose, in the present text they are called optical filters.

The distance between adjacent extrema Δν (or Δλ) in the spectral characteristics for a real single-stage MZI should be formed at the stage of its manufacture by selecting the corresponding difference in arm lengths ΔL and refractive index n. The controlled restructuring of the position of the extreme values of the transmission coefficients relative to the given frequencies {ν _i } (or wavelengths {λ _i }) should be carried out by appropriate adjustment of the phase shift φ when using a single-stage MZI as an optical filter as part of any particular device.

Figure 3 shows the transmission coefficients K _ac (ν, φ) and K _ad (ν, φ) for a single-stage MZI as a function of the optical frequency, which for the corresponding values of the phase delay D and phase shift φ has a distance between adjacent extrema of 50 GHz and can thus be used to separate even and odd channels with an interval between adjacent frequency channels of 50 GHz. Solid lines show the spectral dependence of the transfer coefficient K _ac (ν, φ), according to which one group of channels - odd channels - is output with, dashed lines show the spectral dependence of the transfer coefficient K _ad (ν, φ), which is responsible for outputting another groups of channels - even channels - to the output d.

As can be seen in FIG. 3, the disadvantage of this optical filter is non-planar peaks and slowly falling edges of the spectral bands, which, with a small spectral interval between the channels, can cause crosstalk between adjacent channels. Another known disadvantage is that with a large difference in shoulder lengths ΔL, the introduced dispersion can be very large. These disadvantages limit the possibility of using single-stage MZIs in devices used in communication systems with spectral channel multiplexing.

A significant improvement in the spectral characteristics of the optical filter for devices and spectral densification systems is provided, as is known (US 6,782,158 V), with two-stage MZIs, which can be performed using fiber optic splitters, beam splitters, prism mirrors, polarizers, etc., as well as in the integrated optical form and contain at the same time phase shift devices.

On figa shows a schematic representation of the waveguide version of the two-stage MZI 40, its conditional image is shown in Fig.4b. The device 40 uses three splitters 41, 42 and 43 with coupling coefficients k ₁ , k ₂ and k _3, respectively. The device 40 is placed on a single substrate 46.

The first single-stage MZI 44 is formed by two splitters 41 and 42 and two waveguides 44-1 and 44-2 of unequal length 1 _44-1 and 1 _44-2, respectively. The second single-stage MZI 45 is formed by two splitters 42 and 43 and two waveguides 45-1 and 45-2 of unequal length 1 _45-1 and 1 _45-2, respectively. Phase delays D ₁ = 2πn (1 _44-1 -1 _44-2) / λ and D ₂ = 2πn (1 _45-1 -1 _45-2) / λ are related by: D ₂ = 2 · D _1.

MZI 44 and 45 use phase shift devices 47 and 48; the phase shifts introduced by them are denoted by φ and ϕ, respectively. The two-stage MZI has conclusions on the one hand, a and b, and conclusions on the other, e and f.

The spectral characteristics of the two-stage MZI 40 are not difficult to obtain analytically. For the three splitters 41-1, 41-2 and 41-3, one should introduce matrices T (k _i ) for (i = 1, 2, 3), which connect the light amplitudes at the input and output with the parameters of the splitters:

and for two single-stage MZIs 43 and 44 - matrices T (D ₁ ) and T (D ₂ ):

Then the transmission matrix M (ν, φ, ϕ) of the two-stage MZI is determined by the product of five matrices:

Since the transmission coefficients of the two-stage MZI associate the optical intensities at the output with the optical intensity at the input, expressions of the type should be used to determine them:

From the expressions (6) ÷ (9) all the basic properties can be obtained

two-stage MZI. It is easy to verify that the two-stage MZI, when radiation is input through the inputs a and b, remains a device that performs the function of separating and combining the odd and even channels. So, when applying an optical signal to the input a of a two-stage MZI, the channels will be divided into two groups containing one group — odd channels, and the other group — even channels. We note an important property that is preserved in two-stage MZIs: when the same optical signal is applied to another input, the input in Fig. 4a, the groups with odd and even channels change places at the outputs e and f.

The distances between adjacent extrema Δν and Δλ in the spectral characteristics are also determined by expressions (5), where ΔL is the difference in the length of the shoulders in the first cascade of the two-stage MZI 40, i.e. ΔL = 1 _44-1 -1 _44-2 . The possibility remains of a controlled shift of spectral characteristics, now with the help of two phase shifts φ and ϕ. In order to shift the spectral characteristics K _ac (ν, φ, ϕ) and K _af (ν, φ, ϕ) along the frequency axis by δν, it is necessary to change the phases φ and ϕ using the appropriate phase shift devices:

You can also verify with the help of expressions (6) ÷ (9) that when a signal is input through outputs e and f, the possibility of dividing into odd and even channels and, accordingly, combining odd and even channels is lost. This is a consequence of the fact that matrices (6) and (7) are non-commutative. Thus, two-stage MZIs are not reversible devices - two ports a and b on the one hand can be used only as input, and the other two ports e and f on the opposite side can only be used as output, and therefore two-stage MZIs, as noted above, are not can be used in the known controlled optical input-output multiplexer shown in Fig.1.

5. the transmission coefficients K _ae (ν, φ, ϕ) and K _af (ν, φ, ϕ) are presented as functions of the optical frequency for a two-stage MZI calculated using expressions (6) ÷ (9). This two-stage MZI with coupling coefficients k ₁ = 0.7854, k ₂ = 2.0944, k ₃ = 0.3218, the corresponding phase delays D ₁ and D ₂ and the phases φ and ϕ can be used as a 50 GHz optical filter to separate even and odd channels with an interval between 50 GHz channels adjacent in frequency. The solid lines show the spectral dependence of the transfer coefficient K _ac (ν, φ, ϕ), according to which, when entering through the first input a, one group of channels (odd channels) is output to the first output e, the dashed lines show the spectral dependence of the transfer coefficient K _af ( ν, φ, ϕ), which is responsible for outputting another group of channels (even channels) to the second output f.

As you can see, the two-stage MZI has a much better spectral shape — close to a rectangular one, with a flat top and a steep decline along the edges of the spectral bands. Therefore, a two-stage MZI used as an optical filter provides better crosstalk suppression and high channel isolation. Nevertheless, the dispersion introduced by the two-stage MZI remains large, which limits its use as an optical filter in communication systems with a high data transfer rate.

It is known that the situation can be changed for the better when using filters obtained as a result of cascading two-stage MZIs. In one embodiment of such devices, two-stage MZIs can be used that have identical transmittance but opposite dispersion sign, the so-called complementary two-stage MZIs. Complementarity is ensured by a certain ratio of coupling coefficients k ₁ , k ₂ and k ₃ in the IMC included in their composition (US 6782158 B2).

On figa shows one of the variants of the multi-stage MZI 60, which can be used for separation into odd and even channels; conditional image of a multi-stage MZI (MZI-3) is shown in Fig.6b. The device 60 in planar design is placed on one substrate (chip) 61, has an input port g, a first output port p and a second output port k and includes three two-stage MZIs having a first input a, second input b, first output e and second output f In this case, in the first cascade, two-stage MZI 62 of type I are used, and in the second cascade, two two-stage MZIs 63 and 64 are used, both types I ', that is, with opposite signs of dispersion.

When a signal is input through input port g, the two-stage MZI 62, as usual, divides the channels into two groups: in one group, the odd channels, and in the other even channels; in the second stage, the MZI 63 passes the odd channels to its first output e and then to the external first output port p, and the MZI 64 passes the even channels to its output f and further to the external second output port k. Since the variances of the two-stage MZI 62 and the two-stage MZI 63 and 64 have opposite signs, the dispersion of the multi-stage MZI 60 is compensated — zero or almost zero.

Unfortunately, the disadvantage of multi-stage MZIs is that when an optical signal is input through the second input b of the two-stage MZI, the 62 groups containing odd and even channels do not just change places at the outputs of the two-stage MZIs 63 and 64, but are output to other outputs than the previous ones optical signal input through input a (to outputs f and e of two-stage MZIs 63 and 64, respectively). This disadvantage does not allow the use of multi-stage MZIs in the first embodiment of the controlled optical input / output multiplexer according to the present invention considered below.

The first embodiment of the controlled optical input / output multiplexer according to the present invention is intended for spectral multiplexing systems with a sufficiently wide spectral interval between adjacent channels, for example, for a CWDM system. The circuit of the multiplexer 70 in this embodiment is shown in Fig.7.

The multiplexer has one input port 71, one output port 72, one output port 73, one input port 74 and includes three optical filters 75-1, 75-2 and 75-3, forming a multi-stage structure. The entire device in planar form is made on one silicon substrate 76. Four ports 71 ÷ 74 are made in the form of optical fibers. Filters of all three stages are interconnected and with waveguides-outputs of waveguides 77 formed on a silicon substrate.

Dynamic control of the multiplexer is carried out by adjusting the spectral characteristics of three filters 75-1, 75-2 and 75-3 when applying phase shift devices contained in all three filters, the corresponding voltages. Management is performed using the controller 78, which is connected to the optical filters with an electric bus 79.

As optical filters, single-stage MZIs according to Fig. 2a or two-stage MZIs according to Fig. 4a can be used. The filters are connected in such a way that each filter, except for the first filter 75-1, is connected to one of the outputs and one of the inputs of the previous filter by one of the inputs and one of the outputs, while the first filter 75-1 is connected to the input port by the other input 71 and another output with output port 72, and the last filter 75-3 is connected by another input to input port 74 and another output to output port 73.

Note that the connections of the optical filters in the device 70 are not the only ones possible, and another embodiment of the connection of the optical filters is discussed below. The advantage of this connection is that in the planar design of the device 70, the waveguides 77 do not intersect with each other.

Consider the case when an 8-channel optical signal with a frequency interval between channels Δν = 2400 GHz (average interval between channels Δλ≈20 nm) is fed to the input of multiplexer 70. Since in this example the spectral interval between the channels is large, single-stage MZIs are used as optical filters.

In order to ensure a given interval between channels Δν = 2400 GHz, for three single-stage MZIs, the distances between adjacent extremes in the spectral characteristics (transmittance) are set in such a way that when moving to the next single-stage MZI, the MZI doubles: Δν _75-1 = 2400 GHz, Δν _75-2 = 4800 GHz and Δν _75-3 = 9600 GHz.

Accordingly, according to expression (5), the differences in the lengths of the shoulders in single-stage MZIs are: ΔL _75-1 = 41.6 μm, ΔL _75-2 = 20.8 μm, and ΔL _75-3 = 10.4 μm (it is assumed that n = 1 ,5). The central wavelengths of 8 channels for a given spectral interval between channels Δν can be located as follows: λ ₁ = 1608.5 nm, λ ₂ = 1588.3 nm, λ ₃ = 1568.4 nm, λ ₄ = 1549.0 nm, λ ₅ = 1530.0 nm, λ ₆ = 1511.5 nm, λ ₇ = 1493.5 nm and λ ₈ = 1475.8 nm.

Suppose that for some fixed values of the phases φ * _75-1 , φ * _75-2 and φ * _75-3 , which we denote as {φ * _n }, for one of the waves, for example, for wave ν ₃ , the transmission conditions from the input port 71 to the output port 73. Obviously, these conditions consist in the coincidence of the maximum values of the following transmission coefficients of the three filters at a wavelength of λ ₃ :

In order to better imagine the operation of the device in question, it is necessary to describe in more detail the spectral characteristics of the three optical filters 75-1, 75-2 and 75-3.

With the established distances between adjacent extrema ΔF _75-1 , ΔF _75-2 and ΔF _75-3 and conditions (11), the transmission coefficient K ^75-1 _ad (ν, φ * ₁ ) for the optical filter 75-1 has maximum values for odd waves ν ₁ , ν ₃ , ν ₅ and ν ₇ and minimal for even waves ν ₂ , ν ₄ , ν ₆ and ν ₈ , the transmission coefficient K ^75-2 _ad (ν, φ * ₂ ) for the optical filter 75-2 has the maximum values for waves ν ₃ and ν ₇ and the minimum values for waves ν ₁ and ν ₅ , the transmission coefficient K ^75-3 _ad (ν, φ * ₃ ) for the optical filter 75-3 has a maximum value for wave ν ₃ and a minimum value for wave ν ₇ . One should also bear in mind the invariance of the transmission coefficients of single-stage MZIs when rearranging the subscripts.

So, a multiplexed signal, including 8 spectral channels, comes from VOSS to the input port 71. The optical filter 75-1 in accordance with its transmission coefficient K ^75-1 _ac (ν, φ * ₁ ) directs the waves ν ₁ , ν ₃ , ν ₅ and ν ₇ to the optical filter 75-2, and the waves ν ₂ , ν ₄ , ν ₆ and ν ₈ pass to the output port 72. The optical filter 75-2 in accordance with the transmission coefficient K ^75-2 _ad (ν, φ * 2) directs waves v ₃ and v ₇ to the optical filter 75-3, and waves ν ₁ and ν ₅ - back to the optical filter 75-1, which now pass it at K ^75-1 _bc (ν ₁ φ * 1) = K ^75-2 bc (ν _5, φ * 1) = 1 and are in O bottom port 72. Optical filter 75-3 directs wave ν ₃ in accordance with the transmission factor K ^75-3 _ad (ν _3, φ * ₃₎ to the output port 73, and a wave ν ₇ at K ^75-3 _ac (ν ₇ φ * ₃ ) = 1 first returns to the optical filter 75-2, and then this wave v ₇ at K ^75-2 _bc (ν ₇ , φ * ₂ ) = 1 passes to the optical filter 75-1, with which it K ^75-1 _bc (ν ₇ , φ * ₁ ) = 1 is in the output port 72.

It is easy to trace the trajectory of the wave ν '(with ν' = ν ₃ ) introduced through the input port 74. For this wave, when passing through three optical filters 75-1, 75-2, and 75-3 in series to the output port 72, the values of the corresponding transmission coefficients are all equal to unity: K ^75-3 _bc (ν ', φ * ₃ ) = K ^75-2 _bc (ν', φ * ₂ ) = K ^75-1 _bc (ν ', φ * ₁ ) = 1, and therefore, the wave ν 'passes into the output port 72.

Thus, the connection of the second output of the optical filters 75-2 and 75-3 with one of the inputs of the previous filter allows you to organize the newly introduced channel ν ₃ and channels that do not contain the selected channel ν ', and direct them in the opposite direction to the first optical filter 75 -1, from where they return to VOSS.

Let us now consider the operation of the device 70 in dynamics, when any selected channel may be subject to input / output. For this, the values of {φ _n } phase shifts for the three optical filters should be appropriately changed using expression (10). For example, to switch to the input / output mode of a neighboring wave ν ₄ , it is necessary to change the phase shifts as follows: δφ _75-1 = π, δφ _75-2 = π / 2 and δφ _75-3 = π / 4.

Table 1 shows the changes in the phase shifts {δφ _n } that must be made for the input / output of any of the 8 channels.

Table 1 Frequency of input / output channels and corresponding changes in phase shifts {δφ _n } Channel number I / O Channel Frequency Changes in phase shifts {δφ _n } δφ _75-1 δφ _75-2 δφ _75-3 one ν ₁ 0 -π

2 ν ₂ -π -½π -¼π 3 ν ₃ 0 0 0 four ν ₄ π ½π ¼π 5 ν ₅ 0 π ½π 6 ν ₆ π 1½π ¾π 7 ν ₇ 0 0 π 8 ν ₈ π ½π 1¼π

Note that in Table 1, the changes in phase shifts {δφ _n } can be replaced by equivalent {δφ ' _n } such that δφ' _n = δφ _n ± 2πn, where n = 1, 2, ....

A second embodiment of the controlled optical I / O multiplexer according to the present invention is for DWDM systems. The multiplexer 80 according to this embodiment is shown in FIG. 8. We assume that the input signal contains 64 channels, the channel frequencies correspond to the ITU standard and have a spectral interval between channels Δv = 50 GHz.

The multiplexer has one input port 81, one output port 82, one output port 83, one input port 84 and includes six optical filters 85-1, 85-2, 85-3, 85-4, 85-5, 85-6, also forming a multi-stage structure. The multiplexer further comprises an optical adder 86 having seven inputs and one output. All six filters and the adder are integrated on a single substrate 87. Four ports 81, 82, 83 and 84 are made in the form of optical fibers. Connections of filters with optical fibers, as well as all other connections are made by waveguides 88.

Dynamic control of the multiplexer is carried out by tuning the spectral characteristics of six filters 85-1 ÷ 85-6 when applying to the phase shift device all six filters of the corresponding voltages. Management is carried out using the controller 89, which is connected to the optical filters with an electric bus 89-1.

Since the spectral channels are located much closer to each other in the input signal, this requires the use of elements with higher characteristics, namely with better channel isolation, as well as to use the multiplexer at high transmission speeds with low dispersion. It should be noted that crosstalk in adjacent channels, as well as the introduced dispersion, occur primarily in the filters of the first stages, where the spectral intervals between the channels at the input are small but very large differences in the arm lengths in the MZI and, accordingly, a large introduced dispersion. In subsequent stages, the intervals between the channels become larger, and the introduced dispersion is smaller, respectively, the requirements for optical filters in these stages can be reduced.

Therefore, in the considered second embodiment of the controlled optical input / output multiplexer according to the invention, the first three stages use multi-stage MZIs shown in Fig. 6a, and in the subsequent stages use the two-stage MZIs shown in Fig. 4a. Obviously, in this embodiment, the multiplexer 80 is simpler and cheaper to manufacture than if it were made only on multi-stage MZIs.

The optical filters are connected in series with each other so that the first output of one filter is connected to the input of the other, the second output of each filter is connected to one of the inputs of the optical adder, the input of the first filter 85-1 is connected to the input port 81, the output of the last filter 85-6 connected to the output port 83, and the optical adder 86 with one input connected to the input port 84, and the output to the output port 82.

The distance between adjacent extrema in the spectral characteristics of six optical filters is also established in such a way that when moving to the next optical filter, it doubles: Δν _85-1 = 50 GHz, Δν _85-2 = 100 GHz, Δν _85-3 = 200 GHz , Δν _85-4 = 400 GHz, Δν _85-5 = 800 GHz and Δν _85-6 = 1600 GHz. Accordingly, the difference in the arm lengths of the interferometers in the first steps of the used multistage and two-stage MZIs should be: ΔL _85-1 = 2000 μm, ΔL _85-2 = 1000 μm, ΔL _85-3 = 500 μm, ΔL _85-4 = 250 μm, ΔL _{85 -5} = 125 μm and ΔL _85-6 = 62.5 μm.

Suppose that for one of the waves, for example, wave v ₃ , for some fixed values of the phases {φ * _n } and {ϕ * _n }, respectively, in the first and second stages of the two-stage MCI used in all six optical filters, conditions similar to (11), providing the wave path ν ₃ along the route from the input port 81 to the output port 83.

The operation of the device 80 during these phases {φ * _n } and {ϕ * _n } is as follows. The input signal comes from VOSS to the input port 81, the optical filter 85-1 divides the channels into two groups - the group of odd waves ν ₁ , ν ₃ , ... ν ₆₃ , which are directed to the optical filter 85-2, and the group of even waves ν ₂ , ν ₄ , ..., ν ₆₄ , which are sent to the optical adder 86.

The process is repeated many times: the optical filter 85-2 again divides the waves and directs the waves ν ₃ , ν ₇ , ..., ν ₅₉ , ν ₆₃ to the optical filter 85-3, and the waves ν ₅ , ν ₉ , ..., ν ₅₇ , ν ₆₁ to adder 86, and so on until the last optical filter 85-6 finally finally separates the two waves ν ₃ and ν ₃₅ coming to it. As a result, the wave ν _{3 is released} , which passes to the output port 83, and all other 63 waves after passing the adder 86 are in the output port 82. The wave ν ₃ introduced through the port 84 also arrives at the output port 82.

When the multiplexer 80 is in dynamic mode, that is, to provide input / output of any other waves, it is necessary in accordance with expressions (10) to change the phase values {φ _n } and {ϕ _n } for all used optical filters. As for the multiplexer 70 described above (Fig. 7), it is possible that none of the waves is output, but all are transmitted to VOSS. The number of phase shift devices in the third version of the multiplexer is significantly larger than in the first version, however, the task of the corresponding phase reconstruction {φ _n } and {ϕ _n } does not present fundamental difficulties.

Possible optical losses and different channel levels for transmitted waves can be compensated by using a conventional optical amplifier and / or spectral equalizer in the DWDM technique.

A third embodiment of the controlled optical I / O multiplexer according to the present invention can also be used in DWDM spectral multiplexing systems. The multiplexer 90 corresponding to this embodiment is shown in FIG. 9.

We assume that the input signal again contains 64 channels, the channel frequencies correspond to the ITU standard and have a spectral interval between channels Δν = 50 GHz. Suppose also that the channel frequencies in this case are kept in their denominations more strictly, and the data transfer rates are relatively low. Therefore, here the requirements for channel isolation and insertion dispersion for the used optical filters can be reduced even more than the requirements in the second embodiment of the controlled optical input / output multiplexer discussed above.

Multiplexer 90 has one input port 91, one output port 92, one output port 93, one input port 94 and includes six optical filters 95-1, 95-2, 95-3, 95-4, 95-5 and 95-6 forming two multi-stage structures containing two optical filters 95-1 and 95-2 in the first structure, and four optical filters 95-3, 95-4, 95-5 and 95-6 in the second structure. Optical filters 95-1 and 95-2 are multi-stage MZIs shown in Fig. 6a, filters 95-3 and 95-4 are two-stage MZIs shown in Fig. 4a, and filters 95-5 and 95-6 are single-stage MZIs, shown in Fig. 2a.

The distance between adjacent extrema in the spectral characteristics of six optical filters is also set in such a way that when moving to the next optical filter it doubles: Δν _95-1 = 50 GHz, Δν _95-2 = 100 GHz, Δν _95-3 = 200 GHz , Δν _95-4 = 400 GHz, Δν _95-5 = 800 GHz and Δν _95-6 = 1600 GHzz.

The multiplexer 90 further comprises an optical adder 96 having 3 inputs and one output. All six filters and the adder are integrated on a single substrate 97. Four ports 91 ÷ 94 are made in the form of optical fibers. Connections of filters with optical fibers, as well as all other connections are made by waveguides 98.

Multiplexer 90 is a combination of the first and second embodiments of the multiplexers described above. The first two optical filters 95-1 and 95-2 are connected, as in the multiplexer 80, in series with the connection of the second outputs to the optical adder and form the first multi-stage structure. A second multi-stage structure with four optical filters is shown in FIG. 9 as optical filters arranged in a row; in this second structure, the optical filters are interconnected in the same way as in the multiplexer 70, each filter, except the first one, is connected to one of the outputs and one of the inputs of the previous filter by one of the inputs and one of the outputs.

One of the inputs of the first optical filter 95-1 is connected to the input port 101, one of the outputs of the last optical filter 95-6 is connected to the output port 103 and one of the inputs of the last optical filter 95-6 is connected to the input port 94. The third input of the optical adder is connected with one of the outputs of the optical filter 95-3, the output of the adder is connected to the output port 92.

Dynamic control of the multiplexer is carried out by adjusting the spectral characteristics of six filters 95-1 ÷ 95-6 when applying to the phase shift device all six filters of the corresponding voltages. Management is carried out using the controller 99, which is connected to the optical filters of all optical filters with an electric bus 99-1.

The operation of the multiplexer, which consists of two multistage structures of optical filters, in each structure occurs similarly to those described above in the first and second embodiments of the multiplexer.

In the third embodiment of the controlled optical input / output multiplexer, in the more general case of input / output of one channel from a plurality of 2 ^N channels, the multiplexer should include two multi-stage structures of optical filters: the first structure at multi-stage MZIs (Fig.6a) with the number of stages N ₁ and the second the structure of optical filters on single-stage MZI (Fig.2a) or / and two-stage MZI (Figa) with a total number of steps in the second structure N ₂ .

The total number of optical filters should be N ₁ + N ₂ = N, the distance between adjacent extremes in the spectral characteristics of six optical filters should also be set in such a way that when moving to the next optical filter it doubles.

Separately, the number of single-stage, two-stage and multi-stage MZIs should be selected based on the requirements for the spectral interval between channels Δν and the data transfer rate. An important factor in choosing the optical filters used in both structures may also be the cost of manufacturing the multiplexer.

An additional functionality of all three variants of multiplexers according to the present invention lies in the possibility of the operation of these devices in a mode that provides for one or more dedicated channels simultaneously output and transmission, without introducing new signals on the optical carrier output channels; however, all other channels, as usual, should be passed to the output port.

We illustrate additional functionality using the example of the second variant of multiplexer 80 (Fig. 8). Suppose that 32 channels arrive at input port 81, for example, waves ν ₁ ÷ ν ₃₂ , and it is necessary to simultaneously output and pass a channel with an optical frequency ν ₃ . In order to implement such a regime (let's call it the “output / transmission” mode), it is necessary to preserve the phase shifts {φ * _n } and {ϕ * _n } corresponding to the considered case of input / output of the wave ν ₃ for all optical filters except the last and the value of the phase shifts φ ₆ and ϕ ₆ for the last optical filter 85-6 set so that for the wave ν ₃ provided the division of the optical power of 50:50.

Similarly, with the appropriate settings for the phases {φ _n } and {ϕ _n } of all six optical filters, this mode can be provided for any other wave. In order to perform the “output / transmission” mode for two channels, for example, with frequencies ν ₃ and ν ₁₉ , it is necessary to rearrange the phase shifts for the filter 85-6 to perform a 50:50 division for waves ν ₃ and ν _19. It is easy to continue the description corresponding changes in phase shifts in the optical filters to ensure the mode of "output / transmission" of other pairs of channels, as well as 4 or more channels.

In the described embodiments of the multiplexer according to the present invention, a single operating concept is used. It consists in using a multi-stage structure of optical filters based on asymmetric MZIs. The optical filter of each stage, except for the filter of the last stage, is connected to the input of the filter in the next stage. For each optical filter, the transmission coefficients at the carrier frequencies supplied to the input of the channels have extreme values: for odd channels, the minimum values, for even channels, the maximum values, or vice versa.

When a multi-channel optical signal is passed through a multi-stage structure, each filter divides the channels into two groups, one containing odd and the other even channels, while one group contains a channel to be input / output. The spectral characteristics of the optical filters are adjusted in such a way that the selected channel always appears in the group sent to the optical filter in the next step; as a result, only one channel comes to the output port - the selected input / output channel.

All other channels along with the newly introduced channel are combined and routed to the output port. The combination of channels is carried out using additional connections between the filters, using the properties of their transmission coefficients, or using an optical adder. Thus, a controlled selective input / output of one channel is performed, while the required spectral characteristics of the channels and minimum dispersion are ensured.

The principle of operation, characteristics and possible embodiments of the present invention have been described above using examples of the use of appropriate devices in optical systems in which the wavelengths of the channels are in accordance with ITU standards. Therefore, in the examples considered, the multiplexers functioned as reconfigurable optical input / output multiplexers - ROADM.

However, the controllable optical I / O multiplexers according to the present invention are more flexible and versatile than conventional ROADMs, since they can be used as controllable optical I / O multiplexers in systems in which the optical channel wavelengths are tuned, and therefore a corresponding tuning of the spectral characteristics is necessary multiplexers. The required adjustment of the spectral characteristics can be easily performed using phase shift devices located in optical filters, similarly to what was described in the examples considered.

In all cases, both electro-optical and thermo-optical devices can be used as phase shift devices, while electro-optical phase shift devices can guarantee an extremely high tuning rate of the spectral characteristics of the multiplexer.

The use of integrated optical technologies for manufacturing seems to be a decisive factor in order for the multiplexers according to the present invention to meet the requirements for devices of a similar purpose - a large number of channels, resistance to external influences, high speed, etc. Application of unified standard elements in the design of devices, - single-stage, two-stage and / or multi-stage MZIs, - will allow the use of automated technological operations, which, in turn, it will provide high technical characteristics and a relatively low cost of manufacturing multiplexers.

The choice of one or another embodiment of the method of controlled selective input / output of one channel and the controlled optical input / output multiplexer according to the invention, as well as the optical filters used in them - single-stage, two-stage or multi-stage MZIs - can be made taking into account the specifics of a particular optical system communication.

The examples discussed explain the principle of operation, characteristics and possible design options of the present invention. It will be apparent to those skilled in the art of fiber optic communication systems that other modifications and alternative structural designs of the controlled optical input / output multiplexers according to the invention are possible within the scope of the present invention without departing from the scope of the claims.

Industrial applicability

The method of controlled selective input / output of channels according to the invention and controlled optical input / output multiplexers according to the present invention can be used in fiber-optic lines and communication systems with spectral multiplexing of channels, including trunk lines using DWDM technologies, and regional, city and local communication systems that use CWDM technology.

The controlled optical I / O multiplexers according to the present invention can be implemented using existing integrated optical technologies.

Claims (22)

1. A method of controlled selective input / output of a channel in a fiber-optic communication system with spectral multiplexing of 2 ^N channels, the optical frequencies of which can be tuned, but the spectral interval Δν between adjacent channels is constant, in which:
(a) a multi-channel optical signal is supplied from the optical network to an N-stage structure, in which each stage contains an optical filter having one input or two inputs, and two outputs configured to control the transmission coefficients and characterized in the nth stage, for n = 1, 2, ..., N, the frequency interval Δν _n = 2 ^nl Δν between adjacent extrema in the dependences of the transmission coefficients on the frequency, and the optical filter in each stage, except for the first, one input and one of the outputs is connected respectively to one from the outputs and one input of the optical filter of the previous stage, while one input of the optical filter of the first stage is the input port of the N-stage structure, and one of the outputs of the optical filter of the last stage is the output port in the N-stage structure;
(b) selecting a channel to be input / output;
(c) adjust the optical filter of each stage so that the transmission coefficient of the optical filter from input to output used in the optical filter connections described in a) has a maximum value at the frequency of the selected channel;
(d) pass a multi-channel optical signal through an N-stage structure and get the selected channel at the output of the last-stage optical filter, which is the output port in the N-stage structure;
(e) enter a new channel at the optical frequency of the output channel, combine the new channel and all channels except the output, and return the combined channels to the optical network. 2. The method according to claim 1, characterized in that when using optical filters having two inputs, the input of a new channel is carried out through the input port of an N-stage structure connected to the input of the optical filter of the last stage, not used in the optical filter connections described in a) the combination of the new channel and all channels except the removed one is carried out by connecting the output of the optical filter of each stage, except for the first one, which is not used in the connections of the optical filters described in a), with the input of the optical filter the previous stage is not used in connections of optical filters, described in a), and return the combined channels to optical network is realized through output of optical filter of the first stage that is not used in connections of filters described in a). 3. The method of claim 1, characterized in that when using optical filters having one input, the input of a new channel is carried out through one of the inputs of the optical adder having N + 1 inputs and one output, combining the new channel and all channels except the output is carried out by connecting the output of the optical filter of each stage, not used in the filter connections described in a), with one of the inputs of the specified adder, while through the output of the adder the combined channels are returned to the optical network. 4. A controlled optical input / output multiplexer for a fiber-optic communication system with spectral multiplexing of 2 ^N channels, the optical frequencies of which can be tuned, but the spectral interval Δν between adjacent channels is constant, having one input port (71), one output port ( 72), one output port (73), one input port (74) and including:
N-step structure containing in each step one optical filter (75-1, 75-2, 75-3), made with the possibility of controlled adjustment of transmission coefficients, characterized in the n-th stage, with n = 1, 2, ..., N, the frequency interval Δν _n = 2 ^n-1 Δν between adjacent extrema in the dependence of the transmission coefficients on the frequency and having two inputs (a, b) and two outputs (c, d);
a controller (78) for controlling the adjustment of transmission coefficients of said optical filters (75-1, 75-2, 75-3). 5. The input / output multiplexer according to claim 4, characterized in that in said N-step structure:
the optical filter (75-2, 75-3) of each stage, except the first, is connected to one of the outputs (d) and one of the inputs (b) of the optical filter by one of the inputs (a) and one of the outputs (c), respectively previous step;
the optical filter (75-1) of the first stage by another input (a) is connected to the input port (71),
an optical filter (75-1) of the first stage is connected to the output port (72) by another output (c);
an optical filter (75-3) of the last stage with another output (d) connected to the output port (73);
The optical filter (75-3) of the last stage is connected to the input port (74) by another input (b). 6. The input / output multiplexer according to claim 4, characterized in that the optical filters (75-1, 75-2, 75-3) of the N-stage structure are single-stage asymmetric Mach-Zehnder interferometers (20) and / or two-stage asymmetric Mach-Zehnder interferometers (40). 7. The input / output multiplexer according to claim 4, characterized in that for controlling the adjustment of the transmission coefficients, the optical filters (75-1, ..., 75-6) contain electro-optical or thermo-optical phase shift devices (25; 47, 48). 8. The input / output multiplexer according to claim 4, characterized in that it is made by integrated-optical technology on a single chip. 9. The input / output multiplexer according to claim 4, wherein the input port (71), output port (72), output port (73) and input port (74) are made using optical fibers. 10. A controlled optical input / output multiplexer for a fiber-optic communication system with spectral multiplexing of 2 ^N channels, the optical frequencies of which can be tuned, but the spectral interval Δν between adjacent channels is constant, having one input port (81), one output port 82 ), one output port (83), one input port (84) and including:
An N-step structure containing one optical filter in each stage [85-1, ..., 85-6], configured to control the adjustment of transmission coefficients, characterized in the n-th stage, with n = 1, 2, ..., N, the frequency interval Δν _n = 2 ^n-1 Δν between adjacent extremes in the dependence of the transmission coefficients on the frequency and having one input (g or a) and two outputs (p, k or e, f);
an optical adder (86) having N + 1 inputs and one output connected to the output port (82);
a controller (89) for controlling the adjustment of transmission coefficients of said optical filters [85-1, ..., 85-6]. 11. The input / output multiplexer according to claim 10, characterized in that in said N-step structure:
the optical filter [85-1, ..., 85-5] of each stage, except for the last stage, is connected to the input of the optical filter of the next stage by one of the outputs (p or e), and connected to one of the optical inputs by the other output (k or f) adder;
the optical filter (85-1) of the first stage is connected with its input (g) to the input port (81);
optical filter (85-6) of the last stage with one output (f) connected to another of the inputs of the optical adder, and the other output (e) connected to the port (83) output;
the optical adder (86) is connected to the input port (84) by one input not used in the connections described above. 12. The input / output multiplexer according to claim 10, characterized in that the optical filters [85-1, ..., 85-6] of the N-stage structure are multistage asymmetric Mach-Zehnder interferometers (60). 13. The input / output multiplexer according to claim 10, characterized in that for controlling the adjustment of the transmission coefficients, the optical filters (85-1, ..., 85-6) contain electro-optical or thermo-optical phase shift devices (47, 48). 14. The input / output multiplexer according to claim 10, characterized in that it is made by integrated-optical technology on a single chip. 15. The input / output multiplexer according to claim 10, in which the input port (81), output port (82), output port (83) and input port (84) are made using optical fibers. 16. A controlled optical input / output multiplexer for a fiber-optic communication system with spectral multiplexing of 2 ^N channels, the optical frequencies of which can be tuned, but the spectral interval Δν between adjacent channels is constant, having one input port (91), one output port ( 92), one output port (93), one input port (94) and including:
interconnected first (90a) and second (90b) multi-stage structures containing in each of their stages one optical filter [95-1, ... 95-6], made with the possibility of controlled adjustment of their transmission coefficients, while the first structure has N ₁ steps, the second structure has N ₂ steps and N ₁ + N ₂ = N;
an optical adder (96) having N ₁ + 1 inputs and one output;
a controller (99) for controlling the tuning of the spectral characteristics of the optical filters [95-1, ... 95-6] of the first and second multi-stage structures (90a, 90b). 17. The input / output multiplexer according to clause 16, characterized in that:
the optical filter (95-1, 95-2) in the first multi-stage structure (90a) has one input (g) and two outputs (p, k) and is characterized in the n _1st stage, with n ₁ = 1, 2, ... , N ₁ , with a frequency interval Δν _n1 = 2 ^n1-1 Δν between adjacent extrema in the dependences of the transmission coefficients on the frequency;
the optical filter (95-3, ..., 95-6) in the second multi-stage structure has two inputs and two outputs and is characterized in the n _2nd stage, with n ₂ = 1, 2, ..., N ₂ , the frequency interval Δν _n2 = 2 ^{n2 + N1-1} Δν between adjacent extrema in the dependences of the transmission coefficients on the frequency. 18. The input / output multiplexer according to clause 16, characterized in that:
in the first multi-stage structure (90a), the optical filter (95-1) of each stage, except the last, is connected to the input (a) of the optical filter of the next stage with one output (p), and connected to one of the inputs of the optical adder with the other output (k);
in the first multi-stage structure (90a), the optical filter (95-2) of the last stage with one output (k) is connected to the other from the inputs of the optical adder, and the other output (p) is connected to one of the inputs of the optical filter of the first stage of the second multi-stage structure (90b) ;
in the second multi-stage structure (90b), an optical filter (95-4, 95-5, 95-6) of each stage, except for the first, is connected to one of the outputs (e) by one of the inputs (a) and one of the outputs (f), respectively and one of the inputs (b) of the previous stage optical filter;
in the second multi-stage structure (90b), the optical filter (95-3) of the first stage is connected to another input of the optical adder by another output (f);
in the first multi-stage structure (90a), the optical filter (95-1) of the first stage is connected to the input port (91) by an input (g);
in the second multi-stage structure (90b), the optical filter (95-6) of the last stage is connected to one of the outputs (c) with the output port (93);
in the second multi-stage structure (90b), the optical filter (95-6) of the last stage is connected to another input (b) to the input port (94);
an optical adder (96) is connected to the output port (92) by an output. 19. The input / output multiplexer according to claim 16, characterized in that the optical filters (95-1, 95-2) of the first multi-stage structure (90a) are multistage asymmetric Mach-Zehnder interferometers (60), and optical filters (95-3 , ..., 95-6) the second multi-stage structure (90b) are single-stage asymmetric Mach-Zehnder interferometers (20) and / or two-stage asymmetric Mach-Zehnder interferometers (40). 20. The input / output multiplexer according to clause 16, wherein the optical filters (95-1, ..., 95-6) contain electro-optical or thermo-optical phase shift devices (25; 47, 48) to control the setting of transmission coefficients. 21. The input / output multiplexer according to claim 16, characterized in that it is made by integrated-optical technology on a single chip. 22. The input / output multiplexer according to clause 16, in which the input port (91), output port (92), output port (93) and input port (94) are made using optical fibers.

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