WO2001059515A2

WO2001059515A2 - Optical switch

Info

Publication number: WO2001059515A2
Application number: PCT/CA2001/000134
Authority: WO
Inventors: Michael Gartner
Original assignee: OPTICOM INTERNATIONAL Ltd
Current assignee: OPTICOM INTERNATIONAL Ltd
Priority date: 2000-02-08
Filing date: 2001-02-08
Publication date: 2001-08-16
Anticipated expiration: 2002-08-08
Also published as: WO2001059515A3; AU3352001A

Abstract

An optical switch for routing light signals includes a splitter cell and a recombiner cell. Light signals entering the optical switch are initially split into two polarized light signals having different polarizations. The two polarized light signals are then recombined by the recombiner cell and travel towards one of two output ports. The optical switch also includes a polarization changing device that changes the polarization of the two polarized light signals in response to a control signal. The recombined light signal exiting from the recombining cell will proceed in a direction corresponding to one of the two polarized light signals depending on the polarization of the polarized light signals. By applying the control signal to change the polarization of the polarized light signals, the recombined light signal will travel towards one of two output ports. The optical switch can operate with two input ports and two output ports and can switch light signals entering simultaneously from the two input ports, thereby acting as an optical toggle switch. The optical switch is also bi-directional such that the output ports can act an input ports and the input ports can act as output ports. The optical switch is a 2x2 optical switch, but can be combined with other similar optical switches to create larger switches, such as 4x4 optical switches.

Description

OPTICAL SWITCH

FIELD OF THE INVENTION

This invention relates to switches for routing light signals carrying information. More particularly, the present invention relates to an optical switch and a method for routing light beams between different ports.

BACKGROUND OF THE INVENTION

There has been a growing move in the communication field away from copper wire networks, which transfer information by means of electrical signals, towards fiber optic networks, which transfer information by means of light signals. The move towards fiber optic networks has been made, in large part, because of the increased bandwidth of fiber optic networks which permit fiber optic networks to convey larger amounts of information through a limited number of fiber optic lines as compared to the same number of electrical lines.

In addition, unlike copper wire networks, fiber optic networks do not exhibit electromagnetic interference or radio frequency radiation, resulting in a negligible impact on the surrounding environment. Likewise, fiber optic networks are less susceptible to external sources of electromagnetic interference or radio frequency radiation .

In order for the potential fiber optic networks to be fully realized, a fiber optic network must ideally have the ability to route light signals from the point of initial transmission to the point of final destination. The prior art devices to date for redirecting light in a fiber optic network have been classified into two broad areas, namely (i) opto-electrical switches and (ii) opto-mechanical switches .

Opto-electrical switches do not directly switch light signals, but rather convert the light signals to an electrical signal and then switch the electrical signal, similar to the manner in which electrical signals have been switched in the past. After the electrical signal has been switched, the opto-electrical switches then reconvert the electrical signals back to a light signal, which can continue along the fiber optic network. Opto- electrical switches are fairly reliable because they utilize the same technology that has been used in the past to switch electrical signals. However, opto-electrical switches suffer from the disadvantage that the bandwidth of the system is limited by the electrical switching of the electrical signals. Furthermore, the bandwidth of the system is also constrained by the ability of the converters to convert the light signal to an electrical signal and then convert the electrical signal back to a light signal after the electrical signals have been switched. Therefore, a fiber optic network which utilizes opto-electrical switches has a bandwidth which is constrained by the opto-electrical switch. This may also result in under utilization of a majority of the fiber optic network.

Opto-mechanical switches use a series of mechanical mirrors to redirect the light signals . The mechanical mirrors reflect the light signals and can be mechanically moved to route the light signals towards their final designation. While opto- mechanical switches can redirect light signals without converting them to electrical signals, optomechanical switches are constrained by the accumulative light loss resulting from the mechanical mirrors. This accumulative light loss limits the size of the switch matrix. In particular, it has been difficult to assemble a switching matrix larger than 32 ports. Clearly, this matrix size limitation severely restricts the number of , applications in the fiber optic telecommunication industry that can use this technology. Furthermore, the mechanical switches used in the opto-mechanical switches require large quantities of power to operate and frequently require repair in view of the mechanical parts that are moving to move the mirrors. This further affects the reliability of the opto-mechanical switches in large commercial operations.

Accordingly, the prior art opto-mechanical switches suffer from the disadvantage that there is an accumulative light loss, which decreases the effectiveness of the opto-mechanical switches and limits the size of the opto-mechanical switch. Furthermore, opto-mechanical switches require large quantities of power and frequent repair. While opto-electrical switches can be used to overcome some of the disadvantages of the opto-mechanical switches, opto-electrical switches suffer from the disadvantage that they severely limit the bandwidth of the fiber optic network, leaving other parts of the fiber optic network underutilized.

Accordingly, there is a need in the art for an optical switch which does not limit the bandwidth of the fiber optic network by requiring the light signals to be converted to electrical signals for switching. Furthermore, there is a need in the art for an optical switch which does not require numerous mechanically moved mirrors that consume large quantities of power, frequently require repair, and result in large accumulative light losses . SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to at least partially overcome the disadvantages of the prior art. Also, it is an object of this invention to provide an optical switch which can switch or route light signals without converting the light signals into electrical signals. It is also an object of this invention to provide an optical switch which can redirect light signals without suffering a large accumulative light loss or requiring mechanical movement of mirrors, which consume large amounts of power and require repair.

Accordingly, in one aspect, the present invention provides an optical switch for routing a light signal to a first port or a second port, said optical switch comprising: a splitter cell for splitting the light signal into a first polarized signal having a first polarization and a second polarized light signal having a second polarized signal; a polarization changing device for changing the polarization of the first polarized light signal from the first polarization to the second polarization and for changing the polarization of the second polarized light signal from the second polarization to the first polarization when a light signal is applied to the polarization changing device and for not changing the polarization of the first light signal or the second polarization signal when a second signal is applied to the polarization changing device; a recombiner cell for recombining the first polarized light signal and the second polarized light signal into a recombined light signal; wherein the recombined light signal will travel toward the first port when the first signal is applied to the polarization changing device and the recombined light signal will travel toward the second port when the second signal is applied to the polarization changing device.

In a further aspect, the present invention provides a method of routing light signals, said method comprising steps of: separating the light signal into a first polarized light signal having a first polarization and a second polarized light signal having a second polarization; passing the first polarized light signal and the second polarized light signal through a polarization changing device which changes the first polarization to the second polarization and changes the second polarization to the first polarization when a first signal is applied to the polarization changing device and does not change the polarization of the first polarized light signal and the second polarized light signal when a second signal is applied to the polarization changing device; recombining the first polarized light signal having the first polarization and the second polarized light signal having the second polarization signal after they have passed through the polarization changing device into a recombined light signal; and applying the first signal to the polarization changing device to route the recombined light signal in a first direction and not applying the second signal to the polarization changing device to route of the recombined light signal to a second direction .

Accordingly, one advantage of the present invention is that the light signals can be switched or routed without converting the light signals into electrical signals. In this way, the optical switch according to the present invention provides a large bandwidth, and is not limited by the bandwidth of an electrical switch or a conversion device which converts the light signals to and from electrical signals, as is the case with opto-electrical switches .

A further advantage of the present invention is that, because the light signals are being switched or routed without the light signals being converted to electrical signals, the optical switch according to the present invention will switch the light signals at about the same speed at which the light signals travel through the other components of the optical fiber network. In other words, the other parts of the optical fiber network will not be underutilized. A further advantage of the present invention is that the optical switch according to the present invention has no moving parts. Rather, the optical switch can switch the light signals by changing the polarization of components of the light signal by means of a liquid crystal. Accordingly, this lack of moving parts decreases the likelihood that the optical switch will require repair, and further results in a corresponding increase in the reliability of the optical switch.

A still further advantage of the present invention is that the optical switch can redirect light signals which may comprise light at different wavelengths. This is particularly useful where the light signal has been subject to wave division multiplexing and the light signal comprises a plurality of individual light signals, each individual light signal at a distinct wavelength.

Further aspects of the invention will become apparent upon reading the following detailed description and drawings which illustrate the invention and preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which illustrate embodiments of the invention: Figure 1 shows a schematic side view of a 2x2 optical switch according to one embodiment of the present invention.

Figure 2a shows the optical switch shown in Figure 1 with a light signal entering through one port and the polarization changing device not changing the polarization of the polarized light signals;

Figure 2b shows the optical switch shown in Figure 1 with a light signal entering through one port and the polarization changing device changing the polarization of the polarized light signals;

Figure 3a shows the optical switch shown in

Figure 1 with a light signal entering through a port different than the port illustrated in Figure 2a and the polarization changing device not changing the polarization of the polarized light signals;

Figure 3b shows the optical switch shown in Figure 1 with a light signal entering through a port different from the port illustrated in Figure 2b and the polarization changing device changing the polarization of the polarized light signals; and

Figure 4 shows a 4x4 optical switch comprising 16 2x2 optical switches shown in Figure 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 is a schematic drawing of a side view of a 2x2 optical switch, shown generally by reference numeral 10, according to one embodiment of the present invention.

The embodiment of the optical switch 10 shown in Figure 1 has two input ports I_a, I_B and two output ports O_A, O_B. It is understood that the invention could operate with a single input port, either I_A or IB.

The optical switch 10 further preferably comprises collimating lenses 8A, 8B, 8A' , 8B' for collimating the light signals L_s as they enter and exit the optical switch 10. However, collimating lenses 8A, 8B, 8A' , 8B' are not necessary for the proper operation of the invention.

The optical switch 10 further comprises a splitter cell 11 and a recombining cell 12. The splitter cell 10 splits or separates the light signals L_s (shown in Figures 2a and 2b) entering through either input port I_A or I_B. The splitter cell 11 will split the light signal L_s into two separate polarized light signals L_SPA and L_SPB (shown in Figures 2a and 2b) having different polarizations . In a preferred embodiment, the splitter cell 11 directs the polarized light signal L_SPA, L_SPB along either the first path 21 or the second path 22. For example, the splitter cell 11 may direct the first polarized light signal L_SPA onto the first path 21 and may direct the second polarized light signal L_Sp_B onto the second path 22. Preferably, each path 21, 22 comprises a permanent mirror 24, 26, respectively, to direct the polarized signals.

Preferably, the first path 21 and second path 22 will then intersect at the recombining cell 12. The recombining cell 12 recombines the two polarized signals L_Sp_A, L_Sp_B into a recombined light signal L_Ξc comprising both polarizations. The recombined polarization signal will then travel through one of the output ports 0_A, 0_B in a manner described below.

In a preferred embodiment, the splitter cell 11 comprises a first polarization cell 15. The first polarization cell 15 is transparent to the portion of the light signals L_s having a first polarization and the first polarization cell 15 reflects the portion of the light signals L_s having a second polarization. In this way, the first polarization cell 15 permits a first polarized light signal L_SPA having a first polarization to travel through the first polarization cell 15, but reflects a second polarized light signal L_SPB having a second polarization. Thus, the first polarization cell 15 will both separate the light signal L_s into a first polarized light signal L_Sp_A and a second polarized signal L_SPB, having first and second polarizations, respectively, as well direct the polarized light signals L_Sp_A and L_SPB onto the first light path 21 and the second light path 22, respectively.

In a further preferred embodiment, the first polarization cell 15 comprises a plate of glass having liquid crystal molecules normal to the plate of glass which causes the first polarization cell 15 to be transparent to the portion of the light signals L_s which is horizontally polarized. The horizontal polarization cell 15 will reflect the portion of the light signal L_s which is vertically polarized. However, it is understood that other types of polarization cells, including polarization cells which are transparent to vertically polarized light signals L_s and reflect horizontally polarized light signals L_s, could also be used.

In a preferred embodiment, the recombining cell 12 comprises a second polarization cell 16. The second polarization cell 16 will be transparent to polarized light signals L_SPA^ L_SPB having one type of polarization, such as the first polarization, and will reflect polarized light signals L_SPA/ L_SPB having another type of polarization, such as the second polarization. In this way, the second polarization cell 16 will reflect one polarized light signal L_SPA, L_SPB and transmit the other polarized light signal LSPB_Λ L_SPA, depending on their polarization, to recombine the first and second polarized light signals L_SP ^ L_SPB into the recombined light signal l^*sc-

In a preferred embodiment, the second polarization cell 16 will also have liquid crystal molecules normal to the plate of glass and will therefore also be transparent to horizontally polarized light signals and reflect vertically polarized light signals. In this case, the first and second polarization cells 15, 16 could be formed from a single plate of glass. Moreover, if the first and second polarization cells 15, 16 are co- planar, then the polarization cells 15, 16 could be formed from a single polarization cell comprising a single uncut plate of glass.

In order to decrease light loss, it is preferred that the light signal L_s strike the first polarization cell 15 at an angle of incidence of about 70° with respect to the normal. Likewise, it is preferred that the first and second polarized signals L_Sp_A, L_SPB have an angle of incidence onto the second polarization cell 16 of about 70° with respect to the normal. In order for the recombined light signal L_ΞC to have a significant intensity, it is preferred that the first and second polarized signals L_SPA_Λ LSPB have the same angle of incidence onto the second polarization cell 16 and at about the same longitudinal position on the second polarization cell 16. It is also preferable that the optical distance of the first light path 21 be substantially equivalent to the optical path of the second light path 22.

The optical switch 10 also comprises a polarization changing device, shown generally by reference numeral 30. The polarization changing device 30 will change the polarization of the polarized light signals L_Sp_A, L_Sp_B travelling through the first path 21 and the second path 22.

In a preferred embodiment, the polarization changing device 30 comprises a first liquid crystal cell 31 along the first path 21 and a second liquid crystal cell 32 along the second path 22. The first liquid crystal cell 31 rotates the polarization of the polarized light signal L_Sp_A in the first path 21 by about 90° when the first signal Si is applied to the first liquid crystal cell 31. When a second signal S₂ is applied to the first liquid crystal cell 31, the polarization of the first polarized signal L_SPA travelling along the first path 21 will not be affected. The second liquid crystal cell 32 operates in a similar manner to the first liquid crystal cell 31 by changing the polarization of the polarized light signal L_SPB travelling along the second path 22 and not changing the polarization when the second signal S₂ is applied.

In some cases, the liquid crystal cells 31, 32 may have a stable "off state" when no voltage or signal is applied. In this stable "off state", the liquid crystal cells 31, 32 would not change the polarization of the polarized light signals L_SPA, L_SPB when no voltage or signal is applied. In this case, by simply not applying the first signal Si, the polarized light signals L_Sp_A, L_Sp_B will not be changed. However, in some cases, the liquid crystal cells 31, 32 will require a second signal S₂, which may be a reverse voltage to the first signal Si, to return the liquid crystal cells 31, 32 to a state where the polarized light signals L_SPA^ L_SPB passing through the liquid crystal cells 31, 32 are not being changed. Accordingly, when the liquid crystal cells 31, 32 have a stable "off state", the second signals S₂ can be considered an "off" signal or "0" signal equivalent to the first signal Si not being applied.

The first signal Si and the second signal S₂ are generated and applied by a supervisory control module 40. The supervisory control module 40 determines whether or not to apply the first signal Si or the second signal S₂ based on either an address header or a frequency modulation identification of the light signal L_s. The address header and frequency modulation identification of the light signal L_s indicate the final destination of the light signal L_s, as is known in the art. The optical switch 10 and the supervisory control module 40 together form a system for routing light signals, shown generally by reference numeral 90 in Figure 1. The operation of the optical switch 10 will now be discussed with respect to Figures 2a and 2b. For the purposes of illustration, the splitter cell 11 will be considered as comprising a horizontal polarization cell 15 which is transparent to the portion of light signals L_s having a horizontal polarization and reflective to the portion of light signals L_s having a vertical polarization. Likewise, for the purposes of illustrating the invention, the recombining cell 12 will be considered as comprising a horizontal polarization cell 16 which is also transparent to horizontally polarized light and reflective to vertically polarized light. Nevertheless, it is understood that horizontal polarization cells 15, 16 have been selected only for the purposes of explaining the operation of one embodiment of the invention and other types of splitter cells 11 and recombining cells 12, as well as other types of polarization cells 15, 16 can be used.

In Figure 2a, a light signal L_s is shown entering through input port I_B. Light signal L_s is shown by a solid line and reference numeral L_s .

Initially, the light signal L_s will pass through the collimating lens 8B and then reach the splitter cell 11. The splitter cell 11 will split the light signal L_s into a first polarized light signal L_{S A} travelling along the first path 21 and a second polarized light signal L_Sp_B travelling along the second light path 22. As the splitter cell 11 is considered, for the purposes of illustration, to be a horizontal polarization cell 15, the portion of the light signal L_s which passes through the splitter 11 will have a horizontal polarization and in this case will be the first polarized light signal L_SPA travelling on the first light path 21. The first polarized light signal L_SPA is illustrated in Figure 2a as being horizontally polarized by the dash dot dash line " - ". Similarly, as the horizontal polarization cell 15 will reflect the portion of the light signal L_s having a vertical polarization, the second polarized light signal L_Sp_B travelling in the second path 22 will be vertically polarized. This is illustrated by the dash plus dash line " + " shown in Figure 2a.

In Figure 2a, the second signal S₂ is being applied to the liquid crystal cells 31, 32 which together comprise the polarization changing device 30. Accordingly, in the example illustrated in Figure 2a, the polarization changing device 30 is not changing the polarization of the first polarized signal L_S and the second polarized signal L_SPB. The first polarized signal L_SPA will then travel along the first path 21 being reflected by the permanent reflecting surface 24 and the second polarization signal L_SPB will travel along the second path 22 and be reflected by the permanent reflecting surface 26 and the polarization of both polarized light signals L_SPA, L_SPB will not be changed. The first light path 21 and the second light path 22 intersect at the recombining cell 12. As stated above, for the purposes of illustration, the recombining cell 12 will be considered to be a horizontal polarization cell 16 which is transparent to horizontally polarized light and reflects vertically polarized light. Accordingly, the first and second polarized light signals L_SPA, L_SPB will meet at the second horizontal polarization cell 16. The first polarized light signal L_SPA. which is horizontally polarized, will pass through the horizontal polarization cell 16, but the second polarized light signal L_{S B}, which is vertically polarized, will be reflected by the horizontal polarization cell 16. The result is that both the first polarized light signal L_SPA and the second polarized light signal L_SPB will travel in the same direction, thus recombining into the recombined light signal L_Sc-

The recombined light signal L_Sc is shown as a solid line as it has been recombined and comprises both a horizontally polarized portion and a vertically polarized portion. The recombined light signal L_sc will have properties similar to the light signal L_s and carry the same information as the light signal L_s. The recombined light signal L_sc will travel towards one of the output ports 0_A, 0_B, which in the example shown in Figure 2a is the output port 0_B. Accordingly, it is apparent that the recombining cell 12 will recombine the polarized signals L_SPA, L_SPB into the recombined signal L_sc. Moreover, the recombined signal L_Sc will travel in a direction which is dependent on the relative polarizations of the polarized signals L_SPA, L_SPB, as well as the properties of the recombining cell 12. For example, in this illustration, the recombining cell 12 is a horizontal polarization cell 16 which is transparent to horizontally polarized light providing the result that the recombined light signal L_sc will travel in the same direction as whichever polarized light signal L_SPA, L_SPB is horizontally polarized when the polarized light signals L_{SP C} L_SPB are recombined. As, in the example illustrated in Figure 2a, the first polarized light signal L_SPA is horizontally polarized when the signals L_S A, L_SPB are recombined, the recombined light signal L_sc will travel in the same direction as the first polarized light signal L_Sp_A, which in this case is towards output port 0_B.

Reference is now made to Figure 2b which is similar to Figure 2a except that the first signal S_x is being applied to the liquid crystal cells 31, 32, which together form the polarization changing device 30. Accordingly, in the example illustrated in Figure 2b, the polarization of the first and second polarized light signals L_SPA^ L_SPB will change as they travel along the first and second light paths 21, 22.

As shown in Figure 2b, the light signal L_s again enters through input port I_B and strikes the splitter cell 11. The splitter cell 11 will split the light signal L_s into the first polarization signal L_SPA and the second polarization signal L_SPB- AS we are continuing to consider the beam splitter 11 to be a horizontal polarization cell 15, the first polarized light signal L_SPA.- which passes through the beam splitter 11, will be initially horizontally polarized and the second polarized light signal L_Sp_B, which is reflected by the horizontal polarized cell 15, will be initially vertically polarized.

As the first polarized signal L_SPA travels along the first path 21, it will encounter and interact with the liquid crystal cell 31, which, as the first signal Si is being applied, will change the polarization of the first polarized light signal L_SPA- AS, in this case, the first polarized light signal L_Sp_A is initially horizontally polarized, the liquid crystal cell 31 will change the polarization of the first polarized light signal L_Sp_a to be vertically polarized. This is illustrated in Figure 2b by the dash dot dash line changing into the dash plus dash line.

Likewise, as the second polarized signal L_SPA which is initially vertically polarized, passes through the second liquid crystal cell 32, to which the first signal Si is also being applied, the polarization of the second polarized light signal _SPA will change from being vertically to horizontally polarized. This is illustrated in

Figure 2b by the dash dot dash line changing into a dash plus dash line.

Both the first polarized light signal L_Sp_A, which is now vertically polarized, and the second polarized light signal L_SPB, which is now horizontally polarized, will continue along the first path 21 and the second path 22, respectively, until they intersect at the recombining cell 12. As the recombining cell 12 is considered to be a horizontal polarization cell 16 for this illustration, the second polarized light signal L_SPB, which is horizontally polarized, will pass through the recombining cell 12. The first polarized light signal L_SPA which is now vertically polarized will be reflected by the recombining cell 12 providing the result that the first polarized signal L_SPA and the second polarized signal L_Sp_B will recombine into the recombined light signal L_Sc, similar to Figure 2a. However, as the second polarized light signal L_SPB is now horizontally polarized, the recombined light signal L_sc will travel in the same direction as the second polarized light signal L_Sp_B, namely towards output port 0_A. Accordingly, as shown in Figures 2a and 2b, when the second signal S₂ is applied to the liquid crystal cells 31, 32 such that they do not change the polarization of the polarized light signals L_SPA, L_SPB an input light signal Ls from input port I_B will exit through output port 0_B. However, when the first signal S is applied to the liquid crystal cells 31, 32, a light signal L_s entering through input port I_B will exit through output port 0_A. Accordingly, it is clear that the optical switch 10 will route or switch optical light signals L_s to one of the two output ports O_A, O_B depending on whether the first signal Si or the second signal S₂ is applied to the polarization changing device 30. It is clear that the optical switch 10 will route or switch the light signal L_s without converting the light signal L_Ξ to an electrical signal, and, without the use of moving mirrors or other mechanically moving devices.

It is apparent that optical switch 10 will operate with only one input port, such as input port I_B. In this case, all light signals L_s would enter through input port I_B and exit through either output port 0_A or output port 0_B, depending on whether the first signal Si or the second signal S₂ is applied to the liquid crystal cells 31, 32. However, the optical switch 10 can also operate with a second input port I_A, as illustrated in Figures 3a and 3b.

As shown in Figures 3a and 3b, the light signal L_s entering through input port I_A will be switched or routed to output port 0_A or output port 0_B in a similar manner to which light signal L_s entering through input port I_B was switched or routed to output port 0_A or output port 0_B, as described above with respect to input port I_B.

With respect to Figure 3a, when the second signal S₂ is being applied, the splitter cell 11 splits the light signal L_s into the first polarized signal L_Sp_A and the second polarized signal L_Sp_B. As the first polarized signal L_Sp_A is being reflected from the splitter cell 11, and assuming the splitter cell 11 is a horizontal polarization cell 15, the first polarized light signal L_Sp_A will be initially vertically polarized, as shown by the dash plus dash line. The second polarized light signal L_SPB, which passes through the splitter cell 11, will be horizontally polarized, as shown by the dash line. As the second signal S₂ is being applied in the example shown in Figure 3a, the polarization of the polarized light signals L_SVΆ, L_SPB will not be changed.

As the light paths 21, 22 intersect at the recombining cell 12, the polarized light signals L_SPA. L_SPB will reco bine into the recombined light signal L_sc. Assuming the recombining cell 12 is a horizontal polarization cell 16, the recombined light signal L_Sc will continue in the same direction as the horizontally polarized light signal, which, in the example shown in Figure 3a, is the second polarized light signal L_SPA toward output port 0_A. Accordingly, when the second signal S₂ is applied to the liquid crystal cells 31, 32, and the light signal Ls enter through input port I_A, the recombined light signal L_sc will travel towards and exit output port 0_A.

In Figure 3b, where the first signal Si is applied to the liquid crystal cells 31, 32 of the polarization changing device 30, the polarization of the polarized light signals L_SPA, L_Sp_B will change. This is illustrated in Figure 3b by the first polarized light signal L_Sp_A initially having a dash plus dash line representing a vertically polarized light signal, and then having a dash dot dash line after passing through the first liquid crystal cell 31, representing a horizontally polarized light signal. Likewise, the second polarized light signal L_Sp_B is initially horizontally polarized, represented by the dash dot dash line, and then becomes vertically polarized after passing through the liquid crystal cell 32, represented by the dash plus dash line. Assuming the recombining cell 12 is a horizontal polarization cell 16, the recombined light signal L_sc will travel in the same direction as whichever polarized light signal L_SPA or Ls_PB has a horizontal polarization. As, in this case, the first polarized light signal L_SPA is horizontally polarized, the recombined light signal L_sc will travel towards output port 0_B. Accordingly, when a light signal L_s enters through the input port I_A and the second signal S₂ is applied to the liquid crystal cells 31, 32, the recombined light signal L_Sc will travel towards the first output port 0_A. When the light signal L_s enters through the input port I_A and the first signal Si is applied to liquid crystal cells 31, 32, the recombined light signal L_Sc will travel towards the second output port 0_B.

In a preferred embodiment, the splitter cell 11 and the recombining cell 12 can split or recombine light signals L_s entering through either input port I_A or input port I_B. For example, in the embodiment where the splitter cell 11 and recombining cell 12 comprise horizontal polarization cells 15, 16, the horizontal polarization cells 15, 16 will have two opposed surfaces 15a, 15b, and 16a, 16b, respectively, as shown in Figure 1, upon which light signals L_s can be incident. In this way, light signals L_s can be inputted from both input port I_A and input port I_B and be switched by the optical switch 10. Moreover, given the properties of light, and in particular the fact that one light signal L_s will not interfere with other light signals L_s, it is possible for the optical switch 10 to switch optical signals L_s entering through both the input port I_A and the input port I_B simultaneously.

However, in this case, since the same liquid crystal cells 31, 32 will affect the polarization of the polarized light signals L_Sp_A, L_Sp_B, regardless of whether they entered from the input port I_A or the input port I_B, it is not possible to independently switch the light signals Ls entering simultaneously from input ports I_A, I_B. Rather, the light signal L_s entering through input port I_A will always exit through an output port 0_A, 0_B, which is different from the output port 0_B, 0_A through which the input signals L_s that entered through input port I_B is exiting. In other words, if signal S₂ is applied to the liquid crystal cells 31, 32, then the light signals L_s entering through input ports I_A, I_B will exit through output ports 0_A, 0_B, respectively. If the first signal S is applied to the liquid crystal cells 31, 32, then light signals L_s entering simultaneously through the input ports I_A, I_B will exit through output ports 0_B, 0_A, respectively. Therefore, the switch 10 will operate as a toggle connecting light signals L_s from input port I_A, I_B to output ports 0_A, 0_B or output ports 0_B, 0_A, depending on whether or not the second signal S₂ or the first signal Si is applied to the liquid crystal cells 31, 32.

In a preferred embodiment, the optical switch 10 is bi-directional in that light signals L_s can also enter through the output ports 0_A, 0_B and be switched by the optical switch 10 to exit through one of the input ports I_A/ I_B- Accordingly, in this preferred embodiment, the input ports I_A, I_B and the output ports O , O_B act as input/output ports I/0_A, I/0_B and input/output ports I/0_A», I/0_B' as shown in Figure 1. Using the optical switch 10 in a bidirectional manner to send and receive optical signals 10 to input/output ports is particularly beneficial where a large amount of information is to be sent to and from two separate entities. This is the case, for example, during video conferencing when large amounts of information in the form of video and audio signals, are sent between two locations. As light signals L_s do not interfere with each other, it is possible for the light signals L_s to enter and exit input/output ports I/0_A, I/0_B, I/0_A', I/O_B' simultaneously.

When light signals L_s enter through input/output ports I/0_A', I/O_B', the optical switch 10 will operate in a similar manner to that illustrated in Figures 2a, 2b, 3a and 3b, except in reverse in that the light signals L_Ξ will enter through the input/output ports I/O_A', I/0_B' and the recombined light signal L_Sc will exit through one of the input/output ports I/O_a, I/0_B. Furthermore, the second polarization cell 16 will act to split the light signals L_Ξ entering through the input/output ports I/0_A, I/0_B into polarized light signals L_SPA. L_ΞPB which travel on the first and second light paths 21, 22. The first polarization cell 15 will act to recombine the polarized light signals L_SP , L_SPB into a recombined light signal L_sc which will travel towards one of the input/output ports I/0_A, I/0_B depending on whether the first signal Si or the second signal S₂ is being applied to the liquid crystal cells 31, 32. Accordingly, in this preferred embodiment, the first and second liquid crystal cells 31, 32 act in a bidirectional manner and the first and second polarized cells 15, 16 act as both a splitter cell 11 and a recombiner cell 16.

The light signals L_s will enter the input ports I_A, I_B generally through a fiber optic network, such as through a fiber optic cable. Likewise, the recombined signals L_sc will exit through output ports 0_A, O_B to the fiber optic network, such as through another fiber optic cable. However, it is possible to combine the optical switch 10 with other optical switches, including other optical switches identical to optical switch 10 so that the input and output do not come from and go to the fiber optic network, but rather other optical switches 10. In this way, a larger optical switch having more than two input ports I_A, I_B and two output ports 0_A, 0_B can be formed, as illustrated in Figure 4.

Figure 4 shows a 4x4 optical switch array, shown generally by reference numeral 100. The optical switch array 100 comprises 16 2x2 optical switches 10, as shown in Figures 1, 2a, 2b, 3a, 3b and 4. The optical switches 10 within the optical switch array 100 are arranged such that at least one input/output port I/0_A', I/0_B< is operatively connected to an input/output port I/0_A, I/0_B of a second optical switch 10' . Likewise, at least one input/output port I/0_A, I/0_B will be operatively connected to the input/output port I/0_A-, I/0_B' of a third optical switch 10''. As shown in Figure 4, the optical switch 100 can switch light signals L_s from input/output ports I₀A, I₀B, I₀C, I₀D to input/output ports I₀A' , I₀B' , I₀C , I₀D' . The optical switch 100 will be controlled by sending the first signal Si and the second signal S₂ to each individual optical switch 10 within the optical switch array 100.

The first signal Si and the second signal S₂ to each of the optical switches 10 will be generated and applied by a supervisory control module 140 which controls the operation of optical switch 100. In order to ensure that a light signal L_s entering on any one of input/output ports IoA, IoB, IoC, IoD exits through the correct input/output port IoA' , I₀B' , I₀C , I₀D' , it is necessary that each of the optical switches 10 which the light signal L_s will pass has been correctly configured by the supervisory control module 140. The supervisory control module 140 will determine to which optical switch 10 the first signal S_x and the second signal S₂ should be applied based on either an address header or a frequency modulation identification of the light signal L_s indicating which input/output port I₀A' , IoB', IoC, I₀D' of the optical switch array 100 the light signal L_s should be switched to.

It is understood that optical switch arrays larger than the 4x4 optical switch array 100 are also possible. In particular, optical switch arrays of 16x16 and 256x256 have been used. In addition, 2048x2048 optical switch arrays comprising a plurality of optical switches 10 are possible without significant light loss.

It is understood that the light signal L_s can include any type of light signal carrying any type of information. In particular, the light signal L_s can include information such as uncompressed video signals, either high definition or broadcast quality format, and switched mass data services up to OC 192 (10 gigabits per second) per input I_A or I_B.

It will be understood that, although various features of the invention have been described with respect to one or another of the embodiments of the invention, the various features and embodiments of the invention may be combined or used in conjunction with other features and embodiments of the invention as described and illustrated herein.

Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to these particular embodiments. Rather, the invention includes all embodiments which are functional or mechanical equivalents of the specific embodiments and features that have been described and illustrated herein.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows :

1. An optical switch for routing a light signal to a first port or a second port, said optical switch comprising : a splitter cell for splitting the light signal into a first polarized signal having a first polarization and a second polarized light signal having a second polarized signal; a polarization changing device for changing the polarization of the first polarized light signal from the first polarization to the second polarization and for changing the polarization of the second polarized light signal from the second polarization to the first polarization when a light signal is applied to the polarization changing device and for not changing the polarization of the first light signal or the second polarization signal when a second signal is applied to the polarization changing device; a recombiner cell for recombining the first polarized light signal and the second polarized light signal into a recombined light signal; wherein the recombined light signal will travel toward the first port when the first signal is applied to the polarization changing device and the recombined light signal will travel toward the second port when the second signal is applied to the polarization changing device.

2. The optical switch as defined in claim 1 wherein the splitter cell directs the first polarized light signal onto a first light path and the splitter cell directs the second polarized light signal onto a second light path; and wherein the recombiner cell is located at an intersection of the first light path and the second light path.

3. The optical switch as defined in claim 1 wherein the splitter cell comprises a first polarization cell that is transparent to the first polarization and reflective to the second polarization.

4. An optical switch as defined in claim 3 wherein the first polarization cell comprises a plate of glass having a plurality of liquid crystal molecules arranged normal to the plate of glass, and, the light signal is incident to the first polarization cell at an angle of about 70° with respect to the ■ normal .

5. The optical switch as defined in claim 3 wherein the recombiner cell comprises a second polarization cell that is transparent to one and reflective to another of the first polarization or the second polarization; and wherein the second polarization cell recombines the first polarized light signal and the second polarized light signal into the recombined light signal by transmitting one of the polarized light signals and reflecting the other polarized light signal .

6. An optical switch as defined in claim 5 wherein the recombined light signal will travel in a direction corresponding to the direction of the polarized light signal which the second polarization cell transmits.

7. An optical switch as defined in claim 6 wherein the second polarization cell comprises a plate of glass having a plurality of liquid crystal molecules normal to the plate of glass, and, the first and second polarized light signals are incident to the second polarization cell at an angle of about 70° with respect to the normal.

8. An optical switch as defined in claim 2 wherein the first light path comprises a first permanent reflective surface that reflects the first polarized light signal from the splitter cell to the recombiner cell and wherein the second light path comprises a second permanent reflective surface that reflects the second polarized light signal from the splitter cell to the recombiner cell.

9. An optical switch as defined in claim 2 wherein the first signal and the second signal applied to the polarization changing device is applied by a supervisory control module; and wherein the supervisory control module determines whether to apply the first signal or the second signal based on either an address header or a frequency modulation identification of the light signal indicating a destination of the light signal.

10. An optical switch as defined in claim 2 wherein the polarization changing device comprises a first liquid crystal cell in the first light path and a second liquid cell in the second light path; and wherein applying the first signal to the first and second liquid cells causes the first liquid crystal cell to change the polarization of the first polarized light signal from the first polarization to the second polarization and causes the second liquid crystal cell to change the polarization of the second polarized light signal from the second polarization to the first polarization.

11. An optical switch as defined in claim 5 wherein the first polarization cell has a first surface and a second surface opposed to the first surface upon which the light signal can be incident; and wherein if the light signal is incident on the first surface when the first signal is applied the recombined light signal will travel towards the first output port, and, if the light signal is incident on the second surface when the first signal is applied, the recombined signal will travel towards the second output port.

12. An optical switch as defined in claim 11 wherein a second light signal can be incident on the second surface of the first polarization cell simultaneously as the light signal is incident on the first surface of the first polarization cell; and wherein the first polarization cell separates the light signal into the first polarized light signal travelling on the first light path and the second polarized light signal traveling on the second light path; wherein the first polarization cell separates the second light signal into a third polarized light signal travelling on the first light path and a fourth polarized light signal travelling on the second light path; wherein the second polarization cell recombines the first polarized light signal and the second polarized light signal into the recombined light signal travelling towards either the first port or the second port and the second polarized light signal recombines the third polarized light signal and the fourth polarized light signal into a second recombined light signal travelling towards the first port or the second port; and wherein the recombined light signal and the second recombined light signal will not travel toward the same port.

13. An optical switch as defined in claim 12 further comprising: a third port for receiving the light signal and a fourth port for receiving the second light signal.

14. An optical switch as defined in claim 13 wherein the second polarization cell separates a third light signal entering from the first port into a fifth polarized light signal having the first polarization and a sixth polarized light signal having the second polarization; wherein the polarization changing device changes the polarization of the fifth polarized light signal from the first polarization to the second polarization and changes the polarization of the sixth polarized light signal from the second polarization to the first polarization when the first signal is applied and does not change the polarization of the fifth and sixth polarized light signals when the second signal is applied; and wherein the first polarization cell recombines the fifth and sixth polarized signals into a third recombined light signal; and wherein the third recombined light signal will travel toward the third port when the first signal is applied to the polarization changing device and the third recombined signal will travel toward the fourth port when the second signal is applied to the polarization changing device.

15. An optical switch as defined in claim 13 wherein at least one of the third port and fourth port is operatively connected to a port of a second optical switch and at least one of the first port and second port is operatively connected to a port of a third optical switch such that the optical switch, the second optical switch and the third optical switch form part of an optical matrix of a plurality of optical switches.

16. A method of routing light signals, said method comprising steps of: separating the light signal into a first polarized light signal having a first polarization and a second polarized light signal having a second polarization; passing the first polarized light signal and the second polarized light signal through a polarization changing device which changes the first polarization to the second polarization and changes the second polarization to the first polarization when a first signal is applied to the polarization changing device and does not change the polarization of the first polarized light signal and the second polarized light signal when a second signal is applied to the polarization changing device; recombining the first polarized light signal having the first polarization and the second polarized light signal having the second polarization signal after they have passed through the polarization changing device into a recombined light signal; and applying the first signal to the polarization changing device to route the recombined light signal in a first direction and not applying the second signal to the polarization changing device to route of the recombined light signal to a second direction.

17. A method as recited in claim 16 further comprising the step of determining whether or not to apply the first signal or the second signal based on either an address header or a frequency modulation identification of the light signal indicating a destination of the light signal.

18. A method as recited in claim 16 further comprising the steps of: directing the first polarized light signal onto a first light path and directing the second polarized light signal onto a second light path; recombining the first polarized light signal and the second polarized light signal at an intersection of the first light path and the second light path such that the recombined light signal will travel in a direction of one of the polarized light signals depending on their polarization when they are recombined into the recombined light signal .

19. A system for routing light signals, said system comprising: an optical switch comprising: a splitter cell for splitting the light signal into a first polarized signal having a first polarization and a second polarized light signal having a second polarized signal; a polarization changing device for changing the polarization of the first polarized light signal from the first polarization to the second polarization and for changing the polarization of the second polarized light signal from the second polarization to the first polarization when a light signal is applied to the polarization changing device and for not changing the polarization of the first light signal or the second polarization signal when a second signal is applied to the polarization changing device; a recombiner cell for recombining the first polarized light signal and the second polarized light signal into a recombined light signal; wherein the recombined light signal will travel toward a first output port when the first signal is applied to the polarization changing device and the recombined light signal will travel toward a second output port when the second signal is applied to the polarization changing device; and a supervisory control for applying the first signal and the second signal to the polarization changing device.

20. A system as defined in claim 19 wherein the supervisory control module determines whether to apply the first signal or the second signal based on either an address header or a frequency modulation identification associated with the light signal and indicating a destination of the light signal.