JP4503496B2 - Optical transmission / reception system and optical reception circuit - Google Patents

Description

  The present invention relates to an optical transmission / reception system and an optical reception circuit for improving transmission / reception characteristics in a basic communication system of a communication carrier.

In a conventional backbone optical transmission / reception system, a method of transmitting logic “1” and “0” of digital data to be transmitted in correspondence with the intensity of light is generally used, and is widely used as an IM-DD system. In addition, the data signal itself is converted into light intensity and also modulated into the phase of light for the purpose of effective use of bands in wavelength division multiplexing transmission, transmission speed increase, and transmission distance extension. The addition method is also widely studied. For example, an optical duobinary signal (for example, Non-Patent Document 1) is known.
K. Yonenaga et al., "Dispersion-Tolerant Optical Transmission System Using Duobinary Transmitter and Binary Receiver", Journal of Lightwave Technology, vol.15, no.8, pp.1530-1537, 1997

  By the way, the purpose of phase modulation in the prior art is to reduce intersymbol interference and to compress the occupied band. On the other hand, in an optical duobinary signal or the like, a modulation pattern depending on a transmission data pattern is used for phase modulation. Therefore, it is possible to detect errors in the received data by reading the phase information with the receiver, but conventionally, it has not been used to improve the reliability of the received data and improve the transmission characteristics. It was.

  There is a method of superimposing transmission data only on the optical phase or on both the optical phase and the optical intensity, and a DPSK signal, a QPSK signal, and the like are known. However, these perform data transmission using only the optical phase or both the optical phase and the optical intensity. If the optical phase information is missing, correct information is not transmitted. On the other hand, the optical duobinary signal is different in that information can be transmitted only with light intensity.

  An object of the present invention is to provide an optical transmission / reception system and an optical reception circuit capable of improving the reliability of received data in an optical transmission / reception system for transmitting an optical duobinary signal.

A first aspect of the present invention is an optical transmission / reception system for transmitting an optical duobinary signal between an optical transmission circuit and an optical reception circuit that are connected to each other via an optical fiber transmission line. The optical reception circuit includes an optical fiber transmission line. The optical duobinary signal transmitted via the coupler is bifurcated, and the optical intensity of one of the bifurcated optical duobinary signals is identified by a threshold value, and binary (“0”, “1”) received data is output. The light intensity identification circuit to be connected and the other optical duobinary signal branched into two are input to a 1-bit delay interference circuit, divided into two paths, and one bit delay is given to one of them, and then the signals are combined again. "0" when both 2-bit light intensities are "0", "1" when one of the continuous 2-bit light intensities is "0" and the other is "1", continuous 2-bit light intensities Are both “1” and the two bits When the carrier phase difference is “0”, it is “2”, and when it is “π”, the light intensity is converted to light intensity corresponding to “0”, and the light intensity is identified by two thresholds to obtain a ternary value (“0”). , “1”, “2”), the optical phase identification circuit that outputs the signal and the reception data input from the optical intensity identification circuit are branched into two, one of which is output as a reception data signal, and the other reception data Is logically inverted by a logic inversion circuit, and the logic inversion output is input to a duobinary encoding circuit to generate a ternary (“0”, “1”, “2”) electric duobinary signal to identify the optical phase. When the output of the circuit and the output of the duobinary encoding circuit are input to the comparison circuit, and the output of the optical phase identification circuit is “2”, the output of the duobinary encoding circuit is “0” or “2”. There is no error in the bit, and the output of the duobinary encoding circuit is If it is “1”, the data determination circuit outputs an error detection signal as an error in the bit .

According to a second aspect of the present invention, there is provided an optical reception circuit of an optical transmission / reception system for transmitting an optical duobinary signal between an optical transmission circuit and an optical reception circuit that are connected to each other via an optical fiber transmission line, and the optical transmission line is connected to The optical duobinary signal transmitted in this way is separated into two couplers, and the optical intensity of one of the two branched optical duobinary signals is identified by a threshold value, and binary (“0”, “1”) received data is output. The optical intensity identification circuit and the other two optical duobinary signals branched into two are input to a 1-bit delay interferometer circuit, divided into two paths, a 1-bit delay is given to one of them, and then combined again to obtain 2 “0” when the light intensity of both bits is “0”, “1” when one of the continuous 2-bit light intensities is “0” and the other is “1”, and the continuous 2-bit light intensity is Both are “1” and the 2-bit light When the phase difference of the carrier is “0”, the light intensity is converted to light intensity corresponding to “0” when the phase difference is “2” and “π”, and the light intensity is identified by two threshold values to obtain a ternary value (“0”). , “1”, “2”), the optical phase identification circuit that outputs the signal and the reception data input from the optical intensity identification circuit are branched into two, one of which is output as a reception data signal, and the other reception data Is logically inverted by a logic inversion circuit, and the logic inversion output is input to a duobinary encoding circuit to generate a ternary (“0”, “1”, “2”) electric duobinary signal to identify the optical phase. When the output of the circuit and the output of the duobinary encoding circuit are input to the comparison circuit, and the output of the optical phase identification circuit is “2”, the output of the duobinary encoding circuit is “0” or “2”. The bit is correct and the output of the duobinary encoding circuit is “ If it is 1 ″, the data determination circuit outputs an error detection signal as an error of the bit .

According to a third aspect of the present invention, in the optical receiver circuit of the second aspect , the data determination circuit inputs the output of the optical phase identification circuit input to the comparison circuit in two branches, and the output of the optical phase identification circuit is “2”. If so, a reset comparison circuit for resetting the value of the memory in the duobinary encoding circuit to “1” is provided.

  The present invention reproduces received data from an optical duobinary signal by the IM-DD method, reads optical phase information corresponding to transmission information included in the optical duobinary signal, and compares it with the received data. It is possible to determine whether the received data of each unit is correct. Thereby, the reliability of received data can be improved and transmission characteristics can be improved.

(Embodiment of optical transmission / reception system)
FIG. 1 shows an embodiment of an optical transmission / reception system of the present invention. In the figure, an optical transmission circuit 100 and an optical reception circuit 200 are connected to each other via an optical fiber transmission line 300. The optical transmission circuit 100 is configured to transmit an optical duobinary signal.

  The optical receiving circuit 200 reproduces the received data from the optical duobinary signal transmitted via the optical fiber transmission line 300 in two branches and the one of the two branched optical duobinary signals by direct detection as usual. The optical intensity identification circuit 220, the optical phase identification circuit 230 that performs optical phase identification from the other optical duobinary signal that has been bifurcated, the received data reproduced by direct detection in the optical intensity identification circuit 220, and the optical phase identification circuit 230 A data determination circuit 240 that compares the obtained optical phase identification results and detects an error in the received data.

(Embodiment of optical receiver circuit)
FIG. 2 shows an embodiment of the optical receiver circuit of the present invention. As shown in FIG. 1, the optical receiver circuit includes a coupler 210, a light intensity identification circuit 220, an optical phase identification circuit 230, and a data determination circuit 240.

  The light intensity identification circuit 220 identifies a photodetector (PD) 221 that performs OE conversion of an optical duobinary signal and a space mark of the electrical signal, and converts it into binary (“0”, “1”) received data. It comprises an identification circuit 222 for conversion.

  The optical phase identification circuit 230 divides the input optical duobinary signal into two paths, gives a 1-bit delay to one of them, and then multiplexes them again to convert the optical phase change into a light intensity change. 231, a photodetector (PD) 232 that performs OE conversion of the light intensity signal, and the intensity of the electric signal, and outputs a ternary (“0”, “1”, “2”) signal 3 The value identification circuit 233 is configured.

  Here, if there is no distortion or noise in the received signal, the light intensity signal output from the 1-bit delay interference circuit 231 is a ternary signal. However, in practice, since a voltage width is generated in each signal level due to distortion or noise during transmission, the ternary identification circuit 233 outputs a ternary signal corresponding to two threshold values as shown in FIG. At this time, as shown in FIG. 4, the light intensity signal is “2” only when the light intensity of the received signal pulse is “1” continuously for 2 bits or more and the optical phase between the pulses does not change. Become. Note that the left of each 2 bits is temporally previous, the light phase “−” is indefinite because the light intensity is “0”, and the output level “−” varies depending on the value of the previous bit.

  On the other hand, according to the sign rule of the optical duobinary signal shown in FIG. 5, the optical phase between adjacent pulses where the light intensity is continuously “1” does not change (* in the figure). Therefore, error detection can be performed by comparing the change in light intensity obtained by the light intensity identification circuit 220 with the output of the optical phase identification circuit 230.

  FIG. 6 shows a first configuration example of the data determination circuit 240. In the figure, the output (reception data) of the light intensity identification circuit 220 is branched into two, and one of them is output as it is as a reception data signal as in the conventional IM-DD transmission / reception system. The other received data is input to the duobinary encoding circuit 242 via the logic inversion circuit 241 and converted into a ternary electric duobinary signal in the same manner as the optical duobinary signal generated by the optical transmission circuit 100. The output of the optical phase identification circuit 230 and the output of the duobinary encoding circuit 242 are compared by the comparison circuit 243, and the result is output as an error detection signal. Note that the configuration of the duobinary encoding circuit 242 is general, and an example in which the duobinary encoding circuit 242 includes an exclusive OR circuit (EXOR), two memories (T), and an adder circuit (+) is shown here.

  Here, in the optical duobinary signal, two of the three values (“0”, “2”) are transmitted as “0” and “π” of the optical phase. Therefore, if the binary reception data matches the binary transmission data, the ternary signal output from the duobinary encoding circuit 242 based on the binary transmission data is the output signal of the optical phase identification circuit 230. Will match. However, as shown in FIG. 4, when the adjacent optical pulse is “0”, the optical phase cannot be read by the 1-bit delay interference circuit 231. However, it is possible to check whether there is an error in the received data at least for this part.

  The error detection process will be described in detail with reference to FIGS. First, binary values “0” and “1” are given as transmission data by electrical signals. The optical intensity of the optical duobinary signal transmitted from the optical transmission circuit 100 is binary and coincides with “0” and “1” of the transmission data. The optical phase of the optical duobinary signal changes binary between “0” and “π” according to the optical duobinary encoding rule. The light intensity identification circuit 220 restores received data from only the light intensity. The optical phase identification circuit 230 outputs “2” only when the optical phases of adjacent pulses are equal. Therefore, when the output of the optical phase identification circuit 220 is “2” and the output of the duobinary encoding circuit 242 is “0” or “2”, the bit is correctly received from both the light intensity and the optical phase. Can be verified. On the other hand, as shown in FIG. 8, when the output of the optical phase identification circuit 220 is “2” and the output of the duobinary encoding circuit 242 is “1”, the bit is determined to be an error, and error detection is performed. A signal is output.

  FIG. 9 shows a second configuration example of the data determination circuit 240. Since the duobinary encoding circuit 242 of the data determination circuit 240 has a memory (T) therein and an error of a certain bit may propagate, it is necessary to reset the memory contents at an appropriate timing. 9 includes a reset comparison circuit 245 that branches and inputs the output of the optical phase identification circuit 220. When the output of the optical phase identification circuit 220 indicates “2”, data “1” is input. The value held in the memory (T) is reset to “1”.

The figure which shows embodiment of the optical transmission / reception system of this invention. The figure which shows embodiment of the optical receiver circuit of this invention. The figure which shows the example of identification of the ternary identification circuit 233. The figure which shows the input-output example of the optical phase identification circuit 230. The figure which shows the state transition of an optical duobinary signal. The figure which shows the 1st structural example of the data determination circuit 240. FIG. The figure explaining the example of error detection operation. The figure explaining the example of error detection operation. The figure which shows the 2nd structural example of the data determination circuit 240. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Optical transmission circuit 200 Optical reception circuit 210 Coupler 220 Light intensity identification circuit 221 Photodetector (PD)
222 Identification Circuit 230 Optical Phase Identification Circuit 231 1-bit Delay Interference Circuit 232 Photodetector (PD)
233 Tri-level identification circuit 240 Data determination circuit 241 Logic inversion circuit 242 Duobinary encoding circuit 243 Comparison circuit 245 Reset comparison circuit

Claims (3)

In an optical transmission / reception system that transmits an optical duobinary signal between an optical transmission circuit and an optical reception circuit that are oppositely connected via an optical fiber transmission line,
The optical receiving circuit is:
A coupler for bifurcating an optical duobinary signal transmitted through the optical fiber transmission line;
A light intensity identification circuit for identifying the light intensity of one of the two branched optical duobinary signals with a threshold value and outputting binary (“0”, “1”) received data ;
The other two-duplex optical duobinary signal is input to a 1-bit delay interference circuit, divided into two paths, and after one-bit delay is given to one of them, the signals are combined again to obtain continuous 2-bit light intensity. “0” when both are “0”, “1” when one of the continuous 2-bit light intensities is “0” and the other is “1”, and both the continuous 2-bit light intensities are “1” When the phase difference of the 2-bit optical carrier is “0”, the light intensity is converted to light intensity corresponding to “0” when the phase difference is “2” and “π”, and the light intensity is identified by two threshold values. An optical phase identification circuit for outputting a signal of a value (“0”, “1”, “2”) ;
The reception data input from the light intensity identification circuit is branched into two, and one of them is output as a reception data signal, the other reception data is logically inverted by a logic inversion circuit, and the logic inversion output is a duobinary encoding circuit. To generate a ternary (“0”, “1”, “2”) electric duobinary signal, and input the output of the optical phase discrimination circuit and the output of the duobinary encoding circuit to the comparison circuit. When the output of the optical phase identification circuit is “2”, if the output of the duobinary encoding circuit is “0” or “2”, there is no error in the bit, and the output of the duobinary encoding circuit And a data decision circuit for outputting an error detection signal as an error if the bit is "1" . In an optical receiver circuit of an optical transmission / reception system that transmits an optical duobinary signal between an optical transmitter circuit and an optical receiver circuit that are oppositely connected via an optical fiber transmission line,
A coupler for bifurcating an optical duobinary signal transmitted through the optical fiber transmission line;
A light intensity identification circuit for identifying the light intensity of one of the two branched optical duobinary signals with a threshold value and outputting binary (“0”, “1”) received data ;
The other two-duplex optical duobinary signal is input to a 1-bit delay interference circuit, divided into two paths, and after one-bit delay is given to one of them, the signals are combined again to obtain continuous 2-bit light intensity. “0” when both are “0”, “1” when one of the continuous 2-bit light intensities is “0” and the other is “1”, and both the continuous 2-bit light intensities are “1” When the phase difference of the 2-bit optical carrier is “0”, the light intensity is converted to light intensity corresponding to “0” when the phase difference is “2” and “π”, and the light intensity is identified by two threshold values. An optical phase identification circuit for outputting a signal of a value (“0”, “1”, “2”) ;
The reception data input from the light intensity identification circuit is branched into two, and one of them is output as a reception data signal, the other reception data is logically inverted by a logic inversion circuit, and the logic inversion output is a duobinary encoding circuit. To generate a ternary (“0”, “1”, “2”) electric duobinary signal, and input the output of the optical phase discrimination circuit and the output of the duobinary encoding circuit to the comparison circuit. When the output of the optical phase identification circuit is “2”, if the output of the duobinary encoding circuit is “0” or “2”, there is no error in the bit, and the output of the duobinary encoding circuit And a data decision circuit for outputting an error detection signal as an error if the bit is "1" . The optical receiver circuit according to claim 2,
The data determination circuit inputs the output of the optical phase identification circuit that is input to the comparison circuit in two branches. If the output of the optical phase identification circuit is “2”, the data determination circuit in the duobinary encoding circuit An optical receiver circuit comprising a reset comparison circuit for resetting a memory value to “1”.

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