JP3712400B2 - Optical time separation circuit and optical time separation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical time separation circuit for separating an optical time division multiplexing (OTDM) signal for each multiplexed channel, and an optical time separation method using the circuit.
[0002]
[Prior art]
In optical communication technology, it is difficult to directly receive an ultrahigh-speed optical signal with a modulation speed of, for example, 40 Gbit / s (gigabit / second) or more, due to the limit of the operation speed of a light receiving element or the like.
[0003]
For this reason, signal separation processing (Demultiplexing, hereinafter simply referred to as “Demux”) is performed to convert an ultrahigh-speed optical signal into a bit rate signal that can be directly received by a receiver.
[0004]
For example, an optical time separation circuit and an optical time separation method using an electroabsorption semiconductor optical modulator (hereinafter also simply referred to as EAM) are known (for example, see Non-Patent Document 1).
[0005]
[Non-Patent Document 1]
Scaleable 80Gbit / s OTDM using a modular architecture based on EA modulators ", HT Yamada et.al., Proceedings of ECOC2000, Vol. 1, Paper 1.3.5, pp. 47-48, 2000
[0006]
[Problems to be solved by the invention]
In a conventional optical time separation circuit, N EAMs are required to separate an input optical signal into N (N is a positive number of 2 or more) systems. Therefore, since the configuration of the optical time separation circuit becomes extremely large, it is inevitable to increase the size of the device including the optical time separation circuit. In addition, the manufacturing cost of the device including the optical time separation circuit increases.
[0007]
Accordingly, an object of the present invention is to provide an optical time separation circuit that enables downsizing of the device at a lower cost.
[0008]
[Means for Solving the Problems]
In order to achieve this object, the optical time separation circuit of the present invention has the following structural features.
[0009]
An optical branching unit having an input unit to which an optical time division multiplexing signal is input , and first and second branching unit output units that output the branched optical time division multiplexing signal, respectively , and a first branching unit output unit Connected to the connected clock recovery circuit and the second branching unit output unit, the splitter input unit to which the branched optical time division multiplexed signal is input and the branched optical time division multiplexed signal are separated. an optical demultiplexer having 2n pieces of demultiplexer output unit to output the wave, among the 2n demultiplexer output, two duplexers output portion and the first and second respectively connected And a single electroabsorption semiconductor light connected to the first and second circulators and electrically connected to the clock recovery circuit and driven by a clock signal supplied by the clock recovery circuit A modulator comprising a first circular The first demultiplexed signal output from the data is input, the first demultiplexed signal is output as a first separated signal that is optically separated, and the first demultiplexed signal is output from the second circulator. The second demultiplexed signal given a predetermined time delay corresponding to the channel to be separated is simultaneously input from a direction different from the direction in which the first demultiplexed signal is input, And n unit circuits each having an electroabsorption semiconductor optical modulator that outputs a demultiplexed signal as a second separated signal that is optically separated , and the first and second circulators output two demultiplexers. The input port connected to each part, the input / output port connected to each of the electro-absorption semiconductor optical modulators, and the output port connected to each of the external 2n receivers. , an electric field absorption type semiconductor optical modulator, black A clock signal input port connected to the clock recovery circuit, a first input / output port connected to the input / output port of the first circulator, and a second input connected to the input / output port of the second circulator. Input / output ports.
[0010]
According to the configuration of the optical time separation circuit of the present invention, the same number of Demux signals are separated by half the number of electroabsorption semiconductor optical modulators (EAM) as compared with the conventional optical time separation circuit. It can be received (detected) by a receiver. In addition, the device including the optical time separation circuit can be further downsized. In addition, the manufacturing cost of the device including the optical time separation circuit can be reduced.
[0011]
The light time separation method of the present invention includes the following steps. That is, the optical branching device includes a step of bifurcating an input optical signal that is time-division multiplexed into a first optical signal and a second optical signal.
[0012]
In the optical time separation method, the step of inputting the first optical signal to the input unit of the optical demultiplexer to output the 2n-system demultiplexed signal and the second optical signal to the clock recovery circuit are provided. And a step of supplying a clock signal regenerated by the clock regenerating circuit to n electroabsorption semiconductor optical modulators .
[0013]
Further, the optical time separation method inputs n first demultiplexed signals among 2n demultiplexed signals to input ports of n first circulators, and the remaining n second demultiplexed signals. A step of inputting a wave signal to input ports of n second circulators, an output of n first demultiplexing signals from input / output ports of the first circulator, and a second demultiplexing of n systems simultaneously. wave signal is output from the output port of the second circulator, and enter the first demultiplexing signals on the first input-output ports of the n electric field absorption type semiconductor optical modulator driven by the clock signal At the same time, the second demultiplexed signal given a predetermined time delay corresponding to the channel to be separated is applied to the second demultiplexed signal of the n electroabsorption semiconductor optical modulators. Input to the output port.
[0014]
Still further, the optical time separation method is such that the electroabsorption semiconductor optical modulator converts the inputted first demultiplexed signal into the time-separated first separated signal and the simultaneously inputted second demultiplexed signal. Is converted to a time-separated second separated signal, the first separated signal is input to the input / output port of the second circulator, and the second separated signal is input to the input / output port of the first circulator. Inputting, outputting a first separated signal from the output port of the second circulator, and outputting a second separated signal from the output port of the first circulator to separate the first and second separated signals; Inputting the separated signal to 2n receivers.
[0015]
According to the optical time separation method of the present invention, two systems of demultiplexed signals can be received by a receiver by being simultaneously incident on one electroabsorption semiconductor optical modulator (EAM) from different directions (opposite directions). Two different Demux signals can be obtained.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a configuration example and operation of an optical time separation circuit according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, only the shapes, sizes, and arrangement relationships of the respective constituent components are schematically shown to such an extent that the present invention can be understood, and the present invention is not particularly limited thereby. In the following description, specific configurations, conditions, numerical conditions, and the like may be used. However, these are merely preferred examples, and are not limited to these. In addition, it should be understood that the same components in the drawings used for the following description are denoted by the same reference numerals, and redundant description thereof may be omitted.
[0017]
FIG. 1 is a schematic block diagram for explaining a configuration example and operation of an optical time separation circuit according to the Demux of the present invention.
[0018]
The optical time separation circuit 10 includes an optical branching device 12. The optical branching unit 12 includes an input unit 14 to which an input optical signal time-division multiplexed on the input side is input, a first branching unit output unit 16a that outputs two branched optical signals, and a second branching unit. And an output unit 16b. An optical waveguide such as an optical fiber or a planar waveguide is connected to the input unit 14 of the branching device 12 from the outside. The external optical waveguide propagates an optical signal having a predetermined modulation speed generated by a transmission device (not shown) and inputs the optical signal to the input unit 14. A first optical waveguide 18, which is an optical waveguide (hereinafter simply referred to as an optical waveguide) composed of, for example, an optical fiber or a planar waveguide, is connected to the first branching device output portion 16 a of the branching device 12. Yes. One end of the second optical waveguide 19 is connected to the second branching unit output portion 16 b of the branching unit 12.
[0019]
The other end of the first optical waveguide 18 is connected to the input side of the clock recovery circuit 20. The other end of the second optical waveguide 19 is composed of, for example, an optical coupler that demultiplexes one input optical signal into an optical signal of 2n channels (n is a positive number of 1 or more). An input unit 22a of the optical demultiplexer 22 is connected.
[0020]
The optical demultiplexer 22 includes 2n output units 22b in addition to one input unit 22a. In this example, 2b of 22b-1, 22b-2, 22b-3, 22b-4, ..., 22b- (2n-1) and 22b-2n (in this example, n is a positive number of 3 or more). Output section 22b exists. These 2n output units are combined into n sets of output units each including two output units. Each output unit 22b is connected to an optical waveguide that propagates the demultiplexed optical signal.
[0021]
Hereinafter, in the connection between the components in the time separation circuit 10 of the present invention, the optical waveguide defined above will be used unless otherwise specified.
[0022]
The n sets of optical waveguides, each including two optical waveguides connected to each output unit 22b, are divided into n unit circuits 100 (100-1, 100-2, ..., 100-). n). That is, two optical waveguides for propagating two optical signals demultiplexed by the optical demultiplexer 22 are connected to the input side of one unit circuit 100.
[0023]
The clock recovery circuit 20 is electrically connected to each unit circuit 100 so as to generate a clock signal and supply the clock signal to each unit circuit 100. For example, when a B Gbit / s optical signal is input and a clock signal is supplied to n unit circuits, a B / 2n GHz clock signal may be supplied. At this time, the clock recovery circuit 20 and the unit circuit 100 may be connected with a delay circuit (not shown) including, for example, an RF amplifier interposed between connection paths therebetween. In this way, each clock signal can be input to the unit circuit 100 by giving an appropriate clock time delay to the clock signal input to each unit circuit 100. Therefore, in this way, it is not necessary to give a time delay to the optical signals input to the plurality of unit circuits 100. The specific configuration of the clock recovery circuit 20 can be a conventional configuration of a so-called clock recovery circuit, and a detailed description thereof will be omitted.
[0024]
The unit circuit 100 is connected to one end of each of two systems of optical waveguides that output the two systems of Demux signals processed by the unit circuit 100, and the other ends of these optical waveguides are different from the first to second nth. It is connected to the receiver 200 (200-1, 200-2, ..., 200- (2n)).
[0025]
Here, the configuration of the unit circuit 100 will be described with reference to FIG. FIG. 3 is a circuit block diagram showing one unit circuit in the optical time separation circuit. Note that the EAM described above is preferably applied as the intensity modulator 40 applied to the unit circuit 100 of the optical time separation circuit 10 of the present invention. However, the present invention is not limited to this, and a Mach Zehnder type intensity modulator using a semiconductor, LiNbO ₃ or the like can be applied.
[0026]
Since a conventionally known EAM configuration can be applied to the EAM itself, a detailed description of the specific configuration and a detailed description of the principle aspect will be omitted.
[0027]
As shown in FIG. 3, each of the separation circuits 100 (100-1, 100-2,..., 100-n) of the n unit circuits 100 includes the first and second circulators 32 (32-1). , 32-2, ..., 32-n), 34 (34-1, 34-2, ..., 34-n) and the intensity modulator 40 (40-1, 40-2, ...). 40-n). The first circulator 32 is connected to one output part of a set of output parts 22 b of the n sets of the optical demultiplexer 22. Therefore, the first demultiplexed signal 01 out of the first and second optical signals demultiplexed by the optical demultiplexer 22 is input to the first circulator 32. The first circulator 32 is further connected to the first input / output port 42 of the intensity modulator 40. The second input / output port 44 of the intensity modulator 40 is connected to the second circulator 34. The second circulator 34 is connected to the other output unit of the above-described one set of output units 22b. Among the first and second demultiplexed signals 01 and 02, the second demultiplexed signal 02 is Entered. The intensity modulator 40 is connected to the above-described clock recovery circuit 20 through an electrical path, and is supplied with a clock signal (see FIG. 2).
[0028]
Here, with reference to FIG. 2, in order to explain the connection relationship between the configurations of the unit circuit 100, the connection relationship of the first circulator 32, the second circulator 34, and the intensity modulator 40 of the unit circuit 100 will be described. To do.
[0029]
FIG. 2A is a schematic block diagram for explaining the configuration of the first circulator 32 of the unit circuit 100, and FIG. 2B shows the configuration of the second circulator 34 of the unit circuit 100. It is a schematic block diagram for demonstrating. FIG. 2C is a schematic block diagram for explaining the configuration of the intensity modulator 40 of the unit circuit 100.
[0030]
The first circulator 32 includes an input port 32a, an input / output port 32b, and an output port 32c. A first demultiplexed signal 01 which is one of the optical time division multiplexed signals demultiplexed by the optical demultiplexer 22 is input to the input port 32a. The input / output port 32b outputs the first demultiplexed signal 01 input to the input port 32a to the outside. The output port 32c outputs an optical signal different from the first demultiplexed signal 01 input to the input port 32a to the outside.
[0031]
Similarly, the second circulator 34 includes an input / output port 34a, an output port 34b, and an input port 34c. The input / output port 34a outputs the second demultiplexed signal 02 input from the input port 34c to the outside. Of the optical signals demultiplexed by the optical demultiplexer 22, the second demultiplexed signal 02 is input to the input port 34c. The output port 34b outputs an optical signal that is an optical signal different from the second demultiplexed signal 02 input to the input port 34c to the outside.
[0032]
The intensity modulator 40 includes first and second input / output ports 42 and 44 and a clock signal input port 46. The first input / output port 42 is connected to the input / output port 32 b of the first circulator 32. The second input / output port 44 is connected to the input / output port 34 a of the second circulator 34. The clock signal input port 46 is connected to the clock recovery circuit 22.
[0033]
Next, the operation of the optical time separation circuit 10 according to the first embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, and FIG.
[0034]
In this example, in the configuration example shown in FIG. 1, an optical signal of 80 Gbit / s (gigabit / second) obtained by time-division multiplexing four systems of optical signals is input to the optical time separation circuit 10 of the present invention. An example in which four 20 Gbit / s Demux signals are output to the first to fourth receivers 200-1 to 200-4 will be described.
[0035]
The optical time separation circuit 10 is an n-stage unit circuit 100 (100-1, 100-2,..., 100-n), here two unit circuits. 100, that is, the first unit circuit 100-1 and the second unit circuit 100-2 will be described.
[0036]
At this time, since the operations of the n-stage unit circuits 100 are the same, the specific operation will be described by taking a single unit circuit as an example in order to simplify the description.
[0037]
With reference to FIG. 1 and FIG. 3, the operation of the optical time separation circuit 10 of this embodiment will be described focusing on a single unit circuit 100. FIG.
[0038]
As shown in FIG. 1, an input optical signal having a modulation speed of 80 Gbit / s propagating through a transmission-side optical waveguide (not shown) is input to the optical time separation circuit 10 of the present invention. Specifically, this input optical signal is input from the input unit 14 of the optical branching device 12. The input optical signal is branched into two by the optical splitter 12 into a first optical signal 00A of 80 Gbit / s and a second optical signal 00B of 80 Gbit / s.
[0039]
The first optical signal 00A is output from the first branching unit output unit 16 a of the optical branching unit 12 and input to the input unit 22 a of the optical demultiplexing unit 22.
[0040]
Similarly, the second optical signal 00B is output from the second branching unit output unit 16 b of the optical branching unit 12 and input to the clock recovery circuit 20. The clock recovery circuit 20 outputs a clock signal recovered based on the input second optical signal 00B. This clock signal is supplied to each unit circuit 100 connected to the clock recovery circuit 20, that is, first and second intensity modulators (EAM) 40-1 and 40-2 in this example.
[0041]
The first and second intensity modulators 40-1 and 40-2 are driven by a 20 GHz (Gigahertz) clock signal supplied from the clock recovery circuit 20.
[0042]
On the other hand, the first optical signal input to the optical demultiplexer 22 is demultiplexed into four systems of 80 Gbit / s demultiplexed signals in this example.
[0043]
Among these, two systems of demultiplexed signals, that is, the first demultiplexed signal 01 and the second demultiplexed signal 02 are input to the single unit circuit 100.
[0044]
Here, referring to FIG. 2 (A) to FIG. 2 (C) and FIG. 3, the first and second circulators 32 and 34 to which the first and second demultiplexed signals 01 and 02 are inputted, and The operation of the intensity modulator 40 will be described.
[0045]
As shown in FIG. 2A, the first demultiplexed signal 01 is input to the input port 32 a of the first circulator 32. The input first demultiplexing signal 01 is output from the input / output port 32b. No modulation processing is applied to the demultiplexed signal and the separated signal passing through the first and second circulators 32 and 34 described below.
[0046]
As shown in FIG. 2C, the first demultiplexed signal 01 output from the input / output port 32 b of the first circulator 32 is input to the first input / output port 42 of the intensity modulator 40. .
[0047]
As described above, the 20 GHz clock signal regenerated by the clock regenerating circuit 20 is electrically input from the clock signal input port 46 to the intensity modulator 40.
[0048]
The intensity modulator 40 driven by the 20 GHz clock signal converts the 80 Gbit / s first demultiplexed signal 01 into a first separated signal 01A which is a 20 Gbit / s Demux signal.
[0049]
As shown in FIG. 2B, the converted first separated signal 01A is input to the input / output port 34a of the second circulator 34. The input first separation signal 01A is output from the output port 34b.
[0050]
The first separated signal 01A output from the second circulator 34 is input to the first receiver 200-1. As described above, since the first separated signal 01A is a 20 Gbit / s Demux signal, it can be received (detected) by the first receiver 200-1.
[0051]
On the other hand, as shown in FIG. 2B, the second demultiplexed signal 02 is input to the input port 34 c of the second circulator 34. The input second demultiplexed signal 02 is output from the input / output port 34a.
[0052]
As shown in FIGS. 2B and 2C, the second demultiplexed signal 02 output from the input / output port 34 a of the second circulator 34 is the second input / output of the intensity modulator 40. Input to port 44. In other words, the second demultiplexed signal 02 is input to the intensity modulator 40 from a port different from that of the first demultiplexed signal 01 and thus from a different direction (opposite direction). At this time, the timing at which the input second demultiplexed signal 02 is input to the intensity modulator 40 is adjusted. This timing adjustment is performed, for example, by adjusting the optical path length through which the second demultiplexed signal 02 propagates before being input to the intensity modulator 40, that is, by propagating an optical waveguide longer than the first demultiplexed signal 01. Is preferably performed.
[0053]
By performing such adjustment, the second demultiplexed signal 02 has a uniform timing with respect to the first demultiplexed signal 01 and a predetermined channel in order to separate the optical signal of the predetermined channel. The signal is given a suitable time delay according to the channel. For example, a case where optical signals of two adjacent channels are separated from one optical signal that is time-division multiplexed will be described as an example. For example, when the first demultiplexed signal 01 of 80 Gbit / s obtained by time-division multiplexing four systems of optical signals is separated into four systems of 20 Gbit / s Demux signals, the first demultiplexed signal The second demultiplexed signal 02 delayed by 12.5 ps (picosecond), which is one bit, may be input to the intensity modulator 40. Hereinafter, in the case of sequentially separating the optical signals of adjacent channels, the third demultiplexed signal is a signal delayed by 12.5 ps with respect to the second demultiplexed signal 02, and the fourth demultiplexed signal May be a signal delayed by 12.5 ps with respect to the third demultiplexed signal.
[0054]
If this example is generalized according to the configuration shown in FIG. 1, an input optical signal of B (Gbit / s) is demultiplexed into a demultiplexed signal of 2n (n is a positive number of 1 or more) system. . The 2n-th demultiplexed signal (n is a positive number greater than or equal to 1) is input as a signal that is delayed by one bit, that is, 1 / B (second) from the previous, that is, the 2n-1 demultiplexed signal. The
[0055]
However, by adjusting the time delay of the demultiplexed signal, signals of channels that are not adjacent to each other among the time-division multiplexed optical signals can be extracted by one unit circuit.
[0056]
FIG. 4 shows four 20 Gbit / s Demux signals obtained by dividing the first demultiplexed signal 01 which is an 80 Gbit / s optical time division multiplexed signal obtained by time division multiplexing four optical signals by the time separation circuit 10 of the present invention. It is a graph which shows the example isolate | separated into. In each graph, the vertical axis represents intensity, and the horizontal axis represents time (10 ps / div). FIG. 4A shows the first demultiplexed signal 01, and FIGS. 4B and 4C are graphs showing the first and second separated signals. In this case, a delay of 2 bits, that is, 25 ps was given between the two optical signals input to the intensity modulator 40 in different directions.
[0057]
As shown in FIG. 2C, the 20 GHz clock signal regenerated by the clock regenerating circuit 20 is electrically input from the clock signal input port 46 to the intensity modulator 40. The intensity modulator 40 driven by the 20 GHz clock signal converts the 80 Gbit / s second demultiplexed signal 02 into a second separated signal 02A which is a 20 Gbit / s Demux signal.
[0058]
As shown in FIG. 2A, the converted second separated signal 02A is input to the input / output port 32b of the first circulator 32. The second separated signal 02A input to the first circulator 32 is output from the output port 32c of the first circulator 32. The second separated signal 02A output from the first circulator 32 is input to the second receiver 200-2 and received (detected) by the second receiver 200-2. The second separated signal 02A is a 20 Gbit / s Demux signal different from the first separated signal 01A.
[0059]
【The invention's effect】
As described above, according to the optical time separation circuit 10 of the present invention, in a unit circuit including one intensity modulator, two systems of demultiplexed signals are directed to one intensity modulator (EAM) 40 in different directions (opposite directions). Simultaneously, two different Demux signals that can be received by the receiver 200 can be obtained.
[0060]
Therefore, compared with the conventional optical time separation circuit, the same number of Demux signals can be separated and received (detected) by the receiver by half the number of intensity modulators (EAM). In addition, the device including the optical time separation circuit can be further downsized. In addition, the manufacturing cost of the device including the optical time separation circuit can be reduced.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic block diagram for explaining a configuration example and operation of an optical time separation circuit according to Demux of the present invention.
FIG. 2A is a schematic block diagram for explaining a configuration of a first circulator of a unit circuit, and FIG. 2B is a schematic diagram for explaining a configuration example of a second circulator. It is a block diagram, (C) is a schematic block diagram for demonstrating the structure of EAM of a unit circuit.
FIG. 3 is a schematic block diagram focusing on one unit circuit for explaining the operation of the optical time separation circuit;
FIG. 4A is a graph showing a first demultiplexed signal, and FIGS. 4B and C are graphs showing first and second separated signals.
[Explanation of symbols]
00A: first optical signal 00B: second optical signal 01: first demultiplexed signal 01A: first separated signal 02: second demultiplexed signal 02A: second separated signal 10: optical time separation circuit 12: Optical branching device 14: Input unit 14a: Branching unit input unit 16: Output unit 16a: First branching unit output unit 16b: Second branching unit output unit 18: First optical waveguide 19: Second optical waveguide Waveguide 20: clock recovery circuit 22: optical demultiplexer 22a: input unit 22b: output unit 32: first circulator 32a, 34c: input port 32b, 34a: input / output port 32c, 34b: output port 34: second Circulator 40: Intensity modulator (EAM)
42: first input / output port 44: second input / output port 46: clock signal input port 100: unit circuit 200: receiver

Claims (5)

A first circulator to which the first demultiplexed signal is input out of the first and second demultiplexed signals obtained by demultiplexing the time-division multiplexed input optical signal by the optical demultiplexer ;
A second circulator to which the second demultiplexed signal is input;
A single electroabsorption semiconductor optical modulator electrically connected to a clock recovery circuit and driven by a clock signal supplied by the clock recovery circuit, the first optical output from the first circulator 1 demultiplexed signal is input, the first demultiplexed signal is output as a first separated signal that is time-separated, and is output from the second circulator, with respect to the first demultiplexed signal. Thus, the second demultiplexed signal given a predetermined time delay according to the channel to be separated is simultaneously input from a direction different from the direction in which the first demultiplexed signal is input, optical time separation circuit including a unit circuit equipped with said electric field absorption type semiconductor optical modulator for outputting the demultiplexed signals to the second separation signal light upon separation. An optical branching unit having an input unit to which an optical time division multiplexing signal is input, and first and second branching unit output units for outputting the branched optical time division multiplexing signal, respectively ;
A clock recovery circuit connected to the output of the first branching device;
2n connected to the second branching unit output unit to which the branched optical time division multiplexed signal is input and to demultiplex and output the branched optical time division multiplexed signal. An optical demultiplexer having a number of demultiplexer outputs;
Of the 2n duplexer output units, the first and second circulators connected to the two duplexer output units, respectively, and the first and second circulators, and A single electroabsorption semiconductor optical modulator that is electrically connected to a clock recovery circuit and is driven by a clock signal supplied by the clock recovery circuit, and is a first output from the first circulator. The first demultiplexed signal is input, the first demultiplexed signal is output as a first separated signal that is optically separated, and the second circulator outputs the first demultiplexed signal to the first demultiplexed signal. The second demultiplexed signal given a predetermined time delay according to the channel to be separated is simultaneously input from a direction different from the direction in which the first demultiplexed signal is input, and the second demultiplexed signal Signal light hour Is equipped with a n unit circuits having the electro-absorption type semiconductor optical modulator for outputting a second separated signal,
The first and second circulators include an input port connected to the two duplexer output units, an input / output port connected to the electroabsorption semiconductor optical modulator, and an external 2n And an output port connected to each of the receivers,
The electroabsorption semiconductor optical modulator includes a clock signal input port connected to the clock recovery circuit, a first input / output port connected to the input / output port of the first circulator, and the second An optical time separation circuit comprising: a second input / output port connected to the input / output port of the circulator. An optical branching device bifurcates the time-division multiplexed input optical signal into a first optical signal and a second optical signal;
Inputting the first optical signal to an input unit of an optical demultiplexer and outputting a 2n-system demultiplexing signal;
Inputting the second optical signal to a clock recovery circuit, and supplying the clock signal recovered by the clock recovery circuit to n electroabsorption semiconductor optical modulators ;
Of the 2n demultiplexed signals, the n first demultiplexed signals are input to the input ports of the n first circulators, and the remaining n second demultiplexed signals are input to the nth demultiplexed signals. Input to the input port of the circulator 2;
The n-system first demultiplexed signal is output from the input / output port of the first circulator, and simultaneously the n-system second demultiplexed signal is output from the input / output port of the second circulator. The first demultiplexed signal is input to first input / output ports of the n electroabsorption semiconductor optical modulators driven by the clock signal, and simultaneously with respect to the first demultiplexed signal Inputting the second demultiplexed signal given a predetermined time delay according to the channel to be separated to the second input / output ports of the n electroabsorption semiconductor optical modulators ;
The electroabsorption semiconductor optical modulator has a first separated signal that is time-separated from the input first demultiplexed signal, and a second that is time-separated from the second demultiplexed signal that is simultaneously input. Converting into two separate signals;
Inputting the first separated signal into an input / output port of the second circulator, and inputting the second separated signal into an input / output port of the first circulator;
The first separated signal is output from the output port of the second circulator, and the second separated signal is output from the output port of the first circulator to separate the first and second separated signals. And a step of inputting the separated signal to 2n receivers. The n-system first demultiplexed signal is output from the input / output port of the first circulator, and simultaneously the n-system second demultiplexed signal is output from the input / output port of the second circulator. The first demultiplexed signal is input to first input / output ports of the n electroabsorption semiconductor optical modulators driven by the clock signal, and simultaneously with respect to the first demultiplexed signal. In the step of inputting the second demultiplexed signal given a predetermined time delay according to the channel to be separated to the second input / output ports of the n electroabsorption semiconductor optical modulators,
4. The light according to claim 3, wherein different time delays are provided for each set of the first and second demultiplexed signals input to the single electroabsorption semiconductor optical modulator. 5. Time separation method. In the step of inputting the second optical signal to a clock recovery circuit and supplying the clock signal recovered by the clock recovery circuit to n electroabsorption semiconductor optical modulators ,
The n clock signals supplied to the n electroabsorption semiconductor optical modulators are given different time delays, and the n electroabsorption semiconductor optical modulators are driven at different timings. The optical time separation method according to claim 3, wherein:

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