JP3180962B2 - Light separation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical demultiplexer used in an optical communication apparatus, and more particularly, to an ultra-high-speed optical signal having a bit rate of 10 Gb / s or more and a plurality of channels having a low bit rate. The present invention relates to an optical demultiplexing device for demultiplexing into an optical signal train.

[0002]

2. Description of the Related Art In an optical communication system currently in practical use, data is time-division multiplexed in an electronic circuit in order to increase the transmission line capacity.
Data transmission of 1.8 Gb / s has been realized. Defeat the current electronic circuit's response speed limit (10-20 Gb / s)
As means for achieving higher multiplexing, a method of optically performing time division multiplexing / demultiplexing of data has been considered.

[0003] In this method, a short optical pulse train having a small duty ratio is modulated by an external modulator and data is added thereto, and the data is optically added (multiplexed) to several channels to obtain a high bit rate. In this method, an optical signal train is created and transmitted, and after transmission, it is optically separated for each original channel.
Optical multiplexing of an optical short pulse train can be easily performed by using an optical star coupler, even if the loss does not matter.

[0004] On the other hand, optical separation requires a very high-speed optical gate. To achieve this, an electro-optical effect or an optical card has been described as described below.
A method of using a 2 × 2 optical switch using the (Kerr) effect has been proposed.

FIG. 2 is a diagram for explaining a conventional optical demultiplexer, and shows an example of a configuration in which an optical signal multiplexed by four channels is demultiplexed for each channel. In FIG.
1, 2 and 3 are 2 × 2 optical switches and 2 × 2 optical switches 1
Each of the two output ports is connected to one input port of a 2.times.2 optical switch 2,3. The 2 × 2 optical switches 1, 2, and ₃ change the optical path length of a Mach-zehnder interferometer formed on a LiNbO ₃ crystal by applying an electric field by an electro-optic effect. Alternatively, an interferometer formed of an optical fiber and changing the optical path length through an optical Car effect by transmitting a high-intensity optical pulse is used.

[0006] Regarding the light separating device using the former, RS
“16Gb / s fibertransmission experi” by Tucker et al.
ment using optical time-division multiplexing ”, E
Electronics Letters, vol. 23, pp. 1270-1271, 1987. Regarding the optical separation device using the latter, Takada et al., “Demultiplexing of 40-Gb /
s optical signal to 2.5 gb / s using a nonlinear fib
er loop mirror driven by amplified, again-switched
laser diode ”, Technical digest of OFC'91, YuN
3,1991.

In the configuration of FIG. 2, four channels (C1, C2,
C3, C4) Time-division multiplexed bit rate Mb / s optical signal M
The SC is input to the 2 × 2 optical switch 1 via one of the input ports. The 2 × 2 optical switch 1 has a frequency of M / 2.
(Hz), the input optical signal is alternately output to two output ports. Therefore, the optical signal train MSC of channel C1 and channel C3 is output from one output port of the 2 × 2 optical switch 1.
(1, 3) are output, and the optical signal trains MSC (2, 4) of channel C2 and channel C4 are output from the other output port, respectively, and the 2 × 2 optical switches 2, 3 at the next stage, respectively. Is input to

The 2 × 2 optical switches 2 and 3 have a frequency of M / 4.
(Hz), the input optical signal is alternately output to two output ports. Therefore, the optical signal SC1 of the channel C1 is output from one output port of the 2 × 2 optical switch 2, and the optical signal SC3 of the channel C3 is output from the other output port. Similarly, the optical signal SC2 of the channel C2 is output from one output port of the 2 × 2 optical switch 3, and the optical signal SC4 of the channel C4 is output from the other output port.

[0009]

However, since a 2 × 2 optical switch utilizing the electro-optic effect needs to be driven at a frequency of at most half the transmission bit rate, the transmission bit rate is low. As the number increases, optical switches capable of responding at a higher speed and electric transmitters and amplifiers with higher frequencies must be prepared.

Also, the 2 × 2 optical switch utilizing the optical car effect has a very large peak power and requires the provision of a highly repetitive ultrashort optical pulse. However, integration is difficult.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical switch or an optical switch having a relatively narrow band despite being suitable for integration and capable of operating at a very high speed.
It is an object of the present invention to provide an optical demultiplexing device which can use a high frequency and does not require a high frequency electric transmitter or amplifier.

[0012]

In order to achieve the above object, according to the present invention, the time rate multiplexed bit rate is M
1. An optical demultiplexer that divides an optical signal at a bit rate of 2 bits into an optical signal stream of 2 ^N channels at a bit rate of M / 2 ^N bits / sec and outputs the signal, and divides an input optical signal into two and outputs the signal. An optical coupler and two optical gates arranged on two output sides of the 1 × 2 optical coupler, the phase difference between the two being set to π, and the output of the 1 × 2 optical coupler being turned on / off at a set frequency and output. 1 input 2 output light separation device as one unit,
2N-1 (N is an integer of 2 or more ) 1-input / 2-output optical demultiplexers are cascade-connected by N stages in a tree form, and 2 ⁿ (n is an integer of N or less) n-th stages the on-off frequency of the optical gate, an optical separation device set to M / 2 ^n, the optical gates off at a frequency of the n-th M / 2 ^n, is turned on and off at a frequency of M / 2 n + ¹ characterized in that the two optical gates constructed by cascade connection.

According to a second aspect of the present invention, a time-division multiplexed optical signal having a bit rate of M bits / sec is converted to a bit rate of M / sec.
What is claimed is: 1. An optical demultiplexer that divides an optical signal stream into 2 ^N- bit / sec 2 ^N- channel optical signal streams and outputs the divided optical signal streams. 1 × 2 arranged on two output sides, the phase difference between each other is set to π
A 1-input 2-output optical separation device consisting of two optical gates for turning on and off the output of the optical coupler at a set frequency is defined as 1 unit and 2N-1 (N is an integer of 2 or more ) 1-input 2-output. Light separation devices are connected in tandem in a tree shape by N stages,
And, n-th stage (n is N an integer) 2 ⁿ pieces of off frequency of the optical gates of the optical separation device set to M / 2 ^n, off at a frequency of the n-th M / 2 ⁿ An optical gate to be constructed by cascading two Mach-Zehnder type intensity modulators or directional coupler type intensity modulators, and setting each operating point to a voltage at which the modulator output is zero, M
/ 2 ^{n + 2} .

According to a third aspect of the present invention, a time-division multiplexed optical signal having a bit rate of M bits / sec is converted to a bit rate of M / sec.
What is claimed is: 1. An optical demultiplexer that divides an optical signal stream into 2 ^N- bit / sec 2 ^N- channel optical signal streams and outputs the divided optical signal streams. 1 × 2 arranged on two output sides, the phase difference between each other is set to π
A 1-input 2-output optical separation device consisting of two optical gates for turning on and off the output of the optical coupler at a set frequency is defined as 1 unit and 2N-1 (N is an integer of 2 or more ) 1-input 2-output. Light separation devices are connected in tandem in a tree shape by N stages,
And, n-th stage (n is N an integer) 2 ⁿ pieces of off frequency of the optical gates of the optical separation device set to M / 2 ^n, off at a frequency of the n-th M / 2 ⁿ The optical gate is constructed by cascading two Mach-Zehnder type intensity modulators or directional coupler type intensity modulators, and setting each operating point to a voltage at which the modulator output is zero. , setting the modulation amplitude to approximately 2 ^1/2 [pi, and drives at a frequency of M / ² n + 2.

[0015]

According to the first aspect, time-division multiplexed bit recording is performed.
An optical signal with a rate of M bits / sec is a 1 × 2 optical cup at each stage.
And each divided optical signal is cascaded by two
Is input to the optical gate connected to the. Two columns in the nth row
Connected optical gate to - an input optical signal to the metropolitan, circumference of M / 2 ⁿ
It is turned on and off at the wave number. As a result, the bit rate becomes 1
/ 2,1 / 4, it is to go down one after the other and ... 1/2 ^N
And the light gates connected in a two-stage cascade
On and off in opposite phases, and on and off as a whole
Since it is turned on and off at twice the return frequency,
The number can be doubled. By the above operation, the time-division multiplexed optical signal has a bit rate of M / ^2N bits.
/ S 2 ^N channel optical signal train.

Further, according to claim 2, n-th M / 2
^The optical gate composed of a Mach-Zehnder type intensity modulator or a directional coupler type intensity modulator which is turned on / off at a frequency of ⁿ has an operating point set to a voltage at which the modulator output is zero, and M / 2 ^{n + 2} Driven at a frequency of

Further, according to claim 3, n-th M / 2
^The optical gate composed of a Mach-Zehnder type intensity modulator or a directional coupler type intensity modulator which is turned on / off at a frequency of ⁿ has an operating point set to a voltage at which the modulator output is zero and a modulation amplitude. It is set to approximately 2 ^1/2 π, M
/ 2 ^{n + 2} Driven at a frequency of

[0018]

FIG. 1 is a block diagram showing a first embodiment of an optical demultiplexer according to the present invention, and shows an example of a configuration in which an optical signal multiplexed by four channels is demultiplexed for each channel. In the figure, 1 0 the optical amplifier, 1 × 2 optical cut is 11, 14, 15
Pula, 12,13,16,17,18,19 is light On'ofuge - door (hereinafter, Tan'nihikarige - that the door) is.

The optical amplifier 1 0 is, for example semiconductor laser - is constituted by Zaanpu or rare-earth-doped fiber amplifiers, are 4-channel time division multiplex from the transmission line optical signal M
The SC is amplified with a predetermined gain.

The 1 × 2 optical coupler 11 has an input port connected to the output of the optical amplifier 10 and two output ports connected to the input sides of the optical gates 12 and 13, respectively. The input optical signal is split into two approximately one-to-one.

The 1 × 2 optical coupler 14 has an input port connected to the output side of the optical gate 12, and two output ports connected to the input sides of the optical gates 16 and 17, respectively. And divides the input optical signal into two approximately one-to-one.

Similarly, the 1 × 2 optical coupler 15 has an input port connected to the output side of the optical gate 13 and two output ports connected to the input sides of the optical gates 18 and 19, respectively. They are connected to each other, and divide the input optical signal into two almost one-to-one.

The optical gates 12, 13, 16 to 19 are, for example, an optical intensity modulator using a Mach-Zehnder interferometer, a 2 × 2 optical switch using a Mach-Zehnder interferometer, and a directional coupler. , A 2 × 2 optical switch using a directional coupler, a light intensity modulator using absorption in a semiconductor, and the like. Of these light gates, light gate 12,
Reference numeral 13 turns on / off the input optical signal at a frequency M / 2, and the two optical gates operate with a phase difference of π from each other.
The optical gates 16 to 19 turn on / off the input optical signal at a frequency of M / 4 Hz.

Next, the operation of the above configuration will be described.

The four-channel (C1, C2, C3, C4) time-division multiplexed bit rate Mb / s optical signal MSC is supplied to the optical amplifier 1
After receiving a predetermined amplification action at 0, the 1 × 2 optical coupler 11
Is input to The optical signal MSC is a 1 × 2 optical coupler 11
The light is divided into two approximately one-to-one and output to two output ports, which are input to the optical gates 12 and 13, respectively. In the optical gates 12 and 13, the input signal is turned on and off at a frequency M / 2, and since the two optical gates 12 and 13 operate with a phase difference of π from each other, one of the optical gates 12 and 13 operates. , An optical signal is output every other channel, and the other optical gate 13 outputs the remaining optical signals similarly every other channel.

By the above operation, the time-division multiplexed optical signal MSC is converted into a two-channel optical signal train MSC (1, 3) and MSC (2, 4) having a bit rate of 1/2. . Two-channel optical signal train MSC (1, 3) and M
The SC (2, 4) is then input to the 1 × 2 optical couplers 14 and 15, respectively, and is split into two on a one-to-one basis . 1 × 2 light mosquitoes
Optical signal M output from the two output ports of the coupler 14
SC (1,3) is input to the optical gates 16,17, respectively. Similarly, the optical signals MSC (2, 4) output from the two output ports of the 1 × 2 optical coupler 15 are connected to the optical gates.
Are input to the ports 18 and 19, respectively.

In the two optical gates 16 and 17 connected to the 1 × 2 optical coupler 14, the input signal is turned on and off at a frequency M / 4, and the two optical gates 16 and 17 have a phase difference of π. , The bit rate is reduced to 1/4, and the optical signal S of the channel C1 is output from one of the optical gates 16.
C1 is output, and channel C is output from the other optical gate 17.
3 is output.

Similarly, in the two optical gates 18 and 19 connected to the 1 × 2 optical coupler 15, the input signal is turned on and off at a frequency M / 4, and the two optical gates 18 and 19 are turned on and off.
Operate with a phase difference of π, so that the bit rate is 1
The optical signal SC2 of the channel C2 is output from one of the optical gates 18, and the optical signal SC4 of the channel C4 is output from the other optical gate 19.

As described above, according to the first embodiment, a 1 × 2 optical coupler and a 1-input 2-output optical separation device from the optical gates arranged on the two output sides are provided. 1 unit, 3 (2N-1 (N is an integer of 2 or more )) 1
By connecting two stages of unit light splitters having two inputs and two outputs in cascade in a so-called tree form, a light splitter having one input and four outputs is constructed. 2 and the second-stage optical gates 16 to 19 are turned on and off at a frequency of M / 4, so that the bit rate of M bits / second of the four-channel time-division multiplexed optical signal MSC is calculated. As a result, the four-channel optical signal S divided into each channel can be reduced.
C1, SC2, SC3, and SC4 can be obtained.

The division loss of 3 dB by the 1 × 2 optical coupler or the excessive insertion loss of the optical gate is reduced by the optical amplifier 10.
Can be compensated.

Although the first embodiment has been described in connection with the case where a four-channel time-division multiplexed signal is separated into four channels, a similar optical signal is used to separate a ^2N- channel multiplexed signal. The coupler and the optical gate are connected in an N-stage tree shape, and the optical gate at the n-th stage (n is an integer equal to or less than N) is denoted by M.
By turning on and off at a frequency of / ^2N , the bit rate can be reduced in order of 1/2, 1/4, ... 1 / ^2N .

FIG. 3 is a block diagram showing a second embodiment of the light separating device according to the present invention. FIGS. 4A and 4B show light gates (intensity modulation) used in FIG. FIG. 7 is a diagram for explaining the operation of the device.

The second embodiment is different from the first embodiment in that a light gate arranged on the output side of the first stage 1 × 2 optical coupler 11 is a light which is turned on / off at a frequency of M / 2. Instead of one gate, two optical gates that are turned on and off at the frequency of M / 4 are connected in cascade, and the phases of both are shifted by π. The operating points of the light gates 12a, 12b, 13a and 13b, which are optical intensity modulators using modulators, are reduced to half the voltage of the modulator output as shown by point A in FIG. I have set it. The curve 1 in FIG.
Reference numeral 00 denotes an optical output characteristic with respect to an applied voltage of an optical intensity modulator or a 2 × 2 optical switch using a Mach-Zehnder interferometer or a directional coupler, and a curve 101 represents a time waveform of the applied voltage.

With such a configuration, the single light gates 12a, 12b, 12c, and 12d are turned on / off at a frequency of M / 4, but as a whole M / 2.
The modulation band can be doubled by connecting two cascaded modulators even in a narrow band.

FIG. 4 shows how the modulation band is increased. In the figure, curves 102 and 103 show the modulation waveforms of the first and second optical gates (modulators) alone, and curve 104 shows the modulation waveform when these are connected in cascade.

FIG. 5 is a block diagram showing a third embodiment of the light separating device according to the present invention. FIGS. 6A and 6B show light gates (intensity modulation) used in FIG. FIG. 7 is a diagram for explaining the operation of the device.

The third embodiment differs from the second embodiment in that each of the light gates 12a, 12b, 13a, 13b,
Optical gates 12a and 12b, which are Mach-Zehnder interferometers or cascaded light intensity modulators using directional couplers, which are turned on and off at a frequency M / 8 instead of turning on and off 16 to 19 at a frequency of M / 4. , 13a, and 13b are set to a voltage at which the modulator output is zero.

A curve 110 in FIG. 6A shows an optical output characteristic with respect to an applied voltage of a light intensity modulator or a 2 × 2 optical switch using a Mach-Zehnder interferometer or a directional coupler, and a curve 111 shows an applied voltage. The time waveform of the voltage is shown.

When the operating point is set to the point A where the output is off, the light output changes by two periods within one period of the applied voltage. Therefore, two light intensity modulators to which a sine wave voltage having a frequency of M / 8 is applied instead of one light gate which is turned on and off at a frequency of M / 2 used in the configuration of the first embodiment. By connecting in tandem and shifting the phase of both by π, the single light gate can be turned on and off at the frequency of M / 2 as a whole, despite turning on and off at the frequency of M / 8, The modulation band can be increased four times.

FIG. 6 shows how the modulation band is increased. In the figure, curves 112 and 113 show the modulation waveforms of the first and second optical gates (modulators) alone, and curve 114 shows the modulation waveform when these are connected in cascade.

The curve 114 is given by the following equation, where m is the phase difference amplitude and t is the time, so that I = 1/4 [1-cos (msin 2πt)] [1-cos (msin ( 2πt + π / 2))] when m is 2 ^1/2 [pi, the light output I is 1, i.e., all input is output without loss. Therefore, the phase difference amplitude m is 2 ^1/2 π
By driving with an applied voltage such that the following applies, even if two intensity modulators (optical gates) are connected in tandem, the input optical signal can be turned on and off at a frequency four times the driving frequency without loss.

[0042]

As described in the foregoing, according to claim 1, bit rate - preparative 1 / 2,1 / 4, ... 1 /2 N and turn
And the repetition frequency
It can be doubled and uses a light gate with a relatively narrow band.
However, a double modulation band can be obtained. Therefore,
If such a light gate is used in a light separation device, separation can be achieved.
In spite of the fact that the bit rate can be greatly increased, the optical switch and optical gate having a relatively narrow band can be used in spite of being suitable for integration and capable of operating at a very high speed, a high-frequency electric oscillator or amplifier is required. The light separation device which does not have the above can be provided.

Further, according to claim 2, it is possible to obtain a modulation bandwidth of 2 ^doubled.

According to the third aspect , all inputs can be output without loss.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a light separating device according to the present invention.

FIG. 2 is a configuration diagram of a conventional light separation device.

FIG. 3 is a configuration diagram showing a second embodiment of the light separating device according to the present invention.

FIG. 4 is an explanatory diagram of the operation of a light gate (intensity modulator) used in the light separating device of FIG.

FIG. 5 is a configuration diagram showing a third embodiment of the light separating device according to the present invention.

FIG. 6 is a diagram illustrating the operation of a light gate (intensity modulator) used in the light separation device of FIG.

[Explanation of symbols]

MSC: time division multiplexed optical signal, SC1, SC2, S
C3, SC4: separated optical signal, 10: optical amplifier, 1
1,14,15 ... 1x2 optical coupler, 12,12a, 1
2b, 13, 13a, 13b, 16, 17, 18, 19
... Light on / off gate.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04J 14/00-14/08 H04B 10/00-10/28 G02B 6/28

Claims (3)

(57) [Claims] 1. A time division multiplexed bit rate bit-rate optical signal of M bits / sec M / 2 ^N bits / sec 2 ^N
An optical demultiplexer that divides an optical signal into two optical signal trains and outputs the divided optical signal.
1 input 2 comprising two optical gates arranged on two output sides of the 1 × 2 optical coupler, the phase difference between which is set to π, and the output of the 1 × 2 optical coupler being turned on and off at a set frequency. The output light separation device is defined as one unit, and 2N-1 (N is an integer of 2 or more ) 1-input, 2-output light separation devices are denoted by N.
In an optical demultiplexer in which only the stages are cascaded in a tree shape, and the on / off frequency of 2 ⁿ optical gates of the ^n- th stage (n is an integer of N or less) is set to M / 2 ⁿ , light separation device the optical gate, and characterized by being configured of two light gates off at a frequency of M / 2 n + ¹ by cascade connections off at a frequency of M / 2 ⁿ of. 2. A time division multiplexed bit rate bit-rate optical signal of M bits / sec M / 2 ^N bits / sec 2 ^N
An optical demultiplexer that divides an optical signal into two optical signal trains and outputs the divided optical signal.
1 input 2 comprising two optical gates arranged on two output sides of the 1 × 2 optical coupler, the phase difference between which is set to π, and the output of the 1 × 2 optical coupler being turned on and off at a set frequency. The output light separation device is defined as one unit, and 2N-1 (N is an integer of 2 or more ) 1-input, 2-output light separation devices are denoted by N.
In an optical demultiplexer in which only the stages are cascaded in a tree shape, and the on / off frequency of 2 ⁿ optical gates of the ^n- th stage (n is an integer of N or less) is set to M / 2 ⁿ , An optical gate which is turned on and off at a frequency of M / 2 ⁿ is formed by connecting two Mach-Zehnder type intensity modulators or directional coupler type intensity modulators in cascade, and each operating point is set to a modulator. Output is set to zero voltage, M / 2 ^{n + 2}
A light separating device driven at a frequency of 3. A time division multiplexed bit rate bit-rate optical signal of M bits / sec M / 2 ^N bits / sec 2 ^N
An optical demultiplexer that divides an optical signal into two optical signal trains and outputs the divided optical signal.
1 input 2 comprising two optical gates arranged on two output sides of the 1 × 2 optical coupler, the phase difference between which is set to π, and the output of the 1 × 2 optical coupler being turned on and off at a set frequency. The output light separation device is defined as one unit, and 2N-1 (N is an integer of 2 or more ) 1-input, 2-output light separation devices are denoted by N.
In an optical demultiplexer in which only the stages are cascaded in a tree shape, and the on / off frequency of 2 ⁿ optical gates of the ^n- th stage (n is an integer of N or less) is set to M / 2 ⁿ , An optical gate which is turned on and off at a frequency of M / 2 ⁿ is formed by connecting two Mach-Zehnder type intensity modulators or directional coupler type intensity modulators in cascade, and each operating point is set to a modulator. Set the output to zero voltage and
Set modulation amplitude approximately 2 ^1/2 [pi, optical separation device and drives at a frequency of M / ² n + 2.