JPH10229387A - Optical time division multiplexed circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably perform time division multiplex of signal light of plural channels, altogether with simplified structure. SOLUTION: This circuit is provided with a light frequency selecting means 14 to multiplex a signal light of N channels with light frequencies fS1 , fS2 to fSN, which differ with one another and a pump light pulse column in which N pieces of pulse with the light frequencies fP1 , fP1 , to fPN which are different from one another are successively repeated, to input it in a four-light waves mixing circuit 13, to select and to output four-light waves mixed light with one light frequency from the outputted light. The light frequency of the signal light and the light frequency of the pump light pulse column are defined as 2fP1 -fS1 =2fP2 -fS2 =...=2fPN-fSN or 2fS1 -fP1 =2fS2 -fP2 =...=2fSN-fPN and the light frequency selected by the light frequency selecting means 14 is defined as 2fP1 -fS1 or 2fS1 -fP1 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical time division multiplexing circuit for generating a high speed optical signal by time division multiplexing a plurality of low speed optical signals.

[0002]

2. Description of the Related Art In a conventional optical transmission system, a plurality of low-speed signals are multiplexed in an electric stage to form a high-speed signal, which is converted into an optical signal and transmitted to an optical fiber. However, in this case, the signal speed that can be multiplexed is limited by the operation speed of the electric circuit. Therefore, an optical time division multiplexing circuit that performs multiplexing in the state of an optical signal has been studied.

FIG. 3 shows a first example of a conventional optical time division multiplexing circuit.
An example of the configuration will be described. In the figure, a low-speed repetitive optical pulse train output from a pulse light source 31 is split into two by an optical coupler 32, input to optical modulators 33-1 and 33-2, and modulated by signals 1 and 2, respectively. The signal light modulated by the optical modulator 33-2 is given a predetermined delay via a delay line 34, is multiplexed with the signal light modulated by the optical modulator 33-1 by the optical coupler 35, and has a signal light pulse train. Becomes

In such an optical time division multiplexing circuit,
In order to regularly time-division multiplex the signal light,
It is necessary to strictly set the delay given to one signal light. However, since the propagation time of light fluctuates due to environmental temperature and the like, it is difficult to strictly set the delay time, and it is difficult to stably obtain a regularly time-division multiplexed signal light pulse train.

FIG. 4 shows a second example of a conventional optical time division multiplexing circuit.
Configuration example (S. Kawanishi and O. Kamatani, "All
-optical time devision multiplexing using four-wav
emixing ", Electronics Letters, vol.30, no.20, pp.1
697-1698, 1994). In the figure, a pulse light source 41 outputs a low-speed repetitive optical pulse train having a wavelength λ _S and a wide pulse width. This low-speed repetitive optical pulse train is
The light is split and modulated by the signals 1 and 2 by the optical modulators 43-1 and 43-2, respectively, to become signal light. The signal light modulated by the optical modulator 43-2 is given a delay of approximately one bit after multiplexing via the delay line 44.

On the other hand, the pump light source 45 outputs a high-speed repetitive optical pulse train of wavelength λ _P (hereinafter referred to as “pump light”). The pump light and the signal light are multiplexed by an optical coupler 46 and input to a four-wave mixing circuit (FWM) 47.
Here, the signal light is set to alternately overlap each pulse of the pump light. Since the pulse width of the signal light is wider than the pulse width of the pump light, the setting condition can be easily satisfied even if there is environmental disturbance.

In the four-wave mixing circuit 47, light of a new wavelength λ _F (hereinafter referred to as “FWM light”) is generated by the four-wave mixing phenomenon of the pump light and the signal light. This FW
Since the M light is generated only when the pump light and the signal light are present at the same time, the on / off modulation of the signal light shifts to the FWM light. That is, the signal light is cut out by the pump light, and the pulse width and the time position of the signal light can be matched with the pulse width and the time position of the pump light.

The output light of the four-wave mixing circuit 47 is input to an optical filter 48, where the signal light having the wavelength λ _S and the wavelength λ
_{The P} pump light is removed. The FWM light of wavelength λ _F output from the optical filter 48 is a signal light pulse train in which the signal light is time-division multiplexed, and the pulse position matches the pulse position of the pump light. in this way,
By using the four-wave mixing circuit 47 to perform four-wave mixing of the pump light and the signal light having a stable pulse width and time position, time-division multiplexing can be performed regularly even if the time position of the signal light slightly fluctuates. It is possible to obtain a simplified signal light pulse train (FWM light).

[0009]

By the way, the conventional optical time division multiplexing circuit shown in FIG. 4 is more effective than the conventional optical time division multiplexing circuit shown in FIG. The tolerance is wide. But still, signal light,
Of the pulse width and the time position are limited to the reciprocal of the bit rate after multiplexing. That is, fluctuation exceeding the pulse interval of the pump light is not allowed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical time division multiplexing circuit capable of stably performing time division multiplexing of signal light of a plurality of channels with a simple configuration.

[0011]

An optical time-division multiplexing circuit according to the first aspect of the present invention comprises a plurality of optical frequencies f _S1 , f _S2 ,
, F _SN and a pump light pulse train in which N pulses of different optical frequencies f _P1 , f _P2 ,..., F _PN are sequentially repeated are input to the four-wave mixing circuit. And an optical frequency selecting means for selecting and outputting four-wave mixed light of one optical frequency from the output light. Here, the optical frequency of the signal light and the optical frequency of the pump light pulse train are 2f _P1 −f _S1 = 2f _P2 −f _S2 =... = 2f _PN −f _SN or 2f _S1 −f _P1 = 2f _S2 −f _P2 = ... = 2f _SN -f _PN The optical frequency selected by the optical frequency selecting means is 2f _P1 −f _S1 or 2f _S1 −f _P1 according to the relationship between the signal light and the optical frequency of the pump light pulse train.

Thus, a low-speed N-channel signal light can be sequentially cut out by a high-speed pump light pulse train having a stable pulse width and time position. That is, signal light of a plurality of channels can be collectively time-division multiplexed. The optical time division multiplexing circuit according to claim 2 includes M sets of the optical time division multiplexing circuit according to claim 1 except for a means for generating a pump light pulse train, and the time division multiplexing is performed in each set. The signal light is further wavelength-multiplexed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 shows a first embodiment of the optical time division multiplexing circuit of the present invention. Here, for the sake of simplicity, a case where two-channel signal light is time-division multiplexed will be described. The signal light is an NRZ signal light modulated at a low speed and has different optical frequencies f _S1 and f _S2 .

In the figure, a signal light having an optical frequency f _{S1 and} a signal light having an optical frequency f _S2 are multiplexed by an optical coupler 11 and further multiplexed with a pump light pulse train by an optical coupler 12 to form a four-wave mixing circuit (FWM). 13 is input. Output light of the four-wave mixing circuit 13 is extracted through an optical filter 14. Here, the pump light pulse train is a short light pulse train in which two different optical frequencies f _P1 and f _P2 are alternately repeated. Such a pump light pulse train includes an SC (super continuum) light source 15, an optical demultiplexer 16, a delay line 17,
It is generated by an optical coupler (or optical multiplexer) 18.

The SC light source 15 is a light source utilizing the non-linearity of an ordinary short pulse light source and an optical fiber, and generates short pulse light having a broadened spectrum. The short-pulse light output from the SC light source 15 is input to the optical demultiplexer 16 and separated into short-pulse light having optical frequencies f _P1 and f _P2 . Light frequency f
The short pulse light of _P2 is given a predetermined delay by the delay line 17,
The short pulse light having the optical frequency f _P1 is multiplexed with the optical coupler 18,
A pump light pulse train in which the optical frequencies f _P1 and f _P2 are alternately repeated is obtained.

Here, the optical demultiplexer 16, the delay line 17, and the optical multiplexer 18 used for generating the pump light pulse train can be formed on a waveguide on the same substrate. Further, since each time position of the pump light pulse is determined by the short pulse light of the SC light source 15, it is stable with high accuracy. Therefore, a pump light pulse train with a stable time position can be generated without being affected by environmental disturbance. In the case of the conventional optical time-division multiplexing circuit shown in FIGS. 3 and 4, it is difficult to integrate the optical time-division multiplexing circuit including the optical modulator, and it is difficult to strictly set the delay time against environmental disturbance. Met.

[0017] and the signal light of the optical frequency f _S1, the optical frequency f _S2
The four-wave mixing circuit 13 to which the signal light and the pump light pulse trains of the optical frequencies f _P1 and f _P2 are input generates FWM light of a new optical frequency in accordance with the combination of each optical frequency.
When the pump light pulse of the optical frequency f _P1 , the signal light of the optical frequency f _{S1 and} the signal light of the optical frequency f _S2 are input, the optical frequencies 2f _P1 −f _S1 , 2f _P1 −fs ₂ , 2f _S1 −f _P1 , 2f
_{S2 -f P1, f P1 + f} S1 -f S2, f P1 + f S2 -f S1, ... FWM light is generated of. When a pump light pulse of the optical frequency f _P2 , a signal light of the optical frequency f _{S1 and} a signal light of the optical frequency f _S2 are input, the optical frequencies 2f _P2 −f _S1 and 2f _P2
−f _S2 , 2f _S1 −f _P2 , 2f _S2 −f _P2 , f _P2 + f _S1 −f
_{S2, f P2 + f S2 -f} S1, ... FWM light is generated of.

Here, the optical frequency of the signal light and the optical frequency of the pump light pulse train are set as follows: 2f _P1 −f _S1 = 2f _P2 −f _S2 (1) Thus, among the FWM light generated by four-wave mixing circuit 13, and FWM light of the light frequency 2f _P1 -f _S1 corresponding to the pump light pulse of the light frequency f _P1, corresponding to the pump light pulse of the light frequency f _P2 Optical frequency 2f _P2 −
The FWM light of f _S2 will have the same optical frequency. Therefore, the transmitted light frequency of the optical filter 14 is set to 2f _P1 −f
By setting _S1 (= 2f _P2 −f _S2 ), FWM light corresponding to each pump light pulse can be simultaneously extracted.

By the way, the FWM of the optical frequency 2f _P1 −f _S1
Light is generated only when the signal light is on. That is, on / off modulation of signal light is shifted to this FWM light. FWM light of the light frequency 2f _P2 -f _S2 occurs only when the signal light is on. That is, on / off modulation of signal light is shifted to this FWM light. Therefore, the output light of the optical filter 14 is an optical pulse train in which the signal light is time-division multiplexed. In addition, the time position of the multiplexed optical pulse train coincides with the time position of the pump light pulse train that is stabilized with high precision.

The relationship between the optical frequency f _S1 of the signal light, the optical frequency f _S2 of the signal light, and the optical frequencies f _P1 and f _P2 of the pump light pulse train is not limited to the equation (1). In the equation (1), f _S1 and f _S2 or f _P1 and f _P2 may be exchanged. Further, it may be set so that 2f _S1 −f _P1 = 2f _S2 −f _P2 (2). In this case, the transmitted light frequency of the optical filter 14 is 2f _S1 −f _P1 (= 2f _S2 −
f _P2 ).

The above is a configuration for multiplexing two channels of signal light. Generally, N channels (N> N) are used.
When multiplexing a signal light 2), f _S1, f _S2 the optical frequency of the signal light, respectively, ..., and f _SN, the pump light pulse train optical frequency f _P1, f _P2, ..., sequentially f _PN Shall be repeated. Also, between each optical frequency, for example _{2f P1 -f S1 = 2f P2 -f} S2 = ... = 2f set so that _PN -f _SN ... (3). If the N-channel signal light and the pump light pulse train are collectively input to the four-wave mixing circuit, a time-division multiplexed light pulse train can be obtained in the same manner as in the case of two channels.

(Second Embodiment) FIG. 2 shows a second embodiment of the optical time division multiplexing circuit of the present invention. Here, for the sake of simplicity, two-channel signal light,
Are time-division multiplexed, and on the other hand, two-channel signal light
Will be described below, and the time-division multiplexed optical pulse trains are further wavelength-multiplexed. The signal light is an NRZ signal light modulated at a low speed, and has different optical frequencies f _S1 , f _S2 , f _S3 and f _S4 .

In the figure, a signal light having an optical frequency f _{S1 and} a signal light having an optical frequency f _S2 are multiplexed by an optical coupler 11-1.
Further, it is multiplexed with the pump light pulse train by the optical coupler 12-1 and input to the four-wave mixing circuit (FWM) 13-1. The output light of the four-wave mixing circuit 13-1 is supplied to an optical filter 14-1.
Is taken out through. On the other hand, the signal light of the optical frequency f _{S3 and} the signal light of the optical frequency f _S4 are multiplexed by the optical coupler 11-2, further multiplexed with the pump light pulse train by the optical coupler 12-2, and are mixed with a four-wave mixing circuit (FWM). 13-2. The output light of the four-wave mixing circuit 13-2 is an optical filter 1
4-2.

Here, the pump light pulse train is a short light pulse train in which two different optical frequencies f _P1 and f _P2 are alternately repeated. Such a pump light pulse train is generated by the SC light source 1
5, generated by the optical demultiplexer 16, the delay line 17, and the optical coupler (or optical multiplexer) 18, branched into two by the optical coupler 19, and input to the optical couplers 12-1 and 12-2. Here, the optical frequency of the signal light, and the optical frequency of the pump light pulse train are
(1) is set as equation are set as the signal light, the 2f the optical frequency of the optical frequency and the pump optical pulse train _{P1 -f S3 = 2f P2 -f S4} ... (4). Then, the optical filters 14-1 and 14
The transmitted light frequency of −2 is 2f _P1 −f _S1 (= 2f _P2
−f _S2 ) and 2f _P1 −f _S3 (= 2f _P2 −f _S4 ). Note that this optical frequency setting is an example as described above, and other settings are also possible.

Thus, the output light of the optical filter 14-1 is an optical pulse train in which the signal light is time-division multiplexed, and the output light of the optical filter 14-2 is the time-division multiplexing of the signal light. It becomes an optical pulse train. In addition, the time positions of the multiplexed optical pulse trains coincide with the time positions of the pump light pulse trains that are stabilized with high precision. A multiplexed signal light of the optical frequency 2f _P1 -f _S1 output from the optical filter 14-1, multiplexed signal light of the optical frequency 2f _P1 -f _S3 output from the optical filter 14-2, an optical multiplexer ( Or an optical coupler) 20. The output light of the optical multiplexer 20 is time-division multiplexed with the signal light and the signal light, and further becomes an optical pulse train in which they are wavelength-multiplexed.

In general, when M sets (M is an integer of 2 or more) of N channel signal lights having different optical frequencies for each set are prepared, time-division multiplexed, and wavelength multiplexed, the same applies. This can be dealt with. In the first embodiment and the second embodiment described above,
Although the signal light before multiplexing is the NRZ signal light, it is not limited to this. The pulse width of the signal light may be such that each signal light pulse always overlaps with the pump light pulse in the four-wave mixing circuit even if there is environmental disturbance. Also, NR
In the case of the Z signal light, the signal light and the pump light pulse train need not always be synchronized.

[0027]

As described above, the optical time-division multiplexing circuit of the present invention can collectively time-division multiplex signal light of a plurality of channels with a simple configuration. Further, the time position of the multiplexed optical pulse train coincides with the time position of the pump light pulse train that is stabilized with high accuracy, so that time-division multiplexed light can be stably obtained.

The time division multiplexed light output via the four-wave mixing circuit and the optical frequency selection circuit has one optical frequency. Therefore, by generating time-division multiplexed lights having optical frequencies different from each other via a plurality of four-wave mixing circuits and optical frequency selection circuits and wavelength-multiplexing them, the multiplicity can be further increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of an optical time division multiplexing circuit of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the optical time division multiplexing circuit of the present invention.

FIG. 3 is a block diagram showing a first configuration example of a conventional optical time division multiplexing circuit.

FIG. 4 is a block diagram showing a second configuration example of a conventional optical time division multiplexing circuit.

[Explanation of symbols]

 11, 12, 18, 19 Optical coupler 13 Four-wave mixing circuit (FWM) 14 Optical filter 15 SC (super continuum) light source 16 Optical demultiplexer 17 Delay line 20 Optical multiplexer

Claims (2)

[Claims] 1. Optical frequencies f _S1 , f _S2,.
means for multiplexing N-channel signal light of f _SN , and N pulses of different optical frequencies f _P1 , f _P2 ,..., f _PN are included in the pulse width of the signal light. Means for generating a pump light pulse train in which pulses are sequentially repeated; a four-wave mixing circuit for multiplexing and inputting the multiplexed N-channel signal light and the pump light pulse train to generate four-wave mixing light And an optical frequency selection unit that selects and outputs four-wave mixing light of one optical frequency from the output light of the four-wave mixing circuit, wherein the optical frequency of the signal light and the optical frequency of the pump light pulse train are _{, 2f P1 -f S1 = 2f P2} -f S2 = ... = 2f PN -f SN _{or, 2f S1 -f P1 = 2f S2} -f P2 = ... = set to 2f _SN -f the _PN relationship, the light The optical frequency selected by the frequency selection means is the same as the signal light. Optical time-division multiplexer, characterized in that depending on the relationship of the optical frequency of the pump light pulse train is 2f _P1 -f _S1 or 2f _S1 -f _P1. 2. The optical time-division multiplexing circuit according to claim 1, except for a means for generating a pump light pulse train, wherein the signal time-division multiplexing is performed on signal lights having mutually different optical frequencies.
A set (M is an integer of 2 or more) of optical time-division multiplexing units; and a different optical frequency f within a pulse width of each set of signal light.
Means for generating a pump light pulse train including N pulses of _P1 , f _P2 ,..., F _{PN, and} the N pulses being sequentially repeated; An optical input device comprising: means for inputting to each of the four-wave mixing circuits of the division multiplexing unit; and means for multiplexing the four-wave mixing light output from the M sets of optical time-division multiplexing units. Division multiplexing circuit.