JP3201566B2 - Optical demultiplexing circuit - 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 multiplexing / demultiplexing circuit which collectively separates a time-multiplexed signal light pulse train into a plurality of streams in a time division optical transmission system.

[0002]

2. Description of the Related Art FIG. 5 shows a configuration of a conventional optical demultiplexing circuit using four-wave mixing. The configuration shown here is described in the document `` T.
Morioka, et al., "Multiple-output, 100Gbit / s All-op
ticalDemultiplexer Based on Multi-channel Four
-wave Mixing by a Linearly-chirped Rectangular Pu
mp Pulse ", ECOC'94 vol.1, pp.125-128, 1994". Here, a four-channel batch separation type configuration is shown.

In FIG. 1, a time-division multiplexed optical frequency ν
The signal light of _{S and} the control light having chirping whose optical frequency changes linearly with time at the central optical frequency ν _P and having a time width Δt including the signal light pulse train of four channels are combined by the optical multiplexer 41. And input to the polarization maintaining optical fiber. In general, if the bit rate of the signal light is B and the number of channels to be collectively separated is n, then Δt> n / B.
The instantaneous optical frequency of the control light corresponding to each channel chi (i = 1, 2, 3, 4) of the signal light is ν _P (i). In the polarization-maintaining optical fiber 42, a four-wave mixing effect is induced by the signal light and the control light, and the generated four-wave mixing light is split by the optical splitter 43 for each optical frequency. It becomes light.

Here, the four-wave mixing effect will be described with reference to FIG. In the polarization maintaining optical fiber 42, the signal light (optical frequency ν _S ) and the control light (the instantaneous optical frequency ν _P (i) corresponding to each channel) interact due to the four-wave mixing effect, and ν _i = 2ν _S − Four-wave mixing light having an optical frequency ν _i having a relationship of ν _P (i) is generated. The four-wave mixed light is a case where the signal light of the optical frequency ν _S is degenerate (the case where the optical frequency ν _S is equal to the zero dispersion optical frequency of the polarization maintaining optical fiber 42). By demultiplexing the four-wave mixed light corresponding to each channel by the optical demultiplexer 43, the four channels can be collectively separated.

Here, a method of generating control light having linear chirping will be described. In the first generation method shown in FIG. 7, an optical fiber 51 for generating a white pulse, an optical fiber 52 for chirp adjustment, and an optical bandpass filter 53 are used.
When an optical short pulse train (optical frequency ν ₀ ) is incident on the white pulse generating optical fiber 51, a broadband white pulse (center optical frequency ν ₀ ) is generated. The optical bandpass filter 53 has a rectangular spectral transmission function, and converts a white pulse input through the chirp adjusting optical fiber 52 into a central optical frequency ν.
_After filtering by _P , control light having a predetermined time width and linear chirping is output. The chirp adjusting optical fiber 52 adjusts the absolute value and sign of chirping according to its dispersion characteristics.

In the second generation method shown in FIG. 8, an ordinary dispersion optical fiber 54 having ordinary dispersion (positive dispersion) is used. When an optical short pulse train (optical frequency ν ₀ ) is incident on the ordinary dispersion optical fiber 54, a control light having a predetermined time width and linear chirping (center optical frequency ν _P ) is obtained by a combined effect of its self-phase modulation effect and dispersion. Occurs. This is the same principle as the pulse compression method for optical pulses (GPAgrawal, "Nonl
inear Fiber Optics ", chapter 6, Academic Press, 198
9).

[0007]

However, it is not easy to generate control light having a wide time width and linear chirping by the above-described control light generation method. Further, it has not been easy to continuously generate control light having a predetermined time width and linear chirping as shown in FIG. Therefore, when the number of channels to be demultiplexed by an ultra-high-speed signal is large, it is difficult to cope with the configuration shown in FIG.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical multiplexing / demultiplexing circuit which can collectively separate multiple channels from an ultra-high-speed signal.

[0009]

An optical demultiplexing circuit according to the present invention comprises an optical short pulse light source for outputting an optical short pulse train, and a multi-wavelength light source for outputting wavelength-division multiplexed light obtained by wavelength multiplexing continuous light having a plurality of wavelengths. A first optical AND circuit that inputs a wavelength multiplexed light and an optical short pulse train, outputs a wavelength multiplexed light short pulse train obtained by converting the intensity product thereof into an optical short pulse, and a wavelength multiplexed light short pulse train. A dispersion circuit for inputting and outputting control lights arranged on the time axis with different delays added according to wavelengths, and a signal light and a control light in which a plurality of channels are time-division multiplexed and a control light are inputted. A second optical AND circuit that outputs wavelength-converted light obtained by converting the wavelength of the control light into a wavelength corresponding to each channel of the control light, and demultiplexes the wavelength-converted light for each wavelength, and outputs demultiplexed output light corresponding to each channel. And an optical demultiplexer.

[0010] Further, the first and second optical AND circuits include:
An optical coupler that has a one-to-one branching ratio in a predetermined wavelength region in a two-input two-output configuration and receives wavelength-division multiplexed light or control light at one input port, and has a flat dispersion characteristic in a predetermined wavelength region. An optical fiber loop connecting between two output ports of the optical coupler, and means for inputting an optical short pulse train or signal light to the optical fiber loop so as to propagate only in one direction in the optical fiber loop, The configuration is such that a wavelength multiplexed optical short pulse train or wavelength converted light is output from the other input port of the optical coupler.

[0011] The first and second optical AND circuits may include:
An optical short pulse train and a wavelength multiplexed light, or a device having a saturable absorption characteristic in which a signal light and a control light are respectively incident,
When the optical short pulse train and the wavelength multiplexed light or the signal light and the control light are simultaneously input, respectively, the corresponding wavelength multiplexed light short pulse train or the wavelength converted light is output as the nonlinear reflected light.

[0012]

In the optical demultiplexing circuit according to the present invention, an optical short pulse train and a wavelength multiplexed light are first processed by a first optical AND circuit to generate a wavelength multiplexed light short pulse train having a plurality of wavelength components. By inputting this to the dispersion circuit, the optical short pulse is converted into control light arranged on the time axis according to the wavelength. The signal light to be demultiplexed and the control light output from the dispersion circuit are processed by the second optical AND circuit, whereby the wavelength of the signal light is converted into a wavelength corresponding to each channel of the control light, and output as wavelength-converted light. Is done. By demultiplexing the wavelength-converted light for each wavelength, a plurality of channels can be separated at once.

[0013]

FIG. 1 shows an embodiment of an optical multiplexing / demultiplexing circuit according to the present invention. In the figure, an optical short pulse light source 11 has a wavelength λ _P
Is output. The multi-wavelength light source 12 outputs a wavelength multiplexed light c obtained by wavelength multiplexing continuous lights having wavelengths λ _{1 to} λ _n . The optical AND circuit 13 inputs the optical short pulse train b and the wavelength multiplexed light c, and outputs a wavelength multiplexed optical short pulse train d. The wavelength multiplexed optical short pulse train d is input to the optical fiber 14 and converted into control light e arranged on the time axis according to the wavelengths λ _{1 to} λ _n . The optical AND circuit 15 receives the signal light a having the wavelength λ _S and the control light e, and outputs a wavelength-converted light f obtained by converting the wavelength of each channel into λ ₁ to λ _n . The wavelength-converted light f is input to the optical demultiplexer 16, and is demultiplexed into demultiplexed output light g corresponding to each wavelength (channel).

Here, the operation principle of this embodiment will be described with reference to FIG. 2 in the case where the number n of channels to be collectively separated is four. The optical AND circuits 13 and 15 have two ports,
And when the light is input simultaneously, the light of the port is output to the port. Therefore, the optical AND circuit 1
3 ports, when the wavelength lambda _P of optical short pulse train b and the wavelength-multiplexed light c that the continuous light and wavelength-multiplexed in the wavelength lambda ₁ to [lambda] ₄ is input, the wavelength-multiplexed optical short pulse train of wavelength lambda ₁ to [lambda] ₄ d is output. Since the optical fiber 14 has a different group velocity for each wavelength, the wavelength multiplexed optical short pulse train d is converted into control light e arranged on the time axis according to the wavelengths λ _{1 to} λ ₄ .

When the signal light a having the wavelength λ _S and the control light e having the wavelengths λ _{1 to} λ ₄ are input to the ports of the optical AND circuit 15 in synchronization with the respective channels, the wavelength of each channel of the signal light a is obtained. Is converted from λ _S to λ ₁ to λ ₄ to output a wavelength-converted light f. In the example shown in FIG. 2, signal light of channel 1 (... 111), channel 2 (... 110), channel 3 (... 011...), And channel 4 (. As a result, the wavelength converted light f obtained by converting the signal light of each channel into the wavelengths λ _{1 to} λ ₄ is obtained. By inputting the wavelength-converted light f to the optical demultiplexer 16 and demultiplexing each wavelength, the four channels can be collectively separated.

In this embodiment, the number of wavelengths of the multi-wavelength light source 12, the number of wavelengths,
The wavelength interval and the dispersion characteristics of the optical fiber 14 are optimized, and the corresponding optical demultiplexer 16 is used. FIG. 3 shows the configuration of the first embodiment of the optical AND circuits 13 and 15. In the figure,
The optical AND circuit includes a 2 × 2 optical coupler 21 having no wavelength dependence, an optical fiber loop 22 having flattened dispersion characteristics,
A nonlinear loop mirror (nonlinear Sagnac interferometer) using the optical multiplexer 23 is configured. As the optical fiber loop 22 having a flat dispersion characteristic, there is known an optical fiber such as a double-core fiber in which the dispersion is adjusted to make the dispersion characteristic flat.

In the optical AND circuit 13, the wavelength multiplexed light c input from the port is divided into two equal parts by the optical coupler 21, propagates in the optical fiber loop 22 in the opposite direction, respectively, is again joined by the optical coupler 21, and Output from on the other hand,
The optical short pulse train b input from the port is
3, the light is input to the optical fiber loop 22 and propagates in the optical fiber loop 22 in one direction. At this time, the wavelength multiplexed light c propagating in the same direction as the optical short pulse train b undergoes a phase shift due to the optical Kerr effect of the optical short pulse train b.
Therefore, the wavelength multiplexed light c propagated in the loop in the opposite directions returns to the optical coupler 21 again, and when the phase difference becomes π, the wavelength multiplexed light c is completely switched and output to the other port. Thereby, as shown in FIG. 2, the wavelength multiplexed light c corresponding to the optical short pulse train b is converted into the wavelength multiplexed light short pulse train d and output.

In the optical AND circuit 15, the control light e input from the port is divided into two equal parts by the optical coupler 21, and propagates in the optical fiber loop 22 in the opposite direction, respectively. Is output. On the other hand, the signal light a input from the port is input to the optical fiber loop 22 via the optical multiplexer 23,
2 in one direction. At this time, the control light e propagating in the same direction as the signal light a undergoes a phase shift due to the optical Kerr effect of the signal light a. Therefore, the control light e propagated in the loop in the opposite directions returns to the optical coupler 21 again, and when the phase difference becomes π, the control light e is completely switched and output to the other port. That is,
As shown in FIG. 2, the control light e having a wavelength corresponding to each channel of the signal light a is output as the wavelength-converted light f.

FIG. 4 shows the configuration of the optical AND circuits 13 and 15 according to a second embodiment. In this embodiment, an element having a saturable absorption characteristic is used as an optical AND circuit, and nonlinear reflected light obtained by taking the logical product of the optical short pulse train b and the wavelength multiplexed light c or the signal light a and the control light e is output (reference Reference: R.Takahash
i, et al., "1.55 μm UltrafastSurface-Reflection
All-optical Switching Using Low-temperature-gr
ownBe-doped Strained MQWs ", ECOC'94, Vol.1, pp.113
-116, 1994).

In the drawing, the present device has an Au mirror layer 31,
InAlAs / InP layer 32, InGaAs / InAlAs MQWs layer 33, InG
The structure is such that an aAsP / InP DBR layer 34, an InP layer 35, and an AR coating layer 36 are laminated. The short optical pulse train b and the wavelength multiplexed light c or the signal light a and the control light e are multiplexed to form an AR.
Light is incident from the coating layer 36. Incident light is InGaAs
About 1% of the light is reflected by the P / InP DBR layer 34, and the remaining light is reflected by the Au mirror layer 31. The distance between the InGaAsP / InP DBR layer 34 and the Au mirror layer 31 is set such that the phase difference of the light reflected at the two locations becomes π (or an odd multiple of π). The InGaAs / InAlAs MQWs layer 33 has a property that the transmittance increases when the intensity of the incident light is high, and the light short pulse train b and the wavelength multiplexed light c or the signal light a and the control light e are simultaneously incident respectively. When reflected, the reflected light on the Au mirror layer 31 becomes stronger. On the other hand, the InGaAsP / InP DBR layer 34
Is always 1% of the incident light. Therefore, when the incident light is strong, the influence of the interference of the light reflected at the two places is small, and the light reflected by the Au mirror layer 31 is emitted with almost the same intensity. On the other hand, if the incident light is weak
The light reflected by the Au mirror layer 31 is greatly reduced, and the InGa
It is canceled by interference with light reflected by the AsP / InP DBR layer 34.

As described above, when the light reflected by the Au mirror layer 31 interferes with the light reflected by the InGaAsP / InP DBR layer 34, the light reflected by the Au mirror layer 31 is emitted with almost the same intensity. Whether or not it is canceled depends on the intensity of the incident light, that is, the optical short pulse train b and the wavelength multiplexed light c or the signal light a.
And the control light e are simultaneously input. As a result, the optical AND circuit 13 that generates the wavelength multiplexed optical short pulse train d from the optical short pulse train b and the wavelength multiplexed light c, or the control light e having a wavelength corresponding to each channel of the signal light a is output as the wavelength converted light f. Optical AND circuit 15
Can be configured.

In this embodiment, the size of the circuit can be reduced as compared with the configuration using the optical fiber loop of the first embodiment, and the time from when the signal light enters the circuit to when the signal light exits can be shortened. There are features that you can do.

[0023]

As described above, in the optical demultiplexing circuit of the present invention, the number of wavelengths of wavelength-division multiplexed light, the wavelength interval, and the dispersion characteristics of the dispersion circuit are optimized according to the signal speed of the signal light and the number of demultiplexing. Thus, control light having a wavelength corresponding to each channel of the signal light can be generated. By processing the control light and the signal light with an optical AND circuit, the wavelength of the signal light can be converted into a different wavelength for each channel, and by dividing this for each wavelength, a plurality of channels can be converted. They can be separated at once.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical multiplexing / demultiplexing circuit according to the present invention.

FIG. 2 is a view for explaining an operation example (collective separation of four channels) of the embodiment.

FIG. 3 is a diagram showing a configuration of a first embodiment of optical AND circuits 13 and 15;

FIG. 4 is a diagram illustrating a configuration of a second embodiment of the optical AND circuits 13 and 15;

FIG. 5 is a block diagram showing a configuration of a conventional optical demultiplexing circuit using four-wave mixing.

FIG. 6 is a diagram showing an example of wavelength conversion by the four-wave mixing effect.

FIG. 7 is a view for explaining a first generation method of control light having linear chirping.

FIG. 8 is a diagram illustrating a second generation method of control light having linear chirping.

[Explanation of symbols]

 Reference Signs List 11 short optical pulse train light source 12 multi-wavelength light source 13, 15 optical AND circuit 14 optical fiber 16 optical demultiplexer 21 optical coupler 22 optical fiber loop 23 optical multiplexer 31 Au mirror layer 32 InAlAs / InP layer 33 InGaAs / InAlAs MQWs layer 34 InGaAsP / InP DBR layer 35 InP layer 36 AR coating layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-163006 (JP, A) JP-A-8-110534 (JP, A) JP-A-8-101412 (JP, A) JP-A-4- 19718 (JP, A) JP-A-1-296827 (JP, A) Table 10-508116 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04J 14/00-14 / 08 H04B 10/00-10/28

Claims (3)

(57) [Claims] 1. An optical short pulse light source for outputting an optical short pulse train, a multi-wavelength light source for outputting a wavelength multiplexed light obtained by wavelength multiplexing continuous lights of a plurality of wavelengths, and an input of the wavelength multiplexed light and the optical short pulse train. A first optical AND circuit that outputs a wavelength multiplexed optical short pulse train obtained by converting the wavelength multiplexed light into an optical short pulse by taking the intensity product thereof; and inputting the wavelength multiplexed optical short pulse train and differing according to the wavelength. A dispersion circuit that outputs control light arranged on the time axis by adding a delay, a signal light in which a plurality of channels are time-division multiplexed and the control light are input, and a wavelength of the signal light is set to each of the control lights. A second optical AND circuit that outputs wavelength-converted light converted to a wavelength corresponding to the channel, an optical demultiplexer that splits the wavelength-converted light for each wavelength, and outputs a demultiplexed output light corresponding to each channel. Optical demultiplexing characterized by comprising: Road. 2. The optical demultiplexing circuit according to claim 1, wherein the first and second optical AND circuits have a one-to-one branching ratio in a predetermined wavelength region in a two-input two-output configuration. An optical coupler in which wavelength-multiplexed light or control light is input to an input port of the optical coupler; an optical fiber loop having flat dispersion characteristics in the predetermined wavelength region and connecting between two output ports of the optical coupler; Means for inputting a short pulse train or signal light to the optical fiber loop so as to propagate in the optical fiber loop in only one direction, and a wavelength multiplexed light short pulse train or wavelength conversion light from the other input port of the optical coupler. An optical multiplexing / demultiplexing circuit, which is configured to output a signal . 3. The optical multiplexing / demultiplexing circuit according to claim 1, wherein the first and second optical AND circuits have a saturable absorption characteristic in which an optical short pulse train and a wavelength multiplexed light or a signal light and a control light are respectively incident. When the optical short pulse train and the wavelength multiplexed light, or the signal light and the control light are simultaneously input, respectively, the corresponding wavelength multiplexed light short pulse train or the wavelength converted light is output as the nonlinear reflected light. Optical demultiplexing characterized by the following:
Circuit .