JPH09244077A - Light separating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the polarization dependence of an input light signal in a light separation circuit performing the signal separation of a light domain by a four light wave mix. SOLUTION: In this circuit, an output light signal whose frequency is fk and which is consisting of light pulse strings separated in accordance with a modulation signal is obtained from light pulse strings corresponding to multiple signals by adding the input signal whose signal is fi and which is consisting of light pulse strings correspond to multiple signals and the separation signal having a frequency fj and in which the light beam of a light source 1 is modulated by a modulation signal in a light modulator 2 to a four light wave mix generating element 3. The polarization dependence of the input light signal in the four light wave mix is reduced by providing a light branching unit 5 branching the light beam of the light source 1, a polarized state control part 6 making the branched light beams polarized states different with each other and a light multiplexer 7 multiplexing the branched light beams having different polarized states in between the light source 1 and the light modulator 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a configuration method of an optical circuit for optical communication, and more particularly to an optical separation circuit for enabling signal separation in an optical area.

In order to increase the capacity of optical communication systems, high speed operation of optical transceivers is required. However, in the conventional method of separating the multiplexed signals carried by light at the stage of electric signals, the high speed operation is limited by the high speed characteristics of the electronic circuit.

Therefore, the multiplexing and demultiplexing of signals in the optical region are being studied. In particular, there is a demand for an optical demultiplexing circuit that enables demultiplexing of multiplexed signals in the optical region.

[0004]

2. Description of the Related Art As a conventionally known method for separating multiple signals in the optical domain, a method utilizing the nonlinear effect of four-wave mixing is effective. Four-wave mixing is the frequency fk when two lights of frequencies fi and fj are input to the optical element.
= 2 * fi-fj (or 2 * fj-fi) new light is generated. The optical power of the frequency fk in this case is proportional to the optical power of the frequencies fi and fj.

FIG. 7 shows a conventional light separation circuit, in which 1 is a light source composed of a semiconductor laser or the like, and 2 is a light source 1.
Is a four-wave mixing and generating element including a dispersion shift fiber, an optical semiconductor amplifier, and the like, and 4 is an optical filter including a Mach-Zehnder optical interferometer and the like.

FIG. 8 illustrates the operation of the optical separation circuit. The input optical signal has a frequency fi and consists of a pulse train corresponding to the transmitted signal. The optical modulator output signal has a frequency fj and consists of a pulse train corresponding to the modulated signal. The four-wave mixing and generating element 3 has a frequency fk = 2 × f
New light of i-fj is generated, and the optical filter 4 selectively passes light of frequency fk.

In this case, since the optical signal output of the frequency fk is proportional to the product of the powers of the optical signals of the frequencies fi and fj, the input optical signal is punched out by the optical pulse train (separation pulse) of the output of the optical modulator. Such an output optical signal is obtained. For example, when the modulation signal is a signal that becomes “1” for every 4 bits of the transmission signal, when the transmission signal in the input optical signal is a multiplex signal of nGb / s, the separation pulse starts from n / 4Gb / s. Transmission signal by using
It is possible to obtain an output signal that is divided into / 4 and to separate a multiple signal.

[0008]

The four-wave mixing has a polarization dependence, and when the polarization states of the signals of the frequencies fi and fj are different, the optical output of the frequency fk is not generated, and therefore, the optical region is not generated. No signal separation can be performed. on the other hand,
At the receiver input after optical fiber transmission or the input of ADM (Add Drop Multiplexer) during optical fiber transmission, the polarization state is not fixed, so signal separation in the optical region by four-wave mixing is applied to a practical circuit. It was difficult.

For example, when the polarization state of the input signal light and the polarization state of the optical pulse for separation are orthogonal to each other, the four-wave mixing component does not occur, so that signal separation in the optical region cannot be performed. There was a problem.

The present invention is intended to solve the above-mentioned problems of the prior art, and in performing signal separation in the optical region by four-wave mixing, optical separation in which the polarization dependence of the input optical signal is reduced. It is intended to provide a circuit.

[0011]

The concrete means of the present invention for solving the above-mentioned problems will be listed below.

(1) In the aspect (1) of the present invention, an input optical signal having a frequency fi consisting of an optical pulse train corresponding to a multiplexed signal and a frequency fj obtained by modulating the light of the light source 1 by the modulation signal in the optical modulator 2 are used. In the optical demultiplexing circuit for obtaining the output optical signal having the frequency fk, which is composed of the optical pulse train separated from the optical pulse train corresponding to the multiplex signal according to the modulation signal,
An optical splitter 5 that splits the light from the light source 1, a polarization state control unit 6 that makes the split lights different polarization states, and an optical multiplexer 7 that multiplexes the split lights having different polarization states as the light source 1. It is provided between the optical modulator 2.

(2) In the aspect (2) of the present invention, in the case (1), the polarization state control section 6 includes the optical branching device 5 and the optical multiplexer 7.
Consists of two polarization-maintaining fibers 9 and 10 connecting
One constant polarization fiber is rotated by 90 ° between the input and the output with respect to the other constant polarization fiber.

(3) In the aspect (3) of the present invention, in the case of (1), the polarization state control section 6 includes an optical branching device 5 and an optical multiplexer 7.
One of the two optical lines connecting
The / TM mode conversion element 11 is inserted.

(4) In the cases of (1) to (3), the high dispersion element 8 is inserted between the optical modulator 2 and the four-wave mixing / generating element 3.

(5) In the aspect (4) of the present invention, an input optical signal having a frequency fi consisting of an optical pulse train corresponding to a multiplexed signal and a frequency fj obtained by modulating the light of the light source 1 by the modulation signal in the optical modulator 2 are used. In the optical demultiplexing circuit for obtaining the optical output signal of the frequency fk, which is composed of the optical pulse train separated according to the modulation signal from the optical pulse train corresponding to the multiplexed signal,
An optical modulator including an optical splitter 5 that splits the light from the light source 1, a polarization state control unit 6 that makes the split lights different polarization states, and an optical multiplexer 7 that multiplexes the split lights having different polarization states. Two
And the four-wave mixing and generating element 3. At this time, the optical lengths of the paths of the two branches are equal.

(6) In the aspect (5) of the present invention, in the case (5), the polarization state control section 6 includes the optical branching device 5 and the optical multiplexer 7.
Consists of two polarization-maintaining fibers 9 and 10 connecting
One constant polarization fiber is rotated by 90 ° between the input and the output with respect to the other constant polarization fiber. At this time, the optical lengths of the paths of the two branches are equal.

(7) In the aspect (6) of the present invention, in the case (5), the polarization state control section 6 includes the optical branching device 5 and the optical multiplexer 7.
One of the two optical lines connecting
The / TM mode conversion element 11 is inserted.
At this time, the optical lengths of the paths of the two branches are equal.

(8) In the cases (5) to (7), the high dispersion element 8 is inserted between the optical multiplexer 7 and the four-wave mixing and generating element 3.

(9) In the cases of (5) to (7), the high dispersion element 8 is inserted between the optical modulator 2 and the optical branching device 5.

(10) In the cases of (1) to (9), the optical filter 4 is provided at the subsequent stage of the four-wave mixing and generating element 3, and the frequency fk (=
The optical output signal of 2fi-fj or 2fj-fi) is extracted.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment (1) of the present invention and corresponds to an aspect (1) of the present invention. In the figure, the same parts as those in FIG. 7 are indicated by the same numbers, and these operations are the same as those in FIG. 5 is an optical splitter,
Reference numeral 6 is a polarization state control unit, and 7 is an optical multiplexer. Reference numeral 8 is a high-dispersion element, which is composed of a 1.3-μ band zero-dispersion fiber or the like when used in the 1.5-μ band.

In FIG. 1, the light fj generated by the light source 1 is split into two through the optical branching device 5 and through the polarization state control unit 6, the polarization states of the two split beams are orthogonal to each other or different from each other. The polarization state is controlled so that In the optical multiplexer 7, both output lights of the polarization state control unit 6 are combined and input to the optical modulator 2.

The optical modulator 2 has no polarization dependence, and modulates the combined light composed of polarized waves orthogonal to each other to generate separated pulses. By inputting the optical modulator output to the high-dispersion element 8 to cause pulse compression,
Input into the four-wave mixing and generating element 3.

The four-wave mixing / generating element 3 receives the input optical signal fi
To generate a light output that is punched out by the separation pulse fj,
The optical filter 4 extracts light of frequency fk from the output light of the four-wave mixing and generating element 3 and generates an output optical signal.

In the embodiment (1), the four-wave mixing can be generated for the input optical signal of any polarization state by constructing the separation optical pulse from two polarizations orthogonal to each other. Therefore, signal separation in the optical region can be performed. The magnitude of the four-wave mixing component changes depending on the polarization state of the signal light, which can be dealt with by the gain of the electric circuit in the subsequent stage.

The light source used is 1 as shown in the example of FIG.
The number may be one or two or more as long as they have the same optical frequency. In this case, the optical branching device is unnecessary. Further, the high dispersion element 8 may be omitted if the required optical pulse width can be obtained at the output of the optical modulator.

FIG. 2 shows an embodiment (2) of the present invention and corresponds to the aspect (2) of the present invention. In the figure,
The same components as those in FIG. 1 are indicated by the same numbers, and these operations are similar to those in FIG.

Numerals 9 and 10 are polarization maintaining fibers, which are shown in FIG.
The polarization state control section shown in FIG. Optical splitter 5
The branched optical output of is input to the constant polarization fibers 9 and 10, and one of them is rotated by 90 ° with respect to the other, and the optical multiplexer 7
The light composed of two orthogonal polarizations, which is obtained by inputting to and being combined with, is input to the optical modulator 2 for polarization combination, and the other points are the same.

As described above, in the embodiment (2) of the present invention, the polarization state control section is realized by the constant polarization fiber. In this case as well, the high dispersion element 8 can be omitted if the required optical pulse width is obtained in the output of the optical modulator.

FIG. 3 shows an embodiment (3) of the present invention and corresponds to the aspect (3) of the present invention. In the figure,
The same components as those in FIG. 1 are indicated by the same numbers, and these operations are similar to those in FIG.

11 is a TE / TM mode converter,
The polarization state controller shown in FIG. 1 is formed. The TE / TM mode converter 11 is inserted into one of the optical paths for the branched optical output of the optical branching device 5 to rotate the polarization state by 90 ° and input to the optical multiplexer 7, while the other branched optical output is The light is input to the optical multiplexer 7 via the optical line made of a normal non-polarized optical fiber, multiplexed, and input to the optical modulator 2.

As described above, in the embodiment (3) of the present invention, the polarization state control section is realized by the TE / TM mode converter. In this case as well, the high dispersion element 8 can be omitted if the required optical pulse width is obtained in the output of the optical modulator.

FIG. 4 shows an embodiment (4) of the present invention and corresponds to the aspect (4) of the present invention. In the figure,
Although the same parts as those in FIG. 1 are indicated by the same numbers,
Compared to the case of 1, the positions of the optical modulator 5, the polarization state control unit 6, the optical multiplexer 7, and the optical modulator 2 are different.

In the embodiment (4), the optical output from the light source is modulated and then polarization-multiplexed. In this case, the optical multiplexer 7
It is necessary to make the optical lengths of the paths of the two branches equal to each other in order to prevent the phase difference of the branched optical pulses of different polarizations that are multiplexed by However, there is an advantage that even those having polarization dependency can be used.

Also in this case, if the required optical pulse width is obtained at the output of the optical modulator, the high dispersion element 8 can be omitted. Further, the high-dispersion element 8 is provided in the optical modulator 2
It may be provided immediately after.

FIG. 5 shows the embodiment (5) of the present invention and corresponds to the aspect (5) of the present invention. In the figure,
2 are the same as those shown in FIG.
Compared with the case of, the optical branching device 5, constant polarization fiber 9, 1
0 and the optical multiplexer 7 and the optical modulator 2 are exchanged in position.

The embodiment (5) is for performing polarization multiplexing after modulating the optical output from the light source. The operation principle is the same as that of the embodiment (4), but the optical branching device 5 is used. Output to the polarization-maintaining fibers 9 and 10, and only one of them is 90 °
It is rotated and connected to the optical multiplexer 7 to perform polarization combination, and the other points are the same.

Also in this case, if the required optical pulse width is obtained at the output of the optical modulator, the high dispersion element 8 can be omitted. Further, the high-dispersion element 8 is provided in the optical modulator 2
It may be provided immediately after.

FIG. 6 shows an embodiment (6) of the present invention and corresponds to the aspect (6) of the present invention. In the figure,
3 are the same as those in FIG. 3, but the same numbers are used in FIG.
Compared to the case of 1, the positions of the optical modulator 5, the TE / TM mode conversion element 11 and the optical multiplexer 7, and the optical modulator 2 are different.

The embodiment (6) is for performing polarization multiplexing after modulating the light output from the light source, and the operation principle is the same as that of the embodiment (4), but one optical path Branch light,
The TE / TM mode conversion element 11 is used to change the polarization state to 9
While being rotated by 0 ° and input to the optical multiplexer 7, the other branched optical output is input to the optical multiplexer 7 through an optical line formed of a normal non-polarized optical fiber to be multiplexed and thereby polarized. Wave synthesis is performed, and other points are the same.

Also in this case, if the required optical pulse width is obtained at the output of the optical modulator, the high dispersion element 8 can be omitted. Further, the high-dispersion element 8 is provided in the optical modulator 2
It may be provided immediately after.

[0043]

As described above, according to the present invention, in an optical separation circuit using four-wave mixing, signal separation in the optical region by four-wave mixing is realized regardless of the polarization state of the input optical signal. You will be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment (1) of the present invention.

FIG. 2 is a diagram showing an embodiment (2) of the present invention.

FIG. 3 is a diagram showing an embodiment (3) of the present invention.

FIG. 4 is a diagram showing an embodiment (4) of the present invention.

FIG. 5 is a view showing an embodiment (5) of the present invention.

FIG. 6 is a diagram showing an embodiment (6) of the present invention.

FIG. 7 is a diagram showing a conventional optical separation circuit.

FIG. 8 is a diagram for explaining the operation of the light separation circuit.

[Explanation of symbols]

 1 light source 2 optical modulator 3 four-wave mixing and generating element 4 optical filter 5 optical splitter 6 polarization state control unit 7 optical multiplexer 8 high dispersion element 9 constant polarization fiber 10 constant polarization fiber 11 TE / TM mode conversion element

Claims (10)

[Claims] 1. An input optical signal of frequency fi consisting of an optical pulse train corresponding to a multiplex signal, and a separation pulse of frequency fj obtained by modulating light of a light source by a modulation signal in an optical modulator are applied to a four-wave mixing and generating element. In the optical demultiplexing circuit for obtaining an output optical signal of frequency fk consisting of an optical pulse train separated according to the modulation signal from an optical pulse train corresponding to the multiplexed signal, an optical branching device for branching the light of the light source, An optical separation device, characterized in that a polarization state control unit for making light beams in different polarization states and an optical multiplexer for multiplexing branched lights of the different polarization states are provided between the light source and the optical modulator. circuit. 2. The polarization state control section is composed of two polarization maintaining fibers that connect the optical branching device and the optical multiplexer.
The optical demultiplexing circuit according to claim 1, wherein one of the constant polarization fibers is rotated by 90 ° between the input and the output with respect to the other constant polarization fiber. 3. The polarization state control unit comprises a TE / TM mode conversion element inserted in one of the two optical lines connecting the optical branching device and the optical multiplexer. The optical demultiplexing circuit according to claim 1, which is characterized in that. 4. The optical demultiplexing circuit according to claim 1, wherein a high dispersion element is inserted between the optical modulator and the four-wave mixing / generating element. Optical separation circuit. 5. An input optical signal of frequency fi consisting of an optical pulse train corresponding to a multiplexed signal and a separation pulse of frequency fj obtained by modulating the light of a light source by a modulation signal in an optical modulator are applied to a four-wave mixing generator. In the optical demultiplexing circuit for obtaining an optical output signal of frequency fk consisting of an optical pulse train separated according to the modulation signal from an optical pulse train corresponding to the multiplex signal, an optical branching device for branching the light of the light source, A polarization state control unit that makes light beams in different polarization states and an optical multiplexer that multiplexes branched lights having different polarization states are provided between the optical modulator and the four-wave mixing / generating element. And a light separation circuit. 6. The polarization state control section is composed of two constant polarization fibers connecting the optical branching device and the optical multiplexer.
The optical demultiplexing circuit according to claim 5, wherein one of the constant polarization fibers is rotated by 90 ° between the input and the output with respect to the other constant polarization fiber. 7. The polarization state control section includes the optical splitter 5
6. The optical demultiplexing circuit according to claim 5, wherein a TE / TM mode conversion element is inserted into one of the two optical lines connecting the optical multiplexer and the optical multiplexer. 8. The optical demultiplexing circuit according to any one of claims 5 to 7, wherein a high-dispersion element is inserted between the optical multiplexer and the four-wave mixing / generating element. Optical separation circuit. 9. The optical demultiplexing circuit according to claim 5, wherein a high dispersion element is inserted between the optical modulator and the optical branching device. circuit. 10. The optical demultiplexing circuit according to claim 1, further comprising an optical filter provided in a stage subsequent to the four-wave mixing and generating element, the frequency fk (= 2f).
An optical demultiplexing circuit, wherein an optical output signal of i-fj or 2fj-fi) is extracted.