JPH11119268A - Optical switch and its quenching ratio improving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sufficiently high quenching ratio even though a nonlinear optical waveguide having the dependency to nonlinear phase shift signal optical polarization is used by constituting a nonlinear refractive index variation expressing section of two nonlinear optical waveguides. SOLUTION: The nonlinear refractive index variation expressing section of the optical switch is constituted of two nonlinear optical waveguides 1 and 3. The signal light beams, which are propagated in a first nonlinear optical waveguide with a TE polarization condition, are propagated in a TE polarization state in a second nonlinear waveguide 3. Conversely, the signal light beams, which are propagated in the waveguide 1 with a TM polarization condition, are propagated in the waveguide 3 in a TE polarization state. In other words, the received nonlinear phase shift of the signal light beams becomes independent to the signal beam polarization by the propagation in the waveguides 1 and 3. Thus, the linearly polarized components, which are mutually orthogonal, receive a π radian nonlinear phase shift, the signal light beams, which are outputted immediately after the completion of a switching operation, completely return to an initial condition and the quenching ratio is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch, and more particularly, to an optical switch used in fields such as optical fiber communication and optical information processing.

[0002]

2. Description of the Related Art In order to dramatically improve the transmission and processing speed of information in an optical communication system or an optical information processing system, it is necessary to use an all-optical system. The all-optical system means that signals propagating through transmission lines, multiplexing / demultiplexing circuits, logic circuits, and the like in the system can be transmitted as light without undergoing optical-electrical or electrical-optical conversion on the way. means.

In order to construct such an all-optical system, an element for controlling an optical signal at high speed is required. Conventionally, as a light control element, a method of performing light control by an electric signal (electro-light control) has been adopted. However, in recent years, a method of performing light control by light (light -Light control). In particular, in an optical communication system, if an ultra-high-speed optical-optical control switch (optical-optical switch) is applied to an optical demultiplexing circuit (optical demultiplexer), it is a great factor in realizing high-speed optical communication systems. It becomes a breakthrough. The performance required to put the optical-optical switch into practical use is not limited to the above-described high speed, but also includes a wide range such as low switching energy, high repetition operation, and compact size.

In particular, switching energy is required to be within a range of light pulse energy that can be output by a semiconductor laser, a fiber amplifier, or a semiconductor optical amplifier. The first problem in realizing these performances is the figure-of-merit of the nonlinear optical effect, which is the driving principle of the optical-optical switch ス イ ッ チ⁽³⁾ / τα
(Χ ⁽³⁾ : magnitude of nonlinearity, τ: response time, α: signal loss) obeys the rule that it is almost constant empirically.
That is, the nonlinear optical effect is roughly classified into a non-resonant excitation type and a resonance excitation type. In both cases, it is considered that it is difficult to simultaneously satisfy high efficiency and high speed.

[0005] First, in the non-resonant excitation type, high speed is expected, but efficiency is low. Therefore, a high switching energy or a long interaction length will be required. On the other hand, the resonance excitation type has high efficiency, but has a problem in that relaxation of electrons actually excited in the nonlinear optical medium is slow, which hinders realization of high speed operation. However, in recent years, it has been reaffirmed that the high efficiency of the resonance excitation type is of great appeal in practical use, and various methods for overcoming the problem of slow relaxation and realizing high-speed operation have been proposed.

For example, in an optical-optical switch described in Japanese Patent Application Laid-Open No. 8-179385, a resonance-excited non-linear refractive index change accompanying absorption or amplification of control light is used. It is not limited by the slow relaxation of the excited nonlinear refractive index change. FIG. 3 is a diagram illustrating a configuration of an optical switch according to the related art. The nonlinear optical waveguide 1 is a buried semiconductor optical waveguide having InGaAsP as a core and InP as a clad. InGaAs
The optical waveguide portion made of sP has an absorption edge wavelength of 1.52 μm, and has a wavelength of 1.52 μm when a direct current is applied.
The gain is shown for light ranging from m to 1.35 μm.
The birefringent crystals 4 and 6 are made of rutile single crystal (TiO ₂ ). A rutile single crystal exhibits birefringence in that the propagation time of a light pulse having a linear polarization perpendicular to the optical axis (ordinary ray) and a light pulse having a linear polarization parallel to the optical axis (extraordinary ray) are different.

The analyzer 7 transmits only a certain linearly polarized light. A signal light pulse train having a wavelength of 1.55 μm, a pulse width of 2 ps and a repetition frequency of 160 GHz, and a control light pulse train of a wavelength of 1.40 μm, a pulse width of 2 ps and a repetition frequency of 10 GHz are input to the optical switch. That is, the signal light wavelength is transmitted to the transparent region 20 on the long wave side from the absorption edge,
The control light wavelength is set within the gain band 21 (see FIG.
(B)).

The control light enters the nonlinear optical waveguide 1 via a WDM coupler (wavelength selection coupler) 6 and undergoes optical amplification. Due to the amplification of the control light, the number of carriers in the nonlinear optical waveguide 1 decreases, and a nonlinear phase shift with respect to the signal light occurs with the change in the carrier density. On the other hand, in the birefringent crystal 4, the signal light pulse has an S-1 component having a polarization perpendicular to the optical axis and an S-2 component having a polarization parallel to the optical axis.
A time delay is provided between the components. These signal light pulses pass through the WDM coupler 6 and then pass through the nonlinear optical waveguide 1.
And the S-1 component and the S-2 component are respectively T
It propagates as M polarized light and TE polarized light. The signal light emitted from the nonlinear optical waveguide 1 enters the birefringent crystal 5 such that the polarization of the S-1 component is parallel to the optical axis and the polarization of the S-2 component is perpendicular to the optical axis.

As a result, the time difference between the S-1 component and the S-2 component given by the birefringent crystal 4 is canceled, and the two components are synthesized again. When the relative phase difference between the two components at the time of combining is 0 and at the time of π radian, the polarizations of the signal light at the time of combining are orthogonal to each other. The signal light emitted from the birefringent crystal 5 is input to the analyzer 7, and only one linearly polarized light is output.

Here, the birefringent crystal 5 is used as an initial state.
The case where the relative phase difference between the S-1 component and the S-2 component at the time of emission is 0 and linearly polarized light determined by the combination of both components is completely blocked by the analyzer 7 will be described. FIG. 4 is a waveform diagram showing the operation of the optical switch according to the related art. As shown in FIG. 3A, signal light pulses are input at intervals of 6.25 ps. Here, a signal light pulse train coded as “10111010” is illustrated. The following description focuses on three pulses S1, S2, and S3.

These pass through the birefringent crystal 4 to form two components whose polarizations are orthogonal to each other, S11, S21, S31 and S12, S22, S32, as shown in FIG.
And a time delay is provided. When the control light pulse C is inserted at the position shown in FIG.
Rises and changes almost following the control light pulse and slowly relaxes. Since the relaxation time is longer than the time scale shown in FIG. 4, for the sake of simplicity, it is assumed that the relaxation time is a step-like change as shown in FIG. Signal light pulse S3 incident after control light pulse C
1, S22, S32, etc. receive a non-linear phase shift π.
The signal light pulse emitted from the nonlinear optical waveguide 1 further passes through the birefringent crystal 5 so that the time delay previously given by the birefringent crystal 4 is restored as shown in FIG. It is.

As a result, only the relative phase difference between S21 and S22 becomes π, and the polarization of the synthesized signal light pulse is
Rotate 90 degrees from the initial state. In contrast, S1
Since both 1 and S12 do not undergo the non-linear phase shift, the relative phase difference is 0, and since both S31 and S32 receive the non-linear phase shift π, the relative phase difference is also 0. That is, the polarization direction of S3 synthesized in S31 and S32 is the same as the initial state.

Therefore, by passing through the analyzer 7, only the signal light pulse S2 is output as shown in FIG. With such a mechanism, 160 Gb
It is possible to realize an ultra-high-speed optical-optical switch that separates a ps data string at 10 GHz repetition. The problem with the above-described conventional optical switch is that it is difficult to completely match the nonlinear phase shifts of the TE-polarized light and the TM-polarized signal light received by the nonlinear optical waveguide 1, so that the extinction ratio deteriorates.

The reason will be described below. That is, the suppression ratio of the signal light pulse after S3, which is not desired to be output, is determined by the polarization dependence of the nonlinear phase shift applied to the signal light in the nonlinear optical waveguide 1. For example, in the case of S3, it is determined by how close the relative phase difference between S31 and S32 is to zero. However, it is very difficult to make the nonlinear phase shift of the signal light polarization independent.

In semiconductor optical amplifiers, the polarization independence of gain has been energetically promoted in recent years by improving waveguide cross-sectional shapes and devising waveguide materials. The polarization independence of the gain means that in the optical switch, the carrier change amount caused by the control light does not depend on the polarization of the control light. However, even if the gain for the control light becomes polarization independent, the nonlinear phase shift received by the signal light still has polarization dependency. That is, in the nonlinear optical waveguide, the nonlinear phase shifts of the signal light received by S31 which becomes TM polarized light and S32 which becomes TE polarized light do not completely match. Therefore, the relative phase difference between S31 and S32 does not become 0,
It becomes impossible for the analyzer 7 to completely block S3.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks of the prior art, and in particular, to be sufficiently high even if a nonlinear optical waveguide having a nonlinear phase shift dependent on signal light polarization is used. An optical-optical switch capable of realizing an extinction ratio;
An object of the present invention is to provide a method for improving the extinction ratio of an optical switch.

[0017]

The present invention basically employs the following technical configuration in order to achieve the above object. That is, the first embodiment according to the present invention
As a mode of the present invention, a non-linear refractive index change expressing portion made of a medium that generates a non-linear refractive index change by amplifying the control light, means for dividing the signal light into linearly polarized light components orthogonal to each other, Means for providing a propagation time difference between, and a propagation means for guiding both the control light and the signal light split into the linearly polarized light components orthogonal to each other to the nonlinear refractive index change manifesting unit; and the linearly polarized light components orthogonal to each other. An optical switch comprising means for eliminating a time difference given between the optical switch and the optical switch, wherein the nonlinear refractive index change manifestation unit is configured by two nonlinear optical waveguides, as a second aspect, in addition to the above configuration, Among the two nonlinear optical waveguides, the nonlinear optical waveguide arranged at the subsequent stage compensates for the amount of phase shift by the two nonlinear optical waveguides to be 0 or π radian. As a third mode, there is provided an optical switch in which at least one of the two nonlinear optical waveguides is provided with adjustment means for adjusting the amount of phase shift. According to a fifth aspect, there is provided an optical switch in which polarization rotating means is provided between the two nonlinear optical waveguides. As a fifth aspect, a polarization rotating means is provided between the two nonlinear optical waveguides. Is provided, and T exits from the first nonlinear optical waveguide.
E-polarized signal light enters the second nonlinear optical waveguide as TM polarized light and exits the first nonlinear optical waveguide.
An optical switch configured so that polarized signal light is incident on the second nonlinear optical waveguide as TE polarized light. According to a fifth aspect, in addition to the above configuration, a light in which the polarization rotating unit is a half-wave plate Switch.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical switch according to the present invention is a means for dividing a signal light into a linearly polarized light component orthogonal to each other, and a nonlinear refractive index change manifesting section made of a medium which generates a nonlinear refractive index change by amplifying control light. Means for providing a propagation time difference between the mutually orthogonal linearly polarized light components, and propagation means for guiding both the control light and the signal light split into the mutually orthogonally linearly polarized light components to the nonlinear refractive index change manifesting unit. And an optical switch comprising means for canceling a time difference given between the linearly polarized components orthogonal to each other,
The nonlinear refractive index change manifestation unit is configured by two nonlinear optical waveguides, and, in addition to the above configuration, of the two nonlinear optical waveguides, a nonlinear optical waveguide disposed at a subsequent stage is:
An optical switch configured to compensate so that the amount of phase shift by the two nonlinear optical waveguides becomes 0 or π radian, and a polarization rotating unit is provided between the two nonlinear optical waveguides. The TE-polarized signal light emitted from the one nonlinear optical waveguide enters the second nonlinear optical waveguide as TM polarized light, and the T-polarized signal light exits the first nonlinear optical waveguide.
Since the M-polarized signal light is configured to be incident on the second nonlinear optical waveguide as TE-polarized light, the nonlinear phase shift received by the signal light is transmitted by the first and second nonlinear optical waveguides. Being independent of light polarization.

That is, in the first nonlinear optical waveguide, the nonlinear phase shift of the signal light pumped by the control light is, for example, (2/3) π radian for the TE polarized signal light and TM polarized signal light. Then, it is assumed that (１ ／) π radian. The signal light propagated in the first nonlinear optical waveguide in the state of TE polarization propagates in the second nonlinear optical waveguide in the state of TM polarization, and conversely, propagates in the first nonlinear optical waveguide in the state of TM polarization. The signal light is propagated in the second nonlinear optical waveguide in a state of TE polarization.

Therefore, since the linearly polarized light components orthogonal to each other undergo a nonlinear phase shift of π radians, the signal light output immediately after the end of the switching operation completely returns to the initial state. The extinction ratio is improved. After the control light is amplified by the first nonlinear optical waveguide, it is further amplified by the second nonlinear optical waveguide. Therefore, although the control light pulse energies input to the first and second nonlinear optical waveguides are different from each other, they are used in a state where the output is almost saturated. There is not much difference.

For precise adjustment, it is sufficient to provide adjusting means for adjusting the amount of direct current applied to the first and second nonlinear optical waveguides, respectively.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific example of an optical switch according to the present invention will be described below in detail with reference to the drawings. Figures 1 and 4
A non-linear refractive index change expressing section A made of a medium that generates a non-linear refractive index change by amplifying the control light; means 4 for dividing the signal light into linearly polarized light components orthogonal to each other; A means 4 for providing a propagation time difference between the control light and a propagation means 6 for guiding both the control light and the signal light split into the linear polarization components orthogonal to each other to the nonlinear refractive index change manifesting unit A; In the optical switch provided with the means 5 for canceling the time difference given between the linearly polarized light components, it is shown that the nonlinear refractive index change manifestation part A is constituted by two nonlinear optical waveguides 1 and 3.
Of the two nonlinear optical waveguides 1 and 3, the nonlinear optical waveguide 3 arranged at the subsequent stage is configured to compensate so that the phase shift amount by the two nonlinear optical waveguides 1 and 3 becomes 0 or π radian. It is shown that at least one of the two nonlinear optical waveguides 1 and 3 is provided with adjusting means 8 for adjusting the amount of phase shift. Between the optical waveguides,
It is shown that the polarization rotation means 2 is provided, and the polarization rotation means 2 is provided between the two nonlinear optical waveguides 1 and 3, and TE which emits the first nonlinear optical waveguide 1 is provided.
Polarized signal light enters the second nonlinear optical waveguide 3 as TM-polarized light and exits the first nonlinear optical waveguide 1.
An optical switch configured so that M-polarized signal light enters the second nonlinear optical waveguide 3 as TE-polarized light is shown.

Further, after dividing the signal light into linear polarization components orthogonal to each other and giving a predetermined time difference to the two components of the divided signal light, the two components of the signal light are nonlinearly refracted by amplifying the control light. The first and second nonlinear optical waveguides 1 and 3 are guided to a first nonlinear optical waveguide 1 made of a medium which causes a change in rate, and are phase-shifted. 5 shows a method for improving the extinction ratio of an optical switch in which the extinction ratio is improved by making the total phase shift amount at 0 or π radian.

A polarization rotating means 2 is provided between the two nonlinear optical waveguides 1 and 3 so that the TE-polarized signal light emitted from the first nonlinear optical waveguide 1 is supplied to the second nonlinear optical waveguide 3. There is shown a method for improving the extinction ratio of an optical switch in which a TM-polarized signal light which is incident on the second nonlinear optical waveguide 3 as a TM-polarized light is emitted as TM polarized light and exits the first nonlinear optical waveguide 1. I have.

The embodiment of the present invention will be described in more detail.
The nonlinear optical waveguides 1 and 3 are waveguides having InGaAsP as a core and InP as a clad. The semiconductor optical waveguides 1 and 3 are obtained by growing InGaAsP on an InP substrate by metalorganic vapor phase epitaxy (MOVPE), processing it into a stripe by lithography and wet etching, and again forming an I / O by MOVPE.
It is created by growing InP for embedding nGaAsP. Further, anti-reflection coating is applied to both end surfaces of the semiconductor optical waveguides 1 and 3. InGaAs
The optical waveguide 1a made of P has an absorption edge wavelength of 1.52 μm, a thickness of 0.3 μm, a width of 0.4 μm, and a length of 300 μm. Further, a DC current for adjusting a phase shift is applied to the semiconductor optical waveguide 1 or 3 so that the semiconductor optical waveguide 1 or 3 exhibits a gain with respect to light having a wavelength in the range of 1.52 μm to 1.35 μm.

The half-wave plate 2 inserted between the nonlinear optical waveguides 1 and 3 rotates the polarization directions of the control light and the signal light emitted from the semiconductor optical waveguide 1 by 90 degrees. The birefringent crystals 4 and 6 are made of a rutile single crystal. Rutile single crystal is
Light pulse with linear polarization perpendicular to the optical axis (ordinary ray) and light pulse with linear polarization parallel to the optical axis (extraordinary ray)
Exhibit the birefringence that the propagation times of the light beams are different. The analyzer 7 transmits only a certain linearly polarized light.

This optical switch has a wavelength of 1.55 μm,
A signal light pulse train having a pulse width of 2 ps and a repetition frequency of 160 GHz and a control light pulse train having a wavelength of 1.40 μm, a pulse width of 2 ps and a repetition frequency of 10 GHz are input.
That is, the wavelength of the signal light is longer than that of the absorption edge in the transparent region 20.
Then, the control light wavelength is set within the gain band 21. The control light is incident on the nonlinear optical waveguide 1 via the WDM coupler 6 and is subjected to optical amplification.
The light enters the nonlinear optical waveguide 3 and undergoes optical amplification.

The carriers in the nonlinear optical waveguides 1 and 3 decrease due to the amplification of the control light, and a nonlinear phase shift occurs with respect to the signal light in accordance with the change in the carrier density. On the other hand,
The signal light pulse is given a time delay in the birefringent crystal 4 between the S-1 component having a polarization perpendicular to the optical axis and the S-2 component having a polarization parallel to the optical axis. After passing through the WDM coupler 6, these signal light pulses are incident on the nonlinear optical waveguide 1, and the S-1 component and the S-2 component propagate as TM polarized light and TE polarized light, respectively. The signal light emitted from the non-linear optical waveguide 1 is incident on the non-linear optical waveguide 3 after the polarization is rotated by 90 degrees by the half-wave plate 2 as the polarization rotating means. Therefore, the S-1 component and the S-2 component propagate as TE polarized light and TM polarized light, respectively.

Thereafter, in the birefringent crystal 5, the polarized light of the S-1 component is incident parallel to the optical axis and the polarized light of the S-2 component is perpendicular to the optical axis. As a result, the time difference between the S-1 component and the S-2 component given by the birefringent crystal 4 is canceled, and both components are synthesized again. When the relative phase difference between the two components at the time of combining is 0 and π, the polarizations of the signal light at the time of combining are orthogonal to each other.

The signal light emitted from the birefringent crystal 5 is analyzed by an analyzer 7
And only one linearly polarized light is output. Here, as an initial state, the relative phase difference between the S-1 component and the S-2 component at the time of emission from the birefringent crystal 5 is 0, and linearly polarized light determined by the combination of both components is completely blocked by the analyzer 7. Consider the case. The operation of the optical switch according to the present invention will be described with reference to FIG. As shown in FIG. 4A, 6.25p
Signal light pulses are input at s intervals. Here, “10
Illustrated is a signal light pulse train coded as 1111010 ". Of these, three pulses S1, S2, and S3 are noted.

These pass through the birefringent crystal 4 to form two components whose polarizations are orthogonal to each other, S11, S21, S31 and S12, S22, S22, as shown in FIG.
32 is provided with a time delay. After the control light pulse C is inserted at the position shown in FIG. 3C, the light is incident on the nonlinear optical waveguides 1 and 3, and the nonlinear refractive index rises substantially following the control light pulse and slowly relaxes. Since the relaxation time is longer than the time scale shown in FIG. 4, for the sake of simplicity, it is assumed that the relaxation time is a step-like change as shown in FIG.

The signal light pulses S31, S22, S32, etc. incident after the control light pulse C undergo a nonlinear phase shift of π radian. The signal light pulse emitted from the nonlinear optical waveguide 1 further passes through the birefringent crystal 5 to restore the time delay previously given by the birefringent crystal 4 as shown in FIG. . As a result, only the relative phase difference between S21 and S22 becomes π radian, and the polarization of the combined signal light pulse is rotated by 90 degrees with respect to the initial state. On the other hand, since both S11 and S12 are not subjected to the non-linear phase shift, the relative phase difference is 0, and
Since both S31 and S32 undergo a non-linear phase shift of π radians, the relative phase difference is also zero.

Here, as described above, S31 and S31
The nonlinear phase shift received by the second optical waveguide 32 becomes completely equal by passing through the first and second nonlinear optical waveguides 1 and 3. That is, the polarization direction of S3 synthesized in S31 and S32 is the same as the initial state. Therefore, by passing through the analyzer 7, only the signal light pulse S2 is output as shown in FIG. With such a mechanism,
It becomes possible to realize an ultra-high-speed optical-optical switch that separates from a 160 Gbps data string at 10 GHz repetition.

FIG. 2 is a diagram showing a part of the configuration of an optical switch according to a second embodiment of the present invention. In this example,
On a silicon substrate 11, nonlinear optical waveguides 1 and 3, a half-wave plate 2, and a silica waveguide 1 for optical coupling between them.
2, 13, 14, and 15 are integrated.

First, the nonlinear optical waveguides 1 and 3 are mounted.
11 on silicon substrate etched leaving only part
And SiO_Two-TiO_TwoWith a core of SiO_TwoThe cladding
Embedded silica waveguides 12, 13, 14, 1
5 is formed. The creation method is described in, for example, “1993 March
Mon, Electronics Letters, Vol. 29, No. 5,
444-446 pages, (ELECTONICS LE
TETTRS, VOL, 29, NO5, 444-44
6, MARCH 1993) ".
On a silicon substrate, SiO is deposited by a flame deposition method._Two, S
iO_Two-TiO_TwoAre sequentially deposited and then photolithographically
And dry etching for SiO_Two-TiO_TwoStrike
Process into a lip shape. After that, the SiO_TwoDepositing
By SiO _Two-TiO_TwoEmbed

Further, a portion where the nonlinear optical waveguides 1 and 3 are mounted and a portion where the half-wave plate 2 is inserted are removed by dry etching. The non-linear optical waveguides 1 and 3 are fixed to the portions where the silicon is exposed by soldering. The nonlinear optical waveguides 1 and 3 to be mounted are buried semiconductor optical waveguides having InGaAsP as a core and InP as a clad, similarly to those used in the first embodiment.

The half-wave plate 2 inserted between the nonlinear optical waveguides 1 and 3 is made of polyimide.
The polarization directions of the control light and the signal light emitted from the light are rotated by 90 degrees. By using this integrated element instead of 1, 2, and 3 in the configuration of FIG. 1, it is possible to obtain an optical switch similar to that of the first embodiment. In the above, I
Although an optical switch using a nonlinear optical waveguide having nGaAsP as a core and InP as a clad has been described as an example,
According to the present invention, InGaAs that can be formed on an InP substrate
A similar optical switch can be obtained when a s / InGaAsP multiple quantum well structure is used as a core or when a nonlinear optical waveguide made of another material is used, such as when a material that can be formed on a GaAs substrate is used.

Also, an example has been described in which a combination of a nonlinear optical waveguide alone and another optical component or a combination of an optical circuit in which a nonlinear optical waveguide and a half-wave plate are integrated and another optical component are used. However, according to the present invention, the same effect can be obtained even when all optical components are configured by an integrated optical circuit. Further, the signal light wavelength is not limited to only the transparent region of the nonlinear optical waveguide.
When using a nonlinear optical waveguide having an optical amplification effect,
The same effect can be obtained even if the signal light wavelength is set in the gain region.

[0039]

As described above, according to the optical switch of the present invention, an output having a high extinction ratio can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an optical switch according to the present invention.

FIG. 2 is a diagram showing a part of the configuration of a second embodiment of the optical switch of the present invention.

FIG. 3A is a diagram showing a configuration of an optical switch according to a conventional technique, and FIG. 3B is a graph showing a relationship between wavelength and signal loss.

FIG. 4 is a waveform chart showing the operation of the optical switch according to the present invention and the optical switch according to the related art.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 nonlinear optical waveguide 2 half-wave plate 3 nonlinear optical waveguide 4, 5 birefringent crystal 6 WDM coupler 7 analyzer 11 silicon substrate 12, 13, 14, 15 silica waveguide

Claims (8)

[Claims] 1. A non-linear refractive index change generating section comprising a medium which generates a non-linear refractive index change by amplifying control light, means for dividing signal light into linear polarization components orthogonal to each other, and the linear polarization components orthogonal to each other Means for providing a propagation time difference between the transmission means, propagation means for guiding both the control light and the signal light divided into the mutually orthogonal linearly polarized light components to the nonlinear refractive index change manifesting section, and the mutually orthogonal linearly polarized light. An optical switch comprising means for canceling a time difference given between components, wherein the nonlinear refractive index change generating section is constituted by two nonlinear optical waveguides. 2. The method according to claim 1, wherein, of the two nonlinear optical waveguides, a nonlinear optical waveguide arranged at a subsequent stage compensates for a phase shift amount of the two nonlinear optical waveguides to be 0 or π radian. The optical switch according to claim 1, wherein: 3. The optical switch according to claim 1, wherein at least one of the two nonlinear optical waveguides is provided with adjustment means for adjusting a phase shift amount. 4. The optical switch according to claim 1, wherein a polarization rotation unit is provided between the two nonlinear optical waveguides. 5. A polarization rotating means is provided between the two nonlinear optical waveguides, and TE-polarized signal light emitted from the first nonlinear optical waveguide enters the second nonlinear optical waveguide as TM polarized light. 4. The optical switch according to claim 1, wherein the TM-polarized signal light emitted from the first nonlinear optical waveguide is incident on the second nonlinear optical waveguide as TE-polarized light. 6. An optical switch according to claim 4, wherein said polarization rotating means is a half-wave plate. 7. A signal light is divided into mutually orthogonal linearly polarized light components, and a predetermined time difference is given to the two divided signal light components. Then, the two signal light components are nonlinearly refracted by amplification of control light. Leading to a first nonlinear optical waveguide made of a medium causing a rate change, and phase-shifting, further leading to a second nonlinear optical waveguide, so that the total phase shift in the first and second nonlinear optical waveguides. A method for improving the extinction ratio of an optical switch, characterized in that the extinction ratio is improved by setting the amount to 0 or π radian. 8. A polarization rotating means is provided between the two nonlinear optical waveguides, and TE-polarized signal light emitted from the first nonlinear optical waveguide enters the second nonlinear optical waveguide as TM polarized light. 8. The method for improving the extinction ratio of an optical switch according to claim 7, wherein the signal light of TM polarization emitted from the first nonlinear optical waveguide is made incident on the second nonlinear optical waveguide as TE polarized light.