JP3075199B2 - Light switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-high-speed, large-capacity optical time multiplexing (Optical Time-Domain).
The present invention relates to an optical control optical switch, an optical demultiplexer (optical demux), an optical gate, and the like used for multiplexing (OTDM) optical communication.

[0002]

2. Description of the Related Art As the demand for communication increases, the speed and capacity of optical communication have been energetically advanced. Time-Domain Multiplexin
In the g: TDM) communication system, a time multiplexed optical signal is converted into electric communication by a photodetector, and then demultiplexing is performed by electric signal processing (DeMultiplexing).
Therefore, the speed limit of TDM optical communication is determined by the speed of optical-electrical signal conversion and electric signal processing.
bps is the limit.

In recent years, OTDM optical communication and wavelength multiplexing (Wavel) have been considered as exceeding the speed limit of TDM optical communication.
angle-Domain Multiplexin
g: WDM) Optical communication is being studied. WDM is a technique for multiplexing optical signals having different wavelengths.
Long-distance transmission of about 00 Gbps is the limit.

On the other hand, in a PTDM optical communication system, an optical signal of a single wavelength is multiplexed to 100 Gbps to 1 Tbps or more, and a receiving side uses only the optical signal to transmit a signal of 40 Gbps.
Demultiplexing is performed up to s or less. Therefore, a device (optical Demux) for performing demultiplexing processing is one of the key devices. The optical Demux does not use optical-to-electrical conversion or electrical signal processing, and can operate at high speed.

The conventional optical Demux has a problem that the control light power is very large. However, recently, a cascade type optical switch, a symmetric Mach-Zehnder (Symmetric Matrix) has been used as an optical Demux having a small control light power.
ch-Zehnder: SMZ), and Terahe
rz Optical Asymmetric Dem
There are three proposals of multiplexor (TOAD).

Among them, SMZ and TOAD have problems of heat generation, material deterioration and current generation due to generation of carriers in the semiconductor material constituting the device, and the control light power required for these switches is an optical pulse width. It is constant regardless of.

On the other hand, since the cascade type optical switch does not generate carriers, there is no problem such as heat generation.
Further, since the required control light power is inversely proportional to the light pulse width, the shorter the pulse width, the more the control power can be reduced.

The above-mentioned cascade type optical switch is DeSa.
proposed by Ivo et al. (DeSalvo et a
l. , Opt. Lett. 17, 1992, 28-3
0), which uses a phase change based on the second-order nonlinear susceptibility χ ^(2), and is characterized in that the second harmonic (SHG) light is involved in the mechanism of the phase change.

[0009]

The fundamental wavelength and the second harmonic wavelength used in the cascade type optical switch generally differ in the refractive index of the waveguide material, so that the phase velocity of the fundamental wave and the SHG are shifted. Can be aligned. However, even if the phase matching is performed, since the refractive index dispersion (dn / dλ) of the waveguide material is different between the fundamental wavelength and the second harmonic wavelength, the group velocity (waveguide) of the fundamental wavelength optical signal pulse and the SHG optical pulse is changed. Speed), and the fundamental wave pulse and the SHG pulse are shifted as the light travels through the waveguide. Such a phenomenon is generally a walk
It is called off.

It has been considered in the past studies that when a walkoff occurs in a cascade-type optical switch, the interaction between the mediating SHG pulse and the fundamental wave pulse is extremely reduced so that a phase change does not occur, and therefore the switch does not operate.

Walk of fundamental wave pulse and SHG pulse
The value of off is represented as follows.

[0012]

(Equation 1) Where T _pp is the distance on the time axis between the fundamental wave pulse peak and the SHG pulse peak, T _{0 is} the pulse width of the input fundamental wave pulse, κ ′ _m , κ ′ _{2m is} the reciprocal of the group velocity between the fundamental wave and the SHG wave, L _walkoff : walkoff length, L: cascade region length (optical waveguide length for phase matching).

It can be seen from the above equation that the shorter the pulse width and the larger the refractive index dispersion, the stronger the walkoff occurs.

In a cascaded optical switch using Mach-Zehnder interference, (Y. Baek et a
l. , Opt. Lett. 20, 1995, 2168-
2170) A report using a dielectric (LiNbO ₃ ) as a waveguide material has been reported. In this report, almost no walkoff occurs because a pulse having a long pulse width (90 ps) is used and the dielectric material has a small refractive index dispersion.

Sundheimer et al. Have reported on the cascade phase change incorporating the walkoff effect from both experimental and calculated points (Sundheimer et al.).
et al. , Opt. Lett. 18, 1993,
1397-1399), and in this report the walkoff =
1.9 is reported only for the case where walkoff is small, and there is no study on the cascade phase change when walkoff is large.

Semiconductors have a large value of χ ⁽²⁾ and can be phase-matched and integrated, so they are promising as materials for cascade switches (Y. Ueno, US Pat A).
ppl. No. 08/633882), and the refractive index dispersion is large. Also, when a 1 ps-wide fundamental wave pulse (1.5 μm wavelength) used for 1 Gbps signal transmission is input into a GaAs-based semiconductor optical waveguide, the walkoff length is very short, 300 μm, and a large walk in a cascade type optical switch.
off is likely to occur.

Have considered the case where a semiconductor is used for a cascade type optical switch.
No specific reference is made to the effects of alcohol off (Ironside et al., IEEE).
J. Quantum Electron. Vol. 2
9, pp. 2650-2654, Oct. 1993, H
utchings et al. , Opt. Lett.
Vol. 18, pp. 793-795, May 199
3).

[0018]

An optical switch according to the present invention comprises:
A waveguide type cascade type optical switch, wherein a length (L) of a cascade region generating a phase shift and a walko
The ff length (Lwalkoff) satisfies the relationship of 10 ≦ L / Lwalkoff <30. In addition, waveguide type
The material constituting the optical switch is AlGaAs, Al
GaInP, InGaAsP, AlGaInAs, Cd
It is characterized by being one of ZnSSe, AlGaInN, and SiGe.

Further, the cascade-type optical switch has a cascade region in a portion of the waveguide of the directional coupler formed on the substrate which is closest to the waveguide,
Whether one of the Mach-Zehnder interference type waveguides formed on the substrate has a cascade region in one arm or the Mach-Zehnder interference type waveguide formed on the substrate has a cascade region in both arms. In addition, one of the arms has a phase controller for controlling the bias phase to 0 or π. Further, a polarizer or a wavelength filter is arranged at a stage subsequent to the optical switch.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, first, a simulation result of the effect of Walkoff when a "semiconductor" having a large refractive index dispersion is used for a cascade type optical switch is shown below. Push-pull Mach-Zehnder switch as cascade type optical switch, A as semiconductor
lGaAs was used.

FIG. 4 shows an example of a push-pull type Mach-Zehnder switch. In the push-pull type Mach-Zehnder switch 7 of FIG. 4, an optical waveguide including an incident part 8, an optical branch part, an arm part (11, 12), a merging part, and an emission part is formed on a substrate. Is quasi-phase matching (qu
A cascade region composed of asi phase matching (QPM) structures 13 and 14 is provided.

The principle of the quasi-phase matching is to periodically modulate the second-order nonlinear susceptibility χ ⁽²⁾ (or the refractive index) in the optical waveguide to reduce the difference between the waveguide effective refractive index for the fundamental wave and the SHG wave. They are pseudo matching.

In the push-pull Mach-Zehnder optical switch shown in FIG. 4, the structure period of the QPM is provided so that the phase mismatch (ΔκL) in the cascade region becomes positive and negative in each arm. Further, a phase control region 15 is provided at a stage subsequent to the QPM structure 14 of the arm portion 12 in order to control the bias phase to 0 or π. In this portion, electrodes are provided above and below the waveguide to perform electro-optic effect type phase control.

As shown in FIG. 4, the signal light is a signal light pulse in which the light pulse is time-multiplexed. When the signal light pulse and the control light pulse overlap, a cascade phase difference + π / 2 occurs in the cascade region 13. In the cascade region 14, −π /
2 occurs. Therefore, the difference in the cascade phase change between the arms is π. In a push-pull Mach-Zehnder optical switch, the phase change generated by the cascade effect is half that of a normal Mach-Zehnder optical switch, so that the control light power can be reduced.

The basis of the operation mechanism of the cascade switch is a phase change received when the signal light pulse is guided through the cascade region.

When a single optical pulse (fundamental wave) is incident, the phase change received by the optical pulse is 0 when the optical pulse is weak, and increases from π / 2 to π when the optical pulse is strong. This is the basis of the actual optical switch operation of superposing the control pulse on the pulse.

The operation parameters will be described below while showing an example of a phase change of a pulse propagating in the cascade region.

The operating parameters are the amount of phase mismatch (ΔκL) normalized by the cascade region length, the normalized light pulse intensity (強度 L), and the like.

[0029]

(Equation 2) The three.

The following is an example of the operating conditions. walko
The ff length is proportional to the pulse width as shown in Expression (1). When the pulse width is 3 ps (corresponding to a 300 Gbps signal train), the walkoff length is 1 mm. Therefore, when the cascade region length (L) is 15 mm, walkoff = 15. Next, when L = 15 mm, the pulse peak power =
2W. Here, the value of χ ^{(2) is changed to} the value of the non-resonant region of GaAs (d ₁₄ = 130 pm/V＠10.6 μm).
m), the effective sectional area of the waveguide was set to 10 μm ² .

Therefore, the control light power when the Demux operation is performed at 40 Gbps is 240 mW. Also,
By slightly shifting the QPM period from the phase matching condition, ΔκL = about 3 to 30π is provided. The QPM period is 2-3 μm.

FIG. 6 shows the transitions of the fundamental wave pulse (a) and the SHG pulse (b) during the waveguiding in the case where the walkoff 15 occurs. In the figure, z is the propagation distance, t is the time axis,
ΔκL = π ² and (ΓL) ² = 120.

Since the SHG pulse has a large group velocity, it advances faster than the fundamental wave.
The pulse overlap is very small. However, despite the small overlap, the fundamental receives a large cascade phase change.

FIG. 7 shows the phase change of the fundamental pulse peak when only walkoff is changed. The left vertical axis represents the phase (Φ _NL / π), the right vertical axis represents the pulse waveform distortion, and the horizontal axis represents the walkoff. As shown in FIG.
Although the phase change is reduced as compared with the case where there is no off (10 ⁰ = 1), the decrease is very slow.

From FIG. 7, the normalized light pulse intensity (ΓL) ² =
Using a light pulse intensity equivalent to 120, walkoff
Push-pull interference operation even if is as large as 10 to 15 (Fig. 4)
It can be seen that the phase change (π / 2) required for the above is obtained.
The peak power 2W described above is an estimate based on (ΓL) ² = 120. Also, when a walkoff of about 30 occurs, the overlap between the fundamental wave pulse and the SHG pulse becomes very small, but the phase change of about 1/2 to 1/3 still remains.

The mechanism by which a large phase change occurs even though the overlap between the fundamental wave pulse and the SHG pulse is very small is that although the overlap is small, an SHG electric field having an intensity of about 1/100 exists at the position of the fundamental wave pulse. However, an interaction occurs between them. Therefore, energy exchange between the fundamental wave and the SHG electric field hardly occurs, but the phases of the electric fields are exchanged very efficiently.

FIG. 8 shows the switching operation of the push-pull Mach-Zehnder switch (FIG. 4). In the figure, the vertical axis represents the signal transmittance, and the horizontal axis represents the normalized input light intensity [(ΓL) ² ]. When the bias phase is π (Switch-On operation, solid line): When the signal pulse and the control pulse overlap (the input light intensity is high), the signal pulse is transmitted. When the signal pulse and control pulse do not overlap (input light intensity is low),
Signal pulses are not transmitted. When the bias phase is 0 (S
On the contrary, the signal pulse is transmitted only when the signal pulse and the control pulse do not overlap with each other (switch-off operation, broken line).

In the directional coupler (FIGS. 1 and 2), when the signal pulse and the control pulse overlap, the signal pulse is output as the signal light pulse 32 from the first channel, and when not overlapped, the signal light is output from the second channel. It is output as a pulse 33.

FIG. 9 shows the waveform of the signal light pulse output from the push-pull Mach-Zehnder switch. In the figure,
The vertical axis represents light intensity, and the horizontal axis represents time. The solid line represents the output pulse waveform, the broken line represents the output pulse waveform after passing through the cascade region, and the dotted line represents the input pulse waveform. As shown in the figure, the output pulse waveform has a single peak without disturbance.

As described above, when a semiconductor which is a material having a large refractive index dispersion is used for the cascade type optical switch, the length of the cascade region and the walkoff length are 1 <L / L.
If the relationship of _walkoff <30 is satisfied, the fundamental wave pulse undergoes a sufficiently large phase change, so that it can operate as an optical switch.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Another cascaded optical switch to which the present invention can be applied will be described with reference to the drawings. FIG. 1 shows the structure of an optical Demux according to a first embodiment of the present invention.

In the optical Demux 1 of the first embodiment, upper waveguide channels 2 and 3 are formed on a substrate, and the optical waveguide channels 2 and 3 are so-called directional couplers provided close to each other at a central portion 4. It has a structure.

A cascade region is formed in the central portion 4,
Quasi phase matchi
ng: QPM) structure 5 is provided, and quasi-phase matching between the fundamental wave and the SHG wave is performed in this region. The principle of quasi-phase matching, second-order nonlinear susceptibility of the optical waveguide chi ⁽²⁾
By periodically modulating (or the refractive index), the difference between the waveguide effective refractive index for the fundamental wave and the SHG wave is pseudo-matched.

FIG. 5 shows an example of the QPM structure of the cascade region of this embodiment. A GaAs buffer layer, an AlGaAs cladding layer 20, an asymmetric quantum well (QW) layer 19, and an AlGaAs cladding layer 18 are laminated on a GaAs substrate 22, and a ridge is provided on the AlGaAs cladding layer 18 to form an optical waveguide channel. Next, the AlGaAs cladding layer 1
A mask is provided on the portion 8 except for the portion where the QPM structure 5 is to be formed, ions are implanted from the surface to the AlGaAs cladding layer 20, and the asymmetric quantum well (QW) layer 19 is periodically disordered to form a QPM structure. The QPM period is approximately 2 μm.

The dimensions of the waveguide structure are such that the thickness of the cladding layer is 2 to 5 μm and the channel width is 2 to 4 μm, and the fundamental wave and the SHG wave are guided. The length of the cascade region is
Approximately 200
μm to 10 mm.

In the asymmetric quantum well (QW), SHG
In order to avoid the absorption loss of the fundamental wave, the band gap energy of the QW is set to twice or more the photon energy of the fundamental wave. When 1.5 μm wavelength light (0.8 eV) is used as a fundamental wave for optical communication, the band gap energy is 1.
6 eV or more (0.77 μm or less in wavelength) is necessary, and a material suitable for this is AlGaAs of the embodiment.
In addition, for example, there is AlGaInP.

As described above, an ordered-disordered semiconductor QPM structure (K. Kelaidis, et.
al. , IEEE Trans, Quantum E
electron, vol. 30, pp. 2998-30
05, 1994), but semiconductors such as GaAs and L
Domain-inverted QPM structures reported in dielectrics and organic materials such as iNbO ₃ (MJ Angell, et al.
al. , Appl. Phys. Lett. vol. 6
4, 1994, p. 3107-3109; J. Y
oo, et al. , Appl. Phys. Lett.
vol. 66, 1995, p. 3410-3412)
Can also be used.

Next, the operation of the first embodiment will be described. First
In this embodiment, the time-multiplexed signal light pulse 31 and control light pulse 41 are input to the optical Demuxl. Here, both are polarized light orthogonal to each other.

The optical pulse input to the first channel 2 is
A cascade phase change occurs in the central portion 4 of the light Demux1. The cascade phase change is π when the control light pulse 41 and the signal light pulse 31 overlap, and is 0 when they do not overlap. Therefore, the time-multiplexed signal light is distributed to the first output port and the second output port by the control light pulse.

In the area other than the center, the cascade effect does not occur since the phase matching condition deviates greatly. The control light in FIG. 1 has a polarization orthogonal to the signal light pulse, but is removed by the polarizer 6.

As described above, the cascade phase change using orthogonally polarized light is described in Kobyakov and huching.
et al. (Kobyakov snd)
Lederer, Physical Review
A, vol. 54, no. 4, pp. 3455-347
1, 1996; kobyakov et al. , Op
tics Communications, vol. 1
24, pp. 184, 1996; Huchings e
t al. , Optics Letters, vol.
18, pp. 793-795, May 1993).

In this embodiment, the signal light and the control light have the same wavelength for simplicity, but the present invention can be applied even when the wavelengths are different (Hutchings et al.).
al. , Opt. Lett. Vol. 18, pp. 7
93-795, May 1993). When the wavelengths are different, a wavelength filter can be provided instead of the polarizer 6 to remove the control light component.

The basis of the operation mechanism when the wavelength is the same is the one reported by Asanto et al.
al. , Appl. Phys. Lett. Vol. 6
2, pp. 1323-1325, March 199
Same as 3).

If a semiconductor can be used as the material of the cascade-type optical switch as described above, the optical Demux
And a control light source can be further integrated. The present invention can also be applied to an integrated light Demux.

FIG. 2 shows a second embodiment of the optical Demux to which the present invention is applied.

The light Demux 1 of the second embodiment has the same structure as that of the first embodiment, and the optical waveguide channel 2 is provided on the substrate.
And 3 are formed, and the optical waveguide channels 2 and 3 have a directional coupler structure provided close to each other at the central portion 4. Therefore, specific description is omitted. The second embodiment is different from the first embodiment in the point of the incident signal light pulse.

In the second embodiment, large and small light pulses are time-multiplexed signal light pulses, and the cascade phase change in the second embodiment is π when the input light pulse is large. It becomes 0 when the light pulse is small. Therefore, the time-multiplexed optical pulse is distributed to the first output port and the second output port depending on the difference in the magnitude of the optical pulse between the control light and the signal light.

Also in the second embodiment, the cascading effect does not occur except in the central part because the phase matching condition deviates greatly.

In the second embodiment, the signal light and the control light have the same wavelength for the sake of simplicity. However, as in the first embodiment, the present invention can be applied to the case where the wavelengths are different. It is also possible to remove the control light component.

FIG. 3 shows a third embodiment of a Mach-Zehnder type optical switch to which the present invention is applied. In the Mach-Zehnder optical switch 7 of the third embodiment, an optical waveguide including an incident part 8, an optical branch part, an arm part (9, 10), a junction part, and an emission part is formed on a substrate. Q in part 9
A PM structure is provided. The QPM structure in this embodiment is formed in the same manner as in the first embodiment.

In the third embodiment, a time-multiplexed signal light pulse 31 and control light pulse 41 are input. Here, both are polarized light orthogonal to each other.

On the other hand, the signal light and control light guided through the arm 9 undergo a cascade phase change. The phase change is π when the signal pulse and the control pulse overlap, and is 0 when they do not overlap. The pulse guided through the arm 10 does not cause a cascade phase change. Interference occurs at the junction of the arms 9 and 10.

When the lengths of the arms 9 and 10 are different from each other by 波長 wavelength, the bias of the phase difference between the arms is π. Therefore, when the signal pulse overlaps with the control pulse, the cascade phase change + bias phase difference = 2π, and the signal light reinforces by interference and goes out to the output channel B (On state). If the signal pulse does not overlap with the control pulse, the cascade phase change + bias phase difference = π, and the signals cancel each other out due to interference, and no signal light is emitted (Off state).

In the above embodiments, the dimensions of the waveguide structure are as follows: the cladding layer thickness is 2 to 5 μm, and the channel width is 2 to 4 μm.
The fundamental wave and the SHG wave are guided as μm. The length of the cascade region is about 200 μm to 10 mm, depending on the pulse width of the signal light and operating conditions.

In the asymmetric quantum well (QW), SHG
In order to avoid the absorption loss of the fundamental wave, the band gap energy of the QW is set to twice or more the photon energy of the fundamental wave. When 1.5 μm wavelength light (0.8 eV) is used as a fundamental wave for optical communication, the band gap energy is 1.
6 eV or more (0.77 μm or less in wavelength) is necessary, and a material suitable for this is AlGaAs of the embodiment.
Besides, there is, for example, AlGaInP.

[0066]

As described above, a conventional cascade type optical switch has an L switch.
Only materials having a low refractive index dispersion such as iNbO ₃ , KTP, and organic materials have been used. However, when the length of the cascade region and the walkoff length _satisfy the relationship of 1 <L / L _walkoff <30, the refractive index is reduced. A material having a large rate dispersion (eg, AlGaAs, AlGaInP, InGaAs)
P, AlGaInAs, CdZnSSe, AlGaIn
A cascade-type optical switch can be configured using various semiconductors such as N and SiGe. Also, the use of semiconductor materials has made it possible to integrate elements on the same substrate.

Another advantage of the present invention is that the output pulse waveform breakup is eliminated.
Traditionally, pulse waveform splitting is associated with the choice of ΔκL,
ΔκL for switching operation with small light energy
Is better, but in the conventional case without walkoff, if ΔκL is smaller than 30π, the division becomes remarkable as shown in FIG. In the present invention, as shown in FIG.
No splitting occurs under similar conditions.

The above-mentioned report by Asanto et al. Assumes that a very small ΔκL (0.1π) is obtained and that a good output pulse without pulse waveform splitting can be obtained.
This is based on the fact that the pulse intensity and phase change stepwise (in the report, step-like) at a very small ΔκL. However, it is very difficult to uniformly produce a very small ΔκL of 0.1π over the entire cascade region, and it is not realistic.

Another advantage is that the manufacturing accuracy of the cascade region length is not strict. In the conventional cascade switch, since the energy exchange between the fundamental wave and the SHG wave occurs strongly, the intensity and phase of the fundamental wave largely pulsate during the waveguide. Therefore, high precision was required for producing the cascade region length. On the other hand, in the present invention, since energy exchange hardly occurs, the allowable range of the length is wide, and high precision is not required for producing the cascade region length. Therefore, a cascade-type optical switch having excellent productivity can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a light Demux according to the present invention.

FIG. 2 is a diagram showing an embodiment of a light Demux according to the present invention.

FIG. 3 is a diagram showing an embodiment of a Mach-Zehnder switch according to the present invention.

FIG. 4 is a diagram showing an embodiment of a Mach-Zehnder switch according to the present invention.

FIG. 5 is a diagram showing a QPM structure in a cascade region.

FIG. 6 is a diagram showing transitions of a fundamental wave pulse and an SHG pulse during waveguiding.

FIG. 7 is a diagram illustrating a relationship between a cascade phase change amount and a walkoff.

FIG. 8 is a diagram showing the output intensity of a Mach-Zehnder switch.

FIG. 9 is a diagram showing an output pulse waveform of the present invention.

FIG. 10 is a diagram showing a conventional output pulse waveform.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical Demux 2 Channel A 3 Channel B 4 Cascade area 5 QPM structure 6 Polarization filter

Continuation of the front page (56) References IEEE Journal of Quantum Electronics, Vol. 29, No. 10, p. 2650-2654 Appl. Phys. Lett. Vol. 62, No. 12, p. 1323-1325 4, IEEE Journal of Quantum Electronics, Vol. 29, No. 10, p. 2650-2654 Optics Letters, Vol. 18, No. 10, p. 793-795 3, Appl. Phys. Lett. Vol. 62, No. 12, p. 1323-1325 4, IEEE Journal of Quantum Electronics, Vol. 29, No. 10, p. 2650-2654 Optics Letters, Vol. 18, No. 17, p. 1397-1399 Optics Letters, Vol. 18, No. 10, p. 793-795 3. Appl. Phys. Lett. Vol. 62, No. 12, p. 1323-1325 4, IEEE Journal of Quantum Electronics, Vol. 29, No. 10, p. 2650 -2654 (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/313 G02F 1/377 JICST file (JOIS)

Claims (7)

(57) [Claims] 1. A cascade type optical switch of a waveguide type , wherein the length (L) and the walkoff length (Lwalkoff) of a cascade region for generating a phase shift are 10 ≦ L /
An optical switch characterized by satisfying a relationship of Lwalkoff <30. 2. A cascaded optical switch of the waveguide type.
Is composed of AlGaAs, AlGaInP, In
GaAsP, AlGaInAs, CdZnSSe, Al
2. The optical switch according to claim 1, wherein the optical switch is one of GaInN and SiGe. 3. The cascade type optical switch according to claim 1, wherein the directional coupler formed on the substrate has a cascade region at a position of the waveguide closest to the waveguide. An optical switch as described. 4. The optical switch according to claim 1, wherein said cascade type optical switch has a cascade region in one arm portion of a Mach-Zehnder interference type waveguide formed on a substrate. 5. The optical switch according to claim 1, wherein the cascade type optical switch has a cascade region in both arms of a Mach-Zehnder interference type waveguide formed on a substrate. 6. The cascade type optical switch has a cascade region in both arms of a Mach-Zehnder interference type waveguide formed on a substrate, and a bias phase is set to 0 or π in one of the arms. The optical switch according to claim 1, further comprising a phase control unit for controlling. 7. The optical switch according to claim 3, wherein a polarizer or a wavelength filter is arranged at a stage subsequent to the optical switch.
Or the optical switch according to 5 or 6.