JP2902367B2 - Light modulator - 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 modulator such as a spatial optical switch (hereinafter simply referred to as an optical switch) for switching the traveling direction of an optical signal propagating through an optical waveguide formed on a semiconductor substrate.

[0002]

2. Description of the Related Art The function of an optical switch is to switch the traveling direction of an optical signal (hereinafter referred to as switching).
In particular, it often refers to outputting an optical signal transmitted through an optical waveguide to a target optical waveguide as an output optical signal in accordance with a control signal. In an optical switch that performs such a function, if switching is performed by applying an external voltage, the structure can be simplified, and
The optical switch can function following a control signal that changes at a high speed. The switching by the application of the voltage utilizes the fact that the refractive index and the absorptivity of a part of the material constituting the optical waveguide are changed by the application of the voltage.

At present, the following four types of optical switches are known. That is, a directional coupler optical switch, a Mach-Zehnder interferometer optical switch, a total reflection optical switch, and a gate optical switch.
Kind. These optical switches are utilized in the system in a form that makes use of their respective characteristics.

The directional coupler optical switch includes two adjacent optical waveguides and a control electrode. By controlling the voltage of the control electrode, an optical waveguide through which an output optical signal propagates can be determined. . In the current directional coupling optical switch, lithium niobate (LiNbO ₃ : Lithium Nio) is used.
bate) is used as a basic technology. The primary electro-optic effect (Pockels effect) of this lithium niobate is an ultrafast phenomenon that can directly respond to the electric field frequency of light. However, in practice, the response speed of the actual device is limited by the modulatable frequency of the control voltage and the structure of the control electrode for applying the frequency. Recently, IEE, Journal of Quantum Electron 10, 7 (1980), p. 754 (IEE
As described in EJ Quantum Electron QE107 (1980) p.754), the diffusion loss using titanium diffusion is as low as 0.1 dB / cm, and the electro-optic effect is comparable to that of a single crystal. A technique for fabricating a wave path has been found and is up to the present.

Although the switching speed of such a directional coupler optical switch is very high in principle, the control electrode must be large. Therefore, the switching speed is limited by the large capacitance of the control electrode. It had been. Then, in order to reduce the size of the control electrode, the refractive index modulation rate may be increased. As a method for this, as described in JP-A-63-197915, a directional coupler optical switch composed of an optical waveguide having a quantum well layer provided near the center of a core layer is manufactured. By injecting light of a wavelength that resonates with excitons in the well layer,
It is known that a large refractive index modulation can be obtained. In addition, the control voltage applied to the control electrode can be naturally reduced by the large refractive index modulation rate.

As described in Japanese Patent Application Laid-Open No. 63-197915, a Mach-Zehnder interferometer optical switch also operates at a low voltage and a high speed with a large refractive index modulation factor using exciton resonance. What has been realized is known.

[0007]

The following problems have been encountered when trying to improve the refractive index modulation rate and reduce the size of the optical switch by the above-described method. That is, when the optical switch is operated at a high temperature, the structure in the dispersion relation due to the exciton resonance becomes dull, and the refractive index modulation rate does not increase. In addition, since light that resonates with excitons is used, the loss due to spontaneous emission is large, but if light that is as close to the resonance frequency as possible is used to improve the refractive index modulation rate, the loss in the optical switch increases. .

The present invention has been made to solve the above-mentioned problems, and provides an optical modulator that can operate at high speed, can be downsized, and can reduce a control voltage. The purpose is to:

[0009]

In order to achieve this object, according to the present invention, an electric field is applied to an optical waveguide having two or more adjacent portions, and an electric field is applied to at least one part of the inside of the optical waveguide. An optical modulator having a control electrode for guiding the exciton polariton.
Shall be and, part of the optical waveguide, and the substrate-side cladding layer formed on a semiconductor substrate, a large substrate having a refractive index as compared to the upper portion is formed and the substrate-side cladding layer of the substrate-side cladding layer A side core layer, a quantum well layer formed above the substrate side core layer and for confining excitons, an electrode side core layer formed above the quantum well layer, and an upper side of the electrode side core layer. And an electrode-side cladding layer having a smaller refractive index than the electrode-side core layer, wherein the substrate-side cladding layer and the substrate-side core layer are laminated.
Countercurrent region, the electrode-side core layer, the product of the electrode-side cladding layer
A grating is disposed in at least one of the layer direction regions in the stacking direction region.

In this case, a １ ／ wavelength shift is provided in at least one portion of the grating in which the phase of the grating is shifted by an integral multiple of １ ／.

In this case, the grating is chirped.

The waveguide having the above-mentioned grating is
The direction region and the waveguide direction region having the quantum well layer are separated.

The substrate-side cladding layer and the electrode-side cladding layer each include a layer having a large refractive index and a layer having a small refractive index, each having a wavelength of about ４ of the wavelength of light propagating through the optical waveguide.
Use a structure that is periodically stacked.

In the band diagram of the direct transition semiconductor, the energy of the conduction band at point Γ is larger than the level of electrons in the quantum well layer, and the energy of the valence band is higher than the level of holes in the quantum well layer. A barrier layer made of a smaller material is formed on both sides of the quantum well layer, and the conduction band energy at the point X or L is smaller than the level of electrons in the quantum well layer and the conduction band at the point Γ. A relaxation layer made of a material whose energy is higher than the electron level in the quantum well layer is formed between the barrier layer and the substrate-side core layer and the electrode-side core layer.

Further, at least one pair of the optical waveguides is brought close to both sides of the portion where the control electrode is provided.

[0016]

FIG. 2 is a schematic view showing a directional coupler optical switch according to the present invention, FIG. 1 is an enlarged sectional view taken along line AA of FIG. 2, and FIG. 3 is an enlarged sectional view taken along line BB of FIG. It is. As shown, two adjacent optical waveguides 104 and an optical waveguide 10
Control electrode 103 for applying an electric field to a part of the inside of
Are provided. A substrate-side cladding layer 111 made of n-type Al _0.3 Ga _0.7 As is formed on a semiconductor substrate 110 made of n-type GaAs.
11 has a length of 200 μm and an interval of 2
27.1 nm, depth 100 nm, mode of light (including radiation mode as well as propagation mode in optical waveguide 104)
And a grating (diffraction grating) 117 having a coupling constant of 0.012 μm ⁻¹ between the
Is provided with a quarter wavelength shift (not shown) in which the phase of the grating 117 is shifted by an integral multiple of 1/4. The substrate-side core layer 11 made of undoped Al _0.13 Ga _0.87 As is provided on the substrate-side cladding layer 111.
2 is formed, and undoped A is formed on the substrate side core layer 112.
A quantum well layer 113 made of undoped GaAs sandwiched between l _0.2 Ga _0.8 As and containing the excitons is formed, and the wavelength of the emitted light from the excitons in the quantum well layer 113 is 793 nm. The electrode-side core layer 11 made of undoped Al _0.13 Ga _0.87 As is provided on the quantum well layer 113.
4 are formed, and undoped A
3 is made of _0.16 Ga _0.84 As, is parallel to the surface of the semiconductor substrate 110, and is perpendicular to the optical waveguide 104, that is, FIG.
A rib layer 115 for realizing light confinement in the horizontal direction of the paper is formed, a ridge is formed on the upper surface of the rib layer 115, and an electrode-side cladding layer 116 made of p-type Al _0.3 Ga _0.7 As is formed on the rib layer 115. And the substrate-side cladding layer 11
1. The substrate-side core layer 112, the quantum well layer 113, the electrode-side core layer 114, the rib layer 115, and the electrode-side cladding layer 116 constitute the optical waveguide 104 of the control electrode 103. The thickness of the substrate-side cladding layer 111 is 700 n.
m, the thickness of each of the core layers 112 and 114 is 900 n
m, the thickness of the rib layer 115 is 500 nm, the thickness of the electrode-side cladding layer 116 is 700 nm, and the thickness of the quantum well layer 113 is 7.5 nm. The width of the two optical waveguides 104 is 3 μm, and the interval between the two optical waveguides 104 is 1 μm.

Next, a method of manufacturing the directional coupler optical switch shown in FIGS. 1 to 3 will be described. First, an n-type Al _0.3 Ga _0.7 As layer is epitaxially grown on a semiconductor substrate 110 to form a substrate-side cladding layer 111. Next, a grating 117 is formed on the upper surface of the substrate-side cladding layer 111 by anisotropic chemical etching. Next, MOVPE (Metal Organic Vapor Phase
Epitaxy) undoped Al _0.13 Ga _0.87 A
s layer, undoped GaAs layer sandwiched by undoped Al _0.2 Ga _0.8 As, Al _0.13 Ga _0.87 As layer, Al _0.16 G
a After forming a _0.84 As layer, Al
_A ridge is formed in the _0.16 Ga _0.84 As layer to form a substrate-side core layer 112, a quantum well layer 113, an electrode-side core layer 114, and a rib layer 115. Next, p-type Al _0.3 Ga _0.7 As
The layer is formed by regrowth, and the electrode-side cladding layer 116 is formed.

In this directional coupler optical switch,
When light propagates in the direction of arrow 118, the light field concentrates on the thick portion of the rib layer 115, and the optical waveguide 1
In the region where the two optical waveguides 104 are close to each other, the fields corresponding to the eigenmodes of the two optical waveguides 104 overlap each other, as shown in FIG. The eigenmode of one optical waveguide 104 is no longer an eigenmode. In fact, the power of light propagates between the two optical waveguides 104 while vibrating. Then, by changing the refractive index of the optical waveguide 104 by the voltage of the control electrode 103, the period of vibration between the two optical waveguides 104 can be changed, so that it works as a switching element.

In such a directional coupler optical switch, the grating 117 is provided at the interface between the substrate-side cladding layer 111 and the substrate-side core layer 112.
Since the number of modes of the optical signal coupled to the light emitted from the excitons of the quantum well layer 113 can be reduced, the coupling energy between the light emitted from the excitons and the light increases, so that the refractive index modulation rate increases. Become. For example, at a temperature of 4.2 K, the coupling energy between light emitted from excitons and light is 6.5 times that in the case where no grating is provided, and the refractive index modulation rate with respect to an electric field is also 6 times as much. Becomes Therefore, since the control electrode 103 can be reduced in size, the operation can be performed at a high speed, the size can be reduced, and the control voltage applied to the control electrode 103 can be reduced. Also, the grating 117 has a に wavelength shift, and
Since the wavelength shift plays the same role as a half-wavelength resonator in a microcavity structure, the power of the resonator mode is concentrated around the position of the quarter wavelength shift, and the coupling energy between the light emitted from the exciton and the light. Can be further increased. Therefore, the switching speed can be improved by approximately one digit, the element size can be reduced by approximately one digit, and the operating voltage can be reduced by approximately one digit.

By the way, in order for the binding energy between light emitted from the exciton of the quantum well layer 113 and light to increase,
It is considered that the control of the longitudinal mode parallel to the propagation of light plays a large role. That is, as shown in FIG. 4, the dispersion relation of the polariton in which the light emitted from the exciton propagating in the optical waveguide 104 is coupled with the light is represented by the upper limb represented by the dispersion curve 801 and the lower limb represented by the dispersion curve 802. There is. Then, the dispersion curve 804 of the photon in the semiconductor not bonded to the exciton and the dispersion curve 8 of the exciton constituting the polariton
At the point where 03 intersects, the dispersion curves 801 and 802 are separated without intersecting, and the interaction energy between the exciton of the polariton and the light propagating in the optical waveguide 104 including the quantum well layer 113 is scattered by phonons and the like. Is strongly influenced by the LT split amount 805. However, when the grating 117 is formed, the intensity of light having a specific wave number represented by a straight line 809 increases, and light having this wave number is selected and fixed. Therefore, the split amount representing the energy of the interaction between the exciton and light is the point 8
The energy of the difference between the upper limb energy of the polariton when the wave number represented by 07 is fixed and the energy of the lower limb of the polariton when the wave number represented by the point 808 is fixed, that is, the Rabi splitting amount 806, and the Rabi splitting 806
Is increased, the refractive index modulation rate is increased.

FIGS. 5A and 5B are schematic diagrams each showing a part of another directional coupler optical switch according to the present invention.
As shown in the figure, an extension line 601 of the convex portion is provided on the optical waveguide 104.
Concentric grating 117a that intersects at one point
Or a grating 117b having a convex portion parallel to the curved optical waveguide 104a. That is, the chirped grating 11
7a and 117b are formed. The gratings 117a and 117b are provided with a 波長 wavelength shift.

As is well known, when the line width of spontaneous light emission from an exciton is smaller than the line width of a grating including a quarter wavelength shift and the resonator formed by an optical waveguide structure, the excitation The coupling efficiency of the emitted light from the element to the propagation mode is maximized. However, the line width of spontaneous emission from excitons is determined by parameters such as the temperature of the device, the flatness of the interface of the quantum well layer where the excitons are excited, and the density of the excited excitons. Reducing the line width of the spontaneous emission from the exciton by use restricts the use environment and conditions. Therefore, a method of increasing the line width of the resonator without greatly lowering the Q value of the cavity is required. In the directional coupler optical switch shown in FIGS. 5A and 5B, since the chirped gratings 117a and 117b are provided, the peaks of the light reflectance by the gratings 117a and 117b are obtained. Moves, and the resonator created by the 波長 wavelength shift is simultaneously chirped and continuously distributed within a certain range in the optical waveguides 104 and 104a, so that the line width of the resonator can be increased. The device can be operated under wider excitation and temperature conditions while maximizing the coupling efficiency to the propagation mode. Therefore, since the refractive index modulation factor is further increased, the control electrode can be further reduced, so that the operation can be performed at an extremely high speed.

FIG. 6 is a schematic sectional view showing another directional coupler optical switch according to the present invention. As shown in the figure, the region in the waveguide direction where the quantum well layer 113 is located,
Direction in which the pad layer 111, the substrate-side core layer 112, and the like are stacked
A region in a direction perpendicular to the direction (the left-right direction in FIG. 6) is separated from a region in the waveguide direction where the grating 117c exists.

In this directional coupler optical switch,
Since the length of the grating 117c can be increased, the number of modes of an optical signal coupled with the radiated light from the excitons in the quantum well layer 113 can be reliably reduced. Since the binding energy with the refractive index increases, the refractive index modulation rate further increases.

FIG. 7 is a schematic sectional view showing another directional coupler optical switch according to the present invention. As shown in the figure, Al _0.4 Ga _0.6 As having a thickness of 61.5 nm and 57 nm
The substrate-side cladding layer 311 and the electrode-side cladding layer 316 are formed of a multilayer film (15 periods) of Al _0.16 Ga _0.84 As. That is, a structure in which a layer having a large refractive index and a layer having a small refractive index are stacked at a period of about a quarter of the wavelength of light propagating in the optical waveguide 104 (hereinafter referred to as DBR (Distributed Br)
agg reflector))
Are formed. The thickness of the core layers 112 and 114 is determined so that the optical length is a half integral multiple of the wavelength of light emitted from the exciton, and the quantum well layer 113 is disposed at the center of the core layers 112 and 114. ing.

In this directional coupler optical switch,
Since the cladding layers 311 and 316 of the DBR are formed, light emitted from excitons having a large incident angle is not emitted from the core layer 11.
Since the light is strongly reflected at the interface between the cladding layers 311 and 316, the loss can be reduced. Also,
The thickness of the core layers 112 and 114 is determined so that the optical length thereof is a half integral multiple of the wavelength of light emitted from the exciton, and the quantum well layer 113 is disposed at the center of the core layers 112 and 114. Therefore, since the quantum well layer 113 is located at the position of the node of the standing wave of light formed in the core layers 112 and 114, the loss can be further reduced. The effect of mode reduction is greater when the difference in refractive index between the two types of layers of the DBR is larger.

FIG. 8 is a band diagram near the quantum well layer of another directional coupler optical switch according to the present invention. As shown in the figure, the conduction band energy a at the Γ point of the direct transition semiconductor is larger than the electron level b in the quantum well layer 701, and the valence band energy c is the hole level in the quantum well layer 701. A barrier layer made of a material smaller than the position d, that is, a barrier layer 702 made of Al _0.3 Ga _0.7 As and having a thickness of 5 nm is formed on both sides of the quantum well layer 701, and the conduction band energy e at the X point or the L point is reduced. Quantum well layer 7
01, ie, a relaxation layer made of a material having a conduction band energy f at the Γ point larger than the electron level b in the quantum well layer 701.
The relaxation layer 703 having a thickness of 10 nm
2 and the core layers 112 and 114.

By forming a grating in a single-mode optical waveguide, the coupling efficiency from natural light emission from excitons to the waveguide mode is improved to some extent. Therefore, there is a corresponding reduction in loss. However, the quantum interference effect due to Fano resonance is also important for reducing the loss. This is a well-known matter, but will be described in some detail. FIG. 9 shows an energy diagram in which the interference effect due to the Fano resonance occurs. The important thing is that two adjacent bound levels 2, 3 are interacting with one continuous level, and the transition from the ground level 1 to the continuous level is forbidden. Now, when the relaxation time from the level 3 is longer than the relaxation time from the level 2, the path that relaxes from the ground level 1 to a state having the continuous spectrum with the level 2 as an intermediate state, and the path from the ground level 1 to the level The loss of light having the same energy as the energy E ₀ is greatly reduced by the interference effect between the path having the position 3 as an intermediate state and a path having a continuous spectrum.
lly-Induced Transparency (EIT)). In the directional coupler optical switch shown in FIG. 8, the ground level 1 is a state where no exciton is excited in the quantum well layer 701, and the levels 3 and 2 are points 807 and 8 in FIG.
08, the continuous level is a state in which electrons exist near the X point of the relaxation layer 703. The transition from the ground level 1 to the vicinity of the point X of the relaxation layer 703 which is a continuous level is an indirect transition in terms of both space and momentum, and the transition from the ground level 1 to the vicinity of the point X of the relaxation layer 703 is made. The probability of the formation of an exciton in the quantum well layer 701 and the probability of an electron transitioning to the relaxation layer 703 are sufficiently smaller. Further, since the quantization level of the relaxation layer 703 resonates with the level 2, the tunnel probability from the level 2 becomes larger than the tunnel probability from the level 3.
Therefore, in the directional coupler optical switch shown in FIG. 8, the EIT appears remarkably, and the loss is reduced by one digit or more.

FIG. 10 is a schematic diagram showing a Mach-Zehnder interferometer optical switch according to the present invention. As shown in the figure, the optical waveguides 104 are close to each other on both sides of the portion where the control electrode 103 is provided, a loop closed by the optical waveguides 104 is formed, and the substrate-side cladding layer 111 and the substrate-side core layer 112 A grating 117 is formed at the interface of
A quarter wavelength shift is provided at the center of the grating 117.

In this Mach-Zehnder interferometer optical switch, too, the control electrode 103 can be made small because the refractive index modulation factor becomes large, so that the operation can be performed at high speed and the size can be reduced. In addition, the control voltage applied to the control electrode 103 can be reduced.

Although the directional coupler optical switch and the Mach-Zehnder interferometer optical switch have been described in the above embodiments, the present invention can be applied to other optical modulators. In the above embodiment,
Although the grating 117 is formed at the interface between the substrate-side cladding layer 111 and the substrate-side core layer 112, the region in the stacking direction of the substrate-side cladding layer 111 and the substrate-side core layer 112, that is,
Substrate-side cladding layer 111, substrate-side core layer 112, etc. are laminated
Region direction (FIG. 1 up and down direction) which is, the electrode-side core layer 114 may be disposed a grating on at least one of the stacking direction region of the stacking direction region of the electrode-side cladding layer 116. That is, the rib layer 115 and the electrode-side cladding layer 1
16, the substrate-side cladding layer 111, the substrate-side core layer 112, the electrode-side core layer 114, and the electrode-side cladding layer 116.
A grating may be arranged inside the device. Further, in the above-described embodiment, the grating 117 is formed by anisotropic chemical etching. However, as a manufacturing method of the grating, an ultraviolet two-beam interference exposure method using a He-Cd laser or an Ar laser, a mask exposure method, There are an X-ray mask exposure method, an electron beam direct writing method, and the like. Also, by increasing the refractive index difference between the substrate-side core layer and the substrate-side cladding layer and the refractive index difference between the electrode-side core layer and the electrode-side cladding layer, the critical angle for total reflection (the core layer and the cladding layer) is increased. (In the case where the light is incident parallel to the interface with 0 °), it is assumed to be 0 °).

[0032]

In the optical modulator according to the present invention, since the number of modes of the optical signal coupled with the light emitted from the excitons in the quantum well layer can be reduced, the light emitted from the excitons and the light can be reduced. , The refractive index modulation rate increases. Therefore, since the control electrode can be made smaller, the operation can be performed at high speed, and
The size can be reduced, and the control voltage applied to the control electrode can be reduced.

Further, when a quarter wavelength shift in which the phase of the grating is shifted by an integral multiple of 1/4 is provided in at least one portion of the grating, the quarter wavelength shift is equal to the half wavelength resonator in the microcavity structure. Since they fulfill the same role, the binding energy between light emitted from excitons and light can be further increased.

When the grating is chirped, the line width of the resonator can be increased, and the element can be operated under wider excitation and temperature conditions while maximizing the coupling efficiency to the propagation mode. In addition, the refractive index modulation rate can be further increased.

When the region in the waveguide direction where the grating is located is separated from the region in the waveguide direction where the quantum well layer is located, the length of the grating can be increased. Since the number of modes of the optical signal coupled with the light emitted from the exciter can be reliably reduced, the coupling energy between the light emitted from the exciton and the light is further increased, so that the refractive index modulation rate is further increased. Can be.

Further, the substrate-side cladding layer and the electrode-side cladding layer have a structure in which a layer having a large refractive index and a layer having a small refractive index are laminated at about a quarter of the wavelength of light propagating through the optical waveguide. When is used, the loss can be further reduced.

In the band diagram of the direct transition semiconductor, the energy of the conduction band at point Γ is larger than the level of the electrons in the quantum well layer, and the energy of the valence band is larger than the level of the holes in the quantum well layer. A barrier layer made of a small material is formed on both sides of the quantum well layer, and the energy of the conduction band at point X or L is smaller than the level of electrons in the quantum well layer and the energy of the conduction band at point Γ is quantum. When a relaxation layer made of a material larger than the electron level in the well layer is formed between the barrier layer, the substrate-side core layer, and the electrode-side core layer, the loss is reduced by interference effect due to the Fano resonance. Can be.

Also, when at least one pair of optical waveguides is brought close to each other on both sides of the portion where the control electrode is provided, high speed can be achieved by a large refractive index modulation rate by an electric field, and low voltage driving is possible. It becomes small.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view taken on line AA of FIG. 2;

FIG. 2 is a schematic diagram illustrating a directional coupler optical switch according to the present invention.

FIG. 3 is an enlarged sectional view taken on line BB of FIG. 2;

FIG. 4 is a graph for explaining the operation of the directional coupler optical switch shown in FIGS.

FIG. 5 is a schematic view showing a part of another directional coupler optical switch according to the present invention.

FIG. 6 is a schematic sectional view showing another directional coupler optical switch according to the present invention.

FIG. 7 is a schematic sectional view showing another directional coupler optical switch according to the present invention.

FIG. 8 is a band diagram near a quantum well layer of another directional coupler optical switch according to the present invention.

FIG. 9 is a diagram illustrating the operation of the directional coupler optical switch shown in FIG. 8;

FIG. 10 is a schematic diagram showing a Mach-Zehnder interferometer optical switch according to the present invention.

[Explanation of symbols]

 103 Control electrode 104 Optical waveguide 104a Optical waveguide 110 Semiconductor substrate 111 Substrate-side cladding layer 112 Substrate-side core layer 113 Quantum well layer 114 Electrode-side core layer 116 Electrode-side cladding layer 117 Grating 117a Grating 117b Grating 117c Grating 311 Substrate-side cladding layer 316 Electrode-side cladding layer 601 Extension line 701 Quantum well layer 702 Barrier layer 703 Relaxation layer

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) G02F 1/313 G02F 1/025 JICST file (JOIS)

Claims (7)

(57) [Claims] 1. An optical modulator comprising: an optical waveguide having two or more adjacent portions; and a control electrode for applying an electric field to at least a part of the interior of the optical waveguide. Is the one that guides the exciton polariton
There, a portion of the optical waveguide, and the substrate-side cladding layer formed on a semiconductor substrate, a large substrate side core layer with a refractive index compared to the formed on top of the substrate-side cladding layer and the substrate-side cladding layer A quantum well layer formed above the substrate-side core layer and for confining excitons; an electrode-side core layer formed above the quantum well layer; and a quantum well layer formed above the electrode-side core layer. And having an electrode-side cladding layer having a smaller refractive index than the electrode-side core layer, the substrate-side cladding layer, the lamination direction region of the substrate-side core layer, the electrode-side core layer, the electrode-side cladding layer. optical modulator and characterized in that a grating on at least one of the stacking direction region of the stacking direction region. 2. The apparatus according to claim 1, wherein a 波長 wavelength shift is provided in at least one portion of said grating, the phase of said grating being shifted by an integral multiple of １ ／.
An optical modulator according to claim 1. 3. The optical modulator according to claim 2, wherein said grating is chirped. 4. The optical modulator according to claim 1, characterized in that to separate the waveguide direction region of the waveguide direction region and the quantum well layer with the grating. 5. A high-refractive-index layer and a low-refractive-index layer are laminated as the substrate-side cladding layer and the electrode-side cladding layer at a period of about a quarter of a wavelength of light propagating through the optical waveguide. The optical modulator according to claim 1, wherein the optical modulator has a structure. 6. In the band diagram of the direct transition semiconductor, the energy of the conduction band at point 大 き く is larger than the level of electrons in the quantum well layer, and the energy of the valence band is higher than the level of holes in the quantum well layer. A barrier layer made of a smaller material is formed on both sides of the quantum well layer, and a point X or L
A relaxation layer made of a material in which the conduction band energy at the point is smaller than the electron level in the quantum well layer and the conduction band energy at the Γ point is larger than the electron level in the quantum well layer. The barrier layer and the substrate-side core layer,
The optical modulator according to claim 1, wherein the optical modulator is formed between the electrode-side core layer and the electrode-side core layer. 7. An optical modulator according to claim 1, wherein at least one pair of said optical waveguides is brought into close proximity on both sides of the portion where said control electrode is provided.