JP2004347650A - Semiconductor optical modulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an electro-absorption semiconductor optical modulator which modulates light with respect to a wide wavelength region and does not require temperature control of an element. <P>SOLUTION: The semiconductor optical modulator has a p-type cladding layer 2 disposed on a GaAs substrate 1, a double quantum well structure 3 disposed on the cladding layer 2 and consisting of a first quantum well layer 5 and a second quantum well layer 6 alternately laminated across a barrier layer 4, and an n-type cladding layer 7 disposed on the double quantum well structure 3, and is constructed in such a way that bottom energy of a conduction band of the second quantum well layer 6 is larger than that of the first quantum well layer 5, band gap energy of the second quantum well layer 6 is larger than band gap energy 13 of the first quantum well layer 5, and ground level energy of the first quantum well layer 5 is smaller than that of the second quantum well layer 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electro-absorption type semiconductor light modulation element for converting an electric modulation signal used in optical communication or the like into a light modulation signal.
[0002]
[Prior art]
[Patent Document] Japanese Patent No. 2670051.
[0003]
2. Description of the Related Art Conventionally, as one of semiconductor light modulation elements, an electroabsorption light modulation element using a red shift of an absorption edge due to a Stark effect of an exciton in a quantum well structure has been proposed. The above patent document shows a typical example of this element. The conventional example will be described below with reference to FIGS. FIG. 7 is a perspective view of this conventional device structure, and FIG. 8 is a characteristic diagram showing a light absorption spectrum of the device of FIG.
7, reference numeral 71 denotes an InP substrate; 72, a first cladding layer made of n-type InP disposed on the InP substrate 71; 73, a 100-degree thick In _0.55 Ga _0.45 As _0.97 P _0. The light absorption edge of the ₀₃ quantum well layer is maintained at a wavelength of 1.50 μm. Reference numeral 74 denotes an InP barrier layer having a thickness of 150 °. The quantum well layers 73 and the barrier layers 74 are alternately stacked for 20 periods to form a multiple quantum well layer structure as an active layer. Reference numeral 75 denotes a second cladding layer made of P-type InP, and the upper part thereof has a stripe shape as shown in the figure. The second cladding layer 75 has a thickness of 0.4 μm, and a stripe having a height of 1.6 μm and a width of 6 μm is formed thereon to form a loading clad portion 76. 77 is a p-type In _0.53 Ga _0.47 As cap layer having a thickness of 0.15 μm formed on the stripe, 78 and 79 are electrodes, 81 is input light, and 82 is output light. In this structure, light is incident on the multiple quantum well layer structure in parallel and operates as a light modulator or switch.
FIG. 8A shows a change in the light absorption coefficient when a voltage is applied to the active layer sandwiched between the p-type and n-type cladding layers 75 and 72. In this figure, the horizontal axis represents the wavelength, the vertical axis represents the absorption coefficient, and λg represents the absorption edge. The broken line indicates the presence of an electric field, and the solid line indicates the absence of an electric field. As shown in the figure, the peak of the absorption coefficient shifts to the longer wavelength side by applying a voltage. Therefore, as shown in FIG. 8B, the absorption coefficient greatly changes near the absorption edge λg depending on the presence or absence of the electric field. By controlling the potential difference between the electrodes 78 and 79, the intensity of light passing through the element can be changed.
[0004]
[Problems to be solved by the invention]
However, as can be seen from FIG. 8B, the absorption coefficient changes only in the limited wavelength region of 10 nm around the wavelength of 1.55 μm, and the modulation efficiency for light of wavelengths other than this region rapidly deteriorates. Will be. Therefore, in order to realize an optical modulator that modulates light having a wavelength of 1.54 μm or less, the InP composition for In _0.53 Ga _0.47 As, which is a material used for the quantum well layer 73, is increased to increase the absorption edge λg Needs to be adjusted to the shorter wavelength side. Further, in order to realize an optical modulator that modulates light having a wavelength of 1.56 μm or more, the InP composition with respect to In _0.53 Ga _0.47 As of the material used for the quantum well layer 1103 is reduced to reduce the absorption edge λg Needs to be adjusted to the longer wavelength side. Therefore, when applying the conventional electro-absorption optical modulator to large-capacity wavelength division multiplexing transmission, it is necessary to prepare several types of crystal structures, which is very inefficient.
Further, when the element temperature changes, the wavelength range that can be modulated also shifts because the absorption edge λg shifts with the shift of the band gap energy. Therefore, the light of the assumed wavelength may deviate from the wavelength range that can be modulated by the change in the element temperature. In order to avoid this, in the conventional electro-absorption type optical modulation device, it is essential to use the device together with a device for keeping the device temperature constant, which has been an obstacle to cost reduction and integration.
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to realize an electroabsorption type semiconductor optical modulation device which can modulate over a wide wavelength range and does not require control of the device temperature.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention employs a configuration as described in the claims.
That is, the semiconductor light modulation device of the present invention includes a first conductivity type first clad layer provided on a substrate, a first quantum well layer provided on the first clad layer, and a second quantum well layer provided on the first clad layer. A double quantum well structure in which quantum well layers are alternately stacked with a barrier layer interposed therebetween, and a second cladding layer of a second conductivity type provided on the double quantum well structure; The energy at the lower end of the conduction band of the second quantum well layer is greater than the energy at the lower end of the conduction band of the first quantum well layer, and the bandgap energy of the second quantum well layer is higher than that of the first quantum well layer. The energy is higher than the band gap energy of the layer, and the energy of the ground level of the electrons in the first quantum well layer is smaller than the energy of the ground level of the electrons in the second quantum well layer.
In addition, when a voltage is applied to the double quantum well structure, light is transmitted from the semiconductor light modulation device by utilizing a difference in wavelength dependence of a light absorption coefficient due to resonance / non-resonance of an electron quantum level. The ratio is controlled.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, first, the principle (operation) of the present invention will be described with reference to FIGS. FIG. 5 is a diagram for explaining the relationship between the energy levels of electrons and holes in the double quantum well structure, and FIG. 6 is a diagram showing the double quantum well structure in which the electron levels are in resonance and non-resonance. FIG. 7 is a diagram for explaining a difference in light absorption coefficient of the light.
5, reference numeral 4 denotes a barrier layer, 5 denotes a first quantum well layer, 6 denotes a second quantum well layer, 11 denotes a lower end of the conduction band of the first quantum well layer 5, and 12 denotes a second quantum well layer. 6, 13 is the bandgap energy of the first quantum well layer 5, 14 is the bandgap energy of the second quantum well layer 6, 15 is the ground level of electrons in the first quantum well layer 5. , 16 are the ground levels of the electrons in the second quantum well layer 6, 17 are the ground levels of the holes in the first quantum well layer 5, 18 are the ground levels of the holes in the second quantum well layer 6. , Eg are the transition energies between the ground level 15 of electrons in the first quantum well layer 5 and the ground level 17 of holes, and E1 is the ground level 16 of electrons in the second quantum well layer 6 and the ground level of holes. This is the transition energy between positions 18.
[0007]
In the semiconductor superlattice structure (double quantum well structure) in the semiconductor light modulation device according to the present invention, electrons and holes are formed in the first quantum well layer 5 and the second quantum well layer 6 as shown in FIG. A level is formed. Accordingly, when no voltage is applied to the double quantum well structure, the ground level 15 of electrons and the ground level 17 of holes are formed in the first quantum well layer 5 and the second quantum well layer 6 is formed. A ground level 16 of electrons and a ground level 18 of holes are formed therein. The transition energy between the ground level 15 of electrons in the first quantum well layer 5 and the ground level 17 of holes is Eg, and the ground level 16 of electrons in the second quantum well layer 6 is Assuming that the transition energy between the ground levels 18 is E1, the light absorption coefficient of the superlattice structure has a characteristic that increases stepwise at the transition energies Eg and E1, as indicated by the dashed line in FIG. The superlattice structure absorbs light having an energy larger than the transition energy Eg.
In this structure, the ground level 15 of the electrons formed in the first quantum well layer 5 is the lowest energy level among the quantum levels of the electrons formed in the second quantum well layer 6. The electric field strength at which resonance occurs is defined as Fres. In this case, when the electric field strength Fres is applied to the superlattice structure, the wave function of the ground level 15 of the electrons formed in the first quantum well layer 5 is equal to that of the first quantum well layer 5 and the second quantum well layer 5. , The overlap integral of the wave function of the electron of the ground level 15 of the electron and the hole of the hole of the ground level 17 of the hole becomes small, and the energy larger than the transition energy E1 is obtained. The light absorptivity of the superlattice structure with respect to the light of the above decreases. The light absorption characteristics of the superlattice structure at this time are plotted in FIG.
When the electric field intensity applied to the superlattice structure becomes larger than the electric field intensity Fres, the wave function of the electrons does not seep into the adjacent well beyond the barrier, and the wave function is localized in one of the wells. That is, the light absorptance at each level recovers to the same value as when no electric field is applied to the superlattice structure. That is, the state returns to the state shown by the one-dot chain line in FIG.
Here, when the difference between the light absorption coefficients at F = Fres and F ≠ Fres is plotted on the abscissa, the energy is plotted as shown in FIG. 6B, which corresponds to the light having the energy larger than the transition energy Eg, that is, the transition energy Eg. A change in the absorption coefficient is obtained for light in a wide wavelength region on the short wavelength side of the wavelength to be emitted. Therefore, by employing the proposed superlattice structure, it becomes possible to realize an optical modulation element capable of modulating over a wide wavelength range as compared with a conventional electro-absorption optical modulator. Further, since the wavelength range in which modulation can be performed is widened, even if the element temperature changes and the transition energy Eg shifts, the wavelength does not deviate from the wavelength range in which modulation is possible, and a device for keeping the element temperature constant becomes unnecessary. In addition, cost reduction and high integration can be achieved.
[0008]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, those having the same functions are denoted by the same reference numerals, and repeated description thereof will be omitted.
Embodiment 1
FIG. 1A is a schematic cross-sectional view showing an example of the structure of a semiconductor light modulation device having a semiconductor superlattice structure according to the first embodiment of the present invention. In FIG. 1A, a cladding layer 2 made of p-type Al _0.35 Ga _0.65 As, a double quantum well structure 3 which is a superlattice structure, and an n-type Al _{. A} cladding layer 7 made of ₃₅ Ga _0.65 As is formed, and ohmic electrodes 8 and 9 are formed on the cladding layers 2 and 7, respectively. FIG. 1B is an enlarged cross-sectional detailed view of the double quantum well structure 3 of FIG. 1A. The barrier layer 4 is made of Al _0.35 Ga _0.65 As and has a thickness of 5 nm. First quantum well layer 5 made of Ga _0.68 In _0.32 N _0.01 As _0.99 , Al _0.35 Ga _0.65 As barrier layer 4 having a thickness of 5 nm, and GaN _{0 having a} thickness of 14 nm as one cycle of the second quantum well layer 6 made of _.008 as _0.992, which became _Al 0.35 _{Ga 0.65} as barrier layer 4 was formed structure having a thickness of 3nm on overlaid 20 cycles ing. In this structure, the input light 41 travels in a direction parallel to the hetero interface of the double quantum well structure 3 and becomes an output light 42.
In FIG. 2, 11 is the lower end of the conduction band of the first quantum well layer 5, 12 is the lower end of the conduction band of the second quantum well layer 6, 13 is the band gap energy of the first quantum well layer 5, and 14 is The band gap energy of the second quantum well layer 6, 15 is the ground level of the electrons of the first quantum well layer 5, 16 is the ground level of the electrons of the second quantum well layer 6, and 17 is the first quantum level. The ground level of holes in the well layer 5, 18 is the ground level of holes in the second quantum well layer 6, 19 is the first excitation level of electrons in the first quantum well layer 5, and 20 is the first excited level. , The first excitation level of holes in the quantum well layer 5, Eg is the transition energy between the ground level 15 of electrons and the ground level 17 of holes in the first quantum well layer 5, and E1 is the second quantum level. The transition energy E2 between the ground level 16 of the electrons in the well layer 6 and the ground level 18 of the holes is the first excitation level 19 of the electrons in the first quantum well layer 5. A transition energy between the first excited level 20 of the hole.
[0009]
As shown in FIG. 2A, the quantum levels in the double quantum well structure 3 are such that electron and hole levels are formed in the first quantum well layer 5 and the second quantum well layer 6. Is done. Thus, when no voltage is applied to the double quantum well structure 3, the light absorption coefficients of the wavelengths 1.31, 1.09, and 0.95 μm are stepped, respectively, as shown by the dashed line in FIG. It shows characteristics that increase likewise.
A voltage is applied to the electrodes 8 and 9 of this device so that the electrode 9 becomes positive, and an electric field of 108 kV / cm is formed in the double quantum well structure 3. In this case, in the double quantum well structure 3, the ground level 15 of the electrons in the first quantum well layer 5 and the ground level 16 of the electrons in the second quantum well layer 6 cause resonance. For the reason described in the explanation of the principle, the light absorption coefficient decreases as shown by the solid line in FIG.
In this state, when the voltage applied between the electrodes 8 and 9 is further increased, the ground level 15 of the electrons in the first quantum well layer 5 and the ground level 16 of the electrons in the second quantum well layer 6 are changed. The resonance state is canceled, and the light absorption coefficient recovers as indicated by the dashed line in FIG.
As described above, the semiconductor light modulation device of the first embodiment is provided on the first cladding layer 2 of the first conductivity type (here, p-type) provided on the GaAs substrate 1 and on the two cladding layers, A double quantum well structure 3 in which a first quantum well layer 5 and a second quantum well layer 6 are alternately stacked via a barrier layer 4, and a second quantum well structure 3 provided on the double quantum well structure 3; A second cladding layer 7 of two conductivity type (here, n-type), and (1) the energy at the lower end 12 of the conduction band of the second quantum well layer 6 (2) the bandgap energy 14 of the second quantum well layer 6 is larger than the bandgap energy 13 of the first quantum well layer 5, and (3) the bandgap energy 13 of the first quantum well layer 5. The energy of the ground level 15 of the electron 5 is equal to the energy of the ground level 16 of the electron in the second quantum well layer 6. It has become-saving smaller configuration.
Further, when a voltage is applied to the double quantum well structure 3, the semiconductor is utilized by utilizing the difference in the wavelength dependence of the light absorption coefficient due to the exudation of the wave derivative due to resonance / non-resonance of the electron quantum level. The light modulation element is configured to control the light transmission ratio (transmittance).
The double quantum well structure 3 is determined by selecting a material that satisfies the above requirements (1) and (2), and then selecting the materials of the first quantum well layer 5 and the second quantum well layer 6. By adjusting the layer thickness, the above requirement (3) can be easily satisfied.
[0010]
In this element, a large change in the light absorption coefficient can be obtained by controlling the electric field intensity over a very wide wavelength range from 1.31 to 1.09 μm in wavelength. An optical modulator having a wavelength range that can be modulated by one digit or more can be realized. Further, since the wavelength range in which modulation can be performed is widened, even if the element temperature changes and the transition energy Eg shifts, the wavelength does not deviate from the wavelength range in which modulation is possible, and a device for keeping the element temperature constant becomes unnecessary. In addition, cost reduction and high integration can be achieved.
In the first embodiment, an optical modulator having a wavelength shorter than 1.31 μm is described. However, the wavelength range in which modulation is possible is not limited to the value proposed in the first embodiment. It is obvious that the wavelength can be shifted by changing the well width of the first quantum well layer 5 and adjusting the transition energy Eg. In the first embodiment, GaAs and Al _0.35 Ga _0.65 As, Ga _0.68 In _0.32 N _0.01 As _0.99 , and GaN _0.008 As _{0.992 are} used as semiconductor materials. was used _{but, InP, in x Ga 1-} x As y P 1-y, in 0.52 Al 0.48 As, in other group III-V semiconductors and its mixed crystal, such as, the present invention Obviously, a semiconductor light modulation device can be realized.
[0011]
Embodiment 2
Hereinafter, another example different from the first embodiment will be described. FIG. 3A is a schematic cross-sectional view showing an example of the structure of a semiconductor light modulation device having a semiconductor superlattice structure according to the second embodiment of the present invention. 3A, a cladding layer 32 made of p-type Al _0.45 Ga _0.55 As, a double quantum well structure 33 having a superlattice structure, and an n-type Al _{. A} cladding layer 37 made of ₄₅ Ga _0.55 As is formed, and ohmic electrodes 38 and 39 are formed on the cladding layers 32 and 34, respectively. FIG. 3B is an enlarged cross-sectional detailed view of the double quantum well structure 33 shown in FIG. 3A. The barrier layer 34 is made of Al _0.45 Ga _0.55 As and has a thickness of 5 nm. A first quantum well layer 35 of Al _0.45 Ga _0.55 As barrier layer 34 having a thickness of 5 nm, and a second quantum well layer 36 of Ga _0.51 In _0.49 P having a thickness of 15 nm. As one cycle, this is a structure in which 20 cycles are superposed and an Al _0.45 Ga _0.55 As barrier layer 34 having a thickness of 5 nm is formed. In this structure, the input light 41 travels in a direction parallel to the hetero interface of the double quantum well structure 33 and becomes the output light 42.
4, reference numeral 11 denotes the lower end of the conduction band of the first quantum well layer 35, 12 denotes the lower end of the conduction band of the second quantum well layer 36, 13 denotes the band gap energy of the first quantum well layer 35, and 14 denotes the band gap energy of the first quantum well layer 35. The band gap energy of the second quantum well layer 36, 15 is the ground level of the electrons of the first quantum well layer 35, 16 is the ground level of the electrons of the second quantum well layer 36, and 17 is the first quantum level. The ground level of holes in the well layer 35, 20 is the first excitation level of holes in the first quantum well layer 35, and Eg is the ground level 15 of electrons in the first quantum well layer 5 and the first level. The transition energy between the ground level 17 of holes in the quantum well layer 5, E1 is the transition energy between the first excitation level 18 of electrons and the first excitation level 21 of holes, and Eb is the band gap of the barrier layer 34. Energy.
[0012]
As shown in FIG. 4A, the levels of electrons and holes are formed in the first quantum well layer 35 and the second quantum well layer 36 in the double quantum well structure 33. Is done. As a result, when no voltage is applied to the double quantum well structure 33, the light absorption coefficient increases stepwise at a wavelength of 0.805 μm, as shown by the dashed line in FIG. 4B.
Note that, in this structure, at around 0.727 μm corresponding to the transition between the ground level 16 of electrons in the second quantum well layer 36 and the first excitation level 20 of holes in the first quantum well layer 35. The reason why the light absorption coefficient does not increase is that electrons and holes at this level exist separately in the first quantum well layer 35 and the second quantum well layer 36, and almost no transition occurs.
A voltage is applied to the electrodes 38 and 39 of this device so that the electrode 39 becomes positive, and an electric field of 80 kV / cm is formed in the double quantum well structure 33. In this case, the ground level 15 of electrons and the ground level 16 of electrons cause resonance in the double quantum well structure 33, and therefore, for the reason described in the above description of the principle, FIG. As shown by the solid line, the light absorption coefficient decreases.
Further, if the voltage applied between the electrodes 38 and 39 is further increased from this state, the resonance state of the electron ground level 15 and the electron ground level 16 is canceled, and the dashed line in FIG. Then, the light absorption coefficient recovers.
In this device, a large change in the light absorption coefficient can be obtained by controlling the electric field intensity over a very wide wavelength range from 0.805 μm in wavelength to about 0.623 μm where light absorption in the barrier layer 34 starts. Thus, an optical modulator having a wavelength range that can be modulated by one digit or more compared to the conventional electro-absorption type optical modulator can be realized.
In the above-described second embodiment, an optical modulator having a wavelength shorter than 0.805 μm has been described. However, the wavelength range that can be modulated is not limited to the value proposed in the second embodiment. It is obvious that the wavelength can be shifted by changing the well width of the first quantum well layer 35 and adjusting the transition energy Eg. Although GaAs, Al _0.45 Ga _0.55 As, and Ga _0.51 In _0.49 P are used in the second embodiment, In _0.58 Ga _0.42 As _0. The semiconductor light modulation device of the present invention is applicable to other III-V semiconductors such as ₉ P _0.1 , In _0.53 Ga _0.47 As, In _0.52 Al _0.48 As, and mixed crystal systems thereof. It is clear that it can be achieved.
[0013]
Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and it is needless to say that various modifications can be made without departing from the gist of the present invention.
[0014]
【The invention's effect】
As described above, according to the present invention, since the intensity of light can be modulated over a wide wavelength range as compared with a conventional electro-absorption type optical modulation element, it is possible to prevent the modulation efficiency from deteriorating due to a change in element temperature, An optical modulation element that does not require an element temperature adjustment mechanism can be realized, and low cost or high integration can be realized.
[Brief description of the drawings]
FIG. 1A is a schematic diagram showing a structure of a light modulation element according to a first embodiment of the present invention, and FIG. 1B is an enlarged detailed view of a super lattice structure of the light modulation element shown in FIG.
2A is a schematic diagram illustrating a band structure of a superlattice structure according to the first embodiment of the present invention, and FIG. 2B is a diagram illustrating light absorption characteristics of the superlattice structure according to the first embodiment of the present invention. FIG.
FIG. 3A is a schematic diagram illustrating a structure of a light modulation element according to a second embodiment of the present invention, and FIG. 3B is an enlarged detailed view of a superlattice structure of the light modulation element of FIG.
FIG. 4A is a schematic diagram illustrating a band structure of a superlattice structure according to the second embodiment of the present invention, and FIG. 4B is a diagram illustrating light absorption characteristics of the superlattice structure according to the second embodiment of the present invention. FIG.
FIG. 5 is an explanatory diagram showing the relationship between the energy levels of electrons and holes in a double quantum well structure.
FIG. 6 is an explanatory diagram showing a difference in light absorption coefficient between a state where an electron level resonates and a state where it does not resonate in a double quantum well structure.
FIG. 7 is a perspective view showing a structure of a conventional electro-absorption light modulation element.
FIG. 8 is an explanatory diagram showing a relationship between a wavelength and an absorption coefficient of a conventional electro-absorption light modulation element.
[Explanation of symbols]
1. Insulating GaAs substrate 2 p-type Al _0.35 Ga _0.65 As cladding layer 3 double quantum well structure 4 Al _0.35 Ga _0.65 As barrier layer 5 Ga _0.68 In _{0. 32} N _0.01 As _0.99 First quantum well layer 6 GaN _0.008 As _0.992 Second quantum well layer 7 n-type Al _0.35 Ga _0.65 As cladding layers 8, 9. Ohmic electrode 11: lower end of conduction band of first quantum well layer 12: lower end of conduction band of second quantum well layer 13: band gap energy of first quantum well layer 14: band of second quantum well layer Gap energy 15: Ground level of electrons in first quantum well layer 16: Ground level of electrons 17 in second quantum well layer 17: Ground level of holes 18 in first quantum well layer 18: Second Ground level 19 of holes in the quantum well layer. The first excitation level 20 of the element 20 The first excitation level 31 of the hole of the first quantum well layer 31 The insulating GaAs substrate 32 The p-type Al _0.45 Ga _0.55 As cladding layer 33 The double quantum Well structure 34 Al _0.45 Ga _0.55 As barrier layer 35 GaAs first quantum well layer 36 Ga _0.51 In _0.49 P second quantum well layer 37 n-type Al _0.45 Ga _0.55 As cladding layers 38 and 39 ohmic electrode 41 input light 42 output light 71 InP substrate 72 n-type cladding layer 73 In _0.55 Ga _0.45 As _0.97 P _0.03 quantum well Layer 74 InP barrier layer 75 P-type clad layer 76 Loading clad part 77 p-type In _0.53 Ga _0.47 As cap layer 78, 79 electrode 81 input light 82 output light Eg first Ground level of electrons in quantum well layer Transition energy E1 between the ground level of the electron and the hole: the transition energy E2 between the ground level of the electron in the second quantum well layer and the ground energy of the hole: the first excitation of the electron in the first quantum well layer Transition energy Eb between the level and the first excited level of holes: Band gap energy of barrier layer

Claims (2)

A first cladding layer of a first conductivity type provided on a substrate;
A double quantum well structure provided on the first cladding layer, wherein a first quantum well layer and a second quantum well layer are alternately stacked via a barrier layer;
A second conductivity type second cladding layer provided on the double quantum well structure,
The energy at the lower end of the conduction band of the second quantum well layer is larger than the energy at the lower end of the conduction band of the first quantum well layer;
A band gap energy of the second quantum well layer is larger than a band gap energy of the first quantum well layer;
A semiconductor light modulation device, wherein the energy of the ground level of electrons in the first quantum well layer is smaller than the energy of the ground level of electrons in the second quantum well layer. When a voltage is applied to the double quantum well structure, the ratio of light transmission of the semiconductor light modulation element is determined by utilizing the wavelength dependence of the light absorption coefficient due to resonance / non-resonance of the quantum level of electrons. The semiconductor light modulation device according to claim 1, wherein the semiconductor light modulation device is controlled.

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