JPH08160368A - Semiconductor light intensity modulation device and semiconductor optical device - Google Patents

Abstract

PURPOSE: To obtain push-pull actions with simple constitution. CONSTITUTION: Incident light passes a light input side waveguide 12 and is branched to two diagonal waveguides 14a, 14b in a Y-shaped branch 13. Voltages are impressed on these diagonal waveguides 14a, 14b by upper electrodes 15a, 15b, by which electric fields are generated therein. At this time, detuning parts largely to the extent that a primary electro-optical effect mainly arises and, therefore, the change rates Δn1 , Δn2 of the refractive indices in the diagonal waveguides 14a, 14b attain Δn1 =-Δn2 . As a result, the push-pull actions are realized by impressing the voltages of the same magnitude and impression direction on the diagonal waveguides 14a, 14b, by which chirping is made zero in principle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to light modulation using a semiconductor, and more particularly to a semiconductor light intensity modulator for light on the light transmitting side and a semiconductor optical device using the same.

[0002]

2. Description of the Related Art Conventionally, techniques in such a field include:
For example, some documents were described in the following documents. Reference; OQE92-50, 1992, Sano et al., "InGa
As / InAlAs MQW Mach-Zehnder type optical modulator ”, p. 37
-41 In an ultra-high-speed long-distance optical communication system, waveform deterioration due to interaction between wavelength dispersion of an optical fiber and spread of a spectrum of signal light (hereinafter referred to as chirping) limits an optical transmission distance. In particular, with the recent practical use of optical amplifiers, the regenerative repeater distance of the optical waveform has been greatly extended, and thus a technique for obtaining signal light with even smaller chirping is required.

In response to this demand, a device for obtaining intensity-modulated light with a small chirping, which mainly has the following structure, has been developed so far. (A) Mach Zehender interferometer (hereinafter referred to as M
Optical modulator of Z type) (b) Electroabsorption effect of semiconductor (hereinafter referred to as EA effect)
Further, (a) is an electro-optic effect of LiNnO ₃ (hereinafter,
It is classified into one using the EO effect) and one using the semiconductor quantum confined Schunker effect (hereinafter referred to as QCSE). Hereinafter, the latter is referred to as a QCSE-MZ type optical modulator. In the MZ type, in principle, the chirping is set to 0 by applying a voltage so that the two optical waveguides have the same magnitude of change in the refractive index and the signs are opposite to each other (hereinafter referred to as push-pull operation). be able to. In (b), the charving can be reduced, but in principle it is impossible to reduce it to zero. The QCSE-MZ type optical modulator
Since a semiconductor material such as InP is used and it is of the MZ type, it is possible in principle to reduce the chirping to 0.

FIG. 2 shows a conventional QC described in the above document.
It is a block diagram of an SE-MZ type optical modulator. As shown in FIG. 2, in the optical input side Y-shaped branch 4 at the tip of the optical input side waveguide 2 located on a straight line, two curved waveguides 6a and 6b are provided.
Are connected. The curved waveguides 6a and 6b are connected to two parallel straight waveguides 7a and 7b. Upper electrodes 8a and 8b are provided on the linear waveguides 7a and 7b for applying an electric field independently of each other. Straight waveguide 7
a and 7b are connected to the curved waveguides 9a and 9b. The curved waveguides 9a and 9b are provided in the Y-shaped branch 5 on the optical output side.
It is connected to the optical output side waveguide 3. 1 is n-InP
It is a substrate and has a (100) crystal plane. The straight waveguides 7a and 7b are in the <011> direction. Further, in the above structure, the difference in incident light wavelength (hereinafter referred to as detuning) with respect to the PL peak wavelength of 1.47 μm of the optical waveguide layer is 90 to 120 so that the change in refractive index due to QCSE can be made large.
It is set to around nm.

Here, the EO effect and QCSE when an electric field is applied
The refractive index change amount Δn caused by the above is quantitatively described as the following equations (1) and (2). Δn = n ³ Γ {r ₄₁ Ecos (2θ) + sE ² } / 2 (1) E = V / d (2) where n: refractive index when no electric field is applied Γ : Optical confinement coefficient r ₄₁ : first-order electro-optical constant E: applied electric field strength θ: direction of optical waveguide (based on <011> direction of crystal) s: second-order electro-optical constant or change in refractive index due to QCSE Coefficient V: Applied voltage d: Thickness of layer to which voltage is applied From the equation (1), the change in refractive index due to the primary EO effect is
The magnitude and sign of the optical waveguide differ depending on the direction of the optical waveguide or the direction of the applied electric field, whereas the change in the refractive index due to the secondary EO effect or QCSE is independent of the direction of the optical waveguide and the direction of the applied electric field. I understand. Therefore, the refractive index changes Δn ₁ and Δn _{2 of} the linear waveguides 7a and 7b.
Is Δn ₁ = n ³ Γ {r ₄₁ E ₁ cos (2θ) + sE ₁ ² } / 2 = n ³ Γ {r ₄₁ V ₁ cos (2θ) / d + s (V ₁ / d) ² } / 2 ...・ (3) Δn ₂ = n ³ Γ {r ₄₁ E ₂ cos (2θ) + sE ₂ ² } / 2 = n ³ Γ {r ₄₁ V ₂ cos (2θ) / d + s (V ₂ / d) ² } / 2 (4)

As described above, in order to realize the push-pull operation in order to reduce the chirping to 0 in principle, the refractive index changes Δn ₁ and Δn _{2 in} the two linear waveguides 7a and 7b when an electric field is applied are The relation of the following expression (5) must be satisfied. Δn ₁ = −Δn ₂ (5) FIG. 3 is a diagram showing how voltage is applied to obtain the conventional push-pull operation. As shown in FIG. 3, when the voltages applied to the linear waveguides 7a and 7b are expressed as V ₁ = V _b1 ± ΔV ₁ and V ₂ = V _b2 ± ΔV ₂ (6), respectively, V _{b1 -ΔV 1 = V b2 + ΔV} 2 by applying a voltage so as to (7), and may be adjusted to a value of V ₁ and V ₂ so as to satisfy the equation (5). This allows
It is possible to obtain light intensity modulation under push-pull operation. FIG. 4 is a diagram showing an extinction ratio obtained by the voltage application method of FIG. In FIG. 4, P _in is the power of the input light, P _out is the power of the output light, and t is the time. By the way, in the above literature, a voltage is applied only to one of the linear waveguides 7a or 7b, and the other linear waveguide 7b or 7a is grounded. Therefore, the push-pull operation is not obtained.

[0007]

However, the conventional semiconductor light intensity modulator has the following problems (a) and (b). (A) In order to realize the push-pull operation to satisfy the expression (7), since the change in the refractive index due to QCSE does not change linearly with the applied electric field, not only the values of V _b1 and V _b2 but also ΔV ₁ and The magnitude of ΔV ₂ must also be different. As the method, two devices for generating a modulation voltage are prepared and synchronized, or the modulation voltage is electrically bisected to adjust the magnitude of the amplitude and the phase is shifted by 180 degrees and then separately. It is conceivable to adopt a method of superimposing the bias voltage on the However, in any case, the electrically driven device becomes large or complicated. (B) Maximum applied voltage V _b1 + Δ in the straight waveguide 7a
V ₁ and the maximum applied voltage V _b2 −Δ in the straight waveguide 7 _b
At V ₂ , since the voltage difference becomes large, EA in the optical waveguide layer
The difference in absorption amount due to the effect cannot be ignored. this is,
This causes deterioration of the extinction ratio.

[0008]

In order to solve the above-mentioned problems, a first aspect of the present invention is to connect an optical input side waveguide for inputting light and a tip of the optical input side waveguide to apply an electric field. Two waveguides having a non-parallel portion having a Zinc-Blend type crystal structure in which the refractive index changes due to and an upper electrode provided in each of the non-parallel portions are provided. A second invention is two waveguides having non-parallel portions having a Zinc-Blend type crystal structure whose refractive index is changed by applying an electric field, and an upper electrode provided on each of the non-parallel portions, And an optical output side waveguide that combines at the tips of the two waveguides.
In a third aspect based on the first or second aspect, the detuning is set so that the amount of change in refractive index mainly produces only a first-order electro-optical effect, and the two electrodes are connected to the upper electrode by the upper electrode. When the same voltage is applied, the non-parallel portions of the two waveguides are arranged in such a direction that the two waveguides have the same magnitude of change in the refractive index and the signs thereof are opposite to each other. According to the fourth invention, the non-parallel portions of the two waveguides of the third invention are n × 90 + 45 [deg.] With respect to the reference orientation of the Zinc-Blend type crystal. ] (However, an integer of n ≧ 0) is arranged at symmetrical positions about a straight line.

[0009]

According to the present invention, since the semiconductor optical intensity modulator is constructed as described above, when the same voltage is applied to two waveguide parts which are not parallel to each other, the refractive index due to the EO effect or QCSE caused by the voltage is caused. Changes Δn ₁ and Δn ₂ of
The non-parallel portions of the two waveguides are arranged so that Δn ₁ = −Δn ₂ . This enables the push-pull operation of the semiconductor light intensity modulator. Therefore, the above problem can be solved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a plan view showing a semiconductor light intensity modulator according to a first embodiment of the present invention. The semiconductor light intensity modulator of the first embodiment is different from the conventional semiconductor light intensity modulator in that first, the optical input side waveguide 12 and the optical output side waveguide 19 are set to <0.
10> direction. Secondly, in the Y-shaped branch 13 on the light input side, Δθ is symmetrical about the <010> direction as an axis,
The oblique waveguides 14a and 14b are arranged at an angle of −Δθ (Δθ = 20 [deg.]) Degrees and are not parallel to each other.
That is, the upper electrodes 15a and 15b are provided on the electrodes 4a and 14b. As shown in FIG. 1, an optical input side waveguide 12 is arranged in the <010> direction on an n-InP substrate 10 having an upper surface having a (100) plane. The optical input side waveguide 12 is
In the Y-shaped branch 13 on the light input side, two oblique waveguides 14a and 14b are arranged at an angle of Δθ (Δθ = 20 [deg.]) And −Δθ with respect to the <010> direction. That is, if the directions of the oblique waveguides 14a and 14b are θ ₁ and θ ₂ , and the direction of the center line of the angle 2Δθ formed by the two waveguides 14a and 14b is θ ₀ , then θ ₁ and θ ₂
Is expressed by the following equations (8) and (9). θ ₁ = θ ₀ + Δθ (8) θ ₂ = θ ₀ −Δθ (9) In the first embodiment, θ ₀ is defined as <01
1> direction as a reference, θ ₀ = n × 90−45 [deg. ] (10) n = 0, 1, 2, ... (11) In FIG. 1, n = 0, that is, θ ₀ = −45 [deg. ], And θ ₀ is the <010> direction. Also, Δ
The range of θ is 0 <| Δθ | ≦ 45 [deg. ] (12) This is Δθ = 45 [deg. ], The refractive index difference or phase difference at the time of applying an electric field in the oblique waveguides 14a and 14b becomes maximum, and it is meaningless to increase Δθ further. Oblique waveguides 14a and 14b
Upper electrodes 15a and 15b are provided on the upper side.

FIG. 5 is a sectional view taken along the line AA in FIG. As shown in FIG. 5, the oblique waveguide 14a is provided with n−I from the lower layer.
The nP lower clad layer 22a / undoped-InGaAsP optical waveguide layer 24a / p-InP upper clad layer 24a. The oblique waveguide 14b is composed of the n-InP lower cladding layer 22b / undoped-InGaAsP optical waveguide layer 24b / p-.
It is composed of the InP upper cladding layer 24b.
Between the p-InP upper cladding layer 24a and the upper electrode 15a, p-InGaAs for ohmic contact is formed.
(P) The ohmic contact layer 25a is formed. p-InP upper cladding layer 24b and upper electrode 15b
P-InGaAs for ohmic contact between
(P) The ohmic contact layer 25a is formed. By applying a voltage to the upper electrodes 15a and 15b, the refractive index of the undoped-InGaAsP optical waveguide layers 24a and 24b changes. Both sides of the waveguides 14a and 14b are provided with Fedope for horizontal light confinement and electrical insulation.
The upper electrode 15 is filled with the d-InP block layer 26.
The p-InGaAs (P) ohmic contact layers 26a and 26b other than the lower portions of a and 15b are removed. n
The lower layers of the -InP lower clad layers 22a and 22b are n-I.
The nP substrate 11. Below the n-InP substrate 11,
The lower electrode 21 is formed. The PL peak wavelengths of the undoped-InGaAsP optical waveguide layers 23a and 23b are different from the incident optical wavelength, that is, detuning is 150 nm or more (when a voltage is applied to the optical waveguide layers, only a primary electro-optical effect is mainly generated. Is set). Diagonal waveguide 14
The tip of a and 14b has a curvature of 5μ to reduce excess loss.
m (for smoothing the connection to suppress reflection and scattering of light output from the oblique waveguides 14a and 14b)
Curved waveguides 16a and 16b are arranged. In the Y-shaped branch 18 on the optical output side, the light is coupled to the optical output side waveguide 19 in the <011> direction. The diagonal waveguides 14a and 14b, the curved waveguides 16a and 16b, and the diagonal waveguides 17a and 17b form a rhombus-shaped MZ type intensity modulator.

Next, the operation of the semiconductor light intensity modulator of FIG. 1 will be described. The incident light passes through the optical input side waveguide 12 and is passed through the Y-shaped branch 13 into the two oblique waveguides 1.
It is branched into 4a and 14b. Oblique waveguides 14a and 14b
A voltage is applied to the electrodes by the upper electrodes 15a and 15b, and an electric field is generated. At this time, the detuning of the undoped-InGaAsP optical waveguide layer 23 with respect to the incident light length is
When the voltage is applied to the optical waveguide layer 23, they are largely separated from each other so that only a primary electro-optical effect is generated. Therefore, the refractive index change amounts Δn ₁ and Δn ₂ in the oblique waveguides 14a and 14b are Δn ₁ = n ³ Γr ₄₁ Ecos (2 (θ ₀ + Δθ)) from the equations (1), (8), and (9). / 2 (13) Δn ₂ = n ³ Γr ₄₁ Ecos (2 (θ ₀ −Δθ)) / 2 (14) Here, assuming that the voltages V applied to the upper electrodes 15a and 15b are equal. There is. Further, substituting the equations (10) and (11) into the equations (13) and (14), Δn ₁ = −Δn ₂ = | n ³ Γr ₄₁ Esin (2Δθ) / 2 | (15) A push-pull operation is realized by applying a voltage having the same magnitude and the same application direction to the oblique waveguides 14a and 14b, and in principle it is possible to reduce the charving to zero. The phase difference Δψ between the two oblique waveguides 14 a and 14 b is Δψ = (2πL / λ) (Δn ₁ −Δn ₂ ) = (2πL / λ) (n ³ Γr ₄₁ E / 2) 2 sin (θ ₀ ) Sin (Δθ) = (2πLn ³ Γr ₄₁ E / λ) sin (2θ ₀ ) sin (2Δθ) (16) where, L is the length of the region applied to the electric field λ is the wavelength Δψ of the incident light The voltage that becomes π, that is, the half-wave voltage V _pi is expressed by the equations (2) and (16) as follows: V _pi = λd / {2πLn ³ Γr ₄₁ sin (2Δθ ₀ ) sin (2Δθ)} (17) Substituting (17) into equation (16) gives Δψ = π (V / V _pi ) ... (18).

The phase difference Δψ expressed by the equation (16) is output to the output side optical waveguide 19 after passing through the oblique waveguides 14a and 14b.
It is maintained until the light is output. Furthermore, the oblique waveguide 1
If the power ratio when no voltage is applied to 4a and 14b is 1: 1, the following equation (19) is established between the power P _out of the output light and the power P _{in of the} input light. P _out = P _in cos ² (πV / 2V _pi ) = P _in cos ² (Δψ / 2) (19) From the equation (19), the ratio of the output light power P _{out to} the input light power P _in Is expressed by the following equation (20). P _out / P _in = cos ² (Δψ / 2) (20) However, the sum of squares of the absolute values of the complex electric field amplitudes of the oblique waveguides 14a and 14b is 1, and the scattering loss in the Y-type branches 13 and 18 is Is ignored and the power division ratio on the input side is set to 1.

FIG. 6 is a cross-sectional view between the oblique waveguides 14a and 14b of FIG.
7 is a diagram showing the applied voltage dependence of the phase difference Δφ between
FIG. 6 is a diagram showing applied voltage dependence of extinction. The horizontal axis in FIG. 6 is the voltage V [V] applied to the upper electrodes 15a and 15b, and the vertical axis is the phase difference Δψ [rad. ] Is shown. The horizontal axis in FIG. 7 indicates the voltage V [V] applied to the upper electrodes 15a and 15b,
The vertical axis represents the ratio P of the output light power to the input light power.
shows _out / P _in . In FIGS. 6 and 7, λ,
n, d, L, and θ ₀ are 1.55 μm and 3.4, respectively.
8, 0.25 μm, 4 mm, θ ₀ = 45 [deg. ]] Further, Γ and r ₄₁ are each 0.3 × 10.
^-10 , 1.4 × 10 ^-10 cm / V is used. And Δ
θ = 5 [deg. ], 10 [deg. ], 15 [de
g. ], 20 [deg. ] In equation (16)
ψ and the extinction ratio P _out / P _in of Expression (20) are shown. The broken line in FIG. 6 indicates the point where the phase difference Δφ is π, 2π. As shown in FIG. 7, Δθ = 20 [de
g. ], It can be seen that sufficient quenching can be obtained at about 4V.

As described above, the first embodiment has the following advantages. (A) To realize the theoretical charving 0, it is only necessary to apply voltages of the same magnitude and direction to the oblique waveguides 14a and 14b. Therefore, the voltage of the oblique waveguides 14a and 14b can be short-circuited. -Only one device that generates the modulation voltage is required. That is, the mounting can be simplified and the driving device can be simplified. (B) Even if absorption due to the EA effect exists in the optical waveguide layer, the same voltage is applied to the oblique waveguides 14a and 14b, so that there is no difference in absorption amount between the oblique waveguides 14a and 14b. , Does not deteriorate the extinction ratio. From the above, in the intensity modulation type optical communication system,
By incorporating the optical intensity modulator of the present embodiment in the transmitter of the optical signal, the transmission distance is improved, the transmission speed is improved,
It is possible to reduce the system cost while improving the minimum received power.

Second Embodiment FIG. 8 is a plan view of a semiconductor light intensity modulation device showing a second embodiment of the present invention, which is common to the elements of the semiconductor light intensity modulation device of the first embodiment of FIG. The same reference numerals are given to the elements of. The semiconductor light intensity modulator of the second embodiment differs from the semiconductor light intensity modulator of the first embodiment in that the upper electrodes 31a and 31b are provided with two non-parallel oblique waveguides 17a,
It is provided on 17b. As shown in FIG. 8, <0 is formed on the n-InP substrate 11 whose upper surface has a (100) plane.
The optical input side waveguide 12 is arranged with an inclination of θ ₀ (set to satisfy the expressions (10) and (11), which is the direction of <10>) with respect to the 11> direction. Optical input side waveguide 1
Reference numeral 2 denotes a Y-shaped branch 13 on the light input side, which is an oblique waveguide 1
4a and 14b are arranged. Oblique waveguides 14a, 1
4b and the oblique waveguides 17a and 17b, curved waveguides 16a and 16 having a curvature of about 5 μm are provided to reduce excessive loss.
b is arranged. The oblique waveguides 17a and 17b are
They are arranged in the directions of θ ₁ and θ ₂ with respect to the 011> direction as shown in the following equations (21) and (22). θ ₁ = θ ₀ −Δθ (21) θ ₂ = θ ₀ + Δθ (22) The upper electrodes 31a and 3 are provided on the oblique waveguides 17a and 17b.
1b is provided. Two oblique waveguides 17a, 17
In the Y-shaped branch 18 on the light output side, b is combined with the light output side waveguide 19 arranged in the <011> direction. The diagonal waveguides 14a and 14b, the curved waveguides 16a and 16b, and the diagonal waveguides 17a and 17b form a rhombus-shaped MZ type intensity modulator.

The operation of the semiconductor light intensity modulator of FIG. 8 will be described below. The incident light passes through the optical input side waveguide 12 and is passed through the Y-shaped branch 13 into the two oblique waveguides 1.
4a and 14b are branched to form diagonal waveguides 14a and 14b.
And the curved waveguides 16a and 16b. Since there is no change in the refractive index so far, no phase difference occurs between the light passing through the curved waveguides 16a and 16b. After that, it passes through the oblique waveguides 17a and 17b. At this time, the upper electrode 3
Since a voltage is applied by 1a and 31b to generate an electric field, the refractive indices Δn ₁ and Δn ₂ are calculated by the formula (2
From 1) and (22), as in equations (13) and (14),
It becomes like (23) and (24). Δn ₁ = n ³ Γr ₄₁ Ecos (2 (θ ₀ −Δθ)) / 2 (23) Δn ₂ = n ³ Γr ₄₁ Ecos (2 (θ ₀ + Δθ)) / 2 (24) , Δn ₁ = −Δn ₂ = | n ³ Γr ₄₁ Esin (2 Δ
θ) / 2 | and the same relational expression as Expression (15) is obtained. Therefore, the push-pull operation is realized and, in principle, the chirping can be set to zero.

As described above, the second embodiment has the same advantages as the first embodiment. The present invention is not limited to the above embodiment, and various modifications are possible. The following are examples of such modifications. (1) The present embodiment is simply shown to the extent that the present invention can be understood, and the dimensions, shapes, and
The composition is not limited. (2) FIG. 9 is a plan view of a semiconductor light intensity modulator showing a first modification of the present invention. In this first modification,
The optical input side waveguide 12, the Y side branch 13 on the optical input side, the oblique waveguides 14a and 14b, and the upper electrodes 15a and 15b are integrated on the n-Inp substrate 11, and the polarization is preserved on the output side. Type M optical fiber combiner 42
This is a Z-type interferometer. Reference numeral 41 is a current injection electrode for amplifying light by injecting current to form an optical amplifier. (3) FIG. 10 is a plan view of a semiconductor light intensity modulator showing a second modification of the present invention. In the second modification, the optical output side waveguide 19 and the optical output side Y-shaped branch 18 are provided.
And the oblique waveguides 17a and 17b and the upper electrodes 31a and 3
1b and 1b are integrated on an n-Inp substrate 11, and an MZ interferometer is configured by a combination using a polarization-maintaining type optical fiber combiner 52 on the input side thereof. Reference numeral 51 is a current injection electrode for forming an optical amplifier. (4) FIG. 11 is a plan view of a semiconductor light intensity modulator showing a third modification of the present invention. In the third modification, the light input side waveguide 12, the light output side waveguide 19, the oblique waveguides 16a, 16b, 17a and 17b, and the upper electrode 31 are provided.
a and 31b are integrated on the n-Inp substrate 11 to form an MZ
This is a type interferometer. Reference numeral 61 is a current injection electrode for amplifying light.

(5) It is possible to replace the Y-shaped branch in the first and second embodiments with a directional coupler that splits the light in a ratio of 1: 2. (6) The substrate 11 of the first and second embodiments is Zin.
InP which is one of the c-Blend type crystals is used, but other Zinc-Blend such as GaAs is used.
The crystal of the mold may be the substrate. (7) In the first and second embodiments, an example in which n in Expression (10) is set to 0 is shown, but in the case of n = 1, 2, 3, ..., Similarly, Expression (15), And (25) hold. (8) Since the semiconductor having a Zinc-Blend type crystal structure has a three-fold rotational symmetry structure, the primary electro-optic coefficient r ₄₁ of the (100) substrate is the primary electro-optic coefficient r _{52 of} the (010) substrate, ( ₅₂ 001) first-order electro-optic coefficient r ₆₃ of the substrate
Is equal to Therefore, it can be applied to the case of using the (010) substrate or the (001) substrate. The direction of θ ₀ in the equation (15) is the (101) direction in the case of the (010) substrate,
In the case of a (001) substrate, the direction is (110).

(9) Although the n-type substrate is used as the substrate, it is also applicable to the case where the p-type substrate is used. The change in the refractive index of the first diagonal waveguide 14a is opposite in positive and negative between the case of using the n-type substrate and the case of using the p-type substrate, but the change of the refractive index in the diagonal waveguides 14a and 14b is also positive and negative. Therefore, the expression (15) is satisfied. (10) The case of using a bulk crystal for the undoped-InGaAs (P) optical waveguide layer 23 in FIG. 5 has been described, but the same applies to the case of using a multiple quantum well structure for the optical waveguide layer 23. (11) The semiconductor light intensity modulator of this embodiment may be integrated on the same substrate as the semiconductor laser arranged on the input side of the optical input side waveguide 12.

[0021]

As described in detail above, according to the first to sixth aspects of the invention, since the portions of the two waveguides to which the voltage is applied are not parallel, the same voltage is applied to the two waveguides. Since the push-pull operation is possible even when applied, it is possible to simplify the configuration of the semiconductor light intensity modulator for obtaining the push-pull operation.

[Brief description of drawings]

FIG. 1 is a plan view of a semiconductor light intensity modulator according to a first embodiment of the present invention.

FIG. 2 is a plan view of a conventional QCSE-MZ type optical modulator.

FIG. 3 is a diagram showing a voltage applying method for obtaining a push-pull operation of the light intensity modulator of FIG.

FIG. 4 is a diagram showing an extinction ratio obtained by applying the voltage of FIG.

5 is a cross-sectional view taken along the line AA in FIG.

6 is a diagram showing an applied voltage dependency of a phase difference Δφ between the oblique waveguides of FIG. 1.

FIG. 7 is a diagram showing applied voltage dependence of extinction.

FIG. 8 is a plan view of a semiconductor light intensity modulator according to a second embodiment of the present invention.

FIG. 9 is a plan view of a semiconductor light intensity modulation device showing a first modified example of the present invention.

FIG. 10 is a plan view of a semiconductor light intensity modulation device showing a second modification of the present invention.

FIG. 11 is a plan view of a semiconductor light intensity modulation device showing a third modification of the present invention.

[Explanation of symbols]

11 n-InP Substrate 12 Optical Input Side Waveguide 13 Optical Input Side Y
Type branching 14a, 14b, 17a, 17b Diagonal waveguide 15a, 15b, 31a, 31b Upper electrode 16a, 16b Curved waveguide 18 Light output side Y
Type branching 19 Optical output side waveguide

Claims (6)

[Claims] 1. A light input side waveguide for inputting light, and a non-parallel portion having a Zinc-Blend type crystal structure which is connected to a tip of the light input side waveguide and whose refractive index changes by applying an electric field. A semiconductor light intensity modulator, comprising: two waveguides provided; and an upper electrode provided in each of the non-parallel portions. 2. Two waveguides each having a non-parallel portion having a Zinc-Blend type crystal structure whose refractive index changes by applying an electric field, an upper electrode provided on each of the non-parallel portions, and A semiconductor optical intensity modulator, comprising: a waveguide on the optical output side that combines at the tips of two waveguides. 3. The detuning is set so that the amount of change in the refractive index mainly produces only a first-order electro-optical effect, and when the same voltage is applied to the two waveguides from the upper electrode, 3. The semiconductor light according to claim 1, wherein the two waveguides are arranged so that the non-parallel portions of the two waveguides are arranged in such directions that the magnitudes of the changes in the refractive index of the two waveguides are the same and the signs thereof are opposite to each other. Intensity modulator. 4. The non-parallel portions of the two waveguides are n × 90 ± 45 [deg.] With respect to a reference orientation of the Zinc-Blend type crystal. ] (However, it is an integer of n ≧ 0) The semiconductor light intensity modulator according to claim 3, wherein the straight line is an axis of symmetry. 5. A semiconductor optical device comprising the semiconductor light intensity modulator according to claim 1, 2, 3, or 4, and a semiconductor laser or an optical amplifier. 6. The semiconductor optical device according to claim 5, wherein the semiconductor light intensity modulator and the semiconductor laser or optical amplifier are integrated on the same semiconductor substrate.