JPH11261168A - Optical semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce troubles due to stray light generated at an interface of an optical waveguide layer section. SOLUTION: A length Zp along a light guide direction of one waveguide part 12b, 12c or 12d, which determines a light outgoing edge face of an optical waveguide 12, satisfies a relation Zp>(dc+Q)/ϕ, where dc is a maximum coupling radius of light emitted from an outgoing edge face, Q is a deviation obtained from a normalized error function of stray light generated at an edge face of the wave guide layer which is other than the outgoing edge face, and ϕis a progressing angle of a stray light with respect to a guided light along the optical waveguide 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is formed by incorporating a plurality of optical semiconductor elements such as a semiconductor laser and a semiconductor optical modulator for modulating laser light from the semiconductor laser on a single semiconductor substrate. Optical semiconductor device.

[0002]

2. Description of the Related Art As an optical functional element using an optical semiconductor,
Light sources such as semiconductor lasers or light emitting diodes, or optical functional devices such as electroabsorption optical modulators, optical amplifiers, wavelength filters, and wavelength converters have been developed. Among such optical functional elements, a light emitting element serving as a light source, if necessary, together with other optical functional elements, is formed on a single semiconductor substrate.
It is integrated. With this integration, a single optical semiconductor device has been reduced in size and cost.

When such a plurality of optical functional elements are integrated, a single semiconductor substrate is provided as an optical waveguide of an optical semiconductor device with an optical waveguide layer portion exhibiting optimal properties for each optical functional element. Are formed in series with each other. On the semiconductor substrate, the above-mentioned optical functional element is incorporated with each optical waveguide layer portion as a core part of each optical functional element.

Light emitted from, for example, an optical functional element incorporated in a single semiconductor substrate passes through an optical waveguide layer portion defining its core portion, and then to an optical waveguide layer portion having a different property, for example, a modulator core portion. When guided, reflection or scattering occurs at the interface of the optical waveguide layer portions having different properties, thereby generating radiation mode light or stray light which does not couple to the waveguide mode. When this stray light is incident on an optical device on the light receiving side such as an optical fiber that receives a guided mode light from the optical semiconductor device, that is, an outgoing optical signal, the extinction ratio of the optical signal is deteriorated.
It causes various adverse effects.

Therefore, conventionally, when integrating a plurality of optical function elements, for example, Watanabe and others et al., "Optical Modulator / DFB-LD" Optical Waveguide Analysis of Integrated Light Source ”, IEICE Techniques OQE90-46, pp. 107-113 (1990
Year) or by Isamu Kodaka and others, "High speed (20Gbit
/ S) ・ Low drive voltage (2Vp-p) strain InGaAsP MQ
W light modulator / DFB laser integrated light source, ”IEICE Transactions C-1, Vol. J77-C-1, No. 5, 26th
As shown on pages 8 to 275 (May 1994), various proposals have been made to reduce stray light at the interface of optical waveguide layer portions having different properties.

[0006]

However, according to the above-mentioned prior art, stray light at the interface of the optical waveguide layer cannot be sufficiently reduced, and various adverse effects due to the stray light can be reduced. Technology was long-awaited.

[0007]

The present invention adopts the following constitution in order to solve the above points. <Structure> The present invention is basically directed to an optical waveguide having a plurality of optical waveguide layers formed in series and continuously on a semiconductor substrate and having different properties and having a light guiding function. In an optical semiconductor device formed by integrating at least two optical functional elements each having one optical waveguide layer portion as a core, one optical waveguide that defines the light emitting end face of the optical waveguide is provided. The length Zp of the wave layer portion along the light guide direction is set so as to satisfy the following expression. Zp> (dc + Q) / φ (1) Here, dc is the maximum coupling radius of the light emitted from the emission end face, and Q is the stray light generated at the other end of the waveguide layer defining the emission end face. Is a deviation obtained from the normalized error function, and φ is a traveling angle of the stray light with respect to the guided light guided along the optical waveguide.

As the maximum coupling radius dc, a value determined according to, for example, the numerical aperture of an optical device such as an optical fiber coupled to the output end to receive the output light from the output end of the optical semiconductor device is adopted. be able to. Also, the deviation Q
Similarly, a design value required for the optical system of the optical semiconductor device and the optical apparatus can be adopted. The stray light traveling angle φ can be obtained by calculation using a computer program or by experiment.

The values dc and Q required for the optical system including the optical device according to the present invention are obtained by substituting the value of the stray light traveling angle φ obtained in advance into the above equation (1). Value Z
By setting one end of the waveguide layer portion having p as the emission end of the optical semiconductor device, stray light generated at the other end of the waveguide layer portion has a large influence on the waveguide mode from the emission end. It is possible to prevent the light from entering another optical device coupled to the emission end.

Therefore, according to the present invention, it is possible to prevent a large decrease in the extinction ratio of an optical signal caused by stray light, and it is possible to prevent various adverse effects caused by the reduction in the extinction ratio. .

One of the plurality of optical functional elements can be constituted by a light emitting element such as a semiconductor laser or a light emitting diode, and the other one of the optical functional elements can be constituted by an optical modulator, for example. . Instead of this optical modulator,
An optical functional element such as an optical amplifier, a wavelength filter, or a wavelength converter as described above can be adopted, and one end of the optical functional element other than such a light emitting element is used as the output end of the optical device according to the present invention. Can be defined.

Instead of forming the emission end at one end of the optical waveguide layer portion into which the optical element as described above is incorporated,
The emission end can be constituted by one end of a waveguide layer portion which functions as a simple optical waveguide in which no optical element is incorporated. In any case, by giving a specific numerical value of 200 μm or more to the length dimension Zp of the optical waveguide layer portion that defines the emission end of the optical device according to the present invention, it is remarkable as compared with the related art and A practically sufficient effect can be obtained.

The optical waveguide layer portion to which the present invention is applied can be formed to have different compositions and thicknesses along the light guiding direction by selective growth of a semiconductor material constituting the optical waveguide layer portion. it can. By the selective growth, by gradually decreasing or gradually increasing the composition and thickness of the optical waveguide layer portion, it is possible to continuously form the optical waveguide layer portions having different properties while relatively suppressing the generation of stray light. It becomes possible.

Further, the present invention relates to a combination of an optical semiconductor device in which the light emitting element and the modulation function element are integrated, and a base made of, for example, ceramics provided with a high-frequency power supply line as a modulation power supply for the modulation function element. Can be applied.

That is, a groove for accommodating the optical semiconductor device is formed in the base, and the optical semiconductor device is inserted into the groove so that the extending direction of the groove is along the optical waveguide of the optical semiconductor device. When one end of the optical waveguide layer portion of the modulation function element that is housed and becomes the emission end of the optical semiconductor device is disposed toward the open end of the groove, the extension portion is inserted into the optical waveguide layer portion of the modulation function element. Can be provided.

By adopting a value derived on the basis of the above equation (1) as the length dimension of the extension portion, for example, as described above, for example, optically connected to the output terminal of the optical semiconductor device. It is possible to effectively prevent stray light from entering the optical fiber. Further, the extending portion allows the light-emitting end of the optical semiconductor device according to the present invention to be coupled to the light-receiving end of the optical device such as an optical fiber which cannot be dimensionally arranged in the groove. The distance from the surface can be reduced, thereby increasing the optical coupling efficiency between the two.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. <Example 1> FIG. 1 is a longitudinal sectional view schematically showing Example 1 of an optical semiconductor device according to the present invention. The optical semiconductor device 10 according to the present invention includes a semiconductor substrate 1 made of, for example, n-type InP.
1, and the semiconductor substrate is used as a lower cladding layer 11,
An optical waveguide 12 is formed on the cladding layer. An upper cladding layer 13 made of, for example, p-type InP is formed on the optical waveguide 12. The lower clad layer 11, the optical waveguide 12, and the upper clad layer 13 form a laminate.

The optical waveguide 12 is made of, for example, undoped InGaAs.
It consists of an optical waveguide layer composed of P. This optical waveguide layer 12
Consists of an active layer portion 12a, a waveguide layer portion 12b, and an absorption layer portion 12c formed in series with each other. In the illustrated example, the waveguide layer portion 12b and the absorption layer portion 12c are integrally formed with the same configuration.

The active layer portion 12a is set to have a small light confinement coefficient for a laser to be described later. For example, the active layer portion 12a can adopt a multiple quantum well structure. On the contrary, the absorption layer portion 12c and the waveguide layer portion 12b are set to have a large light confinement coefficient for an optical modulator to be described later, and these layer portions 12c and 12b In addition, if necessary, a multiple quantum well structure or a bulk structure can be adopted.

A diffraction grating 14 is formed in a region below the active layer portion 12a on the upper surface of the lower cladding layer 11. A common electrode 15 is formed on the lower surface of the lower cladding layer 11, and a common electrode 15 is formed on the upper surface of the upper cladding layer 13.
a On the region where the diffraction gratings 14 and 12a are provided,
An upper electrode 17a for laser is formed via the contact layer 16a. Thereby, the active layer portion 12
a in a first area A having a length dimension L ₁ corresponding to
A DFB laser A, which is a well-known optical functional element having the active layer portion 12a as a core, is incorporated. One end of the laminate composed of cleavage planes, that is, the active layer portion 1
On the outer end side of 2a, a well-known reflection film 18 is formed.

An upper electrode 17b for an optical modulator is formed on a region of the upper surface of the upper cladding layer 13 where the absorption layer portion 12c is provided via a contact layer 16b. Thus, in the second region B having a length dimension L ₂ which corresponds to the absorption layer portion 12c, the optical modulator B is incorporated an absorbent layer portion 12c is a well-known optical functional element prior to the core portion Have been. An anti-reflection film 19, which is well known in the art, is formed on the other end of the stacked body composed of cleavage planes, that is, on the outer end side of the absorption layer portion 12c.

Active layer portion 12a and absorption layer portion 12c
The third region C corresponding to the length L ₃ of the waveguide layer portion 12b between the laser beam and the optical modulator B becomes a separation region for electrically separating the laser A and the optical modulator B.
Acts as a guide path for guiding the laser light from the laser A to the modulator B.

That is, when a forward bias voltage is applied between the two electrodes 17a and 15 of the laser A, a laser beam is emitted from the inner end of the active layer portion 12a. The laser light is guided to the absorption layer portion 12c that is continuous with the absorption layer portion 12c via the absorption layer portion 12c having one end contacting the inner end of the active layer portion 12a. The laser beam guided to the absorption layer portion 12c is subjected to intensity modulation in accordance with a high-frequency voltage applied between the electrodes 17b and 15 of the optical modulator B, and the absorption layer portion 12c forming the core portion of the modulator B is formed. Is emitted from the emission end toward another optical device such as an optical fiber.

Accordingly, in the optical semiconductor device 10, the laser light is guided from the active layer portion 12a to the absorption layer portion 12c defining the emission end via the waveguide layer portion 12b. If they are different, reflection or scattering occurs at their interface, thereby producing stray light, which is radiation mode light that does not couple the optical waveguide 12 to the guided mode. In the illustrated example, the waveguide layer portion 12b
Since the absorption layer portion 12c and the absorption layer portion 12c are formed integrally and continuously by the same configuration, stray light is generated at the interface between the active layer portion 12a and the waveguide layer portion 12b. When strong stray light is incident on another optical device coupled to the optical semiconductor device 10, various adverse effects occur, such as a reduction in the extinction ratio of an optical signal due to a guided mode.

In order to reduce the adverse effects of the stray light, in the optical semiconductor device 10 according to the present invention, the distance Zp (L ₂ + L ₃ ) from the emitting end to the point where the stray light is generated is set as follows. .

FIG. 2A shows a relationship between stray light and guided light along a guided mode, and FIG. 2B shows an intensity distribution of the stray light. A position indicated by a point P in FIG. 2A is a point where stray light is generated, and a position separated by a distance Zp from the point P indicates an emission end. The stray light travels toward the emission end at an angle of φ (radian) with respect to the guided light at the point P where the stray light is generated. Separate. The maximum coupling radius determined by the numerical aperture and the like of an optical device such as an optical fiber that receives light from the emission end is indicated by dc.

It is assumed that the stray light and the guided light have the same intensity ratio, and that their intensity distributions are both standard normal distributions as shown in FIG. 2B.

At this time, the following equation Zp = dp / tan φ (1) Here, since φ is considered to be extremely small, equation (1) can be rewritten as Zp = dp / φ (2) Can be.

In the design of the optical system, if the deviation expressed by an error function indicating the ratio of stray light that can enter the optical device is Q, the following equation is obtained from the design: dp = dc + Q (3) Is derived.

Therefore, Zp = (dc + Q) / φ (4) is derived from the relationship between Expressions (2) and (3), and an allowable design requirement for stray light is as follows: (Dc + Q) / φ (5) is obtained.

From this, the design conditions of the optical system are given.
The maximum coupling radius dc, deviation Q and stray light traveling angle obtained
Is obtained by substituting these into equation (5).
To the absorption layer portion 12c and the waveguide layer portion.
The sum of the length dimensions of the minute 12b (L _Two + L_Three )
To obtain the optical semiconductor device 10 capable of suppressing the influence of stray light.
Can be.

The above-mentioned deviation Q is obtained from the above-mentioned error function. This error function corresponds to a saturation extinction ratio E which is an intensity at which extinction is saturated. For example, when a saturation extinction ratio E of 30 dB is given by design. , And the corresponding error function is 10
A value of ^-3 is given, and a value of ³ is given to the deviation Q represented by this error function.

In determining the value Zp that satisfies the relationship of equation (5), the stray light traveling angle φ can be determined by, for example, executing a computer program called BPM or experimentally.

FIG. 3 shows the relationship between the saturation extinction ratio E required for optical design and the propagation distance Zp satisfying the relationship of the equation (5) at the predetermined maximum coupling radius dc in the optical design. It is a graph represented as an X-axis and a Y-axis, respectively.

By preparing such a graph in advance, for example, when a value of 30 dB is required as the saturation extinction ratio E, the propagation distance Zp of 250 μm, which is the value of the Y axis corresponding to the X axis, can be read. it can. Therefore, in this case, by setting the sum (L ₂ + L ₃ ) of the lengths of the absorption layer portion 12c and the waveguide layer portion 12b to 250 μm or more, the active layer portion 12a and the waveguide layer portion 12b can be separated from each other. The effect of stray light generated at the interface can be substantially eliminated. Under general design conditions, it is sufficient if the sum of the lengths (L ₂ + L ₃ ) of the absorption layer portion 12c and the waveguide layer portion 12b is 200 μm or more.

<Embodiment 2> FIG. 4 shows Embodiment 2 of the optical semiconductor device 10 according to the present invention. In the specific example 2, the other components except the optical waveguide 12 are the same as the specific example 1, and the same reference numerals are shown. In the specific example 2, the active layer portion 12a and the waveguide layer portion 12b connected to the active layer portion 12a are constituted by optical waveguide layer portions having different properties from each other. The absorption layer portion 12c to be connected is constituted by an optical waveguide layer portion having different properties.

In the optical semiconductor device 10 of the second embodiment, the interface where the stray light is generated from the guided light from the active layer portion 12a toward the emission end is formed between the active layer portion 12a and the waveguide layer portion 12b and the waveguide layer. It is present between the portion 12b and the absorbing layer portion 12c. However, among the distances from the output end face to each interface, this distance is smaller in the waveguide layer portion 12b.
The stray light at the interface between the layer and the absorbing layer portion 12c has a stronger effect. Therefore, by the distance L ₂ between the interface closer to this and the exit end face is designed such that the propagation distance Zp than described above, it is possible to effectively prevent the influence of stray light.

<Embodiment 3> FIG. 5 shows Embodiment 3 of the optical semiconductor device 10 according to the present invention. As shown in the specific example 3, the active layer portion 12a and the waveguide layer portion 12b are formed by contact bonding (butt-joint). On the other hand, the absorption layer portion 12c and the waveguide layer portion 12b are formed integrally. With respect to integrally forming the absorption layer portion 12c and the waveguide layer portion 12b, for example, by combining a selective growth method with a metal organic chemical vapor deposition or another growth method, the absorption layer portion 12c and the waveguide layer portion 12b are respectively formed. , Different optimal thickness dimensions and compositions can be applied. In the specific example 3, as in the specific example 1, the absorption layer portion 12c and the waveguide layer portion 12c are formed.
The value of the sum (L ₂ + L ₃ ) of the lengths of b is set to be equal to or longer than the propagation distance Zp.

<Embodiment 4> Embodiment 4 shown in FIG. 6 shows an example in which the selective growth method shown in Embodiment 3 is applied to a common waveguide structure. In the common waveguide structure, the waveguide layer portion 12b extends below the active layer portion 12a, but a substantial interface exists between the active layer portion 12a and the waveguide layer portion 12b. Therefore, also in the specific example 4, as in the specific example 1, the sum of the lengths (L ₂ + L ₃ ) of the lengths of the absorption layer portion 12c and the waveguide layer portion 12b is set to be equal to or longer than the propagation distance Zp. Is set.

<Embodiment 5> In the optical semiconductor device 10 of Embodiment 5 shown in FIG. 7, a contact is provided at an intermediate position on the waveguide layer portion 12b and the absorption layer portion 12c which are continuously formed in the same configuration. A layer 16b and an upper electrode 17b for an optical modulator are formed.

Therefore, one end of the optical modulator B formed in relation to the area of the upper electrode 17b, that is, the laser A
On the side, but the separation region having a length dimension L ₃ similar to the above is formed, while the second isolation region C having an optical modulator length L ₄ in the other end of B ' Is formed. Of the absorption layer portion 12c, the optical waveguide layer portion 12d of the second separation region C 'forms an extension 12d from the modulator B to the emission end.

In the fifth embodiment, since the waveguide layer portion 12b and the absorption layer portion 12c including the extension 12d are formed continuously with the same configuration as described above, the waveguide layer portion 12b extends from the emission end. The distance (L ₂ + L ₃ + L ₄ ) to the interface between the portion 12b and the active layer portion 12a is set to be equal to or longer than the propagation distance Zp.

<Embodiment 6> In the embodiment 6 shown in FIG. 8, the extending portion 12d and the absorbing layer portion 12c excluding the extending portion 12d are used.
1 and 2 show examples in which optical waveguide layers are different from each other. In this specific example 6, the waveguide layer portion defining the output end is the extension 12d, and the interface between the extension and the absorption layer portion 12c is the interface closest to the output end. Thus, as the length L ₄ of the extension portion 12d is the propagation distance Zp above, is set.

Referring to the graph of FIG. 3, for example, when a saturation extinction ratio of 20 dB is given, in order to suppress the influence of stray light, the length L ₄ of the elongated portion 12 d is set as follows.
About 230 μm is provided.

FIG. 9 shows an optical semiconductor device 10 according to the sixth embodiment shown in FIG. 8 using a ceramic base 21 provided with a high-frequency power supply line 20 (20a and 20b) as a power supply line to the optical modulator B. An example is shown below.

The ceramic base 21 has a rectangular block shape as a whole, and the surface 21a of the ceramic base 21 has
A concave groove 22 penetrating from one end to the other end and having a width of 2d is formed. In addition, ceramic base 2
The high-frequency power supply lines 20a and 20b described above are arranged on the front surface 21a of the one side so as to be aligned with each other in a direction crossing the extending direction of the groove 22 on both sides of the groove 22. A high-frequency power supply (not shown) is connected to one power supply line 20a. The other power supply line 20b is grounded via a terminating resistor R.

The optical semiconductor device 10 has an emission end at the groove 2.
2 is accommodated in the groove toward one open end.
In addition, the optical semiconductor device 10 is arranged such that the center line above the optical modulator B 17b is aligned with the center line of the high-frequency power supply lines 20 (20a and 20b).

The lower electrode 15 of the optical semiconductor device 10 is connected to a wiring section (not shown) provided at the bottom of the groove 22. The upper electrode 17a of the laser A is connected to a DC power supply (not shown) via a DC power supply line 23 as in the conventional optical semiconductor device. The upper electrode 17b of the optical modulator B is connected to the high-frequency power supply line 20 (20a and 20b) via the connection line 24, as in the related art.

High-frequency power supply line 20 (20a and 20b)
When the distance Ws from the center line of the optical semiconductor device 10 to the end of the ceramic base 21 close to the emission end of the optical semiconductor device 10 is large, light emitted from the optical semiconductor device 10 may be reflected by both side walls of the concave groove 22. There is. In particular, when the high-frequency power supply line 20 is formed using a microstrip line, the length Ws of the ceramic base 21 is different from the power supply line 20.
Is set to a length several times (500 μm or more) the half value (100 μm or more). For this reason, reflection is likely to occur on both side surfaces of the concave groove 22.

In order to prevent this reflection, it is sufficient to satisfy the following equation: L ₄ > Ws−L ₂ / 2−d / tan θ (6) Here, θ indicates the spread angle of the light emitted from the emission end of the optical semiconductor device 10. As an example,
Ws = 500 μm, L ₂ = 100 μm, d = 200 μm
When each value of θ and 45 ° is given, the value of L ₄ obtained from Expression (6) is 250 μm or more.

Therefore, the value of L ₄ obtained by using the graph of FIG. 3 based on the relationship between this value 250 μm and the above-mentioned stray light 2
By adopting the larger value of L ₄ out of 30 μm, the optical semiconductor that can suppress the influence of stray light and can be coupled to other optical devices with high coupling efficiency without causing reflection at the ceramic base 21. The device 10 can be obtained.

In the above-described example, an example in which InP is used as the semiconductor substrate has been described. However, various semiconductor materials such as GaAs can be used as the semiconductor material, and various types of waveguide such as a laterally buried structure can be used as the waveguide. Structure can be applied. Furthermore, as the optical function element of the optical semiconductor device 10, an example of an optical modulator and a DFB laser has been described.
The present invention can be applied to integration of various optical functional elements such as a DBR laser and a DFB / DBR laser.

[0053]

According to the present invention, as described above, the length of the optical waveguide portion that defines the emission end is set to a length sufficient to suppress the incorporation of stray light into the waveguide mode. Therefore, it is possible to prevent the stray light from deteriorating the extinction ratio of the optical signal, and it is possible to prevent various adverse effects due to the reduction in the extinction ratio.

Further, according to the present invention, by forming the extension portion related to the emission end, it is possible to prevent various adverse effects due to the above-mentioned influence of stray light, and in addition to the optical coupling efficiency by using the ceramic base. Can also be prevented from decreasing.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a specific example 1 of an optical semiconductor device according to the present invention.

FIG. 2 is a graph showing a relationship between stray light and guided light and a light intensity distribution.

FIG. 3 is a graph showing a relationship between an extinction ratio and a transmission plate distance.

FIG. 4 is a longitudinal sectional view showing Example 2 of the optical semiconductor device according to the present invention.

FIG. 5 is a longitudinal sectional view showing Example 3 of the optical semiconductor device according to the present invention.

FIG. 6 is a longitudinal sectional view showing Example 4 of the optical semiconductor device according to the present invention.

FIG. 7 is a longitudinal sectional view showing Example 5 of the optical semiconductor device according to the present invention.

FIG. 8 is a longitudinal sectional view showing Example 6 of the optical semiconductor device according to the present invention.

FIG. 9 is a plan view showing a combination of the optical semiconductor device of Example 6 and a ceramic base.

[Explanation of symbols]

 Reference Signs List 10 optical semiconductor device 11 semiconductor substrate (cladding layer) 12 optical waveguide 12a (active layer portion) optical waveguide layer portion 12b (waveguide layer portion) optical waveguide layer portion 12c (absorption layer portion) optical waveguide layer portion 12d (extended portion) Optical waveguide layer portion 21 Base 22 Concave groove A, B Optical functional element

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hideaki Horikawa 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (5)

[Claims] An optical waveguide formed in series and continuously on a semiconductor substrate and having a plurality of optical waveguide layer portions having different properties, and formed in association with an optical waveguide having a light guiding function, An optical semiconductor device in which at least two optical functional elements each having one optical waveguide layer portion as a core are integrated, wherein one of the waveguide layers defining a light emitting end face of the optical waveguide. An optical semiconductor device, wherein a length dimension Zp of a portion along a light guiding direction is set so as to satisfy the following expression. Zp> (dc + Q) / φ Here, dc is the maximum coupling radius for light emitted from the emission end face, and Q is the normalization of stray light generated at the other end of the waveguide layer defining the emission end face. And φ is the advancing angle of the stray light with respect to the guided light guided along the optical waveguide. 2. The optical semiconductor device according to claim 1, wherein the optical functional element formed in association with the waveguide layer other than the optical waveguide layer defining the emission end face in the waveguide layer is a light emitting element. 3. A core part of an optical modulator for receiving a high-frequency signal for optical modulation, wherein at least a part of the waveguide layer part defining the emission end face functions as a core part of the optical modulator. The length dimension Zp of the waveguide layer portion is 200
2. The optical semiconductor device according to claim 1, wherein said optical semiconductor device has a thickness of not less than μm. 4. The waveguide layer part is made of a semiconductor material.
2. The structure according to claim 1, wherein at least one of the waveguide layers is formed to have a different composition and a different thickness along a light guiding direction by selective growth of the semiconductor material. Optical semiconductor device. 5. A light guide formed in series and continuously on a semiconductor substrate and having a plurality of optical waveguide layers having different properties, and formed in association with an optical waveguide having a light guiding function, An optical semiconductor device in which a light emitting element and a modulation function element for modulating the intensity of light from the light emitting element are integrated, each having one of the optical waveguide layer portions as a core, wherein at least one end of the groove is open. Is disposed on the surface of the base on which a high-frequency power supply line for the modulation function element is formed, with the light emitting end face facing the open end of the groove. Is formed with an extended portion that defines a light emitting end face, and a length dimension Zp of the extended portion along the light guiding direction is set to satisfy the following expression. Semiconductor device. Zp> (dc + Q) / φ Here, dc is a maximum coupling radius for light emitted from the emission end face, and Q is a normalized value of stray light generated at the other end of the extension portion defining the emission end face. Is a deviation obtained from an error function, and φ is a traveling angle of the stray light with respect to the guided light guided along the optical waveguide.