JP4912719B2 - Semiconductor optical device, optical switching system, and wavelength tunable laser - Google Patents

Description

  The present invention relates to a semiconductor optical device, and more particularly to a semiconductor optical device capable of changing a light emission angle.

  Conventionally, an external cavity type semiconductor laser (hereinafter referred to as EC-LD) is a semiconductor that has a much higher yield in manufacturing and can obtain a laser beam with a narrow spectral line width than a monolithic type distributed feedback semiconductor laser. Useful as a laser.

  EC-LD is comprised by the semiconductor optical element and diffraction gratings, such as a fiber grating, for example. Here, the diffraction grating and the semiconductor optical element are required to align the optical axis with high accuracy so as to function as a resonator.

  Further, in a semiconductor optical device such as an EC-LD, at least one optical waveguide end face needs to be a low reflectivity end face, and an end face serving as a terminal end of at least one waveguide of the semiconductor optical element is an oblique end face. Is used. In such a semiconductor optical device having an oblique end face, there may be a variation in angle formed between the normal direction of the cleavage plane and the waveguide during the manufacturing process. In this case, since the light emission angle varies for each semiconductor optical element, the emission characteristics of the individual semiconductor optical elements are corrected so that the positional deviation of the optical axis between the semiconductor optical element and the external resonator is corrected. It is necessary to align the optical axis according to.

  In the optical axis alignment, there are a method of mechanically moving the semiconductor optical device and a method of changing the emission angle of light emitted from the semiconductor optical device. If the latter method is used, the semiconductor optical device is moved. This is desirable because a small and high performance EC-LD can be configured without the need for a movable part.

  As a method of changing the emission angle of light emitted from the semiconductor optical device, there is a method of changing the current injected into the active layer according to the position in the horizontal direction within the cross section of the active layer (for example, Patent Document 1). reference).

  As shown in FIG. 10, the semiconductor laser 50 of Patent Document 1 includes a semiconductor substrate 51 in which an active layer 52 and a cladding layer 53 are stacked. First and second channels 53 a and 53 b are formed as current flow paths from the second electrodes 55 and 56 to the active layer 52.

When the amount of current injection supplied to the first channel 53a is increased, the carrier density in the active layer 52 in the vicinity of the first channel 53a increases. Here, the greater the carrier density, the lower the equivalent refractive index of the active layer 52. Therefore, the light in the active layer 52 propagates inside the active layer 52 so as to be pulled in a direction with a low equivalent refractive index. As a result, the emission angle of light emitted from the semiconductor laser 50 has also changed.
JP-A-1-293683

  However, the semiconductor laser 50 disclosed in Patent Document 1 requires two-channel current control in order to adjust the emission angle of the emitted light. Therefore, there is a problem that the control circuit becomes complicated. In addition, it is necessary to manufacture the insulating portion 54 by proton or ion implantation, which makes it difficult to manufacture.

  The present invention has been made to solve the conventional problems, and it is an object of the present invention to provide a semiconductor optical device that can adjust the light emission angle by one-channel current control and can be easily manufactured.

  In order to solve the above problems, a semiconductor optical device according to claim 1 of the present invention includes a semiconductor substrate, a lower clad layer, an active layer and an upper clad layer which are stacked on the semiconductor substrate and form a part of a waveguide. And an emission end face formed by cleavage from which light from the waveguide is emitted, and the waveguide is in the emission end face within a plane parallel to the substrate surface of the semiconductor substrate. The optical axis of light emitted from the waveguide intersects with the normal of the end surface at a first angle, and the optical axis of the light exits from the output end surface within the plane parallel to the substrate surface of the semiconductor substrate. In the semiconductor optical device that intersects with the normal line at a second angle, the semiconductor optical device includes a partial heating means above the upper cladding layer and in the vicinity of the emission end face, and the waveguide is heated by the partial heating means. Changing the equivalent refractive index of the waveguide And by and characterized by changing the second angle.

  With this configuration, the semiconductor optical device of the present invention can adjust the light emission angle only by adjusting the current supplied to the partial heating means, so that the light emission direction is changed by current control of only one channel. be able to. Further, since the partial heating means heats only the vicinity of the emission end face, the reliability can be improved. Furthermore, since it is not necessary to provide an insulating part, manufacture becomes easy.

  According to another aspect of the semiconductor optical device of the present invention, the partial heating means includes an insulating film, a thin film resistor formed on the insulating film, and at least two terminals for supplying power to the thin film resistor. It is characterized by having.

  With this configuration, the semiconductor optical device according to the present invention can reliably prevent the power supplied to the partial heating means from flowing into the upper cladding layer, the lower cladding layer, and the active layer. The emission angle can be changed while maintaining reliability while the power is relatively stable.

  A semiconductor optical device according to a third aspect of the present invention is characterized in that a temperature control element is provided below the semiconductor substrate.

  With this configuration, in the semiconductor optical device of the present invention, the temperature control element cools the upper clad layer, the lower clad layer, and the active layer heated by the partial heating means, so that the time from heating to cooling is shortened. As a result, it is possible to shorten the time required for the change of the emission angle. Further, the temperature rise of the entire semiconductor optical device is suppressed, and the output and the reliability are improved.

  An optical switching system according to the present invention includes at least two optical waveguides and the semiconductor optical device according to any one of claims 1 to 3, wherein the optical switching system includes the semiconductor optical device according to a change in the equivalent refractive index. The optical waveguide coupled with the emitted light is switched.

  With this configuration, in the optical switching system of the present invention, the semiconductor optical device can adjust the light emission angle by controlling the current of only one channel, so that light can be switched by a simple control circuit.

  A wavelength tunable laser according to the present invention includes a diffraction grating and the semiconductor optical device according to any one of claims 1 to 3, and a wavelength of light diffracted by the diffraction grating is incident on the diffraction grating. It is characterized by changing according to the angle of light.

  With this configuration, the wavelength tunable laser according to the present invention can adjust the light emission angle by controlling the current of only one channel, and therefore the wavelength can be changed by a simple control circuit.

  In the semiconductor optical device according to the present invention, only the power supplied to the partial heating means can adjust the emission angle by controlling the current of only one channel by changing the equivalent refractive index of the waveguide near the emission end face. It is possible to provide a semiconductor optical device that can be manufactured easily.

  Hereinafter, a semiconductor optical device, an optical switching system, and a wavelength tunable laser according to embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
A semiconductor optical device according to a first embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the semiconductor optical device 1 includes a semiconductor substrate 2, an active layer 4, an upper cladding layer 5, a lower cladding layer 6, and a contact layer 7. A part of the active layer 4, the upper cladding layer 5, and the lower cladding layer 6 forms a waveguide through which light is guided.

  Here, the active layer 4, the upper cladding layer 5, the lower cladding layer 6, and the contact layer 7 form the semiconductor layer 3. The semiconductor substrate 2 and the semiconductor layer 3 are formed by cleavage, and have a light emission end face 8 which becomes a terminal end of the waveguide.

  The semiconductor optical device 1 further includes an upper electrode 11 for injecting current into the active layer 4 and a partial heating means 14 for heating the active layer 4, the upper cladding layer 5 and the lower cladding layer 6 in the vicinity of the emission end face 8. And a lower electrode 17.

The emission end face 8 is formed so that the normal line of the emission end face 8 and the optical axis of the waveguide intersect at a _first angle θ ₁ in a plane parallel to the substrate surface of the semiconductor substrate 2. The The first angle θ ₁ is such that the optical axis of the waveguide in the vicinity of the exit end face 8 and the normal line of the exit end face 8 are not parallel, and light propagating through the waveguide is not totally reflected by the exit end face 8. Thus, a value of 0 ° <θ ₁ <18 ° may be taken. In the present embodiment, the first angle θ ₁ is 6 °.

In the present embodiment, as shown in FIG. 1, the waveguide is formed by a curved waveguide having a curved portion in the vicinity of the emission end face 8, and the optical axis and the straight line of the waveguide at the emission end face 8 of the curved waveguide. The angle between the optical axis and the optical axis is 6 °, but the waveguide may be formed only by the straight portion, and the emission end face 8 may be cleaved so that the first angle θ ₁ is 6 °. . That is, it is only necessary that the emission end face 8 is formed so as to function as an oblique end face with respect to the waveguide.

  The partial heating means 14 includes a thin film resistor 12, an insulating film 13, and terminals 15 and 16. The insulating film 13 prevents power supplied to the thin film resistor 12 from flowing into the active layer 4. The thin film resistor 12 is disposed above the upper electrode 11 with the insulating film 13 interposed therebetween, and is formed on the curved waveguide with a predetermined length in the direction parallel to the emission end face 8 and a predetermined width in the vertical direction. ing. Terminals 15 and 16 formed to be connected to both ends of the thin film resistor 12 supply power sent from a power source (not shown) to the thin film resistor 12. The material of the thin film resistor 12 is preferably a material that can be formed by vapor deposition, such as Au or Pt, and can form a stable metal film. In particular, the use of Pt is more preferable because the resistance value is high and the heat generation amount is large. As shown in FIG. 1C, the thin film resistor 12 may be formed to have a predetermined length and a predetermined width along a curved waveguide.

  The electric power supplied to the partial heating means 14 causes the thin film resistor 12 to generate heat while being prevented from flowing into the active layer 4 by the insulating film 13. Therefore, the power supplied to the partial heating means 14 does not affect the carrier density in the active layer 4, and the output end face 8 is in a state where the power of the light emitted from the semiconductor optical device 1 is relatively stable. The nearby semiconductor layer 3 can be heated.

When the partial heating means 14 generates heat, the active layer 4, the upper cladding layer 5 and the lower cladding layer 6 in the vicinity of the emission end face 8 are heated through the insulating film 13, and the equivalent refractive index of the waveguide in the vicinity of the emission end face 8 is reached. n ₁ changes.

The light propagating through the waveguide has Snell's law n ₁ sin θ ₁ = n ₂ sin θ ₂ (1) at the oblique end face.
Is emitted in the emission direction. Here, n ₂ is a refractive index in the air and is approximately 1.0. Therefore, the second angle (hereinafter referred to as the emission angle) θ ₂ formed by the optical axis of the light emitted from the semiconductor optical device 1 and the normal direction of the emission end face 8 is equivalent to the vicinity of the emission end face 8 of the waveguide. It depends on the refractive index _{n 1.} As a result, in the semiconductor optical device 1 of the present invention, the emission angle θ _{2 of the} light emitted from the semiconductor optical device 1 depends on the temperature of the waveguide near the emission end face 8.

As described above, the semiconductor optical device 1 of the present invention has a configuration in which the power supplied to the partial heating means 14 does not flow into the active layer 4. Therefore, a current control only one channel, while maintaining the power of the emitted light relatively stable, it is possible to change the equivalent refractive index n ₁ of the waveguide. Further, in order to change the emission angle θ ₂ , it is only necessary to change the equivalent refractive index n ₁ in the vicinity of the emission end face 8 of the waveguide. Need only be provided. Therefore, reliability can be improved.

  The semiconductor optical device 1 of the present invention may be provided with a temperature control element (Peltier element) (not shown) below the semiconductor substrate 2. In this case, since the semiconductor layer 3 heated by the partial heating means 14 is immediately cooled by the temperature control element, the cycle time for heating and cooling the semiconductor layer 3 can be greatly shortened. Further, the temperature rise of the entire semiconductor optical device is suppressed, and the output and the reliability are improved.

  Hereinafter, the case where the semiconductor optical device 1 of the present invention is applied to EC-LD will be described.

  FIG. 2 is a schematic view showing an optical system of EC-LD configured using the semiconductor optical device 1 of the present invention. The semiconductor optical device 1 and the fiber 20 are coupled via a lens 21, and a grating (not shown) is formed inside the fiber 20.

  By forming a resonator by the semiconductor optical device 1 and the grating in the fiber 20, the semiconductor optical device 1 emits light having a wavelength of 1550 nm.

The waveguide of the semiconductor optical device 1 has an equivalent refractive index n ₁ of 3.23 at room temperature for light having a wavelength of 1550 nm. Here, when heating the semiconductor layer 3 by the partial heating means 14, the equivalent refractive index n ₁ of the waveguide is changed.

FIG. 3 is a graph showing the relationship between the temperature of the waveguide near the exit end face 8 and the equivalent refractive index n ₁ of the waveguide. When the waveguide is heated to room temperature by 50 ° C., the equivalent refractive index n ₁ changes to 3.24.

The emission angle θ _{2 of} light emitted from the emission end face 8 of the semiconductor optical device 1 changes according to the change in the equivalent refractive index n ₁ of the waveguide. FIG. 4 is a graph showing the relationship between the temperature of the waveguide near the exit end face 8 and the exit angle θ ₂ . In the normal temperature state, the emission angle θ ₂ is about 19.73 °. On the other hand, when the temperature of the waveguide is increased to 50 ° C., the emission angle θ ₂ changes to about 19.8 °.

The coupling efficiency between the semiconductor optical device 1 having the emission angle change Δθ ₂ as described above and the fiber 20 is calculated.

  In the present embodiment, the distance z between the semiconductor optical device 1 and the lens 21 is 400 μm. The image magnification m of this optical system is 4.

For example, it is assumed that the light emitted from the semiconductor optical device 1 is emitted with an angle Δθ ₂ shifted from the optical axis connecting the semiconductor optical device 1 and the fiber 20. Since Δθ ₂ takes a sufficiently small value, the semiconductor optical device 1 has x ₁ = z · tan Δθ ₂ (2)
It can be considered that the position has shifted. At this time, the light incident on the fiber 20 is x ₂ = (m + 1) x ₁ (3) from the center of the fiber 20.
Incident light is incident on a shifted position.

In the optical system as described above, the coupling efficiency between the semiconductor optical device 1 and the fiber 20 is expressed by the following equation.

Here, w ₁ is the spot radius of the exit end face 8 of the emitted light, w ₂ is the spot radius of the fiber, and w ₁ = w ₂ = 5 μm. Further, it is regarded as an ideal optical system, and the coupling constant κ = 1 is set.

In this case, for the positional deviation x ₁ of the semiconductor optical device 1, showing the normalized coupling efficiency in FIG.

For example, it is assumed that when an EC-LD optical system is constructed, the light emitted from the semiconductor optical device 1 is shifted by Δθ ₂ = 0.07 ° from the ideal emission angle. At this time, since Δθ ₂ is sufficiently small, it can be considered that the semiconductor optical device 1 is displaced by 0.43 μm. The normalized coupling efficiency in this state is −0.9 dB compared to the coupling efficiency in the ideal state from FIG.

  FIG. 6 is a graph showing the relationship between the temperature change of the waveguide near the emission end face 8 and the normalized coupling efficiency.

  From FIG. 6, it can be seen that the normalized coupling efficiency of −0.9 dB corresponds to the case where the temperature of the waveguide near the emission end face 8 changes by 50 ° C.

  Here, in the present embodiment, for example, an object is to correct a manufacturing error of an angle of the emission end face 8 with respect to the waveguide. That is, the emission direction of the emitted light is assumed to be parallel to the substrate surface of the semiconductor substrate 2 and in the same plane passing through the center of the core of the fiber 20.

  Therefore, when the normalized coupling efficiency with respect to the temperature change of the waveguide is reversible and the power of the light incident on the fiber 20 is monitored, the value is 0.9 dB lower than the expected value. By making the waveguide near the emission end face 8 50 ° C. higher than room temperature, the angle of the light emitted from the semiconductor optical device 1 can be changed by 0.07 °, and the coupling efficiency can be corrected by 0.9 dB.

  According to the semiconductor optical device 1 of this embodiment as described above, the partial heating means 14 can adjust the light emission angle by changing the equivalent refractive index of the waveguide in the vicinity of the emission end face 8, so that the oblique end face Even when the output angle causes an error in the output angle and the coupling efficiency of the light emitted from the semiconductor optical device 1 to the fiber decreases, the partial heating means 14 adjusts the output angle of the light to increase the coupling efficiency to the fiber. Can be optimized.

  Further, according to the semiconductor optical device 1 of the present embodiment, since the optical axis is not likely to be angularly shifted in the direction perpendicular to the substrate surface, the optical axis is not shifted when the EC-LD is constructed. It occurs in the same horizontal plane that is parallel to the substrate surface of the substrate 2. Therefore, the emission angle of the light emitted from the semiconductor optical device 1 is changed using the partial heating means 14 even when the coupling efficiency is reduced due to the positional deviation of the semiconductor optical device 1 when the EC-LD is constructed. By doing so, the coupling efficiency can be corrected.

  In addition, when the semiconductor optical device 1 is used for a long time, the light output with respect to the current decreases due to an increase in the threshold value for oscillation, and carriers are accumulated in the active layer 4. It will be. However, even in such a case, according to the semiconductor optical device 1 according to the present embodiment, the partial heating means 14 heats the active layer 4, the upper cladding layer 5 and the lower cladding layer 6 in the vicinity of the emission end face 8. The equivalent refractive index of the waveguide in the vicinity of the emission end face 8 can be corrected. Therefore, even when the semiconductor optical device 1 is used for a long time, it is possible to always keep the light emission angle to the semiconductor optical device 1 constant. Note that the waveguide up to the emission end face 8 must be heated. Therefore, when the thickness of the upper clad layer 5 is 1 to 3 μm, the distance d between the emission end face 8 and the thin film resistor 12 is preferably 50 μm or less.

(Second Embodiment)
An optical switching system according to a second embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 7, the optical switching system according to the present embodiment includes a semiconductor optical device 31 and first and second fibers 32 and 33. Here, the first and second fibers 32 and 33 constitute an optical waveguide.

  A semiconductor substrate, semiconductor layer, upper electrode, lower electrode, partial heating means and insulating film (not shown) constituting the semiconductor optical device 31 are the semiconductor substrate 2 constituting the semiconductor optical device 1 according to the first embodiment of the present invention. The semiconductor layer 3, the upper electrode 11, the lower electrode 17, the partial heating means 14, and the insulating film 13 have the same configuration, and a description thereof is omitted.

In the present embodiment, the semiconductor optical device 31 has an emission end face so that the first angle θ ₁ is 17.9 °.

  As the first and second fibers 32 and 33, for example, tip-spherical fibers are used. The distance L between the emission end face of the semiconductor optical device 31 and the first and second fibers 32 and 33 is 2 mm.

  FIG. 8 is a graph showing the relationship between the temperature change of the waveguide near the emission end face and the positional deviation of the light at a distance L from the semiconductor optical element 31 at this time.

  For example, when the temperature change of the waveguide near the emission end face is 50 ° C., the position of the light is shifted by about 60 μm at the position of the distance L from the semiconductor optical device 31.

  Therefore, the optical system is installed so that the distance between the centers of the cores of the first fiber 32 and the second fiber 33 is 60 μm, and the waveguide near the emission end face is heated by 50 ° C. by the partial heating means. A switching system can be configured.

  Here, when the temperature control element (Peltier element) is provided below the semiconductor substrate of the semiconductor optical element 31, the semiconductor layer heated by the partial heating means is immediately cooled by the temperature control element (Peltier element). The cycle time for heating and cooling the semiconductor layer can be greatly reduced. In this case, the optical switching system according to the present embodiment can have a switching speed of several ms.

  Further, instead of the first and second fibers 32 and 33, a quartz-based planar lightwave circuit (PLC) may be used. In this case, a pair of optical waveguides are formed on the quartz substrate so as to be 60 μm apart from each other at the light incident end face.

  According to such an optical switching system of the present embodiment, switching can be performed while the output of light emitted from the semiconductor optical device 31 is stabilized. Further, since a switching speed of several ms can be realized, it is useful as an optical switching system constituting an optical burst switching network.

(Third embodiment)
A wavelength tunable laser according to a third embodiment of the present invention will be described with reference to FIG.

  As shown in FIG. 9, the wavelength tunable laser 40 according to the present embodiment includes a semiconductor optical element 41, a diffraction grating 42, and a mirror 43.

  A semiconductor substrate (not shown) constituting the semiconductor optical device 41, a semiconductor layer, an upper electrode, a partial heating means, an insulating film, and a lower electrode are the semiconductor substrate 2 constituting the semiconductor optical device 1 according to the first embodiment of the present invention. The semiconductor layer 3, the upper electrode 11, the partial heating means 14, the insulating film 13, and the lower electrode 17 have the same configuration, and a description thereof is omitted.

  The diffraction grating 42 has a diffraction grating period p. The light emitted from the semiconductor optical element 41 is diffracted by the diffraction grating 42, reflected by the mirror 43, returns to the semiconductor optical element 41, resonates between the semiconductor optical element 41 and the mirror 43, and The light is emitted from the end face 41 a opposite to the diffraction grating to the outside of the wavelength tunable laser 40. In addition, the mirror 43 may be configured by a transmission mirror, and may be transmitted to the outside of the wavelength tunable laser 40 through the mirror 43.

At this time, the wavelength λ of the light emitted from the wavelength tunable laser 40 is
λ = p (sin (α) + sin (β)) (5)
It is expressed as Here, α is an angle with respect to the diffraction grating normal of the light emitted from the semiconductor optical element 41, and β is an angle with respect to the diffraction grating normal of the light diffracted by the diffraction grating 42.

The angle α changes according to the emission angle θ _{2 of the} light emitted from the semiconductor optical device 41. Therefore, the wavelength of the light emitted from the wavelength tunable laser 40 can be changed by changing the equivalent refractive index n ₁ in the vicinity of the emission end face of the waveguide by the partial heating means.

  According to the wavelength tunable laser 40 of this embodiment as described above, the light emission angle can be adjusted by controlling the current of one channel of the semiconductor optical device 41, so that the light incident on the diffraction grating 42 can be controlled by a simple control circuit. The incident angle can be changed. Therefore, the tunable laser 40 can be configured with a simple control circuit.

  In addition, as compared with a wavelength tunable laser that changes the wavelength by mechanically moving a semiconductor optical element or a diffraction grating, a movable part is not required, so that a small and high-performance wavelength tunable laser can be configured.

  As described above, the semiconductor optical device according to the present invention changes the equivalent refractive index of the waveguide by heating and can control the emission angle of the emitted light. This has the effect that correction for misalignment can be easily performed, and is effective in optical communication and the like.

(A) Top view schematically showing the semiconductor optical device according to the first embodiment of the present invention (b) AA sectional view in FIG. Schematic diagram showing an optical system of EC-LD configured using a semiconductor optical device Graph showing the temperature change of the waveguide exit end face neighborhood, the relationship between the effective refractive index n ₁ of the waveguide A graph showing the relationship between the temperature change of the waveguide near the exit end face and the exit angle θ ₂ Graph showing the normalized coupling efficiency with respect to the position deviation x ₁ in the semiconductor optical device Graph showing the relationship between the temperature change of the waveguide near the exit end face and the normalized coupling efficiency Schematic diagram of an optical switching system according to a second embodiment of the present invention A graph showing the relationship between the temperature change of the waveguide near the exit end face and the amount of positional deviation of the optical axis at a distance L from the exit end face Schematic diagram of a wavelength tunable laser according to a third embodiment of the present invention Schematic diagram of conventional semiconductor optical device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor optical device 2 Semiconductor substrate 3 Semiconductor layer 4 Active layer 5 Upper clad layer 6 Lower clad layer 7 Contact layer 8 Outgoing end surface 11 Upper electrode 12 Thin film resistor 13 Insulating film 14 Partial heating means 15, 16 Terminal 17 Lower electrode 20 Fiber 21 Lens 31 Semiconductor optical device 32 First fiber 33 Second fiber 40 Tunable laser 41 Semiconductor optical device 42 Diffraction grating 43 Mirror 50 Semiconductor laser 51 Semiconductor substrate 52 Active layer 53 Clad layer 53a First channel 53b Second channel 54 Insulating portion 55 First electrode 56 Second electrode

Claims (5)

A semiconductor substrate (2);
A lower clad layer (6), an active layer (4) and an upper clad layer (5) stacked on the semiconductor substrate and forming a part of the waveguide;
An emission end face (8) formed by cleavage, from which light from the waveguide is emitted;
The waveguide intersects with the normal of the emission end face at a first angle (θ ₁ ) at the emission end face in a plane parallel to the substrate surface of the semiconductor substrate,
The optical axis of the light emitted from the waveguide forms a _second angle (θ ₂ ) with the normal of the emission end face at the emission end face in a plane parallel to the substrate surface of the semiconductor substrate. In the intersecting semiconductor optical device,
A partial heating means (14) is provided above the upper cladding layer and in the vicinity of the emission end face,
A semiconductor optical device characterized in that the second angle is changed by heating the waveguide by the partial heating means to change the equivalent refractive index of the waveguide.   The partial heating means includes an insulating film (13), a thin film resistor (12) formed on the insulating film, and at least two terminals (15, 16) for supplying power to the thin film resistor. The semiconductor optical device according to claim 1.   The semiconductor optical device according to claim 1, wherein a temperature control element is provided below the semiconductor substrate. At least two optical waveguides (32, 33);
A semiconductor optical device according to any one of claims 1 to 3,
An optical switching system, wherein an optical waveguide coupled with light emitted from the semiconductor optical device is switched in accordance with a change in the equivalent refractive index. A diffraction grating (42);
A semiconductor optical device according to any one of claims 1 to 3,
A wavelength tunable laser, wherein a wavelength of light diffracted by the diffraction grating changes according to an angle of light incident on the diffraction grating.

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