JPH10107359A - Semiconductor optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the temperature change in, for example, the differential efficiency of the output of an optical fiber by enabling the reflection factor of a light-transmitting film on the surface of a light-receiving element to have a large wavelength dependence and maximizing the connection efficiency between a semiconductor element and an optical fiber at a temperature higher than the room temperature. SOLUTION: Output from the front of a laser diode(LD) 15 is connected to an optical fiber via a lens 2, and rear output is inputted to a light-receiving element (PD) for monitoring. Coating films 12-14 are forned on a surface 11 of the PD 16 as a light- transmitting film, thus achieving a wavelength dependence, where a reflection factor decreases as the wavelength increases. The oscillation wavelength of the LD 15 increases as the temperature increases, and the reflection factor of the light transmitting film decrease as the temperature increases, thus improving the transmission rate of the light-transmitting film as the temperature increases. A position is adjusted so that the connection efficiency between the LD 15 and an optical fiber 3 can be maximized at a temperature higher than the room temperature, and the differential efficiency of fiber output 6 and the temperature change in the current value for monitoring the PD 16 are mode decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an optical communication system,
The present invention relates to an optical measuring device or a semiconductor optical device used for optical information processing and a method of manufacturing the same.

[0002]

2. Description of the Related Art With the development of an optical communication system which is a fundamental technology of the advanced information society, a semiconductor optical device having stable output characteristics and transmission characteristics at a wider temperature is required. As a light source of a communication system, a light emitting diode (LED; Light) is used in a communication application for a relatively short distance.
An emitting diode (LD) may be used, but usually a laser diode (LD; Laser).
Diode) is used.

When an LD is used as a light source for communication, a bias current I _b near an oscillation threshold current I _th is usually used.
Flushed, it is generating optical pulses to be transmitted signal by adding a pulse current I _p to I _b (FIG. 15). At this time, it is necessary to keep the peak value of the optical pulse input to the optical fiber as constant as possible due to the problem of the dynamic range of the receiving device. The bias current I _b is the threshold current I _th
If it is too large, the 01 level difference (extinction ratio) of the digital optical signal will be reduced, causing the reception sensitivity to deteriorate.
_If it is smaller than _th , the transmission code error rate deteriorates due to an increase in relaxation oscillation amplitude and oscillation delay time in the optical output signal waveform of the LD. Therefore, it is necessary to control I _p and I _b with high accuracy.

On the other hand, the output characteristics of the LD element itself greatly change with the ambient temperature. As shown in FIG. 16, the current-optical output characteristics show that the threshold current I _th increases and the differential efficiency η _d decreases as the temperature increases. I do. For this reason, a temperature control device for keeping the LD at a constant temperature has conventionally been used in semiconductor optical devices. However, this temperature control device is not only expensive but also reduces the size and power consumption of the semiconductor optical device. There was a problem of making it larger.

In recent years, by adopting a multiple quantum well structure or a strained multiple quantum well structure for an LD active layer,
Temperature characteristics are greatly improved, for example, −40 ° C. to +85
The LD can be used in a wide temperature range of ° C. without using a temperature control device. In this case, a constant light intensity P _f which is output from the semiconductor optical device to an optical fiber,
And, as the means for controlling the bias current I _b to the threshold current I _th vicinity of the LD, the monitoring light-receiving element installed in the LD rear; output current I _m from (Monitor Photo Diode monitor PD) is used However, when the temperature change of the differential efficiency η _d of the semiconductor optical element is large, the load on the drive circuit system becomes large, so that the size, power consumption, and price of the semiconductor optical device that can operate in a wide temperature range are reduced. For this purpose, it is desired that the change in temperature of the differential efficiency η _f of the fiber output light intensity be small.

On the other hand, in Japanese Patent Application Laid-Open No. Sho 62-211979, relative displacement due to temperature change is caused in an optical system by using materials having different expansion coefficients for components supporting an optical fiber and an LD. Differential efficiency η
_A support mechanism that maximizes the optical coupling efficiency η _c between the optical fiber and the LD under the condition where _d is the lowest, or a light compensating for the temperature change of the differential efficiency η _d between the optical fiber and the LD The temperature change of the differential efficiency of the optical fiber output is reduced by inserting a filter having transmission characteristics. However, in this case, since the coupling efficiency between the LD front output light and the monitor PD hardly changes while the coupling efficiency between the front output light of the LD and the optical fiber greatly changes depending on the temperature, the optical fiber output light intensity P proportionality relationship between the monitor current value I _m from _f and monitor PD are not satisfied. Therefore, I _m for a given P _f varies with temperature, it becomes impossible to accurately control the I _b and I _p, will give a significant adverse effect on optical transmission properties including transmission code error rate.

Hereinafter, these points will be described in more detail. FIG. 17 schematically shows a conventional LD module structure.
_{The front} is coupled to an optical fiber 3 via a lens 2.
As the fiber coupling efficiency at this time fiber output P _f is the module of eta _c, the _{P f = η c · P front} .

On the other hand, a part of the light output P _rear from the rear of the LD 1 is incident on the monitor PD 4.
Monitor current value I _m output from D4 is, I _m = P _rear
· Η _r · (1-R) · η _PD Here, eta _r is the reflectivity coupling efficiency in backward output light is incident on the light receiving surface of the monitor PD4, R is comprising a light transmitting film of the monitor PD light receiving surface surface, eta _PD light monitor PD4 - current converter Efficiency.
Assuming that the front-to-back output ratio of LD1 is a, P _front = a ·
Since the P _rear, I _m is expressed by the following equation.

[0009]

[0010]

_{Accordingly, η r, R, η PD} , a, η if the temperature dependency exists in the coefficient of _c I _m and P _f are made to show a constant proportional relationship regardless of the temperature, In practice, the temperature dependence of _Im and P
There is a temperature change in the proportionality of _f .

Generally, since the light receiving diameter of the monitor PD is sufficiently large, the influence of the thermal expansion of the support member on η _r is small.
η _r is a substantially constant value regardless of the temperature. η _{PD is} also usually L
It shows a substantially constant value in the operable temperature range of D. Conventionally, the reflectance R of the PD surface has hardly been considered in the design of the monitor PD, or the reflectivity R of the PD due to a temperature change as disclosed in JP-A-63-128773.
It has been designed so that the change in the reflectance R becomes small even when the oscillation wavelength changes.

On the other hand, the temperature change of the coupling efficiency η _c due to the change of the optical system alignment due to the thermal expansion of the support material is much larger than the temperature change of the coupling efficiency η _r with the monitor PD, for example, 1994. Proceedings of the 4th IEICE Spring Conference 4th page 287 pages or 1995 IEICE General Conference Proceedings Electronics 1
As described on page 185 of this publication, even when good bonding characteristics with a relatively small temperature change are obtained, the temperature can be reduced from 25 ° C to 85 ° C.
About 0.5 dB, ie about 12%
There are even temperature changes.

Further, as disclosed in Japanese Patent Application Laid-Open No. Sho 62-211979, the temperature change of the fiber coupling efficiency η _c is intentionally increased, and η _c is maximized under the condition that the differential efficiency η _{d of the} LD is the lowest. For example, as shown in FIG. 18, when η _c changes from −5 dB to −3 dB due to a temperature rise from 25 ° C. to 85 ° C., the differential efficiency of the LD front output light P _{front by} a difference of 2 dB While reduction is compensated simultaneously monitor current value I _m for a given fiber output P _f by the change in the eta _c will 2dB change, as a result, control of the LD driving conditions by I _m becomes extremely difficult As a result, the optical transmission quality is greatly deteriorated.

[0015]

The first problem in the prior art is as follows.
The problem is that it is difficult to reduce the size, power consumption, and cost of a semiconductor optical device that can operate in a wide temperature range. The reason is that a device that keeps the temperature of the optical semiconductor element constant or a complex input signal control circuit that keeps the optical output from the optical semiconductor device constant to compensate for the temperature change of the output characteristics of the optical semiconductor element. It is necessary.

The second problem is that the temperature change of the coupling efficiency between the LD and the optical fiber is intentionally increased, and the temperature dependence of the differential efficiency η _d of the LD light output is compensated for. If it becomes difficult to control the LD driving condition by monitoring current I _m, it is that deteriorates the transmission quality. The reason is that only the temperature change in the coupling efficiency eta _c to fiber LD output light in the LD module, because temperature changes occur in a proportional relationship between the fiber output light intensity P _f and the monitor current I _m .

Further, as described above, the fiber coupling efficiency η _c compensating for the temperature change of the differential efficiency η _d of the LD light output.
As a means to have a, when using a material having a different expansion coefficient for each part supporting the optical fiber and the LD, or when inserting a filter having a light transmission characteristic to compensate for the differential efficiency between the optical fiber and the LD, Third, the reliability of the module is significantly reduced due to an increase in the number of parts and assembly due to an increase in the number of parts, and a strain stress generated at a joint when materials having different coefficients of expansion are used. This is a problem.

An object of the present invention is to provide a semiconductor optical device which has a small difference in temperature of a monitor current value with respect to a differential efficiency of a fiber output and a constant fiber output value and which is excellent in reliability and is inexpensive.

[0019]

SUMMARY OF THE INVENTION The present invention relates to a semiconductor optical device (LD) used for assembling an LD module used in a semiconductor optical device.
By adjusting the position of the coupling system such that the coupling efficiency between D) and the optical fiber is maximized at a temperature higher than room temperature, the temperature change of the differential efficiency of the optical output from the LD can be compensated, and the conventional LD can be used. In the module design, the wavelength dependence of the reflectance of the monitor PD surface, which is hardly considered or designed to be small, is controlled by the material, thickness, and total number of the light transmitting films formed on the PD surface. In addition, a characteristic of reducing a temperature change of a monitor current value with respect to a constant fiber output value caused by a temperature change of a fiber coupling efficiency or the like is provided.

It should be noted that a special mechanism for providing a coupling efficiency for compensating for the temperature characteristic of the differential efficiency of the LD, that is, a support material having a different thermal expansion coefficient and a filter having a light transmission characteristic for compensating for the differential efficiency are not used. An LD module having a large temperature change in fiber coupling efficiency depending on the design of the module itself (eg, the material of the module, the type or focal length of the lens, the distance between the optical fiber, the lens and the LD, etc.), the ambient temperature at the time of position adjustment and the positioning method Therefore, the cost of members and assembly due to an increase in the number of parts and the reliability of the module are not reduced.

By using the present invention, the temperature change of the differential efficiency η _f of the fiber output is extremely small without using expensive materials and parts or complicated mechanical mechanisms, and
Monitor current value I for a given fiber output light intensity P _f
It is possible to manufacture an LD module having a small temperature change of _m . As a result, it is possible to provide an inexpensive semiconductor optical device for optical fiber communication that can operate in a wide temperature range and that can control the driving of the LD with high accuracy.

[0022]

Next, the present invention will be described in detail with reference to the drawings. FIGS. 1A and 1B show the LD module structure according to the first embodiment of the present invention and the structure of a light transmitting film on the surface of a light receiving element used for the LD module, respectively. The LD module uses a Fabry-Perot resonator type LD (FP-LD) as a light source, and its front-to-back output ratio a is determined by the reflectance of the LD end face, and has a substantially constant value regardless of the temperature. Have. Therefore, in the present LD module configuration, the main factor that causes a temperature change in the monitor current value Im with respect to a constant fiber output Pf is a temperature change in the fiber coupling efficiency η _c due to a temperature change in the optical system alignment.

F used as a light source in the present embodiment
As shown by the broken line in FIG.
2.0 dB (approximately 37
%)descend. On the other hand, the LD module according to the present embodiment is designed so that the temperature change of the coupling efficiency η _c is large, and the ambient temperature at the time of assembly is 85 ° C., and the position is adjusted so that the coupling efficiency becomes maximum at the ambient temperature. Is performed, the temperature dependence is given such that the coupling efficiency η _c at 85 ° C. becomes 1.3 dB (about 35%) larger than 25 ° C. as shown in FIG. As a result, the temperature change of the differential efficiency η _f of the fiber output is 2-1.3 = 0.7d.
B (solid line in FIG. 2).

On the other hand, the transmission film on the surface of the light receiving element according to the present embodiment has a coating film 12 of amorphous silicon (refractive index 3.2) and a film thickness of 109.4 nm (optical path) with a wavelength λ = 1400 nm as a design center. (Length λ / 4) Coating film 13: silicon nitride film (refractive index: 1.
8), film thickness = 194.4 nm (optical path length λ / 4) Coating film 14: silicon nitride film (refractive index 1.
8), the film thickness = 388.9 nm (optical path length λ / 2) was changed to the monitor PD light receiving surface 11-12-13-12-14-1.
By forming in the order of 2, the reflectance R has a wavelength dependency as shown in FIG.

As shown in FIG. 5, the oscillation wavelength of the FP-LD used as a light source in this embodiment is output from the rear of the LD in order to increase the wavelength by about 0.4 nm for a temperature rise of 1 ° C. The reflectance R of the light transmitting film on the surface of the monitor PD has a temperature dependency as shown in FIG. Therefore, the transmittance (1-R) of the light transmitting film is 85 ° C.
It is 65.7% at an oscillation wavelength of 1330 nm, whereas it is 53.7% at 25 ° C. (an oscillation wavelength of 1310 nm). This proportion contributes to the monitor current I _m of the light that reaches the PD surface including the light transmitting film, from 25 ° C. 85
A 0.88 dB (18.4%) improvement would be achieved by increasing the temperature to ° C.

As can be seen from the equation (1), such a temperature change in the transmittance (1-R) of the light transmitting film compensates for a temperature change in the tracking characteristic caused by a temperature change in the fiber coupling efficiency η _c. Has an action. Therefore, in a module having the same structure as that of the present embodiment, when there is no wavelength dependency in the reflectance R of the light transmitting film, P depends on the temperature change of η _c.
f = 1 mW when I _m whereas also changes 1.3dB as shown in broken lines in FIG. 7, by which the wavelength dependency is present in R, the temperature change in 85 ° C. as shown in solid line in FIG. 7 1.3-0.88 = 0.42 dB (10%) at 0 ° C.
± 0.5 dB (12%) even in the temperature range of ~ 85 ° C
Within

FIGS. 8A and 8B show the LD module structure according to the second embodiment of the present invention and the structure of the transmission film on the surface of the light receiving element used for the LD module, respectively. In the LD module according to the present embodiment, a distributed feedback LD (DFB-LD) is used as a light source. The temperature dependence of the oscillation wavelength is 0.09 m / ° C. as shown in FIG. Is 1/4 or less. Generally, the differential efficiency η _d of the optical output of the DFB-LD
Is larger than that of the FP-LD, and in the case of the present embodiment, is 3.0 dB due to the temperature rise from 25 ° C. to 85 ° C.
(See broken line in FIG. 10). For this reason, the LD module according to the present embodiment is designed to have a larger temperature change of the fiber coupling efficiency η _c than that used in the first embodiment of the present invention, and the temperature change of the fiber output differential efficiency η _f is reduced. I am trying to do it. Specifically, as shown in FIG. 11, the coupling efficiency at 85 ° C. is 2.0 dB higher than that at 25 ° C.
The LD module was designed and assembled to be higher, and the decrease in differential efficiency of the fiber output was suppressed to 3.0-2.0 = 1.0 dB at 85 ° C. (FIG. 10)
solid line).

The assembly of the LD module in this embodiment is performed at room temperature. After detecting the position where the coupling efficiency becomes maximum at room temperature, the position of the coupling system is intentionally shifted and fixed at 85 ° C. In which the coupling efficiency is maximized. At this time, the shift amount and the shift direction can be analytically obtained from the shape and the coefficient of thermal expansion of the supporting material, but based on the temperature dependence of the coupling efficiency when the shift amount and the shift direction are changed somewhat. It is also possible to experimentally determine the amount that maximizes the coupling at the desired temperature.

On the other hand, in order to prevent the temperature change of the monitor current value with respect to the constant fiber output light intensity due to the temperature change of the fiber coupling efficiency, the light transmitting film on the light receiving element surface in the second embodiment of the present invention has a wavelength of With the design center at 1330 nm, coating film 12: amorphous silicon (refractive index 3.2), film thickness = 103.9 nm (optical path length = λ / 4) coating film 17: silicon oxide film (refractive index 1.
5), film thickness = 221.7 nm (optical path length = λ / 4) Coating film 18: silicon oxide film (refractive index 1.
5), film thickness = 443.3 nm (optical path length = λ / 2) monitor PD light receiving surface 11-12-17-12-17-1
By forming in the order of 2-18-12-17-12, the reflectance R has a wavelength dependency as shown in FIG. Therefore, the DFB used as the light source in this embodiment having the temperature dependency of the oscillation wavelength as shown in FIG.
-The temperature dependence of the transmittance (1-R) of the light transmitting film on the monitor PD surface to the output light from the LD is based on 25 ° C (0d
B) As shown in FIG. 13, 1.8 dB higher at 85 ° C.
At 0 ° C., it is reduced by −0.67 dB. As a result, a constant P
temperature change of I _m for _f, as shown in solid line in FIG. 14, 0~ + 85 0.5dB (% ) in the temperature range of ℃ is reduced below performs well controlled with high precision I _b and I _p It becomes possible.

As described above, both the fiber coupling efficiency η _c and the temperature change of the light transmittance (1-R) of the monitor PD surface are designed to be large, and the respective temperature dependencies take appropriate values. By designing and assembling,
It is possible differential efficiency eta _f the fiber output, and the temperature variation of the monitor current value I _m for a given fiber output light intensity P _f constitutes the small LD module.

In the present invention, many other modifications can be realized without being limited to the above embodiments.
For example, in the above embodiment, application to a semiconductor laser (LD) having a wavelength band of 1.3 μm has been described. However, the present invention is not limited to this, and other wavelengths, for example, 1.55
The present invention is also applicable to the μm band and the 1.48 μm band, or the 0.98 μm band and the 0.63 μm band. Also, LD
However, the present invention is not limited to FP-LD and DFB-LD, but includes λ / 4 shift distribution reflection type LD, gain-coupled diffraction grating type DFB-LD, complex-coupled diffraction grating type DFB-LD, and multiple phase shift type DFB-LD. The present invention can be applied to all types of semiconductor optical devices such as an LD and an LD having a strong wavelength dependency on the reflectance of the cavity end face. Further, the material, film thickness, number of layers, and the like of the light transmitting film on the surface of the monitor PD are not limited to those in the above-described embodiment, and various LD structures, oscillation wavelengths, LD module structures, or operating temperatures of the semiconductor optical device are used. Various materials, film thicknesses, and number of layers are applied in order to have the effect of reducing the temperature change of the differential efficiency of the fiber output and the temperature change of the monitor current value for a constant fiber output light intensity corresponding to the range. be able to.

In the above-described embodiment, 0 to 85 ° C. is used as an example of the range showing the temperature change of the fiber output differential efficiency of the LD module and the temperature change of the monitor current with respect to a constant fiber output. Is not limited to this temperature range.
It goes without saying that the present invention can be used for a semiconductor optical device used in a wide temperature range of 5 ° C. or more. Further, the temperature at which the fiber coupling efficiency becomes maximum does not need to be the maximum temperature in the operating temperature range, and like the wavelength at which the reflectance of the light transmitting film on the surface of the monitor PD becomes minimum.
Appropriate values can be used so that various characteristics of the LD module fall within a desired range in the operating temperature range.

[0033]

According to the present invention, it is possible to realize an LD module in which the differential efficiency of the fiber output and the temperature change of the monitor current value with respect to a constant fiber output light intensity are small without using expensive materials and parts or complicated mechanical mechanisms. . This makes it possible to provide a large number of semiconductor optical devices for optical fiber communication that can operate in a wide temperature range at low cost.

The reason is that the coupling efficiency between the LD and the optical fiber is designed to have a large temperature dependency,
By adjusting the position of the coupling system and assembling it so that the fiber coupling efficiency becomes maximum in a high-temperature portion where the differential efficiency of the D output is reduced, the temperature change of the differential efficiency of the LD light output is compensated. In the module design, the wavelength dependence of the reflectance of the monitor PD surface, which is hardly considered or designed to be small, is controlled by the material, thickness, and total number of the light transmitting films formed on the PD surface. This is because the effect of reducing the temperature change of the monitor current value with respect to a constant fiber output value caused by the temperature change of the fiber coupling efficiency or the like is provided.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams schematically showing the structure of an LD module according to a first embodiment of the present invention, and FIGS.
It is a figure showing the structure of the light transmission film on the light sensing element surface used for the D module.

FIG. 2 is a diagram showing the temperature dependence of the optical output differential efficiency η _d and the fiber output differential efficiency η _f of the FP-LD used in the LD module according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the temperature dependence of the fiber coupling efficiency η _c of the LD module according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the wavelength dependence of the reflectance R of the light transmitting film on the light receiving element surface according to the first embodiment of the present invention.

FIG. 5 is a diagram showing the temperature dependence of the oscillation wavelength of the FP-LD as the light source according to the first embodiment of the present invention.

FIG. 6 is a diagram showing the temperature dependence of the reflectance R of the light transmitting film on the light receiving element surface according to the first embodiment of the present invention.

[7] monitor current value I _m for a given fiber output P _f of the LD module according to the first embodiment of the present invention
FIG. 5 is a diagram showing the temperature dependence of the light transmission film on the surface of the monitor PD in comparison with the case where there is no wavelength dependence.

FIGS. 8A and 8B are diagrams schematically showing an LD module structure according to a second embodiment of the present invention, and FIGS.
It is a figure showing the structure of the light transmission film on the surface of the light receiving element used for the module.

FIG. 9 is a diagram illustrating the temperature dependence of the oscillation wavelength of a DFB-LD as a light source according to the second embodiment of the present invention.

FIG. 10 is a diagram showing the temperature dependence of the optical output differential efficiency η _d and the fiber output differential efficiency η _f of the DFB-LD used in the LD module according to the second embodiment of the present invention.

FIG. 11 is a diagram showing the temperature dependence of the fiber coupling efficiency η _c of the LD module according to the second embodiment of the present invention.

FIG. 12 is a diagram showing the wavelength dependence of the reflectance R of the light transmitting film on the light receiving element surface according to the second embodiment of the present invention.

FIG. 13 is a diagram showing the temperature dependence of the transmittance (1-R) of the light transmitting film on the light receiving element surface according to the second embodiment of the present invention.

[14] a constant fiber output P monitor current for _f value I LD module according to the second embodiment of the present invention
FIG. 7 is a diagram showing the temperature dependence of _m in comparison with the case where the light transmission film on the surface of the monitor PD has no wavelength dependence.

FIG. 15 is a diagram for explaining a driving method of the LD for optical communication.

FIG. 16 is a diagram showing temperature dependence of current-light output characteristics of an LD.

FIG. 17 is a diagram schematically showing a conventional LD module structure.

FIG. 18 is a diagram showing a temperature change of a fiber coupling efficiency η _c in a conventional LD module.

[Explanation of symbols]

1 a semiconductor laser (LD) 2 optical lens 3 optical fiber 4 for monitoring light receiving element (monitor PD) 5 front output P _front 6 fiber output P _f 7 rear output P _rear 8 driving current 9 monitors current I _m 10 ground electrode 11 monitor PD Light receiving surface 12 amorphous silicon (refractive index 3.2, optical path length = λ / 4) 13 silicon oxide film (refractive index 1.5, optical path length = λ /
4) 14 silicon oxide film (refractive index 1.5, optical path length = λ /
2) 15 Fabry-Perot resonator type LD (FP-LD) 16, 20 Monitor PD 17 Silicon nitride film (refractive index 1.8, optical path length = λ /
4) 18 silicon nitride film (refractive index 1.8, optical path length = λ /
2) 19 Distributed feedback LD (DFB-LD)

Claims (5)

[Claims] In a semiconductor optical device having a semiconductor optical element and a light output monitoring light receiving element, the reflectance of a light transmitting film on the surface of the light receiving element has a large wavelength dependency, and the semiconductor light-emitting element has a high temperature above room temperature. A semiconductor optical device wherein the coupling efficiency between an optical element and an optical fiber is maximized. 2. The semiconductor optical device according to claim 1, wherein
A semiconductor optical device, wherein the reflectance of the light transmitting film on the surface of the light receiving element changes by 1% or more with respect to a wavelength change of 20 nm from the wavelength at which the reflectance becomes minimum. 3. The semiconductor optical device according to claim 1, wherein the wavelength dependency of the reflectance of the light transmitting film on the surface of the light receiving element reduces a temperature change of a monitor current value with respect to a constant fiber output light intensity. A semiconductor optical device having an effect. 4. The semiconductor optical device according to claim 1, wherein the position of the coupling system is adjusted by setting the ambient temperature to be higher than room temperature, so that the semiconductor optical device and the optical fiber are connected at a temperature higher than room temperature. A semiconductor optical device assembled so as to maximize coupling efficiency. 5. The semiconductor optical device according to claim 1, wherein after detecting a position where the coupling efficiency becomes maximum by adjusting the position of the coupling system at room temperature, the coupling efficiency at a high temperature is intentionally increased. A semiconductor optical device which is assembled so that the coupling efficiency between a semiconductor optical element and an optical fiber is maximized at a temperature higher than room temperature by shifting and fixing a position of a coupling system.