JP2003347651A - Optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical module in which a monitoring photodetector is not brought into unstable operating conditions or not broken down, an optical module in which the mounting cost is reduced by preventing the output from being saturated by the heat accumulated in a semiconductor laser to fuse the exist end face thus breaking down the element, and an optical module in which the coupling efficiency is prevented from lowering due to displacement of the optical axis of an optical fiber caused by thermal expansion of the semiconductor laser. <P>SOLUTION: The optical module comprises a light transmitter 19, the semiconductor laser 12 being coupled optically with the light transmitter 19, and a photodetector 15 for monitoring the exit light from the semiconductor laser 12 arranged on a substrate 10 of single crystal silicon. The photodetector 15 having a light absorption layer of metal silicide is integrated on the substrate 10 and the semiconductor laser 12 is arranged on an underlying layer consisting of an insulator layer 16 and a metal layer 17 formed sequentially on the substrate 10. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical module equipped with a semiconductor laser used in the field of optical communication and communication, and more particularly to an optical module for an optical fiber amplifier (optical amplification utilizing stimulated emission transition to a low energy level). The present invention relates to an optical module capable of monitoring the output of a high-power excitation laser used in the optical module.

[0002]

2. Description of the Related Art At present, from a low-speed telephone-centric communication business,
It is beginning to shift to a broadband communication business represented by digital multimedia services. As described above, the communication system has begun to shift from the conventional metallic system to the optical communication system in accordance with the communication demand for a wide band. In the optical communication system, the backbone called the trunk system has been mainly used in the past, but recently, the optical communication has been advanced to the metro system and the access system. Further, the use of optical communication has also been advanced in LANs and the like in offices of companies.

[0003] With the progress of the optical communication system, demand for modules used for optical communication is anticipated, and there is a demand for a small-sized, low-cost mass-produced type from a high-mix low-volume production type.

In recent years, high-density wavelength division multiplexing (DWDM) has become mainstream in trunk line long-distance systems.
In this case, since the transmission loss of the optical fiber limits the transmission distance, it is required to increase the optical output and extend the reach of the signal light.

[0005] Therefore, at present, the optical fiber doped with a rare earth element is irradiated with a laser beam to increase the number of carriers existing at a high energy level by light excitation (formation of population inversion).
Accordingly, there is a demand for an optical fiber amplifier that performs optical amplification using stimulated emission transition to a low energy level. Also, the number of multiplexed wavelengths is increasing,
There is a demand to collectively amplify a plurality of signals having different wavelengths to obtain high output characteristics.

[0006] As an optical module to meet these requirements, there is a surface mount type optical module. FIG. 2 shows an example of the surface mount optical module. In this optical module, a groove 2 having a V-shaped cross section for installing an optical fiber 29 on a mounting substrate 20 is provided.
1 (V-groove) and a concave portion 23 in which the semiconductor laser 22 is installed are provided, and a mounting method (passive alignment) in which these optical components are only mechanically arranged is used. Further, in the optical module using the passive alignment, the mounting method of the light receiving element for monitoring the output light of the semiconductor laser 22 leads to a reduction in cost because of automatic power control (APC) for keeping the optical output of the semiconductor laser 22 constant. One way. in this way,
Conventionally, the monitor light receiving element 25 is a semiconductor laser 22
Has been adopted in which the light receiving surface 24 inclined backward is mounted vertically.

Japanese Patent Application Laid-Open No. 2000-208858 proposes using b-FeSi2 as a light receiving element and monolithically integrating the light receiving element on a substrate on which a semiconductor laser is mounted. Here, b-FeSi
Reference numeral 2 denotes a direct transition type semiconductor, which realizes light emission of λ ≒ 1.5 mm (D. Leong et al., Na
cure, Vol. 387, pp. 686, 1997,
See). Further, since it exhibits a large absorption coefficient of 10 ⁵ cm ^-1 at the above-mentioned wavelength, application research to infrared detectors has been conducted (Y. Maeda et al., Mat.
Res. Soc. Symp. Proc. , Vol. 60
7, pp. 315, 2000). This allows
Since the light receiving element for the monitor is not separately prepared and mounted, the mounting cost is reduced.

[0008]

However, in the above-mentioned technology, since the light receiving element for monitoring is monolithically integrated on the substrate on which the semiconductor laser is mounted, heat is stored on the substrate by the heat generated by the semiconductor laser, and the integrated light is accumulated. The operation of the light receiving element becomes unstable.

In addition, the mounted optical fiber is displaced due to thermal expansion in the substrate. This causes a problem that the coupling efficiency between the light emitted from the semiconductor laser and the optical axis of the optical fiber is reduced.

Particularly, in the case of a pumping semiconductor laser for an optical fiber amplifier, a high reflectance coating is applied to one side of the end face of the emitted light in order to increase the light output. In such a high-output pump laser, since the amount of heat generated by the element is large, the substrate stores a large amount of heat. The heat may destroy the monolithically integrated monitoring light receiving element. Further, the heat storage may saturate the output of the pumping semiconductor laser, or may melt the emission end face and destroy the element.

Accordingly, the present invention has been completed in view of the above, and its object is to prevent the operation of the monitor light receiving element from becoming unstable due to the heat generated by the semiconductor laser, or to destroy this element. An object of the present invention is to provide an optical module that can reduce the mounting cost without using the optical module. It is another object of the present invention to provide an optical module capable of reducing the mounting cost without saturating the output due to the heat of the semiconductor laser due to the heat storage and dissolving the emission end face of the semiconductor laser to destroy the element. It is still another object of the present invention to provide an optical module in which a reduction in coupling efficiency caused by displacement of an optical axis of an optical fiber due to thermal expansion due to heat generated by a semiconductor laser is minimized.

[0012]

In order to achieve the above-mentioned object, an optical module according to the present invention comprises an optical transmitter, a semiconductor laser optically connected to the optical transmitter, and a base made of single crystal silicon. An optical module in which light-receiving elements for monitoring emitted light of the semiconductor laser are disposed, wherein the light-receiving elements each having a metal silicide as a light absorption layer are integrated on the base, and the semiconductor laser is It is characterized in that a metal layer and an insulator layer formed on a base are disposed on a base layer which is sequentially laminated.

[0013] Further, the base may include a high position surface, a low position surface,
And forming an inclined surface between the high position surface and the low position surface, respectively, the optical transmitter on the high position surface, the semiconductor laser on the low position surface, and the inclined surface on the inclined surface. A light receiving element is provided. Further, the metal silicide is iron silicide. Furthermore, the inclined surface is (11)
1) A plane or a plane equivalent thereto, or a (001) plane or a plane equivalent thereto. The semiconductor laser is a high-output pump laser for an optical fiber amplifier.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an optical module according to the present invention.
In this embodiment, an optical fiber is exemplified as an optical transmission line, but an optical waveguide formed on a substrate, for example, may be used as the optical transmission line.

As shown in FIG. 1, an optical module according to the present invention comprises, on a substrate 10 made of single-crystal silicon, an optical transmitter such as an optical fiber 19 or an optical waveguide, and a semiconductor laser 12 optically connected to the optical transmitter. And a light receiving element 15 for monitoring the emitted light of the light receiving element.
The semiconductor laser 12 is disposed on a base layer in which a metal film 16 as a metal layer formed on the base 10 and an insulating film 18 as an insulator layer are sequentially laminated.

The base 10 has a high position surface, a low position surface,
And an inclined surface 13 existing between the high position surface and the low position surface, respectively, the optical fiber 19 as the optical transmission body on the high position surface, and the semiconductor laser 12 on the low position surface. The light receiving element 15 is provided on the inclined surface 13.

Further, the metal silicide is preferably iron silicide. Furthermore, the inclined surface 13 is preferably a (111) plane or a plane equivalent thereto, or (00)
1) A surface or a surface equivalent thereto. The semiconductor laser 12 is a high-power pump laser for an optical fiber amplifier.

More specifically, the substrate 10, which is a Si platform (Si optical bench), is mainly composed of a single crystal Si substrate, and has a V-shaped V-shaped groove 11 in which an optical fiber 19 is installed on the same substrate, and a semiconductor laser. 12 has an inclined surface 13 facing the emission end face, and the inclined surface 13 is a single crystal S
i (111) plane (notation by Miller index;
The same applies to notations such as 11)), and the V-groove 11 and the inclined surface 13 are formed by, for example, anisotropic etching using an alkali aqueous solution of single crystal Si.

A light absorbing layer in the light receiving element of the present invention.
As shown in FIG. 3, b-FeSi2 has an orthorhombic crystal structure (a = 9.86 °, b = 7.79 °, c = 7.83).
Å), and as shown in FIG.
b-FeSi2 (101) / Si (001), b-FeS
i2 (110) / Si (111).

The light receiving element 15 having b-FeSi 2 as a light absorbing layer is formed on the inclined surface 13. In the present embodiment, the inclined surface 13 is formed as a Si (111) surface, but the inclined surface 13 is formed on the Si (001) surface (and an equivalent Si (1) surface).
(00) plane or Si (010) plane).

Here, the light absorbing layer of b-FeSi2 is formed by a molecular beam epitaxial growth method, an ion implantation method, a laser ablation method, a growth method of depositing and annealing Fe, and the like. Note that it is optimal to form the layer to a thickness of about 0.2 to 0.4 μm by an ion implantation method, since Fe having high purity can be used and the crystal growth region can be controlled with high accuracy.

The insulating film 16 is made of SiO2, SiNx, etc.
It is formed to a thickness of about 0.2 to 0.8 μm by the VD method.
It is desirable to use the method.

The metal film 17 is made of Au, Pt, Al, Ag or the like having good heat conduction and good heat dissipation, and is formed to a thickness of about 0.3 to 0.6 μm by a vapor deposition method. Of these metal elements, use of Au is optimal in terms of heat dissipation and adhesion to the insulating film 16.

Substrate 18 on which semiconductor laser 12 is mounted
Is a ceramic made of Al2O3, CuTa, Si or the like.

Thus, according to the optical module of the present embodiment, the heat generated by the semiconductor laser 12 is radiated well by interposing the metal film 17 having good heat radiation between the substrate 18 and the base 10 of the Si platform. A light-receiving element 1 having b-FeSi2 monolithically integrated on a base 10 of a Si platform as a light absorbing layer.
The optical module 5 can be provided at low cost without the operation becoming unstable and without the element being destroyed.

Further, it is possible to provide an optical module in which the heat generated by the semiconductor laser 12 does not accumulate, the output of the semiconductor laser 12 is saturated, the emission end face is melted, and the element is not broken, thereby reducing the mounting cost. .

Further, it is possible to provide an excellent optical module in which a decrease in coupling efficiency caused by a displacement of an optical axis of an optical fiber due to thermal expansion due to heat generated by a semiconductor laser is prevented.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

The substrate 10 of the Si platform was formed of a single-crystal Si substrate, and the n-type (110) plane was used as a main surface. Further, a mask pattern is formed on the Si substrate using a predetermined photomask and photoresist by a photolithography process, and a strong alkaline aqueous solution KO is used.
Etching was performed with an H aqueous solution. By performing etching using this KOH aqueous solution, a (111) plane inclined by 54.7 ° from the (100) plane toward the [110] direction was formed. Thereby, the inclined surface 13 facing the emission end face of the semiconductor laser 12 could be formed.

Next, a V-shaped groove 11 was formed by dicing using a dicing blade having a V-shaped cross section.

Next, Fe ions are implanted by an ion implantation method, and annealing is performed at a high temperature of 800 to 1000 ° C. to form a 0.2 μm b-FeSi 2 layer 31. In the grown b-FeSi2, the site of Si (II) is distorted from the crystal lattice position, and the vacancy is vacancy.
It becomes. This vacancy acts as an acceptor, and the grown b-FeSi2 has a carrier density of about 1 × 10 ¹⁸
It exhibits p-type conductivity of cm ^-3 .

Thereafter, an insulating film 15 made of SiNx was formed to a thickness of 0.7 μm by the p-CVD method. After passing through a photolithography process, an Al contact electrode is formed by sputtering, so that the monitoring light-receiving element 1 is formed.
5 was formed.

Next, after the pattern is formed again in the photolithography step, the metal film 17 is formed to a thickness of 0.3 μm by Au evaporation.
Formed.

Then, the CuTa substrate 18, the semiconductor laser 12, and the optical fiber 19 were mounted at predetermined positions.

Thus, in the present embodiment, a Si platform (Si optical bench) in which light receiving elements using metal silicide as a light absorbing layer are monolithically integrated.
An insulating film and a metal film were sequentially formed thereon, and a substrate on which a semiconductor laser was mounted was mounted thereon. Particularly, the metal silicide is iron silicide, and the surface of the Si platform facing the emission end face of the semiconductor laser is (1).
11) By using the surface, the operation of the light receiving element does not become unstable or the element is not destroyed,
An excellent low-cost optical module that prevented displacement of the optical axis of the optical fiber due to thermal expansion of the Si platform could be provided.

[0037]

As described above in detail, according to the optical module of the present invention, the operation of the monitor light receiving element does not become unstable due to the heat generated by the semiconductor laser, and the monitor light receiving element is not destroyed because of its reliability. It is possible to provide a low-cost optical module with excellent performance.

Further, it is possible to provide an excellent optical module in which the output due to the heat of the semiconductor laser is saturated by the heat storage, the emission end face is melted, and the element is not destroyed.

Further, it is possible to provide an excellent optical module in which a reduction in coupling efficiency caused by a displacement of an optical axis of an optical fiber due to thermal expansion due to heat generated by a semiconductor laser is minimized.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically illustrating an embodiment of an optical module according to the present invention.

FIG. 2 is a perspective view illustrating a conventional optical module.

FIG. 3 is a crystal structure diagram of β-FeSi2.

FIG. 4 is a plan view illustrating an epitaxial relationship.

FIG. 5 is a sectional view taken along line A-A ′ in FIG. 1;

[Explanation of symbols]

10: Si platform (base) 11: V groove 12: Semiconductor laser 13: Slope 14: V groove inclined side surface 15: Light receiving element 16: insulating film (insulator layer) 17: metal film (metal layer) 18: Substrate 19: Optical fiber (optical transmission body)

Claims (5)

[Claims] An optical module comprising a substrate made of single-crystal silicon, an optical transmitter, a semiconductor laser optically connected to the optical transmitter, and a light receiving element for monitoring light emitted from the semiconductor laser. The light receiving element using a metal silicide as a light absorbing layer is integrated on the base, and the semiconductor laser is disposed on an underlayer formed by sequentially laminating an insulator layer and a metal layer on the base. An optical module, which is provided. 2. A high position surface, a low position surface, and an inclined surface existing between the high position surface and the low position surface are respectively formed on the base, and the optical transmission body is formed on the high position surface. The optical module according to claim 1, wherein the semiconductor laser is provided on the low position surface, and the light receiving element is provided on the inclined surface. 3. The optical module according to claim 1, wherein the metal silicide is iron silicide. 4. The optical module according to claim 1, wherein the inclined surface is a (111) plane or a plane equivalent thereto, or a (001) plane or a plane equivalent thereto. . 5. The optical module according to claim 1, wherein said semiconductor laser is a high-power pump laser for an optical fiber amplifier.