JPH04275483A - Semiconductor laser light amplifier - Google Patents

Abstract

PURPOSE:To increase stability for a mechanical vibration by reducing aligned parts of an optical system. CONSTITUTION:Grating lenses 9, 10 and mirrors 15, 21 are respectively provided on front and rear surfaces 8a, 8b of a flat substrate 8 to constitute an optical component on the substrate, and a semiconductor laser 7 having input, output waveguide 16, 19 including grating lenses 13, 22 is provided on the surface 8a of the substrate.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser optical amplifier, and in particular is used as a repeater for optical fiber communications.

0002

2. Description of the Related Art A semiconductor laser optical amplifier commonly used in the past, as shown in FIG. (3), laser (1) and each fiber (
It consists of coupling lenses (4) and (5) such as rod lenses inserted between lenses 2) and (3). The role of each component will be explained along the propagation of signal light. Fiber (2
) The weak signal light propagated through the core of the fiber end (2
The light is emitted from a), condensed by a coupling lens (4), and guided to the active layer (6) of the laser (1). The signal light within the active layer 6 causes optically stimulated emission within the laser and is optically amplified. Therefore, a high-output optical signal having the same wavelength as the incident optical signal is emitted from the end face (1a) of the laser (1). The emitted signal light is coupled to the fiber (3) by the coupling lens (5) and propagates through the fiber (3). In this case, in the case of a single mode fiber, the core diameter of the fiber is usually 5 to 10 μm, although it depends on the wavelength used. On the other hand, the spread width of the laser beam is about 3 to 8 μm for InP systems, and therefore, the alignment accuracy of the optical system between the fiber and the laser must be at least about 2 μm when considering the coupling efficiency. A great deal of precision is required for axis alignment.

0003

[Problems to be Solved by the Invention] However, in the conventional configuration described above, since the coupling lens is separated from each component including the laser section, the position of the coupling lens with respect to the laser can be determined with an accuracy of several μm. It was necessary to fit them together and fix them with welding, adhesive, etc. Therefore, if the alignment accuracy is poor, the loss of light between the fiber (2) and the laser (1) or between the laser (1) and the fiber (3) will be large, and the effect of amplifying the light with the optical amplifier will not be sufficient. The problem arose that it became impossible to do so. For this reason, it is necessary to assemble the optical axes of the coupling lenses with precision on the order of microns, but alignment on the order of microns is extremely difficult from the standpoint of assembly accuracy and reproducibility. Furthermore, even if the coupling lens is fixed with an adhesive or the like, it is unstable against temperature changes, mechanical vibrations, etc., and there are extremely problems in terms of quality.

0004

[Means for Solving the Problems] The present invention has a planar substrate having a grating lens and a mirror on its front and back surfaces, respectively, and an input waveguide and an output waveguide including the grating lens on the surface of the planar substrate. This is a semiconductor laser optical amplifier comprising a semiconductor laser. That is, in the present invention, for example, as shown in FIG. 2, crystal growth is performed on an InP compound semiconductor substrate (8), and an active layer (17) of InGaAsP or the like is formed using a known technique.
Grating lenses (9), (10), (13) and (22) are formed on the optical axis of the element (7) and on the substrate surface (8a), respectively, using photofabrication technology and 2 using dry etching processes such as reactive ion etching and plasma etching.
Au, Ag, and C having a high reflectance are formed with a preferable width of ~0.5 μm intervals, and are further coated on the back surface (8b) of the substrate.
A reflective film for a mirror (15) (2) is formed on the substrate surface by vapor deposition of U, Al, etc. in alignment with the optical axis of the laser element formed on the surface of the substrate.
1) is formed by photo-etching technology. In this process, optical components are fabricated on a single substrate to configure a semiconductor laser amplifier, so each optical component can be arranged with the precision of photo-etching, and these optical components can be configured on a single substrate, resulting in high efficiency. Accuracy and high reliability are achieved. At the same time, it has the advantage that it can handle wafer processes and the manufacturing process can be extremely simplified.

[0005]

[Operation] According to the present invention, for example, a quaternary laser element such as InGaAsP is formed on the surface of a compound semiconductor substrate such as InP using epitaxial growth, and a grating lens is further formed on the optical axis. Incoming light and outgoing light from a fiber can be converted into parallel light beams (plane waves) or diverging light beams (spherical waves), and light can be efficiently introduced into and led out from a waveguide type laser chip. As mentioned above, a reflecting mirror is provided on the back side of the substrate at a position opposite to the position of the laser element on the substrate, and reflects the incident light from the fiber or the emitted light from the laser element.
A structure has been realized in which these lights are confined within a compound semiconductor substrate such as InP, which also serves as an optical waveguide to effectively guide the light. Therefore, it is possible to construct optical components using photofabrication technology, which is often used in ICs, etc., so alignment can be performed with high precision, the size is extremely small, and many parts can be formed simultaneously on one wafer. This method has many advantages over conventional techniques, such as being able to realize a semiconductor laser optical amplifier at a lower cost.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view of a semiconductor laser optical amplifier according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the structure of the optical amplifier. The optical amplifier according to the present invention basically consists of a semiconductor laser section (7) that amplifies light, and an InP compound semiconductor substrate (8) having gratings, mirrors, etc. on both sides. Grating (9)
, (10). The role of each part will be explained along the propagation of signal light. The weak signal light that has propagated through the fiber (11) is emitted from the end face of the fiber (11) as output light (12), and is emitted by the grating (13) formed on one side (front surface) (8a) of the substrate (8). It is collimated and guided into the substrate at a certain angle. The signal light (14) guided into the substrate is reflected by a mirror (15) formed on the other surface (back surface) (8b) of the substrate (8), and then reflected by a grating (9) in the semiconductor laser section (7). ) enters the active layer (17) of the semiconductor laser section (7) via the input waveguide (16). At this time, a current is injected into the active layer (17) of the semiconductor laser section (7), forming a population inversion. When an optical signal is transmitted to the active layer (17) in this state, the optical signal is amplified by stimulated emission. The amplified signal light is propagated to the output waveguide (19) and output to the substrate (8) by the grating (10). After the light (20) emitted to the substrate (8) is reflected by the mirror (21), the reflected light (24) becomes focused light (25) which is focused onto the fiber (23) by the grating (22). , the fiber (
23). The manufacturing method will be explained below. A compound semiconductor such as InP is used for the substrate, a laser element is formed by crystal growth on the compound semiconductor substrate, and a grating lens is placed on the optical axis of the element using photofabrication technology, reactive ion etching, and plasma etching. A desired spacing of 2 to 0.5 μm is created using an iso-dry etching process. Furthermore, Au, Ag, Cu, Al, or the like having high reflectivity is vapor-deposited on the back surface of the substrate, and aligned with the optical axis of the laser element formed on the surface.
A reflective film for the mirror is formed using photo-etching technology. Since optical components are fabricated on a single substrate using this process to configure a semiconductor laser optical amplifier, each optical component can be arranged with the precision of photo-etching. Further, in the above process, it is possible to handle wafers. In this example, a semiconductor laser element is fabricated on a compound semiconductor substrate such as InP, and a grating lens and a reflecting mirror are formed on the same substrate using photofabrication technology that has a proven track record in IC technology. Compared to the conventional method of mechanically aligning individual optical components with high precision and fixing them with welding, adhesive, etc., these optical amplifiers can be realized easily and with high positional precision. High reliability can also be achieved. Note that when the amplification factor of the optical amplifier is low and it is necessary to improve the coupling efficiency in the grating lens, it is possible to improve the efficiency by making the cross-sectional shape of the grating blazed.

[0007]

[Effects of the Invention] In the semiconductor laser optical amplifier of the present invention, optical components such as gratings and mirrors and the laser can be fabricated on the same substrate, so there is no need to align the optical components and the laser after fabrication. The number of adjustment points can be reduced. Furthermore, by manufacturing the optical component and the laser on the same substrate, stability against misalignment due to thermal expansion, mechanical vibration, etc. can be improved, and reliability can be improved. Furthermore, since it is possible to simultaneously form a large number of optical amplifiers on a semiconductor substrate using photofabrication technology, it is possible to realize a small, robust, and inexpensive semiconductor laser optical amplifier, which has an extremely large ripple effect.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a view taken along line A-A in FIG. 1;

FIG. 3 is a configuration explanatory diagram showing a conventional example.

[Explanation of symbols]

7 Semiconductor laser 8 Substrate 9, 10, 13, 22 Grating lens 1
5, 21 Mirror 16 Input waveguide 19 Output waveguide

Claims (1)

[Claims] 1. A semiconductor comprising a planar substrate having a grating lens and a mirror on its front and back surfaces, respectively, and a semiconductor laser having an input waveguide and an output waveguide including the grating lens on the surface of the planar substrate. Laser light amplifier.