JP2009212176A - Semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode structure of DFB-LD, which can fuse an electrode on an active layer side of the DFB-LD to an electrode on a heatsink for high heat exhaust characteristics and high single mode characteristics yield as well. <P>SOLUTION: In a semiconductor laser 1, a mesa structure is formed on its surface and an electrode pad 5 having sufficient area is formed directly above the mesa as well as on both sides of a separation groove 3. The electrode directly above the mesa and the electrodes on both sides of the separation groove are connected together through electrodes formed, being divided in two or more pieces, in the grooves on both sides of the mesa. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor laser.

  With the recent widespread use of high-speed, large-capacity WDM (wavelength division multiplexing) optical networks, optical communication devices are required to operate in a wide range of temperatures.

  In particular, in a single-core bidirectional optical transceiver used in an access network, a semiconductor laser element is required to operate in a wide temperature range of −40 to + 85 ° C. without temperature adjustment such as cooling using a Peltier element or the like.

  In particular, as a light source of an optical transceiver used at a distance of about 20 km, a distributed feedback semiconductor laser (DFB-LD) that generally has a narrow line width and oscillates in a single mode is used. The axial mode characteristics change very sensitively to stress application. Usually, in order to maintain single-axis mode oscillation, the substrate side is solder-fused onto a heat sink while avoiding the light emitting part side including the active layer.

  Patent Document 1 discloses the structure of a conventional array type laser diode, and Patent Document 2 discloses a conventional optical semiconductor module.

Japanese Patent Laid-Open No. 11-233877 JP 2002-314184 A

  However, when soldering the substrate side on the heat sink while avoiding the light emitting part side including the active layer described above, since the LD light emitting part that generates heat is far from the heat sink, the active layer side is fused on the heat sink. Since the exhaust heat characteristic is inferior to that of the LD, the light output characteristic of the LD is lowered.

  On the other hand, some single-core bidirectional optical transceivers employ an optical module using a PLC, in order to maintain the coupling efficiency between the optical waveguide constituting the PLC and the DFB-LD at a certain level. It is desirable to eliminate the influence of the variation in polishing thickness of the LD substrate by fusing the electrode on the PLC and the active layer side electrode of the LD.

  That is, in an optical module using PLC, it is more advantageous to fuse the electrode on the active layer side to the electrode on the PLC from the viewpoint of either exhaust heat efficiency or coupling efficiency, but from the viewpoint of maintaining single mode oscillation. It is advantageous to fuse the electrode on the substrate side to the electrode on the PLC, resulting in a trade-off.

  From the above description, the electrode structure shown in FIG. 3 is usually used for a communication semiconductor laser that requires single mode characteristics, and the electrode structure shown in FIG. 4 is used for a high output semiconductor laser that requires high temperature and high output characteristics. The substrate side, the latter, is generally used by mounting the active layer side on a heat sink or PLC.

  In FIG. 3, 1 is an edge-emitting semiconductor laser, 2 is an active layer, 3 is a separation groove, 4 is a protective film such as a dielectric, 5 is an electrode, and 31 is an extraction electrode. is there.

  In FIG. 4, 1 is an edge-emitting semiconductor laser, 2 is an active layer, 3 is a separation groove, 4 is a protective film such as a dielectric, and 5 is an electrode.

  That is, in order to improve the temperature characteristics of the semiconductor laser, it is essential to improve the exhaust heat characteristics in order to suppress the rise of the active layer temperature due to the heat generation of the active layer. It is effective to fuse the electrode directly to the electrode on the heat sink or PLC.

  However, in the above structural example, due to the mismatch of the thermal expansion coefficients of the semiconductors constituting the DFB-LD, the solder, and the Si constituting the PLC, a strong stress is applied to the active layer of the DFB-LD to cause refraction near the diffraction grating. The rate changes and the oscillation condition is affected, and the single mode oscillation characteristic is degraded with high probability. For this reason, it is very difficult to maintain the single mode oscillation characteristic at a high yield while maintaining high exhaust heat efficiency and high coupling efficiency.

The inventions described in Patent Document 1 and Patent Document 2 also have the same problem.
(Object of invention)
An object of the present invention is to provide an electrode structure of a DFB-LD in which an active layer side electrode of the DFB-LD can be fused to an electrode on a heat sink, and both a high heat removal characteristic and a high single mode characteristic yield can be achieved. It is to be.

In solving the above-described problems, the semiconductor laser of the present invention has a mesa structure formed on the surface, electrode pads having a sufficient area directly on the mesa and on both sides of the separation groove, and the electrodes on the mesa and the separation groove. The electrodes on both sides are connected to each other through two or more electrode groups formed in the grooves on both sides of the mesa.
(Function)
According to the present invention, an electrode pad is formed on both sides of the mesa, and an electrode divided at an appropriate interval is formed inside the separation groove, whereby the active layer side electrode and heat sink of the DFB-LD, or the PLC Even if the electrode on the surface is directly soldered, the solder melted at the time of fusion does not enter the separation groove on the side of the mesa, and the stress applied to the active layer inside the mesa compared to when the solder enters the groove Is greatly reduced. As a result, it is possible to maintain single mode characteristics with a high yield even after the DFB-LD is soldered to the PLC, and it is possible to achieve both high heat exhaustion characteristics or high coupling characteristics.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode structure of DFB-LD which can fuse | bond the electrode of the active layer side of DFB-LD to the electrode on a heat sink, and can make a high heat exhaust characteristic and a high single mode characteristic yield compatible is provided. can do.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The present invention relates to an electrode structure of an edge-emitting semiconductor laser device and a mounting method thereof, and in particular, an electrode on a mesa structure including an active layer and an electrode in another region are connected by a plurality of divided electrodes and discharged. The present invention relates to an electrode structure excellent in thermal efficiency and suitable for use in combination with a planar optical circuit (PLC), and a mounting method thereof.
(Description of configuration)
Next, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic perspective view of a distributed feedback semiconductor laser according to a first embodiment of the present invention.

  In FIG. 1, 1 is an edge emitting semiconductor laser, 2 is an active layer, 3 is a separation groove, 4 is a protective film such as a dielectric, 5 is an electrode, and 6 is a separation slit. is there.

  Separation grooves 3 are provided on both sides of the active layer 2 of the edge-emitting semiconductor laser 1, and the surface is covered with a protective film 4 such as a dielectric, except for the region immediately above the active layer 2. Electrodes 5 are formed in other regions.

  The electrode 5 is divided into a plurality of regions by separation slits 6 in the separation grooves 3 on both sides of the active layer 2. The division shape of the electrode 5 is optimized so that the solder does not flow into the separation groove 3 during solder fusion by the solder wettability of both the protective film 4 such as a dielectric and the electrode 5 and the shape of the separation groove. Although not shown in FIG. 1, an electrode is also formed on the back surface of the semiconductor laser 1 so that a current flows through the active layer.

  FIG. 2 is a schematic perspective view showing a mounting form of the semiconductor laser shown in FIG. 1 on a PLC.

  2, 11 is the semiconductor laser shown in FIG. 1, 12 is a Si substrate, 13 is a PLC electrode, and 14 is solder.

  According to the present invention, the electrode pad 5 is formed on both sides of the mesa on the active layer 2 and the electrode 5 divided at an appropriate interval is formed inside the separation groove 3, thereby enabling the active layer of the DFB-LD. Even if the electrode on the 2 side and the heat sink 12 or the electrode on the surface of the PLC 13 are directly fused with the solder 14, the solder 14 melted at the time of the fusion does not enter the separation groove 3 on the mesa side, and the solder 14 enters the groove 3. Compared with the case of entering, the stress applied to the active layer 2 inside the mesa is greatly reduced.

  As a result, even after the DFB-LD is fused to the PLC with the solder 14, it is possible to maintain the single mode characteristics with a high yield, and it is possible to realize both high heat exhaustion characteristics or high coupling characteristics.

  When the semiconductor laser and the heat sink (Si substrate) are fused, if the solder enters the separation groove on the side of the mesa, there is a problem that stress distortion occurs and the characteristics of the laser deteriorate. The electrode metal is excellent in thermal conductivity and is desired to be formed in as wide an area as possible. However, the metal has high wettability with respect to the solder, and in the structure shown in FIG.

Therefore, in the present invention, the electrode metal in the groove portion is divided as shown in FIG. Solder wettability of the exposed portion (protective film 4, usually SiO ₂ , SiN or the like is used) is extremely low, so that the solder does not get on the electrode portion in the groove portion 3 due to the surface tension of the solder itself.

  Therefore, the groove 3 is not filled with solder, and the influence of thermal stress can be avoided.

  Further, in the electrode structure of FIG. 3, although conduction can be obtained, the heat radiation area is small and the heat radiation property is insufficient. This is a structure in which a heat sink is mounted on the lower side of the laser element, and the heat dissipation efficiency is not high.

  On the other hand, the structure of the present invention is effective when mounting the laser element 11 upside down as shown in FIG. 2 so that the active layer 2 side is mounted on the substrate (for example, mounting on a PLC), and heat dissipation. This is also advantageous.

  The present invention can provide a semiconductor laser module that can be used in a wide temperature range without using a temperature control device, and an optical transceiver using the semiconductor laser module.

1 is a schematic perspective view showing a first embodiment of a stress-reducing electrode type semiconductor laser according to the present invention. It is a schematic perspective view which shows the mounting form to PLC using 1st Embodiment of the stress reduction electrode type semiconductor laser of this invention. It is a schematic perspective view of Structural Example 1 with a semiconductor laser electrode structure. It is a schematic perspective view of the structural example 2 of a semiconductor laser electrode structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 End surface emitting semiconductor laser 2 Active layer 3 Separation groove 4 Dielectric film 5 Electrode 6 Separation slit 11 Stress reduction electrode type semiconductor laser 12 Si substrate 13 PLC electrode 14 Solder 31 Extraction electrode

Claims (6)

  A mesa structure is formed on the surface, electrode pads are formed immediately above the mesa and on both sides of the separation groove, and two electrodes on the mesa and electrodes on both sides of the separation groove are in the groove on both sides of the mesa. A semiconductor laser, wherein the semiconductor lasers are connected via an electrode group formed as described above.   2. The semiconductor laser according to claim 1, wherein the mesa structure is formed by providing separation grooves on both sides of an optical waveguide including an active layer.   3. The semiconductor laser according to claim 1, wherein the mesa structure side is fused to a heat sink by solder.   A mesa structure is formed on the surface, electrode pads are formed immediately above the mesa and on both sides of the separation groove, and two electrodes on the mesa and electrodes on both sides of the separation groove are formed in the groove on both sides of the mesa. A method of manufacturing a semiconductor laser, characterized in that the connection is made through the electrode group formed as described above.   5. The method of manufacturing a semiconductor laser according to claim 4, wherein the mesa structure is formed by providing separation grooves on both sides of an optical waveguide including an active layer.   6. The method of manufacturing a semiconductor laser according to claim 4, wherein the mesa structure side is fused to a heat sink by solder.

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