JPS60187085A - Distribution feedback semiconductor laser - Google Patents

Abstract

PURPOSE:To realize a distribution feedback semiconductor laser characterized only in TE mode oscillation by a method wherein an optical waveguide constituted of a layer with its forbidden band width larger than that of an activation layer is coupled to a distribution feedback waveguide and its surface is coated with a metal layer with the intermediary of an insulating layer. CONSTITUTION:To an activation waveguide 10 including an activation layer having an uneven periodic structure 100, an optical waveguide 50 is coupled, with its forbidden band width larger than that of said activation layer. The waveguide 10 is provided with a clad layer 30 thereon. On the waveguide 50, through the intermediary of an insulating film 200, a metal layer 300 of Au or the like is provided. The end face of the activation region is so structured as to suppress the Fabry-Perot mode. Oscillation is generated by an oscillating frequency that is determined by the diffraction lattice organized by the periodic structure of the activation waveguide 10. Said light is coupled with the optical waveguide layer 50, to be reflected by its end face and return to the activation waveguide 10. Due to the metal layer 300, loss is greater in the TM mode than in the TE mode. Accordingly, a distribution feedback semiconductor laser oscillating only in the TE mode is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a semiconductor laser, and particularly to a distributed feedback semiconductor laser.

(Prior art and its problems) Distributed feedback semiconductor lasers (hereinafter referred to as DFB lasers) oscillate in a single-axis mode, so when used as a light source for optical fiber communication, they are greatly affected by wavelength dispersion caused by the optical fiber. It is promising as a high-capacity, long-distance light source. 1st
The figure is a schematic cross-sectional view of a conventional DFB laser in the cavity direction. An active waveguide 10 having an uneven diffraction grating 100 with a constant period and including an active layer is sandwiched between cladding layers 20 and 30 whose forbidden band width is wider than that of the semiconductor constituting the active waveguide. In conventional DFB lasers, TE mode oscillation and TM mode oscillation occur simultaneously, and the transition from TE mode to TV mode occurs easily depending on the current injection level, and the L type has a linear current-optical output characteristic. observed as the king of In addition, when applied to optical integrated circuits, etc., T
Oscillation must be limited to either E mode or TM mode (G).

(Object of the Invention) An object of the present invention is to increase the difference in threshold current between TB mode oscillation and TM mode oscillation in order to eliminate the above problems.
It is an object of the present invention to provide a structure of a distributed feedback semiconductor laser capable of oscillating only in the l1li mode.

(Structure of the Invention) The structure of the distributed feedback semiconductor laser of the present invention has a structure in which an active waveguide having a periodic structure with irregularities on the surface including an active layer is sandwiched between cladding layers having a larger forbidden band width than the active layer. Further, the active waveguide has a structure in which the active waveguide is continuous with an optical waveguide made of a layer having a forbidden band width larger than that of the active layer, and the optical waveguide has a metal on the surface with an insulator interposed therebetween. .

(Operations and Effects of the Invention) According to this configuration, the DFB laser oscillates in a single axis mode at an oscillation wavelength determined by the periodic structure of the irregularities of the active waveguide. Oscillation is mainly controlled by the active waveguide, and the light coupled from the active waveguide to the optical waveguide is reflected at the end face of the optical waveguide.
The active waveguide also contributes to the oscillation of the active layer. Since the surface of the optical waveguide has metal in the vicinity via an insulator, the loss in the TE attitude and the TM attitude in the optical waveguide layer is greater in the TM attitude. Therefore, the light that returns to the active waveguide and contributes to oscillation is larger in the TE attitude, and the oscillation of the active waveguide is fixed in the TE attitude. This will be explained below using the drawings. FIG. 2 is a schematic cross-sectional view of the distributed feedback semiconductor laser of the present invention in the cavity direction. An active waveguide 10 including an active layer having an uneven periodic structure 100 is connected to an optical waveguide layer 504 having a larger forbidden band width than the active layer. The active waveguide 10 is a waveguide that provides gain, and the leading waveguide layer 50 has a forbidden band width larger than that of the oscillation light beam. The end face of the active region has a structure such as a diagonally etched end face which is commonly used to suppress Fabry-Perot mode. This structure does not have to be an obliquely etched end face, but may be any structure as long as it suppresses the Fabry-Perot mode. The oscillation occurs at an oscillation wavelength determined by a diffraction grating made of a periodic structure of concavities and convexities formed in the active waveguide. The light is coupled to the optical waveguide layer 50i, reflected at the end face of the optical waveguide layer, and redirected to the active waveguide 10.
In the TE mode and TM mode, the loss from the active waveguide to the optical waveguide and back to the active waveguide is as follows:
Since the metal 300 is present on the surface of the optical waveguide layer via the insulating film 200, the TE mode is smaller. Therefore, the light returning to the active waveguide is thicker in the TE mode, and the active waveguide is fixed to TE mode oscillation.

(Example) The following will be explained using examples.

FIG. 3 shows the manufacturing process of the laser of the present invention, and is a 1.3 μm Mi
g of Ga I nAs P , 0. I Jim and 1.2
A DH wafer including an active waveguide layer 10 consisting of two layers of Ga I nAs po and i 5 μm having a μm composition was fabricated. Cladding layer 2 () with an uneven period of 3900A
, 30 are both InP, and the fabrication is exactly the same as that of a conventional DFB laser. The cladding layer 30 on top of the l)H wafer obtained in FIG.
The active waveguide 1 (H) was selectively etched with a mixed solution of H2SO and H,0 (Fig. 3(b)).As shown in Fig. 3(C), Then, G with a composition of 1 to 2 μm is grown again by liquid phase growth to become the optical waveguide layer 50.
a 1 nAs Po, 25 ttm and InPo, 2
It grew by μm. A semiconductor layer forming an optical waveguide layer is also laminated on top of the C and C layers 30, but there is no problem. Thereafter, a 3000A insulating film 200 was formed on the entire surface using the pyrolysis OVD method, and the upper part of the active waveguide was etched to remove the deposited metal at the end of the active waveguide and form an obliquely etched surface. Furthermore, the back side electrode & was made and the third
An FB laser was used as shown in Figure <d) (the electrodes are not shown). The oscillation was in the TE mode, and no oscillation in the TM mode was observed.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional DFB laser, FIG. 2 is a sectional view of a DFB laser of the present invention, and FIGS. 3(a), (bl,
(C8(d) is a manufacturing process diagram of 1) FB laser of the present invention. In the figure, 10 is an active waveguide, 20 and 30 are cladding layers, 50 is an optical waveguide layer, 100 is an uneven periodic structure, and 200 is an active waveguide.
3 is an insulating film, 300 is a metal, and 400 is an etching mask.爾心ズ e MiQ

Claims (1)

[Claims] It has a structure in which an active waveguide having a periodic structure with irregularities on the surface including an active layer is sandwiched between cladding layers having a forbidden band width larger than that of the active layer. 1. A distributed feedback semiconductor laser having a structure in which the optical waveguide is connected to a leading waveguide made of a wide layer, and has metal interposed on the surface of the optical waveguide through an insulating material.