JP2005039150A - Edge-emitting-type semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser of large output power in which variation of oscillating conditions by variation of external optical conditions such as dirt on the emission edge face or the arrangement of optical parts is reduced. <P>SOLUTION: The active layer 14 of the semiconductor laser has a DBR reflecting layer 15 on the emission-edge side, while a space for phase adjustment, where no DBR reflecting layer is formed, is provided between the emission edge 16 and the end of the emission-edge side of the DBR reflecting layer 15. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-power edge-emitting semiconductor laser.

  In recent years, a laser beam that has been enhanced by combining laser beams from a plurality of light emitting points of a high-power laser light source or a semiconductor laser bar has been used for workpiece processing such as surface modification, welding, and cutting. A conventional high-power end-face emission semiconductor laser used for laser processing forms a half mirror by a cleavage plane at the emission end or a dielectric multilayer film, and satisfies oscillation conditions (see Patent Document 1). On the other hand, among the low-power semiconductor lasers used for communication, a semiconductor laser having a periodic refractive index distribution on the front surface of the active layer for the purpose of narrowing the spectrum width of the oscillation wavelength, or the oscillation wavelength is made variable. Therefore, a semiconductor laser having a distributed Bragg reflection region is known (see Patent Document 2).

JP 2001-77457 A JP 2002-232070 A

  When a laser resonator is configured with a cleaved surface of the emission end or a dielectric multilayer film, if dirt is attached to the laser emission end surface, the oscillation condition changes, causing a reduction in laser light output and a reduction in light emission efficiency. Further, the oscillation condition changes even if an optical component such as a lens is disposed adjacent to the emission end face or covered with another dielectric. When a dielectric multilayer film is formed at the emission end, there are problems such as deterioration and peeling of the film.

  A conventional semiconductor laser having a distributed Bragg reflection region is a small-power semiconductor laser for communication in which the reflectance of the distributed Bragg reflection region is generally as high as 90% or more. On the other hand, a high-power semiconductor laser used for laser processing or the like has a reflectance of about 10% at the emission end and the optical conditions of the resonator are different. It cannot be adopted.

  It is an object of the present invention to provide a high-power semiconductor laser in which fluctuations in oscillation conditions due to changes in external optical conditions such as dirt on the emission end face and arrangement of optical components are reduced.

  The edge-emitting semiconductor laser of the present invention achieves the above object by adding a DBR (distributed black reflection mirror) structure inside the active layer. By appropriately designing the positional relationship between the position of the DBR and the emission end, a resonant mirror having a desired reflectance that is not easily affected by dirt on the laser emission end face can be configured. Further, even if an optical component such as a lens is arranged adjacent to the laser emission end face or the end face is covered with a dielectric or the like, the oscillation characteristics are not affected, so that the subsequent optical system is not limited.

  According to the present invention, the adoption of the DBR reflection layer can prevent fluctuations in oscillation characteristics due to contamination of the laser emission end face. Further, even if an optical component such as a lens is arranged adjacent to the laser emission end face or covered with a dielectric or the like, the influence on the oscillation characteristics is eliminated.

  According to the present invention, it is possible to obtain a high-power semiconductor laser in which the change in the oscillation state due to contamination of the emission end is reduced.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic view of an edge-emitting semiconductor laser according to the present invention, FIG. 1 (a) is a schematic view of the whole, and FIG. 1 (b) is a schematic cross-sectional view of the broken line portion.

  This edge-emitting semiconductor laser has an active layer 14 formed between a clad layer 12 and 13 on a substrate 11. The active layer 14 has a DBR (distributed black reflection mirror) structure 15 inside. A portion where no DBR is formed exists between the end of the DBR 15 on the emission end side and the emission end face 16 of the semiconductor laser by a distance L. The distance L is set so that the following equation (1) is established. λ is the oscillation wavelength, and n is the refractive index of the active layer. δ is the phase difference between the reflected light from the emission end and the reflected light from the DBR.

  In order to reduce the combined reflectance for a large output, it is necessary to cause both reflected lights to cancel each other, and therefore the phase δ is limited to a range larger than 90 ° and smaller than 270 °. (However, due to the nature of the phase, a value obtained by adding an integer multiple of 360 ° to this is also valid). Further, the reflectivity of DBR is conventionally 90% or more, but is used at 60% or less in the present invention.

As schematically shown in FIG. 2, the resonant mirror on the output side of the semiconductor laser according to the present invention is realized by combining the output end and the DBR. The combined reflectance r at the exit end is the combined reflectivity of the reflected light A from the exit end and the reflected light B from the DBR. Although the combined reflectance varies depending on the phase difference between the reflected lights A and B, this phase difference depends on the distance L between the end face and the DBR. The reflected light A from the end face is not a simple end face reflectivity because it is affected by multiple reflections between the DBR and the end face. Now, the facet reflectivity r _a, the DBR reflectivity r _b, When the phase difference between the reflected light A and B [delta] due to the distance L, synthetic reflectance r is given by the following equation (2).

Here, (strength) reflectance is represented by R. There is a relationship of R = | r | ² . For example, if R _a = 30%, R _b = 30%, and δ = 101.4 °, then R = 30%. In this state, even if R _a is reduced to 10%, the change is small as R = 26.1%. In this way, even if the end surface reflected light A changes, a design in which the change in the combined reflectance R (ie, r) is small is possible.

R _a is, since the reflectance at the end face, if subjected to particular processing on the end surface, the refractive index of the active layer n and the outside of the refractive index n _o (for air n _o = 1), the following equation It is decided.
R _a = | (n−n _o ) / (n + n _o ) | ²
Therefore, if the value of n _o changes due to a disturbance such as dust, _Ra also changes.

Taking an example of a near-infrared high-power laser, the refractive index of GaAs, which is a material, is about 3.6. Therefore, if there is no particular disturbance, R _a = 31.9%. If the DBR is attached so that R _b = 30% and δ = 137 °, the combined reflectance R becomes 10%, which is a value suitable for high power (this R _b and δ can be combined in various ways). ). In this case, synthesized reflectivity R in the case of facet reflectivity R _a by disturbance has changed is as shown in FIG. 3, it is possible to reduce the amount of change with respect to an end face reflectance R _a.

1 is a schematic view of an edge emitting semiconductor laser according to the present invention. Explanatory drawing of the resonant mirror of the output side where the output end and DBR were compounded. The figure which shows the change of the synthetic | combination reflectance R when end surface reflectance _Ra changes.

Explanation of symbols

  11: substrate, 12, 13: clad layer, 14: active layer, 15: DBR, 16: emitting end

Claims (2)

In an edge-emitting semiconductor laser having an active layer on a substrate and a cladding layer sandwiching the active layer,
The active layer has a DBR reflection layer on the output side, and a phase adjustment region in which no DBR reflection layer is formed is provided between the output end and the end of the DBR reflection layer on the output end side. A featured edge-emitting semiconductor laser.   2. The edge-emitting semiconductor laser according to claim 1, wherein the phase adjustment region has a length difference between the reflected light from the emitting end and the reflected light from the DBR of more than 90 ° and less than 270 °. A featured edge-emitting semiconductor laser.

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