CN109638640B

CN109638640B - Semiconductor laser device

Info

Publication number: CN109638640B
Application number: CN201910015103.8A
Authority: CN
Inventors: 林宏翔; 刘佟; 崔晗; 蔡昭权; 魏晓慧
Original assignee: Huizhou University
Current assignee: HUIZHOU ZHONGBANG ELECTRONICS Co.,Ltd.
Priority date: 2019-01-08
Filing date: 2019-01-08
Publication date: 2020-08-14
Anticipated expiration: 2039-01-08
Also published as: CN109638640A

Abstract

The invention relates to a semiconductor laser, which defines an XYZ space rectangular coordinate system, and then the semiconductor laser comprises: electrodes located forward and rearward in the Z-axis direction; an active region for generating laser light when the electrode is energized; the waveguide layers are positioned in front of and behind the active layer in the Z-axis direction and positioned on the periphery side of the active region; and reflection layers located in front and rear of the waveguide layer in the Y-axis direction, the laser emission port of the semiconductor laser being formed on the reflection layer located in front in the Y-axis direction. And a Brewster window for screening out laser with the polarization direction parallel to the X-axis direction is further formed in at least one of the front and the back of the Y-axis direction of the active region. The semiconductor laser can directly output linear polarization laser without adding an optical device externally, has a simple structure, and can be used as a laser and applied to a dielectric laser accelerator.

Description

Semiconductor laser device

Technical Field

The invention relates to a laser, in particular to a semiconductor laser.

Background

Semiconductor lasers are widely used in various fields of science and technology and life, and are devices which generate laser by using certain semiconductor materials as working substances. The operating principle is that the population inversion of the non-equilibrium carriers is realized between the energy bands (conduction band and valence band) of the semiconductor substance or between the energy bands of the semiconductor substance and the energy levels of the impurities (acceptor or donor) by a certain excitation mode, and when a large number of electrons in the population inversion state are recombined with holes, the stimulated emission action is generated. The excitation modes of semiconductor lasers are mainly three, namely, an injection mode, an optical pump mode and a high-energy electron beam excitation mode. An electric injection type semiconductor laser is generally a semiconductor junction diode made of materials such as gallium arsenide (GaAs), cadmium sulfide (CdS), indium phosphide (InP), zinc sulfide (ZnS), and the like, and is excited by injecting current along a forward bias to generate stimulated emission in a junction plane region. In many fields such as fiber optic gyroscope, fiber optic sensing, nonlinear frequency conversion, coherent light beam combination and the like, stable polarization characteristics of output laser are required to be kept, so that the research on a semiconductor laser with single polarization output characteristics and a certain extinction ratio has very important significance. At present, the conventional method is to add a polarizing device outside the laser, for example, a polarizing plate, a nicol prism, etc. to screen out single-polarization laser in laser with any polarization state output by the laser, which has a complex structure and a large light loss.

Disclosure of Invention

The invention aims to provide a semiconductor laser with a simple structure.

A semiconductor laser, defining an XYZ rectangular coordinate system, comprising: electrodes located forward and rearward in the Z-axis direction; an active region located between the electrodes for generating laser light when the electrodes are energized, a major extension plane of the active region being parallel to a plane defined by the XY axes; the waveguide layers are positioned in front of and behind the active layer in the Z-axis direction and positioned on the periphery side of the active region; and reflection layers located in front and rear of the waveguide layer in the Y-axis direction, the laser emission port of the semiconductor laser being formed on the reflection layer located in front in the Y-axis direction. And a Brewster window for screening out laser with the polarization direction parallel to the X-axis direction is further formed in at least one of the front and the back of the Y-axis direction of the active region.

Preferably, the brewster window is formed by etching on the semiconductor material, and when the brewster angle is defined as theta, the inclination angle of the brewster window relative to the Y axis is theta or pi-theta, and the relation between the brewster angle theta and the vacuum refractive index n2 and the refractive index n1 of the semiconductor material is

。

Preferably, the equivalent width of the vacuum in the Brewster window in the Y-axis direction is defined as D ', the equivalent width of the medium in the laser resonant cavity in the Y-axis direction is defined as L', and the laser wavelength is defined as lambda, then

And m is a positive integer.

Preferably, the width of the single-layer vacuum area in the Brewster window is 50um-100 um.

In one embodiment, the active region and the semiconductor material forming the brewster window comprise InGaAsP semiconductor material.

In one embodiment, brewster windows for screening out laser beams having polarization directions parallel to the X-axis direction are formed in front of and behind the Y-axis direction of the active region.

In one embodiment, the semiconductor laser is a distributed bragg reflector laser, the brewster window is located between the active region and the distributed bragg reflector region and between the insulating layer and the substrate layer in the Z-axis direction, and the width in the Z-axis direction is 50um to 100 um.

The semiconductor laser can directly output linear polarization laser without adding an optical device externally, has a simple structure, and can be used as a laser and applied to a dielectric laser accelerator.

Drawings

Fig. 1 is a front sectional view of a semiconductor laser according to an embodiment.

Fig. 2 is a top cut-away view of a portion of a semiconductor laser of an embodiment.

Fig. 3 is a schematic perspective view of a portion of a semiconductor laser according to an embodiment.

FIG. 4 is a schematic diagram of the path of polarized light in a Brewster window.

Fig. 5 is a front sectional view of a semiconductor laser according to another embodiment.

Detailed Description

The semiconductor laser device of the present invention will be described in further detail with reference to the following embodiments and the accompanying drawings.

For convenience of description, an XYZ rectangular coordinate system is defined, and the laser emission direction of the semiconductor laser is directed forward in the Z-axis direction and parallel to the Z-axis. In the first embodiment, as shown in fig. 1 to 3, the semiconductor laser 100 of the present invention includes at least electrodes 20 respectively disposed in front and rear in the Z-axis direction, an active region 30 disposed between the electrodes 20, a waveguide layer 40 disposed around the active region 30, and a reflecting layer 60 disposed in front of and behind the waveguide layer 40 in the Y-axis direction. The laser light exit is located on the reflective layer 60 in front in the Y-axis direction. To facilitate the distinction of the various portions of the semiconductor laser 100, fig. 3 shows a perspective view of the layer 30 in which the active region of the semiconductor laser 100 is located and the waveguide layer 40 in which the active region is forward and rearward in the Z-axis direction, omitting the electrode 20, the reflective layer 60, and the brewster window 44 located within the waveguide layer 40, in a particular embodiment, the active region is located only at a central location of the layer 30, surrounded by waveguide material at its periphery; only a cross-sectional view of the semiconductor laser 100 taken along a plane defined in fig. 3 parallel to the YZ axis is shown in fig. 1, with only the active region 30, the reflective layer 60, and the brewster window 44 cross-sectional lines omitted, and the electrode 20 and waveguide layer 40 cross-sectional lines omitted, to avoid viewing too much of the cross-sectional lines; a cross-sectional view of waveguide layer 40 of semiconductor laser 100 located forward in the Z-axis direction along a plane parallel to the plane defined by the XY-axes in fig. 3 is shown in fig. 2. It will be appreciated that the semiconductor laser 100 should include a housing with components inside the housing and the interior of the housing preferably being in a vacuum.

Wherein the main extension plane of the active region 30 is parallel to the plane defined by the XY-axis, in the present embodiment, the active region 30 is entirely made of a semiconductor material for generating laser light when the electrodes are energized, such as, but not limited to, InGaAsP (indium gallium arsenic phosphide) semiconductor material. In the present embodiment, the active region 30 and the waveguide layer 40 are formed in a rectangular parallelepiped structure having six planes parallel to planes defined by the XY axis, the YZ axis, and the XZ axis, respectively. The reflecting layer 60 is attached to two faces of the cuboid structure in the Y-axis direction, so that the radiation laser generated by the active region is coupled into the waveguide layer at a certain coupling ratio, reflected by the reflecting layer and returned to form an optical resonant cavity. The electrodes 20 may each have one or more metal layers, which may include, for example, but not limited to, alloys made of one or more of Ag, Au, Sn, Ti, Pt, Pd, Rh, and Ni. The reflective layer 60 may comprise a high reflectivity film or be a high reflectivity coating such as, but not limited to, a metal layer having a bragg mirror layer sequence or reflectivity.

It will be appreciated that other functional layers may also be included between the waveguide layer and the electrodes, such as, but not limited to, passivation layers, insulating layers, growth substrates, and the like.

The present invention forms brewster windows 44 for screening out laser light having a polarization direction parallel to the X-axis direction in front of and behind the Y-axis direction of the active region 30. In this embodiment, brewster window 44 is formed by etching in the semiconductor material. In one embodiment, two semiconductor material regions tilted with respect to the Y-axis and located within waveguide layer 40 and separated from active region 30 may be grown on the semiconductor material of the active region, and then etched to form brewster window 44. Preferably, the width of the single-layer vacuum region in the brewster window in the Y-axis direction is 50um-100um, which is much larger than the laser wavelength, and belongs to the field of geometrical optics, and the brewster window size in the figure is a schematic diagram.

Defining the Brewster's angle as theta, the tilt angle of the Brewster's window 44 with respect to the Y-axis is either theta (the angle between the Brewster's window 44 located forward in the Y-axis direction in FIG. 2 and the Y-axis) or pi-theta (the angle between the Brewster's window 44 located rearward in the Y-axis direction in FIG. 2 and the Y-axis), and the Brewster's angle theta and the vacuum refractive index n are equal to theta₂And refractive index n of semiconductor material₁In a relationship of

. Defining the width of the brewster window 44 in the Y-axis direction as D, the equivalent width of the vacuum in the brewster window 44 in the Y-axis direction as D ', the equivalent width of the medium in the brewster window 44 in the Y-axis direction as D, the equivalent width of the medium in the laser resonator in the Y-axis direction as L ', then L ' = 2L 1 ' + L2 ' +2 ' + D, D = D ' + D, the laser wavelength is λ, then L ' = L1 ' + L2 ' +2 ' + D

And m is a positive integer.

Taking InGaAsP as an example of a semiconductor material, the refractive index n₁=3.5, trueRefractive index n of void₂=1, brewster's angle θ can be calculated, i.e., the following equation is satisfied

，

Then 15.94 ° and 164.16 ° are the tilt angles required for etching.

According to the stimulated radiation mechanism, because the laser passes through the Brewster window and then the line bias laser, the generated laser is also the line bias laser when the laser passes through the gain medium of the active region again. The laser thus travels back and forth in the cavity formed with the brewster window 44 and the laser is screened for a polarization direction parallel to the X-axis. As shown in fig. 4, the laser traverses the cavity formed to meet the brewster angle condition each time the vacuum enters the medium in the brewster window 44, so that the s-polarized light is reflected and the reflected light deviates from the central axis path and cannot be gained, gradually attenuating. The single refracted light still contains s-polarization, but the refracted light rapidly reduces the s-polarization component after passing through the Brewster window for multiple times in the single round trip process, and finally achieves good p-polarization. Therefore, high-energy electrons in the semiconductor active region are irradiated by linearly polarized laser light, and the laser light after gain has the same polarization direction. Although the laser still contains a small part of s polarization, the quantity of the s polarization is greatly different from the p direction, the electron acceleration is not influenced, and the same acceleration field and the same electron movement direction can be realized, namely the accelerated laser is linear polarization laser.

In one embodiment, the semiconductor material is selected to be InGaAsP,

in summary, the electrodes 20 and the active region 30, the waveguide layer 40, the reflection layer 60 and possibly further functional layers between the electrodes 20 form a semiconductor laser. The active region realizes population inversion under the action of external excitation current to achieve the basic laser gain condition, and laser generated by the active region is coupled into the waveguide layer with a certain coupling coefficient. According to the invention, the Brewster window is arranged on the waveguide layer, so that the laser in the resonant cavity achieves good linear polarization characteristic, and an external optical polarizer is omitted.

In the above embodiments, InGaAsP is used as the semiconductor material, and it is understood that other semiconductor materials used for lasers may be used.

In the above embodiments, the shape of the laser is a cuboid as a whole, and it is understood that the shape of the semiconductor laser may be changed in various ways, for example, in other embodiments, the front end and the rear end of the semiconductor laser in the Y-axis direction may be arc-shaped protrusions or hemispheres, and in still other embodiments, the front end and the rear end of the semiconductor laser in the Z-axis direction may be stepped or substantially triangular or trapezoidal.

In the above embodiments, the brewster windows are symmetrically disposed with respect to the active region, and in other embodiments, the brewster windows on both sides of the active region may have different equivalent widths in the Y-axis direction.

In the above embodiments, both sides of the active region are provided with gratings, and in other embodiments, only one side may be provided with gratings.

For example, in a second embodiment as shown in fig. 5, a Distributed Bragg Reflector (DBR) laser 200 may be divided into a DBR region 70, a brewster window region 80 and an active region 90 from the rear to the front in the Y-axis direction, and overall has a rectangular parallelepiped structure with six sides parallel to planes defined by the XY-axis, the YZ-axis and the XZ-axis, respectively. The reflective layer 60' is attached on both faces of the rectangular parallelepiped structure in the Y-axis direction. Wherein a bragg grating 71 acting as a mirror is located in the DBR region 70. A brewster window 44' is formed in brewster window region 80, i.e., on the side of active region 90, for screening out laser light having a polarization direction parallel to the X-axis direction. Brewster window 44' is to be located between the insulating layer and the substrate layer in the Z-axis direction and has a width in the Z-axis direction of 50um to 100 um. A reflective layer in the active region 90, in which the active gain semiconductor substance 30 'is located between the waveguide materials 40' in the Z-axis direction and the laser light emitting port is located forward in the Y-axis direction60' of the main body. The main extension plane of the semiconductor substance 30' is parallel to the plane defined by the XY-axes. In this embodiment, where the Brewster's angle is defined as θ, the angle at which the Brewster's window 44 'is tilted with respect to the Y-axis is also the same as that of the first embodiment, the Brewster's angle θ being the same as the vacuum refractive index n₂And refractive index n of semiconductor material₁In a relationship of

. The relationship between the dimensions of the brewster window 44' and the dimensions of the medium in the laser cavity is the same as in the first embodiment and will not be described further.

The laser 200 can also perform a similar function to that of the first embodiment, so that the laser light inside the cavity can achieve a good linear polarization characteristic.

While the invention has been described in conjunction with the specific embodiments set forth above, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and scope of the appended claims.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

Claims

1. A semiconductor laser defining an XYZ rectangular coordinate system, comprising:

electrodes located forward and rearward in the Z-axis direction;

an active region located between the electrodes for generating laser light when the electrodes are energized, a major extension plane of the active region being parallel to a plane defined by the XY axes;

the waveguide layers are positioned in front of and behind the active layer in the Z-axis direction and positioned on the periphery side of the active region; and

reflection layers positioned in front and rear of the waveguide layer in the Y-axis direction, the laser emission port of the semiconductor laser being formed on the reflection layer positioned in front in the Y-axis direction;

the Brewster window used for screening out the laser with the polarization direction parallel to the X-axis direction is further formed in at least one of the front and the back of the Y-axis direction of the active region;

the Brewster window is formed by etching on a semiconductor material, the Brewster angle is defined as theta, the inclination angle of the Brewster window relative to the Y axis is theta or pi-theta, and the Brewster angle theta and the vacuum refractive index n₂And refractive index n of semiconductor material₁In a relationship of

。

2. A semiconductor laser as claimed in claim 1 wherein, defining an equivalent width of the vacuum in the brewster window in the Y-axis direction as D ', an equivalent width of the medium in the laser cavity in the Y-axis direction as L', and a laser wavelength as λ, then

And m is a positive integer.

3. A semiconductor laser as claimed in claim 1 wherein the width of the monolayer vacuum region in the brewster window is between 50um and 100 um.

4. A semiconductor laser as claimed in claim 2 wherein the active region and the semiconductor material forming the brewster window comprises InGaAsP semiconductor material.

5. A semiconductor laser as claimed in claim 2 wherein the active region is formed with brewster windows both in front of and behind the Y-axis direction for screening out laser light having a polarization direction parallel to the X-axis direction.

6. A semiconductor laser as claimed in claim 2 which is a distributed bragg reflector laser, wherein the brewster window is located between the active region and the distributed bragg reflector region and between the insulating layer and the substrate layer in the Z-axis direction, and has a width in the Z-axis direction of 50um to 100 um.