阅读说明：本技术 一种集成有源布拉格反射器的单模太赫兹量子级联激光器 (Single-mode terahertz quantum cascade laser integrated with active Bragg reflector ) 是由 徐刚毅 何力 俞辰韧 朱欢 常高垒 朱海卿 王凯 白弘宙 王芳芳 陈建新 林春 于 2019-09-10 设计创作，主要内容包括：本发明公开了一种集成有源布拉格反射器的单模太赫兹量子级联激光器。本发明中,由解理形成的腔面和一阶光子晶体形成的布拉格反射器构成了一个谐振腔,靠近解理腔面一侧有若干个空气狭缝构成的耦合光栅。当解理腔面与布拉格反射器构成的谐振腔与有源光子晶体产生共振时,形成耦合腔,并且反射器对于该耦合模式提供一定的相位补偿以满足谐振腔的相位条件,该耦合模式通过光栅耦合器向自由空间辐射。通过调节耦合光栅的几何结构,可以控制激光器的辐射效率。该器件最大的优点是：该谐振腔结构能独立控制模式选择与辐射效率,器件的尺寸不再受到模式选择的限制。所获得的输出功率高,功率效率高,温度性能好,远场光斑发散角小。(The invention discloses a single-mode terahertz quantum cascade laser integrated with an active Bragg reflector. In the invention, a cavity surface formed by cleavage and a Bragg reflector formed by a first-order photonic crystal form a resonant cavity, and one side close to the cleavage cavity surface is provided with a coupling grating formed by a plurality of air slits. When the resonant cavity formed by the cleavage cavity surface and the Bragg reflector resonates with the active photonic crystal, a coupling cavity is formed, and the reflector provides certain phase compensation for the coupling mode to meet the phase condition of the resonant cavity, and the coupling mode radiates to a free space through the grating coupler. By adjusting the geometry of the coupling grating, the radiation efficiency of the laser can be controlled. The device has the following advantages: the resonant cavity structure can independently control mode selection and radiation efficiency, and the size of the device is not limited by the mode selection. The obtained output power is high, the power efficiency is high, the temperature performance is good, and the far-field light spot divergence angle is small.)

1. The utility model provides an integrated active Bragg reflector's single mode terahertz quantum cascade laser which characterized in that:

the single-mode terahertz quantum cascade laser integrated with the active Bragg reflector adopts a metal-metal waveguide structure, and the specific structure is as follows: the n-type doped GaAs substrate layer (1), the lower metal layer (2), the lower contact layer (3), the active region (4), the upper contact layer (5) and the upper metal layer (6) are arranged from bottom to top in sequence; one end of the laser is an active Bragg reflector region and an absorption boundary, the other end of the laser is a cleavage end face, and a surface emitting region is arranged between the cleavage end face and the Bragg reflector region;

the active Bragg reflector region adopts an active first-order photonic crystal structure; the first-order active photonic crystal is composed of an n-type doped GaAs substrate layer (1), a lower metal layer (2), a lower contact layer (3), an active region (4), an upper contact layer (5), an upper metal layer (6) and a photonic crystal (7) combined with the upper metal layer (6); the photonic crystal (7) is a parallel air slit periodically arranged on the upper metal layer (6) along the ridge waveguide direction or an air small hole periodically arranged along both the ridge waveguide direction and the vertical ridge waveguide direction, and the sum of the slit length or the diameter of the small hole along the vertical ridge waveguide direction is less than the two sides of the waveguide;

the absorption boundary is composed of an n-type doped GaAs substrate layer (1) which is not covered by an upper metal layer (6), a lower metal layer (2), a lower contact layer (3), an active region (4) and an upper contact layer (5);

the emitting surface emitting region is composed of an n-type doped GaAs substrate layer (1), a lower metal layer (2), a lower contact layer (3), an active region (4), an upper contact layer (5), an upper metal layer (6) and a coupling grating (8) combined with the upper metal layer (6); the coupling grating (8) is a parallel slit which is periodically arranged on the upper metal layer (6) along the ridge waveguide direction, and the length of the slit is less than the two sides of the waveguide;

the Bragg reflector has extremely high reflectivity for a mode meeting the Bragg condition, when a resonant cavity formed by the cleavage cavity surface and the Bragg reflector resonates with the active photonic crystal, a coupling cavity is formed, and the reflector provides certain phase compensation for the coupling mode to meet the phase condition of the resonant cavity, and the coupling mode radiates to a free space through the grating coupler.

2. The integrated active bragg reflector single-mode terahertz quantum cascade laser of claim 1, wherein: an air slit is arranged on the surface of the ridge waveguide to separate the active Bragg reflector region from the emitting surface emitting region, and the distance between the air slit and the Bragg reflector region is equal to the period of a first-order photonic crystal in the Bragg reflector region; the width of the air slit is equal to the width of the ridge waveguide; the air slits open both the upper metal layer (6) and the upper contact layer (5).

Technical Field

The invention belongs to the technical field of laser semiconductors, relates to a terahertz quantum cascade laser, and particularly relates to a single-mode terahertz quantum cascade laser integrated with an active Bragg reflector.

Background

The frequency of a terahertz (THz) Quantum Cascade Laser (QCL) covers 1-5THz, has the advantages of high energy conversion efficiency, small volume, easy integration and the like, and is a coherent light source with a very potential terahertz waveband. The single-mode high-power THz-QCL has important application prospects in the fields of material detection, spectral analysis, imaging, communication, gas analysis and the like. The device is required to have the performances of high working temperature, high output power, high conversion efficiency, single-mode spectrum, small far-field divergence angle and the like.

At present, THz-QCL has two basic waveguide structures, namely a single-sided metal waveguide structure and a double-sided metal waveguide structure. The THz-QCL of the single-sided metal waveguide has high output power but poor temperature performance. And the THz-QCL of the double-sided metal waveguide has higher working temperature due to smaller loss and mode limiting effect close to 1. The bimetallic waveguide THz-QCL is the focus of current research, since poor temperature performance is an intrinsic disadvantage of single-sided metallic waveguides THz-QCL. However, the double-sided metal waveguide structure has impedance mismatch of cavity surfaces due to the cavity surfaces with sub-wavelength scale, and the reflectivity is about 0.8, resulting in lower output power and a more divergent light beam.

Efforts are made to improve the output power and beam quality of double-sided metal waveguide single-mode THz-QCLs. The successful cases currently available include: three-level distributed feedback lasers, double-slit distributed feedback lasers, graded photon heterojunction lasers, hybrid grating lasers, two-dimensional photonic crystal lasers and the like. However, in the above scheme, both the output power and the mode selection are mutually restricted: the output power of the device is in direct proportion to the area of the device, so the area of the device is as large as possible; to obtain a stable single-mode output, the length of the device needs to be short, and a too long device introduces a high-order mode. Therefore, the device cavity length of the single-mode terahertz quantum cascade laser is limited.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a surface-emitting single-mode terahertz quantum cascade laser, which can maintain single-mode operation when increasing the cavity length of the laser by independently adjusting and controlling the mode selection and radiation efficiency, so as to realize surface emission of terahertz laser with high power, single mode, high operating temperature and small divergence angle.

To achieve the above and other related objects, the present invention provides an active bragg reflector integrated single-mode terahertz quantum cascade laser.

The single-mode terahertz quantum cascade laser integrated with the active Bragg reflector adopts a metal-metal waveguide structure, and the specific structure is as follows: the n-type doped GaAs substrate layer 1, the lower metal layer 2, the lower contact layer 3, the active region 4, the upper contact layer 5 and the upper metal layer 6 are arranged from bottom to top in sequence; one end of the laser is an active Bragg reflector region and an absorption boundary, the other end of the laser is a cleavage end face, and a surface emitting region is arranged between the cleavage end face and the Bragg reflector region;

the active Bragg reflector region adopts an active first-order photonic crystal structure; the first-order active photonic crystal is composed of an n-type doped GaAs substrate layer 1, a lower metal layer 2, a lower contact layer 3, an active region 4, an upper contact layer 5, an upper metal layer 6 and a photonic crystal 7 combined with the upper metal layer 6; the photonic crystal 7 is a parallel air slit periodically arranged on the upper metal layer 6 along the ridge waveguide direction or an air small hole periodically arranged along both the ridge waveguide direction and the vertical ridge waveguide direction, and the sum of the lengths of the slits or the diameters of the small holes along the vertical ridge waveguide direction is less than the two sides of the waveguide;

the absorption boundary is composed of an n-type doped GaAs substrate layer 1 which is not covered by an upper metal layer 6, a lower metal layer 2, a lower contact layer 3, an active region 4 and an upper contact layer 5;

the emitting surface emitting region consists of an n-type doped GaAs substrate layer 1, a lower metal layer 2, a lower contact layer 3, an active region 4, an upper contact layer 5, an upper metal layer 6 and a coupling grating 8 combined with the upper metal layer 6; the coupling grating 8 is a parallel slit periodically arranged on the upper metal layer 6 along the ridge waveguide direction, and the length of the slit is less than that of two sides of the waveguide;

the Bragg reflector has extremely high reflectivity for a mode meeting the Bragg condition, when a resonant cavity formed by the cleavage cavity surface and the Bragg reflector resonates with the active photonic crystal, a coupling cavity is formed, and the reflector provides certain phase compensation for the coupling mode to meet the phase condition of the resonant cavity, and the coupling mode radiates to a free space through the grating coupler.

An air slit is arranged on the surface of the ridge waveguide to separate the active Bragg reflector region from the emitting surface emitting region, and the distance between the air slit and the Bragg reflector region is equal to the period of a first-order photonic crystal in the Bragg reflector region; the width of the air slit is equal to the width of the ridge waveguide; the air slit cuts through both the upper metal layer 6 and the upper contact layer 5.

A manufacturing method of a single-mode terahertz quantum cascade laser integrated with an active Bragg reflector comprises the following steps:

step one, taking semi-insulating GaAs as a substrate, epitaxially growing a corrosion barrier layer, and epitaxially growing an upper contact layer 5 on the corrosion barrier layer; epitaxially growing an active region 4 on the upper contact layer; epitaxially growing a lower contact layer 3 on the active region, and then evaporating a lower metal layer 2 on the lower contact layer by electron beams; thus, a substrate is formed;

step two, evaporating a Ti/Au film on the surface of the other heavily doped n-type GaAs substrate 1 by an electron beam to form another substrate;

step three, the metal surfaces of the two substrates are opposite and bonded together;

polishing the semi-insulating GaAs substrate until the semi-insulating GaAs substrate is away from the corrosion barrier layer by a preset distance, then corroding the semi-insulating GaAs substrate to the corrosion barrier layer by adopting wet corrosion, and removing the corrosion barrier layer by using HF acid; then using wet etching to thin the upper contact layer to a set thickness; photoetching an absorption boundary on the upper contact layer by using a photoetching technology; then using wet etching to thin the upper contact layer and the active region to a set thickness; photoetching small holes or slits on the active region layer and part of the upper contact layer by utilizing a photoetching technology; evaporating a metal layer on the active region layer and part of the upper contact layer by adopting a stripping technology, and forming air pores or slits on the upper metal layer to form a first-order photonic crystal 7 and a coupling grating 8 which are used as a Bragg reflector region and a surface emitting region; then, photoetching a waveguide structure and an absorption boundary on the active region and part of the upper contact layer by utilizing a photoetching technology; etching to the lower metal layer to form a ridge waveguide; the cavity surface of the ridge waveguide close to the surface emitting region is a cleavage end surface.

As described above, the single-mode terahertz quantum cascade laser integrated with the active bragg reflector and the manufacturing method thereof according to the present invention have the following beneficial effects:

the terahertz laser surface emission with high power, single mode, high working temperature and small divergence angle of the terahertz quantum cascade laser is realized, wherein the mode selection is determined by the gain peak value of the active Bragg reflector and the active area material, the radiation efficiency is determined by the surface emission area, the length of the device has no influence on the mode selection in a certain range, the area of the device is greatly increased, and the output power is improved; on the other hand, the grating area of the surface emitting region is larger, and the beam quality can be improved.

Description of the drawings:

fig. 1 is a schematic structural diagram of an active bragg reflector integrated single-mode terahertz quantum cascade laser with a bragg reflector composed of a first-order two-dimensional photonic crystal according to the present invention.

FIG. 2 is a schematic structural diagram of an active Bragg reflector integrated single-mode terahertz quantum cascade laser with a Bragg reflector composed of a first-order grating according to the present invention

FIG. 3 is a schematic structural diagram of an active Bragg reflector integrated single-mode terahertz quantum cascade laser with a Bragg reflector and a surface emitting region separated by an air slit according to the present invention

Description of the element reference numerals

1. Heavily doped n-type GaAs substrate;

2. a lower metal layer;

3. a lower contact layer;

4. an active region;

5. an upper contact layer;

6. an upper metal layer;

7. a photonic crystal;

8. a coupling grating;

9. air slit

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

Please refer to the attached drawings. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.

In view of the problems of the waveguide of the single-mode terahertz quantum cascade laser, the invention provides the single-mode terahertz quantum cascade laser integrated with the active Bragg reflector, which is expected to have the performances of single-mode output, high output power, small far-field divergence angle and the like, starting from a waveguide structure and integrating the advantages of a plurality of concepts, wherein one side of the single-mode terahertz quantum cascade laser is a Bragg reflector region waveguide sensitive to frequency, the other side of the single-mode terahertz quantum cascade laser is a cleavage end surface, and a surface emitting region waveguide is arranged between the cleavage end surface and the Bragg reflector region waveguide; the Bragg reflector has extremely high reflectivity for a mode meeting the Bragg condition, a coupling cavity is formed when a resonant cavity formed by the cleavage cavity surface and the Bragg reflector and the active photonic crystal resonate, and the reflector provides certain phase compensation for the coupling mode so as to meet the phase condition of the resonant cavity, and the coupling mode radiates to a free space through the grating coupler.

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.