CN111416277B

CN111416277B - Multipole quantum cascade ring laser

Info

Publication number: CN111416277B
Application number: CN202010125064.XA
Authority: CN
Inventors: 王卓然; 张鹏年; 袁国慧; 林志远
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2020-02-27
Filing date: 2020-02-27
Publication date: 2021-07-20
Anticipated expiration: 2040-02-27
Also published as: CN111416277A

Abstract

The invention discloses a multi-pole quantum cascade ring laser, which comprises a substrate, a collector, a quantum cascade structure layer, a quantum energy level matching layer, a base and an emitter which are sequentially arranged from bottom to top, wherein the emitter and the base are arranged in a step shape, and the quantum cascade structure layer and the collector are arranged in a step shape; the laser also comprises a collector electrode arranged on the top of the collector or below the substrate, a base electrode arranged on the top of the base electrode, and an emitter electrode arranged on the top of the emitter. And the laser is also etched with a ring waveguide and a strip-shaped straight waveguide coupled with the ring waveguide. The multi-pole quantum cascade ring laser is simple in design, good in tunable characteristic, capable of outputting multi-wavelength or wide-spectrum or chaotic laser or frequency comb, and capable of effectively reducing application cost of mid-infrared and terahertz sources in wide mid-infrared and terahertz applications.

Description

Multipole quantum cascade ring laser

Technical Field

The invention belongs to the technical field of semiconductor lasers, and particularly relates to a multi-pole quantum cascade ring laser.

Background

Compared with a carrier conduction band-valence band stimulated radiation transfer mechanism of a traditional Quantum well laser, a Quantum Cascade Laser (QCLs) can directly generate mid-infrared and terahertz waveband outputs due to the unique carrier conduction band intra-valence band transfer Cascade mechanism. Compared with the existing generation methods of mid-infrared and terahertz outputs, such as a photoconductive mixing method, a semiconductor built-in electric field method, an optical rectification method, an electro-optical sampling method and the like, the mid-infrared and terahertz output structure based on the QCLs has the advantages of high conversion efficiency, simple cavity structure, good on-chip integratability and the like, and is widely applied to various civil and military applications including DNA detection, biological tissue imaging, non-contact testing, public safety monitoring, gas component detection, THz wireless communication and the like. In order to improve the versatility of QCLs in different applications and reduce the application cost, it is required that the mid-infrared or terahertz output of QCLs has a good tunable characteristic, or has a multi-wavelength or wide-spectrum output characteristic.

In order to improve the tunable characteristics of QCLs, the methods adopted at present mainly include: an external cavity grating tuning method, a strong magnetic field method, a distributed feedback structure method, a Sampled Grating Reflector (SGR) method, and the like. However, these methods are too complicated, have low stability and high energy consumption, and are not suitable for the application of low-power-consumption and miniaturized on-chip integration in the future.

In order to obtain infrared or terahertz output in multi-wavelength or wide-spectrum QCLs, the current main method is to design an active region of a quantum cascade structure of the QCLs, so that energy states of an upper sub-band and a lower sub-band of the active region are transferred to a single energy state, a double energy state, a single energy state, a continuous state, a multi-core and multi-stack QCL structure and the like.

Under the condition of a certain external light injection signal, the laser can generate noise-like wide-spectrum random output with the intensity, frequency and phase changing rapidly in a limited interval, namely chaotic laser. In recent years, chaotic laser has been widely researched and applied in fields of secure optical communication, laser ranging, optical fiber breakpoint detection and the like.

The frequency comb is coherent radiation generated by a laser light source, the spectrum of the frequency comb is composed of a plurality of modes which are completely equidistant and have definite phase relation, and the frequency comb is widely applied to the fields of nano-scale distance measurement, femtosecond time-frequency transfer, accurate measurement of physical quantity and the like. At present, the application of the frequency comb gradually extends from a far ultraviolet band to a middle infrared band and a terahertz band. In the middle infrared band, the frequency comb can be widely applied to the fields of environment perception, gas component detection and the like; in the terahertz waveband, the frequency comb can also be used for the aspects of noninvasive imaging, wireless communication, public safety monitoring and the like. The frequency comb has great application value in a plurality of military and civil applications.

At present, aiming at the application in the fields of wide mid-infrared and terahertz, a quantum cascade structure which is simple in design, good in tunable characteristic and capable of outputting multi-wavelength or wide-spectrum or frequency comb or chaotic laser and a device applied by the quantum cascade structure are lacked.

Disclosure of Invention

The invention aims to solve the problems and provides a multipole quantum cascade ring laser which is simple in design, good in tunable characteristic, capable of outputting multi-wavelength or wide-spectrum or chaotic laser or frequency comb, and capable of effectively reducing the application cost of mid-infrared and terahertz sources in wide mid-infrared and terahertz applications.

In order to solve the technical problems, the technical scheme of the invention is as follows: a multi-pole quantum cascade ring laser comprises a substrate, a collector, a quantum cascade structure layer, a quantum energy level matching layer, a base and an emitter which are sequentially arranged from bottom to top, wherein the collector and the quantum cascade structure layer, and the base and the emitter are arranged in a step shape;

the multi-pole quantum cascade ring laser also comprises a collector electrode arranged on the top of the collector or below the substrate, a base electrode arranged on the top of the base electrode, and an emitter electrode arranged on the top of the emitter;

the laser is also etched with an annular waveguide and a bar-shaped straight waveguide coupled with the annular waveguide, the etching depths of the annular waveguide and the bar-shaped straight waveguide are any depths from the top of the emitter to the top of the base, the top of the quantum energy level matching layer, the top of the quantum level connection structure layer or the top of the collector, wherein at least one side of the annular waveguide in the circular area or outside the circular area has the etching depth only from the top of the emitter to the top of the base, and the bar-shaped straight waveguide comprises an input section and a coupling section;

the quantum cascade structure layer is formed by two at least QCL stack unit series connection stacks that the structure is the same, QCL stack unit includes the QCL subelement that two at least structures are the same, every QCL subelement comprises active area and injection region, the injection region includes a plurality of sections doping area, it is different to have the doping concentration parameter in one section doping area at least between the different kind QCL subelement.

The quantum level junction structure layer comprises N QCL stack units: the first QCL stack unit AB, the ith QCL stack unit AB and the Nth QCL stack unit AB, or the first QCL stack unit ABB, the ith QCL stack unit ABB and the Nth QCL stack unit ABB, wherein i and N are integers which are larger than 1, and i is not larger than N.

It should be noted that the structural composition of the ring waveguide and the bar-shaped straight waveguide may be controlled by controlling the corresponding etching depth, and the ring waveguide and the bar-shaped straight waveguide may be etched only from the top of the emitter to the top of the base, that is, the ring waveguide and the bar-shaped straight waveguide structure only include the emitter, or the ring waveguide and the bar-shaped straight waveguide may be etched from the top of the emitter to the top of the base, the top of the quantum level matching layer, the top of the quantum level connection structure layer, or the top of the collector, or the ring waveguide and the bar-shaped straight waveguide structure may include the emitter, the base, the quantum level matching layer, and the quantum level connection structure layer. In particular, in order to maintain the characteristics of the three-terminal transistor, it is necessary to etch at least one of the two regions inside the circular region of the annular waveguide or outside the circular region only to the top of the base region.

Furthermore, the waveguide structure only comprises an emitter type, the cavity structure of the quantum cascade structure layer of the device is mainly an F-P type, and the annular waveguide structure can finely adjust the mode distribution and the traveling wave mode in the F-P cavity of the device. When the ring waveguide structure comprises an emitter, a base, a quantum energy level matching layer and a quantum level connection structure layer, the resonant cavity structure of the quantum level connection structure layer of the whole device is completely changed into a ring resonant cavity, and the mode distribution and the traveling wave mode are completely distributed according to the device characteristics of the ring resonant cavity. That is to say, the etching depth determines the cavity resonance characteristic of the device, and as the etching depth increases, the cavity resonance gradually changes from the F-P type resonance conversion characteristic to the ring resonant cavity resonance characteristic.

The multipole quantum cascade ring laser adopting the ring waveguide structure can obtain a cascade enhanced four-wave mixing effect by utilizing strong third-order nonlinearity of the ring structure, and is very favorable for locking the uniformity and the relative phase of different tooth comb mode intervals of an output frequency comb, thereby generating the frequency comb with excellent performance. In addition, the traveling wave mode of the ring waveguide structure laser can avoid the spatial hole burning effect caused by the standing wave mode of the laser with the common Fabry-Perot (F-P) structure, and the characteristics of the obtained high-performance frequency comb can be further stabilized and improved.

In the above technical solution, preferably, each QCL subunit has only one segment of doped region, and doping concentration parameters of the doped regions between different QCL subunits are different. Preferably, at least one of the QCL sub-units comprises two or more doped regions, and at least one doped region exists in the QCL sub-unit, and the doping concentration parameter of the doped region is different from the doping concentration parameters of the doped regions in other segments. Further preferably, each QCL stack unit structure only includes two QCL subunits, each QCL subunit has only one doped region, and the doping concentration parameters of the doped regions of the two QCL subunits are different. More preferably, each QCL stack unit structure only includes two QCL subunits, each QCL subunit only includes two doping regions with different doping concentration parameters, and the doping concentration parameter of at least one doping region between the two QCL subunits is different from the doping concentration parameter of the other doping regions.

It should be noted that the doping concentration parameter of each doped region is unique, i.e., there are no two doping concentration parameters in the same doped region. In addition, for comparison, the same doped region in the same segment may be further subdivided into a plurality of segments, except that the doping concentrations of the subdivided segments are the same. In addition, different QCL subunits only have different doping concentration parameters, and other parameters including layer thickness sequence, layer material composition sequence and layer doping position of the subunit structure are all the same.

In the above technical solution, the active region of the QCL subunit adopts a U-L state transfer design, the U state and the L state are any one of a single energy state, a multiple energy state or a continuous state, and the multiple energy state includes at least two energy states. The working or lasing wavelength corresponding to the active region of the QCL subunit is in the mid-infrared or terahertz waveband.

It should be noted that the quantum level connection structure layer in the present invention can also be applied to the existing periodic sub-unit structure with the active region for mid-infrared and terahertz output, that is, the QCL sub-unit structure is not limited to the structure provided by the present invention, and the existing periodic sub-unit that is designed and can work can be used as the middle "QCL sub-unit" of the quantum cascade structure layer in the present invention, and is configured into a corresponding quantum cascade structure layer. Under the guidance of the idea of the invention, quantum cascade structure layers constructed by adopting other existing periodic substructure units are all within the protection scope of the invention.

In the above technical solution, the multi-pole quantum cascade ring laser is a multi-pole device in which a QCL stack unit is used as an active region, and the "multi-pole" refers to a plurality of end-face electrodes perpendicular to a growth direction of a quantum level junction structure layer, and the multi-pole structure at least includes three types of electrode structures of an emitter, a base, and a collector.

In the above technical solution, for the structure of the multi-pole quantum cascade ring laser with a common collector, it is preferable that the ring waveguide and the base are provided with a plurality of insulating layers, so that the laser becomes a multi-stage control type multi-pole quantum cascade ring laser having a plurality of stages of control subunits.

In the above technical solution, the multi-pole quantum cascade ring laser is used as a subunit to form a multi-stage control type multi-pole quantum cascade ring laser, and collector electrodes, base electrodes and emitter electrodes of adjacent subunits are insulated from each other.

Furthermore, at least one collector electrode, at least one base electrode and at least one emitter electrode are arranged in the multi-pole quantum cascade ring laser. On the same control segment structure, a plurality of electrodes of the same type can exist, a collector electrode can be respectively grown on the left side and the right side of the quantum level connection structure layer on the top of the collector layer, and although the spatial positions of the two collector electrodes are different, the roles in the device are the same, and the two collector electrodes can be classified into the electrodes of the type of 'collector electrodes'. Likewise, if the spatial position allows, a base electrode may also be grown on top of the base layer on each of the left and right sides of the emitter layer, both base electrodes being classified as "base electrodes".

In the multi-stage control type multi-pole quantum cascade ring laser, each stage of the multi-stage control type multi-pole quantum cascade ring laser at least comprises three electrode structures of an emitter, a base and a collector. In particular, base-emitter bias (V)_be) Controlling the current density, base-collector bias voltage (V), of the quantum cascade structure layer injected into the control section_bc) And controlling the device bias voltage of the quantum cascade structure layer in the control section. Each electrode in each type of electrode structure can be controlled by an independent section voltage, the value of the independent section voltage can be any one of positive voltage, zero voltage and negative voltage, all the independent section voltages can be combined differently according to different values, and the output characteristics of the output of the multi-section quantum cascade structure layer in a time domain or a wavelength domain are controlled according to different independent section voltage combinations. The multi-stage control structure is mainly used for respectively controlling the working output of each sub-unit, and further combines the characteristics of the laser to develop corresponding applications, such as frequency comb, ultrafast mode locking, optical switch characteristics and the like.

In the above solution, the applied V_beAnd said V_bcUnder the bias combination of devices, at least one of the QCL subcells in each QCL stack unit can work or lase. Further preferably, said V is applied_beAnd said V_bcUnder the bias combination of the device, at least two QCL stack units can work or radiate, and at least one QCL subunit in each work or radiate QCL stack unit can work or radiate.

In the above solution, the applied V is specified_beAnd said V_bcUnder the bias combination of devices, at least one of the QCL subcells in each QCL stack unit can work or lase. Further preferably, the V applied is specified_beAnd said V_bcAt least two QCL stack units can work or lase simultaneously under the bias combination of devicesAnd at least one QCL subunit in each working or lasing QCL stack unit can work or lase.

In the above technical solution, the applied V_beAnd said V_bcWhen the device bias combination is changed, at least one QCL subunit in each QCL stack unit can work or lase. Further preferably, said V is applied_beAnd said V_bcWhen the bias combination of the device is changed, at least two QCL stack units can work or radiate simultaneously, and at least one QCL subunit in each work or radiate QCL stack unit can work or radiate.

In the above technical solution, the applied V_beAnd said V_bcWhen the device bias voltage combination is changed, at least one QCL subunit in each QCL stack unit can work or lase, and the working or lasing output wavelength is changed along with the change of the applied device bias voltage. Preferably, said V is applied_beAnd said V_bcWhen the bias combination of the device is changed, at least two QCL stack units can work or radiate simultaneously, at least one QCL subunit in each work or radiate QCL stack unit can work or radiate, and the output wavelength of the work or radiate is along with the applied V_beAnd said V_bcThe change in the combination of device biases changes. Further preferably, the V applied_beAnd said V_bcWhen the bias combination of the devices is changed, at least two QCL subunits in each QCL stack unit can work or radiate simultaneously, and the output wavelength of the work or the radiation is along with the applied V_beAnd said V_bcThe change in the combination of device biases changes. More preferably, said V is applied_beAnd said V_bcWhen the bias combination of the device is changed, at least two QCL stack units can work or radiate simultaneously, at least two QCL subunits in each working or radiating QCL stack unit can work or radiate simultaneously, and the working or radiating output wavelength is along with the applied V_beAnd said V_bcChanges in the combination of device biases.

The working or lasing outputs are superimposed into a multi-wavelength output or a broad spectrum output or a frequency comb output. Further, the working or lasing outputs are superimposed into a multi-wavelength output or a wide-spectrum output or a frequency comb output, which is dependent on the applied V_beAnd said V_bcThe device bias combination changes.

In the above technical solution, when an external optical signal is injected into the input section of the bar-shaped straight waveguide, the external injection signal can interact with a signal in the ring waveguide structure through the coupling section of the bar-shaped straight waveguide, so as to affect phase or mode locking of the signal in the ring waveguide structure, thereby changing the output characteristic of the multi-pole quantum cascade ring laser. In particular, the injected external optical signal enables the multi-pole quantum cascade ring laser to form chaotic laser capable of generating noise-like wide-spectrum random output with intensity, frequency and phase rapidly changing in a limited interval in the wavelength range of the tunable multi-wavelength output or wide-spectrum output, and the chaotic laser output is changed along with the injected external optical signal or along with the applied V_beAnd said V_bcThe change in the combination of device biases changes.

The multipole quantum cascade ring laser provided by the invention has the following beneficial effects:

1. according to the quantum cascade structure in the multipole type quantum cascade ring laser, at least two QCL stack units are stacked in series, and at least two QCL subunits with different doping concentration parameters contained in each QCL stack unit or at least one QCL subunit contained in each QCL stack unit works or radiates on different wavelengths, so that the output spectrum window of an applied device is enlarged;

2. the quantum-level connection structure layer in the multi-pole quantum cascade ring laser can also be applied to the existing periodic subunit structure with an active region for middle infrared and terahertz output, the structural design of a device can be effectively simplified, and the scheme universality is high;

3. when the multi-pole quantum cascade ring laser is appliedPlus said V_beAnd said V_bcThe spectral output obtained may be dependent on the applied V when the device bias combination is varied_beAnd said V_bcThe device bias combination changes, or when the device is at said applied V_beAnd said V_bcWhen the device is biased under the bias combination, the frequency spectrum output is stable;

4. the multipole quantum cascade ring laser can be further applied to the application of time domain or frequency domain spectral characteristics of QCLs, such as the application fields of optical frequency comb output, mid-infrared chaotic laser output, mode-locked mid-infrared, terahertz output, multi-wavelength multiplexing mid-infrared and terahertz sources and the like.

Drawings

Fig. 1 is a schematic diagram of two arrangement structures of a quantum cascade structure layer QCL stack unit in the invention.

Fig. 2 is a diagram of A, B QCL subunits in the quantum cascade structure layer of the present invention.

FIG. 3 is a schematic diagram of QCL subcells of the quantum cascade structure layer of the present invention with at least one doping concentration parameter; fig. 3 (a): the doping concentration parameter of the A QCL subunits is N_d,1＝N₁，N_d,2＝N₁The doping concentration parameter of the B QCL subunits is N_d,1＝N₁，N_d,2＝N₂(N₁≠N₂) (ii) a Fig. 3(b): the doping concentration parameter of the A QCL subunits is N_d,1＝N₁，N_d,2＝N₂(N₁≠N₂) The doping concentration parameter of the B QCL subunits is N_d,1＝N₁，N_d,2＝N₃(N₃≠N₂)。

Fig. 4 is a schematic diagram of the electric field in one QCL stack unit in the quantum cascade structure layer of the present invention.

Fig. 5 is a schematic structural diagram of a feedback type multipole quantum cascade ring laser in embodiment 3.

Fig. 6 is a top view of a feedback multipole quantum cascade ring laser.

Fig. 7 is a schematic energy band diagram of a feedback type multipole quantum cascade ring laser.

Fig. 8 is a schematic structural diagram of another feedback type multipole quantum cascade ring laser in embodiment 3.

Fig. 9 is a top view of another feedback type multipole quantum cascade ring laser according to embodiment 3.

Fig. 10 is a schematic structural view of a multipole quantum cascade ring laser according to another mode of embodiment 3.

Fig. 11 is a plan view of a multipole quantum cascade ring laser according to another mode of embodiment 3.

Fig. 12 is a schematic diagram of a corresponding wide gain spectrum of the multipole quantum cascade ring laser in embodiment 3.

Fig. 13 is a schematic diagram of two tunable bandwidth gain spectrums corresponding to the multi-pole quantum cascade ring laser in embodiment 3; fig. 13 (a): base-emitter voltage V_be＝V₁Constant, collector-base voltage from V₂Change to V_2’(ii) a FIG. 13(b) base-emitter voltage V₁From changing into V_1'Collector-base voltage V_cb＝V₂And is not changed.

FIG. 14 is a schematic diagram of two tunable gain spectrums corresponding to the multi-pole quantum cascade ring laser in example 3; fig. 14 (a): v_be＝V₁Constant, collector-base voltage V_cbAre each V_2”、V_2’And V₂A time device gain spectrum; fig. 14 (b): v_cb＝V₂Constant, base-emitter voltage V_beAre each V_1”、V_1’And V₁The gain spectrum of the device.

Fig. 15 is a schematic structural view of a multipole quantum cascade ring laser according to embodiment 4.

Fig. 16 is a top view of a multipole type quantum cascade ring laser in embodiment 4.

Fig. 17 is a schematic structural view of another multipole type quantum cascade ring laser in embodiment 4.

Fig. 18 is a top view of another multipole type quantum cascade ring laser according to embodiment 4.

Fig. 19 is a schematic structural view of a multipole quantum cascade ring laser according to another mode of embodiment 4.

Fig. 20 is a plan view of a multipole quantum cascade ring laser according to another mode of embodiment 4.

Fig. 21 is a schematic diagram of two kinds of wide gain spectra corresponding to the multi-pole quantum cascade ring laser in embodiment 4; fig. 21 (a): v_be1＝V₁，V_be2＝V₁，V_be3＝V₁，V_cb1＝V₂，V_cb2＝V_2’，V_cb3＝V_2”Gain spectrum in the case; fig. 21 (b): v_cb1＝V₂，V_cb2＝V₂，V_cb3＝V₂，V_be1＝V₁，V_be2＝V_1’，V_be3＝V_1”Gain spectrum in the case.

Fig. 22 is a schematic diagram of two tunable bandwidth gain spectrums corresponding to the multi-pole quantum cascade ring laser in embodiment 4; FIG. 22(a) V_be1＝V₁，V_be2＝V₁，V_be3＝V₁The collector-base bias voltages of the first segment, the second segment and the third segment control segment are respectively set from V₂Becomes V₃、V_2’Becomes V_3’、V_2”Becomes V_3”I.e. V_cb1＝V₃，V_cb2＝V_3’，V_cb3＝V_3”A time gain spectrum change schematic diagram; FIG. 22(b) V_cb1＝V₂，V_cb2＝V₂，V_cb3＝V₂The base-emitter bias voltage of the first segment, the second segment and the third segment control segment is respectively changed from V₁Becomes V₃、V_1’Becomes V_3’、V_1”Becomes V_3”I.e. V_be1＝V₃，V_be2＝V_3’，V_be3＝V_3”And (3) a schematic diagram of the gain spectrum change in time.

Fig. 23 is a schematic diagram of two types of super-wide gain spectra corresponding to the multi-pole quantum cascade ring laser in embodiment 4; FIG. 23(a) V_be1＝V₁，V_be2＝V₁，V_be3＝V₁，V_cb1＝V₂，V_cb2＝V_2’，V_cb3＝V_2”An ultra-wide spectrum overlay schematic under circumstances; FIG. 23(b) V_cb1＝V₂，V_cb2＝V₂，V_cb3＝V₂，V_be1＝V₁，V_be2＝V_1’，V_be3＝V_1”. Ultra-wide spectrum overlap diagram under the circumstances.

Fig. 24 is a frequency domain output power distribution diagram of the frequency comb output corresponding to the multipole type qc ring laser in embodiment 4.

Description of reference numerals: 1. a first QCL stack unit AB; 2. an ith QCL stack unit AB; 3. an Nth QCL stack unit AB; 4. a first QCL stack unit ABB; 5. an ith QCL stack unit ABB; 6. an Nth QCL stack unit ABB; 7. a substrate; 8. a collector electrode; 9. a quantum cascade structure layer; 10. a quantum energy level matching layer; 11. a base electrode; 12. an emitter; 13. a collector electrode; 14. a base electrode; 15. an emitter electrode; 16. a coupling section; 17. an input section; 18. a strip-shaped straight waveguide; 19. an annular waveguide; 20. an insulating layer.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described with reference to the accompanying drawings and specific embodiments. It should be noted that directional terms and sequential terms such as "upper", "lower", "front", "rear", "left", "right", and the like, which are used in the following embodiments, are only directions with reference to the drawings, and thus, the directional terms are used for illustration and are not intended to limit the present invention.

The invention relates to a multi-pole quantum cascade ring laser, which comprises a substrate 7, a collector electrode 8, a quantum level connection structure layer 9, a quantum level matching layer 10, a base electrode 11 and an emitter electrode 12 which are sequentially arranged from bottom to top, wherein the collector electrode 8 and the quantum level connection structure layer 9 and the base electrode 11 and the emitter electrode 12 are arranged in a step shape. The step-like arrangement is provided for laying collector electrode 13, base electrode 14, and emitter electrode 15.

The multi-pole quantum cascade ring laser further comprises a collector electrode 13 disposed on the collector 8 or below the substrate 7, a base electrode 14 disposed on the base electrode 11, and an emitter electrode 15 disposed on the emitter 12.

The laser is also etched with a ring waveguide 19 and a bar-shaped straight waveguide 18 coupled with the ring waveguide 19, the etching depth of the ring waveguide 19 and the bar-shaped straight waveguide 18 is any depth from the top of the emitter to the top of the base 11, the top of the quantum energy level matching layer 10, the top of the quantum level connection structural layer 9 or the top of the collector 8, wherein, at least one side of the inside or outside of the circular area of the ring waveguide 19 is etched with a depth only from the top of the emitter to the top of the base, and the bar-shaped straight waveguide 18 comprises an input section 17 and a coupling section 16;

as shown in fig. 1, the quantum cascade connection structure layer 9 in the multipole quantum cascade ring laser of the present invention is formed by stacking at least two QCL stack units having the same structure in series, where each QCL stack unit includes at least two QCL sub-units having the same structure, each QCL sub-unit is composed of an active region and an implanted region, the implanted region includes a plurality of doped regions, and at least one doped region has different doping concentration parameters between different QCL sub-units.

In order to facilitate the understanding of the quantum cascade connection structure layer 9 in the multipole quantum cascade ring laser of the present invention, the following detailed description is given by way of example 1 and example 2, taking as an example that each QCL stack cell includes two QCL subcells:

example 1

As shown in fig. 1, two arrangement structures of the quantum level junction structure layer 9 in the present embodiment are schematically shown, wherein each of the QCL stack units in fig. 1(a) is an AB stack, and includes a first QCL stack unit AB1 and an ith QCL stack unit AB 2; the quantum level coupling layer 9 is formed by stacking N QCL stack units AB3 to form AB/…/AB/…/AB stack structure. In fig. 1(b), the QCL stack units are ABB stacks, and include a first QCL stack unit ABB4, an ith QCL stack unit ABB5, and an nth QCL stack unit ABB6, and the quantum level coupling layer 9 is formed by stacking N QCL stack units, so as to form an ABB/…/ABB/…/ABB stack structure.

Each QCL stack cell in fig. 1(a) and 1(b) contains only A, B QCL subcells, A, B QCL subcells are composed of an active region and an implant region, and each implant region contains only one doped region. Wherein, the doping concentration parameter N of the A QCL subunits_d,1Doping concentration parameter N of B QCL subunits_d,2，(N_d,1≠N_d,2). It should be noted that the doping concentration parameter of the a-type QCL sub-units may be greater than or less than the doping concentration parameter of the B-type QCL sub-units, as long as the doping concentration parameters are different, in this embodiment, the doping concentration parameter N of the a-type QCL sub-units_d,1QCL subunit doping concentration parameter N greater than B_d,2. As shown in fig. 2, A, B the two QCL subcells are identical in other parameters than the doping concentration parameter, where the other parameters include: the layer thickness order, layer material composition order, layer doping location, etc. of the QCL subcells are conventionally known parameters in the art. Specifically, in this embodiment, the length of both A, B QCL subunits is L_pThe active region length is L_aThe length of the implanted region is L_p-L_aThe doping positions are all L_d,l～L_d,rThe length of doping is L_d。

In fig. 1(a), 1(b), electrons are injected from the 1 st QCL stack unit and then sequentially enter the second, …, ith, …, and up to the nth QCL stack unit. Wherein, in each QCL stack unit of fig. 1(a), electrons are injected from the a QCL subcells and then enter the B QCL subcells of the QCL stack unit; in each of the QCL stack units of fig. 1(B), electrons are injected from the a-type QCL subcell, then enter the first B-type QCL subcell of the QCL stack unit, and then enter the second B-type QCL subcell of the QCL stack unit.

In each QCL subunit, electrons are injected from the injection region, and are tunneled into the active region after being scattered by electrons and phonons; in the active region, electrons at the upper lasing level are excited to emit a photon, and the photon is transited downwards to the lower lasing level; and then, the electrons rapidly enter a carrier emptying energy level after electron-phonon scattering, and then enter an injection region energy level of the next QCL subunit through electron-electron and electron-phonon scattering coupling.

Fig. 4 is a schematic diagram of the electric field of the quantum cascade connection structure layer 9 of the present embodiment under current injection, wherein the electric field of the ith QCL stack unit is shown in the frame, and the corresponding structure is the ABB/…/ABB/…/ABB stack structure in fig. 1 (b). For convenience of illustration, the QCL stack unit ABB in fig. 1(B) is labeled as three QCL subunits A, B1, B2, respectively, from top to bottom. From left to right, the corresponding electric fields of the three QCL subcells B2, B1, a, respectively, are shown in the box. Wherein L represents the length of the ith QCL stack unit, L_dDenotes the doped region length, L, of each QCL subcell_aThe active area length of each QCL subcell is indicated by the dashed rectangular box.

Due to the effect of the injected electrons, the net charge of the undoped region of each subcell is negative constant, so its electric field is linearly decreased. Due to the presence of positively charged ionized donor ions, the net charge amount of the doped region of each QCL subunit can be a positive number, zero, or a negative constant, here taken to be a positive number, so its electric field rises linearly. In addition, the doping concentration parameter N of the A QCL subunits is set here_d,1QCL subunit doping concentration parameter N greater than B_d,2The positive net charge of the doped regions of the a-type QCL subcells is greater than the positive net charge of the doped regions of the B-type QCL subcells, further resulting in a greater electric field rise slope for the doped regions of the a-type QCL subcells than for the doped regions of the B-type QCL subcells. In addition, when the current density injected into the quantum cascade layer 9 is such that the total equivalent net charge amount of each QCL stack unit ABB is zero, the electric field of the quantum cascade layer 9 will exhibit a periodic variation due to the periodicity of the ABB/…/ABB/…/ABB stack structure.

It should be noted that, the specific length of the QCL subunit is not limited in the present invention, and can be designed according to practical requirements. Similarly, the doping concentration parameter is not particularly limited. In a special case, the doping concentration parameters of the different QCL sub-units in each QCL stack unit should be such that the net charge amount of each QCL stack unit is about zero, the corresponding device injection current is I above the device threshold, which is the case for cascade lasing of each QCL stack unit, and the gain spectrum corresponds to a curve of the type shown in fig. 12 (taking a multi-polar quantum cascade ring laser device as an example). In general, the net charge amount of each QCL stack unit may not be zero, so that only one QCL subcell in each QCL stack unit can operate under a specific bias, and the gain spectrum thereof is as shown in fig. 14 (taking a multi-polar quantum cascade ring laser device as an example). Therefore, when the injection current I is above the device threshold, the net charge per QCL stack cell should not be too large.

Example 2

As shown in fig. 3, in the present embodiment, each QCL subcell of the quantum level junction structure layer 9 has two doped regions. In FIG. 3(a), the doping concentration parameters of the two doped regions of the A QCL subcells are the same and are both N₁. The doping concentration parameters of the two doping regions of the B QCL subunits are respectively N₁And N₂(N₁≠N₂)。

In FIG. 3(b), the A QCL subcells have two doped regions with doping concentration parameters of N₁And N₂(N₁≠N₂). The B-type QCL subunits are provided with two doped regions, and the doping concentration parameters of the two doped regions are N respectively₁And N₃(N₃≠N₂)。

Similarly, in fig. 3, A, B the two QCL subcells are identical in other parameters than the doping concentration parameter, where the other parameters include: the layer thickness order, layer material composition order, layer doping location, etc. of the QCL subcells are conventionally known parameters in the art. Specifically, in this embodiment, the length of both A, B QCL subunits is L_pThe active region length is L_aThe length of the implanted region is L_p-L_aThe doping positions are all L_d,l～L_d,rThe positions of the left first segment doping are L_d,l～L_d,mThe total doping length of the doped region is L_d,r-L_d,l。

Example 3

As shown in fig. 5, which is a schematic structural diagram of the multi-pole quantum cascade ring laser of the present invention, the multi-pole quantum cascade ring laser includes, from bottom to top, a substrate 7, a collector 8, a quantum level junction structure layer 9, a quantum level matching layer 10, a base 11, and an emitter 12, which are sequentially arranged along a z direction, and the emitter 12 is etched to form a straight waveguide 18 and a ring waveguide 19. The base electrode 11 and the emitter electrode 12 are arranged in a step shape, and the collector electrode 8 and the quantum level junction structure layer 9 are also arranged in a step shape. Further, the collector 8 may include a lower cladding layer therein, and the emitter 12 may include an upper cladding layer therein. Specifically, the device is sequentially distributed from bottom to top along the z direction into a heavy n-doped substrate 7, an n-doped collector 8, a quantum level connection structure layer 9, a quantum level matching layer 10, a p-doped base 11 and a heavy n-doped emitter 12. On top of the collector 8, emitter 12 and base 11 are grown a collector electrode 13 (electrode c), an emitter electrode 15 (electrode e) and a base electrode 14 (electrode b). The collector 8 comprises a heavy n-doped lower cladding layer and the emitter 12 comprises a top heavy n-doped upper cladding layer.

Fig. 6 is a top view of the multipole quantum cascade ring laser of fig. 5. The strip-shaped straight waveguide 18 includes an input section 17 and a coupling section 16 coupled to a ring waveguide 19. When an external optical signal is injected into the input section 17 of the straight strip waveguide 18, the external injection signal can interact with the signal in the structure of the annular waveguide 19 through the coupling section 16 of the straight strip waveguide 18, so that the phase or mode locking of the signal in the structure of the annular waveguide 19 is influenced, and the output characteristic of the multi-pole quantum cascade ring laser is changed. Particularly, the injection of the external optical signal can enable the multi-pole quantum cascade ring laser to form chaotic laser capable of generating noise-like wide-spectrum random output with rapidly changing intensity, frequency and phase in a limited interval in a tunable multi-wavelength output or wide-spectrum output wavelength range, and the chaotic laser output is changed along with the injection of the external optical signal or along with the applied V_beAnd V_bcThe change in the combination of device biases changes.

It should be noted that: the collector electrode 13 position may also be grown under the substrate 7, in a role consistent with growing the collector electrode 13 on top of the collector 8 layer. In addition, there may be more than one electrode of the same type on the same device structure, for example, in fig. 5, a second collector electrode 13 may be grown on top of the collector 8 layer on the left side of the quantum cascade structure layer 9. Although the two collector electrodes 13 are spatially located differently, the roles in the device are the same and can be assigned to the class of "collector electrodes 13". Likewise, if the spatial position allows, a second base electrode 14 can also be grown on top of the base 11 layer on the left side of the emitter 12 layer, both base electrodes 14 belonging to the class of "base electrodes 14".

Meanwhile, the voltages of the emitter electrode of the strip-shaped straight waveguide 18 and the emitter electrode of the ring waveguide 19 may be the same or different, depending mainly on the relevant application scenario. In the embodiment of the present application, for convenience, unless otherwise specified, it is assumed that the emitter electrodes of the strip waveguide 18 and the emitter electrode of the ring waveguide 19 are the same in voltage. Similarly, the base electrode voltage at the center of the ring waveguide 19 and the base electrode voltage outside the ring waveguide 19 may be controlled separately according to the application scenario, and in this patent, it is also assumed that the base electrode voltage at the center of the ring waveguide 19 and the base electrode voltage outside the ring waveguide 19 are the same without specific description.

Further, the quantum cascade structure layer 9 may be the quantum cascade structure layer 9 shown in fig. 1(a) or fig. 1(b), and the QCL stack unit of the quantum cascade structure layer 9 in this embodiment is an ABB/…/ABB/…/ABB stack structure corresponding to fig. 1 (b). The layer plane of the quantum cascade connection structure layer 9 is parallel to the x-y plane and the growth direction is along the z direction. The multi-pole quantum cascade ring laser device is etched into a ridge waveguide structure along the y direction, the reflecting end face of the structure is parallel to an x-z plane, the rear end face is an enhanced reflecting end face, and the front end face is an anti-reflecting end face, namely a device light output end face.

As shown in FIG. 5, a voltage V is applied to three electrodes of the collector 8, the emitter 12, and the base 11, respectively_c、V_eAnd V_bThen the base-emitter voltage is V_be＝V_b-V_eCollector-base voltage of V_cb＝V_c-V_b. In order for the multi-polar type F-P device to operate normally, it is necessary to make V, as shown in fig. 7_be>0，V_cb>0, i.e. base-emitter in forward bias state and collector-base in reverse bias state, the energy level difference between quasi-fermi energy levels of emitter 12 and base 11 is eV_beThe difference between the quasi-Fermi levels of the base electrode 11 and the collector electrode 8 is eV_cbWhere e represents the amount of elementary charge. At this time, electrons are injected from the emitter 12 region into the base 11 region, enter the quantum level matching layer 10, and then are injected into the quantum cascade structure layer 9. As known from the common triode knowledge, the current of the collector 8 is controlled by the voltage V from the base electrode 11 to the emitter electrode 12_beControl, i.e. V_beThe current density of the quantum cascade structure layer 9 is controlled, and the working or lasing output intensity of the whole quantum cascade structure layer 9 is controlled. At the same time, V_cbAnd the device bias voltage of the quantum cascade connection structural layer 9 is controlled, so that the electric field intensity of the magnitude cascade structure is controlled, the energy level interval of the upper sub-band and the lower sub-band of the QCL sub-unit is determined, and the working or lasing wavelength of the whole quantum cascade connection structural layer 9 is controlled. By the multi-pole quantum cascade ring device shown in fig. 5, the intensity and wavelength of the working or lasing output of the quantum cascade structure layer 9 can be decoupled and divided by V_beAnd V_cbAnd respectively controlling.

In addition, it should be noted that, in general, V is passed_beWhen the current density injected into the quantum cascade layer 9 is controlled such that the total equivalent net charge of each QCL stack unit is zero, the electric field of the quantum cascade layer 9 will exhibit periodic variation due to the periodicity of the stack structure, similar to the variation of the electric field intensity in FIG. 4, when the working or lasing output wavelength of the quantum cascade layer 9 is mainly from V_cbAnd (5) controlling.

Particularly when V is_beThe current density of the injected quantum level junction structure layer 9 is controlled such that the total equivalent net charge amount of each QCL stack unit is not zero, but V can be adjusted by trimming V as long as the total equivalent net charge amount of each QCL stack unit is less than a certain critical value_beTo change the current density of the implanted quantum cascade connection structure 9 such that each QCL stackThe poisson potential of the linear periodic variation when the total equivalent net charge amount of the unit is zero has appropriate nonlinear variation, so that the working or lasing output wavelength of the quantum cascade connection structural layer 9 can be tuned and controlled.

As shown in fig. 8 and fig. 9, which are schematic structural diagrams of a multi-pole quantum cascade ring laser according to another embodiment of the present invention, in this embodiment, the straight stripe waveguide 18 and the ring waveguide 19 are etched back, that is, the straight stripe waveguide 18 and the ring waveguide 19 each include an emitter, a base, a quantum level matching layer, and a quantum level junction structure layer. Wherein the material of the outer region of the ring waveguide 19 is etched away while the inner region of the ring waveguide 19 remains etched only to the top of the base region. Of course, it is also possible to etch away the material in the circular region of the ring waveguide 19, while keeping the outer region of the ring waveguide 19 etched only to the top of the base region.

The waveguide structure only comprises an emitter type, the cavity structure of the quantum cascade structure layer of the device is mainly F-P type, and the annular waveguide 19 structure can finely adjust the mode distribution and the traveling wave mode in the F-P cavity of the device. When the ring waveguide 19 structure comprises an emitter, a base, a quantum energy level matching layer and a quantum cascade connection structure layer, the resonator structure of the quantum cascade connection structure layer of the whole device is completely changed into a ring resonator, and the mode distribution and the traveling wave mode are completely distributed according to the device characteristics of the ring resonator. That is, the etching depth determines the cavity resonance characteristic of the device, and as the etching depth increases, the cavity resonance gradually changes from the F-P type resonance conversion characteristic to the ring resonant cavity resonance characteristic.

As shown in fig. 10 and fig. 11, the schematic structural diagrams of a multipole quantum cascade ring laser according to still another embodiment of the present invention are shown, in which the straight-bar waveguide structure is also a multipole quantum cascade F-P structure, and this embodiment can represent a coupling structure between a multipole quantum cascade device and a ring-structured device in an F-P structure, and can be used for applications such as injection locking generation and chaotic laser generation.

As shown in fig. 12, the schematic diagram of the wide gain spectrum of the multi-pole quantum cascade ring laser of this embodiment is that when the single-stage control type multi-pole quantum cascade ring laserBase-emitter voltage V of optical device_be＝V₁Collector-base voltage of V_cb＝V₂The gain spectra of the three QCL subunits are given by the dashed lines and the superimposed broad gain spectra are given by the solid lines. Since the electric fields of the active regions of the three QCL sub-cells B2, B1, a decrease sequentially as shown in fig. 4, the central energies of the gain spectra of the three QCL sub-cells B2, B1, a decrease from high energy to low energy accordingly. By designing the corresponding QCL subunit parameters, the gain spectrums of the three subunits can be superposed into a flat wide spectrum.

As shown in fig. 13, two tunable wide gain spectra of the multi-pole quantum cascade ring laser of this embodiment are schematically shown, and the bias combination V is used in a specific device_be＝V₁，V_cb＝V₂The gain spectra of the three QCL subcells are shown as the profiles shown in dashed lines. In FIG. 13(a), V is held_be＝V₁Unchanged when the collector-base voltage is from V₂Change to V_2’At this time, the gain spectra of the three QCL subcells shift in the high energy direction, becoming the profile shown by the solid line. Alternatively, in FIG. 13(b), V is held_cb＝V₂Constant, when base-emitter voltage V_beFrom V₁Change to V_1’At this time, the gain spectra of the three QCL subcells shift in the high energy direction, becoming the profile shown by the solid line. For clarity of the curve variation, the superposition of the gain spectra of the three QCL subunits is not given in fig. 13. However, similar to fig. 12, it is easy to know that when the device bias combination changes as shown in fig. 13(a) or fig. 13(b), the total gain spectrum of the device is also shifted to the high energy direction, which is the wide-spectrum tunable gain characteristic of the quantum cascade structure layer 9 provided by the present invention.

As shown in fig. 14, two tunable gain spectrums of the multipole quantum cascade ring laser of the present embodiment are schematically illustrated. In FIG. 14(a), V is held_be＝V₁When unchanged, the three QCL subcells B2, B1 and A are at collector-base voltage V respectively_cbIs a V_2”、V_2’And V₂The working is performed. Bias combination V at a specific device_be＝V₁And V_cb＝V₂In the following, only a of the three QCL subunits of each QCL stack unit of the quantum level coupling layer 9 can work normally. Bias combination V at a specific device_be＝V₁And V_cb＝V_2’In the following, only B1 QCL subcells of the three QCL subcells of each QCL stack cell of the quantum level coupling structure layer 9 can work normally. Bias combination V at a specific device_be＝V₁And V_cb＝V_2”In the following, the quantum level couples the gain spectrum lasing of only B2 QCL subcells of the three QCL subcells of each QCL stack cell of the layer 9. It should be noted that B1 and B2 are both B QCL subunits, and for convenience of explanation, B1 and B2 are referred to as B1 QCL subunits and B2 QCL subunits, respectively. Then V is maintained_be＝V₁Constant, when the collector-base voltage V of the device is_cbFrom V₂Change to V_2’Or V_2”The gain spectrum of the quantum cascade connection structural layer 9 can be tuned from the gain spectrum of the a QCL subunits to the gain spectrum of the B1 or B2 QCL subunits, so that the tunable output of the quantum cascade connection structural layer 9 of the device is realized.

In addition, as previously described, the collector-base bias voltage V can also be maintained_cbWithout change, by fine tuning the base-emitter bias voltage V_beTo change the current density of the quantum cascade structure layer 9 and thus the operating or lasing output wavelength of the quantum cascade structure layer 9, as shown in fig. 14(b), keeping V_cb＝V₂When unchanged, the three QCL subcells B2, B1 and A are biased at the base-emitter bias voltage V respectively_beIs a V_1”、V_1’And V₁The working is performed. Bias combination V at a specific device_cb＝V₂And V_be＝V₁In this case, only a of the three QCL subunits of each QCL stack unit of the configured metrology sub-level-coupling layer 9 can operate normally. Bias combination V at a specific device_cb＝V₂And V_be＝V_1’In this case, only B1 QCL subunits in the three QCL subunits of each QCL stack unit of the configured metrology sub-level-coupling layer 9 can work normally. In a specific devicePressing combination V_cb＝V₂And V_be＝V_1”In the next place, the metering sub-stage is coupled to gain spectrum lasing, in which only B2 QCL sub-units of the three QCL sub-units of each QCL stack unit of the layer 9 can normally operate. Then V is maintained_cb＝V₂Constant, when base-emitter bias voltage V of the device_cbFrom V₁Change to V_1’Or V_1”The gain spectrum of the quantum cascade connection structural layer 9 can be tuned from the gain spectrum of the a QCL subunits to the gain spectrum of the B1 or B2 QCL subunits, so that the tunable output of the quantum cascade connection structural layer 9 of the device is realized.

Example 4

Fig. 15 and 16 are schematic structural diagrams of a multi-segment controlled multi-pole quantum cascade ring laser capable of being controlled in segments according to the present invention. In the present embodiment, the laser is a three-segment controlled multipole quantum cascade ring laser, and similar to fig. 5, the three-segment controlled multipole quantum cascade ring laser device includes a substrate 7, a collector 8, a quantum level junction structure layer 9, a quantum level matching layer 10, a base 11, and an emitter 12, which are sequentially arranged from bottom to top along a z direction. Further, the collector 8 comprises a heavy n-doped lower cladding layer and the emitter 12 comprises a top heavy n-doped upper cladding layer. Specifically, the device is sequentially distributed from bottom to top along the z direction into a heavy n-doped substrate 7 layer, an n-doped collector 8, a quantum level connection structure layer 9, a quantum level matching layer 10, a p-doped base 11 and a heavy n-doped emitter 12. On top of the collector 8, emitter 12 and base 11 are grown a collector electrode 13 (electrode c), an emitter electrode 15 (electrode e) and a base electrode 14 (electrode b).

Similarly, the position of the collector electrode 13 can also be grown under the substrate 7, in a working role consistent with the growth of the collector electrode 13 on top of the collector 8 layer. In addition, in the same segment of device structure, as in the single-segment multi-pole quantum cascade ring laser shown in fig. 5, there may be a plurality of electrodes of the same type, for example, in fig. 15 and 16, a second collector electrode 13 may be grown on top of the collector 8 layer on the left side of the quantum cascade structure layer 9. Although the two collector electrodes 13 are spatially located differently, the roles in the device are the same and can be assigned to the class of "collector electrodes 13". Likewise, if the spatial position allows, a second base electrode 14 can also be grown on top of the base 11 layer on the left side of the emitter 12 layer, both base electrodes 14 belonging to the class of "base electrodes 14".

Wherein the quantum cascade structure layer 9 may be a quantum cascade structure layer 9 as shown in fig. 1(a) or fig. 1(b), and the QCL stack unit of the quantum cascade structure layer 9 in this embodiment is an ABB/…/ABB/…/ABB stack structure corresponding to fig. 1 (b). The layer plane of the quantum cascade connection structure layer 9 is parallel to the x-y plane and the growth direction is along the z direction. The multipole quantum cascade ring laser is etched into a ridge waveguide structure along the y direction, the reflecting end face of the structure is parallel to an x-z plane, the rear end face is an enhanced reflecting end face, and the front end face is an anti-reflecting end face, namely a device light output end face.

Unlike fig. 5, in the present embodiment, six strip-shaped windows with a certain depth are etched on the top of the ring waveguide 19 of the three-segment controlled multi-pole type quantum cascade ring laser and the base layer outside the ring waveguide 19, and as shown in fig. 16, the strip-shaped windows are filled with an insulating material to form an insulating layer 20, so as to form the three-segment controlled multi-pole type quantum cascade ring laser. The top electrodes of the three-section control type multipole quantum cascade ring laser are mutually insulated, so that the bar-shaped straight waveguide 18 emitter electrode of the three-section control type multipole quantum cascade ring laser is V-shaped_ewIndependently controlled, the emitter electrodes 15 corresponding to the three segments of annular waveguides 19 are respectively V-shaped_e1，V_e2，V_e3Independently controlled, the base electrode in the circular region of the annular waveguide 19 is V_biIndependently controlled, and the three base electrodes outside the circular area of the annular waveguide 19 are V_b1，V_b2，V_b3Are independently controlled. It should be noted that each control segment may also correspond to a different control terminal of the collector, and for simplicity, the collectors of the three control segments are common in this embodiment, that is, a circuit bias model of a common collector is adopted, and at this time, the collector electrode 13 is set to be V_cAre independently controlled. Each control section is controlled by a set of bias combinations, the firstThe first section, the second section and the third section of the control section are respectively composed of (V)_e1，V_b1，V_c)、(V_e2，V_b2，V_c) And (V)_e3，V_b3，V_c) The three sets of biases are independently controlled. Specifically, the length of each segment of the sub-structure of the annular waveguide 19 in the three control segments along the axial direction of the annular waveguide 19 is not particularly limited, and the width of the insulating layer 20 along the axial direction of the annular waveguide 19 is also not particularly limited, and can be correspondingly changed and optimized according to the actual device design and application field.

As shown in fig. 17 and 18, a schematic structural diagram of a three-stage controlled multipole quantum cascade ring laser according to another embodiment of the present invention is shown, in which the multipole quantum cascade ring laser structure shown in fig. 8 and 9 is formed by adding an insulating layer 20.

As shown in fig. 19 and 20, a schematic structural diagram of a three-segment controlled multi-polar qc ring laser according to still another embodiment of the present invention is shown, in which a single-segment controlled multi-polar qc ring laser as shown in fig. 8 and 9 is used as a subunit, and the subunits are repeatedly arranged to form a multi-segment controlled multi-polar qc ring laser, and collector electrodes 13, base electrodes 14, and emitter electrodes 15 of adjacent subunits are insulated from each other. It should be noted that, the radius and the waveguide width of the ring waveguide structure of different segments and the length of the straight strip waveguide in this embodiment are not particularly limited, and may be adjusted and optimized according to different actual device designs and application fields.

Fig. 21 is a schematic diagram of two kinds of wide gain spectrums corresponding to the three-stage control type multipole quantum cascade ring laser in this embodiment. In FIG. 21(a), the base-emitter bias voltages of the first, second and third segment control segments are all V₁I.e. V_be1＝V_b1-V_e1＝V₁，V_be2＝V_b2-V_e2＝V₁，V_be3＝V_b3-V_e3＝V₁. As shown in FIG. 9, in the specific caseCollector-base bias voltage V₂Lower, i.e. V_cb1＝V_c-V_b1＝V₂In the first control section, only a kinds of QCL subunit structures of the three subunit structures of each QCL stack unit of the configuration layer 9 of the metering subunit are able to work normally. At a specific collector-base bias voltage V_2’Lower, i.e. V_cb2＝V_c-V_b2＝V_2’And only B1 QCL subunit structures in the three subunit structures of each QCL stack unit of the metering subunit linkage structure layer 9 arranged in the second control section can work normally. At a specific collector-base bias voltage V_2”Lower, i.e. V_cb3＝V_c-V_b3＝V_2”And the metering sub-stage arranged in the third control section is connected with the gain spectrum lasing, which can only enable B2 QCL sub-unit structures to work normally, in the three sub-unit structures of each QCL stack unit of the structural layer 9. Therefore, the gain spectrum of the finally designed three-segment controlled multipole quantum cascade ring laser is equivalent to the superposition of the gain spectra shown by three dotted lines in fig. 21(a), and a wide gain spectrum shown by a solid line in fig. 21(a) is formed.

Similarly, in FIG. 21(b), the collector-base bias voltages of the first, second and third segment control segments are all V₂I.e. V_cb1＝V₂，V_cb2＝V₂，V_cb3＝V₂. At a specific base-emitter bias, i.e., V, as shown in FIG. 14(b)_be1＝V₁In the first control section, only a kinds of QCL subunit structures of the three subunit structures of each QCL stack unit of the configuration layer 9 of the metering subunit are able to work normally. At a specific base-emitter bias, i.e. V_be2＝V_1’And only B1 QCL subunit structures in the three subunit structures of each QCL stack unit of the metering subunit linkage structure layer 9 arranged in the second control section can work normally. At a specific base-emitter bias, i.e. V_be3＝V_1”And the metering sub-stage arranged in the third control section is connected with the gain spectrum lasing, which can only enable B2 QCL sub-unit structures to work normally, in the three sub-unit structures of each QCL stack unit of the structural layer 9. Thus, the last designed three-segment control schemeThe gain spectrum of the multipole type quantum cascade ring laser is equivalent to the superposition of the gain spectra shown by the three dashed lines in fig. 21(b), resulting in a broad gain spectrum shown by the solid line in fig. 21 (b).

Fig. 22 is a schematic diagram of two tunable bandwidth gain spectrums corresponding to the three-segment control type multipole quantum cascade ring laser in this embodiment. In particular, when the voltages of the independent segments in the three-segment controlled multi-polar quantum cascade ring laser shown in FIG. 21(a) are changed, the base-emitter bias voltage of each segment of the controlled ring laser is kept constant and is still V₁I.e. V_be1＝V₁，V_be2＝V₁，V_be3＝V₁. Simultaneously making the collector-base bias voltages of the first segment, the second segment and the third segment control segment respectively from V₂Becomes V₃、V_2’Becomes V_3’、V_2”Becomes V_3”I.e. V_cb1＝V₃，V_cb2＝V_3’，V_cb3＝V_3”The gain spectrum of each control segment structure is changed from a dashed line spectrum to a solid line spectrum as shown in fig. 22 (a). For clarity of curve variation, the superposition of the gain spectra of the three subunit structures is not shown in fig. 22 (a). However, similar to fig. 13(a), it is readily appreciated that when the collector-base bias voltages of the three independent control segments are changed, the superimposed broad gain spectrum shown in fig. 21(a) also changes as the collector-base bias voltages of the three independent segments change.

Similarly, when the voltages of the individual segments in the three-segment controlled multi-polar quantum cascade ring laser shown in FIG. 21(b) are changed, the collector-base bias voltage of each segment control segment is kept constant and is still V₂I.e. V_cb1＝V₂，V_cb2＝V₂，V_cb3＝V₂. Simultaneously making the base-emitter bias voltage of the first segment, the second segment and the third segment control segment respectively from V₁Becomes V₃、V_1’Becomes V_3’、V_1”Becomes V_3”I.e. V_be1＝V₃，V_be2＝V_3’，V_be3＝V_3”Each ofThe gain spectrum of each control segment structure is changed from a dashed line spectrum to a solid line spectrum as shown in fig. 22 (b). For clarity of curve variation, the superposition of the gain spectra of the three subunit structures is not shown in fig. 22 (b). However, similar to fig. 13(b), it is readily appreciated that when the base-emitter bias voltages of the three independent control segments are changed, the superimposed wide gain spectrum shown in fig. 21(b) also changes as the base-emitter bias voltages of the three independent segments are changed.

Fig. 23 is a schematic diagram of two super-wide gain spectrums corresponding to the three-segment control type multipole quantum cascade ring laser in this embodiment. In FIG. 23(a), the base-emitter bias voltages of the first, second and third segment control segments are all V₁I.e. V_be1＝V₁，V_be2＝V₁，V_be3＝V₁. Meanwhile, the three corresponding collector-base bias voltages are respectively V_cb1＝V₂，V_cb2＝V_2’，V_cb3＝V_2”. As shown in fig. 12, each control segment can work normally under the combination of base-emitter bias and collector-base bias of a specific device, and the gain spectrum of the corresponding QCL stack unit is a gain spectrum with flat and wide spectrum characteristics, as shown by the dashed line in fig. 23 (a). Similar to fig. 13(a), when the base-emitter bias voltage of the single-segment control segment is kept constant, the wide gain spectrum of the QCL stack unit can be tuned under different collector-base bias voltages, and each segment control segment has different wide gain spectrum under the control of different collector-base bias voltages, as indicated by three dotted lines shown in fig. 23 (a). As shown by the solid line in fig. 23(a), the gain spectrum corresponding to the designed three-segment controlled multi-pole quantum cascade ring laser is the superposition of three broad gain spectrums, thereby forming an ultra-wide gain spectrum.

Similarly, in FIG. 23(b), the collector-base bias voltages of the first, second and third segment control segments are all V₂I.e. V_cb1＝V₂，V_cb2＝V₂，V_cb3＝V₂. Meanwhile, the bias voltages of the corresponding three bases and the emitters are respectively V_be1＝V₁，V_be2＝V_1’，V_be3＝V_1”. As shown in fig. 12, each control segment can work normally under the combination of base-emitter bias and collector-base bias of a specific device, and the gain spectrum of the corresponding QCL stack unit is a gain spectrum with flat and wide spectrum characteristics, as shown by the dashed line in fig. 23 (b). Similar to fig. 13(b), the wide gain spectrum of the QCL stack unit can be tuned under different base-emitter bias voltages while the collector-base bias voltage of a single segment of the control segment remains constant, and each segment of the control segment has a different wide gain spectrum under control of a different base-emitter bias voltage, as indicated by the three dashed lines shown in fig. 23 (b). As shown by the solid line in fig. 23(b), the gain spectrum corresponding to the designed three-segment controlled multi-pole quantum cascade ring laser is the superposition of three broad gain spectrums, thereby forming an ultra-wide gain spectrum.

It should be noted that the changes in the collector-base bias and the base-emitter bias combinations of the same segment of the control segment in the above embodiments are such that one of the biases is kept constant and only the other bias is changed. However, the implementation process can also obtain similar beneficial effects by adopting the method of simultaneously changing the collector-base bias voltage and the base-emitter bias voltage of the device aiming at different application fields.

As shown in fig. 24, it is a frequency domain output power distribution diagram of the frequency comb output corresponding to the three-segment controlled multipole type quantum cascade ring laser in this embodiment. In fig. 24, the dashed lines indicate the gain spectrum of the corresponding three-segment controlled multipole qc ring laser, and the solid lines indicate the frequency comb output of the device. When combining the strong four-wave mixing effect caused by the strong third-order nonlinearity of the quantum cascade structure and the mode screening effect of the F-P cavity, the multi-section multi-polar quantum cascade ring laser with any one of the wide gain spectra of fig. 12, 13, 21 or 22, or the multi-section multi-polar quantum cascade ring laser with the ultra-wide gain spectrum of fig. 23 can generate a high-performance frequency comb with good tooth comb spacing and tooth comb power uniformity. In particular, in conjunction with the tunable characteristics of the broad gain spectrum of either of fig. 21 or fig. 22, the designed multipole quantum cascade ring laser can produce a tunable high performance frequency comb.

It should be noted that, only the distribution of the output high-performance frequency comb on the photon energy spectrum is given here, the corresponding output change diagram of the frequency comb in time is not given, but based on the definition of the frequency comb, the various tooth combs of the high-performance frequency comb have a fixed phase relationship, and the phase relationship can be enhanced and fixed by the strong cascade enhanced four-wave mixing effect caused by the strong third-order nonlinearity of the quantum cascade structure and the annular waveguide 19 structure.

In the dual-stage multipole quantum cascade ring laser having the structure shown in fig. 19 and 20, the first-stage sub-unit and the second-stage sub-unit can generate two frequency combs with slightly different mode frequency intervals by independently controlling the voltages of the different electrodes of the two-stage structure, so that applications of corresponding dual-frequency technologies and the like can be further explored.

An external optical signal is injected into the input section 17 of the straight strip waveguide 18, and the external injection signal can interact with the signal in the structure of the annular waveguide 19 through the coupling section 16 of the straight strip waveguide 18 to influence the phase or mode locking of the signal in the structure of the annular waveguide 19, so that the output characteristic of the frequency comb is changed. In particular, the injection of the external optical signal can enable the multi-pole quantum cascade ring laser to form chaotic laser capable of generating noise-like wide-spectrum random output with rapidly changing intensity, frequency and phase in a limited interval in a wavelength range of tunable multi-wavelength output or wide-spectrum output. In particular, in a multi-segment multipole quantum cascade ring laser structure, different collector-base bias and base-emitter bias combinations of different segments can be controlled, even changing the emitter electrode bias V of the slab straight waveguide 18_ewThe phase locking effect among the teeth of the output frequency comb is enhanced, and the time domain waveform of the teeth of the output frequency comb can be compressed and shaped.

It will be appreciated by those of ordinary skill in the art that the examples provided herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited examples and embodiments. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.

Claims

1. A multipole quantum cascade ring laser is characterized in that: the laser comprises a substrate (7), a collector (8), a quantum level connection structure layer (9), a quantum level matching layer (10), a base (11) and an emitter (12) which are sequentially arranged from bottom to top, wherein the collector (8) and the quantum cascade structure layer (9) and the base (11) and the emitter (12) are arranged in a step shape;

the multi-pole quantum cascade ring laser further comprises a collector electrode (13) arranged on the top of the collector electrode (8) or below the substrate (7), a base electrode (14) arranged on the top of the base electrode (11), and an emitter electrode (15) arranged on the top of the emitter electrode (12);

the laser is further etched with an annular waveguide (19) and a bar-shaped straight waveguide (18) coupled with the annular waveguide (19), the etching depths of the annular waveguide (19) and the bar-shaped straight waveguide (18) are any depths from the top of an emitter to the top of a base (11), the top of a quantum energy level matching layer (10), the top of a quantum cascade structure layer (9) or the top of a collector (8), wherein at least one side in a circular area or outside the circular area of the annular waveguide (19) is etched to a depth from the top of the emitter to the top of the base, and the bar-shaped straight waveguide (18) comprises an input section (17) and a coupling section (16);

the quantum cascade structure layer (9) is formed by stacking at least two QCL stack units with the same structure in series, each QCL stack unit comprises at least two QCL sub-units with the same structure, each QCL sub-unit consists of an active region and an injection region, each injection region comprises a plurality of sections of doping regions, and the doping concentration parameters of at least one section of doping region are different among different QCL sub-units; at least one QCL subunit comprises two or more doping areas, and at least one doping area exists in the QCL subunit, and the doping concentration parameter of the QCL subunit is different from that of the other doping areas;

a plurality of insulating layers (20) are arranged on the annular waveguide (19) and the base electrode (11) to enable the laser to be a multi-section control type multi-polar quantum cascade annular laser which can be controlled in a segmented mode;

each section of the multi-section control type multipole quantum cascade ring laser can be controlled by a group of independent section voltages, the group of independent section voltages at least comprise three electrode control voltages of a collector (8), a base (11) and an emitter (12), and the value of each group of independent electrode control voltages is any one of positive voltage, zero voltage or negative voltage.

2. The multipole quantum cascade ring laser of claim 1, wherein: the quantum cascade structure layer (9) comprises N QCL stack units: the first QCL stack unit AB (1), the ith QCL stack unit AB (2) and the Nth QCL stack unit AB (3) or the first QCL stack unit ABB (4), the ith QCL stack unit ABB (5) and the Nth QCL stack unit ABB (6), wherein i and N are integers which are larger than 1, and i is not more than N.

3. The multipole quantum cascade ring laser of claim 1, wherein: the QCL subunit adopts a U-L state transfer design, the U state and the L state are any one of a single energy state, a multi-energy state or a continuous state, and the multi-energy state comprises at least two energy states.

4. The multipole quantum cascade ring laser of claim 1, wherein: the working or lasing wavelength corresponding to the active region of the QCL subunit is in the mid-infrared or terahertz waveband.

5. The multipole quantum cascade ring laser of claim 1, wherein: at least one collector electrode (13), at least one base electrode (14) and at least one emitter electrode (15) in the multi-pole quantum cascade ring laser are provided.

6. The multipole quantum cascade ring laser of claim 1, wherein: the multi-pole quantum cascade ring laser is used as a subunit to form a multi-stage control type multi-pole quantum cascade ring laser, and collector electrodes (13), base electrodes (14) and emitter electrodes (15) of adjacent subunits are insulated from each other.

7. The multipole quantum cascade ring laser of claim 6, wherein: in each section of the multi-section control type multipole quantum cascade ring laser, the base-emitter bias voltage controls the current density of the quantum cascade structure layer (9) in the section, and the base-collector bias voltage controls the device bias voltage of the quantum cascade structure layer (9) in the section.

8. The multipole quantum cascade ring laser of claim 6, wherein: under the combination of the applied base-emitter bias voltage and the applied base-collector bias voltage device bias voltage, at least two QCL stack units can work or lase, and at least one QCL subunit in each work or lase QCL stack unit can work or lase.

9. The multipole quantum cascade ring laser of claim 6, wherein: at least two of the QCL stack units can operate or lase simultaneously under a specific applied base-emitter bias voltage and base-collector bias device bias voltage combination, and at least one QCL subunit in each operating or lasing QCL stack unit can operate or lase.

10. The multipole quantum cascade ring laser of claim 6, wherein: when the applied bias voltage combination of the base electrode-emitter and the bias voltage of the base electrode-collector device is changed, at least two QCL stack units can work or radiate simultaneously, and at least one QCL subunit in each work or radiate QCL stack unit can work or radiate.

11. The multipole quantum cascade ring laser of claim 6, wherein: when the applied bias voltage combination of the base electrode-emitter and the bias voltage device of the base electrode-collector is changed, at least two QCL stack units can work or lase simultaneously, at least one QCL subunit in each work or lase QCL stack unit can work or lase, and the work or lase output wavelength is changed along with the change of the applied bias voltage combination of the base electrode-emitter and the bias voltage device of the base electrode-collector.

12. The multipole quantum cascade ring laser of claim 11, wherein: the working or lasing outputs are superimposed into a multi-wavelength output or a broad spectrum output or a frequency comb output.

13. The multipole quantum cascade ring laser of claim 11, wherein: the working or lasing outputs are superimposed into a multi-wavelength output or a wide-spectrum output or a frequency comb output that changes as the applied base-emitter bias and base-collector bias device bias combination changes.

14. The multipole quantum cascade ring laser of claim 13, wherein: under specific external light injection, chaotic laser can be formed in the wavelength range of the tunable multi-wavelength output or wide-spectrum output, and the chaotic laser output changes along with the change of an injected external signal or along with the change of the applied base-emitter bias voltage and the bias voltage combination of the base-collector bias device.