CN109244822B - Device and method for measuring gain of terahertz quantum cascade laser - Google Patents
Device and method for measuring gain of terahertz quantum cascade laser Download PDFInfo
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- CN109244822B CN109244822B CN201811292367.XA CN201811292367A CN109244822B CN 109244822 B CN109244822 B CN 109244822B CN 201811292367 A CN201811292367 A CN 201811292367A CN 109244822 B CN109244822 B CN 109244822B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
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- G—PHYSICS
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- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
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Abstract
The invention discloses a device and a method for measuring terahertz quantum cascade laser gain. The invention adopts the grating coupler and the absorption boundary to manufacture a monolithic integration structure of the laser and the two amplifiers with different lengths, and obtains gain or loss by measuring the coupling emergent power of the laser after the laser is transmitted in the two amplifiers and combining the transmission rule of the laser in the amplifiers. The method can obtain the change relation of the gain of the bimetal waveguide terahertz quantum cascade laser along with the bias voltage, and has the spectral resolution characteristic. The method has the following advantages: the self-oscillation of the amplifier is fully inhibited, the gain clamping effect is broken through, and the maximum gain of the bimetallic waveguide can be measured.
Description
Technical Field
The invention relates to a device and a method for measuring gains of a bimetal waveguide terahertz quantum cascade laser under different voltages.
Background
The terahertz quantum cascade laser (THz-QCL) has the advantages of wide frequency coverage range, high energy conversion efficiency, small volume, easy integration and the like, is a coherent light source with very competitive terahertz waveband, and has important application prospects in the fields of substance detection, spectral analysis, imaging, communication and the like. The THz-QCL of the bimetallic waveguide has higher working temperature and is the current research focus.
The gain is a very important parameter in the laser, the gain has very great influence on the threshold, the power and the working temperature of the laser, and the rapid and accurate acquisition of the gain of the laser is very important for the material characterization and the design of the resonant cavity structure of the laser.
At present, few studies on the gain of the THz-QCL are carried out, and only a Time Domain Spectroscopy (TDS) method for measuring the gain spectrum of the THz-QCL is reported in experiments. Of the Unterrainer group, Vienna university of Austria, 2007
Et al first measured the gain of the THz-QCL using a time-domain spectroscopy system. They use an 80fs laser pulse (800 nm wavelength) to irradiate on a GaAs photoconductive switch and radiate a broad-spectrum terahertz wave pulse in the frequency range of 0.5-3.5 THz. The terahertz pulse is focused on the cavity surface of the THz-QCL through the lens and is incident into the FP cavity of the THz-QCL, and the incident terahertz pulse is reflected for a plurality of times in the FP cavity of the THz-QCL and then is emitted through the cavity surface on the other side. The amplitude and the phase of the emergent terahertz pulse can be obtained by a coherent detection method of electro-optic sampling, and the power of the emergent pulse can also be measured by a power meter. By means of the method, it is possible to obtain,
the first time, et al obtained a phase jump in the emitted light as the laser was converted from light absorption to stimulated emission. And then the quantum description of the light stimulated radiation in the population inversion system is verified experimentally for the first time. By means of the method, the user can select the target,
the gain spectrum of the THz-QCL and its evolution with the bias voltage were also measured and gain clamping and gain hole burning phenomena were found. However, the method for measuring THz-QCL by using the TDS method needs a complex and expensive experimental device, and the experimental method is complex and is not beneficial to the conventional measurement of THz-QCL gain.
The invention provides a device and a method for measuring the gain of THz-QCL in a bimetallic waveguide. By utilizing a monolithic integration structure of a terahertz quantum cascade laser and two amplifiers with different lengths, the coupling emergent power of terahertz waves passing through the amplifiers under different bias voltages of the amplifiers is measured, and the gain of the terahertz waves in the bimetallic waveguide structure THz-QCL under different bias voltages is obtained by combining the propagation rule of the terahertz waves in the amplifiers.
Disclosure of Invention
The invention designs a device and a test method capable of conveniently and rapidly measuring the gain of a terahertz quantum cascade laser, solves the difficulty that the traditional TDS method needs a complex and expensive experimental device, and tests the gain of the terahertz quantum cascade laser in a bimetallic waveguide structure in a simple and rapid mode.
As shown in fig. 1, the device for measuring the gain of THz-QCL in a bimetallic waveguide according to the present invention has the following parts: lower electrode 1, lower contact layer 2, active region structure 3, upper contact layer 4 and upper electrode 5.
The lower contact layer 2 is made of GaAs with the thickness of 30-60nm and the n-type doping concentration of 2 multiplied by 1018-3.5×1018cm-3。
The active region 3 comprises 90 modules with periodic repetition, and each module comprises 9 layers of GaAs and 9 layers of Al0.15Ga0.85As mutually overlapped structures, the thicknesses of the As mutually overlapped structures from GaAs are As follows: 11.4, 2.0, 12.0, 2.0, 12.2, 1.8, 12.8, 1.5, 15.8, 0.6, 9.0, 0.6, 14.0, 3.8, 11.6, 3.5, 11.3 and 2.7(nm), the GaAs layer of the first two layers is a doped layer, and the n-type doping concentration is 1015-1016cm-3。
The upper contact layer 4 is made of GaAs with a thickness of 150-300nm and an n-type doping concentration of 2 × 1018-3.5×1018cm-3。
The lower electrode 1 and the upper electrode 5 are made of Ti and Au, the Ti is adjacent to the contact layer, the thickness of the Ti is 10-20nm, the thickness of the lower electrode Au is 800-1000nm, and the thickness of the upper electrode Au is 300-500 nm.
Periodic air slits are formed in the upper electrode to constitute three grating structures. As shown, the grating structure in the top electrode divides the device into 7 parts, Z1, Z2, Z3, Z4, Z5, Z6, and Z7.
The grating in Z1 is a first-order distributed feedback grating, the period length is 19.8-21 μm, the air slit width is 3-5 μm, and the number of periods is 30-45. The grating structure makes Z1 a first order dfb laser.
The grating structures in Z3 and Z6 are the same, the period length is 42-50 μm, the air slit width is 14-16 μm, and the number of periods is 10-20. The grating structure makes Z3 and Z6 grating couplers.
The upper contact layer of Z4 and Z7 is not covered by the upper electrode, and its length is 200-350 μm. The exposed contact layer makes Z4 and Z7 absorption boundaries.
The lengths of Z2 and Z5 were 100-1000. mu.m. The presence of three grating structures and absorption boundaries makes it an amplifier.
The optical power-current-voltage test is carried out on the structure, so that the gain of the bimetallic waveguide terahertz quantum cascade laser can be obtained, and the specific test comprises the following steps:
1) the bias voltage of the first-stage feedback laser is fixed to enable the first-stage feedback laser to radiate, and the output wavelength is lambda0Output power of P0；
2) Bias voltage of fixed amplifier Z2 set to V0Measuring the power P emitted by the grating coupler Z31；
3) The bias voltage of the fixed amplifier Z5, again V0Measuring the power P emitted by the grating coupler Z62；
4) According to the propagation rule of the terahertz waves in the amplifier:
p1＝p0×exp(g×L1)×κGC，p2＝p0×exp(g×L2)×κGCobtaining a wavelength of λ0The bias voltage of the terahertz wave in the bimetallic waveguide is V0Gain of time is
Wherein L is1And L2Respectively, the length of Z2 and Z5, where g is the gain of the terahertz wave in the bimetallic waveguide, κGCIs the coupling coefficient of the grating coupler.
Description of the drawings:
fig. 1 is a structure for measuring gain in a double-metal waveguide terahertz quantum cascade laser, in which 1 is a lower electrode TiAu, 2 is lower contact layer n-type GaAs, 3 is an active region, 4 is upper contact layer n-type GaAs, and 5 is an upper electrode TiAu, in which periodic air slits are made in the upper electrode to form three grating structures.
Detailed Description
Example 1:
according to the invention, we have prepared a device for measuring the gain of THz-QCL in a bimetallic waveguide structure, the specific structure is as follows:
the lower electrode 1 is made of Ti and Au, wherein the thickness of Ti is 10nm, and the thickness of Au is 1000 nm.
The lower contact layer 2 is made of GaAs with a thickness of 50nm and an n-type doping concentration of 3.5 × 1018cm-3。
The active region structure 3 comprises 90 modules of periodic repetition, each module comprising 9 GaAs potential wells and 9 Al layers0.15Ga0.85As potential barriers are overlapped, and the thickness from GaAs is As follows: 11.4, 2.0, 12.0, 2.0, 12.2, 1.8, 12.8, 1.5, 15.8, 0.6, 9.0, 0.6, 14.0, 3.8, 11.6, 3.5, 11.3 and 2.7(nm), the GaAs layer of the first two layers is a doped layer, and the n-type doping concentration is 1016cm-3。
The upper contact layer 4 is made of GaAs with a thickness of 300nm and an n-type doping concentration of 3.5 × 1018cm-3。
The upper electrode 5 is made of Ti and Au, wherein the thickness of Ti is 10nm, and the thickness of Au is 500 nm.
The grating period in the first order dfb laser Z1 was 20 μm with an air slit width of 5 μm for 30 periods.
The amplifiers Z2 and Z5 were 100 μm and 300 μm in length, respectively.
The grating period in grating couplers Z3 and Z6 was 46 μm, with an air slit width of 14 μm for 10 periods.
The absorption boundaries Z4 and Z7 were 300 μm in length.
Example 2:
according to the invention, we have prepared a device for measuring the gain of THz-QCL in a bimetallic waveguide structure, the specific structure is as follows:
the lower electrode 1 is made of Ti and Au, wherein the thickness of Ti is 10nm, and the thickness of Au is 1000 nm.
The lower contact layer 2 is made of GaAs with a thickness of 50nm and an n-type doping concentration of 3.5 × 1018cm-3。
The active region structure 3 comprises 90 modules of periodic repetition, each module comprising 9 GaAs potential wells and 9 Al layers0.15Ga0.85As potential barriers are overlapped, and the thickness from GaAs is As follows: 11.4, 2.0, 12.0, 2.0, 12.2, 1.8, 12.8, 1.5, 15.8, 0.6, 9.0, 0.6, 14.0, 3.8, 11.6, 3.5, 11.3 and 2.7(nm), the GaAs layer of the first two layers is a doped layer, and the n-type doping concentration is 1016cm-3。
The upper contact layer 4 is made of GaAs with a thickness of 300nm and an n-type doping concentration of 3.5 × 1018cm-3。
The upper electrode 5 is made of Ti and Au, wherein the thickness of Ti is 10nm, and the thickness of Au is 500 nm.
The grating period in the first order dfb laser Z1 was 20 μm with an air slit width of 5 μm for 30 periods.
The amplifiers Z2 and Z5 were 100 μm and 500 μm in length, respectively.
The grating period in grating couplers Z3 and Z6 was 46 μm, with an air slit width of 14 μm for 10 periods.
The absorption boundaries Z4 and Z7 were 300 μm in length.
Example 3:
according to the invention, we have prepared a device for measuring the gain of THz-QCL in a bimetallic waveguide structure, the specific structure is as follows:
the lower electrode 1 is made of Ti and Au, wherein the thickness of Ti is 10nm, and the thickness of Au is 1000 nm.
The lower contact layer 2 is made of GaAs with a thickness of 50nm and an n-type doping concentration of 3.5 × 1018cm-3。
The active region structure 3 comprises 90 modules of periodic repetition, each module comprising 9 GaAs potential wells and 9 Al layers0.15Ga0.85As potential barriers are overlapped, and the thickness from GaAs is As follows: 11.4, 2.0, 12.0, 2.0, 12.2, 1.8, 12.8, 1.5, 15.8, 0.6, 9.0, 0.6, 14.0, 3.8, 11.6, 3.5, 11.3 and 2.7(nm), the GaAs layer of the first two layers is a doped layer, and the n-type doping concentration is 1016cm-3。
The upper contact layer 4 is made of GaAs with a thickness of 300nm and an n-type doping concentration of 3.5 × 1018cm-3。
The upper electrode 5 is made of Ti and Au, wherein the thickness of Ti is 10nm, and the thickness of Au is 500 nm.
The grating period in the first order dfb laser Z1 was 20 μm with an air slit width of 5 μm for 30 periods.
The amplifiers Z2 and Z5 were 300 μm and 500 μm in length, respectively.
The grating period in grating couplers Z3 and Z6 was 46 μm, with an air slit width of 14 μm for 10 periods.
The absorption boundaries Z4 and Z7 were 300 μm in length.
Claims (2)
1. The utility model provides a device for measuring terahertz quantum cascade laser gain now, includes bottom electrode (1), lower contact layer (2), active area (3), goes up contact layer (4) and top electrode (5), its characterized in that:
the device adopts a bimetal waveguide structure, and the structure of the device is that a lower electrode (1), a lower contact layer (2), an active region (3), an upper contact layer (4) and an upper electrode (5) from bottom to top;
the lower electrode (1) and the upper electrode (5) are made of Ti and Au, and the Ti is adjacent to the contact layer;
the lower contact layer (2) and the upper contact layer are made of n-type doped GaAs;
the active region (3) is used by a conventional terahertz quantum cascade laser;
periodic air slits are formed in the upper electrode to form three grating structures, and the grating structures in the upper electrode divide the device into the following regions: z1, Z2, Z3, Z4, Z5, Z6, and Z7, wherein:
the grating in Z1 is a first-level distributed feedback grating, the period length is 19.8-21 μm, the width of the air slit is 3-5 μm, the number of periods is 30-45, and the grating structure enables Z1 to become a first-level distributed feedback laser;
the upper electrodes in Z2 and Z5 do not contain grating structures, and the length of the grating structures is 100-1000 μm;
the grating structures in Z3 and Z6 are the same, the period length is 42-50 μm, the width of the air slit is 14-16 μm, the number of periods is 10-20, and the grating structures enable Z3 and Z6 to be grating couplers;
the upper contact layer of Z4 and Z7 is not covered by the upper electrode and has a length of 200-350 μm, and the exposed contact layer makes Z4 and Z7 as absorption boundaries.
2. A terahertz quantum cascade laser gain measurement method based on the device for measuring terahertz quantum cascade laser gain of claim 1, characterized by comprising the steps of:
1) the bias voltage of the first-stage feedback laser Z1 is fixed to make it radiate, and the output wavelength is lambda0Output power of P0；
2) Bias voltage V of fixed amplifier Z20Measuring the power P emitted by the grating coupler Z31；
3) The bias voltage of the amplifier Z5 is fixed, likewise V0Measuring the power P emitted by the grating coupler Z62；
4) Obtaining the wavelength lambda from the above measurement results0The bias voltage of the terahertz wave in the bimetallic waveguide is V0The gain of (A) is:
wherein L is1And L2The lengths of Z2 and Z5, respectively, and g is the gain of the terahertz wave in the bimetallic waveguide.
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| US20150248047A1 (en) * | 2014-02-28 | 2015-09-03 | The University Of Manchester | Terahertz Mixer and Optical Fiber Coupled Terahertz Mixer |
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