Low-Threshold High-Temperature Operation of ～7.4μm Quantum Cascade Lasers

We report low-threshold high-temperature operation of 7.4#m strain-compensated InGaAs/lnAIAs quantum cascade lasers （QCLs）. For an uncoated 22-μm-wide and 2-mm-long laser, the low-threshold current densities, i.e. 0.33kA/cm^2 at 81 K in pulsed mode and 0.64kA/cm^2 at 84K in cw mode, are realized. High-temperature operation of uncoated devices, with a high value of 223K, is achieved in cw mode.     

High-Temperature Operation of 8.5 μm Distributed Feedback Quantum Cascade Lasers

We present a distributed feedback quantum cascade laser （DFB-QCL） emitting at a wavelength of 8.5μm and operating up to 420K （147℃） with a low-threshold current density in pulsed mode. The DFB-QCLs studied are based on a four-well active design; the central portion of the waveguide consists of 60 periods of lattice matched InP-based InGaAs/AlInAs. In the design of the device, an active structure with lower doping and a deep-top grating process are utilized to achieve high temperature operation with a lower-threshold current density. At 420K, a low-threshold current density of 3.28 kA/cm^2 and a single mode peak power of 15mW are achieved on an epilayer-up mounting device with ridge width of 26μm and cavity length of 3.0mm. A side mode suppression ratio of 25 dB at 420 K is obtained.     

A novel 2-μm pulsed fiber laser based on a supercontinuum source and its application to mid-infrared supercontinuum generation

A new method to achieve 2-μm pulsed fiber lasers based on a supercontinuum(SC) is demonstrated. The incident pump light is a pulsed SC which contains a pump light and a signal light at the same time. The initial signal of the seed laser is provided by the incident pump light and amplified in the cavity. Based on this, we obtain a 2-μm pulsed laser with pulse repetition rate of 50 kHz and pulse width of 2 ns from the Tm-doped fiber laser. This 2-μm pulsed laser is amplified by two stages of fiber amplifiers, then the amplified laser is used for mid-infrared(mid-IR) SC generation in a 10-m length of ZrF4–BaF2–LaF3–AlF3–NaF(ZBLAN) fiber. An all-fiber-integrated mid-IR SC with spectrum ranging from 1.8 μm to4.3 μm is achieved. The maximal average output power of the mid-IR SC from the ZBLAN fiber is 1.24 W(average output power beyond 2.5 μm is 340 mW), corresponding to an output efficiency of 6.6% with respect to the 790-nm pump power.     

Room—Temperature A1GaAsSb／InGaAsSb Multi—Quantum—Well Lasers with High Chraracteristic Temperature

Planar structure A1GaAsSb/InGaAsSb lasers operated at 2.01/zm with high characteristic temperature have been fabricated from a strained multiple quantum-well heterostructure. To decrease the free carrier induced absorption of optical mode in the mid-infrared, we design a broaden waveguide layer in the laser structures to decrease the optical mode distribution in the heavy doped cladding layer, therefore it can be absorbed easily. To enhance the characteristic temperature of laser diodes, A1 constituent up to 80% was applied to the A1GaAsSb cladding layer. The laser diodes with a threshold current density of 1.8 kA/cm2 can be pulsed operating up to 340 K. The characteristic temperature To is 125 K and 90 K in the operating temperature ranges 170-220 K and 230-340 K, resDectivelv. The emission spectrum shows a multiple longitudinal mode.     

A 10.7 μm InGaAs/InAlAs Quantum Cascade Detector

A 10.7μm quantum cascade detector based on lattice matched InGaAs/InAlAs/InP is demonstrated and characterized in terms of responsivity, resistivity and detectivity. The device operates in the 8 14μm atmospheric window up to 140 K and shows a peak reponsivity of 14.4mA/W at 78K. With a resistance-area product value of 159Ωcm^2, the Johnson noise limited detectivity D^＊J is 2.8 × 10^9 Jones （cmHz^1/2W^-1） at 78K.     

High-Power and Low-Threshold-Current-Density GaAs/AlGaAs Quantum Cascade Lasers

We report on the realization of GaAs/AlGaAs quantum cascade lasers with an emission wavelength of 9.1 μm above the liquid nitrogen temperature. With optimal current injection window and ridge width of 24 and 60μm respectively, a peak output power more than 500mW is achieved in pulsed mode operation. A low threshold current density Jth = 2.6 kA/cm^2 gives the devices good lasing characteristics. In a drive frequency of i kHz, the laser operates up to 20% duty cycle.     

Room-Temperature Operation of 2.4 μm InGaAsSb/A1GaAsSb Quantum-Well Laser Diodes with Low-Threshold Current Density

GaSb-based 2.4μm InGaAsSb/AIGaAsSb type-I quantum-well laser diode is fabricated. The laser is designed consisting of three In0.35 Ga0.65As0.1Sb0.9/Al0.35 Ga0.65 As0.02Sb0.98 quantum wells with 1% compressive strain located in the central part of an undoped Al0.35Ga0.65As0.02Sb0.98 waveguide layer. The output power of the laser with a 50-μm-wide i-ram-long cavity is 28roW, and the threshold current density is 400A/cm2 under continuous wave operation mode at room temperature.     

Low Threshold Distributed Feedback Quantum Cascade Lasers with Widely Spaced Emission Wavelengths

We report lasing properties of distributed feedback quantum cascade lasers （DFB QCLs） including a doublephonon-resonance active region, at wavelength of about 8.4 μm. A broad gain spectrum is generated due to the coupling between the lower laser level in the active region and the levels in the injector, and is demonstrated by the lasing spectrum of the corresponding Fabry-Perot QCLs whose width is 0.5 μm at 1.5 times of the threshold current. As a result, the DFB QCLs employing different grating periods exhibit a wavelength span of 0.18μm at room temperature and total wavelength coverage of 0.28μm at various heat sink temperatures. A high side mode suppression ratio of about 30dB and a low threshold current density of 1.78kA/cm^2 are achieved as the lasers operate at room temperature in pulsed mode.     

Continuous Wave Performance and Tunability of MBE Grown 2.1μm InGaAsSb/AlGaAsSb MQW lasers

InCaAsSb/AlGaAsSb multi quantum well ridge waveguide lasers at 2.1 μm wavelength are fabricated by using molecular beam epitaxy. Continuous wave performance and tunability of the lasers are evaluated in a wide temperature range extend to 80℃. Output power of the laser at 30℃ exceeds 30 m W/facet at driving current of 0.5 A, the characteristic temperature To is 89K in 0-50℃ range. No fast degradation is observed in accelerated aging test at 90℃ for those lasers with lower Al content in cladding layers. Temperature tunability of the lasers is 1.36 nm/K. Single-mode output with side mode suppression ratios greater than 20 dB is achieved in a certain driving current region; current tunability is 8 × 10^-3 nm/mA regardless of mode hopping.     

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well vertical-cavity surface-emitting laser

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) based on an intra-cavity contacted structure is fabricated. A threshold current of 1.5 mA for a 22 μm oxide aperture device is achieved, which corresponds to a threshold current density of 0.395 kA/cm². The peak output optical power reaches 17.5 mW at an injection current of 30 mA at room temperature under pulsed operation. While under continuous-wave (CW) operation, the maximum power attains 10.5 mW. Such a device demonstrates a high characteristic temperature of 327 K within a temperature range from -12℃ to 96℃ and good reliability under a lifetime test. There is almost no decrease of the optical power when the device operates at a current of 5 mA at room temperature under the CW injection current.     

Terahertz Quantum Cascade Laser Operating at 2.94THz

The development of quantum cascade laser at 2.94 THz is reported. The laser structure is based on a bound-to-continuum active region and a semi-insulating surface-plasmon waveguide. Lasing is observed up to a heat-sink temperature of 70 K in pulsed mode with light power of 4.75 mW at 10 K and 1 mW at 70 K. A threshold current density of 296.5 A/cm2 and an internal quantum efficiency of 1.57 × 10-2 per cascade period are also observed at 10 K. The characteristic temperature of this laser is extracted to be T0 = 57.5 K.     

High-Power Operation of Uncoated Strain-Compensated Quantum Cascade Lasers at 4.8μm

High-power operation of uncoated 22μm-wide quantum cascade lasers （QCLs） emitting at λ～ 4.8μm is reported. The emitting region of the QCL structure consists of a 30-period strain-compensated Ino.68 Gao.32 As/In0.37 Alo.63 As superlattice. For a 4-mm-long laser in pulsed mode, a peak output power is achieved in excess of 2240mW per facet at 81K with a threshold current density of 0.64 kA/cm^2. The effects of varying the cavity lengths from 1 to 4 mm on the performances of the QCLs are analysed in detail and the low waveguide loss of only about 1.4 cm^-1 is extracted.     

Optical properties of InGaAsBi/GaAs strained quantum wells studied by temperature-dependent photoluminescence

The effect of bismuth on the optical properties of InGaAsBi/GaAs quantum well structures is investigated using the temperature-dependent photoluminescence from 12 K to 450 K.The incorporation of bismuth in the InGaAsBi quantum well is confirmed and found to result in a red shift of photoluminescence wavelength of 27.3 meV at 300 K.The photoluminescence intensity is significantly enhanced by about 50 times at 12 K with respect to that of the InGaAs quantum well due to the surfactant effect of bismuth.The temperature-dependent integrated photoluminescence intensities of the two samples reveal different behaviors related to various non-radiative recombination processes.The incorporation of bismuth also induces alloy non-uniformity in the quantum well,leading to an increased photoluminescence linewidth.     

Room temperature continuous wave operation of 1.33-um InAs/GaAs quantum dot laser with high output power

Continuous wave operation of a semiconductor laser diode based on five stacks of InAs quantum dots (QDs) embedded within strained InGaAs quantum wells as an active region is demonstrated. At room temperature, 355-mW output power at ground state of 1.33-1.35μm for a 20-μm ridge-waveguide laser without facet coating is achieved. By optimizing the molecular beam epitaxy (MBE) growth conditions, the QD density per layer is raised to 4×10~(10) cm-2. The laser keeps lasing at ground state until the temperature reaches 65℃.     

Room temperature continuous wave operation of 1.33-μm InAs/GaAs quantum dot laser with high output power

Continuous wave operation of a semiconductor laser diode based on five stacks of InAs quantum dots (QDs) embedded within strained InGaAs quantum wells as an active region is demonstrated. At room temperature, 355-Mw output power at ground state of 1.33-1.35μm for a 20-μm ridge-waveguide laser without facet coating is achieved. By optimizing the molecular beam epitaxy (MBE) growth conditions,the QD density per layer is raised to 4 × 1010 cm-2. The laser keeps lasing at ground state until the temperature reaches 65 ℃.     

Simulation of quantum-well slipping effect on optical bandwidth in transistor laser

An optical bandwidth analysis of a quantum-well （16 nm） transistor laser with 150-μm cavity length using a charge control model is reported in order to modify the quantum-well location through the base region. At constant bias current, the simulation shows significant enhancement in optical bandwidth due to moving the quantum well in the direction of collector-base junction. No remarkable resonance peak, limiting factor in laser diodes, is observed during this modification in transistor laser structure. The method can be utilized for transistor laser structure design.     

High-Duty-Cycle Operation of GaAs/AlGaAs Quantum Cascade Laser above Liquid Nitrogen Temperature

We present a detailed study of λ- 9.75 μm GaAs/AlGaAs quantum cascade lasers. For a coated 2-rmm-long and 40-μm-wide laser, an optical power of 85 μ W is observed at 95% duty cycle at 80K. At a moderate driving pulse （1 kHz and 1% duty cycle）,the device presents a peak power more than 20mW even at 120K. At 80K, the fitted result of threshold current densities shows evidence of potential cw operation.     

Strain Compensated AlInGaAs/InGaAs/InAs Triangular Quantum Wells for Lasing Wavelength beyond 2μm

The subband energy and lasing wavelength of compressively strained triangular Ino.53Ga0.47As/InAs quantum well are calculated and compared with the conventional rectangular ones with the same strain contents. The strain compensation using Al0.33In0.36Ga0.31As barrier is introduced. The results show that lasing wavelength can be extended dramatically to beyond 2.8μm by changing the energy band from the conventional rectangular shape to a triangular one, the realization of such a structure using molecular beam epitaxy technology is also discussed.     

Tunable Diode Laser Absorption Spectroscopy Detection of N2O at 2.1μm Using Antimonide Laser and InGaAs Photodiode

Tunable diode laser absorption spectroscopy detection of N2 0 around 2.1 μm is demonstrated by using a homemade InGaAsSb/AlGaAsSb MQW laser diode and an InGaAs wavelength extended photodiode. Details of the devices and the detection system are described. In the system, the laser is driven by low frequency pulses with long duration to form a wavelength scan around 4741 cm^-1; the absorption information is obtained from the detected signal of the photodiode. By using a gas cell with 15cm path length, a detection limit is estimated to be smaller than 0.2 Torr.     

Temperature-dependent rectifying and photovoltaic characteristics of an oxygen-deficient Bi_2Sr_2Co_2O_y/Si heterojunction

A Bi2Sr2Co2Oy/Si heterojunction is obtained by growing a layer of p-type oxygen-deficient Bi2Sr2Co2Oy film on a commercial n-type silicon wafer by pulsed laser deposition. Its rectifying and photovoltaic properties are studied in a wide temperature range from 20 K to 300 K. The transport mechanism under the forward bias can be attributed to a trap- filled space-charge-limited current conduction mechanism. Under the irradiation of a 532-nm continuous wave laser, a clear photovoltaic effect is observed and the magnitude ofphotovoltage increases as the temperature decreases, The results demonstrate the potential application of a Bi2SrzCo2Oy-based heterojunction in the photoelectronic devices.