Ultra-low temperature sensitive deep-well quantum cascade lasers (λ - 4.8 μm) via uptapering conduction band edge of injector region

A new design feature for deep-well quantum cascade (QC) lasers, in which the conduction band edge of the injector region is uptapered, results in virtual suppression of carrier leakage out of the active regions of 4.8 mm emitting devices. For heatsink temperatures in the 20?90°C range the characteristic temperature coefficients for threshold, T₀, and slope efficiency, T₁, reach values as high as 278 and 285 K, respectively, which are nearly twice the values for conventional QC lasers. At 20°C, the threshold current density for uncoated, 30 period, 3 mm-long devices is only ~1.8 kA/cm².     

Nanofaceting and alloy decomposition: From basic studies to advanced photonic devices

Most of the modern epitaxial structures for semiconductor lasers serving the needs of optical storage and fiber pumping are grown on misoriented GaAs(0 0 1) substrates. It has been found in metal-organic vapor-phase epitaxy that surface misorientation helps to achieve better epitaxial quality of the alloy layers. On the other hand, these misoriented or, in other definition, high-index surfaces are known to undergo phase transformations, depending on the misorientation angle, from nanofaceting (like (3 1 1)A, (3 1 1)B, (3 3 1), (2 1 1)B GaAs surfaces) to arrays of step bunches (like (7 7 5) GaAs, etc.). In the present paper, we consider growth-related effects during growth of both standard and advanced laser structures on GaAs substrates which are typically used for growth of 650 nm GaAlInP devices. We show that the active region of the laser structures represents a corrugated superlattice with a 25 nm in-plane periodicity, while the surrounding layers are natural superlattices with a 5 nm vertical periodicity. Corrugated superlattice used as an active region manifests itself through a strong modification of optical properties. Strong in-plane polarization evidences the formation of arrays of quantum wires. Both standard and advanced red laser have been grown and processed. The advanced lasers have demonstrated a vertical beam divergence of only 7–8° full-width at half-maximum (FWHM). The advanced lasers with 10 μm-wide stripes demonstrate continuous wave (CW) power up to 200 mW and the lateral beam divergence of 4°, and those with 4 μm-wide stripes show CW power up to 120 mW and the lateral beam divergence of 6.5°. No facet passivation has been applied and the power is limited by the catastrophic optical mirror damage (COMD). 20 W pulsed power has been achieved in 100 μm-wide stripes for the advanced design and 6 W has been obtained for the standard design. The advantage comes from the design optimization of the laser waveguide using the concept of the longitudinal photonic bandgap crystal. We believe that also the optimization of the active region with better utilization of the nanofaceting effects may enable, in addition, a dramatic extension of the emission wavelength towards bright red (620–630 nm) and, probably, yellow (580 nm) spectral ranges.     

(InAs)/sub 1//(GaAs)/sub 4/ superlattice strained quantum well laser at 980 nm

The first successful MBE growth of (InAs)/sub 1//(GaAs)/sub 4/ short-period superlattice (SPS) strained quantum well lasers emitting at approximately 980 nm is reported. The SPS consists of six periods of one and four monolayers of InAs and GaAs, respectively. The measured threshold current density was approximately 100 A cm/sup -2/ for 0.96 mm long lasers. Devices have operated up to 170 degrees C with a characteristic temperature T/sub 0/ of 148 K. The (InAs)/sub m//(GaAs)/sub n/ superlattice is an ordered counterpart of the InGaAs random alloy, and provides an alternative method fabricating high speed electronic and photonic devices.<>     

120°C 20 Gbit/s operation of 980 nm VCSEL

980 nm VCSELs show under 20 Gbit/s large signal modulation clearly open eyes without adjustment of the driving conditions between 0 and 120°C.     

Optimization of GaAsP/AlGaAs-based QW laser structures for high power 800 nm operation

We present a detailed study of the MOVPE growth of 800 nm diode laser structures based on the combination of a GaAsP quantum well with well-established AlGaAs waveguide structures. By optimizing the strain and thickness of the quantum well highly-reliable diode lasers with low threshold current and high efficiency were demonstrated. 100 μm aperture “broad area” devices mounted epi-side up achieve a CW output power of 8.9 W with a wall-plug efficiency of 50%. These output powers represent record values for diode lasers in this wavelength range. Reliability measurements at 1.5 W and 50°C ambient temperature suggest lifetimes >10 000 h.     

High-power laser diodes based on asymmetric separate-confinement heterostructures

Asymmetric separate-confinement laser heterostructures with ultrawide waveguides based on AlGaAs/GaAs/InGaAs solid solutions, with an emission wavelength of ～1080 nm, are grown by MOCVD. The optical and electrical properties of mesa-stripe lasers with a stripe width of ～100 μm are studied. Lasers based on asymmetric heterostructures with ultrawide (>1 μm) waveguides demonstrate lasing in the fundamental transverse mode with an internal optical loss of as low as 0.34 cm^?1. In laser diodes with a cavity length of more than 3 mm, the thermal resistance is reduced to 2°C/W, and the characteristic temperature T ₀= 10°C is obtained in the range 0–100°C. A record-breaking wallplug efficiency of 74% and an output optical power of 16 W are reached in CW mode. Mean-time-between-failures testing for 1000 h at 65°C with an operation power of 3–4 W results in the power decreasing by 3–7%.     

High-power and low-threshold-current operation of 1.3 μm strain-compensated AlGaInAs/AlGaInAs multiple-quantum-well laser diodes

Low-threshold-current and high-temperature operation of 1.3 μm wavelength AlGaInAs/AlGaInAs strain-compensated multiple-quantum-well laser diodes (LDs) with a linearly graded index separate confinement heterostructure also made up of AlGaInAs has been successfully fabricated. The threshold current density and differential quantum efficiency are 400 A/cm² and 22% for the as-cleaved broad-area LDs with a 900 μm cavity length, respectively. The calculated internal quantum efficiency, internal optical loss, and threshold gain are 23%, 6.5 cm⁻¹, and 45 cm⁻¹, respectively. The threshold current and slope efficiency at room temperature for the 3 μm-ridge-stripe LDs without facet coating are 12 mA and 0.17 W/A, respectively. The peak wavelength is at 1295 nm with an injection current of 60 mA. With increasing the temperature up to 100 °C, the threshold current will increase up to 41 mA. The characteristic temperature is around 78 K in the range from 20 to 60 °C and 56 K in the range from 60 to 100 °C. The wavelength swing varied with temperature is 0.43 nm/°C for the LDs operated at 60 mA and room temperature.     

Excimer laser with high repetition rate for DUV lithography

The 248nm wavelength of the KrF excimer laser is the accepted tool for the production of structures in the range of 0.25μm. When going to below 0.20μm, the even shorter excimer wavelength of 193nm will be used. The demands on the laser source have changed over the last years for both the reflective and the refractive Step&Scan tools. The cost-effective operation of such lithography tool requires excimer lasers with high power and repetition rates of ≥ 1kHz. Precise dose control of the exposure requires high repetition rate and stability of the laser output energy.     

Wideband uniplanar 180° phase switch

A wideband 180° phase switch is developed at millimetre-wave frequencies (31 GHz centre frequency) using uniplanar technology. The circuit is designed using coplanar-to-slotline transitions and commercial pin diodes as switching devices. The implementation is straightforward, fast in terms of fabrication and low-cost. The circuits tested, made on an alumina substrate, show a phase difference between states of 180° ± 2°, providing 40% bandwidth with in-band insertion loss lower than 2.5 dB and a return loss better than 10 dB. The phase switch provides a ±5° phase error in a bandwidth of around 60%, from 18 to 38 GHz.     

MOVPE growth of AlGaAs/GaInP diode lasers

GaAs-based diode lasers for emission wavelengths between 800 nm and 1060 nm with AlGaAs-cladding and GaInP-waveguide layers were grown by MOVPE. For wavelengths above 940 nm broad area devices with InGaAs QWs show state-of-the-art threshold current densities. Ridge-waveguide lasers fabricated by selective etching achieve 200 mW CW monomode output powers. (In)GaAsP QW-based diode lasers with an emitting wavelengths around 800 nm suffer from problems at the upper GaInP/AlGaAs interface. Asymmetric structures with a lower AlGaAs/GaInP and an upper AlGaAs/AlGaAs waveguide not only avoid this interface but also offer better carrier confinement. Such structures show very high slope efficiencies and a high T₀. Maximum output powers of 7 W CW are obtained from 4 mm long devices.     

Power stabilisation of uncooled 980 nm pump laser modules from 10to 100°C

Efficient fibre Bragg grating wavelength and power stabilisation of 980 nm pump lasers at high fibre-coupled output power (250 mW at 10°C and 95 mW at 100°C) over a wide temperature range of 90°C is demonstrated     

Spread spectrum clock generator with hybrid controlled oscillator

A spread spectrum clock generator (SSCG) with a hybrid controlled oscillator (HCO) is presented. By using the proposed HCO, the modulation ratio of an SSCG can be made insensitive to process, voltage and temperature variations without a ΣΔ fractional-N phase-locked loop. The simulated modulation ratio sensitivities are as low as -1.3%/ 100°C and 7.0%/V for temperature and V_DD, respectively. The SSCG IC, designed in a 0.18 μm 1P4M CMOS process, operates from 40 to 90 MHz and consumes 5.5 mA from a 1.8 V supply voltage.     

High-temperature operation of 650-nm wavelength AlGaInPself-pulsating laser diodes

Low-coherence self-pulsating laser diodes operating at a wavelength of 650 nm and at temperatures in excess of 70°C are required for high density optical storage systems. We report on AlGaInP lasers operating at this wavelength which exhibit stable self-pulsation up to a temperature of 100°C. The lasers are 50-μm-wide oxide-isolated stripe devices in which the saturable absorption necessary for pulsation is provided by multiple-quantum wells placed within the p-doped cladding layer. The pulsation frequency of the devices increases linearly with increasing drive current and is present up to 1.5 times, lasing threshold     

高功率266 nm全固态单频连续波激光器研究进展

高功率单频连续波266 nm激光在大容量信息存储、高分辨光谱监测及高精度紫外光刻等领域具有重要应用价值,近年来已成为国内外紫外激光领域的研究热点之一。文中首先综合比较了用于产生高功率266 nm紫外激光的非线性光学晶体基本性能,并根据主要的激光器频率锁定方法,重点分析了H?nsch-Couillaud (H-C)频率锁定和Pound-Drever-Hall (PDH)频率锁定方法的优缺点以及连续波单频266 nm激光器发展现状,介绍了本课题组最新研究成果,即基于H-C频率锁定方法实现了功率1.1 W的单频连续波266 nm紫外激光稳定输出。最后,针对进一步提升全固态单频连续波266 nm激光器性能亟需解决的问题和可能解决路径进行了简要分析和展望。     

Spectroscopy, modeling, and laser operation of thulium-dopedcrystals at 2.3 μm

Pulsed room-temperature lasers based on the thulium 2.3-μm ³H₄-³H₅ transition have been achieved in 1.5% Tm:YAG, 2% Tm:LuAG, and 1.5% Tm:YLF crystals using a pulsed alexandrite laser at 785 nm as the pump source in a collinear geometry. The absorbed energy thresholds (slope efficiencies) for 1.5% Tm:YAG, 2% Tm:LuAG, and 1.5% Tm:YLF lasers are measured to be 1.2 mJ (14%), 1.8 mJ (13%), and 1.0 mJ (18%), respectively, which are in good agreement with the theoretically predicted results. The experimental results indicate 1.0 mJ thulium to be the most optimum concentration for 2.3-μm laser action. The thulium lasers are tuned around 2.3 μm using an intracavity single birefringent plate of quartz     

High quality compressively strained InP-based GaInAs(P)/GaInAsP multi-quantum well laser structures grown by metalorganic vapor phase epitaxy

The growth and characterization of strained GaInAs and GaInAsP multiquantum well (MQW) laser structures has been investigated. The use of triple axis x-ray diffraction (XRD), in addition to the conventional high resolution double crystal XRD, yields further information about the structural integrity of these complex structures. Buried heterostructure lasers with eight GaInAsP wells (+1.0% strain, 80Å thick) exhibit a record low threshold current of 3.1 mA. By using a constant As/P ratio in the wells and barriers of an MQW laser structure, we have shown that the structure can be annealed at 700°C for 1 h with only a minimal shift (-4 nm) in the photoluminescence emission wavelength. Conventional lattice-matched GaInAs/GaInAsP MQW structures exhibit a shift of-46 nm under the same conditions.     

Monolithic multiple wavelength surface emitting laser arrays

A two-dimensional (2-D) surface emitting laser array emitting 140 unique, nonredundant, uniformly separated, single-mode wavelengths in the 980-nm regime is described. The wavelength separation between neighboring lasers is as small as 0.3 nm. A large total wavelength span of 43 nm was obtained without compromising the performance of the lasers. All 140 lasers have nearly the same threshold currents, voltages, and resistances. The techniques used are generic and can be readily extended to both longer and shorter wavelength lasers. The authors also report the first wavelength division multiplexing system experiment using part of this laser array. A BER (bit-error ratio) of 10 ^-9 at 155 Mb/s was obtained with simultaneous operation of four lasers at a wavelength separation of 1.5 nm. Negligible optical and electrical crosstalk was observed between the lasers     

Complex-coupled quantum cascade distributed-feedback laser

Quantum-cascade distributed-feedback lasers (QCDFB) with a grating close to the active region are reported. Feedback is provided by the grating in a refractive index-dominated coupling scheme. Reliable single-mode emission at /spl lambda//sub cm//spl ap/5.4 /spl mu/m with a side-mode suppression ratio (SMSR) /spl ap/30 dB is observed. The laser is continuously tunable over 40 nm with a coefficient of /spl Delta//spl lambda///spl Delta/T/spl ap/0.37 nm/K in the temperature range from 200 K to 300 K. Comparison with Fabry-Perot QC lasers shows an overall improved performance of QC-DFB lasers.     

Highly uniform operation of high-performance 1.3-μm AlGaInAs-InPmonolithic laser arrays

We describe the fabrication of monolithically integrated 1×12 arrays of 1.3-μm strain-compensated multiquantum-well AlGaInAs-InP ridge lasers. The laser array shows highly uniform characteristics in threshold current, slope efficiency, and lasing wavelength with a standard deviation of 0.08 and 0.27 mA, 0.012 and 0.007 W/A, and 0.59 and 0.57 nm, respectively, at 20°C and 100°C. Besides, each laser on the array exhibits a low threshold current of 8 mA at 20°C and 21 mA at 100°C, a characteristic temperature of 92 K, and a slope efficiency drop of 0.7 db between 20°C and 80°C. A low thermal crosstalk of less than -4 dB can be obtained from one diode as the injected current of other elements is increased to 70 mA. Also, each laser on the array has a negligible degradation after a 24-hr burn-in test at 80 mA and 100°C. An expected lifetime of more than 20 years is estimated for the lasers when operating at 10 mW and 85°C. The lasers have a small-signal modulation bandwidth of about 9 GHz at 25°C and a low relative intensity noise of -155 dB/Hz without an isolator at 2.5 GHz. It can transmit a 2.5-GHz signal to 50 km through standard single-mode fiber and to 308 m through multimode fiber, with a clear eye opening in OC-48 data-rate tests     

High T0 long-wavelength InGaAsN quantum-well lasersgrown by GSMBE using a solid arsenic source

We demonstrate high performance, λ=1.3- and 1.4-μm wavelength InGaAsN-GaAs-InGaP quantum-well (QW) lasers grown lattice-matched to GaAs substrates by gas source molecular beam epitaxy (GSMBE) using a solid As source. Threshold current densities of 1.15 and 1.85 kA/cm² at λ=1.3 and 1.4 μm, respectively, were obtained for the lasers with a 7-μm ridge width and a 3-mm-long cavity. Internal quantum efficiencies of 82% and 52% were obtained for λ=1.3 and 1.4 μm emission, respectively, indicating that nonradiative processes are significantly reduced in the quantum well at λ=1.3 μm due to reduced N-H complex formation. These Fabry-Perot lasers also show high characteristic temperatures of T₀ =122 K and 100 K at λ=1.3 and 1.4 μm, respectively, as well as a low emission wavelength temperature dependence of (0.39±0.01) nm/°C over a temperature range of from 10°C to 60°C