Temperature dependent characteristics of InAs/GaAs quantum dot laser grown by gas source molecular beam epitaxy

We report on the temperature dependent lasing characteristics of InAs/GaAs quantum dot lasers under continuous wave mode. The five-stacked InAs quantum dots were grown by gas-source molecular beam epitaxy with slightly different thickness. Ridge waveguide laser with stripe width of 6 μm was processed on the growth structure. The characteristic temperature was measured as high as infinity in the temperature range of 80–180 k. With the increase of injection current, the lasing spectra of laser diode broaden gradually at low temperature of 80 k. However, when the operation temperature increases from 80 to 300 K, the width of lasing spectrum reduces gradually from 40 to 2.0 nm. The lasing process is obviously different from that of a reference quantum well laser which widens its width of lasing spectra by increasing operation temperature. These experiments demonstrate that a carrier transfer from the smaller size of dots into larger dots caused by thermal effect play an important role in the lasing characteristic of quantum dot lasers. In addition, the laser can operate at maximum temperature of 80 °C under continuous wave mode with a maximum output power of 52 mW from one facet at 20 °C. A wavelength thermal coefficient of 0.196 nm/K is obtained, which is 2.8 times lower than that of QW laser. The low wavelength thermal coefficient of quantum dot laser is mainly attributed to its broad gain profile and state filling effects.     

Below-band-gap waveguiding behaviors of a weakly index-guided GaAs/AlGaAs quantum well laser

We report the reduced waveguiding efficiency for the signals around 1560 nm as the injection current of an GaAs/AlGaAs multiple quantum well laser diode (lasing wavelength at 840 nm) with a ridge-loading waveguide configuration increased. This reduction trend stopped when the injection current reached the threshold condition of the laser diode. The decreased waveguide transmission and the more expanded mode profile indicated the variation of the effective refractive index gradient in the lateral dimension with injection current. This variation was due to the refractive index decrease with increasing carrier density even below band gap. A slab waveguide model was used to simulate the lateral mode profile variation with injection current. The refractive index differences between the guiding layer and claddings in the slab waveguide model provided estimates of refractive index contrasts of the laser diode at a concerned wavelength under various injection conditions.     

Mid-infrared spectroscopic studies and lasing in GaAs–AlGaAs quantum cascade devices

Complementary intersubband and interband optical measurements have been employed in order to study GaAs–AlGaAs quantum cascade light-emitting diode and laser structures. Using these techniques, we have measured the redistribution of electrons throughout the bridging regions and upper states in the active regions of the diode device with increasing bias. The high quality of the sample gives very narrow line widths in the optical spectra, permitting the resolution of transitions involving closely spaced energy levels. This has allowed the direct observation of level alignment at the onset of current flow through the device. In addition, stimulated emission at λ=9.7 μm has been observed from a GaAs–AlGaAs laser structure under pulsed operation. A threshold current density of 6.5 kA/cm² and peak power 300 mW are measured at 10 K and lasing operation is observed up to 200 K.     

670 nm AlGaInP/GaInP strained multi-quantum well laser diode with high characteristic temperature (T 0)

A 670 nm AlGaInP/GaInP strained multi-quantum well laser diode with a high characteristic temperature (T ₀) has been achieved by optimization of quantum well structures and the metal-organic chemical vapour deposition process. The hole concentration of 5×10¹⁷ cm^-3 in the p-AlGaInP cladding layer on a (100) 5° off GaAs substrate has been obtained with very small ratio, 0.35, of mole flow rate of zinc source to the group III sources ([DEZn]/[III]) of 0.35. The threshold current and maximum temperature for continuous wave operation of lasers with cavity length of 300 m have been measured as 45 mA and 80°C, respectively. The characteristic temperature (T ₀) of the lasers has been measured as high as 153 K. The laser without facet protections could operate for more than 1000 h at 50°C and 5 mW.     

Low-threshold mid-IR MgO:PPLN optical parametric generation with high reflectivity mirror for signal wavelength

A low-threshold middle-infrared(mid-IR) MgO:PPLN optical parametric generation(OPG)pumped by a laser diode(LDl end-pumped Z-type Nd:YLF laser at 1047 nm is realized with high reflectivity(HR) mirror for signal.At repetition rate of 10 kHz,the OPG threshold of 50μJ has been achieved with HR mirror for signal.Compared with the threshold without mirror,the threshold decreases by 17%.Using HR mirror for pump at output side of crystal,the threshold of 40μJ is achieved.The 2.7-4.1μm continuous tunable output is produced with seven grating periods from 28.5 to 31.5μm and temperatures from 30 to 200℃.When the incident average pump power is 3 W.the OPG idler output power is 0.46 W at 3.26 μm,which corresponds to optical-to-optical conversion efficiency up to 15.3%.     

Temperature and injection current dependent electroluminescence study of GaInP/AlGaInP quantum well laser diode grown using tertiarybutylarsine and tertiarybutylphosphine

GaInP/AlGaInP triple quantum well (TQW) lasers, grown by metalorganic chemical vapor deposition (MOCVD) using tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP), were fabricated with a pulsed anodic oxidation (PAO) process. The devices worked at room temperature (RT) with the lowest threshold current density (J_th) of 1.5 kA/cm² ever reported for GaInP/AlGaInP lasers grown using TBAs and TBP. Temperature dependent (35–250 K) electroluminescence (EL) study of the GaInP/AlGaInP laser diode showed almost the same luminescence quenching behavior at a high temperature region (120–250 K), independent of the injection current (100–150 mA). A model involving a nonradiative recombination mechanism was presented to interpret the EL quenching behavior over the experimental temperature range. The nonradiative recombination centers in the Al-containing barrier or cladding layer are believed to contribute to the loss of carriers via nonradiative recombination. PACS 78.60.Fi; 71.20.Nr; 78.67.De; 81.15.Gh; 42.55.Px     

1.06 μm InGaAs/InGaAsP量子阱半导体激光器的温度特性

研究了1.06 μm InGaAs/InGaAsP量子阱半导体激光器厘米bar模块的温度特性,测试分析了该模块的输出光功率、阈值电流、转换效率和光谱随注入电流及管芯温度变化的特性。结果表明,器件在15~55 ℃范围内所测的输出光功率由40.7 W降低到29.4 W,阈值电流由9.29 A升高到17.24 A,转换效率由54.22%降低到37.55%,光谱漂移为0.37 nm/℃,特征温度为68.6 K。实验结果表明,为保持器件性能的稳定,在实际应用过程中应该使器件的温度控制在15~25 ℃范围内。     

Watt-level ~2 μm laser output in Tm3+-doped tungsten tellurite glass double-cladding fiber

We report, for the first time to the best of our knowledge, a watt level cw fiber laser at ~2 μm from a piece of 40-cm-long newly developed highly thulium-doped (3.76 × 10(20) ions/cm(3)) tungsten tellurite glass double cladding fiber pumped by a commercial 800 nm laser diode. The maximum output power of the fiber laser reaches 1.12 W. The slope efficiency and the optical-optical efficiency with respect to the absorbed pump are 20% and 16%, respectively. The lasing threshold is 1.46 W, and the lasing wavelength is centered at 1937 nm.     

GaSb-based type-I quantum well cascade diode lasers emitting at nearly 2-μm wavelength with digitally grown AlGaAsSb gradient layers

We report a GaSb-based type-I quantum well cascade diode laser emitting at nearly 2-μm wavelength. The recycling of carriers is realized by the gradient AlGaAsSb barrier and chirped GaSb/AlSb/InAs electron injector. The growth of quaternary digital alloy with a gradually changed composition by short-period superlattices is introduced in detail in this paper. And the quantum well cascade laser with 100-μm-wide, 2-mm-long ridge generates an about continuous-wave output of 0.8 W at room temperature. The characteristic temperature T₀ is estimated at above 60 K.     

Amplified luminescence in InGaAs/AlGaAs laser diode arrays at high pump levels

The development of amplified luminescence fluxes in powerful InGaAs/AlGaAs laser diode arrays (lasing wavelength 940–960 nm) has been studied experimentally and theoretically at pump levels above the threshold value. Flux density values for amplified luminescence propagation along (1.88⋅10⁹ W/m²) and across (1.21⋅10⁹ W/m²) the laser diode array cavity axis have been evaluated for the threshold pump level at room temperature (293 K). The contribution of the recombination rate induced by the amplified luminescence to the threshold current generation of the laser diode array reaches 7%. It has been shown that the amplified luminescence flux density is increased by 49% as the pump level rises from one to three threshold values.     

Widely tunable continuous-wave Raman laser in diatomic hydrogen pumped by an external-cavity diode laser

What is to the authors' knowledge the first experimental demonstration of a nonresonant cw Raman laser pumped by a tunable external-cavity diode laser (ECDL) is presented. The ECDL is phase-frequency locked to a high-finesse Raman laser cavity containing diatomic hydrogen (H(2)) by the Pound-Drever-Hall locking technique. The Stokes lasing threshold occurs at a pump power of 400 +/- 30 muW, and a maximum photon conversion efficiency of 12.0 +/- 1.3% is achieved at 1.6 mW of pump power. A 40-nm tuning range of the cw Stokes emission, 1174-1214 nm, is obtained by tuning of the wavelength of the ECDL pump source.     

Experimental modulation bandwidth beyond the relaxation oscillation frequency in a monolithic twin-ridge laterally coupled diode laser based on lateral mode locking

Monolithic twin-ridge laterally coupled diode lasers emitting at 1.3microm are presented that have a small-signal modulation bandwidth beyond the relaxation oscillation frequency of a single ridge. Spectra and spectrally resolved far fields are presented for three bias conditions: only one ridge lasing, both ridges lasing just above threshold, and both ridges lasing at biases well above threshold. In the first two cases the spectrum has single-peaked longitudinal modes, whereas the third cases shows splitting to in-phase and out-of-phase modes. The splitting frequency of the optical spectrum is measured to be 7.7 GHz. Small-signal modulation measurements reveal a strong resonance at 7.7 GHz, demonstrating an effect of lateral mode locking. As a result of this effect, the twin-ridge laser can be made to have a -3-dB bandwidth beyond that associated with its relaxation oscillation frequency.     

大功率780 nm半导体激光器的设计与制备

设计并制备了一款780 nm半导体激光器,并进行了外腔反馈锁模研究。利用金属有机化学气相沉积技术制备了激光器外延层,采用GaAsP/GaInP作为量子阱/波导层有源区,限制层采用低折射率AlGaInP材料。采用超高真空解理钝化技术,在激光器腔面蒸镀无定形ZnSe钝化层。未钝化器件在输出功率2.5 W时发生腔面灾变损伤（COD）,钝化后器件未发生COD现象,电流在10 A时输出功率10.1 W,电光转换效率54%。体布拉格光栅（VBG）外腔锁定前后,器件的光谱半峰全宽分别为2.6 nm和0.06 nm,VBG变温调控波长范围约230 pm。     

High power red-light GaInP/AlGaInP laser diodes with nonabsorbing windows based on Zn diffusion-induced quantum well intermixing

The layer structure of GaInP/AlGaInP quantum well laser diodes (LDs) was grown on GaAs substrate using low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique. In order to improve the catastrophic optical damage (COD) level of devices, a nonabsorbing window (NAW), which was based on Zn diffusion-induced quantum well intermixing, was fabricated near the both ends of the cavities. Zndiffusions were respectively carried out at 480, 500, 520, 540, and 580 ℃ for 20 minutes. The largest energy blue shift of 189.1 meV was observed in the window regions at 580 ℃. When the blue shift was 24.7 meV at 480 ℃, the COD power for the window LD was 86.7% higher than the conventional LD.     

一种结构新颖的L波段掺铒光纤激光器

提出了一种结构新颖的L波段环形腔掺铒光纤激光器。用掺铒光纤作为增益介,采用980nm激光器作为前向抽运源,利用起偏器和偏振控制器获得L波段激光,利用光环形器将后向的放大自发辐射再引入铒光纤的前端,重复利用。当抽运功率为103mW时得到了阈值功率约为23．87mW,输出功率达6．34mW的激光输出,斜率效率约为8．05％,与没有重复利用后向放大自发辐射谱的掺铒光纤激光器做比较,该结构对L波段掺铒光纤激光器的性能有明显的提升作用。对于长度不合适的铒纤,在没有重复利用后向放大自发辐射谱时没有获得激光输出;而在利用后向放大自发辐射后,在阈值功率约为88mW时得到了激光输出,从而很好地证明了上述结论。     

MOCVD growth of A1GaInP/GaInP quantum well laser diode with asymmetric cladding structure for high power applications

In order to improve the characteristics of the general broad-waveguide 808-nm semiconductor laser diode （LD）, we design a new type quantum well LD with an asymmetric cladding structure. The structure is grown by metal organic chemical vapor deposition （MOCVD）. For the devices with 100-ttm-wide stripe and 1000-/zm-long cavity under continuous-wave （CW） operation condition, the typical threshold current is 190 mA, the slope efficiency is 1.31 W/A, the wall-plug efficiency reaches 63%, and the maximum output power reaches higher than 7 W. And the internal absorption value decreases to 1.5 cm^-1.     

The study of a Tm:YLF laser pumped by a Raman shifted Erbium fiber laser at 1678 nm

A Tm:YLF laser pumped by a Raman shifted Er-fiber laser at 1.678 μm was studied at two Tm³⁺ ion concentrations equal to 1.5% and 5%. At output powers up to 460 mW the measured lasing efficiency at a wavelength of ~ 1.93 μm was as high as ~ 50%. The lasing performance was compared with that obtained under pumping by a 792-nm laser diode. The temporal structure of the laser pulse was recorded and the beam propagation factor M² was measured for all pumping conditions.     

Lasing spectra of 1.55 μm InAs/InP quantum dot lasers: theoretical analysis and comparison with the experiments

In this paper, a theoretical model is used to investigate the lasing spectrum properties of InAs/InP (113)B quantum dot (QD) lasers emitting at 1.55 μm. The numerical model used is based on a multi-population rate equation (MPRE) analysis. It takes into account the effect of the competition between the inhomogeneous broadening (due to the QD size dispersion) and the homogenous broadening as well as a nonlinear gain variation associated to a multimode laser emission. The double laser emission and the temperature dependence of lasing spectra of self-assembled InAs/InP quantum dot lasers is studied both experimentally and theoretically.     

Spectroscopic and travelling-wave lasing characterisation of tetraphenylbenzidine and di-naphtalenyl-diphenylbenzidine

The organic light emitting diode (OLED) hole transport molecules N,N,N’,N’-tetraphenylbenzidine (TPB, triphenylamine dimer TAD or TPD) and N,N’-bis(2-naphtalenyl)-N,N’-bis(phenylbenzidine) (β-NPB, naphtyl-diphenylamine dimer β-NPD), dissolved in tetrahydrofuran (THF) and as neat film, are characterized by optical absorption and emission spectroscopy. The absorption and stimulated emission cross-section spectra, the fluorescence quantum distributions, fluorescence quantum yields, degrees of fluorescence polarization, and fluorescence lifetimes are determined. The lasing behaviour is studied by picosecond laser pulse excitation (excitation wavelength 347.15 nm, pulse duration 35 ps). The excited-state absorption at the pump laser wavelength is determined by saturable absorption measurement. Low-Q laser oscillation of TPB in THF is achieved by transverse pumping of the dye in a cell. The excited-state absorption of TPB in THF at the laser wavelength is extracted from the laser threshold. In TPB neat films, wave-guided travelling-wave lasing was obtained. No laser action was achieved for β-NPB because of small S₁-S₀ stimulated emission cross-section, and the presence of excited-state absorption in the fluorescence wavelength region. The TPB and β-NPB results are compared with the corresponding spectroscopic and lasing behaviour of the related methyl-substituted triphenylamine dimers, 3-methyl-TPD and 4-methyl-TPD, which are well established OLED hole transport materials.     

Structure Optimisation of a Possible 1.5-μm GaAs-based Vertical-cavity Surface-emitting Laser Diode with the GaInNAsSb/GaNAs Quantum-well Active Region

Structure optimisation of the GaAs-based GaInNAsSb/GaNAs quantum-well (QW) vertical-cavity surface-emitting diode lasers (VCSELs) has been carried out using the comprehensive three-dimensional self-consistent physical model of their room-temperature (RT) continuous-wave (CW) threshold operation. The model has been applied to investigate a possibility to use these devices as carrier-wave lasing sources in the third-generation optical-fibre communication. In this simulation, all physical (optical, electrical, thermal and gain) phenomena crucial for a laser operation including all important interactions between them are taken into consideration. As expected, the 1.5λ-cavity VCSEL has been found to demonstrate the lowest RT CW threshold. However, for many VCSEL applications, the analogous VCSEL equipped with a longer 3λ-cavity should be recommended because it exhibits only slightly higher threshold but manifest much better mode selectivity – the desired single-fundamental-mode operation has been preserved in these devices up to at least 380 K. The Auger recombination has been found to be decidedly the main reason of the threshold current increase at higher temperatures. A proper initial red detuning of the resonator wavelength with respect to the gain spectrum may drastically decrease CW lasing thresholds, especially at higher temperatures.