High-performance λ=1.3 μm InGaAsP-InP strained-layerquantum well lasers

Compressively and tensile strained InGaAsP-InP MQW Fabry-Perot and distributed feedback lasers emitting at 1.3-μm wavelength are reported. For both signs of the strain, improved device performance over bulk InGaAsP and lattice-matched InGaAsP-InP MQW lasers was observed. Tensile strained MQW lasers show TM polarized emission, and with one facet high reflectivity (HR) coated the threshold currents are 6.4 and 12 mA at 20 and 60°C, respectively. At 100°C, over 20-mW output power is obtained from 250-μm-cavity length lasers, and HR-coated lasers show minimum thresholds as low as 6.8 mA. Compressively strained InGaAsP-InP MQW lasers show improved differential efficiencies, CW threshold currents as low as 1.3 and 2.5 mA for HR-coated single- and multiple quantum well active layers, respectively, and record CW output powers as high as 380 mW for HR-AR coated devices. For both signs of the strain, strain-compensation applied by oppositely strained barrier and separate confinement layers, results in higher intensity, narrower-linewidth photoluminescence emissions, and reduced threshold currents. Furthermore, the strain compensation is shown to be effective for improving the reliability of strained MQW structures with the quantum wells grown near the critical thickness. Linewidth enhancement factors as low as 2 at the lasing wavelength were measured for both types of strain. Distributed feedback lasers employing either compressively or tensile strained InGaAsP-InP MQW active layers both emit single-mode output powers of over 80 mW and show narrow linewidths of 500 kHz     

High-performance long-wavelength (λ~1.3 μm) InGaAsPNquantum-well lasers

We demonstrate high-performance InGaAsPN quantum well based long-wavelength lasers grown on GaAs substrates, nitrogen containing lasers emitting in the λ=1.2- to 1.3-μm wavelength range were grown by gas source molecular beam epitaxy using a RF plasma nitrogen source. Under pulsed excitation, lasers emitting at λ=1.295 μm exhibited a record low threshold current density (J_TH) of 2. 5 kA/cm². Lasers grown with less nitrogen in the quantum well exhibited significantly lower threshold current densities of J_TH =1.9 kA/cm² at λ=1.27 μm and J_TH=1.27 kA/cm² at λ=1.2 μm. We also report a slope efficiency of 0.4 W/A and an output power of 450 mW under pulsed operation for nitrogen containing lasers emitting at 1.2 μm     

λ=8.3 μm GaAs/AlAs quantum cascade lasers incorporatingInAs monolayers

The development of GaAs-based quantum cascade lasers incorporating indirect bandgap AlAs barriers in conjunction with ultrathin InAs layers in the active regions of the device is reported. The InAs layers produce a downshift of the energies of the lower lasing states, allowing laser emission to be observed at λ=8.34 μm. The GaAs/InAs/AlAs devices operate in pulsed mode up to a maximum temperature of 250 K, with a characteristic temperature of around 200 K for T>100 K     

Low-threshold strain-compensated InGaAs(N) (λ = 1.19-1.31μm) quantum-well lasers

Highly strained (Δa/a ~ 2.5%) In_0.4Ga_0.6 As and In_0.4Ga_0.6As_0.995N_0.005 -quantum-well (QW) active lasers utilizing strain-compensating InGaP-GaAsP buffer layers and GaAs_0.85P_0.15 barrier layers, grown by metal-organic chemical vapor deposition (MOCVD), are demonstrated with lasing emission wavelength of 1.185 and 1.307 μm, respectively. Threshold and transparency current density for the strain compensated InGaAsN QW lasers, with emission wavelength of 1.295 μm, are measured to be as low as 290 A/cm² (L = 1500 μm) and 110 A/cm², respectively, with characteristic temperature of T₀ and T₁ of 130 K and 400 K     

Strained-layer InGaAsP diode lasers with tapered gain region foroperation at λ=1.3 μm

A report is given of the first high-power InP-based tapered lasers. Continuous output powers of 0.5 W with nearly 80% of the power in the central lobe have been obtained. This is the highest reported brightness of a 1.3 μm source     

Pulsed and continuous-wave operation of long wavelength infrared(λ=9.3 μm) quantum cascade lasers

The operation of quantum cascade lasers at a wavelength (λ≃9.3 μm) well within the 8-13-μm atmospheric window is reported. A detailed study of intersubband luminescence in a vertical transition structure shows linewidths as narrow as ~10 meV at cryogenic temperatures, increasing to 20 meV at room temperature. Pulsed operation is demonstrated up to 220 K with a peak power ≈10 mW and ≈35 mW at 140 K. The temperature dependence of the threshold current density (J _th) is described by a high T₀ (128 K), J_th is also systematically studied as a function of cavity length to determine the peak gain and waveguide losses. Continuous-wave, single-mode operation is demonstrated up to 30 K with powers ≈2 mW     

Low-temperature sensitive, compressively strained InGaAsP active(λ=0.78-0.85 μm) region diode lasers

This letter reports comparative studies between (Al)GaAs versus InGaAsP active region edge-emitting semiconductor lasers for emission wavelength in the IR regime (λ=0.78-0.85 μm). High characteristic temperature T₀(200 K) and T₁ (450 K) edge-emitting diode lasers have been demonstrated by using the compressively strained (Δa/a=0,6%) Al-free (InGaAsP) active region with an emission wavelength of 0.85 μm. The high T₀ and T ₁ a result of low active-layer carrier leakage, will be beneficial for high-temperature and high-power operation. Implementation for InGaAsP-active VCSEL's with compressively strained InGaAsP-active layers and conventional DBR's is also discussed     

Temperature analysis and characteristics of highly strainedInGaAs-GaAsP-GaAs (λ > 1.17 μm) quantum-well lasers

Characteristic temperature coefficients of the threshold current (T₀) and the external differential quantum efficiency (T₁) are studied as simple functions of the temperature dependence of the physical parameters of the semiconductor lasers. Simple expressions of characteristic temperature coefficients of the threshold current (T₀) and the external differential quantum efficiency (T₁) are expressed as functions as physical parameters and their temperature dependencies. The parameters studied here include the threshold (J_th) and transparency (J_tr ) current density, the carrier injection efficiency (η_inj ) and external (η_d) differential quantum efficiency, the internal loss (α_i), and the material gain parameter (g_o). The temperature analysis is performed on low-threshold current density (λ = 1.17-1.19 μm) InGaAs-GaAsP-GaAs quantum-well lasers, although it is applicable to lasers with other active-layer materials. Analytical expressions for T ₀ and T₁ are shown to accurately predict the cavity length dependence of these parameters for the InGaAs active lasers     

Long-wavelength (λ=10 μm) quadrupolar-shaped GaAs-AlGaAsmicrolasers

In this paper, we present experimental results of our investigations on deformed GaAs-AlGaAs microlasers emitting around λ=10 μm. These quantum cascade lasers exhibit interesting features regarding the threshold current densities, optical output, and far-field pattern. A slight aberration from a circular cross section decreases the threshold current density for microlasers (which have a radius of 50 μm). For larger deformations ϵ, the threshold starts to increase because of the increasing mirror losses. For smaller microlasers (radii between 22 and 34 μm), the threshold current density increases already for slight deformations due to the increase of the mirror losses. The experimental results can be fitted very well with the mirror losses as a fitting parameter using a well-known and simple model. Threshold currents as low as 170 mA are measured for a cylindrical microlaser with a radius of 22 μm. The peak optical output is increasing quasi-exponentially with rising deformation. Lasing emission from slightly concave resonator shapes is detected. The bow-tie mode and other modes-different from Whispering-gallery modes-are responsible for highly directed emission along the diagonal axis and along the short axis, respectively, of the microlasers. Single-mode emission with a side-mode suppression ratio larger than 25 dB is shown over the entire drive current range for a highly deformed microlaser. The laser line can be temperature tuned with Δν/T=-0.027 cm^-1/K. A dual mode switching depending on the drive current with a mode spacing of Δν=8.1 cm^-1 between 999 and 1007.1 cm^-1 is observed for a less deformed microlaser     

Improved performance of GaAs-AlGaAs superlattice quantum cascadelasers beyond λ=13 μm

Highly improved quantum cascade lasers based on intraband transitions in a chirped AlGaAs-GaAs superlattice have been realized. Lasing in a liquid nitrogen environment with a laser wavelength centered at 13 μm and with a peak optical power per facet exceeding 80 mW is achieved. A threshold current density of 8.6 kA/cm² at 80 K has been measured. Multimode lasing spectra ranging from 12.4 to 13.3 μm and single mode spectra in a short cavity at 13 μm are obtained. To improve the gain in the structure, the design of the injector is optimized. The minibands in the active region are more strongly confined beneath the conduction band edge of the barriers to decrease electron losses into the continuum. The maximum operating temperature exceeds 230 K with T₀ values of 170 K     

Room-temperature long-wavelength (λ=13.3 μm) unipolarquantum dot intersubband laser

Long-wavelength (λ=13.3 μm) unipolar lasing at 283 K from self-organised In_0.4Ga_0.6As/GaAs quantum dots, due to intersubband transitions in the conduction band, is demonstrated for the first time. The threshold current density under continuous wave operation is 1.1 kA/cm² for a 60 μm×1.2 mm broad-area plasmon-enhanced waveguide device and the maximum power output is ≈ μW. The long intersubband relaxation time in quantum dots, together with the short lifetime in the ground state, due to interband stimulated emission, help to achieve the necessary population inversion and gain     

High-performance 1.5 μm wavelength InGaAs-InGaAsP strainedquantum well lasers and amplifiers

Improved performance of 1.5-μm wavelength lasers and laser amplifiers using strained In_xGa_1-xAs-InGaAsP quantum well devices is reported. The device structures fabricated to study the effects of strained quantum wells on their performance are described. These devices showed TM mode gain, demonstrating the strain-induced heavy-hole-light hole reversal in the valence band. Lasers using these tensile strained quantum wells show higher and narrower gain spectra and laser amplifiers have a higher differential gain compared to compressively strained quantum well devices. Consequently, the tensile strained quantum well lasers show the smallest linewidth enhancement factor α=1.5 (compression α=2.5) and the lowest K-factor of 0.22 ns (compression K=0.58 ns), resulting in an estimated intrinsic 3 dB modulation bandwidth of 40 GHz (compression 15 GHz)     

1.5 μm λ/4 shifted multiple quantum well distributedfeedback laser diodes

1.5 μm λ/4 shifted multiple quantum well distributed feedback laser diodes have been achieved for the first time. A characteristic temperature value for a threshold current at around room temperature was as high as 88 K. Spectra at 0.9 times the threshold current showed substantial TM mode suppression. The MQW active region consists of four GaInAs wells (75 Å thick) and GaInAsP barriers (λ_g=1.15 μm, 150 Å thick) grown by metalorganic vapour phase epitaxy (MOVPE). 1.3 μm GaInAsP was grown as an optical guide layer     

InGaAsP (λ=1.3 μm) strip buried heterostructure lasersgrown by MOCVD

The authors describe InGaAsP-InP index guides strip buried heterostructure lasers (SBH) operating at 1.3 μm with a 1.1-μm guiding layer grown by a two-step atmospheric pressure metalorganic chemical vapor deposition (MOCVD) growth procedure. These lasers are compared with buried heterostructure lasers having similar guiding layers under the active layer but terminated at the edge of the active layer. SBH lasers with 0.15-μm-thick active layer strips, 5-μm wide, and guide layers varying from 0 to 0.7 μm have threshold currents increasing from 34 to 59 mA, and nearly constant differential external quantum efficiencies of 0.2 mW/mA. The threshold current increases more rapidly with temperature with increasing guide layer thickness, with T₀ decreasing from 70°C for lasers without a guide layer to 54.3°C for lasers without a guide layer to 54.3°C for lasers with 0.7-μm-thick guide layers. Output powers of up to 30 mW/facet have been obtained from 254-μm-long lasers and were found to be insensitive to guide layer thickness     

Gain-coupled strained layer MQW-DFB lasers with an essentiallysimplified fabrication process for λ=1.55 μm

A gain-coupled (GC) strained-layer (SL) multi-quantum-well (MQW) distributed-feedback (DFB) laser with a metallized surface grating and a substantially simplified fabrication process made by single-step epitaxy without corrugation overgrowth is described. The complex coupling coefficient can be adjusted by the contact metallization. Room-temperature single-mode continuous-wave (CW) operation with a threshold current of 22 mA, an output power of 20 mW, and a linewidth of 2.5 MHz is demonstrated     

Continuous wave operation of long wavelength (λ≃11μm) inter-miniband lasers

A long wavelength (λ≃11 μm) quantum cascade laser based on inter-miniband transitions in semiconductor superlattices is reported. The device operates continuous wave up to a temperature of 85 K, with a maximum output power of 75 mW at 25 K. Both record values for unipolar lasers of comparable wavelength     

Germanium-diffused waveguides in silicon for λ=1.3 μm andλ=1.55 μm with losses below 0.5 dB/cm

The authors present a simple technique for the fabrication of integrated optical channel waveguides that are prepared by indiffusion of an E-beam evaporated amorphous alloy of germanium and silicon into commercially available silicon with low dopant concentration, using only simple technological processes such as standard lithography, PVD, and diffusion. The waveguides are polarization independent and have waveguide losses as low as 0.3 dB/cm at wavelengths of λ=1.3 μm and λ=1.55 μm. The spot sizes are well suited for low-loss single-mode fiber device coupling, being on the order of a few microns in both horizontal and vertical directions     

High-power long-wavelength (λ~11.5 μm) quantum cascadelasers operating above room temperature

High-temperature operation (T=320 K) of quantum cascade lasers has been extended to 11.5-μm wavelengths with high performances. Peak-pulsed optical power of 55 mW is obtained at 300 K with a high T ₀=172 K, in good agreement with our theoretical model     

Room-temperature long-wavelength (λ=13.3 μm) unipolarquantum dot intersubband laser [and reply]

For original paper see Krishna et al., ibid., vol. 36, p.1550-1555 (2000). Krishna et al. reported a “quantum dot far infrared (λ = 13.3 μm) laser, based on transitions between discrete bound electron states in self-organised quantum dots”. Weber et al. argue that insufficient experimental evidence for such a claim was presented in the work. Krishna et al. reply to the comment and report that they have carried out further work which makes them believe that they observe dominant stimulated emission and gain in these devices, with a distinct threshold and polarisation of the output     

Continuous wave operation of λ~19 μm surface-plasmonquantum cascade lasers

Continuous wave laser action has been achieved in a superlattice quantum cascade device operating on surface plasmon waveguide modes. The emission wavelength λ~19 μm is by far the longest ever reported for continuous wave III-V semiconductor lasers. The output power at cryogenic temperature is of the order of the mW