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     

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     

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     

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     

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     

Reliability in InGaAsP/InP buried heterostructure 1.3 µm lasers

A study was conducted of aging-induced Sn whisker growth at the surface of Au-Sn bonding solder layers around a laser chip, as well as metallurgical reactions, especially in p-side down lasers, at the interface of the solder and laser crystal just below the active layer. These phenomena cause electrical shorts in InGaAsP/InP laser diodes, which occur suddenly in devices operated for long periods without any previous symptoms having appeared in their aging characteristics. To completely eliminate such failures, a novel assembling method in which chips were mounted p-side up on semiinsulating SiC submounts using Pb-Sn solder, was applied to InGaAsP/InP buried heterostructure (BH) lasers emitting at 1.3 μm. BH lasers assembled by this method do not suffer any shorting failure even after 8000 h operation under 60°C and 5 mW/facet output conditions. The small degradation rates obtained, for example, 3 percent/kh (median) at 60°C, certify the reliability of these improved lasers. As long as the stripe width of the active layer was optimized to be in the range of1.5-2.5 mum necessary for obtaining kink-free light output versus current properties, no detrimental changes in laser characteristics, including transverse and longitudinal modes and dynamic output response, were observed in aged lasers. In this paper, the long-term degradation modes observed are presented, and possible causes are discussed.     

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     

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     

15 Gb/s multichannel optical interconnect laser array transmitteroperating at λ=1.3 μm

We have fabricated and measured detailed bit error rate experiments on a 12 channel optical interconnect transmitter operating at rates up to 1.25 Gb/s per channel, using InGaAsP/InP λ=1.3 μm lasers. The lasers are highly uniform, the channel crosstalk is less than 1 dB, and the mode selective losses are low (<1 dB). This transmitter has been demonstrated in an architecture which would allow the transmission of 120 channels of 100-Mb/s uncompressed video signals     

High-performance strain-compensated InGaAs-GaAsP-GaAs(λ=1.17 μm) quantum well diode lasers

This letter reports studies on highly strained and strain-compensated InGaAs quantum-well (QW) active diode lasers on GaAs substrates, fabricated by low-temperature (550°C) metal-organic chemical vapor deposition (MOCVD) growth. Strain compensation of the (compressively strained) InGaAs QW is investigated by using either InGaP (tensile-strained) cladding layer or GaAsP (tensile-strained) barrier layers. High-performance λ=1.165 μm laser emission is achieved from InGaAs-GaAsP strain-compensated QW laser structures, with threshold current densities of 65 A/cm² for 1500-μm-cavity devices and transparency current densities of 50 A/cm². The use of GaAsP-barrier layers are also shown to significantly improve the internal quantum efficiency of the highly strained InGaAs-active laser structure. As a result, external differential quantum efficiencies of 56% are achieved for 500-μm-cavity length diode lasers     

1.3 μm multiquantum well decoupled confinement heterostructure(MQW-DCH) laser diodes

A 1.3-μm multi-quantum-well decoupled confinement heterostructure (MQW-DCH) laser diode has been developed. This structure introduces internal barriers between the active quantum wells and the optical waveguide. It is thus possible to have, at the same time, deep quantum wells to prevent carrier leakage and a strong optical waveguide with a high confinement factor. The barrier parameters have been optimized using numerical modeling tools, and the DCH laser diode has been built using chemical beam epitaxy. The broad-area transparency current density is 140 A-cm^-2, the internal efficiency is 0.83, the waveguide loss is 5 cm^-1. and T₀ = 62 K. Ridge waveguide laser diodes have a room temperature threshold of 8 mA and an efficiency of 0.32 mW/mA     

V-grooved substrate buried heterostructure InGaAsP/InP laser emitting at 1.3 µm wavelength

Details of the fabrication, optimization of the dimensions of the active region, characteristics, and the aging results of theV- grooved substrate buried heterostructure (VSB) InGaAsP/InP laser are described. It is shown that the VSB laser can be fabricated in one-step epitaxy as well as two-step epitaxy. The active region width below 2.5 μm and the thickness of0.15-0.2 mum are shown to give stable fundamental mode operation and good temperature characteristics. The fundamental mode operation up to the optical output of 20 mW/facet at 25°C and the CW operation above 100°C are obtained. The pulse response showed the strongly damped relaxation oscillation with a frequency as high as 4.5 GHz. The spectral width under the modulation of 400 Mbit/s RZ single is as narrow as 25 Å in full width at half maximum. Highly stable aging characteristics at an elevated temperature of 50°C are obtained in both two-step epitaxy lasers and one-step epitaxy lasers.     

InGaAs-InGaAsP buried heterostructure lasers operating at 2.0 μm

Buried heterostructure lasers with highly strained InGaAs-InGaAsP active regions, emitting at 2 μm have been fabricated and tested. The lasers exhibited threshold current densities of 500 A/cm² for 1-mm-long cavities, an internal loss of 11 cm^-1, and characteristic temperatures as high as 50°C. The gain characteristics were also investigated and a linewidth enhancement factor of 8 was determined     

Miniature Mach-Zehnder InGaAsP quantum well waveguideinterferometers for 1.3 μm

Electrooptic Mach-Zehnder interferometers with active lengths as small as 350 μm are discussed. These strip-loaded waveguide devices utilize the electrooptic effect in InGaAsP/InP quantum wells to achieve pi phase shift with single arm drive voltages of 12 V and 6 V drive in push-pull operation     

High speed III-V electrooptic waveguide modulators at λ-1.3μm

Traveling wave GaAs electrooptic waveguide modulators at a wavelength of 1.3 μm with bandwidth in excess of 20 GHz have been developed and characterized. The design and characteristics of both p-i-n modulators in microstrip configuration and Schottky barrier on n ^--GaAs/semi-insulating (SI) GaAs in the coplanar strip configuration modulators are discussed. It is shown that microwave loss and slowing on n⁺ GaAs substrates will limit the bandwidth of the microstrip modulator to less than 10 GHz for a device 8 mm in length. Modulators with bandwidths in excess of 10 GHz are fabricated on SI GaAs substrates     

Optimization of Si1-xGex/Si waveguidephotodetectors operating at λ=1.3 μm

This paper analyzes the influence of various design parameters in the external quantum efficiency (QE) of waveguide detectors based on Si/Si_1-xGe_x strained-layer superlattices (SLSs), for use in optical communications at λ=1.3 μm. The study presents an algorithm that automatically generates structurally stable SLSs. This generation is completed by intensive simulation of the generated SLSs to calculate the external QE. The simulation embraces optical waveguiding, absorption, quantum size effect, as well as thermodynamics of the strained layers. Two sets of data were created using two different models for the SiGe layer critical thickness, h_c(x). A conservative model for h_c, corresponding to the equilibrium regime, yielded discrete maximum values for QE (around 12%) that were mainly dependent on the alloy absorption. A second model for h_c, corresponding to the metastable regime, produced considerably higher QEs (around 60%), and shows the great importance of fiber-to-waveguide coupling efficiency. The importance of the passive-waveguide coupler geometry is investigated using the beam propagation method     

High reliability low-threshold InGaAsP ridge waveguide lasersemitting at 1.3 μm

The fabrication, performance, and reliability of InP/InGaAsP ridge waveguide lasers emitting at 1.3 μm is described. The structure requires only one stage of planar wafer growth and simple fabrication steps and is therefore an inherently low-cost product. Threshold currents are typically 25-30 mA, and the external quantum efficiency is 20-25% per facet. Output power in the fundamental mode is maintained to above 10 mW, while total power in excess of 100-mW CW at 20° has been obtained. The life test data have been fitted to a power-law drift model to predict long-term behavior and is consistent with total lifetimes in excess of 25 years. The device is eminently suited for applications in high-reliability high-capacity fiber-optic communications systems     

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     

High-temperature CW operation of planar buried-ridge structurelasers at λ=1.5 μm

GaInAsP/InP-PBRS lasers emitting at 1.5 μm have been fabricated by multiple liquid-phase epitaxy. Effective current confinement is achieved without current blocking layers. CW threshold current is as low as 9 mA at 25°C. Output powers per facet of up to 10 mW at 80°C and 3.5 mW at 100°C are obtained. The maximum operation temperature of 110°C is the highest value yet achieved with this type of laser at 1°5 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