High Wall-plug Efficiency Research Articles

High performance quantum cascade lasers based on three-phonon-resonance design

A quantum cascade laser structure based on three-phonon-resonance design is proposed and demonstrated. Devices, emitting at a wavelength of 9 μm, processed into buried ridge waveguide structures with a 3 mm long, 16 μm wide cavity and a high-reflection (HR) coating have shown peak output powers of 1.2 W, slope efficiencies of 1 W/A, threshold current densities of 1.1 kA/cm2, and high wall-plug efficiency of 6% at 300 K. A 3 mm long, 12 μm wide buried-heterostructure device without a HR coating exhibited continuous wave output power of as high as 65 mW from a single facet at 300 K.

Beam quality of blue InGaN laser for projection

AbstractThe blue light sources of choice for laser projection will be long wavelength nitride lasers because of their high wall plug efficiency and their small form factor compared to blue light sources using second harmonic generation. High quality of the far field is required for laser projection. However, optical confinement of GaN/AlGaN structures becomes increasingly difficult when wavelength shifts from 405 nm to the true blue spectrum. We will show excellent far fields by suppression of higher order laser modes and by improved waveguiding, respectively. We present simulations of laser modes as a function of ridge width. The slow axis far field is improved by absorber layers that guarantee in‐plane values of M2 < 1.5. Sufficient vertical confinement of the laser light by thick cladding layers is necessary to suppress laser modes guided within the substrate. We present 440 nm lasers for projection with threshold currents of 20 mA and slope efficiencies more than 0.8 W/A. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

1.6 W high wall plug efficiency, continuous-wave room temperature quantum cascade laser emitting at 4.6μm

A strain-balanced, InP-based quantum cascade laser structure designed for light emission at 4.6μm was grown by metal-organic chemical vapor deposition. A maximum total optical power of 1.6W was obtained in continuous-wave mode at 300K for uncoated devices processed in buried heterostructure geometry with stripe dimensions of 5mm by 9.5μm. Corresponding maximum wall plug efficiency and threshold current density were measured to be 8.8% and 1.05kA∕cm2, respectively. Fully hermetically packaged laser of identical dimensions produced in excess of 1.5W under the same conditions.

The scalability of the tunnel-regenerated multi-active-region light-emitting diode structure

The scalability of the tunnel-regenerated multi-active-region (TRMAR) structure has been investigated for the application in light-emitting diodes (LEDs). The use of the TRMAR structure was proved theoretically to have unique advantages over conventional single-active-layer structures in virtually every aspect, such as high quantum efficiency, high power and low leakage. Our study showed that the TRMAR LED structure could obtain high output power under low current injection and high wall-plug efficiency compared with the conventional single-active-layer LED structure.

Buried heterostructure quantum cascade lasers with high continuous-wave wall plug efficiency

The authors report on the development of λ∼4.7μm strain-balanced InP-based quantum cascade lasers with high wall plug efficiency and room temperature continuous-wave operation. The use of narrow-ridge buried heterostructure waveguides and thermally optimized packaging is presented. Over 9.3% wall plug efficiency is reported at room temperature from a single device producing over 0.675W of continuous-wave output power. Wall plug efficiencies greater than 18% are also reported for devices at a temperature of 150K, with continuous-wave output powers of more than 1W.

High power temperature-insensitive 1.3 µm InAs/InGaAs/GaAs quantum dot lasers

We report on GaAs-based broad area (100 µm) 1.3 µm quantum dot (QD) lasers with high CW output power (5 W) and wall-plug efficiency (56%). The reliability of the devices has been demonstrated beyond 3000 h of CW operation at 0.9 W and 40 °C heat sink temperature with 2% degradation in performance. P-doped QD lasers with a temperature-insensitive threshold current (T0 > 650 K) and differential efficiency (T1 = infinity) up to 80 °C have been realized.

Tapered diode lasers at 976 nm with 8 W nearly diffraction limited output power

High-efficiency tapered diode lasers with ridge-waveguide structure emitting at 976 nm have been realised. High wall-plug efficiencies of more than 57% result in output powers of more than 12 W for a single emitter with 3.5 mm resonator length. A nearly diffraction limited behaviour has been demonstrated up to 8.3 W CW.

The electrical turn-on characteristics of vertical-cavity surface-emitting lasers

We present a detailed comparison of the electrical turn-on characteristics of 980 nm vertical-cavity surface-emitting lasers (VCSELs) with simulations using a recently extended laser simulator. It is shown that the three recombination mechanisms, spontaneous emission, Shockley–Read–Hall recombination, and Auger recombination, result in distinctly different exponential current–voltage dependencies below threshold. Therefore, information can be extracted about the relative strength of the recombination rates due to those processes, and their relative contributions to the threshold current can be assessed. We show that for the VCSELs studied in this work, spontaneous emission is the dominant contribution to the threshold current.

A simulation study on energy recovery from spent electron beams in an S-band linac

The feasibility of energy recovery with an S-band linac was studied based on two-dimensional particle-in-cell simulations. A 1-m standing-wave accelerating tube with 20 cells was chosen for the numerical model, with a 4.5-cell RF gun as the injector which is to be used for our IR FEL project. For ample reduction of beam energy to the dump with a typical beam energy from the gun of 5.49MeV, the phase acceptance of the re-injection of the spent beam is found to be ±0.16πrad which corresponds to a feasible longitudinal deviation of ±27ps. Furthermore, for a lower beam energy to the dump and a higher wall plug efficiency, simulations with a lower beam energy of 2.42MeV from the gun were carried out. Counter re-injection of the spent beam is found to be effective for compensating longitudinal velocity variations of low-energy beams along the tube, while degradation in the transverse emittance due to enhanced space–charge effect was found.

Intersubband quantum-box semiconductor lasers

It is shown that semiconductor lasers utilizing intersubband transitions in quantum boxes, so-called intersubband quantum-box (IQB) lasers, can have significantly lower threshold current densities and operating voltages than quantum cascade (QC) lasers. In order to achieve this result, an enhancement factor of about 20 in the LO-phonon-assisted electron relaxation time is necessary. The increased gain for the radiative stage in an IQB laser eliminates the need for a multiradiative-stage structure (typically 25 stages in QC lasers). In turn, the electron injector and Bragg mirror regions on either side of the active region can be separately optimized. Due to their inherently lower input power requirements, IQB lasers operating in the mid-IR wavelength range should be capable of higher average-output powers than QC lasers at all temperatures. Furthermore, continuous-wave (CW) operation at room temperature with high wallplug efficiency becomes possible.

Low-threshold vertical-cavity surface-emitting lasers based on oxide-confinement and high contrast distributed Bragg reflectors

The interest in low-threshold vertical-cavity surface-emitting lasers (VCSEL's) is increased by the demonstration of the small size, low loss optical mode due to oxide-confinement in the Fabry-Perot microcavity laser. Intense recent work in this area has resulted in numerous record breaking demonstrations of low-threshold current, high wall-plug efficiency, and high speed. In this paper, we discuss the impact of the dielectric cavity design to enhance control of the optical mode. We argue that high contrast dielectric mirrors can become an important design approach, especially for small apertures limited by diffraction loss. Experimental results are compared for different types of mirror and aperture designs.

Energy spread analysis of a waveguide optical klystron

Waveguide free electron lasers (FELs) based on electrostatic accelerator have many advantages including CW operation and high wall-plug efficiency, and therefore are an excellent candidate for many potential applications in medicine, science and industry. One drawback of electrostatic accelerators is that their beam current is usually small and this results in a low beam-wave interaction gain. To reduce this problem, one possible approach is to employ an FEL configuration having an intrinsically higher gain such as a waveguide optical klystron configuration. However because of the enhanced electron bunching process, the interaction gain of waveguide optical klystrons may become more susceptible to electron energy spread. To assess this quantitatively, energy spread effects in a waveguide optical klystron are analysed and formulated in the small signal limit. Through numerical examples, it is shown that the higher interaction gain of waveguide optical klystron devices can be realistically achieved with the nominal electron beam quality of electrostatic accelerators.

Planar Be-doped VCSELs with highwallplug efficiencies

The fabrication of planar, proton implanted vertical-cavity lasers (VCSELs) with low threshold voltages of 1.8 V and high wallplug efficiencies of 17.6% for top surface emission is reported. The maximum output power of 25 µm devices is 12.5 mW. Layer structures containing simple single-step graded AlGaAs-GaAs Bragg reflectors were grown by solid source molecular beam epitaxy with beryllium as p-type dopant.

Optimization of planar Be-doped InGaAs VCSEL's with two-sided output

Threshold current, output power, wall-plug efficiency and operating voltage of epitaxially grown InGaAs-AlGaAs planar vertical-cavity surface-emitting lasers (VCSEL's) are strongly influenced by the electrical and optical properties of the p-doped Bragg reflector. Here we study in some detail the dependence of output behavior on the composition, interface grading, and modulation doping of the Be-doped AlGaAs-GaAs Bragg reflector. Using optimized p-doped mirrors VCSEL's with low threshold current densities of 300 A/cm/sup 2/, low driving voltages of 1.6 V and high wall-plug efficiencies of 17.6% are obtained. Transverse single-mode emitting devices show a record low emission linewidth of 30 MHz and a linewidth-power product of 2.2 mW/spl middot/MHz. >

High wallplug efficiency vertical-cavity top-surface emitting laser diodes

Wallplug efficiencies as high as 12.7% have been achieved for top-emitting VCSELs (vertical cavity surface emitting lasers) by addressing the associated complication of peripheral contacts on proton-bombarded regions in addition to mirror resistance. The two major technical advances that have resulted in the improved wallplug efficiencies are low-resistance p-type DBRs (distributed Bragg reflectors) and low resistance contacts to implanted regions of the DBR. VCSELs designed for 980-nm wavelength have been fabricated from epitaxial material incorporating these advances. Typical device characteristics including 2 mW in the fundamental mode and 2 V thresholds are routinely accomplished. Initially, wallplug efficiencies of 10% were typical; however, subsequent rapid thermal anneals increased the typical efficiency of 11% due to slight decreases in threshold current and slight increases in the initial slope efficiency. The efficiency increased further after an 8 h burn-in at a current of 10 mA. The highest efficiency measured after burn-in was 12.7% and occurred at 1.5 mW in the fundamental mode.

High wallplug efficiency vertical-cavity surface-emitting lasers using lower barrier DBR mirrors

A lower energy barrier p-type Al 0.67 Ga 0.33 As/GaAs DBR mirror has been incorporated into a previously reported vertical-cavity surface-emitting laser structure. CW measurements at room temperature demonstrate lower threshold voltages or 1.86V, and a record high power-conversion efficiency or 14.9% was achieved