High-power single-frequency semiconductor lasers

The AlGaAs photocathode can be used in the field of underwater optical communication because of its fast response speed and adjustable spectral response range. In order to solve the problem that the low light absorption of the AlGaAs emission layer limits the improvement of its quantum efficiency, the distributed Bragg reflector (DBR) structure is used to reflect the light at a specific wavelength back to the emission layer to further increase the absorption rate, thus improving the response capability of the photocathode at 532 nm. The spectral response model of the AlGaAs photocathode with DBR structure is obtained by solving one-dimensional continuity equation. The optical model of the AlGaAs photocathode with enhanced response at 532 nm is established by the finite-difference time-domain method. The effects of the sublayer periodic pairs, the sublayer material and the thickness of emission layer and buffer layer on the absorption rate of emission layer are analyzed. The light absorption distributions of AlGaAs photocathode with and without DBR structure are compared, and the influence mechanism of DBR structure on the blue-green light absorption capacity of AlGaAs photocathode emission layer is clarified, which can provide a theoretical basis for designing its structural parameters. The results show that the DBR structure with a periodic pair of 20 and Al<sub>0.7</sub>Ga<sub>0.3</sub>As/AlAs has the best reflection effect on 532 nm light. Based on the DBR structure, when the thickness of the emission layer and buffer layer are 495 nm and 50 nm, respectively, the emission layer has the best absorption rate of 532 nm light. Furthermore, two kinds of AlGaAs photocathodes with and without DBR structure are prepared by the metal-organic chemical vapor deposition technology, and the reflectivity and profile structure of the grown samples are characterized. Then the Cs/O activation experiments are performed to compare the spectral response curves. It is found that the spectral response of the AlGaAs photocathode sample with DBR structure at 532 nm wavelength is about twice that of the sample without DBR structure.

Threshold current density and differential quantum efficiency are analyzed for a surface emitting (SE) lambda /4-shifted distributed feedback (DFB) laser consisting of alternating active and passive layers with a distributed Bragg reflector (DBR). It is shown that the threshold current density can be reduced by using the DFB action induced by alternating active and passive layers in the active region of the SE DFB laser structure, as compared to SE DBR lasers with a homogeneous active region. It is also shown that the differential quantum efficiency of the DFB laser with a DBR can be higher than that of conventional DBR lasers without increasing the threshold current density. >

Enhanced optical absorption of monolayer WS2 using Ag nanograting and distributed Bragg reflector structures

Structural analysis of distributed Bragg reflector mirrors

Diode lasers emitting single-frequency, diffraction limited beams at a continuous-wave (CW) optical power of several Watts are required for many applications including frequency conversion, free-space communications, and pumping of fibre lasers and fibre amplifiers. The spectral region around 980 nm is of particular interest for the pumping of erbium and ytterbium doped fibres as well as for the second harmonic generation of laser radiation at 488 nm replacing Ar ion lasers in material analytics. One of the most promising devices is the monolithically integrated master-oscillator power-amplifier (MOPA), where either a distributed Bragg reflector (DBR) laser or a distributed feedback (DFB) laser acting as the master oscillator and a straight or tapered gain-region power-amplifier are combined on a single chip. Here, a MOPA consisting of a DBR laser and a tapered amplifier is demonstrated which emits a CW power of more than 10 W at 977 nm in a nearly diffraction limited beam and narrow spectral bandwidth of 40 pm. To the authors' knowledge, the 10 W reported here is the highest nearly diffraction-limited single-frequency power ever demonstrated from a single-chip diode laser at any wavelength.

In this study, high performance nitride-based flip-chip (FC) light-emitting diodes (LEDs) using optimized distributed bragg reflector (DBR) were fabricated and compared with conventional FC-LED using silver (Ag) reflector. Most of FCLEDs are using the silver (Ag) as reflector due to its superior reflectance at visual spectrum region. However, A silver has detrimental problems such as electro-chemical migration and agglomerations, which resulting in reliability issues such as degradation of power drop, unstable operating voltage and leakage issues. Our DBR structure was designed to have 99% at whole visible spectrum range (400~750nm), which is higher reflectance than silver reflector (90~95%). Optical power is higher than higher than the Ag-LED up to 30% @ 500mA. As the current increases up to 1A, the gap slightly decreased. Reliability test results show stable optical power, operating voltage, and leakage maintenance.

A key element in any optical system is the light source and semi-conductor lasers have become the most attractive candidates for many applications due to their small size, low drive voltages and high output powers. However, their linewidths need to be reduced for operation at ever-increasing modulation rates. Monolithic laser designs such as the distributed feedback (DFE) and distributed Bragg reflector (DER) produce line-narrowed outputs by including an internal grating within the laser cavity [1). If the cavity is extended beyond the active semi-conductor chip then this long external cavity arrangement, with a reflector at the end, can produce far greater line-width reductions provided that a mechanism is included for selection of a single longitudinal lasing mode [2). Applications for tunable LEC lasers have increased dramatically in recent years and now extend from local oscillators in coherent detection schemes to testing of optical components such as filters and amplifiers and they might in future also be employed in sophisticated fibre optic sensor systems. Various designs have been proposed for mechanical arrangements which would enable wide-range tuning whilst maintaining a single longitudinal mode [3-5) but, in practice, suffer from backlash, hysteresis and slow operation which make them non—ideal for field operation. In the present work we seek an improved control system which will enable wavelength tuning to be performed with the ease and consistency of the electronic tuning schemes.

Since 1976, the Laser Hardened Materials Evaluation Laboratory (LHMEL) has been characterizing material responses to laser energy in support of national defense programs and the aerospace industry. Now, that capability is available to commercial industry as well. LHMEL’s power levels, beam uniformity, and diagnostics capabilities make it an ideal facility for proof-of-concept testing or process development.Located at Wright-Patterson Air Force Base, Ohio, LHMEL is managed by the Wright Laboratory Materials Directorate and operated by Lawrence Associates, Incorporated. The facility’s advanced hardware is centered around two carbon dioxide laser systems: the LHMEL I laser producing 15 kW of continuous wave (CW) power on target and LHMEL II producing 150 kW of CW power on target. Both lasers operate at 10.6 microns and can deliver stable, full power irradiations for durations of up to 80 seconds.Both LHMEL devices use a multi-mode resonator configuration producing a flat-top spatial intensity distribution. This beam profile delivers a uniform amount of energy over the entire beam diameter and ensures a controlled and repeatable laser exposure on target.The singular capabilities of the LHMEL facility provide unique opportunities for commercial materials processing. Uses of LHMEL might include demonstration of the feasibility of a new material processing technique before investing capital in its development, simulating the high service life temperatures experienced by parts within an automobile or jet engine, performing a limited production run to laser cut thick steel plates for a special custom order, or using LHMEL’s high power to perform deep-penetration welds of steel, aluminum, or titanium. LHMEL has already performed extensive work in the area of thermal load simulation and has begun initial testing efforts in other areas of materials processing.LHMEL’s capabilities are perhaps most beneficial in the surface treatment of materials. Applications requiring uniform irradiation of large surface areas to produce the ideal heat treatment with limited or single passes could be satisfied by LHMEL. Initial heat treatment tests have been performed at LHMEL. Other techniques to increase wear resistance, extend service life, or even inhibit surface corrosion might be developed using LHMEL.Tests are performed on a cost-reimbursement basis or, if appropriate, a Cooperative Research and Development Agreement (CRDA) can be negotiated.Since 1976, the Laser Hardened Materials Evaluation Laboratory (LHMEL) has been characterizing material responses to laser energy in support of national defense programs and the aerospace industry. Now, that capability is available to commercial industry as well. LHMEL’s power levels, beam uniformity, and diagnostics capabilities make it an ideal facility for proof-of-concept testing or process development.Located at Wright-Patterson Air Force Base, Ohio, LHMEL is managed by the Wright Laboratory Materials Directorate and operated by Lawrence Associates, Incorporated. The facility’s advanced hardware is centered around two carbon dioxide laser systems: the LHMEL I laser producing 15 kW of continuous wave (CW) power on target and LHMEL II producing 150 kW of CW power on target. Both lasers operate at 10.6 microns and can deliver stable, full power irradiations for durations of up to 80 seconds.Both LHMEL devices use a multi-mode resonator configuration producing a flat-top spatial intensity distribution. T...

Down-conversion in Tm3 +/Yb3 + doped glasses for multicrystalline silicon photo-voltaic module efficiency enhancement

Optimized Tamm-plasmon structure by Differential Evolution algorithm for single and dual peaks hot-electron photodetection

GaN growth on Si with rare-earth oxide distributed Bragg reflector structures

A low-threshold-current distributed reflector laser consisting of phase-shifted distributed feedback (DFB) grating and quantum-wire distributed Bragg reflector (DBR) sections was realized. The device with a DFB length of 150µm, a DBR length of 240µm and a stripe width of 1.5µm achieved a threshold current as low as 1.2mA and a differential quantum efficiency of 13% from the front facet under RT-CW conditions. A good single-mode operation was also realized at a mode determined by the phase-shifted grating.

A Michelson interferometer with balanced detection, built to study semiconductor lasers, is analyzed. The quantum noise due to vacuum fluctuations, coupling losses, detector quantum efficiency, and spatial mode mismatches are included in the analysis. The limits for frequency noise detection and the sensitivity of the interferometer are examined. It is observed that under ordinary measurement conditions the frequency noise can only be measured up to slightly above the cavity bandwidth of the laser. Comprehensive measurement procedures are proposed, and experimental results showing the frequency modulation response, measured from 10 kHz to 8 GHz, of a three-section distributed feedback (DFB) laser and the frequency noise spectra, measured from 30 MHz to 8 GHz, of a two-section distributed Bragg reflector (DBR) laser are presented. These results reveal new cavity detuning effects in the noise characteristics of tunable DBR lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An 8-wavelength distributed Bragg reflector (DBR) array for narrow channel wavelength division multiplexing (WDM) has been fabricated with a new technique for printing first-order Bragg gratings using a phase mask and a conventional incoherent source. All the distributed gratings were printed in a single photolithographic step with a slightly modified mask aligner. The DBR's excellent wavelength control for channels separated by as little as 0.8 nm is described. Many advanced photonic devices relying on gratings like quarter-wave shifted distributed feedback (DFB) lasers and wavelength division multiplexing (WDM) components can potentially be manufactured with this technique in a simple and cost-effective way. >

This paper reports on the design and simulation of a Multi Quantum Well (MQW) AlGaAs/GaAs single p-i-n junction solar cell with a Distributed Bragg Reflector (DBR) placed at back surface. The DBR structure reflects the part of the spectrum that benefits from absorption in the AlGaAs QW structure, while being transparent to the IR spectrum. The efficiencies and short-circuit currents for the AlGaAs MQW cell with and without DBR are simulated. The efficiencies and short-circuit currents of an optimized AlGaAs MQW cell with and without DBR are simulated. Results obtained show improvement in short circuit current, open circuit voltage and efficiency when both MQW and DBR were used. Simulation results predict an efficiency of about 28.4% for the MQW AlGaAs-DBR single p-i-n junction photovoltaic cell under the presence of both radiative and non-radiative recombination mechanisms.