Strong Doping of the n-Optical Confinement Layer for Increasing Output Power of High- Power Pulsed Laser Diodes in the Eye Safe Wavelength Range

Abstract—An analytical model for internal optical losses at high power in a 1.5 μm laser diode with strong n-doping in the n-side of the optical confinement layer is created. The model includes intervalence band absorption by holes supplied by both current flow and two-photon absorption, as well as the direct two-photon absorption effect. The resulting losses are compared with those in an identical structure with a weakly doped waveguide, and shown to be substantially lower, resulting in a significant improvement in the output power and efficiency in the structure with a strongly doped waveguid

A low noise, wide dynamic range TOF laser radar receiver based on pulse shaping techniques

Abstract A time of flight (TOF) laser radar receiver based on unipolar-to-bipolar pulse shaping at its input is presented. The pulse shaping and the non-linear feedback of the transimpedance preamplifier give low timing error and jitter over a wide input pulse amplitude range. This receiver is realized in a 0.35μm CMOS technology and intended to be used in laser ranging with laser pulses of width ~1ns. Post-layout simulations show a dynamic range of more than 1:200000, a trans-impedance gain of 117dbΩ, a bandwidth of 260MHz and an input-referred equivalent current noise of 70nA. These results are achieved while keeping the walk error less than ±55ps (9mm) without any need for complicated calibration methods

Laser diode structures with a saturable absorber for high-energy picosecond optical pulse generation by combined gain-and Q-switching

Abstract The performance of gain-switched Fabry-Perot asymmetric-waveguide semiconductor lasers with a large equivalent spot size and an intracavity saturable absorber was investigated experimentally and theoretically. The laser with a short (~ 20 μm) absorber emitted high-energy afterpulse-free optical pulses in a broad range of injection current pulse amplitudes; optical pulses with a peak power of about 35 W and a duration of about 80 ps at half maximum were achieved with a current pulse with an amplitude of just 8 A and a duration of 1.5 ns. Good quality pulsations were observed in a broad range of elevated temperatures. The introduction of a substantially longer absorber section lead to strong spectral broadening of the output without a significant improvement to pulse energy and peak power

Modified high-power nanosecond Marx generator prevents destructive current filamentation

Abstract A traditional Marx circuit (TMC) based on avalanche transistors with a shortened emitter and a base was investigated numerically by using a two-dimensional (2-D) physics-based approach and experimentally, and compared with a special Marx circuit (SMC) suggested here, in which an intrinsic base triggering of all the stages protects the transistors, especially the second one, from thermal destruction due to current filamentation. This is because the entire emitter-base perimeter in the SMC participates in switching, whereas in a TMC the switching is initiated across the entire area of the emitter but then changes to current filamentation due to certain 3-D transient effects reported earlier. Very significant difference in local transient overheating in the transistors operating in TMC and SMC determines the difference in reliability of those two pulse generators. The results suggest a new circuit design for improving reliability and explain the difference in the operating mode of different transistors in the chain which makes the second transistor most prone to destructive thermal filamentation. This new understanding points additionally to ways of optimizing the design of the transistors to be used in a Marx circuit

Strong doping of the n-optical confinement layer for increasing output power of high- power pulsed laser diodes in the eye safe wavelength range

Abstract An analytical model for internal optical losses at high power in a 1.5 μm laser diode with strong n-doping in the n-side of the optical confinement layer is created. The model includes intervalence band absorption by holes supplied by both current flow and two-photon absorption (TPA), as well as the direct TPA effect. The resulting losses are compared with those in an identical structure with a weakly doped waveguide, and shown to be substantially lower, resulting in a significant improvement in the output power and efficiency in the structure with a strongly doped waveguide

Time-domain terahertz imaging of layered dielectric structures with interferometry-enhanced sensitivity

Abstract This article presents a time-domain imaging technique for layered dielectric slabs using a solid-state wavelet generator with subterahertz carrier frequency. The technique utilizes the dual nature of a wavelet, i.e., both the applicability of time-of-flight measurements and the ability of wavelets to interfere in thin dielectric layers at a carrier frequency that is preserved in spite of the ultrawideband character of the signal. This results in a very high sensitivity of the time delay of the resultant pulse to variations in the effective thickness (thickness × refractive index) of the dielectric layer. It is shown using a plane-wave analysis of the pulse propagation that under certain conditions, this sensitivity enhancement can reach an order of magnitude. The experimental setup for the reflection-mode operation is described and its performance in the discrimination of healthy and malignant tissues and in the detection of corrosion under paint is demonstrated

Increasing output power of pulsed-eye safe wavelength range laser diodes by strong doping of the n-optical confinement layer

Abstract A semi-analytical model for internal optical losses at high power in a 1.5 μm laser diode with strong n-doping in the n-side of the optical confinement layer is created. The model includes intervalence band absorption by holes supplied by both current flow and two-photon absorption. The resulting losses are shown to be substantially lower than those in a similar, but weakly doped structure. Thus a significant improvement in the output power and efficiency by strong n-doping is predicted

Optical loss suppression in long-wavelength semiconductor lasers at elevated temperatures by high doping of the n-waveguide

Abstract We show that strong n-doping of the n-waveguide layer substantially decreases the thermal carrier leakage from the active layer and the associated optical losses in III–V semiconductor lasers. The effect is particularly pronounced in devices operating at the wavelength region where the free hole absorption cross-section is much greater than that of free electrons. This is predicted to decrease the threshold current and improve the output efficiency of the lasers. An example of a bulk InGaAsP/InP pulsed lasers is used to demonstrate that lasers with highly doped n-InGaAsP side of the waveguide can retain high output powers at ambient temperatures substantially above room temperature

Asymmetric-waveguide, short cavity designs with a bulk active layer for high pulsed power eye-safe spectral range laser diodes

Abstract It is shown, by calculations calibrated against the authors’ recent experimental data, that an eye-safe wavelength range InGaAsP/InP high pulsed power laser design using a bulk active layer, which has a large refractive index step with respect to the optical confinement layer and is located close to the p-cladding, can provide substantial performance improvement compared to the best results achieved so far for this operating regime and wavelength. The dependence of the laser performance on the design parameters such as the thicknesses of the active layer and the waveguide, as well as the cavity length, are analysed. It is shown that the relatively thick bulk active layer in such InGaAsP/InP lasers allows the use of short cavity lengths (~1 mm or even shorter), for achieving high pulsed power while maintaining a low p-cladding series resistance (making for high efficiency) and a narrow far field (making for high brightness). A single-asymmetry structure with the asymmetric active layer location but symmetric optical confinement layer/cladding refractive index steps gives performance only marginally inferior to that of a double-asymmetric one including asymmetric refractive index steps

High Power 1.5 μm pulsed semiconductor laser design with a bulk active layer and an asymmetric waveguide

Abstract InGaAsP/InP high pulsed power lasers operating in the range of 1.3–1.6 μm have been intensely studied recently, with LIDAR technology being the primary application. We present and analyse a design with a bulk active layer which has a large refractive index step with respect to the optical confinement layer and is located close to the p-cladding. It is shown that such lasers can allow a noticeable performance increase over the state of the art. The dependence of the laser performance on the design parameters including the thicknesses of the active layer and the waveguide, the cavity length, and the waveguide asymmetry, is analysed. It is shown that short cavity lengths (~1 mm or even shorter) can be used in the design considered for achieving high pulsed power. Due to the significant waveguiding properties of the active layer, the use of both symmetric and asymmetric waveguide designs is possible, with only slightly higher output predicted for the asymmetric one. Both designs allow operation with a single, broad transverse mode enabling high brightness