Deriving of Single Intensive Picosecond Optical Pulses from a High-Power Gain-Switched Laser Diode by Spectral Filtering

Single 25 ps/16 W optical pulses were achieved by spectral filtering from a multiheterostructure gain-switched laser diode with its quasisteady-state modes suppressed by a factor of 103 as compared with the peak power. A significant transient spectrum broadening makes this possible provided that a very high dI/dt rate of the pumping current pulse is used. A simple numerical model is suggested which describes adequately both the spectral and transient features of the observed phenomenon. It follows from the model that single picosecond optical pulses can be obtained from any type of high power semiconductor laser

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

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 leads to strong spectral broadening of the output without a significant improvement to pulse energy and peak power

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

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

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

Time-gated CMOS SPAD and a quantum well laser diode with a CMOS driver for time-resolved diffuse optics imaging

Abstract Single-Photon Avalanche Photodiodes (SPADs) were fabricated and characterized in 150 nm CMOS technology. The SPAD is based on a p+/nwell junction with a p-substrate guard ring. In addition, a compact gain switched quantum well (QW) laser diode with a CMOS driver was used with the proposed SPAD for time-resolved diffuse optics measurements. The measured impulse response function (IRF) of the SPADs was ∼50 ps at best. Two phantoms were measured to demonstrate the suitability of SPADs for time-resolved diffuse optics imaging (TRDOI)

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

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

Asymmetric waveguide design of laser diodes for pico- and nanosecond pulse generation in the eye safe spectral range:linear and nonlinear electromagnetic effects

Abstract High energy optical pulse generation using semiconductor lasers has attracted significant attention recently, for applications such as high-precision laser radars, three-dimensional time imaging, spectroscopy, and lifetime studies. Depending on the resolution required, pulses of either several to several tens of nanoseconds or ~ 100 picoseconds in duration can be required. In the former case, from the laser dynamics point of view, the laser is operating in a steady state with a transient at the start of the pulse; in the latter case, the main techniques used are gain switching (pumping the laser with a current pulse of a nanosecond duration or somewhat shorter, but still significantly longer than the desired optical pulse), active or passive Q-switching (using a laser incorporating an active voltage-controlled modulator or a saturable absorber respectively), or a combination of these techniques. In our recent work (see [1,2] and references therein), we have used gain-switched Fabry-Perot asymmetric-waveguide semiconductor lasers with a large equivalent spot size d/Γα ≫ 1 μm (d being the active layer thickness and Γα, the active layer confinement factor). A saturable absorber can be monolithically integrated within the laser cavity to facilitate high-energy afterpulse-free optical pulse emission in a broad range of injection current pulse amplitudes by combined gain- and Q-switching. Optical pulses with a peak power of about 35 W and a duration of about 80 ps at half maximum, without a substantial afterpulse structure, were achieved with a current pulse with an amplitude of just 8 A and a duration of 1.5 ns. Good quality, after pulsing-free optical pulses were observed in a broad range of elevated temperatures. It has also been shown [3] that a similarly asymmetric laser structure, with a Quantum Well active layer, is advantageous for quasi-CW operation (that is, pumped by current pulses long enough for the output power transients to die out, but short enough to avoid heating), correspondingly emitting optical pulses with a similar duration, of a few nanoseconds to hundreds of nanoseconds long