Lauri Toikkanen

1.3-µm optically-pumped semiconductor disk laser by wafer fusion

We report a wafer-fused high power optically-pumped semiconductor disk laser operating at 1.3 µm. An InP-based active medium was fused with a GaAs/AlGaAs distributed Bragg reflector, resulting in an integrated monolithic gain mirror. Over 2.7 W of output power, obtained at temperature of 15 °C, represents the best achievement reported to date for this type of lasers. The results reveal an essential advantage of the wafer fusing technique over both monolithically grown AlGaInAs/GaInAsP- and GaInNAs-based structures.

3 nJ, 100 ps laser pulses generated with an asymmetric waveguide laser diode for a single-photon avalanche diode time-of-flight (SPAD TOF) rangefinder application

An asymmetric waveguide laser diode with a thick active layer operated with enhanced gain switching is shown to be able to produce ?100 ps, ?25 W optical pulses in fundamental transverse mode with ?15 A, ?1.5 ns injection current pulses. A pulsed time-of-flight distance measurement demonstration utilizing this laser diode and a SPAD detector indicates centimetre-level precision and compensated accuracy from uncooperative targets at tens to hundreds of metres in a measurement time of a fraction of a second.

SS-MBE-grown short red wavelength range AlGaInP laser structures

Short-wavelength GaInP/AlGaInP quantum-well (QW) laser diodes emitting in the 618-650 nm range at room temperature have been fabricated and characterized. Several variations in laser structures have been tested, including changes in QW composition, thickness, strain and number; changes in the barrier/waveguide composition and thickness; changes in cladding structure; use of multi-quantum-barriers and changes in the doping profile. The experiments showed that the threshold current characteristic temperature (T0) increases with the number of QWs and is higher for compressive strain. The use of graded-index (GRIN) waveguides and higher p-cladding doping induced both a reduction in threshold current density and an increase in T0, mostly at shorter wavelengths. Waveguide thickness optimization can be carried out, for both constant composition and GRIN waveguides, using the QW optical confinement as a first-approximation optimization criterion. Modified cladding structures reduced the vertical far-field full-width-at-half-maximum below 20° without significantly affecting the threshold current. Devices designed using some of the guidelines resulted from our study achieved, with different structures and under different operating conditions, performances like emitting more than 2W at 650 nm in continuous wave operation or lasing down to 618 nm at room temperature, which is among the shortest wavelengths from lasers grown by solid-source molecular-beam-epitaxy.

1.3-

We report 1.3-μm mode-locked optically pumped semiconductor disk laser (SDL) made by wafer fusion. The gain medium and the saturable absorber, both based on an InP material system, were integrated with AlGaAs-GaAs distributed Bragg reflectors by localized wafer fusion. An intracavity wedged diamond heat spreader capillary bonded to the gain chip prevents the disruption of 6.4-ps pulse spectrum and supports 100 mW of average power. The results reveal an advantage of wafer fusion process of disparate materials over monolithically grown InP-based gain/absorber structures and demonstrate practical potential of the technique for long-wavelength SDLs.

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In this paper we review the recent development of resonant cavity light emitting diodes (RC-LEDs), intended for short-haul polymer optical fibre (POF) data transmission systems. The RC-LEDs with emission windows of 84 μm in diameter, suitable for standard POFs, exhibit bandwidths up to 200 MHz and light power of 3 mW (cw). The maximum external quantum efficiency is 9.5%. Larger devices, 500 μm in size, launch light power up to 15 mW. Record high transmission rates, 622 Mbit s−1, with bit-error rate <1×10−11 have been demonstrated for a 1 m long step-index POF. The devices are robust. Neither sudden unexpected failure, nor gradual power degradation has been observed after operation under accelerated ageing conditions for about 100000 device-hours. The alignment tolerance of the coupling efficiency is found to be very large, ±0.5 mm in all x–y–z, directions, suggesting that fibre pigtail packaging is inexpensive.

m Mode-Locked Disk Laser With Wafer Fused Gain and SESAM Structures

Room temperature lasing operation at 599 nm for a AlGaInP/AlInP/GaAs edge-emitting laser structure is reported. The structure was grown on GaAs substrate and pumped optically with a 532 nm Q-switched laser. The lasing threshold for a 2 mm long and 25 μm wide ridge waveguide structure was 30 mW of average pump power. The orange output beam had an optical spectral width of 1.7 nm.

Resonant cavity light emitting diode for a polymer optical fibre system

In this letter, we present the first 2-W flip chip quantum-dot (QD) semiconductor disk laser operating at 1200 nm. Compared to other techniques used for thermal management, e.g., intracavity heat spreader approach, the flip chip design preserves undisturbed optical spectrum and exhibits low intracavity losses. The latter is particularly essential for power scaling of lasers with QD gain media.

Optically Pumped Edge-Emitting GaAs-Based Laser With Direct Orange Emission

We have examined a possibility to use an AlxIn1-x P layer as an active region of a 650-nm semiconductor laser. Encouraging results have been obtained with compressively strained oxide-stripe AlInP-AlGaInP quantum-well lasers, which operated in continuous-wave mode at room temperature, producing an optical power of 460 and 320 mW per uncoated facet at 10 degC and 20 degC, respectively. In pulsed mode, a power level of 780 mW/facet was achieved at 2-A drive current at 5 degC. The results indicate that wide-bandgap AlInP affords an opportunity to develop lasers for the wavelengths 600leslambdales650 nm, which is difficult to achieve by any semiconductor heterostructure

Flip Chip Quantum-Dot Semiconductor Disk Laser at 1200 nm

Visible laser light is needed for a number of applications including life science and laser projection displays. To produce red light from a semiconductor disk laser (SDL) via frequency doubling, laser should generate light around the wavelength of 1.2 µm. This spectral range is challenging with typically used InGaAs and GaAs structures due to an increased lattice mismatch between the two materials. We report a novel approach based on a wafer fused optically-pumped semiconductor disk laser operating at 1.2 µm. This technique allows integrating materials with different lattice constants and provides convenient means to extend the operation wavelength of an SDL [1].

AlInP–AlGaInP Quantum-Well Lasers Grown by Molecular Beam Epitaxy

We report the use of partially relaxed tensile as well as compressively strained GaInP layers for lateral ordering of InAs quantum dots with the aid of misfit dislocation networks. The strained layers and the InAs QDs were characterized by means of atomic force microscopy, scanning electron microscopy, and X-ray reciprocal space mapping. The QD-ordering properties of compressive GaInP are found to be very similar with respect to the use of compressive GaInAs, while a significantly stronger ordering of QDs was observed on tensile GaInP. Furthermore, we observed a change of the major type of dislocation in GaInP layers as the growth temperature was modified.