Pietari Tuomisto

2.7 W tunable orange-red GaInNAs semiconductor disk laser

We report on a GaInNAs/GaAs semiconductor disk laser frequency-doubled to produce orange-red radiation. The disk laser operates at a fundamental wavelength of 1224 nm and delivers an output power of 2.68 W in the visible region with an optical-to-optical conversion efficiency of 7.4%. The frequency-converted signal could be launched into a singlemode optical fiber with 70-78% coupling efficiency, demonstrating good beam quality for the visible radiation. Using a Fabry-Pérot glass etalon the emission wavelength could be tuned over an 8 nm spectral range.

High power frequency doubled GaInNAs semiconductor disk laser emitting at 615 nm

We report on an optically-pumped intracavity frequency doubled GaInNAs/GaAs -based semiconductor disk laser emitting around 615 nm. The laser operates at fundamental wavelength of 1230 nm and incorporates a BBO crystal for light conversion to the red wavelength. Maximum output power of 172 mW at 615 nm was achieved from a single output. Combined power from two outputs was 320 mW. The wavelength of visible emission could be tuned by 4.5 nm using a thin glass etalon inside the cavity.

High-power (>1 W) dilute nitride semiconductor disk laser emitting at 1240 nm

We report on a high-power GaInNAs/GaAs optically pumped semiconductor disk laser operating at a wavelength of 1240 nm. The laser structure consisted of 12 dilute nitride (GaInNAs) quantum wells placed on top of a GaAs/AlAs distributed Bragg reflector, the whole structure being grown by molecular beam epitaxy. A diamond heat spreader was bonded onto the sample for improved heat dissipation. When cooled down to 8°C, the laser produced continuous-wave output power up to 1.46 W in the TEM00 mode, demonstrating the potential of dilute nitrides for high-power disk laser applications.

Semiconductor saturable absorbers with recovery time controlled through growth conditions

We discuss a new method to shape the temporal response of saturable absorption in semiconductors. In particular, we investigate the possibility to control independently the absorption recovery time of each quantum-well forming the semiconductor absorber. The recovery time is tailored by irradiation with nitrogen ions produced by an RF-plasma source. The irradiation is performed in-situ as one step of the epitaxial growth process; the quantum-wells are individually exposed to a flux of N-ions after they are grown. The amount of non-radiative recombination centers within the quantum-wells is strongly related to the time interval during which the N-ions flux is active and to the thickness of the semiconductor layer grown on top of each quantum-well before the irradiation is performed. We apply this method to fabricate fast semiconductor saturable absorbers operating in the 1-&mgr;m wavelength range. The absorption recovery time could be changed from 300 ps to 10 ps without degradation of the nonlinear optical response. The practicality of the design is finally proved by using the semiconductor saturable absorbers for mode-locking Yb-doped fiber lasers.

3.5 W GaInNAs disk laser operating at 1220 nm

We report an essential progress towards the development of efficient GaInNAs-based semiconductor disk lasers operating at 1220 nm spectral range. The gain mirrors were fabricated by molecular beam epitaxy using a radio frequency plasma source for incorporating the nitrogen. The typical structure consisted of a 30-pair GaAs/AlAs distributed Bragg reflector and 10 GaInNAs quantum wells with relatively low content of nitrogen. The growth parameters and the composition of the structures have been optimized to reduce the detrimental effect of nitrogen on the emission efficiency. We have achieved a maximum output power of 3.5 W and a differential efficiency of 20%.

Recent Progress in Development of GaInNAs- Based Photonic Devices

The GaInNAs/GaAs semiconductor heterostructures have emerged as promising alternatives to InP-based compound semiconductors for the fabrication of 1.3-mum METRO and LAN telecommunications lasers. We shall review the recent advances made in the field of the GaInNAs technology. An emphasis is put on the development of low-threshold double-quantum-well (DQW) and triple-quantum-well (TQW) ridge waveguide lasers (RWG) grown by molecular beam epitaxy. A record slope efficiency of 0.28 W/A and a low threshold current density of 278 A/cm2/QW are demonstrated in this paper for the TQW single-mode lasers. We shall also discuss the first measurements of electron-spin relaxation in dilute nitride quantum-wells. Excitation of spin-polarized electrons is potentially attractive for implementing all-optical polarization switches in a broad wavelength range

Optically-Pumped Semiconductor Disk Lasers for Second-Harmonic and Sum-Frequency Generation

We report on intracavity frequency-doubling and sum-frequency generation in optically-pumped semiconductor disk lasers. High power second-harmonic red emission from a GaInNAs-based disk laser and aquamarine sum-frequency emission from a dual-wavelength semiconductor disk laser were obtained.

Fiber laser mode-locked with a semiconductor saturable absorber etalon operating in transmission

We demonstrate a resonant semiconductor saturable absorber used in transmission for mode-locking of fiber lasers. The cavity-enhanced modulation depth corresponding to low-loss transmission state enables a robust self-starting mode-locking highly tolerant to cavity dispersion.

Fast-switching frequency-converted laser light source for display applications

We report a passively Q-switched two-component visible laser light source based on frequency conversion. The device consists of a monolithic single transverse mode ridge-waveguide infrared laser diode and a waveguide-type periodically poled magnesium oxide doped lithium niobate crystal for second harmonic light generation. An integrated 45-degree folding mirror and a coupling lens are formed by etching on opposite sides of the monolithic gallium arsenide -based laser diode for coupling the infrared emission into the waveguide-type nonlinear crystal for efficient single pass frequency conversion. Passively Q-switched operation is realized by an integrated electro-absorber section coupled with the in-plane multi-quantum well gain structure. Stable high-repetition rate self-pulsating operation was achieved by reverse-biasing the electro-absorber section and reduced speckle visibility of the second harmonic light was observed when compared to continuous-wave operation of the same laser.

Low-cost frequency-converted laser light sources

We report a fast-switching two-component frequency-converted laser with reduced speckle visibility. A bottom-emitting passively Q-switched laser with integrated electroabsorber, folding mirror and coupling lens was successfully applied with a waveguide-type periodically poled magnesium oxide doped lithium niobate crystal to generate second harmonic light at 532 nm. Reduced speckle visibility was demonstrated when operating the laser in self-pulsating mode when compared to continuous-wave operation even when using a nonlinear crystal with narrow acceptance bandwidth of 0.24 nm @ 1064 nm. The spectral width of the infrared light was 0.33 nm in pulsed mode and 0.08 nm in continuous-wave mode resulting in visible light spectral width of 0.12 nm and 0.03 nm in self-pulsating and continuous-wave mode.