Quantum-dot Saturable Absorber Research Articles

Temperature dependence of electroabsorption dynamics in an InAs quantum-dot saturable absorber at 1.3 μm and its impact on mode-locked quantum-dot lasers

We report temperature-dependent absorption recovery times in an InAs p-i-n ridge waveguide quantum-dot modulator under low reverse bias, investigated via subpicosecond pump-probe measurements. The measured decrease in absorption recovery time with increasing temperature (293–319 K) is in excellent agreement with a thermionic emission model. A similar trend in pulse duration with increasing temperature is also observed from a two-section mode-locked quantum-dot laser fabricated from a similar epitaxial structure. These measurements confirm the key role of the absorber recovery time in the reduction in the pulses generated by two-section mode-locked quantum-dot lasers, both at room and elevated temperatures.

Passive Mode-Locking of a Ti : Sapphire Laser by InGaP Quantum-Dot Saturable Absorber

We demonstrate the use of a novel InGaP quantum-dot (QD) saturable absorber (SA) to induce passively mode-locked (ML) operation of a Ti : sapphire laser. Pulses as short as 518 fs are obtained at 752 nm with an average output power of up to 190 mW for 2.3 W of absorbed pump power at 532 nm. The absorption recovery of the SA is characterized by two decay coefficients: a fast and a slow component having time constants of 0.4 and 300 ps, respectively. The saturation fluence of the InGaP QDs was measured to be 28 ¿J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the initial low-signal absorption was 1.5%, where 1.15% was nonsaturable loss.

Ultrafast absorption recovery dynamics of 1300 nm quantum dot saturable absorber mirrors

We compare the performance of two quantum dot saturable absorber mirrors with one device operating at the quantum dot ground state transition whereas the other operates at the first excited state transition. Time-resolved photoluminescence and heterodyne four-wave mixing experiments demonstrate faster recovery of the excited-state device compared to the ground-state device. Femtosecond pulses were achieved with both devices, with the ground-state device producing 91 fs pulses and the excited-state device producing 86 fs pulses in a Cr:forsterite laser. The fast absorption recovery dynamics indicates the potential of devices exploiting excited-state transitions for use in high repetition rate lasers.

Dispersionless saturable absorber mirrors with large modulation depths and low saturation fluences

We show that it is possible to eliminate group delay dispersion over wide bandwidths in low-finesse, resonant saturable absorber mirrors, whilst maintaining a low saturation fluence and a high modulation depth. By modelling the mirror structure we demonstrate that these properties can be produced by capping a resonant device with a single dielectric layer of carefully selected refractive index. We show that a specially capped dispersionless structure minimises the temporal broadening of femtosecond pulses reflected from the mirror. We compare this device against uncapped-resonant and anti-resonant structures. The superior performance of the capped, dispersionless device was verified experimentally by comparing resonant, anti-resonant and dispersionless quantum-dot (QD) saturable absorber mirrors incorporated into a Cr4+:forsterite laser system. We found that a minimum pulse duration of 86 fs could be achieved for the dispersionless structure at 1290 nm with an output power of 55 mW compared to 122 fs in an anti-resonant structure and several-picosecond pulses for a resonant structure.

Post-growth tailoring of quantum-dot saturable absorber mirrors by chemical etching

We have designed and grown a resonant, low-finesse quantum-dot saturable absorber mirror and subsequently modified the important parameters using chemical etching. The modulation depth and saturation fluence at the design wavelength of 1064 nm were modified by etching the sample to tune the cavity resonance. The device properties were characterised using normal incidence spectroscopic reflectivity measurements, intensity dependent reflectivity measurements and modelled using a transfer matrix approach. The saturable absorber mirror was used to facilitate self-starting, passively mode locked pulses in a neodymium vanadate laser operating at 1064 nm. The etching was found to affect the duration of the pulses, leading to temporal width tuning over a range of 94 ps. The shortest pulse duration of 84 ps was achieved for the cavity resonance close to 1064 nm, with an output power of 3 W. This method is an effective technique for post-growth engineering of the properties of semiconductor saturable absorber mirrors (SESAMs) with nanometre precision.

Low-loss quantum-dot-based saturable absorber for efficient femtosecond pulse generation

We report the efficient generation of femtosecond pulses from a diode-pumped solid-state laser that has been passively mode locked using a quantum-dot-based saturable absorber. Average output powers up to 1.15W and transform-limited pulses as short as 114fs were obtained around 1040nm with a pulse repetition frequency of 107MHz from a diode-pumped Yb3+:KY(WO4)2 laser. The InGaAs quantum-dot saturable absorber was characterized to have a saturation fluence of 25μJ∕cm2 and nonsaturable losses of less than 0.2% with an initial low-signal absorption of 2.5% at 1040nm.

Quantum dot saturable absorber for passive mode locking of Nd:YVO4 lasers at 1064 nm

An InAs/GaAs quantum dot saturable absorber mirror was used to mode lock a Nd:YVO4 solid-state laser at the operation wavelength of 1064.6 nm. Multi-watt average power was obtained during stable cw mode locking with pulses as short as 24 ps, and with a repetition rate of 65 MHz.

Characterization of highly stacked InAs quantum dot layers on InP substrate for a planar saturable absorber at 1.5 µm band

We examined the absorption saturation properties in the 1.5 µm band of novel highly stacked InAs quantum dot layers. The transmission change at vertical incidence based on the saturable absorption of the quantum dots was more than 1%. This value is as large as the reflection changes of previously reported 1-µm-band quantum dot saturable absorber with interference enhancement. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Semiconductor quantum-dot saturable absorber mode-locked fiber laser

We demonstrate self-starting passive mode-locking of an ytterbium fiber laser by using a multilayer quantum-dot saturable absorber mirror. A high modulation depth of the absorber ensures robust pulse operation of the fiber laser with a threshold pump power of 30 mW. The 2.8-ps pulses with an average power of 5 mW have been generated at 1042 nm.

InAs?GaAs quantum-dot saturable absorber for a diode-pumped passively mode-locked Nd:YVO_4 laser at 1342?nm

We report that InAs/GaAs quantum dots were developed to be saturable absorbers as well as output couplers in diode-pumped passively mode-locked Nd:YVO4 lasers at 1342 nm. With an incident pump power of 12.6 W, an average output power of 0.85 W with a mode-locked pulse width of 26 ps at a repetition rate of 152 MHz was obtained.

InAs/GaAs quantum-dot saturable absorbers for diode-pumped passively Q-switched Nd-doped 13-µm lasers

A low-loss semiconductor saturable absorber based on InAs/GaAs quantum dots was developed for Q switching of a diode-pumped Nd-doped laser operating at 1.3 microm. With an InAs/GaAs quantum-dot saturable absorber, a diode-pumped Nd:YVO4 laser at 1342 nm was achieved. With an incident pump power of 2.2 W, an average output power of 360 mW with a Q-switched pulse width of 90 ns at a pulse repetition rate of 770 kHz was obtained.

Quantum-dot-based saturable absorber with p-n junction for mode-locking of solid-state lasers

We demonstrate stable mode-locking in a Yb : KYW laser by using a quantum-dot (QD) saturable absorber structure that incorporates a p-n junction. A reduction in the output pulse duration was measured when a reverse bias was applied to the QD saturable absorber mirror.

Fast Quantum-Dot Saturable Absorber for Passive Mode-Locking of Solid-State Lasers

We demonstrate stable mode-locking in a Yb : KYW laser by using a quantum-dot (QD) saturable absorber. A fast component in the absorption decay in this QD structure has been measured by pump-probe technique to be /spl sim/1 ps.

Passive mode-locking in 1.3 μm two-section InAs quantum dot lasers

Passive mode locking was achieved at 1.3 μm in oxide-confined, two-section, bistable quantum dot (QD) lasers with an integrated intracavity QD saturable absorber. Fully mode-locked pulses at a repetition rate of 7.4 GHz with a duration of 17 ps were observed under appropriate bias conditions. No self-pulsation accompanied the mode locking. These results suggest that a carefully designed QD laser is a candidate for ultrashort pulse generation.

Bistable operation of a two-section 1.3 μm InAs quantum dot laser-absorption saturation and the quantum confined Stark effect

Room temperature, continuous-wave bistability was observed in oxide-confined, two-section, 1.3 /spl mu/m quantum-dot (QD) lasers with an integrated intracavity quantum-dot saturable absorber. The origin of the hysteresis and bistability were shown to be due to the nonlinear saturation of the QD absorption and the electroabsorption induced by the quantum confined Stark effect.

PbS quantum-dot-doped glasses for ultrashort-pulse generation

We investigate the use of PbS quantum-dot-doped glasses as saturable absorbers for ultrashort-pulse lasers by means of absorption bleaching experiments and numerical analysis of the pulse shaping process using the Haus’ master equation. We explain the mode-locking mechanism and the limitations of these absorbers. The generation of transform-limited fs pulses is predicted by soliton mode locking initiated by the absorption saturation of higher excited states of the quantum-dot saturable absorber.

Bistability and self-pulsation in quantum-dot lasers with intracavity quantum-dot saturable absorbers

Self-organized In0.4Ga0.6As/GaAs quantum-dot single-mode ridge waveguide lasers with intracavity absorber were grown by molecular beam epitaxy. Bistability in the light–current characteristics of 3 μm single-mode edge-emitting laser was obtained by controlling the intracavity absorber voltage. Self-pulsation was also observed with a center frequency of 1.6 GHz and linewidth &amp;lt;10 MHz.