Quantum-dot Semiconductor Saturable Absorber Research Articles

InAs/GaAs quantum dot semiconductor saturable absorber for controllable dual-wavelength passively Q-switched fiber laser

We experimentally demonstrate the first use of 1550-nm InAs/GaAs quantum dot semiconductor saturable absorber mirror (QD-SESAM) in the dual-wavelength passively Q-switched (QS) erbium doped fiber (EDF) laser. The dual-wavelength QS lasing was obtained at a pump threshold of 180 mW with the average output power of 2.2 mW and the spacing between the two lasing wavelengths is 14 nm. A large absorption ranging from 1520 to 1590 nm has been realized when no substrate rotation was employed during the molecular beam epitaxy growth of the QD-SESAM indicating the potential to generate a 60 nm spacing of the dual-wavelength QS lasing peaks by changing the positions in the QD-SESAM and replacing EDF by co-doped fiber as gain medium. These results have provided a new opportunity towards achieving the stable and wide wavelength-tunable dual-modes fiber lasers.

Femtosecond Alexandrite laser passively mode-locked by an InP/InGaP quantum-dot saturable absorber

An Alexandrite laser passively mode-locked using an InP/InGaP quantum-dot semiconductor saturable absorber mirror (QD-SESAM) was demonstrated. The laser was pumped at 532nm and generated pulses as short as 380fs at 775nm with an average output power of 295mW. To the best of our knowledge, this is the first report on a passively mode-locked femtosecond Alexandrite laser using a SESAM in general and a QD-SESAM in particular.

10 GHz pulse repetition rate Er:Yb:glass laser modelocked with quantum dot semiconductor saturable absorber mirror.

Semiconductor saturable absorber mirror (SESAM) modelocked high pulse repetition rate (≥10 GHz) diode-pumped solid-state lasers are proven as an enabling technology for high data rate coherent communication systems owing to their low noise and high pulse-to-pulse optical phase-coherence. Compared to quantum well, quantum dot (QD)-based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the first 10 GHz pulse repetition rate QD-SESAM modelocked laser at 1.55 μm, exhibiting 2 ps pulse width from an Er-doped glass oscillator (ERGO). The 10 GHz ERGO laser is modelocked with InAs/GaAs QD-SESAM with saturation fluence as low as 9 μJ/cm2.

A diode-pumped 1.5 μm waveguide laser mode-locked at 6.8 GHz by a quantum dot SESAM

We report a passively mode-locked, diode-pumped waveguide laser operating in the 1.5 μm spectral region using a quantum dot semiconductor saturable absorber mirror as the saturable absorber element. A repetition rate of up to 6.8 GHz and an average power as high as 30 mW were obtained during mode-locked operation. A minimum pulse duration of 2.5 ps was produced at a wavelength of 1556 nm. The repetition rate of the source was tuned by more than 1 MHz by changing the pump power, demonstrating a possible route towards integrated pulse repetition rate stabilization.

Timing Jitter Characterization of a Free-Running SESAM Mode-locked VECSEL

We present timing jitter measurements of an InGaAs quantum well vertical external cavity surface emitting laser (VECSEL) passively mode locked with a quantum dot semiconductor saturable absorber mirror (SESAM) at 2-GHz repetition rate. It generates 53-mW average output power in 4.6-ps pulses at 953 nm. The laser housing was optimized for high mechanical stability to reduce acoustic noise. We use a fiber-coupled multimode 808-nm pump diode, which is mounted inside the laser housing. No active cavity length stabilization is employed. The phase noise of the free-running laser integrated over a bandwidth from 100 Hz to 1 MHz corresponds to an RMS timing jitter of ≈212 fs, which is lower than previously obtained for mode-locked VECSELs. This clearly confirms the superior noise performance expected from a high-Q-cavity semiconductor laser. In contrast to edge-emitting semiconductor diode lasers, the cavity mode is perpendicular to the quantum well gain layers, which minimizes complex dispersion and nonlinear dynamics.

Femtosecond high-power quantum dot vertical external cavity surface emitting laser

We report on the first femtosecond vertical external cavity surface emitting laser (VECSEL) exceeding 1 W of average output power. The VECSEL is optically pumped, based on self-assembled InAs quantum dot (QD) gain layers, cooled efficiently using a thin disk geometry and passively modelocked with a fast quantum dot semiconductor saturable absorber mirror (SESAM). We developed a novel gain structure with a flat group delay dispersion (GDD) of ± 10 fs2 over a range of 30 nm around the designed operation wavelength of 960 nm. This amount of GDD is several orders of magnitude lower compared to standard designs. Furthermore, we used an optimized positioning scheme of 63 QD gain layers to broaden and flatten the spectral gain. For stable and self-starting pulse formation, we have employed a QD-SESAM with a fast absorption recovery time of around 500 fs. We have achieved 1 W of average output power with 784-fs pulse duration at a repetition rate of 5.4 GHz. The QD-SESAM and the QD-VECSEL are operated with similar cavity mode areas, which is beneficial for higher repetition rates and the integration of both elements into a modelocked integrated external-cavity surface emitting laser (MIXSEL).

Compact ultrafast semiconductor disk laser: targeting GFP based nonlinear applications in living organisms

We present a portable ultrafast Semiconductor Disk Laser (SDL) (or vertical extended cavity surface emitting laser—VECSELs), to be used for nonlinear microscopy. The SDL is modelocked using a quantum-dot semiconductor saturable absorber mirror (SESAM), delivering an average output power of 287 mW, with 1.5 ps pulses at 500 MHz and a central wavelength of 965 nm. Specifically, despite the fact of having long pulses and high repetition rates, we demonstrate the potential of this laser for Two-Photon Excited Fluorescence (TPEF) imaging of in vivo Caenorhabditis elegans (C. elegans) expressing Green Fluorescent Protein (GFP) in a set of neuronal processes and cell bodies. Efficient TPEF imaging is achieved due to the fact that this wavelength matches the peak of the two-photon action cross section of this widely used fluorescent marker. The SDL extended versatility is shown by presenting Second Harmonic Generation images of pharynx, uterus, body wall muscles and its potential to be used to excite other different commercial dyes. Importantly this non-expensive, turn-key, compact laser system could be used as a platform to develop portable nonlinear bio-imaging devices.

Electronically Controlled Pulse Duration Passively Mode-Locked Cr : Forsterite Laser

A passive mode-locked Cr:forsterite laser with electronically controlled pulse duration is demonstrated. A DC voltage controlled p-n junction quantum-dot semiconductor saturable absorber mirror is presented. Output pulse durations varying from 17.4 to 6.4 ps were obtained by applying a DC voltage between 0 and -4.5 V. No dispersion compensation was used.

Subpicosecond quantum dot saturable absorber mode-locked semiconductor disk laser

We report the generation of subpicosecond pulses from a passively mode locked, optically pumped quantum well semiconductor disk laser using a quantum dot semiconductor saturable absorber mirror (SESAM). We obtained 870 fs pulses at a repetition rate of 895 MHz with average output power of 45 mW at 1027.5 nm. The mode locking operation was insensitive to SESAM temperature over the range of −10 to 85 °C, with the pulse duration variation thought to be dominated by the temperature dependence of the group delay dispersion.

Tailoring Quantum Dot Saturable Absorber Mirrors for Ultra-Short Pulse Generation

ABSTRACTWe have designed and grown a series of quantum dot semiconductor saturable absorber mirrors (QD-SESAMs) for a range of operating wavelengths, incorporating innovative design and processing features to optimise the device performance. Using a range of reflectivity studies, ellipsometric measurements and both time-integrated and time-resolved spectroscopic studies, we have conducted detailed investigations of device performance. Extensive modelling work of dielectric multilayers has been undertaken which supports our experimental findings and allows us to understand and design novel structures in order to improve and tailor device characteristics, including dielectric capping and non-normal incidence. We demonstrate samples designed for operation with the higher excited-states of the QDs which produced a self-starting train of mode-locked pulses with a temporal duration of 200 ps at a repetition rate of 78 MHz in a Nd:YVO4 solid-state laser. We also present SESAMs incorporating electronically coupled QD bilayers, allowing long wavelength operation.

Quantum-dot-based saturable absorber for femtosecond mode-locked operation of a solid-state laser

A quantum-dot-based saturable absorber has been demonstrated to initiate the generation of femtosecond pulses from a passively mode-locked solid-state laser. Control and tuning of the pulse duration from 58 ps to 158 fs was achieved. The 158 fs transform-limited pulses at 1280 nm are the shortest pulses that were produced from the Cr:forsterite laser passively mode locked by an InAs/InGaAs quantum-dot semiconductor saturable absorber mirror.