Compact all-quantum-dot-based tunable THz laser source

We demonstrate an ultracompact, room temperature, tunable terahertz (THz) generating laser source based on difference-frequency-driven photomixing in a coplanar stripline InAs/GaAs quantum-dot (QD) antenna pumped by a broadly tunable, high power, continuous wave InAs/GaAs QD laser diode in the double-grating quasi-Littrow configuration. The dual-wavelength QD laser operating in the 1150- 1301 nm wavelength region with a maximum output power of 280 mW and with tunable difference-frequency (277 GHz to 30 THz) was used to achieve tunable THz generation in the QD antenna with a photoconductive gap of 50 μm. The best THz output performance was observed at pump wavelengths around the first excited state of the InAs/GaAs QDs (∼1160 nm), where a maximum output power of 0.6 nW at 0.83 THz was demonstrated

Investigation of the Chromatic Dispersion in Two-Section InAs/GaAs Quantum-Dot Lasers

We present the measurements of the dispersion of InAs/GaAs quantum-dot lasers emitting at 1230 nm (ground state) and 1160 nm (excited state) from the analysis of their subthreshold emission spectra. Measurements from devices with various lengths allow us to deduce that the group velocity dispersion is as high as 2270 fs2mm−1 and is mainly due to the dispersion of bulk GaAs. The gain-induced dispersion varies with the injected current at a rate of ≃−2 fs2 mA−1mm−1, whereas the effect of a saturable absorber on the dispersion is found to be negligible. These results suggest that the implementation of integrated dispersion compensation could significantly reduce the pulse duration of these lasers in mode-locked regime and lead to an enhancement of the formation of optical frequency combs in these devices

Photoconductivity of an InAs/GaAs self-assembled quantum dot photoconductive THz antenna

A broadband terahertz (THz) source is desirable for applications such as imaging, spectroscopy and security. Towards this, an InAs/GaAs quantum dot (QD) based photoconductive antenna (PCA) is a promising and compact solution for THz generation. Coherent THz radiation in the pulsed and the CW regime has been generated with a QD PCA under a resonant and off-resonant pumps [1, 2]. While photoconductivity of QD materials in mid- and far-IR at lower temperatures has been studied for cryogenic sensors and attributed to interlevel transitions, near-IE interband photoconductivity needs further investigation [3, 4]. In this work, we report on the photoconductive properties of an InAs/GaAs QD PCA pumped by a broadly-tunable InAs/GaAs QD external-cavity diode laser

Photoelectric Properties of InAs/GaAs Quantum Dot Photoconductive Antenna Wafers

In this paper, the study of the photoconductivity in self-assembled InAs/GaAs quantum dot photoconductive antenna in the wavelength region between 1140 nm and 1250 nm at temperatures ranging from 13 to 400 K is reported. These antennas are aimed to work in conjunction with quantum dot semiconductor lasers to effectively generate pulsed and continuous wave terahertz radiation. For the efficient operation, laser wavelengths providing the highest photocurrent should be determined. To study the interband photoconductivity of quantum dot photoconductive antennas, at room and cryogenic temperatures, we employed a broadly-tunable InAs/GaAs quantum dot based laser providing a coherent pump with power exceeding 20 mW over a 100 nm tunability range. The quantum dot antenna structure revealed sharp temperature-dependent photoconductivity peaks in the vicinity of wavelengths, corresponding to the ground and excited states of InAs/GaAs quantum dots. The ground state photoconductivity peak vanishes with a temperature drop, whereas the excited state peak persists. We associate this effect with different mechanisms of photoexcited carriers extraction from quantum dots

Efficient generation of orange light by frequency-doubling of a quantum-dot laser radiation in a PPKTP waveguide

Orange light with maximum conversion efficiency exceeding 10% and CW output power of 12.04 mW, 10.45 mW and 6.24 mW has been generated at 606, 608, and 611 nm, respectively, from a frequency-doubled InAs/GaAs quantum-dot external-cavity diode laser by use of a periodically-poled KTP waveguides with different cross-sectional areas. The wider waveguide with the cross-sectional area of 4×4 μm demonstrated better results in comparison with the narrower waveguides (3×5 μm and 2×6 μm) which corresponded to lower coupling efficiency. Additional tuning of second harmonic light (between 606 and 614 nm) with similar conversion efficiency was possible by changing the crystal temperature

Conical refraction of a high-M2 laser beam

We report on experiments with conical refraction of laser beams possessing a high beam propagation parameter M2. With beam propagation parameter values M2=3 and M2=5, unusual Lloyd's distributions with correspondingly three and five dark rings were observed. In order to explain this phenomenon, we extend the dual-cone model of the conical refraction that describes it as a product of interference of two cones that converge and diverge behind the exit facet of the crystal. In the extended model, these converging/diverging cones are represented as the cone-shaped quasi-Gaussian beams possessing the M2 parameter of an original beam. In this formalism, a beam-waist of these cone-shaped beams is proportional to the M2 value and defines the area of their interference which is a width of the Lloyd's ring. Therefore, the number of dark rings in the Lloyd distribution is defined by the M2 value and can be much greater than unity. The results of the numerical simulations within the extended dual-cone model are in excellent agreement with the experiment

Tunable single- and dual-wavelength SHG from diode-pumped PPKTP waveguides

A compact, all-room-temperature, widely tunable, continuous wave laser source in the green spectral region (502.1–544.2 nm) with a maximum output power of 14.7 mW is demonstrated. This was made possible by utilizing second-harmonic generation (SHG) in a periodically poled potassium titanyl phosphate (PPKTP) crystal waveguide pumped by a quantum-well external-cavity fiber-coupled diode laser and exploiting the multimode-matching approach in nonlinear crystal waveguides. The dual-wavelength SHG in the wavelength region between 505.4 and 537.7 nm (with a wavelength difference ranging from 1.8 to 32.3 nm) and sum-frequency generation in a PPKTP waveguide is also demonstrated

Generation of tunable visible picosecond pulses by frequency-doubling of a quantum-dot laser in a PPKTP waveguide

We demonstrate a compact all-room-temperature picosecond laser source broadly tunable in the visible spectral region between 600 nm and 627 nm. The tunable radiation is obtained by frequency-doubling of a tunable quantum-dot external-cavity mode-locked laser in a periodically-poled KTP multimode waveguide. In this case, utilization of a significant difference in the effective refractive indices of the high- and low-order modes enables to match the period of poling in a very broad wavelength range. The maximum achieved second harmonic output peak power is 3.25 mW at 613 nm for 71.43 mW of launched pump peak power at 1226 nm, resulting in conversion efficiency of 4.55%

Pulse dynamics in SESAM-free electrically pumped VECSEL

Self-starting pulsed operation in an electrically pumped (EP) vertical-external-cavity surface-emitting-laser (VECSEL) without intracavity saturable absorber is demonstrated. A linear hemispherical cavity design, consisting of the EP-VECSEL chip and a 10% output-coupler, is used to obtain picosecond output pulses with energies of 2.8 pJ and pulse widths of 130 ps at a repetition rate of 1.97 GHz. A complete experimental analysis of the generated output pulse train and of the transition from continuous-wave to pulsed operation is presented. Numerical simulations based on a delay-differential-equation (DDE) model of mode-locked semiconductor lasers are used to reproduce the pulse dynamics and identify different laser operation regimes. From this, the measured single pulse operation is attributed to FM-type mode-locking. The pulse formation is explained by strong amplitude-phase coupling and spectral filtering inside the EP-VECSEL