High-power ultrafast solid-state laser using graphene based saturable absorber

We demonstrate a graphene based saturable absorber mode-locked Nd:YVO4 solid-state laser, generating ~14nJ pulses with ~1W average output power. This shows the potential for high-power pulse generation. © 2011 Optical Society of America.

Radio over free space optical link using a directly modulated two-electrode high power tapered laser

The analog modulation performance of a high-power two-electrode tapered laser is investigated. A 25dB dynamic range for 2.4GHz 802.11g signals is achieved with a 26dB loss budget, showing a >1km free space range is possible. © 2010 Optical Society of America.

APSK coded modulation schemes for nonlinear satellite channels with high power and spectral efficiency

A new class of 16-ary Amplitude Phase Shift Keying (APSK) coded modulations deemed double-ring PSK modulations best suited for (satellite) nonlinear channels is proposed. Constellation parameters optimization has been based on geometric and information-theoretic considerations. Furthermore, pre- and post-compensation techniques to reduce the nonlinearity impact have been examined. Digital timing clock and carrier phase have been derived and analyzed for a Turbo coded version of the same new modulation scheme. Finally, the performance of state-of the art Turbo coded modulation for this new 16-ary digital modulation has been investigated and compared to the known TCM schemes. It is shown that for the same coding scheme, double-ring APSK modulation outperforms classical 16-QAM and 16-PSK over a typical satellite nonlinear channel due to its intrinsic robustness against the High Power Amplifier (HPA) nonlinear characteristics. The new modulation is shown to be power- and spectrally-efficient, with interesting applications to satellite communications. © 2002 by the American Institute of Aeronautics and Astronautics, Inc.

Fabrication and Characterization of High Power InGaN Blue-Violet Lasers with an Array Structure

InGaN/GaN multi-quantum-well-structure laser diodes with an array structure are successfully fabricated on sapphire substrates. The laser diode consists of four emitter stripes which share common electrodes on one laser chip. An 800-mu m-long cavity is formed by cleaving the substrate along the < 1 (1) over bar 00 >. orientation using laser scriber. The threshold current and voltage of the laser array diode are 2A and 10.5 V, respectively. A light output peak power of 12W under pulsed current injection at room temperature is achieved. We simulate the electric properties of GaN based laser diode in a co-planar structure and the results show that minimizing the difference of distances between the different ridges and the n-electrode and increasing the electrical conductivity of the n-type GaN are two effective ways to improve the uniformity of carrier distribution in emitter stripes. Two pairs of emitters on a chip are arranged to be located near the two n-electrode pads on the left and right sides, and the four stripe emitters can laser together. The laser diode shows two sharp peaks of light output at 408 and 409 nm above the threshold current. The full widths at half maximum for the parallel and perpendicular far field patterns are 8 degrees and 32 degrees, respectively.

High-power quantum-dot superluminescent LED with broadband drive current insensitive emission spectra using a tapered active region

High-power and broadband quantum-dot (QD) superluminescent light-emitting diodes are realized by using a combination of self-assembled QDs with a high density, large inhomogeneous broadening, a tapered angled pump region, and etched V groove structure. This broad-area device exhibits greater than 70-nm 3-dB bandwidth and drive current insensitive emission spectra with 100-mW output power under continuous-wave operation. For pulsed operation, greater than 200-mW output power is obtained.

High-power operation of uncoated strain-compensated quantum cascade lasers at 4.8 mu m

High-power operation of uncoated 22-mu m-wide quantum cascade lasers (QCLs) emitting at lambda approximate to 4.8 mu m is reported. The emitting region of the QCL structure consists of a 30-period strain-compensated In0.68Ga0.32As/In0.37Al0.63As superlattice. For a 4-mm-long laser in pulsed mode, a peak output power is achieved in excess of 2240mW per facet at 81K with a threshold current density of 0.64kA/cm(2). The effects of varying the cavity lengths from 1 to 4mm on the performances of the QCLs are analysed in detail and the low waveguide loss of only about 1.4 cm(-1) is extracted.

Enhancement of the spectral width of high-power 1.5 mu m integrated superluminescent light source by quantum well intermixing process

A novel type of integrated InGaAsP superluminescent light source was fabricated based on the tilted ridge-waveguide structure with selective-area quantum well (QW) intermixing. The bandgap structure along the length of the device was modified by impurity free vacancy diffusion QW intermixing, The spectral width was broadened from the 16 nm of the normal devices to 37 nm of the QW intermixing enhanced devices at the same output power level. High superluminescent power (210 mW) was obtained under pulsed conditions with a spectral width of 37 nm.

High-power electroabsorption modulator for radio over fibre system

An electroabsorption modulator using an intra-step quantum well (IQW) active region is fabricated for a radio over fibre system. The strain-compensated InGaAsP/InGaAsP IQW shows good material quality and improved modulation properties, high extinction ratio efficiency (10 dB V-1) and low capacitance (< 0.42 pF), with which high frequency (> 15 GHz) can be obtained. High-speed measurement under high-power excitation shows no power saturation up to an excitation power of 21 dBm. To our knowledge, the input optical power is the highest reported for a multi-quantum well EAM without a heat sink.

High-power electroabsorption modulator using intrastep quantum well

An electroabsorption modulator using the intrastep quantum well (IQW) active region is fabricated for optical network systems. The strain-compensated InGaAsP/InGaAsP IQW shows good material quality and improved modulation properties, high extinction ratio elliciency 10 dB/V and low capacitance (< 0.42 pF), with which an ultra high frequency (> 15 GHz) can be obtained. High-speed measurement under high-power excitation shows no power saturation up to excitation power of 21 dBm. To our knowledge, the input optical power is the highest reported for multi-quantum well EAMs without heat sinks.

Comparison of two kinds of active layers for high-power narrow-stripe distributed feedback laser diodes

Usually GaAs/AlGaAs is utilized as an active layer material in laser diodes operating in the spectral range of 800 850 nm. In this work, in addition to a traditional unstrained GaAs/AlGaAs distributed feedback (DFB) laser diode, a compressively strained InGaAlAs/AlGaAs DFB laser diode is numerically investigated in characteristic. The simulation results show that the compressively strained DFB laser diode has a lower transparency carrier density, higher gain, lower Auger recombination rate, and higher stimulated recombination rate, which lead to better a device performance, than the traditional unstrained GaAs/AlGaAs DFB laser diode.