Resonant cavity based compact efficient antireflection structures for photonic crystals

We propose an effective admittance ( EA) method to design antireflection structures for two-dimensional photonic crystals (PCs). We demonstrate that a compact and efficient antireflection structure, which is difficult to obtain by the conventional admittance matching method, can be readily designed by the EA method. The antireflection structure consists of an air slot resonant cavity that is constructed only with the materials that constitute the PC. Compared with a bare PC, the reflection from a PC with an antireflection structure is reduced by two orders of magnitude over a wide bandwidth. To confirm the presented EA method, finite-difference time-domain (FDTD) simulations are performed, and the results from the FDTD and the EA method are in good agreement.

Simulation research of nonlinear behavior induced by the charge-carrier effect in resonant-cavity-enhanced photodetectors

In this paper, we have calculated and discussed in detail the nonlinear effect induced by three carrier effects: free-carrier absorption, bandgap filling, and bandgap shrinkage. The central wavelength of response of resonant-cavity-enhanced (RCE) photodetectors shifts according to the change of the refractive index, and the response of a given optical wavelength simultaneously changes.With an increasing As composition of ln(1-x)Ga(x)As(y)P(1-y) and the spacer thickness, the nonlinear effect increases, but the -1-dB input saturation optical power and the -1-dB saturation photocurrent decrease. Bistable-state operation occurs when the input optical power is in the proper bistable region.

Passively Q-switched mode-locking of diode-pumped Nd : YVO4 laser with GaAs intracavity absorber grown at low temperature

Using a low temperature grown GaAs wafer as an intracavity saturable absorber, a temporal envelope duration of 11 ns of Q- switched and mode- locked ( QML) 1064 nm operation was achieved in a very simple compact plane- concave cavity Nd: YVO4 laser, it was so short that the pulses can be used as Q- switching pulses. The maximal average output power is 808 mW with the repetition rate of 25 kHz, and the corresponding peak power and energy of a single Q- switched pulse was 2.94 kW and 32.3 mu J, respectively. The mode- locked pulse trains inside the Q- switched pulse envelope had a repetition rate of 800 MHz.

The effect of proton radiation on a superlumine scent diode (SLD)

The effect of proton radiation on a superluminescent diode (SLD) was studied, and the radiation damage from different energies was compared. The results reveal that the optical power degradation is greater from 350 KeV protons than from 1 MeV protons. Analysis of SLD characteristics after irradiation shows that the main effect of radiation is damage within the active region. At the same time, the results also show that quantum-well (QW) SLDs are far less sensitive to radiation than double-heterojunction (DH) SLDs. (C) 2007 Elsevier B.V. All rights reserved.

A bidirectionall diode-pumped, passively mode-locked Nd : YVO4 ring laser with a low-temperature-grown semiconductor saturable absorber mirror

We report the operation of a bidirectional picosecond pulsed ring Nd:YVO4 laser based on a low-temperature-grown semiconductor saturable absorber mirror. Except for the laser crystal, the six-mirror ring laser cavity has no intra-cavity elements such as focusing lens or mirror. The bidirectional mode locked pluses are obtained at the repetition rate of 117.5 MHz, pulse duration of 81 ps, power of 2 x 200 mW.

Experiments of a diode-pumped Nd : GdVO4/LT-GaAs Q-switched and mode-locked laser

A diode-pumped passively Q-switched mode-locked (QML) Nd:GdVO4 laser with a low temperature GaAs (LT-GaAs) saturable absorber is presented. The maximal Q-switched mode-locked average output power was 798 mW with the Q-switched envelop having a repetition rate of 125 kHz. The mode-locked pulse trains inside the Q-switched pulse envelope had a repetition rate of similar to 750 MHz. The laser properties of the operational parameters on the pump power were also investigated experimentally.

Unselective regrowth buried heterostructure long-wavelength superluminescent diode realized with MOVPE

A novel unselective regrowth buried heterostructure (BH) long-wavelength superluminescent diode (SLD), which has a grade-strained bulk InGaAs active region, was developed by metalorganic vapor-phase epitaxy (MOVPE). The 3 dB emission spectrum bandwidth of the SLD is about 65 nm with the range from 1596 to 1661 nm at 90 mA and front 1585 to 1650 nm at 150 mA. An output power of 3.5 mW is obtained at 200 mA injection current under CW operation at room temperature. (c) 2006 Elsevier B.V. All rights reserved.

Design and fabrication of 1.06 mu m resonant-cavity enhanced reflective modulator with GaInAs/GaAs quantum wells

A resonant-cavity enhanced reflective optical modulator is designed and frabricated, with three groups of three highly strained InGaAS/GaAs quantum wells in the cavity, for the low voltage and high contrast ratio operation. The quantum wells are positioned in antinodes of the optical standing wave. The modulator is grown in a single growth step in an molecular beam epitaxy system, using GaAs/AIAs distributed Bragg reflectors as both the top and bottom mirrors. Results show that the reflection device has a modulation extinction of 3 dB at -4.5 V bias.

Diode-end-pumped passively CW mode-locked Nd : YLF laser by the LT-In0.25Ga0.75As absorber

We have demonstrated a self-staring passively continuous-wave mode-locked diode end-pumped Nd:YLF laser with a semiconductor saturable absorber mirror of single-quantum-well (In0.25Ga0.75As) grown by metal-organic chemical-vapor deposition technique at low temperature. The saturable absorber was used as nonlinear absorber and output coupler simultaneously. Stable pulse duration of 3 ps has been achieved at the repetition rate of 98 MHz. The average output power was 530 mW at 1053 nm under the incident pump power of 10 W, corresponding to the peak power of 1.8 kW and pulse energy of 5.4 nJ.

High-performance 1.55 mu m low-temperature-grown GaAs resonant-cavity-enhanced photodetector

A 1.55 mu m low-temperature-grown GaAs (LT-GaAs) photodetector with a resonant-cavityenhanced structure was designed and fabricated. A LT-GaAs layer grown at 200 degrees C was used as the absorption layer. Twenty- and fifteen-pair GaAs/AlAs-distributed Bragg reflectors were grown as the bottom and top mirrors. A responsivity of 7.1 mA/W with a full width at half maximum of 4 nm was obtained at 1.61 mu m. The dark current densities are 1.28x10(-7) A/cm(2) at the bias of 0 V and 3.5x10(-5) A/cm(2) at the reverse bias of 4.0 V. The transient response measurement showed that the photocarrier lifetime in LT-GaAs is 220 fs. (c) 2006 American Institute of Physics.

Experimental investigation of intracavity absorber low temperature GaAs in diode-pumped Nd : GdVO4 laser

A passively Q-switched and mode-locked diode-pumped Nd:GdVO4 laser was demonstrated using a low-temperature-grown GaAs wafer (LT-GaAs) as an intracavity saturable absorber. The maximal Q-switched mode-locked average output power was 750 mW with the Q-switched envelop having a repetition rate of 167 kHz. The mode-locked pulse trains inside the Q-switched pulse envelope had a repetition rate of similar to 790 MHz.

Effects of phase-breaking on long-range charge transfer in DNA: Partially-coherent-tunneling model study

The mechanism of hole charge transfer in DNA of various lengths and sequences is investigated based on a partially coherent tunneling theory (Zhang et al., J Chem Phys 117:4578, 2002), where the effects of phase-breaking in adenine-thymine and guanine-cytosine base pairs are treated on equal foot. This work aims at providing a self-consistent microscopic interpretation for rate experiments on various DNA systems. We will also clarify the condition under which the simple superexchange-mediated-hopping picture is valid, and make some comments on the further development of present theory.

GaAs absorber grown at low temperature used in passively Q-switched diode pumped solid state laser

We report, for the first time to the best of our knowledge, on a passively Q-switched Nd:YVO4 laser with a GaAs absorber grown at low temperature (LT) by metal organic vapor phase expitaxy. Using the LT GaAs absorber as well as an output coupler, a passively Q-switched laser whose pulse duration is as short as 90 ns, was obtained.

Q-switched and mode-locked diode-pumped Nd : GdVO4 laser with low temperature GaAs saturable absorber

Low temperature GaAs (LT-GaAs) was successfully grown at the temperature of 550 degrees C by metal organic vapor phase epitaxy on a semi-insular GaAs substrate. With such an absorber as well as an output coupler we obtain Q-switched mode-locked (QML) 1064 nm Nd:GdVO4 laser pumped by diode laser with high repetition rate, formed with a simple flat-flat cavity. The repetition rate of the Q-switched envelope increased from 100 to 660 kHz as the pump power increased from 2.28 to 7.29 W. The mode-locked pulses inside the Q-switched pulse envelope had a repetition rate of similar to 1.36 GHz. A maximum average output power of 953 mW was obtained. The dependence of the operational parameters on the pump power was also investigated experimentally. (C) 2005 Elsevier B.V. All rights reserved.

1.55-mu m resonant cavity enhanced photodiode based on MBE grown Ge quantum dots

Self-assembly Ge quantum dots (QD) on Si and Si/Ge mutli-quantum-wells (MQW) are grown by MBE. The island size and island density was investigated by atomics force microscopy. Ten-layer and twenty-layer MQW were selected for photodiode device fabrication. In photoluminescence (PL), a broad peak around 1.55-mu m wavelength was observed with higher peak intensity for the 10-layer MQW which had less defects than the 20-layer sample. Resonant cavity enhanced (RCE) photodiodes were fabricated by bonding on a SOI wafer. Selected responsivity at 1.55 mu m was successfully demonstrated. (c) 2005 Elsevier B.V. All rights reserved.