Monolithically integrated semiconductor optical amplifier and electroabsorption modulator with dual-waveguide spot-size converter input and output

We have demonstrated an electroabsorption modulator and semiconductor optical amplifier monolithically integrated with novel dual-waveguide spot-size converters (SSC) at the input and output ports for low-loss coupling to a planar light-guide circuit silica waveguide or cleaved single-mode optical fibre. The device was fabricated by means of selective-area MOVPE growth, quantum well intermixing and asymmetric twin waveguide technologies with only a three-step low-pressure MOVPE growth. For the device structure, in the SOA/EAM section, a double ridge structure was employed to reduce the EAM capacitances and enable high bit-rate operation. In the SSC sections, buried ridge structure (BRS) was incorporated. Such a combination of ridge, ATG and BRS structure is reported for the first time in which it can take advantage of easy processing of the ridge structure and the excellent mode characteristic of BRS. At the wavelength range of 1550-1600 nm, lossless operation with extinction ratios of 25 dB dc and more than 10 GHz 3 dB bandwidth is successfully achieved, The beam divergence angles of the input and output ports of the device are as small as 8.0 degrees x 12.6 degrees, resulting in 3.0 dB coupling loss with a cleaved single-mode optical fibre.

Controlled growth of III-V compound semiconductor nano-structures and their application in quantum-devices

This paper reviews our work on controlled growth of self-assembled semiconductor nanostructures, and their application in light-emission devices. High-power, long-life quantum dots (QD) lasers emitting at similar to 1 mu m, red-emitting QD lasers, and long-wavelength QD lasers on GaAs substrates have successfully been achieved by optimizing the growth conditions of QDs.

Q-switched and mode-locked diode-pumped Nd : YVO4 laser with an intracavity composite semiconductor saturable absorber

We have demonstrated a passively Q-switched and mode-locked Nd:YVO4 laser with an intracavity composite semiconductor saturable absorber (ICSSA). Stable Q-switched and mode-locked pulses with Q-switched envelope pulse duration of 180 ns and pulse repetition rate of 72KHz have been obtained. The maximum average output power was 1.45W at 8W incident pump power. The repetition rate of the mode-locked pulses inside the Q-switched envelope was 154 MHz. Experimental results revealed that this ICSSA was suitable for Q-switched and mode-locked solid-state lasers. (c) 2007 Elsevier Ltd. All rights reserved.

Status and trends of short pulse generation using mode-locked lasers based on advanced quantum-dot active media

In this review, the potential of mode-locked lasers based on advanced quantum-dot ( QD) active media to generate short optical pulses is analysed. A comprehensive review of experimental and theoretical work on related aspects is provided, including monolithic-cavity mode-locked QD lasers and external-cavity mode-locked QD lasers, as well as mode-locked solid-state and fibre lasers based on QD semiconductor saturable absorber mirrors. Performance comparisons are made for state-of-the-art experiments. Various methods for improving important characteristics of mode-locked pulses such as pulse duration, repetition rate, pulse power, and timing jitter through optimization of device design parameters or mode-locking methods are addressed. In addition, gain switching and self-pulsation of QD lasers are also briefly reviewed, concluding with the summary and prospects.

High-average-power and high-conversion-efficiency continuous wave mode-locked Nd : YVO4 laser with a semiconductor absorber mirror

A high-power continuous wave (cw) mode-locked Nd:YVO4 solid-state laser was demonstrated by use of a semiconductor absorber mirror (SAM). The maximum average output power was 8.1 W and the optic-to-optic conversion efficiency was about 41 %. At the maximum incident pump power, the pulse width was about 8.6 ps and the repetition rate was 130 MHz. Experimental results indicated that this absorber was suitable for high power mode-locked solid-state lasers. (C) 2006 Elsevier Ltd. All rights reserved.

Measurement of chirp parameter and modulation index of a semiconductor laser based on optical spectrum analysis

A novel and simple method for measuring the chirp parameter, frequency, and intensity modulation indexes of directly modulated lasers is proposed in a small-signal modulation scheme. A graphical approach is presented. An analytical solution to the measurement of low chirp parameters is also given. The measured results agree well with those obtained using the conventional methods.

Passively mode-locked Nd : YVO4 laser using semiconductor saturable absorption mirrors of interface states relaxation region

Semiconductor saturable absorber mirrors (SESAMs) with GaAs/air interface relaxation region have less nonsaturable loss than those with low temperature grown In0.25Ga0.75As relaxation region. A thin layer Of SiO2 and a high reflectivity film Of Si/(SiO2/Si)(4) were coated on the SESAMs, respectively in order to improve the SESAM's threshold for damage. The passively continuous wave mode-locked lasers with two such SESAMs were demonstrated, and the SESAM with high reflectivity film of Si/(SiO2/Si)(4) is proved to be helpful for high output power. (c) 2006 Elsevier GmbH. All rights reserved.

Post-growth and in situ annealing on GaInNAs(Sb) and their application in 1.55 mu m lasers

Rapid thermal annealing (RTA) has been demonstrated as an important way to improve the crystal quality of GaInNAs(Sb)/GaAs quantum wells. However little investigation has been made into their application in laser growth, especially at a wavelength of 1.55 mu m. When a GaAs-based laser is grown, AlGaAs is usually used for cladding layers. The growth of the p-cladding layer usually takes 30-45 min at a growth temperature higher than that of the GaInNAs(Sb) active region, which affects the material quality. To investigate this effect, various post-growth annealing processes were performed to simulate this process. Great enhancement of the PL intensity was obtained by a two-step process which consisted of annealing first at 700 degrees C for 60 s and then at 600 degrees C for 45 min. We transferred this post-growth annealing to in situ annealing. Finally, a GaInNAsSb laser was grown with a 700 degrees C in situ annealing process. Continuous operation at room temperature of a GaAs-based dilute nitride laser with a wavelength beyond 1.55 mu m was realized for the first time.

Analysis of mode quality factors for equilateral triangle semiconductor microlasers with rough sidewalls

The eigenmode characteristics for equilateral triangle resonator (ETR) semiconductor microlasers are analysed by the finite-difference time-domain technique and the Pade approximation. The random Gaussian correlation function and sinusoidal function are used to model the side roughness of the ETR. The numerical results show that the roughness can cause the split of the degenerative modes, but the confined modes can still have a high quality factor. For the ETR with a 3 mum side length and the sinusoidal fluctuation, we can have a quality factor of 800 for the fundamental mode in the wavelength of 1500 nm, as the amplitude of roughness is 75 mn.

Size limit and spontaneous emission factor for equilateral triangle semiconductor microlasers

The size of equilateral triangle resonator (ETR) needed for confining the fundamental mode is investigated by the total reflection condition of mode light rays and the FDTD numerical simulation. The confinement of the TM modes can be explained by the total reflection of mode light rays, and the confinement of the TE modes requires a larger ETR than the TM modes, which may be caused by excess scattering or radiation loss for the TE modes. With the multilayer staircase approximation, it is found that the spontaneous emission factor of the ETR lasers has the same form as that of strip waveguide lasers.

Analysis of semiconductor microlasers with an equilateral triangle resonator by rate equations

Semiconductor microlasers with an equilateral triangle resonator (ETR) are analyzed by rate equations with the mode lifetimes calculated by the finite-difference time-domain technique and the Pade approximation. A gain spectrum based on the relation of the gain spectrum and the spontaneous emission spectrum is proposed for considering the mode selection in a wide wavelength span. For an ETR microlaser with the side length of about 5 mum, we find that single fundamental mode operation at about 1.55 mum can be obtained as the side length increases from 4.75 to 5.05 mum. The corresponding wavelength tuning range is 93 nm, and the threshold current is about 0.1 to 0.4 mA.

High-performance strain-compensated InGaAs/InAlAs quantum cascade lasers

We report on the realization of quantum cascade (QC) lasers based on strain-compensated InxGa(1-x)As/In(y)A((1-y))As grown on InP substrates using molecular beam epitaxy. X-ray diffraction and cross section transmission electron microscopy have been used to ascertain the quality of the QC laser materials. Quasi-continuous wave lasing at lambda approximate to 3.54-3.7 mum at room temperature was achieved. For a laser with 1.6 mm cavity length and 20 mum ridge-waveguide width,quasi-continuous wave lasing at 34 degreesC persists for more than 30 min, with a maximum power of 11.4 mW and threshold current density of 1.2 kA cm(-2), both record values for QC lasers of comparable wavelength.

Influence of output waveguide on mode quality factor in semiconductor microlasers with an equilateral triangle resonator

Semiconductor microlasers with an equilateral triangle resonator (ETR) and an output waveguide are proposed and analyzed by the finite-difference time-domain technique and the Pade approximation. The numerical results show that microlasers with an output waveguide still have a high-quality factor (Q factor) and are suitable to realize directional emission. For the ETR with a 0.46-mum-width opening in one of the vertices connected to the output waveguide, we have the Q factor of 1.5x10(3) and 2.5x10(2) for the TM fundamental mode at the wavelength of 1.55 mum, as the side length of the ETR is 5 and 3 mum. The simulated intensity distributions are presented for the fundamental mode in the ETR with a side length of 3 mum and an opening of 0.23 mum. (C) 2000 American Institute of Physics. [S0003-6951(00)01749-6].

Investigation on anisotropy of vertical-cavity surface-emitting lasers

We have studied the spontaneous emission of polarized excitons in the GaInP/AlGaInP vertical-cavity surface-emitting lasers from 50 K to room temperature. It is observed that the spontaneous emission peak enters and leaves the resonant regime. At the resonant regime, the emission intensities of the perpendicularly and horizontally polarized excitons are enhanced and their proportions are different from that in nonresonant regime. These experimental results are explained by the dressed exciton theory of the semiconductor microcavity device. Based on this theory, the intensity enhancement and the polarization dependence are understood as cooperative emission and the microcavity anisotropy. (C) 2000 American Institute of Physics. [S0021-8979(00)05315-9].

High-speed and high-power 1.3 mu m InGaAsP/InP selective proton-bombarded buried crescent lasers with optical field attenuation regions

High-speed and high-power InGaAsP/lnP selective proton-bombarded buried crescent (SPB-BC) lasers with optical field attenuation regions were reported. The defect of proton bombardment can not affect the lifetime of the SPB-BC laser because the optical field attenuation region obstructs the growth and propagation of defects. A CW light output over 115 mW was achieved at room temperature using a 500 mu m long cavity SPB-BC laser. The 3 dB bandwidth was 8.5 GHz, and the lifetime was about 8.5 x 10(5) h. The capacitance of four kinds of current blocking structures was first measured in our experiment, and the results shown that the capacitance of proton-bombarded pnpn structure was not only less than that of pnpn current blocking structure, but also less than that of semi-insulating Fe-InP structure.