Passively mode-locking Nd : Gd0.5Y0.5VO4 laser with an In(0.25)Ga(0.75)Aa absorber grown at low temperature

We have demonstrated stable self-starting passive mode locking in a diode-end-pumped Nd:Gd-0.8-Y0.5VO4 laser by using an In0.25Ga0.75As absorber grown at low temperature (LT In0.25Ga0.75As absorber). An In0.25Ga0.75As single-quantum-well absorber, which was grown directly on the GaAs buffer by use of the metal-organic chemical-vapor deposition technique, acts simultaneously as a passive mode-locking device and as an output coupler. Continuous-wave mode-locked pulses were obtained at 1063.5 nm. We achieved a pulse duration of 2.6 ps and an average output power of 2.15 W at a repetition rate of 96.4 MHz. (c) 2005 Optical Society of America.

Low power-consumption and high response frequency thermo-optic variable optical Attenuators based on silicon-on-insulator materials

A novel silicon-on-insulator thermo-optic variable optical attenuator with isolated grooves based on a multimode interference coupler principle is fabricated by the inductive coupled plasma etching technology. The maximum fibre-to-fibre insertion loss is lower than 2.2 dB, the dynamic attenuation range is from 0 to 30 dB in the wavelength range 1500-1600 nm, and the maximum power consumption is only 140 mW. The response frequency of the fabricated variable optical attenuator is about 30 kHz. Compared to the variable optical attenuator without isolated grooves, the maximum power consumption decreases more than 220 mW, and the response frequency rises are more than 20 kHz.

A study on the realization of radio frequency energy AC/DC charge pump based on MOS FET

This paper presents a novel efficient charge pump composed of low Vth metal-oxide-semiconductor (MOS) field effect transistors (FET) in the course of realizing radio frequency (RF) energy AC/DC conversion. The novel structure eliminates those defects caused by typical Schottky-diode charge pumps, which are dependent on specific processes and inconsistent in quality between different product batches. Our analyses indicate that an easy-fabricated, stable and efficient RF energy AC/DC charge pump can be conveniently implemented through reasonably configuring the MOS transistor aspect ratio, and other design parameters such as capacitance, multiplying stages to meet various demands on performance.

Passive mode locking of diode-end-pumped Nd : GdVO4 laser with an In0.25Ga0.75As output coupler

Passive mode locking of a diode-pumped Nd:GdVO4 laser was demonstrated using In0.25Ga0.75As as saturable absorber as well as output coupler. The pulse width was measured to be about 16 ps with a repetition rate of 146 MHz. The average output power was 120 mW with pump power of 6 W. To our knowledge, this is the first demonstration on a passively mode-locked Nd:GdVO4 laser by using an In0.25Ga0.75As output coupler. (C) 2004 Elsevier B.V. All rights reserved.

A novel hybrid phase-locked-loop frequency synthesizer using single-electron devices and CMOS transistors

This paper proposes a novel phase-locked loop (PLL) frequency synthesizer using single-electron devices (SEDs) and metal-oxide-semiconductor (MOS) field-effect transistors. The PLL frequency synthesizer mainly consists of a single-electron transistor (SET)/MOS hybrid voltage-controlled oscillator circuit, a single-electron (SE) turnstile/MOS hybrid phase-frequency detector (PFD) circuit and a SE turnstile/MOS hybrid frequency divider. The phase-frequency detection and frequency-division functions are realized by manipulating the single electrons. We propose a SPICE model to describe the behavior of the MOSFET-based SE turnstile. The authors simulate the performance of the PILL block circuits and the whole PLL synthesizer. Simulation results indicated that the circuit can well perform the operation of the PLL frequency synthesizer at room temperature. The PILL synthesizer is very compact. The total number of the transistors is less than 50. The power dissipation of the proposed PLL circuit is less than 3 uW. The authors discuss the effect of fabrication tolerance, the effect of background charge and the SE transfer accuracy on the performance of the PLL circuit. A technique to compensate parameter dispersions of SEDs is proposed.

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.

Frequency mixing and phase detection functionalities of three-terminal ballistic junctions

Three-terminal ballistic junctions (TBJs) are fabricated from a high-mobility InP/In0.75Ga0.25As heterostructure by electron-beam lithography. The voltage output from the central branch is measured as a function of the voltages applied to the left and right branches of the TBJs. The measurements show that the TBJs possess an intrinsic nonlinearity. Based on this nonlinearity, a novel room-temperature functional frequency mixer and phase detector are realized. The TBJ frequency mixer and phase detector are expected to have advantages over traditional circuits in terms of simple structure, small size and high speed, and can be used as a new type of building block in nanoelectronics.

Silicon bench for passive coupling and packaging of high-frequency optoelectronic devices

Coupling and packaging have become decisive factors in the final performance and cost of high-frequency optoelectronic devices. Here, we report the design and successful fabrication of a silicon bench that integrates a V-groove and high-frequency coplanar waveguide (CPW) on the same high-resistivity silicon wafer as an effective optoelectronic packaging solution.

Simultaneous Q switching and mode locking with narrow envelope width in a microchip Nd : YVO4 laser with a composite semiconductor absorber

By using a composite semiconductor absorber and an output coupler, we demonstrated a Q-switched and mode-locked diode-pumped microchip Nd:YVO4 laser. With a 350-mu m-thick crystal, the width of the Q-switched envelope was as short as 12 ns; the repetition rate of the mode-locked pulses inside the Q-switched pulse was more than 10 GHz. The average output power was 335 mW at a maximum pump power of 1.6 W. Q-switched envelope widths of 21 and 31 ns were also achieved with crystals 0.7 and 1.0 mm thick, respectively.

Small-signal power measuring technique for measuring the frequency response of electroabsorption modulators

We propose and demonstrate measurement of the frequency response of an electroabsorption (EA) modulator using an extended small-signal power measuring technique. In this technique, the modulator is driven by a microwave carrier amplitude modulated by a low-frequency signal, and the modulator frequency response is obtained without the need of a high-speed photodetector. Based upon the nonlinear characteristics of the EA modulator and the underlying principle of the present method, equations have been derived. A measurement scheme using a network analyzer and a low-speed photodetector has been proposed and constructed, and the experimental results confirm that our proposed method is as accurate as the swept-frequency measurement using a network analyzer directly.

Estimation of frequency response of directly modulated lasers from optical spectra

A simple method for estimating the frequency responses of directly modulated lasers from optical spectra is presented. The frequency-modulation index and intensity-modulation index of a distributed feedback laser can be obtained through the optical spectrum analyses. The main advantage is that the measurement setup is very simple. Only a microwave source and an optical spectrum analyser are needed and there is no need to use a calibrated broadband photodetector. Experiment shows that the proposed method is as accurate as the swept frequency method using a network analyzer and is applicable to a wide range of modulation powers.

p-type Zn1-xMgxO films with Sb doping by radio-frequency magnetron sputtering

Sb-doped Zn1-xMgxO films were grown on c-plane sapphire substrates by radio-frequency magnetron sputtering. The p-type conduction of the films (0.05 <= x <= 0.13) was confirmed by Hall measurements, revealing a hole concentration of 10(15)-10(16) cm(-3) and a mobility of 0.6-4.5 cm(2)/V s. A p-n homojunction comprising an undoped ZnO layer and an Sb-doped Zn0.95Mg0.05O layer shows a typical rectifying characteristic. Sb-doped p-type Zn1-xMgxO films also exhibit a changeable wider band gap as a function of x, implying that they can probably be used for fabrication of ZnO-based quantum wells and ultraviolet optoelectronic devices. (c) 2006 American Institute of Physics.

Potential frequency bandwidth estimation of TO packaging techniques for photodiode modules

Scattering parameters of photodiode chip, TO header and TO packaged module are measured, and the effects of TO packaging network on the high-frequency response of photodiode are investigated. Based on the analysis, the potential bandwidth of TO packaging techniques is estimated from the scattering parameters of the TO packaging network. Another method for estimating the potential bandwidth from the equivalent circuit for the TO packaged photodiode model is also presented. The results obtained using both methods show that the TO packaging techniques used in the experiments can potentially achieve a frequency bandwidth of 22 GHz.

Probing deep level centers in GaN epilayers with variable-frequency capacitance-voltage characteristics of Au/GaN Schottky contacts

Under identical preparation conditions, Au/GaN Schottky contacts were prepared on two kinds of GaN epilayers with significantly different background electron concentrations and mobility as well as yellow emission intensities. Current-voltage (I-V) and variable-frequency capacitance-voltage (C-V) characteristics show that the Schottky contacts on the GaN epilayer with a higher background carrier concentration and strong yellow emission exhibit anomalous reverse-bias I-V and C-V characteristics. This is attributed to the presence of deep level centers. Theoretical simulation of the low-frequency C-V curves leads to a determination of the density and energy level position of the deep centers. (c) 2006 American Institute of Physics.

A novel fast lock-in phase-locked loop frequency synthesizer with direct frequency presetting circuit

This paper proposes a novel, fast lock-in, phase-locked loop (PLL) frequency synthesizer. The synthesizer includes a novel mixed-signal voltage-controlled oscillator (VCO) with a direct frequency presetting circuit. The frequency presetting circuit can greatly speed up the lock-in process by accurately the presetting oscillation frequency of the VCO. We fully integrated the synthesizer in standard 0.35 mu m, 3.3 V complementary metal-oxide-semiconductors (CMOS) process. The entire chip area is only 0.4 mm(2). The measured results demonstrate that the synthesizer can speed up the lock-in process significantly and the lock-in time is less than 10 mu s over the entire oscillation frequency range. The measured phase noise of the synthesizer is -85 dBc/Hz at 10 kHz offset. The synthesizer avoids the tradeoff between the lock-in speed and the phase noise/spurs. The synthesizer monitors the chip temperature and automatically compensates for the variation in frequency with temperature.