Dingli Wang

Modeling Widely Tunable Sampled-Grating DBR Lasers Using Traveling-Wave Model With Digital Filter Approach

A theoretical model for simulating widely tunable sampled-grating distributed Bragg reflector (SGDBR) lasers has been developed. The model integrates both time-domain traveling-wave method and frequency-domain transfer-matrix method into a single procedure. The active region of the device is still operated in the conventional time domain, while the passive parts are firstly performed by the transfer-matrix method and then transformed to the time domain via digital filters. Both the static and dynamic characteristics of SGDBR lasers, such as L-I curve, output spectrum, tuning characteristics, large-signal modulation, and dynamic wavelength switching, can be clearly visible in our model and in qualitative agreement with the published experimental results.

Widely Wavelength-Selectable Lasers With Digital Concatenated Grating Reflectors—Proposal and Simulation

A digital concatenated grating is presented to tackle that problem of creating a flat ldquotop-hatrdquo comb reflector for tunable lasers. A novel, monolithic, widely tunable semiconductor laser with these gratings is proposed and demonstrated theoretically.

Slightly tapered optical fiber with inner air-cavity as a miniature and versatile sensing device

A long-standing goal of optical fiber sensors is the development of a miniature and versatile optical fiber device, which is capable of performing multiple sensing functions, and supporting a simple and efficient system. Here, we demonstrate an elegant way of achieving such a device by use of an inner air-cavity in a slightly tapered optical fiber. Owing to the small size of only a few tens microns and inner cavity structure, a spatially precise “point sensing” with high sensitivity and good robustness can be readily achieved. The refractive index, strain, and temperature sensitivities obtained are ~1060 nm/RIU (refractive index unit), 22.5 pm/με, and 80 pm/°C, respectively. The inner air-cavity-based device is flexible, ultracompact, versatile, and highly efficient, which provides a promising new way for a wide range of optical fiber sensing applications.

Modeling Wavelength Switching of Widely Tunable Sampled-Grating DBR Lasers Using Traveling-Wave Model With Digital Filter Approach

A dynamic theoretical model has been proposed for simulating the wavelength switching performance of widely tunable sampled-grating distributed Bragg reflector lasers. The active region of the device is still operated in time domain while the passive parts are first modeled by transfer-matrix method and then transformed into the time domain via digital filter approach. The switching performance and corresponding mode-competition behaviors can be clearly demonstrated by the transient spectrum traced by the switching time.

Angled stripe InGaAsP/InP SLED fabricated by low-damage inductively coupled plasma dry etching

We successfully fabricated the angled strip DC-PBH style SLED devices by using low damage ICP dry etching technology. The mesa of DC-PBH SLED was formed by Cl2/N2 ICP dry etching process. The low DC bias (<100 eV) of ICP etching technology can reduce the damage caused by ordinary RIE technique and Cl2/N2 based process can get rid of chemical damage caused by CH4/H2. High out-put power SLED device was obtained by using low damage ICP dry etching, the out-put power is 2 mW at 100 mA inject current (CW) at 25°C. Through optimized the angle of the active strip and AR optical film design, the full width of the half maximum (FWHM) of the spectrum at 2 mW out-put power can reach 46.4nm and the ripple of the SLED spectrum is low down to 0.4 dB.

High-speed directly modulated and uncooled long-wavelength DFB semiconductor lasers

This paper summarizes the recent advances and results of uncooled, high-speed directly modulated long-wavelength DFB laser diodes. It discusses ways of obtaining high temperature operation of laser diodes. By assessing the effect of carrier transport, doping and strain in active region, as well as the non-active region factor, such as laser waveguide properties and microwave parasitic parameters, various methods are discussed to improve the direct modulation bandwidth.

Nano-patterns fabricated by soft press and temperature-pressure variation imprint

Nano-devices are increasingly required, the fabrication cost of nano-devices is quite high due to high resolution requirement. Nanoimprint lithography(NIL) is a promising technology for nano devices fabrication due to its low cost and high resolution. However, it still suffers from the large area uniformity and imprint defects problems. Herein, temperature-pressure variation soft press process are used in Simultaneous Thermal and UV (STU) imprint to enhance the uniformity and quality of pattern. This method is used to pattern high quality photonic crystals and gratings.

Application of reflection-spectrum envelope for sampled gratings

An analytical expression is proposed for evaluating the performances of reflection-spectrum envelope for sampled gratings. The accuracy of the expression has been verified by the simulated reflectivity spectrum by use of transfer matrix method. A new technique of multiple reflection-spectrum envelope concatenation is introduced to demonstrate a 23-channel grating with uniform characteristics in all channels. The proposed technology can densify sampled grating both in spectral channel number and in spatially physical corrugation.

Nonlinear phenomena analysis of tunable external cavity semiconductor laser with sampled fiber grating

The theoretical model considering nonlinear effects in the external cavity semiconductor laser with sampled fiber grating has been presented. Such effects are including the asymmetric side mode suppression ratio (SMSR) or power characteristics, and hysteresis phenomena. This theoretical model is based on the transmission line theory on compound cavity. The parameters of the laser, e.g. active section length and phase section length, have been optimized to suppress such nonlinear effects, which makes the device control simple and reliable, while the performances such as 16nm tuning range, 40dB SMSR, 8.5mW output power can be maintained.

Effects of external magnetic trap on two dark solitons of a two-component Bose-Einstein condensate

Two dark solitons are considered in a two-component Bose-Einstein condensate with an external magnetic trap, and effects of the trap potential on their dynamics are investigated by the numerical simulation. The results show that the dark solitons attract, collide and repel periodically in two components as time changes, the time period depends strictly on the initial condition and the potential, and there are obvious self-trapping effects on the two dark solitons.