Xiyao Chen

Effect of external cavity length on self-mixing signals in a multilongitudinal-mode Fabry–Perot laser diode

The effect of external-cavity length on self-mixing signals in a multilongitudinal-mode Fabry-Perot laser diode (FP-LD) was investigated experimentally. It has been shown that the output waveforms of self-mixing signals vary periodically when the length of the external cavity changes. This result agrees well with our theoretical calculations for the self-mixing effect of two adjacent longitudinal modes in a FP-LD. Moreover, the time-averaged output intensities of self-mixing signals has also been measured and compared with theoretical analysis.

Single-frequency Q-switched erbium-doped fiber ring laser by combination of a distributed Bragg reflector laser and a Mach-Zender interferometer

A single-frequency Q-switched erbium-doped fiber ring laser is implemented for producing a single frequency with 25-Mhz laser linewidth, Q-switched pulses with a high peak power at 1557.5 mm. The single longitudinal mode is selected by a distributed Bragg reflector fiber laser, and a fiberoptic Mach-Zehnder interferometer acts as a Q-switch. The peak power and the average power of the Q-switched pulses vary with the repetition rate.

Independent control of upper and lower cutoff frequencies in two-dimensional photonic crystal waveguides

The independent control of the upper and lower cutoff frequencies of the guided modes in coupled-cavity wavguides (CCWs) is investigated numerically. The CCWs are formed in a two-dimensional photonic crystal (2D PhC) consisting of a square array of dielectric rods in the air. The dielectric constant and radius of the rods in the perfect PhC is 11.56 and 0.18α, respectively, in which α is lattice constant. By using the plane wave expansion method (PWEM), the impact of two influencing factors on cutoff frequencies in CCWs is calculated systematically. Efficient methods have been demonstrated for tuning one cutoff frequency while keeping the other unchanged. The indepent control ranges of the upper and lower cutoff can be up to 67.85% and 68.57% of photonic band gap (PBG), respectively. The results can be applied to the design of PhC-based optical devices such as band filters and optical switches.

Photo-induced polarized emission of the Eu3+-doped Azo-polymer waveguide

The polarized emission behaviors of the Eu3+ doped azo-polymer waveguide were reported in this paper. Affected by the azobenzene groups in the photoinduced orientation process by the 532nm linearly polarized laser, the ligands were realigned orderly perpendicular to the direction of the orientation direction. This leads to the polarized absorption and emission of the waveguide in the orientation direction. By an m-line apparatus based on the prism coupling technique, two guided modes propagation were observed in the waveguide at 650nm in TE polarizations.

Theoretical and numerical analysis of polarization properties used as Doppler velocimetry in vertical-cavity surface-emitting lasers

This paper presents a theoretical and numerical analysis of polarization properties used as Doppler velocimetry in Vertical-Cavity Surface-Emitting lasers. A good match is found between numerical results and reported experiment results. We show that condition of generating square waves is the VCSELs must operated inside the bistable region and frequency difference between two linear polarization modes is equal to several certain values. We can select proper VCSELs which frequency difference between two linear polarization modes is multiple of ±3G to obtain asymmetric waveform of self-mixing signal.

Optical reflector based on two-dimensional photonic crystal constructed by a square lattice of air holes

The optical reflector based on two-dimensional photonic crystal constructed by a square lattice of dielectric rods has already been reported in recent years, But the enormous difficulties to fabricate this structure are well-known, because the height of the rods must be finite in a real system so in this case no guided modes appears when air waveguides are created. On the contrary, there is not this inherent limitation for the photonic crystal waveguide made of air holes. In this paper, I will demonstrate an optical reflector based on photonic crystal,which constructed by air holes introduced into high index material. We design a monomode waveguide with even symmetry and discuss the characteristic of the reflector obtained by inserting several defects into the monomode waveguide in FDTD method.This kind of reflectors still have guided mode even if it possess finite thickness. This will make optical reflector based on two-dimensional photonic crystal nearer to practical application.

Optical filter in two-dimension photonic crystal waveguide

The factors that affect the properties of the filters in a two-dimensional photonic crystal (2-D PC) waveguide are investigated quantitatively. The waveguide is constructed by omitting one line rods in a perfect 2-D PhC composed of circular dielectric rods located at a square lattice. The 2-D PC filters (2-D PCF) are formed by adding some defect rods in the waveguide. The numerical calculation results show that the reflectivity and transmission of the filter are dependent on the size, dielectric constant and number of defect rods. Moreover, the transmission spectrum of a PCF is also obtained by using fast fourier transform (FFT) method and comb-like curve shape similar to that in the transmission spectrum of Fabry-Perot etalons is found in it .

Tunable polarization interference filter for high-resolution wavelength monitoring of a DWDM transmitter

A temperature-tunable polarization interference filter (PIF) made of YVO4 crystal has been presented and applied for wavelength monitoring of a distributed feedback (DFB) laser in a dense wavelength-division-multiplexing (DWDM) optical communication system. This novel device offers a flexible way to monitor the operating wavelength of the transmitter over a wide capture range. Monitoring resolution of 0.02 nm can be obtained by measuring the temperature variation of the filter while its transmission value is kept at a constant value.