Jianxin Geng

Polarization analysis and experimental implementation of PLZT electro-optical switch using fiber Sagnac interferometers

The polarization characteristics of electro-optical (EO) switches using fiber Sagnac interferometer (FSI) structures are theoretically investigated. Analytical solutions of output fields are presented when the twists and birefringence in a Sagnac loop are considered. Numerical calculations show that the twists of fiber, the orientation of the inserted phase retarder, and the splitting ratio of the coupler will influence both the output intensity and the output polarization properties of the proposed switch. A polarization-independent EO switch based on a Sagnac interferometer and a PUT bar was experimentally implemented, which showed good coincidence with the analytical results. The experiment showed a switch with 22 dB extinction ratio and less than 31.1 ns switching time. (c) 2006 Optical Society of America.

Specklegram in a multiple-mode fiber and its dependence on longitudinal modes of the laser source

A specklegram in a multimode fiber (MMF) has successfully been used as a sensor for detecting external disturbance. Our experiments showed that the sensitivity in the sensor with a multiple longitudinal-mode laser as its source was much higher than that with a single longitudinal-mode laser. In addition, the near-field pattern observations indicated that the coupling between different transverse modes in the MMF is quite weak. Based on the experimental results, a theoretical model for the speckle formation is proposed, taking a bend-caused phase factor into consideration. It is shown in the theoretical analysis that the interferences between different longitudinal modes make a larger contribution to the specklegram signals.

Single-frequency phosphate glass fiber laser with 100-mW output power at 1535 nm and its polarization characteristics

We demonstrated a single-frequency Phosphate glass fiber laser with 100 mW output power in this paper. Single-frequency single-polarization operation with ≪5 KHz linewidth and 65dB SNR is realized by using external cavity polarization feedback technology.

Instabilities in a grating feedback external cavity semiconductor laser

Output power fluctuations in a grating external cavity diode laser with Littman configuration are described, showing peculiar chaotic behaviors of self-pulsation at the L-I curve kink points. Different spectral characteristics with multiple peaks are observed at upper and lower state of the self-pulsation. It is found also that P-N junction voltage jumps in a same pace with the pulsation. The observed phenomena reflect competition between different longitudinal modes, and transient variation of transverse modes in addition. These experimental results may contain information about the mechanisms of the chaotic instability in strong filtered feedback semiconductor lasers.

Optic fiber-based dynamic pressure sensor

This paper shows the way to turn birefringence of single-mode fiber into a prime quality for a powerful and reliable sensor. This paper presents preliminary results for the development of a weigh-in-motion (WIM) technique based on sagnac-loop sensor. After a brief description of the sensor and its principle of operation, the theoretical model is developed.Then, a full characterization made in static conditions is presented.

Logarithmic conversion of absorption detection in wavelength modulation spectroscopy with a current-modulated diode laser

Logarithmic-conversion data processing used in wavelength modulation spectroscopy (WMS) with a current-modulated diode laser as its source is analyzed and compared with second-to-first ratio detection. Analytic Fourier coefficients of logarithmic-converted residual amplitude modulation (RAM) of a light source are given. An experimental setup for methane absorption detection at 1650 nm is described. It is shown theoretically and experimentally that logarithmic-converted WMS cannot only eliminate the fluctuation of received light power, but also improve the signal-to-noise ratio significantly.

Narrow line width phosphate glass fiber laser

An Er³⁺/Yb³⁺ codoped phosphate glass fiber laser is presented which output a single mode with SNR>50dB and the line-width of 4.5kHz. The output power of 79mW and slope efficiency of 21% were obtained under temperature control at 11°C. The output power varies with ambient temperature periodically.

Single-frequency Phosphate glass fiber laser with 100mW output power at 1535nm and its polarization characteristics

We demonstrated a single-frequency Phosphate glass fiber laser with 100 mW output power in this paper. Single-frequency single-polarization operation with ≪5 KHz linewidth and 65dB SNR is realized by using external cavity polarization feedback technology.

Fiber optic methane sensing system based on wavelength modulation spectroscopy by using logarithm method

A new method based on logarithm calculation for wavelength modulation spectroscopy is proposed and analyzed. It is shown that in the algorithm the second harmonic signal keeps linear relation with the gas concentration in the whole concentration scale. A fiber optic methane sensing system with much higher SNR was built.

Detuning behaviors of fiber Bragg grating external cavity laser

The mode hopping and lasing spectral linewidth broadening of fiber Bragg grating external cavity laser associated with frequency detuning between external cavity mode and intracavity mode have been experimental observed and analyzed. Through optimizing the parameter of device, wavelength stabilized single mode emission without mode hopping and spectral linewidth broadening was obtained experimentally over 70/spl deg/C range.