An effective method to implement room temperature operation of multiwavlength erbium-doped fiber ring laser (MW-EDFL) employing equivalent low frequency shift feedback (ELFSF) is presented. Simultaneous multiwavelength lasing with 0.5nm wavelength spacing is experimentally demonstrated by applying a sawtooth signal of the order of 10kHz to a phase modulator inserted in the ring cavity to prevent single-wavelength oscillation. A LiNbO3 multifunction chip of fiber gyro has been used as the phase modulator, the output coupler, and the polarizer of Lyot periodic filter. The MW-EDFL output is linearly polarization light that meets the requirement of external modulation for WDM applications.
All polarization maintaining fiber Sagnac interferometers with linearly birefringence are proposed for the construction of stable comb filters. The transfer functions of the filters can be determined if stress-induced birefringence fiber is used because its birefringence is more or less independent of wavelength. The transfer function of the simplest filter, which acts as a comb filter, with only one polarization mode-coupling point is obtained. Several filters have been realized; they exhibit channel isolation of about 22 dB and can be used as frequency selectors in multi-wavelength fiber lasers. We also discuss the potential applications of the proposed filter that include add-drop multiplexers in wavelength division multiplexing (WDM) systems, gain flattening in fiber amplifiers, and switches/modulators.
Ultrasonic Lamb waves have been proved to be a potentially desirable method for quick interrogation of large plate structures. Integrating fiber optic sensors offer great potential to monitor large areas due to their geometric flexibility. To date this potential has not been widely exploited and there have been only a few reports of non-destructive testing with integrating fiber optic sensors. In this report we present our preliminary measurements for the interrogation of hole defects in plate-like materials with surface-bonded integrating fiber optic sensors. Due to the signal integrating characteristics of fiber sensors very complicated signals were obtained. Therefore signal processing is needed to interpret waveforms for flaw detection.