Single-stage gain-clamped L-band EDFA with C-band ASE self-oscillation in ring cavity

We demonstrate single-stage gain-clamped L-band Er3+-doped fiber amplifier (EDFA) utilizing self-oscillation modes as the control light. The amplifier structure exploits the characteristics of C/L-band coupler to isolate between lasing modes and L-band signal. The self-lasing cavity modes are obtained without any tunable bandpass filter in the loop and generated from the amplified spontaneous emission in the C-band region. The amplifier configuration has lower noise figures as opposed to a dual-stage partially gain-clamped amplifier. The gain and noise figure fluctuations are less than ±0.4 dB in the gain clamping region. The transient analysis confirms that the maximum power excursion is less than 0.3 dB for 10-dB add/drop

Temperature and current dependence of doppler SNR in a VCSEL based self-mixing sensor

This paper proposes a method for maintaining the maximum signal-to-noise ratio (SNR) of the signal obtained from the self-mixing sensor based on a Vertical-Cavity Surface-Emitting Laser (VCSEL). The SNR of the Doppler self-mixing signal was investigated experimentally as a function of laser driving current and ambient temperature. It was found that the locus of the maximum SNR in the current-temperature space can be well approximated by the simple analytical model based on the temperature behaviour of the VCSELs threshold current. A selfmixing Doppler signal was acquired from the variation in VCSEL junction voltage rather than from a conventional variation in laser optical power to reduce the complexity of the system. It was found that the optimum sensor performance over a wide range of ambient temperatures can be achieved by tuning the laser current according to the proposed model. This enables the sensor to operate without temperature stabilisation making it attractive for mobile applications and applications with limited power supply. ©2009 IEEE