Intracavity Laser Diode Pumped and Modulated Er³ + Doped Fiber Lasers

Abstract

We report on a pulsed compound Er³+-doped laser, that simultaneously uses an intracavity laser diode for optical pumping, gain or phase modulation and as a bandwidth control etalon. We demonstrate a simple method to produce high-energy pulses with peak powers up to 100 times the average power and with durations on the order of 1 μs using the synchronization of relaxation oscillations by drive current modulation of the intracavity pump laser diode. The forced sustained relaxation oscillations is shown to depend on wavelength, and the frequency locking curve exhibits strong asymmetry with hysteresis behavior. Tunable locked spiking operation provides interesting tool for characterization of the laser dynamics.

Mode-locked pulses with durations adjustable from 200 ps to less than 50 ps were generated by current modulation of a 1.48 μm pump laser diode incorporated in an Er-doped fiber laser cavity. The laser diode exhibits sufficient phase modulation without degradation in pump ability, and thus demonstrates a very practical and simple approach to optical pulse generation.

We propose and demonstrate a novel mechanism for Q-switching an Er-doped fiber laser. The fiber laser cavity includes a current modulated laser diode that serves both as a pumping source and nonlinear etalon, and is terminated by a diffraction grating that serves as a frequency dependent reflector. Current modulation of the intracavity laser diode produces strong frequency modulation effects in the pumping diode laser modes. The laser is effectively Q-switched when diode mode frequency is swept through the reflection window of the diffraction grating in the fibre laser cavity acted as frequency-dependent reflector. The use of pump laser diode switch has the advantage of maintaining the light in a guided waveform and permits the extraction of pulse average power close to cw average power. High switch hold-off with switch time <lns can be easily obtained by frequency modulation of the laser diode modes in dispersive resonator.