Abstract: An external cavity laser system comprises a reflective optical amplifier 3, an input waveguide 4 for receiving an optical input signal from the reflective optical amplifier 3, a Bragg grating 5 for reflecting a portion of the optical input signal back along the input waveguide 4 to define a resonant cavity with the optical amplifier, and a reflection photodiode 30 for detecting the signal portion reflected by the grating 5 and for supplying an electrical feedback signal indicative of the signal portion. A transmission photodiode 6 is also provided for detecting the signal portion transmitted by the grating 5 and for supplying an electrical feedback signal indicative of that signal portion. These feedback signals are supplied to a control circuit which controls a phase modulator to modulate the phase of the optical input signal so as to ensure zero detuning between the dominant signal mode and the peak of the grating.

Abstract: A hybridized fiber amplifier/waveguide system for amplifying a multichannel signal comprises a planar waveguide structure (1) incorporating a pump laser (2) providing an output signal of a defined wavelength, a doped optical fiber (8) attached to the structure and having an absorption wavelength corresponding to the wavelength of the laser output signal, and coupling means (5) for supplying the output signal of the laser and the multichannel signal to the doped fiber to amplify the multichannel signal.