A method of and device for generating an amplified optical signal directly in an optical fiber by way of phase-sensitive amplification based on one or more four-wave mixing processes. The silicon substrate has a plurality of cavities defined therein. The second limb 26 is exposed to the pressure in a chamber 34 which assists the resilience of the sealing ring 20 in maintaining sealing contact between the sealing face 30 and the abutment surface 32.