Patent ID: 7038782

Claim:
A device for determining frequency of a laser producing an output light beam having a laser frequency, comprising: a fringe-producing optical element to generate an interference pattern from light derived from the output light beam, the fringe-producing optical element being a non-parallel etalon and the interference pattern defining a pattern period; a detector unit disposed to detect the interference pattern, the detector unit including at least three detector elements disposed to detect respective portions of the pattern period and including additional detector elements disposed to detect similarly phased portions of the interference pattern as associated detector elements of the at least three detector elements, signals from the at least three detector elements being summed together with signals from their respective associated detector elements to produce detection signals associated with each of the at least three detector elements; and a control unit coupled to the detector unit and adapted to generate a laser frequency control signal in response to the detection signals associated with the at least three detector elements for controlling the laser frequency.