COMPLEX OPTICAL CAVITIES

摘要

A complex optical cavity system comprises a hybrid laser source, based on a traditional Mach-Zender Interferometer (MZI), consisting of three mirrors (1, 2 and 3) of reflectivity less than or equal to (1) and a beam splitter (5). The source additionally includes an extra mirror (4) of reflectivity less than (1), and a phase shifting element (PSE) (8) constituting a tunable Fabry-Perot filter. The mirrors (1 and 4) define a first cavity of length L1, and the mirrors (1 and 3) define a second cavity of length L2. An active medium (6) is provided to produce amplification of the light needed for stimulated (laser) emission within each of these cavities. The mirrors (2 and 4) form a FP cavity of length L3 within which the PSE (8) is positioned so as to allow the optical passband to be tuned to the required wavelength range. Any radiation of a wavelength that does not lie within the passband of the FP cavity of length L3 is confined to the MZI complex cavity consisting of the first cavity of length L1 and the second cavity of length L2. Since the optical lengths L1 and L2 differ by an odd number of lambda /4, the modes of the first and second cavities interfere destructively, with the result that the modes of the whole complex cavity defined by the components (1, 3, 4 and 5) are suppressed. For any radiation of a wavelength that is within the passband of the FP, this FP cavity is transparent and such radiation is confined to the complex cavity. Since the optical lengths L1 + L3 and L2 of these cavities differ by an even number of lambda /4, the light in the two cavities interferes constructively and the modes of the whole cavity defined by the components (1, 2, 3 and 5) are enhanced.