High-order achromatic quarterwave combination plates and tuners.
Achromatic quarterwave combination plates are formed from two high-order birefringent plates having even and odd multiples of quarterwave retardation at some nominal wavelength. Eleventh- and twelfth-order plates at 1315 nm combined with their axes 77 degrees apart are shown to have 90 +/- 0.25 degrees of retardation between 1275 and 1355 nm. They can be used to construct two- and four-waveplate tuners for birefringent filters.
A technique for modelling the performance of birefringent wave plates
By considering the phase delay introduced by a birefringent wave plate to each frequency component of a finite bandwidth light source we establish the polarisation state of the transmitted light. Realisable designs of achromatic, zero-order and high-order quarter wave and half wave plates are analysed for use with a variety of light sources with different bandwidths.
Tunable birefringent wavelength-division multiplexer/demultiplexer
A tunable wavelength-division multiplexer/demultiplexer, based on a polarisation-insensitive birefringent optical filter design, is described. The two channels of the device can each be tuned, with the channel separation adjustable over a wide range. Experiments with 6 to 30 nm laser channel separations have yielded optical crosstalk values of less than −20 dB.