Polarization independent wavelength tunable filter based on birefringence compensation

DETAILED DESCRIPTION It is an object of the present invention to provide a tunable, polarization independent wavelength filter utilizing birefringence compensation.
It is a further object of the present invention to provide a polarization independent tunable filter employing material compositional and geometrical tailoring to facilitate coupling of both polarization modes from a first waveguide to a second adjacent waveguide.
It is a still further object of the invention to provide the polarization independent filter in semiconductor material and more preferably in III-V alloy material.
Therefore in accordance with the present invention there is provided a polarization independent wavelength tunable filter comprising a first waveguide for receiving an optical signal on at least one wavelength carrier and a second waveguide for receiving from the first waveguide a selected wavelength.
A coupling region lies immediately between the two waveguides.
According to the invention the physical characteristics of the waveguides and coupling region are tailored so as to facilitate coupling of the selected wavelength from the first waveguide to the second.
Preferably, the waveguides and coupling region are fabricated in an epitaxially grown III-V semiconductor alloy.
The balancing of propagation constants required to ensure complete coupling of the central wavelength including TE and TM polarization modes is achieved through selection of geometrical configuration, compositional ratios, and birefringence compensation.
The birefringence compensation is accomplished by utilizing multi-quantum wells preferably in the coupling layer.