Abstract: A disk shaped tunable optical filter is formed by a transparent substrate in a disk shape, and a filter layer formed on a top surface of the substrate, having such a filter characteristic that a transmission central wavelength varies along a circumferential direction as a monotonic function of a viewing angle. This disk shaped tunable optical filter can be advatageously utilized in realizing a wavelength discrimination apparatus, a reference wavelength light generation apparatus, an optical packet generation apparatus, and a tunable optical filter module, which are also disclosed.

Abstract: An inexpensive polarization independent optical nonreciprocal circuit which does not require a use of expensive birefringent crystals, optical branching circuits, and a phase adjustment. The optical nonreciprocal circuit is formed by at least one lens through which a light propagating between two waveguides passes; and a polarization rotation circuit for sequentially applying a nonreciprocal rotation and a reciprocal rotation to a first half of the light propagating between two waveguides, and sequentially applying a reciprocal rotation and a nonreciprocal rotation to a second half of the light propagating between two waveguides, so that the first half and the second half of a light propagating forward are set to have an identical polarization to form an even guided mode and coupled, while the first half and the second half for a light propagating backward are set to have opposite polarizations to form an odd non-guided mode and dissipated.

Abstract: An optical device is presented which is useful for optical signal transmission and switching systems by multiplexing and demultiplexing optical signals in looped optical paths, consisting of a plurality of individual loop-back optical paths. The device is essentially a multi/demultiplexer having an arrayed waveguide grating disposed between a plurality of input sections and output sections which are joined by the plurality of individual loop-back optical paths. Because the modulated signals are looped back into the same optical paths using the same devices, problems of mismatching performance introduced by using different optical devices are avoided. The device processes individual optical signals of different wavelengths, minimizes splitting losses, and reduces noise components by producing narrow bandpass signals of high signal to noise ratio. Optical signal splitting and insertion, delay line memory and delay equalization circuits can all be handled by the same circuit configuration.