Abstract: A widely-tunable laser apparatus comprises a plurality of tunable lasers having different ranges that overlap to encompass a desired operating range of wavelengths (for example from 1250 nm to 1650 nm) of the widely-tunable laser apparatus. The tunable lasers are tunable synchronously and selectively with their respective outputs connected in common to sweep the output of the widely-tunable laser apparatus substantially continuously over said operating range. The tunable lasers share the same tuning means which has a plurality of independent channels, each for light from a respective one of the tunable lasers.

Abstract: A polarization independent optical spectrum analyzer comprises a diffraction grating, input and output slit means and polarization-maintaining multi-pass optics for directing a light beam to and fro across the diffraction grating while maintaining its linear state of polarization. The optical spectrum analyzer further comprises a polarization control unit for decomposing a light beam for analysis into first and second beams having mutually orthogonal states of polarization (SOPs) and then adjusting one or both SOPs so that they are parallel to each other and to one of the dispersion plane of the diffraction grating which is rotated to select different wavelengths of the first and second light beams. The first and second light beams are passed across the diffraction grating repeatedly by multi-pass polarization-maintaining optics and are outputted and detected separately.

Abstract: A dual-channel, double-filtering, multi-pass OSA having a narrow spectral linewidth response and high ORR comprises a diffraction grating (DG), two input ports (P1?, P1?) for directing first and second input light beams (LR, LT) onto the grating; a retroreflector (RAM1) for returning the dispersed light beams to the grating for dispersion again; two intermediate output ports (P2?, P2?) for receiving the twice-dispersed light beams; two secondary input ports (P3?, P3?) coupled to the intermediate output ports by polarization-maintaining waveguides (PMF2?, PMF2?) for directing the light beams onto the grating a third time, with their SOPs having a predetermined orientation relative to the SOPs of the first and second light beams when first incident upon the grating, the retroreflector (RAM1) returning the three-times-dispersed light beams to the grating for dispersion a fourth time; and two output ports (P4?, P4?) for receiving the light beams after dispersion the fourth time.

Abstract: A polarization independent optical spectrum analyzer comprises an inherently polarization sensitive angle-tuned filter element and polarization-maintaining multi-pass optics for directing a light beam to and fro through the tunable filter element while maintaining its linear state of polarization. The optical spectrum analyzer comprises such a tunable optical filter in combination with a polarization control unit for decomposing a light beam for analysis into first and second beams having mutually orthogonal states of polarization (SOPs) and then adjusting one or both SOPs so that they are parallel to each other and to one of the principal axes of the angle-tuned filter which selects different wavelengths of the first and second light beams. The first and second light beams are passed through the filter repeatedly by multi-pass polarization-maintaining optics.

Abstract: An optical spectrum analyzer comprises a diffraction grating (DG), a polarization decomposing unit (PDM) for decomposing the input light beam into first and second light beams having mutually-perpendicular linear states of polarization, and two output ports (FP2/1, FP2/2) each for receiving from the grating, substantially exclusively, a respective one of the polarized light beams (LT, LR) after diffraction by the diffraction grating (DG).