Abstract: A polarization-related characteristic of an optical path is determined from a predetermined function of the mean-square of a plurality of differences between polarization-analyzed optical power parameters corresponding to pairs of wavelengths mutually spaced about a midpoint wavelength by a small optical frequency difference. At least some of the said differences correspond to wavelength pairs measured under conditions where at least one of midpoint wavelength, input state of polarization (I-SOP) or analyzed state of polarization (A-SOP) of a pair is different.

Abstract: A polarization-related characteristic of an optical path is determined from a predetermined function of the mean-square of a plurality of differences between polarization-analyzed optical power parameters corresponding to pairs of wavelengths mutually spaced about a midpoint wavelength by a small optical frequency difference. At least some of the said differences correspond to wavelength pairs measured under conditions where at least one of midpoint wavelength, input state of polarization (I-SOP) or analyzed state of polarization (A-SOP) of a pair is different.

Abstract: A laser for generating laser light pulses comprises a cavity containing an active optical gain medium (102) and a spectral filtering device (104), a delay device (110) for delaying light by a predetermined delay time (?t), means (106) for extracting a portion of laser light from the cavity, launching said portion into said delay means (110) and returning the delayed portion to the optical gain medium (102), control means (116) operable to activate the gain medium for a first time period (C1) to produce a first laser light pulse (LP1) having a duration that is less than the delay time (?t), and activate the gain medium for a second time period (C2) while a said delayed portion of the first light pulse that has been delayed by the delay means (UO) is traversing the gain medium (102), thereby to produce a second laser pulse (LP2) having a shorter duration and faster risetime than the first laser light pulse (LP1), and output means (108) for outputting the second laser light pulse (LP2).

Abstract: First and second optical fibers are spliced by a mechanical splice-based connecting device having a portion whereby light leaked from the splice can leave the connecting device. A reference power level (PREF) of light leaked while only the first fiber is inserted into the connecting device, and a measured power level (PM) light leaked while both fibers are inserted are measured. Insertion loss of the splice is derived from the measured power level (PM), the measured reference power level (PREF) and a calibration factor (C) previously obtained by using the same or substantially identical measuring apparatus and connecting device to measure a corresponding calibration input power level (P?IN) and calibration reference power level (P?REF) with only the first fiber inserted, and a calibration measured power level (P?M) and output power level (P?F) of light coupled into a second fiber after the second fiber has been inserted.

Abstract: A laser for generating laser light pulses comprises a cavity containing an active optical gain medium (102) and a spectral filtering device (104), a delay device (110) for delaying light by a predetermined delay time (?t), means (106) for extracting a portion of laser light from the cavity, launching said portion into said delay means (110) and returning the delayed portion to the optical gain medium (102), control means (116) operable to activate the gain medium for a first time period (C1) to produce a first laser light pulse (LP1) having a duration that is less than the delay time (?t), and activate the gain medium for a second time period (C2) while a said delayed portion of the first light pulse that has been delayed by the delay means (UO) is traversing the gain medium (102), thereby to produce a second laser pulse (LP2) having a shorter duration and faster risetime than the first laser light pulse (LP1), and output means (108) for outputting the second laser light pulse (LP2).

Abstract: A method of estimating loss of a splice between first and second optical fibers spliced together by a mechanical splice or a mechanical splice-based connector having a portion through which light leaked from the splice can emerge comprises the steps of launching light into the first fiber, collecting light leaked from the portion using a multiplicity of ports, measuring the power level of the collected light and deriving the insertion loss from the measured power level, a predetermined power level and a collection factor C representing a relationship between measured power level, predetermined power level, power level of light in the first fiber, and power level of light coupled into the second fiber previously obtained for the same or similar connecting device. The ports may be angularly spaced about the axis of the connector or splice. The predetermined power level may be obtained by measuring light emerging from the connector but without the second fiber in position.

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 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).

Abstract: A photodetector device comprising a photosensitive detector (12; 96) and one or more interfaces (20′, 20″, 28, 98) between dissimilar media is configured so that a light beam (LB) for detection will pass through the interface(s) along a beam axis that is not normal to the interface(s). The deviation (&thgr;) from the normal will be such that polarization dependent transmission introduced at the interface(s) will compensate for inherent polarization dependency of the detector (12; 96). The deviation may be achieved by inclining the interface(s) relative to a predetermined direction along which the light beam will be incident. Where the photosensitive detector is in a housing (84) with a window (20) through which the light beam enters the housing, the housing can be tilted. In such as case, there are three interfaces, one (28; 98) at the surface of the detector (12; 96), and one at each surface (20′, 20″) of the window (20).

Abstract: A polarization independent tunable optical filter 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. An optical spectrum analyzer apparatus 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 an inherently polarization sensitive angle-tuned filter which selects different wavelengths of the first and second light beams. The light beams are passed through the filter repeatedly by multi-pass polarization-maintaining optics.

Abstract: A photodetector device comprising a photosensitive detector (12; 96) and one or more interfaces (20′, 20″, 28, 98) between dissimilar media is configured so that a light beam (LB) for detection will pass through the interface(s) along a beam axis that is not normal to the interface(s). The deviation (&thgr;) from the normal will be such that polarization dependent transmission introduced at the interface(s) will compensate for inherent polarization dependency of the detector (12; 96). The deviation may be achieved by inclining the interface(s) relative to a predetermined direction along which the light beam will be incident. Where the photosensitive detector is in a housing (84) with a window (20) through which the light beam enters the housing, the housing can be tilted. In such as case, there are three interfaces, one (28; 98) at the surface of the detector (12; 96), and one at each surface (20′, 20″) of the window (20).

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).