Abstract: There is provided a method and an apparatus for determining quality parameters on a polarization-multiplexed optical signal based on an analysis of the power spectral density of the Signal-Under-Test (SUT). The method is predicated upon knowledge of the spectral shape of the signal in the absence of significant noise or spectral deformation. This knowledge is provided by a reference optical spectrum trace. Based on this knowledge and under the assumption that ASE noise level is approximately constant in wavelength over a given spectral range, the spectral deformation of the signal contribution of the SUT may be estimated using a comparison of the spectral variations of the optical spectrum trace of the SUT with that of the reference optical spectrum trace.

Abstract: There is provided a method for determining the in-band noise in agile multichannel Dense Wavelength Division Multiplexing (DWDM) optical systems, where the interchannel noise is not representative of the in-band noise in the optical channel. The method relies on the analysis of two observations of the same input optical signal. In the two observations, the linear relationship between the optical signal contribution and the optical noise contribution (e.g. the observed OSNR) is different, which allows the discrimination of the signal and noise contributions in the input optical signal. In a first approach, the two observations are provided by polarization analysis of the input optical signal. In a second, the input optical signal is obtained using two different integration widths.

Abstract: There is provided a method of determining at least one linear-crosstalk-related parameter of an optical signal-under-test having, within an optical channel bandwidth, at least a data-carrying signal contribution and a wavelength-dependent linear-crosstalk contribution arising from a data-carrying signal contribution of an adjacent optical signal associated with an adjacent channel to the optical signal-under-test, the method comprising: acquiring at least one optical spectrum trace encompassing a quasi-continuum of closely-spaced wavelengths over a spectral range extending to at least part of both the signal under test and the adjacent optical signal; and estimating said linear-crosstalk contribution using at least spectral properties of said at least one optical spectrum trace; wherein one of said at least one linear-crosstalk-related parameter is the linear-crosstalk contribution and is determined from said estimating.

Abstract: There is provided a method for determining a noise parameter characterizing an optical Signal-Under-Test (SUT) having a signal contribution, an Amplified Spontaneous Emission (ASE) noise contribution and a non-ASE optical noise contribution, such as a carrier-leakage contribution or a depolarized-signal contribution, within an optical-signal bandwidth. The method comprises acquiring optical spectrum trace(s) of the SUT, discriminating at least the non-ASE optical noise contribution from the ASE-noise contribution using the optical spectrum trace(s) and/or a trace obtained from the optical spectrum trace(s); and determining the noise parameter using discriminated non-ASE optical noise contribution and/or the discriminated ASE-noise contribution.

Abstract: A method comprises: acquiring, for a number nSOP of varied State-Of-Polarization analysis conditions of the input optical signal, nSOP polarization-analyzed optical spectrum traces; mathematically discriminating said signal contribution from said noise contribution within said optical signal bandwidth using said polarization-analyzed optical spectrum traces, said mathematically discriminating comprising: obtaining a differential polarization response that is related to the optical spectrum of said signal contribution by a constant of proportionality; estimating the constant of proportionality of a differential polarization response to the optical spectrum of said signal contribution; estimating the optical spectrum of said noise contribution from said input optical signal, within said optical signal bandwidth using said constant of proportionality and said differential polarization response; and determining said in-band noise parameter on said input optical signal from the mathematically discriminated noise c

Abstract: There is provided a method for determining the in-band noise in agile multichannel Dense Wavelength Division Multiplexing (DWDM) optical systems, where the interchannel noise is not representative of the in-band noise in the optical channel. The method relies on the analysis of two observations of the same input optical signal. In the two observations, the linear relationship between the optical signal contribution and the optical noise contribution (i.e. the observed OSNR) is different, which allows the discrimination of the signal and noise contributions in the input optical signal. In a first approach, the two observations are provided by polarization analysis of the input optical signal. In a second, the input optical signal is obtained using two different integration widths.

Abstract: There is provided a method for determining an in-band noise parameter, such as the Optical Signal-to-Noise Ratio (OSNR), on an optical signal-under-test (SUT) propagating along an optical communication link and comprising a data-carrying signal contribution of any arbitrary degree of polarization and a noise contribution. A spectral shape trace of signal contribution in the SUT is estimated using a reference optical spectrum trace of a reference signal which comprises a signal contribution that is spectrally representative of the signal contribution of the SUT and a noise contribution which is at least approximately known. The signal contribution is mathematically discriminated from said noise contribution in the SUT using the spectral shape trace and the test optical spectrum trace. The in-band noise parameter is then determined at least from the mathematically discriminated noise contribution.

Abstract: A method comprises: acquiring, for a number nSOP of varied State-Of-Polarization analysis conditions of the input optical signal, nSOP polarization-analyzed optical spectrum traces; mathematically discriminating said signal contribution from said noise contribution within said optical signal bandwidth using said polarization-analyzed optical spectrum traces, said mathematically discriminating comprising: obtaining a differential polarization response that is related to the optical spectrum of said signal contribution by a constant of proportionality; estimating the constant of proportionality of a differential polarization response to the optical spectrum of said signal contribution; estimating the optical spectrum of said noise contribution from said input optical signal, within said optical signal bandwidth using said constant of proportionality and said differential polarization response; and determining said in-band noise parameter on said input optical signal from the mathematically discriminated noise c

Abstract: There is provided a method for determining the in-band noise in agile multichannel Dense Wavelength Division Multiplexing (DWDM) optical systems, where the interchannel noise is not representative of the in-band noise in the optical channel. The method relies on the analysis of two observations of the same input optical signal. In the two observations, the linear relationship between the optical signal contribution and the optical noise contribution (i.e. the observed OSNR) is different, which allows the discrimination of the signal and noise contributions in the input optical signal. In a first approach, the two observations are provided by polarization analysis of the input optical signal. In a second, the input optical signal is obtained using two different integration widths.

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 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 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).

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: 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: An apparatus for simultaneously stabilising the output power and wavelength of a semiconductor laser is disclosed. A wavelength discriminating scheme is used to provide a wavelength error signal and an output power detection scheme is used to provide an output power level signal. The wavelength error signal is used to adjust the behaviour of a temperature sensor such that an automatic temperature control (ATC) module configured to maintain a pre-determined output from the temperature sensor, adjusts the actual laser temperature to minimize said signal. The output power level signal is directly delivered to an automatic power control (APC) module, which adjusts the drive current fed into the laser to minimize said signal using known control circuitry means.