Abstract: Optical unit for a projective optical metrological system, which receives a light signal coming from a light constellation comprising a number of light sources; the optical unit includes: an optoelectronic image acquisition system and a first and a second optical circuit, which receive the light signal and are traversed by a first and a second optical beam, respectively. The first and the second optical circuits direct, respectively, at least a first part of the first optical beam and at least a first part of the second optical beam on the optoelectronic image acquisition system, so as to cause the simultaneous formation of two different images of the constellation in the optoelectronic image acquisition system. The optical unit further includes an electronic processing unit coupled to the optoelectronic image acquisition system, which determines a number of quantities indicative of the position and/or attitude of the light constellation with respect to the optical unit, based on the two images.

Abstract: Optical unit for a projective optical metrological system, which receives a light signal coming from a light constellation comprising a number of light sources; the optical unit includes: an optoelectronic image acquisition system and a first and a second optical circuit, which receive the light signal and are traversed by a first and a second optical beam, respectively. The first and the second optical circuits direct, respectively, at least a first part of the first optical beam and at least a first part of the second optical beam on the optoelectronic image acquisition system, so as to cause the simultaneous formation of two different images of the constellation in the optoelectronic image acquisition system. The optical unit further includes an electronic processing unit coupled to the optoelectronic image acquisition system, which determines a number of quantities indicative of the position and/or attitude of the light constellation with respect to the optical unit, based on the two images.

Abstract: An optical system and method for seeding an optical transmitter includes a first optical transmitter comprising a first reflective optical amplifier and a second optical transmitter comprising a second reflective optical amplifier. The second optical transmitter is optically coupled to the first optical transmitter. The optical system also includes an optical cavity for seeding the first reflective optical amplifier with a first optical seed signal. The optical cavity is formed between the first reflective optical amplifier of the first optical transmitter and the second reflective optical amplifier of the second optical transmitter. The first reflective optical amplifier is configured to transmit a first optical signal to the second reflective optical amplifier and the second reflective optical amplifier is configured to provide the first optical seed signal by reflecting a portion of the first optical signal back to the first reflective optical amplifier.

Abstract: An optical system and method for seeding an optical transmitter includes a first optical transmitter comprising a first reflective optical amplifier and a second optical transmitter comprising a second reflective optical amplifier. The second optical transmitter is optically coupled to the first optical transmitter. The optical system also includes an optical cavity for seeding the first reflective optical amplifier with a first optical seed signal. The optical cavity is formed between the first reflective optical amplifier of the first optical transmitter and the second reflective optical amplifier of the second optical transmitter. The first reflective optical amplifier is configured to transmit a first optical signal to the second reflective optical amplifier and the second reflective optical amplifier is configured to provide the first optical seed signal by reflecting a portion of the first optical signal back to the first reflective optical amplifier.

Abstract: An optical source comprises a first laser arranged to generate a first optical signal having a first state of polarization (SOP) and a first optical frequency; a second laser arranged to generate a second optical signal having a second SOP, substantially orthogonal to the first SOP, and having a second optical frequency, different from the first optical frequency by a preselected frequency difference; a polarisation beam coupler arranged to combine the first optical signal and the second optical signal into a composite optical signal comprising both the first optical signal and the second optical signal having said substantially orthogonal SOPs; and an output arranged to output the composite optical signal.

Abstract: An optical source comprises a first laser arranged to generate a first optical signal having a first state of polarization (SOP) and a first optical frequency; a second laser arranged to generate a second optical signal having a second SOP, substantially orthogonal to the first SOP, and having a second optical frequency, different from the first optical frequency by a preselected frequency difference; a polarisation beam coupler arranged to combine the first optical signal and the second optical signal into a composite optical signal comprising both the first optical signal and the second optical signal having said substantially orthogonal SOPs; and an output arranged to output the composite optical signal.

Abstract: An optical source (10) comprising: a first laser (12) arranged to generate a first optical signal (14) having a first state of polarization and a first optical frequency; a second laser (16) arranged to generate a second optical signal (18, 48, 78) having a second state of polarization, substantially orthogonal to the first state of polarization, and having a second optical frequency, different to the first optical frequency by a preselected frequency difference, ??; a polarization beam coupler (20) arranged to combine the first optical signal and the second optical signal into a composite optical signal comprising both the first optical signal and the second optical signal having said substantially orthogonal states of polarization; and an output (22) arranged to output the composite optical signal (24).

Abstract: An optical source (10) comprising: a first laser (12) arranged to generate a first optical signal (14) having a first state of polarization and a first optical frequency; a second laser (16) arranged to generate a second optical signal (18, 48, 78) having a second state of polarization, substantially orthogonal to the first state of polarization, and having a second optical frequency, different to the first optical frequency by a preselected frequency difference, ??; a polarization beam coupler (20) arranged to combine the first optical signal and the second optical signal into a composite optical signal comprising both the first optical signal and the second optical signal having said substantially orthogonal states of polarization; and an output (22) arranged to output the composite optical signal (24).

Abstract: An optical access network comprises an optical network unit having a first port for connecting to a first optical link, a second port for connecting to a second optical link and an optical source. The optical source is arranged to generate a first optical signal, to transmit the first optical signal via the first port, to receive an optical seed signal via the first port and to amplify the optical seed signal. The optical seed signal has a narrower bandwidth compared to the first optical signal. A modulator is arranged to modulate the amplified optical seed signal with upstream data to form an upstream optical signal and to transmit the upstream optical signal via the second port. A polarisation modifier can modify polarisation of the first optical signal.

Abstract: In a coherent optical receiver, a received signal and an oscillator-generated signal, having frequency difference such that the receiver operates under intradyne conditions, are made to beat in a 3×3 optical coupler. A polarizing beam-splitter splits one of the signals into components with orthogonal polarization which are applied to inputs of the coupler, which receives the other of the received or oscillator-generated signal. After photoelectric conversion, the signals are fed to analog processing devices generating an electrical signal representing the received signal that is fed to a low pass filter before being demodulated. The frequency difference between the signals and the passband of the filter are such that a component of the electrical signal, oscillating at a frequency depending on the frequency difference and having amplitude and phase depending on the instant state of polarization of the received signal, is suppressed. A method is also provided.

Abstract: An optical source (10) comprising: a first laser (12) arranged to generate a first optical signal (14) having a first state of polarisation and a first optical frequency; a second laser (16) arranged to generate a second optical signal (18, 48, 78) having a second state of polarisation, substantially orthogonal to the first state of polarisation, and having a second optical frequency, different to the first optical frequency by a preselected frequency difference, Av; a polarisation beam coupler (20) arranged to combine the first optical signal and the second optical signal into a composite optical signal comprising both the first optical signal and the second optical signal having said substantially orthogonal states of polarisation; and an output (22) arranged to output the composite optical signal (24).

Abstract: An optical access network comprises an optical network unit having a first port for connecting to a first optical link, a second port for connecting to a second optical link and an optical source. The optical source is arranged to generate a first optical signal, to transmit the first optical signal via the first port, to receive an optical seed signal via the first port and to amplify the optical seed signal. The optical seed signal has a narrower bandwidth compared to the first optical signal. A modulator is arranged to modulate the amplified optical seed signal with upstream data to form an upstream optical signal and to transmit the upstream optical signal via the second port. A polarisation modifier can modify polarisation of the first optical signal.

Abstract: In a coherent optical receiver, a received signal and an oscillator-generated signal, having frequency difference such that the receiver operates under intradyne conditions, are made to beat in a 3×3 optical coupler. A polarising beam-splitter splits one of the signals into components with orthogonal polarisation which are applied to inputs of the coupler, which receives the other of the received or oscillator-generated signal. After photoelectric conversion, the signals are fed to analogue processing devices generating an electrical signal representing the received signal that is fed to a low pass filter before being demodulated. The frequency difference between the signals and the passband of the filter are such that a component of the electrical signal, oscillating at a frequency depending on the frequency difference and having amplitude and phase depending on the instant state of polarisation of the received signal, is suppressed. A method is also provided.

Abstract: An optical access network comprises an optical network unit having a first port for connecting to a first optical link, a second port for connecting to a second optical link and an optical source. The optical source is arranged to generate a first optical signal, to transmit the first optical signal via the first port, to receive an optical seed signal via the first port and to amplify the optical seed signal. The optical seed signal has a narrower bandwidth compared to the first optical signal. A modulator is arranged to modulate the amplified optical seed signal with upstream data to form an upstream optical signal and to transmit the upstream optical signal via the second port. A polarization modifier can modify polarization of the first optical signal.

Abstract: Chromatic dispersion (CD) processing apparatus comprises an equalizer loop comprising: a frequency domain equalizer (FDE) arranged to receive samples of an electrical representation of an optical communications signal having CD and to apply CD compensation to the samples, to form dispersion corrected samples having a residual CD value; a time domain equalizer arranged to receive the corrected samples and to generate a representation of a channel linear transfer function of the signal from the corrected samples, to generate and transmit a monitoring signal comprising said representation; optical performance monitoring apparatus arranged to receive the monitoring signal and to estimate the residual CD value; and a processor arranged to receive the estimated residual value and to compare it to a threshold value and to generate and transmit to the FDE an estimation signal comprising the estimated value unless it is less than the threshold.

Abstract: Optical transmitter apparatus 10 comprising a reflective optical amplifier 12, a driver 14, an optical splitter 16, polarisation compensation apparatus 18 and an optical router 20. The reflective optical amplifier is arranged to receive an optical seed signal. The driver is arranged to generate a drive signal arranged to cause the reflective optical amplifier to amplify the optical seed signal to form an optical signal. The optical splitter is arranged to receive the optical signal and to split off a part of the optical signal to form a further optical signal. The polarisation compensation apparatus is arranged to receive the further optical signal and to rotate a polarisation of the further optical signal by a pre-determined amount, to form a further optical seed signal. The optical router is arranged to receive the further optical seed signal and to direct the further optical seed signal to the reflective optical amplifier for amplification thereby.

Abstract: Chromatic dispersion (CD) processing apparatus comprises an equalizer loop comprising: a frequency domain equaliser (FDE) arranged to receive samples of an electrical representation of an optical communications signal having CD and to apply CD compensation to the samples, to form dispersion corrected samples having a residual CD value; a time domain equaliser arranged to receive the corrected samples and to generate a representation of a channel linear transfer function of the signal from the corrected samples, to generate and transmit a monitoring signal comprising said representation; optical performance monitoring apparatus arranged to receive the monitoring signal and to estimate the residual CD value; and a processor arranged to receive the estimated residual value and to compare it to a threshold value and to generate and transmit to the FDE an estimation signal comprising the estimated value unless it is less than the threshold.

Abstract: All-optical phase-modulated data signal regenerator apparatus (10) comprising an optical input (12), an optical signal converter (16), an optical carrier signal source (18), optical signal forming apparatus (20) and an optical output (14). The input (12) is arranged to receive a phase-modulated optical data signal. The signal converter (16) is arranged to receive the data signal and to convert phase modulation of the data signal into a corresponding intensity modulation of an intermediate optical signal. The carrier signal source (18) provides an optical carrier signal.

Abstract: A free space optical communications link node 10 comprising transmitter apparatus 12 comprising a first optical transmitter 14, arranged to transmit high priority traffic on a first upstream optical signal having a first wavelength and at a first optical signal power, and a second optical transmitter 16 arranged to transmit low priority traffic on a second upstream optical signal having a second wavelength, different to the first wavelength, and at a second optical signal power. The node 10 further comprises receiver apparatus 18 comprising a first optical amplifier 20 arranged to receive and amplify a first downstream optical signal having a third wavelength and carrying high priority traffic and a second downstream optical signal having a fourth wavelength, different to the third wavelength, and carrying low priority traffic.

Abstract: An optical access network comprises an optical network unit having a first port for connecting to a first optical link, a second port for connecting to a second optical link and an optical source. The optical source is arranged to generate a first optical signal, to transmit the first optical signal via the first port, to receive an optical seed signal via the first port and to amplify the optical seed signal. The optical seed signal has a narrower bandwidth compared to the first optical signal. A modulator is arranged to modulate the amplified optical seed signal with upstream data to form an upstream optical signal and to transmit the upstream optical signal via the second port. A polarisation modifier can modify polarisation of the first optical signal.