Abstract: The invention relates to an optical modulator control system implemented in an optical burst mode transmitter, said control system comprising means for measuring a plurality of optical power sample values and associated optical wavelength data values from a modulator at a first sampling rate, wherein an average power table is generated from said values for each sample period and stored in a memory. The control system also comprises means for performing a control error calculation from two or more stored average power tables at a second sampling rate to calculate a single error value to provide gain and/or bias control signals, wherein the second sample rate is sampled at a slower rate than the first sample rate. The control system described optimises the modulator performance over temperature and lifetime in an optical network.

Abstract: A device and method for depolarising the total field of a wavelength division multiplexed (WDM) signal is provided. A polarization maintaining multiplexor combines a plurality of optical signals to form a polarized multiplexed signal. The multiplexed signal is then passed through a differential group delay (DGD) element adapted to modify the polarization state of one or more optical source signals within the multiplexed signal and thereby to at least partially depolarise the multiplexed signal.

Abstract: The invention relates to an optical modulator control system implemented in an optical burst mode transmitter, said control system comprising means for measuring a plurality of optical power sample values and associated optical wavelength data values from a modulator at a first sampling rate, wherein an average power table is generated from said values for each sample period and stored in a memory. The control system also comprises means for performing a control error calculation from two or more stored average power tables at a second sampling rate to calculate a single error value to provide gain and/or bias control signals, wherein the second sample rate is sampled at a slower rate than the first sample rate. The control system described optimises the modulator performance over temperature and lifetime in an optical network.

Abstract: The invention provides an optical transmitter comprising a differential encoder having first and second outputs, the first and second outputs being of opposite polarity to one another, a first RZ converter connected to the first output of the differential encoder and a second RZ converter connected to the second output of the differential encoder, and a dual electrode Mach Zehnder modulator to which an unmodulated coherent light source is coupled, wherein the output of the first RZ converter is connected to a first electrode of the Mach Zehnder modulator and the output of the second RZ converter is connected to a second electrode of the Mach Zehnder modulator. The invention provides improved signal integrity as compared with existing RZ-DPSK solution through the use of high quality RZ drivers. Furthermore, the invention gives rise to controllable RZ pulse edge chirping, providing rapid pulse compression or broadening through a dispersive fibre length.

Abstract: A device and method for depolarising the total field of a wavelength division multiplexed (WDM) signal is provided. A polarisation maintaining multiplexor combines a plurality of optical signals to form a polarised multiplexed signal. The multiplexed signal is then passed through a differential group delay (DGD) element adapted to modify the polarisation state of one or more optical source signals within the multiplexed signal and thereby to at least partially depolarise the multiplexed signal.

Abstract: A method, apparatus, and computer program product are provided for optimizing the pulse shape of optical signals output from an optical transmitter. The optical transmitter includes an optical modulator controlled by a bias voltage and a signal drive level, wherein the bias voltage and signal drive level are controlled automatically in a systematic way in dependence on one another to adapt the pulse shape of an optical output signal for optimal transmission over a transmission line.

Abstract: An apparatus and method are provided for filtering an optical signal by wavelength. An initially polarised signal is passed through a DGD element effective to alter the polarisation state of the components of the signal according to wavelength. A polarisation filter (polariser) is then provided to attenuate light having given polarisation states from the signal, thereby attenuating the wavelengths associated with said polarisation states. The invention finds particularly utility in the domain of vestigial sideband filtering, allowing the bandwidth of signals within a wavelength division multiplexed system to be reduced without introducing the deleterious effects associated with conventional wavelength filters.

Abstract: An optical communications system comprising: an optical input and an output, a source of input signals in an asymmetric format and having a duty cycle, a modulator for modulating the input signals, to produce an asymmetric signal, the modulator comprising a Mach-Zehnder interferometer; drive means for driving the modulator at a predetermined modulator drive voltage; bias means for applying a bias voltage to the modulator; adjustment means for adjusting a first variable chosen from one of the bias voltage, gain voltage, or duty cycle in response to the relationship existing between changes in the amplitude of the asymmetric signal and changes in the first variable, characterized in that the system further comprising varying means for varying a second variable, different to the first variable and chosen from one of the bias voltage, gain voltage or duty cycle in response to adjustments made to the first variable; and a monitor for recording the average optical output power.

Abstract: The present invention provides both a method and an apparatus for optically encoding data. Light from a coherent source is split into two separate light signals, and each of these light signals is modulated with the data such that the data levels output correspond to the points of maximum optical power. One of the modulated light signals is phase biased to be in phase or in anti-phase with the other modulated light signal and the two light signals are then combined to form a combined optical output. The present invention enables the resulting combined optical output to be a data format with a high extinction ratio compared with conventional optical data formats. It can be used to produce a wide variety of optical data modulation formats.

Abstract: A wavelength division multiplexing optical transmission system, an optical loading-channel transmitters, a WDM optical transmitter and a method of optically loading an optical transmission line with multiple optical loading channels. The multiple optical loading channels are produced in the form of an optical comb by using a periodic optical filtering apparatus incorporated within a resonator constructed as an optical loop. A plurality of optical loading channels of the generated optical comb are then output without data being modulated thereon.

Abstract: The invention provides an optical transmitter comprising a differential encoder having first and second outputs, the first and second outputs being of opposite polarity to one another, a first RZ converter connected to the first output of the differential encoder and a second RZ converter connected to the second output of the differential encoder, and a dual electrode Mach Zehnder modulator to which an unmodulated coherent light source is coupled, wherein the output of the first RZ converter is connected to a first electrode of the Mach Zehnder modulator and the output of the second RZ converter is connected to a second electrode of the Mach Zehnder modulator. The invention provides improved signal integrity as compared with existing RZ-DPSK solution through the use of high quality RZ drivers. Furthermore, the invention gives rise to controllable RZ pulse edge chirping, providing rapid pulse compression or broadening through a dispersive fibre length.

Abstract: An optical communications system comprising: an optical input and an output, a source of input signals in an asymmetric format and having a duty cycle, a modulator for modulating the input signals, to produce an asymmetric signal, the modulator comprising a Mach-Zehnder interferometer; drive means for driving the modulator at a predetermined modulator drive voltage; bias means for applying a bias voltage to the modulator; adjustment means for adjusting a first variable chosen from one of the bias voltage, gain voltage, or duty cycle in response to the relationship existing between changes in the amplitude of the asymmetric signal and changes in the first variable, characterised in that the system further comprising varying means for varying a second variable, different to the first variable and chosen from one of the bias voltage, gain voltage or duty cycle in response to adjustments made to the first variable; and a monitor for recording the average optical output power.

Abstract: A method, apparatus, and computer program product are provided for optimising the pulse shape of optical signals output from an optical transmitter. The optical transmitter includes an optical modulator controlled by a bias voltage and a signal drive level, wherein the bias voltage and signal drive level are controlled automatically in a systematic way in dependence on one another to adapt the pulse shape of an optical output signal for optimal transmission over a transmission line.

Abstract: A wavelength division multiplexing optical transmission system, an optical loading-channel transmitters, a WDM optical transmitter and a method of optically loading an optical transmission line with multiple optical loading channels are disclosed. The multiple optical loading channels are produced in the form of an optical comb by means of a periodic optical filtering apparatus incorporated within a resonator constructed as an optical loop. A plurality of optical loading channels of the generated optical comb are then outputted without data being modulated thereon.