Abstract: A grating coupler is disclosed. The grating coupler comprises a grating formed in a waveguide formed in a silicon layer of a silicon on insulator photonic component. The grating has a series of sequentially arranged grating elements i, each comprising an alternating etched trench section having a length Le and an etch depth e, and an unetched tooth section having a length L0. Each grating element has a total length of ?i and a fill factor Fi. The fill factor Fi of each grating element varies across the grating coupler according to an apodization function dependent on the location of the grating element. The total length of each grating element ?i varies across the grating coupler such that the effective refractive index of each grating element causes the Bragg condition to be satisfied for all of the grating elements of the grating.

Abstract: An optical regenerator for regenerating a multi-level phase encoded signal. A first non-linear medium (HNLF1) generates a comb of frequency harmonics from the signal under the action of a coherent pump, each component bearing the phase encoded data. A filter selects the first and (M?1)th order components. The filtered signal is then input to a second non-linear medium (HNLF2) where a further pump is applied, to coherently add the first and (M?1)th order components and regenerate the signal by reducing phase noise.

Abstract: An optical device, suitable for use either as a coherent receiver or analog-to-digital converter, of optical phase modulated signals borne on a carrier. The signal is four-wave mixed with a pump to generate a non-linear comb of a series of harmonic components of the signal. The modulation-free carrier is also combined with the pump to generate an equivalent linear comb matched in frequency to the components of the non-linear comb. The harmonic and modulation-free components are linearly combined so they interfere in a pairwise manner, and then the interfered frequency components are separated out in an optical wavelength division demultiplexer into a plurality of frequency-specific optical output channels. A plurality of photodetectors connected to respective ones of the optical output channels then converts the analog values in each channel to respective electronic signals which are then digitized using a processor into binary digits using a thresholding process.

Abstract: An optical regenerator for regenerating a multi-level phase encoded signal. A first non-linear medium (HNLF1) generates a comb of frequency harmonics from the signal under the action of a coherent pump, each component bearing the phase encoded data. A filter selects the first and (M?1)th order components. The filtered signal is then input to a second non-linear medium (HNLF2) where a further pump is applied, to coherently add the first and (M?1)th order components and regenerate the signal by reducing phase noise.

Abstract: Apparatus for providing timing jitter tolerant optical modulation of a first signal by a second signal, the first signal having a first wavelength, the second signal including a plurality of second signal pulses having a second pulse shape and a second wavelength. The apparatus includes a first signal input port, a second signal input port, a coupler, a grating and a non-linear optical device. The apparatus is configured to direct the second signal at the second signal input port to the non-linear optical device via the coupler and the grating, and to direct the first signal at the first signal input port to the non-linear optical device. The grating is a superstructured fibre Bragg grating that converts the second signal pulses into intermediary pulses each having an intermediary pulse shape. The intermediary pulse shape is such that it provides a switching window within the non-linear optical device.

Abstract: Apparatus for providing timing jitter tolerant optical modulation of a first signal by a second signal, the first signal having a first wavelength, the second signal including a plurality of second signal pulses having a second pulse shape and a second wavelength. The apparatus includes a first signal input port, a second signal input port, a coupler, a grating and a non-linear optical device. The apparatus is configured to direct the second signal at the second signal input port to the non-linear optical device via the coupler and the grating, and to direct the first signal at the first signal input port to the non-linear optical device. The grating is a superstructured fibre Bragg grating that converts the second signal pulses into intermediary pulses each having an intermediary pulse shape. The intermediary pulse shape is such that it provides a switching window within the non-linear optical device.

Abstract: An optical transmission system comprising transmitter, link and receiver. At the receiver a decoder is connected to receive the encoded optical signal from the link and decode it according to a decoding signature carried by the decoder that is complementary to the encoding signature at the transmitter coder. The signal is thus decoded to produce a decoded optical signal having a broadened autocorrelation peak and an unwanted background pedestal component. After amplification (EDFA3) the decoded signal is supplied through a non-linear optical element in the form of a non-linear optical loop mirror (NOLM). The NOLM enhances the autocorrelation peak intensity relative to the pedestal and compresses its pulse width, to return the pulse width to the same or narrower than prior to coding at the transmitter.

Abstract: Optical code division multiple access (OCDMA) coder:decoder gratings have been fabricated. The modulated refractive index profile that makes up the OCDMA coder:decoder grating incorporates changes in polarity between OCDMA chips by discrete phase shifts, thereby to provide bipolar coding through phase modulation. (In another embodiment quadrupolar coding is achieved). For NRZ modulation, each grating section is either in phase with, or has a predetermined phase shift relative to, the preceding grating section, depending on whether the OCDMA signature has a change in polarity between chips. RZ modulation is also possible. Results are presented from specific examples of bipolar OCDMA with NRZ modulation, which show higher data rates (10 Gbit/s), shorter chip-lengths (6.4ps) and far longer code sequences (63 bits) than previously demonstrated. Other embodiments relate to optical packet switching, for example using the Internet Protocol (IP) or Asynchronous Transfer Mode (ATM).

Abstract: A hybrid optical transmission system comprising an optical transmitter and receiver. The transmitter includes an input for receiving an encoding signal and an encoder arranged to encode an optical signal with any one of a plurality of encoding signatures according to the encoding signal. The optical receiver comprises a grating decoder connected to receive the encoded optical signal from the input, the grating decoder incorporating a decoding signature complementary to a matched one of the encoding signatures so as to decode the encoded optical signal when encoded with the matched one of the encoding signatures. A hybrid system is thus provided that uses (passive) grating decoders at the receiver in combination with active drive-signal-based encoders at the transmitter. In this way, flexibility can be retained for the transmitter hardware, whereas the advantages of grating decoders can be exploited at the receivers.