Abstract: A non-linear optical device includes a frequency-conversion waveguide and first and second input waveguides. The longitudinal axes of the input waveguides are inclined to that of the frequency-conversion waveguide such a first transverse mode is excited in the latter at the input frequency in operation of the device. The frequency-conversion waveguide supports a second transverse mode at an output frequency of the device, such that the phase velocity of the second transverse mode at the output frequency is substantially equal to that of the first transverse mode at the input frequency, thus providing phase-matching by balancing the effects of chromatic and modal dispersion.

Abstract: A non-linear optical device includes a frequency-conversion waveguide and first and second input waveguides. The longitudinal axes of the input waveguides are inclined to that of the frequency-conversion waveguide such a first transverse mode is excited in the latter at the input frequency in operation of the device. The frequency-conversion waveguide supports a second transverse mode at an output frequency of the device, such that the phase velocity of the second transverse mode at the output frequency is substantially equal to that of the first transverse mode at the input frequency, thus providing phase-matching by balancing the effects of chromatic and modal dispersion.

Abstract: A novel method of fabrication of periodic dielectric composites involving a flexible computer design stage, rapid growth of a second dielectric component. Laser stereolithography is used to form the polymer material layer by layer by photopolymerisation of a liquid. Certain materials constructed in this fashion exhibit a complete loss-free barrier to microwave propagation through the material for a desired band of frequencies and are commonly known as photonic band gap crystals. Such materials could provide a novel medium for all-angle wide- and narrow-band blocking filters, narrow-band transmission filters, reflective and loss-free substrates for planar antennas, and novel loss-free media for oscillator cavities and waveguides. In addition a novel crystal structure, particularly suited to the fabrication method mentioned above and consisting of concatenated polyhedrons, is revealed.

Abstract: A method of growing robust large area colloidal photonic crystals and devices produced thereby. A suspension of monosized colloidal spheres (1) is subjected to a composite shear (6) by applying a sequential set of shearing forces. The crystalline layers within the colloid experience shearing forces with components in both x and y directions, forcing the colloid into a singe face-centered-cubic structure in preference to a twinned face-centered-cubic structure. The method may also comprise the use of a dispersion medium which is capable of undergoing a controllable phase change from a liquid phase to a solid phase. The crystal may be fixed into a single face-centered cubic structure.

Abstract: A novel method of fabrication of periodic dielectric composites involving a flexible computer design stage, rapid growth of a second dielectric component. Laser stereolithography is used to form the polymer material layer by layer by photopolymerisation of a liquid. Certain materials constructed in this fashion exhibit a complete loss-free barrier to microwave propagation through the material for a desired band of frequencies and are commonly known as photonic band gap crystals. Such materials could provide a novel medium for all-angle wide- and narrow-band blocking filters, narrow-band transmission filters, reflective and loss-free substrates for planar antennas, and novel loss-free media for oscillator cavities and waveguides. In addition a novel crystal structure, particularly suited to the fabrication method mentioned above and consisting of concatenated polyhedrons, is revealed.

Abstract: A method of fabricating a dielectric medium comprising two materials with discrete interfaces between the two materials and media formed from the dielectric medium.

Abstract: A cryptographic receiver (10) includes photon detectors (52, 54, 56, 58) arranged to detect photons arriving from filters (22) and (24). A fiber coupler (14) randomly distributes each received photon (16) from an optical fiber toone of two photon channels (18, 20). The filters (22, 24) are each unbalanced Mach-Zehner interferometers with a phase modulator (34, 44) in one arm (28, 38). The filters (22, 24) impose non-orthogonal measurement bases on photons within the respective channels (18, 20). A signal processor (60) derives a cryptographic key-code by analysis of signals received from the photon detectors (52, 54, 46, 58).

Abstract: An optical communications system (10) comprises a transmitter (12) and a receiver (14). A source (16) of correlated pairs of photons of conjugate energies provides first and second photon beams (38, 36). The first photon beam (38) passes through a modulated filter (50) to which a communications signal (52) is applied. A variable spectrum beam (54) is produced which is converted to a timing signal (68) of macroscopic optical pulses (66). The second photon beam (36) and timing signal (68) are transmitted to the receiver (14). The received timing signal (84) is converted to a series of electrical timing pulses (90). The received second photon beam (82) passes through an unmodulated filter (94) matched to the modulated filter (50) when the signal (52) is not applied. The unmodulated filter splits the beam (82) into two conjugate spectra photon beams (96, 98) which are then converted to first and second series of electrical pulses (108, 110) respectively.