Ofidium Pty. Ltd.

Analog Devices,inc.

Beijing University of Technology

Jean Armstrong

Arthur James Lowery

Cuiwei He

Brendon James Schmidt

Simon W Brewer

Qian Wang

Arthur Lowery

An optical receiver () for detection of light from one or more sources () comprises an opaque layer () disposed on a first surface. An aperture () is formed in the opaque layer. An optical detector () has a detection region disposed on a second surface. The first and second surfaces are spaced apart from one another such that light passing through the aperture () illuminates a corresponding illumination region () on the second surface, and is detected by the optical detector () In the event that the detection region overlaps the illumination region. Multiple apertures may be formed in the opaque layer, and/or multiple optical detectors may be disposed on the second surface. The optical receiver may thereby enable optical signals originating at different locations to be detected, and distinguished, over a wide field of view.

Multi-directional optical receiver

A receiver for recovering transmitted information carried by a received optical signal that has been affected by dispersion includes an optical splitter having an input port arranged to receive the received optical signal, and a plurality of output ports. A proportion of optical power at the input port is transmitted to each of the output ports. A plurality of optical detectors is operably connected to respective output ports of the optical splitter, for generating a corresponding plurality of electrical signals. Optical phase shifters are disposed between the output ports of the optical splitter and respective optical detectors. As a result, each optical phase shifter applies a frequency dependent phase shift to an optical signal passing therethrough. An electronic processor includes analog and/or digital electronic components configured to combine two or more of the plurality of electrical signals, or information recovered separately therefrom, in order to provide improved accuracy or reliability of information recovery as compared with detecting and processing only the received optical signal. The receiver is advantageously able to mitigate the effects of frequency-dependent fading which may occur in intensity modulation/direct detection optical transmission systems due to dispersion in optical transmission paths.

Reception of signals transmitted over a dispersive optical channel

A system () for transmitting digital information includes a transmitting apparatus () for generating an optical signal bearing digital information, a dispersive optical channel (), and a receiving apparatus () for receiving the optical signal. The dispersive optical channel () is disposed to convey the optical signal from the transmitting apparatus () to the receiving apparatus (). The transmitting apparatus includes an encoder () for encoding digital information into a series of blocks, each including a plurality of data symbols corresponding with one or more bits of digital information. A signal generator () generates a time-varying signal corresponding with each of said blocks. An optical transmitter () is arranged to apply the time-varying signal to an optical source () to produce an optical signal which includes an optical carrier and substantially only a single information bearing optical sideband in an optical frequency domain, the sideband corresponding with the time-varying signal. The receiving apparatus () includes an optical detector () for detecting the optical signal to produce a corresponding received time-varying electrical signal. The receiver further includes means () for generating a series of received data blocks from the time-varying electrical signal. An equalizer () performs an equalization of received data symbols included in each data block to mitigate the effect of dispersion of the optical channel, thereby enabling the transmitted data symbols to be recovered.

Methods and apparatus for optical transmission of digital signals

An apparatus and method are provided for receiving an optical signal having an optical carrier component and at least one information-bearing optical sideband. In general, an optical filter arrangement () is used to separate the optical carrier component from the information-bearing optical sideband. First and second optical splitters () divide the optical power in the optical carrier and the optical sideband, respectively, into corresponding sub-components. The sub-components of the optical carrier have substantially orthogonal polarisation states, which is an optional characteristic of the sideband sub-components. First and second optical coupling devices () respectively each combine one of the optical carrier sub-components with a corresponding one of the optical sideband sub-components. Optical detectors () detect the outputs of the combiners (). The arrangement is able to achieve a number of the benefits of coherent optical heterodyne receivers, particularly when used in combination with advanced coding and modulation methods, while avoiding the need, and associated complexity, of providing an optical oscillator at the receiver.

Method and apparatus for reception of optical signals

A method of communicating digital information over a dispersive optical channel includes encoding the digital information into a plurality of data blocks, each of which includes a number of bits of the information. A time-varying electrical signal is generated which corresponds with each of said data blocks. The time-varying electrical signal is applied to an optical transmitter () to generate an optical signal which includes an asymmetrically amplitude limited transmitted signal modulated onto an optical carrier. The optical signal is then transmitted over the dispersive optical channel (). At a receiving apparatus () the optical signal is detected to produce an electrical signal which corresponds with the asymmetrically amplitude limited transmitted signal. A frequency domain equalization of the electrical signal mitigates the effect of dispersion of the optical channel () on the transmitted optical signal, and the equalized signal is decoded to recover the encoded data blocks and the corresponding transmitted digital information. The method enables bipolar signals to be transmitted over a dispersive unipolar optical channel, and reduces or eliminates the need to apply a high optical bias level at the transmitter, thereby improving optical power efficiency and enabling output power levels to be maintained below applicable safe levels, while simultaneously enabling the effects of channel dispersion to be substantially mitigated.

The invention provides a new approach which is better suited to FFT design as applied to multicarrier modulation systems such as OFDM. The signals are scaled so that overflow, rather than being completely avoided, occurs with low probability throughout the IFFT and FFT structures. The size of the error that results from an overflow depends on how overflow is handled in the DSP. To minimize the degradation, overflow should result in saturation of the value at the maximum positive or negative value option. This is equivalent to clipping the signal. Using the new technique, signals within the FFT structure are scaled to balance the effect of clipping and round-off. Clipping may result in comparatively large errors in a few signal values but because of the spreading effect of the FFT and because OFDM systems typically include error coding/correction, system performance depends on the total error or, in other words the total noise power, across all of the FFT outputs rather than on any individual value.

Multicarrier modulation systems

Methods and apparatus () for composing, generating and transmitting information-bearing optical signals are provided. An information-bearing electrical signal is composed () having desirable spectral properties, preferably configured to ensure that undesired interference between electrical spectral components generated in a square-law direct detection process () at a corresponding optical receiver () is substantially avoided. Predistortion () is advantageously applied to transmitted signals, in order to account for a nonlinear relationship arising in a modulation process () between electrical signal amplitude and corresponding optical field amplitude. Orthogonal frequency division multiplexing (OFDM) techniques may be applied to composed signals having the desired characteristics, and additionally may facilitate the application of frequency domain equalisation () in order to mitigate transmission impairments, including dispersion. Improvements in received signal quality, and/or transmission distance, may thereby be achieved, along with simplification of receiver configuration and operation.

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North Balwyn, Australia

Jean Armstrong