Abstract:
Disclosed herein is a method of encoding and/or decoding data for optical data transmission along a transmission link, as well as corresponding transmitters and receivers. The data is encoded based on an adaptive constellation diagram in a 2-D plane, said constellation diagram including a first and a second pair of symbols, wherein the symbols of the first pair of symbols are located at opposite sides of the origin of the 2-D plane at a first distance di from each other, and wherein the symbols of the second pair of symbols are located at opposite sides of the origin of the 2-D plane at a second distance d2 from each other. The method comprises a step of adapting the constellation diagram by varying the ratio of the first and second distances d 1, d 2 such as to minimize or nearly minimize a bit error rate in the transmitted data.
Abstract:
An apparatus comprises a front end configured to receive an optical signal, and convert the optical signal into a plurality of digital signals, and a processing unit coupled to the front end and configured to determine a best-match chromatic dispersion (CD) estimate in the optical signal by optimizing a cost function based on signal peaks of the plurality of digital signals.
Abstract:
An optical receiver that uses a coherent optical quadrature-detection scheme to demodulate an amplitude-modulated optical input signal in a manner that enables the use of a free-running optical local-oscillator source. The optical receiver employs a signal combiner that combines, into an electrical output signal, the in-phase and quadrature-phase electrical signals generated as a result of the quadrature detection of the optical input signal. Depending on the frequency offset between the local- oscillator signal and the input signal, the electrical output signal produced by the signal combiner can be a desired baseband signal or an intermediate-frequency signal. The latter signal can be demodulated to recover the baseband signal in a relatively straightforward manner, e.g., using a conventional intermediate-frequency electrical demodulator coupled to the signal combiner.
Abstract:
An approach is provided that uses diversity to compensate fading of free-space optical (FSO) signals propagating through an environment characterized by atmospheric scintillation. One embodiment involves collecting at least one FSO beam, demultiplexing the beam by wavelength into at least two sub-beams, detecting each sub- beam to produce an electrical output therefrom, and recovering a signal using complementary information from at least two of the electrical outputs. Another embodiment involves collecting the FSO beam onto an array of spatially separated sub- apertures, detecting the light entering each sub-aperture to produce an electrical output therefrom, and recovering a signal using complementary information from at least two of the electrical outputs. This second embodiment enables both electronic adaptive processing to coherently integrate across the sub-apertures and in the case of multiple transmit apertures a free space optical Multiple Input Multiple Output (MIMO) system.
Abstract:
It is disclosed an optical coherent receiver for an optical communication network. The optical coherent receiver is configured to receive a modulated optical signal and to process it for generating an in-phase component and a quadrature component. The optical coherent receiver comprises a power adjuster in turn comprising a multiplying unit and a retroactively connected digital circuit. The multiplying unit is configured to multiply the in-phase and quadrature components by in-phase and quadrature gains, respectively, thereby providing power-adjusted in-phase and quadrature components. The digital circuit is configured to compute: a common gain indicative of a sum of the powers of the power-adjusted in-phase and quadrature components; a differential gain indicative of a difference between the powers of the power-adjusted in-phase and quadrature components; and the in-phase and quadrature gains as a product and a ratio, respectively, between the common gain and the differential gain.
Abstract:
Embodiments for optical communication are provided in which tunable receiver selects and demodulates a first channel of a WDM signal. An example receiver includes a tunable local oscillator for generating a local oscillator signal approximately centered at a first channel wavelength. An optical hybrid of the receiver receives at a first input a wavelength-division-multiplexed (WDM) signal with a M-ary modulation scheme, wherein M is an integer greater than 2, and at a second input the local oscillator signal. A plurality of detectors detect in-phase and quadrature components of the first channel wavelength output of the optical hybrid, which are digitizing by a plurality of analog-to- digital converters. A digital signal processor processes the digitized in-phase and quadrature components in order to recover data carried by the first channel of the WDM signal.
Abstract:
An exemplary apparatus for digital coherent detection of a multi -wavelength signal includes a polarization-diversity optical hybrid, at least four Wavelength De- Multiplexing (W-DMUX) filters, 4M detectors, and 4M analog-to-digital converters (ADCs), with M an integer greater than one. The hybrid has a first input for receiving a multi -wavelength signal including M sub-channels at different wavelengths, and a second input for receiving a reference light source including M continuous-wave references at different wavelengths that approximates center wavelengths of the M sub-channels. The hybrid has at least four outputs. A W-DMUX input for each W-DMUX filter is provided a corresponding one of the hybrid outputs, and each W-DMUX filter provides M filtered optical channel outputs. Each detector converts at least one of the filtered channel outputs into a corresponding electrical signal. Each ADC converts one of the electrical signals into a corresponding digital signal. The corresponding digital signals represent the M sub-channels.