Multiplexer and modulation arrangements for multi-carrier optical modems

Abstract

Consistent with the present disclosure, data, in digital form, is received by a transmit node of an optical communication system, and converted to an analog signal by a digital-to-analog converter (DAC) to drive a modulator. The modulator, in turn, modulates light at one of a plurality of wavelengths in accordance with the received data forming a plurality of corresponding carriers. The carriers are modulated according to one of a plurality of modulation formats and then optically combined to form a superchannel of a constant maximum capacity, for example. Accordingly, the number of carriers and the bit rate for each carrier remain constant for each modulation format to realize a constant maximum capacity. The superchannel is then transmitted over an optical communication path to a receive node. At the receive node, the superchannel is optically demultiplexed from a plurality of other superchannels. The plurality of carriers of the superchannel are then supplied to a photodetector circuit, which receives additional light at one of the optical signal carrier wavelengths from a local oscillator laser. An analog-to-digital converter (ADC) is provided in the receive node to convert the electrical signals output from the photodetector into digital form. The output from the ADC is then filtered in the electrical domain, such that optical demultiplexing of the carriers is unnecessary.

Description

Background technique [0001] As is well known, in a wavelength division multiplexing (WDM) optical communication system, a plurality of optical signals or channels, each having a different wavelength, are combined onto an optical fiber. Such systems typically include a laser associated with each wavelength, a modulator configured to modulate the optical signals output by the lasers, and an optical combiner for combining each of the modulated optical signals. These components are usually arranged at the transmitting end of the WDM optical communication system to transmit the optical signal to the optical fiber. At the receiving end of a WDM optical communication system, optical signals are often separated and converted into corresponding electrical signals, which are then further processed. [0002] Known WDM optical communication systems are capable of multiplexing 40 channels at 100 GHz intervals or 80 channels at 50 GHz intervals. These WDM optical communication systems occ...

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Problems solved by technology

Thus, it may be advantageous to limit the maximum data capacity available on each superchannel

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