Optical Receiver Separating Carrier and Sidebands for Coherent Detection
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Solution Overview
Problem
Coherent optical heterodyne receivers are not widely deployed due to their complexity and cost, particularly in systems with high bandwidth signals and significant polarization mode dispersion, where direct-detection receivers fail to provide adequate performance for emerging modulation formats like OFDM.
Innovation Solution
An apparatus and method that separates an optical signal into a carrier component and information-bearing sidebands, splits these into orthogonal polarizations, and combines them for detection, mimicking coherent detection without a local oscillator, using optical filters, splitters, and detectors to reduce noise and mitigate polarization mode dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coherent optical heterodyne receivers are used, then receiver noise performance is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the local oscillator component from the coherent detection system, retaining only the essential heterodyne detection functionality. By removing the complex local oscillator and its associated frequency control mechanisms, the system achieves simplified architecture while maintaining the noise performance benefits of coherent detection through optical filtering and direct detection of the optical signal combined with a local oscillator beam.
Solution Approach 2:
The invention replaces expensive, complex coherent detection components with simpler, more cost-effective alternatives. Specifically, it substitutes the need for a stable narrow-linewidth local oscillator laser with a broader linewidth laser combined with optical filtering, and replaces complex polarization control systems with polarization-diversity detection, thereby reducing system cost and complexity while maintaining performance.
2Measurement precision
If coherent optical heterodyne receivers are used, then signal detection capability is improved, but ease of operation deteriorates due to polarization alignment requirements
Solution Approach 1:
The patent segments the detection process into two independent polarization channels (parallel and perpendicular components). By detecting both polarization components separately and combining their signals, the system eliminates the need for precise polarization alignment between the local oscillator and the incoming signal, thereby maintaining signal detection capability while significantly improving ease of operation.
Solution Approach 2:
The polarization-diversity detection structure makes the receiver universally applicable to signals with any polarization state. The system can detect both horizontally and vertically polarized components simultaneously, making it insensitive to polarization changes in the optical fiber transmission medium, thus improving ease of operation without sacrificing detection capability.
3Device complexity
If direct-detection receivers are used, then device complexity is reduced, but performance deteriorates in systems with polarization mode dispersion and high bandwidth signals
Solution Approach 1:
The patent transitions from scalar intensity detection to vectorial polarization-resolved detection by measuring both the parallel and perpendicular polarization components. This dimensional expansion allows the system to process signals affected by polarization mode dispersion effectively, maintaining performance in high bandwidth systems while keeping device complexity relatively low through the use of standard optical components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves benefits of coherent detection with reduced complexity, balancing receiver noise and polarization control, enhancing signal quality without the need for a local oscillator, and is cost-effective, suitable for systems with PMD and emerging modulation formats.
Implementation Method 1
an optical filter arrangement having an optical input and at least first and second optical outputs, the optical signal being coupled to the optical input, wherein optical power in substantially only the optical carrier component is transmitted to said first optical output, and optical power in substantially only the optical sideband is transmitted to said second optical output
Implementation Method 2
a first optical splitter, having an input coupled to said first optical output of the optical filter arrangement, which splits the optical power in the optical carrier component into two sub-components having first and second substantially orthogonal polarisation states
Implementation Method 3
first and second optical coupling devices, each having at least two inputs and at least one output at which power from the two inputs is combined
Implementation Method 4
at least first and second optical detectors coupled to corresponding ones of each said output of the first and second coupling devices, to generate received electrical signals corresponding with the detected optical signals
Data Source
AI summary
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 (110) is used to separate the optical carrier component from the information-bearing optical sideband. First and second optical splitters (126, 128) 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 (142, 144) respectively each combine one of the optical carrier sub-components with a corresponding one of the optical sideband sub-components. Optical detectors (158, 160) detect the outputs of the combiners (142, 144). 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.