Optical Receiver Demodulator for M-ary Modulation
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Solution Overview
Problem
Current parallel optical communication receivers face challenges in achieving high sensitivity, reduced electrical bandwidth, simplified implementation, and lower size, weight, and power (SWAP) while handling high data rates and various modulation formats, particularly in space-based communications where power is limited.
Innovation Solution
An optical demodulator comprising an optical processor and a comparison module that transforms M parallel input optical signals into 2×log2 M intermediary optical signals, allowing for the determination of logical data representation through optical power comparison, enabling wide-band parallel optical communication receivers with improved sensitivity and scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional M-FSK receivers use M separate detectors followed by M-to-1 winner-take-all analog comparison circuitry, then the receiver can demodulate M-ary orthogonal modulation formats, but the implementation becomes difficult at high rates (more than a few GHz-class rates)
Solution Approach 1:
The patent segments the demodulation process into two distinct stages: (1) optical processing stage that transforms M parallel input optical signals into 2×log2 M intermediary optical signals using optical processors, and (2) comparison stage that compares optical power of intermediary signals to determine logical representation. This segmentation reduces the complexity of the comparison circuitry from M-to-1 to a hierarchical structure with 2×log2 M comparators, making high-rate demodulation feasible.
Solution Approach 2:
The patent introduces intermediary optical signals as a mediator between the M input optical signals and the final demodulated output. These intermediary signals are generated by optical processors that perform preliminary processing, transforming the input signals into a form that requires fewer comparison operations. This intermediary representation reduces the burden on the comparison circuitry and enables higher operating rates.
2Measurement precision
If M analog-to digital converters (ADC) are used to convert optical signals, then digital outputs can be digitally compared to determine which received frequency signal is the largest, but high-speed ADCs are power-hungry and expensive, especially at high symbol bandwidths
Solution Approach 1:
The patent replaces the conventional approach of using M ADCs for optical-to-electrical conversion and digital comparison with an all-optical processing approach. Optical processors perform the transformation of input signals into intermediary signals, and optical power comparison is used to determine the logical representation. This substitution eliminates the need for high-speed ADCs and their associated power consumption, while maintaining detection accuracy through optical power measurement.
3Reliability
If space-based communications use traditional receiver implementations, then communication over distances exceeding typical Earth orbit is possible, but power consumption is high which limits link margin and distance
Solution Approach 1:
The patent implements a receiver architecture where optical signals are processed and compared directly in the optical domain without conversion to electrical signals. The optical processors and optical power comparators operate using optical energy, eliminating the need for power-hungry ADCs and digital processing circuits. This self-service approach within the optical domain significantly reduces power consumption while maintaining reliable detection, thereby increasing link margin for space-based communications.
Data Source
AI summary
The present invention provides a simple means of demodulating optical signals, e.g. wideband M-ary orthogonal. The demodulator comprises an optical processor and a comparison module. The optical processor transforms M input optical signals into 2 log2(M) intermediary optical signals and the comparison module determines the logical representation of the input data based on log2(M) binary comparisons of the optical power of the intermediary signals. Example embodiments may be reconfigurable to receive optical signals using M-FSK, M-PPM, M-PolSK, and hybrid M-ary orthogonal modulation formats. Example embodiments also offer small size, weight and power consumption for both free-space and fiber optic environments as well as improved receiver sensitivity and reduced electron bandwidth requirements.