Rate Adjustable DPSK Modulator for Optical Sensitivity
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Solution Overview
Problem
Conventional optical broadband communication systems face challenges in rate adaptability and sensitivity, particularly in free space optical communication links affected by atmospheric variability and turbulence, where existing methods like binary pulse-position modulation and fixed-rate DPSK are cumbersome or inadequate.
Innovation Solution
The implementation of a rate adjustable differential phase shift key (DPSK) system that eliminates the need for multiple interferometric delays by using a multi-symbol DPSK technique, where the temporal separation between compared symbols is adjusted based on data rate, allowing for flexible modulation and demodulation through variable multi-symbol delay modules in both transmitter and receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fixed-rate DPSK is used to achieve near-quantum limited performance, then sensitivity is improved, but rate adaptability deteriorates and device complexity increases due to the need for many integrated waveguides
Solution Approach 1:
The patent implements rate adaptability by dynamically adjusting the delay line length in the DPSK modulator based on the desired data rate. The delay line can be configured to different lengths (e.g., 1 unit delay for 10 Gb/s, 2 units delay for 5 Gb/s) allowing the system to adapt to different transmission rates while maintaining near-quantum limited sensitivity through optimized DPSK detection
2Adaptability or versatility
If multiple integrated waveguides are used to achieve rate adaptability, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent employs a universal DPSK modulator design where a single integrated waveguide structure with a variable delay line can perform multiple data rates. By adjusting the delay line configuration rather than using separate waveguides for each rate, the system achieves rate adaptability while reducing overall device complexity
Solution Approach 2:
The system achieves rate adaptation by changing the delay parameter (time delay or path length) in the interferometric modulator rather than changing the physical structure. This parameter adjustment allows flexible rate adaptation without adding complex integrated waveguide networks
3Productivity
If binary pulse-position modulation is used to trade link margin for throughput, then productivity is improved, but measurement precision deteriorates due to inadequate sensitivity
Solution Approach 1:
The patent transitions from BPPM to DPSK modulation, changing the modulation parameter from pulse position encoding to differential phase encoding. This parameter change enables the system to achieve both high throughput and near-quantum limited sensitivity by utilizing the phase domain for data encoding while maintaining robust detection performance
Data Source
AI summary
In a fixed delay optical communication system, rate adjustable differential phase shift key (DPSK) techniques eliminate the need for multiple comparing modules, each corresponding to a different data rate. Setting alternative data rates at integer multiples of the fundamental data rate of the optical communication system allows the system to process the respective integer number of symbols per period of the system, wherein the period of the system is the inverse of the fundamental data rate. Pulse carving techniques may be used to set the duty cycle of clock levels associated with a clock signal. The clock levels may be combined with respective symbols to provide optical symbols having a duty cycle less than 100%.