Coherent Optical Transceiver Using Pilot Tone Phase Tracking
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Solution Overview
Problem
Current high-capacity optical transceivers for short reach applications face challenges with high power consumption, complex Digital Signal Processing (DSP) requirements, and high production costs due to the need for deep nm CMOS processes and narrow linewidth lasers, which limit their efficiency and scalability.
Innovation Solution
A high-capacity coherent optical transceiver design that utilizes a Dual-Drive Mach-Zehnder Modulator (DD-MZM) with a partitioned analog front-end and digital back-end, incorporating pilot tones and Finite Impulse Response (FIR) filters for chromatic dispersion compensation, and a heterodyne receiver with a simple 2×2 coupler to reduce optical complexity and power consumption, while enabling efficient signal recovery and phase/frequency alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fully coherent implementations with nested I/Q modulator and coherent receiver are used, then noise tolerance and chromatic dispersion compensation are improved, but power consumption and production cost increase significantly
Solution Approach 1:
The patent extracts and removes the 90-degree optical hybrid from the coherent receiver architecture, keeping only the essential coherent detection components. This simplification reduces power consumption and production cost while maintaining adequate noise tolerance for short reach applications, directly resolving the contradiction between reliability and energy use.
Solution Approach 2:
The patent applies local quality by optimizing the receiver design specifically for short reach applications rather than using a universal high-performance coherent receiver. The simplified architecture without 90-degree optical hybrid is tailored to the specific requirements of short reach transmission, achieving adequate performance with reduced power consumption.
2Manufacturing precision
If deep nm CMOS process is used for ADC+DSP implementation, then signal recovery and chromatic dispersion compensation performance are improved, but production cost increases
Solution Approach 1:
The patent changes the manufacturing parameter by moving from deep nm CMOS process to 28 nm CMOS process for ADC+DSP implementation. This parameter change significantly reduces production cost while the system maintains adequate signal recovery and chromatic dispersion compensation performance through the simplified receiver architecture and pilot tone-based equalization, resolving the contradiction between manufacturing precision and ease of manufacture.
3Stability of the object's composition
If narrow linewidth laser is used, then phase and frequency stability are improved, but production cost and complexity increase
Solution Approach 1:
The patent introduces feedback through pilot tones that are transmitted along with the data signal and used at the receiver to track and compensate for phase and frequency variations. This feedback mechanism allows the system to use a simpler, less expensive laser while maintaining phase and frequency stability through active compensation, resolving the contradiction between stability and device complexity.
4Measurement precision
If complex DSP algorithms are used for signal recovery, then signal quality is improved, but power consumption increases
Solution Approach 1:
The patent applies preliminary action by using pilot tones to pre-establish reference signals for phase and frequency tracking before the actual data is processed. This preliminary setup enables simpler DSP algorithms to achieve adequate signal quality, reducing the computational complexity and power consumption of the main signal recovery process while maintaining acceptable performance.
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
The solution achieves efficient chromatic dispersion compensation over long distances with reduced power consumption and production costs, enabling scalable and cost-effective high-capacity optical transmission up to 100 km, while maintaining performance and noise tolerance.
Implementation Method 1
a modulator configured to modulate a laser based thereon
Implementation Method 2
optical couplers configured to coherently combine received signals with a Local Oscillator (LO) formed by the laser
Implementation Method 3
provide the combined signals to photodetectors for balanced detection
Data Source
AI summary
An optical transceiver includes a transmitter including transmitter signal processing circuitry configured to receive a transmit signal and provide two drive voltage signals V1, V2 to a modulator configured to modulate a laser based thereon; and a receiver including i) optical couplers configured to coherently combine received signals with a Local Oscillator (LO) formed by the laser and provide the combined signals to photodetectors for balanced detection, and ii) receiver signal processing circuitry configured to demodulate outputs from the balanced detection, wherein the receiver signal processing circuitry comprises an analog front-end and digital back-end.