M-PAM Optical Transmitter with Constellation Control
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Solution Overview
Problem
Metro networks require cost-effective optical transmission systems capable of high data rates over long distances, as existing solutions are sensitive to cost, footprint, and power consumption, and struggle with transmission distances beyond a few hundred kilometers at high data rates.
Innovation Solution
The use of directly modulated optical sources, such as VCSELs, to generate M-level amplitude-shift keyed (ASK) optical signals, combined with polarization division multiplexing and digital coherent detection, reduces complexity and power consumption, enabling 100 Gb/s transmission over 960 km without the need for carrier and phase recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If digital coherent detection with carrier and phase recovery is used, then transmission distance and data rate are improved, but device complexity and power consumption increase
Solution Approach 1:
The patent extracts and removes the carrier and phase recovery functions from the coherent detection system. By using directly modulated laser diodes that inherently encode both amplitude and phase information in the optical signal, the system eliminates the need for separate carrier recovery and phase detection circuits, thereby reducing device complexity while maintaining transmission performance
Solution Approach 2:
The laser diode is designed to self-generate the carrier signal through direct modulation. The optical carrier is embedded within the modulated signal itself, allowing the system to serve its own carrier generation needs without external carrier sources or complex recovery mechanisms, thus simplifying the overall system architecture
2Productivity
If digital coherent detection with carrier and phase recovery is used, then transmission distance and data rate are improved, but power consumption increases
Solution Approach 1:
The patent removes the power-intensive carrier and phase recovery modules from the system. By using directly modulated laser diodes that provide inherent carrier embedding, the system eliminates the need for high-power local oscillators and complex phase-locked loops, thereby significantly reducing overall power consumption while maintaining 100 Gb/s transmission capability
Solution Approach 2:
The system uses the laser diode's own modulated output as the carrier source, eliminating the need for separate high-power local oscillators. This self-service approach reduces power consumption by avoiding redundant high-power components while still enabling coherent detection functionality
3Ease of manufacture
If cost-effective optical transmission systems are used, then metro network deployment is improved, but transmission distance is limited to a few hundred kilometers
Solution Approach 1:
The patent changes the modulation parameter by using direct modulation of laser diodes instead of external modulation. This parameter change enables the system to achieve both cost-effectiveness (through simpler, cheaper laser diodes) and extended transmission distance (through optimized direct modulation schemes and advanced signal processing) simultaneously
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 significantly extends transmission distance and reduces costs by eliminating the need for carrier frequency and phase recovery, achieving error-free operation at 100 Gb/s over 960 km with reduced complexity and power consumption, a substantial improvement over previous methods.
Implementation Method 1
The optical transmitter may include a vertical cavity surface-emitting laser (VCSEL) configured to generate the optical signal in response to the drive signal
Implementation Method 2
The optical transmitter may include an electro-absorption modulator configured to modulate light from the laser into the M different levels in response to the drive signal
Implementation Method 3
The optical transmitter may include a Mach-Zehnder modulator (MZM) configured to modulate light from a laser into the M different levels in response to the drive signal
Data Source
AI summary
An apparatus includes an optical transmitter configured to provide an optical signal amplitude-modulated among M different levels. A constellation control module is configured to provide a drive signal to control the optical signal. A feedback module is configured to receive a measure of spacing between amplitude peaks of a symbol constellation of the optical signal. The feedback module is further configured to regulate the constellation control module to adjust the optical signal in response to the measure of spacing.