Sinusoidally Modulated Optical Transmitter for High-Speed PAM Signals
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Solution Overview
Problem
In short-range optical transmission systems, the increasing transmission speed per channel requires optical transmitters with wide bandwidths, which is challenging due to the bandwidth limitations of optical transmitters, especially when using PAM4 modulation, and existing methods for generating high-extinction-ratio optical pulses with low jitter are complex and difficult to integrate.
Innovation Solution
An optical-time-division multiplexed transmission system using sinusoidally modulated optical signals, where a sinusoidal electrical signal is applied to generate optical pulses, split and modulated by external modulators to create orthogonal pulses, and a MIMO equalizer is used to demultiplex and determine signal levels, overcoming bandwidth limitations and achieving high-speed multi-level PAM signals with a single optical receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an optical transmitter with wide bandwidth is used to generate high-speed signals, then transmission speed is improved, but manufacturing difficulty and cost increase significantly
Solution Approach 1:
The patent divides a high-speed data stream into multiple lower-speed channels that are transmitted sequentially over the same optical carrier. Instead of requiring a single wide-bandwidth transmitter for high-speed operation, the system segments the data into multiple lanes (e.g., 4 lanes for 100G, 8 lanes for 200G) operating at lower speeds, which can be generated by standard bandwidth transmitters. This segmentation approach resolves the contradiction by achieving high aggregate transmission speed through multiple parallel low-speed channels rather than a single high-speed channel.
2Productivity
If actively mode-locked laser is used to generate optical pulses with high repetition rate, then pulse repetition rate is improved, but device complexity increases due to complex control circuits
Solution Approach 1:
The patent replaces the mechanically complex actively mode-locked laser system with an electro-optic modulation approach. Instead of using complex control circuits to actively control the resonance distance of the laser, the system uses a standard laser source combined with electro-optic modulators that are driven by electrical clock signals. This substitution eliminates the need for complex mechanical control circuits while achieving the same pulse generation function through electrical modulation of the optical carrier.
3Manufacturing precision
If two modulators and dispersion compensating fiber are used to generate pulses, then pulse quality is improved, but insertion loss increases and integration becomes difficult
Solution Approach 1:
The patent merges multiple separate components (laser source, modulators, dispersion compensating fiber) into an integrated photonic circuit platform. Instead of using discrete two-modulator configurations with long-distance dispersion compensating fiber that cause high insertion loss and integration difficulties, the system integrates the pulse generation functionality directly into a compact photonic chip. This integration combines the laser source and modulation functions in a unified structure, reducing insertion loss and enabling scalable deployment.
4Productivity
If PAM4 modulation is used to achieve high frequency efficiency, then bandwidth requirement is reduced, but transmission speed per channel still requires wide bandwidth transmitter
Solution Approach 1:
The patent applies segmentation by dividing the high-speed data stream into multiple parallel channels, each operating at lower speed with PAM4 modulation. For example, to achieve 100G transmission, the system uses 4 channels operating at 25G each; for 200G, it uses 8 channels at 25G each. This segmentation allows PAM4 modulation to be effective at each channel level while the aggregate transmission speed meets high-speed requirements, resolving the contradiction between frequency efficiency and per-channel speed requirements.
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 allows for cost-effective generation of high-speed multi-level PAM signals, minimizing optical spectrum and facilitating expansion through wavelength division multiplexing, while using a low-complexity linear equalizer to optimize receiver performance and reduce inter-symbol interference.
Implementation Method 1
an optical detector to convert the optical-time-division-multiplexed PAM signal transmitted through an optical fiber into an electrical signal
Data Source
AI summary
Disclosed are an optical-time-division-multiplexed transmission method and system using a simple sinusoidally modulated optical signal as an input pulse source. An optical-time-division-multiplexed transmission system comprises: an optical-time-division-multiplexed transmitter by applying a sinusoidal electrical signal, a first multi-level electrical PAM signal, and a second multi-level electrical PAM signal so as to generate an optical-time-division-multiplexed multi-level PAM signal; an optical detector for converting the transmitted optical-time-division-multiplexed PAM signal into an electrical signal; a time-division-demultiplexer for demultiplexing the detected electrical signal into two signals; a MIMO equalizer; and two decision elements for determining the levels of two demultiplexed signals obtained from the MIMO equalizer.