Optical Transmitter Master-Slave Laser Injection Locking
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Solution Overview
Problem
Current optical transmitters face challenges in transmitting high spectral efficiency coherent modulation formats due to high chirp associated with direct semiconductor laser modulation, and existing solutions like LiNbO3-based external IQ modulators are costly, have significant insertion loss, limited optical power handling, and require high drive voltage RF booster amplifiers.
Innovation Solution
An optical transmitter design using a master laser to injection-lock one or more slave lasers, reducing chirp and enabling complex modulation schemes by destructively interfering the carrier part of the slave laser output with a signal derived from the master laser, allowing for coherent multiplexing of slave laser outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If direct modulation of semiconductor laser is used, then cost is reduced, but chirp increases significantly limiting transmission distance
Solution Approach 1:
The system segments the laser functions into a master laser that provides the carrier signal and slave lasers that are injection-locked to it. This segmentation allows the master laser to maintain stable frequency while slave lasers provide modulation capability, reducing overall chirp while maintaining cost-effectiveness compared to external modulators.
Solution Approach 2:
The master laser acts as an intermediary that injection-locks the slave lasers, providing a stable reference frequency. This intermediary mechanism enables the slave lasers to operate with reduced chirp while still allowing direct modulation for cost-effective implementation.
2Adaptability or versatility
If LiNbO3-based external IQ modulator is used, then complex modulation formats are achieved, but insertion loss increases and optical power handling is limited
Solution Approach 1:
The system merges the carrier generation function (master laser) with the modulation function (slave lasers) in a unified injection-locked architecture. This combination eliminates the need for separate external modulators, reducing insertion loss while maintaining the capability to generate complex modulation formats through coherent multiplexing of slave laser outputs.
Solution Approach 2:
The master laser serves multiple functions: providing the carrier signal, injection-locking the slave lasers, and enabling complex modulation formats. This multi-functionality eliminates the need for dedicated external modulators, reducing overall system loss while maintaining versatility for various modulation schemes.
3Adaptability or versatility
If LiNbO3-based external IQ modulator is used, then complex modulation formats are generated, but device complexity increases due to multiple high-speed data streams
Solution Approach 1:
The system replaces electronic multiplexing of multiple high-speed data streams with optical injection locking. Instead of electronically combining multiple modulated signals (which requires complex electronic multiplexers), the master laser optically locks the slave lasers, enabling complex modulation through optical interference and coherent combination, thereby reducing electronic complexity.
4Power
If RF booster amplifiers are used with external modulators, then sufficient drive voltage is achieved, but power consumption and noise increase
Solution Approach 1:
The slave lasers self-generate the required drive voltage through the injection locking mechanism from the master laser. This self-service approach eliminates the need for external RF booster amplifiers, reducing power consumption and noise while still achieving sufficient modulation depth through the optical injection locking process.
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 low chirp and complex modulation capabilities without the need for high-cost external modulators or RF amplifiers, enabling efficient transmission of high spectral efficiency signals over long distances with reduced power consumption and noise.
Implementation Method 1
a master laser device for generating a master signal; one or more slave laser devices, injected with the master signal such that signals generated by the one or more slave laser devices are phase-locked with the master signal
Implementation Method 2
an interfering arrangement, for destructively interfering the signals generated by the one or more slave laser devices with a signal derived from the master signal, so as to generate an output signal in which the carrier part is at least partially cancelled
Data Source
Figure 1~2
Figure 3
AI summary
An optical transmitter, comprising: a master laser device for generating a master signal; one or more slave laser devices, injected with the master signal such that signals generated by the one or more slave laser devices are phase-locked with the master signal; an input for receiving one or more data streams to be transmitted, the one or more data streams being used to modulate respectively the one or more slave laser devices, such that each signal generated by the one or more slave laser devices respectively comprises a modulated part and a carrier part; and an interfering arrangement, for destructively interfering the signals generated by the one or more slave laser devices with a signal derived from the master signal, so as to generate an output signal in which the carrier part is at least partially cancelled. In embodiments, the transmitter comprises multiple slave laser devices, whose outputs can be coherently multiplexed together to generate multiple-bit output signals.