Optical Modulator Linear Response via Injection Locked Slave Laser
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Solution Overview
Problem
Conventional optical modulators have nonlinear optical modulation transfer functions, limiting their spurious free dynamic range (SFDR) and often suffer from chirp and inefficient power handling in direct laser modulation approaches.
Innovation Solution
An optical modulator with a linear response is achieved by phase modulating the output of an injection locked slave laser, specifically by tuning the cavity resonance of the slave laser and combining it with the injection source signal from the master laser, resulting in an arcsine phase modulation within a Mach-Zehnder interferometer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electro-optic modulators are used, then optical modulation is achieved, but the optical modulation transfer function is inherently nonlinear, limiting the spurious free dynamic range (SFDR)
Solution Approach 1:
The system divides the modulation function into two separate components: a master laser that provides a stable optical carrier and a slave laser that performs the actual phase modulation. This segmentation allows the master laser to maintain frequency stability while the slave laser handles modulation, achieving both linearity and stability that cannot be obtained with a single conventional modulator.
Solution Approach 2:
The slave laser acts as an intermediary between the electrical modulation signal and the optical carrier from the master laser. It converts the electrical signal into phase modulation of the optical wave, providing a linear transfer function. The injection locking mechanism ensures the slave laser operates at the master laser's frequency while maintaining linear phase response to the modulation signal.
2Productivity
If direct modulation of optical intensity of a laser is used, then modulation is achieved, but chirp and inefficient power handling are typical drawbacks
Solution Approach 1:
The system replaces direct intensity modulation (analogous to mechanical adjustment) with phase modulation achieved through injection locking. By modulating the phase rather than directly adjusting intensity, the system avoids the chirp effects that occur when direct intensity modulation causes frequency excursions. The phase modulation is achieved through electrical control of the slave laser's resonance frequency, providing efficient power handling without harmful chirp.
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 enhances the spurious free dynamic range (SFDR) by providing a linear optical modulation transfer function, improving transmission characteristics and addressing the limitations of conventional modulators.
Implementation Method 1
The slave laser is injection locked to the master laser, such that the output frequency of the slave laser is locked to the output frequency of the master laser
Implementation Method 2
The modulated optical signal from the slave laser is combined with the unmodulated optical signal from the master laser
Data Source
AI summary
Apparatuses and methods for modulating an optical signal are disclosed. One embodiment is a method comprising: phase modulating a slave laser which is injection locked to a master laser to produce an arcsine phase modulated optical signal, and combining the arcsine phase modulated optical signal with an output optical signal from the master laser.