External Resonator Laser Phase Control With Rectangular Dither
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Solution Overview
Problem
Existing optical transceivers require complex circuits to generate sinusoidal dither signals for phase control of laser light, which complicates downsizing and reducing power consumption.
Innovation Solution
A light source unit using a semiconductor optical amplifier and an external resonator with a wavelength-tunable filter, where a heater in the optical waveguide controls the phase of laser light, and a dither signal with a periodic rectangular wave is used to minimize intensity fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sinusoidal dither signal is used for phase control of laser light, then phase control is achieved, but circuit complexity increases
Solution Approach 1:
The patent replaces the mechanical/electrical system for generating sinusoidal signals with a digital system. A rectangular wave dither signal is generated by a digital signal generator and applied to a digital-to-analog converter (DAC), which converts it to an analog signal for controlling the laser diode current. This substitution of digital electronics for traditional analog signal generation simplifies the circuit architecture while maintaining phase control functionality.
Solution Approach 2:
The patent changes the waveform parameter of the dither signal from sinusoidal to rectangular wave. This parameter change allows the use of simpler digital circuitry to generate the dither signal, as rectangular waves can be easily generated by digital logic circuits and DACs, whereas sinusoidal waves require more complex analog signal generation circuits. The rectangular wave signal is converted to analog form and applied to modulate the laser diode current, achieving the desired phase control effect.
2Reliability
If complex circuits are used to generate sinusoidal dither signals, then phase control is achieved, but power consumption increases
Solution Approach 1:
The patent replaces power-hungry analog sinusoidal signal generation circuits with low-power digital signal generation and DAC conversion. The digital signal generator and DAC consume significantly less power than traditional analog oscillators and signal conditioning circuits, thereby reducing the overall power consumption of the optical transceiver while maintaining the phase control function.
3Reliability
If sinusoidal dither signal generation circuits are included, then phase control is achieved, but device size increases
Solution Approach 1:
The patent substitutes bulky analog circuit components with compact digital integrated circuits. The digital signal generator and DAC can be implemented on a small semiconductor chip, significantly reducing the device footprint compared to traditional analog signal generation circuits that require larger components for frequency stabilization and signal conditioning.
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 configuration allows for effective phase control of laser light using a simpler digital signal, enabling downsizing and reducing power consumption in optical transceivers.
Implementation Method 1
a semiconductor optical amplifier configured to amplify an input light
Implementation Method 2
a heater provided in an optical waveguide of the external resonator through which the laser light is propagated and configured to control a phase of the laser light
Data Source
AI summary
An external resonator outputs a laser light. A heater controls a phase of the laser light. A drive signal output unit outputs a drive signal to the heater. A control unit controls a drive signal provided to the heater by the drive signal output unit. A light monitoring unit monitors intensity of the laser light. The control unit superimposes an applied dither signal having a rectangular wave on the drive signal. The light monitoring unit detects an amplitude of the fluctuation of the laser light caused by the applied dither signal, and outputs a detection result. The control unit monitors the detection result by changing power of the drive signal, searches for the power at which an amplitude of the fluctuation of the laser light becomes a minimum, and determines the searched power as the power of the drive signal.