Semiconductor Laser Wavelength Control Using Dual Filters
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Solution Overview
Problem
Conventional wavelength-tunable semiconductor lasers have limited wavelength-tunable ranges due to narrow free spectral ranges (FSRs) of wavelength-selective filters, making it difficult to accurately control emission wavelengths when variations exceed the filter's FSR, especially in wavelength-division multiplexing (WDM) optical transmission systems where reduced wavelength intervals are desired.
Innovation Solution
A semiconductor laser device incorporating a laser diode with a gain waveguide, multiple photodiodes, and two wavelength-selective filters with different periodic transmission peaks, where two photodiodes are optically coupled through these filters to monitor and control the laser beam's wavelength, allowing for wider variation correction and precise emission wavelength maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single wavelength-selective filter with narrow FSR is used for wavelength control, then wavelength selection precision is improved, but wavelength-tunable range is limited
Solution Approach 1:
The wavelength monitoring function is segmented into two independent channels: one using a ring resonator for wide-range wavelength detection and another using an etalon filter for precise wavelength selection. Each filter operates independently with its own photodiode, allowing the system to combine the advantages of both narrow and wide FSR filters without interference.
Solution Approach 2:
The invention adds a dimensional aspect to wavelength monitoring by introducing a second filter with different FSR characteristics. Instead of relying on a single filter's one-dimensional wavelength response, the system uses two filters with different periodic transmission peak patterns, creating a two-dimensional wavelength detection space that simultaneously provides wide range and high precision.
2Adaptability or versatility
If current injection is used to change transmission peak wavelengths for wavelength tuning, then wavelength adjustment capability is improved, but control accuracy deteriorates when variation exceeds FSR
Solution Approach 1:
The system implements feedback control by monitoring the output of both photodiodes and comparing the detected wavelengths. When the wavelength shifts exceed the etalon filter's FSR range, the ring resonator's wide FSR detection provides feedback information that helps the control circuit determine the correct transmission peak alignment, ensuring accurate wavelength control even for large wavelength variations.
Solution Approach 2:
The invention dynamically switches between relying on the etalon filter for precise control and the ring resonator for wide-range detection based on the magnitude of wavelength variation. For small variations within the etalon's FSR, the etalon provides precise feedback. For larger variations exceeding the FSR, the system dynamically utilizes the ring resonator's wide detection range to maintain control accuracy.
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 device effectively maintains the original emission wavelength even with significant variations, enabling accurate control and reducing wavelength intervals in WDM systems by utilizing a ring resonator with a wider FSR and an etalon filter for enhanced wavelength monitoring and control.
Implementation Method 1
a first wavelength-selective filter having periodic transmission peaks, and a second wavelength-selective filter having periodic transmission peaks
Implementation Method 2
two wavelength-selective filters with different periodic transmission peaks
Implementation Method 3
Two photodiodes among the plurality of photodiodes are optically coupled to the first optical waveguide through the first and second wavelength-selective filters, respectively
Data Source
AI summary
A semiconductor laser device includes a laser diode provided on a semiconductor substrate, the laser diode including a first optical waveguide having a gain waveguide, a plurality of photodiodes, a first wavelength-selective filter having periodic transmission peaks, and a second wavelength-selective filter having periodic transmission peaks, the period of the transmission peaks of the second wavelength-selective filter being different from the period of the transmission peaks of the first wavelength-selective filter. Furthermore, two photodiodes among the plurality of photodiodes are optically coupled to the first optical waveguide through the first and second wavelength-selective filters, respectively.