DBR Laser Thermal Chirp Compensation
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Solution Overview
Problem
Semiconductor distributed Bragg reflector lasers face performance degradation due to inhomogeneous thermal chirp induced by optical absorption and thermal cross-talk, leading to broadened reflective peaks and reduced side mode suppression ratio (SMSR), especially in longer DBR sections with narrow reflective peaks.
Innovation Solution
A semiconductor distributed Bragg reflector laser with a first DBR section that compensates for thermal chirp along its length by incorporating a built-in effective chirp, either through varying the grating pitch or waveguide width, to minimize thermal-induced chirp effects, thereby maintaining high SMSR and reducing the length of the DBR section without compromising optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the DBR section is made longer to narrow the reflective peak for single longitudinal mode operation, then the mode selectivity and SMSR are improved, but the thermal chirp induced by optical absorption becomes more inhomogeneous and degrades performance
Solution Approach 1:
The patent applies preliminary anti-action by designing a DBR grating with a built-in chirp profile that is the inverse of the expected thermal chirp distribution. The grating pitch is varied along the length of the DBR section to pre-compensate for the inhomogeneous thermal expansion that will occur during operation, thereby maintaining narrow reflective peaks and high SMSR despite the presence of thermal effects
Solution Approach 2:
The patent implements local quality by making the grating pitch non-uniform along the DBR section. Different regions of the grating have different pitch values, with the pitch variation specifically tailored to compensate for the local thermal chirp at each position. This allows each part of the DBR to maintain optimal reflective properties despite inhomogeneous heating
2Reliability
If the DBR section is made longer to achieve narrow reflective peaks, then the SMSR is improved, but the device length and complexity increase
Solution Approach 1:
The patent applies parameter changes by varying the grating pitch parameter along the length of the DBR section. Instead of using a uniform pitch that would require a long DBR to achieve narrow peaks, the pitch is systematically varied to create a chirped grating that achieves the same or better spectral selectivity in a shorter length
3Reliability
If the grating pitch is varied to compensate for thermal chirp, then the effective chirp is reduced and SMSR is enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-programming the exact pitch variation profile needed to compensate for thermal effects. The grating is fabricated with this predetermined chirp pattern, which is designed based on thermal modeling to achieve optimal compensation under operating conditions, thereby reducing the need for post-fabrication adjustments
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 effectively compensates for inhomogeneous heating, achieving a substantially reduced or eliminated effective chirp, enhancing the SMSR and allowing for a shorter DBR section while maintaining high optical performance, with the built-in chirp varying monotonically and continuously along the DBR section.
Implementation Method 1
a first distributed Bragg reflector (DBR) section comprising a grating configured to produce a reflection spectrum having a comb of first reflective peaks
Implementation Method 2
The gain section is electrically driven to emit light by stimulated emission
Implementation Method 3
a thermal gradient in the first distributed Bragg reflector section throughout the first distributed Bragg reflector section, away from the optical gain section
Data Source
Figure 1A
Figure 1B~1C
Figure 2A~2C
AI summary
A semiconductor distributed Bragg reflector laser configured for single longitudinal mode operation, having an optical waveguide comprising an optical gain section, a first reflector being a first distributed Bragg reflector (DBR) section comprising a grating configured to produce a reflection spectrum having one or more first reflective peaks, and a second reflector, wherein the first DBR section is configured to compensate for thermal chirp that is induced inhomogeneously along the length of the DBR section, in use.