Tunable Laser Diode Wavelength Control via Thermal Phase Compensation
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Solution Overview
Problem
The instability of manufacturing processes and stress-induced phase disorders in diffraction gratings within wavelength tunable laser diodes (LDs) with sampled grating distributed feedback (SG-DFB) and chirped sampled grating distributed Bragg reflector (CSG-DBR) regions lead to undesired variations in optical interaction, affecting the emission wavelength and side mode suppression ratio (SMSR).
Innovation Solution
A method to tune the emission wavelength of tunable LDs by adjusting the power supplied to heaters in segments of the CSG-DBR region, using relations such as P1=P3·Rth3/Rth1+(P2·Rth2/Rth1−P3·Rth3/Rth1)×K, where Rth1 to Rth3 are thermal resistances, and K is an optimization factor, to compensate for phase mismatches and maximize the wavelength tunable range and SMSR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If diffraction gratings are formed in segments of CSG-DBR region, then wavelength selection function is improved, but phase disorder occurs due to manufacturing instability and stress
Solution Approach 1:
The patent changes the optical path length parameter of the first segment relative to the second and third segments by introducing a deviation controlled by factor K (0.3<K<0.7). This parameter modification compensates for phase disorders caused by manufacturing variations and stress-induced deformations, thereby maintaining the wavelength selection precision despite manufacturing imprecision
Solution Approach 2:
The patent applies preliminary compensation by pre-adjusting the optical path length of the first segment before the device enters practical operation. By designing the segment lengths to satisfy L1=L3+(L2-L3)×K from the outset, the system proactively counteracts expected phase disorders from manufacturing instability, ensuring accurate wavelength selection from the start
2Stability of the object's composition
If temperature distribution is made homogeneous, then optical interaction stability is improved, but temperature control complexity increases
Solution Approach 1:
The patent modifies the optical path length parameter to compensate for temperature-induced phase disorders. By setting L1=L3+(L2-L3)×K, the system creates a built-in compensation mechanism that maintains optical interaction stability across temperature variations without requiring complex active temperature control systems
3Ease of manufacture
If segment optical lengths are made equal, then manufacturing simplicity is improved, but phase disorder increases due to stress and temperature variations
Solution Approach 1:
The patent introduces a controlled deviation in the optical path length of the first segment (L1=L3+(L2-L3)×K) to compensate for stress-induced phase disorders. This moderate parameter change maintains manufacturing simplicity while significantly improving optical interaction reliability by counteracting the effects of mechanical stress and temperature variations on the grating phases
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 stabilizes the emission wavelength and enhances the wavelength tunable range by compensating for phase disorders, thereby improving the side mode suppression ratio and maintaining laser oscillation stability even with deviations in segment lengths.
Implementation Method 1
The segments have respective optical lengths, L1 to L3 and heaters... supplying power, P1 to P3, to respective heaters of the segments... the disorder of the diffraction gratings between segments may be compensated
Data Source
AI summary
A method to control a wavelength tunable laser diode (tunable LD) is disclosed. The tunable LD includes a SG-DFB region and a CSG-DBR region to tune the emission wavelength thereof. The CSG-DBR region includes three segments, where the refractive indices of respective segments are variable by heaters provided therein. When the electrical power supplied to two segments is optionally selected, the power supplied to the rest segment is corrected by an offset from a value reflecting physical dimensions of the heaters. The offset is determined such that the tunable LD shows the best side mode suppression ratio (SMSR).