Acoustically Tunable DFB Laser Self-Heating Mitigation
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Solution Overview
Problem
Conventional acoustically tunable distributed feedback (ADFB) lasers experience self-heating induced wavelength drifts during burst-mode operation, leading to signal degradations when used in networks with narrowband wavelength filters, such as TWDM-PONs with filter widths of 50 GHz or less, and existing mitigation techniques result in suboptimal operation with system penalties.
Innovation Solution
A laser assembly and method that utilize a controllable oscillator to generate a surface acoustic wave in the semiconductor laser, creating a diffraction grating structure whose periodicity compensates for self-heating induced wavelength shifts by adjusting the frequency of the periodic electric signal, allowing the emission wavelength to remain constant without modifying the laser itself, using a control signal based on the input signal and pulse shaping circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional ADFB lasers are used in burst-mode operation, then the laser can operate in high-speed transmission modes, but self-heating induced wavelength drifts occur leading to signal degradations
Solution Approach 1:
The patent applies preliminary anti-action by generating a surface acoustic wave before and during laser operation that creates a diffraction grating structure with periodicity opposing the thermal expansion-induced wavelength drift. The acoustic wave is activated in advance and maintained throughout burst-mode transmission to preemptively counteract the self-heating effect, preventing wavelength drift rather than correcting it after occurrence
Solution Approach 2:
The patent implements dynamics by using a controllable oscillator to dynamically adjust the frequency of the surface acoustic wave in real-time during burst-mode operation. The oscillator frequency is modulated according to the burst transmission timing, allowing the diffraction grating periodicity to adapt dynamically to the changing thermal conditions while maintaining wavelength stability throughout the high-speed transmission cycles
2Manufacturing precision
If generic mitigation techniques such as accelerated heating or elevated subthreshold bias current are applied, then wavelength drift can be reduced, but the laser operates at non-optimal points resulting in system penalties
Solution Approach 1:
The patent introduces a surface acoustic wave as an intermediary mechanism that mediates between the thermal effects and the laser emission wavelength. The acoustic wave creates a mechanical diffraction grating that acts as a intermediary structure, physically coupling the compensation mechanism to the optical field without requiring electrical bias adjustments or thermal pre-heating, thus avoiding system penalties while achieving wavelength stability
Solution Approach 2:
The patent replaces electrical and thermal control mechanisms with a mechanical/acoustic approach. Instead of using elevated bias currents or pre-heating (electrical/thermal systems), the invention uses surface acoustic waves to create a mechanical diffraction grating that compensates for wavelength drift, substituting a mechanical field-based solution for traditional electrical control methods
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 effectively cancels self-heating induced wavelength drifts in a non-signal-degrading manner, enabling the use of ADFB lasers in TWDM-PONs with narrow filter widths without system penalties, maintaining constant emission wavelength and reducing costs by not requiring modifications to the semiconductor laser.
Implementation Method 1
The periodic electric signal may be applied to layers or regions of the semiconductor laser that comprise piezoelectric electrodes and are arranged in proximity to the active semiconductor region. By applying the periodic electric signal to the semiconductor laser, a surface acoustic wave is generated in the semiconductor material.
Implementation Method 2
Due to the presence of the surface acoustic wave, a diffraction grating structure (i.e. a periodic modulation of the diffraction index of the semiconductor material) is created in the semiconductor laser and may interact with the laser mode in the active semiconductor region.
Data Source
AI summary
The laser assembly includes a semiconductor with an active semiconductor region, a controllable oscillator for generating a periodic electric signal that is applied to the semiconductor laser to generate a surface acoustic wave in or near the active semiconductor region such that a diffraction grating structure is created in or near the active semiconductor region by the surface acoustic wave, an emission wavelength of the active semiconductor region being determined by a periodicity of the diffraction grating structure, wherein the controllable oscillator is configured to set a frequency of the periodic electric signal in accordance with a control signal, and a control circuit for generating the control signal for the controllable oscillator in such a manner that a shift of the emission wavelength from heating of the active semiconductor region during emission of the optical signal is at least partially compensated by an opposite shift of the emission wavelength from a change of the periodicity of the diffraction grating structure in or near the active semiconductor region.