Tunable Laser Side Mode Suppression via Asymmetric Facets
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Solution Overview
Problem
Existing wavelength-tunable lasers face challenges in achieving sufficient side-mode suppression ratio and enlarged free-spectral-range over extended wide-band wavelengths, particularly in the silicon photonics platform, which is crucial for high-bandwidth optical communication networks.
Innovation Solution
The method involves configuring a gain chip with a high-reflection facet for long-wavelength side-mode suppression and an absorption layer for short-wavelength side-mode suppression, combined with a Vernier-ring-reflector tuner to generate a joint interference spectrum with isolated spectral peaks, allowing for tunability over the extended C-band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional gain chip with uniform reflectivity is used, then the device structure is simple, but the side-mode suppression ratio is insufficient
Solution Approach 1:
The patent applies local quality by creating non-uniform reflectivity distribution across the gain chip facets. Specifically, one facet is designed with high reflectivity while the other facet has low reflectivity, allowing different regions of the device to perform different functions: the high-reflectivity facet suppresses short-wavelength side modes through strong feedback, while the low-reflectivity facet allows long-wavelength side modes to pass with minimal reflection, thereby achieving superior side-mode suppression ratio.
Solution Approach 2:
The gain chip is segmented into distinct functional regions with different optical properties. The device divides the spectral control function into two separate facets: one dedicated to suppressing short-wavelength side modes and another for suppressing long-wavelength side modes. This segmentation allows each facet to be optimized independently for its specific suppression task, resolving the contradiction between suppression performance and structural simplicity.
2Adaptability or versatility
If the free-spectral-range is enlarged for wide-band tuning, then the wavelength tuning range is extended, but the side-mode suppression becomes more difficult
Solution Approach 1:
To achieve both wide wavelength tuning range and effective side-mode suppression, the patent employs local quality by assigning different reflectivity characteristics to different facets. The high-reflectivity facet provides strong feedback for wavelengths at one end of the tuning range, while the low-reflectivity facet provides minimal feedback for wavelengths at the other end. This localized optimization allows the device to maintain high side-mode suppression ratio across the entire extended tuning range.
Solution Approach 2:
The patent implements dynamic spectral control by using the interference between light reflected from the two facets with different reflectivities. As the wavelength tunes across the extended range, the relative phases and amplitudes of the reflected lights change dynamically, creating wavelength-dependent feedback that automatically suppresses side modes at different positions in the spectrum, thereby maintaining high suppression ratio throughout the wide tuning range.
3Adaptability or versatility
If a Vernier-ring-reflector tuner is added for wide-band tuning, then the wavelength tunability is improved, but the device complexity increases
Solution Approach 1:
The patent merges the tuning function with the gain chip structure itself by integrating the Vernier-ring-reflector tuner directly into the laser device. The tuner is combined with the gain chip and facet structure, allowing wavelength tuning to be achieved through the interference spectrum generated by the combined structure. This merging reduces the need for separate, independent tuning components, thereby improving wavelength tunability while limiting the increase in overall device complexity.
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 effectively suppresses both long- and short-wavelength side modes, enhancing the spectral efficiency and mode selectivity of the wavelength-tunable laser, resulting in improved performance for wide-band optical communication applications.
Implementation Method 1
coupling a light excited in the active layer and at least partially reflected from the second facet
Implementation Method 2
reconfiguring the gain chip with an absorption layer disposed in the N-type cladding layer near the active layer to induce a gain loss for wavelengths shorter than a longest wavelength associated with a short-wavelength side mode JFSR peak
Implementation Method 3
wavelength tuner configured to generate a joint interference spectrum with multiple modes in isolated spectral peaks separated by a joint-free-spectral-range (JFSR)
Data Source
AI summary
A method for improving wide-band wavelength-tunable laser. The method includes configuring a gain region between a first facet and a second facet and crosswise a PN-junction with an active layer between P-type cladding layer and N-type cladding layer. The method further includes coupling a light excited in the active layer and partially reflected from the second facet to pass through the first facet to a wavelength tuner configured to generate a joint interference spectrum with multiple modes separated by a joint-free-spectral-range (JFSR). Additionally, the method includes configuring the second facet to have reduced reflectivity for increasing wavelengths. Furthermore, the method includes reconfiguring the gain chip with an absorption layer near the active layer to induce a gain loss for wavelengths shorter than a longest wavelength associated with a short-wavelength side mode. Moreover, the method includes outputting amplified light at a basic mode via the second facet.