Wavelength Tunable Surface Emitting Laser With Reflection Suppressing Layer
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Solution Overview
Problem
Wavelength tunable surface emitting lasers face challenges in maintaining high light emission efficiency and preventing an increase in threshold current due to excessive reflectance over a wide wavelength range, which affects their performance in optical coherence tomography applications.
Innovation Solution
Incorporating a reflection suppressing layer with a specific optical thickness and refractive index on the reflectors, particularly the upper reflector, to balance reflectance and reduce excessive reflection around the center wavelength, thereby optimizing reflectance characteristics for efficient light emission across a wide wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of layers in DBR is increased to achieve high reflectance over a wide wavelength range, then the reflection range and reflectance increase, but the reflectance becomes too high and light emission becomes difficult
Solution Approach 1:
The patent applies local quality by providing the third layer only at the wavelength region where reflectance becomes excessively high, rather than uniformly across all wavelengths. This localized modification suppresses reflection only in the problematic high-reflectance region while maintaining high reflectance in other wavelength regions, thus resolving the contradiction between achieving wide wavelength range reflectance and preventing excessive reflection that blocks light emission.
Solution Approach 2:
The patent changes the optical characteristics parameter by introducing a third layer with specific refractive index properties (lower than the first layer but higher than adjacent layers) and specific optical thickness (λ0/8 to λ0/2). This parameter change modifies the reflectance characteristics locally, suppressing excessive reflection at specific wavelengths while preserving overall high reflectance across the wide wavelength range.
2Reliability
If the reflectance of the light emission side reflector is increased to achieve high reflectance over a wide wavelength range, then the reflection range increases, but the light emission efficiency is reduced
Solution Approach 1:
The patent applies local quality by introducing the third layer only in the wavelength region where reflectance becomes excessively high. This localized structural modification reduces reflection only where needed, thereby improving light emission efficiency in that specific region while maintaining high reflectance across the overall wide wavelength range, thus resolving the contradiction between wide wavelength reflectance and light emission efficiency.
Solution Approach 2:
The patent changes the optical parameters by specifying the third layer's refractive index (between that of the first and adjacent layers) and optical thickness (λ0/8 to λ0/2). This parameter optimization allows the reflector to maintain high reflectance over a wide wavelength range while preventing excessive reflectance that would reduce light emission efficiency.
3Productivity
If the reflectance of the light emission side reflector is decreased to improve light emission efficiency, then light emission efficiency improves, but the threshold current for laser oscillation increases
Solution Approach 1:
The patent applies local quality by providing the third layer only in the wavelength region where reflectance is excessively high. This localized approach reduces reflection only where it becomes problematic, thereby improving light emission efficiency without significantly reducing overall reflectance. The maintainment of adequate overall reflectance ensures that the threshold current for laser oscillation does not increase excessively.
Solution Approach 2:
The patent optimizes the parameters of the third layer (refractive index between first and adjacent layers, optical thickness of λ0/8 to λ0/2) to achieve a balance: reducing reflectance only in regions where it becomes excessively high, thereby improving light emission efficiency while maintaining sufficient overall reflectance to keep the threshold current at acceptable levels.
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 ensures efficient light emission and stable threshold current over a wide wavelength range, enhancing the performance of surface emitting lasers in optical coherence tomography by preventing excessive reflectance and maintaining high reflectance within an optimal range.
Implementation Method 1
a third layer provided on at least one end of the stacked body and configured such that an optical thickness nd of the third layer satisfies λ0/8≤d＜λ0/4... the third layer having a refractive index that is lower than the refractive index of the first layers and higher than a refractive index of a layer provided adjacent to the third layer
Data Source
AI summary
A surface emitting laser includes a lower reflector, an active layer, a gap portion, an upper reflector, and a driving unit. The lower reflector, the active layer, the gap portion, and the upper reflector are arranged in that order. The surface emitting laser is capable of varying a wavelength of emitted light by changing a distance between the upper and lower reflectors. The driving unit moves one of the upper and lower reflectors in an optical axis direction of the emitted light. At least one of the upper and lower reflectors includes a stacked body in which first layers and second layers are alternately stacked, the second layers having a refractive index lower than a refractive index of the first layers, outermost layers of the stacked body being the first layers, and a third layer provided on at least one end of the stacked body.