VCSEL Light Shielding for Atomic Oscillator Stability
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Solution Overview
Problem
Vertical cavity surface emitting lasers (VCSELs) face challenges in achieving both miniaturization and high frequency stability due to their narrow divergence angle, which limits the diameter of the laser light passing through an alkali metal cell, and manufacturing reproducibility issues related to film thickness variations during semiconductor layer growth, making it difficult to produce multiple lasers with the same wavelength accurately.
Innovation Solution
The design incorporates a light shielding part with a central opening to increase the divergence angle of the laser light and forms multiple VCSELs with different wavelengths on a single substrate using a wavelength adjustment layer, allowing for selective emission of light with specific wavelengths and improved manufacturing precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a VCSEL with narrow divergence angle is used, then the device size can be reduced, but the frequency stability deteriorates due to limited light diameter passing through the alkali metal cell
Solution Approach 1:
The patent introduces a light shielding part with a specific opening area to control the lateral dimension of light emission. By adjusting the opening area of the light shielding part, the divergence angle is increased, which allows the light beam to expand laterally before entering the alkali metal cell, thereby increasing the effective light diameter without increasing the overall device volume.
Solution Approach 2:
The light shielding part is strategically positioned between the VCSEL and the alkali metal cell to locally modify the light propagation characteristics. The opening area of the light shielding part is specifically designed to control the light beam's divergence angle, creating a localized optical field that achieves both miniaturization and high frequency stability.
2Productivity
If multiple VCSELs are manufactured on a single substrate, then productivity increases, but manufacturing precision deteriorates due to film thickness variations during semiconductor layer growth
Solution Approach 1:
The patent introduces a wavelength adjustment layer between the VCSEL and the light shielding part, whose thickness is precisely controlled to compensate for film thickness variations. By adjusting the thickness of this wavelength adjustment layer, the optical path length is modified to ensure that multiple VCSELs on the same substrate emit light at the same wavelength, thereby maintaining manufacturing precision while achieving high productivity.
3Reliability
If the opening area of the light shielding part is increased, then the divergence angle increases improving frequency stability, but the light intensity decreases
Solution Approach 1:
The patent uses the wavelength adjustment layer to compensate for the light intensity reduction caused by the increased opening area. By optimizing the thickness of the wavelength adjustment layer, the optical path is adjusted to maintain both the increased divergence angle (for frequency stability) and sufficient light intensity for effective atomic clock operation.
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 enhances the divergence angle of the laser light, enabling miniaturization of atomic oscillators while maintaining high frequency stability and improving the reproducibility and cost-effectiveness of producing VCSELs with desired wavelengths.
Implementation Method 1
a resonator area that includes an active layer... light of an oscillation wavelength λ is emitted
Implementation Method 2
the upper and lower reflecting mirrors are formed by alternately laminating and forming materials having different refractive indexes... the optical thickness of the low refractive index material(s) and the high refractive index material(s) is λ/4
Implementation Method 3
an alkali metal cell 940 in which an alkali metal is sealed... two transitions of electrons in alkali metal atoms are carried out simultaneously at side band wavelengths... a transparency phenomenon of absorptivity of light being reduced in the alkali metal occurs
Data Source
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AI summary
A surface emitting laser element includes a lower DBR formed on a substrate; an active layer formed above the lower DBR; an upper DBR formed on the active layer. The upper DBR includes a dielectric multilayer that is formed as a result of dielectrics having different refractive indexes being alternately laminated and formed, a light shielding part is formed above the upper DBR, and the light shielding part has an opening at a central area for emitting light.