VCSEL Emitter Mirror Absorbing Layer for Feedback Reduction
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Solution Overview
Problem
Vertical cavity surface emitting lasers (VCSELs) are vulnerable to optical feedback, particularly from their own reflections, which can lead to relative intensity noise and power modulation issues, and existing solutions either provide inadequate feedback protection or compromise other performance specifications like light output slope and threshold current.
Innovation Solution
An improved VCSEL structure with an emitting mirror that incorporates an absorbing region with specific layer configurations, such as a half-wave thick low-index layer, a quarter-wave thick high-index layer, an absorption layer, and another half-wave thick low-index layer, integrated into the emitting mirror to lock the absorption layer in a standing wave null, reducing optical feedback while allowing adjustments to meet performance requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an absorbing layer is integrated into the emitting mirror to reduce optical feedback, then feedback protection is improved, but parasitic losses increase and light output slope deteriorates
Solution Approach 1:
The emitting mirror is designed with spatially varying properties: the absorbing layer is positioned only in the peripheral region outside the aperture, while the central aperture region maintains high transmission. This local differentiation allows feedback reduction at the edges without compromising the main light output path, thus reducing parasitic losses while protecting against feedback.
Solution Approach 2:
The emitting mirror structure is segmented into distinct functional zones: a central aperture region for primary light transmission and a peripheral region containing the absorbing layer for feedback suppression. This segmentation allows each zone to optimize its function independently, maintaining light output slope while providing feedback protection.
2Object-affected harmful factors
If an absorbing layer is integrated into the emitting mirror to reduce optical feedback, then feedback protection is improved, but light output slope and power output performance worsen
Solution Approach 1:
The absorbing layer is strategically positioned in the peripheral region of the emitting mirror, creating a local quality difference between the central aperture area (high transmission, maintains light output slope) and the peripheral area (absorption, reduces feedback). This localized approach preserves overall productivity while achieving feedback protection.
Solution Approach 2:
The mirror aperture is segmented into a central transmission zone and a peripheral absorption zone. The central zone maintains high transmission characteristics essential for light output slope, while the peripheral zone provides feedback suppression, thus maintaining overall device productivity.
3Object-affected harmful factors
If the absorbing layer is positioned outside the aperture, then feedback protection is improved, but the structure complexity increases
Solution Approach 1:
The absorbing layer is merged with the emitting mirror structure, forming an integrated hybrid mirror rather than a separate component. This combination reduces overall device complexity by eliminating the need for separate feedback protection elements while achieving feedback suppression in the peripheral region.
Solution Approach 2:
The emitting mirror structure serves multiple functions: it provides the primary optical interface for light extraction, defines the aperture boundary, and incorporates the absorbing layer for feedback protection. This multi-functionality reduces the need for additional separate components, thereby reducing 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
The solution effectively reduces the impact of optical feedback on VCSELs, maintaining desired light output slope and power output while minimizing parasitic losses, thus addressing the vulnerability to feedback and ensuring reliable operation.
Implementation Method 1
an absorptive layer (28) is provided and integrated adjacent a top surface of the emitting mirror (42)
Implementation Method 2
the reflectivity of the whole structure is very robust at approximately 99.8% or higher over a wavelength range of almost 300 nm
Implementation Method 3
the 0.5% of the incident photons that penetrate the front mirror from the outside begin to bounce back and forth between the two mirrors in an amplification process of trapping
Data Source
AI summary
A VCSEL is provided that integrates an absorbing layer sandwiched within a null of the standing wave in the emitting mirror to reduce the reflectivity and transmissivity of the emitting mirror as seen by the feedback optical wave, with minimal effect on the reflectivity of the emitting mirror as seen by the light exiting the cavity. The absorbing layer may be made of a suitable absorbing material, such as a GaAs layer in a laser emitting near 850 nm or highly doped p-layer, for instance, and may be disposed epitaxially in a semiconductor or metamorphic mirror. The absorbing layer sandwich may be incorporated into the VCSEL after the last mirror pair or at any desired position with the emitting mirror array.