Mesa VCSEL Reduces Relative-Intensity Noise
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Solution Overview
Problem
Mesa VCSELs exhibit higher relative-intensity noise (RIN) compared to oxide-apertured VCSELs, particularly at data rates above 4 Gbit/s, due to lasing sustained in the active layer under the contact annulus, leading to varying optical power emission.
Innovation Solution
Incorporating a second DBR mesa of dielectric material on the window region of the first DBR mesa, ensuring sufficient total reflectance to sustain lasing mainly under the window region, while the first DBR mesa provides insufficient reflectance alone, thereby reducing RIN.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single DBR mesa is used for current confinement, then the device is easier to manufacture, but the relative-intensity noise increases due to lasing under the contact annulus
Solution Approach 1:
The single DBR mesa is segmented into two separate DBR mesas: a first DBR mesa for current confinement and a second DBR mesa positioned on the window region for optical feedback. This segmentation allows the current confinement function to be separated from the lasing sustenance function, preventing lasing under the contact annulus while maintaining ease of manufacture through modular structure.
Solution Approach 2:
The second DBR mesa acts as an intermediary element that provides the necessary optical feedback for lasing without requiring the first DBR mesa to sustain lasing. This intermediary structure enables the first DBR mesa to focus solely on current confinement, thereby reducing RIN while maintaining manufacturability.
2Power
If the inner circumference of the contact annulus is decreased, then the optical power emission increases, but the relative-intensity noise increases due to enhanced lasing under the contact annulus
Solution Approach 1:
The optical feedback function is segmented from the current confinement function by using a separate second DBR mesa. This allows the contact annulus inner circumference to be optimized for maximum optical power emission without the harmful side effect of enhanced lasing under the contact annulus, since the second DBR mesa is specifically positioned to provide feedback only from the window region.
3Device complexity
If lasing is sustained under the contact annulus, then the device structure is simpler, but the optical power varies randomly over time due to transverse mode competition
Solution Approach 1:
The device structure is segmented into two functional mesas, which increases structural complexity but eliminates transverse mode competition by preventing lasing under the contact annulus. The second DBR mesa provides optical feedback exclusively from the window region, ensuring stable optical power output.
Solution Approach 2:
The second DBR mesa is locally positioned on the window region to provide targeted optical feedback. This local quality enhancement ensures that lasing is sustained only in the desired region, preventing the optical power variations caused by transverse mode competition while maintaining overall device simplicity.
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 RIN by ensuring stimulated emission dominates over spontaneous emission under the window region, even at maximum bias current, and reduces electrical resistance.
Implementation Method 1
a DBR layer of semiconductor material, for reflecting light at a lasing wavelength
Implementation Method 2
an active layer of semiconductor material, disposed on a top surface of the DBR layer, for lasing at the lasing wavelength
Implementation Method 3
a first DBR mesa of semiconductor material, disposed on a mesa region of a top surface of the active layer, for reflecting light at the lasing wavelength
Implementation Method 4
a second DBR mesa of dielectric material, disposed on the window region of the top surface of the first DBR mesa, for reflecting light at the lasing wavelength
Data Source
AI summary
The present invention provides an improved mesa vertical-cavity surface-emitting laser (VCSEL), in which a first distributed Bragg reflector (DBR) mesa of semiconductor material is disposed on a top surface of an active layer. A contact annulus is disposed on a contact region of a top surface of the first DBR mesa, such that an inner circumference of the contact annulus defines a window region of the top surface of the first DBR mesa. A second DBR mesa of dielectric material is disposed on the window region. Whereas the first DBR mesa has a first reflectance at a lasing wavelength that is insufficient to sustain lasing in the active layer, the first DBR mesa and the second DBR mesa together have a total reflectance at the lasing wavelength that is sufficient to sustain lasing in the active layer under the window region.