Substrate-Emitting VCSEL for High-Speed Optical Links
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Solution Overview
Problem
Standard top-emitting VCSELs face issues with parasitic inductance from wire bonding, which reduces modulation speed and complicates assembly with external optical elements, and have weak lateral mode suppression, especially at high driving currents, making them less effective for high-speed fiber optic communication.
Innovation Solution
The development of a single-mode vertical-cavity surface-emitting laser (VCSEL) with an Indium phosphide-based active region and an overgrown tunnel junction, configured for flip-chip mounting to a circuit board, utilizing a high reflectivity composite mirror to reduce parasitic capacitance and enhance mode and polarization selection, allowing for increased modulation speed and efficient emission through the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If wire bonding is used for electrical connection in standard top-emitting VCSELs, then electrical connection is achieved, but parasitic inductance increases and modulation speed decreases
Solution Approach 1:
The patent inverts the conventional VCSEL structure by making the VCSEL substrate-emitting rather than top-emitting. This allows the VCSEL to be flip-chip mounted directly to the circuit board, eliminating wire bonds and their associated parasitic inductance, thereby achieving higher modulation speeds
2Ease of manufacture
If wire bonds are used in standard VCSELs, then electrical connection is established, but assembly with external optical elements becomes difficult
Solution Approach 1:
By inverting the emission direction to substrate-emitting, the patent enables flip-chip mounting configuration where the VCSEL is mounted face-down directly to the circuit board. This eliminates wire bonds and simplifies assembly with external optical elements like lenses and fibers
3Reliability
If lateral index variation in overgrown tunnel junction is used for mode suppression, then mode selection is achieved, but suppression strength is weak at high driving currents
Solution Approach 1:
The patent modifies the tunnel junction structure by introducing compositional grading in the InP-based active region, creating local variations in refractive index that enhance lateral mode suppression. This local quality modification strengthens mode selection even at high driving currents where conventional uniform structures fail
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 enables higher modulation speeds and improved mode selection, enabling data transmission rates exceeding 50 Gb/s, overcoming the limitations of standard VCSELs by reducing parasitic capacitance and facilitating easier integration with optical fibers.
Implementation Method 1
a VCSEL comprises an emission structure mounted and/or formed on a substrate... The VCSEL is configured to emit laser light through the substrate
Implementation Method 2
a high reflectivity mirror... In various embodiments, the high reflectivity mirror is a composite mirror composed of a partial semiconductor distributed Bragg reflector in combination with a metal reflector
Data Source
AI summary
A vertical-cavity surface-emitting laser (VCSEL), substrate emitting VCSEL, and multi-beam emitting device and corresponding manufacturing processes are provided. An example VCSEL comprises a substrate having a first surface and a second surface; an output coupling mirror disposed on the second surface of the substrate; a high reflectivity mirror; and an active cavity material structure disposed between the output coupling mirror and the high reflectivity mirror. The active cavity material structure comprises a first current-spreading layer, a second current-spreading layer, an active region disposed between the first current-spreading layer and the second current-spreading layer, and a tunnel junction overgrown by the second current spreading layer, wherein the tunnel junction is disposed adjacent the active region. The VCSEL is configured to emit radiation outward through the first surface of the substrate.