Three-Terminal VCSEL with Collector for Reduced Fall Time
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Solution Overview
Problem
Three-terminal VCSELs fail to achieve higher speeds without sacrificing optical output due to limitations in the interaction between electrical carriers and photons in the active region, and existing designs result in lower optical output at logical HIGH states.
Innovation Solution
A three-terminal VCSEL configuration with a reduced fall time is achieved by applying electrical potentials across the base-emitter and base-collector junctions to optimize optical signal modulation, using refractive index layers and quantum wells for electro-absorption modulation, and employing a push-pull modulation scheme to decouple photon density from carrier density, allowing faster transition between logical states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a three-terminal VCSEL configuration is used to increase modulation speed, then the speed is limited by carrier-photon interaction in the active region, but adding a collector does not increase the speed
Solution Approach 1:
The VCSEL structure is segmented into distinct functional regions: an emitter region with n-type DBR, an active region with intrinsic layer and p-type DBR, and a collector region with additional n-type DBR. This segmentation allows independent optimization of each region's function, enabling the collector to provide electrical control without interfering with the active region's carrier-photon interaction that generates light.
Solution Approach 2:
The collector terminal acts as an intermediary control mechanism that modulates the laser output without directly participating in carrier injection. By applying reverse bias to the collector, the patent controls the electrical field in the active region, thereby modulating the laser output speed independently of the carrier-photon interaction processes.
2Power
If the base region is made thin to allow electron passage to collector for amplified electrical signal, then fewer electrons are available for recombination to produce light, but optical output at logical HIGH state is lower
Solution Approach 1:
The patent separates the electrical amplification function (performed in the collector region) from the optical generation function (performed in the active region). The thin base region enables electron passage for electrical signal amplification, while the dedicated active region with intrinsic layer ensures sufficient carrier recombination for high optical output, resolving the trade-off between electrical and optical performance.
Solution Approach 2:
The collector terminal serves as an intermediary that provides electrical signal amplification without directly consuming carriers needed for light generation. The collector's reverse-biased junction allows it to extract and amplify electrical signals while the active region maintains its carrier population for optimal optical output.
3Ease of operation
If electrical modulation signal is applied across base-emitter junction to switch laser between logical states, then modulation is achieved but fall time is not reduced, limiting operating speed
Solution Approach 1:
The collector terminal acts as an intermediary control mechanism that directly influences the fall time of the laser modulation. By applying reverse bias to the collector, the patent creates an electric field that rapidly extracts carriers from the active region, thereby reducing the fall time. This intermediary control mechanism enables fast switching without complicating the base-emitter modulation scheme.
Solution Approach 2:
The patent implements dynamic control of the collector bias to actively manage the fall time characteristic. During the fall edge of the modulation signal, reverse bias is applied to the collector to accelerate carrier extraction, dynamically adjusting the extraction rate to achieve reduced fall time and enable higher operating speeds.
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 VCSEL operates at higher speeds with maintained optical output by reducing photon recycling and carrier recombination, enabling faster switching between logical states and increased modulation speeds.
Implementation Method 1
an n-type distributed Brag reflector (DBR) disposed on the top surface of the substrate... The first plurality of n-type layers... comprise pairs of layers of alternating high and low refractive index that operate as a first distributed Bragg reflector (DBR)
Implementation Method 2
pairs of layers of alternating high and low refractive index that operate as a distributed Bragg reflector
Implementation Method 3
using refractive index layers and quantum wells for electro-absorption modulation
Implementation Method 4
electrons from the n-type layers that are adjacent the intrinsic layer and holes from the p-type layers that are adjacent the intrinsic layer are injected into the active region of the intrinsic layer where they combine to produce photons. This combining of holes and electrons in the active region to produce photons is a phenomenon known as spontaneous emission
Implementation Method 5
As the photons pass out of the active region, they are repeatedly reflected by the DBRs back into the active region, which results in more recombination of electrons and holes in the active region. This is a phenomenon known as stimulated emission
Data Source
AI summary
A three-terminal VCSEL is provided that has a reduced fall time that allows the VCSEL to be operated at higher speeds. Methods of operating the three-terminal VCSEL are also provided. The VCSEL can be operated at higher speeds without decreasing the optical output of the VCSEL when its in the logical HIGH state.