Transistor Laser Bistable Switching via Photon-Assisted Tunneling
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Solution Overview
Problem
Existing electro-optical circuits face limitations in achieving and exploiting bistability and fast switching, with previous approaches like laser-photothyristor pairs being slow due to saturated switching operations and external optical components being limited by low coupling efficiencies and large device dimensions, making them unsuitable for high-density integrated logic applications.
Innovation Solution
A semiconductor transistor laser with a quantum size region in the base region, enclosed in an optical cavity, enables electrical and optical bistable switching by controlling photon density through intra-cavity photon-assisted tunneling, allowing for voltage-tuned and current-controlled switching between coherent and incoherent states, and stimulated and spontaneous recombination processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If laser-photothyristor pairs are used for electro-optical switching, then optical switching is achieved, but switching speed is limited to MHz range due to saturated switching operation and charge storage in PNPN device
Solution Approach 1:
The patent merges the laser and transistor into a single integrated transistor laser device, combining the optical generation capability with the electrical switching function in one monolithic structure. This integration eliminates the need for separate laser-photothyristor pairs and their associated interconnections, enabling faster switching speeds while reducing device complexity through consolidation.
Solution Approach 2:
The patent replaces the saturated PNPN switching mechanism with a transistor-based switching mechanism that operates in the unsaturated regime. This substitution eliminates the charge storage effect that limits switching speed, allowing the device to operate at much higher frequencies while maintaining optical switching capability.
2Quantity of substance
If external optical components such as SOA, EAM, and MZM are used, then optical modulation is achieved, but coupling efficiency is low and device dimensions are large (∼mm)
Solution Approach 1:
The patent combines the optical amplification, modulation, and detection functions into a single transistor laser device. The laser cavity is formed within the transistor structure itself, eliminating the need for separate external optical components. This integration dramatically reduces device size from millimeter scale to micrometer scale while improving coupling efficiency through direct monolithic integration.
Solution Approach 2:
The patent embeds the optical cavity within the transistor structure, nesting the optical functionality inside the electrical device. The cavity is formed by the transistor's inherent layers and interfaces, creating a compact nested structure where the optical path is contained within the electrical device boundaries, achieving both small size and high coupling efficiency.
3Speed
If PNPN photothyristor is used for optical switching, then optical bistability is achieved, but switching speed is slow due to charge accumulation in base region
Solution Approach 1:
The patent replaces the PNPN photothyristor bistable mechanism with a transistor laser bistable mechanism. The transistor operates in a regime where charge accumulation is minimized, allowing for fast switching while maintaining bistability through the laser's optical feedback mechanism rather than charge storage. This substitution enables both fast switching and reliable bistability simultaneously.
Solution Approach 2:
The patent changes the operating parameters of the transistor to achieve unsaturated switching operation. By controlling the base current and collector voltage to maintain the transistor in an unsaturated regime, the device avoids charge accumulation while preserving bistability through optical feedback, thereby achieving fast switching speeds without sacrificing reliability.
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 transistor laser achieves high-speed digital computation by enabling ultra-high-speed integrated optical switches and electro-optical bistability, with room temperature operation and sharp voltage thresholds, facilitating high-speed optical logic gate and flip-flop applications.
Implementation Method 1
switching between coherent and incoherent states, and stimulated and spontaneous recombination processes
Implementation Method 2
switching between coherent and incoherent states, and stimulated and spontaneous recombination processes
Implementation Method 3
providing an optical resonant cavity that encloses at least a portion of said base region
Implementation Method 4
providing an optical resonant cavity that encloses at least a portion of said base region
Implementation Method 5
modifying said input electrical signals to switch back and forth between a first state wherein the photon density in said cavity is below a predetermined threshold and said optical output is incoherent
Data Source
AI summary
A method for electrical and optical bistable switching, including the following steps: providing a semiconductor device that includes a semiconductor base region of a first conductivity type between semiconductor collector and emitter regions of a second conductivity type, providing a quantum size region in the base region, and providing base, collector and emitter terminals respectively coupled with the base, collector, and emitter regions; providing input electrical signals with respect to the base, collector, and emitter terminals to obtain an electrical output signal and light emission from the base region; providing an optical resonant cavity that encloses at least a portion of the base region and the light emission therefrom, an optical output signal being obtained from a portion of the light in the optical resonant cavity; and modifying the input electrical signals to switch back and forth between a first state wherein the photon density in the cavity is below a predetermined threshold and the optical output is incoherent, and a second state wherein the photon density in the cavity is above the predetermined threshold and the optical output is coherent, said switching from the first to the second state being implemented by modifying the input electrical signals to reduce optical absorption by collector intra-cavity photon-assisted tunneling, and the switching from the second to the first state being implemented by modifying the input electrical signals to increase photon absorption by collector intra-cavity photon-assisted tunneling.