VCSEL Gain Modulation for Compact Physical Random Number Generation
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Solution Overview
Problem
Current random number generators based on quantum phase diffusion in semiconductor lasers face complexity due to the need for external interferometric elements or spectrally matched lasers, leading to increased device dimensions and instability.
Innovation Solution
A method utilizing a single mode vertical-cavity surface-emitting laser (VCSEL) with gain modulation from below to above threshold, producing pulses of varying amplitude without requiring an external interferometer or second laser, allowing for compact and robust random number generation using a photodiode to detect the intensity patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an external interferometer or two spectrally matched lasers are used to generate random numbers from quantum phase diffusion, then random number quality is improved, but device complexity and dimensions increase
Solution Approach 1:
The invention extracts and eliminates the external interferometer from the system by using a VCSEL cavity that inherently functions as an interferometer. The random phase information is extracted directly from the intensity fluctuations of the laser output without requiring separate interferometric measurement equipment.
Solution Approach 2:
The VCSEL cavity serves multiple functions simultaneously: it generates the laser output, provides the interferometric path for phase measurement, and acts as the resonant cavity for mode beating. This multi-functionality eliminates the need for separate dedicated components for each function.
2Measurement precision
If an external interferometer or two spectrally matched lasers are used to generate random numbers, then random number quality is improved, but device dimensions increase
Solution Approach 1:
The invention merges the laser cavity and interferometer into a single integrated VCSEL structure. The Fabry-Perot cavity of the VCSEL serves as both the laser resonator and the interferometric measurement path, eliminating the need for separate external interferometric components and reducing overall device footprint.
3Measurement precision
If two spectrally matched lasers are used for random number generation, then random number quality is improved, but stability deteriorates due to intrinsic instability and environmental changes
Solution Approach 1:
The invention segments the dual-laser system into a single-laser system with multiple longitudinal modes. Instead of using two separate lasers that must be spectrally matched, a single VCSEL generates multiple modes within its cavity, eliminating the need for spectral matching between separate sources and reducing sensitivity to environmental changes.
4Device complexity
If a multimode laser is used for random number generation without external interferometer, then device complexity is reduced, but mode instability increases
Solution Approach 1:
The invention changes the operating parameters of the VCSEL to ensure stable multimode operation. By controlling the injection current and cavity design parameters, the system maintains stable mode beating frequencies that are suitable for random number generation while keeping the device compact.
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 approach results in a high-speed, high-quality, and compact random number generator with reduced dimensions and improved stability, eliminating the need for external interferometers and maintaining high bitrates while being easier to implement and maintain.
Implementation Method 1
The present invention is based on the random gain of a single mode vertical-cavity surface-emitting laser (VCSEL) which produces pulses of differing amplitude (intensity) when its current is modulated from below to above threshold
Implementation Method 2
By modulating the laser from below to above threshold, optical pulses with nearly identical intensities and completely randomized phases are generated
Implementation Method 3
The random intensity patterns can subsequently be detected with a photodiode
Data Source
AI summary
A method for physical random number generation includes the steps of: modulating the gain of a vertical-cavity surface-emitting laser periodically from the lower threshold to the upper threshold and back; maintaining the gain per round trip positive for a longer period than the round trip time of the cavity; maintaining the net gain per round trip negative for a longer period than the round trip time of the cavity, in order to create optical pulses of random amplitude; detecting the optical pulses; converting the optical pulses into electrical analog pulses; and digitising the electrical analog pulses into random numbers.