Double-Pass Entangled Photon Source Using a Single Nonlinear Crystal
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Solution Overview
Problem
Existing entangled photon sources are complex to adjust and maintain, and often require temporal compensation for the walk-off effect, leading to reduced quality or unsuitable mass production.
Innovation Solution
A simplified entangled photon source design using a laser, nonlinear element, dichroic element, and polarization rotation/reflection elements to generate polarization entangled photon pairs with a double-pass configuration through a periodically poled Lithium Niobate or potassium titanyl phosphate crystal, eliminating the need for additional compensation elements and maintaining equal pump power for high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a complex design with multiple optical components is used (e.g., Sagnac configuration), then the generation of entangled photon pairs is achieved, but the device becomes difficult to adjust and maintain
Solution Approach 1:
The patent combines multiple functions into a single nonlinear crystal by using a double-pass configuration where the laser beam passes through the same crystal twice. The first pass generates entangled photon pairs, the beam is reflected back, and the second pass generates additional pairs, eliminating the need for separate crystals or complex Sagnac loop configurations while maintaining high entanglement quality
Solution Approach 2:
The patent divides the single pass through the nonlinear crystal into two separate passes by using a mirror to reflect the beam back through the crystal. This segmentation allows the same crystal to be used twice, effectively doubling the pump power utilization while simplifying the overall device structure compared to using two different crystals or complex interferometric configurations
2Manufacturing precision
If temporal compensation for the walk-off effect is implemented, then the quality of entangled state is improved, but the device becomes more complex and unsuitable for mass production
Solution Approach 1:
The patent changes the polarization state parameter of the laser beam between the two passes through the nonlinear crystal. By rotating the polarization angle by 45 degrees between passes, the system naturally compensates for walk-off effects and generates high-quality entangled states without requiring additional compensation elements or complex adjustments
Solution Approach 2:
The system uses the same nonlinear crystal for both passes without requiring external compensation mechanisms. The polarization rotation inherent in the double-pass configuration automatically handles the walk-off effect compensation, making the device self-compensating and suitable for mass production
3Reliability
If two different crystals are used in crossed-crystal sources, then the generation of entangled photon pairs is achieved, but the entangled state quality is reduced due to crystal property differences
Solution Approach 1:
The patent merges the function of two different crystals into a single crystal by using a double-pass configuration. The same nonlinear crystal is used for both the first and second passes, eliminating the issues arising from crystal property differences while maintaining high entanglement quality through consistent nonlinear optical properties throughout the system
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 source provides a stable and efficient generation of high-quality entangled photon pairs with reduced complexity, eliminating the need for complex adjustments and compensation, and enabling high efficiency and ease of maintenance.
Implementation Method 1
generating photon pairs by the transmission of the laser beam through a nonlinear element
Implementation Method 2
a dichroic element configured to separate the entangled photon pairs and the laser beam
Implementation Method 3
a polarization rotation element configured to rotate the polarization of the laser beam
Data Source
AI summary
An entangled photon source for the generation of polarization entangled photon pairs comprising a laser configured to generate a polarized laser beam in the range of 630 nm to 790 nm, and a nonlinear element configured to generate photon pairs by the transmission of the laser beam, and a dichroic element configured to separate the entangled photon pairs and the laser beam. The source comprises in addition a polarization rotation element and a reflection element configured to reflect the laser beam after the first transmission through the nonlinear element for a second transmission through the nonlinear element.