Bright Entangled Photon Sources With Integrated Pump Filtering
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Solution Overview
Problem
Existing entangled photon sources face issues with optical insertion loss, inefficient photon collection and delivery, and integration challenges due to the use of discrete components, which degrade efficiency and brightness, and require additional filters that introduce further optical loss and size constraints.
Innovation Solution
Integration of a fiber-based polarization Sagnac interferometer with a periodically poled nonlinear waveguide (PPNW) into a compact module, incorporating built-in pump-removal filters and using polarization maintaining fibers to enhance photon pair generation and delivery, while minimizing temporal walk-off and optical loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If discrete components are used in entangled photon sources, then the system is easier to manufacture and assemble, but optical insertion loss increases and photon collection efficiency decreases
Solution Approach 1:
The patent integrates multiple discrete optical components (nonlinear waveguide, filters, coupling lenses, isolators) into a single monolithic chip structure. This merging eliminates the need for external optical alignment and reduces the number of optical interfaces, thereby minimizing optical insertion loss while maintaining ease of manufacture through standardized chip fabrication processes
2Reliability
If additional filters are added to remove pump light, then pump removal efficiency improves, but optical loss increases and device size increases
Solution Approach 1:
The patent embeds pump removal filters directly within the chip structure, nesting them inside the monolithic device rather than placing them as external components. This nested configuration allows the filters to be positioned optimally close to the generation region, improving pump removal efficiency while minimizing the light path and reducing overall optical loss. The device size increase is minimized through integrated design
3Ease of manufacture
If discrete optical components are used, then the system is easier to assemble, but alignment stability decreases and susceptibility to vibrations increases
Solution Approach 1:
The patent merges all optical components into a single monolithic chip where relative positions are fixed during fabrication. This eliminates the need for post-assembly optical alignment and makes the system inherently resistant to vibrations and thermal fluctuations, as there are no loose optical interfaces that can misalign. The ease of assembly is maintained through standardized chip manufacturing and mounting procedures
4Loss of energy
If integration is performed to reduce loss, then optical efficiency improves, but device complexity increases
Solution Approach 1:
The patent replaces the mechanical system of discrete optical components requiring manual alignment with an integrated photonic system where optical paths are defined by fixed waveguide structures on the chip. This substitution eliminates the complexity of mechanical alignment and mounting while achieving lower optical loss through direct waveguide coupling. The integration complexity is managed through established photonic chip fabrication techniques
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 high-fidelity, stable, and compact entangled photon sources with reduced noise floor, suitable for satellite communication, offering efficient photon conversion and reliable operation with minimal maintenance, low power consumption, and robustness against vibrations and thermal fluctuations.
Implementation Method 1
Spontaneous parametric down conversion (SPDC) is one of the most passive optical processes implemented in generating correlated photons. In SPDC, a pump photon at high frequency ωp travelling in a non-linear medium is converted into two correlated lower energy photons.
Implementation Method 2
All pump photons and generated daughter photons are confined to a crystal waveguide and routed via polarization maintaining (PM) fibers and are efficiently coupled to their output ports
Implementation Method 3
The inherent phase stability of Sagnac interferometers is remarkable. It is attributed to the common interferometric path of pump photons and photon pairs that are combined into a single spatial mode.
Data Source
AI summary
Bright entangled photon sources including an alignment-free, fiber-based, mechanically-rugged and generic interferometric module are disclosed. The inherent phase-stability of a Sagnac interferometer is deployed. High down-conversion efficiency of periodically poled nonlinear-waveguides is combined with the optical gain of semiconductor optical amplifiers and immunity of fiber optics. A single compact interferometric engine combines these attributes, allowing highly stable, integrable and bright polarization entangled-photon sources operating at room temperature. Using a minimum number of in-line optical parts, the compact module is based on a novel method that enhances the long-term stability and efficiency without compromising the entanglement quality. Besides energy entanglement, polarization entanglement is presented and set through the operational conditions. An optional periodically poled nonlinear waveguide can be hosted to achieve the desired spectral bandwidth and photons generation rate. The result is a zero-maintenance, lightweight, low-power consumption engine of compact and fully-integrable bright polarization-entangled photon sources.