Photonic Integrated Circuit Pump Filtering for Low-Loss Squeezed Light
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Solution Overview
Problem
Loss in squeezed-light devices degrades the squeezing factor due to mechanisms like absorption, scattering, and reflection, which is exacerbated by off-chip filtering and interferometers, leading to reduced performance in applications requiring long-distance transmission.
Innovation Solution
Incorporating a pump filter and on-chip interferometer on a photonic integrated circuit (PIC) to minimize loss by using a second microresonator for pump filtering and optimizing waveguide couplers, thereby reducing propagation and insertion losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If off-chip filtering and interferometers are used in squeezed-light devices, then pump light can be filtered and interference patterns can be generated, but loss increases due to absorption, scattering, and reflection, degrading the squeezing factor
Solution Approach 1:
The patent combines the pump filter and interferometer functions onto a single photonic integrated circuit chip. The microresonator serves as both the squeezing light generator and the pump filter, while the waveguide integrally forms the interferometer structure. This integration eliminates multiple off-chip optical components and their associated coupling interfaces, thereby reducing propagation losses from absorption, scattering, and reflection that degrade the squeezing factor.
Solution Approach 2:
The patent uses an evanescently coupled microresonator as an intermediary element to filter pump light without requiring direct physical contact or additional optical components. The microresonator is evanescently coupled to the waveguide, allowing it to selectively filter pump wavelengths while maintaining low loss transmission of the squeezed light signal. This intermediary approach achieves pump filtering with minimal insertion loss.
2Reliability
If off-chip filtering components are used, then pump light can be removed, but insertion loss increases due to additional coupling interfaces
Solution Approach 1:
The patent merges the pump filtering function directly into the photonic integrated circuit waveguide structure using an evanescently coupled microresonator. This eliminates the need for separate off-chip filtering components and their associated coupling interfaces. By integrating the filter functionality into the waveguide itself, the patent removes multiple insertion loss points that would otherwise be introduced by discrete filtering components.
3Adaptability or versatility
If squeezed light is transmitted over long distances, then quantum communication applications can be enabled, but loss degrades the squeezing factor and reduces transmission efficiency
Solution Approach 1:
The patent integrates all necessary functions (squeezing light generation, pump filtering, and interferometry) onto a single photonic integrated circuit chip. This compact integration minimizes the total optical path length and reduces the number of coupling interfaces where loss occurs. The integrated design enables efficient squeezed light generation with minimal initial loss, preserving the squeezing factor for long-distance transmission in quantum communication applications.
Solution Approach 2:
The patent employs a high-Q microresonator with carefully engineered resonant parameters to enhance the squeezing light generation efficiency. By optimizing the resonator quality factor and coupling parameters, the system achieves high squeezing factors at the source. This parameter optimization ensures that the squeezed light maintains sufficient signal quality for long-distance transmission, compensating for inevitable propagation losses.
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
Preserves squeezing factor by minimizing loss, enabling efficient generation and transmission of squeezed light over long distances, particularly at telecom wavelengths, suitable for quantum communication applications.
Implementation Method 1
A first microresonator converts two pump photons into a pair of entangled signal and idler photons through spontaneous four-wave mixing
Implementation Method 2
A second microresonator is evanescently coupled to the first bus waveguide at a different wavelength than the signal light and the idler light to resonantly couple unconverted pump light
Implementation Method 3
A waveguide coupler minimizes propagation loss
Implementation Method 4
This is typically accomplished with anti-reflection coatings, minimizing changes in the refractive index (which create reflections)
Data Source
AI summary
A photonic integrated circuit (PIC) includes a first microresonator that generates a two-mode squeezed vacuum using spontaneous four-wave mixing. Specifically, the first microresonator uses a nonlinear optical medium to convert two pump photons into a pair of entangled signal and idler photons. Due to imperfect conversion efficiency, some of the pump light may co-propagate with the signal light and idler light. To remove this “unconverted” pump light, the PIC includes a second microresonator that is tuned to resonate with only the pump light. The second microresonator is located after the first microresonator and couples the unconverted pump light into a waveguide that guide the light off the PIC. Thus, the second microresonator acts as a notch filter. Integrating this pump filter onto the PIC adds negligibly to the path length of the squeezed light, and therefore saves the propagation losses incurred when using a much larger off-chip filter.