On-Chip Long-Pass Filter Using Silicon Absorption for Pump Rejection
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Solution Overview
Problem
Current optical filters for on-chip quantum photonic circuits require precision fabrication processes and active wavelength alignment, limiting their efficiency and flexibility in rejecting pump photons while maintaining high extinction ratio and broad bandwidth.
Innovation Solution
A long-pass filter design utilizing a waveguide core with a selective-absorber layer made of indirect-bandgap semiconductor materials like α-Si, which absorbs undesired short-wavelength pump light without attenuating desired longer-wavelength photons, achieving high extinction ratio and broad bandwidth without the need for precision fabrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cascaded optical microring-based filters or Mach-Zehnder interferometers are used to attain wavelength-selective isolations, then the extinction ratio is improved, but the device complexity and manufacturing precision requirements increase
Solution Approach 1:
The patent extracts the filtering function from complex cascaded filter stages and implements it through a single integrated long-grating waveguide structure. The grating is directly written into the waveguide core, separating the filtering mechanism from the need for multiple discrete filter components and their cascaded arrangement, thereby reducing device complexity while maintaining high extinction ratio
Solution Approach 2:
The patent employs a composite structure combining the waveguide core material (e.g., lithium niobate) with an embedded long-grating structure. This composite design allows the grating to be integrated directly into the waveguide, enabling wavelength-selective filtering without requiring separate filter components or precise cascaded alignments, thus simplifying the overall device architecture
2Adaptability or versatility
If active thermal and electric controls are used for aligning filter wavelengths, then the adaptability is improved, but the energy consumption increases
Solution Approach 1:
The long-grating waveguide filter is designed to be inherently wavelength-selective through its grating period and length, which are fixed during fabrication. The filter operates passively without requiring active thermal or electric controls for wavelength alignment, thereby eliminating the energy consumption associated with such control mechanisms while maintaining its filtering function
Solution Approach 2:
The patent achieves wavelength selectivity through the physical parameters of the grating structure (grating period, length, and depth) rather than through active control parameters like temperature or voltage. By optimizing these structural parameters during fabrication, the filter is tuned to the desired wavelength without requiring post-fabrication active adjustment, thus reducing energy consumption
3Adaptability or versatility
If long gratings or directional coupler-based filters are used to enable broad bandwidth, then the adaptability is improved, but the insertion loss increases
Solution Approach 1:
The patent applies local quality by varying the grating depth and period along the waveguide length to optimize the filtering performance. The grating structure is designed with different local characteristics to achieve both broad bandwidth and low insertion loss simultaneously, with stronger coupling regions providing filtering and weaker coupling regions maintaining low loss transmission
Solution Approach 2:
The patent uses a long-grating structure that extends over a significant portion of the waveguide length, providing sufficient filtering action to achieve high extinction ratio and broad bandwidth. The grating length is optimized to provide just enough filtering action to achieve the desired performance without excessive length that would cause high insertion loss
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 filter effectively rejects pump photons by over 120 dB while maintaining negligible loss for signal photons, achieving a compact footprint and flexible design suitable for integrated quantum photonic chips.
Implementation Method 1
The selective-absorber layer is composed of an indirect-bandgap semiconductor material selected to have a bandgap energy greater than a maximum photon energy associated with the one or more first constituent wavelengths and less than a minimum photon energy associated with the one or more second constituent wavelengths such that when the desired and undesired light components interact with the selective-absorber layer during propagation inside the waveguide core, the undesired light component is attenuated
Data Source
AI summary
A passive on-chip optical long-pass filter for removing residual pump photons at short wavelengths after nonlinear generation of photons. A thin layer (<100 nm) of amorphous or poly-crystalline silicon is deposited onto a section of a waveguide to absorb light with a wavelength shorter than the silicon bandgap wavelength of ˜1.1 μm, while the nonlinearly generated light in longer wavelengths than the silicon bandgap wavelength propagates in the waveguide with a negligible absorption loss. The filter is applicable to attain an on-chip optical pump light rejection ratio exceeding 120 dB for nonlinear and quantum photonic chips. The filter is conceptually simple to design and can be fabricated by a CMOS process with potentially a high wafer-level scalability and manufacturability at a low cost. The filter can be realized in various integrated photonic platforms, including silicon carbide, silicon nitride, lithium niobate and aluminum nitride.