Bulk Illumination RF Resonator for Low Power Photonic Control
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Solution Overview
Problem
Conventional photonic control of RF signal propagation in microwave devices is limited by the confinement of free carriers to the substrate surface, leading to reduced interaction with the resonant field and limited sensitivity, as most devices rely on surface illumination and compound semiconductors for monolithic integration, which complicates the fabrication and reduces performance.
Innovation Solution
The use of a longer optical wavelength that penetrates beyond the substrate surface for bulk illumination, combined with a resonant RF structure, allows for enhanced interaction between the RF field and photogenerated carriers, achieving increased sensitivity and performance by recirculating unabsorbed optical power within the high RF field region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If surface illumination is used to generate photo carriers, then the device structure is simplified, but the interaction between RF field and photo carriers is reduced
Solution Approach 1:
Instead of illuminating from the top surface, the patent inverts the illumination direction by using a substrate-transparent material and illuminating from the bottom through the substrate. This allows optical power to reach the sensitive region without being absorbed by metal layers, resolving the contradiction between structural simplicity and effective interaction.
Solution Approach 2:
The substrate acts as an intermediary medium that allows optical power to pass through. By selecting a substrate-transparent material and appropriate wavelength, the substrate enables bulk illumination while maintaining structural simplicity, thus resolving the contradiction.
2Use of energy by moving object
If top illumination is used to avoid absorption, then optical power reaches the sensitive region, but free carriers are confined to the surface
Solution Approach 1:
The patent inverts the illumination approach by shining light from the bottom through the substrate rather than from the top. This enables optical power to penetrate into the bulk and generate free carriers throughout the volume, not just at the surface, thus resolving the contradiction between optical power delivery and carrier distribution volume.
Solution Approach 2:
The invention transitions from surface-level (2D) carrier generation to bulk (3D) carrier generation by changing the illumination dimension. Light propagates through the substrate thickness to illuminate the entire sensitive region volume, increasing the quantity of photo-generated carriers.
3Reliability
If compound semiconductors are used for monolithic integration, then photosensitivity is improved, but fabrication complexity increases
Solution Approach 1:
The patent changes the optical parameter (wavelength) to match the absorption characteristics of silicon substrate. By selecting a wavelength where silicon is transparent, the invention achieves effective photosensitivity in standard silicon-based microwave devices without requiring compound semiconductors, thus resolving the contradiction between photosensitivity and fabrication complexity.
Solution Approach 2:
The invention uses homogeneous silicon substrate material throughout the device structure rather than integrating different compound semiconductor materials. This maintains uniform fabrication processes while achieving the desired photosensitivity through appropriate wavelength selection and bulk illumination geometry.
4Power
If short wavelength (600-900 nm) is used for maximum absorption, then carrier generation is enhanced, but optical penetration depth is reduced
Solution Approach 1:
Instead of using short wavelengths that are strongly absorbed at the surface, the patent inverts the approach by using longer wavelengths that penetrate deeper into the substrate. The bottom-illumination geometry compensates for lower absorption coefficient by allowing light to travel through the substrate and illuminate the bulk region effectively.
Solution Approach 2:
The patent changes the optical wavelength parameter from the conventional 600-900 nm range to longer wavelengths where the substrate is transparent. This parameter change enables deep penetration while bulk illumination ensures sufficient carrier generation throughout the sensitive region volume.
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 significant increase in RF transmission change per unit optical power, with 5.5 dB achieved with less than 1 mW of optical power, and up to 11 dB with 2 mW, surpassing previous devices in sensitivity and efficiency, while maintaining monolithic integration on a silicon substrate without the need for bias voltage or p-n junctions.
Implementation Method 1
low-loss optical waveguides cannot be easily integrated with the device to deliver light directly to the sensitive region
Implementation Method 2
Bulk illumination of an interior region of a resonant configuration having a high intensity RF field results in a large RF-optical (and therefore RF-free carrier) overlap integral
Implementation Method 3
by using an RF resonator/resonant structure (as opposed to traveling wave configurations) the RF field is confined in a small volume and passively amplified
Implementation Method 4
an optional optical boundary condition that recirculates the unabsorbed optical power inside the high RF field region until it is fully absorbed
Data Source
AI summary
A photonically controlled microwave device having a photosensitive substrate having an interior region comprising a high radio frequency (“RF”) field for a resonant RF mode. An RF resonator is patterned on a surface of the substrate, the pattern includes an aperture in the resonator positioned to direct light received from a light source to the interior region. The light source may have a wavelength that enables illumination of the interior region to generate free carriers or other photo-induced changes in RF permittivity. An optical boundary may be provided that recirculates the unabsorbed optical power inside the high RF field region until it is fully absorbed.