-
Real-time ultrasound sensing with a mode-optimized photonic crystal slab
Authors:
Eric Y. Zhu,
Maria Charles-Herrera,
Cory Rewcastle,
Raanan Gad,
Li Qian,
Ofer Levi
Abstract:
Integrated photonic sensors can provide large scale, flexible detection schemes. Photonic crystal slabs (PCS) offer a miniaturized platform for wideband, sensitive ultrasound detection by exploiting the photoelastic effect in water. However, poor modal overlap with the sensing medium and non-negligible absorption loss of the aqueous medium have previously limited PCS sensor performance. In this st…
▽ More
Integrated photonic sensors can provide large scale, flexible detection schemes. Photonic crystal slabs (PCS) offer a miniaturized platform for wideband, sensitive ultrasound detection by exploiting the photoelastic effect in water. However, poor modal overlap with the sensing medium and non-negligible absorption loss of the aqueous medium have previously limited PCS sensor performance. In this study, we detail the development and optimization of a PCS-based acoustic sensor, by adding to it a low-loss high-index polymer cladding layer. Exploiting a mode-optimized TM-like optical resonance present in a PCS, with high bulk index sensitivity (>600 nm/RIU) and quality factor Q (>8000), we demonstrate real-time ultrasound-sensing at a noise equivalent pressure (NEP) of 170 Pa (1.9 Pa/rt Hz). The PCS sensor is backside-coupled to optical fiber which, along with its intensity-based ultrasound-sensing architecture, will allow us to scale up easily to a 2D array. This work paves the way to a sensitive compact ultrasound detector for photoacoustic-based diagnostics and monitoring of tissue.
△ Less
Submitted 14 August, 2021; v1 submitted 2 May, 2021;
originally announced May 2021.
-
Refractive-Index-based ultrasound sensing with photonic crystal slabs
Authors:
Eric Y. Zhu,
Cory Rewcastle,
Raanan Gad,
Li Qian,
Ofer Levi
Abstract:
We demonstrate ultrasound detection with 500-$μ\mathrm{m}$-diameter photonic-crystal slab (PCS) sensors fabricated from CMOS-compatible technology. An ultrasound signal impinging a PCS sensor causes a local modulation of the refractive index (RI) of the medium (water) in which the PCS is immersed, resulting in a periodic spectral shift of the optical resonance of the PCS. The acoustic sensitivity…
▽ More
We demonstrate ultrasound detection with 500-$μ\mathrm{m}$-diameter photonic-crystal slab (PCS) sensors fabricated from CMOS-compatible technology. An ultrasound signal impinging a PCS sensor causes a local modulation of the refractive index (RI) of the medium (water) in which the PCS is immersed, resulting in a periodic spectral shift of the optical resonance of the PCS. The acoustic sensitivity is found to scale with the index sensitivity $S$ and quality factor $Q$. A noise equivalent pressure (NEP) of 650 Pa with averaging (7.4 Pa$/\sqrt{\mathrm{Hz}}$) and relative wavelength shifts of up to 4.3$\times10^{-5}$ MPa$^{-1}$ are measured. The frequency response of the sensors is observed to be flat from 1-20 MHz, with the range limited only by our measurement apparatus.
△ Less
Submitted 8 June, 2019; v1 submitted 30 October, 2018;
originally announced December 2018.
-
Improved spot formation for flexible multi-mode fiber endoscope using partial reflector
Authors:
Ruo Yu Gu,
Elaine Chou,
Cory Rewcastle,
Ofer Levi,
Joseph M. Kahn
Abstract:
Multi-mode fiber (MMF) endoscopes are a new type of endoscope that use only a single optical fiber to transmit images, achieving much higher spatial resolution for a given diameter than commercial fiber bundle endoscopes. However, a drawback of MMF endoscopes is that imaging quality degrades substantially as the MMF is perturbed. We propose a method for improving spot formation at the distal end o…
▽ More
Multi-mode fiber (MMF) endoscopes are a new type of endoscope that use only a single optical fiber to transmit images, achieving much higher spatial resolution for a given diameter than commercial fiber bundle endoscopes. However, a drawback of MMF endoscopes is that imaging quality degrades substantially as the MMF is perturbed. We propose a method for improving spot formation at the distal end of a perturbed MMF, and thus improving imaging quality, by attaching a partial reflector to the distal end of the MMF. We experimentally find that the perturbation of the light reflected from the partial reflector is highly correlated with the perturbation of the light transmitted through the MMF. We demonstrate a simple method exploiting this correlation that enables formation of spots at the distal fiber end with quality 10-15% higher than if the perturbation of the MMF is ignored. In the future, more advanced algorithms exploiting the correlation may enable further improvements in spot formation and imaging through perturbed fibers.
△ Less
Submitted 19 May, 2018;
originally announced May 2018.