Angle-misaligned chirp-enhanced delay (ACED) cavity - enabling optical time-stretch imaging in a new wavelength regime

Grant Data
Project Title
Angle-misaligned chirp-enhanced delay (ACED) cavity - enabling optical time-stretch imaging in a new wavelength regime
Principal Investigator
Dr Tsia, Kevin Kin Man   (Principal investigator)
Start Date
Completion Date
Conference Title
Presentation Title
optical time stretch, ultrafast optical imaging, biophotonics
Engineering (E)
RGC General Research Fund (GRF)
HKU Project Code
Grant Type
General Research Fund (GRF)
Funding Year
1) Develop the prototypes of the ACED cavity operating in VIS-sNIR – ACED cavity is essentially a free-space Fabry-Perot cavity with two non-parallel (i.e. angle-misaligned) mirrors, which is the key feature enabling enormous (also dynamically tunable) GDD, yet with low optical loss, within a reasonable footprint. In contrast to the standard dispersive-fiber-based OTS, this is a new concept of OTS. We will thus first devise the optimal ACED-cavity design rules, which can be done adequately based on geometric optics, i.e. ray-tracing, for efficient OTS operation in VIS-sNIR. Design considerations include the achievable GDD, optical loss, spectral and spectral/temporal resolutions. According to the optimal designs, the prototypes will be constructed by the commercially-available optics, e.g. high-reflectivity plane mirrors and diffraction grating. Its OTS performance will be characterized and optimized in two selected wavelength ranges: ~500 nm and ~800 nm – the windows to be adopted in the OTS-based imaging systems; 2) Establish two OTS bioimaging modalities in VIS-SNIR based on ACED cavity – Leveraging on our current expertise in varies modalities of OTS-related imaging, we will then exemplify the utility of the new ACED-cavity concept for OTS bioimaging in the unexploited VIS-sNIR range by developing two imaging modalities based on our prior work – (i) optofluidic cellular quantitative phase OTS imaging at ~500nm: To demonstrate its better compatibility with standard tools used in biomedicine (e.g. bioassays), this quantitative phase OTS imaging system will also be integrated with a non-imaging single-cell fluorescence detection module for multiparametric quantitative cellular imaging in ultrafast microfluidic flow (>1 m/s), particularly valuable for highly multiplexed cellular assays; (ii) OTS-based swept-source OCT (SS-OCT) at ~800nm with an A-scan rate of multi-MHz: OTS-based OCT has been restricted in 1500–1600nm while many successful OCT applications, e.g. retinal imaging in ophthalmologic diagnosis, demand the operation window of 800–1000nm; 3) Exploit a new modality: "spectral-encoding-free" OTS imaging in VIS-sNIR – Spectral-encoding of image has long been the pre-requisite in OTS imaging. However, it is this feature making OTS imaging generally incompatible with fluorescence imaging – the workhorse in life sciences and biomedicine. Intriguingly, ACED cavity also works with non-spatially-dispersed light for efficient OTS in VIS-sNIR. It implies that broadband spectral encoding is no longer necessary. Together with its giant stretched-time and low-loss operation, ACED cavity represents a unique concept enabling ultrafast OTS fluorescence imaging. We will exploit this entirely new approach, i.e. spectral-encoding-free OTS imaging, using a narrowband source in VIS-sNIR. Specifically, the prototype development will be focused on demonstrating fluorescence OTS imaging.