New detection paradigms for laser-scanning microscopy leveraging fiber optical amplifiers

SUMMARY Laser scanning microscopy (LSM) – including optical coherence tomography (OCT), confocal and multiphoton microscopy (MPM) – allows imaging thick, living tissue at depth, and thus has been widely adopted for many biological contexts. To facilitate further research and discovery, increase in the total information capacity with

larger fields-of-view, faster imaging, or deeper penetration is desired, but is ultimately limited by tissue heating. This project will employ distributed amplification in optical fibers – a technique pioneered and honed for telecommunications – in order to bypass this limitation. Two fiber-based amplifier and detection systems (F-

BADS) will be constructed leveraging both the sensitivity of optical amplification, and the bandwidth and dynamic range of photodiode detectors in order to increase the signal-to-noise ratio (SNR) and acquisition speed of LSM by ~100-fold relative to conventional detection modalities. The first F-BADS will employ Raman amplification in

multi-mode fibers to provide gain in the visible spectrum. The module will be installed into an existing two-photon microscope and characterize the benefits in SNR and speed afforded by this technique relative to photo- multiplier-tube-based detection. The second F-BADS will use four-wave mixing in single-mode fiber (SMF) to

provide gain in the 13XX tissue transparency window. The SMF-based design of this amplifier will facilitate alignment-free integration into a fiber-based reflectance microscope. SNR, speed, and penetration depth achievable with this method will be characterized for both confocal microscopy and OCT. Both proposed F-BADS

are drop-in compatible as add-on modules for any microscope, and can amplify spatially coherent or incoherent light across the visible and near-infrared spectrum, including broadband fluorescent signals. Therefore, these proof-of-principle demonstrations of the utility of nonlinear fiber optical amplification will encourage wide adoption

for a broad range of optical imaging applications, as well as facilitate further scaling of LSM information capacity.