Optical imaging techniques that measure changes in calcium or voltage provide a promising route toward to large-scale measurement of neural activity and high spatial resolution to resolve individual neurons. However, acquiring images through significant depths of the brain is difficult since brain tissue is extremely heterogeneous, which results in strong scattering by the various tissue components and limited penetration depth as well as achievable imaging resolution. To overcome the effects of scattering, optical imaging measurement techniques have been proposed ranging from laser scanning microscopy of submicron structures to diffuse optical tomography of large volumes of tissue.

    Recent advances in imaging technology such as light-sheet microscopy have enabled high-speed, high-resolution, three-dimensional volumetric imaging of large volumes of neural tissue. However, the light sheet microscopy technique fails to be compatible with opaque or scattering samples and has a limitation of the sample size by the two compact orthogonal illumination and detection objectives. In this work, I will show an implantable light sheet photonic probe integrated with a microlens  that can produce a thin layer of illumination. With this planar illumination, the probe can image more than 500 microns deep below the surface of a brain tissue phantom, which is confirmed experimentally.  

First, I will make an introduction of the current optical imaging techniques, such as epi-fluorescence microscopy, laser scanning confocal microscopy, two-photon microscopy and conventional light sheet microscopy. Also, I will discuss the limitations and drawbacks of each method.

Second, I will present the design and principle of the integrated light sheet photonic probe with a microlens that can produce a thin layer of light illumination perpendicular to the device plane. In addition, I will show the structure of the photonic probe and components of the imaging setup.

Also, I will numerically and experimentally illustrate the light sheet can be created by a microlens diffraction. Then I will show the imaging result of inserting the photonic probe inside the brain tissue phantom and compare it to the conventional wide field microscopy.

Finally, I will make a summary of my work and then talk about the future work of my research.