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Facilities and equipment in the Visual and Biomedical Optics Lab

 

In the past two and a half years, with the support of the Department of Ophthalmology and Visual Science and Department of Electrical and Computer Engineering and also the support from the funding agencies, Dr. Li and his team members have installed a diamond turning machine for fabrication of passive and active adaptive optical elements and have built several biomedical optical imaging systems in the lab located at 1330 Kinnear Road. The lab contains a room over 2,000 square feet for experiments, where seven optical tables are housed, a room with a fume hood and a spin processor, and an additional room with the diamond turning machine. The state-of-the-art cleanroom facilities at NanoTech West (http://nanotech.osu.edu/), which is right across Dr. Li’s lab, are also available for daily use. The lab is well equipped with three wavelength-tunable laser systems (continuous wave, femtosecond, and nanosecond), various optical elements, electronic devices, and optical testing setups.

 

1. Diamond turning machine for optical fabrication

We have a 4-axis diamond turning machine (Nanoform 250 Ultra from Ametek) installed in our lab. We have successfully designed, programmed, and fabricated different types of phase plates for passive adaptive optical imaging and for assembly of active adaptive lens. This is a great advantage for us to complete versatile research in house. It is very convenient for us to use the machine to fabricate any phase plate and various lenses for vision correction.

 

 

2. Several custom built biomedical imaging systems

Dr. Li and his team members have custom built an ultrafast parallel confocal imaging system with adaptive focus, ultrahigh-resolution optical coherence tomography imaging system for eye imaging (both cornea and retina), photoacoustic imaging system, and wavefront-coded wide-field microscope with extended depth of field. Dr. Li was also involved in building the most advanced scanning laser polarimeter for diagnosis of glaucoma. Currently Dr. Li is building polarization–sensitive optical coherence tomography system and two-photon / second-harmonic-generation imaging system for eye imaging. Dr. Li’s lab has also built a setup for generation of cylindrical vector beams with arbitrary amplitude, phase, and polarization states, and this setup will be useful for optical imaging. Dr. Li is actively collaborating with faculty members at OSU for interdisciplinary research.

 

(1) Ultrafast parallel confocal imaging system with adaptive focus

By introducing electro-optic varifocal lens and reconfigurable digital micromirror device (DMD) for rapid depth scanning and parallel pinhole array generation, we have built an ultrafast 3D confocal / fluorescence microscope which allows more than 2000 frames per second. Such a system has very important applications in imaging dynamic behaviors inside a cell and in large-scale imaging and recording of neural activities in the eye and brain. Our paper presented at Frontiers in Optics was among the top downloaded papers at OSA webpage.

 

 

(2) Ultrahigh-resolution optical coherence tomography imaging system for eye imaging (both cornea and retina)

We have built an ultrahigh-resolution OCT imaging system using a light source with an ultra broad bandwidth from 760 nm to 940 nm. This allows a 3-micron depth resolution in sample. An important feature of the system is that a spectrometer which is linear in wave number is used. Custom optical design in the reference arm, the sample arm, and the spectrometer allows high signal-to-noise ratio. The x-y fast scanners are equipped with the system to provide 3D image.

 

(3) Polarization-sensitive optical coherence tomography imaging system

Many biomedical tissues such as cornea, Henle nerve fibers, retinal nerve fiber layer, choroid, sclera, skin, bone have birefringent properties. Quantitative measurement of the birefringence and thickness of these tissues are critical for objective diagnosis of diseases and wounds of these tissues. The system has been built in the lab.

 

(4) Full-field optical coherence microscope

By using the parallel confocal imaging system as the sample arm, we have built a full-filed optical coherence microscope. Previous full-field OCT microscopes did not use confocal imaging geometry. Our system can provide better transverse resolution and signal-to-noise ratio.

 

 

(5) Photoacoustic microscopic imaging

Photoacoustic microscope is a new imaging modality that measures 3D absorption map of a biomedical sample. It provides the complementary property of the sample in comparison with the other imaging techniques based on scattered light. For eye imaging, the photoacoustic ophthalmoscope can be used for diagnosis of eye diseases such as diabetic retinopathy, tumor, etc. We have built a scanning laser photoacoustic ophthalmoscope and our goal is to achieve optical resolution in 3D.

 

(6) Wavefront-coded wide-field microscope with extended depth of field

High-resolution 3D volume microscopic imaging with rapid data acquisition and no moving components is extremely important for life science, especially for live cell imaging where dynamic behaviors inside cells need to be recorded in real time for better understanding of the cell functions and diagnosis of various diseases. The depth of field (DoF) of a microscope objective is inversely proportional to the square of the numerical aperture (NA). For high resolution imaging, high NA objective lenses are used and hence the depth of field is limited. As a result, objects outside this thin region cannot be clearly imaged by the microscope. Extension of the DoF allows for the investigation of a sample’s 3D structure. This is especially important in biological and medical research conducted with high NA objectives. Based on wavefront coding technique, we have been working on new microscopes with simultaneous extended DoF and quantitative depth extraction for real-time 3D imaging. Both reflective and transmissive microscopes are investigated. Such a new microscope with simultaneous extended DoF and quantitative depth extraction will have revolutionary impact in the field of biomedical imaging. The research will provide a simple and low-cost microscope that allows video-rate 3D medical imaging.

 

(7) Two-photon/second-harmonic-generation imaging system

The periodic fiber structures in the eye can generate second harmonic signal upon excitation of femtosecond laser pulses in the near infrared and hence changes in these structures can be monitored. Two-photon fluorescence imaging also plays an important role in structural and functional imaging of the retina. The system is being built.

 

(8) Generation of unconventional polarized beam for imaging

Unconventional polarized beam (radially and azimuthally polarized beams with special amplitude and phase distributions) can be focused to a sharper spot and this property can be exploited for super resolution imaging. We have built a 4-f optical system using programmable spatial light modulator that can generate unconventional polarized beams with arbitrary amplitude, phase, and polarization.

 

 


 

Equipment

 

Dr. Li’s lab in the Department of Ophthalmology and Visual Science and the Department of Electrical and Computer Engineering has the following equipment:

 

  • Laser systems: Ti:Sapphire femtosecond laser (Mira 900 from Coherent), wavelength tunable continuous wave laser (MBR laser system from Coherent) nanosecond laser working at 1064 nm and 532 nm (SPOT-10-250-1064 from Elforlight), wavelength-tunable nanosecond laser (Pulsed Nd:YAG laser GCR series Quanta-Ray MOPO-730 from Spectra Physics), several He-Ne lasers working at 633 nm, Verdi laser working at 532 nm, , , near IR semiconductor lasers (from CVI Melles Griot), broadband superluminascent laser diode.

  • Optical test: 7 optical tables, setups for characterization of the liquid crystal lens, phase-shifting interferometer, various optical components (lenses, beam splitter, polarizers, waveplates, filters, attenuaters, fiber couplers, microscope objectives), adaptive optics kit from ALPAO (Hi-speed DM 97-15 deformable mirror with 97 elements and 32x32 element wavefront sensor), spatial light modulator (Pluto NIR-2 from HoloEye), digital micromirror device, pairs of beam scanning mirrors, many translation stages, a few piezo transducers, spectrometer.

  • Electronics: electronic circuit design software, oscilloscopes, various detectors, lock-in amplifiers, power suppliers, wire bonding machine, various data acquisition boards, etc.

  • Microfabrication: Nanotech West (OSU microfabrication facility); Diamond truning machine (Nanoform 250 from Ametek)

  • Visual test: various eye charts for visual acuity and contrast sensitivity tests

  • Zemax optical design software, FDTD simulation software, BPM simulation software, COMSOL, AutoCAD, etc.

  • High-speed photo detectors, various CCD and CMOS cameras of different frame rates, National Instrument frame grabber board, Visual Studio, LabView control.

  • Custom built parallel confocal imaging system with adaptive focus and high-resolution optical coherence tomography imaging system; photoacoustic imaging system and second-harmonic-generation imaging system.

  • We have the cleanroom/wet lab to prepare various samples.