Diffraction Phase Microscopy (DPM) is a common-path, single shot QPI technique that has found applications in studies of red blood cell morphology and dynamics, cell growth measurement, as well as in Fourier Transform Light Scattering. In DPM, the phase is retrieved by interfering two orders of diffraction from a grating placed at the image plane. The reference field has been, in the past, generated by low pass filtering the zero order via a pinhole placed in the Fourier plane. For achieving the desired spatial coherence, the pinhole is often only 5-10 µm in diameter, making the system difficult to align every time an imaging study is performed. In this work, we eliminated the pinhole from the DPM optical path and generated instead the reference field by magnifying strongly the zero order. We show that a gradient-index (GRIN) lens (effective focal length of 300 µm) can be used to magnify the Fourier transform of the zero order to the point where the DC component fills the camera sensor. We show that the resulting Magnified Object Spectrum Interference Microscopy (MOSIM) system can successfully reconstruct quantitative phase images, without the need for tedious alignment. Because it conserves the common path geometry, MOSIM is characterized by 1.1 nm spatiotemporal pathlength noise. Since it is single shot, we demonstrated 400 frames/s acquisition. We anticipate that this new method can potentially lead to a more robust and less vibration sensitive QPI instrument for carrying out biological studies at various spatiotemporal scales.
Optical projection tomography is a new optical imaging method for visualizing small biological specimens in three dimension. The most important advantage of OPT is to fill the gap between MRI and confocal microscope for the specimen having the range of 1-10 mm. Thus, it has been mainly used for whole-mount small animals and developmental study since this imaging modality was developed. The ability of OPT delivering anatomical and functional information of relatively large tissue in 3D has made it a promising platform in biomedical research. Recently, the potential of OPT spans its coverage to cellular scale. Even though there are increasing demand to obtain better understanding of cellular dynamics, only few studies to visualize cellular structure, shape, size and functional morphology over tissue has been investigated in existing OPT system due to its limited field of view.
In this study, we develop a novel optical imaging system for 3D cellular imaging with OPT integrated with dynamic focusing technique. Our tomographic setup has great potential to be used for identifying cell characteristic in tissue because it can provide selective contrast on dynamic focal plane allowing for fluorescence as well as absorption. While the dominant contrast of optical imaging technique is to use the fluorescence for detecting certain target only, the newly developed OPT system will offer considerable advantages over currently available method when imaging cellar molecular dynamics by permitting contrast variation. By achieving multi-contrast, it is expected for this new imaging system to play an important role in delivering better cytological information to pathologist.
We propose a dual-channel fiber scanning probe for simultaneous measurement of swept source optical coherence tomography (SS OCT) and fluorescence spectroscopy (FS) signals. For the purpose, SS OCT and FS system were combined by adopting the specially fabricated double cladding fiber (DCF) and wavelength division multiplexer (WDM) coupler, and DCF fiber was directly connected to sample arm of DCF coupler for fiber-based probe. Moreover, for sample scanning, the fiber was driven by piezoelectric bender. Since DCF has dual-channel configuration consists of core and inner cladding, both OCT and FS signals propagate through the two channels at the same time. Therefore, the suggested system enables multifunctional imaging that would make it possible to determine a more specific diagnosis. To demonstrate the feasibility of the probe, a photosensitizer injected in-vivo mice were imaged with scanning speed of 16 Hz and scanning range of 2 mm.
We present a birefringence analysis method based on polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) for distinguishing pearls. To cope with the round shape of general pearls, a rotation stage was used for the sample scanning. With the system, the birefringence of several cultured pearls including south sea, Akoya, freshwater cultured pearls, and imitation pearls are analyzed and compared. Interestingly, PS-SS-OCT surely shows well developed birefringence patterns of phase retardation and fast axis orientation with the cultured pearls, whereas the pattern does not appear in the imitation pearls. In addition, the intensity image can help to distinguish the cultured pearls. Therefore, PSSS-OCT enables a more accurate interpretation for identifying the cultured pearls from imitation pearls.
Optical coherence tomography (OCT) has been developed particularly for biomedical and industrial fields owing to the
advantage of in vivo real time optical imaging with a micro-scale high resolution. Depending on specific imaging
purposes, various dedicated OCT systems have been proposed and implemented. We present the recent achievements of OCT systems and their applications such as monitoring of cross-sectional biological specimen, discrimination of living human breast cancer cells, and characterization of wet pad surface in chemical mechanical polishing (CMP) process.
We propose full-range spectral domain optical coherence tomography equipped with a fiber-based sample scanner,
which is used for sample scanning and phase shifting for full-range image at the same time. For a fiber-based sample
scanner, since the fiber tip oscillates as a free standing cantilever in general, unintentional phase shift occurs inevitably.
The unintentional phase shift was used for eliminating the bothersome complex conjugate ghost image of OCT. In
addition, fiber was tilted a few degree to give proper phase shift. In this scheme, moreover, image can be obtained
without any physical modification of the scanner. To realize this technique, we constructed the SD-OCT system and
fabricated a magnetically actuated single-body lensed fiber scanner due to advantages of simple design, low operating
voltage, cost-effectiveness and low insertion loss. The scanner was made of lensed fiber loaded with an iron-based bead
and a solenoid which is placed perpendicular to the lensed fiber. When a sinusoidal current is applied into the solenoid,
the lensed fiber oscillated due to magnetic force between the iron-based bead and the solenoid. With the suggested full
range method, we obtained contrast enhanced full-range SD OCT images of pearl and tooth. This simple and effective
method can be applied to any fiber-based scanner and it has great potential as a handheld probe/endoscopic probe in
biomedical imaging field.
We report the development and performance of high resolution spectral domain optical coherence tomography
(SD-OCT) system based on 2×2 planar lightwave circuit (PLC) splitter that was designed as a single mode splitter at
near infrared and used as the beam splitter for a SD-OCT system. The splitter has been made by coupling SMFs to a
planar lightwave circuit (PLC) splitter chip. The PLC splitter chip was fabricated to have a single mode property with
740 nm cutoff wavelength and the SMFs, which have 730 nm cutoff wavelength, were securely connected to the PLC
chip through fiber block arrays having lithographically fabricated V grooves. With the implemented PLC splitter, we
have obtained a low excess loss of 0.4 dB at 840 nm with wide band coupling property. With the proposed 2×2 PLC
splitter and fabricated WDM coupler, SD-OCT images of samples successfully obtained by using combined source with
840 nm and 880 nm SLDs.
We report the fabrication and performance of the 2×2 photonic crystal fiber (PCF) splitter that was designed as a single
mode splitter at the visible and near infrared and used as the beam splitter for a spectral domain optical coherence
tomography (SD-OCT) system. The PCF splitter has been made by coupling PCFs to a planar lightwave circuit (PLC)
splitter chip. The PLC splitter chip was fabricated to have a single mode property with 630 nm cutoff wavelength and the
PCFs were securely connected to the PLC chip through PCF block arrays having lithographically fabricated V grooves.
The core width of the splitter chip was about 4 μm×4 μm and the core-cladding index difference was about 0.15%. With
the implemented PCF PLC splitter, we have obtained a low excess loss of 1.2 dB and a low polarization-dependent loss
of 0.19 dB at 680 nm with wide band coupling property. With the proposed 2×2 PCF splitter, SD-OCT images of human
finger, nail, and tooth successfully obtained by using 680 nm, 840 nm, and 930 nm SLD source. This PCF PLC splitter is
expected to have high resolution OCT.
We propose a single piece optical fiber-based two-dimensional scanning hand-held probe suitable for three-dimensional
optical coherence tomography. The probe consists of only a single piece of optical fiber loaded with a bead
of ferromagnetic material, which acts as a vibrating cantilever. The fiber cantilever is two dimensionally actuated with a
single miniaturized solenoid. For effective beam focusing, a fiber lens is formed at the end of the fiber. The inductance
and input current of the solenoid were 100 μH and 216 mA, respectively. The iron-bead on the fiber is located at the off-axis
of solenoid for two-dimensional scanning. Then, by modulating the input current to the solenoid, it was possible to
mechanically oscillate the fiber cantilever in an elliptically spiral pattern. With the proposed probe, 2-dimensional
scanning could be experimentally achieved in a rate of 4 s/vortex across a scanning area of approximately 30 mm2,
which could be controlled with the length of the fiber or/and the weight of the iron-bead. Three-dimensional tomographic
image of a coin was successfully obtained with the spectral domain optical coherence tomography equipped with the
proposed scanner. It is expected that the scheme of 2-dimentional scanning with a single actuator might be useful in
various real-time imaging applications including OCT owing to the advantages of low cost, low power consumption,
simple fabrication process and versatile design.
We report the fabrication and performance of the 2x2 photonic crystal fiber (PCF) splitter that was designed as a single
mode splitter at the 800 nm optical band and used as the beam splitter for a spectral domain optical coherence
tomography system. The PCF splitter has been made by coupling PCFs to a planar lightwave circuit (PLC) splitter chip.
The PLC splitter chip was fabricated to have a single mode property at the 800 nm wavelength band and the PCFs were
securely connected to the PLC chip through PCF block arrays having lithographically fabricated V grooves. The core
size of the splitter chip was about 5 μmx5 μm and the core-cladding index difference was about 0.15 %. With the
implemented PCF PLC splitter, we have obtained a low excess loss of 1.2 dB at 850 nm and a low polarization-dependent
loss of 0.19 dB. With the proposed 2x2 PCF splitter, optical coherence tomography images of pearls were
successfully obtained.
We propose a fiber-based hand-held scanning probe suitable for the sample arm of spectral domain optical coherence
tomography (SD-OCT). To achieve a compact and miniaturized probe, a single-body lensed-fiber, on which an
iron-bead ferromagnetic material is loaded was fabricated and a solenoid actuator driven by readily available driving
voltage (10 V) and current (120 mA) was utilized. A focusing lens was directly formed in a single-body onto the distal
end of a fiber, which eliminated any complement optical components in front of a conventional sample probe and
removes any optical alignment problem. By using the soft-iron solenoid actuator, the fiber in the probe is activated
which gives the sample scanning for the OCT imaging. Moreover, the simple design of the solenoid allowed easy
fabrication and a good practicality. With the implemented probe, OCT images of a pearl and a human finger tip were
obtained at an imaging speed of 30 Hz and a scanning range of 4 mm.
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