A holey optical fiber (HOF) wavelength division multiplexing (WDM) coupler, which divides optical waves according
to their wavelengths, has been made by using the Fused Biconical Tapered (FBT) method. The transmission band of the
proposing HOF WDM coupler could be easily tuned by adjusting the pulling length during the FBT process. The HOF
used for the WDM coupler was designed to be bending insensitive, which could withstand a bending radius of up to 6
mm. Interestingly, it was observed that the air hole structure of the HOF should be maintained to have the property of a
WDM coupler. The cross sectional SEM images of the implemented HOF WDM coupler are presented along with the
light intensity distribution at the coupling region. The proposed HOF couplers may find applications as optical CWDM
(coarse wavelength division multiplexing) filters and as optical fiber sensors also.
Novel wavelength-swept Raman laser is newly demonstrated to implement an arbitrary gain band for a swept-source optical coherence tomography (SS-OCT). Instead of conventional semiconductor optical amplifier, we adapt optical fiber Raman amplification, which can easily generate an instant femto-second optical gain at arbitrary wavelength region from 1.1 to 1.6 micrometer using a high-power optical pump power. We also experimentally demonstrate OCT images using the novel wavelength-swept Raman laser source.
Several technical problems have to be overcome before Optical Coherence Tomography (OCT) can be accepted among
the established endoscopic imaging modalities. Most of conventional Michelson-based OCT systems need to have two
separated paths of the sample and reference arms, which limits the flexibility of endoscopic probe. Recently, common-path
interferometer based OCT have been demonstrated to circumvent the mismatch problems of length, polarization,
and dispersion between the reference and sample arms, but the interferometric scanning methods have been realized with
time-domain PZT or spectral-domain CCD. In this work, we demonstrate a novel Fourier-domain common-path OCT
based on sweeping laser source, which shows superiority in the speed and robustness. Using a holey optical fiber with
low bending loss, a novel curled optical patch cord, like a curl cord of telephone, is also adapted for the convenient
access to the biological target at the flexible distance. The freedom to use an arbitrary length and wiring of the probe can
provide more flexibility for use in endoscopic OCT.
We demonstrate a novel implementation of spectral domain OCT by using a proposed sweeping detector at 1320 nm
wavelength range. A fiber pigtailed Fabry-Perot tunable filter is newly adapted to receive spectral interferometer
information using a photo-receiver instead of using charged couple detector arrays. In order to show a possibility of the
scheme in other view point, we have changed the position of the Fabry-Perot tunable filter of the interferometer. The
combination of a super luminescent LED and a semiconductor optical amplifier was used as an optical source. Its output
power is about 10 mW and the spectral bandwidth is about 60 nm. The filtered light after passing thorough the Fabry-
Perot tunable filter has 0.15 nm instantaneous spectral linewidth with 1.3 mW average output power. The system with an
axial resolution of 12 μm performed OCT imaging of a cornea of a rat eye proving potential about the application of the
proposed sweeping detector OCT.
There have been several technologies to enable high resolution cross-sectional images of biological tissues in optical coherence tomography (OCT) method. Optical frequency comb (OFC) source has been proposed to overcome the crosstalk problem among the CCD detector pixels of the continuous spectrum of light source. Recently, a passive-type OFC is demonstrated simply placing a Fabry-Perot interferometer filter right after the broadband light source, but it shows a high loss of output light power and limited tenability of channel spacing of multi-wavelength. In this work, we experimentally demonstrate a spectral comparison of a novel multi-wavelength source based on a fiber Sagnac interferometer. The channel spacing is flexibly tuned by the effective length control of polarization-maintaining fiber (PMF). The uniform and stable multi-wavelength spectral distribution is also helpful to obtain the higher sensitivity from the lower exposure intensity source to get a better quality spectral OCT image.