We developed a swept source laser using a micro electro mechanical systems(MEMS) scanner mirror, and demonstrated
optical coherence tomography. To enable both the wide tuning wavelength range and high scanning frequency, we
introduced 2-degree-of-freedom(2-DOF) MEMS scanner mirror. A tunable optical filter is composed of a MEMS
scanner mirror and a diffraction grating which is arranged in Littrow configuration. We built a swept source laser which
has a wavelength range of 143 nm, center wavelength of 1304 nm, and a peak power of 16 mW. OCT measurements are
performed at a rate of 17.9 kHz and doubled 35.9 kHz at unidirectional and bidirectional sweeps, respectively. The
system sensitivity is 101.5 dB.
A novel processing technique called Non-Harmonic Analysis (NHA) is proposed for high-resolution OCT imaging.
Conventional Fourier-Domain OCT relies on the FFT calculation which depends on the window function and length.
NHA can resolve high frequency without being influenced by window function or frame length of sampled data. The
results show that NHA process realizes practical image resolution equivalent to 100nm swept range by using significantly reduced wavelength range, and also implies the potential of high resolution imaging capability without the need of a broadband source.
This paper reports on a high-speed, wavelength-swept laser operating at 1310nm for optical coherence tomography
(OCT) applications. The simple and reliable laser comprises a pigtailed semiconductor optical amplifier (SOA) and a
wavelength-scanning filter in a fiber ring cavity configuration. The tunable filter consists of a diffraction grating and
polygon mirror scanner in Littrow configuration. A photodiode is used to generate a start trigger signal synchronized to
the start of each frequency sweep. Intracavity prisms plays important role to provide constant and narrow laser linewidth
and linear frequency sweep at the same time. The laser exhibits a peak power of over 20mW. The tuning range of the
laser is as wide as 120nm maximum, and 100nm FWHM at a scanning frequency of 20kHz. Coherence length was
measured to be 4mm. By utilizing a novel double pass configuration in the scanning filter an improvement in coherence
length to 7mm is also achieved. OCT system configured with the light source exhibits 106dB sensitivity and 12μm axial
resolution in imaging.
This paper reports on a wide-range, high-speed, wavelength-swept laser operating at 1310nm for optical coherence
tomography (OCT) applications. The laser comprises a pigtailed wideband, high-gain semiconductor optical amplifier
(SOA) and a wavelength-scanning filter in a fiber ring cavity configuration. The tunable filter consists of a diffraction
grating and polygon mirror scanner in Littrow configuration. A photodiode is used to generate a start trigger signal
synchronized to start of each frequency sweep. Intracavity prisms are aligned to provide constant and narrow laser
linewidth and linear frequency sweep. This arrangement also generates a wide tuning range for a given beam deflection
angle by the polygon scanner while maintaining narrow laser linewidth. The laser exhibits a peak power of 20mW. The
measured tuning range of the laser is 170nm maximum, with 160nm FWHM at a scanning frequency of 20kHz using a
single custom engineered SOA device. Laser output is coupled via HI1060 fiber with a cut-off wavelength of 980nm
ensuring single-mode propagation over the 1230nm to 1400 nm tuning range.
We propose an all-optical fiberscopic endoscope for medical diagnosis by using a MEMS optical scanner with the
wavelength-division multiplex approach. An infrared light of 1.3 microns was used for medical inspection through the
endoscope fiber, and it was scanned over the tissue of interest by using a MEMS scanning mirror. The mirror was
electrostatically operated not by using external voltage line but by co-located photovoltaic cell, which generated
operation voltage from another input light of 1.5-micron-wavelength. The entire sensor head (fiber, beam splitter,
photovoltaic cell, and MEMS chip) was encapsulated in a Pyrex glass tube of 5 mrn outer diameter. Drive voltage of 5
V was obtained by the optical modulation, and the MEMS scanner chip operated at 300 Hz resonance for optical scan
angle of 10 degrees. In this paper, we present the MEMS device structure, optical system, and preliminary imaging of
human skin tissue by the optical coherent tomography.
We demonstrate a high-speed tuneable, continuous wave laser source at 1550nm for Fourier domain OCT imaging. The light source was based on a pigtailed semiconductor optical amplifier and a diffraction grating and polygon mirror for fast frequency tuning. This source provides frequency scan rate of up to 20kHz over a wavelength range of 80nm (60nm FWHM) at the central wavelength of 1550nm, offering an axial resolution of ~17 microns.
A two- and three- dimensional swept source optical coherence tomography (SS-OCT) system which uses a ready-to-ship scanning light source is demonstrated. The light source has the center wavelength of 1.31 μm, the -3 dB wavelength range of 110 nm, the scanning rate of 20 KHz and high linearity of frequency scanning. A simple calibration method using a fringe analysis technique for spectral rescaling is presented. This SS-OCT is capable of realtime display of two-dimensional OCT, and can take three-dimensional OCT with the measurement time of 2 s. In vivo human anterior eye segments are investigated both two- and three- dimensionally. The system sensitivity is experimentally determined as 113 dB.
In this paper, we report a MEMS-variable attenuator (VOA) with unique SOI based electrostatic torsion mirror structure to realize simple fabrication process and low voltage, stable operation, as well as high production yield. In the proposed device, attenuation principle is a simple beam deflection method by using tilt mirror, which deflects the incoming optical beam, and thus changes coupling loss at the output fiber end with respect to the beam mode profile. The whole MEMS structure is made of silicon-on-insulator (SOI) wafer, where a shaped through-hole made by deep RIE (DRIE) under the half side of the rotational mirror suspended by torsion bars automatically defines the electrode on the opposite side with respect to the upper device silicon layer. A number of careful design tips are taken into account for high temperature stability and anti-shock/vibration performance. Fabrication process of the chip is also as simple as it is designed so that it only requires two DRIE processes and three photolithography steps. For the finished pigtail module, dual fiber with an aspherical collimator lens, and a CAN package with MEMS chip mounted inside are tightly welded by YAG laser in order to ensures both environmental reliability and operational stability. Driving voltage as low as 5V provides attenuation range over 45dB while maintaining anti-shock/vibration characteristics. Selective deposition of metal layer coating on the circular mirror section suppresses temperature dependent fluctuation less than 0.5dB at 20dB attenuation over 0 to 70degC range by decoupling bimorph effect of metal layer from the electrostatic operation.
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