Based on the analysis of the noise source in the optical coherence tomography (OCT) system, a fractional integral denoising algorithm is proposed to denoise the OCT image. The algorithm is simple and easy to implement, and the experiment is compared with the median filter and Wiener filter method. The results show that the algorithm can effectively preserve the important detail information in the OCT image while effectively removing the noise, so that the detail of the image is clear and the image quality can be improved, which indicates that the method can achieve the purpose of reducing the image noise.
In this study, we have demonstrated a wavelength-swept fiber laser based on an acousto-optic tunable filter(AOTF) as a selective element and a semiconductor optical amplifier(SOA) as a gain medium in an internal fiber ring cavity. The light deriving from one port of the SOA goes through an optical isolator, the AOTF, a fiber coupler and a polarized controller successively, then it goes back to the other port of the SOA to form a ring cavity. The laser output is from another port of the fiber coupler. The laser made by this method is mainly used for swept-source optical coherence tomography(SS-OCT). The application of the SOA provides a sufficiently broad range and can ensure an increased axial resolution of SS-OCT. AOTF offers a wide tuning range, high switching speed and stable operation against vibration for the non-mechanical structure. The proposed wavelength-swept fiber laser ensures a high axial resolution of tomographic images and has a stable laser output. We have discussed the influence of the SOA injection current to the tuning range of the laser. In the SOA injection current of 280 mA, a continuous wavelength tuning range from 1295 to 1370 nm centered at a wavelength of 1330nm is obtained at the sweep rate of 1.06 kHz, and the power of the swept source was 1.14 mW. In addition, for quantitative characterization of the wavelength-swept performance with a AOTF, we have theoretically and experimentally analyzed the influence of the following controllable parameters: injection current, output power and sweeping frequency.
The design and development of the swept laser for optical coherence tomography is presented. It is manifested by a semiconductor optical amplifier, a fiber coupler, two fiber isolators, a semiconductor optical amplifier (SOA) and an acousto-optic tunable filter (AOTF) for frequency tuning within a unidirectional all-fiber ring cavity. Light output from the coupler is further amplified and spectral shaped by a booster SOA terminated at both ends with two isolators. The total loss in ring cavity is 8.2 dB. The gain SOA provides fiber-to-fiber small signal gain of 22.2 dB with saturation output power of 9.0 dBm. The developed laser source provides up to 100 kHz over a full-width wavelength tuning range of 140 nm at center wavelength of 1308 nm with an average power of 8 mW, yielding an axial resolution of 5.4 μm in air for OCT imaging. Theoretically, the measurement principle and the feasibility of the system are analyzed. Implementing the laser source in swept source based OCT (SS-OCT) system, real-time structural imaging of biological tissue is realized.
An infrared endoscopic system has been developed to investigate thermal spread and
collateral damage during energized laparoscopic surgery, the system consists of an infrared endoscope
and a thermal camera (3-5 μm) with combined thermal sensitivity of 0.05°C. The system performance
was evaluated in live animals with electrosurgical devices to monitor intraoperative thermal changes.
During activation periods, the peak temperature of the jaws averaged 100.5 ± 5.8 ℃ with a thermal
spread of 3.0 ± 0.9 mm. For laparoscopic dissections of the esophagus-gastric junction with the 10 mm
Atlas, the maximum jaw temperature was 105.2 ± 2.1 ℃ with a bigger thermal spread of 11.5 ± 7.2
mm). The study has confirmed that infrared endoscopy is a very useful tool adjunct to conventional
endoscopy, which may improve the safety of energized laparoscopic dissections.
We demonstrate a novel ultra-broad tunable bandwidth and narrow instantaneous line-width swept laser source using combined tunable filters working at 1290 nm center wavelength for application in optical coherence tomography. The combined filters consist of a fiber Fabry-Perot tunable filter (FFP-TF) and a polygon mirror with scanning grating based filter. The FFP-TF has the narrow free spectral range (FSR) but ultra-high spectral resolution (narrow instantaneous bandwidth) driven at high frequency far from resonant frequency. The polygon filter in the Littrow configuration is composed of fiber collimator, polygon mirror driven by function generator, and diffractive grating with low groove. Polygon filter coarsely tunes with wide turning range and then FFP-TF finely tunes with narrow band-pass filtering. In contrast to traditional method using single tunable filter, the trade-off between bandwidth and instantaneous line-width is alleviated. The combined filters can realize ultra wide scan range and fairly narrow instantaneous bandwidth simultaneously. Two semiconductor optical amplifiers (SOA) in the parallel manner are used as the gain medium. The wide bandwidth could be obtained by these parallel SOAs to be suitable for sufficient wide range of the polygon filter’s FSR because each SOA generates its own spectrum independently. The proposed swept laser source provides an edge-to-edge scanning range of 180 nm covering 1220 to 1400 nm with instantaneous line-width of about 0.03 nm at sweeping rate of 23.3 kHz. The swept laser source with combined filters offers broadband tunable range with narrow instantaneous line-width, which especially benefits for high resolution and deep imaging depth optical frequency domain imaging.
The design and development of the miniaturized interferometer for measurement of the refractive index or concentration
of sub-microliter volume aqueous solution in microfludic chip is presented. It is manifested by a successful measurement
of the refractive index of sugar-water solution, by utilizing a laser diode for light source and the small robust
instrumentation for practical implementation. Theoretically, the measurement principle and the feasibility of the system
are analyzed. Experimental device is constructed with a diode laser, lens, two optical plate and a complementary metal
oxide semiconductor (CMOS). Through measuring the positional changes of the interference fringes, the refractive index
change are retrieved. A refractive index change of 10-4 is inferred from the measured image data. The entire system is
approximately the size of half and a deck of cards and can operate on battery power for long time.
A high speed swept source optical coherence tomography (SS-OCT) system capable of full-range imaging is presented. Wave-number carrier frequency is introduced into the spectral interference signal by a transmissive dispersive optical delay line (TDODL). High carrier frequency in the spectral interference signal corresponding to an equivalent distance-shift is exploited to obtain full-range OCT imaging. Theoretical development is conducted with the instantaneous coherence function introduced for a complete description of a spectral interference signal. Performance advantage of the TDODL-based method over the conventional approach where only one side (positive or negative path length difference) is used for imaging to avoid overlaying mirror artifacts is confirmed by the measured envelopes of spectral interference signal. Feasibility of the proposed method for full-range imaging is validated in a custom-built SS-OCT system by in vivo imaging of a biological sample.
A portable choroidal laser Doppler flowmeter (LDF) with enhanced sensitivity based on a scattering plate is developed. The portable LDF is weighted 2 kg operated at center wavelength of 780 nm, leading to a better penetration into the eye fundus in contrast to the previous LDF operated at center wavelength of 670 nm. Enhancement of number of detected photons that undergo Doppler scattering and improved measured speed of choroidal blood flow are achieved with the use of a scattering plate positioned in front of the eye. The mechanism of detection and sensitivity enhancement is theoretically analyzed. Evaluation of system performance is done by in vivo measurements on ten volunteers. The results demonstrate that an increased percentage of backscattering light at high Doppler shift frequency is collected due to utilization of the scattering plate. However, this kind of light detection influences spatial resolution of the system and decreases the total signal measured. The proposed method for detection and sensitivity enhancement might be useful in a case where the perception of very slight alternation of blood flow is pursued and the spatial resolution is not as critical as that in a choroidal vascular bed.
A high-speed linear wavelength-swept laser source working at center wavelength of 1309 nm is demonstrated.
Wavelength tuning is performed using a compact polygon filter in Littrow telescope-less configuration. The repetition
frequency of the wavelength-swept laser source is up to 50 kHz with the polygon scanned at a speed of 694 rotations per
second. The turning range is 130 nm and full width at half maximum (FWHM) is 61 nm. The average output power can
reach to 7 mW. The developed swept laser source can be implemented in optical frequency domain imaging, optical
reflectometry, and other test or measurement applications.
Optical coherence tomography (OCT) is an emerging cross-sectional imaging technology. It uses broadband light sources
to achieve axial image resolutions on a few microns scale. In this paper, the principle of Fourier domain mode-locked
(FDML) wavelength swept laser for swept source optical coherence tomography (SS-OCT) is presented and crucial
parameters of the laser system are discussed. On analysis of different methods and system configurations, a new
configuration of swept laser system is put forward. We theoretically demonstrate a high-speed, broad bandwidth, Fourier
domain mode-locked (FDML) wavelength swept laser around 1310 nm for high-resolution frequency domain optical
coherence tomography (FD-OCT). The laser has a fiber ring cavity with a semiconductor optical amplifier gain medium.
Intra-cavity mode selection is achieved with an in-fiber tunable fiber Fabry-Perot filter. The laser is designed to generate
32 kHz sweeping rate with a tuning range of 165 nm full width, 3 dB sweep range of 91 nm. In SS-OCT applications the
swept laser will achieve about 8.3 μm axial resolution in air and 5.9 μm axial resolution in biological tissue. The
instantaneous linewidth is 0.103 nm corresponding to a coherence length of several mm, enabling OCT imaging over a
large axial range. The swept laser implemented in the FD-OCT system can provide information of biological tissue
imaging in real time.