Significance: Selective retina therapy (SRT) selectively targets the retinal pigment epithelium (RPE) and reduces negative side effects by avoiding thermal damages of the adjacent photoreceptors, the neural retina, and the choroid. However, the selection of proper laser energy for the SRT is challenging because of ophthalmoscopically invisible lesions in the RPE and different melanin concentrations among patients or even regions within an eye.
Aim: We propose and demonstrate SRT monitoring based on speckle variance optical coherence tomography (svOCT) for dosimetry control.
Approach: M-scans, time-resolved sequence of A-scans, of ex vivo bovine retina irradiated by 1.7-μs duration laser pulses were obtained by a swept-source OCT. SvOCT images were calculated as interframe intensity variance of the sequence. Spatial and temporal temperature distributions in the retina were numerically calculated in a 2-D retinal model using COMSOL Multiphysics. Microscopic images of treated spots were obtained before and after removing the upper neural retinal layer to assess the damage in both RPE and neural layers.
Results: SvOCT images show abrupt speckle variance changes when the retina is irradiated by laser pulses. The svOCT intensities averaged in RPE and photoreceptor layers along the axial direction show sharp peaks corresponding to each laser pulse, and the peak values were proportional to the laser pulse energy. The calculated temperatures in the neural retina layer and RPE were linearly fitted to the svOCT peak values, and the temperature of each lesion was estimated based on the fitting. The estimated temperatures matched well with previously reported results.
Conclusion: We found a reliable correlation between the svOCT peak values and the degree of retinal lesion formation, which can be used for selecting proper laser energy during SRT.
We report on development of optical parametric oscillator (OPO) based mid-infrared laser system, which utilizes periodically poled nonlinear crystal that was pumped by near-infrared (NIR) laser. We have obtained 8 W of mid-infrared average output at the injection current of 20A from a quasi-phase-matched OPO using external cavity configuration. The laser tissue ablation efficiency was investigated which is substantially affected by several parameters such as, optical fluence rate, wavelength of the laser source and the optical properties of target tissue. Wavelength and radiant exposure dependent tissue ablation dimension were quantified by using SD-OCT (spectral domain optical coherence tomography) and the ablation efficiency was compared to that of non-converted NIR- laser system.
We propose and demonstrate a highly sensitive micro-fluidic temperature sensor based on a two-core photonic crystal fiber (TCPCF). TCPCF has two cores of small asymmetry in sizes that serves as two arms in the inline Mach-Zehnder interferometer (MZI). Using manual gluing and subsequent infiltration technique, the cladding air holes near one core are selectively filled with polymer of high thermo-optic coefficient, which makes its core-mode effective index sensitive to temperature variation and induces large thermo-optic mismatch between the two cores. A high sensitivity of 1.595 nm/ oC is achieved in our experiment, which is almost 200 times improved from that of the sensor device before polymer infiltration process.
We experimentally demonstrate a novel all-fiber Sagnac loop hybrid interferometer (SLHI) based on a highlybirefringent photonic crystal fiber with two asymmetric cores. Two cores exhibit unique birefringence properties and the light launched into them propagates with negligible coupling. Fast Fourier transform analysis of the transmission spectrum shows six frequency peaks in the spatial domain due to multiple interferences comprising the intra-core and inter-core mode interferences characterized by the four-beam interference model. The device response is investigated under the application of torsion, strain and temperature by measuring the phase-shift responses of three fiber interferences in the SLHI. The device application in simultaneous multi-parameter measurement is also discussed.
We investigate the strain and temperature sensing characteristics of an inline hybrid Mach-Zehnder interferometer (HMZI) formed by splicing a short section of asymmetric twin-core photonic crystal fiber (ATC-PCF) between two single mode fibers. For fixed polarization state of input light, two cores due to their asymmetric construction strongly support the propagation of few dominant core-modes, specifically, a lowest-order, and a set of lowest- and higher-order core-modes, respectively; this leads to a unique phase difference between inter-core and intra-core mode fiber interferometers in our ATC-PCF based HMZI. Experimental results reveal that, among different orders of interferometers involved in the HMZI, the interferometer with higher-value of modal refractive index difference exhibit larger phase-shift sensitivity to the surrounding perturbations.
The studies on microstructured optical fibers (MOF) have drawn considerable interest and played an important role in
many applications. MOFs provide unique optical properties and controllable modal properties because of their
flexibilities on manipulation of the transmission spectrum and the waveguide dispersion properties. MOFs are especially
useful for optical sensing applications because the micro-structured air channels in MOF can host various types of
analytes such as liquids, gases, and chemical molecules. Recently, many studies have focused on the development of
MOF-based optical sensors for various gases and chemical molecules. We propose a compact, and highly sensitive
optical micro-cavity chemical sensor using microstructured fiber. The sensor probe is composed of a hollow optical fiber
and end cleaved microstructured fiber with a solid core. The interference spectrum resulting from the reflected light at
the silica and air interfaces changes when the micro-cavity is infiltrated with external chemical molecules. This structure
enables the direct detection of chemical molecules such as volatile organic compounds (VOCs) without the introduction
of any permeable material.
We propose and experimentally demonstrate a new chemical molecule sensing scheme using multi-wavelength fiber laser based on inter-core interference in twin-core photonic crystal fiber. In our proposed multi-wavelength fiber laser, two separated cores are integrated in a single photonic crystal fiber and surrounded by air channels. The anti-symmetrical super-modes participate in inter-core interference, which leads to the formation of twin-core photonic crystal fiber-based wavelength-selective comb filter. Most of the evanescent waves are localized in the 13 air channels around the two integrated cores, where light-matter interaction takes in place. The presence of chemical molecules in the air channels of TC-PCF leads to perturbation of the inter-core effective index difference between the two propagating core modes and the associated lasing wavelength shift.
This paper presents chemical vapor sensing properties of twin-core photonic crystal fiber-based in-reflection
interferometer. The interferometer is composed of end-cleaved twin-core photonic crystal fiber (TC-PCF) and fiber
circulator. Infiltrating chemical molecules in the air holes of TC-PCF lead to change in inter-core effective index
difference and associated fringe shift in the interferometer. As an example we demonstrate acetone vapor detection and
discuss the potential applications of the proposed device.
We fabricated asymmetric two-core photonic crystal fiber (AS-TC-PCF) and observed the temperature and strain
responses of the Michelson interferometer based on it. The asymmetric two cores induce optical path length difference
and produce polarization-dependent interference fringes. The temperature and strain sensitivities of the AS-TC-PCF
were measured using the interference fringe shift. With increasing temperature, the interference fringes shifted to longer
wavelengths, and the temperature sensitivities were measured to be 5.06 pm/°C and 11.05 pm/°C, respectively, for
different polarizations. However, with increasing strain, the interference fringes shifted to shorter wavelengths, and the
strain sensitivities were measured to be -0.50 pm/με and -1.87 pm/με, respectively.
An inline Mach-Zehnder interferometer (MZI) is demonstrated using liquid filled twin-core photonic crystal fiber (TCPCF).
The TC-PCF is filled selectively with liquid ethanol, increasing the effective refractive index contrast between
twin cores, resulting in interference fringe spectrum with narrower free spectral range (FSR). Strain induced wavelength
shift of the interference fringes is experimentally monitored. Wavelength shifts to the shorter wavelength side with a
sensitivity of about -1.48 pm/με for applied strain change. Selectively liquid filled TC-PCF based MZI is simple to
fabricate and expected to have wide range of applications in optical sensors, multi-wavelength laser source and tunable
optical devices.
Multi-wavelength fiber lasers have attracted a lot of interest, recently, because of their potential applications in
wavelength-division-multiplexing (WDM) systems, optical fiber sensing, and fiber-optics instruments, due to their
numerous advantages such as multiple wavelength operation, low cost, and compatibility with the fiber optic systems.
Semiconductor optical amplifier (SOA)-based multi-wavelength fiber lasers exhibit stable operation because of the SOA
has the property of primarily inhomogeneous broadening and thus can support simultaneous oscillation of multiple lasing
wavelengths. In this letter, we propose and experimentally demonstrate a switchable multi-wavelength fiber laser
employing a semiconductor optical amplifier and twin-core photonic crystal fiber (TC-PCF) based in-line interferometer
comb filter. The fabricated two cores are not symmetric due to the associated fiber fabrication process such as nonuniform
heat gradient in furnace and asymmetric microstructure expansion during the gas pressurization which results in
different silica strut thickness and core size. The induced asymmetry between two cores considerably alters the linear
power transfer, by seriously reducing it. These nominal twin cores form effective two optical paths and associated
effective refractive index difference. The in-fiber comb filter is effectively constructed by splicing a section of TC-PCF
between two single mode fibers (SMFs). The proposed laser can be designed to operate in stable multi-wavelength lasing
states by adjusting the states of the polarization controller (PC). The lasing modes are switched by varying the state of
PC and the change is reversible. In addition, we demonstrate a tunable multi-wavelength fiber laser operation by
applying temperature changes to TC-PCF in the multi-channel filter.
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