Diameter Multimode Fiber Research Articles

Fabrication of PANI/GO/Pd nanocomposite based tapered optical fiber for hydrogen gas sensing applications

Hydrogen (H2) is viewed as a promising solution for future energy demands because of its effectiveness, widespread availability, environmentally friendly properties, and sustainability. The study focuses on developing and evaluating H2 gas sensors based on optical fiber coated with nanocomposites such as polyaniline (PANI), graphene oxide (GO), and palladium (Pd) as sensing layers. An optical transducing channel was developed using a 125 μm diameter multimode optical fiber to improve the light field. The optical fiber was reduced to 20 μm and coated with the PANI/GO/Pd nanocomposite using drop casting. The proposed optical fiber sensor achieved a sensitivity of 9.79/vol%. The response and recovery time were calculated at room temperature and found to be 60 and 190 s, respectively. Overall, the developed optical fiber sensor shows high stability and excellent selectivity to H2 gas when compare to other gases such as NH3 and CH4.

Kilowatt level Raman amplifier based on 100 µm core diameter multimode GRIN fiber with M2 = 1.6.

In this Letter, we demonstrate a high-power Raman fiber amplifier with excellent beam quality based on graded-index fiber. The Yb-doped fiber laser (YDFL) and bandwidth-tunable amplified spontaneous emission (ASE) source are employed as the pump source to compare the laser performance separately. When the ASE with a bandwidth of 8 nm is employed, a maximum power of 943 W at 1130 nm is achieved, which is twice that pumped by YDFL. The beam quality factor M2 at maximum output power is 1.6, with a brightness enhancement (BE) factor of 27. To the best of our knowledge, this is the best beam quality and BE factor based on pure Raman gain with output power of over 100 W.

Photoacoustic tomography for imaging the prostate: a transurethral illumination probe design and application

In vivo imaging of prostate cancer with photoacoustic tomography is currently limited by the lack of sufficient local fluence for deep tissue penetration and the risk of over-irradiation near the laser-tissue contact surface. We propose the design of a transurethral illumination probe that addresses those limitations. A high energy of 50 mJ/pulse is coupled into a 1000-µm-core diameter multimode fiber. A 2 cm diffusing end is fabricated, which delivers light in radial illumination. The radial illumination is then reflected and reshaped by a parabolic cylindrical mirror to obtain nearly parallel side illumination with a doubled fluence. The fiber assembly is housed in a 25 Fr cystoscope sheath to provide protection of the fiber and maintain a minimal laser-tissue contact distance of 5 mm. A large laser-tissue contact surface area of 4 cm2 is obtained and the fluence on the tissue surface is kept below the maximum permissible exposure. By imaging a prostate mimicking phantom, a penetration depth of 3.5 cm at 10 mJ/cm2 fluence and 700 nm wavelength is demonstrated. The results indicate that photoacoustic tomography with the proposed transurethral probe has the potential to image the entire prostate while satisfying the fluence maximum permissible exposure and delivering a high power to the tissue.

Double-Loop Wavefront Tilt Correction for Free-Space Quantum Key Distribution

Both free-space and optical fiber quantum key distribution (QKD) links will coexist in future quantum networks, requiring efficient coupling between both types of channels. However, wavefront distortions introduced by the atmospheric channel can severely affect this efficiency. Active mechanisms such as precise beam tracking or steering can correct for some of these wavefront distortions, considerably improving the signal-to-noise ratio of the received quantum signal in many scenarios. A tracking system that uses two, instead oftypically one, controlling loops for tilt correction, stabilizes the beam in the whole optical axis of the receiver relaxing the restrictions of the receiver's optical design, and reduces the area of beam fluctuations in the receiver's focal plane a 24% more than a single-loop configuration. The tracking system was characterized in a QKD system at a 300 meter-link in moderate to strong turbulent conditions (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> - 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-14</sup> - 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2/3</sup> ) and an improved coupling efficiency of a factor of 2.1 and 1.6 was obtained for a 9.5 μm-core diameter standard telecommunications Single Mode Fiber (SMF) and a 25 μm-core diameter multimode fiber (MMF), respectively. This reduces the quantum bit error rate (QBER) caused by solar background photons in a 52 % for the former and 39% for the latter, enabling an increase in the secret key rate ofmore than one order ofmagnitude for SMF and a factor of five for MMF. These results are promising for enabling QKD free-space links and their interconnection to fiber optic infrastructure in realistic scenarios of communication networks of high turbulence regimes and daylight conditions.

Ultraminiature optical design for multispectral fluorescence imaging endoscopes.

A miniature wide-field multispectral endoscopic imaging system was developed enabling reflectance and fluorescence imaging over a broad wavelength range. At 0.8-mm diameter, the endoscope can be utilized for natural orifice imaging in small lumens such as the fallopian tubes. Five lasers from 250 to 642 nm are coupled into a 125 - ? m diameter multimode fiber and transmitted to the endoscope distal tip for illumination. Ultraviolet and blue wavelengths excite endogenous fluorophores, which can provide differential fluorescence emission images for health and disease. Visible wavelengths provide reflectance images that can be combined for pseudo-white-light imaging and navigation. Imaging is performed by a 300 - ? m diameter three-element lens system connected to a 3000-element fiber. The lens system was designed for a 70-deg full field of view, working distance from 3 mm to infinity, and 40% contrast at the Nyquist cutoff of the fiber bundle. Measured performance characteristics are near design goals. The endoscope was utilized to obtain example monochromatic, pseudo-white-light, and composite fluorescence images of phantoms and porcine reproductive tract. This work shows the feasibility of packaging a highly capable multispectral fluorescence imaging system into a miniature endoscopic system that may have applications in early detection of cancer.

A Distributed Antenna System for Indoor Accurate WiFi Localization

Specific infrastructures are a key challenge for indoor geo-localization systems. In particular, an accurate narrowband localization technique using 802.11 g WiFi signals is proposed in this letter. The related system architecture is built on the basis of radio over fiber topology of distributed antennas systems that are increasingly deployed in buildings. In particular, the system proposed collects the microwave signals using remote and local access points linked by ${\hbox {62.5-}}\mu\hbox{m}$ core diameter multimode fibers and enables to determine the location transmitter with an accuracy of less than 6.4 cm.

Design and evaluation of a device for fast multispectral time-resolved fluorescence spectroscopy and imaging

The application of time-resolved fluorescence spectroscopy (TRFS) to in vivo tissue diagnosis requires a method for fast acquisition of fluorescence decay profiles in multiple spectral bands. This study focusses on development of a clinically compatible fiber-optic based multispectral TRFS (ms-TRFS) system together with validation of its accuracy and precision for fluorescence lifetime measurements. It also presents the expansion of this technique into an imaging spectroscopy method. A tandem array of dichroic beamsplitters and filters was used to record TRFS decay profiles at four distinct spectral bands where biological tissue typically presents fluorescence emission maxima, namely, 390, 452, 542, and 629 nm. Each emission channel was temporally separated by using transmission delays through 200 μm diameter multimode optical fibers of 1, 10, 19, and 28 m lengths. A Laguerre-expansion deconvolution algorithm was used to compensate for modal dispersion inherent to large diameter optical fibers and the finite bandwidth of detectors and digitizers. The system was found to be highly efficient and fast requiring a few nano-Joule of laser pulse energy and <1 ms per point measurement, respectively, for the detection of tissue autofluorescent components. Organic and biological chromophores with lifetimes that spanned a 0.8-7 ns range were used for system validation, and the measured lifetimes from the organic fluorophores deviated by less than 10% from values reported in the literature. Multi-spectral lifetime images of organic dye solutions contained in glass capillary tubes were recorded by raster scanning the single fiber probe in a 2D plane to validate the system as an imaging tool. The lifetime measurement variability was measured indicating that the system provides reproducible results with a standard deviation smaller than 50 ps. The ms-TRFS is a compact apparatus that makes possible the fast, accurate, and precise multispectral time-resolved fluorescence lifetime measurements of low quantum efficiency sub-nanosecond fluorophores.

A novel spectroscopic filter used in rotational Raman lidar for the temperature profiling

We perform the rotational Raman temperature measurements in the troposphere and lower stratosphere with high performance. Depending on the aerosol content and presence of clouds in the lower troposphere, the rotational Raman lidar (RRL) is the lidar technique of choice for temperature measurements. However, the Raman filter design is a technical difficulty in RRL systems. Considering the higher spectral resolution and compactness, we select several photonic crystals to construct a novel spectroscopic filter for extracting the required rotational Raman spectrum (RRS) signals of atmospheric molecules. We describe in detail the principle to design the photonic-crystal filter. To verify the feasibility of the novel spectroscopic filter, we carry out some numerical calculations, and our results show that the novel spectroscopic filter has the capability to fine draw the required RRS signal and suppress sufficiently elastic signals. For the RRL system which uses the novel spectroscopic filter, we obtain that a statistical temperature error is less than 1 K up to a height of 3.2 and 5.6 km for daytime and nighttime measurements, respectively. Our simulation conditions are as follows: 532 nm laser with 500 mJ energy, and 10 Hz pulse repeating rate, a 300 mm diameter Cassegrain reflecting telescope with 1000 mm focus length, 0.2 mm diameter multimode optical fiber which sets the field of view (FOV) of receiving system to 0.2 mrad, 45 m range resolution, 9 min observation time, overall optical-system efficiency of 0.6, and a special atmospheric model which integrates the US standard model of 1976 with an actual Mie scattering profile obtained from practical observations.

Subcarrier modulated transmission of 2.5 Gb/s over 300 m of 62.5-&amp;#x03BC;m-core diameter multimode fiber

We report for the first time the transmission of a 2.5-Gb/s SCM channel over a 300-m length of installed-grade 62.5-μm core-diameter multimode fiber. This result demonstrates that, in a "worst-case" scenario, subcarrier modulation can be successfully used to allow improved quality transmission over multimode fiber links compared with conventional baseband transmission techniques.

Novel MEMS pressure and temperature sensors fabricated on optical fibers

We present the fabrication and initial testing of novel optically interrogated pressure and temperature sensors fabricated directly on optical fibers using microelectromechanical systems (MEMS) technology. A new micromachining process for use on a flat fiber end face that includes photolithographic patterning, wet etching of a cavity and anodic bonding of a silicon diaphragm is utilized. Two prototype pressure sensors, fabricated on 400 μm diameter multimode fibers, have been tested displaying an approximately linear response to static pressure (14–80 psi). A prototype temperature sensor, fabricated by anodically bonding an ultra-thin crystalline silicon onto a fiber end face, has been tested in the range 25–300 °C. A minimum detectable temperature variation of 6 °C is observed. Since these sensors are significantly miniaturized, they will find application in situations where small size is advantageous and where dense arrays may be useful.

Fluorescent fiber-optic calcium sensor for physiological measurements.

A new optical sensor based on covalent immobilization of a newly synthesized calcium-selective, long-wavelength, fluorescent indicator has been constructed, with a response dynamic range optimal for physiological measurements. Immobilization occurs via photoinitiated copolymerization of the indicator with acrylamide on the distal end of a silanized 125 micrograms diameter multimode optical fiber. The working lifetime of this sensor is limited only by photobleaching of the indicator. Due to the inherent hydrophilic nature of the acrylamide polymer, the response time of this new sensor is governed by simple aqueous diffusion of the ionic calcium. This results in sensor response times fast enough to monitor some concentration fluctuations at physiological rates. The ability to monitor calcium concentration fluctuations in a high background level of magnesium is also demonstrated with a calculated selectivity of 10(-4.5).

System design methodology for power budgeting of 62.5 mu m multimode fiber systems

The authors present the data to support a recommendation of a new system loss budgeting rule applicable to high-component-count systems using 62.5 mu m core diameter multimode fiber. The limited phase space or restricted launch characterization of fiber is demonstrated again to give the most accurate system loss prediction. However, for this fiber size, components such as connectors, switches, and couplers are shown to exhibit loss equivalent to the overfilled launch loss. Two mechanisms are found to explain why the overfilled launch component loss best characterizes their actual loss in common multimode fiber systems. Both are related to the large numerical aperture (NA) of the power distribution launched by the light-emitting diode (LED) system sources. It is important to note that these mechanisms only have been observed on components made with 62.5 mu m multimode fiber. This behavior is likely to be different in other fiber sizes. >

Development of proposed federal standard 1070: 62.5/125-μm graded-index, multimode optical fiber waveguides for on-premises applications

Abstract This paper describes a process that has been successful in generating a specification to guide the user community in the procurement of single-size, multimode optical fiber for on-premises applications. This process began with an attempt to adopt an industry standard as a federal standard that would eliminate a multiplicity of choices available from the marketplace. The initial EIA-458-A Standard contained four “preferred” sizes. Discussions both in a government standards committee and in an applications-oriented industry (EIA) working group indicated the desirability of recommending a single fiber size. The process by which the industry committee selected the 62.5-μm core diameter/125-μm cladding diameter multimode fiber is presented. The next element of the process was that of selecting the appropriate standard performance measures and attributes that would assure minimum performance of graded parameters such as attenuation and bandwidth, as well as a uniform specification of the product. The v...