• Journal of the Korean Institute of Telematics and Electronics
• /
• v.27 no.4
• /
• pp.604-611
• /
• 1990

One of the confronting problems in using optical fibers under radiation environments is producing of color centers in optical materials due to nuclear radiation. These centers increase transmission loss by absorbing propagating light. In this study, the radiation effects on optical fiber are studied theoretically. Also, optical attenuation induced by \ulcorner-ray irradiation from Co**60 for single mode and multimode optical fibers is measured at the optical wavelength of 0.85\ulcorner and 1.3\ulcorner, and the results are analyzed. Gammaray is irradiated for 5hours at the rate of 300rads/min, which is corresponding to 90 krads of integrated dose. In case of multimode optical fibers, the induced loss at 0.85\ulcorner wavelength has been twice higher than that at 1.3\ulcorner. The loss in multimode fibers has been significantly larger by 7-20 times than that in single mode fibers, dependently on fiber materials at 1.3\ulcorner.

• Journal of the Optical Society of Korea
• /
• v.13 no.2
• /
• pp.234-239
• /
• 2009

This paper presents a theoretical and experimental investigation of the transmission and sensing characteristics of the biconically tapered cladded multimode fibers. The beam propagation method was used to examine the transmission characteristics with various structural parameters. The results show that the transmission of the biconically tapered cladded multimode fibers is sensitive to the mode of the input optical beam and the refractive index of the external medium. A refractive index sensor for the external medium was proposed based on the theoretical analysis, and its feasibility was demonstrated experimentally.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.27 no.12
• /
• pp.1900-1905
• /
• 1990

In this study, the thermal neutron effects on optical fiber are examined theoretically. Also, the induced loss by thermal neutron irradiation in optical fibers is measured at the optical wavelengths of 0.85 and 1.3\ulcorner, respectively, and the results are analyzed. Thermal neutrons cause nuclear reaction with fiber compositions. So secondary ionizing radiations of high energy are generated. Color centers formed by these secondary ionizing rasiations increase transmission loss of optical fiber by absorbing propagating light in fiber core. As a result of experiment, owing to Ge, P, and B doping effects, the induced loss in multimode fibers has been 5 tmes larger than that in single mode fibers at 1.3 \ulcorner wavelengh. In case of multimode fibers, the loss at 0.8 \ulcorner wavelength region more suceptible for radiations has been twice higher than at 1.3\ulcorner.

• Journal of the Optical Society of Korea
• /
• v.18 no.1
• /
• pp.15-22
• /
• 2014

We present a novel bandwidth measurement scheme for multimode optical fibers. Amplified spontaneous emission (ASE) radiation was utilized for a source of intrinsically modulated light with a wide modulation bandwidth. In our measurement scheme, the continuous-wave (CW) ASE light that passed through a multimode fiber (MMF) under test was analyzed by the fourth-order power with a high-speed photodetector and an electric spectrum analyzer. The modulation transfer function of the multimode fiber could be directly measured with the photoelectric spectra in the modulation frequency domain. The measurement result of our method was experimentally compared to that of the conventional measurement scheme based on the impulse response measurement. It has been found that our scheme provides a stable measurement means of MMF characterization that is suitable for the field testing due to the simplicity of the system.

• 제어로봇시스템학회:학술대회논문집
• /
• 2004.08a
• /
• pp.484-487
• /
• 2004

Symmetric directional couplers are widely used in interferometers, switches, and various signal processing devices. Recently, several optical couplers using multimode fibers were reported, but these suffer from inefficient coupling of light into a branching fiber and/or low directivity. This paper presents the measurement and analysis of loss in the connection of optical fibers via the optical directional couplers. The functionality of the device is based on the principle that is symmetrical, the power in excited mode can be unambiguously directed into one of the output channel by varying and of its parameters. In this experiment, we measure the power of loss in the optical directional coupler at various radius of curvature. Before the measurement of loss in x-coupler, we polish the contact of the fiber surface in order that light can penetrate through another port. The results show that, when the radius of curvature is increased, the loss power is decreased and also approaches of the straight line case.

• Journal of information and communication convergence engineering
• /
• v.14 no.3
• /
• pp.163-170
• /
• 2016

Because of rapid technological advancements, increased data rate support has become the key criterion for future communication medium selection. Multimode optical fibers and multicore optical fibers are well matched to high data rate throughput requirements because of their tendency to support multiple modes through one core at a time, which results in higher data rates. Using the numerical mode solver OptiFiber, we have designed a concentric core fiber by investigating certain design parameters, namely core diameter (µm), wavelength (nm), and refractive index profile, and as a result, the number of channels, material losses, bending losses, polarization mode dispersion, and the effective nonlinear refractive index have been determined. Space division multiplexing is a promising future technology that uses few-mode fibers in parallel to form a multicore fiber. The experimental tests are conducted using the standard second window wavelength of 1,550 nm and simulated results are presented.

• Proceedings of the KIEE Conference
• /
• 1986.07a
• /
• pp.599-603
• /
• 1986

• Journal of Sensor Science and Technology
• /
• v.11 no.5
• /
• pp.273-278
• /
• 2002

An intrusion-sensitive capability of multimode graded-index (GRIN) optical fibers under bending has been investigated. In this system, the data light is transmitted in the fundamental mode while alarm monitor light is launched in a high-order mode at the same time. An attempted intrusion to drain data by bending the fiber results in greater attenuation of a monitor signal in higher order modes, thereby setting off an alarm at the receiver. Light propagation in a multimode graded-index fiber is also analyzed theoretically when the fundamental mode is selectively excited and the fiber is bent around a constant radius mandrel. The bending generates coupling between the various modes of the fiber. Power transitions of the fundamental mode by changing the bending radius were also analyzed numerically using program simulation. It is shown that Asawa-Taylor model[4] is valid up to 1cm of the radius of curvature of the fiber bend.

• Korean Journal of Optics and Photonics
• /
• v.4 no.4
• /
• pp.420-427
• /
• 1993

Dielectric thin film mirrors are embedded in multimode and single-mode fibers by a fusion splicing technique. The fibers with $45{\circ}$ angled embedded mirrors serve as ultra-compact directional couplers with low excess optical loss of 0.2 dB for multimode and 0.5 dB for single mode at 1.3 ${\mu}m$ and excellent mechanical properties. The reflectance is wavelength dependent and strongly polarization depencient. Far-field scans of the reflected output power measured with a white-light source show a pattern which is almost circularly symmetric with aspect ratio of 1.09 at 5% of the peak power. The splitting ratio in a multimode coupler measured with a diode laser source is much less dependent on input coupling conditions than in conventional fused biconical-taper couplers, indicating that these couplers are less susceptible to modal noise occuring in optical fiber communication systems. Spectral properties of multilayer internal mirrors normal to the fiber axis have been investigated experimentally, and a matrix analysis has been used to explain the results.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2003.04a
• /
• pp.388-399
• /
• 2003

Light losses in optical fibers are investigated by a fiber optic OTDR (Optical Time Domain Reflectometry) sensor system to develop fiber optic probes for structural strain measurement. The sensing fibers are manufactured 3 kinds of fibers: one is single mode fiber, and second is multimode fiber, and the third is low-cladding-index fiber. Fiber bending tests are performed to determine the strain sensitivity according to the strain of gage length of optical fibers. In the result of this experiments, the strain sensitivity of the single mode fiber was shown the highest value than others. The fiber optic strain probe was manufactured to verify the feasibility of the structural strain measurement. In this test, the fiber optic strain probe of the OTDR sensor could be easily made by the single mode fiber.