Polished Optical Fiber Research Articles

Hindering effect of the core-cladding interface in thermally poled optical fibers.

In this paper, the hindering effect of the core-cladding interface (CCI) in thermally poled optical fiber is investigated based on the two-dimensional charge dynamics model. The influence of the mobility of charge carriers at the CCI, and the mobility and concentration of charge carriers in the fiber core on the thermal poling process is presented. It is found that lower mobility of charge carriers at the CCI is responsible for the hindering effect of the CCI. The hindering effect of the CCI could either be enhanced by increasing the mobility and concentration of charge carriers in the fiber core or be overcome by decreasing the mobility and concentration of sodium ions in the fiber core, which could increase the χ(2) in propagation mode. The results provide theoretical insight into the underlying mechanism of the hindering effect and may find applications in thermal poling optical waveguides and multilayered structures.

Fiber optic polarization beam splitter using a reduced graphene oxide-based interlayer

A fiber-optic polarization beam splitter (PBS) incorporating reduced graphene oxide (rGO) as a metallic interlayer material is proposed and demonstrated. It is experimentally shown that the polarization beam splitting function can readily be obtained using a coupler structure with a thin rGO layer embedded between two side-polished fibers due to induced transverse magnetic (TM) surface waves. The rGO layer was prepared by a simple method of dielectric GO spraying and ultraviolet irradiation-based reduction. The polarization extinction ratio of our implemented PBS was measured to be 14.5dB at a wavelength of 1550nm for both through- and cross-port. Its operating bandwidth was shown to be at least 100nm (from 1500 to 1600nm), which was limited by the maximum tuning range of the input tunable laser used.

UV-Induced Absorption in All-Fiber Frequency Doublers: Characterization and Photobleaching

Periodic UV exposure of thermally poled optical fibers is usually used to produce efficient all-fiber frequency doublers based on second-order nonlinearity. To date, no data regarding UV-induced absorption in poled fibers have been reported. In this study, we measured this absorption and showed how it affects the conversion efficiency of second harmonic generation at wavelengths below ~800 nm. Color centers responsible for induced absorption in poled GeO2 -doped fibers were identified and photobleached by continuous-wave radiation at 532 nm. We demonstrated that photobleaching does not affect the value of nonlinearity but improves the conversion efficiency of all-fiber frequency doublers. The results obtained can be used to improve the efficiency of all-fiber second harmonic generation in the blue-green part of the spectrum.

Birefringent crystal-clad fiber-optic polarizer based on fused biconical taper

Birefringent crystal-clad fiber-optic polarizer based on fused biconical taper

Optical fiber with nanostructured cladding of TiO2 nanoparticles self-assembled onto a side polished fiber and its temperature sensing.

We demonstrated temperature sensing of a fiber with nanostructured cladding, which was constructed by titanium dioxide TiO2 nanoparticles self-assembled onto a side polished optical fiber (SPF). Significantly enhanced interaction between the propagating light and the TiO2 nanoparticles (TN) can be obtained via strong evanescent field of the SPF. The strong light-TN interaction results in temperature sensing with a maximum optical power variation of ~4dB in SPF experimentally for an external environment temperature varying from -7.8°C to 77.6°C. The novel temperature sensing device shows a linear correlation coefficient of better than 99.4%, and a sensitivity of ~0.044 dB/°C. The TN-based all-fiber-optic temperature sensing characteristics was successfully demonstrated, and it is compatible with fiber-optic interconnections and high potential in photonics applications.

Automated quality control DFB laser-diodes based system for single-mode fiber-optic devices polarization dependent loss measurements

This article describes the development of an automated quality control polarization-dependent loss (PDL) measurement system which incorporates 978nm, 1310nm and 1550nm DFB (distributed feedback laser) lasers and two internal fiber optic standards for monitoring the system stability and drift overtime. PDL measurements collected with the system for a WDM (wavelength division multiplexer) is presented. The system PDL measurements repeatability is <±0.023dB and the % CV (coefficient of variance) is <±24%.

Enhanced photo-H₂ production by unsaturated flow condition in continuous culture.

A biofilm photobioreactor under unsaturated flow condition (BFPBR-U) is proposed using a polished optical fiber as the internal light source for photo-H2 production in continuous culture. The main chamber was filled with spherical glass beads to create the reaction bed and the cells were immobilized to form a biofilm under unsaturated flow condition obtained by pumping substrate solution over a packing bed at a rate to create a thin fluid film and injecting the argon to maintain the gas phase space. The effects of operational conditions, including flow rate and influent substrate concentration, on the photo-H2 production performance were investigated. The unsaturated flow conditions eliminated the inhibition caused by high organic loading rate and enhanced light transmission efficiency, leading to an improvement in the photo-H2 production performance.

Fiber-optic polarization diversity detection for rotary probe optical coherence tomography

We report a polarization diversity detection scheme for optical coherence tomography with a new, custom, miniaturized fiber coupler with single mode (SM) fiber inputs and polarization maintaining (PM) fiber outputs. The SM fiber inputs obviate matching the optical lengths of the X and Y OCT polarization channels prior to interference and the PM fiber outputs ensure defined X and Y axes after interference. Advantages for this scheme include easier alignment, lower cost, and easier miniaturization compared to designs with free-space bulk optical components. We demonstrate the utility of the detection system to mitigate the effects of rapidly changing polarization states when imaging with rotating fiber optic probes in Intralipid suspension and during in vivo imaging of human airways.

带输入、输出端口的双芯光纤偏振分束器研究

带输入、输出端口的双芯光纤偏振分束器研究

Quasi-phase-matched second-harmonic generation in thermally poled twin-hole silica-glass optical fiber by mercury-lamp exposure

Second-harmonic generation (SHG) from a twin-hole fiber by thermal poling was studied. Quasi-phase-matching (QPM) was performed with a low-pressure mercury lamp. Erasure of the second-order nonlinearity was studied by uniform exposure, and after that QPM was performed using a photomask erasing the nonlinearity periodically. SHG was measured with a Q-switched Nd3+:YAG laser. The second-harmonic power increased by a factor of 7 after QPM. A ray-tracing analysis on the light distribution of the lamp after the photomask was performed, and the effect on QPM is discussed. A model for the second-order nonlinearity by charge layers is also discussed.

MEMS Fabry-Perot sensor interrogated by optical system-on-a-chip for simultaneous pressure and temperature sensing

We present a micro-electro-mechanical systems (MEMS) based Fabry-Perot (FP) sensor along with an optical system-on-a-chip (SOC) interrogator for simultaneous pressure and temperature sensing. The sensor employs a simple structure with an air-backed silicon membrane cross-axially bonded to a 45° polished optical fiber. This structure renders two cascaded FP cavities, enabling simultaneous pressure and temperature sensing in close proximity along the optical axis. The optical SOC consists of a broadband source, a MEMS FP tunable filter, a photodetector, and the supporting circuitry, serving as a miniature spectrometer for retrieving the two FP cavity lengths. Within the measured pressure and temperature ranges, experimental results demonstrate that the sensor exhibits a good linear response to external pressure and temperature changes.

Fiber-optic polarization interferometer with an additional phase modulation for electric field measurements

A fiber-optic polarization interferometer with two electrooptic elements (sensor and additional modulator) designed for measuring electric field intensity is suggested and analyzed. The paper focuses on the theoretical and experimental demonstration of the principles of operation of fiber-optic circuits that generate and process the optical signals and provide measurement. The advantage offered by our interferometer is that it allows, in contrast to conventional configurations, additional modulation of the phase difference between interfering waves by a modulator in the instrumental part of the device and the use of available methods of phase detection developed for fiber-optic interferometric sensors. A laboratory prototype has been successfully tested.

A 2-Axis Optical Force–Torque Fingertip Sensor for Dexterous Grasping Using Linear Polarizers

This paper presents a two-axis force/torque sensor (one force and one torque) that uses light-intensity modulation techniques to measure the contact force and torque between a robotic finger and an object. The sensor has a diameter of 9 × 10-3 m and a height of 10 × 10-3 m. The sensor incorporates linearly aligned fiber-optic cables, linear polarizers, and nitinol wire strips into a rigid structure made of plastic. The nitinol wire strips allow certain parts of the structure to deform under applied forces. A model of the sensor is presented, and calibration experiments were conducted, validating the model. The sensor was also incorporated into the fingertip of a Barrett Hand, and experiments were conducted on three objects, i.e., a power adapter, a partially filled plastic bottle, and a curved paper punch to identify the sensor's response to different surface profiles. The sensor's data are also compared with data from a Nano17 force and torque sensor, and the results from the two sensors are discussed.

Poincare Sphere Method in the Analysis of Fiber Polarization Mode Dispersion

With the continuous improvement of the optical fiber communication rate, polarization mode dispersion (PMD: Polarization mode dispersion) is gradually depth. PMD will cause the light pulse signal wide during transmission, and in the signal transmission process continuous accumulation, damage to the transmission performance of the system, limit the system's transmission rate and transmission distance, PMD began to be the main obstacle which constrained optical fiber communication system upgrade and further development. PMD is a random value and difficult to calculate and test in the actual optical fiber communication systems. Poincare method is intuitive, easy to understand, easy measurement to study the characteristics of the PMD, and avoid a lot of tedious calculations. In the paper, analysis the single-mode fiber and its PMD, and the polarization state transmission process of polarization maintaining fiber and its nonlinear effects using the Poincare method, and simulate PMD characteristics by using Matlab software. Based on these, introduce the measurement principle of an improved Poincare method. Analysis showed that the Poincare sphere is a unique method in the analysis of fiber-optic polarization state transmission. Poincare method for the study of polarization mode dispersion has become an important direction of today's communications field.

OFS research over the last 10 years at CQU &amp; UESTC

This article reviews my new optical fiber sensing (OFS) research activities in China for the last ten years at Chongqing University and University of Electronic Science and Technology of China, since I returned from UK in 1999. The research progress in long period fiber gratings (LPFGs), distributed fiber sensing systems and microfiber sensors is introduced. For LPFGs, the processing method with high-frequency CO2 laser pulses types of LPFGs fabricated and the related applications for both optical sensing and optical communication are described. For distributed fiber sensing systems, the fiber-optic polarization optical time domain reflectometer (POTDR), fiber-optic phase-sensitive optical time domain reflectometer (Φ-OTDR) and Brillouin optical time-domain analyzer (BOTDA) are developed, respectively. For microfiber sensors, we mainly focus on the knot resonator and its application for sensing of the refractive index and acceleration, etc.

Artificially disordered birefringent optical fibers

We develop and experimentally verify a theory of evolution of polarization in artificially-disordered multi-mode optical fibers. Starting with a microscopic model of photo-induced index change, we obtain the first and second order statistics of the dielectric tensor in a Ge-doped fiber, where a volume disorder is intentionally inscribed via UV radiation transmitted through a diffuser. A hybrid coupled-power & coupled-mode theory is developed to describe the transient process of de-polarization of light launched into such a fiber. After certain characteristic distance, the power is predicted to be equally distributed over all co-propagating modes of the fiber regardless of their polarization. Polarization-resolved experiments, confirm the predicted evolution of the state of polarization. Complete mode mixing in a segment of fiber as short as ∼ 10cm after 3.6dB insertion loss is experimentally observed. Equal excitation of all modes in such a multi-mode fiber creates the conditions to maximize the information capacity of the system under e.g. multiple-input-multiple-output (MIMO) transmission setup.

Differential Rayleigh scattering method for measurement of polarization and intermodal beat length in optical waveguides and fibers

We propose a modification of the Rayleigh scattering method, which allows for measurement of polarization and intermodal beat length in single-mode and few-mode channel waveguides and optical fibers. A significant sensitivity increase is achieved by taking two high-resolution photographs in oblique scattered light of π-shifted intensity distributions produced by interference of polarization or spatial modes and applying Fourier analysis to the differential image. In the case of polarization beat length measurements, the π-phase shift is obtained by switching the polarization state at the fiber input, while in intermodal measurements, the π-phase shifting is realized by changing the excitation conditions. The usefulness of the method for characterization of channel waveguides and optical fibers is demonstrated in several examples. Moreover, we show that the combination of the spectral interferometry method with the proposed method allows for broadband measurements of differential phase and group effective indices.

Fiber Temperature Sensor Based on Micro-mechanical Membranes and Optical Interference Structure

A novel fiber temperature sensor is presented theoretically and experimentally in this paper. Its working principle is based on Optical Fabry-Perot interference structure that is formed between a polished optical fiber end and micro-mechanical Bi-layered membranes. When ambient temperature is varying, Bi-layered membranes will be deflected and the length of Fabry-Perot cavity will be changed correspondingly. By detecting the reflecting optical intensity from the Fabry-Perot cavity, the ambient temperature can be measured. Using finite element software ANSYS, the sensor structure was optimized based on optical Interference theory and Bi-layered membranes thermal expansion theory, and theoretical characteristics was simulated by computer software. In the end, using optical fiber 2×2 coupler and photo-electrical detector, the fabricated sample sensor was tested successfully by experiment that demonstrating above theoretical analysis and simulation results. This sensor has some favorable features, such as: micro size owing to its micro-mechanical structure, high sensitivity owing to its working Fabry-Perot interference cavity structure, and optical integration character by using optical fiber techniques.

측면 연마 광섬유를 이용한 휘발성 유기 화합물 가스센서

In this study, a novel gas sensor based on evanescent field coupling between single mode side polished fiber and solvatochromic dye dispersed polymer waveguide was demonstrated. We fabricated a side polished optical fiber device as a volatile organic compounds gas detector. Solvatochromic dye was coated on the top of the side polished optical fiber to take advantage of evanescent field coupling. The solvatochromism can be defined as the phenomenon whereby a compound changes color, either by a change in the absorption or emission spectra of molecule, when reacted in different VOCs. The device reacted to polarity gases like a hexane, butane, xylene etc. The resonance wavelength was shifted by the xylene concentration which range was 0.1 ppm ~ 100 ppm. Also, the response with the concentration was lineer and the detection limit was 0.1 ppb.

Investigation on all-optical regeneration of asynchronous dual-wavelength signals based on fiber-optic parametric amplification

With the continued development of the wavelength division multiplexing (WDM) network, there arises an urgent demand for the research of multi-wavelength all-optical 3R regeneration. In this paper, a novel multi-wavelength all-optical regeneration scheme has been proposed. Using phase clock in the fiber-optic parametric amplification and polarization multiplexing, all-optical regeneration of dual-wavelength signals generated by two independent WDM transmitter is realized. Theoretical analysis is carried out for the operation mechanism of the amplitude noise suppression using the gain saturation of the parametric amplification, and re-timing using phase modulation with cascading dispersion. Dual-wavelength 10 Gbit/s signal optical regeneration is demonstrated experimentally. Experimental results show that the inter-channel nonlinearities like four-wave mixing and cross phase modulation are effectively reduced. In the single and dual-wavelength cases, signal to noise ratio improvements of at least 6.5 dB and 4.5 dB have been achieved, respectively, after regeneration. Bit error rate test shows that about 2 dB power penalty improvement is obtained in both single- and dual-wavelength operations.