Fiber Loop Length Research Articles

Multivariable Analysis of Nonlinear Optical Loop Mirror Operating Parameters Using Jones Matrices and Three-Dimensional Renderings

Nonlinear optical loop mirrors (NOLMs) are used in modern fiber optic devices and optical communications. In this study, we present numerical analyses of the multiple variables involved in the operation of an NOLM in low- and high-power transmissions. The Jones matrix formalism was used to model linear and circular polarization inputs. We used three-dimensional (3D) plots to identify the characteristics required in the experimental operation of the NOLM. These characteristics, including the critical power, low- and high-power transmission, and dynamic range, depend on parameters such as the fiber loop length, input power, angle of retarder plate, and input polarization. A standard single-mode fiber (SMF-28) with high twist loop lengths of 100, 300, and 500 m and input powers of 0–100 W was simulated. Three-dimensional surface graphics provided a comprehensive view of the NOLM transmission and considerably enhanced the optimal transmission by manipulating adjustable device components including the power and polarization control plates. Optimal transmission facilitates its use in integrating ultrafast pulse generation, optical signal processing, optical communication systems, and photonic integrated circuit applications.

Study of Straight-Line-Type Sagnac Optical Fiber Acoustic Sensing System

A straight-line-type Sagnac optic fiber acoustic sensing system is proposed in this paper to adopt the application needs of no man’s plateau borderline for monitoring mechanical invasion. The Sagnac interference fiber loop is replaced by a straight-line fiber and a 1 × 2 coupler, and the length of the Sagnac interference fiber loop is shortened by close to 50%. The influences of delay fiber and sensing fiber on the sensing system are analyzed by theory calculation and simulation and the optimal lengths of delay fiber and sensing fiber were decided. The experiment system was set, and the sensing fiber was wound into titanium alloy cylinder to compose the sensing element. Experimental results show that the sensing system has a good response to 50−8000 Hz and 70 dB sinusoidal acoustical signals and can well distinguish the signals of different frequencies. Using a small-scale helicopter audio signal as the acoustical signal, the test results show that the response curve is consistent with the simulation results and the sensitivity reaches 30.67 mV/Pa.

A Precisely Frequency-Tunable Parity-Time-Symmetric Optoelectronic Oscillator

Mode selection is crucial for a stable single-mode oscillation of an optoelectronic oscillator (OEO). In this article a parity-time (PT)-symmetric frequency-tunable OEO is proposed and experimentally demonstrated, to realize the precise frequency tuning without using any narrowband filter. The proposed PT-symmetric OEO is implemented based on two identical optoelectronic hybrid loops mainly consisting of a shared dual-parallel Mach-Zehnder modulator (DPMZM) and a photodetector. The PT-symmetry condition can be achieved by enabling antisymmetric gain/loss in the two loops through manipulating the bias voltages of the two child-MZMs of DPMZM, and continuous frequency tunability is realized by adjusting the bias voltage of the parent-MZM. A theoretical model is developed for the proposed PT-symmetric OEO to analyze the dynamics of the PT-supermodes as the gain/loss coefficient changing. Furthermore, an experiment is performed. Without high-Q filter, stable single-mode oscillation of the PT-broken supermode at 4.2 GHz with side-mode suppression ratios of 60 and 50 dB is demonstrated in the OEO with 6 and 2000 m fiber loop lengths, respectively. The frequency tuning ranges are 1.4 MHz and 1.5 kHz for two OEOs with different fiber loop lengths.

Refractive Index Sensing Based on Chaotic Correlation Fiber Loop Ring Down System Using Tapered Fiber

A novel refractive index sensing using the tapered single mode fiber (TSMF) is proposed based on the chaotic correlation fiber loop ring down system (FLRDs). A chaotic fiber laser is used to drive the fiber loop cavity. The performance of the proposed TSMF chaotic correlation FLRDs refractive index sensing was demonstrated by measuring the ring down time of the peaks of correlation coefficient of the sensing system at different refractive index. The sensing demonstrates a good stability and repeatability. The influence of the change in fiber loop length on the sensing system was also investigated. The results show that the sensitivity of chaotic correlation FLRDs increases with the decrease of the loop length and the change of the loop length has little effect on the detection limit (DL) of the system. The DL of 10−4 RIU were achieved. Compared with the pulsed FLRDs, the chaotic correlation FLRDs significantly simplify the light source of sensing system and eliminate the trade-off problem between the length of fiber loop cavity and the light source, and makes fiber loop length more flexible.

All optical Millimeter-wave signal generation and transmission for radio over fiber (RoF) link

<span>Fiber-based wireless system has become a promising solution as a cost- effective communication and it offers high capacity network with millimeter- wave (mm-wave) signal transmission. The system significantly offers superior possible bandwidths for both fiber and free-space applications. Hence, with the increased capacity as well as wireless mobile network applications particularly at mm-wave signal, radio over fiber (RoF) technology is the utmost option. Nevertheless, when high frequency signal transmission is involved, power fading or dispersion effect limits the performance of RoF link. Therefore, this work proposed a RoF system by integrating remote optical local oscillator (LO) with frequency up-conversion at the base station (BS). All optical mm-wave signals are generated and transmitted for the RoF link. The effects of the changes of fiber loop length, optical power of the continuous wave (CW) optical laser carrier and responsivity value of the p-i-n photodiode (PD) mainly at 40 GHz are investigated and the power fading effects are discussed.</span>

RF Up-Conversion and Waveform Generation Using a Frequency-Shifting Amplifying Fiber Loop, Application to Doppler Velocimetry

We investigate the radio-frequency (RF) up-conversion and waveform generation properties of an optical fiber loop including a frequency shifter and an amplifier. By seeding the loop with a single-frequency continuous-wave laser, one can develop a wide optically carried RF comb, whose spectral extension is governed by the loop net gain. In addition, by choosing the fiber loop length and the RF shifting frequency, arbitrary waveforms can be generated. We present an analytical interference model that includes the time delay, the frequency shift, and the gain. Experiments are conducted with 1.06-μm fiber-optic components. Using a 200-MHz acousto-optic frequency shifter, we find a 19-fold up-conversion up to 3.8 GHz with a typical in-loop gain of 3. Various waveforms including bright and dark pulses, square- or triangle shaped are achieved by properly adjusting the loop length and the frequency shift. A good agreement between experimental and theoretical results is obtained. The fully fibered microwave-photonic source is applied to a laboratory Doppler velocimetry demonstration. The gain in sensitivity obtained with the up-converted signal is readily observed.

Implementing BosonSampling with time-bin encoding: Analysis of loss, mode mismatch, and time jitter

It was recently shown by Motes, Gilchrist, Dowling & Rohde [PRL 113, 120501 (2014)] that a time-bin encoded fiber-loop architecture can implement an arbitrary passive linear optics transformation. This was shown in the case of an ideal scheme whereby the architecture has no sources of error. In any realistic implementation, however, physical errors are present, which corrupt the output of the transformation. We investigate the dominant sources of error in this architecture --- loss and mode-mismatch --- and consider how it affects the BosonSampling protocol, a key application for passive linear optics. For our loss analysis we consider two major components that contribute to loss --- fiber and switches --- and calculate how this affects the success probability and fidelity of the device. Interestingly, we find that errors due to loss are not uniform (unique to time-bin encoding), which asymmetrically biases the implemented unitary. Thus, loss necessarily limits the class of unitaries that may be implemented, and therefore future implementations must prioritise minimising loss rates if arbitrary unitaries are to be implemented. Our formalism for mode-mismatch is generlized to account for various phenomenon that may cause mode-mismatch, but we focus on two --- errors in fiber-loop lengths, and time-jitter of the photon source. These results provide a guideline for how well future experimental implementations might perform in light of these error mechanisms.

A Self-Synchronized Optoelectronic Oscillator Based on an RTD Photodetector and a Laser Diode

We propose and demonstrate a simple and stable low-phase noise optoelectronic oscillator (OEO) that uses a laser diode, an optical fiber delay line and a resonant tunneling diode (RTD) free-running oscillator that is monolithic integrated with a waveguide photo-detector. The RTD-OEO exhibits single-side band phase noise power below -100 dBc/Hz with more than 30 dB noise suppression at 10 kHz from the center free-running frequency for fiber loop lengths around 1.2 km. The oscillator power consumption is below 0.55 W, and can be controlled either by the injected optical power or the fiber delay line. The RTD-OEO stability is achieved without using other high-speed optical/optoelectronic components and amplification.

Response characteristic analysis of polarization maintaining fiber ring resonator with dual-coupler for sensing application

A polarization maintaining fiber ring resonator with dual-coupler (PMDC-FRR) for sensing application is presented in this paper. Polarization maintaining directional fiber couplers and fiber loop are employed to eliminate the polarization fading in the fiber ring resonator. Three important characteristic parameters associated with the sensing application, which are the visibility of the output intensities, the free spectral range and the finesse, are discussed as functions of the coupler coefficients and the fiber loop length in detail. In addition, the critical drive voltage of the tunable laser to keep the output intensities stable is also analyzed, when the fiber ring resonator with dual-coupler is utilized as fiber sensor with phase modulation. A PMDC-FRR is designed practically in experiment with the power coupling coefficients of 0.5 and the loop length of 22 m. The experimental results provide sufficient arguments for the theoretical predicts. The theoretical and experimental analysis results will be useful to the sensing application of the PMDC-FRR.

니트소재의 영상정보 제시 방법에 따른 주관적 질감 비교

The purpose of this study is to compare the subjective texture of actual objects and their picture images on the Internet to find out a method to present visual images in order to supply information similar real objects. For this study, seven knit fabrics and four presentation methods of visual images including twice magnifications and two dimensions of 2D and 3D. The results of this study were as follows: There are significant differences among subjective textures evaluated by touching seven fabrics actually and we can verify the effects of fiber contents and loop length of knit on textures. We can find out differences of texture depending on presentation methods. In case of 2D evaluation of knits fabrics, visual images of real size present a little exact information on roughness and heaviness whereas those of twice magnification do roughness, wetness, softness and luster. And 3D images give us more exact information of textures on softness, heaviness and warmness, but rather twice enlarged 3D image can`t supply an information of heaviness texture.

Wavelength-tunable picosecond pulses from a passively mode-locked figure-eight Erbium-doped fiber laser with a Sagnac fiber filter

We experimentally demonstrated a wavelength-tunable passively mode-locked Erbium-doped figure-eight fiber laser. Wide tunability is achieved using a high-birefringence (hi-bi) fiber Sagnac loop. The filter transmission pass wavelength is controlled by thermally adjusting the hi-bi fiber loop length. The output pulses are wavelength tunable over a range from 1525 nm to 1555 nm. The FWHM of the autocorrelation trace is about 3.1 ps and the pulse spectrum has a FWHM of 1.5 nm. The pulse temporal and spectral widths remain constant over the tunable range.

LOW-POWER ALL-OPTICAL SWITCHING USING A FIBER SAGNAC INTERFEROMETER WITH A PUMPED NONLINEAR COUPLER

We propose a novel Sagnac interferometer (SI) optical switch consisting of a pumped erbium-doped fiber 3dB coupler for a signal at 1.55 μm and a short fiber loop. The switching between the reflected and transmitted output powers can be accomplished by two approaches: using 980nm-pump power in the cross-pumping mode or using an additional signal power in the self-pumping mode. In the two modes, the switching powers are 40mW and 20mW, and the switching times are sub-nanoseconds and milliseconds, respectively. In the both cases, the switching powers are independent of the fiber-loop length, so that the power-length products for proposed SI switch can be smaller than that of other kind of nonlinear SI switches.

A study on subjective assessment of knit fabric by ANFIS

The purpose of this study was to examine the effects of the structural properties of plain knit fabrics on the subjective perception of textures, sensibilities, and preference among consumers. This study, then, aimed to provide useful information with respect to planning and designing knitted fabrics by predicting the subjective characteristics analyzed according to their structural properties. For this purpose, we employed statistical analysis tools, such as factor and regression analysis and an adaptive-network-based fuzzy inference system(ANFIS), thereby combining the merits of fuzzy and neural networks and presupposing a non-linear relationship. Through factor analysis, we also categorized the subjective textures into ‘roughness’, ‘softness’, ‘bulkiness’ and ‘stretch-ability’ with R2=70.32 %: and categorized the sensibilities into ‘Stable/Neat’, ‘Natural/Comfortable’ and ‘Feminine/Elegant’ with R2=68.12 %. We analyzed subjective textures, sensibilities, and preference with ANFIS, assuming non-linear relationships; consequently, we were able to generate three or four fuzzy rules using wool/rayon fiber content and loop length as input data. The textures of roughness and softness exhibited a linear relationship, but other subjective characteristics demonstrated a non-linear input-output relationship. Compared with linear regression analysis, the ANFIS exhibited had higher predictive power with respect to predicting subjective characteristics.

Tunable All-Optical Microwave Filters Based on Fiber Loop and Chirped Fiber Bragg Gratings

All-optical microwave filters are important parts of fiber-optic microwave/millimeter wave processing systems. In this paper, two novel passive tunable all-optical microwave filters based on fiber loop and chirped fiber Bragg gratings (CFBGs) are demonstrated, where the frequency response of the both filters can be continuously tuned by adjusting the wavelength of the input light. The required free spectral range (FSR) of the filters can be obtained by carefully controlling the length of fiber loop and the positions of the CFBGs in the fiber loop. Experimental results prove the feasibility of the proposed filtering structures.

Fiber-connectorized multiwavelength 2×2 switch structure using a fiber loop mirror

A fiber-connectorized multiwavelength 2×2 switch structure is introduced for the first time that deploys a fiber loop mirror (FLM) arrangement with polarization control. Switch operation is achieved via a programmable waveplate effect rather than an optical power consuming long fiber loop length non-linear optical effect. The results from an experimental four-wavelength (i.e., 1546.92 nm, 1548.52 nm, 1550.12 nm, and 1551.72 nm) proof of concept switch using two mechanical fiber-based polarization controllers embedded in a short 7 m fiber loop indicates an average optical coherent crosstalk of −31.2 dB. Presently, optical loss is mainly limited by the WDM devices used in our experimental setup. Hence, without the WDM multiplexers, an average optical loss of 2.22 dB is measured over a 50 nm optical bandwidth. Also, an average 0.08 dB polarization dependent loss is measured for this broadband switch.

Low-drift modulator without feedback

A low-drift amplitude modulator has been demonstrated using a fiber Sagnac interferometer with a lithium-niobate phase modulator. Although the fiber-loop length must be adjusted for the modulation rate, this type of modulator structure is inherently insensitive to variations in the voltage bias of the drive signal, as well as to temperature variations. >

Jones calculus analysis of single-mode fiber Sagnac reflector

It is postulated that stray birefringence degrades the performance of the single-mode fiber Sagnac reflector. An expression for the birefringence dependence of reflector performance is derived using the Jones calculus and is used as the basis for a theoretical model of the spectral response of a real Sagnac reflector. The experimental behavior of the reflector with (1) different levels of stress applied to the fiber loop and (2) different lengths of highly birefringent fiber spliced into the loop are compared with the model. This comparison confirms the initial postulate.