Fiber-optic interferometric point thermometer

A modulation technique suitable for short optical fiber interferometric sensors is presented. This is a passive technique that makes use of modal properties of highly birefringent fiber to generate quadrature output components. Experimental results are presented for 2 miniature, remote Fabry-Perot interferometers fabricated from 2 different types of highly birefringent fiber using this signal processing method.     

Interference method of measuring the extinction coefficient of birefringent optical fibers

The extinction coefficient of a birefringent optical fiber (the ratio between the radiation power output of the polarization mode and the radiation power transferred from this mode to another one) characterizes the capability of a birefringent fiber to retain the polarization state of the radiation. In relatively short birefringent fibers (1–100 m), the extinction coefficient may reach 10⁴–10⁶. Such high values of the extinction coefficient are difficult to measure by standard techniques (excitation of one polarization mode by an incoherent source with subsequent recording of the light intensity at the output of the analyzer). An interference method of measuring the extinction coefficient of birefringent fibers is suggested. It is based on using a coherent source and measuring interference oscillations caused by an additional phase modulation at the input of the fiber. This method does not require precise polarization matching between the laser source and fiber and considerably loosens requirements for the polarizer-analyzer extinction and resolution of the photodetector. As a result, using simple standard components (semiconductor laser, film polarizer, and photodetector), one can measure extinction coefficient as high as 10⁶. The suggested interference method of measuring the extinction coefficient of birefringent fibers receives a theoretical analysis, and experimental data obtained for 2- to 1000-m-long fibers are presented.     

Multiwavelength fiber laser based on a photonic crystal fiber loop mirror with cooperative Rayleigh scattering

In this work, a multiwavelength fiber Raman laser based on a highly birefringent photonic crystal fiber loop mirror is presented. A laser resonator is formed when the Raman amplification with cooperative Rayleigh scattering in a dispersion-compensating fiber is used as a distributed mirror and combined with a photonic crystal fiber loop mirror filtering structure. Stable multiwavelength lasing at room temperature is achieved due to the low temperature sensitivity of the highly birefringent photonic crystal fiber.     

Fiber-optic sensing of high static pressure

Abstract

This paper describes a new fiber-optic sensor for pressures up to 200 MPa, based on the effect of hydrostatic stress on the polarization-mode coupling which occurs in highly birefringent fibers. Sensor construction, measurement set-up and typical output are presented. Results show that this new sensor displays far greater sensitivity when compared to solid-state pressure sensors.     

Correlation between the birefringence and the structural parameter in photonic crystal fiber

In order to simply design a highly birefringent photonic crystal fiber (HB-PCF), we numerically simulated the correlation between the birefringence and the structural parameter of photonic crystal fiber with square-lattice or triangle-lattice air-holes by using multipole method. It is shown that the phase birefringence B(λ) and the group birefringence G(λ) can be modulated by the structure parameter of normalized wavelength λ/Λ and the relative air-hole size d/Λ. Numerical results show very high phase and group birefringence of the order of 10⁻². The group birefringence becomes negative in the region where phase birefringence increases with an increase in normalized wavelength that does not appear in traditional highly birefringent fibers.     

Temperature sensing using the spectral interference of polarization modes in a highly birefringent fiber

The spectral interference of polarization modes in a highly birefringent (HB) fiber to measure temperature is analyzed theoretically and experimentally. A tandem configuration of a birefringent delay line and a sensing HB fiber is considered and the spectral interferograms are modelled for the known birefringence dispersion of the HB fiber under test. As the delay line, a birefringent quartz crystal of a suitable thickness is employed to resolve a channeled spectrum. The channeled spectra are recorded for different temperatures and the polarimetric sensitivity to temperature, determined in the spectral range from 500 to 850 nm, is decreasing with wavelength. It is demonstrated that the temperature sensing is possible using the wavelength interrogation, i.e., the position of a given interference maximum is temperature dependent. The temperature sensitivity of the HB fiber under test is −0.25 nm/K and the resolution is better than 0.5 K.     

Highly Birefringent Microstructure Fiber with Zero Dispersion Wavelength at 0.64 Micrometer

Abstract

In this article, we have designed a microstructure fiber, which consists of elliptical air holes at the core region. We have investigated its optical properties using finite difference time domain method. The fundamental mode of the proposed microstructure fiber can induce very high birefringence. It has been realized that the value of birefringence is mainly decided by the shape of the air holes present in the first and second rings. The zero dispersion wavelengths of both fast and slow axes have been shifted to 0.64 micrometer. The proposed birefringent microstructure fiber may be useful in optical communication and sensors.     

Elliptically birefringent optical fiber transmission characteristics

Abstract

This paper presents a rigorous analysis of spun hi-bi (highly birefringent) fibers, loosely categorized as elliptically bi fibers, via the initial value problem approach. Two kinds of transmission problem are treated. In the single-eigenmode transmission regime, it is found that the major technological difficulty inherent to spun hi-bi fibers concerns excitation of the eigenmode, which strictly requires that the launched light be exactly oriented in conformity with one or the other local principal axes of the fiber and, meanwhile, that the ellipticity of the launched light be exactly equal to the eigen-ellipticity of the same fiber. In the second kind of problem that involves the interaction of two eigenmodes, a basic result is derived to show that an arbitrary polarization mode of excitation will reproduce itself in integer multiples of the local beat length. Such a kind of transmission regime is relieved of the excitation difficulty but, because of being severely length-sensitive, is inherently impractical from the application viewpoint.     

A high-precision optical metrology system for determining the thickness of birefringent wave plates

This study develops a non-destructive measurement system for determining the thickness and refractive indices of birefringent optical wave plates. Compared to previous methods presented in the literature, the proposed metrology system provides the ability to measure the thickness of the birefringent optical plate in high-precision. The results show that for a commercially available birefringent optical wave plate with refractive indices of n_e=1.5518, n₀=1.5427 and a thickness of 452.1428 μm, the experimentally determined value for the error in the wave plate thickness measurement is just 0.046 μm. The measurement resolution of the proposed system exceeds that of the interferometer hardware itself. The proposed method provides a simple yet highly accurate means of measuring the principal optical parameters of birefringent glass wave plates.     

Design of hybrid photonic crystal fiber: Polarization and dispersion properties

A highly birefringent dispersion compensating hybrid photonic crystal fiber is presented. This fiber successfully compensates the chromatic dispersion of standard single mode fiber over E- to L-communication bands. Simulation results reveal that it is possible to obtain a large negative dispersion coefficient of about −1054.4 ps/(nm km) and a relative dispersion slope of 0.0036 nm⁻¹ at the 1550 nm wavelength. The proposed fiber simultaneously provides a high birefringence of order 3.45 × 10⁻² at the 1550 nm. Moreover, it is confirmed that the designed fiber successfully operates as a single mode in the entire band of interest. For practical conditions, the sensitivity of the fibers dispersion properties to a ±2% variation around the optimum values is carefully studied and the nonlinearity of the proposed fiber is also reported and discussed. Such fibers are essential for high speed transmission system as a dispersion compensator, sensing applications, fiber loop mirrors as well as maintaining single polarization, and many nonlinear applications such as four-wave mixing, etc.     

Thermal characteristics of a fiber Fabry-Perot etalon made of highly birefringent fiber

Fiber Fabry-Perot etalon (FFPE) is a device designed as an optical frequency filter, and its transmission characteristics change depending on temperature. The temperature dependence of the transmission frequency of an FFPE made of a highly birefringent fiber was found to be −2:31 GHz/deg, which is almost the same as that of a conventional etalon. On the contrary, its temperature dependence of the transmission frequency separation due to birefringence was found to be −140 MHz/deg. This is about 18 times larger than that for a conventional FFPE, and it implies that an FFPE made of highly birefringent fiber is promising as a temperature sensor with a high precision.     

Challenges and Solutions in Fabrication of Silica-Based Photonic Crystal Fibers: An Experimental Study

Abstract

The fabrication process of photonic crystal fibers based on a stack-and-draw method is presented in full detail in this article. In addition, improved techniques of photonic crystal fiber preform preparation and fabrication are highlighted. A new method of connecting a handle to a preform using only a fiber drawing tower is demonstrated, which eliminates the need for a high-temperature glass working lathe. Also, a new technique of modifying the photonic crystal fiber structural pattern by sealing air holes of the photonic crystal fiber cane is presented. Using the proposed methods, several types of photonic crystal fibers are fabricated, which suggests potential for rapid photonic crystal fibers fabrication in laboratories equipped with and limited to only a fiber drawing tower.     

Highly birefringent soft glass rectangular photonic crystal fibers with elliptical holes

In this paper we report on the fabrication of highly birefringent photonic crystal fiber with a photonic cladding composed of elliptical holes ordered in a rectangular lattice. The fiber features a group birefringence G of 0.82×10^?4 at 725 nm. We discuss the influence of structural parameters including the ellipticity of the air holes and the aspect ratio of the rectangular lattice on the birefringence and on the modal properties of the fiber.     

Wavelength Shift of Cladding Mode Resonances in a Mechanically Induced LPFG by Twisting the Fiber

Abstract

The long-period fiber grating is mechanically induced over a twisted fiber and its characteristics are investigated. The amplitude as well as the wavelength shift of the resonance is studied in response to the applied twist and pressures. These resonances decrease in amplitude and shift to shorter wavelength side as the applied twist increases. The spectral responses of a grating assembly formed by two grating sections in series, one section with a twisted fiber and other with an untwisted fiber, are also investigated. Shearing stress and photo-elasticity causes the fiber to be circularly birefringent and the mechanically induced grating formed over the twisted fiber region causes the appearance of two resonances shifted away from the resonances of the untwisted grating section. At higher twist rates, resonant wavelength shift becomes insensitive to applied pressures, showing a reduction in the induced linear birefringence. The wavelength shift is almost symmetric with respect to the applied twist rate in clockwise and counterclockwise directions.     

Optical Kerr coefficient measurement at 1.15 μm in single mode optical fibers

We have measured the optical Kerr coefficient n_2B in a SiO₂-GeO₂ birefringent single mode fiber at 1.15 μm. We have observed experimentally a 100% modulation depth with a low pump power of 390 mW launched into a 580 m long single mode optical fiber.     

在保偏光纤上制作光纤光栅的应用研究

提出一种在保偏光纤上计算光纤拍长的方法，即在保偏光纤上制作光纤光栅，利用光纤光栅的特性可以方便地求得光纤的拍长，同时，发现在保偏光纤上写入光纤光栅，其过程等效于在两个主轴上分别写入了一个光纤光栅，并且这两个光栅对于光的偏振态具有选择性，它们分别作用的偏振态是相互正交的。利用此特性，可以得到偏振消光比比较高的偏振分束器。     

Interference of white light in tandem configuration of birefringent crystal and sensing birefringent fiber

Spectral interference of white-light beams propagating through a tandem configuration of birefringent crystal and sensing birefringent fiber is analyzed theoretically and experimentally. The spectral interference law is expressed analytically under the condition of a Gaussian response function of a spectrometer taking into account the dispersion of birefringence in the crystal and in the fiber. Two types of spectral interferograms are modeled knowing dispersion characteristics of the sensing fiber and using a quartz crystal of the positive or a calcite crystal of the negative birefringence. The theoretical analysis is accompanied by two experiments employing a highly birefringent fiber and a birefringent quartz crystal of two suitable thicknesses. Within both experiments the spectral interference fringes are resolved in accordance with the theory with phases dependent on the fiber length.     

基于小圆孔结构纤芯的高双折射光子晶体光纤

为了实现高双折射光子晶体光纤,提出了一种在纤芯中引入微小圆孔的方法.利用全矢量有限元方法和完美匹配层条件研究了基于圆孔微细结构纤芯的光子晶体光纤的双折射特性.讨论了纤芯圆孔数量、孔径、间隔距离对光纤双折射特性的影响;设计了一种双折射达到10－2量级的光子晶体光纤.模拟结果表明采用三个以上圆孔可以获得较大的双折射,增大外包层数目可以有效减小约束损耗.     

Theoretical Analysis of the Polarization- and Frequency-Dependent Gain for Fiber Optical Parametric Amplifier

Abstract

We develop the gain expression of fiber optical parametric amplifier with birefringent effect and loss. The simulations show that the optical parametric amplifiers' gain is frequency-dependent and polarization-dependent. If the signal polarization state goes along the fast axis, when the average half-difference of two pump frequencies is smaller, the gain flatness is better; if the signal polarization state goes along the slow axis, when half-difference of two pump frequencies is smaller, the gain flatness is worse, and the gain bandwidth becomes wider. We still find that the signal gain is different under the distinct signal polarization state.     

Tunable photonic delay lines in optical fibers

A comprehensive overview is presented about optical fiber‐based tunable photonic delay lines, which have been steadily developed over the last decade for the realization of all‐optically controlled timing functions. The most widely used techniques, such as those based on slow & fast light and wavelength conversion associated to dispersion, are described and their physical limitations are discussed in terms of the maximal achievable delay, the associated signal distortion and signal bandwidth. Besides, an entirely different approach for all‐optical signal delaying is introduced. This technique is based on movable grating reflectors dynamically generated in highly birefringent optical fibers. This type of delay line has experimentally demonstrated large tunable delaying with a moderate signal distortion for high capacity optical data streams and even for wideband analog signals.