Polarization-maintaining Fiber Coupler Research Articles

Utilization of telecommunication optical routes to power fiber-optic polarization sensors

A single-mode telecommunication optical route can be used for reliable power supplies of a remote non-electric temperature fiber-optic polarization sensor, but the optical route, due to many physical factors, affects an immediate state of polarization during the transmission. This negative phenomenon changes the sensitivity of the sensor itself. The thesis proposes two main approaches to solving that problem. The first approach is based on the suitable connection of a depolarizer and linear polarizers. The second approach is based on signal interference, which takes place in a polarization-maintaining fiber coupler. This article also evaluates the advantages and disadvantages of the two approaches and graphically demonstrates the functionality of the fiber-optic sensor, which was tested by applying a container with water of different temperatures. A big advantage of this type of sensor is that it is not necessary to have components, that are dependent on electricity, near the monitored place, where there may be no access to electricity, or the place may be sensitive to an electric charge. Paper demonstrates the possibility of successfully powering the non-electric sensor via a classical optical route.

10-Hz, 636-ps, 1064-nm, all polarization-maintaining fiber front-end based on ultrafast optical fiber pulse chopping

We demonstrate a robust 10-Hz, 1064-nm, all polarization-maintaining (PM) fiber laser front-end for a joule-level solid-state amplification system applying ultrafast optical pulse chopping. A 1064-nm single frequency continuous wave (CW) laser is chopped by an in-line acousto-optic modulator (AOM) to generate ∼7 ns duration pulses at 500-kHz repetition rate, followed by a Sagnac loop (SL) consisting of a 50:50 PM fiber coupler and an electro–optical (EO) phase modulator, which further shortens the pulse duration from 7 ns to 636 ps via a passively fixed optical chopping gate. Finally, the pulse energy is amplified to the sub-µJ level and its repetition rate is further reduced to 10-Hz by another in-line AOM stage. This 10-Hz, 636-ps, sub-µJ level fiber laser realized in an all-PM-fiber configuration can be used as a robust front-end for joule-level solid-state amplification and follow-on nonlinear frequency conversion experiments.

基于全保偏光纤结构的高稳定性激光相位解调系统

基于全保偏光纤结构的高稳定性激光相位解调系统

Fiber-Based Polarization Diversity Detection for Polarization-Sensitive Optical Coherence Tomography

We present a new fiber-based polarization diversity detection (PDD) scheme for polarization sensitive optical coherence tomography (PSOCT). This implementation uses a new custom miniaturized polarization-maintaining 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 two orthogonal OCT polarization channels prior to interference while the PM fiber outputs ensure defined orthogonal axes after interference. Advantages of this detection scheme over those with bulk optics PDD include lower cost, easier miniaturization, and more relaxed alignment and handling issues. We incorporate this PDD scheme into a galvanometer-scanned OCT system to demonstrate system calibration and PSOCT imaging of an achromatic quarter-wave plate, fingernail in vivo, and chicken breast, salmon, cow leg, and basa fish muscle samples ex vivo.

Investigation on the Data Processing Method for High-Precision Alignment of PM Fibers

The extinction ratio is the characteristic parameter of polarization-maintaining (PM) fiber couplers. The detection accuracy of polarization angle is related to the extinction ratio, and affects the thin-diameter PM fiber coupler performances greatly. A series of image processing steps including median filtering, adaptive image morphology, and maximum variance threshold segmentation method are used to get the outline of optical fibers. The minimum squares method is used to get the maximum intensity of the light. The experimental data is processed using the Fourier filtering method and influences of the manufacturing error and random errors of fibers are reduced. By fitting the experiment data with cubic spine method, and its mean square error of fitting is 0.05458, then the polarization angle of the PM fiber is determined. Experiments show that this method can precisely determine the fast axis position of PM fibers, and it can achieve the high precision alignment of 80 um PM fibers.

Birefringence analysis of directional fiber coupler induced by fusion and coupling parameters

The effect of fusion and coupling parameters to the form of birefringence of coupling region directional fiber coupler is reported. Vector of polarization was determined by using perturbation method that describes the propagation of electric field in single mode fiber coupling induced by stress which is caused by fusion and coupling parameters during fabrication. It is found that the geometrical change, such as radius of coupling cross section, refractive index difference, normalized frequency, and twisting angle significantly affect the polarization and birefringence. However, change of temperature during fusion in range 27–1350°C gives only small increment in birefringence directional fiber coupler. By knowing these parameters, the polarization and birefringence can be maintained and optimized for polarization maintaining fiber coupler application.

A linearly-polarized tunable Yb-doped fiber laser using a polarization dependent fiber loop mirror

A Ytterbium-doped linearly-polarized fiber laser is constructed with a polarization maintaining fiber Sagnac loop mirror. The fiber loop mirror made of polarization maintaining fiber coupler has a polarization dependent reflectivity, which provides the necessary polarization discrimination between the slow and fast axes. With a fiber Bragg grating written in normal polarization maintaining fiber as an output coupler, laser output of up to 5.6W at 1070nm is generated with a polarization extinction ratio of >20dB and an overall efficiency of 55%. The broadband polarization dependent reflection of the fiber loop mirror offers advantages of easy spectral tuning and simple linearly-polarized laser generation.

Revised minimum reciprocity configuration and actualization methodology of interferometric all-fiber-optic gyroscopes

We propose a revised minimum reciprocity configuration (MRC) of an interferometric all-fiber-optic gyroscope (all-fiber I-FOG), based on our design of a fused-taper polarization-maintaining fiber coupler. This MRC reduces the insertion loss and production cost of the optical path, yet maintains the principle of reciprocity. Experimental results show that this I-FOG with five optical components exhibits better performance than a conventional I-FOG with six optical components. Using the revised MRC, the angle random walk and the bias instability of an I-FOG are improved from 0.025 deg/√hr to 0.011 deg/√hr, and 0.48 deg/hr to 0.21 deg/hr, respectively.

Side-Polished Polarization-Maintaining Fiber Coupler with a Thin Metal Interlay and Its Application as a Polarization Splitter

The polarization-selective characteristics of a side-polished polarization-maintaining (PM) fiber coupler including a thin metal interlay have been investigated theoretically and experimentally. It is theoretically shown that the coupler is suitable for separating two orthogonal polarizations with a short coupling length and for achieving wide operational bandwidth. We have experimentally realized a polarization splitter with 22 dB and 18 dB extinction ratios at 1550 nm for transverse electric (TE) and transverse magnetic (TM) polarizations, respectively. The measured excess losses are less than 1 dB for both TE and TM polarizations.

Periodic microbending-induced core-to-cladding mode coupling in polarization-maintaining fibers.

We investigate codirectional mode coupling induced by periodic microbending in polarization-maintaining (PM) fibers by using both an acoustic flexural wave and a pair of corrugated fixtures. The measured filtering spectra are found to be strongly polarization dependent. In addition, the coupling strength depends on the angle between the birefringence axes and the bending direction. These characteristics can be utilized for a variety of applications, such as fiber polarizers, polarization-dependent-loss compensators, and on-line alignment of birefringence axes for the manufacture of PM fiber couplers.

The manufacturing of an optical fiber coupler by the fusion elongation method

An optical fiber coupler is used for joining or splitting optical signals at optical fiber branch points. It is an essential component for optical communication systems. Nowadays, telecommunication systems providers such as AT&T in America and NTT in Japan are in the process of implementing Fiber To The Home and Fiber To The Curb and therefore optical coupler will be in high demand in the near future. Special optical fibers such as polarization maintaining (PM) fiber also enjoy ever increasing popularity as communication systems and fiber sensor become more sophisticated. Consequently optical fiber couplers made of PM fiber will be in great demand. The fabrication of PM fiber couplers is either by the polishing method or by the fusion and elongation method. The fabrication technique for the polishing type PM fiber coupler has well been developed. However, the properties of the epoxy resin used in a polishing type PM fiber coupler change with temperature and humidity. Consequently, the characteristics of such coupler are also dependent on temperature. This undesired characteristics has imposed severe limitations of the use of the PM polishing type coupler. It is believed that PM couplers made by the fusion and elongation method have a steady characteristics over a wide temperature range. This paper reports a method for the fabrication of Polarization-Maintaining (PM) Optical Fiber Couplers using the fusion and elongation method and confirms that the characteristics of such PM couplers are stable over a temperature range of 110°C. Moreover, the manufacturing time for the fusion and elongation type coupler is reduced tremendously compared with that for the polishing type coupler. As the manufacturing time is reduced, the cost of production should proportionally be decreased. By applying this method, the manufacturing process could be fully automated and a high reliability product would be produced.

Nonlinear Sagnac interferometer switch and its applications

Ultrafast all-optical switching based on the optical Kerr effect in a Sagnac interferometer which consists of a dichroic polarization-maintaining fiber coupler and dispersion-shifted polarization-maintaining fiber loop is reported. This nonlinear Sagnac interferometer switch has the advantage of high stability originating from completely balanced interfering arms. In addition, because dispersion-shifted fibers were used, increases in switching power and switching time were prevented. Moreover, polarization fluctuation was completely suppressed due to the all-polarization maintaining fiber configuration. The required switching power for complete switching was measured to be 1.8 W for a 200-m-long fiber. All-optical time division demultiplexing and logic operations, including inversion and operation, using the nonlinear Sagnac interferometer switch were successfully demonstrated at 5 Gb/s.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Environmental performance of fused PM fiber couplers for fiber gyro application

Environmental test results for fused polarization maintaining (PM) fiber couplers fabricated with PANDA, bow-tie, and elliptically stressed fibers are reported. The packaged couplers are 32 mm long and 2.5 mm in diameter. Excess loss as low as 0.1 dB and polarization extinction ratio as high as 35 dB at the output ports of a coupler have been achieved. Robust couplers that are insensitive to mechanical and acoustic vibrations have been achieved through proper packaging.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ultrafast all-optical logic operations in a nonlinear Sagnac interferometer with two control beams

Ultrafast highly stable all-optical logic operations, including inversion, AND, XOR, and XOR, in a two-wavelength nonlinear Sagnac interferometer with two control beams have been reported. The interferometer consists of a dichroic polarization-maintaining fiber coupler and a 200-m-long dispersion-shifted polarization-maintaining fiber Sagnac loop. The logic operations were successfully demonstrated at multigigabit operation per second, and the required signal power was 1.8 W for a 200-m fiber.

Asymmetric behavior of polished polarization-maintaining couplers

Basic asymmetric behavior is experimentally observed in a polished polarization-maintaining fiber coupler. As the two half-couplers are made to slide on top of each other, the output extinction ratio exhibits relatively large variations whose forms depend on the fiber that is selected for the input. We propose that a local distortion of the fiber birefringent axes, which could be caused by the half-coupler polishing process, can generate such features even when the launched light is perfectly polarized along a principal axis of the input fiber.

Ultrafast, low power, and highly stable all-optical switching in an all polarization maintaining fiber Sagnac interferometer

An ultrafast, low-power, and highly stable all-optical switch in a nonlinear Sagnac interferometer is reported. To achieve low-power, highly stable, and walkoff free switching, use is made of a small-core dispersion-shifted polarization-maintaining fiber loop (200 m in length) which has a small group delay difference between the wavelengths of the input signal and the control pulse. To achieve complete polarization stability, a wavelength-sensitive polarization-maintaining fiber coupler is employed. Highly stable and walkoff free all-optical switching is demonstrated at 5 Gb/s. >

Analysis of mode coupling behavior in fused polarization-maintaining fiber couplers

To achieve low excess loss fiber couplers, analysis on mode coupling behavior in fused fiber couplers has been carried out using a combination of a scalar wave finite element method and a step approximation method, with an emphasis on clarifying the excess loss mechanism in fused polarization-maintaining (PANDA) fiber couplers. Numerical analysis has indicated the following results: First, fused PANDA fiber couplers have a critical outer diameter in the biconical taper region,, at which mode couplings between the symmetric fundamental mode and the symmetric next higher-order mode take place. Second, PANDA fiber couplers in which the waist diameter in the biconical taper region is larger than the critical diameter have small excess loss, because the large waist diameter provides the small mode coupling, although too large a waist diameter does not allow power splitting as a coupler. This analysis shows that excess loss in PANDA fiber couplers largely depends on the outer diameter dimension of the biconical taper region and gives an optimal value of such diameter. This is in good agreement with the experimental results.

Low excess loss conditions of polarization-maintaining fiber couplers

Loss characteristics and field intensity distributions of fused polarization-maintaining fiber couplers are measured. From the results, it is shown that excess loss spectra have a sinusoidal response. Further, the loss peaks of the usual polarization-maintaining and absorption-reducing (PANDA) fiber couplers with indexdepressed stress applying parts are larger than those of PANDA couplers with index-matched stress applying parts. It is also confirmed that low excess loss of <0.1 dB can be obtained for a large waist diameter of the fused region even in conventional PANDA fiber couplers.

Fiber-coupler fabrication with automatic fusion-elongation processes for low excess loss and high coupling-ratio accuracy

A novel fiber-coupler fabrication system which automatically processes fusion and elongation is presented. Not only conventional single-mode fiber couplers but also polarization-maintaining fiber couplers with excellent characteristics such as excess losses less than 0.11 dB and coupling-ratio accuracy better than 1.3 percent were obtained. In addition, it was confirmed that polarization crosstalk for polarization-maintaining fiber couplers in the present system was lower than that for the conventional manual method. The fabrication yield and reliability of the present system have been much higher than those of the conventional method and the processing time for fabrication could also be reduced.