PANDA Fiber Research Articles

Mode shape convertor produced by the thermal diffusion of different dopants

A novel method is proposed for producing mode shape convertors by the controlled thermal diffusion of different dopants. Mode shape convertors with an aspect ratio of up to 3.5 are produced by using PANDA fibers. >

INVESTIGATION OF IMPURITIES IN THE STRESS APPLYING PARTS (SAPS) DOPED WITH B2O3 FOR POLARIZATION-MAINTAINING FIBERS

OH-radical concentration in the (SAPS) doped with B2O3 for PANDA fibers is measured by infrared absorption method. B, Si, 0 and N in SAPS are analysed X-ray photoelectron spectroscopy (XPS). The Ge distribution in the core and the cathod luminescence at core-cladding interface of SAPS are measured by scanning electron microscopy, The ratio of absorption coefficient between the fundamental stretching vibration and its first overtone of OH bond is explained theoretically by using a vibrator model.

Fused polished polarisation-maintaining fibre couplers

A fused polished polarisation-maintaining fibre coupler with extinction ratio of greater than 17 dB has been made with standard PANDA fibre, using a recently reported technique where the ease of fabrication is comparable to that for fused tapered couplers. >

Stress calculations based on point-matching method for mechanically inhomogeneous optical fibers

A point-matching method is introduced to calculate the stress distribution in mechanically inhomogeneous fibers in which the Young's modulus and Poisson ratio differ from region to region over the whole of the fiber cross section. Thus, it is best suited for the stress analysis in birefringent fibers such as elliptic-clad circular core fiber, bow-tie fiber, or panda fiber, all of which belong to the class of multiply connected elasticity problems. The formulation of the method is detailed, and its accuracy is compared with that of analytical calculation, where possible, and that of numerical methods, such as finite-element and boundary-element techniques. The comparisons show that the point-matching method can produce very accurate results and is very flexible in its application to fibers of different geometries. >

General solutions for stress-induced polarization in optical fibers

General solutions of thermal stresses and material birefringence in polarization-maintaining optical fibers are presented. The solutions give the stresses and birefringence at every point in the cross section of various fibers. The fundamental solution of the stress field is constructed by using the complex variable method in elasticity. When the cores, inner claddings, or stress-inducing regions are ellipses, circles, or bow-tie shapes, exact closed-form solutions can be found. The average core birefringence and center core birefringence of elliptical core, elliptical cladding, twin core, Panda, and bow-tie fibers are calculated and compared. Among these fibers, the bow-tie fiber shows the highest birefringence. >

Fiber-optic dual-coil sensor for simultaneous measurements of mechanical displacement and temperature change

A dual-fiber-coil polarization interferometric sensor using paired fibers is fabricated by use of a newly developed high-birefringence single-mode PANDA fiber with rectangular-shaped cladding. The birefringent axes of the paired fibers are aligned at right angles with the help of the flat sides of the cladding while a length of the paired fibers is being coiled. This right-angle arrangement gives opposite bending-induced retardations to the paired fibers. The difference measurement of these retardations result in twice the bending-induced retardation alone and is immune to environmental temperature disturbances. The mechanical displacement can be obtained from this bending-induced retardation. High sensitivity is feasible if the number of turns is maximized and the diameter of the paired fiber coil minimized in the fabrication process.

Temperature insensitive fiber coil sensor for altimeters

A displacement sensor using a pair of flat Panda fiber coils with a 90 degrees connection is demonstrated. The dual coils are squeezed differentially. The phase retardations caused by the compression are constructively added, while the retardations caused by the environmental temperature are destructively added, thereby removing the temperature effect. Both the birefringence and loss effects induced by the deformation of the coils are utilized for high accuracy detection and emergency detection, respectively. In experiments using thirty turn coils, the guaranteed sensitivity of 357 degrees /mm (retardation/displacement) and the long term stability of 4 degrees /h (retardation/period) were obtained.

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.

Transmission loss of a 125- mu m diameter PANDA fiber with circular stress-applying parts

The transmission loss of a 125- mu m diameter polarization-maintaining and absorption-reducing optical fiber (the PANDA fiber) with circular stress-applying parts (SAPs) has been investigated. The loss is calculated at a 1.55- mu m wavelength for SAPs consisting of B/sub 2/O/sub 3/ doped silica glasses. The experimental measurements show the validity of the analysis. It is shown that, when the half distance between SAPs is more than 2.2 times the core radius, the additional transmission loss due to B/sub 2/O/sub 3/ absorption is less than 0.05 dB/km with normalized frequency of 2.2 to 2.4 and a B/sub 2/O/sub 3/ dopant concentration of 20 mol.%. As a result, it has been confirmed that transmission losses of 125- mu m diameter PANDA fibers can be comparable to those of commercially available single-mode optical fibers. >

Polarisation-maintaining optical fibres with Al 2 O 3 stress-applying parts

Polarisation-maintaining optical fibres have been drawn from VAD synthesized preforms with Al/sub 2/O/sub 3/ single-crystal rods as stress-applying parts (SAPs). Measured X-ray diffraction patterns have shown that the Al/sub 2/O/sub 3/ SAPs are crystallised after heating in and drawing from a carbon furnace. The model birefringence is more than twice that of conventional PANDA fibre with B/sub 2/O/sub 3/.SiO/sub 2/ as SAPs.

Crosstalk characteristics of a 100 km-long spliced polarisation maintaining optical fibre

Crosstalk of −10.1 dB in a 100 km-long spliced polarisationmaintaining optical fibre has been achieved at 1.56 μm wavelength. The fibre has been constructed from 14,125 μm-diameter PANDA fibres, with an average modal birefringence of 4.8×10−4, by conventional arc-fusion splice techniques. An average transmission loss of 0.37 dB/km, including the splice loss, has been obtained at 1.56 μm wavelength.

Polarization-dependent chromatic dispersion in birefringent optical fibers

Chromatic dispersion of two orthogonal polarization modes has been investigated for various kinds of PANDA fibers. In high-birefringence fiber with modal birefringence B = 7.9 x 10(-4), the zero-dispersion wavelength for the x-polarization mode (lambda(0x) = 1.307 microm) was 6 nm shorter than that for the y-polarization mode (lambda(0y) = 1.313 microm). Chromatic dispersion of the fiber at 1.55-microm wavelength was sigma(x) = 18.3 psec/km-nm and sigma(y) = 16.1 psec/km-nm for the x- and y-polarization modes, respectively.

26 km-long polarisation-maintaining optical fibre

The letter describes the development of a long-length and large-diameter preform for polarisation-maintaining optical fibres. The preform was 470 mm in length and 48 mm in diameter. As a result, a 26 km-long PANDA fibre is developed. This fibre achieves crosstalk of –22 dB, corresponding to h = 2.4 × 10-7m-1 and a transmission loss of 0.3 dB/km at a wavelength of 1.56 μm. These fibres will be useful for future high-speed and medium-span coherent optical communications.

Fiber devices using polarization- maintaining fibers

Abstract Fiber devices using polarization-maintaining fibers called PANDA fibers are presented. They are polarization-maintaining couplers and polarization-splitting couplers, optical isolators and optical circulators, and multi/demultiplexers designed for 1.3 μm wavelength. Crosstalk of-32 dB and excess loss of 0.03 dB for the polarization-maintaining coupler, and polarization-splitting ratio of 17 dB and excess loss of 0.5 dB for the polarization-splitting coupler have been fabricated by a fusion-elongation method. A fiber polarizer with the extinction ratio of more than 40 dB has been presented by using the difference of bending loss between the orthogonal modes in the PANDA fibers. Multi/demultiplexer with narrow band-pass of 1.4 nm utilizing combination of PANDA fiber polarization dispersion and the polarization-splitting coupler has been realized. An optical isolator consisting of fiber polarizers and a spherical YIG with a lens function and an optical circulator consisting of polarizing-splitting c...

Side-hole fiber for fiber-optic pressure sensing

An optical fiber whose structure is similar to that of the PANDA fiber, but with two open channels in the place of the stress members, is investigated. Variations of the internal or external gas pressure permit tuning of the fiber birefringence (10−4 rad m−1 Pa−1) over a wide range, including sign reversal, and application as a pressure sensor.

FSK transmission experiment using 10.5 km polarisation-maintaining fibre

A 400 Mbit/s FSK transmission experiment is performed using 10.5 km PANDA fibre with crosstalk of −23 dB. The polarisation state is stable and excess errors are not found in the presence of forced fibre fluctuations. The influence of polarisation direction of the incident light on transmission characteristics is discussed.

Analysis of fiber-optic polarizing beam splitters consisting of fused-taper couplers

The characteristics of polarization splitting in fiber-optic couplers employing both nonbirefringent and birefringent fibers (PANDA fibers) are investigated. An analytical method that takes into account the cores, stress-applying parts, and stress birefringence in the coupling region is proposed. From comparison between the theory and experiments, the validity of the present analytical method is confirmed. It is shown that the length of the coupling region in birefringent-fiber polarizing beam splitters (BPBS) is several times shorter than that in nonbirefringent-fiber polarizing beam splitters (NPBS).

Design and fabrication of low-loss and low-crosstalk polarization-maintaining optical fibers

Low-loss and low-crosstalk polarization-maintaining optical fibers (called PANDA fibers), which are potentially useful for coherent optical communication systems, have been fabricated based on the optimum design. Transmission loss of 0.22 dB/km, comparable to that of commercially available single-mode fibers, and crosstalk of -27 dB in a 5-km length, corresponding to the polarization-mode-coupling coefficient of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4.0 \times 10^{-7}</tex> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , have been demonstrated in the 1.56-μm wavelength.

Stress‐applied polarization‐maintaining optical fibers. Design and fabrication

AbstractTo realize low‐loss low‐crosstalk long‐length polarization‐maintaining fibers, this paper examines the “PANDA fibers” having a circular stress‐applying part which has a high design accuracy and ease of fabrication. Stress‐applied type polarization‐maintaining optical fibers generally have two orthogonal polarized modes, and their coupling causes crosstalk which makes the transmission of polarized mode through a long‐length of fibers difficult. To suppress this mode‐coupling, it is important (a) to make the modal birefringence larger, and (b) to reduce the deterioration of the symmetry of the stress applied. This paper examines the circular stress‐applying type PANDA fiber and compares it with two other types of PANDA fiber having the typical shapes of the stress‐applying part. As a result, (1) the structure parameters of the stress‐applying part which gives the maximum modal birefringence and a low loss, and (2) the mode‐coupling parameter, with the stress‐applying part deviated, which can evaluate the crosstalk characteristics, have been obtained. Based on the results of these theoretical analyses, the symmetry in the stress‐applying part is improved by using a large preform, and the increase of the modal birefringence by increasing the outer diameter of the fiber is carried out. The circular stress‐applying type PANDA fiber having a crosstalk as low as ‐42 dB in 1 km has been realized.

High-birefringence polarizing fiber with flat cladding

This paper presents the theoretical and experimental investigations on polarization characteristics of PANDA fiber with flat cladding. It is theoretically shown that the modal birefringence in the flat-clad fiber is almost the same as that in the circular-clad fiber. The flat-clad PANDA fiber has been fabricated by grinding off the preform cladding on the opposite faces and then drawing with a low furnace temperature. The modal birefringence of the fiber is B = 5.9 \times 10^{-4} and the separation of the bending loss edges for the two polarization modes is \Delta\upsilon = 0.51 in the normalized frequency. The polarizing region can be tuned from 1.3 to 1.56 μm by varying the fiber-bending diameter from 3.5 to 4.5 cm. A 1.5-m length of polarizing fiber exhibits extinction ratios of 44.9 and 44.4 dB with insertion losses for the guided mode of 0.25 and 0.41 dB at 1.3 and 1.56 μm, respectively.