Index Matching Oil Research Articles

Tunable spectral enhancement of fiber supercontinuum

We demonstrate tunable spectral enhancement of the supercontinuum generated in a microstructured fiber with a fiber long-period grating. The long-period grating leads to phase distortion and loss that, with subsequent high-intensity propagation in uniform fiber, evolves into an enhancement around the grating's resonant wavelengths. Wavelength tunability is achieved by varying the temperature or the ambient refractive index, and the spectral peak can be extinguished by immersing the grating in index-matching oil.

A refractometer based on a micro-slot in a fiber Bragg grating formed by chemically assisted femtosecond laser processing

A liquid core waveguide as a refractometer is proposed. Microtunnels were created in standard optical fiber using tightly focused femtoscond laser inscription and chemical etching. A 1.2(h)x125(d) x500(l) mum micro-slot engraved along a fiber Bragg grating (FBG) was used to construct liquid core waveguide by filling the slot with index matching oils. The device was used to measure refractive index and sensitivity up to 10- 6/pm was obtained.

Anisotropic fluorescence emission of a dye-doped fibre ring that is pumped by a ring laser beam

The fluorescence characteristics of a dye-doped polymer fibre were studied by exciting the fibre ring with a ring laser beam. An efficient excitation was achieved from the fibre side owing to the high absorbance of the organic dye. The pump-laser power could be raised to over 400 kW (pulse duration: 5 ns), which was unattainable by the conventional fibre-end pumping method because of the poor laser power durability of the dye-doped polymers. The fibre ends, which were polished obliquely (45°) to pick up the circulating fluorescence, were coupled to each other with an index-matching oil. When the pump power density exceeded 0.2 kW mm−2 (total power: 40 kW), the circulating beam exhibited both a nonlinear peak-growth and a spectral narrowing that were caused by the stimulated emission. By contrast, the fluorescence in the radial direction became weaker as the pump power increased, indicating that the stimulated emission in the axial direction suppressed the fluorescence in the radial direction.

MEMS compatible micro-GRIN lenses for fiber to chip coupling of light

Graded-Index (GRIN) lenses with a diameter of 125 mum are presented. This diameter enables the assembly of the GRIN lenses onto an optical micro-system using the same passive alignment grooves as used for the light carrying optical fibers. In contrast to refractive lenses, GRIN lenses have flat endfaces and the focal distance of a GRIN lens is defined by its length. Therefore, GRIN lenses can be diced from a selected multimode optical fiber with a regular wafer dicing machine. The effects of the resulting surface roughness are reduced by immersing the optical parts into index matching oil, which can not be applied for refractive lenses. This has a further advantage since an anti-reflective coating becomes dispensable. The coupling efficiency of a collimator set-up using the GRIN lenses is studied using paraxial ray calculations. The calculated minimal coupling losses of less than 0.3 dB are in excellent agreement with the measured results. Losses smaller than 2 dB over a coupling length of 2 mm have been measured.

Design and characteristics of large displacement optical fiber switch

Plastic optical fiber (POF) is suitable for indoor local area network (LAN), for example, in-home or office networks, because of its flexibility and its ease of connection due to its relatively large core diameter. A 1/spl times/2 optical switch for indoor LAN using POF and a shape memory alloy (SMA) coil actuator with magnetic latches was successfully fabricated and tested. In this paper, the design concept and the characteristics of this switch are described. To achieve switching by the movement of a POF, large displacement is necessary because the core diameter is large (e.g., 0.486 mm). A SMA coil actuator is used for large displacement and a magnetic latching system is employed for fixing the position of the shifted POF. For this design, the insertion loss is 0.40 to 0.50 dB and crosstalk is more than -50 dB without index-matching oil. Switching speed is less than 0.5 s at a driving current of 80 mA. A cycling test was performed 1.4 million times at room temperature. Another optical fiber switch was fabricated and successfully actuated using plastic clad fiber (PCF). PCF also has a large core diameter (e.g., 0.20 mm) and optical switches using PCF will be useful for short distance networks between buildings.

Nondestructive measurement of refractive index profile for holey fiber preforms

A non-destructive technique is presented to determine the refractive index profile of holey fiber preforms. The holes are filled with index matching oil and the holey preform deflection data is measured. An improved optical path-length formula and back projection method is used to reconstruct the two-dimensional filled holey fiber preform refractive index distribution.

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.

Design of High-Performance Latching Typle Single-Mode Fiber Switches and Theri Characteristice

This paper describes the optical, mechanical, and magnetic design of compact latching type single-mode fiber switches and demonstrates their characteristics including several reliability tests.To reduce the switch size and power, we designed a simple electro-magnetic driving mechanism composed of a solenoid coil and magnets that can move an ultra-light micro-magnetic-alloy pipe fixed on a movable fiber. Insertion loss and reflected light were reduced by injecting refractive- index-matching oil into the switches. We investigated precise optical coupling condition between a movable fiber and stationary fiber in terms of magnetic attraction forces.The fabricated 1×2 switches exhibited a low insertion loss of 0.31dB, a high return loss of 51dB, a relatively fast switching time of <2ms, and low driving power of 9mW. When subjected to endurance (108 switchings), heat cycle, shock and vibration, and long-term (6.5years) intermittent operating tests, they revealed no significant optical or mechanical degradation.

Extension of the useful focal length range of microlenses by oil immersion

A technique is investigated for increasing the focal length of an existing microlens or microlens array to realize long focal length microlenses. Photoresist microlens arrays have been fabricated and immersed in oils of various refractive indices (index-matching oil), extending the range of easily achievable numerical apertures towards lower values. The focal length can be altered by exchanging the oil for another with a different refractive index. We derive simple design relations which predict the changes in focal length, spherical aberration and astigmatism due to the oil immersion of the lens. Using these relations and oils of various refractive indices we have calculated the photoresist refractive index to be . The effects of altering the focal length on the on- and off-axis aberrations have also been measured and agreement with our design equations has been demonstrated.

Proposal of human eye's crystalline lens-like variable focusing lens

The variable focusing lens is designed and fabricated like the human eye's crystalline lens. The lens consists of glass diaphragm, microchannels and working fluid. The chamber between a glass diaphragm and a substrate is filled with the working fluid. Refractive index matching oil such as silicone oil can be used as working fluid, which is pumped into or out of the chamber through the microchannel. The curvature of the lens can change due to the oil pressure built by micropump outside. The change of curvature of the lens produces the focal plane shift. In addition, both convex lens and concave lens can be realized by pressurized working oil. Commercial micropump is used for the test of a fabricated variable focusing lens. The designed variable focusing lens has a square diaphragm with side length of 10 mm. Thickness of the glass diaphragm is 40 μm.

Lateral-shearing interferometer using square prisms for optical testing of aspheric lenses

We present a lateral-shearing interferometer specially devised for production-line inspection of aspheric lenses. The interferometer constitutes four right-angle prisms, whose relative sliding motions provide the lateral shearing and phase shifts necessary for measuring the beam wavefront collimated by the lens under test. The prisms are held together face to face using index-matching oil, so environmental disturbances from external vibration and atmospheric turbulence can be minimized. Furthermore, a special phase-measuring algorithm of least-squares type is adopted to compensate for the phase shift error caused by the variation in thickness of the index-matching oil holding the prisms. Experimental results prove that the interferometer provides a measuring reproducibility of the order of one hundredth of the light's wavelength.

Cladding-surrounding interface insensitive long-periodgrating

A long period grating is presented, the resonant peak of which is not sensitive to the interface between the cladding and the surrounding media of a fibre. The spectral behaviour of the resonant peak is investigated using index matching oils and mechanical scratching on the cladding surface of the fibre.

Enhanced coupling to microsphere resonances with optical fibers

Morphology-dependent resonances (MDR's) of polystyrene microspheres were excited by an optical fiber coupler. For optical elimination of the air–cladding interface at the optical fiber coupler surface, the microsphere was immersed in an index-matching oil. MDR's were observed, even though the relative refractive index between the microsphere and the oil was only 1.09. The observed MDR spectra are in good agreement with the generalized Lorenz–Mie theory and the localization principle. The scattering efficiency into each MDR is estimated as a function of the impact parameter by means of generalized Lorenz–Mie theory.

A Simple Method for Calculating Scattering Patterns of Light from Optical Fibres

Abstract A simple method using a wave optics approach has been developed to calculate scattering patterns of light from optical fibres. The refraction inside fibres is formulated into the calculation, removing the need for refractive index matching oil in experiments. Refractive indices and diameters of both unclad and clad step-index fibres are recovered from measured scattering patterns.

Tunable erbium fiber laser using a novel overlay bandpass filter

A unidirectional erbium fiber laser incorporating a novel LiNbO(3) overlay fiber-optic bandpass filter is demonstrated. By applying index-matching oils of different refractive indices to the surface of the overlay filter, we could tune the operating wavelength of the laser from 1531 to 1556 nm while maintaining a bandwidth of less than 0.2 nm (resolution limited). Output powers as high as 3 mW for 36 mW of pump power have been recorded.

Automated optical main-distributing-frame system

This paper describes the key technologies of an automated optical main-distributing-frame system for the fiber-to-the-home network. The system consists of an optical matrix-board with a groove at each cross-point and a precision robot mechanism that manipulates refractive index matching oil. Experimental results for a prototype model confirm the feasibility of lightwave cross-connection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Tunable couplers fabricated in K + /Na + ion exchanged glass

The characteristics of optical directional couplers fabricated in K/sup +//Na/sup +/ ion exchanged glass are shown to be dependent on the refractive index of the overlayer material. This effect was experimentally observed using index matching oils, and electrical switching using liquid crystal overlayers was demonstrated. >

Fluoropolymer barriers to stress corrosion in optical fibers

Some recent studies on fluoropolymers that exhibit substantially increased barrier properties against the migration of moisture when compared to conventional fiber coating materials, and as a result may offer unique advantages for use in optical fiber applications, are reported. Moisture vapor permeability studies of cis-trans fluoropolyol polyacrylate indicate that it can offer up to an order of magnitude reduction in H2O permeability relative to commercially available UV curable acrylate coatings. Experimentally determined permeability coefficients were of the order of 10−12 g cm−2 s−1 cm/mm Hg and diffusion coefficients were of the order of 10−10 cm2 s−1. In addition to improved barrier properties, incorporation of fluorine into the polymer structure lowers the index of refraction of the polymer enabling a material to be tailored for use as a cladding in conjunction with silica glass. The index of refraction of cis-trans fluoropolyol polyacrylate was determined, using index matching oils, to be 1.437 (lower than the silica core) permitting its use as a cladding. Other material parameters relevant to fiber coatings have also been measured. The elastic modulus E of the material was determined to be 1010 dyn/cm2 with a slow drop to 108 dyn/cm2 at the glass transition temperature ∼45°C. In addition, an improved formulation of cis-trans fluoropolyol polyacrylate is presented that allowed in-line coating of the optical fiber in an oxygen environment.

Refractive-index profiling of single-mode optical fibers and performs

The application of the focusing method to measure the refractive-index profiles of single-mode optical fibers and preforms is described. In this automatic and nondestructive technique, the fiber or preform is immersed in index-matching oil, and collimated light is passed transversely through it. The intensity distribution of the transmitted light is detected with a video camera and processed with the aid of a computer-controlled video analysis system that provides the profile within a few minutes. The profiles of boron-doped and germanium-doped fibers and preforms with maximum Deltan varying from 0.0006 to 0.012 were measured with a repeatability of better than 1% and with a resolution better than 1 microm. The profiles of the preforms are in good agreement with those of the fibers and also with those of slab samples taken from the tips of the same preforms.