Interfacial-gel Polymerization Research Articles

Fabrication of defocus graded-index optical waveguide for evanescent wave optical amplifier

This is the first report on an evanescent wave optical amplifier with a plastic waveguide that can amplify a CW signal transmitted by a plastic optical fiber. The waveguide with a concave refractive index distribution was fabricated by an interfacial-gel polymerization technique. Since the waveguide increases the number of reflections at the boundary surface of the waveguide and the laser dye solution, the enhancement of amplification efficiency can be realized. The function of the fabricated waveguide was confirmed by calculations and experiments. The obtained results indicate that the fabricated fiber generated a larger evanescent field than the waveguide without a refractive index distribution.

Methodological Approach To Control the Refractive Index Profile of Graded-Index Polymer Optical Fiber

The graded-index polymer optical fiber (GI-POF) is a promising candidate for high-speed communication medium for very short reach networks such as home networks and office local area networks (LANs). It is well-known that there is an optimum refractive index profile to maximize bandwidth properties of GI-POF when the profile is expressed by the power law equation. The interfacial-gel polymerization technique, one of the major conventional fabrication methods of GI-POF, has many processes, and the formation mechanism of refractive index profiles intricately depends on many parameters of fabrication conditions. Thus is very difficult to control and form an optimum radial refractive index profile in the GI-POF. Recently, the coextrusion process has been proposed for mass production of GI-POF. In this process, the forming process of refractive index profiles can be expressed by a simple advection−diffusion equation. Therefore, we investigated the general methodology to control refractive index profiles by numerically solving the advection−diffusion equation. On the basis of our data, it was determined that refractive index profiles could be controlled by adjusting diffusion temperature and core ratio.

Design and synthesis of graded index plastic optical fibers by copolymeric system

AbstractGraded index plastic optical fibers (GI POF) based on the copolymer of 2,3,5,6‐tetrafluorophenyl methacrylate (TFPMA) and methyl methacrylate (MMA) were prepared. The copolymers of 10 wt% and 20 wt% of TFPMA with MMA were prepared in bulk using di‐tert‐butyl peroxide as the radical initiator at 90–120°C for 48 hr. The glass transition temperatures (Tg) of the copolymers were 115 and 118°C, and the refractive indexes were 1.4912 and 1.4901 at 589 nm, respectively. The transmittances of the copolymers were a slightly higher than that of pure PMMA. Copolymer tubes (diameter 18 mm, length 600 mm) were prepared by the copolymerization of TFPMA (10 and 20 wt%) with MMA (90 and 80 wt%) as the cladding of the optical fiber. In order to prepare GI POF based on these copolymers, a high refractive index compound, diphenyl sulfide (DPS) $\left( {n_{\rm D}^{20} \, = \,1.6330} \right)$, was added to the mixture of the monomers in the tube (as a core material) and then copolymerized by an interfacial gel polymerization technique. The material dispersion and optimum index exponent g were calculated and found to be very close to that of GI POF prepared from pure PMMA. The obtained copolymer preforms were drawn by heating at 220–250°C with controlling of drawing velocity. The resulting fiber diameter was 0.75 mm and the length was 50–150 m. The attenuation spectra of the fibers were measured and found to be similar to GI POF prepared using pure PMMA. The results indicate that the core material of GI POF can be prepared by a copolymer system in which the refractive indexes of homopolymers are very close to each other and the monomers yield a random copolymer. Copyright © 2008 John Wiley & Sons, Ltd.

Fluorescence characterization and gain studies on a dye-doped graded index polymer optical-fiber preform

Preparation of an appropriate optical-fiber preform is vital for the fabrication of graded-index polymer optical fibers (GIPOF), which are considered to be a good choice for providing inexpensive high bandwidth data links, for local area networks and telecommunication applications. Recent development of the interfacial gel polymerization technique has caused a dramatic reduction in the total attenuation in GIPOF, and this is one of the potential methods to prepare fiber preforms for the fabrication of dye-doped polymer-fiber amplifiers. In this paper, the preparation of a dye-doped graded-index poly(methyl methacrylate) (PMMA) rod by the interfacial gel polymerization method using a PMMA tube is reported. An organic compound of high-refractive index, viz., diphenyl phthalate (DPP), was used to obtain a graded-index distribution, and Rhodamine B (Rh B), was used to dope the PMMA rod. The refractive index profile of the rod was measured using an interferometric technique and the index exponent was estimated. The single pass gain of the rod was measured at a pump wavelength of 532 nm. The extent of doping of the Rh B in the preform was studied by axially exciting a thin slice of the rod with white light and measuring the spatial variation of the fluorescence intensity across the sample.

Doped Colloidal Photonic Crystal Structure with Refractive Index Chirping to the [111] Crystallographic Axis

A three-dimensionally ordered array of close-packed colloidal spheres, a photonic crystal structure in which the refractive index of the medium interstitial lattice in a colloidal crystal spatially changes in the [111] crystallographic axis, is demonstrated. The colloidal photonic crystal structure with refractive index chirping was produced by infiltration of a monomer and organic dopants with a high refractive index into a silica opal, followed by interfacial gel polymerization. The resulting photonic crystal structure has a gradually varying stop band at each different (111) plane in the face-centered cubic (fcc) crystal structure at a normal incidence. This novel structure exhibited optical characteristics that have band-gap broadening by the superposition of stop bands at each plane of the crystal with different dielectric functions. Moreover, the refractive index perturbation in the [111] fcc opal also showed a defect state within a pseudo-photonic band gap. This new type of photonic crystal structure should be useful for the band-gap engineering of photonic-band-gap materials.

Modeling isothermal free-radical frontal polymerization with gel effect using free volume theory, with and without inhibition

Frontal Polymerization is a process that converts monomers into polymers by means of a propagating spatially localized reaction front. Such fronts exist with free-radical polymerization, where in the simplest case, a mixture of monomers and initiator is placed into a test tube and upon initiation of the reaction at one end of the tube, a self-sustained wave develops and propagates through the tube. Isothermal Frontal Polymerization (IFP), often referred to as interfacial gel polymerization, occurs due to the coupling of mass diffusion of the species and the gel effect. Utilizing the free volume theory of Vrentas and Duda for describing the self-diffusive behavior of the gel effect, we mathematically model and study this IFP process. We determine, both numerically and analytically, characteristics of the process including the propagation velocity of the reaction zone, the structure of the wave, and the distance traveled by the front before it breaks down due to reactions ahead of the front.

Fabrication process and optical properties of perdeuterated graded-index polymer optical fiber

We proposed a graded-index polymer optical fiber (GI-POF) enabling greater-than-gigabit data transmission in a short reach network by applying a two-step interfacial-gel polymerization process to a perdeuterated polymer material. Using this process, it is possible to fabricate a nearly optimum refractive-index profile with good reproducibility. In this paper, the preparation of a perdeuterated polymethyl methacrylate (PMMA-d8)-based GI-POF utilizing a PMMA cladding is described. This means that the low-loss PMMA-d8 material is used only for the core. Because the cladding transmits only a small fraction of the optical power, a low-loss material is not necessarily required for the cladding. It was verified that the low attenuation of the PMMA-d8 was maintained even if the cladding was composed of hydrogenated PMMA. As a result, a gigabit data transmission over 300 m was achieved by the PMMA-d8-core and PMMA-cladding GI-POF, which was impossible by the conventional PMMA-based GI-POF.

Otrzymywanie preform metoda miedzyfazowej polimeryzacji zelowej

A method of preparation of poly(methyl methacrylate) (PMMA) preforms, showing gradient distribution of refractive index difference (An), in interfacial gel polymerization of methyl methacrylate (MMA) (Table 2 and 3) was elaborated. The effects of: radical initiator type [2,2'-azobisisobutyronitrile (AIBN) or benzoyl peroxide (NB)], its amount (0.001 or 0.002 mol/dm 3 ), amount of chain transfer agent (dodecyl mercaptan - MD, 0.01-0.03 mol/dm 3 ) as well as amount of bromonaphthalene (BN, 5-24 wt. %, being unreactive additive showing higher refractive index than polymer matrix, on the character of the curves illustrating An courses in the preforms were investigated (Figs. 1-8). It has been found that the preforms showing An courses nearly ideal were obtained when BN concentration was 17 wt. % and AIBN was used as an initiator. Mutual ratio of AIBN and MD concentrations allowing eliminating the bubbles' forming in the preform has been determined. These preforms can be used as precursors for gradient-index polymer optical fibers.

Preparation of heat‐resistant gradient‐index polymer optical fiber rods based on poly(N‐isopropylmaleimide‐co‐methyl methacrylate)

AbstractUsing the interfacial gel polymerization method, a heat‐resistant gradient‐index polymer optical fiber (GI POF) was developed based on the copolymer of methyl methacrylate (MMA) and N‐isopropylmaleimide (IPMI) as the matrix material and bromobenzene (BB) as dopant. The gradient distribution of IPMI in the GI POF rod was determined by element analysis. IPMI had great advantage in improving glass transition temperature (Tg) and forming a gradient‐index profile. There was a significant enhancement in the heat‐resistant property in comparison with a conventional GI POF rod. The combination of high thermal stability and easy fabrication makes the novel BB–IPMI–MMA system very suitable for heat‐resistant GI POF. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 280–283, 2003

Accurate refractive index profiling in a graded-index plastic optical fiber exceeding gigabit transmission rates

An optimum index profile offering the highest bit rate communication was formed in a poly methyl methacrylate (PMMA)-based graded-index plastic optical fiber (GI-POF) by modifying the polymerization process. The interfacial-gel polymerization process we have proposed to fabricate the PMMA-based GI-POF is capable of forming a nearly optimum refractive index profile. However, the theoretically calculated bandwidth from the measured index profile was reduced compared with a GI-POF with an optimum profile. In this paper, we report how to obtain a PMMA-based GI-POF having exactly the optimum index profile. The bandwidth of this ideal GI-POF was experimentally measured and a very high value of 2.88 GHz, even for a 150-m fiber length, was confirmed. The calculated bandwidth agreed well with the experimentally measured one. These results indicate that very low modal dispersion can be expected in a GI-POF fabricated by the modified interfacial-gel polymerization process.

Refractive index distribution of graded poly(methyl methacrylate) preform described by self-diffusion approaches of free-volume theory in a ternary system

A series of graded index poly(methyl methacrylate) (PMMA) preforms with monomer/dopant=5:1, 7:1, 10:1 have been made by an interfacial-gel polymerization procedure, in which polymerization was performed in a PMMA tube and a dopant, bromobenzene (BB), was used as a higher refractive index molecule. The graded index was formed by the diffusion of the molecules. While describing the process of interfacial-gel polymerization, the distribution of the polymer concentration at the radial direction of the tube was assumed to be ω=a(r/R)2+b. According to the self-diffusion approach of the free-volume theory in ternary systems and its application in a high-conversion polymerization system, a model of forming the graded index is established, and a quadratic refractive index (RI) distribution on the cross-section of the preform is obtained. Compared with the theory in a binary system, the result is more identical with experiments in both the changing trend and the value of RI. The RI distributions of preforms prepared with different MMA/BB were simulated. The effect of MMA/BB on the RI distribution was also discussed.

Mathematical modeling of interfacial gel polymerization for weak and strong gel effects

Mathematical modeling of interfacial gel polymerization for weak and strong gel effects

Mathematical modeling of interfacial gel polymerization for weak and strong gel effects

Frontal polymerization (FP) is a process in which a spatially localized reaction zone propagates into a monomer converting it into a polymer. Two types of FP processes have been observed experimentally. One is exothermic FP, which occurs due to diffusion of heat released in the polymerization reactions and which we have previously studied. The other is an isothermal FP process, also referred to as interfacial gel polymerization, which is due to mass diffusion of the species coupled with the gel effect. In a previous work we proposed and studied analytically a model of interfacial gel polymerization. That work discussed the case of an excessive amount of initiator in the initial mixture. In addition, it was assumed that the parameters of the problem were such that the steady-state assumption (SSA) concerning the total concentration of radicals holds not only in the bulk region, which is typically the case, but also in the gel region, which may limit the applicability of the results. In this work we seek to resolve the limitations associated with these two main assumptions. We relax the SSA in the gel region, analyze the various situations of initiator consumption for a weak gel effect, and study the case of a strong gel effect. We obtain analytical results, including the time-dependent propagation velocity of the reaction zone and the distance traveled by the front before it breaks down due to reactions ahead of the front, which are in good agreement with our numerical simulations.

A New Processing Method for the Fabrication of Cylindrical Objects with Radially Varying Properties

Objects with spatially varying properties are often desirable for some applications such as the functionally gradient materials (FGMs) in the field of powder metallurgy and ceramics or the graded-index plastic optical fibers (GI-POFs) for communications. In the case of FGMs, the material composition of the composite materials may vary spatially, whereas the refractive index varies continuously in the radial direction in the case of GI-POFs. Because of the peculiar property of such objects, they can have very specialized functions. When an optical fiber has a specific refractive index profile, it is capable of transmitting more optical signals per unit time, corresponding to higher bandwidth communications. While the concept of the objects with spatially varying properties has a great potential for various applications, the major obstacle has been limited availability of fabrication techniques. Although there are some methods available, such as the “centrifugal casting” for FGMs and the “interfacial-gel polymerization technique” for GI-POFs, their capabilities are still limited, requiring further development. In this paper, a new fabrication method for cylindrical objects with radially varying properties is introduced with an experimental confirmation. While this method is shown to be capable of producing GI-POFs, its applicability may not be limited to GI-POFs.

Mathematical modeling of interfacial gel polymerization

Frontal Polymerization (FP) is a process in which a spatially localized reaction zone propagates into a monomer converting it into a polymer. Two types of frontal polymerization processes have been observed experimentally. One is exothermic FP, which occurs due to diffusion of heat released in the polymerization reactions and which we have previously studied. The other is an isothermal FP process, also referred to as interfacial gel polymerization, which is due to mass diffusion of the species coupled with the gel effect. We propose and study a model of interfacial gel polymerization. We determine, both numerically and analytically, important characteristics of the process including the time-dependent propagation velocity of the reaction zone, the structure of the wave, and the distance traveled by the front before it breaks down due to reactions ahead of the front.

Preparation of graded index plastic rods doped with Nd3+by interfacial-gel polymerization

A novel graded index (GI) plastic rod was prepared by interfacial-gel polymerization carried out in a poly(methyl methacrylate) (PMMA) tube with one closed end. Bromobenzene (BB) was used to obtain a graded index distribution and neodymium octanate (NOA) as a dye with Nd3+ concentrations from 60 to 700 ppm. For a polymerization system containing methyl methacrylate (MMA) as monomers, azobis-isobutyronitrile (AIBN) as an initiator, and dodecyl mercaptain as chain transfer agents, the difference of the refractive index from the center to the periphery of the rod (Δn) was found to be 0.015 at 18 wt % of BB and 60 ppm of Nd3+. Experimental results also showed that a parabolic profile of refractive index formed on the cross section of the rod and Δn increased with BB contents increasing. NOA has little effect on the profile within the given concentrations. A description for forming the GI distribution is given by the free volume theory. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1431–1436, 1998

Preparation of graded index plastic rods doped with Sm3+ by interfacial-gel polymerization

A novel graded index (GI) poly(methyl methacrylate) (PMMA) rod was prepared by interfacial-gel polymerization carried out in a PMMA tube with one closed end. Bromobenzene (BB), a higher refractive index molecule, was used to obtain a graded index distribution and samarium octanoate (SOA) was used as a dye with Sm3+ concentrations from 60ppm to 700ppm. For a poly-merization system containing methyl methacrylate (MMA) as monomer, azobis-isobutyronitrile (AIBN) as initiator and dodecyl mercaptan as chain transfer agent, the difference of the refractive index from the centre to the periphery of the rod (Δn) with various BB and Sm3+ contents was determined. Experimental results showed that a parabolic profile of refractive index formed on the cross-section of the rod and Δn increased with increase of BB content. SOA has little effect on the profile within the given concentrations. The GI distribution may be calculated by free volume theory. The result is identical with the experimental distribution. © 1998 SCI.

Refractive Index Distribution of Graded Index Poly(methyl methacrylate) Preform Made by Interfacial-Gel Polymerization

A graded index poly(methyl methacrylate) (PMMA) preform has been made by a novel interfacial-gel polymerization procedure, in which polymerization was performed in a PMMA tube and a dopant, bromobenzene (BB), was used as a higher refractive index molecule. A detailed mechanism of the graded index formation is given and simulated according to the free volume theory and its application in a high-conversion polymerization system. Under the assumption that polymer concentration distributes in the form of ω = a exp(r) + b at the radial direction of the tube, a quadratic distribution of refractive index on the cross section of the preform is obtained. The result is identical with experiments performed by the interfacial-gel polymerization.

Formation of the refractive index profile in the graded index polymer optical fiber for gigabit data transmission

Bandwidth characteristics of the large core graded index polymer optical fiber (GI-POF) are theoretically and experimentally clarified. The refractive index profile of the GI-POF was controlled by interfacial-gel polymerization to investigate the relation between the index profile and the bandwidth characteristics. It was experimentally confirmed that the maximum bandwidth of the poly methyl methacrylate (PMMA) base GI-POF is at most 3 GHz for 100 m transmission using a typical laser diode emitting at 650-nm wavelength (3 nm source spectral width) when its refractive index profile is optimized. The maximum bandwidth theoretically estimated by considering both modal and material dispersions is approximately 3 GHz which is exactly the same as the measured value, while higher than 10 GHz for 100 m was expected if only modal dispersion was taken into account. The optimum refractive index profile of the PMMA base GI-POF is theoretically and experimentally clarified by considering the profile dispersion further.

Giga Bit Transmission in High-Bandwidth Low-Loss Perdeuterated Polymer base Graded-Index Polymer Optical Fiber Link.

This paper describes the high speed transmission characteristics of the perdeuterated poly methyl methacrylate (PMMA-d8) base graded-index (GI) polymer optical fiber (POF). The PMMA-d8 base GI POF was obtained by the interfacial-gel polymerization technique. We succeeded in I Gb/s 160m transmission at 650-nm wavelength in the 160-m GI POF link. In general, the possible transmission distance of the PMMA POF link is limited to approximately 100m because of high attenuation. However, substitution of hydrogen atoms in the polymer for deuterium atoms decreases the intrinsic absorption loss. The total attenuation of the PMMA-d8 base GI POF at 650-nm wavelength was about 60dB/km which is approximately half of the attenuation of PMMA base GI POF. Therefore the low-loss PMMA-d8 base GI POF enables longer distance communication. We also analyzed the dispersion property of the PMMA-d8 base GI POF by utilizing WKB method in which both modal and material dispersion were taken into consideration. It was clarified that approximately 2Gb/s transmission can be achieved by the PMMA-d8 base GI POF with 200-m length when 650-nm wavelength is adopted as the signal wavelength. The PMMA-d8 base fiber has two optical windows of light transmission which are located around 650-680-nm and 780-nm wavelengths. As the material dispersion decreases with increasing the signal wavelength, the use of the light source operating at 780nm is effective for higher bit rate transmission. It was also confirmed that the PMMA-d8 base GI POF can transmit about 3Gb/s for 200m when the signal wavelength is 780nm. These experimental and theoretical results indicate that the PMMA-d8 base GI POF could be one of the promising candidate of the physical layers in the high speed multimedia network.