Electrically tunable Bragg gratings in single-mode polymer optical fiber

Abstract

We present what is to our knowledge the first demonstration of a tunable fiber Bragg grating device in polymer optical fiber that utilizes a thin-film resistive heater deposited on the surface of the fiber. The polymer fiber was coated via photochemical deposition of a Pd/ Cu metallic layer with a procedure induced by vacuum-ultraviolet radiation at room temperature. The resulting device, when wavelength tuned via joule heating, underwent a wavelength shift of 2 nm for a moderate input power of 160 mW, a wavelength to input power coefficient of −13.4 pm/ mW, and a time constant of 1. There are many important applications for tunable fiber devices in optical sensing and lightwave communication systems. The use of fiber Bragg gratings (FGBs) as tunable filtering candidates has been demonstrated in glass fibers with wavelength and bandwidth tunability shown by use of strain 1 and temperature.2,3 FBG filters coated with thin-film heaters on the surface have been promoted as wavelength-tunable devices because of their compact nature, fast response, and high efficiency. It has been noted recently that polymer optical FBGs have a high temperature sensitivity, 4 and hence they may be suitable candidates for producing a widely tunable filter by heating the fiber. Thermally tuned gratings in polymer waveguides have resulted in large wavelength tuning, but in polymer material that cannot be extruded into fiber. 5 In this Letter we demonstrate what is believed to be the first wavelength-tunable polymer optical FBG filtering device that relies on thin-film resistive load heating to produce wavelength changes.FBGs were inscribed into step-index single-and few-mode polymer optical fiber [polymethylmethacrylate (PMMA)] by use of a 30 mW Kimmon IK series HeCd laser emitting at 325 nm by means of the standard phase mask technique. The phase mask had a pitch of 1060.85 nm and was designed to produce a FBG at 1568 nm in the polymer optical fiber, in contrast with the 1536 nm design wavelength for silica fiber. Further details of the inscription procedure may be found in Ref. 6.The surface region around the grating was coated with a Pd/ Cu metallic layer; the former aided adhesion to the PMMA, and the latter acted as the thinfilm heater element. Metal deposition was initiated by use of a vacuum-ultraviolet (VUV) light source operating at 172 nm and at low (room) temperature using the arrangement in Fig. 1. At this wavelength the penetration depth of the light source is of the order of 1 m, and therefore there is no damage to the grating device, but the surface of the sample undergoes chemical roughening, as the light initiates bond Fig. 1. Schematic diagram of the coating procedure.

Microfluidic Flows and Heat Transfer and Their Influence on Optical Modes in Microstructure Fibers

“…The results are shown in Figure 3, where the steady-state temperature of the water channel is plotted vs. time. This shows that the time taken to reach thermal equilibrium within the water channel of the MOF is ~0.6 s and is consistent with the experimental work of Kalli et al [28,29]. This confirms the response of the MOF, and as such, only steady-state solutions are considered further in this study.…”

Tunable Bulk Polymer Planar Bragg Gratings Electrified via Femtosecond Laser Reductive Sintering of CuO Nanoparticles

“…With a Bragg wavelength shift of −547 pm at a consumed electrical power of 18.3 mW, the tunable COC‐PPBGs electro‐optic efficiency is about two times higher than that of a thermo‐optically tunable Bragg grating within a poly(methyl methacrylate) fiber, coated with a Pd/Cu thin film, and that of a silica fiber Bragg grating coated with a Ti/Pt/Ni alloy. [ 56,57 ] It is worthwhile to note that the demonstrated devices, especially but not solely the shown Cu conducting path geometries and configurations, are not yet finally optimized for efficient electro‐optic tuning. It is therefore expected that the adaptation of various parameters such as conducting path positioning, cross section, and general design yields noticeable further improvement of the electrified COC‐PPBG's tuning capabilities.…”

Challenges in the fabrication of fibre Bragg gratings in silica and polymer microstructured optical fibres

“…Finally, gratings in polymer fibres have been reported to exhibit significant temperature sensitivity . This has been exploited, for example, to obtain electrically tuneable Bragg grating filter devices . On the other hand this sensitivity to temperature may lead to an undesirably large cross‐sensitivity to temperature changes in sensor applications.…”

“…The main idea was that reducing the amount of air holes would facilitate the passage of the inscription laser beam to the core region, which led to using MOFs with a limited amount of air hole rings, fibres with rows of air holes instead of rings of air holes , and MOFs with holes missing in the lattice . Other features such as a flattened outer surface or a sleeve in the cladding in view of facilitating the alignment have also been proposed.…”