Polymer Optical Fiber Gratings Research Articles

Potential of high-sensitivity tactile sensing using polymer optical fiber gratings

We characterize fiber gratings inscribed line-by-line in perfluorinated graded-index polymer optical fibers (PFGI-POFs) for tactile sensing. First, we measure the dependence of the wideband transmitted light spectrum on the distance between the fiber grating and an object composed of metal or rubber, clarifying that the spectral power is significantly dependent on the object position in a wide wavelength range. Subsequently, we experimentally show that this behavior is caused by the light scattering at the fiber grating, indicating that PFGI-POF gratings are potentially applicable to simple low-cost tactile sensors or high-sensitivity short-range displacement sensors with no need for additional supportive tools.

Fabrication and Application of Polymer Optical Fiber Gratings: A Review

Fabrication and Application of Polymer Optical Fiber Gratings: A Review

Latest Achievements in Polymer Optical Fiber Gratings: Fabrication and Applications

Grating devices in polymer optical fibers (POFs) have attracted huge interest for many potential applications in recent years. This paper presents the state of the art regarding the fabrication of different types of POF gratings, such as uniform, phase-shifted, tilted, chirped, and long period gratings, and explores potential application scenarios, such as biosensing and optical communications.

Advances on Polymer Optical Fiber Gratings Using a KrF Pulsed Laser System Operating at 248 nm

This paper presents the achievements and progress made on the polymer optical fiber (POF) gratings inscription in different types of Fiber Bragg Gratings (FBGs) and long period gratings (LPGs). Since the first demonstration of POFBGs in 1999, significant progress has been made where the inscription times that were higher than 1 h have been reduced to 15 ns with the application of the krypton fluoride (KrF) pulsed laser operating at 248 nm and thermal treatments such as the pre-annealing of fibers. In addition, the application of dopants such as benzyl dimethyl ketal (BDK) has provided a significant decrease of the fiber inscription time. Furthermore, such improvements lead to the possibility of inscribing POF gratings in 850 nm and 600 nm, instead of only the 1550 nm region. The progress on the inscription of different types of polymer optical fiber Bragg gratings (POFBGs) such as chirped POFBGs and phase-shifted POFBGs are also reported in this review.

Etching Process Related Changes and Effects on Solid-Core Single-Mode Polymer Optical Fiber Grating

Etching process related material and mechanical changes on solid-core single-mode polymer optical fiber (POF) and their influence on the characteristic properties of polymer fiber Bragg gratings (PFBGs) are studied. A poly(methyl methacrylate)-based POF is etched to different diameters, and it is experimentally demonstrated that etching can lead to a change in the Young's modulus of the fiber. It is found that etching process induced material changes of the polymer fiber can enhance the reflectivity and inherent sensitivity of PFBGs. It is demonstrated that gratings based on etched POF exhibit higher reflectivity with a shorter exposure time compared with unetched ones. Highest reflectivity of 98.54% is observed within 7 seconds of exposure for a diameter of 85 $\mu\text{m}$ . The stability of fabricated Bragg gratings is also studied. By tailoring the etching diameter of POF, Bragg gratings with high sensitivity and high reflectivity can be fabricated.

Analysis of viscoelasticity of POF gratings in the stress sensing

The time-dependent behavior of polymer optical fiber (POF) grating under constant tensile stresses has been studied. We show that the evident time-dependence is due to the viscoelastic nature of POF grating materials that can be described with the Kelvin Model. Based on the Kelvin Model, the time-dependent relationship between the Bragg wavelength shift and stress has been analyzed in detail. The results show that the viscoelasticity has a great impact upon the stress response of POF gratings. With the increment of stress level, the visco response part increases faster than that of elastic response part. Especially, the response and recovery with and without stress can be fitted with dual exponential decay and the time constant of fast response and relaxation is ∼102s and that of the slow is ∼103s, which corresponds to the fast and slow movements of polymer segments, respectively. Experiments and regressions also show that the stress sensitivity is observed to be 369pm/MPa for the immediate response and 598pm/MPa for response balance, showing high stress sensitivity. All the spring stiffness and dashpot viscosity of Kelvin elements are larger than 1010Pa and 1013Pas. The dashpot viscosity of slow Kelvin element (1014Pas) is around one order larger than that of fast Kelvin element (1013Pas) with stress. Further analysis demonstrate the response and recovery of POF gratings with and without the stress displays an evident non-linear viscoelasticity, which will bring more complexity for POF gratings in the mechanical sensing applications.

Analysis of multimode BDK doped POF gratings for temperature sensing

We report a temperature sensor based on a Bragg grating written in a benzil dimethyl ketal (BDK) doped multimode (MM) polymer optical fiber (POF) for the first time to our knowledge. The thermal response was further analyzed in view of theory and experiment. In theory, with the order of the reflected mode increasing from 1st to 60th order, for MM silica fiber Bragg grating (FBG) the temperature sensitivity will increase linearly from 16.2pm/°C to 17.5pm/°C, while for MM polymer FBG the temperature sensitivity (absolute value) will increase linearly from −79.5pm/°C to −104.4pm/°C. In addition, temperature sensitivity of MM polymer FBG exhibits almost 1 order larger mode order dependence than that of MM silica FBG. In experiment, the Bragg wavelength shift will decline linearly as the temperature rises, contrary to that of MM silica FBG. The temperature sensitivity of MM polymer FBG is ranged from −0.097nm/°C to −0.111nm/°C, more than 8 times that of MM silica FBG, showing great potential used as a temperature sensor.

Optical manipulable polymer optical fiber Bragg gratings with azopolymer as core material

Polymer optical fiber (POF) with a core of azopolymer has been fabricated. Based on the photoinduced birefringence of azopolymer materials, a mechanism for writing POF gratings is presented. After writing in azopolymer optical fiber (APOF) by two beams of mutually orthogonal polarizations, a birefringence grating was formed, and then the gratings could be erased almost totally for a short time by the circularly polarized beam at the same wavelength. By manipulating the APOF gratings, the transmittance through APOF at 632.8nm can be adjustable as revealed by the transmittance change during write-erase-write procedure.

Polymer Optical Fiber Photosensitivities and Highly Tunable Fiber Gratings

In this paper, recent progress in the investigation of photosensitivities of polymer optical fibers and the development of polymer optical fiber grating is reported. Photosensitivities in various polymer fibers, including doped and undoped, multimode and single-mode polymer fibers, have been experimentally characterized and evaluated for fiber grating application. In particular, the wavelength dependence of material absorption and photosensitivity has been found essential to the fabrication of polymer optical fiber grating. Based on the results of photosensitivity research, polymer optical fiber gratings have been successfully fabricated. More importantly, polymer optical fiber grating has been demonstrated highly tunable, with a tuning range more than 70 nm. The unique feature of high tunability in polymer optical fiber grating has great potential in various applications including optical fiber WDM systems and fiber sensor systems. Several important issues that remain to be investigated will also be discussed.

Highly tunable Bragg gratings in single-mode polymer optical fibers

A Bragg grating in a single-mode polymer optical fiber (POF) has been created. The novel grating has a length of 1 cm with a reflectivity of 80% and a linewidth of about 0.5 nm. The wavelength tunability of the POF grating by stretching was investigated and a wavelength tunable range of 20 nm has been achieved. Based on the properties of the polymer, we believe that this kind of grating has a wavelength tuning potential of more than 100 nm.