3D-printed Tilt Sensor based on an embedded Two-mode Fiber Interferometer

A 3D-printed tilt fiber sensor using a two-mode fiber interferometer (TMFI) as the sensing mechanism has been demonstrated. The TMFI was constructed by splicing single-mode fibers (SMF28s) at both ends of a two-mode fiber (TMF) to generate a comb-like interference spectrum that is sensitive to bending. A 3D-printed cantilever with a weight attached to one end was used to induce bending as the structure was tilted and by embedding the TMFI onto the 3D printed cantilever, different tilt angles can be measured, as a result of the bending of the fiber. The TMFI exhibited a linear response towards the tilt angles, θ, with a responsivity of 1 × 10-2 nm/deg at negative θ (0 to -90°) and 5 × 10-3 nm/deg at positive θ (0 to 90°), respectively. The sensor was able to detect small angle changes in increments as small as 1° and it performs better than embedded FBG sensors. The tilt sensor proposed has a small form factor and simple design, as well as being cost-effective and light-weight, thus showing significant potential for a variety of civil engineering applications

Air-holes induced multimodal fiber design to increase the effective index difference between higher order guided modes

A novel technique is proposed to increase the effective index difference (△neff) between higher order modes of a multimode step-index fiber. Multimode fibers provide a higher effective area and their higher order modes are also resistant to area reduction due to bending. However, the larger effective area comes with an increased number of modes which are more prone to mode coupling and mode mixing. The modal stability is directly related to the effective index difference between the mode of propagation and its neighboring modes. We have shown here that the modal stability between LP06 mode and its neighboring antisymmetric LP15 and LP16 modes can be increased more than 54% by the introduction of air-holes array along the circumference of the fiber. We have also shown variation in the effective index difference with possible fabrication tolerances that may occur in air-holes size and change in their locations. Furthermore, the technique presented here can also be applied to increase the stability of other higher modes of a multimode fiber

Augmenting data rate performance for higher order modulation in triangular index profile multicore fiber interconnect

A triangular profile multicore fiber (MCF) optical interconnect (OI) is investigated to augment performance that typically degrades at high data rates for higher order modulation in a short reach transmission system. Firstly, probability density functions (PDFs) variation with inter-core crosstalk is calculated for 8-core MCF OI with different index profile in the core and it was observed that the triangular profile MCF OI is the most crosstalk tolerant. Next, symbol error probability (SEP) for higher order quadrature phase shift keying (QPSK) modulated signal due to inter-core crosstalk is analytically obtained and their dependence on typical characteristic parameters are examined. Further, numerical simulations are carried out to compare the error performance of QPSK for step index and triangular index MCF OI by generating eye diagram at 40 Gbps per channel. Finally, it is shown that MCF OI with triangular index profile supporting QPSK has double spectral efficiency with tolerable trade off in SEP as compared with those of binary phase shift keying (BPSK) at high data rates which is scalable up to 5 Tbps

Computer modelling of photonic devices for optical measurements

The emergence and progress of optical technologies have enabled them to have a profound effect in telecommunications and consumer electronics and also for optical sensing and measurements. To exploit fully the potential of the available faster transmission rates, higher bandwidths, and low transmission losses available with optics, the aim is to increase the capability of optical systems by introducing approaches based on new physical principles and on the optimization of such devices. Analytic modelling techniques are available, but however, lightwave systems do not lend themselves well to such models, due to the frequent use of unrealistic assumptions and design restrictions in some cases. A better approach is computer aided modelling which can be flexible and has been developed for the range of lightwave systems, with the potential to take into account important systems features. A wide range of computer-aided design and simulation packages have been developed for a considerable number of photonic devices. Modelling work carried out on MMI (multimode interference) devices is presented, as representative of thi

Novel 3D-printed biaxial tilt sensor based on fiber Bragg grating sensing approach

In this work, a novel 3D-printed biaxial sensor system for tilt measurement, based primarily on the use of four Fiber Bragg Grating (FBG) devices, has been developed and its performance characterized. The tilt sensor system created is of a compact design and relatively small dimensions, making it ideally suited to a variety of industrial applications. In the system developed, the four FBGs used were spliced in a serial formation and attached to four different sides of the sensor structure designed, to allow biaxial measurements to be made. The wavelengths' shift of the FBGs used were monitored as a function of the tilt of the device, using an Optical Spectrum Analyzer (OSA) for this development work. In the sensor, an average FBG-based responsivity of 0.01 nm/° of tilt was measured for each of the different FBGs used. To provide compensation for temperature changes in the system itself, a further FBG-based approach was used (in which they were configured to be insensitive to the effect of the tilt). They were thus calibrated by being exposed to a range of operational temperatures for the system, showing, as a result, a calibration of 0.011 nm/°C. Prior work on the sensor system had proved it to be highly linear in response, over the tilt range of 0° ± 90°. The experimental results obtained from the performance characterization indicate that the small, compact design of this type yields excellent responsivity, compared to other larger and more complex designs discussed in the literature. The sensor system was also relatively easy to fabricate using the 3D-printing method, creating in that way an inexpensive, temperature-compensated tilt monitoring device that had a wide variety of potential industrial applications

Enhanced spectral sensitivity of fibre long period gratings to refractive index of aqueous solutions utilising copper patterned coatings

A set of long period grating devices have been fabricated in photosensitive single mode fibre coated with a series of copper rings (period of 380μm, 50% duty cycle and length of 4cm). The long period gratings were inscribed with a uniform UV-laser exposure across the entire length of the copper ring patterned coating. The devices ranged in copper thickness from 0.5μm to 1.5μm. In addition, a control long period grating was fabricated in the same type of fibre with the same period for comparison. The refractive index and temperature spectral sensitivity of these devices were investigated and it was found that the index and temperature sensitivity is a function of the thickness of the copper rings, as supported by theoretical modelling. Furthermore, the index sensitivity of these devices in the 1.333 index region is greater than the control long period grating. The patterned 0.5μm coated long period grating gave a sensitivity of Δλ/Δn = -74 nm leading to a resolution of 1.4×10-3 compared to the control which had a sensitivity of Δλ/Δn = -32 nm with a resolution of 3.2×10-3 in the index region of 1.320 to 1.380 (aqueous solution regime). This demonstrates a two fold increase in the sensitivity. This novel fibre long period grating device shows potential for increasing the resolution of measurements of the index of aqueous solutions