Ultra-compact single-mode fiber optical tweezer based on a 3D printed hybrid micro-optical structure (Conference Presentation)

Frequency fluctuation in a single-mode optical fiber is briefly discussed, and a preliminary experiment for optical heterodyne communication in a single-mode fiber is carried out with the aid of frequency-stabilized He-Ne lasers operating at a wavelength of 0.633 microm. As a result, we have obtained clear demodulated signals, having sinusoidal, triangular, and rectangular waveforms, through an optical fiber 100 m in length.

We study the problem of coupling partially coherent radially polarized (PCRP) vortex beams into a single-mode optical fiber. Using the well-known concept of the cross-spectral density (CSD) matrix, we derive a general expression for the coupling efficiency of the partially coherent beam into a single-mode fiber. We adopt PCRP vortex beams for incident beams and use our general results to discuss the effects of the coherence, topological charge, and wavelength on the coupling efficiency of an optical beam focused onto a single-mode fiber with a lens. Our results should be useful for any application that requires coupling of partially coherent beams into optical fibers.

Fiber optic sensors offer a high-performance alternative because they provide a low-cost solution, resistance to electromagnetic interference, multiplexing capabilities, and high integration. The performance of fiber optic sensors applies to measuring physical parameters such as pressure, bending, and temperature. This study aims to determine the optimal value of using optical fiber types in landslide early detection sensors. The method used is bending in the form of deflection on the optical fiber. The deflection values used are 0 mm - 15 mm, 0 mm - 20 mm, and 0 mm - 25 mm. The optical fiber is placed horizontally in the middle of the bending tool. This bending affects the deflection of the optical fiber, resulting in the attenuation of light in the optical fiber. The deflection phenomenon results in light attenuation in the optical fiber. The sensitivity level of a single-mode fiber optic sensor is higher than a multimode. It shows the greater linearity value in each deflection treatment. Single-mode optical fiber linearity data on deflection variations of 0 - 15 mm, 0 - 20 mm, and 0 - 25 mm, respectively, are 0.9833, 0.9871, and 0.9847. At the same time, the linearity data of multimode optical fiber is 0.8926, 0.9841, and 0.9687. Single-mode optical fiber is more sensitive than multimode optical fiber. It is caused by the core diameter of single-mode optical fiber, which is much smaller than that of multimode optical fiber. The difference in core diameter results in differences in light propagation in the optical fiber. The small diameter of the core has a low dispersion level so that more light intensity is reflected into the core. Light attenuation occurs in a single-mode optical fiber due to macro bending treatment. Meanwhile, the attenuation of light in Multimode fiber optics is due to the bending and dispersion of light. Therefore, a landslide early detection sensor design is more optimal by using a single-mode optical fiber.

For several decades silica-based optical fibres have been used for telecommunication and sensor purposes. The single-mode fibre is frequently employed in long-distance networks, whereas the multi-mode fibre is the preferred means of signal transport in campus and in-building networks. Because of the huge bandwidth of optical fibres in comparison to its electrical wireless and copper-based counterparts, the demand for optical fibres keeps increasing. In a competitive market, fibre manufacturers aim to produce ever better fibres that are as cheap and easy to employ as possible. As fibre research, development and manufacturing is a mature discipline, improvements in fibre design can only be achieved through the construction of robust, accurate and efficient numerical fibre models for the computation of those quantities that determine the behaviour of the fibre. We have developed a modular software code, based on Maxwell’s equations, to compute these quantities in a vectorial full-wave way for both single-mode and multi-mode optical fibres. Key is the refractive-index profile, or, more specifically, the dopant profile, as it defines the propagation, splicing and bending-loss characteristics of the fibre. For the single-mode fibre, the fibre quantities that we have concentrated on are dispersion, dispersion slope, mode-field diameter, effective area, bending loss, effective and theoretical cut-off wavelength and MAC-value. We highlight one fibre quantity in particular, viz. the computation of the bending loss in a single-mode fibre. Many approximate modelling techniques have been developed to estimate this loss in a fast way. Our numerical scheme, however, is the first rigorous one, as we have performed a vectorial full-wave analysis of the bent optical fibre. In this context, triple integrals involving products of Bessel functions with large, complex order and argument appear. Due to cancellations in the pertaining computation, a high relative accuracy is needed for the computation of each product. As a result, it takes weeks on a contemporary computer to compute the bending loss as a function of the radius of curvature. We have used the vectorial full-wave bending-loss results to determine the most appropriate approximate method. Subsequently, we have extended that approximate method to compute the bending losses of higher-order modes, since the required effective cut-off wavelength depends on the bending loss of the first higher-order mode. The selected approximate method has been used in the ensuing bending-loss calculations. Since the fibre properties are often conflicting, it is a challenging task to adapt the radial dopant profile to meet a set of predefined design goals. A design goal is a combination of desired values for (some of) the aforementioned fibre quantities, and can mathematically be translated into a cost function. The minimisation of this cost function provides us with the optimal dopant profile for that specific set. For the single-mode fibre, we have performed this minimisation for piecewise-linear profiles, by employing various global and gradient-based local optimisation strategies to speed up the design step considerably. Frequently,these optimisation strategies lead to counter-intuitive dopant profile designs that could not have been contrived otherwise. We have selected a deliberate mix of several optimisation routines and have compared their performances. Perhaps the most important conclusion is that there still appears to be room for improvement in the design of the radial dopant profile of commercially available fibres. For the multi-mode fibre, vectorial full-wave optimisation is not feasible yet because of the long computation times for the large number of propagating modes. Still, our numerical scheme allows for a manual fine-tuning of the popular power-law profile to minimise differential mode delay. Further, we have included mode coupling and differential mode attenuation in our model to obtain intensity patterns that match closely with measurements. We have also analysed the influence of profile variations, e.g. on-axis dips and kinks, on the intensity pattern. A selective excitation of different mode groups in a multi-mode fibre, offers the possibility to create several independent transmission channels, and thus a higher information capacity. Recently, the feasibility of this so-called mode group diversity multiplexing technique has been demonstrated. Simulations provide us with a means to better understand its operation and possibly increase its efficiency. The channel separation may be enhanced by employing a lens between the fibre and the detector, which is called mode-selective spatial filtering. Our numerical simulations of a mode group diversity multiplexing link, with and without mode-selective spatial filtering, are in agreement with the measurements. The above discussion makes clear that the developed software code has a wide range of applicability. Moreover, it is built in a modular way and thus extensions, like the inclusion of more fibre quantities or different profile dopants, are straightforward.

In this work, we develop a fluidic laser beam shaper based on the thermal lens effect in MoS2 suspensions. It is demonstrated that another weak unfocused Gaussian beam (probe beam) is transformed into an annular beam due to the thermal lens effect resulting from a strong focused Gaussian beam (pump beam). The time evolution of the generated annular beam is studied, and the result shows that the annular beam exhibits asymmetric caused by heat convection with the high pump beam power. In addition, the tunability of the generated annular beam is investigated. Furthermore, the optical trapping of micro-sized particles in air using the annular beam is researched. It is found that this method exhibits stable performance capture for 3 h. The advantages of adjustable size, flexible setup and low cost of annular beam generated method are significant for lots of laser applications, such as optical trapping, optical imaging and laser machining.

A Raman OTDR (ROTDR) fault location for a 100-km-long single-mode optical fiber has been tested. A Ge p-i-n photodiode cooled by liquid nitrogen has been used as a backscattered light receiver. The signal-to-noise ration (SNR) improvement of the cooled Ge p-i-n photodiode from a Ge avalanche photodiode (Ge APD), which operates at room temperature, is 14 dB. Spectral Stokes light power distributions, which have been emitted from a long single-mode fiber, have been measured to estimate the maximum locatable length for a single-mode fiber. It has been shown, from the measurements and calculations, that a 100- km-long and a 30-dB total attenuation at a 1.55-μm wavelength single-mode fiber fault location can be achieved with the aid of an averaging technique. On the basis of these results, a 102-km-long single-mode fiber fault location experiment has been successfully carried out.

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The optical fibres that will be used in SLHC detectors will be exposed to high doses and low temperatures in the inner detectors. A number of Single-Mode (SM) and Multi-Mode (MM) fibres have been tested for radiation hardness by exposure beyond a full SLHC dose to 500 kGy(Si) in the -25°C operating temperatures expected in the upgraded inner detectors. From these measurements conservative estimates of the level of Radiation Induced Absorption (RIA) have been calculated for these fibres in realistic paths through an upgraded inner detector. Two SM fibres have been found whose total calculated RIAs were much lower than the budgeted 1 dB, despite the high dose rates used in the experiment. The RIAs for the DrakaElite Super RadHard Single-Mode Fiber and Fibre X were calculated to be 0.142 and 0.064 dB respectively. Another SM and a MM fibre showed high levels of RIA during the experiment, however they cannot be ruled out as candidate fibres due the the high dose rate of 27 kGy(Si)/hr used.

Bend-induced retardation and twist-induced rotation in single-mode optical fibers are important variables in the design of optical fiber current measurement systems. Bend-induced retardation varies with the square of the curvature and is believed caused by a waveguide geometry effect. Twist-induced rotation varies with the angle through which the fiber is twisted and is produced by torsional strain in the fiber. Both effects were found highly reproducible and to have small temperature dependence. Neither effect should significantly limit the performance of optical measurement systems using single-mode fibers.

Propagation characteristics of annular laser beams passing through the reflection Bragg grating with deformation

Optical trapping is widely used in different areas, ranging from biomedical applications, to physics and material sciences. In recent years, optical fiber tweezers have attracted significant attention in the field of optical trapping due to their flexible manipulation, compact structure, and easy fabrication. As a versatile tool for optical trapping and manipulation, optical fiber tweezers can be used to trap, manipulate, arrange, and assemble tiny objects. Here, we review the optical fiber tweezers-based trapping and manipulation, including dual fiber tweezers for trapping and manipulation, single fiber tweezers for trapping and single cell analysis, optical fiber tweezers for cell assembly, structured optical fiber for enhanced trapping and manipulation, subwavelength optical fiber wire for evanescent fields-based trapping and delivery, and photothermal trapping, assembly, and manipulation.

The special optical fibers, with large mode field, are developed for fabricating high power optical fibers passive components. If a conventional fiber optical laser is used as optical source, the coupling efficiency between special optical fibers and conventional single mode fibers (SMFs) need to be improved. We investigate the specialty optical fibers property and its effect on the coupling efficiency using an electric arc fusion splicer. Improper splicing parameters can lead to coupling efficiency sharply decreased. Several splicing methods are utilized, and all the results are proposed. Comparing these results, we find a set of splicing parameters for reducing the scattering loss at the splice point. It was demonstrated that properly splicing parameters can make coupling efficiency greatly increased; furthermore, a balance between splicing strength and coupling loss was achieved.

Optical tweezers is a powerful tool which is used to capture and manipulate microscopic particles such as dielectric microspheres and cells. In the single optical trap the beam is strongly focused to a diffraction limited spot by a high numerical aperture objective. Resently a new version of optical trap was demonstrated with optical fibers. Compared with the common optical tweezers which required high power microscope objective and carefully adjusted optical path, the fiber optical tweezers are compact in size and less expensive. Moreover, they have also a working distance not necessarily close to the objective as for a typical optical tweezers.In this work we present the development of a single beam optical fiber trapping system integrated with an optical fiber ablation system for micromanipulation of biological objects. The fiber trap was formed using a continuous wave He-Ne laser operating at 632.8 nm. The fiber ablation system was formed using a free-running Er:YAG laser operating at 2.94 μm with pulse duration of 80 μm. The ablation beam was coupled into the front end of a fluoride glass optical fiber via a focusing lens of 100 mm and a pinhole of 50 μm. We evaluated the fluoride glass optical fiber as far as attenuation and as far as the spatial distribution of the energy output is concerned. We verified that optical trapping and the micromanipulation of micro objects were easily achieved, by a focused laser beam, emerging from optical fiber inclined at 42 degrees to the sample.

A detailed investigation of the nonlinear multimodal interference in a short graded-index multimode optical fiber is presented. The analysis is performed for a specific device geometry, where the light is coupled in and out of the multimode fiber via single-mode fibers. The same device geometry was recently used to obtain ultra-low-loss coupling between two single-mode optical fibers with very different mode-field diameters. Our results indicate the potential application of this simple geometry for nonlinear devices, such as in nonlinear switching, optical signal processing, or as saturable absorbers in mode-locked fiber lasers. Saturable absorption in this all-fiber configuration is discussed and it is shown that it provides attractive properties that can potentially be used in high pulse energy mode-locked fiber lasers.

This paper describes results of a recent study that characterizes effective index of refraction for commercially available matched-clad, single-mode optical fibers. Effects of product parameter, stress, and temperature ranges on the index are reported. Direct measurements of flight times, fiber lengths, tensile loads, elongations, and temperatures provide index of refraction accuracy to four decimal places. Nominal effective index of refraction values found for unshifted fiber were 1.4675 and 1.4681 at 1300 nm and 1550 nm wavelengths, respectively; values for dispersion-shifted fiber were 1.4718 and 1.4711. Both fiber types at each wavelength displayed index versus stress slopes of -0.000024/kpsi, and index versus temperature slopes of 0.000012/°C.