Single-mode-multimode-multimode device: sensitivity of the single mode to the fiber parameters and geometrical misalignments
01 Feb 2016-Journal of The Optical Society of America B-optical Physics (Optical Society of America)-Vol. 33, Iss: 2, pp 211-219
TL;DR: In this paper, the sensitivity of single-mode quality to small variations in the fiber parameters and geometrical misalignments is studied in detail, and different methods are suggested to mitigate the mode quality degradation caused by errors in fiber parameters.
Abstract: Single-mode–multimode–multimode (SMm) fiber structure provides an all-fiber solution for exciting a single radial mode in a multimode fiber (MMF). The proposed SMm design essentially exploits the interfering modes of the first MMF for exciting a single mode in the second. In this paper, the sensitivity of single-mode quality to small variations in the fiber parameters and geometrical misalignments is studied in detail. Different methods are suggested to mitigate the mode quality degradation caused by errors in the fiber parameters. An estimate of the acceptable geometrical misalignments in the structure is also given for achieving a high-quality single mode from the device.
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TL;DR: A singlemode-multimode-singlemode (SMS) fiber structure consists of a short section of multimode fiber fusion-spliced between two SMS fibers as mentioned in this paper.
Abstract: A singlemode-multimode-singlemode (SMS) fiber structure consists of a short section of multimode fiber fusion- spliced between two SMS fibers. The mechanism underpinning the operation of an SMS fiber structure is multimode interference and associated self-imaging. SMS structures can be used in a variety of optical fiber systems but are most commonly used as sensors for a variety of parameters, ranging from macro-world measurands such as temperature, strain, vibration, flow rate, RI and humidity to the micro-world with measurands such as proteins, pathogens, DNA and specific molecules. While traditional SMS structures employ a short section of standard multimode fiber, a large number of structures have been investigated and demonstrated over the last decade involving the replacement of the multimode fiber section with alternatives such as a hollow core fiber or a tapered fiber. The objective of replacing the multimode fiber has most often been to allow sensing of different measurands or to improve sensitivity. In this paper, several different categories of SMS fiber structures, including traditional SMS, modified SMS and tapered SMS fiber structures are discussed with some theoretical underpinning and reviews of a wide variety of sensing examples and recent advances. The paper then summarizes and compares the performances of a variety of sensors which have been published under a number of headings. The paper concludes by considering the challenges faced by SMS based sensing schemes in terms of their deployment in real world applications and discusses possible future developments of SMS fiber sensors.
80 citations
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TL;DR: In this article, an all-fiber passively mode-locked laser operation based on the nonlinear multimode interference of step-index multimode fiber was demonstrated. But the authors did not investigate the influence of total cavity dispersion on the optical spectrum, pulse width, and output power.
Abstract: We experimentally demonstrate for the first time, to the best of our knowledge, an all-fiber passively mode-locked laser operation based on the nonlinear multimode interference of step-index multimode fiber. Such a structure couples the light in and out of the multimode fiber via single-mode fibers, and its physical mechanisms for saturable absorption have been analyzed theoretically based on the third-order nonlinear Kerr effect of multimode fiber. Using the nonlinear multimode interference structure with 48.8 mm length step-index multimode fiber, the modulation depth has been measured to be ∼5%. The passively mode-locked laser output pulses have a central wavelength of 1596.66 nm, bandwidth of 2.18 nm, pulsewidth of ∼625 fs, and fundamental repetition rate of 8.726 MHz. Furthermore, the influence of total cavity dispersion on the optical spectrum, pulse width, and output power is investigated systematically by adding different lengths of single-mode fiber and dispersion compensation fiber in the laser cavity.
52 citations
TL;DR: A method is proposed that constructs the inverse transformation matrix of the MMF based on principal component analysis (PCA), which can reconstruct the grayscale images of natural scene at high frame rate and high resolution and shows high reconstruction accuracy with few training samples.
13 citations
TL;DR: This paper combines principal component analysis (PCA) method, deep learning based speckle classification (DLSC) anddeep learning based image enhancement (DLIE) to improve imaging definition and shows imaging capability with high definition for complex natural scenes, which may provide a feasible method for high definition images transmission through the MMF.
9 citations
TL;DR: In this article, the authors present an analysis of the propagation of a nearly diffraction-limited laser beam through 5 to 10m long multimode step-index fibers with a numerical aperture of 0.111 and core diameters of up to 80m.
Abstract: In view of the growing demand for fiber beam delivery in manufacturing systems with close to diffraction-limited beam quality, we present an analysis of the propagation of a nearly diffraction-limited laser beam through 5 to 10 m long multimode step-index fibers with a numerical aperture of 0.111 and core diameters of up to 80 $\mu$ m. The influence of the launching conditions are investigated theoretically and experimentally by varying the beam size of the input beam. At a core diameter as high as 80 $\mu$ m, corresponding to a mode field area of 2800 $\mu$ m2, and an optimum launching condition, the transmitted M2 was measured to be around 1.3. It is shown that bending of the fibers down to radii as small as 2 cm barely influences the beam quality factor of the transmitted beam for all the tested fibers as the M2 was always found to be smaller than 1.5. The threshold of stimulated Raman scattering was measured to be around 60 kW for a fiber loosely placed on the table ( $\text{r}_{\text{bend}}$ $\geq$ 25 cm) with a total length of 10 m and a core diameter of 80 $\mu$ m.
5 citations
References
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TL;DR: The first experimental investigation of nondiffracting beams, with beam spots as small as a few wavelengths, can exist and propagate in free space, is reported.
Abstract: It was recently predicted that nondiffracting beams, with beam spots as small as a few wavelengths, can exist and propagate in free space. We report the first experimental investigation of these beams.
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TL;DR: In this article, simultaneous transmission of six spatial and polarization modes, each carrying 40 Gb/s quadrature-phase-shift-keyed channels over 96 km of a low-differential group delay few-mode fiber, is reported.
Abstract: We report simultaneous transmission of six spatial and polarization modes, each carrying 40 Gb/s quadrature-phase-shift-keyed channels over 96 km of a low-differential group delay few-mode fiber. The channels are successfully recovered by offline DSP based on coherent detection and multiple-input multiple-output processing. A penalty of ;28 dB.
901 citations
TL;DR: This technique will permit scaling of pulsed fiber lasers and amplifiers to significantly higher pulse energies and peak powers and cw fiber sources to higher average powers while maintaining excellent beam quality.
Abstract: The authors report a new approach to obtain single-transverse-mode operation of a multimode fiber amplifier, in which the gain fiber is coiled to induce significant bend loss for all but the lowest-order mode. They have demonstrated this method by constructing a coiled amplifier using Yb-doped, double-clad fiber with a core diameter of 25 {micro}m and NA of {minus}0.1 (V {approx} 7.4). When operated as an ASE source, the output beam had an M{sup 2} value of 1.09 {+-} 0.09; when seeded at 1,064 nm, the slope efficiency was similar to that of an uncoiled amplifier. This technique does not require exotic fiber designs or increase system complexity and is inexpensive to implement. It will allow scaling of pulsed fiber lasers and amplifiers to significantly higher pulse energies and peak powers and cw fiber sources to higher average powers while maintaining excellent beam quality.
630 citations
TL;DR: In this article, an experimental and theoretical study of bandwidth enhancement in multimode fiber links achieved by using offset launch techniques is presented. But offset launch is not suitable for low bandwidth "worst case" fibers.
Abstract: This paper reports an experimental and theoretical study of bandwidth enhancement in multimode fiber links achieved by using offset launch techniques. It is found, both from theory and experiment, that an up to four-fold bandwidth enhancement can be obtained compared to standard overfilled launch techniques despite exciting over 50% of the fiber modes, thus allowing good stability. The enhancement technique is found to be achieved for a range of fibers with different core diameters and core refractive index profiles. The level of bandwidth enhancement depends upon the inherent bandwidth of the fiber, being particularly effective in improving the performance of low bandwidth "worst case" fibers. The launch is found to be stable with respect to environmental variations, showing bandwidth enhancement for injection positions or connector offsets of up to 5 /spl mu/m from optimum. In addition, unlike many restricted launch techniques, it is found to be tolerant to angular fiber misalignment for angles up to 6/spl deg/ from normal.
322 citations