Fiber-optic distributed acoustic sensor (DAS) has been deployed for real-time monitoring of various physical phenomena. The operational principle of DAS relies on monitoring backscattered light from a fiber while leaving the pump optical pulses to get wasted at the fiber distal end. Here, we report on energy harvesting from the DAS pump optical signal to supply energy to passive devices. In this work, a DAS over a ∼1.1-km single-mode fiber (SMF) detects a 200-Hz vibration event produced by a piezoelectric transducer (PZT) while harvesting a 1.58–mW optical signal to charge a 10-F supercapacitor.
Optical wireless communication (OWC) is envisioned to become an indispensable technology in future wireless networks. However, one of the main issues hindering the widespread of OWC systems is the strict alignment required to maintain connectivity. This is due to the tradeoff between the receiver’s active area and its response speed, which necessitates the use of a lens to focus the light, limiting the field of view (FOV). Taking inspiration from the wide-FOV eyes of horseflies to address this issue, we propose the use of a convex-surface fused fiber-optic taper (FFOT) that can effectively expand a planar array of photodetectors and project it onto a spherical dome, respectively improving the light collection of individual photodetectors and expanding the overall FOV of the array. In our proof-of-concept demonstration, we show an optical receiver with a FOV semi-angle of around 25° and optical power density gain up to 120 in a 1-GHz link whose bandwidth is limited only by the photodetector. Moreover, reducing of the FOV of each individual fiber that results from tapering and the extra-mural absorption material incorporated around the fibers’ cores reduce the crosstalk between them, preserving the image quality. Therefore, unlike non-imaging light focusing elements, FFOTs can potentially be used in applications in which preserving the image is necessary, such as in imaging multiple-input and multiple-output systems and light detection and ranging (LiDAR). We also show the performance of FFOTs in collecting light from color-converting materials, a technique used in expanding the FOV beyond the étendue limit.
Relaxing the alignment in underwater wireless optical communication systems is highly favorable for practical use. Employing wavelength-division-multiplexing (WDM) adds to the requirement of alignment since multiple filters are used at the receiver side to separate the incoming wavelengths. We report the use of scintillating fibers in WDM systems as signal detectors that offer valuable advantages such as large-area detection, widefield- of-view and high data rates. We demonstrate the optimal selection of wavelengths based on the fibers’ characteristics, and realise an aggregated data rate of 400-Mb/s using on-off keying modulation format with zero-forcing equalization and maximum ratio combining in an outdoor diving pool in a maximum separation distance of 10-m.
Current optical communication technologies are predicted to face a bandwidth capacity limit in the near future. The nature of the limitation is fundamental rather than technological and is set by nonlinearities in optical fibers. One solution, suggested over 30 years ago, comprises the use of spatial modes of light as information carriers. Along this direction, light beams endowed with orbital angular momentum (OAM) have been demonstrated as potential information carriers in both, free space and fibres. However, recent studies suggest that purely OAM modes does not increase the bandwidth of optical communication systems. In fact, in all work to date, only the azimuthal component of transverse spatial modes has been used. Crucially, all transverse spatial modes require two degrees of freedom to be described; in the context of Laguerre-Gaussian (LGp`) beams these are azimuthal (l) and radial (p), the former responsible for OAM. Here, we demonstrate a technique where both degrees of freedom of LG modes are used as information carrier over free space. We transfer images encoded using 100 spatial modes in three wavelengths as our basis, and employ a spatial demultiplexing scheme that detects all 100 modes simultaneously. Our scheme is a hybrid of MIMO and SMM, and serves as a proof-of-principle demonstration. The cross-talk between the modes is small and independent of whether OAM modes are used or not.
We numerically study the supercontinuum (SC) generation in a six modes photonic crystal fiber (PCF). By solving the multimode generalised Schrdinger equation, we demonstrate the generation of SC by initially exciting the fundamental mode or one of the higher order modes and then observe the energy transfer to the other high order modes. We analyze the energy transfer between degenerate modes during propagation through the few mode PCF. A detailed investigation of the nonlinear effects on the SC process through linear and nonlinear coupling is provided which confirms the energy transfer between optical degenerate modes during propagation inside the few- mode fiber.
We experimentally demonstrate an information encoding protocol using the two degrees of freedom of Laguerre Gaussian modes having different radial and azimuthal components. A novel method, based on digital holography, for information encoding and decoding using different data transmission scenarios is presented. The effects of the atmospheric turbulence introduced in free space communication is discussed as well.
KEYWORDS: Holograms, Digital holography, Multiplexing, Wavefronts, Spatial light modulators, Modes of laser operation, Optical communications, Data transmission, Single mode fibers, Signal detection
High-capacity data transmission has been implemented using single channel optical systems. This technique is limited and soon it will be unable to fulfill the growing needs for higher bit rate data transmission. Hence multi-mode transmission has been recently given attention as a potential solution to the current problems. In this context, we demonstrate a method of multiplexing laser modes using spatial light modulators (SLMs). In our proposed technique, we use Laguerre Gaussian (LG) modes, which form a complete basis set; hence multi-mode masks can be created by taking a linear combination of the LG modes. Since LG modes are characterised by two degrees of freedom, the azimuthal index ` and radial index ρ, this allows for multi-dimensional states. There are however some experimental challenges which include the sensitivity of the setup to misalignment, that leads to mode-coupling. It is also important that the injected modes ha a uniform power spectrum so that are weighted equally. The size of the multi-modes is highly dependent on the resolution of the SLM.
We analyze the effect of atmospheric turbulence on the propagation of multiplexed Laguerre Gaussian modes. We present a method to multiplex Laguerre Gaussian modes using digital holograms and decompose the resulting field after encountering a laboratory simulated atmospheric turbulence. The proposed technique makes use of a single spatial light modulator for the generation of superimposed beam and a second spatial light modulator and a CCD camera for the modal decomposition. The obtained results demonstrate how sensitive the Laguerre Gaussian beams are to atmospheric distortions.
We propose a 2-dimensional method for Bessel Gaussian beam azimuthal and radial decomposition using digital holograms. We illustrate the reconstruction of a Bessel Gaussian beam after encountering an obstruction. From the measured decomposition we show the reconstruction of the amplitude, phase and azimuthal index of the field with high degree of accuracy.
We propose a new and versatile design of a directional coupler able to generate and multiplex high order modes in few mode fibers. The designed device can selectively generate five high order modes and multiplex them in a few mode fiber with an overall insertion loss not exceeding 3dB at the telecommunication wavelength λ = 1550 nm. The mode dependent loss is found to be weakly dependent to the wavelength. The proposed device is very promising for high order mode multiplexing and suitable for high bit-rate optical communication systems.
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