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We report on an all-fiber setup capable of generating complex intensity patterns using interference of few guided modes. Comprised by a few-mode fiber (FMF) spliced to a multimodal interference (MMI) fiber device, the setup allows for obtaining different output patterns upon adjusting the phases and intensities of the modes propagating in the FMF. We analyze the output patterns obtained when exciting two family modes in the MMI device using different phase and intensity conditions for the FMF modal base. Using this simple experimental arrangement we are able to produce complex intensity patterns with radial and azimuthal symmetry. Moreover, our results suggest that this approach provides a means to generate beams with orbital angular momentum (OAM).
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The transmission properties of a photonic crystal immersed in several different oils have been characterized using terahertz time domain spectroscopy in the spectral range of 0.3-1.5 THz. As in previous works, oil samples can be distinguished using terahertz transmission measurements. When the same oils are introduced into a photonic crystal, we find that the effective refractive index of the photonic crystal is sensitive to the properties of the oils and shows differences not seen in bulk measurements. These effects are described in detail and have potential applications in both the sensing of very small volumes of oils and in the fine control of the refractive indices of photonic crystals.
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We report on a simple fabrication technique for Fabry-Perot (FP) sensors formed by a microbubble within a polymer drop deposited on the tip of an optical fiber. Polydimethylsiloxane (PDMS) drops are deposited on the tips of standard single-mode fibers incorporating a layer of carbon nanoparticles (CNPs). A microbubble inside this polymer end-cap, aligned along the fiber core, can be readily generated on launching light from a laser diode through the fiber, owing to the photothermal effect produced in the CNP layer. This approach allows for the fabrication of microbubble end-capped FP sensors with reproducible performance, showing temperature sensitivities as large as 790 pm/°C, larger than those reported for regular polymer end-capped devices. We further show that these microbubble FP sensors may also prove useful for displacement measurements, with a sensitivity of â¼5.4 nm/µm.
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We demonstrate optical fiber sensors based on highly coupled multicore fibers operating with the optical Vernier effect. The sensors are constructed using a simple device incorporating single-mode fibers (SMFs) and a segment of a multicore fiber. In particular, we evaluated the performance of a sensor based on a seven-core fiber (SCF) spliced at both ends to conventional SMFs, yielding a versatile arrangement for realizing Vernier-based fiber sensors. The SMF-SCF-SMF device can be fabricated using standard splicing procedures and serve as a "building block" for both, reflection and transmission sensing configurations. As demonstrated with our experimental results, the Vernier arrangements can yield a ten-fold increase in sensitivity for temperature measurements compared to a conventional single SMF-SCF-SMF device, thereby confirming the enhanced sensitivity that can be attained with this optical effect. Furthermore, through theoretical analysis, we obtain the relevant parameters that must be optimized in order to achieve an optimal sensitivity for a specific application. Our findings thus provide the necessary guidelines for constructing Vernier-based sensors with all-fiber devices based on highly coupled multicore optical fibers, which constitutes an ideal framework to develop highly sensitive fiber sensors for different applications.
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We demonstrate tunable microring resonators (TMRs) based on light-activated functional polymer coatings deposited on glass optical fibers. TMRs were fabricated using two layers of polydimethylsiloxane-based compounds: one incorporating an azobenzene dye and one using a fluorescent ytterbium and erbium-doped sodium yttrium fluoride powder. The latter yields a photoluminescent composite producing green up-conversion emission under infrared pumping. This visible emission triggers photoinduced birefringence effects in the azobenzene layer, thereby modifying the spectral features of the TMR devices. The shift in the resonance peaks as a function of pump power is linear, yielding a tuning range of 1.3 nm. Aside from the observed photoinduced effects, we also discuss the photothermal effects involved in the tuning mechanism.
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We present a new technique allowing the fabrication of large modal count photonic lanterns for space-division multiplexing applications. We demonstrate mode-selective photonic lanterns supporting 10 and 15 spatial channels by using graded-index fibres and microstructured templates. These templates are a versatile approach to position the graded-index fibres in the required geometry for efficient mode sampling and conversion. Thus, providing an effective scalable method for large number of spatial modes in a repeatable manner. Further, we demonstrate the efficiency and functionality of our photonic lanterns for optical communications. Our results show low insertion and mode dependent losses, as well as enhanced mode selectivity when spliced to few mode transmission fibres. These photonic lantern mode multiplexers are an enabling technology for future ultra-high capacity optical transmission systems.
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We demonstrate a simple approach based on a photonic lantern spatial-mode multiplexer and a few-mode fiber for optical and manipulation of multiple microspheres. Selective generation of linearly polarized (LP) fiber modes provides light patterns useful for trapping one or multiple microparticles. Furthermore, rotation of the particles can be achieved by switching between degenerate LP modes, as well as through polarization rotation of the input light. Our results show that emerging fiber optic devices such as photonic lanterns can provide a versatile and compact means for developing optical fiber traps.
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The fibre-optic microwave photonic link has become one of the basic building blocks for microwave photonics. Increasing the optical power at the receiver is the best way to improve all link performance metrics including gain, noise figure and dynamic range. Even though lasers can produce and photodetectors can receive optical powers on the order of a Watt or more, the power-handling capability of optical fibres is orders-of-magnitude lower. In this paper, we propose and demonstrate the use of few-mode fibres to bridge this power-handling gap, exploiting their unique features of small acousto-optic effective area, large effective areas of optical modes, as well as orthogonality and walk-off among spatial modes. Using specially designed few-mode fibres, we demonstrate order-of-magnitude improvements in link performances for single-channel and multiplexed transmission. This work represents the first step in few-mode microwave photonics. The spatial degrees of freedom can also offer other functionalities such as large, tunable delays based on modal dispersion and wavelength-independent lossless signal combining, which are indispensable in microwave photonics.
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We demonstrate adaptive-spatial mode control (ASMC) in few-moded double-clad large mode area (LMA) fiber amplifiers by using an all-fiber-based photonic lantern. Three single-mode fiber inputs are used to adaptively inject the appropriate superposition of input modes in a multimode gain fiber to achieve the desired mode at the output. By actively adjusting the relative phase of the single-mode inputs, near-unity coherent combination resulting in a single fundamental mode at the output is achieved.
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The advent of nanotechnology has triggered novel developments and applications for polymer-based membranes with embedded or coated nanoparticles. As an example, interaction of laser radiation with metallic and carbon nanoparticles has shown to provide optically triggered responses in otherwise transparent media. Incorporation of these materials inside polymers has led to generation of plasmonic and photothermal effects through the enhanced optical absorption of these polymer composites. In this work, we focus on the photothermal effects produced in polydimethylsiloxane (PDMS) membranes with embedded carbon nanoparticles via light absorption. Relevant physical parameters of these composites, such as nanoparticle concentration, density, geometry and dimensions, are used to analyze the photothermal features of the membranes. In particular, we analyze the heat generation and conduction in the membranes, showing that different effects can be achieved and controlled depending on the physical and thermal properties of the composite material. Several novel applications of these light responsive membranes are also demonstrated, including low-power laser-assisted micro-patterning and optomechanical deformation. Furthermore, we show that these polymer-nanoparticle composites can also be used as coatings in photonic and microfluidic applications, thereby offering an attractive platform for developing light-activated photonic and optofluidic devices.
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A bending sensor is demonstrated using the combination of a mode-selective photonic lantern (PL) and a multicore fiber. A short section of three-core fiber with strongly coupled cores is used as the bend sensitive element. The supermodes of this fiber are highly sensitive to the refractive index profiles of the cores. Small bend-induced changes result in drastic changes of the supermodes, their excitation, and interference. The multicore fiber is spliced to a few-mode fiber and excites bend dependent amounts of each of the six linearly polarized (LP) modes guided in the few-mode fiber. A mode selective PL is then used to demultiplex the modes of the few-mode fiber. Relative power measurements at the single-mode PL output ports reveal a high sensitivity to bending curvature and differential power distributions according to bending direction, without the need for spectral measurements. High direction sensitivity is demonstrated experimentally as well as in numerical simulations. Relative power shifts of up to 80% have been measured at radii of approximately 20 cm, and good sensitivity was observed with radii as large as 10 m, making this sensing system useful for applications requiring both large and small curvature measurements.
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To unlock the cost benefits of space division multiplexing transmission systems, higher spatial multiplicity is required. Here, we investigate a potential route to increasing the number of spatial mode channels within a single core few-mode fiber. Key for longer transmission distances and low computational complexity is the fabrication of fibers with low differential mode group delays. As such in this work, we combine wavelength and mode-division multiplexed transmission over a 4.45 km low-DMGD 6-LP-mode fiber by employing low-loss all-fiber 10-port photonic lanterns to couple light in and out of the fiber. Hence, a minimum DMGD of 0.2 ns (maximum 0.357 ns) is measured after 4.45 km. Instrumental to the multi-mode transmission system is the employed time-domain-SDM receiver, allowing 10 spatial mode channels (over both polarizations) to be captured using only 3 coherent receivers and real-time oscilloscopes in comparison with 10 for conventional methods. The spatial channels were unraveled using 20 × 20 multiple-input multiple-output digital signal processing. By employing a novel round-robin encoding technique, stable performance over a long measurement period demonstrates the feasibility of 10x increase in single-core multi-mode transmission.
