The field of hybrid optical fibers is one of the most active research areas in current fiber optics and has the vision of integrating sophisticated materials inside fibers, which are not traditionally used in fiber optics. Novel in-fiber devices with unique properties have been developed, opening up new directions for fiber optics in fields of critical interest in modern research, such as biophotonics, environmental science, optoelectronics, metamaterials, remote sensing, medicine, or quantum optics. Here the recent progress in the field of hybrid optical fibers is reviewed from an application perspective, focusing on fiber-integrated devices enabled by including novel materials inside polymer and glass fibers. The topics discussed range from nanowire-based plasmonics and hyperlenses, to integrated semiconductor devices such as optoelectronic detectors, and intense light generation unlocked by highly nonlinear hybrid waveguides.

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Hybrid Optical Fibers – An Innovative Platform for In-Fiber Photonic Devices

Advancements in semiconductor core optical fiber

The nonlinear properties of a low loss hydrogenated amorphous silicon core fiber have been characterized for transmission of high power pulses at 1540nm. Numerical modelling of the pulse propagation in the amorphous core material was used to establish the two-photon absorption, free-carrier absorption and the nonlinear refractive index, which were found to be larger than the values typical for crystalline silicon. Calculation of a nonlinear figure of merit demonstrates the potential for these hydrogenated amorphous silicon core fibers to be used in nonlinear silicon photonics applications.

Nonlinear transmission properties of hydrogenated amorphous silicon core optical fibers

This paper reviews recent progress in the nascent field of semiconductor optical fibres, from the fundamentals through to device demonstration. The incorporation of semiconductor materials into both the step-index and microstructured fibre geometries provides a route to introducing new optoelectronic functionality into existing glass fibre technologies. Herein, the various fabrication methods that have been developed as of to date are described, and their compatibility with the different semiconductor materials and fibre designs discussed. Results will be presented on the optical transmission properties of several fibre types, with particular attention being paid to the observation of nonlinear propagation in silicon core fibres. Finally, some speculation regarding the future prospects and applications of this new class of fibre will be provided.

Semiconductor optical fibres: progress and opportunities

We demonstrate the ability to pull small diameter silicon-core fibers with low oxygen content by using interface modifiers between the silica cladding and the semiconductor. Alkali earths scavenge oxygen and form a fine-structured eutectic that accommodates thermal strain and may be useful as an intermediate index cladding layer for optical applications. NaO, MgO, SrO, CaO and BaO interface modifiers were tested. CaO coated fibers were made with core diameters down to 10 microns, small bending radii, low oxygen incorporation, and optical losses below 4 dB/cm at 1.55 microns.

Alkaline oxide interface modifiers for silicon fiber production

In this research, for the first time, an n-type silicon optical fiber is demonstrated. The fiber is fabricated by drawing from a powder-in-tube-type preform. Outside diameters in the range of several hundred micrometers were made with core diameters in the range of tens of micrometers. Optical and material characterizations have been made in order to understand the structural and compositional properties of this device. Fibers fabricated have a polycrystalline core with a few large grains as determined by electron backscatter diffraction analysis. Grains' dimensions in the core are on the order of tens to hundreds of micrometers. The doped silicon optical fiber may pave the way for in-fiber silicon photonics in the near future.

Fabrication of n-Type Silicon Optical Fibers

We experimentally demonstrate the fabrication of silicon optical fibers by using the powder-in-tube technique. The fibers are drawn from a preform utilizing a custom-made fiber drawing system. Silicon optical fibers having cladding diameters in the range of 40 to 240 µm, core diameters in the range of 10 to 100 µm, and an approximate overall length of 7 cm have been fabricated. The powder-in-tube technique is versatile and can be utilized to fabricate fibers with different dimensions and core/cladding materials.

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Fabrication of silicon optical fiber

Recently, silicon‐integrated optical circuits have attracted intensive interests, thanks to the compatibility with the complementary metal‐oxide‐semiconductor (CMOS) technology that enables mass production at low cost. The optical switch is an essential part of optical integrated circuits, with broad applications in optical communications and networks, optical computing, and sensing such as LiDAR. In general, the silicon‐integrated optical switch adopts thermo‐optic or carrier dispersion effect to realize reconfigurable signal routing. However, the use of thermo‐optic effect leads to high power consumption, and the carrier dispersion effect has the disadvantage of small refractive index change. In addition, both effects are non‐latching, and hence, continuous power consumption is required even when switching is not needed. For overcoming these drawbacks, phase‐change materials (PCMs) have been introduced into silicon‐integrated optical switches. In this paper, silicon‐integrated optical switches are classified according to the underlying structure and recent research is reviewed. Recent studies on silicon‐integrated optical switches incorporating PCMs are also reviewed. Furthermore, the pros and cons of different types of integrated optical switches with and without PCMs are compared and discussed.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/lpor.202200571

A Review of Silicon‐Based Integrated Optical Switches

We have demonstrated the fabrication of long period gratings in random hole optical fibers. The long period gratings are fabricated by a point-by-point technique using a CO2 laser. The gratings with a periodicity of 450 µm are fabricated and a maximum coupling efficiency of −9.81 dB has been achieved. Sensing of different refractive indices in the surrounding mediums is demonstrated by applying standard liquids with refractive indices from 1.400 to 1.440 to the long period grating.

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Ke Wang

Papers

Fabrication of n-Type Silicon Optical Fibers

Fabrication of silicon optical fiber

A Review of Silicon‐Based Integrated Optical Switches

Long Period Gratings in Random Hole Optical Fibers for Refractive Index Sensing

P‐Type Silicon Optical Fiber