Semiconductor optical fibres for infrared applications: a review

Over the last decade a new class of optical fibre has emerged that incorporates semiconductor materials within the core. These fibres are rich in optoelectronic functionality and offer extended transmission bands across the infrared spectral region so that their application potential is vast. Various fabrication methods have been developed to produce fibres with a range of unary and compound semiconductor core materials, which can be either amorphous or crystalline in form. This review discusses the main fabrication procedures and the infrared optical properties of the semiconductor fibres that have been fabricated to date, then takes a look at the future prospects of this exciting new technology

Flat-top temperature tuning response in periodically-poled nonlinear crystals

Second harmonic generation via periodically-poled nonlinear materials offers an efficient means of generating high-quality visible light that would be otherwise unattainable with traditional laser sources. While this technology has the potential for implementation in many mass-industrial applications, temperature stability requirements of 0.1 deg.C can make packaging with a pump source problematic. Using our high fidelity poling technique we have achieved precise placement of poled domains in Lithium Niobate based on the resulting mathematical models. These initial devices provide more than 4 deg.C flat-top temperature stability, albeit with a corresponding loss in operational efficiency. Our aim is to implement improved designs in magnesium-doped Lithium Niobate for packaging with near-room temperature diode-based pump sources, as could be applied towards RGB TV and projector applications

Non-isothermal phase-field simulations of laser-written in-plane SiGe heterostructures for photonic applications

Advanced solid-state devices, including lasers and modulators, require semiconductor heterostructures for nanoscale engineering of the electronic bandgap and refractive index. However, existing epitaxial growth methods are limited to fabrication of vertical heterostructures grown layer by layer. Here, we report the use of finite-element-method-based phase-field modelling with thermocapillary convection to investigate laser inscription of in-plane heterostructures within silicon-germanium films. The modelling is supported by experimental work using epitaxially-grown Si0.5Ge0.5 layers. The phase-field simulations reveal that various in-plane heterostructures with single or periodic interfaces can be fabricated by controlling phase segregation through modulation of the scan speed, power, and beam position. Optical simulations are used to demonstrate the potential for two devices: graded-index waveguides with Ge-rich (>70%) cores, and waveguide Bragg gratings with nanoscale periods (100–500 nm). Periodic heterostructure formation via sub-millisecond modulation of the laser parameters opens a route for post-growth fabrication of in-plane quantum wells and superlattices in semiconductor alloy films

Towards in-fiber silicon photonics

We review the recent advancements in the fabrication and application of silicon optical fibers. Particular focus is placed on novel materials and device designs for use in optical signal processing systems

Semiconductor optical fibers

We review the recent advancements in the fabrication and application of semiconductor optical fibers. Particular focus is placed on novel materials and device designs for use in optical signal processing systems

Graphene-based fiber polarizer with PVB-enhanced light interaction

Graphene is a two-dimensional material which, as a result of its excellent photonic properties, has been investigated for a wide range of optical applications. In this paper, we propose and fabricate a commercial grade broadband graphene-based fiber polarizer using a low loss side-polished optical fiber platform. A high index polyvinyl butyral layer is used to enhance the light-graphene interaction of the evanescent field of the core guided mode to simultaneously obtain a high extinction ratio ~37.5 dB with a low device loss ~1 dB. Characterization of the optical properties reveals that the polarizer retains low transmission losses and high extinction ratios across an extended telecoms band. The results demonstrate that side-polished fibers are a useful platform for leveraging the unique properties of low-dimensional materials in a robust and compact device geometry

Development of polycrystalline silicon waveguides by laser crystallization

Silicon (Si) is an excellent material for integrated photonics devices as its high refractive index allows for small device footprints. To date, most of the work in this area has leveraged the single crystal silicon-on-insulator platforms, which are relatively expensive to produce and thus drive up component costs. Here we propose an alternative method to fabricate crystalline silicon waveguides by laser processing of an amorphous starting material. As well as reducing production costs, this approach has the added advantage of removing the substrate dependence so that more flexible alternatives can be considered. This method has previously been applied to a-Si wires grown inside silica capillaries and shown to produce very large crystallites [1]. Here we demonstrate preliminary results of laser-induced crystallization of a-Si films and micro-patterned wires produced by chemical vapor deposition (CVD) on SiO2 substrates. The samples have been crystallized using a c.w. argon-ion laser at 488nm. Crystallized tracks have been written by scanning the focused beam across the samples using different laser intensities and scanning speeds. The resulting material quality is then studied using Raman spectrometry, optical and electronic microscopy and X-ray diffraction. For the planar films, we have produced crystallite sizes on the order of hundreds of nanometers to a few microns; similar to those obtained via conventional pulsed Excimer laser crystallization [2]. However, for the micro-patterned samples, we have found that it is possible to grow crystals that almost cover the entire width of the wire, over lengths of up to 18µm, considerably larger than what is typically reported for polysilicon waveguide devices [3]. Furthermore, this laser crystallization method has been observed to reform the surface of the Si wires resulting in very smooth sidewall profiles (as shown in Fig. 1) which is very important for low loss optical transmission in photonic devices

Nonlinear applications in the mid-infrared regime based on germanium on silicon platform

This abstract reviews our progress in characterizing nonlinear properties of low loss germanium-on-silicon waveguides in the mid-infrared wavelength. All-optical modulation is demonstrated in these waveguides and indicates the suitability of this platform for nonlinear applications in this long wavelength regime

Low loss tapered polysilicon core fibers

We have fabricated small core polysilicon waveguides by tapering bulk, as-drawn silicon optical fibers. The taper process acts to improve the local crystallinity of the core, resulting in a significant reduction in the material los

Programmable long period grating in a liquid core optical fiber

A programmable fiber long-period grating (LPG) is experimentally demonstrated in a liquid core optical fiber with a low insertion loss. The LPG is dynamically formed by a temperature gradient in real time through a micro-heater array. The transmission spectrum of the LPG can be completely reconfigured by digitally changing the grating period, index contrast, length, and design. The phase shift inside the LPG can also be readily defined to enable advanced spectrum shaping. Owing to the high thermo-optic coefficient of the liquid core, it is possible to achieve high coupling efficiencies with driving powers as low as a few tens of milliwatts. The proposed thermo-programmable device provides a potential design solution for dynamic all-fiber optics components