Optical characterisation of germanium optical fibres

Semiconductor core optical fibres are currently generating great interest as they promise to be a platform for the seamless incorporation of optoelectronic functionality into a new generation of all-fibre networks [1,2]. Although recent attentions have primarily focused on silicon as the material of choice for semiconductor photonics applications, germanium has some advantages over its counterpart. For example, it has higher nonlinearity, extended infrared transparency and has recently been demonstrated as a direct band gap laser medium [3]. Here we present the first optical characterisation of a germanium core optical fibre. The fibre was fabricated using a chemical micro fluidic deposition process [1] that uses GeH4 (germane) as a precursor to deposit amorphous germanium into the hole of a silica capillary. Figure 1 (a) shows an optical microscope image of the polished end face of a germanium fibre, with a 5.6 µm core diameter, which has been completely filled with the semiconductor material. Optical transmission measurements have been conducted over the wavelength range 2 µm to 11 µm, to confirm the broad mid-infrared operational window, and the guided output at 2.4 µm, imaged using a Spiricon Pyrocam III pyroelectric array camera, is shown in Figure 1 (b). At this wavelength the optical loss has been measured to be 20 dB/cm, which is comparable to losses measured for amorphous silicon fibres in the infrared. The potential for these germanium optical fibres to be used as optical modulators and infrared detectors will be discussed

Deposition of electronic and plasmonic materials inside microstructured optical fibres

Optical fibres are the transport medium of today's digital information. However, current telecommunications fibre systems require external solid state circuits to generate, amplify, receive, and manipulate the light. The fusion of the two technologies, namely fibre photonics and semiconductor electronics is expected to have a major impact on next generation of optoelectronic devices, exploiting both the guiding capabilities of optical fibres and the processing properties of semiconductors devices. Only recently, with the advent of microstructured optical fibres and templating material processing methods, it has been possible to create optical fibres with solid-state material inclusions. TEM, SEM and micro-Raman analysis was used to determine the structural characteristics of silicon and germanium modified microstructured optical fibres. These studies demonstrate that single crystal, poly-crystalline and amorphous semiconductors can be conformally deposited within the capillary voids of microstructured optical fibres. As a step towards fibre-integrated optoelectronic devices, it is demonstrated that in-fibre silicon and germanium wires and tubes can function as field effect transistors and light waveguides

Electrical and Raman characterization of silicon and germanium-filled microstructured optical fibers

Extreme aspect ratio tubes and wires of polycrystalline silicon and germanium have been deposited within silica microstructured optical fibers using high-pressure precursors, demonstrating the potential of a platform technology for the development of in-fiber optoelectronics. Microstructural studies of the deposited material using Raman spectroscopy show effects due to strain between core and cladding and the presence of amorphous and polycrystalline phases for silicon. Germanium, in contrast, is more crystalline and less strained. This in-fiber device geometry is utilized for two- and three-terminal electrical characterization of the key parameters of resistivity and carrier type, mobility and concentration

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Wavelength-dependent loss measurements in polysilicon modified optical fibres

The recent advancements in on-chip silicon photonics has lead to the demonstration of a number of compact optoelectronic devices owing to the unique material properties of the semiconductor. Although to date most of the major advancements have been based on single-crystal silicon waveguides, lately there has been an increased interest in polycrystalline structures for integrated devices as the deposition process is easier, allowing for more design flexibility. As a photonics material, polysilicon offers good optical and electronic properties but it is typically associated with large losses due to scattering off grain boundaries and surface imperfections at the corecladding interface

High pressure thermal chemical deposition of a Si-H from Silane within microstructured optical fibers

We report a simple high pressure thermal chemical deposition technique capable of infiltrating high aspect ratio structures such as microstructured optical fibers with a-Si:H tubes and wires. High quality films and structures of a-Si:H are generally produced via PECVD, or hot wire CVD. However, because these techniques rely on remote generation of reactive radicals for deposition they are not suitable for the infiltration of deep high aspect ratio structures. Template organization of materials is a powerful tool for developing new and exciting functionalities and light matter interactions. We show that thermal deposition from silane at temperatures as low as 400°C is possible when using high pressures. Raman and IR spectroscopy give confirmation to the presence of hydrogen in the deposited material. Without optimization of the deposition process we have already achieved optical loss values at 1.55 µm that are greater than a 20 fold improvement as a result of the hydrogenation. The best non-hydrogenated microwires deposited under similar pressure conditions have losses of 17dB/cm, we have already achieved loss values as low as 3dB/cm. Generally high pressure pyrolysis of silane leads to the formation of Si fines that are a result of gas phase homogeneous reactions. We have found that the increased surface area to volume ratio within high aspect ratio templates such as the capillaries of microstructures optical fibers favors heterogeneous surface deposition allowing the formation of highly conformal structures and solid micro wires centimeters in length. We have investigated the deposition within fused silica microstructured optical as well as polyimide and PTFE substrates. Infiltration of a-Si:H into high aspect ratio structures would enable the production of waveguides capable of long, intense light matter interactions. Such interactions could be exploited for the production of new in-fiber photonic, photovoltaic, and optoelectronic devices that would, for example, allow manipulation of light in transmission

Array of tapered semiconductor waveguides in a fiber for infrared image transfer and magnification

The proof-of-concept of an infrared imaging tip by an array of infrared waveguides tapered as small as 2 µm is demonstrated. The fabrication is based on a high-pressure chemical fluid deposition technique to deposit precisely defined periodic arrays of Ge and Si waveguides within a microstructured optical fiber template made of silica to demonstrate the proposed concept at wavelengths of 10.64 µm and 1.55 µm, respectively. The essential features of the imaging system such as isolation between adjacent pixels, magnification, optical throughput, and image transfer characteristics are investigated. Near-field scanning at 3.39 µm wavelength using a single tapered Ge core is also demonstrated