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Nanoelectronics and Nanophotonics
Published in M S Shur, R A Suris, Compound Semiconductors 1996, 2020
Traveling-wave or distributed photodetectors are currently being developed to overcome the bandwidth limitation arising from the RC time constant in conventional lumped-element photodetectors [1–7]. Moreover, the concept of distributed photodetection is particularly well suited for wide-band operation at large optical power levels [6] where the frequency response of conventional lumped-element devices starts to degrade due to field screening effects of the photo-generated space charge [8,9]. The potential fields of application thus include optical microwave links, optical heterodyne detection, and opto-electronically generated millimeter waves and microwaves which all will considerably benefit from distributed photodetectors with a high optical saturation power. A distributed or traveling-wave photodetector can be considered as a pair of unidirectionally coupled waveguides. The optical input signal traveling down the optical waveguide is continuously attenuated by conversion of photons into photo-carriers. The resulting photocurrent excites forward- and reverse-propagating electrical waves of equal amplitude. Matching between the optical group velocity and the electrical phase velocity results in virtually capacitance-free photodetection.
Sensing for the Perfectly Firm Tomato
Published in Denise Wilson, Sensing the Perfect Tomato, 2019
In the first method, an optical waveguide in the shape of a fiber, rectangle, or other structure is applied to the tomato with some pressure. An optical waveguide is a structure that restricts where and how light can travel. Changes in the shape of the waveguide, through contact with the fruit surface, cause a change in how light propagates or travels through the waveguide. Changes in light transmission characteristics can mean a change in phase, wavelength, polarization, or intensity of the light traveling through the waveguide. In turn, these changes in light properties are proportional to sheer and vertical stresses on the waveguide as well as other mechanical properties that are a direct indication of firmness. Using an optical waveguide and sensor to determine firmness through the force vs. deformation approach provides some advantages over mechanical sensors. An optical output is inherently immune to electronic noise and can provide more consistent and reliable readings. However, an optical output also requires that the fruit under evaluation be antireflective and that interference from ambient light sources be kept to a minimum. While these two issues are of concern for any optical sensor or sensing system, they are less of a concern with the optical force vs. deformation approach because the waveguide does not depend on propagation of light through the ambient environment to provide an accurate indication of firmness.
Future Semiconductor Devices
Published in Lambrechts Wynand, Sinha Saurabh, Abdallah Jassem, Prinsloo Jaco, Extending Moore’s Law through Advanced Semiconductor Design and Processing Techniques, 2018
Wyn Lambrechts, Saurabh Sinha, Jassem Abdallah, Jaco Prinsloo
There are multiple types of planar optical interconnects that may be built on a substrate, such as embedded/buried optical waveguides, optical rib waveguides, slab waveguides and others, as shown in Figure 5.5 (Miller 2009; Zimmermann 2010; Orcutt et al. 2013; Filipenko et al. 2015). Optical waveguides can be made from a variety of materials, including organic polymers, semiconductors and dielectric materials (Zimmermann 2010; Miller 2009; Orcutt et al. 2013; Tong 2014a). Optical waveguides work via the confinement and propagation of discrete modes of electromagnetic waves inside patterned waveguide cores (depicted as material 1 in Figure 5.6 and as the darker regions of Figure 5.5) (Heebner et al. 2008; Wang et al. 2016). The waveguide cores have higher refractive indices than the surrounding (cladding) materials, and confinement of the light within the cores is accomplished via total internal reflection (Heebner et al. 2008; Wang et al. 2016).
Research of the bending loss of S-shaped waveguides with offsets and trenches
Published in Journal of Modern Optics, 2021
Yuling Shang, Wenjie Guo, Jiaqi Wang, Chunquan Li, Yamin Zhao
Several material systems have been used to fabricate optical waveguide devices include Si/SiO2, SiN/SiO2, and polymers. The index difference between the waveguide core and cladding significantly influences the bending loss of the curved waveguides. Waveguides with high index contrast materials, such as Si/SiO2, SiN/SiO2 systems, have a maximum index difference [8], which allows for high confinement of light and a small bending radius of a few microns to achieve low-loss transmission [9]. However, the high index contrast waveguides show large scattering losses caused by the sidewall roughness of the waveguide [10,11]. Moreover, they contribute to a low coupling between the fibre and the waveguide due to the mismatch of different modes and sensitivity to alignment. In contrast, low index contrast waveguides, such as polymers waveguides, can provide low transmission loss and low waveguide-fibre coupling losses [7]. However, there is a downside to the low index contrast waveguides: the low bending loss requires a centimeter-level radius [9], which is not suitable for compact and low-loss optical circuits.
Fabrication of ridge waveguide on the ion-implanted TGG crystal by femtosecond laser ablation
Published in Journal of Modern Optics, 2020
Jing-Yi Chen, Jie Zhang, Liao-Lin Zhang, Chun-Xiao Liu
The optical waveguide structure confines the light to a guiding area with a width of several micrometers, which can not only enhance the density of the light intensities but also significantly reduce the dimensions of optical devices. Therefore, researches on the arts of optical waveguide fabrication are particularly important. Ion implantation/irradiation is an effective material surface modification technology, which can precisely select the ion energy and ion dose to change the refractive index within a specific area of the material, and hence the optical waveguide is fabricated [10–12]. Planar or slab waveguides, the most common optical waveguide structures, restrict light in one dimension. However, in the tremendous demand for fabricating miniaturized and integrated optical devices, two-dimensional (2D) waveguides such as channel and ridge waveguides are more widely applied, owing to their higher intensity density in the waveguide region confined by horizontal and vertical directions [13]. On the basis of ion-implanted planar waveguide wafer, surface patterning technology needs to be incorporated for preparing the bi-directional confinement ridge waveguide. Recently, the femtosecond laser ablation reported in some literatures has proved to be a simple and precise means in micromachining ridge waveguide structures [14–17]. Controlling the trajectory of the ablating laser, the ridge region could be prepared without a mask in the whole process [16,18].