Review on Optical Waveguides

Abstract

Optical devices are necessary to meet the anticipated future requirements for ultrafast and ultrahigh bandwidth communication and computing. All optical information processing can overcome optoelectronic conversions that limit both the speed and bandwidth and are also power consuming. The building block of an optical device/circuit is the optical waveguide, which enables low-loss light propagation and is thereby used to connect components and devices. This chapter reviews optical waveguides and their classification on the basis of geometry (Non-Planar (Slab/Optical Fiber)/Planar (Buried Channel, Strip-Loaded, Wire, Rib, Diffused, Slot, etc.)), refractive index (Step/Gradient Index), mode propagation (Single/Multimode), and material platform (Glass/Polymer/Semiconductor, etc.). A comparative analysis of waveguides realized in different material platforms along with the propagation loss is also presented.

Light waveguiding in bioinspired peptide nanostructures

“…Passive light waveguides are obeyed to the classical optical laws of reflection, refraction, and diffraction. They guide the input light waves directly through their spectral transmission window . The waveguiding property is based on optical confinement‐light trapping of the propagating electromagnetic light wave in this dielectric layer.…”

“…The waveguides are composed of a dielectric or semiconductor material with lower refractive index that surrounds the guided dielectric layer having higher refractive index. According to Snell's law, if the light impinges the cladding layer that surrounds the guiding core at an angle equal or greater than a critical angle, the light is confined within the core and propagates along the waveguide …”

“…These factors include region of optical transparency, defining minimum optical absorption coefficient in the working spectral range, high refractive index contrast, and multifunctional properties such as electro‐optic and nonlinear optical effects. Optical fibers are made of a wide range of inorganic materials such as elementary semiconductors like Si and Ge; semiconductor compounds, Si 3 N 4 , ZnSe, CdTe, InP, GaAs, based on alloys from IV, II to VI, and III to V groups; dielectrics (silica glass, SiO 2 ); and ferroelectrics (LiNbO 3 , LiTaO 3 ) . The main advantage of the semiconductor light waveguiding materials is their unique property to tune the region of optical transparency from ultraviolet (UV) to infrared (IR) region by the use of either modulated bandgap energy technology or applying quantum confinement engineering .…”

“…It is worth to note that such a common approach of peptide optical waveguiding takes into account the classical optics based on diffraction, reflection, and refraction. Such a classical mode is characterized by light wave propagation through optical transmission window and known as passive waveguiding …”

“…It is also higher than those of other biocompatible counterpart optical waveguiding biomaterials such as silk fibers, polymers, hydrogels, and more. The second condition requires optical transparency of waveguiding materials in a spectral region of their specific applications to minimize the optical losses in the waveguide core. Most of integrated bio‐optical devices use optical spectrum of biological transmission window in the visible NIR range (0.4‐2.0 μm). The third condition requires specific functional waveguiding properties when the light guiding is combined with electro‐optical modulation (electro‐optical effect) of the propagating electromagnetic wave and/or nonlinear optical conversion. The fourth requirement is related to optimal geometrical dimensions of the waveguides defining the minimum thickness of the waveguiding layer, d w , in order to allow light propagation inside its core only and design single mode waveguides. The considered optical waveguiding requirements take into account the conventional approach related to classical optical waveguiding based on diffraction, reflection, and refraction. Such a classical mode is characterized by light wave propagation through optical transmission window and known as passive waveguiding.…”