Radiation- and Bound-Mode Propagation in Rectangular, Multimode Dielectric, Channel Waveguides With Sidewall Roughness

Abstract

Abstract-This paper calculates and displays accurate radiation modes for rectangular, multimode dielectric, channel waveguides, for the first time, and introduces the new semianalytical calculation method used to find them, the radiation-mode Fourier decomposition method (RFDM), which is an extension of the Fourier decomposition method (FDM) for finding bound propagating modes. The optimum choice of non-linear conformal transformation parameters is discussed for achieving highest accuracy. Once the radiation modes are known, the coupling coefficients can be found between the bound and radiation modes, as well as those between the bound modes themselves, andhence, the propagation loss can be found. The paper adapts Marcuse's coupled power theory, for the first time, to enable it to model propagation in rectangular, multimode dielectric, channel waveguides suffering from one dimensional sidewall roughness enabling the equilibrium distance to be calculated, at which rate of loss to radiation modes becomes constant, and to find that equilibrium propagation loss, and the dependence on the statistical properties of the wall roughness. This leads to the conclusion that at sufficient distance there exist two uncoupled modes, a symmetric and an asymmetric lowest order mode.

Fabrication of Polymer Waveguides by Laser Ablation Using a 355 nm Wavelength Nd:YAG Laser

“…[29] noted that both photothermal and photochemical processes were present during the fabrication, due to the higher wavelength (355 nm) of the UV Nd:YAG compared to the KrF excimer laser; although, waveguide loss measurements were not yet reported and the values of wall roughness were not stated. The first measurements of side wall roughness of polymer waveguides have only been reported recently [31]. Therefore, this paper investigates the use of UV Nd:YAG lasers and the optimisation of the fabrication process using another polymer popularly used for optical waveguides due to its inherently low loss for use in Optical Interconnects (OI).…”

Passive assembly of parallel optical devices onto polymer‐based optical printed circuit boards

“…surface roughness (Papakonstantinou et al, 2009) of the waveguide, the scattering caused by imperfections along the "walls" of the waveguide; and . propagation loss, due to the natural (wavelength dependent) absorption of light by the material comprising the waveguide.…”

“…Additional losses have been identified in other waveguide components such as bends , tapers (Papakonstantinou et al, 2007) and tapered bends (Papakonstantinou et al, 2009). Typically, polymer waveguides become more absorbing at longer infrared wavelengths, however, most commercially available formulations are tuned to provide excellent transmissivity in the near infrared, specifically 850 nm.…”

Polymer optical waveguides with reduced in-plane bend loss for electro-optical PCBs

“…In particular when considering the need for commercially viable design and fabrication techniques for embedded stepindex optical waveguides in printed circuit boards, one must operate within a limiting trade-off space, which includes insertion loss, signal dispersion, refractive index difference between core and cladding, waveguide size, misalignment tolerance, minimum bend radius, maximum waveguide length and sidewall roughness [7][8][9][10].…”