Deposition and characterization of metal sulfide dielectric coatings for hollow glass waveguides

Abstract

Metal sulfide dielectric thin films have been deposited using dynamic wet chemistry processing on silver coated hollow glass waveguides (HGWs). The sulfides used were cadmium sulfide (CdS) and lead sulfide (PbS); both films have excellent infrared transparency and high refractive index contrast. The thickness of these thin films can be tailored to minimize the attenuation of the HGW over specific infrared wavelengths. We have made both single and multiple dielectric (2 and 3 layer) metal coated HGWs using CdS and PbS deposited over an inner Ag layer. The straight lowest loss measured at 1.55 microm for a 1,000-microm bore Ag/CdS/PbS/CdS HGW was 0.06 dB/m. This loss is three times less than that measured for a single layer Ag/CdS coated HGW at 1.55 microm.

Characterization of metal-sulfide-coated hollow glass waveguides

“…The growth rates were then given by the slopes when data was plotted as thickness vs. time. The method has been shown to have good correlation between the calculated layer thickness and the thickness measured directly using FESEM microscopy 14 . The growth rate of PbS is shown in Fig.…”

Theory and practical considerations of multilayer dielectric thin-film stacks in Ag-coated hollow waveguides

“…For all calculations in this study, with the exception of the forthcoming analysis of waveguide loss as a function of bore size, a constant waveguide bore size of a 350 μm (ID 2a 700 μm) will be assumed, as this bore size is often used for the majority of practical HGW applications. Furthermore, as mentioned in the introduction, the dielectric thin film materials considered will remain constant throughout with CdS being used as the low index material and PbS as the high index material, with the film adjacent to the silver film composed of the low index material (CdS) [1,11]. These dielectric materials will be assumed to be lossless in the λ 1-12 μm region of interest, an assumption which is largely valid except for PbS close to λ 1.0 μm.…”

“…Of the commonly deposited dielectric film materials, CdS (n CdS n L ≈ 2.25) and PbS (n PbS n H ≈ 4.25) pose as excellent candidates for the development of such multilayer stacks, due to their high IR transparency, well-developed deposition procedures, chemical compatibility and. above all, their high index mismatch (n PbS ∕n CdS n H ∕n L ≈ 1.85) [1,11,12]. As such, this study will focus exclusively on the use of these two materials in HGWs for the theoretical analysis of said proposed multilayer structures.…”

Optofluidic waveguides: II. Fabrication and structures

“…Bragg fibers were also constructed in a coating procedure that mimics the silver coated capillaries cited above. Layers of cadmium sulfide and lead sulfide were placed over silver coatings using a liquid-phase deposition process with specific applications in the infrared wavelengths (Gopal and Harrington 2003). One millimeter inner diameter tubes with these coating exhibited an attenuation of 6 × 10 −4 dB/cm at a wavelength of 1.55 µm when filled with air.…”