Multilayer Silver / Dielectric Thin-Film Coated Hollow Waveguides for Sensor and Laser Power Delivery Applications Theory, Design, and Fabrication Carlos M. Bledt a, James A. Harrington a, and Jason M. Kriesel b a Dept. of Material Science & Engineering Rutgers, the State University of New Jersey b Opto-Knowledge Systems, Inc. January 21, 2012

Background on Hollow Glass Waveguides Used in the low loss broadband transmission from λ = 1 – 16 μm Light propagation due to enhanced inner wall surface reflection Silica Wall Dielectric Film Polyimide Coating Silver Film Structure of HGWs SiO2 capillary tubing substrate Ag film ~200 nm thick Dielectric(s) such as AgI, CdS, PbS Multilayer structures of interest Theoretical loss dependence * ∝ 1/a3 (a is bore radius) ∝ 1/R (R is bending radius) * Harrington, J. A., Infrared Fiber Optics and Their Applications 1/11

Attenuation Considerations in HGWs Practical losses in HGWs: Propagating modes Dielectric thin film materials Thickness of deposited films Quality and roughness of films Number of films deposited ↑ Throughout ∝ ↓ mode quality Ray Optics Attenuation Equation 𝟐𝜶 𝜽 = 𝟏−𝑹 𝜽 𝟐𝒂 𝒄𝒐𝒕 𝜽 α = power attenuation coefficient a = HGW inner radius size R = power reflection coefficient θ = angle of propagating ray R(θ) term dependence on: Angle of incidence Thin film structure Thin film materials HE11 mode is lowest loss mode in metal / dielectric coated HWs R(θ) is main design parameter 2/11

Motivation for Multilayer Designs Multilayer thin film designs Alternating low (nL) and high (nH) refractive index films Metal chalcogenides as film materials (compatible) Periodic structure resulting in 1-D photonic band gap structure Benefits of photonic band gap structures: Ultra-low loss at discrete λ ranges Omnidirectional properties (no bending loss) nH Film nL Film Silver Film Attenuation in multilayer HGWs * Loss ↓ as NL+H ↑ (asymptotic behavior) Loss ↓ as nH/nL (with nL > 1) Issues with multilayer designs Surface roughness ↑ with total film thickness (increased scattering losses) Precise film thickness control necessary for photonic band gap structure n Index profile * Miyagi, M. and Kawakami, S. "Design theory of dielectric- coated circular metallic waveguides for infrared transmission 3/11

Spectral Simulation of Multilayer HGWs Proposed PBG design Use metal sulfide thin films: PbS (nH ≈ 3.80 – 4.10 at IR λ) * CdS (nL ≈ 2.25 – 2.45 at IR λ) * Theoretical spectral calculations of 1-D PBG coated HGWs: Ray-Transfer matrix Method Simulation parameters for λT = 1.064 µm CdS Film PbS Film N 5 δ 131 nm 68 nm n 2.280 4.385 κ N/A CdS Film PbS Film N 1 δ 131 nm 68 nm n 2.280 4.385 κ ≈ 0 CdS Film PbS Film N 2 δ 131 nm 68 nm n 2.280 4.385 κ N/A CdS Film PbS Film N 4 δ 131 nm 68 nm n 2.280 4.385 κ N/A CdS Film PbS Film N 3 δ 131 nm 68 nm n 2.280 4.385 κ N/A CdS Film PbS Film N 6 δ 131 nm 68 nm n 2.280 4.385 κ N/A * Note: θi = 89.93° - HE11 Mode* 𝑬 𝒛 𝑭 𝒛 = 𝒊=𝟏 𝑵 𝑨 𝒊 𝑩 𝒊 𝑪 𝒊 𝑫 𝒊 𝑬 𝟎 𝑭 𝟎 Multilayer structure design High film index contrast (nH/nL) nL > 1 for hollow air core HWs Low κ materials at design λ Careful film thickness control Surface roughness excluded * Palik, E. D. and Ghosh, G., Handbook of Optical Constants of Solids 4/11

Experimental Approach Research objectives: CdS (nL) / PbS (nH) alternating film pairs Optimize CdS and PbS thin film deposition procedures Determine film growth kinetics of CdS and PbS films in HGWs Analyze optical response of multilayer coated HGWs Optimize multilayer coated HGW to develop 1-D PBG structure Experimental Approach HGW dimensionality constant at ID = 700 μm Film thickness as function of time for: CdS on Ag & CdS on PbS thin films PbS on Ag & PbS on CdS thin films Deposition of CdS / PbS based multilayer dielectric thin film stacks Characterization to include: FTIR spectroscopy Optical attenuation measurements 5/11

Fabrication Methodology Films deposited via dynamic liquid phase deposition process (DLPD) [8] The DLPD process: Peristaltic pumps used to flow precursor solutions through HGW Constant flow of solutions allows for deposition of films Strong reaction kinetics temperature & concentration dependence Advantages of DLPD process: No solution concentration depletion Flow speed adjusted to improve film quality Precursor Solution #1 Precursor Solution #2 HGW   Waste Peristaltic Pump x.xx rpm 1. Sn2+ Sensitization Step 2. Silver Film Deposition 3. Dielectric Thin Film Cadmium Sulfide (CdS) Lead Sulfide (PbS) 6/11

Deposition of Metal Chalcogenide Films Deposition of metal sulfide films involves hydrolysis of thiourea in an alkaline medium containing complexed metal cation species [9,10,11,12] Possible deposition mechanisms Competing homogeneous & heterogeneous (desired) deposition processes [10,12] Homogeneous Growth Heterogeneous Growth Cluster by cluster deposition Low overall film quality Rapid growth rate Poor stability & high porosity High surface roughness Ion by ion deposition High overall film quality Slow growth rate Good film adherence Low surface roughness 7/11

Cadmium Sulfide Film Growth Kinetics CdS on Ag HGW kinetics: [Cd(NO3)2] = 7.49 mM [SC(NH2)2] = 75 mM [NH4OH] = 1.85 M (pH ≈ 11.75) Volumetric Flow Rate: 17.35 mL/min Growth rate: 3.62 nm/min Temperature: 24 °C ± 0.5 𝜹 𝒂 𝑪𝒅𝑺 =𝟏.𝟒𝟑×𝟏 𝟎 −𝟑 𝒕 𝑪𝒅𝑺 −𝟎.𝟎𝟑𝟔 CdS on Ag / PbS HGW kinetics: [Cd(NO3)2] = 7.49 mM [SC(NH2)2] = 75 mM [NH4OH] = 1.85 M (pH ≈ 11.75) Volumetric Flow Rate: 17.35 mL/min Growth rate: 4.79 nm/min Temperature: 24 °C ± 0.5 𝜹 𝒂 𝑪𝒅𝑺 =𝟒.𝟕𝟗×𝟏 𝟎 −𝟒 𝒕 𝑪𝒅𝑺 +𝟎.𝟑𝟒𝟖 8/11

Lead Sulfide Film Growth Kinetics CdS on Ag HGW kinetics: [Pb(NO3)2] = 2.72 mM [SC(NH2)2] = 27.2 mM [NaOH] = 37.5 mM (pH ≈ 12.05) Volumetric Flow Rate: 17.35 mL/min Growth rate: 3.62 nm/min Temperature: 24 °C ± 0.5 𝜹 𝒂 𝑷𝒃𝑺 =𝟑.𝟔𝟐×𝟏 𝟎 −𝟑 𝒕 𝑷𝒃𝑺 +𝟎.𝟎𝟒𝟕 PbS on Ag / CdS HGW kinetics: [Pb(NO3)2] = 2.7 mM [SC(NH2)2] = 27.2 mM [NaOH] = 37.5 mM (pH ≈ 12.05) Volumetric Flow Rate: 17.35 mL/min Growth rate: 6.71 nm/min Temperature: 24 °C ± 0.5 𝜹 𝒂 𝑷𝒃𝑺 =𝟔.𝟕𝟏×𝟏 𝟎 −𝟑 𝒕 𝑷𝒃𝑺 +𝟎.𝟏𝟒𝟗 9/11

CdS / PbS Multilayer Stack HGWs High compatibility seen between CdS & PbS films Characteristics spectral shift with additional layers Surface roughness increase with time Losses measured with Synrad CO2 laser emitting at λ = 10.6 μm Drop in attenuation seen with successive layers up to 5 layers Lower losses achieved relative to Ag/CdS & Ag/PbS only HGWs 10/11

Considerable progress achieved towards 1-D PBG structures in HGWs Conclusion Considerable progress achieved towards 1-D PBG structures in HGWs Experimental Goals Achieved: Theoretical calculations for 1-D CdS / PbS PBG structures Film growth kinetics study for: CdS films on Ag and PbS substrates PbS films on Ag and CdS substrates Deposition of CdS / PbS multilayers Important considerations: Substrate has pronounced effect on growth kinetics Fabrication difficulty increases considerably with: Total number of deposited films Increasing individual film thickness Future research: Continue study of multilayer stacks – Incorporate novel materials Optimize structure for appearance of PBG at NIR wavelengths Study possibility of omnidirectional propagation – FDTD analysis 11/11

Thank you for your attention! End of Presentation Thank you for your attention!

References Harrington, J. A., Infrared Fiber Optics and Their Applications, (SPIE Press, Bellingham, WA, 2004). Miyagi, M. and Kawakami, S. "Design theory of dielectric-coated circular metallic waveguides for infrared transmission,“ IEEE Journal of Lightwave Technology. LT-2, 116-126 (1984). J. D. Joannopoulos, S. G. Johnson, R. D. Mead, and J. N. Winn, Photonic Crystals: Molding the Flow of Light, Second Edition, (Princeton Univ. Press), 2008 Palik, E. D. and Ghosh, G., Handbook of optical constants of solids, (Academic, London, 1998). O. S. Heavens, Optical Properties of Thin Film Solids, First Edition, (Dover Publications, Inc.), 1991 S. G. Johnson, M. Ibanescu, M. Skorobogatiy, O. Weisberg, T. D. Engeness, M. Soljacic, S. A. Jacobs, J. D. Joannopoulos, Y. Fink, “Breaking the glass ceiling: hollow OmniGuide fibers,” Proceeding of SPIE Vol. 4655 (2002) Fink, Y., Winn J.N., Fan, S., Michel, J., Chen, C., Joannopoulos, J.D., Thomas, E.L., "A Dielectric Omnidirectional Reflector," Science 282, 1679–1682, November 1998. Gopal, V., Harrington, J. A., “Deposition and characterization of metal sulfide dielectric coatings for hollow glass waveguides,” Optics Express, 11, 24 (2003). Niesen, T. P., De Guire, M. R., “Review: Deposition of Ceramic Thin Films at Low Temperatures from Aqueous Solutions.” Journal of Electroceramics, 6, 169 – 207 (201). R. S Mane and C. D Lokhande, “Chemical deposition method for metal chalcogenide thin films,” Mat. Chem. Phys. 65, 1-31 (2000). Chaparro, A. M., “Thermodynamic analysis of the deposition of zinc oxide and chalcogenides from aqueous solutions,” Chem. Mater., 17 (16), 4118-4124 (2005) Guillen, C., Martinez, M. A, Herrero, J., “Accurate control of thin film CdS growth process by adjusting the chemical bath deposition parameters,” Thin Solid Films, 335, 37 – 42 (1998).