1. 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

2. 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
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3. 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
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4. 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

5. 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 = 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

6. 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

7. 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

8. 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

9. 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: 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: 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

10. 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: 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: 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
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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

12. 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
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13. Thank you for your attention!
End of Presentation
Thank you for your attention!

14. 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, (1984).
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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
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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).
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Chaparro, A. M., “Thermodynamic analysis of the deposition of zinc oxide and chalcogenides from aqueous solutions,” Chem. Mater., 17 (16), (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).