Passive long-range surface plasmon-polariton devices in Cytop

Abstract

Passive elements operating with long-range surface plasmon polaritons and constructed as Au stripes embedded in Cytop were investigated theoretically and experimentally at wavelengths near 1310 nm. The elements investigated consist of straight waveguides, S-bends, Y-junctions, couplers, and Mach-Zehnder interferometers. The measured performance of these devices is close to theoretical expectations, although uniformity issues were noted, likely because of fabrication imperfections. Cytop is a low-index polymer suitable for biosensing applications involving aqueous buffers. The elements demonstrated thus could form the basis of integrated biosensing devices operating with long-range surface plasmons.

Thermo-optic characterization of long-range surface-plasmon devices in Cytop

“…The slope of Eq. (3a) was extracted by fitting and found to be m 1.35 rad∕mW, which is close to the value obtained in the previous case (m 1.25 rad∕mW, previous subsection); fabrication inconsistencies among structures and waveguide deformation could be causes for the discrepancy [19,20]. Again, it is observed that at a dissipated power of ∼12 mW (5 mA injected current), the measurements deviate from sinusoidal, probably for the same reasons as discussed in the previous subsection.…”

“…7 and compared with Eq. (3d), in which the value used for the input power was P in 1.83 mW, the attenuation was α 0.691 mm −1 (mode power attenuation of 6 dB∕mm), the total radiation coefficient was ρθ 0 0.039 (total radiation loss 0.34 dB), the total transition coefficient was τ 0 0.599 (total TL 5.2 dB), and the nominal phase shift between the arms was ϕ 0 −02π, all adjusted by optimizing the fit between the theoretical and experimental responses, with α, ρθ 0 , and τ 0 remaining very close to modeling results reported in [20]. The slope of Eq.…”

“…5(a), and from the mosaic of a full sequence of mode output images as shown in Fig. 5(b), it is observed that the curves generally follow the same trend: at lower current the mode power is generally stable with only small fluctuations caused by the beating between the LRSPP mode and cladding modes excited due to imperfect input coupling into the LRSPP mode (∼90% coupling efficiency [20]). As the current increases, the fluctuations in mode power gradually become larger, reaching a peak value before steeply dropping off.…”

“…A radiation coefficient ρ at a curved section θ is defined (for convenience) as e −2ρθ R, where the radiation loss of the section is determined in decibels as −10log 10 R. τ 0 and Δτ s are coefficients that characterize the total transition loss and the difference in transition loss between the arms. Transition losses include buttcoupling losses at the input and output facets of the die, transition losses at the taper of the two Yjunctions, and transition losses at the intersections between curved sections bending in opposite directions [20]. A transition coefficient τ at a junction is defined (for convenience) as e −2τ T r , where T r is the transmittance of the junction and TL −10log 10 T r is the transition loss in decibels.…”

“…Recently, work has focused on developing metal stripe waveguides and devices in Cytop [19,20]. Cytop is an amorphous fluoropolymer with a refractive index that is close to that of water [21] (n ∼ 1.334), motivating interest in this material, and in Teflon [22] which is a similar polymer, for biosensors where microfluidic channels confining the sensing fluid (usually aqueous) must be integrated with waveguides.…”