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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 25 — Dec. 3, 2012
  • pp: 27636–27649
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Efficient photo-thermal activation of gold nanoparticle-doped polymer plasmonic switches

J.-C. Weeber, K. Hassan, L. Saviot, A. Dereux, C. Boissière, O. Durupthy, C. Chaneac, E. Burov, and A. Pastouret  »View Author Affiliations


Optics Express, Vol. 20, Issue 25, pp. 27636-27649 (2012)
http://dx.doi.org/10.1364/OE.20.027636


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Abstract

We report on the photo-thermal activation of dielectric loaded plasmonic switches comprised of gold nanoparticle-doped polymer deposited onto a gold film. The plasmonic switches rely on a multi-mode interferometer design and are fabricated by electron beam lithography applied to a positive resin doped with gold nanoparticles at a volume ratio of 0.52%. A cross-bar switching is obtained at telecom wavelengths by pumping the devices with a visible beam having a frequency within the localized surface plasmon resonance band of the embedded nanoparticles. By comparing the switching performances of doped and undoped devices, we show that for the modest doping level we consider, the power needed to activate the doped switches is reduced by a factor 2.5 compared to undoped devices. The minimization of activation power is attributed to enhanced light-heat conversion and optimized spatial heat generation for doped devices and not to a change of the thermo-optic coefficient of the doped polymer.

© 2012 OSA

1. Introduction

2. Samples fabrication

The samples were fabricated by electron-beam lithography applied to NP-doped or undoped polymethyl methacrylate (PMMA) layer spin-coated onto a 80 nm-thick gold layer thermally evaporated onto a glass substrate. The NP-doped PMMA was obtained by dissolving solid PMMA (molecular weight 120K) into toluene and by subsequently mixing the resulting solution with commercially available (Aldrich, Ref. 660434) gold nanoparticles (diameter ranging from 3 to 5nm) dispersed into toluene as well. When spin-coated onto a gold layer, the NP-doped PMMA layers feature pronounced colors ranging from light green to dark pink depending on layer thickness. Prior to the exposure, the PMMA layers were baked on a hot plate. For the NP-doped PMMA solution used for the fabrication of the samples investigated in the following, the volume occupied by the gold NP into the baked doped PMMA layers was estimated to be 0.52% of the solid polymer volume. This volume ratio has been computed from the density (0.9308) and gold concentration (2 % w/v) of the NP solution and from the known density of the 120K PMMA (1.118) and the experimentally measured concentration (0.22g/mL) of solid PMMA into the prepared PMMA-toluene solution. The volume ratio of 0.52% corresponds to a doping level of 2 × 1017 NP per cm3 of solid polymer and a side-to-side average distance between the NPs in the range of 10 to 15nm. PMMA being a positive electron-beam resin, the switches were fabricated by exposing and eventually dissolving areas surrounding the plasmonic waveguides. In spite of the presence of the NPs, the optimum exposure doses (165μC/cm2) were found to be similar for the doped and undoped PMMA layers.

Scanning Electron Microscope (SEM) images of the switches fabricated following this process with the NP-doped PMMA resin are shown in Fig. 1. The MMI switches we considered are equipped with an input grating coupler (period= 2.45μm) (see Fig. 1(a)) allowing a very efficient excitation of the device by means of a moderately focused beam (spot size = 30μm) impinging at an angle of incidence of 30° for free-space wavelengths ranging from 1500nm to 1600nm [28

28. M. G. Nielsen, J.-C. Weeber, K. Hassan, J. Fatome, C. Finot, S. Kaya, L. Markey, O. Albrektsen, S. I. Bozhevolnyi, G. Millot, and A. Dereux, “Grating couplers for fiber-to-fiber characterizations of stand-alone dielectric loaded surface plasmon waveguide components,” J. Lightwave Technol. 30, 3118–3125 (2012). [CrossRef]

]. The switch is comprised of the single-mode DLSPPW (labeled as SM in Fig. 1(b)) and a multi-mode waveguide with a typical length of 140μm and finally a Y-junction at the output end of the device. For a switch relying on a dual-mode interference, the optimum length L of the multi-mode waveguide is given by 2L=λ0/|Δne(1)Δne(2)| where λ0 is the free space wavelength and where Δne(i) (i = 1, 2) denote the change of effective index of each mode involved in the switching process for a given change in temperature.

Fig. 1 (a) SEM image of a NP-doped plasmonic MMI switch (scale bar=50μm). The dark regions are coated with polymer, light-gray regions correspond to bare gold film. (b) Zoom onto the region corresponding to the dashed perimeter shown in (a) showing the single-mode (SM) and multi-mode (MM) waveguides (Scale bar=10μm). (c) Detail of the transition between the single-mode and multi-mode regions (Scale bar= 1 μm). The nanoparticles are clearly visible on the DLSPPWs.

The excitation of the MMI waveguide is achieved by a straight single-mode DLSPPW laterally shifted with respect to the multi-mode waveguide as shown on the SEM image displayed in Fig. 1(c). This lateral shift is used to control the relative amplitude of the modes excited in the MMI region. The presence of the NP is clearly visible in Fig. 1(b) and 1(c). In particular, we note in Fig. 1(c) that the NPs have coagulated during the fabrication process. The NP distribution observed at the top surface of the polymer was also visible on the SEM images of the vertical side walls of the waveguides indicating that the NPs are distributed in the volume of the doped PMMA layer. We note however, that, from the SEM images of the waveguide side-walls, we could only hardly estimate the NP density in the polymer as a function of the distance to the gold film. Finally, an atomic force microscope imaging of the waveguides reveals a roughness at the top surface of the doped waveguides with an average peak-to-peak height of 12nm significantly degraded compared to undoped structures (average peak-to-peak roughness around 4nm).

3. Radiation leakage characterizations of the MMI swicthes

3.1. Experimental set-up and MMI imaging

Fig. 2 (a) Leakage radiation microscope set-up used for the observation and the photo-thermal activation of the switches. (b) (resp. (c)) Typical LRM images at λ0 =1580nm of a doped (resp. undoped) MMI waveguide (scale bar=100μm). (c) Single-exponential fits (solid lines) of the experimental LRM intensity (dots) along the doped and undoped MMI waveguide axis.

The near-infrared signal and the visible pump beam transmitted through the gold film were collected by a high-numerical aperture objective (NA=1.49) forming the image of the surface onto the detector of an InGaAs camera. A longpass filter with a cut-on wavelength of 900nm was used to remove the contribution of the visible light from the LRM images. LRM images of a NP-doped and undoped MMI switch are shown in Fig. 2(b) and 2(c) respectively for an incident free-space wavelength of λ0=1580nm. The MMI DLSPPWs we consider are expected to support a fundamental symmetric DLSPPW mode with an effective index nes and an higher-order anti-symmetric mode (effective index nea) [26

26. A. Pitilakis and E. E. Kriesis, “Longitudinal 2x2 Switching Configurations Based on Thermo-Optically Addressed Dielectric-Loaded Plasmonic Waveguides,” J. Lightwave Technol. 29, 2636–2646 (2011). [CrossRef]

] where the symmetric and anti-symmetric nature of the modes refers to the electric field component perpendicular to the thin metal film on which the polymer ridge is deposited. On the LRM images, we observe a two modes beating pattern with a period of p = 6.5μm and p = 6.3μm for the doped and undoped waveguides respectively. The beating period being given by:
p=λ0(nesnea)
(1)
we conclude that the effective index difference ( nesnea) for the two DLSPPW modes is only slightly changed by the NP doping. On the contrary the damping distance along the MMI waveguide is clearly affected by the presence of the NPs. By integrating the LRM image intensity over the width of the waveguide for each observation point along the waveguide axis, we find that the intensity profile is well fitted by a single-exponential function corresponding to a 1/e damping distance (at 1580nm) of respectively Lspp = 40 ± 2μm and Lspp = 56 ± 2μm for the NP-doped and undoped MMI (see Fig. 2(d)).

3.2. Finite-element analysis of the MMIs

In order to correlate our experimental results to the properties of the MMI waveguides, we perform a finite-element eigenmode analysis. The modeled MMI we consider is made of undoped PMMA and has a width w and height h of respectively 900nm and 400nm extracted from the SEM and AFM characterizations of the fabricated waveguides. As said before, the experimental waveguides are obtained by exposing and dissolving the (doped or undoped) PMMA resin on each side of the waveguides leaving the waveguide itself unexposed. The PMMA, once exposed and developed, is known to create undercut sidewalls. In our situation, these undercuts result in trapezoidal cross-section waveguides. For a reasonable 15°-tilt of the waveguide side walls with respect to the normal, we found an effective index for the symmetric and anti-symmetric mode of respectively nes=1.251 and nea=1.005 leading to a beating length (at 1580nm) with a period of p = 6.4μm in fair agreement with the experimental value (p = 6.3μm).

Fig. 3 (a) Opto-geometrical parameters for the finite-element analysis of an undoped MMI waveguides, W =900nm, h =400nm (see Fig. 3(a)), npmma = 1.489, nAu = 0.57+i11.7 for a wavelength of λ0=1580nm. The trapezoidal shaped cross-cut of the DLSPPW accounts for the undercut of the vertical side-walls produced by PMMA processing. (b) (resp. (c)) Spatial distribution of the guided power for the fundamental symmetric (resp. higher-order anti-symmetric) DLSPPW mode.

4. Photo-thermal activation of MMI plasmonic switches

A quantitative comparison of the photo-thermal activation power for doped and undoped MMI switches is only possible provided that devices operating an optimized light-heat conversion are used. The waveguides we consider being obtained by processing a positive resin, the reference system (in absence of waveguide) is a polymer thin film deposited onto a gold thin film. Characterizing this reference configuration for the doped and undoped polymer is then necessary for an optimization of the photo-thermal behavior of the MMI switches.

4.1. Optical properties of the NP-doped PMMA layers

With the aim of extracting the optical properties of the NP-doped polymer, we first characterize the optical response of the NP in solution into toluene diluted PMMA. A dual beam spectrophotometer has been used to record the normal incidence absorbance spectra displayed in Fig. 4(a). These spectra have been recorded by comparing the transmission through 1 mm-thick calibrated cells filled with NP-doped PMMA solutions with NP concentration corresponding to gold volume fraction of 0.0038% and 0.0074%. For these measurements, a cell filled with undoped PMMA was placed on the path of the reference beam of the spectrophotometer. As expected for gold NP embedded into a liquid matrix with a refractive index close to 1.5, the NP-doped solution exhibits a maximum absorbance at a free-space wavelength around 520nm. Starting from a NP-doped polymer solution diluted into toluene with a gold volume ratio of 0.04%, NP-doped PMMA films have been prepared by spin-coating at different speeds onto bare (without gold film) glass substrates. After spin-coating, and prior to absorbance measurements, the PMMA films were baked according to the process used for electron-beam lithography leading to a gold volume fraction of 0.52% in the solid PMMA layers.

Fig. 4 (a) Absorbance spectra of NP-PMMA solutions with gold volume fractions of 38 part per million (ppm) and 74 ppm. (b) Absorbance spectra for NP-doped PMMA layers of different thicknesses deposited on a glass substrate. The gold volume fraction of solid PMMA is 5200ppm (0.52%).

The absorbance spectra shown in Fig. 4(b) have been obtained for baked NP-doped PMMA films deposited on the glass substrate with a bare glass slide placed on the reference arm of the spectrophotometer. On these spectra, we note a red-shift of the maximum absorbance of about 40nm compared to the NP-doped PMMA solutions. This red-shift results from the combined effect of the refractive index increase of the polymer host matrix when the solvent is evaporated and from the fact that the NP particles are closely-packed in the solid PMMA layer as previously noticed on the waveguide SEM images (see Fig. 1). Despite the red-shift of the absorbance peak, we note that the 532nm pump beam is still within the absorbance peak of the NP-doped solid PMMA layers. The radius of the NP we use in this study being very small compared to visible wavelengths, their scattering efficiency is more than three order of magnitude smaller than their absorption efficiency over the whole visible range [30

30. C. F. Bohren and D. R. Huffman, Absorption and Scattering of Light by Small Particles (John Wiley and sons, Inc., New York, 1983), page 136.

]. Thus, the spectra of the NP-doped PMMA layers are characteristic of the absorption of the composite medium. The absorbance Abs measured with the dual-beam of the spectro-photometer is defined as Abs=log10IIref where I and Iref are the powers transmitted through the coated and the bare substrate respectively. Neglecting the scattering of the NPs and the change of reflectivity due to the presence of the PMMA layer (compare to the bare substrate), the power I can be expressed as I = Iref exp(−2κpk0h) where k0 is the incident wavevector, h is the thickness of the doped layer and where κc is the extinction coefficient of the doped polymer defined as n̂p = np + p with n̂p the complex effective index of the composite medium. Knowing the thickness h of the NP-doped PMMA layers from AFM measurements, the effective extinction coefficient κp can be evaluated from:
κp=λ0×Abs×ln104πh
(2)
By averaging the extinction coefficients extracted from the spectra displayed in Fig. 4(b), we find that the effective extinction coefficient for the NP-doped PMMA is equal to κp = 0.031 at λ0 = 532nm.

We have considered so far NP-doped PMMA layers deposited on a glass substrate whereas the MMI switches are implemented onto optically thick gold films. The quantity of interest for the photo-activation of the MMI switches is obviously the amount of incident pump light which is absorbed by the system. This quantity is difficult to extract from absorbance spectra in the presence of metal due to the high gold film reflectivity. However, by recording the transmittance T and the near-normal incidence reflectance R spectra of PMMA layers deposited onto gold coated glass substrates, the absorption can be extracted according to A = 1− (R + T) (assuming once again that the scattering of NPs is negligible). This measurement procedure is illustrated in Fig. 5(a) showing the experimental transmittance and reflectance spectra along with the experimental absorption spectrum in the case of a bare gold film (thickness=80nm) evaporated onto a glass substrate. These experimental spectra are compared to the theoretical ones (dashed-lines) computed with the dielectric function of gold extracted from ref. [31

31. E. D. Palik, Handbook of Optical Constants of Solids (Academic Press Inc., London, 1985).

]. For this configuration, we note that only 23% of the incident light is converted into heat at 532nm making light-heat conversion rather inefficient at this wavelength for this configuration. The same measurements have been performed for undoped and NP-doped PMMA layers with different thickness. For each PMMA layer, the absorption at 532nm has been computed and plotted in Fig. 5(b). For the undoped PMMA, the experimental values are in good agreement with the computed absorption when the refractive index of PMMA at 532nm is 1.502 in agreement with PMMA specifications. Note that for the undoped PMMA layer thicknesses leading to an anti-reflecting effect (for example h = 403nm), the maximum absorption level is about 38±2%. For NP-doped PMMA layers, a fairly good agreement between computed and experimental values is obtained when the complex refractive index at 532nm is 1.57 + i0.031. In agreement with Maxwell-Garnett effective medium approach, the real refractive index of NP-doped PMMA layers is larger than for undoped layers, however the refractive index of 1.57 is about 0.02 larger compared to the refractive index returned by the Maxwell-Garnett theory. In spite of the rather low gold volume ratio, Maxwell-Garnett approach fails to provide an accurate value for the real effective index of the composite medium likely due to the coagulation of the NPs [29

29. M. A. Garcia, J. Llopis, and S. Paje, “A simple model for evaluating the optical absorption spectrum from small Au-colloids in sol-gel films,” Chem. Phys. Lett. 315, 313–320 (1999). [CrossRef]

]. Finally, we note that for a NP-doped PMMA layer with a thickness of h = 396nm, the absorption is about 79±2.5%, two-fold larger than for an undoped layer of same thickness. Hence, light-heat conversion for optimized layers is improved by a factor 2 for doped polymer.

Fig. 5 (a) Solid lines: Experimental normal incidence transmittance (T) and near-normal incidence reflectance (R) spectra of a 80nm-thick gold film deposited onto a glass substrate using a titanium adhesion layer with a thickness of 3nm. The Absorption spectra (A) is computed from T and R. Dashed lines: comparison of the experimental spectra with computed spectra using the gold dielectric function tabulated in Ref. [31] and neglecting the effect of the adhesion layer. (b) Dots: Experimental absorption values at 532nm for doped and undoped PMMA layers deposited on a gold film. Solid lines: computed absorption at 532nm for PMMA layers deposited on a gold film. For undoped PMMA, the best fit is obtained for nPMMA=1.502, for doped PMMA, nNP–PMMA=1.57+i0.031.

4.2. Doped and undoped MMI switches

We consider first a MMI fabricated in an undoped PMMA layer with a thickness of 406nm. Figure 6(a) shows the intensities ICROSS and IBAR at the outputs of the Y-junction obtained by integrating the LRM images over the two ports when sweeping the incident wavelength. The BAR (resp. CROSS) port is located on the same (resp. opposite) side of the MMI waveguide than the laterally shifted single-mode input waveguide. The cold spectrum displayed in Fig. 6(b) is obtained by computing the extinction ratio ER given by:
ER(dB)=10log10IBARICROSS
(3)
Symmetric ERs of +15 and −15 dB are measured at respectively λB=1563nm and λC=1535nm. The corresponding LRM images are displayed on Fig. 6(c) and (d) respectively. For the photo-activation, the incident wavelength is adjusted at 1540nm and the pump beam with an increasing power is focused onto the MMI region of the switch. For each pump power, the ER is computed in the cold (pump OFF) and hot state (pump ON) and plotted in Fig. 6(e). When the pump power is increased, we observe an increase of the ER for the MMI we consider. This trend results from the negative thermo-optic coefficient of PMMA ( dndT=1.05e104) causing a blue-shift of the ER spectrum when the temperature is increased [27

27. K. Hassan, J.-C. Weeber, L. Markey, A. Dereux, O. Pitilakis, and E. E. Kriesis, “Thermo-optic plasmo-photonic mode interference switches based on dielectric loaded waveguides,” Appl. Phys. Lett. 99, 241 110 (2011). [CrossRef]

] and hence an increase of the ER in the case of the MMI we consider at λ0 = 1540nm. For a pump power of 40mW, the ER jumps from −8 to +12dB in the cold and hot state respectively as shown on the corresponding LRM images displayed in Fig. 6(f) and 6(g). Note that for recording the image of Fig. 6(f), the longpass filter has been intentionally removed in order to show the elongated pump beam produced by the arrangement of two cylindrical lenses. Finally, the change of ER resulting from the MMI photo-activation is correlated to a change of wavelength by using the cold spectrum (see Fig. 6(b)). The result of this procedure is the curve plotted in Fig. 6(h) showing that the wavelength shift Δλ depends almost linearly on the pump power with a slope P = 0.5nm/mW. Note that the value of P is not an intrinsic property of the MMI device but depends also on the pump illumination conditions. For the purpose of comparison of the undoped and NP-doped MMIs, it is then critical to keep the pump illumination conditions unchanged when switching from a sample to another.

Fig. 6 (a) LRM intensity integrated over the CROSS and the BAR output port of an un-doped MMI switch for a signal sweeping the telecom frequency range. (b) CROSS-BAR Extinction ratio spectrum computed using the results of (a). (c) (resp.(d)) LRM image of the CROSS (resp. BAR) state. (e) For a fixed wavelength of 1540nm, change of extinction ratio at the output port as a function of the pump power. (f) (resp.(g)) LRM image taken at λ0=1540nm in the hot (resp. cold) state. The elliptically shaped pump (532nm) beam with a power of 40mW is visible in (f). (h) Activation power efficiency obtained by correlating the extinction ratio change in (e) to a wavelength shift in the cold state given in (b).

The same experiment has been conducted for a NP-doped MMI switch fabricated in a doped PMMA layer with a thickness of 396nm. The extinction ratio observed for this NP-doped MMI is plotted in Fig. 7(a). The MMI switch is in the BAR state at λB=1522nm (ER=+20dB) and in the CROSS state (ER=−18 dB) at λC=1558nm. The incident wavelength being fixed to 1536nm, the photo-thermal activation of the MMI leads to a decrease of the extinction ratio as shown in Fig. 7(b). This time, the ER drops from +6dB in the cold state to −4.5 dB for a pump power of only 8mW. The image displayed in Fig. 7(c) shows the difference of the LRM image in the hot and cold state for such a pump power. On this image, the build-up process along the MMI region leading to the switching at the Y-junction is clearly visible. Using once again the cold ER spectrum as a calibration curve, the drop of the ER is correlated to the wavelength shift plotted in Fig. 7(d) with a slope of P = 1.37 nm/mW. Similar characterizations have been repeated for several undoped and NP-doped switches fabricated respectively on the same substrate as the devices considered above. The values of the slope P obtained in each case are summarized in table (1). Based on the values of the slope P, we conclude that the pump power needed for the photo-thermal activation of the NP-doped MMIs is about 2.5 times smaller than for undoped ones, a factor that is even larger than the absorption enhancement obtained for the doped and undoped PMMA unstructured layers. This activation power ratio can in principle originate from the enhanced absorption of the NP-doped polymer and/or an increase of the thermo-optic coefficient of the composite medium. In our situation, the contribution of the thermo-optic coefficient of the NP-doped polymer can be safely neglected. Indeed, the infrared signal being far from the plasmon resonance of NPs, the thermo-optic coefficient (TOC) of the composite medium can be approximated as the volume fraction average of the TOCs of each compound of the composite medium [32

32. M. Rashidi-Huyeh and B. Palpant, “Counterintuitive thermo-optical response of metal-dielectric nanocomposite materials as a result of local electromagnetic enhancement,” Phys. Rev. B 74, 075 405 (2006). [CrossRef]

]. Using the data of bulk gold [32

32. M. Rashidi-Huyeh and B. Palpant, “Counterintuitive thermo-optical response of metal-dielectric nanocomposite materials as a result of local electromagnetic enhancement,” Phys. Rev. B 74, 075 405 (2006). [CrossRef]

], we find that the TOC of the doped polymer at 1550nm for a gold volume ratio of 0.52% is changed by less than 2% compared to the undoped one. Thus, the decrease of the photo-thermal activation power is due to the enhanced light-heat conversion for the doped switches.

Fig. 7 (a) CROSS-BAR exctinction ratio for a doped MMI switch. (b) For a fixed wavelength of 1536nm, change of extinction ratio at the output port as a function of the pump power. (c) Differences of the LRM images recorded in the hot and cold state for a pumping power of 8mW. (d) Activation power efficiency obtained from (b) and (a).

Table 1. Activation efficiency obtained for three different NP-doped and undoped MMI switches

table-icon
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In fact, not only the total amount of absorbed light is changed when doping the polymer but also the spatial distribution of the heat source density. The volume density of heat sources is given by:
h(r)=12ωε0(ε(r))|E(r)|2
(4)
where ℑ(ε(r⃗)) and E(r⃗) denote respectively the imaginary part of the relative dielectric function of the material and the electric field of the pump beam at the observation point r⃗. We have computed this density by using the differential method [33

33. M. Nevière and E. Popov, Light Propagation in Periodic Media (Marcel Dekker, Inc. New-York-Basel, 2003).

] for a DLSPPW (h = 400nm, W = 900nm, see Fig. 8(a)) illuminated at normal incidence by a cylindrical Gaussian beam with a waist of 10μm. The heat source density calculated along the vertical axis of the waveguide (see Fig. 8(b)) shows that for undoped waveguides (np =1.502), the heating power is localized at the metal film surface as a consequence of the skin depth effect whereas for doped polymer (n̂p = 1.57 + i0.031), heat is generated also in the volume of the DLSPPWs. By integrating the heat density over the volume of the active area, we find that for the doped MMI DLSPPWs, about 50% of the heat is generated within the polymer leading to a temperature distribution in the core of the waveguides that could enhance the thermo-optical response of the switches. We note also that, for the configuration we consider, the polarization of the pump beam (parallel or perpendicular to the waveguide axis) plays only a minor role since the topographic steps at the surface of the gold film achieve a very poor excitation of surface plasmon modes at a wavelength of 532nm. Finally, we emphasize that the spatial distribution of heat sources in the presence of the NPs could impact the response time of the switches. This topic is out of the scope of the present work but deserves a careful examination as it may help in the development of faster thermo-plasmonic devices.

Fig. 8 (a) Configuration for the heat source density computation. The parameters are W =900nm, h =400nm and g =2.5μm. The thickness of the gold film is 80nm. (b) Heat source density at 532nm computed for along the vertical (z-axis) of the waveguide for the doped and undoped polymer.

5. Conclusion

In summary, we have investigated the photo-thermal activation of 1×2 dielectric loaded plasmonic switches. The switches which rely on a MMI design were fabricated by electron beam lithography using a NP-doped positive resin. For a doping level corresponding to a gold volume ratio of 0.52%, the radiation leakage microscope images of the doped MMI waveguides reveal an decrease by about 30% of the plasmon modes propagation distance attributed to waveguide walls scattering losses. By inspecting the spectral response at room temperature of 140μm-long MMI waveguides, we note a switching between the CROSS and the BAR state with typical extinction ratios around 20dB over a wavelength range of 30±5nm for both doped and un-doped devices. For the purpose of comparing the power needed to thermally activate doped and undoped switches, the thickness of polymer leading to an optimum light-heat conversion when illuminated at 532nm has been determined by analyzing absorbance spectra of homogeneous layers. For an optimized thickness of 400nm, the light-heat conversion efficiency at 532nm is enhanced by a factor 2 by the presence of the NPs.

In this study, the polymer material has been engineered to enhance light-heat conversion. Following this approach, many improvements can be suggested such as for example the use of silver NPs which are known to generate about ten times more heat when illuminated at their resonance frequency compared to gold NPs [17

17. A. O. Govorov and H. H. Richardson, “Generating heat with metal nanoparticles,” Nano today 2, 30–38 (2007). [CrossRef]

]. Finally, and beyond polymer doping, the metal film supporting the plasmon mode of interest can also be patterned to become fully absorbing at the pump frequency leading to an optimum light-heat conversion. Actions in this direction are currently in progress and will be reported elsewhere.

Acknowledgments

This work has benefited from the financial support of the Agence Nationnale de la Recherche through the PNANO program project FenoptiX (Grant number ANR-09-NANO-023) and from the FP7 European Project PLATON (Grant Number: 249135).

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O. Tsilipakos, E. E. Kriesis, and S. I. Bozhevolnyi, “Thermo-optic microring resonator switching elements made of dielectric-loaded plasmonic waveguides,” J. Appl. Phys. 109, 073 111 (2011). [CrossRef]

12.

K. Hassan, J.-C. Weeber, L. Markey, and A. Dereux, “Thermo-optical control of dielectric loaded plasmonic racetrack resonators,” J. Appl. Phys. 110, 023 106 (2011). [CrossRef]

13.

G. Giannoulis, D. Kalavrouziotis, D. Apostolopoulos, S. Papaioannou, A. Kumar, S. Bozhevolnyi, L. Markey, K. Hassan, J.-C. Weeber, A. Dereux, M. Baus, M. Karl, T. Tekin, O. Tsilipakos, A. K. Pitilakis, E. E. Kriesis, K. Vyrsokinos, H. Avramopoulos, and N. Pleros, “Data transmission and thermo-optic tuning performance of dielectric-loaded plasmonic structures hetero-integrated on a silicon chip,” IEEE Photon. Technol. Lett. 24, 374–376 (2012). [CrossRef]

14.

D. Kalavrouziotis, S. Papaioannou, G. Giannoulis, D. Apostolopoulos, K. Hassan, L. Markey, J.-C. Weeber, A. Dereux, A. Kumar, S. I. Bozhevolnyi, M. Baus, M. Karl, T. Tekin, O. Tsilipakos, A. Pitilakis, E. E. Kriesis, H. Avramopoulos, K. Vyrsokinos, and N. Pleros, “0.48Tb/s (12x40Gb/s) WDM transmission and high-quality thermo-optic switching in dielectric loaded plasmonics,” Opt. Express 20, 7655–7662 (2012). [CrossRef] [PubMed]

15.

D. Perron, M. Wu, C. Horvath, D. Bachman, and V. Van, “All-plasmonic switching based on thermal nonlinearity in a polymer plasmonic microring resonator,” Opt. Lett. 36, 2731–2733 (2011). [CrossRef] [PubMed]

16.

H. H. Richardson, Z. N. Hickman, A. O. Govorov, A. C. Thomas, W. Zhang, and M. E. Kordesch “Thermooptical properties of gold nanoparticles embedded in ice: characterization of heat generation and melting,” Nano Lett. 6, 783–788 (2006). [CrossRef] [PubMed]

17.

A. O. Govorov and H. H. Richardson, “Generating heat with metal nanoparticles,” Nano today 2, 30–38 (2007). [CrossRef]

18.

H. H. Richardson, M. T. Carlson, P. J. Tandler, P. Hernandez, and A. O. Govorov, “Experimental and theoretical studies of light-to-heat conversion and collective heating effects in metal nanoparticle solutions,” Nano Lett. 9, 1139–1146 (2009). [CrossRef] [PubMed]

19.

E. Boisselier and D. Astruc, “Gold nanoparticles in nanomedicine; preparations, imaging, diagnostics, therapies and toxicity,” Chemical Soc. Rev. 38, 1759–1782 (2009). [CrossRef]

20.

A. S. Urban, M. Fedoruk, M. R. Horton, J. O. Rädler, F. D. Stefani, and J. Feldmann, “Controlled nanometric phase transitions of phospholipid membranes by plasmonic heating of single gold nanoparticles,”, Nano Lett. 9, 2903–2908 (2009). [CrossRef] [PubMed]

21.

S. Maity, L. N. Downen, J. R. Bochinski, and L. I. Clarke, “Embedded metal nanoparticles as localized heat sources: An alternative processing approach for complex polymeric materials,” Polymer 52, 1674–1685 (2011). [CrossRef]

22.

D. Hühn, A. Govorov, P. Rivera Gil, and W. J. Parak, “Photostimulated Au nanoheater in polymer and biological media: characterization of mechanical destruction and boiling,” Adv. Funct. Mater. 22, 294–303 (2012). [CrossRef]

23.

C. Fang, S. Lei, Y. Zhao, J. Wang, and H. Wu, “A Gold Nanocrystal/Poly(dimethylsiloxane) composite for plasmonic heating on microfluidic chips,” Adv. Mater. 24, 94–98 (2012). [CrossRef]

24.

G. Baffou, C. Girard, and R. Quidant, “Mapping heat origin in plasmonic structures,” Phys. Rev. Lett. 104, 136 805 (2010). [CrossRef]

25.

A. Sanchot, G. Baffou, R. Marty, A. Arbouet, R. Quidant, C. Girard, and E. Dujardin, “Plasmonic nanoparticle network for light and heat concentration,” ACS Nano 4, 3434–3440 (2012). [CrossRef]

26.

A. Pitilakis and E. E. Kriesis, “Longitudinal 2x2 Switching Configurations Based on Thermo-Optically Addressed Dielectric-Loaded Plasmonic Waveguides,” J. Lightwave Technol. 29, 2636–2646 (2011). [CrossRef]

27.

K. Hassan, J.-C. Weeber, L. Markey, A. Dereux, O. Pitilakis, and E. E. Kriesis, “Thermo-optic plasmo-photonic mode interference switches based on dielectric loaded waveguides,” Appl. Phys. Lett. 99, 241 110 (2011). [CrossRef]

28.

M. G. Nielsen, J.-C. Weeber, K. Hassan, J. Fatome, C. Finot, S. Kaya, L. Markey, O. Albrektsen, S. I. Bozhevolnyi, G. Millot, and A. Dereux, “Grating couplers for fiber-to-fiber characterizations of stand-alone dielectric loaded surface plasmon waveguide components,” J. Lightwave Technol. 30, 3118–3125 (2012). [CrossRef]

29.

M. A. Garcia, J. Llopis, and S. Paje, “A simple model for evaluating the optical absorption spectrum from small Au-colloids in sol-gel films,” Chem. Phys. Lett. 315, 313–320 (1999). [CrossRef]

30.

C. F. Bohren and D. R. Huffman, Absorption and Scattering of Light by Small Particles (John Wiley and sons, Inc., New York, 1983), page 136.

31.

E. D. Palik, Handbook of Optical Constants of Solids (Academic Press Inc., London, 1985).

32.

M. Rashidi-Huyeh and B. Palpant, “Counterintuitive thermo-optical response of metal-dielectric nanocomposite materials as a result of local electromagnetic enhancement,” Phys. Rev. B 74, 075 405 (2006). [CrossRef]

33.

M. Nevière and E. Popov, Light Propagation in Periodic Media (Marcel Dekker, Inc. New-York-Basel, 2003).

OCIS Codes
(160.3900) Materials : Metals
(160.6840) Materials : Thermo-optical materials
(240.6680) Optics at surfaces : Surface plasmons
(130.4815) Integrated optics : Optical switching devices
(130.5460) Integrated optics : Polymer waveguides

ToC Category:
Integrated Optics

History
Original Manuscript: October 18, 2012
Revised Manuscript: November 14, 2012
Manuscript Accepted: November 14, 2012
Published: November 28, 2012

Citation
J.-C. Weeber, K. Hassan, L. Saviot, A. Dereux, C. Boissière, O. Durupthy, C. Chaneac, E. Burov, and A. Pastouret, "Efficient photo-thermal activation of gold nanoparticle-doped polymer plasmonic switches," Opt. Express 20, 27636-27649 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-25-27636


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References

  1. B. Steinberger, A. Hohenau, H. Ditlbacher, A. L. Stepanov, A. Drezet, F. R. Aussenegg, A. Leitner, and J. R. Krenn, “Dielectric stripes on gold as surface plasmon waveguides,” Appl. Phys. Lett.88, 094 104 (2006). [CrossRef]
  2. T. Holmgaard and S. Bozhevolnyi, “Theoretical analysis of dielectric-loaded surface plasmon waveguides,” Phys. Rev. B75, 245405 (2007). [CrossRef]
  3. A. V. Krasavin and A. V. Zayats, “Passive photonic elements based on dielectric-loaded surface plasmon waveguides,” Appl. Phys. Lett.90, 211101 (2007). [CrossRef]
  4. S. Massenot, J. Grandidier, A. Bouhelier, G. Colas des Francs, L. Markey, J.-C. Weeber, A. Dereux, J. Renger, M. U. Gonzalez, and R. Quidant, “Polymer-metal waveguides characterization by Fourier plane leakage radiation microscopy,” Appl. Phys. Lett.91, 243102 (2007). [CrossRef]
  5. T. Holmgaard, S. Bozhevolnyi, L. Markey, A. Dereux, A. Krasavin, P. Bolger, and A. Zayats, “Efficient excitation of dielectric-loaded surface plasmon-polariton waveguide modes at telecommunication wavelengths,” Phys. Rev. B78, 165431 (2008). [CrossRef]
  6. J. Grandidier, G. Colas des Francs, L. Markey, A. Bouhelier, S. Massenot, J.-C. Weeber, and A. Dereux, “Dielectric loaded surface plasmon polariton waveguides on a finite width metal strip,” Appl. Phys. Lett.96, 063 105 (2010). [CrossRef]
  7. R. M. Briggs, J. Grandidier, S. P. Burgos, E. Feigenbaum, and H. A. Atwater, “Efficient Coupling between Dielectric-Loaded Plasmonic and Silicon Photonic Waveguides.” Nano Lett.10, 4861–4867 (2010). [CrossRef]
  8. S. S. Papaioannou, K. Vyrsokinos, O. Tsilipakos, A. Pitilakis, K. Hassan, J.-C. Weeber, L. Markey, A. Dereux, S. I. Bozhevolnyi, A. Miliou, E. E. Kriesis, and N. Pleros, “A 320 Gb/s-Throughput Capable 2 × 2 Silicon-Plasmonic Router Architecture for Optical Interconnects,” J. Lightwave Technol.29, 3185–3195 (2011). [CrossRef]
  9. D. Kalavrouziotis, G. Giannoulis, D. Apostolopoulos, S. Papaioannou, A. Kumar, S. Bozhevolnyi, L. Markey, K. Hassan, J.-C. Weeber, A. Dereux, M. Baus, M. Karl, T. Tolga, O. Tsilipakos, A. Pitilakis, E. Kriesis, H. Avramopoulos, K. Vyrsokinos, and N. Pleros, “10 Gb/s Transmission and Thermo-Optic Resonance Tuning in Silicon-Plasmonic Waveguide Platform,” in Proceedings 37th European Conference on Optical Communication (ECOC2011), 6066097, Geneva, Switzerland, 18–22 September 2011.
  10. J. Gosciniak, S. I. Bozhevolnyi, T. B. Andersen, V. S. Volkov, J. Kjelstrup-Hansen, L. Markey, and A. Dereux, “Thermo-optic control of dielectric loaded plasmonic waveguide components,” Opt. Express18, 1207–1216 (2010). [CrossRef] [PubMed]
  11. O. Tsilipakos, E. E. Kriesis, and S. I. Bozhevolnyi, “Thermo-optic microring resonator switching elements made of dielectric-loaded plasmonic waveguides,” J. Appl. Phys.109, 073 111 (2011). [CrossRef]
  12. K. Hassan, J.-C. Weeber, L. Markey, and A. Dereux, “Thermo-optical control of dielectric loaded plasmonic racetrack resonators,” J. Appl. Phys.110, 023 106 (2011). [CrossRef]
  13. G. Giannoulis, D. Kalavrouziotis, D. Apostolopoulos, S. Papaioannou, A. Kumar, S. Bozhevolnyi, L. Markey, K. Hassan, J.-C. Weeber, A. Dereux, M. Baus, M. Karl, T. Tekin, O. Tsilipakos, A. K. Pitilakis, E. E. Kriesis, K. Vyrsokinos, H. Avramopoulos, and N. Pleros, “Data transmission and thermo-optic tuning performance of dielectric-loaded plasmonic structures hetero-integrated on a silicon chip,” IEEE Photon. Technol. Lett.24, 374–376 (2012). [CrossRef]
  14. D. Kalavrouziotis, S. Papaioannou, G. Giannoulis, D. Apostolopoulos, K. Hassan, L. Markey, J.-C. Weeber, A. Dereux, A. Kumar, S. I. Bozhevolnyi, M. Baus, M. Karl, T. Tekin, O. Tsilipakos, A. Pitilakis, E. E. Kriesis, H. Avramopoulos, K. Vyrsokinos, and N. Pleros, “0.48Tb/s (12x40Gb/s) WDM transmission and high-quality thermo-optic switching in dielectric loaded plasmonics,” Opt. Express20, 7655–7662 (2012). [CrossRef] [PubMed]
  15. D. Perron, M. Wu, C. Horvath, D. Bachman, and V. Van, “All-plasmonic switching based on thermal nonlinearity in a polymer plasmonic microring resonator,” Opt. Lett.36, 2731–2733 (2011). [CrossRef] [PubMed]
  16. H. H. Richardson, Z. N. Hickman, A. O. Govorov, A. C. Thomas, W. Zhang, and M. E. Kordesch “Thermooptical properties of gold nanoparticles embedded in ice: characterization of heat generation and melting,” Nano Lett.6, 783–788 (2006). [CrossRef] [PubMed]
  17. A. O. Govorov and H. H. Richardson, “Generating heat with metal nanoparticles,” Nano today2, 30–38 (2007). [CrossRef]
  18. H. H. Richardson, M. T. Carlson, P. J. Tandler, P. Hernandez, and A. O. Govorov, “Experimental and theoretical studies of light-to-heat conversion and collective heating effects in metal nanoparticle solutions,” Nano Lett.9, 1139–1146 (2009). [CrossRef] [PubMed]
  19. E. Boisselier and D. Astruc, “Gold nanoparticles in nanomedicine; preparations, imaging, diagnostics, therapies and toxicity,” Chemical Soc. Rev.38, 1759–1782 (2009). [CrossRef]
  20. A. S. Urban, M. Fedoruk, M. R. Horton, J. O. Rädler, F. D. Stefani, and J. Feldmann, “Controlled nanometric phase transitions of phospholipid membranes by plasmonic heating of single gold nanoparticles,”, Nano Lett.9, 2903–2908 (2009). [CrossRef] [PubMed]
  21. S. Maity, L. N. Downen, J. R. Bochinski, and L. I. Clarke, “Embedded metal nanoparticles as localized heat sources: An alternative processing approach for complex polymeric materials,” Polymer52, 1674–1685 (2011). [CrossRef]
  22. D. Hühn, A. Govorov, P. Rivera Gil, and W. J. Parak, “Photostimulated Au nanoheater in polymer and biological media: characterization of mechanical destruction and boiling,” Adv. Funct. Mater.22, 294–303 (2012). [CrossRef]
  23. C. Fang, S. Lei, Y. Zhao, J. Wang, and H. Wu, “A Gold Nanocrystal/Poly(dimethylsiloxane) composite for plasmonic heating on microfluidic chips,” Adv. Mater.24, 94–98 (2012). [CrossRef]
  24. G. Baffou, C. Girard, and R. Quidant, “Mapping heat origin in plasmonic structures,” Phys. Rev. Lett.104, 136 805 (2010). [CrossRef]
  25. A. Sanchot, G. Baffou, R. Marty, A. Arbouet, R. Quidant, C. Girard, and E. Dujardin, “Plasmonic nanoparticle network for light and heat concentration,” ACS Nano4, 3434–3440 (2012). [CrossRef]
  26. A. Pitilakis and E. E. Kriesis, “Longitudinal 2x2 Switching Configurations Based on Thermo-Optically Addressed Dielectric-Loaded Plasmonic Waveguides,” J. Lightwave Technol.29, 2636–2646 (2011). [CrossRef]
  27. K. Hassan, J.-C. Weeber, L. Markey, A. Dereux, O. Pitilakis, and E. E. Kriesis, “Thermo-optic plasmo-photonic mode interference switches based on dielectric loaded waveguides,” Appl. Phys. Lett.99, 241 110 (2011). [CrossRef]
  28. M. G. Nielsen, J.-C. Weeber, K. Hassan, J. Fatome, C. Finot, S. Kaya, L. Markey, O. Albrektsen, S. I. Bozhevolnyi, G. Millot, and A. Dereux, “Grating couplers for fiber-to-fiber characterizations of stand-alone dielectric loaded surface plasmon waveguide components,” J. Lightwave Technol.30, 3118–3125 (2012). [CrossRef]
  29. M. A. Garcia, J. Llopis, and S. Paje, “A simple model for evaluating the optical absorption spectrum from small Au-colloids in sol-gel films,” Chem. Phys. Lett.315, 313–320 (1999). [CrossRef]
  30. C. F. Bohren and D. R. Huffman, Absorption and Scattering of Light by Small Particles (John Wiley and sons, Inc., New York, 1983), page 136.
  31. E. D. Palik, Handbook of Optical Constants of Solids (Academic Press Inc., London, 1985).
  32. M. Rashidi-Huyeh and B. Palpant, “Counterintuitive thermo-optical response of metal-dielectric nanocomposite materials as a result of local electromagnetic enhancement,” Phys. Rev. B74, 075 405 (2006). [CrossRef]
  33. M. Nevière and E. Popov, Light Propagation in Periodic Media (Marcel Dekker, Inc. New-York-Basel, 2003).

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