Optical Field Probing in Photonic Structures by Atomic Force Microscopy combined with optical heterodyne detection

Sylvain Blaize, Gilles Lérondel, Aurélien Bruyant, Renaud Bachelot, Pascal Royer, Institut Charles Delaunay, Laboratoire de Nanotechnologie et d’Instrumentation Optique, CNRS

(FRE2848), Université Technologique de Troyes, BP 2060, 10010 Troyes, France

ABSTRACT

This article presents recent advances in scattering-type near field optical scanning microscopy used as a powerful characterization tool for integrated optics. By significant examples, it is shown that this specific probe microscopy based on an Atomic Force Microscope setup with optical heterodyne detection functionalities allows for in situ quantitative study of the complex field propagating in compact silicon on insulator photonic structures (single channel waveguides, MMI splitters and microdisk resonators).

Keywords: Integrated optics, SOI, Silicon on Insulator waveguides, SNOM, NSOM, AFM, near-field optics, scanning near-field optical microscopy and spectroscopy, waveguide, apertureless, heterodyne interferometry

1. INTRODUCTION Recent advances in Near-Field Optics have given rise to unprecedented characterization techniques for integrated optical elements of continuously increasing complexity, including that down to the level of submicron or nanoscale optical confinement. More precisely, since 1985, Scanning Near-Field Optical Microscopy (SNOM) has appeared to be an efficient method for mapping the optical field propagating in photonic components at the nanometer scale. This approach of microscopy was first suggested by E. Synghe1 in 1928 and implemented for the first time by D. Pohl2 and coworkers in 1984. In the context of optoelectronics and integrated optics (IO), SNOM has been used, for example, to study the correlation between the pump intensity and the spontaneous emission in a vertical cavity surface emitting laser, to characterize the transition between waveguide modes and lattice modes in a 1D refractive index lattice and to determinate the dispersion relation in a photonic crystal (see for a review by Hsu3 and references therein). The increasing interest especially for photonics and the variety of the associated structures makes the SNOM a very promising tool of characterization. To understand the full potential of SNOM in these fields, one has to consider that both the characterization technique and the samples under investigation are in constant evolution. As another significant example, a pulse-tracking experiment has been made possible in a waveguide by use of a heterodyne SNOM (Balistreri4). More recently, light localisation in a point defect has been clearly observed in a 2D photonic crystal where inner surface scattering losses have been minimised (Kramper5). As a last significant example, Campillo and Hsu recently carried out intensity and phase mapping of guided light in LiNbO3 waveguides with an interferometric near-field scanning optical microscope using a tapered optical fiber6. So far, most of the near-field studies have been carried out with a SNOM probe made from tapered optical fibers. On the other hand, although often presented as a very promising approach, there are only very few reports about the use of apertureless scanning near-field optical microscopy (ASNOM) for the characterization of IO structures. In this report, we summarize the results we obtained in the past few years using a home-made phase sensitive heterodyne ASNOM devoted to the study of such related components. After introducing heterodyne ASNOM principles and advantages, recent results obtained on Silicon on Insulator (SOI) IO devices like channel silicon waveguide’s dispersion measurement, complex field mapping inside a Multimode Interferometric (MMI) splitter, and finally preliminary results on whispering gallery modes characterization inside very high-Q silicon microdisk resonators.

*blaize@utt.fr; utt.fr

Invited Paper

Integrated Optics: Devices, Materials, and Technologies XII, edited by Christoph M. Greiner, Christoph A. Waechter Proc. of SPIE Vol. 6896, 689616, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.763854

Proc. of SPIE Vol. 6896 689616-12008 SPIE Digital Library -- Subscriber Archive Copy

2. HETERODYNE APERTURELESS NEAR-FIELD OPTICAL MICROSCOPY: PROMISING APPROACH FOR NEAR-FIELD CHARACTERIZATION OF IO

DEVICES Since the introduction of Scanning Near-field Optical Microscopy, numerous approaches have been developed and revisited (e.g., see Courjon7 and references therein). Despite the diversity of these approaches, they share a main principle: at each position of the scanning probe on the sample surface, one detects, far from the sample, the optical field scattered by the interaction between three elements, namely the incident electromagnetic field, the probe extremity, and the sample surface. Thanks to this controlled near-field interaction, this principle allows for the optical investigation of samples with a lateral resolution, which does not depend on the light wavelength anymore but rather on both the probe size and its distance to the sample, opening the door to the optical investigation of the nanomaterials.

Nowadays, it is usual to consider two main families of SNOM probes. The first one involves the apertured probes. In this case, the probe’s end presents a small aperture surrounded by metal, whose role is to confine the electromagnetic field. The aperture can be used either to illuminate locally the sample surface (illumination mode) or to pick up the sample near-field (detection mode). In general, apertured probes are produced from optical fibers, the later being used as a guide for the incident light or to collect the light scattered by the aperture. This technique has been applied successfully to observe the optical field propagation in various confined waveguiding structures with a subwavelength resolution. Conventional detection with a quadratic detector leads to the intensity mapping of the propagated optical field8-9, whereas homodyne or heterodyne interferometric detection leads to the complex optical field mapping (amplitude and phase)10-11. Time-resolved SNOM measurements using interferometric setups have also been reported12-13.

Figure 1 depicts schematically the second family of SNOM probes. In that case, the tip is made of homogeneous dielectric or metallic material presenting no aperture and its extremity can be viewed as a nano-antenna that scatters the sample’s nearfield into the farfield14-16 The far field scattered by the tip end is collected by an external optical detection system most often based on a confocal-type microscope. This configuration is called either apertureless-SNOM (ASNOM) or scattering SNOM (s-SNOM).

The apertureless probe seems to arouse an increasing interest in the SNOM community for numerous advantages compared to the aperture probe:

ASNOM does not require the challenge of SNOM probe development because it can use probes for Atomic Force Microscopy (AFM) or Scanning Tunneling Microscopy (STM). Consequently, apertureless SNOM can be developed from any commercial Scanning Probe Microscope (SPM), letting us envisage the potential economic impact of this technique.

Apertureless probes do not suffer from wavelength limitation. Indeed, while it seems difficult to extend the performance of aperture SNOM to the mid- and the far-IR region (due to the strong attenuation of the light power transmitted by the silica fibers and the severe cutoff problem for metallised waveguides), ASNOM demonstrated a very high resolution (up to λ/600) in the infrared region of the spectra17-18 .

Several theoretical works 19-20 and experiments21-24 have showed that the end of apertureless metal tip can present an electromagnetic singularity resulting in a strongly confined nano-source. This effect possibly involves local second harmonic generation or white light emission. As a consequence, the ASNOM tip can be used also as a local optical source.

However, in conventional ASNOM, the use of an external detection system in the far-field entails several difficulties.

The main negative aspect is that a background field corresponding, for example in the case of waveguide probing, to the scattering propagation losses (figure 2), is added to the object field (coming from the tip’s scattering). Numerous authors have stated that this background signal could not be totally suppressed because of the coherent adding of the different collected fields in the confocal volume of the far field detection25. The intrinsic interferometric nature of the ASNOM

Proc. of SPIE Vol. 6896 689616-2

AFM probe

/iuace.c.

Undesirable scatters

signal has been investigated in detail in a previous paper26. The main consequence is the appearance of tilted fringes (fig.2) which result from interference between the field scattered by the probe and a scattered background field in the direction of detection. In particular we have experimentally shown that the s-SNOM signal can be described by a mix of intensity, amplitude and phase signals26. One crucial issue for s-SNOM is thus related to the control of the coherent background field.

Another difficulty in ASNOM experiments is that the detected optical power remains very weak. This is explained by the very low scattering efficiencies of the probes which have a terminal radius of curvature often as low as 30nm. Several methods have been proposed to extract the weak signal issued from the local interaction between the tip end and the sample. Among them are tip-to-sample distance modulation with lock-in detection, demodulation at high harmonics of the modulation frequency27, classical heterodyne detection28-29 and excitation of a local field singularity at the tip apex30 In many experiments, these methods have permitted the extraction of near-field components in the presence of a strong background field

Fig. 1 : A) Schematic principle of the ASNOM. B) Typical ASNOM raw optical image of a waveguide’s optical nearfield.

Tilted fringes appear due to a coherent adding between the field scattered by the probe and a background field scattered in the direction of detection.

We have shown in previous papers 31-32 that these two technical hitches can be counteracted by means of heterodyne interferometry detection.

The advantages listed above appear especially important in the field of IO. Heterodyne-ASNOM can be implemented from today’s standard AFM equipment. Apertureless probes can be used for characterization of a wavelength broad band working device, i.e., from NIR integrated sources to blue or UV emitters, for example. Finally heterodyne interferometry enables low signal detection as in the case of buried integrated waveguides.

3. EXPERIMENTAL APPARATUS The experimental setup is sketched in fig.2. It is based on a fibre Mach-Zehnder interferometer. After splitting of a laser diode beam (frequency ω/2π = 1.9 1014 Hz ) by a fibre coupler (ratio 90/10%), a reference beam at frequency ω+∆ω is generated by two crossed acousto-optic modulators. The optical shift ∆ω can be set from 10 kHz to a few MHz. In the other arm, the object beam (frequency ω) is launched into the optical chip after a polarisation control.

On the waveguide surface, the local guided field (evanescent tails of the guided modes and eventually radiated fields) is converted into radiating modes by a silicon tip for AFM (Atomic Force Microscopy). The tip to surface distance is

A

Proc. of SPIE Vol. 6896 689616-3

Polarisationcontroller

AFM

Opticalchip (TbpogrDI)

LASER 0)

10%

AO shifter

Detector

controlled by the AFM in intermittent-contact mode (also called “tapping mode”). In this mode the probe oscillates along the z direction, perpendicularly to the sample usually at a frequency closed to ω0/2π ≈ 300 kHz and with amplitude around 100 nm. The device under test is mounted on an x-y piezoelectric stage and is scanned beneath the AFM probe. The atomic force feedback ensures constant vibration amplitude during the scan acquisition and leads to a precise topography image.

Simultaneously, the light scattered by the nano-probe is collected by a confocal-type microscope. More details on the optical collection system can be found elsewhere 27.

Finally, the object beam and the reference beam are combined in a single mode fibre coupler and detected by a standard photodiode detector.

In order to extract both the amplitude and phase of the local optical field, the photocurrent is demodulated by a dual output lock-in amplifier.

Fig.2 : Experimental setup. The ASNOM is a combination of an Atomic Force Microscope (AFM) with a confocal optical

microscope. The complex amplitude of the guided field is obtained by incorporating the ASNOM into one arm of a heterodyne mach-zehnder interferometer (see text for details)

Assuming a vertical cosine vibration of the probe around a mean position z0, with amplitude A, the position of the probe end can be written as

( )0 0( ) cosz t z A tω= +

In the case of the AFM tapping mode, Az =0 so that

( )0( ) cosz t A A tω= +

Proc. of SPIE Vol. 6896 689616-4

With the two hypotheses of (1) a linearly polarized verticaly confined field described by a penetration depth 1/γ and (2) a passive probe (the probe does not perturb the near-field), the electric field scattered by the probe can be written analytically:

( ) ( )( ) pj t j z t

p pt E e eω ϕ γ+=pE u

Where

( )p scanE r and ( )p scanϕ r are respectively the local amplitude and phase of the guided optical field at the waveguide

surface at the scanner position defined by the Cartesian coordinates ( , 0scan z =r ).

pu is an unitary vector directed along the direction of the polarisation of the electric field

γ can be the imaginary transverse optical constant of a guided mode, related to the effective index effn by 1/ 22

2

2

4γ

πβ

λ= −

⎛ ⎞⎜ ⎟⎝ ⎠

with 2 effnπ

βλ

= .

As mentioned in the introduction, the field collected by the external detection also contains a background field ( )Bgj t

Bg Bg BgE e ω ϕ+=E u produced by propagation losses in the waveguide. The radiated field BgE consists of scattered waves which propagate directly toward the detector, and thus, are not modulated by the probe (independent from the tip height modulation). In other words, all undesirable propagating waves which are not diffracted by the probe compose this background.

The total electric field after combination into the fibre coupler is the sum of three terms:

tot p Bg ref= + +E E E E

Where (( ) )( ) refj t

ref ref reft E e ω ω ϕ+∆ +=E u is the reference field (reference arm).

Finally the detected intensity on the quadratic detector is given by: 2

( ) Bg ref pI t = + +E E E

The lock-in demodulation can extract the harmonics of the detected signal. A rigourous analysis of the ASNOM signal processed by the lock-in amplifier can be found in Stefanon et al. 31 where we have shown that in presence of strong background field BgE , a lock-in demodulation at frequencies 0nω ω∆ + is particularly interesting. For these frequencies,

even for an important BgE weight, the lock-in outputs will give:

⎪⎩

⎪⎨⎧

=∝

+∆

−+∆

Pscann

ArefscanPscann

reErErR

φφ ωω

γωω

)()()(

0

0

A perfect separation of optical phase and amplitude is obtained with no influence of the background field. Furthermore, a gain factor Eref increase the scattered signal Ep. (SeeStefanon et al. 31 for more details)

In conclusion, heterodyne detection offers an elegant way to increase the electronic signal for a given object optical power: the signal to noise ratio will be increased up to a point where shot noise will dominate the Johnson noise from the detector. Furthermore, it allows measuring the complex amplitude (real amplitude and phase) of the waveguide near field signal even in presence of strong background light.

Proc. of SPIE Vol. 6896 689616-5

e Lema

10 20 30 40 80 80 70

Distance (pm)

TM lunUame tel!muds

TElundamentalmuds -

3 4 8 8 7 8 8 10

EffecIiueindeun

80

2.2 -

2.1 -mode TE (FEMsoIver

2 —e—modeTM (FEM solver)X mode TE (Het-ASNOM)

1.9 L? mode TM (Het-ASNOM)

1.8l5 --1.6 1.61 1.62 1.63 1.64 1.66 1.68 1.67 1.68

Wavelength (pm)

4. RESULTS: OPTICAL MAPPING OF COMPACT SOI-BASED DEVICES

4.1 Effective index dispersion in single channel SOI waveguide

Fig 3: A) scheme of the SOI waveguide cross section, B) Real part of the propagating field measured by heterodyne

ASNOM, C)Fast Fourier Transform spectrum of a longitudinal profile along the propagation axis. The spatial frequencies can be directly linked to the effective index

As a first example, we present the measurement by heterodyne-ASNOM of the TE (transverse electric) mode effective index dispersion inside a silicon wire of rectangular section. The structure is schematically shown in fig. 3. A complete description of the device and details on the fabrication process can be found in Le Coarer et al. 33. The aim of this work was to bring a precise evaluation of the effective index dispersion around 1.55 µm in order to calibrate the response of a compact IO Fourier transform spectrometer realized on an SOI substrate. The result of the heterodyne-ASNOM mapping above the waveguide at lock-in demodulation frequency set to 0ω ω∆ − is given in figure 3B and 3.C at wavelength 153µm.

Fig.4: Dispersion curves of the effective indices of TE and TM fundamental modes measured by heterodyne-ASNOM and

corresponding theoretical dispersion curves calculated with Comsol Femelab.

Silicon substrate

Buried Silicon oxyde layer

Si waveguide

Silica cap layer

500 nm

100 nm

200 nm

1 µm

A B

C

Proc. of SPIE Vol. 6896 689616-6

0• 5pm

3.6 pm I4 rI

10 orn

radLock-in Amplitude @ Aw—o A.U. It

30 . 1

09

25 08

07a20

I::

10 15 20 25 30Dintance in pm

Lock-in Phase @ Aco—o0

Dintance in pm

For measuring the mode effective index dispersion, we have used a single mode laser tunable between wavelengths 1.51µm and 1.6 µm. A longitudinal 1D Fast Fourier Transform (FFT) of the longitudinal complex field profile is useful to extract the complete set of the guided modes effective index 35. Indeed, in the FFT spectrum, the spatial frequencies are directly linked to the waveguide’s modes wavenumbers and thus to their effective index, and the intensity of the FFT spectrum gives a relative value of the mode excitation power weight.

By tuning the laser wavelength, it is thus possible to extract the effective index dispersion law for the complete set of guided mode. In fig. 4 are presented the obtained dispersion curves for fundamental TE and TM mode. The theoretical dispersion curves calculated with Comsol Femlab are also shown for comparison. A good agreement is found for the modal group velocities whereas the absolute effective index is over-estimated by the simulation. This over-estimation mainly comes from the imperfection of the technologic fabrication process (Cf. fig 5.b for example).

4.2 Optical field mapping of an SOI MMI splitter

Below we present results of the observation of a very compact waveguide splitter. The device mask is sketched on the fig. 5.A). It is composed of a straight singlemode input waveguide at wavelength 1.55µm, an MMI cell (MultiMode Interfometer) which split the light with an expected ratio of 3dB into two output singlemode waveguides which then undergoes a 90° turn.

Fig. 5: Scheme of the MMI waveguide splitter. A) design of the mask. B) SEM picture of the input waveguide cross-section.

Fig. 6: Complex optical near-field mapping of the MMI splitter with the heterodyne ASNOM. Raw data from lock-in

amplitude (left image) and phase(right image) outputs at frequency ∆ω−ω0

Proc. of SPIE Vol. 6896 689616-7

0' __GUIDEDMODES

i'RADIATIONMODES

_____:, _____f

___ __ 05 0

4T

A SEM picture (Scanning Electron Microscope) of the waveguide cross section is shown on figure 5.B. For this experiment, we launched a DFB laser source at wavelength 1.55µm into the input waveguide by means of a micro-lensed fiber. The optical amplitude and phase mapping were then performed by the heterodyne ASNOM, with the lock-in detection set at frequency 0ω ω∆ − . The raw data are shown on fig. 6. Both amplitude and phase images show an optical field either inside or outside the waveguide. In particular, the vertical and quasi-plane wave fronts all across the phase image reveal that despite the use of a micro-lensed fibre for light injection, the spatial filtering of radiated modes at the input waveguide facet is not perfect.

It is clear that a part of the light is confined into the structure, by means of guided mode excitation, and also that an efficient coupling on substrate and/or totally radiated modes occurs in the MMI cell. More precisely, the losses are revealed by the concentric wave fronts formed in the phase image.

A 2D Fast Fourier Transform (FFT) spectral filter on the complex field can be useful to extract the complete set of guided modes 34. The 2D FFT of the complex optical field corresponds physically to a projection in a base of plane waves. The spatial frequencies in the 2D FFT spectrum are thus related to the propagation constants of the optical modes. Waveguide radiation modes are linked to low spatial frequencies (neff < silica refractive index) whereas waveguide guided modes are linked to high spatial frequencies (silicon refractive index < neff < silica refracted index).

Fig. 7: A) and B), 2D Fast Fourier Transform of the complex optical field (raw data from Figure 6). C) and D), respectively filtered amplitude and phase of the guided field after radiation modes subtraction on the 2D FFT spectrum. (See text for details)

As shown in figure 7, if we compute the optical field after a subtraction of the low spectral frequencies which correspond to radiating modes, the remaining field is the contribution of spectral frequencies related to the guided modes. We can then measure with accuracy a single transverse electric mode with an effective index corresponds to 2.09 in the input waveguide. The intensity splitting ratio in the MMI cell in is of 48%/52%, the MMI insertion losses are measured to be 1.5 dB .

Furthermore, it is possible under specific conditions which are discussed by Bruyant et al. 32 to evaluate the reflection coefficient of the MMI cell from the FFT analysis of the complex field propagating upstream the MMI cell. Here, the back reflections losses are estimated to be as low as -31dB.

Proc. of SPIE Vol. 6896 689616-8

Dis

tanc

e (p

m)

U. S

Finally a zoom into the MMI cell (see fig.8) shows an excellent agreement between the probed optical field and the predicted simulated with a 3D commercial FDTD method (Fullwave by Rsoft)

Fig.8: Comparison between the experimental optical field (here the real par of the field is plotted) and the simulated field

using a 3D FDTD method.

4.3 Whispering gallery modes (WGM) mapping of High-Q SOI microdisk

As a last example, we present preliminary results on field mapping on a resonant SOI microdisk.

Fig.9: Heterodyne ASNOM results (raw images) A) AFM topography, B) optical amplitude image C) optical phase image.

The aim of this study is to observe the WGM’s modes structure involved into the spectral resonance which presents a quality factor of about 90000. Fig. 9.A) shows the microdisk’s topographic image. Raw amplitude and phase signals of the complex field recorded at the resonant wavelength of 1579.9 nm are depicted respectively in fig.9.B) and 9.C). The

Proc. of SPIE Vol. 6896 689616-9

WGM was excited with TE-polarized light from a tunable laser. The amplitude image clearly shows a stationary mode structure with a strong confinement along the perimeter of the microdisk. The azimuthal order of the WGM is measured to be 29. Current investigations are made to understand the origin of this stationary field which could be due to the disk edge’s roughness for example.

5. CONCLUSION

From the studies presented in the present report, the Apertureless Scanning Near-Field Optical Microscope with optical heterodyne detection turns out to be a new alternative and very promising tool for in situ high-resolution investigation of modern photonic and optoelectronic components of integrated optics. This technique allows for the optical mapping of both amplitude and phase of a guided optical field. The advantages of ASNOM are numerous compared to aperture SNOM techniques. For example the ASNOM can be easily developed from a commercial AFM and we emphasize that low near-field optical signal can be detected along with high spatial resolution (thanks to the low apex radius of AFM probes) even in presence of high background light, which is inherent in ASNOM techniques. In particular, the potential of the technique has been shown through the local near-field observation of various SOI waveguides. Further investigations in the area of integrated nano-optic devices are being conducted and increasing exploitation of interferometric detection techniques for ASNOM is foreseen.

6. AKNOWLEDGEMENTS This work was partially financially supported by the “région Champagne Ardennes”, and is part of the strategic research program on “s-SNOM photonics devices characterization” of the “Université de Technologie de Troyes (UTT)”. The authors want to thank J.M. Fedelli from LETI/CEA and the “Laboratoire de Physique de la Matière (LPM/INSA-Lyon)” for providing the SOI MMI structures and also Dr. A. Morand from the “Institut de Microélectronique Electromagnétisme et Photonique (IMEP)” for providing the resonant SOI microdisk.

REFERENCES

1 E.H. Synghe, “A suggested method for extending the microscopic resolution into the ultramicroscopic region”, Phil Mag 6,356, (1928) 2 D. Pohl, W. Denk, M. Lanz ,”Optical stethoscopy: Image recording with resolution λ/20”. Appl Phys Lett 44,651–653, (1984) 3 J.W.P. Hsu , “Near-field scanning optical microscopy studies of electronic and photonic materials and devices”, Mat Sci Eng Rep 33, 1–50 ( 2001) 4 M.L.M. Balistreri, J.P. Korterik, G.J. Veldhuis, L. Kuipers, N.F. van Hulst, “Quantitative photon tunneling and shear-force microscopy of planar waveguide splitters and mixers”, J Appl Phys 89,3307–3314 (2001) 5 P. Kramper, M. Kafesaki, C.M. Soukoulis,A. Birner,F. Mueller, U. Goesele, R.B. Wehrspohn, J. Mlynek, V. Sandoghdar, “Near-field visualization of light confinement in a photonic crystal microresonator”. Opt Lett 29,174–176. (2004) 6 A.L. Campillo, J.W.P. Hsu, “Intensity and phase mapping of guided light in LiNbO3 waveguides with an interferometric near-field scanning optical microscope”, Appl Opt 42,7149–7156.( 2003) 7 D. Courjon , Near-field microscopy and near-field optics, Imperial College Press.(2003) 8 S. Bourzeix, J.M. Moisson, F. Mignard, F. Barthe, A.C. Boccara, C. Licoppe, B. Mersali, M. Allovon, ans A. Bruno, “Near-field optical imaging of light propagation in semiconductor waveguide structures,” Appl. Phys. Lett. 73, 1035-1037 (1998).

Proc. of SPIE Vol. 6896 689616-10

9 M.L.M. Balistreri, D.J.W. Klunder, F.C. Blom, A. Driessen, H.W.J.M. Hoekstra, J.P. Korterik, L. Kuipers, and N.F. van Hulst “ Visualizing the whispering gallery modes in a cylindrical optical microcavity,” Optics Letters 24, 1829-1831 (1999). 10 M.L.M Balistreri,J.P. Korterik, L. Kuipers, and N.F. van Hulst, N.F. “Visualization of mode transformation in a planar waveguide splitter by near-field optical phase imaging,” Appl. Phys. Lett. 79, 910-912 (2001). 11 A.L. Campillo, J.W.P. Hsu, C.A. White, and C.D.W. Jones, “Direct measurement of the guided modes in LiNbO3 waveguides,” Appl. Phys. Lett. 80, 2239-2241 (2002). 12 M.L.M. Balistreri, H. Gersen, J.P. Korterik, L. Kuipers and N.F. van Hulst, ”Tracking femtosecond laser pulses in space and time,” Science 294, 1080–1082 (2001). 13 H. Gersen, J. P. Korterik, N. F. van Hulst, and L. Kuipers, “Tracking ultrashort pulses through dispersive media: Experiment and theory,” Phys. Rev. E 68, 026604 (2003). 14 R. Bachelot, P. Gleyzes, A.C. Boccara, “Near-field optical microscopy by local perturbation of a diffraction spot. Microsc Microanal Microstruct” 5, 389–397.(1994) 15 Y. Inouye, S. Kawata, “Near-field scanning optical microscope with a metallic probe tip”, Opt Lett 19, 159–1961, (1994) 16 F. Zenhausern, M.P. O’Boyle, H.K. Wickramasinghe, “Apertureless near-field optical microscopy”, Appl Phys Lett 65, 1623–1625. (1994) 17 B. Knoll, F. Keilmann, “Infrared conductivity mapping for nanoelectronics”, Appl Phys Lett 77, 3980–3982. (2000) 18 A. Lahrech, R. Bachelot, P. Gleyzes, A.C. Boccara, “Infrared nearfield imaging of implanted semiconductors: evidence of a pure dielectric contrast”. Appl Phys Lett 71, 575–577.(1997) 19 L. Novotny, R.X. Bian, X.S. Xie, “Theory of the optical tweezers.” Phys Rev Lett 79, 645–648 (1997). 20 Martin OJF, Girard C.. “Controlling and tuning strong optical field gradients at the local probe microscope tip apex”. Appl Phys Lett 70:705–707. (1997) 21 L. Aigouy, A. Lahrech, S. Gresillon, H. Cory, A.C. Boccara, J.C. Rivoal, “Polarization effects in apertureless scanning near-field optical microscopy: an experimental study”. Opt Lett 24, 187–189.(1999) 22 F. H’Dhili, R. Bachelot, G. Lerondel, D. Barchiesi, P. Royer, “Nearfield optics: direct observation of the field enhancement below an apertureless probe using a photosensitive polymer”, Appl Phys Lett 7,4019–4021.(2001) 23 R. Bachelot, F. H’Dhili, D. Barchiesi, G. Lerondel, R. Fikri, P. Royer, N. Landraud, J. Peretti , F. Chaput, G. Lampel G, J.P. Boilot, K. Lahlil, “Apertureless near-field optical microscopy: a study of the local tip field enhancement using photosensitive azobenzene-containing films”, J Appl Phys 94, 2060–2072, (2003) 24 A. Bouhelier, M.R. Beversluis, L. Novotny, “Characterization of nanoplasmonic structures by locally excited photoluminescence”, Appl Phys Lett 83,5041–5043.(2003) 25 R. S. Taylor, K.E. Leopold, M. Wendman, G. Gurley, and V. Elings, “Scanning probe optical microscopy of evanescent fields,’’ Rev. Sci. Instrum. 69, 2981–2987 (1998). 26 S. Aubert, A. Bruyant S. Blaize, R. Bachelot, G. Lerondel, S. Hudlet, and P. Royer, ”Analysis of the interferometric effect of the background light in apertureless scanning near-.eld optical microscopy,” J. Opt. Soc. Am. B 20, 2117–2124 (2003). 27 G. Wurtz, R. Bachelot and P. Royer, “Imaging a GaAlAs laserdiode in operation using apertureless scanning near-field optical microscopy,” Eur. Phys. J.: Appl. Phys. 5, 269–275 (1999). 28 R. Hillenbrand, B. Knoll, and F. Keilmann, “Pure optical contrast in scattering-type scanning near-field microscopy,” J. Microsc. (Oxford) 202, 77–83 (2000). 29 R. Hillenbrand, T. Taubner, and F. Keilmann, “Phonon enhanced light matter interaction at the nanometre scale,” Nature 418, 159–162 (2002). 30 E.J. Sanchez, L. Novotny, and. X.S. Xie, “Near-field fluorescence microscopy based on two-photon excitation with metal tips,” Phys. Rev. Lett. 82, 4014–4017 (1999). 31 I. Stefanon, S. Blaize, A Bruyant, S. Aubert, G. Lerondel, R. Bachelot and P. Royer " Heterodyne detection of guided waves using a scattering-type optical near-field microscope " , Optics Express, 13(14), 5554-5564 (2005) 32 Bruyant, G. Lerondel, S. Blaize, I. Stefanon, S. Aubert, R. Bachelot, and P. Royer, " Local complex reflectivity in optical waveguides" , Phys. Rev. B, 74, 075414-1 – 075414-16 (2006) 33 E. Le Coarer, S. Blaize, nature photonics 34 A. Bruyant, I. Stefanon, G. Lerondel, S. Blaize, S. Aubert, R. Bachelot, P. Royer, P. Pirasteh, J. Charrier, and P. Joubert, “light propagation in porous silicon waveguide : an optical modes analysis in near field,” phys. stat. sol. (a) 202(8) , 1417–1421 (2005)

Proc. of SPIE Vol. 6896 689616-11