**3. SRS in nanophotonics**

In order to control a signal light, its intensity or phase has to be modified by a control signal. In a nonlinear optics device, a control light-wave is employed to modify the optical proprieties of the medium as seen by a signal light-wave. Of course, higher nonlinearity requires shorter interaction length *L*. In order to reduce *L* in a nonlinear device with physical dimensions greater than the wavelength, the efficiency of nonlinear effects can be enhanced taking advantage of optical resonators (see Section 2.1 for examples) [2]. In nanoscale devices, which should be able to control light with light in a nanoscale layer or in a nanoparticle of nonlinear material, the trick of using optical resonators cannot be used. Therefore, we have to develop nanostructured materials having enough large nonlinearities [16].

The search for new materials, from an experimental point of view, should satisfy a number of technological and economical requirements, while, from a theoretical point of view, it should be combined with a deep understanding of nonlinear polarization mechanisms, elucidating their relation to the structure of nanostructures (average radius, volume fraction and size dispersions) [17]. In the past few decades, a number of nanomaterials proved remarkable nonlinear optical (NLO) properties, which encourage the fabrication of ultra-compact, low-loss and high-performance nanoscale photonic devices [18].

**133**

*Stimulated Raman Scattering in Micro- and Nanophotonics*

–106

Recent interest in the optical responses of metal nanoparticles and metamaterials is focused on enhancing local electromagnetic fields [19]. The significant

for nonlinear optical processes [19]. However, although plasmonics structures and metamaterials can provide substantial size reduction for optical components, their optical losses are often undesired [20]. Therefore, in order to control the flow of light, an all-dielectric platform is highly attractive. Although r*esonant nonlinearities* are significant, they are not appealing for applications, due to their long response times. In addition, at resonance the incident radiation is absorbed by materials [17]. On the other hand, *nonresonant nonlinearities* take place at frequencies below the absorption edge (i.e. when the light linear absorption is negligible) and they are very fast (typical recovery times are of the order of picoseconds). Recently, thirdorder NLO properties of Si-nc have been widely investigated and a large variation of the nonlinear refractive index (n2) values has been reported, complicating the

As far as the investigation of SRS at the nanoscale is concerned, there have been a few number of fundamental investigations, both experimental and theoretical. In Ref. [22], a large Raman gain, measured by resonant Raman spectra excited at 632.8 nm, was obtained from individual single-walled carbon nanotubes. The theoretical interpretation takes in to account both the exceptional nonlinear properties and the efficient electron-phonon interaction in single-walled carbon nanotubes. In Ref. [23], SRS from GaP nanowires was measured by Raman spectra in backscattering configuration, using CW laser excitation (514.5 nm). Strong nonlinear SRS, obtained by crystalline nanowires with a diameter of 210 nm and with length of about 1 micron, were discussed in terms of theoretical results developed for dielec-

In the following, the observation of SRS in nanostructured silica-based materials (Section 3.1) and nanostructured silicon-based materials (Section 3.2) are reported

Among the innovative materials for Raman amplification, one of the most interesting classes is oxide glasses, above all silicon dioxide-based glasses due to their compatibility with the current optical fibers technology. To try to improve their SRS efficiency, a useful strategy is to add suitable dopants (heavy metal oxides as Ta2O5, Bi2O3, and Nb2O5) to silica [24–27]. We note that in other systems, such as niobiumphosphate glasses, characterized by a high concentration of niobium, a higher peak Raman gain (but in the best case of ≈ 10 times) and a broadening of the bandwidth

In this paragraph, in order to increase SRS optical features of silica-based glasses, we propose an alternative approach: instead of to investigate new glass compositions, we change the glass arrangement. We note that a glass structural variations can be obtained as a result of an appropriate heat treatments made in the glass transition range, generating glass-ceramics with nanocrystals uniformly dispersed in the glass matrix (glass-crystals nanocomposites) [30]. We consider glasses, belonging to the K2O-Nb2O5-SiO2 (KNS) system, forming transparent and stable glasses and showing interesting non-linear optical properties. For glasses in the class of the KNS glass-forming system, an interesting glass nanostructuring process has been considered. The process contains two partially overlapped processes, namely, phase separation and crystallization [31]. We note that a clear relationship between glass nanostructuring and Raman gain has not been proven yet, although, in our previous paper, a connection between local structure and SRS in bulk

, predicted at a flat metal surface, are significant

*DOI: http://dx.doi.org/10.5772/intechopen.80814*

interpretation of experimental results [21].

**3.1 SRS in nanocomposities silica-based materials**

with respect to silica glass has been demonstrated [28, 29].

enhancement factors of 103

tric cavities.

and discussed.

*Stimulated Raman Scattering in Micro- and Nanophotonics DOI: http://dx.doi.org/10.5772/intechopen.80814*

*Nonlinear Optics - Novel Results in Theory and Applications*

To have a rapid idea of the Raman enhancement reported by the different approaches in microstructures described in this section, in **Figure 3** we summarized

In order to control a signal light, its intensity or phase has to be modified by a control signal. In a nonlinear optics device, a control light-wave is employed to modify the optical proprieties of the medium as seen by a signal light-wave. Of course, higher nonlinearity requires shorter interaction length *L*. In order to reduce *L* in a nonlinear device with physical dimensions greater than the wavelength, the efficiency of nonlinear effects can be enhanced taking advantage of optical resonators (see Section 2.1 for examples) [2]. In nanoscale devices, which should be able to control light with light in a nanoscale layer or in a nanoparticle of nonlinear material, the trick of using optical resonators cannot be used. Therefore, we have to develop nanostructured materials having enough large

The search for new materials, from an experimental point of view, should satisfy a number of technological and economical requirements, while, from a theoretical point of view, it should be combined with a deep understanding of nonlinear polarization mechanisms, elucidating their relation to the structure of nanostructures (average radius, volume fraction and size dispersions) [17]. In the past few decades, a number of nanomaterials proved remarkable nonlinear optical (NLO) properties, which encourage the fabrication of ultra-compact, low-loss and high-performance

**132**

them.

**Figure 3.**

**3. SRS in nanophotonics**

*SRS enhancement reported in different kind of microstructures.*

nonlinearities [16].

nanoscale photonic devices [18].

Recent interest in the optical responses of metal nanoparticles and metamaterials is focused on enhancing local electromagnetic fields [19]. The significant enhancement factors of 103 –106 , predicted at a flat metal surface, are significant for nonlinear optical processes [19]. However, although plasmonics structures and metamaterials can provide substantial size reduction for optical components, their optical losses are often undesired [20]. Therefore, in order to control the flow of light, an all-dielectric platform is highly attractive. Although r*esonant nonlinearities* are significant, they are not appealing for applications, due to their long response times. In addition, at resonance the incident radiation is absorbed by materials [17]. On the other hand, *nonresonant nonlinearities* take place at frequencies below the absorption edge (i.e. when the light linear absorption is negligible) and they are very fast (typical recovery times are of the order of picoseconds). Recently, thirdorder NLO properties of Si-nc have been widely investigated and a large variation of the nonlinear refractive index (n2) values has been reported, complicating the interpretation of experimental results [21].

As far as the investigation of SRS at the nanoscale is concerned, there have been a few number of fundamental investigations, both experimental and theoretical. In Ref. [22], a large Raman gain, measured by resonant Raman spectra excited at 632.8 nm, was obtained from individual single-walled carbon nanotubes. The theoretical interpretation takes in to account both the exceptional nonlinear properties and the efficient electron-phonon interaction in single-walled carbon nanotubes. In Ref. [23], SRS from GaP nanowires was measured by Raman spectra in backscattering configuration, using CW laser excitation (514.5 nm). Strong nonlinear SRS, obtained by crystalline nanowires with a diameter of 210 nm and with length of about 1 micron, were discussed in terms of theoretical results developed for dielectric cavities.

In the following, the observation of SRS in nanostructured silica-based materials (Section 3.1) and nanostructured silicon-based materials (Section 3.2) are reported and discussed.
