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Second-harmonic (SH) reflection and diffraction measurements are performed, at the wavelengths of a Ti:sapphire laser on a GaAs/AlGaAs photonic crystal waveguide patterned with a square lattice, the basis consisting of rings of air in the dielectric matrix. The measured angles of diffracted SH beams agree with those predicted from nonlinear diffraction conditions. Results for reflected and diffracted SH intensities as a function of incidence angle, polarization, and pump wavelength show that, due to the low air fraction of the photonic crystal, the reflected one is dominated by the crystalline symmetry of GaAs, while the diffracted one is related to the photonic crystal structure. The large diffraction-to-reflection ratio points to the importance of nonlinear diffraction in photonic crystals. Preliminary measurements in the 1500nm range reveal explicit features related to photonic modes.

A study was conducted to investigate the antireflective properties of layers of GaP nanorods using wavelength- and angle-dependent transmission and reflection measurements. The broadband reduction of reflection was demonstrated by zero-order or direct transmission and specular reflection measurements. The nanorods were fabricated by chemical vapor deposition (CVD) using the VLS method. It was demonstrated that the enhanced transmission and reduced reflection of the layers was related to a graded refractive index in the nanorod layer. The enhanced direct transmission, along with the total transmission and reflection revealed that scattering and absorption were weak in these layers. It was observed that the antireflection behavior over a broad wavelength and angular range, along with low amount of light scattered improved the potential of the nanorod antireflection coatings for enhanced coupling in solar cells or for more efficient light extraction from light-emitting diodes (LEDs). U7 - Export Date: 2 August 2010 U7 - Source: Scopus

Recent experimental and theoretical work on two-dimensional (2D) and waveguide-embedded photonic crystals is reviewed. The investigated systems are 2D macroporous silicon and photonic crystal slabs based on silicon-on-insulator as well as GaAs/AlGaAs. In all these structures, reflectance at varying angles of incidence allows to determine the dispersion of photonic modes above the light line. For macroporous silicon, reflectance from the side yields a complementary measurement of the photonic gaps. In the GaAs-based system, second-harmonic generation in reflection shows a resonant enhancement when the pump beam is frequency- and momentum-matched to a photonic mode in the slab. A theory of photonic states in waveguide-embedded photonic crystals leads to a determination of mode dispersion and diffraction losses for leaky photonic modes.

Second-harmonic (SH) radiation generated in reflection is measured from the surface of a two-dimensional triangular photonic crystal in a GaN layer. A very large SH enhancement is observed when the incident radiation is resonant with a leaky photonic mode. The potential of second-harmonic generation as a tool for photonic band mapping is also envisaged. The extended transparency window of III-nitride wide band gap semiconductors coupled with large nonlinearities is an appealing feature pointing toward light control and manipulation in photonic structures.

We demonstrate the coupling of bright and dark Surface Lattice Resonances (SLRs), which are collective Fano resonances in 2D plasmonic crystals. As a result of this coupling, a frequency stop-gap in the dispersion relation of SLRs is observed. The different field symmetries of the low and high frequency SLR bands lead to pronounced differences in their coupling to free space radiation. Standing waves of very narrow spectral width compared to localized surface plasmon resonances are formed at the high frequency band edge, while subradiant damping onsets at the low frequency band edge leading the resonance into darkness. We introduce a coupled oscillator analog to the plasmonic crystal, which serves to elucidate the physics of the coupled plasmonic resonances and to estimate very high quality factors (Q>700) for SLRs, which are the highest known for any 2D plasmonic crystal., 13 pages (in preprint), 4 figures, 1 table

Lattice surface modes in two-dimensional plasmonic crystals of metallic nanoantennas are sustained by the diffractive coupling between localized plasmon resonances. We have investigated experimentally the dispersion of these modes by combining variable-angle transmittance and reflectance spectroscopy. Transmittance spectra through plasmonic crystals reveal quality factors for these modes exceeding 150 in the near infrared, 30 times higher than the quality factor associated to localized plasmon resonances. We have derived the characteristic lengths of the lattice surface modes, distinguishing a regime in which the group velocity is reduced while the mode intensity is strongly confined near the nanoantennas and a regime in which the surface mode propagates over several unit cells of the plasmonic crystal.

We demonstrate that the emission of light by fluorescent molecules in the proximity of periodic arrays of nanoantennas or plasmonic crystals can be strongly modified when the arrays are covered by a dielectric film. The coupling between localized surface plasmon resonances and photonic states leads to surface modes which increase the density of optical states and improve light extraction. Excited dye molecules preferentially decay radiatively into these modes, exhibiting an enhanced and directional emission., Comment: 5 figures

This work demonstrates pulsed and continuous-wave (cw) operations of photonic band-edge lasers at telecom wavelength (1.55 μm). This InP-based two-dimensional photonic crystal (2DPC) laser is integrated over a silicon wafer, opening new perspectives towards practical silicon-based photonics.

We present continuous-wave laser operation at room temperature at 1.55 μm by optically pumping a photonic crystal structure containing an InGaAs/InP quantum well active layer. The active layer is integrated onto a Silicon chip by means of Au/In bonding technology. This metallic layer provides the reduction of heating by thermal dissipation into the substrate, and increases the quality-factor by reducing the radiative losses.

We manufactured an optically active InP-on-insulator structure using spin-on-glass bonding. A ninefold improvement of photoluminescence was obtained by patterning a photonic crystal with graphite lattice into the InP layer.

Ultrafast optical bistability is demonstrated at 1550 nm in an InP-based two-dimensional photonic crystal distributed resonator. A low intensity threshold of 4 kW/cm2 is observed, with a contrast of 65% between the high and low reflectivity states.

Two-dimensional photonic crystals etched into GaAs/AlGaAs waveguides have been investigated by means of second-harmonic generation (SHG) from the surface of the samples. 130-fs laser pulses from a tunable Ti:sapphire source at 800 nm and from an optical parametric oscillator in the range 1.4-1.6 micron have been chosen to excite SH signals in reflection and diffraction directions. Their observed behavior reflects the GaAs crystalline symmetry and the photonic crystal structure, respectively.

We report on third-harmonic (TH) generation emitted from 1D photonic slabs etched into Silicon-on-Insulator (SOI) planar waveguides, as compared to the bare waveguide and (100) Silicon bulk responses. 130-fs laser pulses at ~ 810 nm and ~1550 nm have been chosen as a pump to excite TH signals in reflection and diffraction directions. The measured angles of in-plane diffracted third-harmonic beams agree with those predicted by nonlinear diffraction equations. The nonlinear reflectance as a function of the angle of incidence and azimuthal orientation of the structure has been measured. The near-infrared measurements have revealed that, whenever the pump frequency is resonant with a photonic mode, a substantial enhancement of the harmonic signal occurs. This nonlinear mechanism is in principle a very sensitive spectroscopic tool in determining and mapping the photonic band diagram of the system above the light line. The agreement between experimental data and ad hoc simulations of the nonlinear behavior of the system sheds new light on the nonlinear optical response of these nanostructured materials.

This paper reports on nonlinear optical investigations of 2D photonic crystals etched into GaAs/AlGaAs waveguides by means of second-harmonic generation (SHG) from the surface of the samples. 130-fs laser pulses from a tunable Ti:sapphire source at 800 nm and from an optical parametric oscillator in the range 1.4 to 1.6 micron have been chosen to excite SH signals in reflection and diffraction directions. The measured angles of diffracted second-harmonic beams agree with those predicted from nonlinear diffraction conditions. The intensities of the reflected and diffracted SH signals are measured by varying the angle of incidence, input polarization and wavelength. Their observed behavior reflects the GaAs crystalline symmetry and the photonic crystal structure, respectively. Moreover, the measured high diffraction-to-reflection intensity ratio suggests the possibility of tailoring the nonlinear response using diffraction modes.

Summary form only given. Second and third harmonic signals generated in reflection and diffraction from the surface of photonic crystal (PC) waveguides are considered as a spectroscopic diagnostic tool in two leading material systems: GaAs and Silicon. Measurements of second harmonic generation (SHG) in reflection from GaAs-based 2D patterned planar waveguides reveal resonant interaction of the impinging radiation with the quasi-guided modes of the photonic structure. Spectral and angular dependence of these effects reflects the structure of the sample and may be used for an accurate energy and momentum positioning of the photonic bands. Preliminary results of third harmonic generation (THG) from Si-based 1D patterned planar waveguides in the visible spectral range are also presented, indicating harmonic generation as a possible route towards systematic characterization and description of photonic structures.

Linear and nonlinear optical measurements on GaAs/AlGaAs photonic crystal waveguides with square lattice are reported. Second-harmonic generation in reflection shows a resonant enhancement when the pump beam is frequency- and momentum-matched to a photonic mode in the slab. A full three-dimensional theory of waveguide-embedded photonic crystals allows to determine the dispersion of photonic modes and the intrinsic radiative losses of quasi-guided modes lying above the light line.

We present measurements of iso-frequency dispersion surfaces of light scattered from metallic micro-gratings with different periods. The dispersion surfaces, obtained using an infinity-corrected microscope objective, exhibit maxima attributed to diffracted orders as they become evanescent and pronounced minima due to the resonant excitation of surface plasmon polaritons (SPPs). We have also measured the enhanced photoluminescence of a thin layer of dye molecules on top of the grating. This enhanced luminescence is attributed to the local field enhancement close to the surface due to the coupling of the excitation frequency to SPPs. Moreover, we obtain a directional emission of the luminescence, which is attributed to the grating-assisted coupling of SPPs excited by the dye to free space light. The technique used for the measurements presented in this paper can be extended to characterize the angular emission patterns of emitters coupled to micro- and nano-plasmonic structures.

We report on the continuous-wave operation of a band edge laser at room temperature near 1.55 mum in an InGaAs/InP photonic crystal. A flat dispersion band-edge photonic mode is used for surface normal operation. The photonic crystal slab is integrated onto a Silicon chip by means of Au/In bonding technology, which combines two advantages, efficient heat sinking and broad band reflectivity.

We demonstrate experimentally all-optical bistable operation in an InP-based two-dimensional photonic crystal slab lying on top of a Bragg reflector. Bistability is obtained around 1550nm, using a low group velocity mode at the band edge of the photonic dispersion characteristic. The origin of the bistable regime is shown to be the fast (275ps relaxation time), electronically induced nonlinear refraction index. A low intensity threshold of 4kW∕cm2 was observed, with a contrast of 65% between the high and low reflectivity states.

We observed visible second-harmonic and ultraviolet third-harmonic fields generated in reflection from the surface of a two-dimensional triangular GaN/sapphire photonic crystal. When the pump radiation resonates with a photonic mode, enhancement factors as high as 250 and 3500 occurred for the second- and third-harmonic signals, respectively, as compared to the unpatterned GaN slab. The very large increase of third-harmonic field, with a photon energy exceeding that of the electronic band gap, was used as an efficient mechanism to induce GaN photoluminescence.

An InP-based two-dimensional photonic crystal slab laser is optimized in order to exhibit low group velocity modes both at the pumping and the lasing wavelength. Laser operation is demonstrated at 1566nm in the pulsed regime. A threshold of 4kW∕cm2 is demonstrated by pumping at the photonic mode lying in the bound quantum well electronic levels, one longitudinal optical phonon energy below the lasing photonic mode.

Nonlinear reflection and diffraction measurements have been performed on a GaAs/AlGaAs photonic-crystal waveguide patterned with a square lattice: The basis in the two-dimensional unit cell consists of rings of air in the dielectric matrix. The measured angles of diffracted second-harmonic beams agree with those predicted for nonlinear diffraction conditions, Results for second-harmonic intensities as a function of incidence angle, polarization, and pump wavelength show that the reflected second-harmonic signal is dominated by the crystalline symmetry of GaAs, whereas nonlinear diffraction is determined by the photonic-crystal structure.

Second-harmonic generation (SHG) measurements in reflection on a ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{0.25}{\mathrm{Ga}}_{0.75}\mathrm{As}$ photonic crystal waveguide show a resonant enhancement when the pump beam is frequency and momentum matched with the photonic modes in the slab. The enhanced SH signal is observed in the form of resonant peaks, unlike in linear reflectance spectra. The observations are in very good agreement with a full 3D calculation of the anisotropic mode dispersion in the photonic crystal slab. The present results open the way towards realizing the extraordinary enhancement of SHG which was recently predicted [A. R. Cowan and J. F. Young, Phys. Rev. B $65,$ 085106 (2002)], and also demonstrate the potential of SHG as a nonlinear spectroscopic tool for optical studies of photonic crystals.

In an InP-based two-dimensional photonic crystal slab laser effect is improved 10-fold by optically pumping at a low group velocity mode situated one longitudinal optical phonon energy below the lasing mode.