Active Planar Waveguides Research Articles

VARIABLE-ANGLE OPTICAL REFLECTIVITY AND ANGLE-RESOLVED PHOTOLUMINESCENCE STUDIES OF 2D ACTIVE PHOTONIC CRYSTAL BASED ON QUANTUM DOTS

A two-dimensional photonic crystal with hexagonal lattice of air-holes is patterned into an active planar waveguide containing InAs / InGaAs quantum dots. Variable-angle reflectivity spectroscopy is used to map out the photonic band structure. Fano-type resonances observed in the measured reflectivity spectra in TE (TM) polarizations along the Γ–K (Γ–M) lattice direction are attributed to resonance coupling of the optically active photonic bands to external light. Angle-resolved photoluminescence measurements are shown to trace the band structure of the leaky mode. The revealed three-fold emission intensity enhancement of photonic crystals is ascribed to both Purcell and Bragg scattering effects.

Active planar optical waveguides with silicon nanocrystals: Leaky modes under different ambient conditions

We study both experimentally and theoretically the propagation of light emitted from silicon nanocrystals forming planar waveguides buried in SiO2. Photoluminescence spectra detected from the sample facet show significant spectral narrowing—leaky modes—with respect to the spectra measured in standard photoluminescence configuration. The spectral position of the leaky modes responds strongly to a local change of refractive index (liquid drop) on the sample surface. Higher refractive index of the liquid induces higher redshift of the mode position. Experimental data agree with the previously proposed leaky mode model.

Silicon nanocrystals in silica—Novel active waveguides for nanophotonics

Nanophotonic structures combining electronic confinement in nanocrystals with photon confinement in photonic structures are potential building blocks of future Si-based photonic devices. Here, we present a detailed optical investigation of active planar waveguides fabricated by Si +-ion implantation (400 keV, fluences from 3 to 6×10 17 cm −2) of fused silica and thermally oxidized Si wafers. Si nanocrystals formed after annealing emit red-IR photoluminescence (PL) (under UV-blue excitation) and define a layer of high refractive index that guides part of the PL emission. Light from external sources can also be coupled into the waveguides (directly to the polished edge facet or from the surface by applying a quartz prism coupler). In both cases the optical emission from the sample facet exhibits narrow polarization-resolved transverse electric and transverse magnetic modes instead of the usual broad spectra characteristic of Si nanocrystals. This effect is explained by a theoretical model which identifies the microcavity-like peaks as leaking modes propagating below the waveguide/substrate boundary. We present also permanent changes induced by intense femtosecond laser exposure, which can be applied to write structures like gratings into the Si-nanocrystalline waveguides. Finally, we discuss the potential for application of these unconventional and relatively simple all-silicon nanostructures in future photonic devices.

Preparation and infrared emission of silica–zirconia–alumina doped with erbium for planar waveguide

The sol–gel synthesis of Er 3+ (1–5%) doped silica(83)–zirconia(17) waveguide materials with addition of aluminum (6–20 at%) giving a FWHM ( 4I 13/2– 4I 15/2)>60 nm is reported. Zirconia with high refractive index of 1.9 and low phonon energy is a good material compared with titania. The films were deposited on silicon or silica substrate by dipcoating technique using the precursors of Si(OC 2H 5) 4 (Aldrich), Zr(C 3H 7O) 4, CH 3–CH(OH)–CH 3, C 5H 8O 2 , Al(NO 3) 3·9H 2O, Er(NO 3) 3·5H 2O and Yb(NO 3) 3·5H 2O (Merck). The dipcoating rate of 2 and 3 mm/s were controlled by computer. Samples were calcinated at temperatures from 70 to 900 °C. The optical properties were studied by photoluminescent spectra and decay time. Influence of the Al 3+ concentration and the heat treatment conditions for the Er 3+ luminescent properties were studied. An energy transfer from 2F 5/2 (Yb 3+) to 4I 11/2 (Er 3+) multiplets is followed by a relaxation to the 4I 13/2 (Er 3+) and an efficiency luminescence of Er 3+ ( 4I 13/2– 4I 15/2) was clearly measured. It is interesting to indicate that the lifetime of few ms of Er 3+ at 1530 nm in the sample Si(83)Zr(17)Al(6%)Er(1%)Yb(1%) is longer than for the sample without Yb ions. Multilayer thin films were prepared. The thickness, refractive index, the roughness about 2 nm and a propagation loss<2.5 dB/cm were studied for active planar waveguide applications.

Light propagation in planar optical waveguides made of silicon nanocrystals buried in silica glass

Silicon nanocrystals fabricated by Si +-ion implantation (400 keV, fluences from 4 to 6 × 10 17 cm − 2 ) of fused silica form interesting active planar optical waveguides. The nanocrystals emit orange-red photoluminescence (PL) (under UV-blue excitation) and define a region of high refractive index that guides part of the PL along the layer. Light from external light sources can also be coupled into the waveguides (directly to the polished edge facet or from the surface by applying a quartz prism coupler). In both cases the optical emission from the sample facet exhibits narrow (10–20 nm full-with-at-half-maximum) polarisation-resolved transverse electric and transverse magnetic modes instead of the usual broad nanocrystal spectra. This effect is explained by our theoretical model, which identifies the microcavity-like peaks as leaky modes propagating along the waveguide/substrate boundary (not the usual modes guided inside the nanocrystal plane due to its graded index profile). The unconventional properties of this relatively easy-to-make all-silicon structure may be interesting for future photonic devices and sensors.

Stimulated emission in the active planar optical waveguide made of silicon nanocrystals

Thin layers of silicon nanocrystals prepared by silicon-ion implantation into silica substrate form active planar optical waveguides. Testing experiments of optical gain have been performed on a sample implanted to a dose of 4 × 1017 cm–2 by using the variable stripe length (VSL) technique. The photoluminescence collected from the sample facet shows spectrally narrow, polarization-resolved transverse electric (TE) and transverse magnetic (TM) substrate modes. Continuous wave VSL revealed a reduction of optical losses in both modes only. On the contrary, a fast decay component due to amplified spontaneous emission is observed in time-resolved VSL experiments. This fast component shows positive net modal optical gain of ∼12 cm–1. The observed superlinear emission as a function of pump intensity, accompanied by shortening of the fast component lifetime, supports further the observation of stimulated emission. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Reflection and emission of Brillouin zone edge states for active photonic crystal waveguides

A one-dimensional photonic crystal is patterned into an active planar waveguide containing multiple InGaAs quantum wells. External coupling reflectivity is used to map out the photonic band structure, revealing a clear anti-crossing at ~1.37 eV in the 45° TM polarized spectrum. The band structure is compared to and confirmed by scattering-matrix calculations. Photoluminescence measurements are performed in the same geometry on the patterned and unpatterned regions of the sample. The latter shows conventional quantum-well emission and GaAs emission with increasing pump power. In contrast, the spectra from the patterned sample contain a sharp mode from the dielectric-like band of the anti-crossing, corresponding to the Brillouin zone edge. Power-dependent excitation shows this mode to be strongly super-linear, indicative of band edge lasing.

Photoluminescence from an active planar optical waveguide made of silicon nanocrystals: dominance of leaky substrate modes in dissipative structures

Samples with the structure of asymmetric planar waveguides are fabricated by implanting Si + ions with energy of 400 keV and doses from 3 to 6 × 10 17 cm −2 into synthetic silica slabs. Broad photoluminescence spectrum is observed when collecting photoluminescence (PL) signal in the direction perpendicular to the plane of waveguides while PL collected from the edge of the sample reveals narrow (FWHM of 10–20 nm) polarization-resolved transverse electric (TE) and transverse magnetic (TM) peaks. This peculiar observation is explained using a theoretical model, developed within the framework of wave optics. The TE and TM modes are identified as radiative leaky modes of the planar waveguide. Conditions under which the narrow modes can be seen in the edge PL spectra are described.

Active planar optical waveguide made from luminescent silicon nanocrystals

We show experimentally that a layer of silicon nanocrystals, prepared by the Si-ion implantation (with the energy of 400 keV) into a synthetic silica slab and exhibiting room-temperature red photoluminescence, can serve simultaneously as a single-mode planar optical waveguide. The waveguide is shown to self-select guided transverse electric and transverse magnetic modes from the broad photoluminescence emission of the nanocrystals resulting in a substantially narrower emission spectrum for these modes. We further report on an investigation of optical gain in a sample implanted to a dose of 4×1017 cm−2. Despite the occurrence of strong waveguiding, results of the variable stripe length method turned out not to be able to give unambiguous evidence for optical gain.

Planar waveguides for integrated optics prepared by sol–gel methods

Abstract Sol-gel processing is becoming one of the cheapest and most versatile methods for the fabrication of passive and active planar waveguides for integrated optics, in particular for the silica-on-silicon type. The present paper focuses on some recent work in our group on both passive and active (Er3+-doped) silica–titania inorganic and hybrid waveguides, considering in detail their densification behaviour, structure and optical properties. Recent advanced topics, such as nanocrystalline active waveguides prepared by by sol–gel method, are also addressed. The main results to be presented will deal first with the structural evolution during the densification of inorganic and hybrid silica-titania waveguides. Then, the fluorescence behaviour of active waveguides, doped with Er3+ ions, will also be described. And finally silver co-doped nanocrystalline waveguides, will be considered in detail, with particular emphasis on, firstly, the influence of preparation conditions on optical properties such as the...

Aerosol–gel preparation of optically active layers in the system Er/SiO 2–TiO 2

Er-doped silica–titania multilayer coatings have been successfully deposited using an original sol–gel deposition technique: the Aerosol–gel process. This study is the first step toward Aerosol–gel preparation of active planar wave guides. In this paper, we report on the physical, chemical, optical, microstructural and spectroscopic properties of the multilayer coatings. A new optically active crystalline phase, Er 2Ti 2O 7 (ETO), has been identified. This study shows that, depending on the experimental conditions (titanium and erbium content, heat treatment temperature), ETO can be obtained in the form of nanocrystallites dispersed in a transparent amorphous matrix.

Surface nonlocality effects on an optically active waveguide

A new wave-vector-space method capable of finding electromagnetic wave propagation in bounded nonlocal media without using boundary conditions is used to find the modes of an optically active planar dielectric waveguide. Optical activity involves first-order wave-vector dispersion (nonlocality). The method finds how the altered nonlocal interaction close to the surfaces affects the waveguide modes. It is found that first-order effects of the surface layer nonlocality enter both the dispersion relation and the field profiles. The waveguide geometry is also used as an impetus to generalize several aspects of the wave-vector-space method.

Current-induced guiding and beam steering in active semiconductor planar waveguide

We propose a novel method of achieving beam steering in active GaAs-AlGaAs materials. Carrier-induced refractive index change effect is applied to form a channel waveguide in a slab structure. Current injection is used as a means to control, guide, and steer an optical beam between two active stripes. In a structure that was 710 /spl mu/m long, we have experimentally demonstrated waveguiding of an externally coupled optical beam and electrically induced steering of the beam over a 17-/spl mu/m lateral distance at the output facet. The results of theoretical analysis and modeling of the beam shift fit the experimental data well.

Beam propagation in an active planar waveguide with an angled bragg grating (α laser)

In the angled Bragg grating semiconductor laser (α laser), light does not propagate at a right angle with respect to the two-dimensional corrugated grating of the planar waveguide. A closed-form solution of the coupled-wave theory is used to describe the propagation of both the wave fields with different directions. A constant gain is included. Some properties of the main wave and of the secondary wave are described, which are of interest for the α laser. Additional losses occur during facet reflection of the secondary wave.

Beam propagation in an active planar waveguide with an angled Bragg grating ( α laser)

Beam propagation in an active planar waveguide with an angled Bragg grating ( α laser)

Planar waveguide lasers and structures created by laser ablation — an overview

The parameters of planar and channel waveguide lasers fabricated by different techniques are reviewed. Materials and properties of thin films used for creation of planar waveguide lasers are summarized. The parameters of active and passive planar waveguides created by the method of pulsed laser deposition and problems of laser deposition are described. The aspects of laser generation of planar waveguide lasers, resonators and channel waveguides are presented. The results of our experiments of laser deposition of thin Ti:sapphire layers and thin layers of Nd:YAG and Nd:YAP are briefly discussed.

Thermally bonded planar waveguide lasers

A new technique for fabricating active planar waveguide devices is reported. This process, based on the thermal bonding of precision finished crystal or glass components, allows waveguides to be assembled from very dissimilar materials and could be applied to a wide range of solid state laser or other optical media. The waveguide propagation losses, inferred from the laser performance, are found to be 0.7 dB/cm for Nd:Y3Al5O12 bonded to Y3Al5O12, Nd:Y3Al5O12 bonded to glass, and 0.4 dB/cm for Nd:Gd3Ga5O12 bonded to Y3Al5O12 devices.

Evaporated polyurea optical waveguides: electrooptic and structural properties

Electrooptically active planar waveguides of aromatic polyurea were prepared by simultaneous deposition of 4,4′-diamino-diphenyl-methane and 4,4′-diphenylmethane-diisocyanate from the vapor phase and subsequent corona poling. X-ray diffraction spectra show that part of the films has a pronounced layered structure reminiscent of self-assembling systems. Attenuated total reflectance spectroscopy of the waveguide modes of the polymer films was used to measure the piezoelectric and electrooptic susceptibilities. The contributions of the nonlinear polarizability of the urea groups and their dipolar orientation in the applied field are identified. Possible applications of this material for novel optical modulator geometries are discussed.

Evaporated polyurea films for optical modulators

Abstract Electrooptically active planar waveguides of aromatic polyurea were prepared by simultaneous deposition of 4,4'-diamino-diphenyl-methane and 4,4'-diphenylmethane-diisocyanate from the vapor phase and subsequent corona poling. Attenuated total reflectance spectroscopy of the waveguide modes of the polymer films was used to measure the piezoelectric and electrooptic susceptibilities. The contributions of the nonlinear polarizability of the urea groups and their dipolar orientation in the applied field are identified. Possible applications of this material for novel optical modulator geometries are discussed.

Vapour-phase deposition of rare-earth-doped PZG glasses

Physical vapour deposition has been used in transition metal fluoride glasses (TMFG) systems to prepare fluoride glass films doped with various active ions (3d transition or rare-earth). Active planar waveguides have been realized with PZG doped films on flat ZBLAN or CaF2 substrates.