Theory of design parameters for quasi-phase-matched waveguides andapplication to frequency doubling in polymer waveguides

A theory of dispersion in single-mode symmetric waveguides is presented for phase-matching second harmonic generation (SHG) of the fundamental modes, based on the approximate analytical waveguide theory of Botez. The theory is used to derive new equations for the maximum phase-matching distance allowed when there are random fluctuations in waveguide thicknesses, under critical and noncritical phase-matching conditions. The theory is also used to calculate the overlap integral as a function of the waveguide parameters V^ω and V^2ω. A new expression is derived for the efficiency of SHG in waveguides in terms of waveguide parameters that can be used to optimize SHG. Theoretical results are presented for typical LiNbO₃ and polymer waveguides. Quasi-phase-matched (QPM) waveguides are fabricated from nonlinear optical (NLO) polymers using the techniques of periodic poling and bleaching, and channel waveguides are printed by the bleaching of the NLO polymers. The NLO polymers are characterized for their refractive indexes, optical loss, NLO coefficients, and bleaching characteristics. Phase-matched SHG results are presented for the different fabrication methods over a distance of 0.5 cm, and an assessment is given of the relative strengths and weaknesses of the different fabrication approaches     

Second-harmonic generation in potassium niobate waveguides

We report on our progress in the formation of waveguides in potassium niobate (KNbO₃) using techniques such as ion implantation and ion sputtering. Different methods for the structuring of channel waveguides are presented, and their advantages and disadvantages are discussed in terms of their optical and nonlinear optical properties. The excellent power-handling capability of KNbO₃ waveguides is compared to other waveguide materials, and we highlight the influence of postimplantation annealing and repoling on the waveguide attenuation and the nonlinear optical coefficient. We also review recent results on second-harmonic generation in KNbO₃ waveguides focusing on blue light generation     

The SHG-response of different phases in proton exchanged lithiumniobate waveguides

Reflection second-harmonic generation from the polished waveguide end face is used to investigate the second-order nonlinear optical properties of as-exchanged and annealed proton-exchanged (PE) waveguides in different H_xLi_1-xNbO₃ phases. A detailed correlation is done between the nonlinear properties, the processing conditions, the refractive index changes, and the optical losses of the waveguides. It is found that for the direct PE samples, where the β₄, β₃, and β₁ phases are generated at the surface, the nonlinearity in the guide is strongly reduced by more than 85% of its bulk value, while for waveguides prepared in the β₂ phase, the nonlinear coefficient is about 55% of the bulk one. A consequence is that the step-like β_i-phase PE LiNbO₃ waveguides with large refractive index increase are advantageous for efficient SHG in Cherenkov configuration. The nonlinearity, strongly reduced after the initial proton exchange, is found to be restored and even increased after annealing. However, this apparent increase of the nonlinearity is accompanied by a strong degradation of the quality of the second-harmonic generation reflected beam in the region of initial waveguides due to beam scattering. The graded proton exchange technique and dilute melt proton exchange have been shown to produce high-quality waveguides with essentially undergraded nonlinear optical properties. It has been also shown that the nonlinear properties of annealed proton exchanged LiNbO₃ waveguides can be effectively recovered by the reverse proton exchange technique. The results obtained are important for the design, fabrication, and optimizing of guided-wave nonlinear optical devices in LiNbO₃     

Silicon micromachined hollow optical waveguides for sensingapplications

Novel micromachined optical waveguides useful for sensing applications are proposed. The waveguide is designed as hollow-core antiresonant reflecting optical waveguide (ARROW) and can be easily fabricated using standard silicon micromachining techniques. The hollow structure permits to use the core to confine simultaneously the light and the substance to be probed, leading to an increase of the interaction efficiency. Numerical simulations, performed using finite element method technique, show that with a suitable design these waveguides can be used in sensing applications, where the substances under test can be gases or liquids     

Performance of traveling-wave electroabsorption modulators depending on microwave properties of waveguides calculated using the FDTD method

We present a method to analyze electrical and optical characteristics of traveling-wave electroabsorption modulators (TW-EAMs) using the finite-difference time-domain method. We consider the interaction between electromagnetic fields and optical powers in waveguides in time domain to model electrical and optical behaviors of TW-EAMs. The effects of microwave properties of waveguides on modulation response and output optical power of TW-EAMs are analyzed by the proposed method. The characteristic impedance of TW-EAMs is more important than microwave index to obtain large modulation bandwidth of TW-EAMs when impedance matching techniques are not used. However, effective refractive index match between microwave and lightwave becomes important as the waveguide length increases. The microwave property closely related to the extinction ratio of output optical powers is the microwave loss. When impedance match is achieved by low-impedance termination, the velocity matching between microwave and lightwave becomes important.     

基于NPS的集成光学型光隔离器的研究

本文介绍了集成光学型光隔离器的两种构型,着重讨论了基于非互易相移(NPS)的集成光学型光隔离器.对于构成集成光学型光隔离器的关键构件磁光波导的理论基础,数值计算及仿真进行了研究,给出了实现波导结构优化的手段.     

Time-decorrelated multifocal micromachining and trapping

Temporally decorrelated multifocal arrays eliminate spatial interference between adjacent foci and allow multifocal imaging with the diffraction-limited resolution of a single focus, even for foci spaced by less than the focal diameter. In this paper, we demonstrate a high-efficiency cascaded-beamsplitter array for producing temporally decorrelated beamlets. These beamlets are used to produce a multifocal microscope with which we have demonstrated two-photon fluorescence imaging, multifocal micromachining of optical waveguides, and multifocal optical trapping     

A full-vectorial pseudospectral modal analysis of dielectric optical waveguides with stepped refractive index profiles

A new full-vectorial mode solver based on the pseudospectral method for computing dielectric optical waveguides is proposed. The subdomains with homogeneous refractive indexes are connected with imposing the continuities of E/sub z/ and H/sub z/ at the dielectric interfaces, and thus the coupled equations in terms of the transverse magnetic field components H/sub x/ and H/sub y/ are formulated. The optical fields are expanded by a suitable set of orthogonal basis functions, such as Laguerre-Gauss (LG) functions or Chebyshev polynomials. Furthermore, the a priori determination of the scaling factor in LG functions is introduced by means of the effective index method in order to considerably reduce the extra computational time by lengthy trial and errors used by others. Results calculated by the proposed full-vectorial scheme for dispersion characteristics of rectangular channel and rib waveguides having piecewise uniform refractive indexes, even though a coarse mesh used, show good agreement with previously published data based on other rigorous numerical methods.     

Materials for Photonic Applications From Sol-Gel*

A review of sol-gel materials developed in our laboratory for photonic applications is presented. These materials include planar and strip waveguides for integrated optics (IO) passive devices, Er doped waveguides for IO amplifiers, films doped with semiconductor quantum dots for optical switching and fullerene doped materials for optical limiting.     

Materials for Photonic Applications From Sol-Gel*

A review of sol-gel materials developed in our laboratory for photonic applications is presented. These materials include planar and strip waveguides for integrated optics (IO) passive devices, Er doped waveguides for IO amplifiers, films doped with semiconductor quantum dots for optical switching and fullerene doped materials for optical limiting.     

Internal spatial modes in glass microring resonators

We have used near-field scanning optical microscopy to measure the internal optical modes inside glass waveguides and microring resonators. The period of the observed standing modes provides a direct measure of the local effective index. The measured effective index and modal shape determines the values of all components of the wave vector. The observed standing modes inside the ring resonator are unexpected, but are caused by the standing modes in the coupling waveguide. Last, we describe a technique that can obtain detailed information about the locations of the dielectric interfaces     

Optical MEMS devices based on moving waveguides

The paper deals with optical microelectromechanical systems (MEMS), and in particular with optical MEMS based on moving waveguides. After a short overview of this very attractive novel activity, specific technological problems and solutions are discussed. Then the following examples of recent developments based on silica on silicon technology are presented: optical switch, vibration sensor, and optical scanner     

Compact evanescent optical switch and attenuator withelectromechanical actuation

We report the design and the realization of an out-of-plane bending structure supporting a waveguide that is used as an optical attenuator and an optical switch. Both devices are based on evanescent field interaction induced by spatial confinement either between two waveguides or between one waveguide and an absorbing medium. The attenuator exhibits typical attenuation of 65 dB/cm. Even if the bad quality of the waveguide has prevented the correct operation of the switch, we show that the attenuation figure establishes the feasibility of a compact evanescent optical coupler with mechanical drive featuring a total length below 1 mm     

Coupled resonator optical waveguides

Properties of the recently introduced family of coupled resonator optical waveguides (CROWs) are reviewed, particularly with reference to CROWs designed as planar waveguides in two-dimensional photonic crystal slabs to enhance nonlinear interactions and develop novel all-optical information processing devices. Topics covered include: pulse propagation both in the nondispersive approximation and to all orders of dispersion, and the coupled mode theory of nonlinear optics with pulses in CROWs and its applications to second-harmonic generation and wave coupling via field-induced refractive-index gratings. We also review recent experimental progress in the fabrication and characterization of CROWs, and applications of the CROW concept to fiber gratings and microwave waveguides     

2-D MMI Devices Based on Integrated Hollow ARROW Waveguides

In this paper, the design, fabrication, and characterization of 2-D multimode interference (MMI) devices based on integrated silicon hollow antiresonant reflection optical waveguides (ARROW) is presented. Unlike conventional waveguides, the field in ARROW is not confined in the core region by total internal reflection but by dielectric cladding layers designed to form-high reflectivity Fabry-Perot mirrors. This peculiar structure permits to realize integrated hollow-core waveguides using standard silicon technology. In this paper, we show that these waveguides can be usefully applied in the fabrication of 2-D MMI devices. With a 130 mumtimes 130 mum cross-section waveguide, multiple images are observed from 1times1 to 6times6 image matrices. These devices also exhibit interesting bandpass spectral properties that can be usefully applied in several fields ranging from telecommunications to sensing     

Extraordinary evanescent field confinement waveguide sensor for mid-infrared trace gas spectroscopy

Nanophotonic waveguides are at the core of a great variety of optical sensors.These structures confine light along defined paths on photonic chips and provide light-matter interaction via an evanescent field.However,waveguides still lag behind free-space optics for sensitivity-critical applications such as trace gas detection.Short optical pathlengths,low interaction strengths,and spurious etalon fringes in spectral transmission are among the main reasons why on-chip gas sensing is still in its infancy.In this work,we report on a mid-infrared integrated waveguide sensor that successfully addresses these drawbacks.This sensor operates with a 107%evanescent field confinement factor in air,which not only matches but also outperforms free-space beams in terms of the per-length optical interaction.Furthermore,negligible facet reflections result in a flat spectral background and record-low absorbance noise that can finally compete with free-space spectroscopy.The sensor performance was validated at 2.566μm,which showed a 7 ppm detection limit for acetylene with only a 2 cm long waveguide.     

Design of plasmonic half-adder and half-subtractor circuits employing nonlinear effect in Mach–Zehnder interferometer

Plasmonic metal–insulator–metal (MIM) waveguides have the unique attribute of propagating surface plasmons beyond the diffraction limit. In this paper, basic designs for half-adder and half-subtractor circuits are proposed based on the nonlinear effect in Mach–Zehnder interferometers designed using plasmonic MIM waveguides. The proposed devices are studied in the third optical communications window with transverse magnetic polarization. The designs are verified by the finite-difference time-domain technique with the help of MATLAB simulations.     

Introduction to the Issue on Optical Micro- and Nanosystems

The six invited and 30 contributed papers in this special issue focus on optical micro- and nanosystems. They are grouped into the following categories: spatial light modulators; resonators and waveguides; biophotonics; photonic crystals and plasmonics; optical scanning devices and systems; optical switches; lasers; sensors; and nanoelectromechanical systems (NEMS).     

Waveguide lasers in the C-band fabricated by laser inscription with a compact femtosecond oscillator

Femtosecond laser writing of high-quality optical waveguides by means of a compact diode-pumped cavity-dumped Yb:glass laser oscillator is reported. Waveguides have been written on an erbium-ytterbium co-doped phosphate glass for active device production. A detailed analysis of the optical characteristics of waveguides written with different repetition rates, pulse energies, and translation speeds is presented, and an optimum set of writing parameters is established. Coupling losses as low as 0.1 dB/facet with standard telecom fibers and propagation losses lower than 0.4 dB/cm have been obtained. Characterization of the active properties of the waveguides is also presented, together with the demonstration of waveguide laser action in the whole C-band with peak output power of more than 30 mW.     

Silicon-on-silicon rib waveguides with a high-confiningion-implanted lower cladding

The realization of single-mode rib waveguides in standard epitaxial silicon layer on lightly doped silicon substrate, using ion implantation to form the lower cladding, is reported. The implanted buffer layer enhances' the vertical confinement and improves the propagation characteristics. Respect to similar standard all-silicon waveguides a propagation loss reduction of about 7 dB/cm, in the single-mode regime, has been measured. A numerical analysis has been performed to evaluate the theoretical attenuation and the transverse optical field profiles. As a result of the presence of the ion implanted buffer layer, an increase of the fundamental mode confinement factor from 0.3 to 0.85 has been calculated. This results in a great enhancement of the coupling efficiency with standard single-mode optical fibers. Moreover, the proposed technique is low cost, fully compatible with standard VLSI processes, and allows a great flexibility in the integration of guided-wave devices and electronic circuits. Finally, the very high thermal conductivity characterizing these waveguides makes them attractive host-structures for electrically and thermally controlled active optical devices