This PDF file contains the front matter associated with SPIE Proceedings Volume 6872, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

This paper describes the use of closed-loop adaptive optical system to improve the focusing of femtosecond laser beam. Our adaptive system corrects for the low-order aberrations of laser. But even if the aberrations of the laser beam are compensated the focal spot obtained with parabolic mirror is still far from ideal one. And the reason is the aberrations of the parabolic mirror and its poor adjustment. Comparison of phase-conjugate and multi-dither algorithms to correct for the parabolic mirror aberrations is presented. The principle of proper adjustment of the parabolic mirror based on M² minimization is shown.

Computer calculations of the beam quality and output power of nearly diffraction-limited thin-disk Yb:YAG lasers are presented. The CW lasers have stable resonators. Our calculations include the simultaneous operation of two transverse modes. The simulated lasers are similar to those for which experimental results have been reported by other researchers but we have not attempted to make a precise comparison. Our calculated results show interesting trends that can be used in designing such lasers.

Optical resonator for generation of high-power radially polarized beam is presented. In laser cutting applications, radially polarized beam is advantageous because the beam contacts the cut front always with the highly absorptive p-polarization. The proposed resonator comprises a reflector unit that has three conical faces with polarization sensitive dielectric coating, and an ordinary output coupler. The resonator is compatible with any existing circular mirror standing-wave optical resonators. Numerical simulation shows good polarization selectivity with only 1% of reflectivity difference between p and s polarizations, and M² factor of the output beam is 1.9. No output power degradation is seen compared to the standard spherical mirror resonator. Design and fabrication of the resonator for a 1kW-class commercial cw CO₂ laser is discussed.

The result in laser material processing is controlled mainly by the properties of the focused laser beam. Very special requirements have to be taken into account to characterize such a laser beam, which is finally used for laser micromachining. These specific aspects for the design of a beam diagnostics system ready to measure small spots (down the 10 micrometer range) at power densities up to several GW/cm² will be discussed. Based on a CCD-camera concept, care has to be taken to magnify and to attenuate the beam properly. A special electronics design and algorithms are necessary to optimize the performance and finally to realize such a technical measuring system. Some applications of beam diagnostics within industrial processes (drilling holes, cutting wafers etc.) are demonstrated.

A comprehensive investigation of the main parameters that determine the effective power scaling of diffusion cooled annular CO₂ lasers in the 3kW region is presented. Aspects such as RF excited discharge characteristics; small signal gain, free space resonator configuration, beam stability and quality are discussed in detail. Simulations of the resonator system are presented and different shapes for the azimuthal direction are evaluated for power and stability.

It is very important to analyse phase ingomogenity of high-power laser beam. Usually Shack-Hartmann wavefront sensor or interferometer is used to test both laser beam aberrations and quality of the optical element surface. But we found out that in case of strong distortions the measured aberrations differ from the real ones. To investigate this problem we used bimorph deformable mirror to introduce strong aberrations to the laser beam. The results of our experiments are discussed.

The design of refractive beam shaping optics using (geometrical) ray optics, rather than (physical) diffractive optics, has been justified theoretically in the cases of interest and validated empirically. Measured output beam profiles have matched to design profile with surprising accuracy. As the number of aspheric optics manufacturers increases, beam shaping optics will become affordable, even for prototypes. For those not already familiar with the subject, this paper provides a brief review of the theory and demonstrates how to easily calculate the coefficients of the finite polynomial series used to produce aspheric surfaces. The numerical integration step found in the literature has been eliminated resulting in a simplified algorithm which is easily implemented with math processors such as Mathcad®, MATLAB®, or Excel®.

Optical resonators have micrometer size dimensions and come mostly in two flavors, namely circular and racetrack shaped microrings (MR), and microdisks (MD), although microsphere (MS) and photonic crystal microring (PCMR) resonators are also expected to gain prominence. Highly advanced fabrication techniques in recent years resulted in the reduction of propagation losses and in a remarkable increase of resonator Q factor and finesse. Newly developed microresonators are therefore ideally suited for applications in highly selective communication filters, delay lines, distributed and localized sensing, industrial measurements, microlaser mirrors and high-resolution spectroscopy. Since the optical signal recirculates and spends a relatively long time trapped in a high Q cavity, microresonators enhance light-light and light-particle interactions and are for this reason most promising to exploit nonlinear effects. The talk will focus on advances in multiring photonic devices such as the coupled resonator optical waveguide (CROW) and the side-coupled integrated space sequenced optical resonator (SCISSOR), on the link between photonic and microwave filter design, on the effect of polarization on filter response and its control, on schemes and efficiency of tuning and modulation and on MR composites used as reflectors and laser mirrors. The talk will also cover issues related to design trends and technological advances, such as vertically stacked MRs, coiled optical resonators and resonators not based on propagating waves, as well as techniques to extend the free spectral range (FSR) of periodic filters through the Vernier principle and the use of polymer materials and two-dimensional photonic crystals to fabricate optical resonators.

Coherent coupling of optical resonances in spherical microcavities results in the formation of so called photonic molecules. The name originates from the analogy to chemical molecules. The coupled optical modes are similar to the atomic orbitals of a chemical molecule. In this work, we studied the resonance spectrum of the symmetric photonic molecules. Furthermore, symmetric directional emission of light from the photonic molecules is experimentally shown. The photonic molecules are illuminated in the vertical direction with a defocused laser beam. The emission is attributed to photonic nanojets generated in the structure. Spectral analysis exhibit whispering gallery mode resonances of coupled and uncoupled modes. A benzene molecule-like structure consisting of a 7-microspheres cyclic photonic molecule shows a field emission pattern similar to the spatial distribution of the orbitals of the benzene molecule.

We introduce a light-stopping process that uses dynamic loss tuning in coupled-resonator delay lines. We demonstrate via numerical simulations that increasing the loss of selected resonators traps light in a zero group velocity mode concentrated in the low-loss portions of the delay line. The large dynamic range achievable for loss modulation should increase the light-stopping bandwidth relative to previous approaches based on refractive-index tuning.

Lord Rayleigh's 2 dimensional (2D) whispering gallery mode (WGM) is based upon 2D total internal reflection (TIR) while 3D whispering cave mode (WCM) is based upon 3D TIR. 3D WCM is however irreducible to 2D WGM: The 2D WGM is confined to a thin microdisk with a cylindrical symmetry solvable via Bessel function analysis while the 3D WCM is confined to a virtual toroid with a circular helix symmetry not reducible to a simple 2D symmetry. The 3D WCM laser is surface-normal dominant and has no in-plane resonance while the 2D WGM laser is in-plane dominant. Apart from the regular 2D WGM, the 3D WCM's major polarization state favors a strong carrier-photon coupling for the carriers in the planar quantum wells, such that the powerful transient coupling generates photonic quantum rings (PQRs), or concentric quantum rings with a half-wavelength pitch of imminently recombinant carriers, i.e., a photonic quantum corral effect. This feature is responsible for the low threshold currents and thermally stable spectra, which opens the way for easy optical mega-pixel ('Omega') chip fabrications. For the GaAs device size less than 1 μm, the increasing intermode spacing leads to a single eigenmode PQR laser with a record low threshold current of 300 nA.. Moreover PQR 'holes', or microholes in the quantum well plane, give rise to an unusual 'convex' WCM laser via gain guiding effects. Mega-pixel PQR 'hole' laser chips are easier to fabricate than PQR 'mesa' chips, and both will be useful for optoelectronic VLSI, ITS, and biocell sorting.

Miniaturized, portable sensing systems for medical and environmental diagnostics and monitoring are an excellent application area for microresonator sensors. Polymer microresonators are attractive components for chip scale integrated sensing because they can be integrated in a planar format using standard semiconductor manufacturing technologies. Vertically coupled microresonators, where the waveguides lie below or above the microresonator, can be fabricated using standard photolithography, enabling low cost integrated sensor systems. Microresonators can be surface customized for discrimination in, for example, chemical sensing applications, or the surface can be functionalized for biological sensing applications. To create chip scale integrated sensing systems, microresonators can be integrated with planar optical system components, such as polymer waveguides and thin film photodetectors, onto silicon using heterogeneous integration. Heterogeneous integration can also be used to integrate optical sources with sensors onto host substrates such as silicon.

In this paper, we review experiments performed with silica microspheres as optical resonators. We introduce our approach to utilize scanning optical near-field probes as nano scatterers and nano emitters. Applications of mode mapping techniques to improve selective coupling to high-Q modes and to study Raman lasing are presented. Furthermore, we analyze the emission properties of a single nano emitter interacting with resonator modes and demonstrate long-distance energy transfer between two nano emitters. The controlled splitting of a high-Q mode by a single Rayleigh scatterer is also demonstrated.

A theoretical framework is presented for analyzing and synthesizing coupled microring devices of the most general coupling topology. The approach is based on the modeling of an arbitrary system of coupled microresonators by an equivalent electrical network of coupled LC oscillators. The equivalent circuit model enables well-established microwave filter techniques to be leveraged for the design and synthesis of optical filters, allowing complex coupledmicroring architectures to be explored for advanced applications in high-order filtering, dispersion engineering and other spectral shaping functions.

We use a tunable diode laser operating near 1570 nm to investigate various effects of the heat transfer from fused-silica microspheres, with and without thin-film coatings, to the surrounding gas in a vacuum chamber. The resonance frequencies of microsphere whispering-gallery modes (WGMs), excited by a tapered-fiber coupler, shift with changing temperature (about -1.6 GHz/K at 1570 nm). This shift, primarily due to the temperature dependence of the refractive index of fused silica, enables the measurements whose results are reported here: determination of the thermal accommodation coefficient of air on different surfaces, and measurement of the optical absorption coefficients of surface water layers and of a thin film coating. Our method for determining thermal accommodation coefficients involves deducing the thermal conductivity of the air as a function of pressure by measuring the relaxation rate of an externally heated microsphere to room temperature. Then, in a separate experiment, by observing thermal optical bistability of the WGM resonances caused by absorption of the probe laser, the contribution of water or film absorption to the total loss is found.

We report on the development of versatile, miniaturized optofluidic ring resonator (OFRR) dye lasers that can be operated regardless of the refractive index (RI) of the liquid. The OFRR is a piece of a thin-walled fused silica capillary that integrates the photonic ring resonator with microfluidics. In an OFRR dye laser, the active lasing materials (such as dye) are passed through the capillary whereas the circular cross section forms a ring resonator and supports whispering gallery modes (WGMs) that provide optical feedback for lasing. Due to the high Q-factors (> 10⁹), extremely low lasing threshold can be achieved. The operation wavelength can conveniently be changed by using different dye and fine-tuned with solvent. The laser can be out-coupled through a fiber taper in touch with the capillary, thus providing an easy guiding for the laser emission. Our experiments demonstrate lasing through direct excitation and through efficient energy transfer (ET). Theoretical analysis and experimental results for OFRR lasers are presented.

We demonstrate experimentally that random departure from high-index-contrast periodicity in photonic crystal waveguides gives rise to spectral features that bear signatures of Anderson localization. Disorder-induced high-Q cavities are observed in a narrow frequency band close to the guided mode's cut-off where the light propagates with slow group velocity. Spectrally distinct quasi-states with Qs as high as ~250,000 are distributed at random locations along the waveguide and can find applications for example in optical sensing systems.

Photonic circuits based on silicon wire waveguides have attracted significant interest in recent years. They allow strong confinement of light with moderately low propagation losses. Moreover, the high thermo-optical coefficient of silicon and the small device size in silicon photonics allow for micro-heaters induced trimming, tuning, and switching with relatively low power. In this paper, we review our recent progress towards telecom-grade reconfigurable optical add-drop multiplexers (ROADMs) based on silicon microring resonators. We discuss waveguide and micro-heater design and fabrication as well as the first demonstration of telecom-grade silicon-microring filters and the first demonstration of transparent wavelength switching. The reported devices can be employed in numerous optical interconnect schemes.

We describe our investigations of a CW diode pumped solid state laser based on two Nd:YAG active elements provided with original unstable resonator. Two diffraction limited output beam divergence has been achieved. The laser radiation power of the resonator proposed has been obtained of 40% below but with the 30 times greater on-axis intensity as compared to the ordinary used resonator in a commercial laser of a similar type.