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We report multicore fibers (MCFs) with 10 and 16 linearly distributed cores with single-mode operation in the visible spectrum. The average propagation loss of the cores is 0.06 dB/m at λ = 445 nm and < 0.03 dB/m at wavelengths longer than 488 nm. The low inter-core crosstalk and nearly identical performance of the cores make these MCFs suitable for spatial division multiplexing in the visible spectrum. As a proof-of-concept application, one of the MCFs was coupled to an implantable neural probe to spatially address light-emitting gratings on the probe.

Low-loss broadband fiber-to-chip coupling is currently challenging for visible-light photonic-integrated circuits (PICs) that need both high confinement waveguides for high-density integration and a minimum feature size above foundry lithographical limit. Here, we demonstrate bi-layer silicon nitride (SiN) edge couplers that have ≤ 4 dB/facet coupling loss with the Nufern S405-XP fiber over a broad optical wavelength range from 445 to 640 nm. The design uses a thin layer of SiN to expand the mode at the facet and adiabatically transfers the input light into a high-confinement single-mode waveguide (150-nm thick) for routing, while keeping the minimum nominal lithographic feature size at 150 nm. The achieved fiber-to-chip coupling loss is about 3 to 5 dB lower than that of single-layer designs with the same waveguide confinement and minimum feature size limitation.

We report low-loss silicon nitride bi-layer fiber-to-chip edge couplers on 200-mm silicon wafers for visible spectrum photonic circuits. The minimum per-facet coupling loss at λ=488nm was ~2.6dB (TM), and polarization-independent coupling was achieved with ~3.2-dB loss.

We demonstrate 10- and 16-core multicore fibers with all cores operating in a single- mode with

The shapes of initially spherical Ag nanoparticles in soda-lime glass are persistently changed using fs laser irradiation. With linearly polarized pulses, this shape transformation of the nanoparticles causes optical dichroism of the material. The intensity dependence of this effect is studied comprehensively, addressing the whole intensity range of permanent modifications as well as the influence of the number of laser pulses applied to one spot on the sample. The results are used as basis to develop a complete scenario of the possible mechanisms leading to the laser-induced shape transformation of metallic nanoparticles in glass.

Using the mode splitting that can be achieved by exploiting the effect of photoelasticity and the mode selection properties of coupled resonators, single- and two-frequency operation of a diode pumped cw YAG:Nd3+ laser was observed. In the two-frequency case, a regime with two orthogonal linearly polarized modes was realized. The frequency difference between the adjacent modes could be varied from 50 MHz to 8.4 GHz. A maximum laser output power of 12 mW was achieved at a pump level of 240 mW .

We start this discussion with results obtained by applying laser pulses of quite different peak intensities and ‘writing density’; the latter referring to the question of how many pulses are, on average, hitting one position on the sample.

It was shown in the previous sections that the shapes of the initially spherical Ag NPs in glass can be permanently modified by femtosecond laser irradiation; that in turn leads to the optical dichroism induced in the composite glass. The induced degree of dichroism (spectral gap between the two polarized resonances), being correlated with the aspect ratio (ratio of long and short axis) of the NPs, depends on the irradiation parameters such as wavelength, peak intensity and number of laser pulses applied. We will now explore the fabrication of polarization and wavelength selective micro-devices based on metal-glass nanocomposites.

This chapter is dedicated to the general understanding of laser pulse interaction with metal nanoparticles. The aim is to collect all physical processes, which may occur when the laser pulse starts to interact with nanoparticles, as well as all later events and mechanisms, which are triggered by this interaction.

Spherical silver nanoparticles (NPs) of 30 nm diameter embedded in soda-lime glass were uniformly reshaped (elongated) after irradiation by a linearly polarised 250 fs pulsed laser operating within the NPs' surface plasmon resonance band. We observed second harmonic generation (SHG) and multiphoton-absorption-induced luminescence (MAIL) in the embedded laser-reshaped NPs upon picosecond (10 ps) pulsed laser excitation at 1064 nm. A complementary study of SHG and MAIL was conducted in soda-lime glass containing embedded, mechanically-reshaped silver NPs of a similar elongation ratio (aspect ratio) to the laser-reshaped NPs. This supports the notion that the observed difference in SHG and MAIL in the studied nanocomposite systems is due to the shape modification mechanism. The discrete dipole approximation method was used to assess the absorption and scattering cross-sections of the reshaped NPs with different elongation ratios.

Four widely used electromagnetic field solvers are applied to the problem of scattering by a spherical or spheroidal silver nanoparticle in glass. The solvers are tested in a frequency range where the imaginary part of the scatterer refractive index is relatively large. The scattering efficiencies and near-field results obtained by the different methods are compared to each other, as well as to recent experiments on laser-induced shape transformation of silver nanoparticles in glass.

By irradiating spherical metal nanoparticles embedded in glass with several hundred ultrashort laser pulses at peak intensities of 0.2-1.5 TWcm(2), dichroic microstructures can be written in these nanocomposite materials. The underlying mechanism is transformation of the nanoparticles to prolate shapes. Using a single wavelength, the maximum aspect ratio achievable with this process is limited by partial destruction of particles. Here we show that this limitation can be overcome by simultaneous irradiation with different wavelengths. In particular, adding a relatively weak intensity at 800 nm to the main irradiation at 532 nm increases the maximum aspect ratio of Ag nanoparticles and the resulting separation between polarized surface plasmon bands dramatically. These effects are explained by the efficiency of electric field enhancement in the vicinity of nanoparticles, which influences the directed photoionization needed for particle shape transformation.

Laser-induced permanent shape transformation dynamics of glass-embedded silver nanoparticles is investigated by a pulse-pair irradiation technique, where the nanoparticles are irradiated by pairs of time-delayed femtosecond laser pulses. The temporal evolution of surface plasmon extinction bands is obtained up to a time delay of 1 ns. We find that the aspect ratio of the modified nanoparticles, i.e., the observed dichroism, reduces rapidly to a minimum level within 20 ps after the laser irradiation. From that interpulse delay onward, the resulting aspect ratio stays at that minimum level until 100 ps. Subsequently, for longer time delays, the aspect ratio increases again until 1 ns. Temperature modeling of the nanoparticle-glass system gives evidence that the intermediately reduced dichroism is due to the high diffusion mobility that emitted silver ions can possess within a shell of heated glass around the nanoparticle, in a time window of 100 ps. For longer time delays the size of the heated glass shell gets reduced, thereby limiting the range of ionic diffusion. The theoretical estimations confirm the experimental results and suggest that the nanoparticle shape changes depend strongly on the thermal situation induced to the surrounding glass.

The shapes of initially spherical Ag nanoparticles in glass were permanently changed by fs laser irradiation. This shape transformation of the nanoparticles results in an optical dichroism of the material, strongly depending on the actual irradiation parameters such as intensity, number of pulses per irradiated spot and laser wavelength. The proposed technique allows modifying the optical properties of glass containing metallic nanoparticles and can be used for the production of dichroic or polarizing microstructures in the visible and near infrared region with high polarization contrast.

Irradiation of spherical silver nanoparticles in glass by linearly-polarized intense femtosecond laser pulses close to the surface plasmon resonance results in irreversible shape transformations. In this context, the spectral positions of plasmon resonances as a function of particle size and basic shapes are well-understood theoretically and experimentally; however, the dynamical information regarding the laser-induced shape transformation mechanisms is still a matter of interest. To investigate these dynamics we introduce a single-color double-pulse experiment, where the sample is irradiated by two time-delayed pulses of equal intensity. Different nanoparticle shape elongations can be produced depending on the delay between two irradiating pulses. Analyzing the resultant shifts of absorption bands for each delay gives valuable information on the evolution of nanoparticle shape changes. Possible shape modifying mechanisms including nanoparticle ionization, extreme lattice heating and excess energy transfer from the hot nanoparticle to the glass matrix are observed and discussed.

Femtosecond laser pulses tailored with closed-loop, optimal control feedback were used to excite oscillations in C60 with large amplitude by coherent heating of nuclear motion. A characteristic pulse sequence results in significant enhancement of C2 evaporation, a typical energy loss channel of vibrationally hot C60. The separation between subsequent pulses in combination with complementary two-color pump-probe data and time-dependent density functional theory calculations give direct information on the multielectron excitation via the t(1g) resonance followed by efficient coupling to the radial symmetric a(g)(1) breathing mode.

We demonstrate an all-optical data storage and readout technique on a medium that has proved to be stable over centuries—glass containing metallic nanoparticles. Using ultra-short laser pulses to persistently change the shapes of the nanoparticles dependent of the laser polarization, well-defined local dichroism in the focal volume can be produced. The latter could be utilized for multi-bit encoding in spot sizes down to the diffraction limit, where the information can be read out very fast by wavelength- and polarization-sensitive detection of the transmitted light. The storage capacity of the proposed technique is comparable with that of blu-ray discs.

We prove by help of optical microspectroscopy that spherical Ag nanoparticles embedded in glass can be transformed to oblate (disklike) shapes by irradiation with circularly polarized femtosecond laser pulses. The symmetry axis (short axis) of the oblate spheroids produced by this method is oriented along the laser propagation direction. This observation also confirms the assumption that the mechanism of shape transformation starts with directed photoionization of nanoparticles induced by laser irradiation in combination with the electric field enhancement at the particle-glass interface.

We have studied the influence of irradiation parameters on the laser-induced shape transformation of Ag nanoparticles in glass by fs pulses. The amount of dichroism which can be achieved by this technique is related to the aspect ratio of the prepared spheroidal particles. Looking for maximal dichroism, it was found that 'off-resonant' irradiation with wavelengths considerably larger than the surface plasmon (SP) resonance at 413 nm can produce a larger spectral gap between orthogonally polarized SP bands of the reshaped nanoparticles than resonant excitation. It is also shown that subsequent irradiation with successively larger wavelengths may increase the spectral gap even further. A sequence of only two steps of irradiation at 535 and 670 nm already caused a shape transformation of initially spherical Ag nanoparticles to spheroids with an aspect ratio of (a/c)>3.

The 3D shape of Ag nanoparticles in glass irradiated by fs laser pulses is investigated by optical spectroscopy. It is shown that in general spheroids are produced with their symmetry axis oriented along the direction of the linear laser polarization. Depending on the actual irradiation conditions, oblate or prolate spheroids are obtained. The halo of small Ag clusters and Ag ions around the reshaped particles causes a redshift of the surface plasmon resonances via refractive index increase.

A system for the course control and spatial stabilization of the output beam of a femtosecond laser system is realized. An accuracy of 0.5 microrad is achieved long term in a laboratory environment for a beam with an initially daily deviation of more than 40 microrad. The application and importance of the method is illustrated for laser pulse shortening in a hollow waveguide resulting in a stable output power and an 8 fs pulse duration for more than 10 h operation time.

In recent years, the fabrication, structural modification and characterisation of nanostructured materials have gained a great deal of attention due to their distinctive properties and potential use in technological applications. Glass containing silver (Ag) nanoparticles (NP), or Metal-Glass Nanocomposite (MGN), is routinely used as high-contrast optical polarisers [1], and has been recently shown as a promising medium for high-volume optical storage of information [2]. Strong second and third harmonic generation has been demonstrated when the MGN containing mechanically reshaped NPs was subjected to fs pulse excitation [3], thus showing potential as an effective nonlinear optical medium for photonics nanodevice applications.