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A new technique for mode-locking is demonstrated based on two lasers sharing one leg for sum-frequency generation. When the two lasers had equal round trip time one will produce bright pulses and the other dark pulses. Both lasers used Nd:YVO

Electrical corona discharge is employed in this work to deposit ions on the surface of an optical fiber, creating a strong electric field that is used for poling. Green laser light propagating in the core frees photocarriers that are displaced by the poling field. The technique presented can induce a higher optical nonlinearity than previously obtained in traditional optical poling with internal metal electrodes. To date, a maximum second order nonlinearity 0.13 pm/V has been achieved for a 15 kV corona discharge bias.

In this work, we demonstrate a spot-welding method for fabrication of all-silica fiber components. A CO

By focusing a femtosecond laser beam onto the lateral face of a periodically poled KTP crystal, we generate a THz pulse through optical rectification of the laser pulse. The THz signal is recorded by means of a common THz time-domain technique, which allows us to obtain both the magnitude and sign of the THz waveform, and then the magnitude and phase of its spectral components thanks to a numerical Fourier-transform. By moving the laser beam along the crystal, we record a THz signal that renders for the alternative orientation of the crystal domains, with a lateral resolution as good as 10 μm, whatever the THz wavelength. This demonstrates the potential of the Optical Rectification TeraHertz Imaging (ORTI) technique to produce sub-wavelength THz images.

We demonstrate the use of the electrooptic effect to control the propagation constant of the guided modes in silicate few mode fibers with internal electrodes. The electrooptic effect induces a perturbation of the fiber's refractive index profile that controls intermodal interference. To increase the electrooptic effect the silicate fibers are poled. The response time is in the nanosecond range.

A Nd:YVO

A midinfrared single-photon-counting lidar at 3 µm is presented. The 3 µm photons were upconverted to 790 nm in a periodically poled rubidium-doped

A new technique for mode-locking through sum-frequency generation is presented. The technique produced 200 ps long 1064 nm pulses in a coupled-cavity system with two Nd:YVO4 crystals and a PPRKTP phase-matched for sum-frequency generation.

Cavity-free, precision-tunable source of a nanosecond, mJ-level, pulses consisting of backward optical parametric oscillator pumped by diode-seeded laser amplifier shows a record threshold of 19 MW/cm2 and an optical-to-optical efficiency exceeding 70%.

We demonstrate self-compression of 173 fs pulses centered at 1030 nm down to 19.5 fs through electro-optic phase modulation by the phonon-polariton waves generated in a phase-matched intra-pulse difference-frequency mixing.

We demonstrated the concept of anisotropic off-axis laser oscillator through stimulated Raman scattering and generated the octave-spanning supercontinuum, containing two spectral groups between 540~750 and 1095~1800 nm, in a monolithic KTP crystal.

We report generation of octave-spanning supercontinuum from a high-gain, ultra-broadband, and mirrorless Raman oscillator in a monolithic KTP crystal. The supercontinuum output contains two spectral groups between 540~750 and 1095~1800 nm.

The electrooptic effect is used in a few-mode fiber to control intermodal interference. The fiber has internal electrodes and is poled to increase its electrooptic coefficient. The response time is in the nanosecond range.

Precision-tunable mJ, nanosecond pulses at 1981.1 nm and 2145.6 nm are generated at 5kHz repetition with an efficiency of 70% in a cavity-free arrangement using a PPRKTP BWOPO pumped by a narrowband DPSSL at 1030nm.

We report generation of a visible and near-infrared supercontinuum from a high-gain, ultra-broadband, and mirrorless Raman oscillator in a monolithic KTP crystal. The plane transverse to the pump axis resonates and traps off-axis Stokes waves and their frequency-upconverted components bouncing between two crystal surfaces via total internal reflection. The Raman gain is maximized with the Stokes polarization perpendicular to the plane of reflections. When pumped by a Q -switched Nd:YAG laser, the monolithic oscillator generates quasi-mode-locked Stokes pulses with octave-spanning spectral groups across the visible and near-infrared spectra between 540 and 1800 nm.

By generating terahertz pulses in KTP crystals through optical rectification with a pump photon energy varying from below to above the bandgap, we observe a peak of the THz signal at the bandgap energy but also a second one around half the bandgap. This later one is attributed to a two-photon absorption enhanced nonlinearity, which is validated by the similarity of the two-photon absorption coefficient and THz peak amplitude data versus the pump photon energy. A careful analysis of the KTP sample absorption spectral dependence nearby the bandgap demonstrates that KTP is an indirect bandgap crystal, whose absorption below the bandgap involves emission of a phonon related to the symmetric Ti-O stretching vibration, i.e. the ν

Combining metal and semiconducting components in the core of a glass-clad fibre brings new breadth to the range of structures that can be fabricated using localized thermal gradients. Both axial and lateral structuring of fibres drawn withm ultiple components is demonstrated, as well as the introduction, segregation and chemical reaction of metal components within an initially pure silicon core. Gold and tin longitudinal electrodes fabrication, segregation of GaSb and Si in an initially inhomogeneous fiber into parallel axial layers and Al doping of a GaSb core were demonstrated. Gold was introduced into Si fibers to purify the core or weld an exposed core to a Si wafer. Ga and Sb introduced from opposite ends of a silicon fibre reacted to form III-V GaSb within the Group IV Si host, as confirmed by structural and chemical analysis and room temperature photoluminescence.

Microfluidics has emerged rapidly over the past 20 years and has been investigated for a variety of applications from life sciences to environmental monitoring. Although continuous-flow microfluidics is ubiquitous, segmented-flow or droplet microfluidics offers several attractive features. Droplets can be independently manipulated and analyzed with very high throughput. Typically, microfluidics is carried out within planar networks of microchannels, namely, microfluidic chips. We propose that fibers offer an interesting alternative format with key advantages for enhanced optical coupling. Herein, we demonstrate the generation of monodisperse droplets within a uniaxial optofluidic Lab-in-a-Fiber scheme. We combine droplet microfluidics with laser-induced fluorescence (LIF) detection achieved through the development of an optical side-coupling fiber, which we term a periscope fiber. This arrangement provides stable and compact alignment. Laser-induced fluorescence offers high sensitivity and low detection limits with a rapid response time making it an attractive detection method for in situ real-time measurements. We use the well-established fluorophore, fluorescein, to characterize the Lab-in-a-Fiber device and determine the generation of $$\sim$$ ∼ 0.9 nL droplets. We present characterization data of a range of fluorescein concentrations, establishing a limit of detection (LOD) of 10 nM fluorescein. Finally, we show that the device operates within a realistic and relevant fluorescence regime by detecting reverse-transcription loop-mediated isothermal amplification (RT-LAMP) products in the context of COVID-19 diagnostics. The device represents a step towards the development of a point-of-care droplet digital RT-LAMP platform.

The principles behind up-conversion time correlated single photon counting (TCSPC) lidar are presented. This technique can easily extend the detection range of conventional SPADs to reach into the MIR by utilising nonlinear processes to up-convert the wavelength of the MIR to the visible or NIR. The up-converted light can then be detected by a standard Si-SPAD. This allows for high resolution and sensitivity to be achieved while operating the system at room temperature. The technique is demonstrated through a short-range lidar system measuring off diffusely reflecting targets. The system was operating at 3 μm with pulse energies around 3 nJ and a pulse width of 300 fs. The up-conversion was performed inside a PPRKTP crystal placed within a Nd:YVO4 laser cavity operating at 1064 nm, which generated pulses at 790 nm. The temporal FWHM of the lidar response was 76 ps, and the system showed sub-mm range accuracy, demonstrated by scanning 3D targets.

We perform THz generation by optical rectification in ZnTe, KTP and RKTP with femtosecond laser pulses whose wavelength ranges from UV to IR. We observe a strong THz emission when the pump photon energy reaches the crystal bandgap. This phenomenon is explained by the resonance of material nonlinear susceptibility around its bandgap. Additionally, for the first time, we report of a two-photon enhanced nonlinearity in KTP/RKTP, which leads to an enhanced THz emission near half the bandgap.

Lab-on-a-chip (LOC) is a well-established microfluidic platform that allows the miniaturization of chemical and biological processes onto a single unit. Minimal sample and reagent consumption, the potential for multiplexing, rapid analysis, and portability are some of the key advantages of LOC. However, the chips typically need to be integrated with bulky and expensive external optics. Alternatively, silica fibers and capillaries offer opportunities for more compact integration of optics with microfluidics while adding advantages such as; flexibility within a high aspect ratio format, uniaxial arrangements, and measurement-at-a-distance.

Coupling between electromagnetic fields and distinct mechanical states of matter (e.g., Brillioun modes or phonon modes) can mediate energy transfer between electromagnetic waves and the material lattice. Ferroelectric crystals typically show intense optical phonon modes, which also contribute substantially to the nonlinear susceptibility. One such ferroelectric crystal is KTiOPO 4 (KTP), with a large damage threshold, nonlinear coefficient, and transparency range. Moreover, KTP and isomorphs have already been shown to produce cascades of Raman [1] . Recent developments have shown that KTP can be used as an off-axis oscillator for THz generation, mediated by picosecond stimulated polariton scattering (SPS) [2] . Here, we show highly efficient Raman comb generation with nanosecond pulses without an external cavity (contrary to ref. [1] ) in KTP.

Silicate optical fiber does not exhibit a linear electrooptic effect (Pockels’) because the material is symmetric. Poling can be used to induce the Pockels effect in pieces of fiber with electrodes by creating a permanent electric field by applying high voltage while the fiber is excited thermally [1] or optically [2] . The second-order nonlinear coefficient achieved reproducibly is χ (2) ≈ 0.1-0.3 pm/V. Optical poling uses short-wavelength light to excite the fiber core (e.g., from a UV lamp [3] ) as high voltage is applied to the internal fiber electrodes. Although the recorded field is limited by the voltage applied and silica’s dielectric breakdown strength, low loss devices can be fabricated. Here we describe the use of electrical corona discharge to pole fibers with high electric field across the fiber core. Charges deposited on the fiber surface (due to the electrical corona discharge) create the necessary poling field, as previously demonstrated in planar waveguides [4] .

Narrowband coherent electromagnetic radiation in the region of rotational and vibrational states of matter is of interest for numerous scientific and industrial applications, e.g., Microscopy, LIDAR, and Spectroscopy. In particular, LIDARs for measuring concentration distribution of atmospheric greenhouse gases, such as CO 2 , H 2 O, CH 4 , N 2 O, require frequency-agile ns-pulse sources with transform-limited optical spectra. Optical parametric oscillators (OPOs) are frequently used to realize such sources, but sophisticated spectral control is necessary to obtain narrow line stable output. In contrast to regular OPOs, the backward wave OPO (BWOPO) inherently provides a stable, narrow linewidth output [1] – [3] . It’s realization requires sub-micrometer domain structures for quasi-phase matching, which for bulk samples so far only have been demonstrated using periodically poled Rb-doped KTiOPO 4 (PPRKTP) [1] – [2] . Furthermore, KTP is a well-established material with good transparency in the region of 0.4-3.2 µm, high nonlinear coefficient, and high damage threshold. In this work we investigate a master oscillator-power amplifier setup comprising a BWOPO-seeded optical parametric amplifier (OPA) to generate transform-limited nanosecond pulses in the spectral range close to 2 µm.

In this work, we present the design and fabrication of a fiber device that performs digital droplet microfluidics for molecular diagnostics. A variety of fibers and capillaries were used to build three connected modules dedicated to droplet generation, incubation, and fluorescence detection which enables a uniaxial arrangement. This is in contrast to the traditional 2-dimensional lab-on-a-chip architecture. We characterize our fiber device using a fluorescein dilution series. Our observed detection limit is on the order of 10 nM fluorescein. We demonstrate our all-fiber device for the fluorescence readout after loop-mediated isothermal amplification (LAMP) of synthetic SARS-CoV-2. Our results suggest that this fiber device can successfully distinguish between positive and negative samples in molecular diagnostics. We propose that our fiber device offers benefits over microfluidic chip techniques such as easier optical integration, much simpler sample loading, and faster diagnosis with high specificity and sensitivity.

An all-fiber separation component capable of sorting and counting micron-sized particles based on size is presented. A sequence of silica fiber capillaries with various diameters and longitudinal cavities were used to fabricate the component for separation and detection in an uninterrupted flow. Fluorescence microparticles of 1 μm and 10 μm sizes are mixed in a visco-elastic fluid and infused into the all-fiber separation component. Elasto-inertial forces focus the larger particle to the center of the silica capillary, while the smaller microparticles exit from a side capillary. Analysis of the separated particles at the output showed a separation efficiency of 100% for the 10 μm and 97% for the 1 μm particles. In addition, the counting of the larger particles is demonstrated in the same flow. The separated 10 μm particles are further routed through another all-fiber component for counting. A counting speed of ~1400 particles/min and with the variation in amplitude of 10% is achived. A combination of separation and counting can be powerful tool may find several applications in biology and medicine, such as separation and analysis of exosomes, bacteria, and blood cell sub-populations.

Fused silica glass is a commonly used high-performance material in scientific and industrial applications, due to the exceptional optical, mechanical and thermal properties. However, its production can be challenging and expensive due to the high processing temperatures required, in both manufacturing and geometrical structuring. In this work we have studied additive manufacturing of transparent fused silica glass using the laser cladding process. Here a CO2-laser is used to locally melt the glass, while injecting a stream of glass powder into the hot-zone. A challenge specifically addressed in this work is the shadowing effect, i.e., when the injected powder interacts with the laser beam resulting in non-stable heating dynamics, and partial sintering of powder prior to reaching the substrate surface. To reduce these effects, we have studied the use of sub-micron sized glass powders in order to minimize the laser beam interactions, both absorption and scattering. Using fumed silica powder injected via a single, off-axis nozzle, combined with additional powder cone shaping gas, transparent silica glass has been fabricated with an achieved deposition efficiency of up to 30 %. Typical, single deposition tracks have a width of approximately 850 μm with single layer heights of up to 150 μm.

We demonstrate multi-cycle terahertz (MC-THz) generation in a 15.5 mm long periodically poled rubidium (Rb)-doped potassium titanyl phosphate (Rb:PPKTP) crystal with a poling period of 300 µm. By cryogenically cooling the crystal to 77 K, up to 0.72 µJ terahertz energy is obtained at a frequency of 0.5 THz with a 3 GHz bandwidth. A maximum internal optical-to-terahertz conversion efficiency of 0.16% is achieved, which is comparable with results achieved using periodically poled lithium niobate crystal. Neither photorefractive effects nor damage was observed with up to 900 m J / c m 2 , showing the great potential of Rb:PPKTP for multi-millijoule-level MC-THz generation.

By exploiting the anisotropic radiation pattern of an elementary dipole in a laser material, we report a gain enhancement factor of 1.3104 for an off-axis Raman laser in a monolithic y-cut versus z-cut KTP crystal.

An ion-exchange process has been developed for periodically poled Rb-doped KTiOPO

In this work, we explore the interrogation of an array of fiber Bragg gratings as part of a laser cavity. A semiconductor optical amplifier in a sigma-shaped fiber cavity provides gain and is gated periodically at a rate that matches the roundtrip time associated with each grating of the array. The interrogator exhibits clear laser properties such as a threshold and linewidth narrowing. Besides improving the signal-to-noise ratio and enabling the re-use of wavelengths, it is found that this interrogation scheme enables monitoring of weak gratings spaced by less than 1 cm. Intracavity grating interrogation studied here is found to be a simple and powerful way to increase the number of sensor points for industrial applications.

We worked on a new scheme of quasi-phase matching (QPM) based on the negative first order of the spatial modulation of the sign of the second-order nonlinearity. Applying this scheme in the case of angular-QPM (AQPM) in a biaxial crystal reveals new directions of propagation for efficient parametric frequency conversion as well as "giant" spectral acceptances. The experimental validation is performed in a periodically poled rubidium-doped

ISBN 978-1-943580-84-2; International audience; We propose a new scheme of quasi-phase matching based on the negative first-order of the spatial modulation of the sign of the second-order optical nonlinearity. The experimental validation is done in a periodically-poled Rubidium-doped KTiOPO4 crystal.

Grating couplers on thin-film lithium niobate ridge waveguides were designed and fabricated using UV-laser ablation. The calculated coupling efficiency with a sinusoidal grating can be as large as 53% in a 0.5 µm thin film. The maximum grating depth we fabricated was 130nm, limiting the coupling efficiency to a theoretical value of 18%. We fabricated grating couplers on adhered ridge waveguides of 20 µm thickness. Coupling light to waveguides on thin-film lithium niobate is still challenging, and here we present a fast, cheap and reliable fabrication alternative. It will benefit the on-chip testing of integrated components developed on this novel and promising material platform.

A single-photon-counting mid-infrared LIDAR is presented. 2.4 µm mid-infrared photons were up-converted to 737 nm by intra-cavity mixing in a periodically poled rubidium-doped K T i O P O 4 crystal inside a N d : Y V O 4 laser. The up-converted photons were detected by a Si single-photon avalanche photodiode (SPAD). A temporal resolution of 42 ps and a dark count rate of 500 Hz were achieved, limited by the SPAD and ambient light leakage. It allowed for detection of two targets separated by only a few millimeters. This technique is easily extendable to longer wavelengths, limited primarily by the nonlinear crystal transparency.

We present a novel C-cavity concept for tunable lasers. The laser is based on a semiconductor optical amplifier (SOA), serving both as a gain medium as well as a modulator, and a chirped fiber Bragg grating (C-FBG) which acts as the end mirrors on both cavity ends. Driving the SOA with a pulse pair with variable delay enables wavelength tuning by targeting different regions in the C-FBG with the circulating pulse. The cavity design allows for wide tuning while maintaining a constant repetition rate, we show a tuning range of 35 nm -limited by the C-FBG's reflection bandwidth. Time-multiplexed operation with four different wavelengths is also demonstrated. Furthermore, the laser performance and dynamics under different operating conditions are analyzed and discussed.

We present the performance of an all polarization-maintaining Erbium-doped fiber laser mode-locked by a multilayer graphene based saturable absorber. The cavity incorporates a Martinez-type compressor, based on a transmission grating, which allows for continuous tuning of the net cavity dispersion as well as spectral filtering. By adjusting the dispersion and the spectral bandwidth, we could operate the laser in the soliton, the dispersion managed soliton and the absorber-limited pulse regimes. The pulse durations from the laser ranged between 338 fs to 2.1 ps and the laser could be operated at nearly constant output powers in the anomalous and the normal dispersion regimes. We also conducted stability analyses based on dispersive Fourier transform measurements in the different operating regimes. Comparison of the collected spectra reveals that the soliton regime had the best overall stability.

Established waveguide fabrication technologies on lithium niobate (LN) and potassium titanyl phosphate (KTP) were revisited, and a comparative analysis of their performance for type-0 quasi-phase matched second-harmonic generation at 1.55 µm was provided based on literature data and our simulations. This analysis aided identifying gaps where the waveguide performance is below the theoretical predictions, and the possible reasons are discussed. It provides the reader with a roadmap for choosing the most appropriate waveguide type and material choice between LN and KTP for desired performance of targeted applications.

Up-conversion of 2.4 µm pulses to 737 µm was performed which allowed for range determination measurements with conventional Si-based detectors. Temporal resolution of 42 ps was achieved, allowing distinguishability between targets separated by few millimeters.