Two dimensional gradient-index beam shapers fabricated using ultrafast laser inscription.

In this paper gradient-index beam shapers are fabricated using the ultrafast laser inscription method. This method enables the fabrication of two-dimensional refractive index profiles inside silica glass, resulting in highly robust and compact beam shapers. The magnitude of this refractive index change can be tailored by adjusting the laser pulse energy, enabling arbitrary two-dimensional refractive index profiles to be manufactured.

Quantitative morphology of femtosecond laser-written point-by-point optical fiber Bragg gratings.

We investigate the morphology of femtosecond laser, single pulse-inscribed, point-by-point (PbP) fiber Bragg gratings. Direct measurement of a PbP grating's refractive index profile was carried out with micro-reflectivity analysis. PbP gratings were imaged at sub-micrometer scale with scanning electron microscopy, Raman and photoluminescence studies were performed to probe the structural and electronic changes.

Achromatic photonic tricouplers for application in nulling interferometry.

Integrated-optic components are being increasingly used in astrophysics, mainly where accuracy and precision are paramount. One such emerging technology is nulling interferometry that targets high contrast and high angular resolution. Two of the most critical limitations encountered by nullers are rapid phase fluctuations in the incoming light causing instability in the interference and chromaticity of the directional couplers that prevent a deep broadband interferometric null.

Building hybridized 28-baseline pupil-remapping photonic interferometers for future high-resolution imaging.

One key advantage of single-mode photonic technologies for interferometric use is their ability to easily scale to an ever-increasing number of inputs without a major increase in the overall device size, compared to traditional bulk optics. This is particularly important for the upcoming extremely large telescope (ELT) generation of telescopes currently under construction. We demonstrate the fabrication and characterization of a hybridized photonic interferometer, with eight simultaneous inputs, forming 28 baselines, which is the largest amount to date, to the best of our knowledge.

Scalable photonic-based nulling interferometry with the dispersed multi-baseline GLINT instrument.

Characterisation of exoplanets is key to understanding their formation, composition and potential for life. Nulling interferometry, combined with extreme adaptive optics, is among the most promising techniques to advance this goal. We present an integrated-optic nuller whose design is directly scalable to future science-ready interferometric nullers: the Guided-Light Interferometric Nulling Technology, deployed at the Subaru Telescope.

Record-high positive refractive index change in bismuth germanate crystals through ultrafast laser enhanced polarizability.

Unlike other crystals, the counter intuitive response of bismuth germanate crystals ([Formula: see text], BGO) to form localized high refractive index contrast waveguides upon ultrafast laser irradiation is explained for the first time. While the waveguide formation is a result of a stoichiometric reorganization of germanium and oxygen, the origin of positive index stems from the formation of highly polarisable non-bridging oxygen complexes. Micro-reflectivity measurements revealed a record-high positive refractive index contrast of [Formula: see text].

Channel Waveguides in Lithium Niobate and Lithium Tantalate.

Low-loss photonic waveguides in lithium niobate offer versatile functionality as nonlinear frequency converters, switches, and modulators for integrated optics. Combining the flexibility of laser processing with liquid phase epitaxy we have fabricated and characterized lithium niobate channel waveguides on lithium niobate and lithium tantalate. We used liquid phase epitaxy with KO flux on laser-machined lithium niobate and lithium tantalate substrates.

Boson band mapping: revealing ultrafast laser induced structural modifications in chalcogenide glass.

The formation of femtosecond laser direct-written waveguides in gallium lanthanum sulfide (GLS) chalcogenide glass with a peak index contrast of =0.023 and an average positive refractive index change of =0.0049 is explained for the first time, to the best of our knowledge.

Revisiting ultrafast laser inscribed waveguide formation in commercial alkali-free borosilicate glasses.

Alkali-free borosilicate glasses are one of the most used dielectric platforms for ultrafast laser inscribed integrated photonics. Femtosecond laser written waveguides in commercial Corning Eagle 2000, Corning Eagle XG and Schott AF32 glasses were analyzed. They were studied in depth to disclose the dynamics of waveguide formation.

Towards a photonic mid-infrared nulling interferometer in chalcogenide glass.

Nulling interferometry enables astronomers to advance beyond the resolving power of ground-based telescopes with the goal of directly detecting exo-planets. By diminishing the overwhelming emission of the host star through destructive interference, radiation from young companions can be observed. The atmospheric transmission window centered around 4 μm wavelength is of particular interest because it has a favorable contrast between star and planet as well as a reduced atmospheric disturbance.

Beam shaping of a broad-area laser diode using 3D integrated optics.

Typical high power broad-area semiconductor lasers exhibit a highly astigmatic beam profile. However, many applications require a homogenous and circular symmetric beam. Thus coupling into circular multimode optical fibers is often employed.

Digital waveguide adiabatic passage part 2: experiment.

Using a femtosecond laser writing technique, we fabricate and characterise three-waveguide digital adiabatic passage devices, with the central waveguide digitised into five discrete waveguidelets. Strongly asymmetric behaviour was observed, devices operated with high fidelity in the counter-intuitive scheme while strongly suppressing transmission in the intuitive. The low differential loss of the digital adiabatic passage designs potentially offers additional functionality for adiabatic passage based devices.

Compact integrated actively Q-switched waveguide laser.

A miniaturized deformed helix ferroelectric liquid crystal transducer cell was used in combination with a femtosecond laser inscribed active waveguide to realize a compact actively Q-switched laser source. The liquid crystal cell was controlled by a low-voltage frequency generator and laser pulse durations below 40 ns were demonstrated at repetition rates ranging from 0.1 kHz to 20 kHz and a maximum slope efficiency of up to 22%.

Ultrafast laser inscription in ZBLAN integrated optics chips for mid-IR beam combination in astronomical interferometry.

Astronomical interferometry is a unique technique that allows observation with angular resolutions on the milliarcsec scale by combining the light of several apertures hundreds of meters apart. The PIONIER and GRAVITY instruments at the Very Large Telescope Interferometer have demonstrated that silica-based integrated optics (IO) provide a small-scale and highly stable solution for the interferometric beam combination process. Yet, important science cases such as exoplanet hunting or the spectroscopic characterization of exoplanetary atmospheres are favorable for observation in the mid-IR, namely the atmospheric windows L and L' band (3-4 µm), a wavelength range that is not covered by conventional silica-based IO.

Monolithic mode-selective few-mode multicore fiber multiplexers.

With the capacity limits of standard single-mode optical fiber fast approaching, new technologies such as space-division multiplexing are required to avoid an Internet capacity crunch. Few-mode multicore fiber (FM-MCF) could allow for a two orders of magnitude increase in capacity by using the individual spatial modes in the different cores as unique data channels. We report the realization of a monolithic mode-selective few-mode multicore fiber multiplexer capable of addressing the individual modes of such a fiber.

2 W single-longitudinal-mode Yb:YAG distributed-feedback waveguide laser.

Single longitudinal mode (SLM) lasers are important tools for many scientific and commercial applications. SLM operation can be achieved in distributed-feedback (DFB) lasers based on Bragg structures. Semiconductor waveguide DFB lasers are well-established devices, but their output power is limited to a few hundred milliwatts.

On-chip generation of heralded photon-number states.

Beyond the use of genuine monolithic integrated optical platforms, we report here a hybrid strategy enabling on-chip generation of configurable heralded two-photon states. More specifically, we combine two different fabrication techniques, i.e.

Engineering integrated photonics for heralded quantum gates.

Scaling up linear-optics quantum computing will require multi-photon gates which are compact, phase-stable, exhibit excellent quantum interference, and have success heralded by the detection of ancillary photons. We investigate the design, fabrication and characterisation of the optimal known gate scheme which meets these requirements: the Knill controlled-Z gate, implemented in integrated laser-written waveguide arrays. We show device performance to be less sensitive to phase variations in the circuit than to small deviations in the coupler reflectivity, which are expected given the tolerance values of the fabrication method.

Direct infrared femtosecond laser inscription of chirped fiber Bragg gratings.

We compare and contrast novel techniques for the fabrication of chirped broadband fiber Bragg gratings by ultrafast laser inscription. These methods enable the inscription of gratings with flexible period profiles and thus tailored reflection and dispersion characteristics in non-photosensitive optical fibers. Up to 19.

Influence of photo-inscription conditions on the radiation-response of fiber Bragg gratings.

We compared the sensitivity to X-rays of several fiber Bragg gratings (FBGs) written in the standard telecommunication fiber Corning SMF28 with different techniques. Standard gratings were manufactured with phase-mask and UV lasers, continuum wave (cw) at 244 nm or pulsed in the nanosecond domain at 248 nm, in a pre-hydrogenated fiber. Others gratings were written by exposures to a femtosecond IR-laser (800 nm), with both phase-mask and point by point techniques.

Tunable quantum interference in a 3D integrated circuit.

Integrated photonics promises solutions to questions of stability, complexity, and size in quantum optics. Advances in tunable and non-planar integrated platforms, such as laser-inscribed photonics, continue to bring the realisation of quantum advantages in computation and metrology ever closer, perhaps most easily seen in multi-path interferometry. Here we demonstrate control of two-photon interference in a chip-scale 3D multi-path interferometer, showing a reduced periodicity and enhanced visibility compared to single photon measurements.

Low loss mid-infrared ZBLAN waveguides for future astronomical applications.

Photonic technologies will be at the heart of future terrestrial planet hunting interferometers. In particular the mid-infrared spectral region between 3.5 - 4.

On the use of the Type I and II scheme for classifying ultrafast laser direct-write photonics.

The use of the Type I and Type II scheme, first introduced and used by fiber Bragg grating researchers, has recently been adopted by the ultrafast laser direct-write photonics community to classify the physical geometry of waveguides written into glasses and crystals. This has created confusion between the fiber Bragg grating and direct-write photonics community. Here we propose a return to the original basis of the classification based on the characteristics of the material modification rather than the physical geometry of the waveguide.

Femtosecond direct-written integrated mode couplers.

We report the design and fabrication of three-dimensional integrated mode couplers operating in the C-band. These mode-selective couplers were inscribed into a boro-aluminosilicate photonic chip using the femtosecond laser direct-write technique. Horizontally and vertically written two-core couplers are shown to allow for the multiplexing of the LP11a and LP11b spatial modes of an optical fiber, respectively, with excellent mode extinction ratios (25-37 + dB) and low loss (~1 dB) between 1500 and 1580 nm.