The field of mid-infrared fiber photonics has seen significant progress in recent years [1]. In virtually all molecules, transitions involving changes in both vibrational and rotational states can be excited by illumination with light at midinfrared wavelengths from ~ 2 – 15 Μm, giving rise to a plethora of application in environmental sensing, defense, and medicine, to only name a few. However, for most applications, compact and monolithic laser sources without bulky and sensitive free-space optical components are needed. While in-fiber components in mid-infrared compatible soft-glass fibers [2,3] as well as fiber endcaps [4] for long-term stable operation have both been demonstrated, little work to date has focused on the fabrication of fiber-pigtailed optical chips that could offer additional functionalities. The femtosecond laser direct-write technique is a highly versatile method that enables the inscription of tailored three-dimensional photonic circuits into bulk glasses [5]. Here we summaries our recent progress into the fabrication of linear and nonlinear waveguide chips for the realization of all fiber mid-infrared sources.
Ultrafast Laser Inscription enables the fabrication of arbitrary 3-dimensional optical waveguides in optical glass. The use of material science and glass chemistry has facilitated the creation of substrate materials with properties tailored to Ultrafast Laser Inscription to reach sub-decibel end-to-end insertion losses. Using these 3D waveguide circuits to interface with multicore, few-mode and few-mode multicore fibers has seen the demonstration of record-breaking data rates for space-division-multiplexed optical communication.
Ultrafast laser inscription is a technique to create low-loss three dimensional optical circuits within bulk dielectrics that is compatible with a wide range of optical materials. Its unique capabilities and the ability to rapid prototype and quickly iterate through different designs has made it exceptionally attractive for astrophotonics. This paper will summarize the basic aspects of ultrafast laser inscription and review recent progress in its application to astrophotonics, such as stellar interferometry.
A Dy3+-doped ZBLAN fiber amplifier based on an in-band pumped configuration is designed and optimized via an evolutionary approach. In the proposed model, the rate equations are coupled with the power propagation equations for the pump and signal beams. The complete amplifier model allows the definition of the fitness function to be optimized. Realistic values for optical and spectroscopic parameters are considered. For a fiber with dopant concentration of 2000 ppm, by employing an input pump power of 1 W at 2.72 μm wavelength, an optical gain of about 15.56 dB at 2.95 μm wavelength is obtained.
Diamond’s nitrogen-vacancy (NV) center has been shown as a promising candidate for sensing applications and quantum computing because of its long electron spin coherence time and its ability to be found, manipulated and read out optically. An integrated photonics platform in diamond would be useful for NV-based magnetometry and quantum computing, in which NV centers are optically linked for long-range quantum entanglement due to the integration and stability provided by monolithic optical waveguides. Surface microchannels in diamond would be a great benefit for sensing applications, where NV centers could be used to probe biomolecules.
In this work, we applied femtosecond laser writing to form buried 3D optical waveguides in diamond. By engineering the geometry of the type II waveguide, we obtained single mode guiding from visible to the infrared wavelengths. Further, we demonstrate the first Bragg waveguide in bulk diamond with narrowband reflection. We show the formation of single, high quality NV centers on demand in ultrapure diamond using a single pulse from a femtosecond laser. With these building blocks in place, we fabricated an integrated quantum photonic circuit containing optical waveguides coupled to NV centers deterministically placed within the waveguide. The single NVs were excited and their emission collected by the optical waveguides, allowing easy interfacing to standard optical fibers. We also report high aspect ratio surface microchannels, which we will integrate with laser-written NVs and waveguides, paving the way for ultrasensitive, nanoscale resolution biosensors.
Diamond’s nitrogen-vacancy (NV) centers show great promise in sensing applications and quantum computing due to their long electron spin coherence time and their ability to be located, manipulated and read out using light. The electrons of the NV center, largely localized at the vacancy site, combine to form a spin triplet, which can be polarized with 532- nm laser light, even at room temperature. The NV's states are isolated from environmental perturbations making their spin coherence comparable to trapped ions. An important breakthrough would be in connecting, using waveguides, multiple diamond NVs together optically. However, the inertness of diamond is a significant hurdle for the fabrication of integrated optics similar to those that revolutionized silicon photonics. In this work we show the possibility of buried waveguide fabrication in diamond, enabled by focused femtosecond high repetition rate laser pulses. We use μRaman spectroscopy to gain better insight into the structure and refractive index profile of the optical waveguides.
Strong ion migration in shown to enable the production of high refractive index contrast waveguides by fs-laser writing
in a commercial (Er,Yb)-doped phosphate based glass. Waveguide writing was performed using a high repetition rate fslaser
fibre amplifier operated at 500 kHz and the slit shaping technique. Based on measurements of the NA of
waveguides, the positive refractive index change (Δn) of the guiding region has been estimated to be ∼1-2 x10-2. The
compositional maps of the waveguides cross-sections performed by X-ray microanalysis evidenced a large increase of
the La local concentration in the guiding region up to ~25% (relative to the non-irradiated material). This large
enrichment in La was accompanied by the cross migration of K to a neighbouring low refractive index zone. The
refractive index of the La-phosphate glass increases linearly with the La2O3 content (Δn per mole fraction increase of
La2O3 ≈ 5x10-3) mainly because of the relative mass of the La3+ ions. The density increase without substantial
modification of the glass network was confirmed by space-resolved micro-Raman spectroscopy measurements showing
minor variations in the (PO2)sym vibration Raman band. These results provide evidence for the feasibility of adapting the glass composition for enabling laser-writing of high refractive index contrast structures via spatially selective
modification of the glass composition.
Glass and polymer interstacked superlattice like nanolayers were fabricated by nanosecond-pulsed laser deposition with a 193-nm-ultraviolet laser. The individual layer thickness of this highly transparent thin film could be scaled down to 2 nm, proving a near atomic scale deposition of complex multilayered optical and electronic materials. The layers were selectively doped with Er 3+ and Eu 3+ ions, making it optically active and targeted for integrated sensor application.
We present the fabrication and characterisation of Dy3+-doped tellurite glasses and waveguides for applications in the mid-IR. The low phonon energy and large rare-earth ion solubility of tellurite glasses, as well as having infrared transmission ranges up to <5 μm, make them promising candidates for new mid-IR solid-state laser host materials. This paper presents recent achievements in the fabrication of tellurite glasses, glass characterisation and rare-earth ion spectroscopy which is compared to other glass hosts relevant to the mid-IR such as fluoride glasses. When excited with an 808 nm laser diode source, Dy3+ doped tellurite bulk glasses exhibited very broad fluorescence from the 6H13/2 - 6H15/2 transition which extends from 3 μm to 3.6 μm FWHM compared to 2.9 μm to 3.1 μm in Dy3+ doped ZBLAN glass. This broad and red-shifted fluorescence band in tellurite glass may find use in LIDAR and sensing applications as it coincides with an atmospheric transmission band, compared to the ~3 μm emission of Dy3+ doped ZBLAN lasers which is
absorbed by atmospheric water.
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