The outstanding development of photonic technologies occurred in recent decades has allowed their implementation with great success in a wide variety of areas such as high-speed communications, sensors, high-precision medicine tools, scientific instrumentation, space technologies, etc. Driven by this trend, the Global Photonics Market was valued at USD 722.31 billion in 2021, and it is expected to reach USD 1089.00 billion by 2027^[1]. However, in order to further push forward photonic technologies, two fundamental aspects need to be addressed. On the one hand, to create manufacturing processes for the fabrication at sub-micrometric scales that are cost-efficient and provide reproducible results at industrial level to evolve photonic and nanophotonic technologies in the same way that the integrated circuit evolved electronics in the second half of the 20th century. On the other hand, the design and functional demonstration of a family of versatile and robust photonic devices able to work under harsh environmental conditions (extreme temperatures, pressure, salinity, radiation, vacuum, etc.) to address the requirements of the most demanding applications. 

Funded by the Marie Skłodowska-Curie Actions programme, the GRAIL Project focuses on the study, application and improvement of a novel 3D nanolithography fabrication technique for the development of fully monolithic and crystalline photonic elements (e.g., waveguides, diffraction gratings, etc) and devices (e.g., full laser cavity), emphasizing on miniaturization, reproducibility and capabilities to bring the technique to high levels of integration and mass production.

[1] PHOTONICS MARKET – GROWTH, TRENDS, COVID-19 IMPACT, AND FORECASTS (2022 – 2027), Mordor Intelligence Inc.

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Project overview

The GRAIL project is divided in 2 main phases. The first year is dedicated to the implementation and optimization of a 3DNanoWrite fabrication system oriented to the production of Photonic Crystal Waveguides (PCWs), with the goal of optimizing their optical guiding properties in terms of beam quality, propagation losses and in/out-coupling properties. During the second year, the focus will be on the design and fabrication of a Single-Frequency Laser (SFL) as a cutting-edge demonstrator of the fabrication technique capabilities, as well as a new class of monolithic and fully crystalline photonic system: A Single-Frequency Photonic-Crystal Lasers (SF-PCL). Besides the technological development and prototyping, a collaboration with LightFab GmbH has been stablished to perform fabrication tests under industrial environment, using state-of-the-art commercial production facilities.

The research methodology around the GRAIL’s objectives is carries out as follows:

OBJECTIVE 1.- Demonstration of Single-Mode Photonic-Crystal Waveguides (PCWs)

1.- A new experimental 3DNanoWrite setup will be setup and optimized to enable effective, controllable and reproducible 3D nanolithography of crystalline samples. Thus setup is mainly composed of fs-lasers, multi-axes computerized and programmable platforms and other subsystems such as energy tuning, monitoring, pulse train configuration (pulse picking) stages, etc.

2.- Design and fabrication of PCWs in Er:YAG crystals. YAG has been chosen as crystalline medium for prototyping given its wide popularity in photonic applications and its excellent properties at high temperatures, which makes it a suitable material for harsh-environment operation. The active dopant Er (erbium) enables emission at ~1.6 micrometers, which is a common wavelength for many applications (sensing, telco, etc). Furthermore, high-temperature and high pressure resistance experiments will be conducted. The goal at this stage is to exploit a truly exceptional property of PCFs: their unique capability to be endlessly single-mode. Numerical simulations and experimental studies are planned to optimize different PCWs so that all support a single transversal propagating mode (i.e. optimum beam quality) as well as to minimize in/out-coupling and transmission losses

3.- Two different strategies are planned for the PCWs fabrication: (1) employing a fixed pulse repetition rates from ~kHz to 2 MHz, and (2) applying a burst-mode pattern where a high repetition rate (up to 80MHz) is used over the duration of a limited number of pulses

OBJECTIVE 2.- Demonstration of Single-Frequency laser action in PCW Lasers (SF-PCLs)

1.- The PCW design with better properties in terms of losses and mode area will be selected as well as the optimal laser fabrication conditions found in Phase 1. Since the SF-PCL is meant to demonstrate a full-system monolithic in a single crystal, no extra materials such as external cavity mirrors can be used. Therefore, this second phase attempts to benefit from a concept taken from telecom semiconductor lasers: The integration of Distributed FeedBack (DFB) grating directly fabricated into the PCWs. To achieve SF operation, the fabrication process has to reach the ~10nm resolution in a controllable manner to allow the engineering dispersion curves by tuning the fabricated structures parameters (e.g. pore widths, spacing, core area, etc).

2.- Once the DFB gratings are monolithically incorporated to the PCW, lasing properties of the PCL will be tested (output power and spectrum, optical efficiency and beam quality) at room conditions as well as at high temperature and pressure.