In this paper we show a novel design of high Q‐factor silicon nitride (SiN) 1D photonic crystal (PhC) cavities side‐coupled to curved waveguides, operating with both silica and air cladding. The engineering of the etched 1D PhC cavity sidewalls angle allows for high Q‐factors over a wide range of upper cladding compositions, and the achievement of the highest calculated Q‐factor for non‐suspended asymmetric SiN PhC structures. We show the employment of these type of SiN PhC cavities in hybrid external cavity laser (HECL) configuration, with mode‐hop free single mode laser operation over a broad range of injected currents (from 25 mA to 65 mA), milliwatts of power output (up to 9 mW) and side‐mode suppression ratios in the range of 40 dB. We demonstrate the operation of these devices as compact and energy efficient optical sensors that respond to refractive index changes in the surrounding medium the measurement of sodium chloride (from 0% to 25%) and sucrose (from 0% to 25%) in aqueous solution. In HECL configuration, the RI sensor exhibits a 2 orders of magnitude improvement in detection limit compared to the passive microcavity. We also discuss the possibility for applying these devices as novel transducers for refractive index changes that are induced by analyte specific absorption of infrared radiation by the target analytes present in gas or liquid phase.

Single-photon sources are important for integrated photonics and quantum technologies, and can be used in quantum key distribution, quantum computing, and sensing. Color centers in the solid state are a promising candidate for the development of the next generation of single-photon sources integrated in quantum photonics devices. They are point defects in a crystal lattice that absorb and emit light at given wavelengths and can emit single photons with high efficiency. The landscape of color centers has changed abruptly in recent years, with the identification of a wider set of color centers and the emergence of new solid-state platforms for room-temperature single-photon generation. This review discusses the emerging material platforms hosting single-photon-emitting color centers, with an emphasis on their potential for the development of integrated optical circuits for quantum photonics.

In this paper, we show the experimental results of a thermally stable ${\mathrm{Si}}_3{\mathrm{N}}_4$ external cavity (SiN EC) laser with high power output and the lowest SiN EC laser threshold to our knowledge. The device consists of a 250 μm sized reflective semiconductor optical amplifier butt-coupled to a passive chip based on a series of ${\mathrm{Si}}_3{\mathrm{N}}_4$ Bragg gratings acting as narrow reflectors. A threshold of 12 mA has been achieved, with a typical side-mode suppression ratio of 45 dB and measured power output higher than 3 mW. Furthermore, we achieved a mode-hop free-lasing regime in the range of 15–62 mA and wavelength thermal stability up to 80°C. This solves the challenges related to cavity resonances’ thermal shift and shows the possibility for this device to be integrated in dense wavelength-division multiplexing (WDM) and heat-intensive optical interconnects technologies.

Controlling the optical response of a medium through suitably tuned coherent electromagnetic fields is highly relevant in a number of potential applications, from all-optical modulators to optical storage devices. In particular, electromagnetically induced transparency (EIT) is an established phenomenon in which destructive quantum interference creates a transparency window over a narrow spectral range around an absorption line, which, in turn, allows to slow and ultimately stop light due to the anomalous refractive index dispersion. Here we report on the observation of a new form of both induced transparency and amplification of a weak probe beam in a strongly driven silicon photonic crystal resonator at room temperature. The effect is based on the oscillating temperature field induced in a nonlinear optical cavity, and it reproduces many of the key features of EIT while being independent of either atomic or mechanical resonances. Such thermo-optically induced transparency will allow a versatile implementation of EIT-analogs in an integrated photonic platform, at almost arbitrary wavelength of interest, room temperature and in a practical, low cost, and scalable system.

Laser‐based mid‐infrared (mid‐IR) photothermal spectroscopy (PTS) represents a selective, fast, and sensitive analytical technique. Recent developments in laser design permits the coverage of wider spectral regions in combination with higher power, enabling for qualitative reconstruction of broadband absorption features, typical of liquid or solid samples. In this work, we use an external cavity quantum cascade laser (EC‐QCL) that emits in pulsed mode in the region between 5.7 and 6.4 µm (1770–1560 cm ⁻¹ ), to measure the absorption spectrum of a thin film of polymethyl methacrylate (PMMA) spin‐coated on top of a silicon nitride (Si ₃ N ₄ ) micro‐ring resonator (MRR). Being the PTS signal inversely proportional to the volume of interaction, in the classical probe–pump dual beam detection scheme, we exploit a Si ₃ N ₄ transducer coated with PMMA, as a proof‐of‐principle for an on‐chip photothermal sensor. By tuning the probe laser at the inflection point of one resonance, aiming for highest sensitivity, we align the mid‐IR beam on top of the ring’s area, in a transversal configuration. To maximize the amplitude of the photoinduced thermal change, we focus the mid‐IR light on top of the ring using a Cassegrain reflector enabling for an optimal match between ring size and beam waist of the excitation source. We briefly describe the transducer design and fabrication process, present the experimental setup, and perform an analysis for optimal operational parameters. We comment on the obtained results showing that PTS allows for miniaturized robust sensors opening the path for on‐line/in‐line monitoring in several industrial processes.

O-band InP etched facets lasers were heterogeneously integrated by micro-transfer-printing into a 1.54 μm deep recess created in the 3 μm thick oxide layer of a 220 nm SOI wafer. A 7 × 1.5 μm ² cross-section, 2 mm long multimode polymer waveguide was aligned to the ridge post-integration by e-beam lithography with <; 0.7 μm lateral misalignment and incorporated a tapered silicon waveguide. A 170 nm thick metal layer positioned at the bottom of the recess adjusts the vertical alignment of the laser and serves as a thermal via to sink the heat to the Si substrate. This strategy shows a roadmap for active polymer waveguide-based photonic integrated circuits.