Inverse-designed silicon nitride reflectors.

Reflectors play a pivotal role in silicon photonics since they are used in a wide range of applications, including attenuators, filters, and lasers. This Letter presents six silicon nitride reflectors implemented using the inverse design technique. They vary in footprint, ranging from 4 µm × 3 µm to 4 µm × 8 µm. The smaller device has an average simulated reflectivity of -1.5 dB, whereas the larger one exhibits an average reflectivity of -0.09 dB within the 1530 to 1625 nm range. The latter also presents a 1-dB bandwidth of 172 nm, spanning from 1508 to 1680 nm. Despite their resemblance to circular gratings, these devices are more intricate and compact, particularly due to their non-intuitive features near the input waveguide, which include rough holes and teeth. The roughness of these features significantly contributes to the performance of the devices. The reflectors were fabricated on a silicon nitride multi-project wafer (MPW) through a streamlined process involving only a single etching step. The 4 µm × 8 µm reflector demonstrates a remarkably high reflectivity of -0.26±0.11 dB across the 1530 to 1600 nm range, rendering it suitable for high-quality factor cavities with direct applications in lasers and optical communications.

Design of a silicon Mach-Zehnder modulator via deep learning and evolutionary algorithms.

As an essential block in optical communication systems, silicon (Si) Mach-Zehnder modulators (MZMs) are approaching the limits of possible performance for high-speed applications. However, due to a large number of design parameters and the complex simulation of these devices, achieving high-performance configuration employing conventional optimization methods result in prohibitively long times and use of resources. Here, we propose a design methodology based on artificial neural networks and heuristic optimization that significantly reduces the complexity of the optimization process. First, we implemented a deep neural network model to substitute the 3D electromagnetic simulation of a Si-based MZM, whereas subsequently, this model is used to estimate the figure of merit within the heuristic optimizer, which, in our case, is the differential evolution algorithm. By applying this method to CMOS-compatible MZMs, we find new optimized configurations in terms of electro-optical bandwidth, insertion loss, and half-wave voltage. In particular, we achieve configurations of MZMs with a [Formula: see text] bandwidth and a driving voltage of [Formula: see text], or, alternatively, [Formula: see text] with a driving voltage of [Formula: see text]. Furthermore, the faster simulation allowed optimizing MZM subject to different constraints, which permits us to explore the possible performance boundary of this type of MZMs.

Two-axis MEMS positioner for waveguide alignment in silicon nitride photonic integrated circuits.

Alignment is critical for efficient integration of photonic integrated circuits (PICs), and microelectromechanical systems (MEMS) actuators have shown potential to tackle this issue. In this work, we report MEMS positioning actuators designed with the ultimate goal of aligning silicon nitride (SiN) waveguides either to different outputs within a SiN chip or to active chips, such as lasers and semiconductor optical amplifiers. For the proof-of-concept, suspended SiN waveguides implemented on a silicon-on-insulator wafer were displaced horizontally in the direction of light propagation to close an initial gap of 6.92 µm and couple the light to fixed output waveguides located on a static section of the chip. With the gap closed, the suspended waveguides showed ∼ 345 nm out-of-plane misalignment with respect to the fixed waveguides. The suspended waveguides can be displaced laterally by more than ±2 µm. When the waveguides are aligned and the gap closed, an average loss of -1.6 ± 0.06 dB was achieved, whereas when the gap is closed with a ± 2 µm lateral displacement, a maximum average loss of ∼ -19.00 ± 0.62 dB was obtained. The performance of this positioner does not only pave the way for active chip alignment, but it could also be considered for optical switching applications.

Design of a compact CMOS-compatible photonic antenna by topological optimization.

Photonic antennas are critical in applications such as spectroscopy, photovoltaics, optical communications, holography, and sensors. In most of those applications, metallic antennas have been employed due to their reduced sizes. Nevertheless, compact metallic antennas suffer from high dissipative loss, wavelength-dependent radiation pattern, and they are difficult to integrate with CMOS technology. All-dielectric antennas have been proposed to overcome those disadvantages because, in contrast to metallic ones, they are CMOS-compatible, easier to integrate with typical silicon waveguides, and they generally present a broader wavelength range of operation. These advantages are achieved, however, at the expense of larger footprints that prevent dense integration and their use in massive phased arrays. In order to overcome this drawback, we employ topological optimization to design an all-dielectric compact antenna with vertical emission over a broad wavelength range. The fabricated device has a footprint of 1.78 µm × 1.78 µm and shows a shift in the direction of its main radiation lobe of only 4° over wavelengths ranging from 1470 nm to 1550 nm and a coupling efficiency bandwidth broader than 150 nm.

Characterization of surface-states in a hollow core photonic crystal fiber.

Surface or edge states represent an important class of modes in various photonic crystal systems such as in dielectric topological insulators and in photonic crystal fibers. In the later, strong attenuation peaks in the transmission spectrum are attributed to coupling between surface and core-guided modes. Here, we explore a modified implementation of the spatial and spectral interference method to experimentally characterize surface modes in photonic crystal fibers. Using an external reference and a non-uniform Fourier transform windowing, the obtained spectrogram allows clear observation of anti-crossing behavior at wavelengths in which surface and core modes are strongly coupled. We also detect surface modes with different spatial symmetries, and give insight into mode families couple to the fundamental or high-order core modes, as well as the existence of uncoupled surface modes.

Side-lobe level reduction in bio-inspired optical phased-array antennas.

Phased arrays are expected to play a critical role in visible and infrared wireless systems. Their improved performance compared to single element antennas finds uses in communications, imaging, and sensing. However, fabrication of photonic antennas and their feeding network require long element separation, leading to the appearance of secondary radiation lobes and, consequently, crosstalk and interference. In this work, we experimentally show that by arranging the elements according to the Fermat's spiral, the side lobe level (SLL) can be reduced. This reduction is proved in a CMOS-compatible 8-element array, revealing a SLL decrement of 0.9 dB. Arrays with larger numbers of elements and inter-element spacing are demonstrated through an spatial light modulator (SLM) and an SLL drop of 6.9 dB is measured for a 64-element array. The reduced SLL, consequently, makes the proposed approach a promising candidate for applications in which antenna gain, power loss, or information security are key requirements.