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We propose and demonstrate an ultra-low-power 3×3 unitary matrix multiplier with MEMS-based tunable couplers and phase shifters. The static power consumption and tuning energy per tuning element are less than 0.13 µW and 115 pJ, respectively.

Although hexagonal boron nitride (BN) nanostructures have recently received significant attention due to their unique physical and chemical properties, their applications have been limited by a lack of processability and poor film quality. In this study, a versatile method to transfer-print high-quality BN films composed of densely stacked BN nanosheets based on a desolvation-induced adhesion switching (DIAS) mechanism is developed. It is shown that edge functionalization of BN sheets and rational selection of membrane surface energy combined with systematic control of solvation and desolvation status enable extensive tunability of interfacial interactions at BN-BN, BN-membrane, and BN-substrate boundaries. Therefore, without incorporating any additives in the BN film and applying any surface treatment on target substrates, DIAS achieves a near 100% transfer yield of pure BN films on diverse substrates, including substrates containing significant surface irregularities. The printed BNs demonstrate high optical transparency (>90%) and excellent thermal conductivity (>167 W m-1 K-1) for few-micrometer-thick films due to their dense and well-ordered microstructures. In addition to outstanding heat dissipation capability, substantial optical enhancement effects are confirmed for light-emitting, photoluminescent, and photovoltaic devices, demonstrating their remarkable promise for next-generation optoelectronic device platforms.

Two-dimensional materials such as hexagonal boron nitride (h-BN), graphene, and transition metal dichalcogenides have drawn great attention in various fields of photonics and electronics. Among them, h-BN has recently emerged as a promising material platform to study integrated quantum photonics due to its ultrabright quantum light emission capabilities. However, the fundamental optical properties of h-BN have not yet been investigated in the visible and near-infrared (NIR) spectrum thoroughly. In this Letter, we report the refractive indices of h-BN thin films in the visible to NIR range. To the best of our knowledge, this is the first experimental observation of h-BN birefringence. Accurate parameters of refractive indices enable more precise design of h-BN-based photonic devices in the integrated photonics platforms.

Achieving perfect light absorption at a subwavelength-scale thickness has various advantageous in terms of cost, flexibility, weight, and performance for many different applications. However, obtaining perfect absorbers covering a wide range of wavelengths regardless of incident angle and input polarization without a complicated patterning process while maintaining a small thickness remains a challenge. In this paper, we demonstrate flat, lithography-free, ultrahigh omnidirectional, polarization-independent, broadband absorbers through effective dispersion engineering. The proposed absorbers show day-integrated solar energy absorption up to 96%, which is 32% better than with lossy semiconductor/metal absorbers. The proposed simple yet effective method can be applied to light absorption thin film structures based on various types of highly lossy semiconductor materials, including emerging 2D materials.

Hexagonal boron nitride (hBN) has drawn great attention for its versatile applications in electronics and photonics, and precise estimation of its thickness is critical in many situations. We propose a rapid and broad range (10–500 nm) in situ thickness estimation method for transparent hBN and SiO2 layers on the Si substrate using Raman peak intensity ratios at two wavenumbers and optical microscopy image analysis. We theoretically and experimentally demonstrate our method for a wide range of hBN layer thicknesses, and the estimated results show excellent agreement with the measured results with a percentile estimation error of 2.5%.