We experimentally demonstrated a stimulated Brillouin laser with hybrid modes, utilizing two coupled silica microtoroid cavities. The first cavity consists of paired modes with a frequency difference close, but not exactly equal, to its Brillouin frequency shift. The second cavity has a resonant mode that is close to one of the modes of the first cavity. The strong coupling between the two similar frequency modes induces mode splitting, resulting in the generation of a hybrid paired mode. This hybrid mode comprises one eigenmode from the first cavity and the super-modes of the coupled microtoroids. By finely tuning the coupling strength to match the frequency difference between the paired modes and the Brillouin shift, we achieve Brillouin lasing. Furthermore, the offset of the frequency shifting in the hybrid modes configuration is much smaller than the Brillouin frequency shift, significantly reducing coupling loss and enabling the realization of a lowthreshold Brillouin laser. We experimentally observed a lasing threshold as low as 0.45 mW, which is two orders of magnitude lower than that of the direct super-modes frequency matching method. This novel approach relaxes the strict requirement of exact frequency matching conditions for Brillouin lasing, making it an excellent platform for compact and ultra-low threshold Brillouin lasers.
The ability to manipulate light propagation is crucial for the development of optical communication and information processing systems. Photonic integrated circuits have gained significant attention due to their ability to integrate a large volume of components and operate at high speeds, making them ideal for handling the increasing data capacity and rate. In this study, we proposed and experimentally demonstrated a novel method for beam steering using waveguide arrays with specific distributed spacing profiles. By analyzing the diffraction and coherence properties, we discovered that a single waveguide array can perform imaging and phase transformation functions, which are typically achieved using optical lenses. To further enhance this capability, we fabricated corresponding devices on a silicon nitride waveguide platform and investigated the light propagation process through the arrayed waveguide. We successfully achieved various forms of beam steering, including focusing, expansion, and collimation. This beam control method holds great potential for on-chip optical routing, ranging, sensing, and other applications. It offers high integration density and scalability, making it a promising solution for the development of advanced optical systems.
Optical coupling between fibers and on-chip waveguides is a critical step in photonic testing and packaging. We demonstrated broadband surface-normal fiber-to-chip optical coupling based on free-form micro-optical reflector arrays integrated with foundry-processed SiN photonics. The couplers yield a low fiber-to-waveguide coupling loss of 0.5 dB at 1550 nm wavelength, and an exceptionally broad 1-dB bandwidth encompassing O to L bands (1260 nm to 1640 nm), only limited by the wavelength range of our testing setup. In-plane 1-dB alignment tolerances up to ± 2.4 µm and an out-of-plane 1-dB alignment tolerance up to 20 µm were obtained at 1550 nm. We further show that the Optical Free-Form Couplers for High-density Integrated Photonics (OFFCHIP) platform is universally applicable for chip-to-chip, waveguide to free space, and waveguide to surface-normal device coupling, qualifying it as a universal high-performance optical coupling interface for diverse use scenarios.
We introduce a new class of on-chip optical tweezers with high trapping efficiency, compact footprint, and broadband operation by integrating free-form micro-reflectors and micro-lenses to the facets of waveguides to generate the strong three-dimensional optical field gradient for optical trapping. We demonstrate the design, fabrication, and measurement of both reflective and refractive micro-optical tweezers. The reflective tweezers feature a remarkably small trapping threshold power, and the refractive tweezers are handy for multi-particle trapping and inter-particle interaction analysis. This new class of tweezers is promising for on-chip sensing, cell assembly, particle dynamics analysis, and ion trapping.
We reported a simple, robust, and highly sensitive temperature sensor using intrinsic Mach-Zehnder interferometer formed by means of bending a tapered microfiber, embedded in polydimethylsiloxane. The outer temperature perturbations modulate the refractive index of the polymer through thermo-optic and thermal expansion effects of the polymer. This leads to a phase difference between interfering guided modes through the bent-microfiber, which ultimately results prominent wavelength shift in the transmission spectrum. The sensor exhibits a linear temperature response with a sensitivity as high as -6.25nm/°C over the temperature range from 24° to 40 °C. The sensitivity of the sensor increases as wavelength increases.
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