Microlenses on photonic integrated circuits enable flexible packaging and optical isolator integration

This paper presents a versatile microlens integration platform designed to address key packaging challenges in photonic integrated circuits (PICs), particularly in enhancing coupling efficiency, increasing working distance, and enabling the hybrid integration of external optical components, such as isolators, which are difficult to integrate monolithically. We first describe multiple integration strategies for microlenses with PICs toward achieving relaxed alignment tolerances and extended working distances when interfacing with fiber arrays. To demonstrate the platform’s possibilities, we detail two specific use cases. The first involves a long working distance expanded beam interface for O-band datacom applications, where a microlensed PIC, paired with a microlensed connector, achieves a 3.8 mm working distance with a modest additional insertion loss of 0.85 dB per interface attributed to integration of the lenses. This configuration offers improved lateral and longitudinal alignment tolerances, making it well-suited for pluggable connector applications. The second use case demonstrates the integration of an optical isolator within the coupling interface of a C-band PIC, achieving an isolator insertion loss of 1.2 dB and a broad 1 dB bandwidth of 80 nm, with an extinction ratio of -20 dB at the target 1540 nm wavelength. Together, these use cases highlight the potential of microlens-based solutions to address PIC packaging requirements, offering enhanced tolerance management and enabling new possibilities for hybrid integration of complex optical functionalities.