Chip level fiber coupling

Abstract

For miniaturized optical fiber coupled MOEMS systems, fiber coupling on chip level is necessary. Therefore a silicon chip based optical fiber coupling with high position accuracy is introduced. In this paper, we present the fiber chip coupling on two examples: A superconducting single photon detector (SSPD) and a miniaturized fiber Bragg grating sensor. In case of the SSPD position accuracy between SSPD and optical fiber of ± 1 μm is necessary. In this paper we show the developed alignment system and the proof of the position accuracy on silicon test chips. Further, we show first experiments of a fiber coupled superconducting test structure in a closed cycle cryostat with regard to stability of the chip stack and thermal connectivity to the cryostat. The fiber coupling of the fiber Bragg grating sensor is used to miniaturize the sensor overall construction. The fiber Bragg sensor consists of two stacked Silicon photodiodes. The top photodiode is fabricated in a cavity within a remaining 50 μm Silicon membrane and therefore detects only the shorter wavelength range. The bottom photodiode detects the transmitted longer wavelengths. The fiber coupling chip is mounted on top of the photodiode stack. This leads to a compact chip stack with included fiber coupling, without the need for large fiber connectors or ferrule holders. Further, we demonstrate the mounting of the fiber Bragg sensor on a flexible PCB and its performance.