Precision alignment and assembly of a Fourier transform microspectrometer

Abstract

Integrating optics with MEMS presents numerous challenges in assembly and joining of heterogeneous components, stringent alignment of parts, packaging of the device to protect it, etc. Microspectrometers are examples of MOEMS devices where these issues play a significant role to the performance of the device. The motivation behind miniaturization of the spectrometer is strong, because traditional spectrometers are table-top instruments, and they are generally too large, and too costly to be ported outside of lab environments. Micro-Electro-Mechanical-Systems (MEMS) technology combined with microassembly offers promising possibilities to achieve compact and cost-effective miniaturization in such instruments. In this paper, we present a fiber-coupled Fourier-Transform microspectrometer with a nominal size of 3cmx3cmx3cm, constructed using 3D hybrid microassembly and targeting wavelengths in the visible and NIR spectra. We use modular micro scale parts, including minimum energy compliant MEMS fasteners to configure a die-sized microoptical bench. Light coupling, miniature electronics and power are included in a spectrometer package. In order to achieve the required precision on the microoptical bench we employ automated assembly of microcomponents. We present a systematic two-step assembly & alignment scheme (coarse and fine) using an image-based spot Jacobian algorithm. In this paper we present details related to design, tolerance analysis, calibration, microassembly and visual servoing techniques as well as spectrum data recovery for a completed prototype.