Integrated packaging of 2D MOEMS mirrors with optical position feedback

Abstract

Many applications of MOEMS microscanners rely on accurate position feedback. For MOEMS devices which do not have intrinsic on-chip feedback, position information can be provided with optical methods, most simply by using a reflection from the backside of a MOEMS scanner. By measuring the intensity distribution of the reflected beam across a quadrant diode, one can precisely detect the mirror's deflection angles. Previously, we have presented a position sensing device, applicable to arbitrary trajectories, which is based on the measurement of the position of the reflected laser beam with a quadrant diode. In this work, we present a novel setup, which comprises the optical position feedback functionality integrated into the device package itself. The new device's System-in-Package (SiP) design is based on a flip-folded 2.5D PCB layout and fully assembled as small as 9.2×7×4 mm³ in total. The device consists of four layers, which supply the MOEMS mirror, a spacer to provide the required optical path length, the quadrant photo-diode and a laser diode to serve as the light source. In addition to describing the mechanical setup of the novel device, we will present first experimental results and optical simulation studies. Accurate position feedback is the basis for closed-loop control of the MOEMS devices, which is crucial for some applications as image projection for example. Position feedback and the possibility of closed-loop control will significantly improve the performance of these devices.

A position sensing method for 2D scanning mirrors

“…Various methods have been developed to measure the 2D rotation angle of 2D scanning micromirrors such as the capacitive sensing method [3], piezo-resistors based method [4], electromagnetic internal sensing method [5][6][7] and optical feedback method [8,9]. Capacitive sense method is mainly used for electrostatically driven micromirrors, in which the interference between the driving signal and the sensing signal is a serious challenge [3].…”

“…Moreover, this method requires extra space and separate path for the sensing coil [6]. The optical feedback method has the advantage of the angle measurement being independent of the driving mechanism since it either uses 2D PSD (position sensitive detector) with a laser beam positioned externally [11,12], or a quadrant photodiode at the backside of the 2D mirror plate [9]. Quadrant photodiodes are commonly used as tracking and centering devices, in order to be used as a position sensor, its transfer characteristics needs to be linearized [13].…”

“…Quadrant photodiodes are commonly used as tracking and centering devices, in order to be used as a position sensor, its transfer characteristics needs to be linearized [13]. Nonlinearity specially at high deflection angles is one of the main issues [9] which makes the calibration complicated. In one case, Baumgart et al [9] used a quadrant photodiode with a hole in the middle which is a rare type of quadrant photodiode to reduce the size of the device.…”

“…Nonlinearity specially at high deflection angles is one of the main issues [9] which makes the calibration complicated. In one case, Baumgart et al [9] used a quadrant photodiode with a hole in the middle which is a rare type of quadrant photodiode to reduce the size of the device. In another approach, Tortschanoff et al [14][15][16] used two cross orthogonal laser beams.…”