Laser based displays have been under development over the last 50 years but commercial viability of the technology was limited mainly due to the large size and high cost of laser sources. The quest for miniaturization and higher efficiency realized with the development of directly modulatable laser sources and scanning mirrors based on micro electro mechanical systems (MEMS) technology. Integration of scanners and laser diodes provide a powerful combination for micro-display and imaging applications [1]. This is exemplified by the commercial applications such as laser printers, barcode readers, and by wearable micro-display systems.

A displayed image is formed pixel by pixel using a mirror producing angular motion that scans a modulated light beam on a screen as illustrated in Fig. 1a. In order to construct a two-dimensional (2-D) rectangular image, bidirectional writing with a high frequency resonant horizontal “fast axis” and a non-resonant linear ramp “slow axis” appeared as the preferred system architecture. The scan frequency and the 2-D scan angles must be high enough to handle the many millions of pixels per second. Hence, providing a fast and compact actuator to meet the actuation force requirements is a challenging task.

Figure 1. a) Schematic of a flying spot laser display engine with two mirrors. b) FEM model of rotary stage with a mounted mirror. c) FEM model of PZT torsional scanner.

We developed MEMS scanners to be used in both fast and slow axis directions for laser display applications. Comb actuated rotary stage is modeled, fabricated, and characterized to provide linear ramp scan for the slow axis of two-mirror display engine. In this work, a novel spring design for comb-actuated linear in-plane rotary MEMS scanner is presented. Over 98% linear motion up to 28 deg. optical scan angle is achievable with the new suspension design [2].

Moreover, a high frequency resonant torsional micro-scanner actuated with thin film PZT is modeled, fabricated, and characterized to be used as the fast axis scan. Sinusoidal actuation with 24V at a mechanical resonance frequency of 39870 Hz provides a total optical scan angle of 38.5 deg. for the 1.4 mm wide mirror [3,5]. It has the highest performance specifications in literature and also provides significant power and size advantages comparing to electromagnetically and electrostatically actuated scanners. This scanner is a significant step towards achieving full HD resolution with mobile laser projectors.

REFERENCES

[1] S. Holmstrom*, U. Baran*, H. Urey “MEMS Laser Scanners: a Review”, IEEE JMEMS, (2014) (*co-first authors)

[2] U. Baran, W. Davis, S. Holmström, D. Brown, J. Sharma, S. Gokce, and H. Urey, “Linear-Stiffness Rotary MEMS Stage,” IEEE JMEMS, 2012.

[3] U. Baran, D. Brown, S. Holmstrom, D. Balma, W. Davis, P. Muralt, H. Urey, “High Frequency Torsional MEMS Scanner for Displays,” IEEE MEMS Conference, 2012.

[4] U. Baran, Dean Brown, S. Holmstrom, D. Balma, W. Davis, P. Muralt, H. Urey, “Resonant PZT MEMS Scanner for High Resolution Displays”, IEEE JMEMS, (2012)

[5] U. Baran, S. Holmstrom et.al “Resonant PZT MEMS Scanners with Integrated Angle Sensors”, IEEE Optical MEMS and Nanophotonics (OMN), 2014