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Abstract

This article presents a review of active optical devices. We examine different technologies that can be used for active wavefront modulation in a large range of applications including displays, electronic paper and adaptive optics. We introduce this review by describing different light modulations that can be achieved, namely amplitude, phase or wavelength modulation. We then examine the different criteria used in order to assess the different technologies and we describe in detail each technology including the method of light modulation, its characteristics and its applications. This review is divided into two parts: the first one is devoted to amplitude modulation and the second to phase modulation.

Abstract

This article presents a review of active optical devices. We examine different technologies that can be used for active wavefront modulation in a large range of applications including displays, electronic paper and adaptive optics. We introduce this review by describing the different light modulations that can be achieved namely amplitude, phase or wavelength modulation. We then examine the different criteria used in order to assess the different technologies and describe in detail each technology including the method of light modulation, its characteristics and applications. The review is divided into two parts: the first one is devoted to amplitude modulation and the second to phase modulation.

Abstract

In this paper, we report the advantage of using AC actuating signal for driving MEMS actuators instead of DC voltages. The study is based upon micro mirror devices used in digital mode for optical switching operation. When the pull-in effect is used, charge injection occurs when the micro mirror is maintained in the deflected position. To avoid this effect, a geometrical solution is to realize grounded landing electrodes which are electro-statically separated from the control electrodes. Another solution is the use of AC signal which eliminates charge injection particularly if a bipolar signal is used. Long term experiments have demonstrated the reliability of such a signal command to avoid injection of electric charges.

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Abstract

In this paper we describe the use of thermo-activated PNIPAM nano-material in optical switching devices. In other publications, the PNIPAM is used either as a carrier for crystalline colloidal array self-assemblies or as micro-particles that serve as pigment bags. In this publication we use a simpler-to-fabricate pure PNIPAM solution in a semi-dilute regime. The PNIPAM devices produced are transparent at temperatures below a critical temperature of 32°C and become diffusing above this temperature. We show that at 632 nm the transmission through the devices is about 75% in the transparent state while the additional attenuation achieved in the diffusing state is of the order of 38 dB. The experimental fall and rise times obtained are large (about 300 ms and 5 s, respectively) due to the non-optimised thermal addressing scheme. In addition, spectral measurements taken in the infrared spectrum (7001,000 nm) demonstrate that the cell response is flat over a large portion of the infrared spectrum in both the transparent and the diffusing states.

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Abstract

Since its introduction in the nineties, the negative resist SU-8 has been increasingly used in micro- and nanotechnologies. SU-8 has made the fabrication of high-aspect ratio structures accessible to labs with no high-end facilities such as X-ray lithography systems or deep reactive ion etching systems. These low-cost techniques have been applied not only in the fabrication of metallic parts or molds, but also in numerous other micromachining processes. Its ease of use has made SU-8 to be used in many applications, even when high-aspect ratios are not required. Beyond these pattern transfer applications, SU-8 has been used directly as a structural material for microelectromechanical systems and microfluidics due to its properties such as its excellent chemical resistance or the low Young modulus. In contrast to conventional resists, which are used temporally, SU-8 has been used as a permanent building material to fabricate microcomponents such as cantilevers, membranes, and microchannels. SU-8-based techniques have led to new low-temperature processes suitable for the fabrication of a wide range of objects, from the single component to the complete lab-on-chip. First, this article aims to review the different techniques and provides guidelines to the use of SU-8 as a structural material. Second, practical examples from our respective labs are presented.

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Abstract

The development reported herein is that of a surface micromachining technology using two SU-8 layers as a structural material. Three different processes are presented and discussed: the first process makes use of a solgel as the sacrificial layer; the second process utilizes the SU-8 itself as the sacrificial layer; the third process utilizes silicon dioxide as the first sacrificial layer and the solgel as the second sacrificial layer. These three processes are adapted for one structural layer structure. With a two-layer structure and when release is long, the third process is more adapted.

Abstract

Future adaptive optics (AO) systems require deformable mirrors with very challenging parameters, up to 250 000 actuators and inter-actuator spacing around 500 &mgr;m. MOEMS-based devices are promising for the development of a complete generation of new deformable mirrors. Our micro-deformable mirror (MDM) is based on an array of electrostatic actuators with attachments to a continuous mirror on top. The originality of our approach lies in the elaboration of layers made of polymer materials. Mirror layers and active actuators have been demonstrated. Based on the design of this actuator and our polymer process, realization of a complete polymer-MDM has been done using two process flows: the first involves exclusively polymer materials while the second uses SU8 polymer for structural layers and SiO2 and sol-gel for sacrificial layers. The latest shows a better capability in order to produce completely released structures. The electrostatic force provides a non-linear actuation, while AO systems are based on linear matrices operations. Then, we have developed a dedicated 14-bit electronics in order to "linearize" the actuation, using a calibration and a sixth-order polynomial fitting strategy. The response is nearly perfect over our 3×3 MDM prototype with a standard deviation of 3.5 nm; the influence function of the central actuator has been measured. First evaluation on the cross non-linarities has also been studied on OKO mirror and a simple look-up table is sufficient for determining the location of each actuator whatever the locations of the neighbor actuators. Electrostatic MDM are particularly well suited for open-loop AO applications.

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