C. Marxer

Vertical mirrors fabricated by deep reactive ion etching for fiber-optic switching applications

We report on vertical mirrors fabricated by deep reactive ion etching of silicon. The mirror height is 75 /spl mu/m, covering the fiber core of a single-mode fiber when the latter is placed into a groove of equal depth and etched simultaneously with the mirror. To obtain a uniform etch depth, etching is stopped on a buried oxide layer. Using the buried oxide as a sacrificial layer allows to fabricate mirrors with suspension and actuation structures as well as fiber-alignment grooves in one and the same processing step. A minimal mirror thickness of 2.3 /spl mu/m was achieved, resulting in an aspect ratio higher than 30. The verticality was better than 89.3/spl deg/. In the upper part of the mirror a surface roughness below 40 nm rms was obtained. At a wavelength of 1300 nm the reflectivity of the aluminum-coated mirrors was measured to be higher than 76%. Using a reactive ion etched mirror we have fabricated an optical fiber switch with electrostatic actuation. The coupling loss in the bar state of two packaged prototypes was between 0.6 and 1.7 dB and between 1.4 and 3.4 dB in the cross state. The switching time is below 0.2 ms.

A variable optical attenuator based on silicon micromechanics

In this letter, we describe a variable optical attenuator for single mode fibers. As for its counterparts based on conventional mechanics the micromechanical attenuator operates by moving an obstructing element in the optical beam in order to adjust the light damping. The device is fabricated using the silicon micromachining technology. This allows one to integrate the electrostatic actuator together with the fiber alignment grooves and the obstructing element. With this design, an insertion loss below 1.5 dB was achieved. The response time was below 5 ms and no hysteresis was measured. The maximum attenuation was -57 dB. Backreflection attenuation was below -37 dB.

Micro-opto-mechanical 2/spl times/2 switch for single-mode fibers based on plasma-etched silicon mirror and electrostatic actuation

This paper reports on a new optical 2/spl times/2 switch for single-mode fibers. The switching principle is based on a vertical micro-mirror which can be moved into the optical path to switch light between two pairs of fibers. The micromirror switch is designed for by-pass applications. When power is turned off the mirror spring back into its rest position and brings the switch into its bar state. This operation is very reliable, since the moving parts do not get into contact. Fabrication is based on the silicon micromachining technology, which allows to integrate the switching mirror, its electrostatic actuator and the alignment grooves for the fibers on the same chip. The mechanical switching principle brings with it a number of optical advantages such as a high crosstalk attenuation above 50 dB and wavelength and polarization insensitivity. At a wavelength of 1310 nm a minimum insertion loss of 0.6 dB was measured in the bar state, i.e. when the mirror is out of the optical path. In the cross state the light is reflected on the gold coated micro-mirror which has a reflectivity of about 80%. The insertion loss of the bar state was thus higher and a minimum value of 1.6 dB could be obtained. The switching time was well below 1 ms.

Applications of SOI-based optical MEMS

After microelectromechanical systems (MEMS) devices have been well established, components of higher complexity are now developed. Particularly, the combination with optical components has been very successful and have led to optical MEMS. The technology of choice for us is the silicon-on-insulator (SOI) technology, which has also been successfully used by other groups. The applications presented here give an overview over what is possible with this technology. In particular, we demonstrate four completely different devices: (a) a 2 /spl times/ 2 optical cross connector (OXC)with an insertion loss of about 0.4 dB at a switching time of 500 /spl mu/s and its extension to a 4 /spl times/ 4 OXC, (b) a variable optical attenuators (VOA), which has an attenuation range of more than 50 dB (c) a Fourier transform spectrometer (FTS) with a spectral resolution of 6 nm in the visible, and (d) an accelerometer with optical readout that achieves a linear dynamic range of 40 dB over /spl plusmn/6 g. Except for the FTS, all the applications utilized optical fibers, which are held and self-aligned within the MEMS component by U-grooves and small leaf springs. All devices show high reliability and a very low power consumption.

Vertical mirrors fabricated by reactive ion etching for fiber optical switching applications

We report on vertical mirrors fabricated by deep reactive ion etching of silicon. In view of their application in fiber optical switches the mirror height is 75 /spl mu/m. So the mirror covers well the fiber core of a single mode fiber, when the fiber is placed in a groove of the same depth and etched at the same time as the mirror. A minimal mirror thickness of 2.3 /spl mu/m was achieved, resulting in an aspect ratio over thirty. The verticality was better than 89.3/spl deg/. The surface roughness of the etched surface is 36 nm rms. For an increased reflectivity the silicon mirrors are coated with aluminium. Their reflectivity was measured to be 76%. To obtain an uniform etch depth, etching is stopped on a buried oxide layer. This allows to integrate at the same time mirrors with suspension and actuation structures as well as fiber-alignment grooves in one processing step. Using this technology we have fabricated a fiber optical switch with promising performance: The coupling loss in the OFF position is 2.5 dB and 4 dB in the ON position. The switching time is below 0.2 ms.

Advanced deep reactive ion etching: a versatile tool for microelectromechanical systems

Advanced deep reactive ion etching (ADRIE) is a new tool for the fabrication of bulk micromachined devices. Different sensors and actuators which use ADRIE alone or combined with other technologies such as surface micromachining of silicon are presented here. These examples demonstrate the potential and the design freedom of this tool, allowing a large number of different shapes to be patterned and new smart devices to be realized.

Megahertz Opto-Mechanical Modulator

Note: 152 Reference SAMLAB-ARTICLE-1996-008 Record created on 2009-05-12, modified on 2016-08-08

MEMS compatible micro-GRIN lenses for fiber to chip coupling of light

Graded-Index (GRIN) lenses with a diameter of 125 mum are presented. This diameter enables the assembly of the GRIN lenses onto an optical micro-system using the same passive alignment grooves as used for the light carrying optical fibers. In contrast to refractive lenses, GRIN lenses have flat endfaces and the focal distance of a GRIN lens is defined by its length. Therefore, GRIN lenses can be diced from a selected multimode optical fiber with a regular wafer dicing machine. The effects of the resulting surface roughness are reduced by immersing the optical parts into index matching oil, which can not be applied for refractive lenses. This has a further advantage since an anti-reflective coating becomes dispensable. The coupling efficiency of a collimator set-up using the GRIN lenses is studied using paraxial ray calculations. The calculated minimal coupling losses of less than 0.3 dB are in excellent agreement with the measured results. Losses smaller than 2 dB over a coupling length of 2 mm have been measured.

4X4 matrix switch based on MEMS switches and integrated waveguides

We present the development of a 4×4 matrix of optical switches based on silicon microfabricated switches and integrated waveguides. The device consists of two chips connected together by flip-chip bonding. The first chip has 16 latched silicon switches with micro-mirrors, while the second one contains the integrated waveguides and ensures the electrical connection of the 16 switches. The incorporation of integrated waveguides, patterned using a SU-8 mask and deep reactive ion etching, in our switch devices allows both the size and the packaging complexity to be reduced, and a technology for higher order matrices to be developed.

Reliability considerations for electrostatic polysilicon actuators using as an example the REMO component

Abstract The REMO (REflective MOdulator) component is a micromechanical light modulator fabricated by polysilicon surface micromachining. During operation the maximum tensile stress is 130 MPa and the maximum homogeneous electric field is 60 V μm −1 . The effects of these high operation stresses in combination with humid air have been studied. In dry air the mechanical properties of polysilicon meet the requirements for a highly reliable modulator, i.e., the fracture strength is well above the operation stress and slow crack growth is not expected to occur. In dry air no change of the mechanical or the electrical properties can be observed. The combination of cyclic mechanical stress, high electric field and humid air can lead to membrane rupture. On specimens where the stress cycling is stopped before rupture, an increase of the resonance frequency and a permanent electrical polarization of the air-gap capacitor can be observed. This is explained by the formation of a surface oxide. The oxide stiffens the membrane, which results in an increase of the resonance frequency. Trapped charges in the oxide lead to a permanent polarization of the air-gap capacitor.