While most of the MEMS VOA alternatives are based on electrostatic approaches, electrothermal actuated VOA are rarely reported. Electrothermal actuators have been known for their large displacement and high force output. These characteristics make electrothermal actuators to be an attractive alternative for VOA device. Our research attempts here provide the first insight study on the correlation among the mechanics and optical characteristics of MEMS VOA using novel in-plane electrothermal actuator structures.

We first designed an electrothermal driven MEMS VOA device using a H-shaped structure. Based on its unique structural design, a retro-reflection type VOA of smaller footprint is realized. In addition to the H-shaped electrothermal actuator design, we have also designed a novel planar micro-mechanism comprising of a tilted mirror driven by a V-beam electrothermal actuator via a link beam . This electrothermal driven tilted mirror can have static displacement with a motion trace including rotational and translational movement. The rotational and translational misalignment of reflected light spot toward the core of output port fiber will lead to light attenuation. A 50dB attenuation range is achieved when DC driving voltage of 10.2V or 210mW of power is applied to the H-shaped electrothermal actuator. In the case for the mirror driven by a V-beam electrothermal actuator, the device can achieve 30 dB of attenuation under a 7.5 V dc bias.

Selected Publications:

1. Chengkuo Lee, A MEMS VOA Using Electrothermal Actuators, IEEE/OSA J. Lightwave Technol., vol. 25, no.2, pp. 490-498, Feb. 2007. [PDF] [DOI]
2. Chengkuo Lee, Variable optical attenuator using planar light attenuation scheme based on rotational and translational misalignment., Microsyst. Technol., vol. 13, no.1, pp. 41-48, Jan. 2007. [PDF] [DOI]

Actuators deploying piezoelectric PZT films are attractive alternatives to silicon based actuators, as piezoelectric actuator shows higher output force and smaller driving voltage due to their higher energy density than the other actuators. In addition, limited research effort has also been reported in 3-D MEMS VOA in contrast to the reported activities in planar MEMS VOAs. More importantly, there is yet to be reported data on PZT-driven mirror for VOA application to our knowledge.

In our first work for VOA applications, a new 3-D MEMS VOA device driven by two piezoelectric thin film PZT actuators is proposed. The piezoelectric actuators are fabricated alongside the mirror and is connected to the mirror by torsion and bending springs. In our second work, a novel piezoelectric driven 3-D MEMS VOA using a mechanical supporting beam integrated with multiple cantilever actuators is explored for optical attenuation capabilities. For both the PZT MEMS VOA designs we investigated, only 1 dc volt is required to achieve 42 dB dynamic attenuation range. This low actuation voltage is on par with the operating voltage of many of the state-of-the-art MEMS VOAs already reported in literature

Selected Publications:

1. Kah How Koh, Chengkuo Lee and Takeshi Kobayashi, A piezoelectric-driven three-dimensional MEMS VOA using attenuation mechanism with combination of rotational and translation effects, IEEE/ASME J. Microelectromech. Syst., vol. 19, no. 6, pp. 1370-1379, Dec. 2010. [PDF] [DOI]
2. Chengkuo Lee, Fu-Li Hsiao, Takeshi Kobayashi, Kah How Koh, P. V. Ramana, Wenfeng Xiang, Bin Yang, Chee Wei Tan, and D. Pinjala, A 1-V Operated MEMS Variable Optical Attenuator Using Piezoelectric PZT Thin Film Actuators, IEEE J. Select. Top. Quant. Elect., vol.15, no. 5, pp. 1529-1536, Sep/Oct, 2009. [PDF] [DOI]
3. Chengkuo Lee and Jer-Liang Andrew Yeh, Development and Evolution of MOEMS technology in Variable Optical Attenuators, J. of Micro/Nanolithography, MEMS, and MOEMS , vol. 7 (2), 021003, Apr.-Jun. 2008. [PDF] [DOI]

Special Mention:

1. Mr Koh received a Best Paper Award for his conference article submitted to IEEE Photonics Global Conference 2010 and titled "MEMS VOA based on torsional and bending attenuation mechanism using piezoelectric cantilever integrated with 1x10 PZT thin film actuators." The student paper contest, sponsored by Nature Photonics, consisted of a team of review panel chaired by the chief editor of Nature Photonics. [LINK]

By using a CMOS compatible process technology, a MEMS variable optical attenuator (VOA) is characterized in terms of actuation mechanisms. A dual fiber collimator is aligned perpendicularly to the micromirror in a three-dimensional (3-D) free space configuration, where the micromirror is mechanically connected with an electromagnetic actuator and two sets of electrothermal actuators. Three types of attenuation schemes based on electromagnetic, electrothermal and hybrid, i.e. combination of electrothermal and electromagnetic, actuations have been explored and studied. Dynamic attenuation ranges of 40 dB have been achieved at 4 Vdc, 26 mW and 3 Vdc, 20 mW by electromagnetic and electrothermal attenuation schemes respectively. In hybrid attenuation scheme, various voltage combinations are made to the electromagnetic and electrothermal actuators. An optical attenuation of approximately 40 dB can be obtained when 2 volts are applied to both the electromagnetic and electrothermal actuators simultaneously, while the electrical power consumption of the actuators is 17 mW in total.

Selected Publications:

1. Kah How Koh, You Qian and Chengkuo Lee, Design and characterization of a 3-D MEMS VOA driven by hybrid electromagnetic and electrothermal actuation mechanisms, J. Micromech. Microeng., vol. 22, no. 10, 105031, 2012. [PDF] [DOI]

Special Mention:

1. Mr Koh received a new award: Best Student Paper Award during the 17th Opto-Electronics and Communication Conference (OECC) 2012. His submitted article this time round is "3-D MEMS VOA using electromagnetic and electrothermal actuations." [LINK]

 

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