Large Optical MEMS Switches Architectures for Broadband Applications

Objectives

Large Scale Optical Cross Connect
The development consists of a MEMS-based Optical Cross Connect (OXC) with about 50 input and 50 output fibres. One important application of this OXC is an enabling component for a reconfigurable switching network within a communication satellite. The 2 year objective was to deliver a breadboard to prove the soundness of the concept and to demonstrate a working MEMS-based OXC.

An important longer-term objective is to use the knowledge developed in this program to create a Swiss industrial source for MEMS-based OXCs.

The following schematic shows the general concept of the complete switching system. Input and output of the system is in the RF domain, while the core switching is in the optical domain. The RF signal are converted to optical signals prior to the actual optical switching. After the optical switching the are re-converted into the RF domain. The optical switching makes the overall system potentially very compact at very low cross talk and low insertion loss levels.


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Challenges

The key issue in the project is to develop a 2D electrostatic actuated MEMS micromirror array of 128 mirrors which is extreme stable in position over time to avoid heavy and complex feed back loop. Another task is to develop the necessary high port count collimator. And last but not least a training strategy and software for the switch matrix.

Benefits

One expected benefit is to have spin offs with commercial value. Improvement of the knowledge for space application needs in the MEMS based optical domain. High port count optical switches for ground base applications with potential of satellite integration.

Features

The main development of the OXC system was the optical-fibre-cross-connector core, which is schematically shown below.


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The light exits the fibre and is collimated by a microlens, hits on one of the 128 micromirrors and is redirected by tip/tilt of this micromirror to a fixed mirror. The light reflects to the output port micromirror and enters the fibre through the output microlens.

3D representation of the OXC depicting ray tracing results of the optical simulations:


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Main Features:

  • “folded” optical design with only one micromirror chip - compactness
  • 50x50 ports fully reconfigurable
  • Extreme low drift design of the MEMS chip and the electronics - No Feedback loop
  • High optical isolation because of free space architecture - No crosstalk

Detailed view of the three arrays of fibres, micro lenses, and micromirrors, respectively.


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For the bread board, a compact alignment system was constructed which supports the electrical and mechanical interface:


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On the MEMS side the main development was the microfabrication of the oval micromirror arrays comprising 128 micromirrors, which are arranged in 4 rows of 32 mirrors each. The micromirrors are oval, since they are illuminated at 45° AoI. A detailed view shows the 3 gold coated MEMS micromirrors. The mirrors measure about 600x900 µm². The mirrors are actuated parallel-plate electrostatic actuators. The mirror itself is the ground electrode, while the three actuation electrodes are arranged compactly underneath the mirror.


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Bread Boards Details
The fully assembled and tested breadboard shows the OXC in the upper centre and a close up on the right side of the image. The input and output fibres connect on one end to the optical switch and the other end to the E/O and O/E converters.

Breadboard with close-up of the OXC core.


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Top View of the breadboard depicting the fibre interfaces and the OXC.


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Plan

Work Package Expected Duration Main Actor Other Actors
WP1000: Assessment of large MOEMS switch architecture  2 Months Alcatel Space Sercalo, IMT, EPFL
WP1100: trade-off architectures  2 Months Alcatel Space IMT, EPFL
WP1200: Conceptual design  2 Months Sercalo IMT, EPFL
WP2000: Preliminary Design of breadboard  2 Months Sercalo IMT, EPFL
WP3000: Detailed design of breadboard and test set  14 Months Sercalo  
WP3100: Detailed design of breadboard  14 Months Sercalo IMT, EPFL
WP3200: Detailed design of test set  3 Months Alcatel Space EPFL, Sercalo
WP4000: manufacturing  15 Months Sercalo IMT, Alcatel Space, EPFL
WP4100: MOEMS manufacturing  15 Months Sercalo IMT, EPFL
WP4200: test bed manufacturing  5 Months Alcatel Space Sercalo
WP5000: Test campaign  3 Months Alcatel Space Sercalo
WP6000: Appraisal  1 Month EPFL Alcatel Space, Sercalo, IMT

Current status

Completed. We could successfully demonstrate the function of our design and deliver a demo switch system. The testing on the MOEMS switch breadboard and tests-bed was performed on a 10x10 sub-matrix selected among full connected optical inputs and outputs.

Requirement Object Target Spec. Comments
 RF Requirements
 Frequency band  Ka-band  OK alsofor S band
 RF Input Power  >0 dBm  OK fr Ka and S band
 Opto-microwave gain  0 dB  OK for Ka and S band
 Opto-microwave noise figure  <28 dB  OK for Ka band
 C/I ratio (2 tones)  >50dBc  OK for S band, not for Ka band
 Return Loss  >20 dB  OK for Ka band
 Static Isolation  >50 dB  >70 dB
Requirement Object Target Spec. Comments
System Level Requirements
 Number of I/O ports  >50 x 50 Partial 24x24
Full connectivity 10x10.
Switching time  < 5 ms 65 ms
Time for reconfiguration  < 50 ms 100 ms
Mass  < 1kg 0.86 kg
Size  < 1000 cm3 1400 cm3
Power consumption  < 5 W 6.01 W
Optical Requirements
Wavelength range  1.25–1.63µm 1.25-1.63 µm (measurements performed @ 1.55µm)
Insertion loss absolute value  < 7dB < 6.2 dB
Insertion Loss variation  TBD < 0.5 dB
Repeatability of loss  < 1 dB < 0.06dB
Stability of loss  < 1 dB < 0.9 dB
Max Power  21 dBm  
Return Loss (back-reflection)  > 30 dB 15 - 30 dB
Isolation (crosstalk)  > 50 dB > 70 dB
Polarization dependent loss (PDL)  < 0.1 dB < 0.17 dB

The results obtained during the project encouraged sercalo to start a new project on single 2D analogue driven tilt mirrors for ground based applications, like tunable filters, micro scanners or low cost spectrometers and to commercialize a 25 port fiber collimator for rotary joint applications. Future work will tackle environmental testing at chip and equipment level, yield of MEMS chips, etc.

Contacts

Status date

Thursday, February 27, 2014 - 09:03