Fraunhofer Institute for Photonic Microsystems
Fraunhofer Institute for Photonic Microsystems

Liquid Crystal Waveguides

Polarization independent liquid crystal waveguides

Polarization independent liquid crystal waveguides

© Fraunhofer IPMS
Simulation of light propagation in a waveguide with an LC-EOIW with increasing electric field strength (left). 1×2 LC-EOIW switch chip on a printed circuit board: bonded silicon wafers enclosing an LC layer. (center of image) Processed silicon wafer with Vernier-type LC microresonator filter (right).

Many applications nowadays are sensitive to light polarization and require polarization maintaining components. Likewise, there are applications which demand polarization independent components, for instance when it is important to reduce the complexity of fiber optic networks and costs.

Fraunhofer IPMS electro-optically induced waveguides technology with liquid crystals on silicon backplane is attractive for optical switching applications. Key features stem from employing highly transparent liquid crystal blends as waveguide core materials. In particular, the optical power transmitted along the waveguide structure can be controlled by adjusting the electro-optical Kerr response strength in a liquid crystal layer on a sub-microsecond timescale with an applied electrical field. Essentially due to the underlying electrooptical effect, the propagation behavior of a light wave along the Fraunhofer IPMS liquid crystal waveguide is dependent on its polarization state.

A solution for polarization independent electro-optically induced waveguides in liquid crystals was nevertheless developed at the IPMS. In this case the optical losses in the TE and TM modes propagating along the induced waveguide can be controlled by the applied electric field distribution in the electrode backplane. 

These waveguides are fabricated at the Fraunhofer IPMS by means of precision silicon wafer level technology. This fulfills the prerequisites for high quality, high volume and cost efficient manufacturing. A demonstration of a polarization independent waveguide is available.

Key features

  • Polarization controlled operation: – Polarization sensitive OR insensitive
  • Single mode design
  • Fiber optic coupling to LC waveguide
  • Full variable range optical power splitting
  • Continuously voltage adjustable output characteristics
  • Reliability due to the absence of mechanical parts
  • Wafer scale fabrication with precision silicon micro-technology
  • Scalability and reconfigurability of induced waveguide functions
  • Integrability with other devices on a same chip

 

Advantages

Fraunhofer IPMS has demonstrated, making use of particular arrangements of polarization dependent electro-optically induced waveguides, sub-microsecond switching, and continuously voltage adjustable, full variable range power splitting at low optical loss. With the Fraunhofer IPMS new waveguide design, also polarization independent optical switching and polarization independent variable power splitting with the mentioned characteristics are possible. In particular, optical switching devices based on the Fraunhofer IPMS waveguide concept can provide the following key features: fast switching speeds, polarization insensitive operation, good reliability and stability of the switching process, scalability towards high channel count and integrability with other devices, large number of switching cycles as well as low insertion loss and low crosstalk.

 

Usage

An optical switch device based on polarization independent electro-optically induced waveguides can be used for directing signals from multiplexed fiber optic sensors for their cycling analysis in interrogation instruments. For fiber optic sensor network monitoring, the device can ensure switching between channels at frequencies in the MHz range. Moreover due to the absence of mechanical parts, the device can operate nearly wear-free and can therefore be the technology of choice for long-term monitoring applications. In optical telecommunications networks, devices based on polarization independent electro-optically induced waveguides can ensure dynamic switching between different channels, control of power allocated to network nodes and increased efficiency by utilizing optical resources at a lower cost.

 

Applications

  • Fast switching for fiber-optic sensor network monitoring (MHz)
  • Optical telecommunication networks
  • Signal monitoring
  • Fiber-to-fiber interconnection
  • Signal attenuation and power splitting
  • Laser system technology

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