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Tech enables IR propagation in optical films on silicon substrate

Posted: 03 Apr 2007 ?? ?Print Version ?Bookmark and Share

Keywords:optical communications systems? optical crystal film? compact optical communication devices?

The Tokyo Institute of Technology and Fujitsu Laboratories Ltd have co-developed a technology that enables the propagation of IR light through an optical crystal film on a silicon substrate. The technology paves the way for compact optical communication devices featuring the integration of silicon LSIs with various optical devices such as modulators and switches.

In order to enable the use of communications devices such as optical switches and modulators on a silicon substrate, a material with electro-optic effect must be formed on the substrate and light must be propagated through that material. One material known to have excellent electro-optic coefficient is the ferroelectric material, lead zirconate titanate (PZT). However, since significant loss of propagation is incurred due to disruption of crystals when single crystal film is formed on top of silicon substrate, it had been difficult to propagate light successfully.

To overcome the technical issue, a buffer layer with a three-layer structure was utilized on the surface of a silicon substrate, and a PZT single crystal film was formed over the layer. This enabled minimization of the disruption of the atomic alignment, resulting in a high-quality ferroelectric PZT single-crystal-film with proper atomic alignment, and also prevented reaction between the PZT and silicon.

With the same wavelength of IR light typically used in optical communications (1.55?m), Tokyo Institute and Fujitsu successfully minimized the PZT propagation loss to less than 1dB/cm, approximately one-tenth of the loss incurred with existing technologies.

In addition, the electro-optic coefficient, a figure representing the level of change in the refractive index, was verified at 76pm/V with IR light. This is approximately three times the value of lithium niobate single crystals, which are widely used as optical modulators.

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