Planar circuit fabrication
The sol-gel route has done it again: French start-up Kloé has devised a new way to make planar optical circuits intended for deployment in metropolitan area networks.
By Matthew Peach
When an arrayed waveguide grating (AWG) is fabricated by traditional photolithographic means, detail can be compromised. Definition loss occurs when the design is reproduced into a mask, when the mask is duplicated in the photoresist, after etching of the photoresist, and after etching of the guiding layer.
The new fabrication process proposed by Kloé involves writing the design directly into the photosensitive layer, which constitutes the guide. This offers a new way to fabricate planar optical circuits such as AWGs - in volume and at low cost - specifically for deployment in metropolitan area networks.
Kloé's technology employs new types of materials developed by sol-gel processing. These hybrid organic-inorganic materials are synthesised by hydrolysis polycondensation of organo-mineral precursors. The resulting materials could be cured by various means.
For example, UV exposure can photopolymerise the organic part and a thermal treatment can induce the formation of a mineral network. The process produces an organic network and an inorganic network, both interleaved. So, both networks are independent and can stabilise the other. Such a material can have high stability over time, which is not the case with pure polymer materials.
The process enables a material to be synthesised for a specific application by adjusting the ratio between organic and inorganic components.
This technique has enabled Kloé to develop a large range of applications with the hybrid organic-inorganic materials: waveguide structures; seals for pig-tailing and for packaging of Fibre Bragg Gratings; hydrophobic layers and anti-scratch layers, to name a few.
The fabrication process of waveguides takes place at low temperature (under 150°C). The process sequence is: synthesis of materials; deposition by dip or spin coating; UV exposure (the polymerisation of the organic part induces a local increase of the refractive index creating the guide).
Thermal treatment at low temperature (again under 150°C) creates the mineral network which freezes and stabilises the coating. All these steps are automated and will be made in line in Kloé's planned mass production facility.
Director Paul Coudray told Lightwave Europe, "Our circuits are designed for application in MAN, LAN and CATV applications, based on CWDM systems. Our customers will be suppliers such as Alcatel or Nortel Networks, but also all the integrators of metro and local networks.
"The greatest points of interest in our technology are its suitability for mass production and a very low selling price. These are both fundamental factors for the development of the MAN and LAN, which are still underdeveloped markets in comparison with long-haul networks."
Eventually he expects all steps to be automated and in-line - including the passive pig-tailing and hydrophobic packaging. "The mass production unit will have a capability to produce several hundred pieces per day. The flexibility of the process is such that several types of functions could be produced at the same time within the production unit, which Coudray expects to be finalised by the end of 2003. "We are presently developing a pre-industrialisation unit which should be done early in spring 2003. Its production capacity will be 20 circuits per day."
Kloé is an independent company, spun off from the University of Sciences of Montpellier in 2001. It is based on a collaboration between Coudray and Pascal Etienne, PhDs in photonics and material science respectively.