Stray light absorption

Details Stray light absorption Stray light absorption

1998-05-13

2001-10-02

Lee, John D. (Department: 2874)

Optical waveguides

Integrated optical circuit

C385S129000

Reexamination Certificate

active

06298178

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of absorbing stray light in an integrated optical circuit and to an integrated optical circuit comprising light absorbing means for absorbing stray light.
2. Description of the Related Art
In the design of integrated optical circuits there is often a need to deal with light which is not guided by the components forming the circuit. This stray light, which can arise from many sources, such as fibre or laser couplers, scattering from waveguide couplers and bends or from scattering beam dumps, can have a severe impact on the performance of devices which employ these components. The stray light in the optical chip can enter devices on the chip, and output fibres and may severely limit the performance of these devices.
Conventional methods of dealing with this problem include physically arranging devices on an integrated optical chip such that stray light cannot enter sensitive parts of the chip and the use of isolation trenches to keep stray light away from certain parts of the chip.
The imitation of these approaches is that they do not remove the stray light from the integrated optical chip, but instead attempt to minimise the problem of having stray light within the chip.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a method of absorbing stray light in an integrated optical circuit formed on an optically conductive substrate comprising the step of doping selected areas of the substrate so as to increase the absorption of light which is not guided by components of the optical circuit in those areas.
According to a second aspect of the invention, there is provided an integrated optical circuit formed on an optically conductive substrate comprising light absorbing means for absorbing stray light in the substrate, the light absorbing means comprising one or more doped areas of the substrate where the doping concentration is greater than that of areas of the substrate forming the optical circuit to absorb stray light in the substrate which is not guided by components of the optical circuit.
Other features of the invention will be apparent from the following description and from the subsidiary claims of the specification.


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R.A. Soref et al., “Electrooptical Effects in Silicon,” The Journal of Quantum Electronics, vol. QE-23, No. 1, Jan. 1987: pp. 123-129.
Patent Abstracts of Japan, vol. 16, No. 266, Jun. 16, 1992: p. 1371.

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