Page 164 - Optical Switching And Networking Handbook

07_200023_CH06/Batesx 1/17/01 10:05 AM Page 149

Optical Switching Systems and Technologies 149

The light must pass through several devices, and each device
takes its toll in reducing the strength of the signal by about 4.5 deci-
bels (dB), which is a lot of loss. Therefore, the light signals need to be
regenerated electrically when they exit the cross-connect.

Bubble Bubble, Who Has the
Bubble?

Ink-pen technology, already used by Hewlett-Packard (HP) in its
bubble-jet printers, has been reused to solve many of the intrinsic
problems of mechanical devices employed to switch light. What was
that? Agilent’s switch is composed of a vertical and horizontal array
of fixed, aligned waveguides. Light is transmitted across a horizontal
path from the input to output port until a switch command is issued.
When commanded, a bubble is created at the intersection of the
appropriate waveguides, and the light is reflected down a vertical
path to the switched port.This bubble is formed using the same tech-
nology used in ink-jet printers.
Agilent’s Photonic Switching Platform consists of two layers:
1. A bottom layer of glass through which multiple streams of light
travel
2. A top layer of silicon containing the ink-jet technology
(technology from ink-jet printers that has been around for
years)

In the bottom layer, 32 parallel microscopic trenches are carved
into the silica. These intersect each other at 120-degree angles. The
trenches are filled with a liquid with the same refractive index as the
silica. Light passes straight through each of these trenches unless it
runs into a bubble at one of the intersections. If a bubble is there, the
light bounces off into the trench crossing its path. The bubble is cre-
ated by tiny electrodes in the upper silicon ayer of the device. The
electrodes heat up the liquid to form a gas in exactly the same way
as in a bubble-jet printer.