Page 260 - Introduction to Information Optics

4.4. Optical Switching Based on MEMS 245

Input fiber 1 Output fiber i
1 1 2 £_,
\ X

Output fiber 2 Input fiber 2
X N s ,

' ^

Cross •• • Bar
Fig. 4.34. A 2 x 2 switching array using micromirrors.

driving voltage, and lower switching time need to be developed in order for
MEMS optical switches to have practical applications.
Another issue regarding MEMS optical switches is the need for proper
control circuitry to sample the incoming optical signals and to perform the
switching according to the data content of each channel. In this case, the
incoming optical signals should be redirected on an array of optical sensors,
which are built into the substrate, by using an optical beam splitter. Each
optical sensor would continuously detect the incoming data stream and send
this information to a built-in decision and control unit. Based on the extracted
information in data headers or specific patterns in the data stream, the control
unit will identify the data content of each channel and reconfigure the switch
matrix accordingly. This capability offers truly adaptive switching among a
number of incoming channels, where a change in data content of an incoming
channel during operation will automatically result in redirection of the outgo-
ing channels.

4.4.3.3. MEMS Switches without Moving Parts
Most photonic switches based on MEMS technology have movable mi-
cromirrors. Recently, an unusual optical switch without any moving parts was
proposed and fabricated [43]. The switch uses total internal reflection to route
the optical beam. It combines inkjet technology and planar waveguides
consisting of silica and silicon sections. The silica section includes optical
waveguides intersected, at the cross points, by trenches filled with index-
matching fluid. The waveguides and trenches form a proper angle so that total
internal reflection will occur when the refractive index of the waveguide is
larger than that of the trench. The silicon section includes small heaters as
thermal actuators. The heaters are located near the cross points of the