Integrated Optics - Applied Optics Fundamentals and Device Applications - page 276

Broad range of wavelengths (0.6-1.6 µm)
High reliability
Low loss
Polarization insensitive
FIGURE 5.39
Ion-exchange borosilicate glass waveguide single mode fiber-optic contents.
The next step in device complexity beyond the splitter is the single mode
tree or star coupler. These can be 1 × N , 2 × N , 4 × N , etc. These components
usually have equal split ratios but can be manufactured with asymmetric
ratios. Dual wavelength devices are more complex and costly. Port counts
greater than four usually require splicing of two or more devices and large
enclosures or ultimately integration in photonic circuits.
Multimode trees and stars are similar to the single mode devices, but
rarely fabricated with asymmetric split ratios. Constructed with fibers from
50/125 to 200/230 μm, they are generally used in high power industrial and
medical sensing while the single mode devices are used more in the CATV
and DWDM markets. For example, 200/230 devices are used to couple sig-
nals from intravenous catheters in arterial blood-gas sensor systems. 100/140
devices are used to link pressure catheters to intracranial pressure monitors.
They are also used in rpm monitors for steam turbines.