Integrated Optics - Applied Optics Fundamentals and Device Applications - page 277

1. Branching circuits

1 × 2 branches
1 × 4 branches
1 × 8 branches

Input fiber

Output fiber

Waveguide

2. Star couplers

Waveguide

8 × 8 star
16 × 16 star

Input fiber

Output fiber

3. Access couplers

Waveguide

D

A

A B

θ

B

C

θ

Output fiber

Input fiber

D C

4. Multi/demultiplexer

Optical adhesive Waveguide

2 channel
3 channel

Common

F1

CH1

CH3

F2

F3 CH2

I/O fiber I/O fibers

Substrate

Slot

Slot

FIGURE 5.40
Applications of graded-index waveguides.

Wavelength division multiplexers/demultiplexers are manufactured using
the FBT process for sharp tapers, exploiting interference effects between
guided wave devices. These are usually 1310/1550 or 980/1550 devices.
Typical isolation in a 1310/1550 device is 20 dB. High isolation devices (>40 dB)
can be constructed by splicing two or more devices in series.
Low PDL FBT tap couplers with asymmetric split ratios, typically 1/99 or
5/95, are used in feedback control systems to monitor laser output of sensi-
tive optical instruments where the state of polarization can affect system