Integrated Optics - Applied Optics Fundamentals and Device Applications - page 275

Waveguide configuration

Input

Output

A

B
Directional coupler switched output state

0.85, 1.32, and 1.52 µm
15 V switching voltages
dc to >100 MH Z frequency response

(a)

LiNbO 3 Mach-Zehnder modulator
Modulation
input

50 Ω
terminating
resistor
Port #3

Port #1

Optical output

Optical input

Port #4

Port #2

Thermistor

Thermo-electric
cooler

6 V switching voltage
Operation to 4 GH Z
Fiber pigtailed
12 dB channel separation

(b)

FIGURE 5.38
LiNbO 3 directional couplers modulators. (a) (Courtesy of Pilkington Guided Wave Optics);
(b) (Courtesy of Barr & Stroud, Ltd., Glasgow, U.K.)

• Uniformity—most often used with more than two fiber I/O ports,
uniformity is the maximum difference in insertion loss in dB from
one port to another.
• Polarization—also designated polarization dependent loss (PDL)
in splitters. The optical power transmission of fiber-based devices
is often dependent on the orientation of the electromagnetic wave
entering the device. PDL is a measure of how insertion loss changes
as the orientations or states of polarization (SOP) change. In most
quality devices, PDL measures less than 0.2 dB.