Page 207 - Introduction to Information Optics

! 92 3. Communication with Optics

Example 3.14. A silicon PIN photodiode operates at 850 nm. Assume that the
input optical power is 1 mW with a responsivity of 0,65 A/W and the detector
bandwidth is 100 MHz.

(a) Calculate the photocurrent.
(b) Calculate the shot noise current.
(c) Calculate the thermal noise current if T = 300 K and R L = 500 O.
(d) Calculate the signal-to-noise ratio of this detector (in dB).
Solve:
6
(a) I p = R • P in = 0.65 A/W • 10~ W = 0.65 M-
A
2 e>/
8
6
19
x
(b) V<'Ns> = V ' p' / = v2-1.6x 10~ C-0.65 10~ A-10 Hz = 4,5nA.
23 8
/4^rO8Txl(r J/K x 300 K x 10 Hz _ ._ . A

3.3.3. OTHER COMPONENTS USED IN FIBER-OPTIC
COMMUNICATIONS

Besides optical fibers, transmitters, and receivers, there are also other
components needed in fiber-optic networks, including optical couplers,
switchers, amplifiers, isolators, dispersion compensators, and more. Due to
space limitations, we will not describe each component in detail this chapter.
Interested readers can learn more in special books that deal with fiber-optic
components.

3.4. FIBER-OPTIC NETWORKS
3.4.1. TYPES OF FIBER-OPTIC NETWORKS CLASSIFIED BY
PHYSICAL SIZE

In terms of physical size, networks can be classified into three categories;
1. Local Area Networks (LANs). LAN is up to approximately 2 kilometers
total span, such as Ethernets, token rings, and token buses.