[ Back ] [ Home ] [ Up ] [ Next ]
OPTICAL DETECTORS AND FIBER OPTIC RECEIVERS
LEARNING OBJECTIVES
Upon completion of this chapter, you should be able to do the following:
-
Explain the principal properties of an optical detector and fiber optic receiver.
-
Detail semiconductor optical detector performance and capability requirements necessary
for the successful implementation of fiber optic systems.
-
List the main components of a fiber optic receiver.
-
Discuss receiver sensitivity, dynamic range, and other key operational parameters used
to define receiver performance.
INTRODUCTION TO OPTICAL DETECTORS AND FIBER OPTIC RECEIVERS
Chapter 6 taught you that a fiber optic transmitter is an electro-optic device capable
of accepting electrical signals, converting them into optical signals, and launching the
optical signals into an optical fiber. The optical signals propagating in the fiber become
weakened and distorted because of scattering, absorption, and dispersion. The fiber optic
device responsible for converting the weakened and distorted optical signal back to an
electrical signal is a fiber optic receiver.
A fiber optic receiver is an electro-optic device that accepts optical signals
from an optical fiber and converts them into electrical signals. A typical fiber optic
receiver consists of an optical detector, a low-noise amplifier, and other circuitry used
to produce the output electrical signal (see figure 7-1). The optical detector converts
the incoming optical signal into an electrical signal. The amplifier then amplifies the
electrical signal to a level suitable for further signal processing. The type of other
circuitry contained within the receiver depends on what type of modulation is used and the
receiver electrical output requirements.
Figure 7-1. - Block diagram of a typical fiber optic receiver.
Receiver spectral response, sensitivity, Frequency response, and dynamic range are key
receiver performance parameters that can affect overall system operation. The choice of
optical detector materials and structures determines the spectral response. Silicon (Si),
gallium arsenide (GaAs), and gallium aluminum arsenide (GaAlAs) are typical detector
materials used for receiver operation in the 850-nm wavelength region. germanium (Ge),
indium phosphide (InP), and indium gallium arsenide (InGaAs) are examples of detector
materials used for receiver operation in the 1300-nm and 1550-nm wavelength regions.
The receiver sensitivity is the minimum amount of optical power required to
achieve a specific receiver performance.
For digital transmission at a given data rate and coding, this performance is described
by a maximum bit-error rate (BER). In analog systems, for a given modulation and
bandwidth, it is described by a minimum signal-to-noise ratio (SNR). Dynamic range
refers to the range of optical power levels over which the receiver operates within the
specified values. It usually is described by the ratio of the maximum input power to the
sensitivity. Before discussing receiver sensitivity, bandwidth, dynamic range, and
Frequency response in more detail, we discuss the main types of optical detectors used in
fiber optics.
Q.1 What is a fiber optic receiver?
Q.2 Which part of the receiver amplifies the electrical signal to a level suitable for
further signal processing?
Q.3 Which performance parameter is the minimum amount of optical power required to achieve
a specific bit-error rate (BER) in digital systems or a given signal-to-noise ratio (SNR)
in analog systems?
Q.4 Define receiver dynamic range.
[ Back ] [ Home ] [ Up ] [ Next ]
