Chapter 9
Analog Optical Fiber Channels
Abstract Although usually there is a major emphasis on digital transmission links,
in many instances it is more advantageous to transmit information in its original
analog form instead of first converting it to a digital format. For example, as a result
of the increasing use of broadband wireless communication devices, schemes have
been investigated and implemented for using analog optical fiber links for distributing
broadband microwave-frequency signals in a variety of applications. This chapter
addresses these methods, which have become known as RF-over-fiber techniques.
Historically in optical fiber networks the trend has been to use digital transmission schemes. A major reason for this was that digital integrated-circuit technology
offered a reliable and economic method of transmitting both voice and data signals.
However, in many instances it is more advantageous to transmit information in its
original analog form instead of first converting the information to a digital format.
Key applications are in microwave photonics and radio-over-fiber channels [1–9].
Most analog applications use laser diode transmitters, so the discussion here will
concentrate on this optical source.
When implementing an analog fiber optic system, the main parameters to consider
are the carrier-to-noise ratio, bandwidth, spurious-free dynamic range, and signal
distortion resulting from nonlinearities in the transmission system. Section 9.1
describes the general operational aspects and components of an analog fiber optic
link. Traditionally, in an analog system a carrier-to-noise ratio analysis is used instead
of a signal-to-noise ratio analysis, because the information signal is normally superimposed on a radio-frequency (RF) carrier. Thus in Sect. 9.2 carrier-to-noise ratio
requirements are examined. This is first done for a single channel under the assumption that the information signal is directly modulated onto an optical carrier (e.g., a
constant laser output).
For transmitting multiple signals over the same channel, a multichannel modulation technique can be used. In this method, which is described in Sect. 9.3, the information signals are first superimposed on underlying RF subcarriers. These carriers
then are combined and the resulting electrical signal is used to modulate the optical
carrier. A limiting factor in these systems is the signal impairment arising from
harmonic and intermodulation distortions.
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
G. Keiser, Fiber Optic Communications,
https://doi.org/10.1007/978-981-33-4665-9_9
363
Analog Optical Fiber Channels
Abstract Although usually there is a major emphasis on digital transmission links,
in many instances it is more advantageous to transmit information in its original
analog form instead of first converting it to a digital format. For example, as a result
of the increasing use of broadband wireless communication devices, schemes have
been investigated and implemented for using analog optical fiber links for distributing
broadband microwave-frequency signals in a variety of applications. This chapter
addresses these methods, which have become known as RF-over-fiber techniques.
Historically in optical fiber networks the trend has been to use digital transmission schemes. A major reason for this was that digital integrated-circuit technology
offered a reliable and economic method of transmitting both voice and data signals.
However, in many instances it is more advantageous to transmit information in its
original analog form instead of first converting the information to a digital format.
Key applications are in microwave photonics and radio-over-fiber channels [1–9].
Most analog applications use laser diode transmitters, so the discussion here will
concentrate on this optical source.
When implementing an analog fiber optic system, the main parameters to consider
are the carrier-to-noise ratio, bandwidth, spurious-free dynamic range, and signal
distortion resulting from nonlinearities in the transmission system. Section 9.1
describes the general operational aspects and components of an analog fiber optic
link. Traditionally, in an analog system a carrier-to-noise ratio analysis is used instead
of a signal-to-noise ratio analysis, because the information signal is normally superimposed on a radio-frequency (RF) carrier. Thus in Sect. 9.2 carrier-to-noise ratio
requirements are examined. This is first done for a single channel under the assumption that the information signal is directly modulated onto an optical carrier (e.g., a
constant laser output).
For transmitting multiple signals over the same channel, a multichannel modulation technique can be used. In this method, which is described in Sect. 9.3, the information signals are first superimposed on underlying RF subcarriers. These carriers
then are combined and the resulting electrical signal is used to modulate the optical
carrier. A limiting factor in these systems is the signal impairment arising from
harmonic and intermodulation distortions.
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
G. Keiser, Fiber Optic Communications,
https://doi.org/10.1007/978-981-33-4665-9_9
363