A laser diode emits at 10mW constant optical power with a flat RIN spectral density of -130 db/Hz. Find the electrical bandwidth so that the RMS optical power fluction is less than 0.1 mW?
Answers
Answer:
In semiconductor lasers, output optical power may fluctuate due to the existence of spontaneous emission, thus producing intensity noise. Since the quality of a laser output depends on the ratio between the noise power and the total optical power, a commonly used measure of laser intensity noise is the relative intensity noise (RIN), which is defined as
(1.1.50)
where SP(ω) is the intensity noise power spectral density and Popt is the total optical power. Obviously, SP(ω) increases with the increase of the total optical power. RIN is a convenient way to characterize a laser quality. Generally, RIN is a function of frequency; it peaks around relaxation oscillation frequency because of the interaction between carrier density and photon density. The unit of RIN is [Hz−1] or [dB/Hz], as a relative measure.
Terrestrial Amplified Lightwave System Design
Chungpeng Fan, J.P. Kunz, in Optical Fiber Telecommunications (Third Edition), Volume A, 1997
A APPLICATIONS
The optical amplifier provides a method of increasing the optical output power from an end-terminal system by more than 10 dB. In addition, the optical amplifier can be used in a repeater configuration. These two features allow the optical amplifier to be used to increase the distance between end-terminal equipment. As shown in Fig. 9.6, when a system using traditional regenerators with typical regenerator spacing is compared with an amplified system, it is obvious that the amplified system greatly reduces the amount of equipment needed in the network. The cost of the network is, therefore, reduced. The application, then, for optical amplifier systems occurs in those systems where the amplifier can replace many repeater sites. Which systems require many repeaters? These types of systems include
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Fig. 9.6. Equipment comparison — regenerators versus optical amplifiers. DWDM, dense wavelength-division multiplex; LRBC, line repeater bay controller; OA, optical amplifier; REGEN, regenerator; TCC, telemetry channel controller.
(1)
Systems that cover large physical distances. Examples of these are undersea systems and the terrestrial systems that extend across continents (New York to Los Angeles, for example).
(2)
Systems that use optical fiber that has very high loss. The expense of replacing that fiber is very high. To use the fiber would require regenerators every few miles. An optical amplifier system can extend the distances between repeater sites by two, three, or four times.
(3)
Systems that make use of WDM technology. These components typically add 10–20 dB of loss between terminals. The loss in the WDM technology can be overcome with the addition of an optical amplifier.
Explanation: