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Fiber Optics in Sensors and Contr ol Systems
2. The receiver sensitivity is 2 μW. 159
3. The receiver budget (dB) is calculated as:
dB = 10 log [(available light input)/(required light output)]
= 10 log [(200 μW)/(2 μW)]
= 10 log 100
= 20 dB

4. Three major sources of loss are estimated as:
• 2 to 3 dB loss for each end connector
• 1 to 2 dB loss for each splice
• 1 dB/150 m loss for fiber of 200 μm diameter

Most manufacturers specify the optical power budget and trans-
late this into a recommended distance.

3.12.2 Digital Links—Pulsed
The one-for-one creation of a light pulse for an electrical pulse is
shown in Fig. 3.32. This represents the simplest form of data link. It
does not matter what format and signal level the electrical data takes
(e.g., whether IEEE RS-232 or RS-422 standard format or CMOS or
TTL logic level), as long as the interface circuitry is designed to accept
them at its input or reproduce them at the output. Voltage conversion
may be achieved from one end of the link to the other, if desired,
through appropriate interface selection.
The light pulses racing down the fiber are independent of electri-
cal protocol. Several design factors are relevant to these and other
types of data links as follows:
• Minimum output power. The amount of light, typically mea-
sured in microwatts, provided to a specific fiber size from the
data link’s light source
• Fiber size. Determined from the data link’s light source.
• Receiver sensitivity. The amount of light, typically measured
in microwatts or nanowatts, required to activate the data
link’s light detector.
• Data rate. The maximum rate at which data can be accurately
transmitted.
• Bit error rate (BER). The frequency with which a light pulse is
–9
erroneously interpreted (for example, 10 BER means no
9
more than one of 10 pulses will be incorrect).
• Pulse-width distortion. The time-based disparity between
input and output pulse widths. The simple pulse link is also