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15-GHz & 25-GHz Photodetectors Operation • 5
Operation
Introduction
High-speed measurements are easy with the Models
1480 and 1481 photodetector modules. These
modules convert your optical signals to electronic
signals, in effect giving every high-speed/high-
frequency instrument in your lab an optical input.
Each module connects directly to the test instrument
or amplifier, eliminating the need for coaxial cables,
which could seriously distort picosecond pulses and
attenuate microwave signals. The optical signal is
delivered to the photodiode in the module through a
multimode optical fiber. Moreover, the photodiode
bias circuit and battery are self-contained, eliminating
the hassle of external power supplies and expensive
bias networks and reducing the possibility of
photodiode damage due to overvoltage.
The Models 1480 and 1481 use a GaAs PIN photodiode
designed for high responsivity in the 780–870-nm
wavelength range. The high-speed circuitry produces a
clean impulse response, making these models ideal for
digital communication measurements. A 50-
Ω
terminating resistor minimizes electrical reflections,
which helps to minimize ringing when used with
amplifiers which may not have perfect 50-
Ω
inputs.
The Model 1480 has an internal 62.5-µm multimode
fiber which delivers the input light to the 65-µm-
diameter photodiode, permitting the use of delivery
fibers with core diameters of 62.5 µm or smaller,
1480 FC Det revA.fm Page 5 Monday, March 13, 2000 2:55 PM