10-05-2013, 04:28 PM
Microwave Photonics for Space Applications
[attachment=53715]
INTRODUCTION
• Hardly two decades back, it was almost impossible to convince
an RF engineer that
– direct detection using photo detectors with internal gain
control could be of value and that one didn’t need a
heterodyne receiver at visible wavelengths to achieve good
sensitivity.
– that micro radiation tracking was possible
• It was not well understood that the noise limitations for optical
communication systems were significantly different than for RF
systems and that the quantum noise which was of unconcern to
RF engineer, could dominate the S/N issues.
• Who would have imagined in 1970s
– that the major highways of the terrestrial communication
network would be optical fiber systems instead of analog coaxial
cable systems and microwave radio relay systems.
– that fiber systems would give an option of Gbits/sec system
operation
– that one could have repeaterless system in thousands of
kilometers
– that fiber systems would challenge satellite
communication systems
– that fiber systems would surpass the traffic density
handled by satellite systems
• Where microwave and optics meet
– Although digital transmission over fiber optic links is
commonplace today, the ability to handle analog
signals with arbitrary modulation in photonic systems
is relatively recent development
– The technology makes it possible to bring the
advantages of fiber optics to radio frequency (RF)
and microwave transmission systems, including
systems that use Amplitude Modulation.
– With the devices that are now available, RF or
microwave applications now can make use of fiber
optic links, whether the transmission distance is 10
meters or 20 kilometers
• Analog fiber optic links:
– Compared with digital signal transmission,
analog RF & microwave transmissions cover a
much wider spectrum
– The signal to noise (S/N) ratio for analog
systems - particularly AM systems such as
CATV-must be much higher than in digital
systems.
• Calls for fiber optic laser transmitters with low noise
– With specially engineered devices, a number of
important RF and microwave frequency bands are
now well within the range of current analog fiber
optic technology.
• Analog fiber optic applications:
– Fiber optic technology is now being used in a variety of
demanding analog applications
• Replaces heavy coaxial and spline cable links
• Protect receivers, down converters etc. from harsh
environments without costly repeaters
• absolute signal security
• inter facility links for satellite ground stations at
intermediate frequency (IF), C-band or Ku-band.
• In Telemetry tracking systems, fiber optic links make it
possible to locate receivers at a convenient and safe
distance from the antenna pedestal while maintaining
secure link between antenna and the receiver.
[attachment=53715]
INTRODUCTION
• Hardly two decades back, it was almost impossible to convince
an RF engineer that
– direct detection using photo detectors with internal gain
control could be of value and that one didn’t need a
heterodyne receiver at visible wavelengths to achieve good
sensitivity.
– that micro radiation tracking was possible
• It was not well understood that the noise limitations for optical
communication systems were significantly different than for RF
systems and that the quantum noise which was of unconcern to
RF engineer, could dominate the S/N issues.
• Who would have imagined in 1970s
– that the major highways of the terrestrial communication
network would be optical fiber systems instead of analog coaxial
cable systems and microwave radio relay systems.
– that fiber systems would give an option of Gbits/sec system
operation
– that one could have repeaterless system in thousands of
kilometers
– that fiber systems would challenge satellite
communication systems
– that fiber systems would surpass the traffic density
handled by satellite systems
• Where microwave and optics meet
– Although digital transmission over fiber optic links is
commonplace today, the ability to handle analog
signals with arbitrary modulation in photonic systems
is relatively recent development
– The technology makes it possible to bring the
advantages of fiber optics to radio frequency (RF)
and microwave transmission systems, including
systems that use Amplitude Modulation.
– With the devices that are now available, RF or
microwave applications now can make use of fiber
optic links, whether the transmission distance is 10
meters or 20 kilometers
• Analog fiber optic links:
– Compared with digital signal transmission,
analog RF & microwave transmissions cover a
much wider spectrum
– The signal to noise (S/N) ratio for analog
systems - particularly AM systems such as
CATV-must be much higher than in digital
systems.
• Calls for fiber optic laser transmitters with low noise
– With specially engineered devices, a number of
important RF and microwave frequency bands are
now well within the range of current analog fiber
optic technology.
• Analog fiber optic applications:
– Fiber optic technology is now being used in a variety of
demanding analog applications
• Replaces heavy coaxial and spline cable links
• Protect receivers, down converters etc. from harsh
environments without costly repeaters
• absolute signal security
• inter facility links for satellite ground stations at
intermediate frequency (IF), C-band or Ku-band.
• In Telemetry tracking systems, fiber optic links make it
possible to locate receivers at a convenient and safe
distance from the antenna pedestal while maintaining
secure link between antenna and the receiver.