This document discusses photodetectors and their applications. Photodetectors convert optical signals to electrical signals and are the fundamental component of optical receivers. They work on the principle of the photoelectric effect. Good photodetectors have high sensitivity at desired wavelengths, fast response time, compatibility with system dimensions, low noise, insensitivity to temperature, and long operating life at a reasonable cost. Applications of photodetectors include fiber optic communications, safety and security systems, process control, environmental sensing, astronomy, and defense. The document outlines specific examples and uses of photodetectors in each of these application areas.

1. Presentation By:M RAKESH
1MS13MCM04

2.  INTRODUCTION
 PHOTODETECTOR REQUIREMENTS
 APPLICATIONS
1.
FIBEROPTIC COMMUNICATIONS
2.
3.
4.
5.
6.
SYSTEMS
SAFETY AND SECURITY
PROCESS CONTROL
ENVIRONMENTAL SENSING
ASTRONOMY
DEFENCE

3. • Optical receivers convert optical signal
(light) to electrical signal (current/voltage)
• Photodetector is the fundamental element
of optical receiver, followed by amplifiers
and signal conditioning circuitry
• It works on the principle of Photoelectric
effect

4. • Good sensitivity (responsivity) at the desired
wavelength and poor responsivity elsewhere 
wavelength selectivity
• Fast response time  high bandwidth
• Compatible physical dimensions
• Low noise
• Insensitive to temperature variations
• Long operating life and reasonable cost

5. o COMMUNICATIONS
 The radiation is
simply the carrier for
an encoded signal
 Ex- Fiberoptic
communications
o REMOTE-SENSING
 The radiation is the
signal, conveying
information about an
object or scene.
 Ex- Safety & security
devices

6. • Photodetectors operate at IR region
• Detectors are Photodiodes (InGaAs)
• Data communication rates as high as 2.5
Gbits/s

8. • The detection of the presence or absence
of an object
• Detectors are Photoconductors
• Collision detection in automobile industry
• In factories, electrical arc detection,
automatically cutting off the current where
arcing occurs.

9. • Used as position sensors to check that a
work piece is in the proper place
• Comparison of radiation intensity at
different wavelengths
• In recycling plants
• Non-destructive testing units
• Detector systems can endure extreme
environmental conditions

10. •
•
•
•
Pollution detection by UV spectroscopy
Fluorescence spectroscopy
Chemiluminescence
solid particulates in air and water can be
detected by amount of light scattered
• Lidar scattering for monitoring of pollution
over large areas
• Satellite-mounted IR spectrometers can
measure ozone concentrations

11. • FIRST- by ESA for UV rays
• x-ray telescopes such as ROSAT
• The Fly's Eye detector respond to
ultrahigh-energy cosmic rays entering the
top of Earth's atmosphere
• Visible light photodetectors immersed in
millions of gallons of ocean water

12. • Tunable IR detectors to distinguish the
decoys from real targets
• Satellite-borne staring array detectors to
isolate warm targets against a warm
background
• Infrared scanning from aircraft reveals the
location of land mines
• Work is well advanced on adapting military
night vision IR detector systems to enhance
driver vision beyond the reach of headlights.

13. • The most advanced detectors tend to be
made for low-volume specialized fields
• Thermography, measuring the heat
radiated by the human body
• Observe rapid biochemical reactions with
ultrahigh-speed CCDs
• Cameras used for tracing chemical
diffusion in individual cells