An optical detector converts optical signals into electrical signals, with various types available for different parts of the electromagnetic spectrum, including photon and thermal detectors. Noise, both internal and external, can interfere with the detection of weak optical signals, requiring optimization of the detector and amplification circuitry for effective performance. Sensitivity in optical systems is defined by the minimum signal power needed for certain performance levels, with key specifications being receiver sensitivity and dbrn sensitivity.

1. Optical detector NOISE &SENSITIVITY

2. Optical detector
• An optical detector is a Transducer that converts an optical signal into
an electrical signal.
• Transducers are devices that convert input energy of one form into
output energy of another ..It does this by generating an electrical
current proportional to the intensity of incident optical radiation.
• Optical detectors convert incoming optical energy into electrical
signals.
• Photon detectors produce one electron for each incoming photon of
optical energy.

4. • The electron is then detected by the electronic circuitry.
• Thermal detectors convert the optical energy to heat energy, which
then generates an electrical signal
Example:
• Examples are optical radar, monitoring of laser power levels for
materials prosessiong.
• Different types of optical detector are available, covering the
ultraviolet , visible and infrared portions of the electromegnatic
spectrum..

5. • Photodetector Noise
In fiber optics communication systems, the photodiode is
generally required to detect very weak optical signals.
• Detection of weak optical signals requires that the
photodetector and its amplification circuitry be optimized to
maintain a given signal to noise ratio.

6. Noise:
It is the undesirable signal it marks the signal that it is to be deducted
It can be internal or external
Noise which is generated inside the communication system within a device or a circuit
Example
thermal noise ,shot noise
External noise generated outside the device or circuit system
Example
Atmospheric Noise -----Man made or industrial noise

7. Types of noise
• Short noise:
• Discrete nature of electrons causes a signal disturbance called shot
noise ..
• deutation of actual number of electrons from the average number is
known as shot noise
• thermal noise:
it is generated by thermal fluctuations in conducting materials also
known as Nyquist noise
Thermal noise current i is given by:
i²t=4KTB/R
K= boltzman constant B= post-detection band width
T=Absolute temperature

8. Sensitivity:
• It is defined as the minimum signal optical power level required at the receiver to
achieve a certain BER performance
• Constant sensitivity
• A test measures your ability to distinguish between finer and finer increments of
light various dark contrast
• Receiver sensitivity
• most widely used specification of optical receiver in fibre optics system it is
defined as the minimum signal optical power level required at the receiver to
achieve certain BER performance
• DBrn sensitivity:The ability of a receiver to identify and amplify signal at the
receivers input is called receiver sensitivity it is expressed in dBm
Thank you