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Photonics
Photonics is that branch of Science which deals with the production, control and detection of
photons. In Photonics, photons have more or less the same roles as electrons in Electronics. Photonic
devices have a number of advantages over electronic devices because of the very high speed of light. So the
information transmitted photonically can travel very long distances within a very short time.
Solid State Lighting (SSL): Solid state lighting deals with devices which gives light output by carrying
current. It is a type of lighting that uses mainly LEDs. This type of lighting has higher efficiency, reliability
and environmentally friendly technology compared to the conventional incandescent lighting.
Light Emitting Diode (LED)
LED is a heavily doped pn junction diode of suitable materials that emit light when it is forward biased.
I red
+ - green
P + - N
m
symbol + -
depletion region
o
forward biasing
.c V
Block diagram of LED V- I characteristics
Working
es
During forward bias, free electrons from conduction band of n region, and holes from valence band of p
t
region moves towards depletion region and recombine together.
no
During recombination, electromagnetic radiation is emitted with energy equal to band gap energy.
hc
la
Eg = h = where is frequency; c is the velocity of light and is the wavelength.
ra
The band gap energy determines the colour or wavelength of the emitted light.
Applications
ke
used as indicator light.
used in remote sensor.
used for fancy light and decoration.
used in optical communication.
Advantages
low power consumption.
has lower life.
smaller size.
Disadvantages
Output is low.
Intensity of light is small.
7
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Incoherent light is produced.
Photo detectors
A photo detector is a device which converts optical signal to electrical signals. These devices are widely
used in optical communication systems. They should have high sensitivity, low noise, low cost, low
response time, wide bandwidth etc.
Junction Photodiode
.
symbol
- +
This is a reverse biased p-n junction semiconductor device P N
--- -++
which converts light into current. - -
- - depletion region
Working: RL
In reverse bias condition, a small current is produced due to
m
the flow of minority carriers from P and N sides. This current is called dark current.
o
If light is incident at the junction (depletion region), large number of free electrons and holes are created
known as photocarriers.
.c
es
Due to the flow of these free electrons and holes, a current is created called photocurrent.
Magnitude of current depends on the intensity of light incident on it.
t
no
Uses: Used in CD players, smoke detectors, remote control devices.
la
P-I-N Photodiode (P-type – intrinsic – N-type)
ra
In PIN photodiode, a thick intrinsic semiconducting layer
P I N
is inserted between heavily doped P and N region. This is
ke
to improve the sensitivity of the photodiode.
RL
When light is incident on the diode, electrons are excited from the
valence band to the conduction band producing a large number of electron – hole pairs.
Because of its large width, the intrinsic layer absorbs very large number of incoming photons compared
to the P and N regions.
This increases the photocurrent and improves the efficiency, speed and sensitivity compared to that in
photodiode.
Solar cell (Photovoltaic cell)
Solar cells are PN junction diode, it absorbs radiant energy or
sunlight and converts it into electrical energy.
Solar cell consists of a heavily doped p-n junction.
8
For More Study Materials : www.keralanotes.com
Photonics
Photonics is that branch of Science which deals with the production, control and detection of
photons. In Photonics, photons have more or less the same roles as electrons in Electronics. Photonic
devices have a number of advantages over electronic devices because of the very high speed of light. So the
information transmitted photonically can travel very long distances within a very short time.
Solid State Lighting (SSL): Solid state lighting deals with devices which gives light output by carrying
current. It is a type of lighting that uses mainly LEDs. This type of lighting has higher efficiency, reliability
and environmentally friendly technology compared to the conventional incandescent lighting.
Light Emitting Diode (LED)
LED is a heavily doped pn junction diode of suitable materials that emit light when it is forward biased.
I red
+ - green
P + - N
m
symbol + -
depletion region
o
forward biasing
.c V
Block diagram of LED V- I characteristics
Working
es
During forward bias, free electrons from conduction band of n region, and holes from valence band of p
t
region moves towards depletion region and recombine together.
no
During recombination, electromagnetic radiation is emitted with energy equal to band gap energy.
hc
la
Eg = h = where is frequency; c is the velocity of light and is the wavelength.
ra
The band gap energy determines the colour or wavelength of the emitted light.
Applications
ke
used as indicator light.
used in remote sensor.
used for fancy light and decoration.
used in optical communication.
Advantages
low power consumption.
has lower life.
smaller size.
Disadvantages
Output is low.
Intensity of light is small.
7
For More Study Materials : www.keralanotes.com
, https://www.keralanotes.com/
Incoherent light is produced.
Photo detectors
A photo detector is a device which converts optical signal to electrical signals. These devices are widely
used in optical communication systems. They should have high sensitivity, low noise, low cost, low
response time, wide bandwidth etc.
Junction Photodiode
.
symbol
- +
This is a reverse biased p-n junction semiconductor device P N
--- -++
which converts light into current. - -
- - depletion region
Working: RL
In reverse bias condition, a small current is produced due to
m
the flow of minority carriers from P and N sides. This current is called dark current.
o
If light is incident at the junction (depletion region), large number of free electrons and holes are created
known as photocarriers.
.c
es
Due to the flow of these free electrons and holes, a current is created called photocurrent.
Magnitude of current depends on the intensity of light incident on it.
t
no
Uses: Used in CD players, smoke detectors, remote control devices.
la
P-I-N Photodiode (P-type – intrinsic – N-type)
ra
In PIN photodiode, a thick intrinsic semiconducting layer
P I N
is inserted between heavily doped P and N region. This is
ke
to improve the sensitivity of the photodiode.
RL
When light is incident on the diode, electrons are excited from the
valence band to the conduction band producing a large number of electron – hole pairs.
Because of its large width, the intrinsic layer absorbs very large number of incoming photons compared
to the P and N regions.
This increases the photocurrent and improves the efficiency, speed and sensitivity compared to that in
photodiode.
Solar cell (Photovoltaic cell)
Solar cells are PN junction diode, it absorbs radiant energy or
sunlight and converts it into electrical energy.
Solar cell consists of a heavily doped p-n junction.
8
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