Optical sources and detectors

Characteristics of Optical Sources and detectors

1. Optical Sources and Detectors Subject Teacher Mrs. Pallavi Mahagaonkar Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) Fiber Optics Communication

2. To understand the principles of fiber optic communication system. To learn measure different parameter of optical fibers To understand essential optical components of Fiber Optic Communication To study the applications of fiber optic communication systems Learning Objectives: Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele)

3. LED and LASER diode Principles of operation Concepts of line-width, phase noise, switching and modulation characteristics-typical LED and LD structures PN detector PIN detector Avalanche photodiode-principles of operation, Concepts of responsivity Sensitivity Quantum efficiency Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) Optical sources and detectors

4. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) High intensity output Easy Modulation Size & configuration LED & LASER Monochromatic Highly reliable & Low noise Coupling From One fiber to other Cost Effective Optical source

5. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) Light Emitting Diode

6. Light Emitting Diode Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele)

7. Light Amplification by Stimulated Emission of Radiation Applications – Medical , Scientific and Commercial laser printers barcode scanners DNA sequencing instruments fiber-optic semiconducting chip manufacturing free-space optical communication  laser surgery and skin treatments cutting and welding materials LASER: Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele)

8. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) Photo Detectors CHARACTERISTICS REQUIRED: Capability to sense light power and convert to corresponding varying current Very high efficiency required to convert all of weak input power to desired signal High response or sensitivity in desired wavelength. Minimum noise Fast response speed and high bandwidth Insensitive to temperature variation Physically compatible dimension of optical fiber Low cost and long life

9. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) PHOTO DETECTORS - TYPES Photomultipliers – Photocathode and electron multiplier in vacuum tube High gain, low noise Large size and high voltage required Pyro -electric crystals – Photon to heat conversion Variation in dielectric constant gives change in capacitance Cooling arrangements required Semiconductor photo detectors – Size is large Photodiodes

10. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) PHOTO DETECTORS - ADVANTAGES Small size Suitable material High sensitivity Fast response time Types of photo diodes – PiN diode Avalanche Photodiode APD

11. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) PHOTO DETECTOR A photodiode is a PN-junction diode that consumes light energy to produce electric current. Sometimes it is also called as photo-detector, a light detector, and photo-sensor. These diodes are particularly designed to work in reverse bias condition, it means that the P-side of the photodiode is associated with the negative terminal of the battery and n-side is connected to the positive terminal of the battery.

12. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) PHOTO DETECTOR WORKING  When a photon of ample energy strikes the diode, It makes a couple of an electron-hole This mechanism is also called as the inner photoelectric effect If the absorption arises in the depletion region junction then the carriers are removed from the junction by the inbuilt electric field of the depletion region The holes in the region move toward the anode, and electrons move toward the cathode, and a photocurrent will be generated The entire current through the diode is the sum of the absence of light and the photocurrent So the absent current must be reduced to maximize the sensitivity of the device

13. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) PIN DETECTOR: A PIN diode is a diode with a wide, lightly doped 'near' intrinsic semiconductor region between a p- type semiconductor and an n-type semiconductor region. The p-type and n-type regions are typically heavily doped because they are used for ohmic contacts. The wide intrinsic region is in contrast to an ordinary PN diode. The wide intrinsic region makes the PIN diode an inferior rectifier (one typical function of a diode), but it makes the PIN diode suitable for attenuators, fast switches, photo detectors, and high voltage power electronics applications. The speed of the PIN diode is limited by variation in the time it takes electrons to pass through the device. This time spread can be spread in two ways: By increasing the bias-voltage By reducing the thickness of intrinsic layer TYPES: Metal-Semiconductor PIN diode Hetero junction PIN diode

14. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) PIN DETECTOR: A microwave PIN diode is a semiconductor device that operates as a variable resistor at RF and Microwave frequencies. A PIN diode is a current controlled device in contrast to a varactor diode which is a voltage controlled device. When the forward bias control current of the PIN diode is varied continuously, it can be used for attenuating, levelling, and amplitude modulating an RF signal.

15. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) PIN DETECTOR APPLICATIONS It is used as a Photo Detector for most fiber optic application They are used in electronic pre-amplifier to boost sensitivity They are used as a variable resistor in at RF and microwave frequency Widely used in RF modulator circuit to control RF intermediation distortion In a phase shifter circuit considered as a lumped variable-impedance microwave circuit element PIN diodes are utilized as series or shunt connected switches in phase shifter designs The switched elements are either lengths of transmission line or reactive elements

16. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) Avalanche Photo Diode INTRODUCTION: The performance of Avalanche photo diode depends upon the efficiency. It convert light energy in to electrical signal. Designed to operate in reverse bias condition Photo electric effect:

17. Prepared By Mrs. Pallavi Mahagaonkar for TYB.Sc(Ele) Avalanche Photo Diode  High gain due to avalanche multiplication effect Increased noise Si- InGaAs APD often used(diagram on right) n + p + pi Electricfield Depletion region High resistivity p-doped layer increases electric field across absorbing region High-energy electron-hole pairs ionize other sites to multiply the current Leads to greater sensitivity