1 Optoelectronics Yongcai Yang 13641617342. 2 Chapter 1 General Introduction

Prof. Yang, School of Optical-Electrical and Computer Engineering , USST 1

Optoelectronics

Yongcai Yang

13641617342


Chapter 1General Introduction


Modern Information Technology Includes:1. Information collection----Sensor

3. Information processing----Computer and NetOptoelectronic Information Technology Includes1. Optoelectric Sensor----Detection and Control2. Fiber-Optic Communication3. Optic computer and All-optical network

The Key Technology is the conversion:Electrical signal – Optical, Optical signal--electrical

2. Information transmission----Communication


Optoelectronics:

To research all kind of the elements and devices to realize information conversion .

Semiconductor Optoelectronics:

To study semiconductor elements and devices to realize information conversion.

Including: Principle

Structure

Characteristic

Application


Detection Principle ：Measured Physical quantity is converted into luminous flux and flux is converted into electric signal in order to get exact physical quantityOptoelectric Sensor +signal processing

Characteristics 1 、 Online measurement 2 、 No contacting measurement 3 、 Active measurement 4 、 Electronic vision system--Artificial eye

1. Photoelectric techonologyand application


The schematic diagram


Application 1: Fiber-optic communication


Transmitter: Convert the electrical signal into light one. Using Light-emitting diode(LED) and Laser diode(LD)Receiver: Convert the light signal into electrical one . PIN and APD.Fiber: As a transmission medium which uses principle of total internal reflection of light. Repeater: Convert an optical signal into an electrical one, process the electrical signal and convert it back into optical form for continued transmission. A very good example is Pan American Cable System , a worldwide network which links seven countries in South America with North America, Europe and Asia The total length is 7300km. It’s a 2700km undersea cable with 23 repeaters installed every 120km.The other cable buried in soil has with 40 repeaters every 115km.

It will be instead of the optical amplifier.

Applications: Telephone, Cable TV and Computer Networks.


Application 2: Network



Application 3: Freihgter to hold up the missile


2 、 The basics of optics Light is 1. Electromagnetic (EM) wave ----In the wave view 2. A ray or beam ----In the geometric optics view3. A stream of photons ---- In the quantum view Wavelength:λ Velocity: c Frequency:

The period: T Spectrum

= 1/T λ = c

Interference



Ultraviolet: 190~400nm Violet: 400 - 420 nm Indigo: 420 - 440 nm Blue: 440 - 490 nm Green: 490 - 570 nm Yellow: 570 - 585 nm Orange: 585 - 620 nm Red: 620 - 780 nm


Total internal reflection :

When light travels from a medium with a higher refractive index to a medium with a lower refractive index and it strikes the boundary at more than the critical incident angle, (θ1 >θ1C )all light will be reflected back to the incident medium, meaning it will not penetrate the second medium. Total internal reflection is a necessary condition to make optical fiber work as a communications link.


Light source (illumination) 1879 Lamp --First generation illumination 1938 Fluorescence--Second generation illumination 1959 Halogen lamp 1960 Laser 1961 High voltage sodium lamp 1962 Metal halide lamp 2000 LED began to use as illumination in room--Third generation illumination .


Lens: to focus the beam of light focus, focal length , parallel light, uniformity, i

ntensityMirror: to change the direction of light reflecting mirror, concave mirror, convex mirr

orDimmer: to change the luminous flux filter, diaphragm, light wedge, polarizer Modulator: to change the intensity of the radiat

ed power from maximum to minimum also to change the modulation frequency of light flux

Optic elements and devices


Internal (or direct) modulation:

The intensity of the radiated power is changed from maximum to minimum by simply changing the driving current .

External modulation:

To put a modulating wheel or special modulator in light path to order to modulate the luminous flux .


Mach-Zehnder (MDM) external modulator


Bohr's model Bohr's model assumes that electrons rotate on stationary orbits and possess a stationary value of energy.An atom can be at any of these levels and it can change its energy only by jumping from one level to another; In level only discretely .


A PhotonWhat happens if an atom jumps from an upper level to a lower level, from level E3 to level E2? There is an energy difference, ΔE = E3 – E2 , and this difference will be released as a quantum of energy , which is called a photon . A photon as a particle, an elementary particle that carries a quantum of energy, EP, and that travels with the speed of light c , A photon's energy, EP, is defined as follows: EP = h Where h is Planck's constant (h = 6.626 10-

34 J . s) and is the photon's frequency.The higher the photon's frequency, the more energy it carries. Light is a stream of photons.


Einstein 1879--1955


Atoms want to exist at the lowest possible energy levels. To raise them to higher levels, we must use an external energy. The process of making atoms jump to the higher levels is called pumping.When atoms drop to the lower levels, it radiating photons.


The Energy band theory of

semiconductor


Conclusion:1. The value of Eg determines the conductive (resistive) properties of the material. Good conductors have no gap, good insulators have a big energy gap, and semiconductors have a gap in between.2. If an excited electron falls from a conduction band to a valence band, it may release a photon if the energy gap is greater than the photon energy. 3. To make a semiconductor radiate, it is necessary to excite a significant number of electrons at the conduction band—pumping.4. The wavelength (the color) of radiated light is determined by the energy gap of the radiating material.


Risistance Automatic control the current Capacitance The voltage between two sides can

not be changed suddenly Charge :The voltage between two sides is increase

d. Discharge: The voltage decreased. Coupled C—series connection—to stop the slow c

hanging signals Filter C– to eliminate the noises and disturbances

—parallel connection (Low voltage circuits) Inductance The current through it can not be cha

nged suddenly. To eliminate the noise and disturbance—series connection (High-current circuts)

3 、 The basics of circuits


Input impedance , Output impedance Impedance matching, Amplification coefficient Voltage follower Noninverting amplifier inverting amplifier Adder amplifier Subtracter Frequency selecting amplifier—transistor Sample and hold circuit Field effect transistor Comparator--Schmitt trigger (return difference

, positive feedback)


Integrated Operational amplifier



Schmitt decision circuit

Properties: 1.There is a return difference between the triggering voltages to reduce the effect of the noise and disturbance . 2.There is a positive feedback .


Test 1Please draw up the output waveforms when C is big or small respectively according the input waveforms (intermediate frequency).


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1 Optoelectronics Yongcai Yang 13641617342. 2 Chapter 1 General Introduction