OPTI 6103/8103: Light Sources & Detectors

Instructor: Vasily N. Astratov
Office: Grigg 332 (lab, Grigg 349)
Phone: 704-687-8131
E-mail: astratov@uncc.edu
Webpage: http://pages.charlotte.edu/vasily-astratov/
Office hours: TBD

Prerequisite

Physics students should be enrolled in Optical Science and Engineering or Applied Physics programs, ECE students are welcome to take this course

Lecture

Thu 5:00 – 7:30pm, Grigg 131

Subjects covered

principles of lasers, semiconductor lasers and light emitting diodes, optical detection and detectors, modulation and deflection of optical beams, photonic crystals and microresonators

Mid-term exam on Thursday, October 21, 5:00-7:30pm.

Text

Final selection of the main text will be done in the beginning of the Fall semester. Here is the list of texts which are currently under consideration.

Fundamentals of Photonics by B.E.A. Saleh and M.L. Teich, John Wiley & Sons, 1991 or later edition.
Elements of Optoelectronics and Fiber Optics by Chin-Lin Chen, Irwin, 1996

Grading

Homework	30%
Midterm	25%
Final	25%
Presentation	20%

A ≥ 90; 80 ≤ B ≤ 89; 70 ≤ C ≤ 79; U < 70

Class attendance

Attendance of all lectures, exams and presentation session is expected. If you have to miss an exam because of illness or other circumstances beyond your control please notify the instructor in advance. Only in this case you may be given a make-up test. This can be made only once. There is no make-up for a missed presentation.

Academic integrity

Students have the responsibility to know and observe the requirements of The UNC Charlotte Code of Student Academic Integrity. The standards of academic integrity will be enforced in this course. The code forbids cheating, fabrication or falsification of information, multiple submissions of academic work, plagiarism, abuse of academic materials, and complicity in academic dishonesty. You may work with study partners and discuss the subject matter with them. However, each student is individually responsible for his/her tests, papers, and reports. The UNC Charlotte Code of Student Academic Integrity is published in the current University Catalog.

Motivation

Sources and detectors of light are important components of practically any optical system. The area of photonics and optoelectronics has been created with the invention of lasers in 1960s and with the realization of low-loss optical fibers in 1970. These developments have resulted in creating modern information technology and Internet. This has been achieved with many breakthroughs in physics and technology of light sources and detectors. The examples include development of systems with quantum size quantization (quantum wells, wires and dots), distributed feedback and VCSEL lasers and other structures and devices. By understanding and engineering the materials and structures used for generating and detecting light one can achieve ultimate goals of modern photonics and optoelectronics – integration of electronics and optics at a level where new physical phenomena are observed, and new functionality is created – functionality not possible with electrons or electromagnetic waves separated.

Course Outline

This is only a preliminary course description, some topics can be modified or new topics can be added, the depth and coverage scope of various topics may vary.

1. Principles of Lasers

The nature of light, blackbody radiation, photons, quantized energy levels, emission and absorption of light, optical amplifiers, optical resonators, lasers, continuum and pulsed lasers, selected gaseous and solid-state systems.

2. Semiconductor Lasers and Diodes

Intrinsic and extrinsic semiconductors, light-matter interaction, ternary and quaternary semiconductors, heterostructures, quantum wells, wires and dots, homojunctions and heterojunctions, light emitting diodes, injection lasers, distributed feedback lasers and vertical cavity surface emitting (VCSEL) lasers.

3. Optical Detectors

Thermal detectors and photon detectors, quantum efficiency of semiconductor detectors, photoconductors, photovoltaic detectors, PIN diodes, avalance photodiodes, noise and noise equivalent power.

4. Modulators and Deflectors

State of polarization, acoustooptic, electrooptic and magnetooptic effects, Faraday rotation and magnetooptic modulators, index ellipsoid, linear electrooptic effect, electrooptic modulators, acoustooptic modulators and deflectors, Raman-Nath and Bragg diffraction.

5. Photonic Crystals and Microresonators

Wave propagation in periodic systems, 1D/2D/3D crystal examples, photonic band gap, control of emission, dielectric microspheres and their optical properties.

Home Works

Note: Write down equations if any and solve in detail. Also clearly state if any assumptions or approximations are used in solution. Make diagrams where appropriate.

Home Work 1
Due Date: September 14

Click at this link to get the end of Chapter 3 problems from Chin-Lin Chen book:

Problem #2 (Chapter 3)
Problem #4 (Chapter 3)
Problem #5 (Chapter 3)
Problem #8 (Chapter 3)
Problem #10 (Chapter 3)

Home Work 2
Due Date: September 27

Click at this link to get the end of Chapter 3 problems from Chin-Lin Chen book:

Problem #13 (Chapter 3)
Problem #15 (Chapter 3)
Problem #17 (Chapter 3)
Problem #21 (Chapter 3)

Home Work 3
Due Date: October 11

Click at this link to get the end of Chapter 4 problems from Chin-Lin Chen book:

Note: Write down equations if any and solve in detail. Also clearly state if any assumptions or approximations are used in solutions. Make diagrams when appropriate.

1. An electron in free space has its kinetic energy equal to ħ²k²/(2m_e). Calculate the ration of free-space to crystal momentum of an electron in GaAs for:

(a) Conduction band
(b) Valence band

2. (a) In GaAs what electron density must be put into the conduction band to fill the band to DE_c=0.005 eV above its band-edge at T=0^o K.

(b) If a 1 mm³ GaAs sample is used, and each electron has 1 ns life-time in conduction band, how many electrons must be injected per second to maintain the population constant, and what current this corresponds to?

3. Problem # 1 (Chapter 4)

4. Problem # 5 (Chapter 4)

5. Problem # 8 (Chapter 4)

6. Problem # 10 (Chapter 4)

Home Work 4
Due Date: November 8

1. Problem # 4 (Chapter 5)

2. Problem # 5 (Chapter 5)

3. A pn-junction detector has a quantum efficiency of 50% at a wavelength of 0.9 micron.

(a) What is the responsivity at the wavelength of 0.9 micron?
(b) What is the maximum possible size of the bandgap of the material?
(c) Based on your answer to part b, make a sketch of the responsivity of this detector as a function of wavelength between 0.1 and 1.5 micron (assume that the energy of the photon with the wavelength 0.9 micron corresponds to the bandgap).

4. Using Internet or any other sources find the absorption spectrum (absorption coefficient versus wavelength) for Ge at room temperature. Calculate the optimum thickness (assume 90% absorption in the intrinsic region) of the intrinsic layer for a Ge pin diode for operation at

(a) Wavelength of 0.6 micron
(b) Wavelength of 1.2 micron
(c) Wavelength of 1.8 micron
(d) What is the responsivity for each of these detectors?

Plus 4 additional problems

Problem 1. The concentration of charge carriers in a sample of intrinsic Si is n_i = 2.5 x 10¹⁰ cm^-3 and the recombination lifetime is t_c = 10microsecond. If the material is illuminated with light, and an optical power density of 10 mW/cm³ at lyamda = 1 micron is absorbed by the material, determine how much the increase in its conductivity is. The quantum efficiency is equal to 0.7.

Problem 2. For a particular PIN photodiode, a pulse of light containing 9 x 10¹² incident photons at wavelength of 1.55 micron gives rise to, on average, 3 x 10¹² electrons collected at the terminals of the device. Determine the quantum efficiency and current responsivity of the photodiode at this wavelength.

Problem 3. A conventional avalanche photodiode (APD) with gain M = 30 operates at a wavelength of 1.55 mm. If its current responsivity at this wavelength is equal to 12 A/W, calculate its quantum efficiency. What is the photocurrent at the output of the device if a photon flux F = 2 x 10¹⁰photons/s, at this same wavelength, is incident on it?

Problem 4. a) Assume that the ionization rates for electrons and holes are equal for APD, if applied voltage is V = 0.95 V_B, where V_B ~ L^-1/3 – breakdown voltage (where L = 10 micron – thickness of APD). Calculate the gain M of APD.

b) Calculate the gain of such device if the ionization rate for electrons is fixed on previously found level, but the ionization rate for holes is reduced by half.

Home Work 5
Due Date: To Be Determined

To Be Uploaded

Home Work 6
Due Date: To Be Determined