Photonics Engineering

1. Photonics Engineering Prof. Hosoeng Kim Optical Signal & Laser Application Lab. Chung-Ang University

2. 광응용공학 (PHOTONICS ENGINEERING) 담당교수 (Instructor) 김호성 (Kim Hoseong) 5292 http://prof.cau.ac.kr/~laser 010-2514-5292 강의시간/강의실 (Room/Time) 207관(봅스트홀) 604 강의실 월5,6 / 수6 상담가능시간 (Office Hour for Advice) 월 10-11 E-mail hkim@cau.ac.kr 과목 개요 (Course Description) This course introduces light applications such as optical communication and Flat Panel Display to understand these applications, this course covers properties of light, lenses , optical systems, light sources including lasers, Detectors and Fiber optics. 수업 목표 (Course Goals) Understanding the optical engineering and improve design skill. 강의 진행 방식 Power Point, Demonstration, Design Project (optical receiver design and simulation) 학습 평가 방법 Homework 10%, Midterm 25%, Project 30%, Final 35% 기타 안내 사항 It is not necessary to buy two text books but it is recommended strongly to buy one of two. Slides of PowerPoint can be dowloaded from my homepage. 교재: Optics Hecht, Optoelectronics and Photonics Kasap (2001)

3. 주별강의 내용/과제 (Weekly Course Schedule/Assignments) 1주차 강의내용 (1 week Topic(s)) 1.Propagation of light. 2주차 강의내용 (2 week Topic(s)) 1.Propagation of light. 3주차 강의내용 (3 week Topic(s)) 2.Lenses and aberrations 4주차 강의내용 (4 week Topic(s)) 2.Lenses and aberrations 5주차 강의내용 (5 week Topic(s)) 3.Simple optical instruments. 6주차 강의내용 (6 week Topic(s)) 4.Detectors. 7주차 강의내용 (7 week Topic(s)) 5.Light modulators. 8주차 강의내용 (8 week Topic(s)) 6.Illuminators and condensers. 9주차 강의내용 (9 week Topic(s)) 7.Lasers. 10주차 강의내용 (10 week Topic(s)) 7.Lasers. 11주차 강의내용 (11 week Topic(s)) 8.Diffraction theory. 12주차 강의내용 (12 week Topic(s)) 9.Interference. 13주차 강의내용 (13 week Topic(s)) 10. Optical communication 14주차 강의내용 (14 week Topic(s)) 11. Displays 15주차 강의내용 (15 week Topic(s)) 12. Holography, and 3D Display 16주차 강의내용 (16 week Topic(s)) Exam

4. Prof. Hosoeng Kim(1) • 1976년 2월경복고등학교 졸업(마지막 고교입시) • 1976년 3월 서울대학교 전기공학과 입학 English Discussion 동아리 • 1977년 겨울방학 AFKN 받아 쓰기 • 1978년 9월 English Discussion 동아리 회장 • 1979년 3월 서울시 성수동에서 노동 야학 10월 박정희 서거 운동권? 취업? 진학? 군입대? • 1980년 2월 동 대학 전기공학과 학사 3월 동 대학 전기공학과 대학원 입학 5월 광주사태, 휴교령 9월 개학, 공부에 몰두함 박사 및 교수를 목표로 함 • 1982년 2월동 대학 전기공학과 석사

5. Prof. Hosoeng Kim(2) • 1982년 3월-8월 석사장교 소위 임관 및 전역 • 1983년 3월-1983년 8월 서울대 박사과정 • 1983년 9월 - 1986년 8월 금성전기기술연구소 주임연구원(연구소장 권유) 3년 후 유학보장 Low Noise Amplifier and downconvertor for satellite communication • 1984년 4월 결혼, 86년 장녀 출생 • 1986년 9월 - 1988년 8월(새로운 학문을, 내 돈으로…) State University of NY at Buffalo 공학석사 • 1988년 9월 - 1992년 8월 동 대학 공학박사 “Laser Applications to Superconducting Thin Film Deposition and Laser Drilling” • 1993년 3월 - 현재 중앙대학교 전자전기공학부 교수 • Laser Applications : Laser Metrology, MOEMS, Light sensors, Optical system design, circuits…..

6. What One’s Future Will Be • 성공은 능력이 아니라 의지에 달려 있다. • 4학년의 고민 - 진로: 취업(중앙대생이라면 언제라도 가능) 진학: 본교, 유학, 석사, 박사? (돈, 머리, 체력. 의지는 기본) • 꿈은 이루어진다!!! • 배우자 고르기 (controllable, observable) • CEO되기: 지성인? 지식인 인가? 너 자신을 알라!!!

7. Laser Light Amplification by Stimulated Emission of Radiation (lase (v)) Features Monochromatism Coherence Small divergence Ultra short pulse

8. Red Blue Monochromatism (single frequency or color) • Very narrow bandwidth (linewidth) ex) stabilized HeNe laser: λ=632.8 nm f=4.74x1014 Hz ∆λ= 10-6(nm), ∆f=1 MHz • Very high quality factor: ~108 • Immune to chromatic aberration • Very small focus: a few micrometer diameter • Application to Interferometer.

9. Coherence(可干涉性, 결맞음) • The spatial and temporal phase variation of the electric field of the two waves are the same. • Characteristics of stimulated emission. • Spatial coherence, temporal coherence • Holography, Interference, Speckles.

10. θ Small Divergence • Divergence: The bending of rays away from each other or the spreading of a laser beam with increased distance from the exit aperture. • Divergence angle of typical HeNe laser • 1 mr = 0.0573o • Alignment, distance measurements (earth to moon) • Weapon guiding : Gulf War • Tight focusing • 800 m in diameter on the moon (400,000 km from earth) Apollo 11

11. Ultra Short Pulse • ∆t = 10 fs ~ us - λ=3 x 108 x 10 x 10-15 = 3 x 10-6 m = 3 μm - Diameter of human hair : 100 μm • Ultra high intensity(=power density W/cm2) -1 mJ, 10 ps, on 10-4 cm2 I > 1012 W/cm2 • Laser drilling, cutting, welding • Laser Weapon - SDI (Strategic Defense Initiative), MD

13. E(V/m) A T0 T5 T4 T3 T2 T1 ∙ ∙ ∙ ∙ ∙ ∙ O Z(m) -A Chapter 1 Basic Properties of Light Light is described using 3 pictures. Waves Rays Photons seemingly contradictory! Waves [Reading Assignment: Hecht, Chapter 2 (most of this should be review), 3.2, 3.3, 3.4.4, 3.5, 3.6] A propagating “disturbance” in electric and magnetic field (simultaneously!) Example: • At a fixed point in space, the electric field oscillates in time. At a fixed point in time, we see a wave train frozen. • This is called a plane-wave because the field is constant everywhere in the x-y plane at a given z.

14. Another way to draw the plane wave is “wave-fronts” surface of constant “phase” or “phase-fronts” • The wavefront advances by a distance λ, in a time 1/f. So the velocity is υ = distance/time = λf. One of the many remarkable properties of light is it’s universal, constant speed: • The physics of electromagnetic (EM) wave propagation is valid for arbitraryλ, f. On Earth, we can generate, manipulate and/or detect EM waves with wavelength from ~100 km all the way down to ~ 10-6Ǻ.Usually we describe light by wavelength rather then frequency, except in the microwave and radio regions. • The electromagnetic spectrum encompasses the complete range of frequency/wavelength. Different regions have different names. Radio, microwave, infrared, visible, ultraviolet, x-ray, γ-ray.

15. Red Blue Index of Refraction • When light travels in materials, the speed is modified: Usually n≥ 1. (It can be < 1) • The reason is that the electric field shakes the electrons, which tends to drag the field. • Plane wave still has the same form: But the effective wavelength becomes modified by n. If we define the vacuum wavelength, λvac=c/f ,then in the material, The wavelength becomes shorter, if n≥ 1. Dispersion The index of refraction in most materials depends on wavelength: In air – the index depends also on air pressure, humidity, and temperature which leads to many beautiful atmospheric effects.

16. - All information-bearing signals consist of a band of frequencies. - Waves of the component frequencies travel with different velocities, causing a distortion in the signal wave shape. - This phenomenon is called dispersion. Wavelength units (length) Visible light: 4000~7000 Ǻ, 400 ~700 nm, 0.4 ~0.7 μm

17. Spherical Waves Another type of ideal light wave. Constant phase fronts are circular, emanating from a point source. Far away from the source, the radius of the circle becomes so large that we can approximate the wave as a plane wave. For spherical waves, we have Huygens’ Principle Very useful model for wave propagation. • Every point on a wavefront is regarded as a secondary point source generating a spherical wavelet. • The advance of the wave front is found at the envelope of all these wavelets. • Generally, this seems to give parallel wavefronts. But things get interesting at edges. This leads to diffraction (more later).

18. Rays • Follow a point on the wavefront. As the wavefront advances the point traces a straight line. This is a ray of light. • For many cases, we can forget the waves and just trace rays in optical systems. This allows a vast simplification of our analysis and design processes. Virtually all optical design is done with rays. Highly sophisticated optical design CAD programs are available for ray tracing. Photons (light “particles”) • This picture has light represented by tiny bundles of energy (or quanta), following straight line paths along the rays. • The coexistence of electromagnetic wave physics and photon physics is the central paradox of quantum mechanics. • One photon has an energy given by E = hν, ν: frequency in Hz For 2 eV visible photons, h = 6.62× 10-34 J-s : plank’s constant 1 W = 6.3 × 1018eV/s = 3.15 × 1018 photons/sec 1 W = 1 J per second

19. Photoelectric Effect Novel Prize to Einstein

20. Interaction of Radiation and Matters • Atoms have energy states corresponding to electron orbits. • One atom “jumps” from a higher energy state to a lower energy state and emits one photon. 2 ∆E = hv ∆E = hv 1 • Spontaneous emission • random phase, polarization Stimulated absorption Stimulated emission ∆E = hv • Same Phase • Same polarization • Laser!! • Photons are not point particles. They have a wave-like property. A useful picture is the wave-packet. The typical photon energy unit is the electron-Volt. This is defined as the energy required to push one electron across a one-Volt potential, Many photon packets can be thought of as superimposing to make up a plane wave, spherical wave or any other 1eV= 1.6 ×10-19J Typical visible photon energy : 1.2 ~ 2.3 eV

21. Reflection and Refraction, Snell’s Law [Reading assignment: Hecht 4.3, 4.4, 4.7] An important element of optics is the interface between two materials with different index of refraction. Total Reflection The refracted ray disappears! The light is totally reflected. This usually occurs inside a prism , and is called total internal reflection. θC= “critical angle”. For a typical glass with n = 1.5, the critical angle is: If n1 > n2, then we can have θC = 20.9o

22. Light Impinging at a Surface [Cheng p411, 8-10.2,8-10.3] The plane containing the light ray propagation vector and the surface normal is called the “plane of incidence” • For a general polarization state incident on a surface, we choose s and p directions to decompose the polarization effects. Fresnel Reflection Coefficients Near θ1 = 0, : Fresnel Loss No reflection for p-polarization wave! Brewster angle or Polarizing angle. [Hecht 8.6]

23. Polarization [Cheng p364, Hecht 8.1, 8.2] • Light waves have transverse polarization. • The electric field vector points in a direction perpendicular to the propagation direction (ray direction). • The magnetic field vector is orthogonal to propagation direction. Generally, we can ignore the magnetic field. • The E-field vector can lie anywhere in transverse plane

24. Polarization State • The e-field oscillates in time at a given point in space • For light wave propagating in z-direction, let’s look in the x-y plane. AM: linear polarization, with E field perpendicular to the ground TV: linear polarization, with E field parallel to the ground FM: circular polarization with the surface perpendicular to the ground

25. y α x - Set z=0, - Analytically, - Which leads to the following equation for an ellipse: E(0,t) ω E2 E1 0 - Circularly polarized if <Circular polarization> - Elliptically polarized if

26. 1 Polarizers are devices which select one polarization. • Polarizing sheet has an allowed direction – transmits polarization component of incident light along the allowed direction – transmitted light is linearly polarized (can be used to analyze input polarization state) • Polarizing beamsplitter • Polaroid sunglasses are filter out the light of which E-field is parallel to the ground since