Introduction to Photonics Lecture 1 Introduction(2)

  • Published on
    10-Oct-2015

  • View
    38

  • Download
    0

Embed Size (px)

DESCRIPTION

Photonics lecture

Transcript

  • Introduction to Photonics

    Lecture 1: IntroductionSeptember 3, 2014

    Course syllabus Introduction to photonics Optics for communications Ray optics

  • Syllabus

    Course: ENG EC 560, Introduction to Photonics (4 credits) Lectures: Mon/Wed 2-4pm, PHO 211

    Instructor: Jonathan Klamkin, klamkin@bu.edu, PHO 828 Office Hours: Tue 10-11am, Wed 4-5pm, or by appointment

    Textbook: Fundamentals of Photonics, Saleh & Teich Supplemental Books: Optics, Hecht; Photonics: Optical

    Electronics in Modern Communications, Yariv and Yeh; Integrated Photonics, Pollock and Lipson; Diode Lasers and Photonic Integrated Circuits, Coldren, Corzine and Masanovic

    Grading policy: Homework (30%), Exam 1 (35%), Exam 2 (35%),

    2

  • Our BookFundamentals of Photonics

    Second Edition

    B. E. A. Saleh, M. C. Teich, John Wiley & Sons Inc., NY (2007)

    3

  • Course Objectives

    4

    Introduce physical principles and engineering applications of optical fields and their interactions with materials

    Learn design principles governing the behavior of optical components and photonic devices

    Basic theories and key concepts Basic optical components and devices Ray Optics Wave Optics Fourier Optics Electromagnetic Optics Polarization Optics

    Photonic Crystal Optics Guided Wave Optics Fiber Optics Optical Interconnects and Switches

    Integration and Systems Optical Fiber Communications Integrated Photonics

  • Electromagnetic Spectrum

    c=

    wavelength

    frequencyspeed

    5

  • Optical Spectrum

    6

  • Optics versus Photonics

    7

    Optics = Photonics

  • The Pervasiveness of Optics

    8

    Communications Computing Medicine / Biology Defense applications Navigation systems Data storage Imaging NanotechnologyNew industries emerge!

    Optics is everywhere!

  • Photonics: Technology of Light

    9

    Generate, encode, transmit and detect information with optical carrier signals; optical waves carry information with enormous data rates (~Tb/s)

    Example: nearly 1 million simultaneous TV channels (~6 MHz bandwidth per channel) can be transmitted using only 1% of a typical laser frequency (1014 Hz) bandwidth.

    K.C. Kao, inventor of optical fiberNobel Prize Winner, 2009 PROG. IEE, vol. 113, No. 7, July 1966

  • Fiber Optics

    10

    Extremely low loss near 1.55 m ~15 THz of bandwidth available in low-loss region Telecommunications bands: O-band: 1260 1360 nm; S-band: 1492 1530 nm;

    C-band: 1530 1570 nm; L-band: 1570 1612 nm

    Loss spectrum for silica single mode fiber

    Components to generate, manipulate and detect light near 1.3 and 1.55 m

  • Fiber Optics

    11

    Wavelength Division Multiplexing (WDM) Spectrum

    WDM increases fiber utilization 40 channels 100 GHz spacing 40 Gb/s per channel 1.6 Tb/s capacity

  • Optical Fiber Link

    12

  • 13

    Coaxial Cable Loss

    Optical fiber

  • Miniaturization Higher performance Greater functionality Lower energy

    consumption Lower cost

    WDM fiber-optic networksCo-axial cable lines

    14

    Long Distance Communications

  • 15

    Photonics: A Disruptive Technology

    A hard disk

    A letter

    A word

    A library

  • 16

    Revolution in Long-Haul Communications

    Over 420,000 km of fiber in over 100 undersea fiber optic systems are deployed

    Source: J. X. Cai, Tyco Telecommunications

  • Short-Reach Optical Interconnects

    17

    Data center to data center

    Within data center

    Figure of merit: DistanceData Rate

  • 18

    Computer to computer

    Board to board

    Chip to chip

    On chip

    Short-Reach Optical Interconnects

  • Moores Law (1967)

    19

    The number of transistors on a chip will double every two years.

  • Metal Interconnects

    20

    Many levels of metal interconnects for densely integrated circuits

    Multi-tier metal interconnects

  • Microelectronics E(in)volution

    21

    Technology cut-off 0.18m

    Things get smaller, problems get biggerRC time constantsR = L/AC = kA/d

    Local wire interconnection limits the device performance below the 90 nm

  • The Interconnect Bottleneck

    1996 2000 2004 2008 2012 20161k

    10k

    100k

    1M

    i

    n

    t

    e

    c

    o

    n

    n

    e

    c

    t

    l

    e

    n

    g

    h

    t

    /

    c

    h

    i

    p

    (

    m

    /

    c

    m

    2

    )

    year

    From SIA roadmap 2007

    Interconnects limit device performance

    Power dissipation heating Delay latency Spacing crosstalk Cost per interconnect

    22

  • Power Consumption and Dissipation

    23

  • Integrated Optics/Photonics

    24

    Short-medium reach interconnects

    Long-haul telecommunications

    On-chip interconnects

  • Research Level: Nanophotonics

    Quantum dots Metal nanostructures Carbon nanotubes Molecular sensors Photonic crystals Micro resonators Microcavities Plasmonic elements Random lasers

    25

  • Hierarchy of Optics Theories

    Rays

    Waves

    EM waves

    Photons

    Rayoptics

    Start from the center

    26

  • Narcissus, by Michelangelo Caravaggio,ca. 1598.

    27

    Ray Optics

  • Ray optics: geometrical theory concerned with determination of the path of light rays as they reflect from mirrors of various shapes and traverse boundaries between media of various n

    n1

    n2

    n1 n2

    Mirrors

    Boundariesbetweentransparent(homogeneous)media

    n2n1 n1n1 n1n2

    Graded-indexmedia

    Planar Concave Convex

    Scope of Ray Optics

    28

  • Light travels in the form of rays emitted by light sources and observed by opticaldetectors

    A transparent medium is characterized by its refractive index nc = speed of light in the medium = co/nco = speed of light in free space

    Time taken by light to travel a distance d is d/c = nd/co optical path length nd.

    In an inhomogeneous medium the optical path length along a path =

    Fermat's Principle: rays traveling between two points follow a path such that time of travel (or optical path length) is an extremum relative to neighboring paths:

    The extremum is usually a minimum: rays travel along the path of least time.If the minimum time is shared by more than one path, all paths are followedsimultaneously by the rays.

    Postulates of Ray Optics

    Sir Isaac Newton

    Pierre de Fermat

    29

  • Rays A ray is a line drawn is space corresponding to the

    direction of flow of radiant energy Rays are mathematical constructs, not physical

    entities In uniform media rays are straight For isotropic media (the same in all directions) rays

    are perpendicular to the wavefronts (will be clear in wave optics)

    Rays are a useful concept if we can assume: 0

    30

  • Homogenous Media

    31

    n = constant

    Hero's principle: path of minimum distance (= path of shortest time)

    Path of minimum distance between two points is a straight line

    Shadows

  • Fermat's Principle

    Light chooses to travel only along paths of minimum time minimize Optical Path

    Length (OPL)

    32

    Straight ray path in homogeneous medium

  • Fermats Principle

    ++==B

    A

    dzdydxzyxnndsOPL 222),,(

    Light rays follow optical path extrema

    Light bends in nonhomogeneous media

    The optical path length (OPL) is measured in terms of the refractive index n integrated along the trajectory

    33

  • Observation

    The answer is beyond ray optics need wave optics

    Wave optics resolves this problem because wave emitted at A propagates in all directions (with greatly varying amplitude)

    The path of optical length extremum is place where constructive interference occurs between all possible paths

    Preview

    Fermat's principle shows how the ray's destiny is fulfilled (arrives at point B using certain path) but does not explain why the light ray arrives at B instead

    of some other point

    34

  • Law of Reflection

    35

    ProofAB + BC must be a min.Occurs when AB + BC is a min. when B=B

    =

    Applies to reflection from mirror or a boundary between two different media

  • Snells Law

    Proof

    12

    d1

    d2

    d

    A

    C

    B

    Apply Fermats principle: minimize optical path length

    n1d1sec1 + n2d2sec 2

    subject to condition

    d1tan1 + d2tan2 = d

    Law of Refraction

    2211 sinsin nn =

    36

    n1 n2

  • MiragesRays always take a route that minimizes the OPL

    Refractive index decreases with temperature

    37

    Why does image on road appear to wobble?Why does mirage disappear as you approach?

  • Mirrors

    38

    Planar: creation of a virtual source Paraboloidal: parallel rays focus onto a point

    Elliptical: point to point imaging

    Image

    Spherical: no focusing; parallel rays close to axis approximately focused

    Concave R negative

    Convex R positive

    Focus

  • Applications

    39

    What type of mirror is used here?

  • Paraxial Optics

    40

    Paraxial approximation: consider only rays at small inclination angle to the optical axis

    sin tan

    Paraxial optics = first-order optics = Gaussian optics

  • Paraxial Optics

    41

    For paraxial rays, the spherical mirror approximatesparaboloidal mirror and therefore focuses parallel rays into a single point

    For paraxial rays, the spherical mirror approximateselliptical mirror and therefore focuses rays from a single point into another single point

    In the paraxial approximation ( = only paraxial rays considered), a spherical mirror has a focusing property like that of the paraboloidal

    mirror and an imaging property like that of the elliptical mirror.