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Title: Optoelectronics:%20the%20opportunity%20-%20optoelectronics%20has%20come%20of%20age!

Optoelectronics the opportunity-
optoelectronics has come of age!
Professor Wilson Sibbett, University of St Andrews
This perspective is reproduced from a
presentation given at an inauguration
mini-symposium on the Optoelectronics College
held in November 2007 at the Ballathie House
Hotel .
Introductory remarks
  • Electronic devices are all around us but what
    about devices that exploit optoelectronics?
  • Everyday optoelectronic technologies range from
    flat-screen displays (TVs, computers, mobile
    phones ) through the checkout bar-scanners to
    internet communications links
  • A growing number of healthcare-related
    implementations of optoelectronics are beginning
    to emerge in biology and medicine
  • In Scotland, we have notable research strengths
    in optoelectronics and efforts are being made to
    translate these into more widespread and
    practical applications

Basis of this overview
  • Let us start with an historical perspective on
  • Then, consider semiconductor devices as the
    bridge between electronics and optoelectronics
  • Starting with LEDs we proceed to lasers
  • We can consider the translation of science to
  • We can look at a few representative applications
    of optoelectronics
  • All of this has implications for the teaching of

2007 marks a century of optoelectronics
  • HENRY J. ROUND was a key figure in the histroy of
    optoelectronics. He was
  • One of Marconis Assistants in England and
    later the Chief of Marconi Research he
    published a 24-line note in Electrical World
    reporting a bright glow from a carborundum
  • Round, H. J., Electrical World, 49, 308 (1907)
  • Was Henry Round the discoverer of the LED? Maybe
    not but most definitely he can be credited with
    the discovery of electroluminescence!
  • In any case, 1907 can be pinpointed as the year
    of birth for optical electronics or

Oleg Vladimirovich LOSEV the short life of a
  • We must acknowledge the early work of pioneer, Dr
    Oleg Losev (1903-1942)
  • He was the son of a Russian Imperial Army Officer
    but the politics of the day denied him any career
    path in Bolshevik Russia!
  • Sadly, he died of hunger at the age of 39 during
    the blockade of Leningrad!

Oleg Losev the discoverer of the LED?
  • He was remarkable as self-educated scientist.
    His PhD degree was awarded in 1938 by the Ioffe
    Institute (Leningrad) without a formal thesis
    because he had published 43 journal papers and 16
  • Working in a besieged Leningrad (1941), he
    discovered that a 3-terminal semiconductor device
    could be constructed to have characteristics
    similar to those of a triode valve but
    circumstances prevented publication! Losev had
    probably invented the TRANSISTOR!
  • Mid-1920s Oleg Losev observed light emission
    from electrically-biased zinc oxide and silicon
    carbide crystal rectifier diodes Light Emitting
    Diodes or LEDs!
  • Called the inverse photo-electric effect, Losev
    worked out the theory of LED operation and
    studied the emission spectra and even observed
    spectral narrowing at high drive currents
    evidence perhaps of the stimulated emission that
    applies to lasers?!
  • Notably, the first significant blue LED
    re-invented in the 1990s used silicon carbide!!

Semiconductor LEDs and lasers
  • LEDs are now commonplace in games consoles,
    remote controls, vehicle lights, traffic lights
    and, increasingly, in domestic lighting
  • By the end of this decade, the market value is
    predicted to reach 15B!
  • Semiconductor lasers the LED process is at the
    core of this effect and laser action was first
    reported in 1962 by four US research groups (2 at
    GE, IBM, MIT)
  • The are many everyday applications of
    semiconductor lasers in barcode readers, CD DVD
    players, optical-carrier sources for
    communications and internet data
  • NB The optical frequency for the optimum
    telecommunications wavelength (1500nm) is
    extremely high - equivalent to 200 THz (i.e.

Major areas of commercial growth in the
optoelectronics marketplace
  • Flat-panel displays recorded sales are up 30
    year on year currently, 8 growth in Europe
    USA and 9 in Japan
  • Solid-state vehicle lighting much more than just
    brake lights!
  • Solid-state domestic lighting replacement of
    incandescent lighting with LED-based sources
    would reduce CO2 emissions by many millions of
    tonnes worldwide!
  • Power generation solar cell technologies are
    progressing steadily for example, in Germany a
    new power station based on solar cells is
    producing 5MW to power up 1800 households

Recent advances in LEDs for domestic lighting
  • By way of background
  • Incandescent lights are not efficient and have a
    so-called luminous efficacy of 13-14 lumens/Watt
  • Halogen lighting is a little more efficient at
  • Fluorescent lights are significantly better with
    typical luminous efficacies of 60-70L/W
  • More recently
  • White LEDs have achieved 100L/W and, in the
    laboratory, figures up to 300L/W have been
    reported for tailored warm-white LED lighting!

Organic semiconductors
  • We can now have organic materials that have
    exploitable semiconducting characteristics. These
  • Conjugated molecules
  • Novel types of semiconductors
  • Easy processing schemes
  • LED compatibility
  • Physical flexibility

Organic light emitting diodes (OLEDs)
  • These diagrams illustrate the basic OLED

Examples of some OLED displays
Sony ultra-thin 13 display
Kodak viewfinder
Epson widescreen display
Photo-dynamic therapy (PDT)
ALA cream is applied to the site of the skin
tumour (5-aminolevulinic acid)
Exposure to light induces the PP9 to produce
singlet molecular oxygen that leads to local cell
kill within the tumour
The sensitised tumour region is then exposed
to intense light from a source such as a laser or
A typical scar-free outcome from photo-dynamic
therapy or PDT of a skin cancer
Potential of OLEDs for PDT
  • OLEDs have the advantages of
  • Uniform illumination
  • Light weight so can be worn
  • Relatively low intensity for longer treatment
  • So reduced pain, increased effectiveness
  • Low cost - disposable
  • Attractive for hygiene
  • Widens access to PDT
  • A simple wearable power supply
  • Ambulatory treatment1
  • At work
  • At home

1. See for example, Moseley et al,
Brit.Jour.Derm., 154, 747 (2006)
Typical device application cycle
Device applied
Device worn during normal daily activities
Skin cancer treated with OLED-based PDT
Effective treatment with reduced scarring and pain
Concept of spontaneous emission
  • Consider an excited atom
  • This excited atom will relax over some
    characteristic relaxation time
  • If photons are produced during the relaxation
    process this is called spontaneous emission
  • This emission process is independent of external

Concept of stimulated emission
Excited Atom
Incident Photon
Stimulated Transition
Incident Photon
Emitted Photon
  • An excited atom can be stimulated to emit a
  • This process is called stimulated emission
  • The stimulated photon is an exact copy of the
    photon that induced the transition
  • A repeat of this process leads to the optical
    gain which represents the basis of laser action

A laser or laser oscillator
  • Stimulated emission provides optical gain
  • Photons reflected by the resonator mirrors cause
    an avalanche of stimulated emission along the
    axis of the resonator
  • A high intensity beam of light thus builds up in
    the laser resonator
  • A collimated and directional laser beam emerges
    from a partially transmitting exit mirror

A semiconductor diode laser chip
p-type GaAlAs
200nm active GaAs layer
n-type GaAlAs
  • Cleaved or cleaved-and-coated facets act as the
    mirrors in a diode laser
  • This is the preferred source for optical

Absorption of light by major tissue chromophores
Illumination of a hand and wrist area with light
in 700nm, 800nm, 900nm spectral regions
illustrates clearly the deeper penetration at the
longer wavelengths into the biological tissue
Treatment of varicose veins
  • The laser used produces green pulses of light for
    strong absorption in blood but having durations
    matched to the tissue thermal relaxation time.

Skin resurfacing using lasers
  • Laser skin resurfacing is becoming the method of
  • preferable to chemical peels or dermabrasion
  • A pulsed carbon dioxide laser is used

We can now consider digital optoelectronics
  • Lasers can be made to produce either
  • - constant
    intensity beams, or
  • - sequences of
    discrete optical pulses or optical digits

Why might we wish to use optical digits?
  • The laser pulses or optical digits can have
    very high peak intensity
  • Thus, these light impulses can induce either
    single- photon or rather more interesting
    multiple-photon interactions
  • The advantage is strong near-infrared absorption
    (in tissue) with interactions involving two or
    three photons that are equivalent to green or
    blue/uv light
  • The average power or heating effect can be at a
    modest level to avoid tissue damage
  • Ultrashort pulses picoseconds (10-12s) and
    femtoseconds (10-15s) also imply short exposure
    times and so we have ultrafast (or snapshot)

An example of a multiple-photon excitation
  • This multi-photon excitation is localised both in
    space and in time
  • - interactions occur primarily at the
    beam focus for the ultrashort light pulses
  • - penetration of long-wavelength light
    but interaction may involve 2,3 photons!

Multi-photon excitation for treatment of cancer
tumours (PDT)
For example Melanoma on skin in mice
The laser pulses are in the near-infrared
(1047nm) but 3-photon absorption is exploited for
the photo-dynamic therapy (PDT)
Photogen Inc, Knoxville Tennessee Massachusetts
Eye Ear Infirmary
Snapshots in the millisecond regimeEadweard
Muybridge Galloping Horse, 1887
Flash photography with microsecond exposures
  • The motion can be effectivelt frozen using
    short pulses of light
  • - e.g., using 1 microsecond flashes from a xenon

An example of frozen motion! Harold Edgerton,
MIT, 1964
Concept of prompt imaging
  • An ultrashort laser pulse passing through a
    scattering medium carries image information via
    three components as illustrated

Seeing through raw chicken!
Photograph of two crossed metal needles (0.5mm
The needles viewed through a 6mm slab of raw
chicken breast in ordinary illumination
Snapshot image of the needles using femtosecond
illuminating and gating pulses
Laser beam propagation in optical fibres
many-km-lengths of glass!
  • Intensity
  • either continuous or pulsed
  • Focusability
  • efficient coupling propagation of laser beams
    in optical fibres

Optical fibre
Many applications in endoscopy and
Optical fibres
Optoelectronic communications
Optoelectronic datacomms at 100Tb/s!
  • What data speed does this represent?

High-speed data transfer - DVDs

Other information media?
gt 600 DVD movies!!
in one second
An application in biology involves the poration
of cells to provide access to low penetration
Corrective eye surgery using laser pulses
  • Schematic of a laser-pulse produced flap
  • laser pulses focused 160µm below the tissue
    surface to produce micro-cavitations
  • subsequent micro-machined cut to provide hinged

Femtosecond laser-based eye surgery
  • Femtosecond-laser-based Keratomileusis procedure
  • Laser pulses are focused and scanned to outline
    with micron precision a lens-shaped block of
    corneal stroma or lenticule
  • This lenticule is then removed and the corneal
    flap replaced

Optoelectronics for peace weapons
  • Femtosecond laser pulses cut pellets of
    high-explosive and metals

Cut in PETN (LX-16) with 500ps laser pulses
Cut in HNS (LX-15) with femtosecond laser pulses
KEY ADVANTAGES - this process offers a high
safety status - there are no solid HE waste
products - this offers decommissioning
F Roeske Jr et al
Concluding remarks
  • Optoelectronic devices have come of age and have
    opened up a wide range of exciting possibilities
    both within science and in the products used in
    everyday life
  • These are re-defining many of the boundaries of
    modern life and technology
  • Some knowledge of optoelectronics is vital for
    all of us living in the 21st century
  • It follows, therefore, that the teaching of some
    practical skills in optoelectronics should now
    form an exciting part of a modern science
    curriculum and education!
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