Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Lectures 11 and 12: Lasers, LEDs and Photodiodes ECEN 4606, Fall 2010, Prof. Gopinath
Professor J. GopinathUniversity of Colorado at Boulder
ECEN 4606, Undergraduate Optics Lab
ECEN 4606Undergraduate Optics Lab
Lasers, LEDs and Photodiodes
Professor J. Gopinath
Professor J. GopinathUniversity of Colorado at Boulder
ECEN 4606, Undergraduate Optics Lab
Administrative Details
• No prelab or lab reports this week• Averages
- Lab #6 <av>= 86, σ = 10- Prelab #7 <av>= 16, σ = 2.5
• Lab reports- Most of problems are in analysis- If your score is not what you’d like, focus on analysis
section first!• Handouts
- Lecture notes- Polarization practice for final
• Final project- Need to get it approved by Nov. 17- Prelab #13 (due Wed. Dec. 1, should contain diagram of experimental setup, list of parts needed, and goal of experiment – see revised schedule!
• Office hours- My office hours this week will be 11 – noon Wed., but Friday office hours are cancelled- Dongxue’s office hours will be 11 – 12:30 pm on Friday (not the usual Wed. ones)
Professor J. GopinathUniversity of Colorado at Boulder
ECEN 4606, Undergraduate Optics Lab
Lasers vs. lampsIncandescent lampLaser
Efficiency
Wall-plug efficiency is optical powerout to electrical power in. As high as60% for diode lasers, 30% for diode-pumped solid states.
Luminous efficiency is power in visiblespectrum / electrical power in. As lowas 2% for incandescent bulbs. Filterscan reduce spectral width butdramatically reduce efficiency.
Brightness
[ ][ ]( ) [ ]( )
2
2
2220 radm
W
0
=
=
Mn
MwL
wn
λφ
πφ
πλ
= 1012 [W/m2/Sr] for a perfect 1 W laserat λ = 1 um in air.
[ ][ ]( ) [ ]( )Sr4mareafilament
W2 π
φ=L
= 105 [W/m2/Sr] for a bulb with a 1 mm2
filament emitting 1 WProf. McLeod, CU-Boulder
Professor J. GopinathUniversity of Colorado at Boulder
ECEN 4606, Undergraduate Optics Lab
Indirect vs. Direct Absorption
Fox: Optical Properties of Materials
Professor J. GopinathUniversity of Colorado at Boulder
ECEN 4606, Undergraduate Optics Lab
Modes of photodiode operation
Prof. McLeod, CU-Boulder
Open circuit•aka “Photovoltaic”•Solar cells•Low dark current•Slow response
Short circuit
Reversed biased• Drift field increase speed• Lower capacitance• Larger sensitive area
Larger R allows for:1. More sensitivity2. Smaller range3. Smaller
bandwidth
νη
hPei
ieii
P
PTK
e
rsB
≡
−
−= 1
v
P
P
P
Professor J. GopinathUniversity of Colorado at Boulder
ECEN 4606, Undergraduate Optics Lab
Pn and PIN diodes
• pn: Response time faster than photoconductor (due to E) but limited by diffusion which may be as large as carrier recombination lifetime.
• pin: Increased depletion layer width gives:• larger capture area• decreased capacitance (faster response)
pn:
pin:
1. e- & h+ recombine and do not contribute
to current2. e- & h+ may diffuse
into depletion region3. e- & h+ drift under E
field
Depletion
E
-+
n p i D
iffus
ion
Diff
usio
n
1 32
Depletion
E
-+
n p Diff
usio
n
Diff
usio
n
21 3
Professor J. GopinathUniversity of Colorado at Boulder
ECEN 4606, Undergraduate Optics Lab
Photodiode responsivity
• Only respond to photons with energy above bandgap
• If energies are much, much greater than bandgap, will all be absorbed in bulk and there is no current!
www.thorlabs.comwww.udt.com
Professor J. GopinathUniversity of Colorado at Boulder
ECEN 4606, Undergraduate Optics Lab
Dark Current
Sharp PD412PI
id vs temperature at VR = 10 V id vs bias at 25 oC
Typical dark current for Si photodiode
Prof. McLeod, CU-Boulder
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