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The Laser DiodeThe Laser Diode
Jason HillJason HillPhysics 464Physics 464 –– Applied OpticsApplied Optics3/1/053/1/05
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Agenda Agenda
How a Laser Diode WorksHow a Laser Diode Works•• Laser Diode compared to Diode and LEDLaser Diode compared to Diode and LED•• Homojunction vs. HeterojunctionHomojunction vs. Heterojunction•• Edge emitting lasers vs. VCSELsEdge emitting lasers vs. VCSELs
Industrial Applications of the LDIndustrial Applications of the LD•• Laser PointersLaser Pointers
Red & Green lasersRed & Green lasers•• CD/DVDCD/DVD -- ROMROM
Blue, Violet, UltraBlue, Violet, Ultra -- Violet?Violet?
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How a Laser Diode Works
Edge Emitting Laser DiodeCollimating Lens
Operates similar to a Light Emitting DiodeOperates similar to a Light Emitting DiodeActive medium is a semiconductor pActive medium is a semiconductor p -- n junctionn junctionLED utilizes spontaneous emission of radiationLED utilizes spontaneous emission of radiationFabryFabry -- Perot cavity produces stimulated emission of radiationPerot cavity produces stimulated emission of radiation
Light is emitted diffractedLight is emitted diffractedA collimator is needed to focus the beamA collimator is needed to focus the beam
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Edge Emitting vs. Surface EmittingEdge Emitting vs. Surface Emitting
Edge emitting laser:Edge emitting laser: light emission is through thelight emission is through thecleaved edge of the laser. Edge emitters are difficult tocleaved edge of the laser. Edge emitters are difficult to
integrate in large numbersintegrate in large numbersSurface emitting laser:Surface emitting laser: much smaller and can bemuch smaller and can beintegrated in large numbers on a substrate wafer, muchintegrated in large numbers on a substrate wafer, mucheasier to test individually while still on the wafereasier to test individually while still on the wafer
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VCSELsVCSELs
Vertical Cavity Surface Emitting LasersVertical Cavity Surface Emitting LasersVery short optical cavityVery short optical cavity(1(1 -- 33 λλ ))
Quantum wells are used toQuantum wells are used tocontrol optical propertiescontrol optical properties
Require highly reflectiveRequire highly reflectivemirrors (99.9% vs. 30%)mirrors (99.9% vs. 30%)
Metallic mirrors areMetallic mirrors arereplaced with Distributedreplaced with DistributedBragg Reflectors (DBRs)Bragg Reflectors (DBRs)
Metallic Reflector VCSEL
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VCSELsVCSELs
Vertical Cavity Surface Emitting LasersVertical Cavity Surface Emitting LasersVery short optical cavityVery short optical cavity(1(1 -- 33 λλ ))
Quantum wells are used toQuantum wells are used tocontrol optical propertiescontrol optical properties
Require highly reflectiveRequire highly reflectivemirrors (99.9% vs. 30%)mirrors (99.9% vs. 30%)
Metallic mirrors areMetallic mirrors arereplaced with Distributedreplaced with DistributedBragg Reflectors (DBRs)Bragg Reflectors (DBRs)
Etched Well VCSEL
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VCSELsVCSELs
Vertical Cavity Surface Emitting LasersVertical Cavity Surface Emitting LasersVery short opticalVery short opticalcavity (1cavity (1 -- 33 λλ ))
Quantum wells areQuantum wells areused to controlused to controloptical propertiesoptical properties
Require highlyRequire highlyreflective mirrorsreflective mirrors(99.9% vs. 30%)(99.9% vs. 30%) Air Post VCSEL
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VCSELsVCSELs
Vertical Cavity Surface Emitting LasersVertical Cavity Surface Emitting LasersVery short optical cavityVery short optical cavity(1(1 -- 33 λλ ))
Quantum wells are used toQuantum wells are used tocontrol optical propertiescontrol optical properties
Require highly reflectiveRequire highly reflectivemirrors (99.9% vs. 30%)mirrors (99.9% vs. 30%)
Metallic mirrors areMetallic mirrors arereplaced with Distributedreplaced with DistributedBragg Reflectors (DBRs)Bragg Reflectors (DBRs)
Buried Regrowth VCSEL
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Comparison of Red and Green Laser PointersComparison of Red and Green Laser Pointers
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Potassium titany phosphate (KTiOPO 4 ) nonlinear crystalNeodymiumdoped yttrium orthovanadate
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Use of LDs for Optical StorageUse of LDs for Optical StorageDiffraction limits the size of a focused beam to aDiffraction limits the size of a focused beam to aspot with a width on the order of the wavelengthspot with a width on the order of the wavelengthof the light emitted, therefore the wavelengthsof the light emitted, therefore the wavelengthslimits the density of data storage: shorterlimits the density of data storage: shorterwavelengths enable higher storage densitywavelengths enable higher storage density
* This is actually an inaccurate representationof how the data would be arranged, opticaldevices use EFM, EFM+
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Typical CDTypical CD --ROM Optical PickupROM Optical Pickup
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ResourcesResources “ “ BlueBlue LEDsLEDs and Lasers.and Lasers. ” ” eurotechnology.comeurotechnology.com . 15 Sept. 2004. 26 Feb.. 15 Sept. 2004. 26 Feb.
20052005
Dupuis, Russell D.Dupuis, Russell D. “ “ The Diode Laser, The First 30 Days, 40 Years Ago.The Diode Laser, The First 30 Days, 40 Years Ago. ” ”
Optics & Photonics NewsOptics & Photonics News Apr. 2004. 27 Jan. 2005Apr. 2004. 27 Jan. 2005
Goldwasser, Samuel M.Goldwasser, Samuel M. “ “ Diode Lasers.Diode Lasers. ” ” SamSam ’ ’ s Laser FAQs Laser FAQ . 19 Dec.. 19 Dec.2004. 28 Jan. 20052004. 28 Jan. 2005
“ “ Laser Diode.Laser Diode. ” ” Radio Electronics.comRadio Electronics.com . 28 Jan. 2005. Adrio. 28 Jan. 2005. AdrioCommunications Ltd. 28 Jan. 2005Communications Ltd. 28 Jan. 2005
Suematsu, Y,.Suematsu, Y,. Semiconductor Lasers and Photonic Integrated CircuitsSemiconductor Lasers and Photonic Integrated Circuits ..London: Chapman & Hall, 1994.London: Chapman & Hall, 1994.