The Laser DiodeThe Laser Diode

Jason HillJason HillPhysics 464 Physics 464 –– Applied OpticsApplied Optics3/1/053/1/05

AgendaAgenda

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--ROMROMBlue, Violet, UltraBlue, Violet, Ultra--Violet?Violet?

How a Laser Diode Works

Edge Emitting Laser Diode

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

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

Edge Emitting vs. Surface EmittingEdge Emitting vs. Surface Emitting

Edge emitting laser:Edge emitting laser: light emission is through the light emission is through the cleaved edge of the laser. Edge emitters are difficult to cleaved edge of the laser. Edge emitters are difficult to integrate in large numbersintegrate in large numbers

Surface emitting laser:Surface emitting laser: much smaller and can be much smaller and can be integrated in large numbers on a substrate wafer, much integrated in large numbers on a substrate wafer, much easier to test individually while still on the wafereasier to test individually while still on the wafer

VCSELsVCSELsVertical Cavity Surface Emitting LasersVertical Cavity Surface Emitting Lasers

Very short optical cavity Very short optical cavity (1(1--3 3 λλ))

Quantum wells are used to Quantum wells are used to control optical propertiescontrol optical properties

Require highly reflective Require highly reflective mirrors (99.9% vs. 30%)mirrors (99.9% vs. 30%)

Metallic mirrors are Metallic mirrors are replaced with Distributed replaced with Distributed Bragg Reflectors (DBRs)Bragg Reflectors (DBRs)

Metallic Reflector VCSEL

VCSELsVCSELsVertical Cavity Surface Emitting LasersVertical Cavity Surface Emitting Lasers

Very short optical cavity Very short optical cavity (1(1--3 3 λλ))

Quantum wells are used to Quantum wells are used to control optical propertiescontrol optical properties

Require highly reflective Require highly reflective mirrors (99.9% vs. 30%)mirrors (99.9% vs. 30%)

Metallic mirrors are Metallic mirrors are replaced with Distributed replaced with Distributed Bragg Reflectors (DBRs)Bragg Reflectors (DBRs)

Etched Well VCSEL

VCSELsVCSELsVertical Cavity Surface Emitting LasersVertical Cavity Surface Emitting Lasers

Very short optical Very short optical cavity (1cavity (1--3 3 λλ))

Quantum wells are Quantum wells are used to control used to control optical propertiesoptical properties

Require highly Require highly reflective mirrors reflective mirrors (99.9% vs. 30%)(99.9% vs. 30%) Air Post VCSEL

VCSELsVCSELsVertical Cavity Surface Emitting LasersVertical Cavity Surface Emitting Lasers

Very short optical cavity Very short optical cavity (1(1--3 3 λλ))

Quantum wells are used to Quantum wells are used to control optical propertiescontrol optical properties

Require highly reflective Require highly reflective mirrors (99.9% vs. 30%)mirrors (99.9% vs. 30%)

Metallic mirrors are Metallic mirrors are replaced with Distributed replaced with Distributed Bragg Reflectors (DBRs)Bragg Reflectors (DBRs)

Buried Regrowth VCSEL

Comparison of Red and Green Laser Pointers Comparison of Red and Green Laser Pointers

Potassium titany phosphate (KTiOPO4) nonlinear crystalNeodymiumdoped yttrium orthovanadate

Use of LDs for Optical StorageUse of LDs for Optical StorageDiffraction limits the size of a focused beam to a Diffraction limits the size of a focused beam to a spot with a width on the order of the wavelength spot with a width on the order of the wavelength of the light emitted, therefore the wavelengths of the light emitted, therefore the wavelengths limits the density of data storage: shorter limits the density of data storage: shorter wavelengths enable higher storage densitywavelengths enable higher storage density

*This is actually an inaccurate representationof how the data would be arranged, opticaldevices use EFM, EFM+

Typical CDTypical CD--ROM Optical PickupROM Optical Pickup

ResourcesResources““Blue Blue LEDsLEDs and Lasers.and Lasers.”” eurotechnology.comeurotechnology.com. 15 Sept. 2004. 26 Feb. . 15 Sept. 2004. 26 Feb.

2005 2005

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. Adrio Communications 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.