Lasers Design and Laser Systems

Transcription

1 Lasers Design and Laser Systems Tel: Nir Dahan Tel: Thank You 1

2 If it's green, it's biology, If it stinks, it's chemistry, If it has numbers it's math, If it doesn't work, it's technology -- Unknown Course Subjects Introduction and basic principles The laser medium Resonators Gas lasers Diode lasers Solid-state lasers Other lasers 2

3 Band Gap in Semiconductor Energy Levels in Semiconductor Only direct gap semiconductor can be used for diode lasers The requirement is no momentum change

4 The Doping and the p-n Junction The doping controls the type of charge carriers The doping controls the density of charge carriers The p-n Junction The electron-hole recombination creates photons The recombination happens when we apply forward voltage 4

5 Semiconductor Laser Materials Compound GaN/AlGaN ZnSSe ZnCdSe AlGaInP/GaAs Ga 0.5 In 0.5 P/GaAs GaAlAs/GaAs GaAs/GaAs (pure) In 0.2 Ga 0.5 As/GaAs InGaAsP/InP In 0.7 Ga 0.27 As 0.58 P 0.42 In0.58 Ga 0.42 As 0.9 P 0.1 AlGaAsSb/InGaAsSb GaAs/AlGaAs PbEuSeTe PbSSe PbSnTe Wavelength/nm blue/green Applications Disc data storage Disc data storage Disc data storage Replacements for HeNe lasers, eg bar code scanners Chemical sensors Optical communication, metrology Optical communication, metrology Chemical sensors Quantum cascade laser chemical sensors Cryogenic, high resolution spectroscopy Cryogenic, high resolution spectroscopy Cryogenic, high resolution spectroscopy * Other wavelengths can be obtained by frequency doubling and difference frequency methods The Diode Laser Basic Structure The p-n junction is the laser medium the active region For current above the threshold we get population inversion The population inversion is between bands of energy The gain bandwidth is therefore few nanometers (very wide) The simplest resonator is FP The dimensions enforce elliptical beam 5

6 The Diode Laser Basic Structure More names: Junction Laser or Injection Laser The FP Diode Laser The parallel mirrors are made by lattice cleavage The natural mirror reflectance is due to the refractive index: R=[(n 1 -n 2 )/(n 1 +n 2 )] 2 ( for GaAs (n=.6) R=0.2 ) Simple FP diode laser emits light from both sides In advanced FP diode laser one facet is coated for full reflection 6

7 The diode laser beam Divergence Typical dimensions: Height: 5-200nm, Width: 1-10 micron, Length: -00 micron The beam is therefore non-symmetric (elliptical) Where is the far field? The Longitudinal (Cavity) Modes For single mode we need very short cavity How short for 110nm GaAs FP diode laser? (4nm gain bandwidth) In typical FP diode laser we get 10-0 cavity modes What is the coherence? (time and length) 7

8 The I-V diode curve Experimental curve I Ideal curve The Threshold Current 8

9 The Temperature Effect Gain Guided Diode Laser 9

10 The Fabrication Process The Packaging 10

11 Packages (Cyoptics) Assembly Room 11

12 Assembler Arm and Tool High Power Diode Lasers 12

13 Commercial Specification Communication Application 1

14 DFB Laser DFB Laser 14

15 DFB Laser DFB Laser Spectrum 15

16 How Does a DFB Tune? How Does a DFB Tune? 16

17 Quantum Well IBA Diode Lasers Model Wavelength, nm Output power, mw Operating current, ma Operating voltage, V Threshold current, ma Beam divergence, deg. Spectral width (FWHM), nm Stripe width, µm Visible Laser Diodes MOCVD AlGaInP Quantum Well Types IBA10S x 0 < 5 IBAM x 5 <.0 IBA15S x 0 < 5 IBA0S x 0 < 5 IBAM x 5 <.0 15 IBAM x 5 <.0 0 IBAM C x5 <.0 0 IBA2M x 5 <.0 IBA400M x 5 <.0 10 Metal Organic Chemical Vapor Deposition (MOCVD) 17

18 IBA Diode Lasers IBA10S-770 IBAS-780 IBAS-810 IBAS- 810 IBA10S-820 IBAS-80 IBAS-80 IBA20S-8 D IBAS-8 IBAS-875 IBAS-900 IBAS-915 IBAS-920 IBAS-9 IBAS-9 IBAS-980 IBAS-980 Model IBAS-8 D Wavelength, nm Lasers IBAS-1060 Design and Laser Systems Output power, mw Operating current, ma Operating voltage, V Threshold current, ma Single Mode IR Laser Diodes MOCVD GaAlAs & InGaAs Quantum Well Types Beam divergence, deg. 8 x 0 8 x 0 10 x x 0 9 x x 0 10 x 0 12 x 0 10 x 0 10 x 0 10 x 0 10 x 0 10 x 0 10 x 0 10 x 0 10 x 0 10 x 0 10 x 0 Spectral width (FWHM), nm x 0 Dr. Yacov Malinovich.0.0 Stripe width, µm 0 0 Vertical Cavity Surface Emitting Laser 18

19 VCSEL VCSEL 19

20 Commercial Packaging Commercial Specification 20

21 VCSEL With MEMS Adjustment Micro-Electro- Mechanical Systems (MEMS) Grating-outcoupled Surface Emitting Laser The GSE Laser captures the best attributes of Edge Emitters and VCSELs Advantages over Edge Emitters Narrow beam divergence Wafer level testing Adjustable output aperture Manufacturing efficiencies Lower cost packaging DFB performance at VCSEL prices Photodigm, Inc. Advantages over 110nm VCSELs Proven AlInGaAs material structure Higher power output Long wavelengths Wavelength easily adjusted Adjustable output aperture Suitable for higher integration 21