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  1. ��������������������������������������� ������������������������������������������������� Tunable semiconductor lasers Thesis qualifying exam presentation by Chuan Peng B.S. Optoelectronics, Sichuan University(1994) M.S. Physics, University of Houston(2001) M.S. Physics, University of Houston(2001) Thesis adviser: Dr. Han Le Submitted to the Department of Electrical and Computer Engineering in partial fulfillment of the requirements for the Doctor of Philosophy At the University of Houston Oct. 2003

  2. ��������������������������������������� ������������������������������������������������� Outline Outline 1. Introduction and motivation 2. Semiconductor laser physics 3. Tunable laser fundamentals 3. Tunable laser fundamentals 4. Technologies for tunable lasers 5. Summary and Conclusion

  3. ��������������������������������������� ������������������������������������������������� Introduction: Laser History Introduction: Laser History Milestones: • 1917 Origin of laser can be traced back to Einstein's treatment of stimulated emission and Planck’s description of the quantum. • 1951 Development of the maser by C.H. Townes. • • 1958 Laser was proposed by C.H. Townes and A.L. Schawlow 1958 Laser was proposed by C.H. Townes and A.L. Schawlow • 1960 T.H. Maiman at Hughes Laboratories reports the first laser: the pulsed ruby laser. • 1961 The first continuous wave laser was reported (the helium neon laser). • 1962 First semiconductor laser

  4. ��������������������������������������� ������������������������������������������������� Introduction: Laser types and applications Introduction: Laser types and applications Compact disk Basic Scientific Research Laser printer Spectroscopy Free Electron laser (FEL) Scientific Optical disc drives Nuclear Fusion Applications Optical computer Cooling Atoms Lead-salt As Sb N Bar code scanner Short Pulses Common Daily Holograms against forgery Semiconductor lasers Gas Lasers Applications Ti-Sphire Fiber optic communications Ruby Free space communications X-ray lasers Surgery: Nd:YAG Laser shows Liquid Lasers Liquid Lasers • Eyes • Eyes Alexandrite Alexandrite Holograms Holograms • General Organic Dye Kinetic sculptures • Dentistry Medical Ag (Gold) vapor Solid Lasers • Dermatology Applications Cu vapor Diagnostic fluorescence Laser range-finder Ar+ Soft lasers Military Target designation Kr+ Special Lasers Laser weapons Applications N 2 FIR lasers CO 2 HF Laser blinding He-Ne He-Cd He-Ne Measurements Far infared Infared Visible Ultraviolet Soft x-rays Industrial Straight Lines Energy Transport Special Material Processing Applications Laser Gyroscope 30 µ µ m 10 µ µ m 3 µ µ m 1 µ µ m Applications µ µ µ µ µ µ µ µ 30nm 10nm Spectral Analysis 300nm 100nm Fiber Lasers λ λ λ λ Energy

  5. ��������������������������������������� ������������������������������������������������� Introduction: Semiconductor Laser Introduction: Semiconductor Laser What made the semiconductor lasers the most popular light sources ? • Small physical size • Electrical pumping • High efficiency in converting electric power to light • High speed direct modulation (high-data-rate optical communication systems) systems) • Possibility of monolithic integration with electronic and optical components to form OEICs (optoelectronic integrated circuits) • Optical fiber compatibility • Mass production using the mature semiconductor-based manufacturing technology.

  6. ��������������������������������������� ������������������������������������������������� Motivations Motivations Application interests in tunable mid-IR semiconductor lasers: • Spectroscopy - Single frequency mode, tunable • Environmental sensing and pollution monitoring - Lidar - Requires Ruggedness, Correct Wavelength • • Industrial Process Monitoring Industrial Process Monitoring - Requirements similar to Environmental Monitoring • Medical Diagnostics - Breath analysis; Non-invasive Glucose monitoring, Cancer Detection, etc. • Military and law enforcement • Optical communication A key requirement: A key requirement: Broad, continuous wavelength tunability Broad, continuous wavelength tunability

  7. ��������������������������������������� ������������������������������������������������� Outline Outline 1. Introduction and motivation 2. Semiconductor laser physics 3. Tunable laser fundamentals 4. Technologies of tunable lasers 5. Conclusion

  8. ��������������������������������������� ������������������������������������������������� Laser physics Laser physics Mirror Mirror Active medium Active medium R 1 R 1 R 2 R 2 Laser output Laser output Oscillation condition is reached when G, α i G, α i ~ β i L = R R e 1 / 2 2 ( ) 1 Partially Partially 1 2 transmitting transmitting L L L L mirror mirror mirror mirror ~ β = µ k − α i / 2 Loop Loop Loop Loop Loop Loop Loop Loop Loop Loop Gain Gain Gain Gain Gain Gain Gain Gain Gain Gain 0 ν ν ν = = = mc mc mc µ L µ L µ L / / / 2 2 2 gain gain gain gain gain gain gain gain gain gain m m m curve curve curve curve curve curve curve curve curve curve ∆ν =c/2 µ g L ∆ν =c/2 µ g L ∆ν =c/2 µ g L ∆ν ∆ν =c/2nL ∆ν ∆ν =c/2nL ∆ν ∆ν =c/2nL ∆ν ∆ν =c/2nL ∆ν ∆ν ∆ν =c/2nL ∆ν ∆ν ∆ν ∆ν ∆ν =c/2nL ∆ν =c/2nL ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν ∆ν G L G L G L G L G L G L G L G L G L G L 1 1 = α + g ln | | th i Real part: Threshold condition L R 1 R 2 2 Laser Laser Laser Laser Laser Laser Laser Laser Laser Laser  − α g L = R R e 1 / 2 ( ) threshold threshold threshold threshold threshold threshold threshold threshold threshold threshold ( ) 1 i 1 2  ν o ν ν o ν o ν ν ν ν ν ν ν ν o ν ν ν ν ν ν ν ν ν ν ν o ν ν ν o ν o ν ν ν ν o ν ν ν o ν o ν ν ν ν ν µ = π == k L m m Laser Laser Laser Laser Laser Laser Laser Laser Laser Laser  2 2 , ( 1 , 2 , 3 ,..) Longitudinal Longitudinal Longitudinal Longitudinal Longitudinal Longitudinal Longitudinal Longitudinal Longitudinal Longitudinal output output output output output output output output output output 0 modes modes modes modes modes modes modes modes modes modes power power power power power power power power power power Imaginary part: wavelength condition Linewidth Linewidth Linewidth Linewidth Linewidth Linewidth Linewidth Linewidth Linewidth Linewidth ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν m-2 ν m-2 ν ν m-2 ν ν ν m-2 ν ν m-2 ν ν m-2 ν ν m-2 ν ν m-2 ν m-2 ν ν m-2 ν ν m-1 ν m-1 ν m-1 ν m-1 ν m-1 ν m-1 ν m-1 ν m-1 ν m-1 ν m-1 ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν m+1 ν ν m+1 ν ν m+1 ν ν ν ν ν ν m+1 ν ν ν m+1 ν ν ν ν ν ν ν ν ν m+1 ν ν m+1 ν ν ν ν ν m+1 ν ν ν m+1 ν ν m+1 ν ν ν ν ν ν m+2 ν ν ν m+2 ν m+2 ν ν m+2 ν ν ν ν ν m+2 ν m+2 ν ν ν ν ν m+2 ν ν ν m+2 ν ν ν m+2 ν ν ν ν ν m+2 ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν Frequency (v) Frequency (v) Frequency (v) Frequency (v) Frequency (v) Frequency (v) Frequency (v) Frequency (v) Frequency (v) Frequency (v)

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