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Vertical Cavity Surface Emitting Lasers

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Only allowed modes which satisfy would live, beause of constructive interference. ... Transverse modes are the intensity patterns in a plane perpendicular ... – PowerPoint PPT presentation

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Title: Vertical Cavity Surface Emitting Lasers


1
Vertical Cavity Surface Emitting Lasers
Ravi Kalyanam Oct 27, 2006
2
What is Covered?
  • Operating Principle of VCSELS
  • Cavity Modes
  • Axial Modes
  • Transverse Modes
  • Determination of Cavity Resonance
  • Determination of Material Gain
  • Obtaining Device Performance Parameters from
    Experimental Data

Vertical Cavity Surface Emitting Lasers
3
VCSEL Structure
  • Optical cavity defined by 2 DBR mirrors
  • Optical cavity typically one- ? thick
  • Gain medium usually is MQW
  • Cavity Resonance must overlap Gain Spectrum

Vertical Cavity Surface Emitting Lasers
4
Operating Principles
  • Carriers can be pumped, optically or electrically
    to an excited state
  • An incoming photon stimulates de-excitation of
    the electron
  • Modes supported by cavity survive reflections
    within the cavity

Vertical Cavity Surface Emitting Lasers
5
Threshold Condition
  • Photons generated could be lost
  • Intrinsically within the cavity (ai)
  • At the mirrors on either side of the cavity (am)
  • If gain equals the losses, we have threshold
    condition, medium is ready to lase

Vertical Cavity Surface Emitting Lasers
6
Longitudinal Modes
  • Longitudinal modes are standing wave patterns
    formed by waves confined in the cavity.
  • Only allowed modes which satisfy would
    live, beause of constructive interference.

Cavity Modes
7
Transverse Modes
  • Transverse modes are the intensity patterns in a
    plane perpendicular to the propagation
  • Described by a combination of Gaussian profile
    and Laguerre polynomial.

Cavity Modes
8
Reflectivity Measurement Technique
Determination of Cavity Resonance
9
Cavity Resonance Spectrum
  • Ratiometric Measurement Eliminates System
    Spectral Response

Determination of Cavity Resonance
10
LI Curve
  • L-I curve directly gives
  • Differential QE ?d
  • Threshold Current Ith
  • We also could get
  • Intrinsic QE ?i
  • Cavity loss ai
  • Mirror Loss am
  • Threshold Gain gth

Obtaining Device Parameters
11
Extracting ?i and ai
  • Perform L-I on lasers with different L
  • Plot ?d vs. L
  • Y-intercept is
  • Slope gets us

Obtaining Device Parameters
12
?gth vs. Jth Plot
  • Use previous samples to calculate threshold
    current density Jth
  • Plot modal gain vs. Jth

Obtaining Device Parameters
13
VCSEL Parameters
  • Obtain ?d and Jth from L-I curve.
  • Obtain ?i and Jth from diagnostic lasers
  • Use below relations for am and ai

Obtaining Device Parameters
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