semiconductor injection lasers
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Semiconductor Injection Lasers
Presented By:Maria Willeth SosaHannah Kim MalingKarl LubidChristiane Joseph Aguilar
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Semiconductor Injection Laser
• Also known as “Injection laser diode (ILD)”
• A semiconductor device that produces coherent radiation in the visible or IR spectrum when current passes through it.
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Amplification, Feedback,
and Oscillation
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Laser Amplification
•It is provided by a forward-biased p-n junction fabricated from a direct-gap semiconductor material which is usually heavily doped.
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Feedback•Usually obtained by cleaving the crystal planes normal to the lane of the junction, or by polishing two parallel surfaces of the crystal.
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Oscillation•When provided with sufficient gain, the feedback converts the optical amplifier into an optical oscillator.
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Resonator Loss•The principal source of resonator loss arises from the partial reflection at the surfaces of the crystal. This loss constitutes the transmitted useful laser light.
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Gain Condition: Laser Threshold
•Below the threshold, laser’s output power rises slowly with increasing excitation.•Above threshold, the slope of power vs. excitation is orders of magnitude greater.
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PowerInternal Photon Flux •An injected dc current leads to an increase in the steady-state carrier concentrations
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•Output Photon Flux and efficiency - the product of the internal photon flux and the emission efficiency
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Four Efficiencies in Laser Diode
•Internal Quantum Efficiency – only a fraction of the electron-hole recombinations are radiative in nature
•Emission Efficiency –only a portion of the light loss from the cavity is useful.
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• External Differential quantum efficiency- which accounts for both
•Overall efficiency (power-conversion efficiency) - is defined as the ratio of the emitted laser light power to the electrical input power.
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Spectral and Spatial Distribution
•At low current laser diode acts lie normal LED above threshold current, stimulated emission, thus narrowing of light ray to a few spectral lines instead of broad spectral distribution.
• This enables the laser to easily couple to single mode fiber and educes the amount of uncoupled light, like spatial distribution.
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Comparing (a) spectral and (b) spatial distribution of laser diodes
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Far Field Radiation Pattern•The angular divergence determines the far-field radiation pattern.
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Mode Selection •Transverse modes- Determine the intensity distributions on the cross-sections of the beam.
•Longitudinal modes-correspond to different resonances along the length of the laser cavity which occur at different frequencies or wavelengths within the gain bandwidth of the laser.
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Characteristics of Typical Lasers
•Operate in the visible band are usually fabricated from GaInP and generate light at h, = 670 nm.
•They use either gain-guided or index-guided structures
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Quantum-Well Lasers •Electrons and holes are kept together inside the semiconductor at the center, which has a smaller gap. That makes it easier for electrons to find holes.
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Advantages of Injection Laser Diode
•Small size and weight – typical LD measures less than one millimeter across and weighs a gram making it as portable electronic component
•Low current, voltage, and power requirements – require only few milliwatts of power at 3-12 volts DC and several milliamperes.
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•Low Intensity – its coherent output results in high efficiency and ease of modulation for communications and control application.
•Wide-angle beam – laser diode produces a “cone” of visible light or IR, thus it can be collimated using convex lenses.
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Application of Laser Diode•Fiber optic communication•Barcode readers•Laser pointers•CD/DVD/Blu-ray Disc reading and recording•Laser printing•Laser scanning
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