semiconductor injection lasers

Semiconductor Injection Lasers

Presented By:Maria Willeth SosaHannah Kim MalingKarl LubidChristiane Joseph Aguilar

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.

Amplification, Feedback,

and Oscillation

Laser Amplification

•It is provided by a forward-biased p-n junction fabricated from a direct-gap semiconductor material which is usually heavily doped.

Feedback•Usually obtained by cleaving the crystal planes normal to the lane of the junction, or by polishing two parallel surfaces of the crystal.

Oscillation•When provided with sufficient gain, the feedback converts the optical amplifier into an optical oscillator.

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.

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.

PowerInternal Photon Flux •An injected dc current leads to an increase in the steady-state carrier concentrations

•Output Photon Flux and efficiency - the product of the internal photon flux and the emission efficiency

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.

• 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.

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.

Comparing (a) spectral and (b) spatial distribution of laser diodes

Far Field Radiation Pattern•The angular divergence determines the far-field radiation pattern.

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.

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

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.

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.

•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.

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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