ONLINE ELECTRICAL ENGINEERING STUDY SITE

Laser Diode

Laser diodes are the semiconductor lasers which generate highly intense coherent beam of light. These were developed by Robert N. Hall in early 1960s and are also referred to as injection lasers. It is well known that an incident photon can interact with the atom to release a photon which will be identical to the impinging photon in all respects viz., phase, frequency, polarization and direction of travel. This phenomenon is referred to as stimulated emission and forms the basis of working for Lasers (Light Amplification by Stimulated Emission of Radiations). Further, if this event occurs in case of a p-n junction, then the diode is referred to as Laser diode. Laser Diodes are usually made of three layers (sometimes even two) where Gallium Arsenide (GaAs) like materials are doped with aluminium or silicon or selenium to produce p and n layers while the central, undoped, active layer is intrinsic in nature (Figure 1).

When a large forward bias is applied for such an arrangement, heavy current flows through the junction due to which electrons will gain more energy when compared to holes. This extra energy is released in the form of photons when electrons combine with the holes (during recombination process). All these photons oscillate with a particular frequency and bounce back and forth between the reflective walls of the active layer. During this process, a few of them collide with the other atoms to produce more number of photons. This process continues and thus there will be an increase in the number of excited electrons when compared with those in the non-excited state. This phenomenon is termed as population inversion and at this instant a constant highly coherent beam of light will be emitted from the central layer, in the direction parallel to it, through the partially reflecting surface as shown in Figure 1.laser diode Further it is to be noted that inorder to obtain laser light, the end surfaces of the semiconductor material should be parallel to each other, and are to be cut and polished carefully. Among these, one is to be made fully-reflective in nature while the other should be partially-reflective. Also, the wavelength of the light emitted by the laser diode depends on the distance between these two reflecting surfaces and will usually lie in either visible or IR spectrum. This wavelength decides the size of the spot the laser light can be confined to i.e. shorter the wavelength smaller will be spot size. Laser diodes are compact in size and use little power and are thus preferred over lasers when the question will be of space and power consumption. Moreover laser diodes can be characterized in terms of their threshold current, Ith which indicates the value of current at which stimulated emission overcomes the spontaneous emission as shown by the L-I curve in Figure 2. l i curve of laser diode Laser diodes are available in wide variety of forms. If the active layer is narrow and if it can support only single optical mode of operation, resulting in a highly-focused beam, then such laser diodes are referred to as Single Mode Laser Diodes. On the other hand, Multi Mode Laser Diodes have broader active region which supports multiple lateral optical modes and thus have high output power. However it is possible to obtain the output power greater than that of a single-mode laser diode without compromising on its confinement to narrow spectral range by using Master Oscillator Power Amplifier (MOPA) Laser Diodes, as they use an integrated power amplifier to increase the output power without affecting the narrow spectral output produced by the oscillator section. Further the laser diodes can either be Edge-emitting/Surface emitting depending on whether the laser light is emitted in the direction parallel or perpendicular to the material. Apart from these, there also exist many other variations of laser diodes like Vertical Cavity Surface Emitting Laser Diodes (VCSEL Diodes), High Power Laser Diodes, Stacked Laser Diodes, Distributed Feedback (DFB) Lasers or Distributed Bragg Reflector Lasers, External Cavity Diode Lasers, Broad Area Laser Diodes, Slab-Coupled Optical Waveguide Lasers (SCOWLs), etc.

Applications of Laser Diode

  1. CD and DVD players
  2. Barcode scanners
  3. Cable and High Definition (HD) TV transmission
  4. Medical applications including surgical instruments and to heal retina and brain.
  5. Intrusion detection systems
  6. Remote control applications
  7. Industrial applications including welding, precision cutting of metals, heat treating, cladding, etc.
  8. Fibre Optic Communication
  9. High speed, Long distance communication
  10. Spectroscopic sensing
  11. Range finders
  12. Laser pointers
  13. Printing
  14. Integrated Circuits




Closely Related Articles Vacuum Diode History Working Principle and Types of Vacuum DiodePN Junction Diode and its CharacteristicsDiode | Working and Types of DiodeDiode CharacteristicsHalf Wave Diode RectifierFull Wave Diode RectifierDiode Bridge RectifierWhat is Zener Diode?Application of Zener DiodeLED or Light Emitting DiodePIN Photodiode | Avalanche PhotodiodeTunnel Diode and its ApplicationsGUNN DiodeVaractor DiodeSchottky DiodePower DiodesDiode ResistanceDiode Current EquationIdeal DiodeReverse Recovery Time of DiodeDiode TestingMore Related Articles Op-amp | Working Principle of Op-ampAmplifier Gain | Decibel or dB GainIntegrated Circuits | Types of ICRegulated Power SupplyLaser | Types and Components of LaserWork FunctionMobility of Charge CarrierWhat are Photo Electrons? Electron volt or eVEnergy Quanta | Development of Quantum Physics Schottky EffectHeisenberg Uncertainty PrincipleSchrodinger Wave Equation and Wave FunctionCyclotron Basic Construction and Working PrincipleSinusoidal Wave SignalCommon Emitter AmplifierRC Coupled AmplifierDifferential AmplifierWave Particle Duality PrincipleSpace ChargeInverting AmplifierMOSFET | Working Principle of p-channel n-channel MOSFETMOSFET CircuitsMOS Capacitor | MOS Capacitance C V CurveApplications of MOSFETMOSFET as a SwitchMOSFET CharacteristicsPower MOSFETHalf Wave RectifiersFull Wave RectifiersBridge RectifiersClamping CircuitTheory of SemiconductorIntrinsic SemiconductorExtrinsic SemiconductorsEnergy Bands of SiliconDonor and Acceptor Impurities in Semiconductor Conductivity of SemiconductorCurrent Density in Metal and Semiconductor Intrinsic Silicon and Extrinsic SiliconP Type SemiconductorN Type SemiconductorP N Junction Theory Behind P N JunctionForward and Reverse Bias of P N JunctionZener BreakdownAvalanche BreakdownHall Effect Applications of Hall EffectGallium Arsenide SemiconductorSilicon SemiconductorTypes of TransistorsBipolar Junction Transistor or BJTBiasing of Bipolar Junction Transistor or BJTTransistor BiasingTransistor CharacteristicsCurrent Components in a TransistorTransistor Manufacturing TechniquesApplications of Bipolar Junction Transistor or BJT | History of BJTTransistor as a SwitchTransistor as an AmplifierJFET or Junction Field Effect Transistorn-channel JFET and p-channel JFETApplications of Field Effect TransistorDIAC Construction Operation and Applications of DIACTRIAC Construction Operation and Applications of TRIACPhototransistorNew Articles Ring CounterDischarging a CapacitorCharging a CapacitorElectric PotentialParity GeneratorElectric Flux