Fabry-Perot diodes

Semiconductor laser diodes are widely used in CD players, DVDs, printers, telecommunication or laser pointers. In the structure, they are similar to LEDs but they have a resonant cavity where laser amplification takes place. A Fabry-Perot cavity is established by polishing the end facets of the junction diode (so that they act as mirrors) and also by roughening the side edges to prevent leakage of light from the sides of the device. This structure is known as a homojunction laser and is a very basic one. Contemporary laser diodes are manufactured as double heterojunction structures. 

Figure 12.17. (a) Diode laser band structure. (1) In thermal equilibrium. (2) Under forward bias and high carrier injection. Ec, v, and f are the conduction band, valence band, and Fermi energies respectively, (b) Fabry-Perot cavity configuration fora GaAs diode laser. Typical cavity length is 300//m and width 10/tm. d is the depletion layer. 

Fig. 1. 249.9-GHz FIR-ESR spectrometer. A, 9-T magnet and sweep coils B, phase-locked 250-GHz source C, 100-MHz master oscillator D, Schottky diode detector E, resonator and modulator coils F, 250-GHz quasioptical waveguide G, power supply for main coil (100 A) H, current ramp control for main magnet I, power supply for sweep coil (50 A) J, OC spectrometer controller K, lock-in amp for signal L, field modulator and lock-in reference M, Fabry-Perot tuning screw N, vapor-cooled leads for main solenoid O, vapor-cooled leads for sweep coil P, He bath level indicator Q, He transfer tube R, bath temperature thermometer S, " He blow-off valves. [From Lynch et al. (1988), by permission of the AIP.]...

Although many diode lasers work as multimode lasers, the distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers show a mode selection because of their periodic structure. The mode selectivity is generated by the optical properties of the periodic stmctures because (Mily the modes that are associated with a standing wave/stop band are amplified. DFB structures are photonic structures, which are doped throughout the volume with chromophores (in an optimal case at the maxima of the standing waves), whereas DBR lasers have a miniature Fabry-Perot cavity in which the dye is localized, and the mirrors are replaced by periodic gratings [85]. 

The resonator of the most common diode lasers is a Fabry-Perot (FP) resonator the ends of the crystal are cleaved to be flat and parallel with each other, and... 

The diodes can be also arranged in a two-dimensional array, which allows the detection of two-dimensional intensity distributions. This is, for instance, important for the observation of spatial distributions of light-emitting atoms in gas discharges or flames (Sect. 15.4) or of the ring pattern behind a Fabry-Perot interferometer. 

Figure 9.41 shows a diode junction for generating the inverted population combined with a Fabry-Perot resonant cavity. When the junction is forward biased, one can obtain laser emission from such a structure. To get some of fhe Hght out of the cavity at least one, and often both, of the mirrors are only partially reflecting. It turns out to be easy to fabricate such mirrors in a single crystal material such as a semiconductor... 

FIGURE 9.41 Semiconductor diode laser using a Fabry-Perot cavity. 

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