Laser diodes current injection

Kneissl, M., Teepe, M., Miyashita, N., Johnson, N.M., Chem, G.D., and Chang, R.K., 2004, Current-injection spiral-shaped microcavity disk laser diodes with unidirectional emission, Appl. Phys. Lett. 84(14) 2485-2487. 

C5.1 InGaN/GaN/AlGaN-based laser diodes C5.2 Optically pumped lasing and current injection lasing in GaN-based laser structures... 

Injection-type laser diodes based on GalnN active layers have now been demonstrated by a number of different groups [2,25-30], The threshold current densities range from 1.5 kA/cm2 [31] to about 50 kA/cm2 [26], From measurements of the tum-on delay time Nakamura et al [32] have also estimated the threshold carrier density to be about 1 - 2 x 1019 cm 3. 

Diode lasers have interesting spectroscopic properties. They produce radiation of single spatial and longitudinal modes at a maximum injection current and side modes at low diode current, down to <1% of the radiation power at maximum... 

Problem 4-15. An Application of Optical Scattering/Fluorescence. A currently active area of research is the application of optical scattering and fluorescence for the noninvasive location of tumors. The patient is injected with a fluorescent dye that preferentially absorbs into a tumor. A portion of the patient s skin located near the suspected tumor is illuminated with a source of photons, such as a laser diode. The wavelength or energy of the photons is such that the absorbed dye fluoresces, and the emitted photons are then detected by a photomultiplier also located on the patient s skin. This optical response is then analyzed to determine the location and extent of the tumor. 

The modulation bandwidth of the semiconductor injection laser given by Eq. (15), is determined by the gain coefiicient, photon lifetime, and the steady-state photon density. These parameters are influenced by the structure of the laser, the operating temperature, and the laser diode material system. For a given laser, increasing the injection current, as shown in Fig. 16, can increase the bandwidth. However the maximum current is limited by the... 

The resonance characteristics of the RR were measured through the wavelength modulation of a distributed feedback laser diode by sweeping the injection current. ... 

Fig.7.4a-c. Schematic diagram of a diode laser, (a) Injection laser structure. (b) Mode spectrum within the gain profile, (c) Mode hops of a quasi-continuously tunable cw Pb Sn Te diode laser in an He cryostat. The laser frequency is tuned by changing the diode current. The points correspond to the transmission maxima of an external Ge etalon with a free spectral range of 1.955 GHz [7.2]... 

Finally, an electric current can produce injection luminescence from the recombination of electrons and holes in the contact 2one between differendy doped semiconductor regions. This is used in light-emitting diodes (LED, usually ted), in electronic displays, and in semiconductor lasers. 

Much has been learned in the thirty-five years since the demonstration of the first GaAs injection lasers [1,2], The main lesson from that period is that defect-free material is needed, hi the 1970s MITI set up a successful five year crash programme to make zero-defect GaAs. The reason behind the zero defect goal for diode lasers is that defects cause emission line broadening, and the threshold current for an injection laser is directly proportional to the emission linewidth. Excitons in semiconductors are very fragile. They can be easily destroyed, or have their linewidth broadened by crystal lattice disruptions of any sort. 

The measurement is conducted by frequency modulating a diode laser by superimposing a radio frequency oscillation, Q, onto the diode injection current. The spectral output of a frequency modulated diode laser, shown at the top of Fig. 3, consists of a carrier frequency, a>c and side band frequencies, cOc H. When the laser is scanned through the wavelength of oxygen absorbance, the amount of light absorption, which is proportional to the gas concentration, is written into the side band frequencies by recording the difference in absorption between the two sidebands. 

In lasers, luminescent diodes, power diodes and solar cells it was found that in the low injection region the current noise spectral density is a quadratic function of the forward current. Typically, the excess current is a dominant current component in this region. The current noise spectral density vs. frequency for PN junction is shown in Fig. 19. Curve 1 denotes the current noise spectral density for the low injection range, curve 2 is the current noise spectral density for the... 

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