Jul 30, 2020
LED is the abbreviation of Light Emitting Diode. It is widely seen in daily life, such as indicator lights of household appliances and automobile anti-fog lights. The most notable feature of LED is long service life and high photoelectric conversion efficiency. The principle is that in the PN junction of certain semiconductor materials, when the injected minority carriers and the majority carriers recombine, the excess energy is released in the form of light, thereby directly converting electrical energy into light energy. With reverse voltage applied to the PN junction, it is difficult to inject minority carriers, so it does not emit light. This kind of diode made by injection electroluminescence principle is called light-emitting diode, commonly known as LED.
LD is the English abbreviation of laser diode. The physical structure of laser diode is to place a layer of optically active semiconductor between the junctions of light-emitting diodes, and its end surface has a partial reflection function after polishing, thus forming an optical resonant cavity. In the case of forward bias, the LED junction emits light and interacts with the optical resonant cavity to further stimulate the emission of single wavelength light from the junction. The physical properties of this light are related to the material. The working principle of a semiconductor laser diode is theoretically the same as that of a gas laser. Laser diodes are widely used in low-power photoelectric devices such as CD drives on computers and print heads in laser printers.
The difference in the principle of luminescence: LED uses the spontaneous emission of carriers injected into the active area to recombine light, while LD is recombined light-emitting by stimulated radiation. The direction and phase of the photons emitted by the light emitting diode are random, and the photons emitted by the laser diode are in the same direction and phase.
The difference between the two in principle, structure and performance:
(1) The difference in working principle: LED uses the spontaneous emission of carriers injected into the active region to recombine light, while LD is recombined light-emitting by stimulated radiation.
(2) The difference in architecture: LD has an optical resonant cavity to make the generated photons oscillate and amplify in the cavity, while LED has no resonant cavity.
(3) The difference in efficiency: LED has no critical value characteristics, the spectral density is several orders of magnitude higher than that of LD, the output light power of LED is small, and the divergence angle is large.