The operation principle and characteristics of laser diode

The operation principle and characteristics of laser diode

Nov 24, 2020

The advantages of the laser diode are high efficiency, small volume, lightweight, and low price. Especially, the efficiency of multiple quanta well is 20-40%, and the p-n type is also 15% - 25%, which is the most characteristic of the high energy efficiency. In addition, its continuous output wavelength covers the range of infrared to visible light, and the products with an output of optical pulse up to 50W (pulse width of 100ns) have been commercialized. As a laser radar or excitation light source, it can be said that it is an example of a very easy to use a laser.


The core of the semiconductor laser is a PN junction core composed of p-type and n-type semiconductors. When the minority carriers injected into the PN junction combine with the majority of carriers, they will emit visible light, ultraviolet light, or near-infrared light. However, the photons emitted from the PN junction are non-directional, that is, they have the same probability to emit in all directions. Therefore, not all the light generated by the core can be released, which mainly depends on the quality of semiconductor material, the structure and geometry of the core, the internal structure, and the packaging material of the semiconductor laser. The application requires improving the internal and external quantum efficiency of semiconductor lasers. 

Laser Diode

In the conventional package of Φ 5mm semiconductor laser, a square tube core with a side length of 0.25mm is bonded or sintered on the lead frame. The positive electrode of the die is bonded to the gold wire through the spherical contact point, and the inner lead is connected with a pin. The negative electrode is connected with another pin of the lead frame through a reflecting cup, and then the top of the core is wrapped with epoxy resin. 

The function of the reflecting cup is to collect the light emitted from the side and interface of the tube core and emit the light to the desired direction angle. The epoxy resin coated at the top has several functions: protecting the tube core from external erosion; using different shapes and material properties (with or without dispersing agent) to function as a lens or diffuse lens to control the divergence angle of light; the correlation between the refractive index of the tube core and the air refractive index is too large, resulting in the small critical angle of total reflection inside the tube core, which is generated by the active layer Only a small part of the light is taken out, and most of it is easy to be absorbed by multiple reflections in the tube core, resulting in excessive light loss due to total reflection. 

Therefore, epoxy resin with a corresponding refractive index is selected as a transition to improve the light emission efficiency of the tube core. The epoxy resin used to form the shell must have moisture resistance, insulation, mechanical strength, and high refractive index and transmittance of light emitted from the tube core. With different refractive index packaging materials, the influence of packaging geometry on photon escape efficiency is different. The angular distribution of luminous intensity is also related to the core structure, light output mode, material, and shape of the packaging lens. If a sharp resin lens is used, the light can be focused on the axis direction of the semiconductor laser, and the corresponding angle of view is small; if the resin lens at the top is circular or planar, the corresponding viewing angle will be increased.

Red Laser Modules (200)

Elite provides high-quality OEM&ODM laser diode modules covering the wavelength range of 375 nm-980 nm, visible light ranges up to 1000mW, and in the range of 780 nm-980 nm range up to 10W. We warmly welcome your any requirements about lasers. Contact us at or 86-29-68590616 for quotation or sample.