In today’s technological world, semiconductor lasers are ubiquitous yet often overlooked, from supermarket barcode scanners to fiber optic communication networks, from laser printers to medical devices. This compact and highly efficient light source has become an indispensable part of modern life. This article will guide you through the working principles, development history, and wide-ranging applications of semiconductor lasers.
## What is a Semiconductor Laser
A semiconductor laser, also known as a laser diode, is an electronic device that generates coherent light using semiconductor materials. Unlike traditional light bulbs or LEDs, the light emitted by semiconductor lasers is highly directional, monochromatic, and coherent—these characteristics make lasers irreplaceable in numerous applications.
The core part of a semiconductor laser is only the size of a grain of rice, yet it can produce laser outputs ranging from milliwatts to several watts. This remarkable combination of energy density and compact size makes it an ideal choice for modern optoelectronic systems.
## Working Principle: Electrons Dance to Create Photons
The working principle of semiconductor lasers is based on quantum physics and can be summarized in the following key steps:
1. **PN Junction and Carrier Injection**: The core of a semiconductor laser is a specially designed PN junction. When a forward voltage is applied, electrons move from the N region to the P region, while holes move in the opposite direction.
2. **Population Inversion**: In the active region of the PN junction, electrons and holes recombine, releasing energy. When the injected current is sufficiently large, the number of electrons in the conduction band exceeds that in the valence band, creating a