We all know that the working principle of laser diodes is very simple, but there are still many friends who do not know how laser diodes work. Today, the editor will give you a brief introduction. Many friends still ask if QSI laser diode and avalanche diode are the same thing? Let's answer together with the editor.

1、 Working principle of laser diode

Laser diode is a device that operates by utilizing the stimulated radiation effect of semiconductor materials. Its principle is roughly as follows:

1. Carrier recombination luminescence

Under the forward bias of the PN junction, a large number of electrons are injected into the P region and holes are injected into the N region.

When electrons and holes recombine, photons are released, similar to LED.

2. Stimulated radiation

When a photon passes by, it induces an excited electron to transition and release the same photon.

In this way, the number of photons is doubled, and the frequency, phase, and direction remain consistent, forming the core characteristic of laser coherence.

3. Resonant cavity feedback

The two ends of the laser diode chip are polished to form a mirror like reflective surface.

Photons reflect back and forth inside the cavity, continuously amplifying, and some photons are emitted through the semi transparent end, forming high-intensity laser.

Laser diodes are based on semiconductor PN junctions with stimulated radiation and optical resonant cavities, achieving a "directional high brightness laser" that LEDs cannot achieve.

2、 Are QSI laser diodes and avalanche diodes the same thing?

1. QSI laser diode

Belonging to light-emitting devices.

The working principle is stimulated radiation, which outputs laser light.

Main applications: optical communication, laser ranging, medical instruments, industrial lasers, etc.

2. Avalanche diode

Belonging to voltage stabilizing/breakdown type devices

The working principle is that the PN junction undergoes avalanche breakdown under reverse high voltage, and can stably maintain a specific voltage.

Main applications: overvoltage protection, high-speed switch, detector (avalanche photodiode APD).

3. Key Differences

Laser diode: emits light → outputs laser.

Avalanche diode: voltage limiting/detection → does not emit light (unless damaged).

Principle of laser diode: PN junction forward injection → electron hole recombination luminescence → stimulated radiation amplification → resonant cavity output laser.

QSI laser diode ≠ avalanche diode, the former is an optoelectronic device, and the latter is an electronic protection component, with completely different functions and applications.