Laser diodes are now widely used in civilian applications. Do you know the working principle of laser diodes? Can there be a matching circuit diagram for purchasing a laser diode? Let's take a look from the perspective of the editor below.

1、 Working principle of laser diode

1. Fundamentals of Semiconductor Materials

Laser diodes and ordinary light-emitting diodes (LEDs) are both made of semiconductor materials, but the difference lies in the addition of a "resonant cavity" in their structure. When current is injected, electrons and holes recombine in the active region of the semiconductor, releasing photons.

2. Stimulated radiation effect

Unlike LED self emission, laser diodes utilize the "stimulated radiation" effect: when a photon passes through the active region, it excites new photons to be released in the form of the same phase and frequency. This chain effect causes a rapid increase in the number of photons.

3. Resonant cavity amplification

At both ends of a laser diode, two parallel mirrors (one end being a total reflection mirror and the other end being a partial transmission mirror) are usually used to form an optical resonant cavity. Photons are reflected back and forth inside the cavity, continuously amplified, and finally emitted from the semi transparent end, forming a high-intensity and highly coherent laser.

Current injection → electron hole recombination → stimulated radiation → resonant cavity amplification → laser output.

2、 Design ideas for supporting circuit diagrams

Laser diode is a device with extremely high driving requirements, and cannot be directly connected to a battery to light up like ordinary LED, otherwise it is easily damaged. Common driving circuits include the following key components:

1. Constant current source drive

Laser diodes are extremely sensitive to current and typically require a constant current source circuit to stabilize the driving current and avoid overcurrent burnout caused by fluctuations.

2. Bias and modulation circuit

Bias current: Keep the LD operating above the threshold to ensure that laser can be emitted at any time.

Modulation current: superimposed on bias current, used for signal transmission (such as fiber optic communication).

3. Protect the circuit

Including transient suppression diodes (TVS), current limiting resistors, etc., used to prevent static electricity and voltage spikes from causing damage to the device.

3、 Application scenarios

With the advantages of high efficiency, small size, and fast response, laser diodes have been widely used in:

Fiber optic communication and high-speed transmission in data centers;

Laser printers, scanning guns, optical storage devices;

Vehicle mounted LiDAR and industrial ranging;

Medical laser knife, laser therapy device.

Although laser diodes have a compact structure, their underlying principles involve a deep integration of semiconductor physics and optics. To truly unleash its performance, scientific and rational circuit design and rigorous driving control are indispensable. In the future, with the continuous improvement of material technology and circuit integration technology, laser diodes will play an important role in more cutting-edge fields.