How To Choose The Right Laser Diodes For You？

The Difference Between Ordinary Light-emitting Diodes and Laser Diodes

Differences in the Principle of Luminescence:
LED uses spontaneous emission recombination of carriers injected into the active area to emit light, while LD uses stimulated emission recombination to emit light. The direction and phase of the photons emitted by the light-emitting diode are random, while the photons emitted by the laser diode are in the same direction and phase.

LED is the abbreviation of Light Emitting Diode. It is widely seen in daily life, such as indicator lights of household appliances, rear anti-fog lights of cars, etc. The most notable features of LEDs are their long service life and high photoelectric conversion efficiency. Basically, in the PN junction of some semiconductor materials, when the injected minority carriers recombine with the majority carriers, excess energy will be released in the form of light, thereby directly converting electrical energy into light energy. When a reverse voltage is applied to the PN junction, it is difficult for minority carriers to be injected, so it does not emit light. This type of diode made using the principle of injection electroluminescence is called a light-emitting diode, commonly known as LED.

LD is the English abbreviation of laser diode. The physical structure of the laser diode is to place a layer of photoactive semiconductor between the junctions of the light-emitting diode. Its end surface is partially reflective after being polished, thus forming an optical resonant cavity. In the case of forward bias, the LED junction emits light and interacts with the optical cavity, thereby further stimulating the emission of a single wavelength of light from the junction. The physical properties of this light are material-dependent. The working principle of semiconductor laser diodes is theoretically the same as that of gas lasers. Laser diodes are widely used in low-power optoelectronic devices such as CD drives in computers and print heads in laser printers.

There are Differences in Principles, Architecture, and Performance Between the Two.
(1) Difference in working principle: LED uses spontaneous emission recombination of carriers injected into the active area to emit light, while LD uses stimulated emission recombination to emit light.
(2) Difference in architecture: LD has an optical resonant cavity, which allows the generated photons to oscillate and amplify in the cavity, while LED does not have a resonant cavity.
(3) Difference in performance: LED does not have critical value characteristics, and its spectral density is several orders of magnitude higher than that of LD. The light output power of LED is small and the divergence angle is large.

Introduction to the Structure and Working Principle of Laser Diodes
The physical structure of the laser diode is to place a layer of photoactive semiconductor between the junctions of the light-emitting diode. Its end surface is partially reflective after being polished, thus forming an optical resonant cavity. In the case of forward bias, the LED junction emits light and interacts with the optical cavity, thereby further stimulating the emission of a single wavelength of light from the junction. The physical properties of this light are material-dependent.

The working principle of semiconductor laser diodes is theoretically the same as that of gas lasers. Figure 1(b) is a representative symbol of a laser diode. Laser diodes are widely used in low-power optoelectronic devices such as optical disc drives on computers and print heads in laser printers.

Simple Principles of Laser Diodes
Light emission in semiconductors usually results from the recombination of carriers. When a forward voltage is applied to the PN junction of a semiconductor, the PN junction barrier will be weakened, forcing electrons to be injected from the N region through the PN junction into the P region, and holes from the P region through the PN junction into the N region. The equilibrium electrons and holes will recombine, thus emitting photons with wavelength λ. The formula is as follows:

λ=hc/Eg (1)
In the formula: h—Planck’s constant; c—speed of light; Eg—bandgap width of semiconductor.

The above-mentioned phenomenon of emitting light due to the spontaneous recombination of electrons and holes is called spontaneous emission. When photons generated by spontaneous emission pass through a semiconductor, once they pass near the emitted electron-hole pair, they can be stimulated to recombine and generate new photons. This photon induces the excited carriers to recombine and emit new photons. The phenomenon is called stimulated emission of radiation. If the injected current is large enough, a carrier distribution opposite to the thermal equilibrium state will be formed, that is, the particle number is reversed. When a large number of carriers in the active layer are reversed, a small amount of photons generated by spontaneous emission produce induced radiation due to reciprocal reflection from both ends of the resonant cavity, causing positive feedback of frequency-selective resonance, or a gain at a certain frequency. When the gain is greater than the absorption loss, coherent light with good spectral lines - laser - can be emitted from the PN junction. This is the simple principle of the laser diode.

When Choosing Laser Diodes that's right for you, you can follow these steps:
Determine Application Needs: Identify what application you need a laser diode for. Is it for laser cutting, laser marking, laser measurement or other applications? Different applications have specific requirements for laser power, wavelength and characteristics.
Understand the technical parameters: View the technical parameter table of the laser diode, including output power, wavelength range, divergence, operating temperature, etc. Choose the appropriate parameter range based on your application needs.
Consider economic factors: Consider cost factors based on your budget. The price of a laser diode is related to its power, quality and characteristics. Weigh the required performance and budget and choose the product with the highest cost performance.
Refer to customer reviews and recommendations: Check out reviews and recommendations from other users, especially for cases of similar applications. This can help you understand the performance and reliability of different brands or models of laser diodes in real-world applications.
Seek professional advice: If you are unfamiliar with laser technology or have special needs, it is recommended to consult a professional engineer or supplier in the laser field. They can provide professional advice and technical support based on your specific needs.
Consider supply reliability: Choose a laser supplier with a good reputation and a reliable supply chain. Ensure stable product quality and timely technical support.
Conduct experiments and tests: Based on the selected laser diode model, conduct experiments and tests to verify that its performance meets your needs. If necessary, you can try to purchase a small amount of samples for evaluation first.

Taking the above factors into consideration, you can more accurately determine the laser diode specifications required and select the appropriate laser diode for your application. At the same time, it is recommended to consult us or professional engineers for more detailed technical support and suggestions.

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