Laser diodes are semiconductor lasers that emit coherent light. Laser diodes are widely used in communications, laser printers, barcode scanners, optical drives (such as CD/DVD/Blu-ray drives), laser rangefinders, fiber optic communications, and laser lighting.
What Is a Laser Diode?
A laser diode is a semiconductor device that can convert electrical energy into laser light. It has a similar structure to an LED, but through specific design and material selection, it can emit a laser beam with high monochromaticity, directionality, and brightness. Many distributors like Heisener offer a wide range of laser diode models to cater to diverse application needs.
Laser Diode Luminescence Principle
Laser diodes usually consist of a PN junction, an optical cavity, and a reflector. The optical cavity is an area with two mirrors where light is reflected and amplified, and finally emitted through a tiny exit hole. Laser diodes also contain current injection parts, such as electrodes and wires, which are responsible for injecting current into the semiconductor material.
Laser diodes excite carriers (electrons and holes) in semiconductor materials through current, and these carriers recombine in the active area of the laser diode to generate photons. The photons reflect back and forth in the cavity of the diode, gradually amplifying, and finally emitting a laser beam through a small optical window. The generation of lasers is based on the principle of stimulated emission, that is, the interaction between photons and carriers.
Types of Laser Diodes
Edge-Emitting Laser Diodes (EELDs)
Edge-Emitting Laser Diodes (EELDs) emit light from the edge of a semiconductor chip, where the active region is aligned along the chip’s edge. EELDs are commonly used in telecommunications and high-speed data transmission due to their ability to deliver focused and intense light over long distances.
Vertical-Cavity Surface-Emitting Lasers (VCSELs)
Vertical-Cavity Surface-Emitting Lasers (VCSELs) produce light from the surface of the semiconductor chip, using a vertical cavity with reflective mirrors. This design results in a circular beam with low divergence, offering high efficiency and ease of integration into arrays.Â
Distributed Feedback Lasers (DFBs)
Distributed Feedback Lasers (DFBs) are edge-emitting lasers equipped with a built-in grating structure. This design provides a narrow emission linewidth and consistent wavelength, making DFBs suitable for applications requiring accurate wavelength control. They are commonly employed in fiber optic communications, spectroscopy, and high-resolution sensing.
Quantum Cascade Lasers (QCLs)
Quantum Cascade Lasers (QCLs) utilize quantum well structures to produce laser light through intersubband transitions, operating in the mid-infrared to far-infrared spectrum. QCLs are known for their high power output and tunable wavelength capabilities, making them valuable for advanced sensing and imaging applications. They are used in environmental monitoring, chemical detection, and medical diagnostics where specific wavelength precision is required.
Multi-Mode Laser Diodes (MMLDs)
Multi-Mode Laser Diodes (MMLDs) emit light in multiple optical modes simultaneously, resulting in a broader spectral output compared to single-mode lasers. While they offer higher power output, their beam quality is less focused. MMLDs are used in applications requiring substantial power and a wide spectral range, such as laser printing, industrial applications, and medical therapies, where the broader emission spectrum is advantageous.
AlGaAs Laser Diodes
Aluminum Gallium Arsenide (AlGaAs) Laser Diodes use an alloy of aluminum, gallium, and arsenic to emit light in the red to near-infrared spectrum. They are commonly found in consumer electronics such as CD/DVD players and laser pointers, as w ell as some communication systems, due to their robust performance and cost-effectiveness in these applications.
Advantages & DisadvantagesÂ
Advantages
Compared with other light-emitting devices, it has high efficiency
The laser diode is small in size
It has high beam directivity, narrow spectral linewidth and high light intensity
Long service life
Disadvantages
Laser diodes may be affected by temperature changes and performance may decrease as temperature increases.Â
The emitted beam may be harmful to the eyes.
Detection Methods
Resistance Measurement Method: To check a laser diode, first remove it from the circuit and measure its forward and reverse resistance using a multimeter set to the R×1k or R×10k range. A healthy laser diode should exhibit a forward resistance between 20 to 40kΩ and an infinite reverse resistance. If the forward resistance exceeds 50kΩ, the performance of the laser diode has degraded. If the forward resistance is greater than 90kΩ, the diode is severely aged and should no longer be used.
Current Measurement Method: Measure the voltage drop across the load resistor in the laser diode drive circuit using a multimeter. Then, estimate the current flowing through the diode based on Ohm’s law. If the current exceeds 100mA and adjusting the laser power potentiometer does not significantly change the current, it indicates severe aging of the laser diode. If the current dramatically increases and becomes uncontrollable, this suggests that the optical resonator of the laser diode is damaged.
FAQs
What is the lifespan of a laser diode?
The lifespan of a laser diode varies depending on factors such as operating conditions, power levels, and the quality of the diode. Typically, laser diodes can last from several thousand to tens of thousands of hours of operation.Â
What are the common causes of failure in laser diodes?
Common causes of failure in laser diodes include:
- Excessive heat can damage the diode’s internal structure and degrade performance.
- Operating the diode beyond its maximum current rating can lead to overheating and failure.
- Physical impacts or mishandling can cause damage to the diode’s delicate components.
- Semiconductor materials can degrade over time, leading to reduced efficiency and eventual failure.
- Voltage spikes or surges can damage the diode and affect its operation.
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