Semiconductor lasers, also known as laser diodes, are lasers that use semiconductor materials as their active medium. Due to differences in material structure, the specific processes by which different types of lasers generate laser light are quite unique. Commonly used active media include gallium arsenide (GaAs), cadmium sulfide (CdS), indium phosphide (InP), and zinc sulfide (ZnS). Excitation methods include electrical injection, electron beam excitation, and optical pumping. Semiconductor laser devices can be classified into several types, such as homojunction, single heterojunction, and double heterojunction lasers. Homojunction lasers and single heterojunction lasers are mostly pulsed devices at room temperature, while double heterojunction lasers can achieve continuous operation at room temperature.
Semiconductor lasers were successfully excited in 1962 and achieved continuous output at room temperature in 1970. Later improvements led to the development of double heterojunction lasers and striped laser diodes, which are widely used in fiber optic communications, optical discs, laser printers, laser scanners, and laser pointers (laser pens). They are currently the most widely produced type of laser.
Due to their many unique and excellent characteristics, such as high efficiency, miniaturization, and fast response, semiconductor lasers are widely used in communications, industry, medical, and military fields. Below are some common semiconductor lasers and their characteristics.
1. Side-emitting laser
Edge-emitting lasers (EELs) are the most widely used type of semiconductor laser. Their laser beam is emitted perpendicular to the semiconductor surface and can be optically coupled from both ends. EELs offer good beam quality and are suitable for applications such as long-distance communication and fiber optic sensing.
2. Surface-emitting laser
A surface-emitting laser (SEL) emits a laser beam parallel to the semiconductor surface, allowing for optical coupling in a direction perpendicular to the semiconductor surface. SELs feature low threshold voltage, single-mode output, and ease of integration into two-dimensional arrays, making them suitable for applications such as short-range communication and parallel optical signal processing.
3. Vertical-cavity surface-emitting laser
A vertical-cavity surface-emitting laser (VCSEL) is a semiconductor laser with a unique structure. Its laser beam is emitted perpendicular to the semiconductor surface, offering advantages such as low threshold voltage, single-mode output, and a circular beam pattern, making it suitable for applications in data communication, optical storage, and parallel optical signal processing.
4. Distributed feedback laser
A distributed feedback laser (DFB) is a semiconductor laser with a periodic refractive index change. Its laser beam is emitted perpendicular to the semiconductor surface, offering advantages such as low threshold voltage, single-mode output, and narrow linewidth, making it suitable for applications in fiber optic sensing, optical coherent radar, and DWDM systems.
In addition to the types mentioned above, new semiconductor lasers such as quantum dot lasers and graphene lasers are constantly being researched and developed. Different types of semiconductor lasers have their unique application scenarios and advantages, and choosing the appropriate laser type according to specific needs is key.
Currently, blue semiconductor laser tubes mainly use TO packaging. Taking the NUBM08 blue laser tube as an example, its single-tube output power is 4.35W and its wavelength is 455nm. Measured results show that without a collimating lens, the fast-axis divergence angle is 40° and the slow-axis divergence angle is 10°. With a collimating lens, the fast-axis divergence angle is -0.1° and the slow-axis divergence angle is 0.5°. The number of laser tubes stacked along the fast axis is determined based on the beam product (BPP) after fast-axis and slow-axis collimation to achieve optimal fiber-coupled output.
5. Applications of semiconductor lasers
Semiconductor lasers have wide applications in various fields. For example, in the communications field, they can be used for fiber optic communication, optical switching, optical modulation and demodulation, improving communication speed and capacity; in the industrial field, they can be used for material processing, printing, marking, and testing, improving production efficiency and quality; in the medical field, they can be used for surgery, phototherapy, and spectral analysis, improving medical standards and diagnostic capabilities; and in the military field, they can be used for laser weapons, radar, and navigation, enhancing combat capabilities and effectiveness.
6. Summary
Semiconductor lasers are important optical devices with broad application prospects. Different types of semiconductor lasers have their unique characteristics and advantages, and selecting the appropriate laser type based on specific needs is crucial. With continuous technological advancements, semiconductor lasers will be applied and promoted in more fields, bringing greater convenience and contributions to human production and life.
