The Development History of Semiconductor Lasers

A semiconductor laser, also known as a laser diode (LD), was first conceptualized in the 1950s with the development of semiconductor physics.

In the early 1960s, semiconductor lasers were homojunction-type lasers, which could only operate in pulsed mode. At the International Conference on Solid-State Devices held in July 1962, researchers Keyes and Quist from MIT Lincoln Laboratory reported on light emission phenomena in gallium arsenide (GaAs) materials.

The second phase of semiconductor laser development involved heterostructure semiconductor lasers, composed of thin layers of two different bandgap semiconductor materials, such as GaAs and GaAlAs. Single heterojunction injection lasers (SHLD) utilized the potential barrier provided by the heterojunction to confine injected electrons within the P-region of the GaAsP-N junction, thereby reducing threshold current density.

In 1970, a double heterojunction GaAs-GaAlAs laser capable of continuous operation at room temperature with a laser wavelength of 9000Å was invented. Among semiconductor laser devices, the electrically injected GaAs diode laser with a double heterostructure is currently more mature, better performing, and more widely applied.

From the late 1970s, semiconductor lasers began to develop distinctly in two directions: information-type lasers aimed at transmitting information and power-type lasers focused on increasing optical power. Driven by applications like pumping solid-state lasers, high-power semiconductor lasers (with continuous output power over 100W or pulsed output power over 5W) made significant breakthroughs in the 1990s. This progress was marked by a substantial increase in the output power of semiconductor lasers; kilowatt-class high-power semiconductor lasers have been commercialized abroad, while domestic prototypes have reached outputs of up to 600W.

Additionally, there are high-power aluminum-free lasers, infrared semiconductor lasers, and quantum cascade lasers. Tunable semiconductor lasers can change their wavelengths using external fields, magnetic fields, temperatures, pressures, doping levels, etc., allowing for convenient modulation of the output beam.

At the end of the 1990s, surface-emitting lasers and vertical-cavity surface-emitting lasers (VCSELs) saw rapid development.

Currently, VCSELs are used in high-speed networks for gigabit Ethernet. To meet the needs of broadband information transmission, high-speed information processing, large-capacity information storage, and miniaturization and high precision in military equipment in the 21st century, the development trends of semiconductor lasers mainly focus on high-speed broadband LDs, high-power LDs, short-wavelength LDs, quantum wire and quantum dot lasers, and mid-infrared LDs.

What is the wavelength of a semiconductor laser?

For optical communication research, commonly used semiconductor laser wavelengths are in the 1550nm band, followed by 1310nm, along with others like 850nm and 980nm. Common parameters of semiconductor lasers include wavelength, threshold current Ith, operating current Iop, vertical divergence angle, horizontal divergence angle, and monitor current Im.

1. Wavelength: The operating wavelength of the laser tube, often used in photoelectric switches with wavelengths such as 635nm, 650nm, 670nm, 690nm, 780nm, 810nm, 860nm, and 980nm.

2. Threshold Current Ith: The current at which the laser tube begins to produce laser oscillation. For small-power laser tubes, this value is typically several tens of milliamps, while strain-multi-quantum-well structure lasers can have thresholds below 10mA.

3. Operating Current Iop: The driving current when the laser tube reaches its rated output power, important for designing and debugging laser driver circuits.

4. Vertical Divergence Angle: The angle at which the emission band of the laser diode opens in the direction perpendicular to the PN junction, generally around 15° to 40°.

5. Horizontal Divergence Angle: The angle at which the emission band of the laser diode opens in the direction parallel to the PN junction, typically around 6° to 10°.

6. Monitor Current Im: The current flowing through the PIN diode when the laser tube operates at its rated output power.