What Is a DFB Laser?
A Distributed Feedback (DFB) laser is a type of laser diode that produces a stable output wavelength. This stability is achieved by incorporating diffraction gratings at the boundaries of the diode layers, which amplify and emit only the light wavelength that matches twice the distance between the gratings. Unlike standard laser diodes, DFB lasers maintain a consistent wavelength regardless of current changes, operating environment, or modulation.
Uses of DFB Lasers
DFB lasers are primarily used in high-capacity, long-distance optical communications due to their ability to maintain stable output at a constant wavelength under various conditions. They are also employed in medical endoscopy, Raman spectroscopy, wavelength conversion, and gas testing. When selecting DFB lasers, factors such as allowable current, output wavelength, connection terminals, operating environment, and size should be considered.
Principle of DFB Lasers
DFB lasers consist of a p-type cladding layer, an n-type cladding layer, and an active layer sandwiched between them. During operation, forward voltage applied through the electrodes causes electron and hole recombination in the active layer, emitting light. This light is selectively amplified by the diffraction grating to produce a single wavelength output.
Temperature Characteristics of DFB Lasers
DFB lasers exhibit stable wavelengths with minimal temperature variation. Generally, the wavelength gradient is approximately 0.1 nm/℃. The oscillation wavelength is controlled by the grating period and temperature gradient. Efforts are underway to develop cost-effective, low-current DFB lasers that do not require external temperature control, using new materials and packaging methods.
1550 NM Wavelength, a Typical DFB Laser
In long-distance optical communications, wavelengths like 1550 nm are chosen for their low loss in optical fibers. This wavelength is particularly favored for long-wavelength DFB lasers. Other 1550 nm lasers include λ/4 phase-shifted grating DFB lasers and DBR lasers with gratings positioned away from the active layer.
Comparison With FP Lasers
Fabry-Perot (FP) lasers, another type of semiconductor laser, are often compared with DFB lasers. The main difference is FP lasers’ difficulty in achieving single-mode oscillation. FP lasers are used in CD/DVD optical pickups, laser printers, and similar applications.