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A distributed feedback (DFB) laser uses a periodic structure along its waveguide or gain region to provide optical feedback. That structure acts as a distributed reflector, favoring wavelengths or modes that match its periodicity and fall within the laser’s gain range.
How does a DFB laser work?
In a conventional cavity, light reflects between mirrors at the ends. In a DFB laser, a periodic structure provides feedback along the waveguide instead. Its repeating pattern produces Bragg reflection, reinforcing light at selected wavelengths or modes while the gain region amplifies the selected light.
The periodic structure can work by changing the waveguide’s refractive index, its optical loss, or both. For example, in a terahertz quantum-cascade laser described by the University of Cambridge Semiconductor Physics Group, a metal grating modulates waveguide loss. That is one implementation, not a feature shared by every DFB laser.
What does “distributed feedback” mean?
“Distributed” describes the location of the feedback: it is supplied along a periodic part of the waveguide or gain region rather than only by separate mirrors at the cavity ends. The grating’s periodicity helps select the optical mode or wavelength, while the laser’s gain range determines which selected light can be amplified.
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What is a phase shift in a DFB laser?
Some DFB designs include a phase shift in the grating, often near its center, to help favor a single mode. It is a common design choice, not a requirement for a laser to qualify as a DFB laser. Construction and mode behavior can vary between designs.
DFB vs. DBR lasers
The key distinction in the cited semiconductor-laser comparison is where the grating sits relative to the active gain region:
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| Laser type | Grating placement | How feedback is incorporated |
|---|---|---|
| DFB | Distributed along the active medium | The grating supplies feedback along the gain region. |
| DBR | Outside the active region | The grating forms a reflector separate from the gain region. |
This comparison describes the cited semiconductor-laser distinction; it does not mean every device of either type has identical construction or mode behavior.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Where are DFB lasers used?
DFB structures are used in semiconductor lasers, including quantum-cascade lasers (QCLs). The Cambridge group describes DFB QCLs for terahertz operation, and RP Photonics also identifies QCLs as an application. These examples do not amount to an exhaustive classification of every DFB laser implementation.
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Quick Recap
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- Typical Power : > 60 mW
- InGaAsP MQW DFB Laser Diode
- Narrow Linewidth : 200kHz
- Housed in 9pin mini box package with SM fiber
- Operating temperature -5°C to +75°C
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- 1310nm DFB Single mode coaxial laser diode
- Package: A package with SM Fiber with FC/UPC or FC/APC
- Optical output power: 5mW
- Threshold current: 10mA
- High side mode suppression ratio(typical >35dB)
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