Physics / mechanism
Distributed Feedback (DFB) and Distributed Bragg Reflector (DBR) lasers are single-longitudinal-mode semiconductor lasers that use periodic refractive-index or gain gratings to provide wavelength-selective optical feedback, replacing the broadband mirrors of Fabry-Pérot cavities. In DFB designs the grating runs the full cavity length; in DBR designs discrete grating sections flank the gain region, enabling independent current tuning of wavelength and power. Both operate on the Bragg condition: λ_B = 2nΛ, where Λ is grating pitch and n is effective index. State-of-the-art telecom DFBs achieve side-mode suppression ratios >50 dB, linewidths <1 MHz, and output powers of 10–40 mW CW at 1310/1550 nm. Tunable DBR variants cover >40 nm tuning range. Integration into InP or GaAs PICs is mature; heterogeneous bonding onto silicon photonics is the current scaling frontier.
Competitive landscape
Key competition comes from Fabry-Pérot lasers (cheap, multimode, adequate for short-reach), VCSELs (lower cost, wafer-testable, dominate datacom ≤10 km), and external-cavity lasers (narrower linewidth, <100 Hz, but bulky/expensive). Emerging coherent thin-film lithium niobate and silicon-nitride-integrated laser sources challenge DBR in linewidth-sensitive sensing.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.