Distributed Bragg reflector (DBR) laser
A semiconductor laser using passive Bragg gratings outside the gain region as wavelength-selective mirrors. Tunable variant of the DFB laser.
A distributed Bragg reflector (DBR) laser places one or two passive Bragg gratings outside the gain section to act as wavelength-selective end mirrors. Unlike a DFB laser — which uses a single grating distributed along the active region — a DBR laser separates the gain function (active region with cleaved or anti-reflection-coated facets) from the wavelength-selection function (separate passive grating sections).
Standard configurations:
| Configuration | Sections | Tuning |
|---|---|---|
| Two-section DBR | Gain, rear DBR | Wavelength via DBR current |
| Three-section DBR | Gain, phase, DBR | Independent cavity mode and grating tuning |
| Sampled-grating DBR (SG-DBR) | Gain, phase, front SG, rear SG | Vernier tuning over 40+ nm |
| Y-branch / multi-section | Multiple gain, multiple DBRs | Wide discrete or continuous tuning |
The lasing wavelength satisfies the Bragg condition of the active DBR section. Injecting current into the DBR section perturbs the carrier density and thus the refractive index, shifting the Bragg wavelength. This provides electronic wavelength tuning.
Tuning range and resolution:
| Architecture | Continuous tuning range | Total addressable range |
|---|---|---|
| Two-section DBR | 5 nm | 5 nm (single grating) |
| Three-section DBR | 5 – 10 nm continuous | 10 nm |
| SG-DBR / Vernier | 0.5 nm continuous, mode-hop tuning | 40 – 50 nm |
| Modulated grating Y-branch | 5 nm per section | 40 – 80 nm |
DBR lasers are the dominant tunable laser architecture for telecom wavelength-agile transmitters. Single-channel telecom transmitters generally use DFB lasers (lower cost, no tuning required); tunable systems and coherent transponders use DBR or external-cavity diode lasers.
Disadvantages vs DFB: more complex control, multiple bias currents, mode hops between DBR comb modes during coarse tuning, and generally larger linewidth due to longer effective cavity.