The late 1990s to early 2000s telecom revolution prompted laser manufacturers to innovate and design more varieties of lasers to meet the growing demand in telecom applications. One of the best ways to meet the needs of low-signal lasers is to use distributed feedback lasers.
These lasers have not only contributed to addressing the needs of the telecommunications industry but have also caused the disappearance of DBR lasers (Distributed Bragg Reflectors) from the market.
In this post, the differences between DFB lasers and DBR lasers will be explored. But before that, a quick look at what a DFB laser is and what a DBR laser is will be provided.
What Is DFB Laser?
A DFB laser is a type of diode laser that generates resonance and oscillation within the cavity by utilizing diffraction gratings instead of traditional mirrors. This diffraction grating helps ensure that the laser operates at a single wavelength with a narrow linewidth. The primary purpose of a distributed feedback (DFB) laser is to refine and sharpen the output of conventional Fabry-Perot lasers, offering more stable and precise performance.
The replacement of mirrors with grating imparts distributed feedback lasers with a range of advanced characteristics, including periodic, spatially modulated gain, high efficiency, low threshold current, and single-wavelength operation. These features make DFB lasers highly suitable for applications requiring precise wavelength control, such as telecommunications and spectroscopy.
Let’s take a closer look at what a DBR laser is.
What Is DBR Laser?
DBR lasers, or Distributed Bragg Reflector lasers, are among the earliest, if not the first, single-frequency lasers ever developed. These lasers are tunable single-mode diode lasers that feature a resonator made from a short piece of active fiber sandwiched between two Fiber Bragg Gratings, which serve as wavelength-specific reflectors.
In comparison to DFB lasers, the DBR laser produces a single frequency and phase-coherent photons at a specific wavelength, ensuring precise and stable laser output. The gratings in DBR lasers act as mirrors with variable reflectivity at different wavelengths allowing the laser to achieve tunability across a narrow spectrum, making them ideal for applications like telecommunications, spectroscopy, and sensing.
Now, the significant differences between DFB and DBR lasers will be examined in the following section.
DFB Laser Vs. DBR Laser– The Key Differences
Some of the key differences between the Distributed Feedback Laser and the Distributed Bragg Reflector are listed below. Let’s take a glance at each one to get a better understanding of them.
- DFB Laser vs. DBR Laser– The Architecture
As one may expect, the key difference between these two lasers lies in their construction or the location of the grating zone. On the one hand, where the DBR laser uses a high index contrast and high reflectivity surface grating positioned outside the gain region, the DFB lasers utilize a low index contrast and low reflectivity grating embedded within the gain medium itself. This distinction in design influences the optical feedback mechanism, resulting in DBR lasers being tunable, while DFB lasers typically operate at a fixed wavelength.
- DFB Laser vs. DBR Laser– Defect Levels
In the case of DFB lasers, the EPI surface is subjected to air oxidation, and contamination often occurs during ridge and grating processing, which can result in more unsatisfactory performance and reduced efficiency over time. In contrast, DBR lasers exhibit lower defect levels than distributed feedback lasers due to their external grating configuration, leading to higher output powers, improved operational stability, and longer-lasting reliability in various applications.
- DFB Laser vs. DBR Laser– Mode Selection
The third significant distinction between the DFB and the DBR laser is that the DBR only operates at a single longitudinal mode with the highest gain and gain bandwidth of the EPI, ensuring precise wavelength selection and reduced noise. In comparison, DFB lasers operate in multiple lasing modes, which can vary monotonically as the EPI gain curve shifts, resulting in broader wavelength outputs and potentially more noise in certain applications.
- DFB Laser vs. DBR Laser– Number of Modes
The DFB laser has two modes that are symmetrically separated from the grating’s Bragg wavelength, providing stable operation over a range of conditions. In contrast, the DBR laser operates in a single mode with no symmetry, allowing it to function more consistently in a single mode with fewer spectral variations.
So, those are the four primary distinctions between DFB and DBR lasers. As seen, both of these lasers exhibit variations as well as similarities, which cause the two architectures to exhibit different behaviors that influence their performance in specific applications such as telecommunications, sensing, and precision measurement.
Inphenix is a US-based laser diode and light source manufacturer specializing in manufacturing photonics devices such as Semiconductor Optical Amplifiers (SOA), Superluminescent Diodes (SLDs), Gain Chip, LiDAR Lasers, and many others. The firm also builds customized laser devices based on the client’s needs.
Also See: Difference Between FP Laser and DFB Laser
