Several types of lasers have been invented in the last few decades to tackle the rising need for communication. One such laser is called the DFB laser. It is a type of narrow linewidth laser diode or an optical fiber laser where the grating generally happens along the cavity, and not just at the two ends.
The structure of the diode builds a one-dimensional interference grating, also known as Bragg scattering. Being single-frequency laser diodes, distributed feedback laser provides a narrow linewidth with good side mode suppression.
Unlike other conventional laser diodes, distributed feedback lasers do not use two mirrors to develop the optical cavity. Instead, in this advanced and narrow linewidth laser diode, a diffraction grating is integrated into the active region, which acts as the wavelength-selective element for at least one of the mirrors. This grating provides the necessary optical feedback, which ultimately reflects light back into the cavity to form the resonator. The precision of the grating ensures that the laser operates at a single wavelength, offering superior performance and stability in applications requiring narrow linewidth output.
Primarily, there are two types of DFB lasers – Fiber lasers and Semiconductor lasers. Semiconductor lasers can be defined as compact devices that cause laser oscillation by passing an electric current through a semiconductor material, typically resulting in high efficiency and small form factor. While fiber lasers, on the other hand, are devices in which the light is channeled and amplified through a specially designed fiber optic cable, offering advantages such as high beam quality and excellent power scalability for various industrial and scientific applications.
Below are some of the principal characteristics of the DFB laser.
Principal Characteristics of DFB Laser:
- DFB lasers are used to generate a signal with a single frequency.
- It provides a higher modulation speed of up to 15Gbps.
- Distributed feedback lasers offer distraction grating above the active region.
- It is less susceptible to temperature variations.
- In DFB lasers, the periodic variation of the refractive index is obtained using a diffraction grating.
- Except for the single-mode, all other modes are suppressed by oscillators near the Bragg wavelength.
Application of Distributed Feedback Laser:
DFB lasers offer smooth and tunable control of the wavelength, low noise, and narrow spectral width, making it a cost-effective, ideal narrow linewidth laser for fiber optic communication and sensing applications. Below are some of the key applications of these lasers.
A. Optic Communication:
Distributed feedback lasers are widely used in the telecommunication industry due to their ability to generate stable, single-mode outputs. Besides, integrated DFB lasers are highly preferred in advanced optical communication applications, such as Dense Wavelength Division Multiplexing (DWDM), where a tunable laser signal is desired to transmit multiple data channels over the same fiber, significantly increasing bandwidth efficiency and data transmission capacity.
B. Sensing:
Being a narrow linewidth laser, distributed feedback lasers are also used in precision sensing applications where the extremely narrow linewidth is required for high accuracy. In gas sensing applications, the DFB laser’s tunable wavelength plays a crucial role in detecting the absorbing gas signal. By finely tuning the laser’s wavelength, it can precisely match the absorption lines of specific gases, allowing for accurate and sensitive gas detection across various industries, including environmental monitoring and industrial safety.
C. Medical Uses:
DFB lasers are widely accepted in the medical field too. Its shrinking size, cost, and user-friendliness make it an ideal instrument for minor soft tissue procedures. From dentistry, where it is used for precision cutting and treatment, to spectroscopy, where it aids in the analysis of biological samples, and photodynamic therapy, where it helps in targeting and treating cancerous cells, it is now adopted by almost every medical branch. The versatility and adaptability of DFB lasers make them valuable tools in various therapeutic and diagnostic applications.
A few other DFB laser diodes applications are barcode readers, CD players, image scanning, laser absorption, and spectrometry. Besides, these high power, narrow linewidth laser diodes have a wide-scale use in the industry too. It is used for seam welding, cladding, and heat treating.
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