What is the principle of DBR laser?

Principle of Distributed Bragg Reflector (DBR) Laser

The Distributed Bragg Reflector (DBR) laser is a type of semiconductor laser that is designed to produce highly coherent and monochromatic light. It uses the principle of distributed feedback to select the specific wavelength of operation through the incorporation of a periodic structure that acts as a Bragg reflector.

DBR Laser Structure

A DBR laser typically consists of three main sections: the active region, the Bragg reflector region, and the phase control region. The active region is where the light is generated by electrical or optical pumping. The Bragg reflector regions are positioned at the ends of the active region and consist of periodic variations in the refractive index, creating a wavelength-selective mirror. The phase control region, which may not be present in all DBR lasers, allows for fine-tuning of the lasing wavelength.

Operation of a DBR Laser

The operational principle of the DBR laser is based on the interaction of light with the Bragg reflector. When light of different wavelengths propagates through the reflector, only the light whose wavelength matches twice the periodicity of the Bragg grating is strongly reflected. The other wavelengths are mostly transmitted or weakly reflected. Thus, the Bragg grating acts as a filter, allowing the DBR laser to produce light at a specific, predetermined wavelength. The highly reflective Bragg gratings at each end of the laser cavity form the laser's resonator, which provides feedback necessary for lasing.

Advantages of the DBR Laser

• Precise Wavelength Selection: DBR lasers can be designed to emit light at a very specific wavelength, which is determined by the periodicity of the Bragg grating.
• High Spectral Purity: The Bragg grating provides excellent wavelength selectivity, resulting in a narrow linewidth of the output.
• Stability: DBR lasers are known for their stable output wavelength, even under varying external conditions such as temperature fluctuations.

Applications of DBR Lasers

DBR lasers have a wide range of applications due to their stable and precise wavelength output. They are used in optical fiber communications, high-resolution spectroscopy, sensors, and as sources for coherent light in various instrumentation.