What are Distributed feedback laser (DFB) Laser diodes?
Fiber-coupled DFB laser diode (Butterfly package)
DFB laser diode structure
Reflection in DFB laser diode
DFB or distributed feedback laser diodes are single-frequency laser diodes that usually operate from 783 to 1625 nm (higher wavelength also available). The output wavelength of the DFB laser depends upon the effective refractive index and period of the grating. The laser wavelength can be tuned by varying the temperature and current of the DFB laser. These lasers are available in the Butterfly (BTF), TO-Can, Sub-mount, and C-mount, TO-Can pigtailed, chip, HHL, and DIL packages. DFB laser diodes are ideal for fiber optic sensors, high-speed pulsing, analog RF links, optical communication, near-IR gas analysis, and tunable diode laser absorption spectroscopy (TDLAS) applications.
The internal structure of a DFB laser diode has a diffraction grating on its active region. This diffraction grating is a periodical structure element that acts as a Bragg reflector. A Bragg reflector is a mirror that reflects only a selected wavelength of light. Hence, the grating of the DFB laser diode reflects only the selected wavelength and so it produces a single lasing mode. To get a perfect single-mode output, both ends of the DFB laser diode are coated with the anti-reflection coating.
Specifications of DFB laser diode:
Central wavelength: Represents the wavelength of laser emitted from the DFB laser diode. The wavelength is represented in nm (nanometre). A DFB laser diode can have a wavelength range of 780nm to 1625nm. Higher wavelength DFB laser diode is also available.
Technology: Distributed feedback laser (DFB)
Type: Free space/ Fiber coupled. A free space DFB laser diode emits the laser light in free space, and a fiber coupled DFB laser diode emits light through the fiber optic medium.
Spectral width (FWHM): It is the width of the optical spectrum at the half-maximum power. Typically, the spectral width of DFB laser diodes can vary from 1MHz to 10 MHz.
Output power: Represents the output power of the laser diode. A DFB output power is in the range of mill watts.
Threshold current (Ith): It is the current at which the output optical power increases sharply. When the laser diode is biased below this threshold current, the output optical power will be very low. Mostly, the threshold current of a DFB laser diode can vary from 10mA - 70mA.
Working current: It is the driving current or input currents when the laser diode reaches the rated power. Usually, the operating current of a DFB laser diode can from 2mA to 1.35 A.
Operating voltage: Represents the supply voltage. Normally, a DFB laser diode can have the operating voltage range from 1.1V to 10.4V or in-between this range.
Reverse voltage: Represents the maximum allowable reverse voltage, when it is applied across the laser diode. Beyond the reverse voltage, the diode will damage. Usually the reverse voltage of a DFB laser diode is 2V.
Vertical Divergence Angle (θ⊥): The angle at which the light-emitting band spreads in a direction vertical to the PN junction.
Horizontal Divergence Angle (θ∥): The angle at which the light-emitting band spreads in a direction parallel to the PN junction.
Operating temperature: Represents the safe operating temperature of the DFB laser diode. Typically, it can have the range of -40 °C to +85°C.
Storage temperature: Represents the storage temperature range of DFB laser diode. Typically, it can have the range of -45 °C to +80°C.
Package type: Represents the type package used in the DFB laser diode. Usually, DFB laser diodes are available in the Butterfly (BTF), TO-Can, Sub-mount, and C-mount, TO-Can pigtailed, chip, HHL, or DIL packages.