What is the Quantum dot Laser Diodes?
A quantum dot laser diode is a type of laser diode that uses the quantum dot as the active laser medium in its light-emitting region. A quantum dot laser diode is formed by placing the quantum dots between the P-N junction. The quantum dot laser diodes are available in both fiber-coupled and free-space type. Mostly, the packages such as TO-can, chip, C-mount, and butterfly packages are used to pack the quantum dot laser diodes. These diodes are used in optical transmission, data communication, spectroscopy, telecommunications, display technology (laser TV), the multi-channel source for DWDM communication, and medical applications.
Quantum dot diode (Fiber-coupled butterfly package)
Quantum dot diode structure
Density state N(E) of quantum dot (0-D)
Quantum dots are semiconductor particles with a size range of few nanometers. The quantum dot size is less than or equal to (≤) the de Broglie wavelength of the electron. Hence, a quantum dot laser diode has an active medium thickness less than or equal to (≤) the de Broglie wavelength of the electron. These narrow active region forms the zero-dimensional (0-D) quantization and results in discrete energy level. In a quantum dot, the density of the state is continuous and independent of energy. The optoelectronic property change depends upon the size and shape of the quantum dot. The large quantum dot has a size of 5-6 nm, yielding the color orange or red, and the smaller quantum dot has a size of 2-3 nm, yielding the color blue or green.
This much small active region is formed by epitaxial regrowth on specially processed surfaces (cleaved, etched, vicinal, or V-groove). Because of the unique shape of the density states in the quantum dot system, the quantum dot laser diodes have better performance over the quantum well laser diodes and other conventional laser diodes in the following points.
Advantages of quantum dot laser diodes:
1. The population inversion can be easily achieved because the electron profile in the band edge is much sharper. Hence, the quantum dot laser diode requires a lower threshold current.
2. Higher output power.
3. Insensitive to temperature variation. Because carrier distribution in quantum dot structure is less sensitive to temperature variation.
4. Wider wavelength tuning.
5. High speed.
Specifications details of quantum dot laser diodes:
Central wavelength: Represents the wavelength of laser emitted from the quantum dot laser diode. The wavelength is represented in nm (nanometre).The quantum dot laser diodes have wider wavelength operating range.
Technology: Quantum dot technology
Operation mode: Represents the operation mode CW mode/Pulse mode.
Type: Free space / Fiber coupled
Output power: Represents the output power of the quantum dot laser diode. Usually, the quantum dot laser diodes are available in the power range of milliWatts.
Spectral width: It is the width of the optical spectrum at the half-maximum power. It is represented in nm.
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. It is represented in milli Ampere. Mostly, the quantum dot laser diodes have the threshold current range of 10 mA to hunredas of mA .
Operating current: It is the driving current or input currents when the quantum dot laser diode reaches the rated power. The operating current of quantum dot laser diodes can vary form mA to Ampere range.
Operating voltage: Represents the supply voltage. Usually, it is in the range of 1.3 V to 2.3 V
Reverse voltage: Represents the maximum allowable reverse voltage, when it is applied across the laser diode. Beyond the reverse voltage, the diode will damage. It is usually in the range of 2 V.