What are Multi-Quantum Well Laser Diodes?
Multi-quantum laser diode (TO-Can)
A multi-quantum laser diode is a type of quantum well laser diode that has more than one quantum well. It consists of quantum wells and barriers in the active region. The multi-quantum laser diodes are formed by sandwiching several layers of low bandgap materials (GaAs) in between the higher bandgap materials (AlxGa(1-x)As). The wavelength of laser light emitted from multi-quantum laser diodes can vary from 656 to 1635 nm. It is available in both fiber-coupled and free-space type. These diodes are ideal for optical transmission, data communication, local optical network, FTTH (Fiber to the Home), long haul WDM transmission, RF links, seeding, pulsing, and sensing applications.
Typically, standard multi-quantum well laser diodes have 3 to 6 quantum wells in the active region. The optical mode of all quantum wells is overlapping strongly and form one single optical field that results in more power output.
Advantages of muti-quantum well laser diodes:
They basically have all the benefits of the single quantum well laser diodes with more output power.
1. High output power as compared to the single quantum well laser diodes.
2. Lower threshold current value.
3. Insensitive to temperature variation. This is because the carrier distribution in the quantum wells is less sensitive to temperature variation.
4. The wavelength of the light is based upon the thickness of the active region. But, in a homojunction laser diode, the wavelength is based upon the compositions of material.
Key Specifications of quantum well laser diodes:
Central wavelength: Represents the wavelength of laser emitted from the multi-quantum well laser diode. The wavelength is represented in nm (nanometre). The multi-quantum well laser diodes can have a wavelength range from 656 to 1635 nm.
Technology: Multi-Quantum well (MQW)
Operation mode: Represents the operation mode CW mode/Pulse mode.
Type: Free space / Fiber-coupled
Output power: Represents the output power of the quantum well laser diode. Usually, the multi-quantum well 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. Usually, the spectral width of multi-quantum laser diodes can vary from 0.09 to 15 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 x A. The threshold current is proportional to the output power. Mostly, the multi-quantum well laser diodes have the threshold current range of 10 to 50 mA. A higher rating is also available.
Operating current: It is the driving current or input currents when the multi-quantum well laser diode reaches the rated power. It is represented in x A. The operating current is proportional to the output power.
Operating voltage: Represents the supply voltage. Usually, it is in the range of 1.1 to 2.2 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. Some multi-quantum diodes have a reverse voltage range of 2 to 10 V.
Laser gain medium: Represents the semiconducting material used in the active or gain medium. Usually, InGaAsP is used as the gain medium.
Operating temperature: Represents the safe operating temperature of the multi-quantum well laser diode. Typically, it has a range of -40 °C to + 85 °C.
Storage temperature: Represents the storage temperature range of multi-quantum well laser diode. Typically, it has a range of -40 °C to + 85 °C.
Package type: Represents the type package used to pack the multi-quantum well laser diodes. Usually, the quantum well laser diodes are available in TO-can, TO-can pigtailed, chip, DIP, and butterfly packages.