Laser chips used for optical communication and LiDAR have many differences in wavelength selection, power requirements, modulation rate, mode requirements, etc., as follows:

Wavelength selection:

Optical communication: Usually choose the wavelength band with the lowest fiber loss, such as 850nm, 1310nm, 1550nm, etc. For example, in long-distance backbone network communication, 1550nm wavelength is more commonly used because of its minimal transmission loss in optical fibers.

Lidar: commonly used wavelengths are 905nm and 1550nm. The 905nm wavelength is located in a slightly lower loss window of the atmosphere, but due to its proximity to visible light wavelengths, it has potential harm to the eyes and limits the laser power. The 1550nm wavelength has a higher upper limit for human eye safety, and higher power lasers can be used to improve detection range, but atmospheric losses and water vapor absorption may have an impact on rainy days.

Power demand:

Optical communication: More emphasis is placed on low loss transmission, with relatively low requirements for the output power of laser chips. Long distance communication is mainly achieved through optimizing the transmission characteristics of optical fibers.

Lidar: It relies on the reflected light of the object being measured for distance calculation, and it is necessary to increase the transmission power as much as possible while ensuring human eye safety to accurately detect targets. In addition to connecting multiple PN junctions in series on the same laser chip, an array type high-power VCSEL (vertical cavity surface emitting laser) will also be used to increase the current and improve the luminous power through parallel PN junctions.

Modulation rate:

Optical communication: requires processing high-speed data signals and has extremely high modulation rate requirements. For example, a 50G signal typically uses a 19GHz bandwidth, while a 100G signal uses a 25-30GHz bandwidth. To achieve high-speed modulation, it is necessary to reduce the RC constant of the chip and circuit, and designs such as small aperture and single PN junction will be used to reduce the junction capacitance of the PN junction.

Lidar: The modulation rate requirement is relatively low, usually in the KHz and MHz levels, so the junction capacitance requirement is not high. Multiple PN junctions are usually connected in series to increase optical power.

Mode requirements:

Optical communication: In order to reduce the mode interference of optical signals transmitted in optical fibers and ensure stable operation, the ideal situation is to obtain single-mode output laser chips, such as single-mode VCSEL laser chips or single transverse mode FP (Fabry Perot), DFB (distributed feedback) laser chips, etc.

Lidar: The mode requirements are not as strict as optical communication, and focus more on high-power output. Single mode output is not necessarily required, and multi-mode laser chips can also meet the requirements, such as multi-mode VCSEL, which can be used for lidar.

Wavelength tuning method:

Optical communication: Wavelength tuning is the process of adjusting the wavelength to the desired position and fixing it, requiring the wavelength to be stably locked to the specified "point" to ensure the stability and accuracy of communication.

Lidar: Continuous wavelength scanning (frequency scanning) is required, and attention should be paid to the linearity of the scanning frequency, because frequency scanning can calculate the motion speed of objects through the Doppler frequency shift principle. Poor linearity can affect the detection accuracy of the radar.

Reliability requirements:

Optical communication: usually used in data centers and outdoor communication base stations with relatively stable environments. Although reliability is required, it focuses more on long-term stable low loss transmission and high-speed signal processing.

Lidar: It is often installed on equipment with complex environmental conditions such as cars, and needs to adapt to different weather, temperature, and other environmental changes. It requires high reliability and anti-interference ability of laser chips, and needs to be able to work stably in various harsh environments.