Requirements for LiDAR
Along with the progress of technology related to autonomous driving, LiDAR is required to exhibit high performance. For example, there are needs to detect objects over longer distances, to detect higher resolution, and to reduce the effect of noise when reflected light is received. In order to meet these needs, it is necessary to increase the output power of the emitted light.
However, because high output power laser light has a harmful effect on human eyes, a standard (Eye Safe IEC 60825) was established in order to limit the amount of output energy of the emitted light. In order to satisfy this standard, it is necessary to reduce the time of light emitted if higher output light is emitted.
To emit short pulses of light when emitting light at high output, the pulses must be raised sharply. An effective method of shortening the rise time of these pulses is to reduce the parasitic inductance between the pulse generation capacitor and the laser diode.
Solutions using silicon capacitors
A silicon capacitor features small size and a low profile, enabling it to be placed near a laser diode. Also, because it can be mounted by wire bonding, it can be connected directly to a laser diode. These merits enable the silicon capacitor to reduce the loop parasitic impedance (ESL) between the capacitor and the laser diode. As a result,when compared to ceramic capacitors, silicon capacitors enable narrow light pulses (approx. 1.5 nanoseconds) to be emitted at high output (100 W or higher).
Solutions using silicon IPD
A silicon IPD enables capacitors and wiring to be made inside a silicon interposer. Also, a laser diode, a driver, a switching device, and other components can be mounted on a silicon IPD. Because of these merits, the use of a silicon IPD enables to reduce the overall loop parasitic inductance (ESL)as much as possible. As a result, when compared to ceramic capacitors, silicon IPD realizes ideal narrow light pulses (approx. 0.9 nanoseconds) to be emitted at high output (120 W or higher).