Stanford EE259 I Lidar range and direction of arrival estimation I 2023 I Lecture 18

TL;DR

Direct detection lidar measures the power of the incident light, while coherent lidar detects the full electromagnetic field, making it more versatile.

Transcript

uh now let's do a quick review of uh previous lecture lecture 18. so we talked about uh pin photodiodes which are used to detect uh basically the light that is received by a lidar and we talked about the physics of it so the Pion photodiode it's like a regular diode which is a PN Junction except there is an extra material in between the p and the n... Read More

Key Insights

• 🙂 Direct detection lidar measures the power of the incident light using a PIN photodiode, while coherent lidar detects the full complex electric field using a coherent receiver.
• 📁 Direct detection lidar is simpler and more commonly used in the market, while coherent lidar offers additional capabilities like velocity estimation.
• 🧡 Coherent lidar requires more complex hardware and algorithms but offers better range and SNR performance.
• 😒 Both lidar systems can use different pulse shapes, but direct detection lidar typically uses short pulses, while coherent lidar can use FMCW or PMCW waveforms.
• 💗 The range of a lidar system is determined by the pulse repetition interval (PRI) and pulse duration, with the maximum range being equal to (speed of light * PRI) / 2.

Questions & Answers

Q: What are the two main types of lidar systems based on the detection method?

The two main types of lidar systems are direct detection lidar and coherent lidar.

Q: How does direct detection lidar measure the incident light?

Direct detection lidar uses a PIN photodiode to detect the incident light and measures the power of the light for ranging.

Q: What is the advantage of coherent lidar over direct detection lidar?

Coherent lidar can detect both the range and velocity of targets, while direct detection lidar can only measure the power of the incident light.

Q: How does coherent lidar recover the full electromagnetic field?

Coherent lidar uses a coherent receiver, which combines the received signal with a local oscillator signal to extract the real and imaginary parts of the electric field.

Summary & Key Takeaways

• Direct detection lidar uses a PIN photodiode to detect the received light and measures the power of the incident light for time-of-flight estimation.

• Coherent lidar continuously transmits waveforms using frequency modulation (FMCW) or pulse modulation (PMCW) and can detect both range and velocity by analyzing the complex electric field.