Using frequency comb resolution for long-distance measurement

introduction

Precision ranging plays a crucial role in many fields such as industrial metrology, measurement, autonomous navigation, robotics, and remote sensing. It can accurately locate and map objects, detect small changes in distance, and monitor dynamic environments with high precision.

Precision ranging uses various methods, including laser based technologies such as Time of Flight (ToF) measurement, interferometry, and Frequency Modulated Continuous Wave (FMCW) radar (optical detection and ranging). These methods utilize the principles of light waves or electromagnetic waves to determine distance based on measurements of propagation time or phase shift.

Dual comb laser radar

Dual comb lidar is a cutting-edge sensing technology that combines the principles of time-of-flight (ToF) and interferometry, while also drawing on the coherent signal amplification technology of frequency modulated continuous wave (FMCW) lidar. This innovative method combines the advantages of these technologies and can achieve high-precision and fast absolute distance measurement.

Traditional LiDAR systems typically rely on time-of-flight or interferometric methods for distance measurement. The time-of-flight method measures the time required for laser pulses to travel back and forth to a target object, while the interferometry method analyzes the interference pattern of the laser beam. However, both methods have limitations in terms of measurement accuracy, speed, or range.

The dual comb lidar overcomes these limitations by using two frequency combs with slightly different repetition rates. When the emitted light interacts with the target object, a portion of the light will be reflected back. Some of the light will be reflected by the reference mirror. By interfering the light reflected by one frequency comb through the target and reference mirror with the light of another frequency comb, and measuring the delay between the resulting interference patterns, accurate distance measurement results can be obtained.

The key determining factors of dual comb lidar include pulse bandwidth, repetition frequency, and repetition frequency difference. By utilizing the cursor effect (i.e. swapping the roles of local oscillator and sampling oscillator in the same measurement process), dual comb lidar can achieve an extremely long and unambiguous measurement range. This range can extend to hundreds of kilometers, exceeding the needs of most practical applications. At the same time, the system is able to maintain micrometer level accuracy, which is determined by the pulse duration (usually in the sub picosecond range) and data acquisition speed. In addition, dual comb laser radar can obtain interference signals, thereby achieving sub wavelength measurement accuracy. These comprehensive characteristics make dual comb lidar a powerful technology.

Schematic diagram of distance measurement signal in dual comb laser radar. The distance measurement is repeated every 1/Δ f ᵣₑₚ. The time interval between the target pulse and the reference pulse encodes distance information. Distance can be determined solely based on flight time, or optical phase can be used to optimize distance measurement.

Dual comb laser radar based on single cavity dual comb laser

The use of single cavity dual comb lasers in dual comb lidar systems is crucial for promoting the practical application of this technology. By adopting a single cavity design, the system becomes more compact, which is ideal for integration into various platforms and devices. The use of a single laser source eliminates complex synchronization requirements and simplifies the entire system architecture.

In addition, the single cavity dual comb laser method has scalability in production. Due to simplified design and more efficient manufacturing process, it is possible to achieve efficient and economical production of dual comb LiDAR systems. This scalability is particularly important for the widespread application and commercialization of this technology.

The advantages of K2 Photonics precision ranging

• Fast scanning speed

Single cavity dual comb lasers can perform high-resolution measurements at a fast update rate, up to 100 kHz, and even close to 1 MHz in special cases.

• High precision

The dual comb laser radar provides excellent measurement accuracy by utilizing the time stretching factor for optical sampling, ensuring femtosecond level accuracy in recording return pulses. In addition, the utilization of optical phase information further improves the accuracy of measurement, achieving precise and detailed ranging functions.

• Small size
Compact radar systems can be developed using compact single cavity dual comb lasers, especially those operating at GHz repetition rates or higher.

• High sensitivity

The coherent amplification of the local oscillator in a dual comb laser radar can achieve high sensitivity detection of return reflections. In addition, mode-locked solid-state lasers generate lasers with ultra-low noise (RIN and timing) at high frequencies, thereby achieving high sensitivity and particle noise limited measurements.