Dynamic-gain-matching-based large bandwidth self-mixing laser Doppler velocimetry with notable 10 ⁴ intensity response enhancement

Laser Doppler velocimetry is a powerful method for precise motion monitoring with the advantages of high precision and noncontact. Among them, self-mixing (SM) laser Doppler velocimetry exhibits high sensitivity for noncooperative targets. The spontaneous amplification of Doppler signals through intracavity interference enables the detection of weak echo signals, meeting practical measurement requirements. However, the frequency-dependent gain profile in laser feedback systems exhibits progressive attenuation at higher frequencies due to the inherent gain-frequency constraint, fundamentally limiting their applicability for high-sensitivity velocimetry of high-speed targets. We quantitatively establish for the first time, to our knowledge, that the product of self-mixing interferometry’s gain and frequency (GFP) remains constant for higher frequency. In order to improve the bandwidth of SM laser Doppler velocimetry and further enhance the sensitivity of self-mixing interferometry (SMI), a frequency conversion method is implemented to transcend this intrinsic limit. The electro-optical modulator (EOM) and optical injection locking are employed to shift the frequency of the interference signal into the gain region, enabling the extension of gain bandwidth. Theoretically, the measurement bandwidth of Doppler frequency can extend to tens of GHz (the corresponding speed beyond 1 km/s at 1550 nm) due to the large modulation bandwidth of EOM, and the experimental measurement of Doppler frequency exceeds 44 MHz (34.1 m/s at 1550 nm) limited by the target. The system achieves a Doppler frequency measurement precision within 4 Hz. In the meantime, optical injection locking can provide additional optical gain. The seed light of 10 μW is amplified to 60 mW, providing a gain of 37 dB. The detection limit of the proposed system is −145.52 dB with 10 4 higher intensity response sensitivity than normal heterodyne interference. Therefore, the system has the advantages of large bandwidth, high sensitivity, and high precision. It is expected to be widely used in the monitoring of noncooperative high-speed moving targets.