Self-Mixing Interferometry for Precision Measurement

Self-mixing interferometry exploits the reinjection of a fraction of a laser’s own emission—reflected or scattered from a target—back into its active cavity. This interaction modifies the laser’s output power and frequency, encoding information about displacement, velocity, distance and refractive index changes in the target. As a fundamentally monolithic technique, self-mixing interferometry offers non-contact sensing with minimal external components, nanometre-scale resolution and high bandwidth. Recent advances in laser design, signal-processing algorithms and special feedback regimes have extended its applicability from submicrometre displacement measurements to long-range remote sensing and terahertz imaging. Innovations include random distributed feedback fibre lasers for ultra-long-distance velocimetry, generalised phase-stepping schemes for rapid coherent mapping and hybrid swept-frequency approaches for metre-scale ranging. These developments underscore self-mixing interferometry’s global significance in fields as diverse as precision manufacturing, structural health monitoring, environmental sensing and biomedical diagnostics, allowing compact, robust and cost-effective measurement solutions across visible, infrared and terahertz spectral bands.

Research from Nature Portfolio

An improved coherent sensing framework has been demonstrated through a generalised phase-stepping algorithm applied to laser feedback interferometry at terahertz frequencies. By reducing optical sampling to only a handful of phase-stepped measurements per pixel, this approach bypasses complex post-processing models and accelerates data acquisition. Experimental validation using a terahertz quantum cascade laser achieved far-field and near-field two-dimensional nanoscale imaging of micro-resonator fields. The technique reliably extracted magnitude and phase information with as few as four sampling points, opening prospects for fast, high-resolution coherent imaging across the visible, infrared and terahertz domains.

Research from all publishers

Leveraging random distributed feedback fibre lasers, a compact self-mixing velocimeter achieved unprecedented sensitivity down to femtowatt-level feedback. Integrated into a single-channel system, it measured non-cooperative target velocities at distances exceeding 100 km, demonstrating photon-limited detection of Doppler shifts and suggesting new routes for ultra-long-range remote sensing.

A hybrid swept-frequency feedback interferometer combined frequency-swept interferometry with intracavity mixing to enhance weak echo signals without external amplifiers. This configuration enabled non-cooperative-target ranging over several hundred metres, with sub-millimetre precision maintained by an auxiliary compensation interferometer that monitored path-length drifts and environmental disturbances in real time.

A foundational heterodyne self-mixing system achieved single-spot two-dimensional displacement measurements with submicrometre accuracy and nanometre-scale resolution. By multiplexing frequencies within the laser cavity, the method simultaneously resolved in-plane and out-of-plane motions over sub-millimetre ranges, offering a versatile tool for materials deformation testing, rotor vibration analysis and precision positioning tasks.

Self-Mixing Interferometry for Precision Measurement publication trend

The graph below shows the total number of articles in self-mixing interferometry for precision measurement across all publications each year (not limited to Nature Index journals).

Technical terms

Self-mixing interferometry: A sensing technique in which a portion of the laser’s own emission is reflected back into its cavity, producing measurable modulation in the laser’s output that encodes target information.

Laser feedback interferometry (LFI): A variant of self-mixing where coherent feedback influences both amplitude and phase of the lasing field, enabling sensitive detection of displacement, refractive index changes or surface profiles.

Phase-stepping algorithm: A signal-processing method that acquires multiple interferometric measurements at distinct phase offsets, allowing extraction of amplitude and phase information with reduced sampling requirements.

Random distributed feedback fibre laser (RDFL): A laser architecture where feedback arises from distributed Rayleigh scattering along a doped fibre, delivering narrow linewidth and intrinsic long-distance transmission suitable for sensing applications.

Non-cooperative target: A remote object that does not carry a cooperative reflector or transponder, scattering only a weak portion of the incident laser light back towards the sensor.

References

1. Implementation of Er-doped random fiber laser self-mixing sensor with ultra-limit sensitivity. APL Photonics (2024).
2. Terahertz microscopy using laser feedback interferometry based on a generalised phase-stepping algorithm. Scientific Reports (2024).
3. Single-spot two-dimensional displacement measurement based on self-mixing interferometry. Optica (2017).
4. Frequency-swept feedback interferometry for noncooperative-target ranging with a stand-off distance of several hundred meters. PhotoniX (2022).