High-precision indoor positioning technology is regarded as one of the core components of artificial intelligence (AI) and Internet of Things (IoT) applications. Over the past decades, society has observed a burgeoning demand for indoor location-based services (iLBSs). Concurrently, ongoing technological innovations have been instrumental in establishing more accurate, particularly meter-level indoor positioning systems. In scenarios where the penetration of satellite signals indoors proves problematic, research efforts focused on high-precision intelligent indoor positioning technology have seen a substantial increase. Consequently, a stable assortment of location sources and their respective positioning methods have emerged, characterizing modern technological resilience. This academic composition serves to illuminate the current status of meter-level indoor positioning technologies. An in-depth overview is provided in this paper, segmenting these technologies into distinct types based on specific positioning principles such as geometric relationships, fingerprint matching, incremental estimation, and quantum navigation. The purpose and principles underlying each method are elucidated, followed by a rigorous examination and analysis of their respective technological strides. Subsequently, we encapsulate the unique attributes and strengths of high-precision indoor positioning technology in a concise summary. This thorough investigation aspires to be a catalyst in the progression and refinement of indoor positioning technologies. Lastly, we broach prospective trends, including diversification, intelligence, and popularization, and we speculate on a bright future ripe with opportunities for these technological innovations.

A cube-corner is employed as a photoelectric autocollimator’s reflector to extend the angle measurement range and the corresponding algorithms are deduced. Experimental investigations reveal that the measurement range is extended from 1.2° to 12° without enlarging the objective lens’s aperture. The accuracy is better than 35” when the deflection is less than 8°.

We demonstrate a strain-based fully tunable, near-lossless, whispering gallery mode (WGM) resonator made of an in-fiber rectangular air bubble, which is fabricated by splicing two segments of standard single-mode fibers. Such a resonator, with a 39 μm order radius and 1 μm order wall thickness, contributes to a high quality factor exceeding ${10}^6$. The tuning in resonant wavelength is achieved by applying tensile strain to the resonator, and the voltage-tuning rate of the WGM resonance peaks is about 31.96 pm/V (strain-tuning rate $\sim 14.12\mathrm{pm}/\mathrm{\mu ϵ}$), and the corresponding tuning accuracy is better than 0.03 pm. Since the tensile strain applied on the resonator can reach $1000\mathrm{\mu ϵ}$, the achievable total tunable bandwidth of $\sim 14.12\mathrm{nm}$ is more than two times that of its azimuthal free spectral range.

A broadband tunable orbital angular momentum (OAM) mode converter based on a helical long-period fiber grating (HLPFG) inscribed in a conventional single-mode fiber (SMF) is experimentally demonstrated. The proposed all-fiber OAM mode converter is based on the core-cladding mode dual resonance near the dispersion turning point (DTP). The converter can operate with a bandwidth of 303.9 nm @ −3 dB and 182.2 nm @ −10 dB, which is, as far as we know, the widest bandwidth for a conventional SMF. Furthermore, the bandwidth of the OAM mode can be dynamically tuned within a large dynamic range (>80 nm) by simply twisting the fiber clockwise (CW) or counterclockwise (CCW). The dynamic tunability of the bandwidth of the proposed OAM mode generator may find vital applications in large-capacity optical fiber communication systems.

Flexible polymer-based magnetoelectric (ME) materials have broad application prospects and are considered as a new research field. In this article, FeCoSiB thin films were deposited on poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) substrate by DC magnetron sputtering. The structure of PVDF-TrFE/FeCoSiB heterostructure thin films was similar to 2-2. Under a bias magnetic field of 70 Oe, the composites have a dramatically increased ME voltage coefficient as high as 111 V/cm⋅Oe at a frequency of about 85 kHz. The piezoelectric coefficient of PVDF-TrFE thin films is 34.87 pC/N. The surface morphology of PVDF-TrFE thin films were studied by FESEM, and the results of XRD and FTIR showed that the β-phase of PVDF-TrFE thin films was dominant. Meanwhile, the effects of different heating conditions on the crystallization and piezoelectric properties of PVDF-TrFE films were also studied. The flexible ME heterojunction composite has a significant ME voltage coefficient and excellent piezoelectric properties at room temperature, which allows it to be a candidate material for developing flexible magnetoelectric devices.

Foot-mounted positioning system (FPS) is regarded as an important application for GPS-denied scenes, including but not limited to emergency rescue, medical health, and individual soldier positioning. With the assistance of zero velocity update (ZUPT), the basic positioning function can be realized, while the largest problem is that the accumulation of systematic heading drift and positioning error cannot be completely constrained. This paper presents a robust foot-mounted positioning system based on dual inertial measurement unit data and ultrasonic ranging (FPS-DU). Bi-directional Long Short-Term Memory (Bi-LSTM) network is developed for the recognition of quasi-static period for the performance enhancement of ZUPT, and multi-level constraints are modeled for decreasing the cumulative error of the single foot-mounted model. In addition, a unified Kalman-based location estimator is developed combing dual foot-mounted inertial data and sphere constraint-based ultrasonic ranging results, enhanced by a robust ultrasonic outlier detector. Comprehensive experiments demonstrate that the proposed FPS-DU realizes much more accurate and robust positioning accuracy (between 0.371% to 0.548% under different test environments and traveled distances) compared with traditional single FPSs.