Compact Displacement Sensor Research Articles

Nonlinearities in Fringe-Counting Compact Michelson Interferometers.

Compact Michelson interferometers are well positioned to replace existing displacement sensors in the readout of seismometers and suspension systems, such as those used in contemporary gravitational-wave detectors. Here, we continue our previous investigation of a customised compact displacement sensor built by SmarAct that operates on the principle of deep frequency modulation. The focus of this paper is the linearity of this device and its subsequent impact on sensitivity. We show the three primary sources of nonlinearity that arise in the sensor: residual ellipticity, intrinsic distortion of the Lissajous figure, and distortion caused by exceeding the velocity limit imposed by the demodulation algorithm. We verify the theoretical models through an experimental demonstration, where we show the detrimental impact that these nonlinear effects have on device sensitivity. Finally, we simulate the effect that these nonlinearities are likely to have if implemented in the readout of the Advanced LIGO suspensions and show that the noise from nonlinearities should not dominate across the key sub-10 Hz frequency band.

Design and Characterization of a Birefringent-Type Compact Displacement Sensor for Improving Measurement Sensitivity by a Guided-Wave Beam

A compact displacement sensor (CDS) fabricated with the combinations of a birefringent KTP and cylindrical lens is proposed to be applied for optical displacement measurements in a common-path interferometer. To overcome the beam distortion issues of an original laser beam (OLB) in the small radius of the lens, a guided-wave beam (GWB) is proposed to demonstrate that the GWB (having better measurement characteristics than the OLB) is essential to achieve the improved sensitivity of displacement measurements performed by the CDS.

A compact displacement sensor for non-intrusive concentration measurements of flowing liquid

A compact displacement sensor (CDS) was proposed to be applied as a non-intrusive concentration measurement of flowing liquid by employing a phase-interrogation in a homodyne interferometer. To verify the feasibility of the proposed CDS, a measurement setup was constructed and a series of experiments were performed. The experimental results show that a good linear property between the phase change and the concentration variation are achievable. The disposable and cheap acrylic container potentially provides simple and repeatable concentration measurements. The best measurement resolutions of the weight percentage are 0.015% and 0.013% for the flowing salt and hydrochloric acid solutions, respectively. According to the experimental results, the non-intrusive technique is also useful for real-time quality monitoring of a flowing liquid on a production line.

Development of Flexible Displacement Sensor Using Ultrasonic Sensor for Flexible Pneumatic Robot Arm

In our previous study, the flexible robot arm using the flexible pneumatic cylinders for human wrist rehabilitation was proposed and tested. The low-cost bilateral control system using two embedded controller and tested robot arm was also proposed and tested. In this paper, to miniaturize the displacement measuring system and reduce its cost, the flexible and compact displacement sensor using the ultrasonic sensor is proposed. The measuring characteristics of the tested sensor are investigated. As a result, the flexible displacement sensor with the resolution of about 0.1mm and the measuring sampling period of about 4ms could be realized.

Prototype of a compact displacement sensor with a holographic diffraction grating

This paper discusses a compact displacement sensor which is constructed with a volume holographic diffraction grating. The sensor is integrated with a heterodyne interferometer. The best sensitivity can be better than 1pm and the displacement error better than 28nm within a traveling range of 2.5mm. According to long-term static position observations, the stability of the proposed sensor is 10 times better than the apparatus to which it is compared. Furthermore, measurement of the thermal expansion properties of the hologram shows that the grating pitch variation is less than 0.1nm as long as the temperature variation remains within 1°C. Based on these results, the holographic diffraction grating has the potential to measure displacement with high sensitivity, high stability, and reduced measurement error.

Nanomechanically suspended low-loss silicon nanowire waveguide as in-plane displacement sensor

We have devised an air-suspended nano-optomechanical structure that is capable of precisely detecting in-plane motion up to a precision of subnanometer level. To achieve the detection, we utilized a basic silicon photonic building block (i.e., a nanowire waveguide directional coupler) in conjunction with nanoelectromechanical systems (NEMS). We numerically optimized the design and experimentally demonstrated a displacement sensitivity of 8.83×10−5 V/nm−1 with a low noise-level resolution of 0.172 nm/√Hz in a 1 Hz bandwidth centered at 950 Hz. As the waveguide coupler design does not segmentize nanowire waveguides, we eliminated the undesirable insertion losses and coupling losses irrelevant to the measurand. Furthermore the design is simple, ultracompact, and can be easily integrated with on-chip photonic systems, which may be beneficial for applications that require a compact displacement sensor with high accuracy and precision.

Optical feedback characteristics in a dual-frequency laser during laser cavity tuning

The optical feedback characteristics in a Zeeman-birefringence dual-frequency laser are studied during the laser cavity tuning in three different kinds of optical feedback conditions: (i) only //-light is fed back; (ii) only ⊥-light is fed back; (iii) both lights are fed back. A compact displacement sensor is designed using the experimental result that there is a nearly 90 degrees phase delay between the two lights' cosine optical feedback signals when both lights are fed back into the laser cavity. The priority order that the two lights' intensity curves appear can be used for direction discrimination. The resolution of the displacement sensor is at least 79 nm and the sensor can discriminate the target's moving direction easily.