Non-mechanical Scanning Research Articles

Research of Non-mechanical Beam Scanning Technology

Laser beam scanning technology has been widely used in various fields such as LIDAR, photoelectric detection and space optical communication, etc. Mechanical scanning has problems such as inflexibility and low scanning rate. This paper introduces the basic principles of acoustic-optical scanning, electro-optical scanning, optical phased array and MEMS scanning, and analyses the advantages and disadvantages of several scanning methods and the main application scenarios, and finds that the current optical scanning technology is developing towards large scanning angle, high accuracy, fast response and miniaturization, among which the liquid crystal optical phased array and MEMS scanning technology are relatively mature. The scanning angle of the LCD optical phased array can reach ±10°, and the scanning angle of the MEMS can reach 6.6°*4.4°, which has a broad development prospect.

Laser Doppler velocimetry for three-dimensional distribution measurement of the velocity component by combining two-dimensional spatial encoding and non-mechanical scanning.

We present a differential laser Doppler velocimeter (LDV) for measuring the velocity distribution in a three-dimensional (3D) space. Our conventional research so far has proposed some methods for measuring two-dimensional (2D) distribution measurement. One of the proposed methods was spatial encoding of measurement points arranged on a 2D plane. Besides, we also have proposed laser Doppler cross-sectional velocity distribution measurement based on a non-mechanical scanning method. We propose a 3D method by combining 2D spatial encoding and non-mechanical scanning, in which the measurement points distributed on a 2D plane are spatially encoded with different bias frequencies, and these points are scanned non-mechanically in another direction by changing the wavelength. As a feasibility study of the proposed method, experiments were conducted using a 4×4 channel optical setup and were performed at five wavelengths over 1537-1553 nm. The experimental results indicate that the proposed method could successfully measure the 3D distribution of the velocity component. The spectral peaks of the beat signals for 68 measurement points for the rotational speed of the target of 2.0s-1 and those for 67 measurement points for the rotational speed of -2.0s-1 out of 80 measurement points were successfully observed within the measurement error of 2.8%-4.8%.

Liquid crystal spatial light modulator based non-mechanical beam steering system fractional-order model.

The liquid crystal spatial light modulator (LCSLM) is an optical device that can realise non-mechanical beam scanning. However, the traditional integer-order model cannot adequately characterise the dynamic performance of LCSLM beam steering because of the viscoelasticity of liquid crystals. This paper uses the memory characteristics of fractional calculus to construct a fractional constitutive equation for liquid crystals. Combining this equation with the LCSLM beam steering principle, a fractional-order model of the beam steering system is established, and the Legendre wavelet integration operational matrix method is used to estimate the model parameters. In addition, we established a test platform for the dynamic characteristics of LCSLM beam steering system and verified the effectiveness of the established model through experiments. The fitting effects of the integer-order and fractional-order models are compared, and the influence of different model orders on the dynamic performance of beam steering is analysed. Experimental results show that the fractional-order model can accurately describe the dynamic process of beam steering, and this model can be applied to the study of LCSLM-based two-dimensional non-mechanical beam steering control strategies to achieve fast, accurate, and stable beam scanning.

Telecentric design for digital-scanning-based HiLo optical sectioning endomicroscopy with an electrically tunable lens.

Confocal endoscopy has been widely used to obtain fine optically sectioned images. However, confocal endomicroscopic images are formed by point-by-point scanning in both lateral and axial directions, which results in long image acquisition time. Here, an endomicroscope with telecentric configuration is presented to achieve nonmechanical and rapid axial scanning for volumetric fluorescence imaging. In our system, optical sectioning in wide-field fashion is obtained through HiLo imaging with a digital micromirror device. Axial scanning, without mechanical moving parts, is conducted by digital focus adjustment using an electrically tunable lens, offering constant magnification and contrast. We demonstrate imaging performance of our system with optically sectioned images using fluorescently labeled beads, as well as ex vivo mice cardiac tissue samples. Our system provides multiple advantages, in terms of improved scanning range, and reduced image acquisition time, which shows great potentials for three-dimensional biopsies of volumetric biological samples.

Differential laser Doppler velocimetry for cross-sectional velocity distribution measurements using 48-channel spatial encoding and nonmechanical scanning

A differential laser Doppler velocimeter using 48-channel spatial encoded measurement points is proposed for dense cross-sectional velocity distribution measurements. An asymmetrical push–pull configuration and multiple photodiodes are employed to increase the number of the measurement points. The functionality of the proposed structure is experimentally demonstrated. The results indicate that a cross-sectional velocity distribution is successfully measured with the proposed structure.

Electronic holographic three-dimensional display with enlarged viewing angle using non-mechanical scanning technology

A non-mechanical scanning method based on a liquid-crystal spatial light modulator (LC-SLM) is proposed to increase the viewing angle of electronic holographic three-dimensional (3D) displays. A scanning off-axis Fresnel lens is simulated by the LC-SLM to deflect the reconstructed light beam. Using the time-division multiplexing method, the viewing zones are sequentially projected to different positions. When the eyes of the observer are located at the viewing zones, the reconstructed 3D images can be observed. The experimental results and analyses show the feasibility and advantages of the proposed method.

Proposal and design of integrated probe based on silicon photonics for laser Doppler cross-sectional velocity distribution measurement

An integrated probe based on Si waveguides is proposed for cross-sectional velocity distribution measurements. The measurement principle is based on a combination of simultaneous multipoint measurement using spatial encoding and nonmechanical scanning. Chirped focusing grating couplers used in the transmitting optics of the probe are designed and the output beams from the probe employing the grating couplers are simulated as a feasibility study of the concept. The result reveals that the focusing grating couplers can be used in the proposed probe for realizing a nonmechanical scanning function and measurements of the velocity component along the substrate.

Research on Axial Multi-Focus Scanning in Confocal Microscopy with Liquid Crystal Spatial Light Modulator

In this paper, a non-mechanical axial zoom scanning method based on a phase only liquid crystal spatial light modulator is proposed. This novel method is to overcome the measurement error caused by moving mechanical parts in the axial mechanical scanning methods in the confocal microscopy system. The modulation on the incident wave front is completed by a spatial light modulator, which provides this scanning method some outstanding advantages including the flexibility of control and the absence of moving mechanical parts, especially suitable for the fixed sample imaging occasions. By simulating the multiple Fresnel lens with LCSLM to generate controllable multi-focal points and thus realizing this method of axial multi-focus scanning to enhance the axial scanning efficiency and the range. Simulations and experiments on the axial scanning features of the axial multi-focus zoom scanning method are carried out. Results of simulations and experiments indicate that non-mechanical axial zoom scanning can be realized with the use of a spatial light modulator in the confocal microscopy system.

Nonmechanical compact probe for cross-sectional velocity measurement based on differential laser Doppler velocimetry.

In this study, we propose and demonstrate a nonmechanical compact probe for cross-sectional velocity measurement based on differential laser Doppler velocimetry. The system introduces a method that combines simultaneous multipoint measurement using spatial encoding and nonmechanical scanning of measurement points, in which spatially encoded measurement points aligned along the transverse direction are scanned in the axial direction by changing the wavelength. The use of a waveguide-type LiNbO3 phase shifter array for serrodyne frequency shifting is feasible for the system based on fiber optics with an easily handled probe. To miniaturize the probe, a multimode fiber is introduced in the receiving optics and the parameters of the lens system in the transmitting optics are optimized. For the experiment, an eight-channel probe was assembled on an aluminum plate with an 8 cm × 8 cm area size. The experimental results reveal that the cross-sectional two-dimensional velocity distribution was successfully measured using the easily handled compact probe for the first time.

Anti-spoof touchless 3D fingerprint recognition system using single shot fringe projection and biospeckle analysis

Fingerprint is a unique, un-alterable and easily collected biometric of a human being. Although it is a 3D biological characteristic, traditional methods are designed to provide only a 2D image. This touch based mapping of 3D shape to 2D image losses information and leads to nonlinear distortions. Moreover, as only topographic details are captured, conventional systems are potentially vulnerable to spoofing materials (e.g. artificial fingers, dead fingers, false prints, etc.). In this work, we demonstrate an anti-spoof touchless 3D fingerprint detection system using a combination of single shot fringe projection and biospeckle analysis. For fingerprint detection using fringe projection, light from a low power LED source illuminates a finger through a sinusoidal grating. The fringe pattern modulated because of features on the fingertip is captured using a CCD camera. Fourier transform method based frequency filtering is used for the reconstruction of 3D fingerprint from the captured fringe pattern. In the next step, for spoof detection using biospeckle analysis a visuo-numeric algorithm based on modified structural function and non-normalized histogram is proposed. High activity biospeckle patterns are generated because of interaction of collimated laser light with internal fluid flow of the real finger sample. This activity reduces abruptly in case of layered fake prints, and is almost absent in dead or fake fingers. Furthermore, the proposed setup is fast, low-cost, involves non-mechanical scanning and is highly stable.

Nonmechanical scanning laser Doppler velocimetry for distribution measurements of two-dimensional velocity vectors based on optical quadrature detection.

This paper proposes a nonmechanical scanning laser Doppler velocimeter (LDV) for measuring the distribution of two-dimensional velocity vectors. In the proposed LDV, an optical quadrature detection technique and a nonmechanical axial scanning technique are introduced into a reference-type LDV. Consequently, the LDV has a simple optical system without multiple light sources or frequency shifting and does not have any moving mechanisms in the probe. The experimental results obtained using a sensor probe setup indicate that the function of measuring two-dimensional velocity vectors and the scanning function are successfully demonstrated.

Ultrafast axial scanning for two-photon microscopy via a digital micromirror device and binary holography.

In this Letter, we present an ultrafast nonmechanical axial scanning method for two-photon excitation (TPE) microscopy based on binary holography using a digital micromirror device (DMD), achieving a scanning rate of 4.2 kHz, scanning range of ∼180 μm, and scanning resolution (minimum step size) of ∼270 nm. Axial scanning is achieved by projecting the femtosecond laser to a DMD programmed with binary holograms of spherical wavefronts of increasing/decreasing radii. To guide the scanner design, we have derived the parametric relationships between the DMD parameters (i.e., aperture and pixel size), and the axial scanning characteristics, including (1) maximum optical power, (2) minimum step size, and (3) scan range. To verify the results, the DMD scanner is integrated with a custom-built TPE microscope that operates at 60 frames per second. In the experiment, we scanned a pollen sample via both the DMD scanner and a precision z-stage. The results show the DMD scanner generates images of equal quality throughout the scanning range. The overall efficiency of the TPE system was measured to be ∼3%. With the high scanning rate, the DMD scanner may find important applications in random-access imaging or high-speed volumetric imaging that enables visualization of highly dynamic biological processes in 3D with submillisecond temporal resolution.

Fast Axial-Scanning Widefield Microscopy With Constant Magnification and Resolution

In this paper, we propose the use of electrically-addressable lens devices for performing fast non-mechanical axial scanning when imaging three-dimensional samples. This non-mechanical method can be implemented in any commercial microscope. The approach is based on the insertion of the tunable lens at the aperture stop of the microscope objective. By tuning the voltage, a stack of depth images of 3D specimens can be captured in real time and with constant magnification and resolution. The main advantage of our technique is the possibility of performing fast axial scanning free of mechanical vibrations.

Laser Doppler cross-sectional velocity distribution measurement combining 16-channel spatial encoding and non-mechanical scanning

This paper presents a differential laser Doppler velocimeter (LDV) for measuring the velocity distribution on a two-dimensional cross section. The author has proposed the LDV that combines non-mechanical scanning and simultaneous multipoint measurement using spatial encoding. In this paper, this method is expanded to a 16-channel system that facilitates more dense two-dimensional cross-sectional velocity distribution measurements. The spatially encoded measurement points aligned in the transverse direction are generated and scanned in the axial direction in a non-mechanical manner using diffraction gratings and a tunable laser. Multichannel serrodyne frequency shifting using a LiNbO3 phase-shifter array is used to generate spatially encoded points with a simple structure. An asymmetrical push-pull configuration is introduced to increase the number of the spatially encoded points. The experimental results indicate that the two-dimensional velocity distribution was successfully measured by the proposed configuration.

Compressed Sensing in a Fully Non-Mechanical 350 GHz Imaging Setting

We investigate a single-pixel camera (SPC) that relies on non-mechanical scanning with a terahertz (THz) spatial light modulator (SLM) and Compressed Sensing (CS) for image generation. The camera is based on a 350 GHz multiplier source and a Golay cell detector. The SLM consists of a Germanium disc, which is illuminated by a halogen lamp. The light of the lamp is transmitted through a thin-film transistor (TFT) liquid crystal display (LCD). This enables the generation of light patterns on the Germanium disc, which in turn produce reflecting patterns for THz radiation. Using up to 1000 different patterns the pseudo-inverse reconstruction algorithm and the CS algorithm CoSaMP are evaluated with respect to image quality. It is shown that CS allows a reduction of the necessary measurements by a factor of three without compromising the image quality.

Nonmechanical cross-sectional scanning laser Doppler velocimeter with directional discrimination of transverse velocity component

We propose a nonmechanical cross-sectional scanning laser Doppler velocimeter (LDV) with directional discrimination of the transverse velocity component. In the proposed LDV, a combination of changes in wavelength and the port of the fiber array between the main body and probe are used to scan the measurement position on a two-dimensional (2-D) cross-sectional plane that is perpendicular to the direction of flow. Optical frequency shifting using acousto-optic modulators (AOMs) is employed to discriminate the direction of the transverse velocity component. Polarization multiplexing is used to transmit frequency-shifted beams from the main body to the probe. The experimental results reveal that the 2-D scanning function and introduction of directional sensitivity are successfully achieved.

Directional discrimination for fiber-optic non-mechanical scanning laser Doppler velocimeter using single transmission path

We propose a fiber-optic non-mechanical scanning laser Doppler velocimeter (LDV) with directional discrimination of the velocity component using a single transmission path. The LDV uses a polarization maintaining fiber (PMF) as the transmission path between the main body and probe. Two beams with different frequencies induced by acousto-optic modulators (AOMs) are transmitted to the probe as two orthogonal polarization modes of the PMF. The measurement position is axially scanned using gratings in the probe and the change in wavelength. The functions of the scan and directional discrimination are demonstrated experimentally.

Realization of Non-Mechanical Lateral and Axial Confocal Microscopic Laser Scanning with a Phase only Liquid Crystal Spatial Light Modulator

It is proposed in this paper to use phase only liquid crystal spatial light modulators to realize non-mechanical lateral and axial confocal microscopic laser scanning. With a phase only liquid crystal spatial light modulator used as a scanner to realize laser beam deflection, a confocal microscopic lateral beam scanning system is designed. A zoom illuminating lens is formed by incorporating a liquid crystal spatial light modulator along the confocal illumination light path, and thus the focus of the objective lens is axially shifted to realize the axial non-mechanical scanning. The theoretical analyses indicate that phase only liquid crystal spatial light modulators can be used to realize non-mechanical 3D confocal microscopic laser scanning.

Compressive acoustic imaging with metamaterials

Compressive imaging has brought revolutionary design methodologies to imaging systems. By shuffling and multiplexing the object information space, the imaging system compresses data on the physical layer and enables employing fewer sensors and acquiring less data than traditional isomorphic mapping imaging systems. Recently metamaterials have been investigated for designing compressive imager. Metamaterials are engineered materials with properties that are usually unattainable in nature. Acoustic metamaterials can possess highly anisotropy, strongly dispersion, negative dynamic density, or bulk modulus, and they open up new possibilities of wave-matter interaction and signal modulation. In this work, we designed, fabricated, and tested a metamaterial-based single detector, 360 degree field of view compressive acoustic imager. Local resonator arrays are design to resonate randomly in both spatial and spectrum dimensions to favor compressive imaging task. The presented experimental results show that with only about 60 measured values, the imager is able to reconstruct a scene of more than 1000 sampling points in space, achieving a compression ratio of about 20:1. Multiple static and moving target imaging task were performed with this low cost, single detector, non-mechanical scanning compressive imager. Our work paves the way for designing metamaterials based compressive acoustic imaging system.

Non-mechanical scanning laser Doppler velocimetry with sensitivity to direction of transverse velocity component using optical serrodyne frequency shifting

This paper proposes a non-mechanical axial scanning laser Doppler velocimeter (LDV) with sensitivity to the direction of the transverse velocity component using optical serrodyne frequency shifting. Serrodyne modulation via the electro-optic effect of a LiNbO3 (LN) phase shifter is employed to discriminate the direction of the transverse velocity component. The measurement position is scanned without any moving mechanism in the probe by changing the wavelength of the light input to the probe. The experimental results using a sensor probe setup indicate that both the scan of the measurement position and the introduction of directional sensitivity are successfully demonstrated.