Programmable Liquid Crystal Display Research Articles

Programmable liquid crystal display based noise reduced dynamic synthetic coded aperture imaging camera (NoRDS-CAIC).

Besides traditional lens-based imaging techniques, coded aperture imaging (CAI) can also provide target images but without using any optical lenses, therefore it is another solution in imaging applications. Most CAI methods reconstruct target image only from a single-shot coded image using a fixed coding mask; however, the collected partial information inevitably deteriorates the reconstruction quality. Though multi-exposure CAI methods are designed, these existed algorithms can hardly improve reconstruction signal-to-noise ratio (SNR) and spatial resolution simultaneously; additionally, dynamic coding mask display still requires expensive devices and complicated systems. In order to reconstruct target image with both enhanced spatial resolution and SNR but using cost-effective devices and a simple system, we design a noise reduced dynamic synthetic coded aperture imaging camera (NoRDS-CAIC) in this paper. The NoRDS-CAIC only consists of a programmable liquid crystal display (LCD) and an image recorder, and both of them are integrated with a three-dimensional printed shell with the compact size of 19 cm × 15 cm × 16 cm and controlled by our designed software to automatically realize coding mask display, coded image recording and target image reconstruction. When using the NoRDS-CAIC, the optimized coding mask is first sent to the programmable LCD and displayed, then the corresponding coded image is automatically captured using the image recorder. Next, cycle the above procedures to capture enough coded images with previously known coding masks and measured point spread functions (PSFs), and the target image can be finally reconstructed using our designed NoRDS-CAIC decoding algorithm, which is shown with better noise suppression capability and higher reconstruction resolution compared to other classical CAI algorithms. According to the experimental verifications, the NoRDS-CAIC can reach the high resolution of 99.2 µm and the high SNR of 19.43 dB, proving that the designed NoRDS-CAIC can be potentially used for lensless imaging in practical applications.

Programmable aperture microscopy: A computational method for multi-modal phase contrast and light field imaging

We demonstrate a simple and cost-effective programmable aperture microscope to realize multi-modal computational imaging by integrating a programmable liquid crystal display (LCD) into a conventional wide-field microscope. The LCD selectively modulates the light distribution at the rear aperture of the microscope objective, allowing numerous imaging modalities, such as bright field, dark field, differential phase contrast, quantitative phase imaging, multi-perspective imaging, and full resolution light field imaging to be achieved and switched rapidly in the same setup, without requiring specialized hardwares and any moving parts. We experimentally demonstrate the success of our method by imaging unstained cheek cells, profiling microlens array, and changing perspective views of thick biological specimens. The post-exposure refocusing of a butterfly mouthpart and RFP-labeled dicot stem cross-section is also presented to demonstrate the full resolution light field imaging capability of our system for both translucent and fluorescent specimens.

Creating three-dimensional lattice patterns using programmable Dammann gratings

We demonstrate the creation of a three dimensional (3D) lattice of focus spots using a 3D Dammann grating structure. Such a 3D lattice of focus spots can be used for probing 3D structures or for creating 3D photonic crystal structures in optically sensitive media. Experimental results are included where the patterns are encoded onto a programmable liquid crystal display. We demonstrate the generation of five planar arrays each having 6×6 points surrounding another set of four planar arrays each having 5×5 points with a single pattern.

Development of a Print-Through Phenomenon Measurement System Using the Fringe Reflection Method for the Fiber Reinforced Plastics

Precision noncontact measurement of the print-through phenomenon (PTP) of the fiber-reinforced plastics (FRP) is an urgent problem to be solved in yacht industry, especially for the quantization of the surface roughness and the profile of the yacht surface with PTP. The study presents the development of a surface profile measurement system using a fringe reflection method on a PC-based 3-axis measuring machine. The developed system mainly consists of a PC-based 3-axis machine, a CCD Camera, a programmable liquid crystal display (LCD) as a fringe projector, a screen on which the reflected fringe would be projected, a set of measurement software, and a PC. The surface roughness and the 2D profile of the flat composite specimens with PTP could be measured simultaneously using the fringe reflection method, based on the calibration results. Two-dimensional profile of a specimen with PTP was determined by the triangulation principle. The surface roughness of a test object was determined based on the scattering principle.

Depth of focus increase by multiplexing programmable diffractive lenses

A combination of several diffractive lenses written onto a single programmable liquid crystal display (LCD) is proposed for increasing the Depth of Focus (DOF) of the imaging system as a whole. The lenses are spatially multiplexed in a random scheme onto the LCD. The axial irradiance distribution produced by each lens overlaps with the next one producing an extended focal depth. To compare the image quality of the multiplexed lenses, the Modulation Transfer Function (MTF) is calculated. Finally we obtain the experimental Point Spread Functions (PSF) for these multiplexed lenses and experimental results in which an extended object is illuminated under spatially incoherent monochromatic light. We compare the images obtained in the focal plane and in some defocused planes with the single lens and with three multiplexed lenses. The experimental results confirm that the multiplexed lenses produce a high increase in the depth of focus.

Shape measurement using one frame projected sawtooth fringe pattern

Fringe projection technique is a non-contact, full field shape measurement method. The object depth information is recorded as sinusoidal or square wave fringe patterns. The phase-shifting technique or Fourier transform method can be used to extract wrapped phase data and a continuous phase distribution can be retrieved by a phase unwrapping process. In this paper, a shape measurement method using one frame projected sawtooth fringe pattern is proposed. A computer-generated sawtooth pattern is projected by a programmable liquid crystal display (LCD) projector. The deformed sawtooth pattern encoding object shape is converted to a wrapped phase map without using phase shifting or Fourier transform and a continuous phase distribution is retrieved by a quality-guided phase unwrapping algorithm. A special phase quality map, capable of detecting invalid shadowed phase data, is proposed to facilitate the unwrapping process.

Scanning mechanism based on a programmable liquid crystal display

In this work we propose a new robust optoelectronic scanning system for scanning microscopy. The device is based on a programmable liquid crystal television display (LCTV) that acts as a pixel-by-pixel controlled pure phase spatial light modulator. The computer addressed liquid crystal screen allows synthesize different diffractive optical elements at video rates. The phase shifts introduced by these elements make possible a complete control over the position and focusing of the scanning beam.

New method for measuring dynamic response of small components by fringe projection

We describe the use of an optical fringe projection method to measure the dynamic response of small components. In this method, sinusoidal fringes are projected on a small component using a programmable liquid crystal display (LCD) projector and a long-working-distance microscope (LDM). The image of the fringe pattern is captured by another LDM and a high-speed camera and subsequently processed by the fast Fourier transform (FFT) technique. A simple procedure is described that enables calibration of the optical setup for subsequent amplitude and frequency measurement of small vibrating components. A method that enhances the detection range of the system is also included.

Shape measurement by use of liquid-crystal display fringe projection with two-step phase shifting.

The use of an optical fringe projection method with two-step phase shifting for three-dimensional (3-D) shape measurement of small objects is described. In this method, sinusoidal linear fringes are projected onto an object's surface by a programmable liquid-crystal display (LCD) projector and a long-working-distance microscope (LWDM). The image of the fringe pattern is captured by another LWDM and a CCD camera and processed by a phase-shifting technique. Usually a minimum of three phase-shifted fringe patterns is necessary for extraction of the object shape. In this method, a new algorithm based on a two-step phase-shifting technique produces the 3-D object shape. Unlike in the conventional method, phase unwrapping is performed directly by use of an arccosine function without the need for a wrapped phase map. Hence, shape measurement can be speeded up greatly with this approach. A small coin is evaluated to demonstrate the validity of the proposed measurement method, and the experimental results are compared with those of the four-step phase-shifting method and the conventional mechanical stylus method.

Shape measurement of small objects using LCD fringe projection with phase shifting

This paper describes the use of optical fringe projection method for three-dimensional shape measurement of small objects. In this method, sinusoidal linear fringes are projected on the object surface by a programmable liquid crystal display (LCD) projector and a long working distance microscope (LDM). The image of the fringe pattern is captured by another LDM and a CCD camera and processed by phase-shifting technique. A simple procedure is described which enables calibration of the optical setup for subsequent quantitative measurement of unknown object shapes. The method developed can also be applied to the measurement of the warp of a small component under thermal loading. This method is relatively simple and accurate, and is capable of conducting fully automated measurements.