249 research outputs found
Liquid Crystal on Silicon Devices: Modeling and Advanced Spatial Light Modulation Applications
Liquid Crystal on Silicon (LCoS) has become one of the most widespread technologies for spatial light modulation in optics and photonics applications. These reflective microdisplays are composed of a high-performance silicon complementary metal oxide semiconductor (CMOS) backplane, which controls the light-modulating properties of the liquid crystal layer. State-of-the-art LCoS microdisplays may exhibit a very small pixel pitch (below 4 ?m), a very large number of pixels (resolutions larger than 4K), and high fill factors (larger than 90%). They modulate illumination sources covering the UV, visible, and far IR. LCoS are used not only as displays but also as polarization, amplitude, and phase-only spatial light modulators, where they achieve full phase modulation. Due to their excellent modulating properties and high degree of flexibility, they are found in all sorts of spatial light modulation applications, such as in LCOS-based display systems for augmented and virtual reality, true holographic displays, digital holography, diffractive optical elements, superresolution optical systems, beam-steering devices, holographic optical traps, and quantum optical computing. In order to fulfil the requirements in this extensive range of applications, specific models and characterization techniques are proposed. These devices may exhibit a number of degradation effects such as interpixel cross-talk and fringing field, and time flicker, which may also depend on the analog or digital backplane of the corresponding LCoS device. The use of appropriate characterization and compensation techniques is then necessary
Recommended from our members
Computer-Generated Holography for Areal Additive Manufacture
With a market of approximately $10B, additive manufacture (AM) is an exciting next-generation technology with the promise of significant environmental and societal impact. AM promises to help reduce emissions and waste during manufacture while improving sustainability. Widely used in applications from hip implants to jet engines, AM remains the domain of experts due to the material and thermal challenges encountered.
AM in metals is dominated by Laser Powder Based Fusion (L-PBF). Powder is spread in layers 10s of microns thick and selectively melted by scanning a small laser spot heat source over the bed.
Traditional AM systems have limited ability to manage or compensate for heat generated. The rapidly moving heat source spot results in high thermal cycling and is a major influence on residual stress and distortion. Mechanical limitations in the galvoscanner mean that over or under-heating is common and can lead to voids, boiling and spatter. The scale difference between the part size and the spot size means that predictive modelling is beyond the scope of even today’s best computing clusters. These factors have led to frequent inability to ensure part quality without physical prototyping and destructive testing.
This thesis sets out initial research into creating a radically new AM process that uses computer-generated holography (CGH) to produce complex light patterns in a single pulse. Projecting power to the whole layer at once will mean that the thermal properties of the powders before and after writing can be factored into the processed hologram and part design. It will also significantly reduce thermal gradients and melt-pool instability.
The fields of additive manufacture and computer-generated holography are introduced in Chapter 1. Chapters 2 and 3 then provide more detail on CGH and AM modelling respectively. The first deliverable, a reusable software package capable of generating holograms, is presented in Chapter 4. Algorithms developed for the project are introduced in Chapter 4.3. The first project demonstrator, an AM machine capable of printing in resins using holographic projection is discussed in Section 6.2. This shows performance comparable to modern 3D printing machines and highlights the applicability of computer-generated holography to areal processes. Section 6.3 then discusses the ongoing development of a metal powder demonstrator. As this PhD forms the first stage of a larger project, only preliminary work on the powder demonstrator is discussed. Chapter 7 then draws conclusions and outlines the way forward for future research.
The thesis appendices then discuss an in-depth discussion of algorithm performances in Appendices A and B. Appendices C and D then discuss digressions into the implementation. Appendices E and F present a laser induced damage threshold (LIDT) measurement system developed. Finally, Appendices G and H provide more detail on the software developed and Appendix I gives links to additional project resources.EP/T008369/1;
EP/L016567/1;
EP/V055003/
Central Angle Optimization for 360-degree Holographic 3D Content
In this study, we propose a method to find an optimal central angle in deep
learning-based depth map estimation used to produce realistic holographic
content. The acquisition of RGB-depth map images as detailed as possible must
be performed to generate holograms of high quality, despite the high
computational cost. Therefore, we introduce a novel pipeline designed to
analyze various values of central angles between adjacent camera viewpoints
equidistant from the origin of an object-centered environment. Then we propose
the optimal central angle to generate high-quality holographic content. The
proposed pipeline comprises key steps such as comparing estimated depth maps
and comparing reconstructed CGHs (Computer-Generated Holograms) from RGB images
and estimated depth maps. We experimentally demonstrate and discuss the
relationship between the central angle and the quality of digital holographic
content
Spatial Light Modulation as a Flexible Platform for Optical Systems
Spatial light modulation is a technology with a demonstrated wide range of applications, especially in optical systems. Among the various spatial light modulator (SLM) technologies, e.g., liquid crystal (LC), magneto-optic, deformable mirror, multiple quantum well, and acoustic-optic Bragg cells, the ones based on liquid crystal on silicon (LCoS) have been gaining importance and relevance in a plethora of optical contexts, namely, in telecom, metrology, optical storage, and microdisplays. Their implementation in telecom has enabled the development of high-capacity optical components in system functionalities as multiplexing/demultiplexing, switching and optical signal processing. This technology combines the unique light-modulating properties of LC with the high-performance silicon complementary metal oxide semiconductor properties. Different types of modulation, i.e., phase, amplitude or combination of the two, can be achieved. In this book chapter, we address the most relevant applications of phase-only LCoS SLM for optical telecom purposes and the employment of SLM technology in photonic integrated circuits (PICs) (e.g., field-programmable silicon photonic (SiP) circuits and integrated SLM application to create versatile reconfigurable elements). Furthermore, a new SLM-based flexible coupling platform with applications in spatial division multiplexing (SDM) systems (e.g., to efficiently excite different cores in MCF) and characterization/testing of photonic integrated processors will be described
Optoelectronic speckle shearing interferometry
This thesis describes the implementation of enhanced signal processing techniques in
electronic speckle shearing interferometry, including two-wavelength slope
measurement, phase stepping, and heterodyning and stroboscopic illumination in
vibration analysis. All the techniques were achieved using laser diode emission
wavelength modulation.
Slope measurement using two-wavelength illumination can generate slope fringes in a
mechanically passive manner and the fringe visibility is better compared to other
illumination-shifting and object-tilting methods. Three simple geometric objects were
measured using an x shear of 4 mm and AX ~ 0.45 nm. The results are in agreement
with a theoretical analysis. The measurement accuracy can be further improved by
calculating the simple equations of parameters in the fringe function.
A novel phase stepping technique has been demonstrated using laser diode injection
current modulation. An imbalanced Michelson-interferometer arrangement, with a
perspex block of 25 mm thickness inserted into the longer interferometer arm to
maintain equal image magnification for the two images, was used to obtain a 2n phase
shift for an optical frequency change of 7.25 GHz. The technique provides an additional
phase stepping method in shearography with the advantages of removing an active
phase-shifting component from the interferometer and a greater linearity in the phase
shifts through the diode wavelength modulation.
In vibration measurement, heterodyning and stroboscopic illumination have also been
successfully achieved in a mechanical passive manner. For shearing systems using a
Michelson interferometer, heterodyning was originally difficult to perform. With the
unbalanced optical configuration as used in the phase stepping work, heterodyning has
been demonstrated to measure vibration motion ~5.5 kHz and the diode optical
frequency modulation ~15 GHz. By pulsing the laser diode with an 11% duty cycle,
stroboscopic illumination was performed to obtain cosine fringes along with greatly
improved visibility. Phase stepping methods were then incorporated to automate the
fringe analysis.Ph
Holographic MIMO Communications: Theoretical Foundations, Enabling Technologies, and Future Directions
Future wireless systems are envisioned to create an endogenously
holography-capable, intelligent, and programmable radio propagation
environment, that will offer unprecedented capabilities for high spectral and
energy efficiency, low latency, and massive connectivity. A potential and
promising technology for supporting the expected extreme requirements of the
sixth-generation (6G) communication systems is the concept of the holographic
multiple-input multiple-output (HMIMO), which will actualize holographic radios
with reasonable power consumption and fabrication cost. The HMIMO is
facilitated by ultra-thin, extremely large, and nearly continuous surfaces that
incorporate reconfigurable and sub-wavelength-spaced antennas and/or
metamaterials. Such surfaces comprising dense electromagnetic (EM) excited
elements are capable of recording and manipulating impinging fields with utmost
flexibility and precision, as well as with reduced cost and power consumption,
thereby shaping arbitrary-intended EM waves with high energy efficiency. The
powerful EM processing capability of HMIMO opens up the possibility of wireless
communications of holographic imaging level, paving the way for signal
processing techniques realized in the EM-domain, possibly in conjunction with
their digital-domain counterparts. However, in spite of the significant
potential, the studies on HMIMO communications are still at an initial stage,
its fundamental limits remain to be unveiled, and a certain number of critical
technical challenges need to be addressed. In this survey, we present a
comprehensive overview of the latest advances in the HMIMO communications
paradigm, with a special focus on their physical aspects, their theoretical
foundations, as well as the enabling technologies for HMIMO systems. We also
compare the HMIMO with existing multi-antenna technologies, especially the
massive MIMO, present various...Comment: double column, 58 page
Digital control of light.
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.The objective of this research was to describe innovative ways in which digital holography
can be applied in controlling laser light. The ability to control and manipulate a laser beam
has become an extremely desirable feature since it enables improvement in the efficiency and
quality of a number of applications.
Methods of controlling light make use of optical components to change the properties of a
light beam according to the function of that optical element; therefore, a particular arrange-
ment of optical elements in a system controls light in a certain way.
Technological advancements in the field of optics have developed a versatile device called
a spatial light modulator (SLM), which is a novel instrument that employs computer gener-
ated holographic patterns (or phase masks) to modulate the amplitude and /or phase of a
laser beam and it can therefore perform the function of a number of optical elements.
This research presents novel optical set-ups based on the phase-only liquid crystal spatial
light modulator (LC-SLM) for generating, controlling and exploring different laser beam pat-
terns. The thesis has three main sections, the first one is Holographic beam shaping, where a
Gaussian beam was reshaped using an SLM to produce Vortex, Bessel or Laguerre-Gaussian
beams. These beams were found to agree with theoretically generated beams.
Secondly, we produce o -axis laser beams by constructing coherent superpositions of Gaussian
and vortex modes and then use two measurement techniques, peak intensity ratio and modal
decomposition technique, to obtain the constituent components of these fields.
Finally, we investigate the propagation dynamics of Vortex and Laguerre-Gaussian beams
by using a SLM to digitally propagate these beams in free space, and then perform mea-
surements on the far field intensity pattern. The results show that the Laguerre-Gaussian
beam suffers less spreading and beam distortion compared to the vortex beam in free space
propagation
- …