We demonstrate implementation and performance of microdisplay systems based on liquid-crystal technology in a
variety of applications in holographic mastering. These displays can encode 2D objects information in grey scale or
address holographic patterns in amplitude or phase.
The main advantage is here to address any content dynamically with typically 60 Hz. Furthermore they show a resolution
up to 1920×1200 pixels with a pixel size as small as 6.4 microns. Therefore they are extremely suitable for a dynamic or
multi-exposure mastering process, to incorporate image content,
phase-encode objects or any holographic features. This
technology is already being used in holographic security applications as well as in commercial and display holography.
We report about a few applications/implementations and show experimental results and performance parameters.
Liquid-crystal (LC) based micro-displays can be used to modulate incoming light waves with respect to amplitude,
phase and polarization. Twisted-nematic LC displays produce a combined phase-polarization modulation so that it is
difficult to achieve pure phase modulation without amplitude modulation. We present a new phase-only modulating
LCOS (Liquid Crystal On Silicon) spatial light modulator (SLM) based on an electrically controlled birefringence
(ECB) liquid crystal mode. The device has a HDTV (1920x1080) resolution and a small pixel pitch of only 8&mgr;m (87%
fill factor) on a digital silicon back plane. The LC molecules are aligned parallel to the electrodes and an applied electric
field forces them to tilt towards the direction of the field. This leads to a pure phase modulation with a phase retardation
of 2&pgr; for wavelengths between 420 and 1064nm, with negligible polarization change (<1%) if the light is linearly
polarized parallel to the director axis of the LC molecules. The shape of the back-plane of the LCOS micro-display was
investigated using a Twyman-Green interferometer and the observed deviation from a plane surface was compensated
by addressing the inverse spatially resolved phase retardation function. The interferometer was then used to measure
wave fronts that were generated with the micro-display, representing optical elements like e.g. single lenses, lens arrays
and tilted mirrors.
With this paper we present a new developed phase-only LCOS (Liquid Crystal On Silicon) spatial light modulator (SLM) based on an electrically controlled birefringence (ECB) liquid crystal mode for dynamic diffractive optics applications, optical tweezing, wave front control, digital holography and beam/pulse shaping.
This device is the first phase-only SLM showing HDTV resolution and a small pixel pitch of only 8&mgr;m (87% fill factor) on a digital silicon back plane. Here the LC molecules are aligned parallel to the electrodes and an applied electric field forces them to tilt in the direction of the field. In this way, the refractive index seen by the light is changed for one polarization direction. This leads to a pure phase modulation without any polarization change (<1%) if the incident light is polarized linearly parallel to the director axis of the LC molecules.
We have investigated two versions of this new SLM. One version is optimized for the visible wavelength region (420-800nm) and the other one is designed for 2&pgr; phase retardation up to 1064nm. We will discuss the optical modulation and show measurements on reflectivity, diffraction efficiency as well as measurements of the surface quality (flatness).
With user software one is able to adapt the electro-optical response of the system to different wavelengths and applications. Furthermore, we discuss the optical effect of different sequence encoding for the phase modulation properties.
Electronically addressed spatial light modulators (SLMs) are key elements for the reconstruction of digital holograms. Reflective liquid-crystal-on-silicon displays (LCOS) have great potential to fulfill this task due to their high fill factors of over 90% and their small pixel sizes of less than 15 μm. In order to obtain maximum diffraction efficiency of the holographic reconstruction, analog phase holograms have to be implemented making a maximum phase shift of 2π in each LCOS pixel necessary. Therefore, each LCOS display has to be thoroughly characterized prior to its use as a holographic element. In this publication, we report on a specially designed LCOS test bench. Here, displays can be characterized with respect to their phase and amplitude modulation (i.e. the complex transmittance) under a varying angle of the incident linearly polarized light. Additionally, the Jones matrix of the displays can be measured, which allows computation of the response of the displays to light of arbitrary polarization. The measurement of panel flatness is also possible which is necessary to compensate wave front aberrations. Results of measurements of two LCOS dis-plays are presented and a comparison to other measurement methods is given.
Approaching the ideal high resolution phase addressable modulator is a main task for current SLM (Spatial Light Modulator) development. Different technologies, such as optically addressed, modal and electrically addressed spatial light modulators compete in performance and applicability. The requested high Space-Bandwidth-Product (SBWP) can be served by the actual micro-structuring technology used to fabricate LCoS (Liquid Crystal on Silicon) micro-displays. Liquid crystal displays in different modes are suitable due to their birefringence properties and wide transmission range.
Two new, compact sensor systems for measuring linear and angular displacements are presented. Both systems have been designed with the aim of being compact, reliable, low-priced, yet performs with reasonable accuracy. Common for both systems is the use of Vertical Surface Emitting Lasers (VCSELs) as the coherent light source. The first system is a device for measuring one component of a linear translation, being it of a solid surface or scattering particles in a flow. A VCSEL array constitutes the illuminating source creating a fringe-like pattern in the measuring volume by imaging. Scattered light from the object is detected with a single detector and a spectral analysis of the signal reveals the traverse velocity, the fringe distance being known. For measuring rotation of a semi-reflective steel ball, a compact system has been developed, again based on a single, lensless VCSEL as the source. This system is further reduced in size, as compared to the previous system and provides adequate accuracy for its intended purpose.