Near-eye display performance is usually summarized with a few simple metrics such as field of view, resolution, brightness, size, and weight, which are derived from the display industry. In practice, near-eye displays often suffer from image artifacts not captured in traditional display metrics. This work defines several immersive near-eye display metrics such as gaze resolution, pupil swim, image contrast, and stray light. We will discuss these metrics and their trade-offs through review of a few families of viewing optics. Fresnel lenses are used in most commercial virtual reality near-eye displays in part due to their light weight, low volume and acceptable pupil swim performance. However, Fresnel lenses can suffer from significant stray light artifacts. We will share our measurements of several lenses and demonstrate ways to improve performance. Smooth refractive lens systems offer the option for lower stray-light viewing but usually at the cost of a much larger size and weight in order to get to the same pupil swim performance. This can be addressed by using a curved image plane but requires new display technology. Polarization-based pancake optics is promising and can provide excellent image resolution and pupil swim performance within an attractive form-factor. This approach, however, generally results in low light efficiency and poor image contrast due to severe ghosting. We will discuss some of the main limitations of that technology.
Materials and devices.for compact optical amplification in Si photonics is reviewed. In particular, as the requirement for
high gain per length together with high refractive index renders traditional oxide-based approach problematic, Er-doping
of silicon-rich silicon nitride and erbium silicate nanocrystals are proposed and shown to be promising alternatives.
Using such new materials, microdisk resonators and slot waveguides that concentrate the light in a compact volume for
high functionality are fabricated and characterized.
Recent research progresses in slot waveguide have shown that it is possible to achieve photon confinement in low-refractive index region with nm thickness. To utilize this photon confinement, we propose a multilayer waveguide that could be the optimum design for future silicon light emission devices.
Our device consists of multiple alternating layers of Si and SiO2 with nm thickness, which can be easily fabricated. Both transfer matrix method (TMM) and FDTD simulation are used to simulate the performance of this device. We calculated the propagation mode index, and photon confinement in SiO2 layers. Birefringence as high as 0.8 is achieved with moderate design parameters, although a homogeneous slab waveguide also shows some birefringence, it cannot account for the high birefringence we have calculated. Thus it indirectly indicates that for TM polarization photons are actually confined in SiO2 layers, where the refractive index is lower. Also our photon confinement simulation shows that, for a structure with multilayer region thickness of 0.52 μm, photon confinement in SiO2 layers as high as 75% can be achieved with Si/SiO2 layer thickness ratio close to 1.
We fabricated a few multilayer samples with different Si/SiO2 thickness ratios and performed M-line measurement to measure the propagation mode index. The measurement results agrees well with our simulate results, indicates that for TM polarization photons can be strongly confined in SiO2 layers in this multilayer structure. Thanks to this high confinement in SiO2 layers, this structure could be an excellent choice for future silicon light emitting devices.
In recent years, optical CDMA systems have been proposed for multiple accesses to utilize the vast bandwidth available in optical fiber. Optical CDMA systems are believed to provide asynchronous access for each user in the system, which is especially suitable for usage in LAN. In this paper, we demonstrate a novel optical CDMA scheme in a fiber-based testbed. Using the liquid crystal spatial light modulator (SLM), we are able to construct a reconfigurable optical CDMA system suitable for fiber-optic networks. We address the code for each user in the spectrum domain by using a standard 4-f pulse shaping apparatus. Because of the low coherency of the light source we used in the system, we are able to modulate it in time domain without changing its frequency distribution significantly. We can reconfigure the network connection while keep the information bits un-influenced. Another merit of using analog liquid crystal device is that the transmissions of the different frequency components are analog controllable, we can get a uniform intensity distribution in frequency domain when the spectrum of the light source is not flat. Using the liquid crystal as a programmable optical modulator, the high polarization sensitivity of the components used in the system enables low crosstalk between different codes assigned to different users.
Optical CDMA technology has shown promise in optical communications, particularly in local-area optical fiber networks. We present a novel O-CDMA scheme with programmable and reconfigurable bipolar code capability using liquid crystal (LC) Spatial Light Modulators (SLMs). The key to our system performance depends on constructing a decoder that implements a true bipolar correlation using only unipolar signals and intensity detection. This has been accomplished using two unipolar correlations that can be performed optically, followed by a subtraction. In our coding system, the power spectrum of a broadband light source is encoded and decoded by programming the SLMs. The high polarization selectivity of these components coupled with the polarization rotation ability of liquid crystal elements makes switching possible with high extinction ratio and low crosstalk. Experimental results including the correlation measurements are presented. Good contrast between the autocorrelation and cross correlation values shows that a binary information symbol can be recovered by an appropriate threshold operation.
The emerging technology of micro-optical-electro-mechanical systems (MOEMS) offer promise for automating the alignment of free-space optical systems, especially intra-computer optical interconnects. MOEMS-based microlenses and micromirrors have been fabricated for the purpose of providing initial system alignment and dynamic alignment.