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.
Near-eye display users universally request larger fields of view for enhanced immersion, presence, and device utility. Unlike frame rate or device weight, field of view cannot be represented precisely as a single number. Quoting field of view as a diagonal, a carry-over from the display industry, could refer to either the monocular or stereo field of view and gives no indication of the field of view boundary shape. This work defines an unambiguous metric evaluation of field of view based on solid angle, accounting for eye relief, interpupillary distance, eye rotation, and device alignment. The approach allows optical system designers to identify weak points in the optics/display/rendering pipeline. To accompany modeling, a measurement scheme was developed to metrically compare field of view over various real-world user conditions. Best practices for visualizing and communicating field of view are also presented. This work reviews the methods used to increase field of view, with discussion of the monocular and binocular artifacts that arise in large field of view systems. The limitations and advantages of optical tiling, canting, and extreme distortion are described, using relevant examples in the commercial VR space. The fundamental tradeoffs between resolution, field of view, and optical quality over field are discussed, including a review of methods to maximize field of view without sacrificing on-axis resolution. Until display and optics technology can fully match the human visual system, the intermediate objective is to find the best experience match in field of view, resolution, and optical quality given existing hardware limitations. Qualitative assessments of the relative value of different regions of the human visual field will be provided.
We report on the design, fabrication and performance of high-power and high-modulation-speed 1060-nm DBR lasers for green-light emission by second harmonic generation. Single-spatial-mode and single-wavelength power more than 450 mW of 1060-nm wavelength was achieved with a 3-section DBR laser with non-absorbing DBR and phase sections created by an impurity-free quantum-well intermixing technique. A thermally-induced wavelength tuning of 2.4 nm and a carrier-induced wavelength tuning of -0.85 nm were obtained by injecting current into the DBR section. The green power as high as 104.6 mW was demonstrated by coupling the DBR laser output to a second-harmonic-generation waveguide. Measured rise/fall times of 0.2 ns for direct intensity modulation and 0.6 ns for wavelength modulation make the DBR lasers suitable for >=50-MHz green-light-modulation applications. The detrimental thermally-induced patterning effect and a differential-phase modulation scheme as a solution are discussed.
The Beacon is a powerful non-coherent CW infra-red laser source which is developed under the Semi-conductor Inter-satellite Link Experiment (SILEX). It will provide a high divergence beam used during the first tracking acquisition sequence of the Spot 4/Artemis optical communication link. The Beacon uses high efficiency anamorphic couplers to deliver output from 19 laser diodes into a single multi-mode Mixing Fiber, the exit of which is integrated at the focal plane of a collimator. Beacon output is maintained at the required level during unit life using an Optical Monitoring System and a Beacon output Tele-Command. The Engineering Qualification Model is now complete and overall performance with respect to the SILEX requirements is presented.
The beacon is a powerful non-coherent CW laser source which is developed in the frame of the Semi-conductor Inter-satellite Link Experiment (SILEX). Its functionality is to provide a high divergence beam during the first tracking sequence. It is made up of 19 laser diodes coupled into one multi-mode fiber, the exit face of that fiber being integrated at the focal plane of a collimator. A breadboarding phase has been conducted at the beginning of the phase C/D in order to demonstrate that the requirement of 8 KW/Sr within a divergence of 11.75 mRd will be achieved. That phase is now completed and the overall breadboard performance is discussed in this paper with respect to the SILEX requirements.
The small optical user terminal (SOUT) is part of an experimental program of the European Space Agency, initiated by British Aerospace. One takes advantage of the high antenna gain obtainable at 830 nm to build a very small, lightweight, and comparatively low cost terminal, capable of communicating with SILEX, ESA's full scale optical telecommunication program. SPACEBEL is in charge of developing the transmitting chain of the SOUT, and demonstrating its performances on a breadboard model. In the first part of the paper, we describe the transmitting chain of SOUT, stressing the delicate optical link between the diode and the monomode fiber. In the second part of the paper, we report on the first measurement of the efficiency of the coupling between the laser diode and the fiber as measured on the engineering model of the flight design for the Silex Beacon.