Ricardo Martins

Development of head-mounted projection displays for distributed, collaborative, augmented reality applications

Distributed systems technologies supporting 3D visualization and social collaboration will be increasing in frequency and type over time. An emerging type of head-mounted display referred to as the head-mounted projection display (HMPD) was recently developed that only requires ultralight optics (i.e., less than 8 g per eye) that enables immersive multiuser, mobile augmented reality 3D visualization, as well as remote 3D collaborations. In this paper a review of the development of lightweight HMPD technology is provided, together with insight into what makes this technology timely and so unique. Two novel emerging HMPD-based technologies are then described: a teleportal HMPD (T-HMPD) enabling face-to-face communication and visualization of shared 3D virtual objects, and a mobile HMPD (M-HMPD) designed for outdoor wearable visualization and communication. Finally, the use of HMPD in medical visualization and training, as well as in infospaces, two applications developed in the ODA and MIND labs respectively, are discussed.

A mobile head-worn projection display.

A recent advancement was achieved in the integration and miniaturization of a binocular head-worn projection display (HWPD) conceived for fully mobile users. The devised display, referred to as Mobile HWPD (M-HWPD), offers see-through capability through custom-designed, light-weight projection optics and an integrated commercial-off-the-shelf (COTS) retro-reflective screen to display full color stereoscopic rendered images augmenting the real world. Moreover, the light-weight optical device (i.e., approximately 8g per eye) has the ability to project clear images at three different locations within near- or far-field observation depths without loss of image quality. In this paper, we first demonstrate the miniaturization of the optics, the optical performance, and the integration of these components with the retro-reflective screen to produce an M-HWPD prototype. We then show results that demonstrate the feasibility of superimposing computer-generated images on a real outdoor scene with the M-HWPD.

Design of a wearable wide-angle projection color display

In this paper, we investigate the design and fabrication of ultra-light weight projection lenses for color wearable displays. Driven by field of view requirements from 40 degree to 90 degrees, we employed the combination of plastic, glass, and diffractive optics to yield less than 10g optics per eye. The approach centers on the use of projection optics instead of eyepiece optics to yield most compact and high image quality designs. The implementation of the fabricated 52 degrees lens in a teleportal head-mounted display and remote collaborative environment is demonstrated. We also present the design results for a 70 degrees design.

Projection-based head-mounted displays for wearable computers

The projection based head-mounted display (HMD) constitutes a new paradigm in the field of wearable computers. Expanding on our previous projection based HMD, we developed a wearable computer consisting of a pair of miniature projection lenses combined with a beam splitter and miniature displays. Such wearable computer utilizes a novel conceptual design encompassing the integration of phase conjugate material (PCM) packaged inside the HMD. Some of the applications benefiting from this innovative wearable HMD are for government agencies and consumers requiring mobility with a large field-of-view (FOV), and an ultra-light weight headset. The key contribution of this paper is the compact design and mechanical assembly of the mobile HMD.

Embedded Training Display Technology for the Army's Future Combat Vehicles

Abstract : This paper describes an innovative solution for a low cost, compact, lightweight (i.e. <500g), see-through, deployable head-mounted projection display (HMPD) system for embedded training simulation of out-the window (OTW) scenes for Future Combat System ground vehicles. A unique capability is that virtual images are visible only when the user is looking at strategically located screens that simulate windows in the real environment. The display is inherently see-through with the physical surroundings visible through the display optics. This provides users with unencumbered access to the vehicles controls while viewing the simulated OTW scene. In this paper we shall detail the underlying principle of the display, its optical design and assessment, and show an early integration of the optics in a HMPD prototype for demonstration.

Diffraction of phase conjugate material in a new HMD architecture

Conventional head-mounted displays (HMDs) consisting of a pair of miniature projection lenses, beam splitters, and miniature displays mounted on the helmet, as well as phase conjugate material placed strategically in the environment have been redesigned to integrate the phase-conjugate material into a complete see-through embodiment. Some initial efforts of demonstrating the concept was followed by an investigation of the diffraction effects versus image degradation caused by integrating the phase-conjugate material internally in the HMD. The key contribution of this paper lies in the conception, and assessment of a novel see-through HMD. Finally, the diffraction efficiency of the phase-conjugate material is evaluated, and the overall performance of the optics is assessed in both object space for the optical designer and visual space for possible users for this technology.

Compact microlenslet-array-based magnifier

An ultracompact optical imaging system allowing various magnifications or demagnifications and based on microlenslet arrays is presented for the first time to our knowledge. This research generalizes recent findings regarding microlenslet-array-based 1:1 relay systems [Appl. Opt. 42, 6838 (2003)]. Through optical ray tracing, the feasibility of magnifying gray-scale images through a stack of two dissimilar microlenslet arrays is demonstrated for the first time to our knowledge. Results presented specifically demonstrate that a compact imaging system operating at a magnification of 2 is feasible with an overall length of approximately 9 mm. Optical aberrations of the most basic configuration are evaluated, and optimization is discussed.

Magnifying miniature displays with microlenslet arrays

Current technology trends are focused on miniaturizing displays, although for specific applications such as the use of head-mounted displays (HMD) this limits the advancements for a wider field-of-view (FOV) and a negligible overall weight of the optics. Due to the advancements of electronics that benefit from smaller miniature displays, universities and companies are focused on developing this technology to meet the growing demand of this global market. Higher resolution displays with added brightness are being developed, but these displays are decreasing in their viewable area. HMDs can benefit from these higher resolution and brighter displays but they will undergo an increased optical weight to compensate for the smaller display size. To overcome this hindrance in HMDs, we demonstrate in this paper how to incorporate microlenslet arrays as an optical relay system to magnify miniature displays. Microlenslet arrays provide respectively shorter focal length which yields a smaller overall object to image distance and an incremental overall weight compared to an otherwise increased optical lens assembly. The contribution of this paper is a patented concept of magnifying/demagnifying miniature displays with microlenslet arrays that can be integrated in a spaced limited area.

Design and fabrication of trihedral corner-cube arrays using analog exposure based on phase masks

Trihedral corner cube arrays are efficient retro-reflectors. They are integral parts in numerous imaging and sensing applications. However, the fabrication of these trihedral arrays can prove to be both difficult and cost prohibitive. Using a phase-only mask, we have fabricated an array of analog reflectors which can then be tiled using a photolithographic stepper. The elements are designed using a fixed period and varying fill factor to create the analog slope of each side wall. The overall depth of the array can be controlled by both the exposure and etching processes to ultimately create the desired effect. After etching, a single coating of metal finishes the process, and the elements can then be diced out and integrated into each specific application. The etched arrays may alternatively be used as a mold to create high volumes of the desired element. The design and fabrication parameters for trihedral corner cube arrays will be discussed in detail. The advantages and limitations will then be discussed.

Beyond the desktop : emerging technologies for supporting 3D collaborative teams

The emergence of several trends, including the increased availability of wireless networks, miniaturization of electronics and sensing technologies, and novel input and output devices, is creating a demand for integrated, fulltime displays for use across a wide range of applications, including collaborative environments. In this paper, we present and discuss emerging visualization methods we are developing particularly as they relate to deployable displays and displays worn on the body to support mobile users.