Bernard Kress

A review of head-mounted displays (HMD) technologies and applications for consumer electronics

We review in this paper the various architectures that have been proposed in industry to implement see-through head-mounted display (HMD), especially for the consumer electronics market.

Distributed Bragg reflector structures based on PT-symmetric coupling with lowest possible lasing threshold

A new approach towards the design of optimized distributed Bragg reflector (DBR) structures is proposed by taking advantage of recent developments related to the concept of parity-time (PT) in optics. This approach is based on using unidirectional gratings that provide coupling between co-propagating modes. Such couplers with PT symmetric gratings can provide co-directional mode coupling occurring only in one direction. This specific coupling property is achieved through a combined contribution of superimposed index and gain/loss modulations with same grating periodicity, but shifted with respect to one another by a quarter periods. Based on the transfer matrix approach, the transmission and reflection properties of the structure are modeled. One of the unique characteristics of the structure is very low lasing threshold. Such low threshold can be achieved by 100% reflectivity of the both Bragg grating mirrors, and by releasing the amplified signal in one single direction through a PT symmetric grating assisted co-directional coupler. Besides the lasing applications, the proposed structure can be implemented as an optical memory unit of replicating any input optical waveform.

Free space diffraction on active gratings with balanced phase and gain/loss modulations

A theoretical analysis of asymmetrical diffraction in Raman-Nath, intermediate and Bragg diffraction regimes is presented. The asymmetry is achieved by combining matched periodic modulations of the phase and of the loss/gain of the material, which enables the breakdown of optical symmetry and redirects all resulting optical energy in only positive or only negative diffraction orders, depending on the quarter period shift directions between the phase and the loss/gain modulations. Analytic expressions for the amplitudes of the diffraction orders are derived based on rigorous multimode coupled mode equations in slowly varying amplitude approximation.

Analysis of PT-symmetric volume gratings beyond the paraxial approximation.

We study the diffraction produced by a PT -symmetric volume Bragg grating that combines modulation of refractive index and gain/loss of the same periodicity with a quarter-period shift between them. Such a complex grating has a directional coupling between the different diffraction orders, which allows us to find an analytic solution for the first three orders of the full Maxwell equations without resorting to the paraxial approximation. This is important, because only with the full equations can the boundary conditions, allowing for reflections, be properly implemented. Using our solution we analyze the properties of such a grating in a wide variety of configurations.

Diffractive and holographic optics as optical combiners in head mounted displays

We review in this paper the various architectures that have been developed in industry to implement see-through head-mounted display (HMD) optics, especially for the consumer electronics market. We will focus our investigations on holographic and diffractive optics.

The segmentation of the HMD market: optics for smart glasses, smart eyewear, AR and VR headsets

This paper reviews the various optical technologies that have been developed to implement HMDs (Head Mounted Displays), both as AR (Augmented Reality) devices, VR (Virtual Reality) devices and more recently as smart glasses, smart eyewear or connected glasses. We review the typical requirements and optical performances of such devices and categorize them into distinct groups, which are suited for different (and constantly evolving) market segments, and analyze such market segmentation.

Restocking the optical designers' toolbox for next-generation wearable displays (Presentation Recording)

Three years ago, industry and consumers learned that there was more to Head Mounted Displays (HMDs) than the long-lasting but steady market for defense or the market for gadget video player headsets: the first versions of Smart Glasses were introduced to the public. Since then, most major consumer electronics companies unveiled their own versions of Connected Glasses, Smart Glasses or Smart Eyewear, AR (Augmented Reality) and VR (Virtual Reality) headsets. This rush resulted in the build-up of a formidable zoo of optical technologies, each claiming to be best suited for the task on hand. Today, the question is not so much anymore will the Smart Glass market happen? but rather which optical technologies will be best fitted for the various declinations of the existing wearable display market, one of the main declination being the Smart Glasses market.

Analysis of unidirectional non-paraxial invisibility of purely reflective PT-symmetric volume gratings.

We study the diffraction produced by a slab of purely reflective PT-symmetric volume Bragg grating that combines modulations of refractive index and gain/loss of the same periodicity with a quarter-period shift between them. Such a complex grating has a directional coupling between the different diffraction orders, which allows us to find an analytic solution for the first three orders of the full Maxwell equations without resorting to the paraxial approximation. This is important, because only with the full equations can the boundary conditions, allowing for the reflections, be properly implemented. Using our solution we analyze unidirectional invisibility of such a grating in a wide variety of configurations.

Optical gesture sensing and depth mapping technologies for head-mounted displays: an overview

Head Mounted Displays (HMDs), and especially see-through HMDs have gained renewed interest in recent time, and for the first time outside the traditional military and defense realm, due to several high profile consumer electronics companies presenting their products to hit market. Consumer electronics HMDs have quite different requirements and constrains as their military counterparts. Voice comments are the de-facto interface for such devices, but when the voice recognition does not work (not connection to the cloud for example), trackpad and gesture sensing technologies have to be used to communicate information to the device. We review in this paper the various technologies developed today integrating optical gesture sensing in a small footprint, as well as the various related 3d depth mapping sensors.

1D eyewear: peripheral, hidden LEDs and near-eye holographic displays for unobtrusive augmentation

1D Eyewear uses 1D arrays of LEDs and pre-recorded holographic symbols to enable minimal head-worn displays. Our approach uses computer-generated holograms (CGHs) to create diffraction gratings which project a pre-recorded static image when illuminated with coherent light. Specifically, we develop a set of transmissive, reflective, and steerable optical configurations that can be embedded in conventional eyewear designs. This approach enables high resolution symbolic display in discreet digital eyewear.