Laurent Vaissie

High efficiency surface-emitting laser with subwavelength antireflection structure

We report on a high efficiency tapered grating surface-emitting laser with an antireflection-structured (ARS) substrate. A 64% improvement of the device efficiency is obtained by monolithic integration of a sawtooth-shaped ARS on the GaAs substrate. Slope efficiencies of 0.82 W/A were measured at 975 nm in pulse pumping and are mainly limited by free-carrier absorption in the n-doped GaAs substrate. A maximum peak power of 25 W was obtained without coating the devices cleaved facet. The symmetry of the near-field intensity profile along the grating coupler is improved by varying the grating duty cycle from 20% to 55%.

Advances in high-brightness semiconductor lasers

We present recent advances in high power semiconductor laser bars and arrays at near infrared and eye-safe wavelengths. We report on increased spectral brightness with internal gratings to narrow and stabilize the spectrum and increased spatial brightness in multimode and single mode devices. These devices have the potential to dramatically improve diode pumped systems and enable new direct diode applications.

Analysis of eyepoint locations and accuracy of rendered depth in binocular head-mounted displays

Accuracy of rendered depth in virtual environments includes the correct specification of the eyepoints from which a stereoscopic pair of images is rendered. Rendered depth errors should be minimized for any virtual environment. It is however critical if perception is the object of study in such environments, or augmented reality environments are created where virtual objects must be registered with their real counterparts. Based on fundamental optical principles, the center of the entrance pupil is the eyepoint location that minimizes rendered depth errors over the entire field of view if eyetracking is enable. Because binocular head mounted displays (HMDs) have typically no eyetracking capability, the change in eyepoints location associate with eye vergence in HMDs is not accounted for. To predict the types and the magnitude of rendered depth errors that thus result, we conducted a theoretical investigation of rendered depth errors linked to natural eye movements in virtual environments for three possible eyepoints locations: the center of the entrance pupil, the nodal point, and the center of rotation of the eye. Results show that, while the center of rotation yields minimal rendered depth errors at the gaze point, it also yields rendered angular errors around the gaze point, not previously reported.

Monolithic integration of dual layer optics on broad area semiconductor lasers

A broad area InGaAs semiconductor laser diode with two monolithically integrated optical elements, a 275 nm period diffraction grating and multilevel refractive lens, is presented. We discuss the potential of dual optics integration for beam shaping of high power lasers and amplifiers.

High-power semiconductor lasers at eye-safe wavelengths

InP based diode lasers are required to realize the next generation of eyesafe applications, including direct rangefinding and HEL weapons systems. We report on the progress of high power eyesafe single spatial and longitudinal mode 1550nm MOPA devices, where we have achieved peak powers in excess of 10W with 50ns pulse widths. A conceptual model based on our recent MOPA results show the path towards scaling to high powers based on spatial beam combination with operating conditions suitable for direct rangefinding applications. We also report on the progress towards high power 14xx and 15xx nm pump lasers for eyesafe HEL systems.

Crossed-beam superluminescent diode

We investigate a novel surface-emitting superluminescent diode configuration that uses two detuned grating outcouplers to suppress lasing. This device exhibits a shaped beam with a peak power of 1.5 W quasi-continuous wave with an 11 nm bandwidth centered on 970 nm.

Hybrid mode calculations for novel photonic crystal fibers

Photonic crystal fibers (PCFs) are quite useful for confining and guiding light with interesting modal properties. The scattering matrix method is used to calculate the higher order modes guided in a PCF. The model is derived from the solution of the boundary condition problem taking into consideration the coupling between the electric and the magnetic fields. Results are presented for novel fibers that allow for only azimuthal modes.

Accuracy of rendered depth in head-mounted displays: role of eyepoint location

Eyetracking is typically not available in head-mounted displays, and eye motions are thus simply ignored when 2D virtual images are displayed, giving rise to rendered depth errors in generating stereoscopic image pairs in head- mounted displays. We present an investigation and quantification of rendered depth errors linked to natural eye movements in binocular head-mounted displays, or Albertian errors, for three possible eyepoint locations: the center of the entrance pupil, the nodal point, and the center of rotation. Theoretical computations based on the intersection of chief rays concluded that, while the center of rotation yields minimal depth errors if no eyetracking is used, rendered angular errors may in some cases be significant (i.e. up to six degrees). Based on the analysis presented in this paper, we suggest that the center of entrance pupil be chosen for far field applications. The center of rotation of the eye should be chosen for near field applications under the assumption that they emphasize position accuracy versus angular accuracy. Preventing or minimizing rendered depth errors may be required for some high accuracy tasks related, for example, to medical or military visualization.

Picosecond pulse generation using a saturable absorber section of grating-coupled surface-emitting laser

We report on a passively and hybridly mode-locked grating-coupled surface-emitting laser (GCSEL) using the unpumped section of the GCSEL as a saturable absorber. We obtain 8.8-ps full-width at half-maximum (FWHM) autocorrelation pulses in passive mode-locked operation and an FWHM pulse duration of 3.4 ps in hybrid mode-locked operation, which are the shortest pulses from a GCSEL external cavity. With hybrid mode-locking, a peak power of 0.26 W and a spectral bandwidth of 0.6 nm are obtained. These results demonstrate the potential of multisegment GCSELs in ultrashort pulse generation.

Selective mode excitation by nonaxial evanescent coupling for bandwidth enhancement of multimode fiber links

We present an analysis of conditioned launch in a gradient- index multimode fiber (MMF). Selective mode excitation is obtained by nonaxial evanescent coupling between two highly asymmetric side- polished fibers: a single-mode fiber and an MMF with an exposed core. An index-matching slab improves the coupling efficiency and selectivity. The simulation shows that about 40% of modes, only high-order modes, are excited in the MMF. When compared to an overfilled launch, the bandwidth of a perturbed index fiber is enhanced more than twofold for large parameter variations.