In recent times the importance of Ladar systems for military applications increases rapidly. Prevalent application in this
area is 3D imaging. Conventional 3D scanning systems usually employ mirror-based mechanisms. Often these suffer
from bulky architecture and a fixed scanning pattern.
In this paper we describe an experimental monostatic Ladar setup with micro-optical bidirectional beam control. This
system offers certain advantages like random beam pointing and a compact design due to transmissive optical elements
with combined emitter and receiver channel.
Our publication depicts the setup of a Ladar demonstrator with micro-optical beam steering at lab-level. The range
finding system is based on time-of-flight principle at near infrared wavelength. Due to monostatic configuration a single
detector is used for start and stop pulse generation. The beam steering is accomplished with decentred micro-lens arrays,
which are driven by a precision alignment system. The micro-optical elements act as entrance and exit aperture
simultaneously. The results of laboratory characterization measurements and data evaluations complete our overview of the
High resolution inertialess beam steering systems are required for numerous applications, including laser radar, multitarget
designation or active imaging. We present a 1.55μm operating continuous laser beam steering system based on the
cascading of an electro-optic PMN-PT ceramic optical phased array (OPA) and of two piezoactuated microlenses arrays
(MLA). The function of the single devices and the principle and the operation of the combination of both are explained.
Then we describe the experimental setup which was realized and outline the test results.
The MLA large angle scanner consists of two MLAs, one of which can be moved with respect to the other by piezodrivers.
This setup acts as a blazed grating and thus results in a discrete beam steering. Each steering position
corresponds to a multiple of 2pi phase shift between adjacent beamlets. In order to get a continuous steering, we
combined the MLA scanner with an electro-optic ceramic OPA. The OPA generates the piston distribution that
compensates the phase difference between adjacent beamlets of the MLAs and reconstructs a continuous wavefront.
The PMN-PT OPA consists in 64 phase modulators with 210µm period and a 0.5 fill factor. The maximum required
voltage corresponding to the 2π phase shift is 150 Volts at 1.55µm. The OPA is imaged on the 105μm period MLAs
with a 0.5-magnification telescope. The two MLAs are in a Keplerian telescope with field lenses arrangement. The
steering performances of the MLAs alone are +/-12° scan angle with 28 discrete positions. Using the combined
architecture, we were able to resolve 64 angular directions between each of these 28 positions. We thus experimentally
obtained a continuous steering at 1.55μm over +/-12° with an angular resolution of 0.24mrad, i.e. 1800 resolved
directions, with only 64+1 control voltages.
Micro-lens arrays of large formats are well suited for agile laser beam steering. State-of-the-art beam steering devices
comprise three microlens arrays which are distributed among two cascaded substrates. The substrates are decentered
laterally by piezoelectric transducers. This arrangement acts like a blazed grating structure with variable blaze angle.
Beam steering with blazed grating micro-lens arrays suffers from non-uniformity of the optical parameters across the
aperture which leads to a reduction of the spatial coherence between the interfering beamlets and an increase in the beam
divergence. This disadvantage can be resolved by combining the blazed grating beam steerer with an array of phase
shifting elements. If the number of phase shifting elements (pixels) is sufficiently large, several pixels cover one
subaperture of the blazed grating and phase piston as well as higher wavefront errors (tip/tilt, defocus) may be corrected.
In the VIS and NIR spectral range large format liquid crystal spatial light modulators (SLM) are available for adaptive
correction of the wavefront of each subaperture of the blazed grating beam steerer. Spatial light modulators based on
micro-mirrors or electro-optical ceramics which cover a broader spectral range up to the MWIR are under development.
This paper outlines the concept of adaptive compensation of the wavefront error of each subaperture in a blazed grating
beam steerer. The combination of micro-lens arrays with large format spatial light modulators for the NIR and the
MWIR spectral ranges will be described. Investigations and measurements at component level (micro-lens arrays and a
commercially available liquid-crystal-on-silicon spatial light modulator) at 1.5 μm will be presented in order to support