Band 2, Heft 5-6

Future challenges and problems of Japanese photonics-related industries are discussed by analyzing the statistics of domestic photonics production trend in Japan from the aspects of offshoring and deep integration taking place in East Asia due to the growing of the global digital economy. Mobile phone, digital camera, semiconductor stepper, and fiber to the X. X is home, buildings, factories, shops, government (FTTX) are case studied, and the utilization of the information and communication technology (ICT), together with a free trade policy, is expected for the future challenges.

In the last 20 years, diffractive optics experienced a strong research interest and was in the center of many development projects in applied optics. To offer a side view for optical engineers, here, we discuss selected, business-related aspects of the current status of the transfer process to bring diffractive optics into commercial products. The contribution is divided into two parts. Here, in part I, we focus on the patent landscape of diffractive optics with a closer look on the temporal development and the distribution over main players. As an important result, currently, new strong patent activities are observed especially in the context of imaging systems. In the second part, the business volumes of selected market segments are discussed.

In target-in-the-loop laser beam projection scenarios typical of remote sensing, directed energy, and adaptive optics applications, a transmitted laser beam propagates through an optically inhomogeneous medium toward a target, scatters off the target’s rough surface, and returns back to the transceiver plane. Coherent beam scattering off the randomly rough surface results in strong speckle modulation in the transceiver plane. This speckle modulation has been a long-standing challenge that limits performance of remote sensing, active imaging, and adaptive optics techniques. Using physics-based models of laser beam scattering off a randomly rough surface, we show that received speckle-field spatial and temporal characteristics can be used to evaluate the intensity distribution of the beam projected onto the target. We derive analytical expressions that directly couple the measured target-return wave statistical characteristics, or ‘speckle metrics’, with characteristics of the laser beam intensity distribution on the target surface. We also show how measured speckle metrics can be utilized for evaluation of laser beam quality at the target surface and for adaptive compensation of atmospheric turbulence-induced phase aberrations.

In this article, we want to give a review on the application of laser gated viewing for the improvement of vision cross-diffusing obstacles (smoke, turbid medium, …), the capturing of 3D scene information, or the study of material properties by polarimetric analysis at near-infrared (NIR) and shortwave-infrared (SWIR) wavelengths. Laser gated viewing has been studied since the 1960s as an active night vision method. Owing to enormous improvements in the development of compact and highly efficient laser sources and in the development of modern sensor technologies, the maturity of demonstrator systems rose during the past decades. Further, it was demonstrated that laser gated viewing has versatile sensing capabilities with application for long-range observation under certain degraded weather conditions, vision through obstacles and fog, active polarimetry, and 3D imaging.

The motivation and intended benefits for the use of infrared (IR) detectors for space applications are highlighted. The actual status of state-of-the-art IR detectors for space applications is presented based on some of AIM’s currently ongoing focal plane detector module developments covering the spectral range from the short-wavelength IR (SWIR) to the long-wavelength IR (LWIR) and very long-wavelength IR (VLWIR), where both imaging and spectroscopy applications will be addressed. In particular, the integrated detector cooler assemblies for a mid-wavelength IR (MWIR) push-broom imaging satellite mission, for the German hyperspectral satellite mission EnMAP and the IR detectors for the Sentinel 3 SLSTR will be elaborated. Additionally, dedicated detector modules for LWIR/VLWIR sounding, providing the possibility to have two different PVs driven by one ROIC, will be addressed.

A variety of optical designs for extremely large telescopes (ELTs) can be found throughout the technical literature. Most feature very fast primary mirrors of either conic or spherical figure. For those designs with conic primary mirrors, many of the optical approaches tend to be derivatives of either the aplanatic Cassegrain or Gregorian systems. The Cassegrain approach is more common as it results in a shorter optical system, but it requires a large convex aspheric secondary mirror, which is extremely difficult and expensive to test. The Gregorian approach is physically longer and suffers from greater field curvature. In some design variations, additional mirrors are added to reimage and possibly flatten a Cassegrain focus. An interesting alternative ELT design uses a small Cassegrain system to image the collimated output of a Gregorian-Mersenne concentrator. Another alternative approach, currently in favor for use on the European ELT, uses three powered mirrors and two flat mirrors to reimage a Cassegrain focus out the side similar to a Nasmyth system. A preliminary examination suggests that a small, fast primary mirror, such as that used on the VATT, might be used for a subscale prototype of current ELT optical design options.

Atmospheric effects significantly influence the propagation of light. Conventional adaptive optics systems, based on Shack-Hartmann sensors (SHS), work well for vertical-path propagation. However, for more challenging scenarios like horizontal-path imaging or free-space laser communications through extended-volume turbulence and strong scintillation, the bandwidth of SHS is insufficient. A promising alternative is the holographic wavefront sensor (HWFS). Our paper deals with some dependencies and limitations of the HWFS. First, we show that the sensitivity of the HWFS is highly dependent on the detector size. The smaller the detector, the more sensitive is the sensor. This has consequences in the photon-starved regime, which would naturally occur when the sensor is operated at the intended MHz speed. Second, we show that uncorrected (or residual) tip/tilt has a large impact on the accuracy of the measurement. We present experimental results of measuring an important and also easily correctable aberration, defocus, with the HWFS.

This letter highlights the application of quantum cascade lasers for stand-off detection and remote sensing. In particular, we review the topic of power scaling via beam combining architectures and conclude with remarks on generating axial symmetric irradiance profiles via incoherent aperture beam combining of individual quantum cascade lasers.

Freeform optics has certain characteristics such as complex surfaces and more degrees to be controlled, so that it is capable of achieving optical mapping relationship, which cannot be achieved by the conventional optical surfaces. There is no applicable method for designing all freeform optics in the optical field until now. The selection of design methods should be based on specific applications. The paper introduces the main optical freeform design methods and their typical applications.

The function of a near-infrared (NIR) cutoff filter for imaging sensors is being described. The main purpose of the NIR cut filter is to obtain correct color recognition; therefore, the NIR filter is made of an absorbing filter glass and an interference coating. The absorbing filter glass is needed to minimize multiple reflections inside the lens system, which are the cause for ghost images. An additional interference coating enhances the function of the filter. Coating and filter glass are strongly dependent on each other. This requires high reproducibility and low tolerances of the filter glass and interference coating. In addition, features like inner quality – especially striae – and stability of the refractive index are important. A NIR cut filter may be designed as a flat plate or as a lens. Our analysis provides an estimation about striae level and variation of transmittance and their effect on image quality and color recognition. Furthermore, the use of an absorption filter glass as a lens (shrinking down the overall size) is discussed in terms of the influence on transmission and striae.