Demand for high integration of optoelectronic and micro-optical components into micro-electronic systems for communication, computing, medical, and sensing applications is increasing. Advanced hybrid packaging technologies are used to enhance glass-based substrates featuring electrical, thermal, and optical functionalities with laser diodes, modulators, isolators, photonic integrated circuits (PIC), beam-splitting components, and micro-lenses. Such glass-based substrates can be thin glass layers on large panels or more mini-bench-like boards that can be embedded into organic printed circuit boards (PCBs). Optical fiber interconnects, connectors, and electrical–optical integration platforms are used for higher level system integration and need to be miniaturized on module and board level to fulfill decreasing channel pitch requirements. We provide background on and discuss thin glass as a suitable base material for ion exchanged waveguide panels and interposers, precise glass structuring for posts and holders, the related high precision assembly techniques, and advanced fiber interconnects. Some examples of PCB photonic integration, micro-bench optical sub-assemblies, including PIC, and 3D optical resonator packages that combine most of these approaches will be shown.
Advances in autonomous driving and robotics are creating high demand for inexpensive and mass-producible distance sensors. A laser ranging system (Lidar), based on the frequency-modulated continuous-wave (FMCW) method is built in this work. The benefits of an FMCW Lidar system are the low-cost components and the performance in comparison to conventional time-of-flight Lidar systems. The basic system consists of a DFB laser diode (λ= 1308 nm) and an asymmetric fiber-coupled Mach-Zehnder interferometer with a fixed delay line in one arm. Linear tuning of the laser optical frequency via injection current modulation creates a beat signal at the interferometer output. The frequency of the beat signal is proportional to the optical path difference in the interferometer. Since the laser frequency-to-current response is non-linear, a closed-loop feed-back system is designed to improve the tuning linearity, and consequently the measurement resolution. For fast active control, an embedded system with FPGA is used, resulting in a nearly linear frequency tuning, realizing a narrow peak in the Fourier spectrum of the beat signal. For free-space measurements, a setup with two distinct interferometers is built. The fully fiber-coupled Mach-Zehnder reference interferometer is part of the feed-back loop system, while the other - a Michelson interferometer - has a free-space arm with collimator lens and reflective target. A resolution of 2:0 mm for a 560 mm distance is achieved. The results for varying target distances show high consistency and a linear relation to the measured beat-frequency.
Addressing the need for fast design cycles and tooling in the assembly of small structures, a flexible approach to overcome the obstacles of current time-consuming manufacturing methods is needed. Additionally, assembly of small and especially optical structures is often limited concerning the application and curing of adhesives used for joining. Local heating structures can be seen as an ideal way of solving this issue. This paper shows the simulation and flexible laser structuring of miniaturized heating. Mask-based large panel physical vapor deposition (PVD) processes and subsequent laser processing appear to be economical and flexible, and are compared to standard panel level lithography processes.
Fraunhofer IZM, Technische Universität Berlin and eagleyard Photonics present various implementations of current micro-optical assemblies for high quality free space laser beam forming and efficient fiber coupling. The laser modules shown are optimized for fast and automated assembly in small form factor packages via state-of-the-art active alignment machinery, using alignment and joining processes that have been developed and established in various industrial research projects. Operational wavelengths and optical powers ranging from 600 to 1600 nm and from 1 mW to several W respectively are addressed, for application in high-resolution laser spectroscopy, telecom and optical sensors, up to the optical powers needed in industrial and medical laser treatment.
In recent years there has been considerable progress in utilizing fully automated machines for the assembly of microoptical systems. Such systems integrate laser sources, optical elements and detectors into tight packages, and efficiently couple light to free space beams, waveguides in optical backplanes, or optical fibers for longer reach transmission. The required electrical-optical and optical components are placed and aligned actively in more than one respect. For one, all active components are actually operated in the alignment process, and, more importantly, the placing of all components is controlled actively by camera systems and power detectors with live feedback for an optimal coupling efficiency.
The total number of optical components typically is in the range of 5 to 50, whereas the number of actors with gripping tools for the actual handling and aligning is limited, with little flexibility in the gripping width. The assembly process therefore is strictly sequential and, given that an automated tool changing has not been established in this class of machines yet, there are either limitations in the geometries of components that may be used, or time-consuming interaction by human operators is needed.
As a solution we propose and present lasered glass building blocks with standardized gripping geometries that enclose optical elements of various shapes and functionalities. These are cut as free form geometries with green short pulse and CO2 lasers. What seems to add cost at first rather increases freedom of design and adds an economical flexibility to create very hybrid assemblies of various micro-optical assemblies also in small numbers.
High precision approaches for active and passive alignment and assembly on optoelectronic micro
benches have been realized at Fraunhofer IZM for various material systems and different scales. The
alignment and reliable mounting of optical subcomponents such as semiconductor laser and photo
diodes, micro lenses and micro prisms require far higher mounting and alignment accuracies than for
micro-electronic parts. When connecting from silicon photonics chip level to single mode optical
fibers, even higher precisions are called for (typically < 100 nm). Alignment and assembly
commonly are performed on specialized lab equipment which needs manual operation, consuming a
lot of time, with less possibilities for automation.
To introduce a higher degree of automatized production, like it has become standard in large volume
electronics, one can choose either active or passive alignment processes - or possibly a combination
of both. In this article we will present examples of micro-optic benches and optical interconnections
that include alignment structures for passive alignment - where the accuracy lies in the components
to be assembled, and mounting takes place on a less accurate machine (“fit into place”). But there is
also a lot of progress on optical "pick, measure and place" machines that realize a flexible and fully
automated active alignment using vision systems and activated components of less cost, with
machine and process robustness for usability in industrial environments.
As connecting elements, passive optical components like optical fibers are commonly used. These
fragile and flexible elements pose additional challenges in secure picking, placing and fixing, at long
lengths vs. small diameters. A very recent and specific approach to use more robust plastic optical
fibers (POF) for very short and cost effective optical interconnects by means of wire bonding
machines will be presented.
We present a novel concept to trim the transmission properties of finite two dimensional photonic crystal slab waveguide structures by UV photobleaching. Systematic fabrication inaccuracies may be compensated due to the shift of the spectral properties during the bleaching process. To prove our concept experimentally, we measured the transmission of UV sensitive photonic crystal structures for different doses. A shift of band edges and defect resonance peaks depending on UV dose is observed due to changes in refractive index and geometry.
The motivation to investigate moderate refractive optical polymers in finite 2D photonic crystal waveguides is manyfold. Compared to high index materials like Si, GaAs and InP the optical wavelength inside the waveguide core of a moderate refractive index material is longer and the optical field confinement in most cases is weaker.
Finite two-dimensional (2d) polymer photonic crystal (PC) slab waveguides were fabricated from a benzocyclobutene polymer on a low refractive index substrate from Teflon. Square and triangular air hole lattices were realized by electron beam lithography and reactive ion etching. Polarization and wavelength dependent transmission measurements show TE-like and TM-like stop gaps at 1.3micrometers excitation wavelengths and are in good agreement with the calculated data obtained by 2D and 3D finite difference time domain (FDTD) methods. Transmission was suppressed by 15dB in the center of the TE-like stop gap for a PC length of only ten lattice constants. Defect states were induced within the stopgap by lattice modification and theoretically and experimentally characterized.
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