Micro-optical Assembly Research Articles

Micro-optics assembly for fast axis collimation by means of convolutional neural network.

The manufacture of high-power diode laser systems highly depends on the quality of the collimation of semiconductor laser diodes. The collimation process is conducted by precise alignment of micro-optics, where the first and the most critical step is the placement of the fast axis collimator (FAC) lens. The sub-micron positioning of the FAC lens is conventionally conducted with an active alignment strategy by monitoring changes in the laser beam profile with an external sensitive camera. The optimization of the beam profile characteristics is controlled by a specifically programmed motorized robotic aligner. However, active alignment, a very accurate method, often results in a higher cycle time than the passive approach, where the lens is placed in a pre-measured position. Here, we developed a new active approach, without closed loop control to position the micro-optics, that relies on the use of a pretrained convolutional network (CNN). We trained and evaluated three CNNs that can predict the optimal lens position using the single camera image of the laser beam. We predict that implementation of the best performing CNN-based model would lead to a decrease in alignment time from tens of seconds to hundreds of milliseconds and will be broadly applied in a high-volume manufacturing environment.

Automated UV-Epoxy-Based Micro-Optic Assembly for Kilowatt-Class Laser-Diode Arrays and Modules

This paper outlines the numerous interdisciplinary activities required to implement two ultraviolet (UV) epoxy-based automated micro-optic assembly tools within a “smart factory” for high-power semiconductor laser manufacturing. After a brief overview of the motivation and approach, two examples of automated micro-optic assembly tools [e.g., fast-axis collimation (FAC) lens attach and mirror stripe alignment] for kilowattclass laser-diode arrays and modules are given that demonstrate the breadth of automation activities required within a modern factory. For each system, the complete assembly sequence is outlined, and the steps that presented fully automated challenges are highlighted. In contrast, to the previous published results that focused on the details of the automated micro-optic alignment, the largest challenges primarily involved automation and repeatability of the UV-epoxy dispense and attach processes for these high-power semiconductor devices. These were solved by precise and stable mechanical design, customized lighting, and machine vision solutions. Finally, the complete integration of the tools into a “smart-factory” system is outlined.

A bimodal endoscopic imager in a glass package

We present the first endoscopic imaging probe that combines full-field white light video microscopy and 3D optical coherence tomography (OCT) in a single miniaturized instrument. Designed as an instrument for the working channels of conventional endoscopes, the presented system has dimensions of mm3 (l × w × h) and is an important step towards practical multi-modal optical biopsy systems for clinical use. The video modality has a sensor-limited resolution and a total field of view of 10 μm and 1.17 mm in diameter, respectively. The OCT modality works in a scanned imaging arrangement and provides 3D optical tomograms with a lateral resolution of 43.5 μm. An integrated tubular piezoelectric fiber scanner is used to perform en face scanning necessary for the 3D OCT measurements. The entire system is assembled and encapsulated within a glass package fabricated via 3D laser microstructuring, a technology which addresses the major issues of micro-optic assembly precision and biocompatibility.

High Performance MEMS-Based Micro-Optic Assembly for Multi-Lane Transceivers

Advanced transceivers generally require a multi-lane approach, which necessitates the integration of multiple subcomponents. The use of mature, generally available, and low-cost single element components such as electro-absorption modulated lasers, silica planar lightwave circuits, and direct-modulated distributed feedback lasers, integrated in a hybrid fashion and optically aligned with micro-electromechanical systems provides a practical solution. Standard bonding tools with positioning tolerances of approximately ten micrometers are used to populate a silicon microbench that incorporates micro-adjustable elements with various optical components. After diebonding, the positions of coupling microlenses are adjusted to correct for the poor diebond accuracy, and then these movable elements are fixed in place with built-in heaters and solder. The net result is highly uniform, manufacturable, and low loss coupling between the optical elements, with typically 1 to 2 dB of loss. Using this packaging technique, we demonstrate a 40 Gb/s four-channel (4 × 10 Gb/s) DML-based transceiver and a 100 Gb/s ten-channel (10 × 10 Gb/s) EML-based transceiver for 10 and 80 km reach respectively.

In vivo brain imaging using a portable 29 g two-photon microscope based on a microelectromechanical systems scanning mirror

We present a two-photon microscope that is approximately 2.9 g in mass and 2.0 x 1.9 x 1.1 cm(3) in size and based on a microelectromechanical systems (MEMS) laser-scanning mirror. The microscope has a focusing motor and a micro-optical assembly composed of four gradient refractive index lenses and a dichroic microprism. Fluorescence is captured without the detected emissions reflecting off the MEMS mirror, by use of separate optical fibers for fluorescence collection and delivery of ultrashort excitation pulses. Using this microscope we imaged neocortical microvasculature and tracked the flow of erythrocytes in live mice.

Overview of alternative infrared detectors and focal plane arrays for LWIR applications

For a variety of scientific, space and defence applications, there is an increasing demand for long-wavelength infrared (LWIR) detector focal plane arrays and compact infrared instruments. In the first part, we present an overview of alternative detectors to standard mercury cadmium telluride photodiodes for LWIR detection, such as the HgCdTe avalanche photodiode, the quantum-well infrared photo-detectors, the superlattice detectors and the carbone nanotubes-based bolometers. In the second part, we focus on new concepts developed to meet the requirement of miniaturization of infrared instruments. Original IRFPA-based micro-optical assemblies have been achieved, demonstrating several optical functions such as imagery, spectral filtering, spectrometry and wavefront sensing.

Assembly of hybrid integrated micro-optical modules using passive alignment with LIGA mounting elements and adhesive bonding techniques

Assembling hybrid integrated micro-optical modules for mono-mode applications requires alignment tolerances better than ±1 μm which, so far, were achieved by complex active alignment of the micro-optical components. This article describes a passive assembly concept employing high-precision LIGA structures to simplify assembly and reduce manufacturing costs. The advantages of this passive assembly concept are demonstrated in the micro-optical assembly of a heterodyne receiver. The micro-optical components (ball microlenses, prisms, glass fibers, photodiodes) were aligned passively by means of alignment structures made of PMMA, and were subsequently fixed by UV-curing adhesive. Photodiodes were additionally contacted with electrically conducting adhesive cured at 70 °C. The mono-mode glass fibers were mounted in fiber mounts into the fiber grooves of which the glass fibers were inserted and immobilized with UV-curing adhesive. Measurements of the optical quality of the heterodyne receiver indicated an accuracy of assembly better than 1 μm.

Coupling technology impact on low-cost laser modules performances and reliability

In order to decrease optoelectronic components cost dedicated to the Access Network, new technologies are emerging especially for the optical coupling. Through the investigation of 3 different types of laser diodes modules, a first impact evaluation of coupling technology on both performances and reliability is performed. As far as performances are concerned, especially optical coupled power, the most sensitive devices are receptacle laser diodes. Through temperature cycling, a first evaluation of the long term stability is performed. Again devices based on micro-optics assembly exhibit the weakest behaviour. The most advanced approach combining mounting on Silicon Platform and ⪡detachable pigtail⪢ seems to be the most promising.