Optical Assembly – Active VS Passive
In this article we will describe the prons & cons of optics assembly in both methods .
According to the current industry trends in the fields of Automotive, AR, VR, Medical, Optics etc. it seems that it is going more and more to the use of smart optics to help us make the right decisions or make the decisions for us. This created a need for computers to "see" the outside, physical world. As the use of these models and markets evolve, higher quality imaging systems are needed to enable better optical performance. Consumer expectations for thinner devices and better-quality images contribute to the increased demand for high quality imaging and drive up the complexity of manufacturing these optical systems. As complexity increases, so do manufacturing challenges.
What is Active Alignment ?
The term "Active alignment" is used to describe the process of dynamic assembly. It describes the process of placing an optical component, usually a lens, a sensor or laser while continuously measuring and challenging the power or image quality.
Due to this technology, it is possible to receive the maximal performance of the optical components.
The most common and simplest way to mount optics is by mechanical placement or mechanical alignment.
In Mechanical placement, the optical components are placed relatively to visual marks or by tight mechanics in addition to special gigs. Usually when using this method, the adhesive is applied before the optical placement and the optical performance are tested post assembly.
In Mechanical alignment, the optical components are placed relative to camera image quality or external signal source and adjusted by manual micrometers. Usually when using this method the adhesive is applied after the “dry \ pre-alignment “was measured and confirmed.
In this method, the assembly is tested before adhesive and post curing.
Since augmented reality and virtual reality are intensively entering to our workspace (medical, automotive) and personal life, this industry requires and promotes the appearance of small scale and low-weight optical systems usually mounted on our head or even our nose tips.
As AR and VR headsets get thinner and smaller, the complexity of the mounted optical systems, including both camera and projection optics, are, naturally, increasing.
Other applications for computer vision, like self-driving cars, are mission-critical and require extreme levels of accuracy. For the massive arrays of cameras to properly inform the on-board computers of a self-driving car, they need to capture and send the most accurate images possible, so that the computer algorithms can quickly identify objects, calculate distances, and dictate the appropriate response. For this market, high quality optical systems are a necessity.
To deliver the needs of high image quality, low bill of materials (BOM) cost and high production yield it will be very hard to achieve all this in the old “mechanical alignment“ method.
The manufacture will have to compensate in additional elements to get the high image quality needed. this will “load” additional components on the product and increase the BOM, weight and production.
In addition, it will “load” on the computing power that will use additional power &time to “fix” the image cleanliness, sharpness and focus.
Fine tuning the optics from beginning will reduce the “optical noise” and will deliver the best possible images for the components used. Component alignment offers the most effective way to improve image quality while keeping costs down.
WHY ACTIVE ALIGNMENT?
There are multiple methods of optical components assembly such as laser diode, photo diodes, lenses and more. The components vary in complexity and cost. The Assembly precision can make the difference in the optical performance of the LD’s, PD’s and the image quality.
Active Alignment is a Dynamic method of assembling optics in “closed loop” feedback. The optics position is optimized by a high resolution 3-6 axis stages, the alignment is done relative to the feedback signal coming in\out an optical sensor or camera. Depending on the manufacturing needs of the customer and the capabilities of the equipment and software, active alignment results in higher precision manufacturing and image quality.
Active alignment for laser diode applications is achievable when assembling other optics (beam splitter, output couplers, etc.). These optical devices are “activated” during the assembly using probes or other conductive pads and the laser is coupled to an optical sensor, fiber or lens while measuring the feedback in a closed loop to axis. when reaching the max or desired power UV adhesive is applied and cured.
ACTIVE ALIGNMENT APPLICATIONS
Active alignment process is usually used in optical devices components that require high image quality with low computing compensation for applications in the fields of automotive, AR, drones, photography, security, and VR.
Additional application for active alignment process is when a submicron accuracy is required for coupling lasers to optical wave guides, photodiodes or fibers.
The manufacturing process benefits from using automated active alignment machines that reflect on the high yield of the finished product. The components are activated and tested during the assembly, so if the output result is not “in spec”, the component is “scraped” and replaced by another before final assembly. The optics are placed in the BEST position according to the image quality or coupling power, so the optical “loss penalty "is very low.
Active alignment machines help improve time-to-market, scrap costs, and overall image quality.
Reviewing the current technology trends in the fields of Augmented Reality, Virtual Reality, Autonomous driving flying, action cameras, and even our smart phones, clearly demonstrates the high complexity of the challenges for the optics manufactures.
The need for high quality images using complex optics (dimensions & performance), short “BOM”, and low computing process time is pushi