An Introduction to 2D Arrays

There are multiple ways to create 2D arrays, all of which rely on the precision of the positional alignment of the fibers in the array. Fiberguide makes it easy to choose and apply specific methods depending on the requirements of the customer.

For instance, should a customer require a positional accuracy of 10 µm – 20 µm with multimode fibers, a metal substrate with bored holes can be utilized. The same accuracy can be achieved with a stacked fiber array with fiber to fiber positioning (i.e. no gap between fibers).

Drilled Mask Array

Drilled Mask Array

Stacked Array

Stacked Array

To achieve tighter positional tolerances, the array mask must be made in a silicon wafer using a photolithography process. This process can generate positional tolerances of 0.5 µm – 2 µm with single mode fibers.

2D Fiber Optic Arrays and their Applications

2D fiber optic arrays can be used in several ways. One is via the telecom optical cross connect. Optical switching demands very high tolerances to channel light from one fiber to another, as well as harsh environmental demands.

To attain the alignment requirements, Fiberguide engineers have designed and patented a photolithographic process to develop accurately sized and positioned holes in silicon substrates. The patented silicon wafer arrays were initially developed to meet the demands of the telecom industry and, specifically, to meet Telcordia GR-1221-CORE-RELIABILITY qualification criteria.

Using this process, highly accurate fiber positioning can be achieved, as well as optimal insertion and return loss specifications. Other key characteristics include flatness over the entire face of the array of ≤1 µm (25 mm x 25 mm area) and precisely controlled fiber angularity. Angular misalignment between fibers is as low as 2.5 mRad, with fiber substrates down to 5 mRad.

Typical Optical Cross Connect Switch

Typical Optical Cross Connect Switch

MEMS Tilt Mirror

MEMS Tilt Mirror

When the fibers have been terminated in these substrates they are ground and polished, AR coated and a lenslet array is applied to collimate the light leaving the fibers. Following this, light from one fiber can be passed into another using electromechanically actuated MEMS mirrors.

Moving light directly from one fiber to another eliminates the need for optical-electrical conversion at the switch, as is the case in a usual hub. This offers a more secure and faster transfer rate of information. The higher bandwidth this generates should be considered, as optical networks are forced to handle increasing data rates.

An additional application for 2D arrays is astronomical mapping. Historically, telescopes have been employed to view one source (or object) at a time, but with developments in fiber optics, multiple objects can now be viewed simultaneously.

If a figure is extended on the active area of the array face, then every fiber can be analyzed independently by a spectrograph, and data about different locations on the figure can be obtained. Each fiber in the array effectively functions as its own ‘camera’, collecting light from different areas of the target.

Fiber optic arrays in telescopes are good for measuring the “red shift” of stars. Changes in light frequencies are seen as color changes, i.e. a redder hue represents a star moving away from earth (redshift). Conversely, stars moving towards earth appear bluer (via blueshift). Spectroscopy can be used to measure the red or blue shift of stars to better understand their relative motion.

Applications of Drilled Arrays

Drilled arrays can be used in many applications and are also a more cost-effective choice than silicon wafer arrays. Larger fiber spacing (such as 9 mm center-to-center) can be applied as microplate readers. Fibers are positioned at the place of each of the microplate’s wells and a flash lamp or other source is pumped through the sample to be recorded. Absorbance and fluorescence can subsequently be recorded on 96 wells at one time.

Microplate

Microplate

Microplate Reader

Microplate Reader

Conclusion

Further applications for 2D arrays include free space parallel interconnects, laser profilometry, optical coherence tomography for mapping and measuring, and many more. Therefore, users who require high precision 2D arrays, or low-cost drilled/stacked arrays can look to Fiberguide, who are always available to help design and implement such applications.

38 X 38 Silicon Wafer Array, Fibers On 1 mm Centers

38 X 38 Silicon Wafer Array, Fibers On 1 mm Centers

This information has been sourced, reviewed and adapted from materials provided by Fiberguide Industries.

For more information on this source, please visit Fiberguide Industries.

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