What Is a Fiber Array?

fiber array

What Is a Fiber Array?

A fiber array is an optical circuit with a series of SM, MM or PM fibers. It is commonly used to encapsulate opto-electrical integrated circuits, optical planar structures (PLC power splitter) or sensors.

Cell-based biosensing can be conducted in a fiber array format using cells that express a reporter protein, a fluorescent indicator or both. These arrays enable single cell observations of variations in a population over time.

Optical Fiber Arrays

Optical fiber arrays are bundles of optical fibers that are arranged on a substrate at specified intervals. They are used in optical communication and telecommunications to transport signals between different devices. The substrate may be made of quartz glass, ceramics or other materials.

The accuracy of the positioning of individual optical fibers on an array requires precise fabrication of the ends of the fibers. This is achieved by forming V-grooves or micro-holes on the substrate using ultra-precision cutting and precision etching. The ends of the fibers need to be well aligned in all dimensions, and they need to be packaged such that they can be safely handled.

For 1D and 2D fiber arrays, the ends of the fibers are often housed in metal flanges. These can be bare or covered with anti-reflection coatings. This reduces parasitic reflections that can lead to increased loss and connection failure.

One of the main applications for optical fiber arrays is to connect photonic integrated circuits to optical fibers. Typically, the chips need to be interfaced with optical fibers by means of a chip-based mode size converter that allows for efficient coupling of signals from the chip to the fiber. The mode sizes of the optical fibers are usually much larger than the mode sizes of the chip waveguides; this results in significant loss if there is no accurate conversion between the two.

Another application of optical fiber arrays is in biosensing systems. These arrays can be configured to contain a variety of different materials, including beads, cells or single molecules.

Biologically active compounds can be loaded into the array wells and their individual responses monitored over long periods of time to enable functional screening. The array can also be coupled to a microfluidics platform for screening adherent cell populations or bead libraries for specific binding or functional activities.

Similarly, arrays can be coupled to high-density sonicators to create powerful tools for cellular analysis. This is possible because the sonication enables direct measurements of cellular function and migration, as well as the monitoring of a large number of biological events at once.

Microlens Arrays

Optical microlens arrays (MLAs) are periodic patterns of microlenses, which can be produced by a variety of optical technologies. For example, photolithography, laser direct writing, gray-scale mask, ion beam etching and other methods can be used to produce MLAs. The microlens shape can be square or hexagonal, and the lens pitch may be a few hundred micrometers or even less.

Typically, MLAs are formed using a photolithographic process that produces all the lenses at once. The lens pattern is usually defined by a mask that can be either grayscale or binary. In the area of plastic optics, one can also use molding techniques.

In the past several years, optical microlens arrays have been used in fiber array imaging chips to enable a wide range of applications. For example, micro-lenses have been developed to image biological samples without damaging them. In addition, micro-lenses have been applied in high-end cameras to deliver large field of view angles, excellent imaging resolution and low distortion.

The ability to control the spatial arrangement of individual lenses is essential for optimum performance. For example, for a two-dimensional fiber array, the spacing of the individual fibers should be matched to the centerline of the focal plane of the underlying image projection lens.

However, the ability to create desired spatial arrangements is complicated by a number of factors, including the geometry and physical properties of the MLAs. Here, we present a novel strategy to fabricate hierarchically structured MLAs.

To realize desired spatial arrangements of MLAs, we redesigned the manufacturing process to utilize the strain-controlled tunability of elastomeric polydimethylsiloxane (PDMS). We first exposed a series of prestretched symmetric flat-top PDMS-MLAs under oxygen plasma treatment at a specific prestrain value. The resulting prestrained PDMS-MLAs spontaneously harnessed the formation of highly uniform nanowrinkled structures all over the surface of the elastomeric MLAs.

As a result, the elasticity of the MLAs changed over time to a degree that induced permeability changes. These permeability changes could be exploited to generate multicoordinated overlay images on the MLAs through slight tuning of the focal length in both the vertical and horizontal directions.

Photonic Integrated Circuits (PICs)

Photonic integrated circuits (PICs) are a new technology that replaces electronics with light. They have a number of advantages over traditional electronic integrated circuits, including miniaturization, higher speed, low heat generation, large integration capacity and compatibility with existing processing flows.

The global photonic integrated circuits market is expected to reach USD 1.87 billion by 2023, with a CAGR of 4.6% from 2017 to 2023. This growth is attributed to the rise of cloud computing, the Internet of Things and other technological advances.

PICs also offer several benefits over traditional CMOS-based electronics. For example, they are smaller and less expensive. They can be used in a variety of applications, including fiber optic communication and sensing. They can also be designed for specific functions, such as lasers and modulators.

While the main markets for photonic integrated circuits are telecom, optical fiber networks and sensing, there are many other industries using this technology. These include medical, aerospace and manufacturing.

There are a variety of fabrication techniques for PICs, and each has its own advantages and disadvantages. For example, Indium phosphide (InP) PICs offer active laser generation, amplification, control, and detection.

Silicon nitride (SiN) PICs are a good choice for waveguides due to their vast spectral range and ultra low propagation losses. These features make them suitable for detectors, spectrometers, biosensors and quantum computers.

Indium phosphide-based PICs are also gaining momentum in the market. In addition to being used in high-speed optical communications, they are a key component in sensor technology for autonomous driving vehicles and a wide range of other applications.

For these reasons, it is important to consider the needs of a diverse range of end users when designing and manufacturing PICs. This includes ensuring that the design and characterization methods work for each type of application.

Synopsys offers a full spectrum of PIC design tools, from circuit modeling to wafer fabrication and packaging. This fiber array comprehensive set of solutions provides the support necessary for the development and characterization of PICs, helping designers to quickly create a successful product.

PICs are an essential part of the high-speed technology that will define our future, and they need to be developed now. In addition to providing the next generation of performance, bandwidth, and efficiency, PICs are an emerging platform for a hybrid solution that incorporates conventional circuits in a 3D multiplanar structure.

Applications

Optical fiber arrays are used in a variety of applications. For example, they are used for high-density sensing systems for a range of biological problems. These systems are designed to contain femtoliter wells, which can be filled with individual beads or living cells to provide a powerful substrate for observing cell migration and for functional screening of chemical compounds. Alternatively, DNA can be analyzed using these fiber arrays to enable the detection of single-stranded DNA and of its sequence information.

Arrays of fibers can also be used for coherent beam combining. This is achieved when each fiber is coupled with the output of a single-frequency, phase-stabilized fiber amplifier. However, this requires precise positioning of the components, as well as an accurate collimation of the beam by a lens array.

For these types of applications, a fiber array is usually formed on some solid surface (see Figure 1). This may be a glass or polymer piece or a metal plate. A simple square lattice is most common, although a more irregular structure is possible.

To ensure that the fiber ends are well aligned in all dimensions, a precise spacing fixture may be used. This is especially important for 2D arrays, where one can use a flange around the fibers. In many cases, one can even package the fiber array so that it can be conveniently handled and safely transported.

These packages can be made from various materials, including silica core/clad or silica core/plastic clad. In addition, borosilicate glass and other exotic materials can be used.

The cores of the fibers are inserted into a V-groove, which is then bonded using a special bonding process. This results in a stress-free, high-reliability and thermal expansion coefficient matching package.

Because the fibers are not only positioned in the groove, but also in the corresponding positions on the substrate, they must be carefully fabricated. This can involve applying anti-reflection coatings that significantly reduce the coupling losses. In this case, a metal flange around the fibers is usually also applied to prevent them from being misaligned.

Another application of optical fiber arrays is laser diode arrays, which contain an array of laser emitters. These can be used for a variety of purposes, including scanning of a wavelength range with lasers or for spectral beam combining. Moreover, the array can be used for optical-to-electrical power conversion or for generating scintillations and speckle noise.

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