fiber lenses (original) (raw)

Definition: lenses used at or near fiber ends

Alternative term: lensed fiber ends

Category: fiber optics and waveguides

• lenses

  • achromatic lenses
  • aspheric aspheric
  • ball lenses
  • condensers
  • cylindrical lenses
  • diffractive lenses
  • f–theta lenses
  • fiber lenses
  • field lenses
  • Fresnel lenses
  • gradient-index lenses
  • Kerr lens
  • loupes
  • magnifying glasses
  • microlens arrays
  • microlenses
  • objective lenses
  • ocular lenses
  • rod lenses
  • scanning lenses
  • telecentric lenses
  • zoom lenses
  • (more topics)

• optics

  • fiber optics
    * fibers
    * fiber connectors
    * fiber-optic adapters
    * fiber couplers
    * fiber-optic pump combiners
    * fiber bundles
    * fiber endface inspection
    * cleaving of fibers
    * fiber cleavers
    * fiber joints
    * fiber splices
    * fiber Bragg gratings
    * fiber cables
    * fiber coatings
    * fiber strippers
    * fiber recoaters
    * fiber coils
    * fiber collimators
    * fiber launch systems
    * fiber lenses
    * fiber loop mirrors
    * fiber patch panels
    * fiber shuffles
    * fiber-optic attenuators
    * fiber-optic plates
    * fiber-optic tapers
    * (more topics)

Related: fiber opticsfiberslensesfiber collimators

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Contents

What is a Fiber Lens?

Generally, a fiber lens is a kind of lens used at or close to the end of an optical fiber.

There are quite different types of fiber lenses:

• Some are made by shaping the end of an optical fiber to a convex form such that it focuses the light coming from the fiber to a spot which is smaller than the fiber mode field diameter. Conversely, divergent light from a small source, such as the end facet of a laser diode, can be coupled more efficiently into the fiber with such a lensed fiber end.
• A variant of the former type has a spherical ball (→ ball lenses) on the fiber tip.
• It is possible to attach a microlens on a fiber end, or to directly fabricate it there.
• In some cases, a fiber is used in a very different way as a cylindrical lens, where incoming light (e.g. from a laser diode) hits the fiber mantle.
• There are lenses (often GRIN lenses) which can be attached to fiber endfaces for performing some optical function — typically, collimating the light coming from a fiber to a diameter which is substantially larger than the fiber mode (→ fiber collimators). Conversely, a collimated laser beam can be efficiently coupled into a fiber with such a fiber lens. With a longer GRIN pitch, it is also possible to let the light coming from the fiber first expand and then be focused to a small spot.

Fabrication of Fiber Lenses

As a very wide range of different types of fiber lenses exist, fabrication details also vary greatly. Some typical examples are given in the following.

Lensed Fiber Ends

Lensed fiber ends are often fabricated by heating a fiber end, e.g. with CO2 laser, such that the glass gets somewhat soft and can change its shape. In some cases, tapering is applied, i.e., pulling the fiber to make it thinner. For example, one may in a first step apply tapering to get a convex shape, then cut that piece at a suitable location and again apply a laser to obtain a nicely rounded end.

Another method is 3D printing of lenses to fiber ends. One first deposits liquid material which is then solidified, e.g. by two-photon polymerization.

Besides heating, etching and polishing techniques may also be applied.

Fiber Collimation Lenses

Gradient-index lenses are often used as fiber collimators. These are originally no fiber-optic components (not having a fiber core), but may be attached to fibers, e.g. with fusing, or mounted close to fiber ends. See the article on gradient-index lenses for fabrication details.

Typical Uses of Fiber Lenses

There are many application areas where light needs to be optically manipulated at a fiber end. Some typical examples:

• Light from laser diodes needs to be coupled into fibers in order to be transported to an application.
• Similarly, quantum dots and other very tiny devices may be coupled to fibers.
• Coupling between fiber ends can be achieved with two fiber lenses. Between those, some additional optical elements may be placed, such as an optical filter, a polarizer or a Faraday isolator. Such components, often in packaged form, are needed in areas like optical fiber communications and fiber-optic sensors. Even when no additional components are needed, fiber lenses can allow for easier coupling with reduced positioning tolerances, compared with butt-coupling of fiber ends.
• Some lensed fibers are used for imaging with near-field microscopy, e.g. for biomedical applications.

Frequently Asked Questions

What is a fiber lens?

A fiber lens is a lens used at or near the end of an optical fiber. It can be a specially shaped fiber tip, an attached microlens, or a separate component like a GRIN lens used to manipulate the light entering or exiting the fiber.

How are lensed fiber ends fabricated?

Lensed fiber ends are often made by heating a fiber tip, for example with a CO2 laser, causing the glass to soften and form a rounded shape. Other methods include 3D printing, chemical etching, and polishing.

What are the main applications of fiber lenses?

They are widely used for coupling light from sources like laser diodes into fibers, connecting two fibers, and building in-line components like Faraday isolators. They are also used for imaging with near-field microscopy.

How does a fiber lens improve the coupling of light into a fiber?

A fiber lens, such as a convex-shaped fiber tip, can focus divergent light from a small source like a laser diode into a spot that better matches the fiber's mode field, thus increasing the coupling efficiency.

Suppliers

Sponsored content: The RP Photonics Buyer's Guide contains seven suppliers for fiber lenses. Among them:

⚙ hardware

PHIX lensed fiber arrays (LFAs) are v-groove optical fiber arrays with 3D printed lenses at the ends of the fibers. They are intended for free space coupling to other fiber arrays, photonic integrated circuits (PICs), or other components. The printed microlenses can focus or collimate the light from the fibers, enabling mode field conversion or coupling over larger distances. We can even print periscopic lenses suitable for wafer-level die testing. Our lens printing process is based on two-photon polymerization, offering high accuracy and precise control over many lens design parameters.

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