Fiber Optic Collimators: Types, Applications, and How to Choose

Fiber optic collimators and their applications is the topic of this blog article.

This blog article is brought to you by Ocean Optics - a leading manufacturer of miniature spectrometers, fiber probes, and other optical components and solutions.

Fiber Optic Collimators: Introduction

Fiber optic collimators (also called fiber-optic collimators) are crucial optical components that convert the diverging output from an optical fiber into a collimated (parallel) beam, or conversely focus light from free space into a fiber. They are widely used in telecommunications, sensing, spectroscopy, research and development, laser systems, medical devices, and industrial applications.

This article explains what fiber optic collimators are, the different types available, typical applications, design parameters to watch, and guidelines for choosing the right collimator for your needs.

What is a Fiber Optic Collimator?

A fiber optic collimator generally consists of:

• An optical fiber (single-mode, multimode, or polarization-maintaining)

• One or more lenses (aspheric, GRIN, doublet, triplet, reflective, etc.)

• A housing that ensures alignment and mounting

The basic working principle is that the fiber’s end face is placed at or near the focal point of a lens. Light exiting the fiber spreads out; if positioned correctly relative to the lens, the lens converts that diverging cone into a beam with minimal divergence (a collimated beam). The divergence and spot size depend on the fiber mode field diameter (MFD) (for single-mode or PM fiber), or the core size / NA (for multimode), the focal length of the lens, and lens quality.

Factors like lens aberrations, coatings, alignment precision, and mechanical stability greatly affect performance: wavefront quality, beam divergence, back reflections, insertion loss, etc.

Types of Fiber Optic Collimators

Here are common types and their pros & cons.

Fixed (Aspheric or Singlet/Doublet) Collimators

• These are factory-aligned, non-adjustable collimators designed to produce a specific beam diameter and divergence at a design wavelength.

• Typical lens types: aspheric or singlet/doublet lenses. Aspheric lenses minimize spherical aberration, but for larger beams or broadband use, doublets or achromats may be preferred.

• Advantages: compact, robust, lower cost, less alignment needed.

• Disadvantages: not adjustable, performance drops off if used far from design wavelength or with fiber having different mode or NA.

Adjustable / Focus-Tunable Collimators

• These allow you to shift the fiber-to-lens distance (or lens-to-fiber) to optimize the collimation (spot size / divergence) for the wavelength or distance you care about. Example: YSenser’s  adjustable aspheric collimator with FC/APC connector.

• Useful when you have multiple wavelengths or want to tune alignment, or need to adapt for being farther away.

• Trade-off: more expensive, potentially larger and mechanically more complex; alignment can drift.

An example of an adjustable aspheric fiber optic collimator

GRIN (Gradient-Index) Lens Collimators / Pigtailed Collimators

• GRIN lenses use a refractive index gradient in the lens material to focus light without needing more complex curved optics. They are small, compact, and often pigtailed (fiber built in) for ease of use.

• Good for compact setups, OEM systems, where space is limited.

• Limitations: often smaller clear aperture; limited beam diameter; aberrations if used far off design parameters.

Reflective Collimators (Mirrors / Parabolic / Off-Axis Parabola)

• Use mirrors instead of lenses; e.g. off-axis parabolic mirrors. These have the advantage that focal length does not depend on wavelength, so chromatic aberration is minimal.

• Useful for broadband sources or applications where multiple wavelengths are present.

• Downsides: potentially bulkier, more difficult alignment, possibly more expensive; mirror coatings require care (reflectivity, durability).

Achromatic / Triplet / Doublet Collimators

• Designed to work well over a broader wavelength range (especially visible + NIR). They reduce chromatic aberration and produce better beam quality (lower wavefront error, lower M²).

• Triplet lens designs or achromatic doublets are common in applications needing high beam quality.

Achromatic fiber optic collimator

Miniature / High-Power / Specialty Fiber Optic Collimators

• Miniature designs (for tight space, fiber-probes, OEM modules).

• High power collimators, with higher damage thresholds, special coatings, perhaps air cooling or robust housings.

• Some designs also involve UHV (ultrahigh vacuum) compatibility, special materials (sapphire, fused silica) for extreme wavelength or durability.

Key Performance Parameters & Design Considerations

When selecting a fiber optic collimator, you’ll want to pay attention to: