Source: Nature

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Multimode Beams in Photonics

Understanding Multimode Beams

Multimode beams are light beams that involve multiple spatial modes in free space or optical materials. In waveguide structures like optical fibers, a defined set of waveguide modes carries the optical power. Free-space light beams can also have multiple spatial modes.

Monochromatic Multimode Beams

In monochromatic multimode beams, a single optical frequency is involved. These beams can be created by launching light from a single-frequency laser into a multimode fiber. The intensity profile of such beams exhibits granular patterns due to interference from multiple mode fields.

Polychromatic Multimode Beams

Polychromatic multimode beams involve multiple frequency components with different intensity patterns. Sources like thermal radiation produce smooth intensity profiles due to averaging out different patterns. Laser beams from solid-state lasers or diode bars show correlations between spatial patterns and optical frequencies.

Evolution of Intensity Profiles

Unlike Gaussian beams that maintain their shape, the intensity profile of multimode beams changes during propagation. The beam quality of multimode beams is generally lower than single-mode beams, quantified by parameters like the M2 factor.

Limitations of Multimode Beams

Multimode beams have limitations in beam quality, smooth intensity profiles, and transmission through optical components. They cannot be efficiently transmitted through single-mode fibers or amplified by most fiber amplifiers.

For applications requiring smooth intensity profiles, single-mode beams like Gaussian beams are preferred. Understanding the characteristics and limitations of multimode beams is crucial for designing optical systems and devices.

Source: PowerPhotonic
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