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Optical path (OP) is the trajectory that a light ray follows as it propagates through an optical medium. The geometrical optical-path length or simply geometrical path length (GPD) is the length of a segment in a given OP, i.e., the Euclidean distance integrated along a ray between any two points.^[1] The mechanical length of an optical device can be reduced to less than the GPD by using folded optics. The optical path length in a homogeneous medium is the GPD multiplied by the refractive index of the medium.

Factors affecting optical path

Path of light in medium, or between two media is affected by the following:

Simple materials used

Lenses
Prisms
Mirrors
Transparent materials (e.g. optical filters)
Translucent materials (e.g. frosted glass)
Opaque materials

References

^ Bass, M.; DeCusatis, C.; Enoch, J.M.; Lakshminarayanan, V.; Li, G.; MacDonald, C.; Mahajan, V.N.; Van Stryland, E. (2009). Handbook of Optics, Third Edition Volume I: Geometrical and Physical Optics, Polarized Light, Components and Instruments(set). Handbook of Optics. McGraw-Hill Education. ISBN 978-0-07-162925-6. Retrieved 2021-10-11.

[Bass2009-1] Bass, M.; DeCusatis, C.; Enoch, J.M.; Lakshminarayanan, V.; Li, G.; MacDonald, C.; Mahajan, V.N.; Van Stryland, E. (2009). Handbook of Optics, Third Edition Volume I: Geometrical and Physical Optics, Polarized Light, Components and Instruments(set). Handbook of Optics. McGraw-Hill Education. ISBN 978-0-07-162925-6. Retrieved 2021-10-11.

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