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`!Optical path`! (`!OP`!) is the `F33f`_`[trajectory`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Trajectory]`_`f that a `F33f`_`[light ray`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Ray_(optics)]`_`f follows as it propagates through an `F33f`_`[optical medium`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Optical_medium]`_`f. The `!geometrical optical-path length`! or simply `!geometrical path length`! (`!GPD`!) is the `F33f`_`[length`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Arc_length]`_`f of a `F33f`_`[segment`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Curve_segment]`_`f in a given OP, i.e., the `F33f`_`[Euclidean distance`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Euclidean_distance]`_`f integrated along a ray between any two points.`:cite-ref-bass2009-1-0[`F5bf`_`[1`#cite-note-bass2009-1]`_`f] The mechanical length of an optical device can be reduced to less than the GPD by using `F33f`_`[folded optics`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Folded_optics]`_`f. The `*`F33f`_`[optical path length`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Optical_path_length]`_`f`* in a homogeneous medium is the GPD multiplied by the `F33f`_`[refractive index`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Refractive_index]`_`f of the medium.

>>Contents

• `F0af`_`[Factors affecting optical path`#factors-affecting-optical-path]`_`f

• `F0af`_`[Simple materials used`#simple-materials-used]`_`f

• `F0af`_`[References`#references]`_`f

-─

>>Factors affecting optical path

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

• `F33f`_`[Reflection`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Reflection_(optics)]`_`f

• `F33f`_`[Total internal reflection`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Total_internal_reflection]`_`f

• `F33f`_`[Refraction`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Refraction]`_`f

• `F33f`_`[Dispersion`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Dispersion_(optics)]`_`f of light

• `F33f`_`[Absorption`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Absorption_(optics)]`_`f

>>Simple materials used

• `F33f`_`[Lenses`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Lens_(optics)]`_`f

• `F33f`_`[Prisms`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Prism_(optics)]`_`f

• `F33f`_`[Mirrors`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Mirror]`_`f

• `F33f`_`[Transparent`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Transparency_and_translucency]`_`f materials (e.g. `F33f`_`[optical filters`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Optical_filter]`_`f)

• Translucent materials (e.g. `F33f`_`[frosted glass`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Frosted_glass]`_`f)

• `F33f`_`[Opaque`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=Opacity_(optics)]`_`f materials

>>References

`:cite-note-bass2009-1`!1.`! `F0af`_`[↑`#cite-ref-bass2009-1-0]`_`f `:citerefbassdecusatisenochlakshminarayanan2009`aBass, 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)`*. McGraw-Hill Education. `F33f`_`[ISBN`:/page/wikibook/entry.mu`zim=wikipedia_en_all_nopic_2025-08.zim|entry_path=ISBN_(identifier)]`_`f 978-0-07-162925-6. Retrieved 2021-10-11.

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