thumb|The figure shows the optical path of a Mirau-objective respectively a Mirau-interferometer. Reference beam (4 to 6) and object beam (7) have identical optical path length and can thus cause white light interference.
'''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.<ref name="Bass2009">{{cite book | last1=Bass | first1=M. | last2=DeCusatis | first2=C. | last3=Enoch | first3=J.M. | last4=Lakshminarayanan | first4=V. | last5=Li | first5=G. | last6=MacDonald | first6=C. | last7=Mahajan | first7=V.N. | last8=Van Stryland | first8=E. | title=Handbook of Optics, Third Edition Volume I: Geometrical and Physical Optics, Polarized Light, Components and Instruments(set) | publisher=McGraw-Hill Education | year=2009 | isbn=978-0-07-162925-6 | url=https://books.google.com/books?id=acrmuZpdSFEC | access-date=2021-10-11 | page=}}</ref> 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: * Reflection ** Total internal reflection * Refraction * Dispersion of light * Absorption
==Simple materials used== * Lenses * Prisms * Mirrors * Transparent materials (e.g. optical filters) * Translucent materials (e.g. frosted glass) * Opaque materials
==References== {{Reflist}}
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{{DEFAULTSORT:Optical path}} Category:Physical optics Category:Geometrical optics
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