Types Depolarizer (optics)

1 types

1.1 cornu depolarizer
1.2 lyot depolarizer
1.3 wedge depolarizer

1.3.1 quartz-silica
1.3.2 quartz-quartz

types
cornu depolarizer

cornu depolarizer

the cornu depolarizer 1 of earliest designs, named after inventor marie alfred cornu. consists of pair of 45° prisms of quartz crystal, optically contacted form cuboid. fast axes 90° apart , 45° sides of depolarizer (see figure). ray entering prism passes through 2 wave plates. thickness of these wave plates , therefore retardance varies across beam. phase shift given by

δ
(
y
)
=



2
π

λ


[

n

2


−

n

1


]
(
2
y
−
a
)
.


{\displaystyle \delta (y)={\frac {2\pi }{\lambda }}[n_{2}-n_{1}](2y-a).}

for input beam of uniform polarization output polarization periodic in



y


{\displaystyle y}

. phase shift dependent on wavelength due dispersion.

the use of 2 prisms means output coaxial input. @ interface between prisms refraction take place, refractive indices exchanged. there therefore separation of components of output beam.

this device not commonly used today, similar designs commercially available.

lyot depolarizer

lyot depolarizer

the lyot depolarizer design. invented bernard lyot. consists of 2 wave plates fast axes 45° apart, second plate twice thicker first. output periodic function of wavelength , function of wave-plates thickness. special considerations needed when depolarizer used particular application, because optimal wave-plate thicknesses depend on signal wavelength , optical spectrum used. commercially available broadband visible applications.

this device attractive in fiber optics, 2 pieces of correct length of polarization-maintaining optical fiber spliced @ 45° angle used instead of wave-plates, no other components such beam splitters required.

wedge depolarizer
quartz-silica

quartz-silica wedge depolarizer

the quartz-silica wedge depolarizer common commercial design , similar cornu depolarizer, however, angle between 2 components smaller (2° typical) , first component birefringent. second component made of fused silica, has similar refractive index quartz, not birefringent. fast axis of quartz element @ 45° wedge. whole device more compact cornu depolarizer (for same aperture).

as cornu depolarizer, there separation of output function of polarization, beam deviation due imperfect match in refractive index between quartz , silica. output periodic across depolarizer. because wedge angle smaller in cornu depolarizer period larger, around 6 mm. depolarizer has preferred orientation because of single defined fast axis. in commercial wedge depolarizers marked.

quartz-quartz

quartz-quartz wedge depolarizers commercially available, though not common. similar cornu depolarizers, small wedge angle of silica-compensated wedge.

other birefringent materials can used in place of quartz in above designs.

wedge depolarizers exhibit small beam deviation. true if faces of optic parallel. because each half of optic wedge, , 2 halves not have same refractive index (for particular polarization), depolarizer wedged (optically).