Totally reflecting thin-film phase retarders

Measurement of phase retardation of optical multilayer films based on laser feedback system

The phase property of optical films is becoming a new research focus in optoelectronics. The retardation caused by reflection on multilayer optical films can be utilized to make phase retarders and modulate the polarization state of optical systems. In this paper, a novel method based on laser feedback is presented to measure the retardance. The laser feedback system can realize fast and stable measurement with high accuracy. Two samples of K9 glass covered with different multilayer optical films are measured at different angles of incidence. The results show that the retardance is sensitive to the incident angle and can provide guidance for the usage of reflective optical films.

Total internal reflection without change of polarization using a right-angle prism with half-wavelength-thick optical interference coating

Monochromatic light, which is polarized in an arbitrary state, is totally internally reflected at angle of incidence phi=45 degrees without change of polarization by a right-angle prism of refractive index n0=1+1/Square root of 2=1.70711 (e.g., N-LAK8 Schott glass at wavelength lambda=706 nm), which is coated with a transparent thin film of refractive index n1=(1+1/2)1/2=1.30656 (e.g., vacuum-deposited fluoride material) and of metric thickness equal to half of the vacuum wavelength of incident light, d=lambda/2. The ambient medium of evanescent refraction is assumed to be vacuum, air, or an inert gas. Wavelength shifts of +/-50 nm, or changes of the internal angle of incidence of +/-1 degrees around 45 degrees, cause phase errors of only a few degrees. The reflected and incident polarization states are nearly identical in the presence of such small phase errors.

In-line broadband 270 degrees (3lambda/4) chevron four-reflection wave retarders

The net differential phase shift Delta(t) introduced between the orthogonal p and s linear polarizations after four successive total internal reflections inside an in-line chevron dual-Fresnel-rhomb retarder is a function of the first internal angle of incidence phi and prism refractive index n. Retardance of 3lambda/4 (i.e., Delta(t)=270 degrees) is achieved with minimum angular sensitivity when phi=45 degrees and n=1.900822. Several optical glasses with this refractive index are identified. For Schott glass SF66 the deviation of Delta(t) from 270 degrees is < or = 4 degrees over a wavelength range of 0.55 < or = lambda < or = 1.1 microm in the visible and near-IR spectrum. For a SiC prism, whose totally reflecting surfaces are coated with an optically thick MgF(2) film, Delta(t)=270 degrees at two wavelengths: lambda(1)=0.707 microm and lambda(2)=4.129 microm. This coated prism has a maximum retardance error of approximately 5 degrees over > three octaves (0.5 to 4.5 microm) in the visible, near-, and mid-IR spectral range. Another mid-IR 3lambda/4 retarder uses a Si prism, which is coated by an optically thick silicon oxynitride film of the proper composition, to achieve retardance that differs from 270 degrees by < 0.5 degrees over the 3-5 microm spectral range.

Designs of infrared nonpolarizing beam splitters with a Ag layer in a glass cube

A novel design of a nonpolarizing beam splitter with a Ag layer in a cube was proposed and optimized, based on the needle optimization. The digital simulations of the reflectance and reflection-induced retardance were presented. The simulation results showed that both the amplitude and the phase characteristics of the nonpolarizing beam splitter could realize the design targets. The difference between the simulated and the target reflectance of 50% is less than 0.4% and the simulated and the reflection-induced retardance is less than 0.62 degrees in the 1260 -1360 nm range for both p and s components.

Embedded centrosymmetric multilayer stacks as complete-transmission quarter-wave and half-wave retarders under conditions of frustrated total internal reflection

A centrosymmetric multilayer stack of two transparent materials, which is embedded in a high-index prism, can function as a complete-transmission quarter-wave or half-wave retarder (QWR or HWR) under conditions of frustrated total internal reflection. The multilayer consists of a high-index center layer sandwiched between two identical low-index films with high-index-low-index bilayers repeated on both sides of the central trilayer, maintaining the symmetry of the entire stack and constituting a QWR (Delta(t)=90 degrees or 270 degrees ) or HWR (Delta(t)=180 degrees ) in transmission. A QWR design at wavelength lambda=1.55 microm is presented that employs an 11-layer stack of Si and SiO(2) thin films, which is embedded in a GaP cube prism. The intensity transmittances for the p and s polarizations remain >99% and Delta(t) deviates from 90 degrees by <+/-3 degrees over a 100 nm spectral bandwidth (1.5< or =lambda< or =1.6 microm), and by < or =+/-7 degrees over an internal field view of +/-1 degrees (incidence angle 44 degrees < or = phi(0)< or =46 degrees inside the prism). An HWR design at lambda=1.55 microm employs seven layers of Si and SiO(2) thin films embedded in a Si cube, has an average transmittance >93%, and Delta(t) that differs from 180 degrees by <+/-0.3 degrees over a 100 nm bandwidth (1.5< or =lambda< or =1.6 microm) and by <+/-17 degrees over an internal field view of +/-1 degree . The sensitivity of these devices to film-thickness errors is also considered.

Achromatic angle-insensitive infrared quarter-wave retarder based on total internal reflection at the Si-SiO2 interface

An achromatic infrared (lambda = 1.2-4 microm), Si-prism quarter-wave retarder (QWR) is described that uses total internal reflection at a buried Si-SiO2 interface at an angle of incidence phi near 33 degrees, where deltaDelta/deltaphi = 0. The retardance delta deviates from 90 degrees by < +/- 2 degrees within a field of view of +/- 10 degrees (in air) over the entire bandwidth. Because the SiO2 layer at the base of the prism is optically thick, this QWR is unaffected by environmental contamination.

Phase retarders highly insensitive to the input angle

In the few exceptional cases of total internal reflection phase retarders that are weakly sensitive to variations in the input angle of incidence i, the devices are of increasingly larger size; deviate or translate the emergent beam; are difficult to align in optical systems; or, in coated rhombs, have an impermanent stability of the retardance. Based on new compensating effects, novel devices of high retardance stability and advantageous characteristics are presented. One device is stable to within 0.09 degrees of 90 degrees for i ? 3 degrees . It is a two-reflection quarter-wave retarder that does not alter the path of the compact size light beam, is of compact size (one seventh the size occupied by the achromatic device AD-1 for equal aperture lengths), and can be easily aligned in optical systems or used as a rotating element. The path length of the beam inside the device is less than one third the corresponding length inside the achromatic device AD-1.

Polarization-preserving totally reflecting prisms with a single medium layer

When reflectors with layers are used at non-normal incidence, the two planes of polarization generally have different phase shifts. The difference in the shifts is known as phase retardance. For prisms with a single layer, this retardance depends on four factors: prism index, layer index, the ratio of the optical thickness of the layer to the wavelength, and angle of incidence. When the retardance is kept at zero and the reflectance for both p and s components of a polarized light are controlled at almost 100% after reflection, a polarization-preserving total reflection is realized. Polarization-preserving totally reflecting prisms (PPTRP's) have many applications in scientific research and optical engineering. Designers of the PPTRP's need references concerning the phase properties of the PPTRP's. However, few papers can be found in which the effects of the four factors on the retardance of the PPTRP's were investigated and compared thoroughly, although the theory concerned has been known and the influences from some (not all) factors have been reported. Therefore it is still necessary to study the behavior of the PPTRP's from all aspects. The effects of all four factors on the retardance are analyzed and compared from all aspects. A general method of designing PPTRP's is proposed. As an example, a special PPTRP is designed and both theoretical and experiment results are given.

Achromatic wave retarder by phase subtraction

We analyze the method of phase subtraction in two identical optical structures to build an achromatic phase retarder. The two structures are made of right-angle prisms and are aligned orthogonal to each other. They are also made of materials of different refractive indices so that dispersion compensation can be taken advantage of. Essentially the phase retardation between the s and p waves in the first structure is subtracted from the phase retardation in the second structure. This can be done by reversing the roles of the s and p waves. By choosing the materials of the prisms properly, the phase retardation can be made to be constant over a broad spectral range. Indeed, calculations made with commercial optical glasses show that phase errors in the visible and near-infrared regions can be rather small. For example, for a 90° phase retarder (quarter-wave plate), a phase error of 0.35° can be obtained from 0.35 to 0.81 μm and from 0.59 to 1.26 μm.

Starting designs for the computer optimization of optical coatings

Several generic starting designs are used for the computer optimization of multilayer optical coatings. The first is a stack of many thin layers. Another, which is applicable to the needle-layer optimization method, is at least one thick layer. Examples include the following coatings: antireflection, beam divider, enhanced metallic reflector, dark mirror, and total internal reflection with prescribed differential phase shift.

Analytical relations for thin-film total internal reflection phase retarders

Single-layer coatings on total internal reflection boundaries that produce any specific phase retardation are analyzed. One- and two-reflection phase-retarding systems are considered. Simple quadratic equations are obtained for an unknown layer phase thickness at a given angle of incidence and phase retardation. Equations for specific multilayer coatings that are equivalent to single-layer designs are also deduced. Diagrams of solution zones for refractive indices are given comparatively for one- and two-reflection systems.

Simple relations for thin-film-coated, phase-retarding totally reflecting prisms

An analysis is given of the designs of thin-film coatings on totally reflecting boundaries that produce half-wave, quarter-wave, and half-quarter-wave phase retardations. Particular single-layer, doublelayer, and symmetrical triple-layer coatings that contain only one non-quarter-wave layer are considered. Simple quadratic equations are presented for the non-quarter-wave-layer phase thickness. Useful diagrams of the solution zones for layer refractive indices are obtained.

Phase retarders with variable angles of total internal reflection

Results for three λ/4 phase retarders are reported. One of them is achromatic to within ± 0.06° of 90° in the visible region. It is shown that, under certain conditions, oblique incidence on the entrance face of total internal reflection phase retarders can greatly improve the achromaticity.

Analytical solutions for zero-phase-shift transparent coatings on metallic reflectors at 10.6 µm

The relationships for refractive indices for zero-phase-shift quarter-wave coatings on metallic reflectors are given. Small variations in λ/4-layer phase thicknesses are also considered.

Achromatic thin-film polarization-preserving beam displacers stable for thickness variations

A pair of two-layer-coated totally reflecting thin-film systems that mutually compensate for the polarization changes and have a good stability for the thickness errors is investigated.

Infrared thin-film totally reflecting quarter-wave retarders

Double-layer ThF(4)-ZnS coatings on a prism of KCl, KBr, and KI are optimized to give totally reflecting quarter-wave retarders at a wavelength of 10.6 microm. The influence on the design parameters of the light absorption occurring at high temperatures is described.