偏振起偏器基础

Polariza ti on Components

Polariza ti on components provide the backbone of our business. Polarizers, Retarders and Liquid Crystal Devices are the fundamental building blocks for our line of systems and instrumenta ti on and also for our original equipment manufacturer (OEM) customers.

In addi ti on to the delivered hardware components, an important part of the service Meadowlark Op ti cs provides to our customers includes extensive, precise polariza ti on metrology. Our metrological capability ensures that these components are delivered to you in spec the ? rst ti me, every ti me.

We have broadened our o? ering to include Polarizers for the ultraviolet to the mid-infrared regions of the spectrum.

Retarders (or waveplates) are another key component to Meadowlark Op ti cs customers. Recent new products include Wide Field Retarders, which provide excellent ? eld of view performance out to

30 degrees incidence, or more. Now, we are introducing Dual Wavelength Retarders for polariza ti on control at two ? xed wavelengths.

The Polarizers and Retarders described above are “passive” components, with no ac ti ve control possible. Our line of Liquid Crystal Devices includes compensated and uncompensated LC Variable Retarders,

A tt enuators and Polariza ti on Rotators. With this catalog, we are now introducing Op ti cal Shu tt ers, as well. Naturally, Meadowlark Op ti cs o? ers necessary control electronics to mate with the LC Device required in your applica ti on including the o? ering of an extended warranty program.

A line of Moun ti ng Hardware is also available. We’ve added Beamspli tt er Mounts to our popular Rotary Mount o? ering.

Addi ti onally, we provide the capability for the assembly and calibra ti on of Op ti cal Sub-assemblies giving our customers a valuable, ti me saving and quality improved product. Call for more informa ti on.

Liquid Crystal Controllers Liquid Crystal Devices

Moun ti ng Hardware Retarders Linear Polarizer Principles

Ideal linear polarizers allow the transmission of only one polarization state with zero leakage of all other polarization states. Rotating the linear polarizer about the optical axis changes the output plane of polarization. Thus, a perfect linear polarizer transmits only 50% of an unpolarized input beam and two perfect polarizers with their transmission axes crossed totally extinguish an incident beam. Imperfections in polarizers such as scattering sites, material defects (such as pinholes in thin films) and field-of-view effects reduce ideal polarizers’ contrast.

When choosing a linear polarizer, several key factors must be considered including: cost, wavelength range, aperture size, acceptance angle, damage threshold, transmission efficiency and extinction ratio. Extinction ratio (or contrast ratio) is defined as the ratio of transmitted intensity through parallel polarizers to the transmitted intensity through crossed polarizers. Meadowlark Optics offers polarizers with extinction ratios as high as 10,000,000:1 over the operating wavelength range.

Meadowlark Optics now offers four types of linear polarizers: dichroic (polymer and glass), dielectric beamsplitting, wire grid and calcite crystal.

Dichroic Polarizers – Polymer and Glass

Meadowlark Optics offers an extensive line of dichroic polarizers made from both polymer and treated glass materials. Dichroic refers to the selective polarization absorption of the anisotropic polarizing material (Diattenuation). These polarizers are usually constructed by laminating a thin, stretched and dyed polymer film between two polished and antireflection-coated glass windows. The resulting compact component offers excellent value and is

often the best choice for flux densities below 1 watt/cm 2.

Selecting the appropriate dichroic polarizing material enables excellent extinction ratio performance over the wavelength range from 310 to 5000 nm. Due to small variations in the polarization material, extinction ratios degrade over larger apertures for all dichroic polarizers. Meadowlark Optics has improved the transmission of dichroic polarizers with high-efficiency, broadband antireflection coatings on the glass windows used in our product design. Laminated glass construction contributes to a substantial improvement in transmitted wavefront distortion. Our polarizer assembly greatly improves the product durability, allowing for easy and repeated cleaning.

Meadowlark Optics also offers a line of high contrast dichroic glass polarizers for the near and mid infrared regions of the spectrum up to 5000 nm. High throughput and contrast make these polarizers an excellent choice for near infrared requirements. Key advantages of dichroic polarizers include superior angular acceptance and extreme flexibility for custom shapes and sizes. Please call one of our Sales Engineers for assistance.

Beamsplitting Polarizers

Beamsplitting polarizers divide unpolarized incident light into

two (usually) orthogonal, linearly polarized beams. Low absorption coatings provide an excellent combination of damage resistance and extinction ratio at a moderate price. Rugged beamsplitter cubes are easily mounted and therefore designed into many instrument applications. Beamsplitting polarizers offer the unique advantage of providing two linearly polarized output beams, one transmitting straight through and the second “splitting” off at precisely 90 degrees. When necessary, the extinction ratio of the reflected beam can be dramatically improved by adding a dichroic polarizer to the output face. Meadowlark Optics offers both Laser Line and Broadband Beamsplitting Polarizers, covering visible to near infrared applications. Laser Line Beamsplitting Polarizers offer the advantage of V-type antireflection coatings, improving efficiency by limiting surface losses. Broadband Beamsplitting Polarizers are more versatile for tunable wavelength or broadband sources.

Fig. 1-1 Regardless of input polariza ti on, a linear polarizer transmits only linearly polarized light.Note: Polarizers are available from less than 5mm square to

200 mm and greater diameter

R e t a r d e r s

L i q u i d C r y s t a l D e v i c e s L i q u i d C r y s t a l C o n t r o l l e r s

M o u n ti n g H a r d w a r e

Linear Polarizer Principles

Calcite Polarizers

Calcite is a naturally occurring birefringent crystal with excellent polarization properties including very high extinction ratio and transmission efficiency. Aperture sizes are limited, since large optically uniform pieces of this natural crystal are rare. Calcite material exhibits extremely broadband transmission performance, from 320 to 2300 nm. Meadowlark Optics offers Glan-Thompson calcite polarizers. Manufactured from Grade A optical calcite material, the design takes advantage of total internal reflection to separate the two polarization components. Glan-Thompson Polarizers are recommended where a wide acceptance angle is important for overall system performance. However, the version with cemented construction limits both power handling and ultraviolet performance.

Wire Grid Polarizers

VersaLight wire grid polarizers are the modern outgrowth of

the 1888 experiments by Heinrich Hertz using fine metallic wires wrapped around a non-conductive frame. Instead of manually arranging an array of fine conductive wires, lithographic techniques are used to place sub 100 nm pitch aluminum conductors on glass substrates. When incident unpolarized radiation interacts with the wire grid, differences in boundary conditions drive different behavior for the two orthogonal polarizations. Electromagnetic radiation incident on the “wires” oscillate free electrons which have a much higher mobility along the wires than in the transverse dimension. Ideally, the wires behave as a perfect reflector for the parallel field and pass 100% of the transverse field. Material defects and Joule heating reduce the contrast of the polarizer, which is also strongly affected by the wavelength of the light passing through it. (Longer wavelengths are closer approximations to the ideal solution as their wavelengths become much greater than the wire grid spacing.)

Versalight polarizers are available in large aperture sizes up to 200mm diameter with high contrast across the visible and near infrared spectrum. They can handle relatively high power and are more durable when coated. Specially selected ultraviolet transmissive material is available on a custom basis. Please contact a Meadowlark Optics Sales Engineer for assistance.

Fig. 1-2 Beamspli tti ng Polarizers provide two orthogonally polarized beams, conveniently separated by 90°.

Liquid Crystal Controllers

Liquid Crystal Devices Moun ti ng Hardware Retarders Linear Polarizer Principles

Polarizer and Retarder References:

1. T. Baur and S. McClain, “Polarization Issues in Optical Design”

in Optical System Design , edited by Robert Fischer, (SPIE press, McGraw-Hill, 2008), Chap 19.2. J.M. Bennett, “Polarization,” in Handbook of Optics , edited by

M. Bass, (McGraw-Hill, New York, 1995), Vol. I, Chap. 5; J.A. Dobrowolski, “Optical Properties of Films and Coatings,” ibid ., Vol. I, Chap. 42; J.M.Bennett, “Polarizers,” ibid., Vol. II, Chap. 3; S. Wu, “Liquid Crystals,” ibid., Vol. II, Chap. 14. 3. D. Clarke and J.F . Grainger, Polarized Light and Optical

Measuremen t, (Pergamon Press, New York, 1971).4. D.S. Kliger, J.W . Lewis and C.E. Randall, Polarized Light in

Optics and Spectroscopy , (Academic Press, San Diego, Calif., 1990).5. W .A. Shurcliff, Polarized Light: Production and Us e, (Harvard

University Press, Cambridge, Mass., 1966).6. D.A. Holmes, “Exact Theory of Retardation Plates,” J.Opt. Soc.

Am. 54, 1115 (1964).7. P .D. Hale and G.W . Day, “Stability of Birefringent Linear

Retarders (Waveplates),” Appl. Opt. 27 (24), 5146 (1988).8. D. Malacara, Optical Shop Testing , (John Wiley and Sons, New

York, 1978).9. G. Love, “Wave-front Correction and Production of Zernike

Modes with a Liquid-Crystal Spatial Light Modulator”, Appl. Opt. 36 (7), 1517 (1997).