Optical Components n λ/4 and λ/2 Wavelength Plates l Terms and Definitions Crystal Wavelength Plate: An element that uses the velocity Extinction Ratio: This indicates a value for the phase accuracy of difference between ordinary and extraordinary light beams to a wavelength plate, and the conversion equation of the create a phase difference between both beams; the difference is extinction ratio V [%] and phase difference Г [deg] is as follows: obtained by using the birefringence of a crystal. When this V [%] = 100×cosГ characteristic is used, a λ/4 wavelength plate converts V= Io , 0 – Io , 90 Io , 0 + Io , 90 Г= 360 (ne−no)×t λ linearly-polarized light into circularly-polarized light, and a λ/2 wavelength plate converts circularly-polarized light into linearly-polarized light with its polarization plane rotated by 90 degrees. Io , 0 : Output in a parallel Nicol state Wavefront aberration: This indicates the Peak-to-Valley Io , 90 : Output in an orthogonal Nicol state difference of a measured wavefront as a unit of design wavelength: the Zygo Corporation’ s phase interference system ne : Refractive index of an extraordinary beam is used to provide the data. no : Refractive index of an ordinary beam P – V = (maximum phase angle – minimum phase angle) t : Thickness of a phase plate λ : Design wavelength l Application As shown in the figure below, wavelength plates are used mainly for picking up optical information files (DVD, etc) to prevent the back-talk noise of laser beams. Disk Lens Wavelength plate Detector Laser beam Lens Beam splitter Lens Laser diode Example of how a wavelength plate is used sq15_071106_waveplate1_e Optical Components n λ/4 and λ/2 Wavelength Plates l Features 1. A computer controlled and grown synthetic quartz crystal for optical 3. The bonding-type plate enables the influence on phase components is used, and by accurately processing the thickness accuracy caused by variations in optical rotation and the laser of the plate, the extinction ratio is kept within a range of ±5%. incident angle to be ignored. Therefore, it can be embedded in 2. A single board-type plate has good wavefront aberration and is an optical system more easily. thin. Therefore, it is convenient to use when bonded to a beam splitter, etc. Y factor Y factor X factor Z factor Z factor X factor Z Z Y Y ngth Wavele plate ngth Wavele te la p Mechanism diagram of a λ/4 wavelength plate Mechanism diagram of a λ/2 wavelength plate l Standard specifications Product name Single-board Type I (x or y−cut) Specifications Size Wavelength range Outline l Directional accuracy of the optical axis Single-board Type II (θ°Z−cut) Bonding Type Reference Laser oscillation wavelength between 400 to 2,000 nm Round plate of φ5 to 10 mm or square plate of 5 x 5 to 10 x 10 mm Thickness Wavefront aberration 0.3 to 1.0 mm Extinction ratio Transmittance 0.5 to 1.0 mm Max. λ/4 (λ = 633 nm transmission) ±5 % Min. 99% (AR coating on both surfaces) Directional accuracy of the light axis Min. 98% The reference and the optical axis are parallel. (AR coating on both surfaces) ±60’ (see the right) * The size and thickness of wavelength plates can be changed upon request. Reference The angle between the reference and the optical axis is 45°. * The arrow shows the light axis. l Environment Resistance The following reliability tests guarantee the specified optical characteristics of NDK’ s optical components. Subjected to high temperature For 96 hours at +85 °C Subjected to low temperature For 96 hours at –40 °C Subjected to high temperature and high humidity For 96 hours at +60 °C and 95 % Heat shock 10 cycles (one cycle is conducted for 30 minutes at –40 °C and 30 minutes at +85 °C) Mechanical strength No flaws after the surface is rubbed with absorbent cotton sq16_090217_waveplate2_e Optical Components n λ/4 and λ/2 Wavelength Plates l How to Determine Wavelength Plate Specifications When placing an order or asking for information, please inform us of the following items. (Check the boxes.) 1. Wavelength plate type o Single-board type : o Bonding type 2. Phase difference o 1/4 wavelength plate : o 1/2 wavelength plate 3. Used frequency mm 4. Coating o Both surfaces : o One surface : o None 5. Dimensions × × : * Concerning wavelength plates other than square ones, please give us your individual specifications. 6. Light axis direction A : 0° B : 45° C : 22.5° sq17_071106_waveplate3_e