Birefringent Substrate Research Articles

Polarization-selective computer-generated holograms: design, fabrication, and applications

We constructed polarization-selective computer-generated holograms that apply an independent phase profile during readout by horizontal and vertical light polarizations. These elements are composed of two surface-relief-etched birefringent substrates joined face to face. We describe the design methodology for arbitrary birefringent substrate and gap materials. We show how these holograms are fabricated with standard microelectronics technology and discuss the effects of etching and alignment errors on performance. We demonstrated a diffraction efficiency of 60% with a polarization contrast ratio of >100:1 using a multilevel phase hologram made from two birefringent lithium niobate substrates. We also showed that a single-layer SiO(2) thin-film antireflection coating on all surfaces can reduce reflections from the high-index substrates without significant effect on hologram performance. We also consider some possible applications of this technology and demonstrate experimentally a dual focal-length lens and a self-interconnecting binary 2 × 2 polarization switch.

Temperature measurements of a birefringent substrate (LiNbO3) in a radio frequency discharge by laser interferometry

Temperatures of a birefringent substrate (LiNbO3) have been measured by laser interferometry in a 13.56 MHz rf discharge. The measurement method is based on monitoring the variation of natural birefringence with temperature. The transient temperature rises and equilibrium values are investigated in nitrogen plasma at rf powers of ∼86 W. Owing to the large heat capacity per unit area of the substrate, the time constant of temperature rises is about ten times as large as the previously reported value of a polymer substrate (PMMA).

Holographic Optical Element with Analyzer Function for Magneto-Optical Disk Head

A new holographic optical element, made of a birefringent LiNbO3 substrate, has been developed for magneto-optical, disk heads. The element includes the analyzer function required for magneto-optical signal detection, in addition to focusing and tracking error signal detection functions. The analyzer function was realized by introducing a birefringent grating structure, using proton exchange method. More than 15dB extinction ratios were obtained for the fabricated element.

Construction of multicapacity matched filters using birefringent object film

Target objects used to construct matched filters for correlator applications are generally recorded on photographic film. Most commercial emulsions of interest are coated on birefringent substrate. The authors address the effects of this birefringence upon the interference pattern recorded as a matched filter in coherent optical correlators. Results are then expanded to include several types of multiple matched filters. Finally, techniques are discussed that reduce the deleterious effects of input film birefringence.

Birefringent Coupler for Integrated Optics

An optical coupler has been developed whereby a birefringent prism or substrate is utilized to couple light into thin film optical waveguides. The coupler is designed so that the incident light, polarized as an extraordinary wave, passes through the birefringent material at such an angle that the index of refraction in the input medium is higher than that of the waveguide. In addition, the orientation of the birefringent material is chosen so that the reflected waves within the waveguide are incident on the input medium at such an angle that the medium index of refraction appears lower than that of the waveguide. In this way, the light is trapped within the waveguide and, when the light is incident at the appropriate angle, this light propagates in the waveguide as a single mode. Coupling takes place over the whole area common to the waveguide and input medium; thus, neither a sharp edge nor a trapped evanescent region are required to prevent the light coupled into the waveguide from leaking back into the coupling prism. The absence of a boundary makes it practical to couple wide beams of light into planar guides. Couplers made of calcite have been used to couple TM He-Ne laser light into multimode waveguides formed of liquids and optical cement.