Holographic Filters In Dichromated Gelatin Position Tuned Over The Near-Infrared Region

Holographic interference filters for infrared communications

“…1, and total internal reflection at the film-air interface creates the standing-wave interference pattern that is recorded within the film as index modulation. 2,3 By rotating the prism with respect to the incident beam, one can change the period of the final index modulation; thus the wavelength at which the hologram shows peak reflectivity at normal incidence will depend on the exposure angle. Figure 3 shows the transmission spectra for four such holograms, all recorded with the same exposure wavelength but each at a different exposure angle.…”

“…Total internal reflection at the film-air interface provides the second beam for our holographic exposures. 2,3 For the geometry shown, by using Snell's law we can write the following equations that relate the external angle of the beam, i , to the angle within the film, f :…”

“…1 Of particular interest is the possibility of using a total internal reflection system to record infrared mirrors by using visible laser illumination. 2,3 Such mirrors have wavelength selection properties and bear a striking resemblence to rugate filters in which the index of refraction varies in a continuous, corrugated manner along the direction of propagation. A comprehensive history of the theory of inhomogeneous films has been compiled by Jacobsson.…”

“…The photopolymer requires exposure with visible wavelengths, which necessitates the use of the total internal reflection configuration mentioned above. 2,3 The holograms were measured with a conventional spectrophotometer. Using these data, we demonstrate that the DuPont HRF-800X001 photopolymer has low loss and low index dispersion in the near infrared.…”

Integration of holographic optical elements with polymer gelatin waveguides on GaAs, LiNbO_3, glass, and aluminum

“…The importance of DCG as a holographic material lies in its ability to record phase holograms by modulating the refractive index with values greater than 0.1.4 High-efficiency holographic optical elements based on DCG have been reported by various groups. 5 ' 6 Integration of such devices in the thin-film format is useful. However, DCG itself, owing to the presence of the photosensitizer ammonium dichromate, has serious in-plane scattering loss (>10 dB/cm), which makes the formation of waveguides in conjunction with other integrated-optic devices impractical.…”