Wavelength Pass Research Articles

Optical multi/demultiplexers for single-mode fiber transmission

This paper describes two types of optical multi/demultiplexers using a single-mode fiber for a two-way transmission system. One type, the filter type, consists of four bandpass filters and a short wavelength pass filter or a long wavelength pass filter. The other, the filter-grating type, consists of two bandpass filters and a grating. The present multi/demultiplexers have four channels with 1.05, 1.15, 1.3, and 1.5 μm wavelengths. Total insertion losses are less than 2.3 and 3.2 dB for the filter type and the filter-grating type, respectively. Cross-talk between channels is less than -40 dB.

An electro-optic tunable filter

This letter describes a tunable optical filter that couples light energy between ordinary and extraordinary polarizations in a birefringent electro-optic crystal at the phase-matched wavelength by means of a spatially periodic dc electric field. The specific embodiment described here is a LiTaO3 platelet operating with transverse electric field and located between cross polarizers. Analogies to both the S̆olc birefringent filter and the Harris acousto-optic filter are cited. The electro-optic filter is tuned by varying the spatial period of the electric field via an array of separately addressable finger electrodes. We have demonstrated tunability from 4700 Å to 4.5 μm. Experimental results of transmittance versus applied voltage and of bandwidth versus pass wavelength agree well with theory. The flexibility of this type of electronic filter in allowing synthesis of arbitrary transfer functions through nonperiodic voltage distributions is emphasized.

Continuous Flow Infrared Gas Analyzer Employing Interference Filters

A filter photometer for the continuous determination of a single component of a gaseous mixture is described. The instrument incorporates a combination of band pass and long wavelength pass filters of the interference type, designed to transmit in the near infrared. The analyzer has been calibrated to determine hydrocarbons in automotive exhaust by means of absorbance measurements at 3.43 microns.