Wayne V. Sorin

Highly selective evanescent modal filter for two-mode optical fibers.

Efficient and selective coupling between a single-mode fiber and the LP(11) mode of a double-mode fiber is demonstrated in an evanescent directional coupler. With greater than 90% coupling to the LP(11) mode, suppression of the coupled power to the lower-order LP(01) mode was measured to be at least 24 dB. This device has application as a modal filter for the construction of in-line all-fiber optical components.

Phase-velocity measurements using prism output coupling for single- and few-mode optical fibers

A measurement technique based on evanescent coupling between guided fiber modes and radiation modes in a bulk medium is described. Modal phase velocities have been measured to an accuracy of better than 0.01%. Direct measurement of modal beat lengths and cutoff wavelengths are also possible. For a step-index fiber, refractive indices for the core and cladding were determined to an accuracy of 10−4; the core diameter was determined to an accuracy of 1%.

Single-mode-fiber evanescent polarizer/amplitude modulator using liquid crystals

An in-line polarizer has been demonstrated that uses the birefringent properties of a nematic liquid crystal placed in the evanescent field of a single-mode fiber. A polarization-extinction ratio of 45 dB was measured with an insertion loss of 1.1 dB. Amplitude modulation was also demonstrated by using an external electric field to reorient the liquid-crystal molecules.

Single-mode-fiber ring dye laser

Pulsed dye-laser operation in a single-mode fiber is demonstrated by incorporating an evanescent field amplifier into an all-fiber ring resonator. Laser threshold is obtained with 60 mW of pump power. Characteristics of the vanescent fiber amplifier are investigated as functions of pump power and dye solution index.

Single-mode-fiber saturable absorber

Saturable absorption is performed on a signal in a single-mode fiber by allowing the evanescent field of the guided wave to interact with a saturable-absorbing dye. The evanescent field is exposed by mechanically removing a portion of the fiber cladding. The saturable material is then placed in close proximity to the fiber core. The singlemode-fiber saturable absorber is characterized by a nonlinear transmission versus input optical intensity. Transmissions ranging from 50 to 80% have been demonstrated using Eastman 9860 saturable-absorbing dye and optical pulses from a Q-switched Nd:YAG laser.