Roger H. Stolen

Self-organized phase-matched harmonic generation in optical fibers

We generated second-harmonic light from a single-mode fiber after a few minutes of seeding with 532-nm harmonic light along with 1.064-microm pump light. This experiment supports a mechanism for photoinducing an alternating second-order nonlinearity in the fiber.

Waveguides and fibers for nonlinear optics

We review the operation of, and materials requirements for, a variety of nonlinear-optics guided-wave devices.

A single-polarization fiber

We report an oPtical fiber which guides only one polarization. This fiber polarizer utilizes high modal birefringence ( 4.7 times 10^{-4} ) to split the two polarizations of the fundamental mode and an ellipitcal depressed-index cladding to provide a steep wavelength-dependent tunneling loss to the fast axis mode. The stress-induced birefringence is created by an elliptical SiO 2 -B 2 O 2 inner cladding. A 4.7-m length of polarizer fiber exhibits an extinction ratio of 34 dB at a wavelength of 633 nm, with polarizing behavior over a bandwidth of 50 nm. Insertion loss of less than 1 dB has been observed for the guided linear-polarization mode. The polarizing band may be shifted from 620 to 525 nm by bending the fiber to a radius of 0.67 cm. Such fiber polarizers should find a variety of applications in fiber sensors, attenuators, isolators, wavelength filters, and tuners.

High-birefringence optical fibers by preform deformation

High-birefringence optical fibers have been fabricated using a preform deformation technique in which an initially round preform is locally heated and squeezed from two sides. This technique has been used to make both polarization-preserving and single-polarization fibers. A novel feature of these new fibers is their rectangular shape which facilitates location of the principal axes and increases resistance to polarization breakdown from external perturbations. These fibers have circular cores, low loss, and excellent polarization holding.

A fiber Raman ring laser

A fiber Raman ring laser was synchronously pumped by a cavity-dumped argon laser. The Raman laser was tuned with either a piezoelectric intracavity interferometer or by varying the pump pulse rate.

Calculation of stress birefringence in fibers by an infinitesimal element method

It is shown that stress birefringence in polarization-preserving fibers can be calculated by the simple addition of contributions from infinitesimal elements of the highly doped stress regions. This method provides insight into the properties of stress-birefringent fibers and shows the equivalence between the various types of such fibers. In particular, it is seen that a circular barrier layer around the core does not reduce the birefringence and that high birefringence does not require a large stress cladding.

Polarization-selective fiber directional coupler

A directional coupler has been made which exhibits a 9-dB polarization selectivity. One-half of the coupler is polished parallel and the other half perpendicular to the elliptical stress cladding of a high-birefringence fiber. Measurements on the coupler and on the fiber suggest a procedure for improving the selectivity.

Numerical study of the Raman effect and its impact on soliton-dragging logic gates

Recent experiments in birefringent optical fibers in which a signal pulse in one polarization is used to switch a control pulse in another polarization are affected by the Raman self-frequency shift. These experiments are modeled numerically, with the experimentally measured Raman profiles used as input to the simulations. Both parallel and perpendicular Raman gain are kept. The effect of keeping the full Raman response rather than just an often-used linear approximation is discussed. The experimental results are in good agreement with theory, although some discrepancies exist. The possibility that these discrepancies could be due to errors in the measurements of the low-frequency portion of the perpendicular Raman gain is examined and ruled out. Other possible sources of this discrepancy are then discussed.