Direct measurement of bend-induced mode deformation in large-mode-area fibers.

In 1976 Marcuse developed an equivalent index model to predict the effects of bending in waveguides, and predicted deformation of the spatial modes in bent optical fibers. Perturbative approaches have been previously applied and tested to predict the behavior of single- and few-moded-fibers. However, much more significant mode deformation has been predicted for large-mode-area fibers than for single- or few-moded-fibers. In this paper, the spatial profiles of modes deformed by bending in large-mode-area fibers are measured for the first time. A finite difference method employing the equivalent index model is used to calculate the modes of the helical fiber, which show an offset that is twice as large as that predicted for single-mode fiber, and mode compression that is five times greater. These calculated results are compared to the experimental data, yielding significantly better agreement than previous perturbative approaches.

All-fiber optical magnetic-field sensor based on Faraday rotation in highly terbium-doped fiber.

An all-fiber optical magnetic field sensor is demonstrated. It consists of a fiber Faraday rotator and a fiber polarizer. The fiber Faraday rotator uses a 2-cm-long section of 56-wt.%-terbium-doped silicate fiber with a Verdet constant of -24.5 rad/(Tm) at 1053 nm. The fiber polarizer is Corning SP1060 single-polarization fiber. The sensor has a sensitivity of 0.49 rad/T and can measure magnetic fields from 0.02 to 3.2 T.

Compact all-fiber optical Faraday components using 65-wt%-terbium-doped fiber with a record Verdet constant of -32 rad/(Tm).

A compact all-fiber Faraday isolator and a Faraday mirror are demonstrated. At the core of each of these components is an all-fiber Faraday rotator made of a 4-cm-long, 65-wt%-terbium-doped silicate fiber. The effective Verdet constant of the terbium-doped fiber is measured to be -32 rad/(Tm), which is 27 x larger than that of silica fiber. This effective Verdet constant is the largest value measured to date in any fiber and is 83% of the Verdet constant of commercially available crystal used in bulk optics-based isolators. Combining the all-fiber Faraday rotator with fiber polarizers results in a fully fusion spliced all-fiber isolator whose isolation is measured to be 19 dB. Combining the all-fiber Faraday rotator with a fiber Bragg grating results in an all-fiber Faraday mirror that rotates the polarization state of the reflected light by 88 +/- 4 degrees .

All-fiber optical isolator based on Faraday rotation in highly terbium-doped fiber.

An all-fiber isolator with 17 dB optical isolation is demonstrated. The fiber Faraday rotator uses 56 wt. % terbium (Tb)-doped silicate fiber, and the fiber polarizers are Corning SP1060 single-polarization fiber. The effective Verdet constant of the Tb-doped fiber is measured to be -24.5+/-1.0 rad/(Tm) at 1053 nm, which is 20 times larger than silica fiber and 22% larger than previously reported results.

Single-frequency 1 W hybrid Brillouin/ytterbium fiber laser.

A high-power hybrid Brillouin/ytterbium fiber laser has been demonstrated with an output power of 1 W. The laser operates in the single-frequency regime with an optical signal-to-noise ratio greater than 55 dB in a 0.1 nm bandwidth.

Pump-induced, dual-frequency switching in a short-cavity, ytterbium-doped fiber laser.

Using a short linear cavity composed of a section of highly ytterbium-doped fiber surrounded by two fiber Bragg gratings, dual-frequency switching is achieved by tuning the pump power of the laser. The dual-frequency switching is generated by the thermal effects of the absorbed pump in the ytterbium-doped fiber. At each frequency, the laser shows single-longitudinal-mode behavior. In each single-mode regime, the optical signal-to-noise ratio of the laser is greater than 50 dB. The dual-frequency, switchable, fiber laser can be designed for various applications by the careful selection of the two gratings.

Complete elimination of self-pulsations in dual-clad ytterbium-doped fiber lasers at all pumping levels.

We have demonstrated suppression and elimination of self-pulsing in a watt-level, dual-clad, ytterbium-doped fiber laser. The addition of a long section of passive fiber in the laser cavity makes the gain recovery faster than the self-pulsation dynamics, allowing only stable cw lasing. This scheme provides a simple and practical method for eliminating self-pulsations in fiber lasers at all pumping levels.

Effective Verdet constant in a terbium-doped-core phosphate fiber.

The concept of an effective Verdet constant is proposed and experimentally validated. The effective Verdet constant of light propagation in a fiber includes contributions from the materials in both the core and the cladding. It is measured in a 25 wt.% terbium-doped-core phosphate fiber to be -6.2+/-0.4 rad/(Tm) at 1,053 nm, which is six times larger than silica fiber. The result agrees well with Faraday rotation theory in optical fiber.

High-gain, polarization-preserving, Yb-doped fiber amplifier for low-duty-cycle pulse amplification.

Amplified spontaneous emission (ASE) suppression techniques were utilized to fabricate a double-pass, Yb-doped amplifier with the noise properties of a single-pass amplifier. Simulations based on a rate equation model were used to analyze the ASE and the effectiveness of the suppression techniques. These techniques were implemented in an alignment-free, double-pass, Yb-doped fiber amplifier with a 26 dB gain at a wavelength 23 nm off the gain peak and a -48 dB noise floor while amplifying linearly polarized optical pulses with a low-duty cycle.