Anthony D. Sanchez

Self-Synchronous and Self-Referenced Coherent Beam Combination for Large Optical Arrays

A novel and highly accurate electronic technique for phase locking arrays of optical fiber amplifiers is demonstrated. This is the only electronic phase locking technique that does not require a reference beam. The measured phase error for this system is lambda /20. A model for calculating the signal-shot noise-limited phase errors and the phase-modulation-induced phase errors is developed. For the first time, nine fiber amplifiers are coherently combined. The total power in the phase locked array is 100 W.

All-fiber 50 W coherently combined passive laser array

We experimentally demonstrate 50 W of spontaneously phase-locked two-laser array in an all-fiber and all-passive configuration using large-mode-area (LMA) polarization-maintaining fiber laser cavities and an LMA fiber coupler. We show that both laser cavity length difference and fiber nonlinearity play an important role in achieving efficient and stable coherent beam combining. In addition, we compare the difference in coherent combining efficiency by using fibers with different mode-field diameters and discuss the underlying phase-locking mechanism and its power scalability.

Response of germanium-doped fiber Bragg gratings in radiation environments

Fiber Bragg gratings were examined in situ while exposed to gamma-ray and proton environments that emulated or exceeded nominal low earth orbit radiation doses. Radiation and temperature induced changes to the reflected Bragg grating amplitude and spectral characteristics were observed in fiber gratings not formed under hydrogen loading. THe irradiations were performed in situ, while the ambient temperature near the Bragg grating was allowed to vary. Shifts in the reflected spectra from the Bragg gratings were observed and attributed to ionization and thermal effects. During irradiation, the spectral shifts were observed to move to longer wavelengths, saturate at low dose and to decrease exponentially following the cessation of radiation.

Coherent combination of high power fiber amplifiers in a two-dimensional re-imaging waveguide

Four actively phase-locked beams produced by fiber amplifiers in a master oscillator power amplifier (MOPA) configuration were coherently combined in a glass capillary re-imaging waveguide producing more than 100 W of coherent output with 80% combining efficiency and excellent beam quality. The beam combiner components maintained a temperature below 30 degrees C with no external cooling at >100 W of combined power.

Gamma-ray-induced effects in erbium-doped fiber optic amplifiers

Four Erbium doped fiber optic amplifiers (EDFAs) were irradiated by gamma-rays to dose levels of 40 Krad(Si) and 100 Krad(Si) at dose rates of 0.25 rad(Si) sec-1 and 1.0 rad(Si) sec-1, respectively. All EDFAs were observed to incur radiation induced permanent decreases to their pre-irradiated signal gains. The paper will discuss the influence of gamma-ray irradiations on EDFA parameters such as gain, noise figure, and integrated amplified spontaneous emission. A brief discussion of how changes to these parameters evolve is presented.

New developments in high power eye-safe LMA fibers

In this paper we present advances made in the development and fabrication of highly efficient, large-mode area fibers for eye-safe wavelengths (1.55 μm, 2.0 μm). LMA Er/Yb co-doped and Tm doped fibers have been successfully fabricated, with 25 μm core and 250 to 300 μm clad diameters, that are suitable for nanosecond pulsed amplification in LIDAR applications as well as high power CW amplification. Manufacturing challenges for these novel fibers are discussed. Measured and modeled data, for both types of fibers, are presented. The development of non-PM and PM-LMA fibers for eye-safe applications is expected to spur rapid progress in power scaling at these wavelengths, similar to that witnessed by the industry at 1.06 μm.

Two-dimensional diffractive coherent combining of 15 fiber amplifiers into a 600 W beam

We demonstrate coherent beam combining using a two-dimensionally patterned diffractive optic combining element. Fifteen Yb-doped fiber amplifier beams arranged in a 3×5 array were combined into a single 600 W, M²=1.1 output beam with 68% combining efficiency. Combining losses under thermally stable conditions at 485 W were found to be dominated by spatial mode-mismatch between the free space input beams, in quantitative agreement with calculations using the measured amplitude and phase profiles of the input beams.

Coherent beam combining of fiber amplifiers in a kW regime

Single-frequency coherent beam combination (CBC) of 16 fiber lasers with kW class output power is presented. In addition, kW scale CBC of three Photonic Crystal Fiber (PCF) amplifiers in a filled aperture configuration is reported.

In-situ high-energy proton irradiation of nonlinear organic modulator materials for space environments

The behavior of two nonlinear polymer-modulator materials irradiated by 63.3 MeV protons to a dose of 1 Mrad(Si) is reported. The effects of proton induced ionization and heating in disperse red 1/poly(methylmethacrylate) and in poly(ethylene dioxythiophene)/poly styrene sulphonate/poly(vinyl alcohol) thin films are discussed. Attenuation of the light transmission at an optical wavelength of (lambda) equals 0.6328 micrometers was measured in the polymer films, conductive coatings and their respective substrates. Comparison of these results with a recently reported study of related nonlinear polymer modulator materials exposed to protons is discussed. Conclusions and recommendations regarding the potential application of polymers in the near-Earth space environment are presented.

Laser Communication Intersatellite Links Realized with Commercial- Off-The-Shelf Technology

Experiments were conducted to evaluate the viability of commercial-off-the-shelf (COTS) technology in the design of high-performance optical intersatellite communications links. The optical links were operated at 155, 622 and 2488 Megabits per second (Mbps) and at 1550 nm wavelength. Communications components were evaluated against performance parameters for on-off keyed (OOK) systems. Transmitters, receivers, optical amplifiers, and filters, used to minimize the impact of amplified spontaneous emission (ASE), were characterized individually and within system configurations. Bit error rate (BER) as a function of photons per bit was characterized for several system configurations. Extinction ratio analysis experiments were conducted to determine the limiting factors on the systems performance. Widely varying optical powers in space (for low earth orbit) imply a robust receiver dynamic range requirement. Dynamic range of COTS receivers was examined and resulted in sufficient performance. In addition, gamma radiation tests on fiber amplifiers were also evaluated in a system context.