Real-time transmission of 16 Tb/s over 1020km using 200Gb/s CFP2-DCO.

We demonstrate real-time transmission of 16 Tb/s (80x200Gb/s) over 1020km TeraWave ULL fiber with 170km span length using the world's first 200Gb/s CFP2-DCO module with a record low power consumption less than 0.1W/Gbps.

800Gb/s (8x128Gb/s) unrepeatered transmission over 515-km large-area ultra-low-loss fiber using 2nd-order Raman pumping.

We demonstrate unrepeatered transmission of 8x128Gb/s PDM-QPSK signals over a 515k-m fiber link. This ultra-long distance of 800 Gb/s unrepeatered transmission in a single fiber configuration is achieved by employing enabling techniques such as large-effective-area ultra-low-attenuation fibers, co-propagating and counter-propagating 2nd-order-pumped distributed Raman amplification, and remote optically pumped amplifier (ROPA). The ROPA itself is also counter-propagating 2nd-order Raman pumped. The designs and characteristics of the ROPA and 2nd-order pumped distributed Raman amplification are described, and optimization of the transmission performance of this ultra-long reach 800Gb/s unrepeatered transmission fiber link is discussed in this paper.

Axicons for mode conversion in high peak power, higher-order mode, fiber amplifiers.

Higher-order mode fiber amplifiers have demonstrated effective areas as large as 6000 µm2, allowing for high pulse energy and peak power amplification. Long-period gratings are used to convert the fundamental mode to the higher-order mode at the entrance to the amplifier, and reconvert back to the fundamental at the exit, to achieve a diffraction limited beam. However, long period gratings are susceptible to nonlinearity at high peak power. In this work, we propose and demonstrate axicons for linear bulk-optic mode conversion at the output of higher order mode amplifiers. We achieve an M2 of less than 1.25 for 80% mode conversion efficiency. Experiments with pulsed amplifiers confirm that the mode conversion is free from nonlinearity. Furthermore, chirp pulse amplifier experiments confirm that HOM amplifiers plus axicon mode convertors provide energy scalability in femtosecond pulses, compared to smaller effective area, fundamental mode fiber amplifiers. We also propose and demonstrate a route towards fiber integration of the axicon mode convertor by fabricating axicons directly on the tip of the fiber amplifier end-cap.

Photo-induced SNAP: fabrication, trimming, and tuning of microresonator chains.

We introduce multiple series of uncoupled and coupled surface nanoscale axial photonics (SNAP) microresonators along the 30 micron diameter germanium-doped photosensitive silica optical fiber and demonstrate their permanent trimming and temporary tuning with a CO2 laser and a wire heater. Hydrogen loading allows us to increase the introduced variation of the effective fiber radius by an order of magnitude compared to the unloaded case, i.e., to around 5 nm. It is demonstrated that the CO2 laser annealing of the fabricated microresonator chain can be used to modify the fiber radius variation. Depending on the CO2 laser beam power, the microresonator effective radius variation can be increased in depth up to the factor of two or completely erased. In addition, we demonstrate temporary tuning of a microresonator chain with a wire heater.

Scrambled coherent superposition for enhanced optical fiber communication in the nonlinear transmission regime.

Coherent superposition of light waves has long been used in various fields of science, and recent advances in digital coherent detection and space-division multiplexing have enabled the coherent superposition of information-carrying optical signals to achieve better communication fidelity on amplified-spontaneous-noise limited communication links. However, fiber nonlinearity introduces highly correlated distortions on identical signals and diminishes the benefit of coherent superposition in nonlinear transmission regime. Here we experimentally demonstrate that through coordinated scrambling of signal constellations at the transmitter, together with appropriate unscrambling at the receiver, the full benefit of coherent superposition is retained in the nonlinear transmission regime of a space-diversity fiber link based on an innovatively engineered multi-core fiber. This scrambled coherent superposition may provide the flexibility of trading communication capacity for performance in future optical fiber networks, and may open new possibilities in high-performance and secure optical communications.

Scaling the effective area of higher-order-mode erbium-doped fiber amplifiers.

We demonstrate scaling of the effective area of higher-order mode, Er-doped fiber amplifiers. Two Er-doped higher-order mode fibers, one with 3800 µm(2) A(eff) in the LP(0,11) mode, and one with 6000 µm(2) effective area in the LP(0,14) mode, are demonstrated. Output beam profiles show clean higher order modes, and S(2) imaging measurements show low extraneous higher order mode content. CW and pulsed amplifier experiments are reported. Nanosecond pulses are amplified to 0.5 mJ pulse energy with 0.5 MW peak power.

Cladding-pumped erbium-doped multicore fiber amplifier.

A cladding pumped multicore erbium-doped fiber amplifier for simultaneous amplification of 6 channels is demonstrated. Peak gain over 32 dB has been obtained at a wavelength of 1560 nm and the bandwidth measured at 20-dB gain was about 35 nm. Numerical modeling of cladding pumped multicore erbium-doped amplifier was also performed to study the properties of the amplifier. The results of experiment and simulation are found to be in good agreement.

Coupled high Q-factor surface nanoscale axial photonics (SNAP) microresonators.

We experimentally demonstrate series of identical two, three, and five coupled high Q-factor surface nanoscale axial photonics (SNAP) microresonators formed by periodic nanoscale variation of the optical fiber radius. These microresonators are fabricated with a 100 µm period along an 18 µm radius optical fiber. The axial FWHM of these microresonators is 80 µm and their Q-factor exceeds 10(7). In addition, we demonstrate a SNAP microresonator with the axial FWHM as small as 30 µm and the axial FWHM of the fundamental mode as small as 10 µm. These results may potentially enable the dense integration of record low loss coupled photonic microdevices on the optical fiber platform.

Surface nanoscale axial photonics: robust fabrication of high-quality-factor microresonators.

Recently introduced surface nanoscale axial photonics (SNAP) makes it possible to fabricate high-Q-factor microresonators and other photonic microdevices by dramatically small deformation of the optical fiber surface. To become a practical and robust technology, the SNAP platform requires methods enabling reproducible modification of the optical fiber radius at nanoscale. In this Letter, we demonstrate superaccurate fabrication of high-Q-factor microresonators by nanoscale modification of the optical fiber radius and refractive index using CO2 laser and UV excimer laser beam exposures. The achieved fabrication accuracy is better than 2 Å in variation of the effective fiber radius.

A higher-order-mode erbium-doped-fiber amplifier.

We demonstrate the first erbium-doped fiber amplifier operating in a single, large-mode area, higher-order mode. A high-power, fundamental-mode, Raman fiber laser operating at 1480 nm was used as a pump source. Using a UV-written, long-period grating, both pump and 1564 nm signal were converted to the LP(0,10) mode, which had an effective area of 2700 microm(2) at 1550 nm. A maximum output power of 5.8 W at 1564 nm with more than 20 dB of gain in a 2.68 m long amplifier was obtained. The mode profile was undistorted at the highest output power.

Raman fiber laser with 81 W output power at 1480 nm.

We demonstrate a Raman fiber laser with an operating wavelength of 1480 nm and record output power of 81 W. High-power operation is enabled by a long-period grating used to frustrate backward lasing at the Stokes wavelength in the Yb-doped fiber amplifier. A cascaded Raman fiber with a long-wavelength fundamental mode cutoff enables efficient multiple Stokes scattering from 1117 to 1480 nm while preventing further unwanted scattering to 1590 nm.

Optically driven deposition of single-walled carbon-nanotube saturable absorbers on optical fiber end-faces.

Optical radiation propagating in a fiber is used to deposit commercially available, single-walled carbon nanotubes on cleaved optical fiber end faces and fiber connectors. Thermophoresis caused by heating due to optical absorption is considered to be a likely candidate responsible for the deposition process. Single-walled carbon nanotubes have a fast saturable absorption over a broad wavelength range, and the demonstrated technique is an extremely simple and inexpensive method for making fiber-integrated, saturable absorbers for passive modelocking of fiber lasers. Pulse widths of 247 fs are demonstrated from an erbium-doped fiber laser operating at 1560 nm, and 137 fs pulses are demonstrated from an amplified Yb-doped fiber laser at 1070 nm.

All-optical switching and multifrequency generation in a dual-core photonic crystal fiber.

We demonstrate all-optical switching at 1550 nm between two weakly coupled cores in a photonic crystal fiber for intensities up to 0.5 TW/cm2. Spectrum analysis at higher intensities reveals that the output was dominated by continuum generation primarily towards shorter wavelengths.

Highly nonlinear near-resonant photodarkening in a thulium-doped aluminosilicate glass fiber.

Permanent photoinduced optical attenuation has been observed in Tm(3+)-doped aluminosilicate glass fibers on exposure to near-resonance mode-locked 1064-nm radiation at 300 K. The rate of this darkening was observed to follow a 4.7 +/- 0.4 power dependence on the 1064-nm intensity. The result shows that absorption of infrared light of moderate intensity can lead to photoionization in rare-earth-doped glass, provided that a multiphoton stepwise excitation channel exists.

Observation of resonant enhancement of photoinduced second-harmonic generation in Tm-doped aluminosilicate glass fibers.

We report a 10(3) increase in efficiency of second-harmonic generation in Tm(3+)-doped aluminosilicate glass fibers when the wavelength of the fundamental beam is tuned to the maximum of the (3)H(6) ? (3)F(4) absorption of Tm(3+) at 785 nm. This result shows the role of resonance enhancement in the nonlinear optical process that is responsible for the formation of the X((2)) grating.

Measurement of erbium confinement in optical fibers: a differential mode-launching technique.

We present a selective mode-launching technique to determine the confinement of erbium in optical fibers. The loss per meter, alpha(lm), of the individual LP(lm) modes (LP(01) and LP(11) at 980 nm) is measured, and the ratio gamma = alpha(01)/alpha(11) is related to the concentration of erbium in the core. We assume a Gaussian diffusion profile for erbium and relate the dependence of gamma on erbium confinement by using exact mode profiles. This technique uses only two sets of measurements and is independent of erbium concentration.

Prechirper to relax the timing restrictions for soliton-dragging logic gates.

The timing restrictions for soliton-dragging logic gates can be relaxed by asymmetrizing the interaction between the orthogonally polarized control and signal pulses. In particular, by prechirping the signal pulse in a normal group-velocity dispersion fiber, we find experimentally that the timing restriction can be loosened from less than 2 pulse widths to over 3.3 pulse widths. For this passive prechirper arrangement the timing restrictions are loosened at the expense of increased minimum switching energy. Soliton-dragging logic gates with a signal prechirper can provide timing restoration as well as logic-level restoration, so that two inverter gates can be cascaded to implement an ultrafast, all-optical pulse regenerator.