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.

Measuring higher-order modes in a low-loss, hollow-core, photonic-bandgap fiber.

We perform detailed measurements of the higher-order-mode content of a low-loss, hollow-core, photonic-bandgap fiber. Mode content is characterized using Spatially and Spectrally resolved (S2) imaging, revealing a variety of phenomena. Discrete mode scattering to core-guided modes are measured at small relative group-delays. At large group delays a continuum of surface modes and core-guided modes can be observed. The LP11 mode is observed to split into four different group delays with different orientations, with the relative orientations preserved as the mode propagates through the fiber. Cutback measurements allow for quantification of the loss of different individual modes. The behavior of the modes in the low loss region of the fiber is compared to that in a high loss region of the fiber. Finally, a new measurement technique is introduced, the sliding-window Fourier transform of high-resolution transmission spectra of hollow-core fibers, which displays the dependence of HOM content on both wavelength and group delay. This measurement is used to illustrate the HOM content as function of coil diameter.

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.

WDM/SDM transmission of 10 x 128-Gb/s PDM-QPSK over 2688-km 7-core fiber with a per-fiber net aggregate spectral-efficiency distance product of 40,320 km·b/s/Hz.

We demonstrate 2688-km multi-span transmission using wavelength-division multiplexing (WDM) of ten 50-GHz spaced 128-Gb/s PDM-QPSK signals, space-division multiplexed (SDM) in a low-crosstalk 76.8-km seven-core fiber, achieving a record net aggregate per-fiber-spectral-efficiency-distance product of 40,320 km·b/s/Hz. The demonstration was enabled by a novel core-to-core signal rotation scheme implemented in a 7-fold, synchronized recirculating loop apparatus.

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.

112-Tb/s space-division multiplexed DWDM transmission with 14-b/s/Hz aggregate spectral efficiency over a 76.8-km seven-core fiber.

We describe a new multicore fiber (MCF) having seven single-mode cores arranged in a hexagonal array, exhibiting low crosstalk among the cores and low loss across the C and L bands. We experimentally demonstrate a record transmission capacity of 112 Tb/s over a 76.8-km MCF using space-division multiplexing and dense wavelength-division multiplexing (DWDM). Each core carries 160 107-Gb/s polarization-division multiplexed quadrature phase-shift keying (PDM-QPSK) channels on a 50-GHz grid in the C and L bands, resulting in an aggregate spectral efficiency of 14 b/s/Hz. We further investigate the impact of the inter-core crosstalk on a 107-Gb/s PDM-QPSK signal after transmitting through the center core of the MCF when all the 6 outer cores carry same-wavelength 107-Gb/s signals with equal powers, and discuss the system implications of core-to-core crosstalk on ultra-long-haul transmission.

Amplification and noise properties of an erbium-doped multicore fiber amplifier.

A multicore erbium-doped fiber (MC-EDF) amplifier for simultaneous amplification in the 7-cores has been developed, and the gain and noise properties of individual cores have been studied. The pump and signal radiation were coupled to individual cores of MC-EDF using two tapered fiber bundled (TFB) couplers with low insertion loss. For a pump power of 146 mW, the average gain achieved in the MC-EDF fiber was 30 dB, and noise figure was less than 4 dB. The net useful gain from the multicore-amplifier, after taking into consideration of all the passive losses, was about 23-27 dB. Pump induced ASE noise transfer between the neighboring channel was negligible.

1.12-Tb/s 32-QAM-OFDM superchannel with 8.6-b/s/Hz intrachannel spectral efficiency and space-division multiplexed transmission with 60-b/s/Hz aggregate spectral efficiency.

We demonstrate the generation of a 1.12-Tb/s superchannel based on coherent optical orthogonal frequency-division multiplexing with polarization-division multiplexed 32-QAM subcarriers, achieving a net intrachannel-spectral-efficiency (ISE) of 8.6 b/s/Hz. Using space-division multiplexing (SDM), we transmit this superchannel over a 76.8-km low-crosstalk multi-core-fiber (MCF) with a record aggregate ISE of 60 b/s/Hz per fiber. We also discuss the impact of core-to-core crosstalk on transmission performance, as well as future perspectives of MCF-based SDM transmission.

Surface nanoscale axial photonics.

Dense photonic integration promises to revolutionize optical computing and communications. However, efforts towards this goal face unacceptable attenuation of light caused by surface roughness in microscopic devices. Here we address this problem by introducing Surface Nanoscale Axial Photonics (SNAP). The SNAP platform is based on whispering gallery modes circulating around the optical fiber surface and undergoing slow axial propagation readily described by the one-dimensional Schrödinger equation. These modes can be steered with dramatically small nanoscale variation of the fiber radius, which is quite simple to introduce in practice. Extremely low loss of SNAP devices is achieved due to the low surface roughness inherent in a drawn fiber surface. In excellent agreement with the developed theory, we experimentally demonstrate localization of light in quantum wells, halting light by a point source, tunneling through potential barriers, dark states, etc. This demonstration has intriguing potential applications in filtering, switching, slowing light, and sensing.

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.

Seven-core multicore fiber transmissions for passive optical network.

We design and fabricate a novel multicore fiber (MCF), with seven cores arranged in a hexagonal array. The fiber properties of MCF including low crosstalk, attenuation and splice loss are described. A new tapered MCF connector (TMC), showing ultra-low crosstalk and losses, is also designed and fabricated for coupling the individual signals in-and-out of the MCF. We further propose a novel network configuration using parallel transmissions with the MCF and TMC for passive optical network (PON). To the best of our knowledge, we demonstrate the first bi-directional parallel transmissions of 1310 nm and 1490 nm signals over 11.3-km of seven-core MCF with 64-way splitter for PON.

Visible continuum generation using a femtosecond erbium-doped fiber laser and a silica nonlinear fiber.

Supercontinuum extending to visible wavelengths is generated in a hybrid silica nonlinear fiber pumped at 1560 nm by a femtosecond, erbium-doped fiber laser. The hybrid nonlinear fiber consists of a short length of highly nonlinear, germano-silicate fiber (HNLF) spliced to a length of photonic crystal fiber (PCF). A 2 cm length of HNLF provides an initial stage of continuum generation due to higher-order soliton compression and dispersive wave generation before launching into the PCF. The visible radiation is generated in the fundamental mode of the PCF.

Demonstration of bend-induced nonlinearities in large-mode-area fibers.

We present what we believe to be the first direct measurements of enhanced nonlinearities in large-mode-area fibers due to bend induced reductions in effective area. Both Raman scattering and self-phase modulation are observed to increase in tightly coiled fibers. The measured increase in nonlinearity compares well with predictions from simulations of the modal effective area.

SBS gain efficiency measurements and modeling in a 1714 mum(2) effective area LP(08) higher-order mode optical fiber.

The stimulated Brillouin scattering (SBS) gain efficiencies were measured in the LP(08) and LP(01) modes of a higher-order-mode optical fiber. Gain efficiencies C(B) of 0.0085 and 0.20 (m-W)(-1) were measured for the LP(08) and LP(01) modes at 1083 nm, respectively. C(B) is inversely proportional to the optical effective area Aeff and the same core-localized acoustic phonon seeds the SBS process in each case. An acoustic modal analysis and a distributed phenomenological model are presented to facilitate the data analysis and interpretation. The LP(08) mode exhibits a threshold powerlength product of 2.5 kW-m.

Probing optical microfiber nonuniformities at nanoscale.

We demonstrate a novel, simple, and comprehensive method for probing optical microfiber surface and bulk distortions with subnanometer accuracy. The method employs a regular optical fiber as a probe that slides along a microfiber transmitting the fundamental mode. The fraction of radiation power absorbed in the probe depends on the local distribution of the mode propagating in the microfiber. From the measured variation of the absorbed power, we determine the variation of the effective microfiber radius, which takes into account both the microfiber radius and refractive index variations. Furthermore, we verify the cylindrical symmetry of the microfiber nonuniformities by probing the microfiber from different sides. These results explain observed transmission losses in silica microfibers and open broad opportunities for microfiber investigation.

Distributed suppression of stimulated Raman scattering in an Yb-doped filter-fiber amplifier.

Suppression of stimulated Raman scattering (SRS) is demonstrated in a cladding-pumped fiber amplifier. The Yb-doped amplifier fiber design incorporates a high-index ring that resonantly couples SRS wavelengths out of the gain material, thus filtering the gain. Modeling shows that fiber asymmetry plays an important role in the filtering spectrum.