G. Lopez-Galmiche

Visible supercontinuum generation in a graded index multimode fiber pumped at 1064 nm.

We observe efficient supercontinuum generation that extends into the visible spectral range by pumping a low differential mode group delay graded index multimode fiber in the normal dispersion regime. For a 28.5 m long fiber, the generated spectrum spans more than two octaves, starting from below 450 nm and extending beyond 2400 nm. The main nonlinear mechanisms contributing to the visible spectrum generation are attributed to multipath four-wave mixing processes and periodic spatio-temporal breathing dynamics. Moreover, by exploiting the highly multimodal nature of this system, we demonstrate versatile generation of visible spectral peaks in shorter fiber spans by altering the launching conditions. A nonlinearly induced mode cleanup was also observed at the pump wavelength. Our results could pave the way for high brightness, high power, and compact, multi-octave continuum sources.

Modal analysis of antiresonant hollow core fibers using S 2 imaging

We analyze the higher-order core mode content in various designs of antiresonant hollow core fibers using spatially and spectrally resolved imaging. Hollow core fibers have great potential for a variety of applications, and understanding their mode content is crucial for many of these. Two different designs of hollow core fibers are considered, the first with eight nontouching rings and the second with eight touching rings forming a closed boundary core. The mode content of each fiber is measured as a function of length and bending diameter. Low amounts of higher-order modes were found in both hollow core fibers, and mode specific and bending-dependent losses have been determined. This study aids in understanding the core modes of hollow core fibers and possible methods of controlling them.

Six spatial modes photonic lanterns

Low-loss all-fiber mode selective photonic-lanterns capable of exciting six spatial fiber modes (4 LP modes) are demonstrated. Mode field profile characterization of photonic lanterns using both step and graded index fibers is presented.

Mode-selective amplification in a large mode area Yb-doped fiber using a photonic lantern

We demonstrate selective spatial mode amplification in a few mode, double-clad Yb-doped large mode area (LMA) fiber, utilizing an all-fiber photonic lantern. Amplification to multi-watt output power is achieved while preserving high spatial mode selectivity. We observe gain values of over 12 dB for all modes: LP01, LP11a, and LP11b, when amplified individually. Additionally, we investigate the simultaneous amplification of LP01+LP11a and LP11a+LP11b, and the resultant mode competition. The proposed architecture allows for the reconfigurable excitation of spatial modes in the LMA fiber amplifiers, and represents a promising method that could enable dynamic spatial mode control in high power fiber lasers.

Few-mode erbium-doped fiber amplifier with photonic lantern for pump spatial mode control

We demonstrate a few-mode erbium-doped fiber amplifier employing a mode-selective photonic lantern for controlling the modal content of the pump light. Amplification of six spatial modes in a 5 m long erbium-doped fiber to ∼6.2  dBm average power is obtained while maintaining high modal fidelity. Through mode-selective forward pumping of the two degenerate LP21 modes operating at 976 nm, differential modal gains of <1  dB between all modes and signal gains of ∼16  dB at 1550 nm are achieved. In addition, low differential modal gain for near-full C-band operation is demonstrated.

Bi-directional pump configuration for increasing thermal modal instabilities threshold in high power fiber amplifiers

We present a time dependent computer model for modal instabilities (MI) in high power fiber amplifiers based on beam propagation method. Three regimes of temporal dynamics that are characteristic of the transfer of energy between the fundamental mode and higher order mode are captured and applied to predicting the threshold of these instabilities in absence of any frequency offset between the interfering modes. Simulation results show an increase of the instabilities threshold by a factor of approximately %30 in the case of bi-directional pump scheme with respect to the forward pump configuration. Furthermore, we estimated the MI threshold applying a coupled-mode model of thermally induced instabilities which also takes account of gain saturation to its first order approximation, and obtained reasonably good agreement with respect to our beam propagation simulation results.

Gain-controlled erbium-doped fiber amplifier using mode-selective photonic lantern

For the first time, we demonstrate the implementation of a core pumped few mode erbium amplifier utilizing a mode selective photonic lantern for spatial modal control of the pump light. This device is able to individually amplify the first six fiber modes with low differential modal gain. In addition, we obtained differential modal gain lower than 1 dB and signal gain of approximately 16.17 dB at λs = 1550 nm through forward pumping the LP21 modes at λp = 976 nm.

Asymmetric Very Large Mode Area Fiber with Enhanced Higher Order Mode Delocalization

A novel very-large-mode-area asymmetric rod-type fiber was fabricated and experimentally characterized. The fiber supports effective and robust single-mode operation for a core diameter of 66μm making it attractive for high power amplifier systems.

Six mode erbium-doped fiber amplifier using mode selective photonic lantern

We demonstrate a six-mode erbium doped fiber amplifier incorporating a photonic lantern for modal gain control. Signal gains >20 dB and differential modal gain <3 dB were obtained through mode selective pumping using LP21 mode.