First demonstration and detailed characterization of a multimode amplifier for space division multiplexed transmission systems

Abstract

We present the first demonstration of a multimode (two mode-group) erbium-doped fiber amplifier for Space Division Multiplexed (SDM) applications and demonstrate various design and performance features of such devices. In particular we experimentally demonstrate that differential modal gains can be controlled and reduced both by fiber design and control of the pump field distribution. Using a suitably designed fiber we demonstrate simultaneous modal gains of ~20 dB for different pair-wise combinations of spatial and polarization modes in an EDFA supporting amplification of 6 distinct modes.

Few-mode EDFA Supporting 5 Spatial Modes with Reconfigurable Differential Modal Gain Control

“…Since the current freespace mode multiplexer scheme suffers from a 3dB excess loss for each mode added to the system, the number of spatial modes was limited to three to keep the signal insertion loss within an acceptable level such that the amplifier can be characterized over a wide range of signal input powers. Moreover based on our previous experimental results on 3-mode EDFA [7], we believe that the orthogonal modes of the LP 11 and LP 21 mode groups will behave similarly. The passive 5MF was then spliced directly to a 6m long ring-doped EDF [8], in which the erbium ions are substantially confined within a ring inside the fiber core to help mitigate the DMG.…”

“…To allow simple but effective modal gain measurement, different wavelengths were chosen for the three different signal channels (for example 1550nm for LP 01 , 1555nm for LP 11 and 1560nm for LP 21 respectively) and a tunable narrow bandpass filter (FWHM=2nm) and a power meter were used to determine the output power and hence gain of the individual channels, similar to the setup described in Ref. [7]. Splice losses of 0.3dB for the LP 01 , 0.8dB for the LP 11 and 1.0dB for the LP 21 modes were measured: the variation being due primarily to mode mismatch between the passive 5MF and active 5M-EDF.…”

Review of Space-Division Multiplexing Technologies in Optical Communications

“…This is different from the usage of an equalizer in the MC amplifier because every mode of the MM-amplifier is coupled with each other. The first trials were conducted for 3-mode EDFAs [99,100,101,102] and Raman amplifier [103]. The WDM coupler was fabricated with FSO by using dichroic mirrors.…”

All fiber components for multimode SDM systems

“…The performance of the device was measured using mode strippers on both sides of the grating and coupling into standard SMF giving 30dB coupling at 1530nm (figure 2). Several of these mode converters were used in the dual mode fiber amplifier experiments [6]. Mechanically tunable gratings offer advantages to provide a good quality LP 11 mode at different wavelengths, give a combination of LP 01 and LP 11 or to switch between the two modes.…”