We propose a PLC-based multi/demultiplexer (MUX/DEMUX) with a mode conversion function for mode division multiplexing (MDM) transmission applications. The PLC-based mode MUX/DEMUX can realize a low insertion loss and a wide working wavelength bandwidth. We designed and demonstrated a two-mode (LP01 and LP11 modes) and a three-mode (LP01, LP11, and LP21 modes) MUX/DEMUX for use in the C-band.
The characteristics of a multicore fiber with one-ring structure are reviewed. The one-ring structure, which has no center
core, can overcome issues on the hexagonal close-pack structure that is the most popular multicore structure. The onering
structure has flexibility in the number of cores and is unrelated to the core pitch limitation due to cutoff wavelength
lengthening thank to no center core structure. The one-ring structure is effective to suppress the worst case crosstalk that
is crosstalk assuming all cores carry equal signal power. In the case of hexagonal close-pack structure, the worst case
crosstalk of an inner core is 7.8 dB larger than that between two cores. The different worst crosstalk is observed
depending on the number of nearest neighbor cores. The one-ring structure can limit the degradation to 3.0 dB for all
cores. Fabricated 12-core fiber with the one-ring structure based on the simulation realized effective core area of 80 m2
and very low crosstalk less than -40 dB after 100-km propagation.
The limitations of crosstalk and core-to-core distance in step-index multi-core fibers (SI-MCFs) are clarified for long-haul
transmission, and the low-crosstalk MCF structures of trench-assisted MCFs (TA-MCFs) are investigated for
realizing large effective area (Aeff) and high core density, simultaneously, with a limited cladding diameter. It is shown
that the crosstalk between neighboring cores in TA-MCFs can be greatly suppressed even if the Aeff and the cutoff
wavelength are fixed compared with SI-MCFs. In addition, the possibility of MCFs with heterogeneous core
arrangement is considered for transmission fibers and low-crosstalk heterogeneous MCFs with bending radius
insensitive characteristics are investigated.
We characterize coupling between two identical collinear hollow core Bragg fibers, assuming TE01 launching condition. Using multipole method and finite element method we investigate dependence of the beat length between supermodes of the coupled fibers and supermode radiation losses as a function of the inter-fiber separation, fiber core radius and index of the cladding. We established that coupling is maximal when fibers are touching each other decreasing dramatically during the first tens of nanometers of separation. However, residual coupling with the strength proportional to the fiber radiation loss is very long range decreasing as an inverse square root of the inter-fiber separation, and exhibiting periodic variation with inter-fiber separation. Finally, coupling between the TE01 modes is considered in a view of designing a directional coupler. We find
that for fibers with large enough core radii one can identify broad frequency ranges where inter-modal coupling strength exceeds super-mode radiation losses by an order of magnitude, thus opening a possibility of building a directional coupler. We attribute such
unusually strong inter-mode coupling both to the resonant effects
in the inter-mirror cavity as well as a proximity interaction between the leaky modes localized in the mirror.
We characterize coupling between two identical collinear hollow
core Bragg fibers, assuming T01 launching condition. Using multipole method and finite element method we investigate dependence of the beat length between supermodes of the coupled fibers and supermode radiation losses as a function of the
inter-fiber separation, fiber core radius and index of the
cladding. We established that coupling is maximal when fibers are
touching each other decreasing dramatically during the first tens
of nanometers of separation. However residual coupling with the
strength proportional to the fiber radiation loss is very long
range decreasing as an inverse square root of the inter-fiber
separation, and exhibiting periodic variation with inter-fiber
separation. Finally, coupling between the T01 modes is considered in a view of designing a directional coupler. We find that for fibers with large enough core radii one can identify
broad frequency ranges where inter-modal coupling strength exceeds
super-mode radiation losses by an order of magnitude, thus opening
a possibility of building a directional coupler. We attribute such
unusually strong inter-mode coupling both to the resonant effects
in the inter-mirror cavity as well as a proximity interaction
between the leaky modes localized in the mirror.
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