When few-mode fibers are employed in mode-division multiplexing (MDM), mode coupling between the propagation modes must be suppressed. In this study, the impulse response for a two-mode fiber (TMF) ...is theoretically described to estimate the mode coupling in the fiber and at a splice point. We then propose a technique for measuring the mode-coupling coefficient in a TMF based on the impulse response technique. The mode-coupling behavior in a fiber and at splice points is measured experimentally using the proposed technique for several fabricated TMFs. We clarify the relationship between the effective-index difference Δ n eff between LP 01 and LP 11 modes and the mode-coupling coefficient h for our fabricated TMFs.
A novel technique is proposed for measuring the longitudinal fiber parameters of multi-core fiber (MCF). The mode field diameter (MFD)of a fiber link composed of MCF is successfully estimated with a ...modified optical time domain reflectometer (OTDR). The measurement accuracy of the MFD distribution is revealed by simulation as a function of the mode coupling coefficient. It is also shown that the relative-index difference and chromatic dispersion of MCF can be estimated with the present technique.
We propose two mode optical fibers (TMFs) with minimally low differential modal delay (DMD) slope which are suitable for wavelength division multiplexing and multiple input multiple output (MIMO) ...combined transmission system. We designed and fabricated three different kinds of TMF, nearly zero-DMD (zTMF), positive-DMD (pTMF) and negative-DMD (nTMF) with a graded index core and a depressed inner cladding. We confirmed that the fabricated zTMF has DMD of below 15 ps/km in the C band and the fabricated pTMF and nTMF have the same degree of effective areas. We also confirmed that a DMD compensation line with a length of 100 km composed of pTMF and nTMF can successfully achieve the best properties of low DMD in the C + L band and low mode conversion.
Copper plates were exposed under sheltered outdoor conditions for up to one year, starting in September 2001 in Musashino City, Tokyo, a suburban area. Following various periods of exposure, the ...patinas on the plates were characterized to investigate their evolution by using X-ray fluorescence analysis, X-ray diffraction, field emission scanning electron microscopy, and glow discharge optical emission spectroscopy. The difference in the roles of sulfur and chlorine in the early stages of copper patination were identified by analyzing the depth profiles of these two elements. Sulfur was found on top of the patina as cupric sulfates such as posnjakite (Cu
4SO
4(OH)
6
·
H
2O) or brochantite (Cu
4SO
4(OH)
6). Brochantite appeared only after 12 months of exposure. In contrast, chlorine was found on the surface after only one month of exposure. It gradually penetrated the patina as the exposure period lengthened, forming copper chloride complexes. Chloride ions accumulated at the patina/copper interface, forming nantokite (CuCl), which promoted corrosion.
An optimized two-mode optical fiber (TMF) with the graded index (GI) profile is designed and fabricated. We clarify an appropriate region of GI-TMF satisfying DMD = 0 ps/km, the large effective area ...A(eff), and the low bending loss for LP(11) at 1550 nm. According to our fiber design, GI-TMF is successfully fabricated to have the large effective area A(eff) of 150 μm(2) for LP(01) mode, and low DMD below 36 ps/km including zero in the C-band. We expect that our design GI-TMF is suitable for MDM and can reduce MIMO-DSP complexity.
We propose a two-mode optical fiber (TMF) with a low sensitivity of differential modal group delay (DMD) to change of the core radius and the refractive index of the core in the index profile which ...are major factors for DMD deviation. This was done to achieve high reproducibility of fiber fabrication. The proposed TMF has a graded index (GI) core and a depressed inner cladding, and we optimize structural parameters. We fabricated different kinds of TMFs to confirm the low DMD sensitivity of our proposed fiber. The fabricated TMF showed that the DMD sensitivity to changes in core radius of the TMF was approximately 8 ps/km/μm which is 98% smaller than that of a GI-TMF without a depressed inner cladding.
A two-beam interferometer (TBI) with a two-mode fiber (TMF) as a dispersive medium in one arm and air in the other provides evidence of interference related to the complex degree of coherence
γ
. A ...TMF with a low differential group delay (DGD) is used to measure the interference effect, since the overlapping of each individual mode at the output of a TMF is easily and artificially created in the vicinity of the zero DGD wavelength. When
γ
01
and
γ
11
, respectively, are the complex degrees of coherence for the interferences between the
LP
01
and
LP
11
modes propagating through a TMF and a wave traversing air-path, the interference effect can be verified using the relationship
|
γ
|
2
=
|
γ
01
+
γ
11
|
2
. The experiments are carried out using a low coherence source and three kinds of TMFs with zero DGD wavelengths around 1550 nm. It is clearly observed that
|
γ
|
2
-response waveforms have oscillatory structures due to the interference between
γ
01
and
γ
11
. A
|
γ
|
2
-response measurement employing the TBI reveals that the theoretically obtained
|
γ
|
2
-curves well reflect
|
γ
|
2
-curve obtained experimentally for a temporally overlapped wave composed of the two modes. To the best of our knowledge, this is the first experimental demonstration of the interference between complex degrees of coherence.
A mode-unbundled reconfigurable add/drop multiplexer (ROADM), composed of a fiber-based mode-multiplexer/demultiplexer pair and a multiport microelectromechanical systems switch, is proposed and ...experimentally characterized for higher data granularity in mode-division multiplexing (MDM) deployment of future metro area networks (MAN). For enabling mode-unbundling transmission, crosstalk reduction through bidirectional mode assignment is adopted. Finally, a 62-km MDM-MAN ring, composed of two mode-unbundled ROADMs and few-mode fiber spans, is experimentally demonstrated by taking advantage of bidirectionally mode assigned 40 Gb/s, 16-QAM signals.
The chromatic dispersion of the LP
11
mode in a few-mode fiber with low differential group delay is evaluated experimentally. A differential group delay of less than 100 ps/km around 1550 nm can be ...evaluated with the modal interferometer method. The white-light interferometric method confirms that the LP
11
mode is behind the LP
01
mode in the 1300–1600 nm wavelength region. The difference between the chromatic dispersion values of the two modes is less than 0.5 ps/km/nm, which means that the optical pulse spreading characteristics of the LP
11
mode are similar to those of the LP
01
mode for fibers with depressed claddings.
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