Abstract:In this paper a polarization-independent all-fiber multiwavelength-switchable filter based on a polarization-diversity loop configuration is newly proposed. The proposed apparatus consists of a polarization beam splitter, high birefringence fibers, and polarization controllers. Our theoretical analysis shows that the apparatus exhibits unique feature which allows it to operate as a polarization-independent multiwavelength periodic filter with a good channel isolation and to make its channel wavelength switchab… Show more
“…Basically, in polarization-interference-based comb filters, an interference fringe is created by the phase difference Γ (=2 πBL / λ ) between two orthogonal polarization modes of PMF, where B , L , and λ are the PMF birefringence, PMF length, and wavelength in vacuum, respectively. This fringe spectrum can be shifted by giving an additional phase difference of 0 to 2 π to this phase difference, that is, varying the effective birefringence of PMF, through the use of some waveplates 23 . Figure 1 Schematic illustrations of ( a ) proposed filter, ( b ) optical propagation paths of input beam introduced into filter, and ( c ) equivalent arrangement of birefringent elements for continuous tuning of passband-flattened transmission spectrum.…”
Section: Principles Of Operationmentioning
confidence: 99%
“…Numerous efforts have been made to provide a comb filter with wavelength tunability by incorporating a Sagnac birefringence loop (SBL) 8 , 9 , a double-loop Mach-Zehnder interferometer (MZI) 10 – 12 , a Lyot-type birefringence filter 1 , 13 , 14 , fiber gratings 15 , 16 , and a polarization-diversified loop structure (PDLS) 17 – 20 . Among various approaches, comb filters based on the PDLS 21 , 22 , which is constructed using a polarization beam splitter (PBS), have great advantages in terms of effective and flexible switching or tuning capability of their passbands 17 – 20 , 23 . That is partly because an SBL-based comb filter, which uses a directional coupler, suffers from degradation in extinction ratio (ER) during its passband tuning 8 , 9 , 24 .…”
Continuous wavelength tuning of optical comb filters, which is an essential functionality for flexible signal processing in reconfigurable optical systems, has been challenging in high order filter structures with two birefringent elements (BEs) or more due to cumbersomeness in finding a combination of waveplates and BEs and complexity in determining their individual azimuthal orientations. Here, we propose a continuously tunable polarization-independent passband-flattened fiber comb filter with two BEs using a polarization-diversified loop structure for the first time. The proposed filter consists of a polarization beam splitter and two groups of a half-wave plate, quarter-wave plate, and polarization-maintaining fiber (PMF). The azimuthal orientation of PMF in the second group is fixed as 22.5°. Orientation angle sets of the four waveplates, which can induce an arbitrary phase shift from 0 to 2π in the passband-flattened transmittance function, are found from the filter transmittance derived using Jones matrix formulation. From theoretical spectral analysis, it is confirmed that passband-flattened comb spectra can be continuously tuned. Theoretical prediction is verified by experimental demonstration. Moreover, the wavelength-dependent evolution of the output state of polarization (SOP) of each PMF is investigated on the Poincare sphere, and the relationship between wavelength tuning and SOP evolution is also discussed.
“…Basically, in polarization-interference-based comb filters, an interference fringe is created by the phase difference Γ (=2 πBL / λ ) between two orthogonal polarization modes of PMF, where B , L , and λ are the PMF birefringence, PMF length, and wavelength in vacuum, respectively. This fringe spectrum can be shifted by giving an additional phase difference of 0 to 2 π to this phase difference, that is, varying the effective birefringence of PMF, through the use of some waveplates 23 . Figure 1 Schematic illustrations of ( a ) proposed filter, ( b ) optical propagation paths of input beam introduced into filter, and ( c ) equivalent arrangement of birefringent elements for continuous tuning of passband-flattened transmission spectrum.…”
Section: Principles Of Operationmentioning
confidence: 99%
“…Numerous efforts have been made to provide a comb filter with wavelength tunability by incorporating a Sagnac birefringence loop (SBL) 8 , 9 , a double-loop Mach-Zehnder interferometer (MZI) 10 – 12 , a Lyot-type birefringence filter 1 , 13 , 14 , fiber gratings 15 , 16 , and a polarization-diversified loop structure (PDLS) 17 – 20 . Among various approaches, comb filters based on the PDLS 21 , 22 , which is constructed using a polarization beam splitter (PBS), have great advantages in terms of effective and flexible switching or tuning capability of their passbands 17 – 20 , 23 . That is partly because an SBL-based comb filter, which uses a directional coupler, suffers from degradation in extinction ratio (ER) during its passband tuning 8 , 9 , 24 .…”
Continuous wavelength tuning of optical comb filters, which is an essential functionality for flexible signal processing in reconfigurable optical systems, has been challenging in high order filter structures with two birefringent elements (BEs) or more due to cumbersomeness in finding a combination of waveplates and BEs and complexity in determining their individual azimuthal orientations. Here, we propose a continuously tunable polarization-independent passband-flattened fiber comb filter with two BEs using a polarization-diversified loop structure for the first time. The proposed filter consists of a polarization beam splitter and two groups of a half-wave plate, quarter-wave plate, and polarization-maintaining fiber (PMF). The azimuthal orientation of PMF in the second group is fixed as 22.5°. Orientation angle sets of the four waveplates, which can induce an arbitrary phase shift from 0 to 2π in the passband-flattened transmittance function, are found from the filter transmittance derived using Jones matrix formulation. From theoretical spectral analysis, it is confirmed that passband-flattened comb spectra can be continuously tuned. Theoretical prediction is verified by experimental demonstration. Moreover, the wavelength-dependent evolution of the output state of polarization (SOP) of each PMF is investigated on the Poincare sphere, and the relationship between wavelength tuning and SOP evolution is also discussed.
“…They finally propagate again into the 3-dB coupler and interfere at the output end. Therefore, the transmission of the Sagnac can be described as follows, 9 I out ␣͑I cw + I ccw ͕͒1 + cos͓␦͔͖͑͒, ͑1͒…”
We report the two-stage single-pump configuration of an erbium-doped fiber amplifier, in which a Sagnac interferometer is introduced to reduce the most important contribution of amplified spontaneous emission ͑ASE͒ noise, providing significant improvement on the amplifier performance. A Sagnac interferometer, made from a highbirefringence fiber loop, is included between the first and second stages. It is designed to provide transmittance with a period of 46 nm that allows us to adjust the minimum transmission around 1530 nm ͑peak of ASE noise͒ and maximum transmission at 1550 nm ͑signal wavelength͒. For optimizing the configuration, we measure the erbium-doped fiber parameters and simulate the amplification of the signal along the fiber. In the experiment, a significant absorption coefficient for pump and signal is found. The absorption looks to be too strong for the background absorption, and we suppose that it may be caused at least partly by excitedstate absorption ͑ESA͒. Including the absorption coefficient allows very good correspondence between simulation and experiment. Experimental results show that with a simple configuration, we obtain up to 53-dB amplification with only 73 mW of pump power.
“…Polarization splitters, as an important kind of components in optical systems, can split one light beam into two light beams in orthogonal polarization states, and have bright prospects of applications in optical communication systems, optical fiber sensing system and so on [1,2]. The dual-core fibers are usually used as polarization splitter since a polarization splitter based on a dual elliptical cores optical fiber was demonstrated in 1990 [3].…”
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