A wavelength spacing switchable and TUNABLE high‐birefringence fiber loop mirror filter

2022

Micro & Nano Letters

By incorporating the heterogeneous combination of wave retarders, the authors demonstrated a continuously wavelength-tunable passband-flattened fibre multiwavelength filter comprised of a four-port polarization beam splitter (PBS), two equal-length polarizationmaintaining fibre (PMF) segments, one wave retarder combination (WRC) of dual quarter-wave retarders (QWRs), and another WRC of a half-wave retarder (HWR) and a QWR. The former WRC lies before the first PMF segment, and the latter one is located between the two PMF segments. From the theoretically derived filter transmittance, the authors found the orientation angle (OA) sets of the four wave retarders where the additional phase ϕ of the transmittance function could be continuously modified from 0 • to 360 • . For eight OA sets allowing ϕ to increase from 0 • to 315 • by 45 • , the authors calculated the passband-flattened transmission spectrum of the filter and confirmed its redshift by 0.1 nm per set. Then, this theoretical prediction was verified by the experimental implementation of the filter, which clearly indicates the continuous wavelength tuning capability of the proposed filter.

Section: Introductionmentioning

confidence: 99%

Continuously wavelength‐tunable passband‐flattened fibre multiwavelength filter based on heterogeneous combination of wave retarders

2022

Micro & Nano Letters

“…To date, much efforts have been made on fiber comb filters that can process optical signals or block unwanted signals causing crosstalks in wavelength-routed optical networks owing to their simple structure, ease of fabrication, and good fiber compatibility. They can be applied to multiwavelength lasing or switching [1], [2], microwave signal processing [3], [4], optical label switching [5], [6], optical pulse train generation [7], etc. Absolute wavelength tuning of passbands of a comb filter is highly required for extracting or rejecting the desired wavelength component in wavelength-division multiplexed optical systems.…”

Section: Introductionmentioning

confidence: 99%

Polarization-Independent Wavelength-Tunable First-Order Fiber Comb Filter

2019

IEEE Photonics J.

Here, we propose a polarization-independent wavelength-tunable first-order fiber comb filter based on a polarization-diversified loop configuration. The proposed filter is composed of a polarization beam splitter, two equal-length high birefringence fiber (HBF) segments, three half-wave retarders (HWRs), and two quarter-wave retarders (QWRs). Among these five wave retarders (WRs), a group of an HWR and a QWR is located in front of each HBF. The third remaining HWR is positioned after the second HBF segment and utilized to adjust the effective orientation angle of this HBF. On the basis of the filter transmittance derived through Jones formulation, orientation angle sets of the five WRs, which can induce an arbitrary phase shift from 0 to 2π in the transmittance function, are found at both flat-top and narrow band transmission spectra. From theoretical transmission spectra obtained at eight selected orientation angle sets of the five WRs, which cause phase shifts increasing linearly from 0 to 7π/4 by a step of π/4, it is confirmed that the flat-top or narrow band comb spectrum can be continuously tuned by properly controlling the WR orientation angles. Then, this theoretical prediction is verified by experimental demonstration. In particular, the spectral evolution of the output states of polarization (SOPs) of the third HWR, the last one of optical components contained within the polarization-diversified loop, is investigated on the Poincare sphere. The relationship of the passband shape and wavelength tuning with the spectral evolution of the SOP is also discussed.

“…Due to simple design, ease of use, and good fiber compatibility, fiber comb filters have been considered as useful wavelength-selective elements that can be employed to route and process optical signals or block unwanted signals causing crosstalks in dense wavelength-division-multiplexed (DWDM) optical networks. They can also be applied to multiwavelength fiber lasers or waveband sources 1 – 4 , microwave photonic filters 5 , 6 , optical pulse train generation 7 , and so forth. Continuous wavelength tunability of a comb filter is highly beneficial to its efficiency when the filter is involved to select the desired wavelength component or prevent interference between wavelength components in wavelength-routing devices or multiwavelength sources.…”

Section: Introductionmentioning

confidence: 99%

Continuously wavelength-tunable passband-flattened fiber comb filter based on polarization-diversified loop structure

2017

Sci Rep

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.