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

Abstract

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.

Continuously wavelength‐tuneable general transmittance function in first‐order fibre multiwavelength filter based on composite combination of wave retarders

“…Previous research on first‐order PDFL multiwavelength filters has mainly focused on using a wave retarder combination (WRC) of an HWR and a QWR placed before each HBF segment to continuously adjust the extra phase retardation ψ of the filter transmittance. Even for PDFL multiwavelength filters utilising composite WRCs, such as a combination of a set of dual QWRs and another set of a QWR and an HWR, only continuous wavelength tuning of flattened or squeezed passbands has been achieved [21−23]. To date, continuous frequency tunability of arbitrarily shaped passbands has not been demonstrated in the first‐order PDFL multiwavelength filter that employs a composite WRC.…”

Wavelength-Tunable First-Order Narrowband Fiber Comb Filter Incorporating All-Quarter-Wave Polarization Transformation

“…Wavelength tunability in zeroth-order PDLS comb filters has been achieved theoretically and experimentally in 2017 by incorporating three types of ordered waveplate combinations, such as a set of a half-wave plate (HWP) and a quarter-wave plate (QWP), a set of a QWP and an HWP, and two QWPs [19,20]. Even in the case of firstorder PDLS comb filters, the wavelength tunability of flat-top [21][22][23] and narrowband [24][25][26] comb spectra has been explored until recently using composite waveplate combinations of HWPs and QWPs. However, because it is relatively complex to convert a given input state of polarization (SOP) to the desired output SOP utilizing two QWPs instead of heterogeneous combinations of a QWP and an HWP, there has been no study of a wavelength-tunable narrowband PDLS comb filter employing polarization controllers homogeneously comprised of QWPs.…”

Wavelength-tunable passband-squeezed polarization-diversified fiber loop comb filter using heterogeneous waveplate combination

“…In terms of a first-order PDFL comb filter with two PMF segments, the continuous wavelength tuning of passband-flattened or -squeezed comb spectra was implemented by employing various combinations of half-wave plates (HWPs) and quarter-wave plates (QWPs) 23 – 27 These WCs adopted in the first-order comb filter also control the effective phase difference between two principal states of polarization of two PMF segments and adjust an extra phase shift ϕ in the filter transmittance function. This phase shift ϕ could be modified from 0 deg to 360 deg by changing the orientation angles (OAs) of the waveplates contained in the filter.…”