Polarization-diversity Loop Research Articles

광섬유 빗살 필터의 사분파장 지연기 연속 조합을 이용한 협대역 다파장 스펙트럼의 연속 주파수 조정에 관한 연구

We propose an optical fiber comb filter based on a polarization-diversity loop structure, which can continuously adjust the narrowband multiwavelength spectrum. The proposed comb filter consists of a polarization beam splitter(PBS), a successive combination of quarter-wave retarders(QWRs), a set of a half-wave retarder and a QWR, and two polarization-maintaining fiber(PMF) segments of equal length. For the convenient adjustment of the narrowband multiwavelength spectrum, the successive combination of QWRs was located between the PBS and the first PMF segment. The transmittance function of the proposed filter was theoretically derived using the Jones calculus. Based on the filter transmittance, we theoretically predicted the orientation angle sets of four wave retarders, which allow the extra phase difference φ of the transmittance function to vary from 0˚ to 315˚ with increments of 45˚. Then, the proposed filter successfully demonstrated the predicted results by obtaining ∼0.0915 ㎚ average wavelength shift and a high linearity of 0.99878.

대역 평탄화된 빗살 스펙트럼의 간단한 연속 파장 조정을 위한 이종 파장 지연기 조합 기반 광섬유 1차 빗살 필터에 관한 연구

In this paper, we propose an optical fiber first-order comb filter based on a polarization-diversity loop structure(PDLS), whose passband-flattened comb spectrum can be continuously wavelength-tuned in a convenient way through heterogeneous wave retarder combination. The proposed filter consists of a polarization beam splitter, two equal-length polarization-maintaining fiber(PMF) segments, three quarter-wave retarders(QWRs) and one half-wave retarder(HWR). For convenient wavelength control, we inserted a set of a QWR and an HWR between two PMF segments. Using the filter transmittance theoretically derived with Jones calculus, we found the azimuth angle(AA) sets of four wave retarders, which enable the additional phase difference ø to change from 0° to 360° On the basis of these AA sets, we theoretically calculated passband-flattened transmittance spectra spaced with a wavelength interval of 0.1nm. Then, we experimentally demonstrated theoretical results.

사분파장 편광 변환을 이용한 협대역 다파장 스펙트럼의 연속 파장 조정에 관한 연구

To continuously adjust the wavelength of the narrow band transmission spectrum in a multiwavelength filter based on polarization-diversity loop configuration(PDLC), we harnessed quarter-wave polarization transformation, which was implemented by a combination of four wave retarders. The PDLC-based multiwavelength filter consists of a polarization beam splitter(PBS), two polarization-maintaining fiber(PMF) segments of the same length, one half-wave retarder(HWR), and three quarter-wave retarders(QWRs). By utilizing the filter transmittance derived through the Jones calculus, we found a combination of orientation angles of the four wave retarders, which could induce an extra phase difference φ from 0° to 360° in the narrow band transmittance function. Then the calculated transmission spectrum was obtained from the eight sets of orientation angles combination of the wave retarders, which were selected to make φ vary from 0° to 315° at intervals of 45°. Theoretical prediction results on the continuous wavelength adjustment of narrow band multiwavelength spectrum using quarter-wave polarization transformation were also experimentally validated.

사분파장 편광 변환을 이용하여 파장 조정을 구현한 통과 대역 평탄화된 다파장 필터에 관한 연구

By harnessing quarter-wave polarization transformation, we propose a multiwavelength filter based on polarization-diversity loop configuration, which can continuously adjust the wavelength of the pass-band-flattened transmission spectrum. The proposed filter consists of a polarization beam splitter, two polarization-maintaining fiber segments of the same length, one half-wave retarder, and three quarter-wave retarders. We found a combination of the orientation angles of the four wave retarders, which could induce an extra phase difference φ from 0° to 360° in the pass-band-flattened transmittance function derived using Jones formulation. Then, we implemented the wavelength adjustment of the pass-band-flattened transmission spectrum at a wavelength interval of 0.1nm through the theoretical calculation of transmission spectra. As a result, we experimentally demonstrated the theoretically predicted results by controlling the azimuth angles of the wavelength retarders within the filter.

Frequency-tunable optical fiber passband-squeezed birefringence filter based on quarter-wave polarization conversion

A polarization-diversified loop structure (PDLS) formed by a four-port polarizing beam splitter has been employed to establish the input polarization independence of optical devices. Here we report a PDLS-based optical fiber birefringence filter, which can provide continuous frequency tunability in passband-squeezed comb spectra by harnessing quarter-wave polarization conversion. The birefringence filter is composed of a four-port PBS, two high birefringence fiber (HBF) segments whose lengths are equal, the first polarization controller (PC) comprised of a quarter-wave retarder (QWR) and a half-wave retarder (HWR), which is located in front of the first HBF segment, and a set of two QWRs as the second PC that lies before the second HBF segment. The dual QWRs, chosen for the second PC, are the simplest form of a PC that can convert arbitrary input polarization into desired polarization. The slow axis of the second HBF segment is oriented at 22.5° with respect to the horizontal axis of the PBS. Through the Jones matrix formulation, we derived the sinusoidal passband-squeezed transmittance function of the filter, whose absolute phase (ϕ) should be continuously varied for the contiguous wavelength tuning of filter spectra. Then, using this filter transmittance, we found the possible loci of the orientation angles (OAs) of the four wave retarders as the functions of ϕ. By utilizing the OA loci of the wave retarders, the theoretical passband-squeezed transmission spectra of the filter were calculated for eight equally spaced values of ϕ from 0° to 315° (with an increment of 45°). This theoretical calculation was also verified by measuring the wavelength-tuned passband-squeezed spectra of the fabricated filter. We theoretically and experimentally confirmed that our filter could provide the wavelength tunability of the polarization-independent passband-squeezed comb spectrum by appropriately controlling the OAs of the wave retarders.

Looped Polarization-Insensitive Fiber Optical Parametric Amplifiers for Broadband High Gain Applications

We investigate polarization insensitive fiber optical parametric amplifiers (FOPAs) employing a balanced polarization diversity loop with at least two unidirectional gain fibers. We describe and compare three variants of looped polarization insensitive FOPAs optimized for noise figure, mitigation of nonlinear impairments and their trade-off, respectively. The test scenario consists of amplifying, by up to 14 dB, a set of 21 × 50 GHz-spaced channels including a 35 GBaud PDM-QPSK signal, and evaluating a power of nonlinear crosstalk, noise figure and amplified signal BER for each variant. For the first time we demonstrate a polarization insensitive FOPA amplifying WDM signals with a noise figure as low as 5.8 dB, and a polarization insensitive FOPA with output WDM signal power of 23 dBm. The testing results let us identify likely application scenarios for each looped FOPA variant. We justify potential implementation of polarization-insensitive FOPAs in future optical communication systems by arguing its ability to deliver low noise figure <6 dB for output signal power as high as 29 dBm and to enable polarization insensitive gain for the most prominent single-polarization FOPA achievements realizing ultrawide high gain.

Passband-Flattened Frequency-Tunable Optical Fiber Multiwavelength Filter with Composite Combination of Waveplates.

We propose a passband-flattened frequency-tunable optical multiwavelength filter with a composite combination of waveplates, which is realized by harnessing a polarization-diversified loop structure. The proposed filter comprises a polarization beam splitter (PBS), two polarization-maintaining fiber (PMF) segments of equal length, an ordered waveplate combination (OWC) of a half-wave plate (HWP) and a quarter-wave plate (QWP) before the first PMF segment, and an OWC of a QWP and an HWP before the second PMF segment. The second PMF segment is butt-coupled to one port of the PBS so that its slow axis is oriented at 22.5° for the horizontal axis of the PBS. Based on the filter transmittance derived through the Jones calculus, we found the orientation angle (OA) sets of the four waveplates, which could induce an extra phase shift Φ from 0° to 360° in the passband-flattened transmittance function. From the transmission spectra calculated at the eight selected OA sets, which caused Φ to increase from 0° to 315° by steps of 45°, it was confirmed that the passband-flattened multiwavelength spectrum can be continuously tuned by properly controlling the OAs. This indicates continuous wavelength tunability based on composite OWCs. Then, this theoretical prediction was verified by experimental demonstration.

편광 상이 고리 구조 내 복합 파장판 조합을 이용한 협대역 빗살 스펙트럼의 연속 파장 제어에 관한 연구

In this paper, we propose a novel birefringence filter based on polarization-diversity loop structure(PDLS) for continuous wavelength controlling of narrowband transmission spectrum. This filter consists of a polarization beam splitter(PBS), two high-birefringence fiber(HBF) of the same length, two half-wave plates(HWPs), and two quarter-wave plates(QWPs). We found a combination of the orientation angles of the four waveplates which could induce an additional phase difference φ from 0° to 360° to the narrowband transmittance function by considering the filter transmittance derived from Jones matrices. Then, we experimentally exhibited eight narrowband transmission spectra measured with a channel spacing of ∼0.1nm based on these theoretical calculations. As a result, we verified the effectiveness of the narrowband multiwavelength filter capable of continuously tuning its wavelength position when properly adjusting the combination of the orientation angles.

편광 상이 고리 구조 내 복합 파장판 조합을 이용한 평탄 대역 다파장 스펙트럼의 연속적인 파장 조정에 관한 연구

편광 상이 고리 구조 내 복합 파장판 조합을 이용한 평탄 대역 다파장 스펙트럼의 연속적인 파장 조정에 관한 연구

RFID-Based Dual-Chip Epidermal Sensing Platform for Human Skin Monitoring

Wireless epidermal devices based on Radio frequency Identification (RFID) enable a contactless and non-invasive monitoring of the human body by sampling health parameters directly on the skin. To achieve multi-parametric sensing, while preserving the intrinsic simplicity and the low cost of RFID tags, a dual-chip epidermal device is here proposed. At this purpose a polarization-diversity loop antenna is exploited so that two almost independent current modes are excited. The resulting radiation patterns are both broadside, thus enabling the simultaneous gathering of two independent dataset from the same maximum distance. A 3.5 by 3.5 cm battery-less, flexible and soft prototype provides −13 dBi embedded realized gain with read distances ranging from 0.6m to 1.5m depending on the microchip sensitivity. The electromagnetic performance of the two ports remain similar even when the tag is applied onto rather in-homogeneous body regions. With reference to body temperature monitoring, the device has been experimented in both controlled and real-life environments, demonstrating the possibility of doubling the sensing capabilities of RFID epidermal devices without affecting their size and radiation performances.

Continuously Wavelength-Tunable First-Order Narrowband Fiber Comb Filter Using Composite Combination of Wave Retarders

Here, by harnessing a composite combination of wave retarders, we propose and experimentally demonstrate a first-order narrowband fiber comb filter capable of continuously tuning its wavelength, of which the filter structure is on the fundamental basis of a polarization–diversity loop structure. The demonstrated comb filter consists of a polarizing beam splitter (PBS), two high birefringence fiber (HBF) segments of the same length, an ordered wave retarder combination (WRC) of a quarter-wave retarder (QWR) and a half-wave retarder (HWR) before the first HBF segment, and an ordered WRC of an HWR and a QWR before the second HBF segment. The second HBF segment is butt-coupled to one port of the PBS so that its principal axis should be 22.5° away from the horizontal axis of the PBS. Taking the filter transmittance obtained by Jones calculus into consideration, we found the azimuth orientation angle (AOA) sets of the four wave retarders, which could allow extra phase shifts (ψ’s) ranging from 0° to 360° to be induced in the narrowband transmittance function. From filter transmission spectra calculated according to the AOA sets found above, it is confirmed that the first-order narrowband comb spectrum can be continuously tuned by properly controlling the AOA’s, clearly indicating the continuous wavelength tunability based on a composite combination of ordered wave retarders. This theoretical prediction was verified by actually constructing the proposed filter. Then, it is concluded that our filter employing the composite combination of wave retarders can be continuously frequency-tuned by properly controlling the AOA’s of the wave retarders.

Arbitrary Phase Modulation of General Transmittance Function of First-Order Optical Comb Filter with Ordered Sets of Quarter- and Half-Wave Plates

Here we theoretically and experimentally demonstrated the arbitrary phase modulation of a general transmittance function (GTF) of the first-order optical comb filter based on a polarization-diversity loop structure, which employed two ordered waveplate sets (OWS’s) of a quarter-wave plate (QWP) and a half-wave plate (HWP). The proposed comb filter is composed of a polarization beam splitter (PBS), two equal-length polarization-maintaining fiber (PMF) segments, and two OWS’s of a QWP and an HWP with each set located before each PMF segment. The second PMF segment is butt-coupled to one port of the PBS so that its principal axis should be 22.5° away from the horizontal axis of the PBS. First, we explained a scheme to find four waveplate orientation angles (WOA’s) allowing the phase of a GTF to be arbitrarily modulated, using the way each component of the filter, such as a waveplate or PMF segment, affects its input or output polarization. Then, with the WOA finding method, we derived WOA sets of the four waveplates, which could give arbitrary phase retardations ϕ’s from 0° to 360° to a GTF chosen here arbitrarily. Finally, we showed phase-modulated GTF’s calculated at eight selected WOA sets allowing ϕ’s to be 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°, and then the predicted results were verified by experimentally measured results. It is concluded from the theoretical and experimental demonstrations that the GTF of our filter based on the OWS of a QWP and an HWP can be arbitrarily phase-modulated by properly controlling the WOA’s of the four waveplates.

Tapered Length Dependence of Pressure Sensitivity in Polarimetric Fiber Pressure Sensor Based on Tapered High Birefringence Fiber

Here we investigated the tapered length dependence of the pressure sensitivity in a temperature-independent polarimetric fiber-optic pressure sensor (FPS) based on tapered high birefringence fiber (HBF) and a fiber Bragg grating (FBG) for three different tapered lengths of 200, 300, and 400 $\mu \text{m}$ . The investigation on the tapered length dependence was also done for three different types of HBF including one panda type fiber (PM-1550XP) and two bow-tie type fibers (HB1250T and HB1500). The polarimetric FPS was constructed by incorporating a polarization-diversified loop structure composed of a polarization beam splitter, polarization controllers, and a sensor head comprised of a 10.0-cm-long tapered HBF segment and a 1.8-cm-long FBG. The tapered HBF was used as a birefringence element to create polarization interference (PI). A pressure-induced change in the HBF birefringence leads to the wavelength shift of the PI spectrum. The FBG, which is sensitive to an ambient temperature change but nearly insensitive to a pressure change, was utilized to compensate for the temperature cross-sensitivity of the tapered HBF. From the investigation, the pressure sensitivity of the tapered HBF was found out to be proportional to the tapered length irrespective of the fiber type. Moreover, for the same tapered length, HB1500 showed the largest pressure sensitivity. In consequence, the maximum pressure sensitivity of approximately−35.46 nm/MPa could be obtained using bow-tie type HBF (HB1500) with a tapered length of $400~\mu \text{m}$ . Its adjusted ${R} ^{{{2}}}$ value representing the sensor linearity was measured as ~0.9973 in an applied pressure measurement range of 0–0.5 MPa.

편광상이 고리 기반 광섬유 다파장 필터의 입력 편광으로 제어되는 채널 간격 스위칭에 대한 연구

In this paper, we propose an optical fiber multiwavelength filter based on a polarization-diversified loop (PDL), whose channel spacings (CSs) can be controlled by its input state of polarization (SOP). The PDL-based filter consists of a polarization beam splitter, three half-wave plates (HWPs), a Faraday rotator (FR), and two polarization-maintaining fiber (PMF) segments with equal birefringence and different lengths. At proper orientation angle sets (θ<SUB>h1</SUB>, θ<SUB>h2</SUB>, θ<SUB>h3</SUB>) of the three HWPs, the proposed filter can have its polarization-dependent transmittance, offering the CS-switchable operation realized by switching between two orthogonal input SOPs of linear horizontal polarization (LHP) and linear vertical polarization (LVP). In particular, at a fixed input SOP, a half-period wavelength switching operation, i.e., an interleaving operation, can also be implemented by controlling only one HWP angle (θ<SUB>h1</SUB> or θ<SUB>h3</SUB>). Theoretical prediction was verified by experiments. For orthogonal input SOPs of LHP and LVP, the fabricated PDL-based filter could provide transmission spectra with CSs of ∼0.9 and ∼0.3nm or vice versa at appropriate sets of (θ<SUB>h1</SUB><SUB></SUB>, θ<SUB>h2</SUB>, θ<SUB>h3</SUB>), respectively, and each of the transmission spectra could be interleaved by adjusting only θ<SUB>h1</SUB> or θ<SUB>h3</SUB>.

Polarization-diversified-loop-based optical fiber interleaving filter with polarization-controlled free spectral range

Here we propose an optical fiber interleaving filter based on a polarization-diversified loop (PDL), which can offer a polarization-controlled free spectral range (FSR). The proposed filter consists of a four port polarization beam splitter, two polarization-maintaining fiber (PMF) segments with equal birefringence (B) and different lengths (L and 2L), three half-wave plates (HWPs), and a Faraday rotator. Basically, the PMF segments within the PDL create polarization interference as the birefringence elements of the proposed filter, and the filter can provide different interference comb spectra depending on input polarization due to non-reciprocal polarization rotation caused by a Faraday rotator. For two orthogonal input polarization states, comb spectra of different FSRs or an equal FSR can be obtained, including their interleaved spectra, by controlling the orientation angles (θh1, θh2, θh3) of the three HWPs. More specifically, in a specific set (Set I) of (θh1, θh2, θh3), the FSRs of S1 (∝ 1/BL) and S3 (∝ 1/3BL) can be obtained for input polarization states of linear horizontal polarization (LHP) and linear vertical polarization (LVP), respectively. By varying only θh2 in Set I, which results in a new angle set designated as Set II, S1 can be exchanged with S3. At another set of three HWP angles (, designated as Set III or IV), the comb spectrum of the filter has an FSR of S1 or S2 (∝ 1/2BL) for LHP input, respectively, and this comb spectrum at each set is shifted by half the interference period, i.e., interleaved, for LVP input. In particular, for these FSR switching functions realizable at Sets I-IV, an interleaved version of the two orthogonally polarized comb spectra in each set can be drawn out by adjusting only θh1 or θh3. What is more, in a reverse operation mode with the filter input swapped with its output, four types of filtering operation at Sets I-IV can be reproduced at different four sets (Sets V-VIII) of (θh1, θh2, θh3). This theoretical prediction on the filter operation was experimentally investigated by constructing the filter, and the abovementioned eight types of filtering operation (at Sets I-VIII) were successfully verified.

Universal Wavelength Tuning Scheme for a First-Order Optical Fiber Multiwavelength Filter Based on a Polarization-Diversified Loop Structure.

In this paper, we propose a universal wavelength tuning scheme for a first-order optical fiber multiwavelength filter based on a polarization-diversified loop structure (PDLS), which is comprised of a polarization beam splitter, two sets of a half-wave plate (HWP) and a quarter-wave plate (QWP), and two polarization-maintaining fiber (PMF) segments. First, the polarization conditions, which should be satisfied to continuously tune the absolute wavelength of a transmittance function with an arbitrary transmission spectrum, are explained based on the continuous wavelength tuning mechanism of the flat-top band transmittance, which was previously reported in the PDLS-based passband-flattened first-order multiwavelength filter. Then, by considering the effect of the four waveplates (i.e., two HWPs and two QWPs) and two PMF segments on the output polarization of each element comprising the filter, we suggest a systematic scheme to find the azimuth angles of the four waveplates for continuous wavelength tuning of the arbitrary transmittance function. Three hundred sixty sets of the four waveplate azimuth angles, which give additional phase shifts of 1-360° (with a step of 1°) to an arbitrarily chosen transmittance function, are obtained with the suggested angle finding approach. Wavelength-tuned transmission spectra are displayed at eight waveplate angle sets, which are chosen from among the above angle sets so that they can induce extra phase shifts of 0, 45, 90, 135, 180, 225, 270, and 315° to the original transmittance function. These spectra prove that the proposed scheme can be applied to the wavelength tuning of every transmittance function of the PDLS-based first-order multiwavelength filter.

Tunable Narrowband Fiber Multiwavelength Filter Based on Polarization-Diversified Loop Structure.

In this paper, we propose a wavelength-tunable narrowband fiber multiwavelength filter based on polarization-diversified loop structure. The proposed filter consists of a polarization beam splitter, three half-wave plates (HWPs), two quarter-wave plates (QWPs) and two polarization-maintaining fiber (PMF) segments. The lengths of the two PMF segments are equal with each other. Among the five waveplates within the filter, a pair of an HWP and a QWP and the other pair of an HWP and a QWP are located in front of each PMF segment. The last HWP is placed after the second PMF and used to adjust the effective azimuthal angle of the second PMF. Azimuthal angle sets of the five waveplates, which can give additional phase shifts from 0 to 360° to the narrowband transmittance function derived from the Jones matrix formula, were theoretically found. Narrowband transmission spectra were calculated at eight waveplate angle sets selected among the angle sets derived above, which were designated as sets I, II, III, IV, V, VI, VII, and VIII that induced additional phase shifts from 0 to 315° (step: 45°) in the transmittance function. The calculated multiwavelength spectra clearly show that the narrowband multiwavelength spectrum can be wavelength-tuned by 0.1 nm as the waveplate angle set switches from set I to set VIII. This theoretical prediction was experimentally verified by appropriately controlling the azimuthal angle of each waveplate.

Polarization-Diversity-Loop-Based Optical Fiber Comb Filter with Polarization-Controlled Dual Transmission Channel Spacings.

In this paper, we propose an optical comb filter based on a polarization-diversity loop structure, whose two transmission channel spacings (TCS's) can be alternately switched between two principal axes of the filter by controlling waveplates contained in the filter. The proposed filter consists of a polarization beam splitter (PBS), three half-wave plates (HWPs), one Faraday rotator (FR), and two polarization-maintaining fiber (PMF) segments with different lengths (L and 2L) and equal birefringence (B). As the PMF segments are utilized as birefringence elements, the TCS of the filter is determined by the product of their effective length Le and birefringence B. For an input signal introduced into each principal axis of the filter, Le can be the sum of or difference between the two lengths (L and 2L) of the two PMF segments, that is, L or 3L, resulting in a TCS of S1 or S₂, respectively, according to angular combination of the orientation angles of the three HWPs. At a specific set of the three HWP angles, the proposed filter can create two sinusoidal transmittance functions with different TCS's (S1 and S₂) at the two principal axes, respectively. Also, the two TCS's (S1 and S₂) are switchable with each other depending on three HWP angles for each principal axis. With the fabricated filter, the flexible switching between S1 and S₂ could be successfully implemented for two orthogonally polarized input signals aligned along the two principal axes of the filter by properly controlling the three HWPs, without any modification of the filter configuration.

연속 파장 조절 가능한 편광상이 고리 기반 협대역 복굴절 필터

Here, we present a continuously wavelength-controllable narrowband birefringence filter utilizing polarization-diversity loop. A polarization beam splitter, three half-wave plates, two quarter-wave plates, and two polarization-maintaining fiber with equal length were used to configure the filter. First, the orientation angle sets of the five waveplates that can induce an extra phase difference from 0 to 360° to the narrowband transmittance function derived using Jones matrix formulation were theoretically found. Then, among the found waveplate angle sets, transmission spectra were calculated for eight waveplate angle sets(Sets I－VIII) that can add extra phase differences from 0 to 315° with a step of 45° to the narrowband transmittance function. In the calculated transmission spectra, when the waveplate angle set was sequentially switched from Set I to Set VIII, the wavelength of the narrowband transmission spectrum could be shifted by 0.1nm. In particular, the theoretically predicted wavelength controllability of the filter was experimentally demonstrated.

편광상이 고리 구조 기반 1차 광섬유 복굴절 필터의 임의 스펙트럼 파장 연속 조절을 위한 편광 조건 연구

편광상이 고리 구조 기반 1차 광섬유 복굴절 필터의 임의 스펙트럼 파장 연속 조절을 위한 편광 조건 연구