Pub Date : 2025-12-11DOI: 10.1109/JLT.2025.3641061
{"title":"Journal of Lightwave Technology Information for Authors","authors":"","doi":"10.1109/JLT.2025.3641061","DOIUrl":"https://doi.org/10.1109/JLT.2025.3641061","url":null,"abstract":"","PeriodicalId":16144,"journal":{"name":"Journal of Lightwave Technology","volume":"43 23","pages":"C3-C3"},"PeriodicalIF":4.8,"publicationDate":"2025-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=11297877","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145729406","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Temperature sensing has seen significant advancements across modern scientific applications. While fiber-optic temperature sensors (FOTS) offer multiple advantages, achieving a synergistic combination of cost-effectiveness, compact dimensions, and high integration remains a critical challenge for practical implementations. This work presents an artificial intelligence (AI)-driven solution featuring a miniaturized, cost-efficient fiber-optic leaky-mode temperature speckle sensor with integrated optoelectronic transceiver functionality. The system employs a fiber microsphere at the emission end for light source coupling and collection, while a fiber taper at the detection end facilitates modal leakage from the fiber core. Temperature-sensitive material integrated within the sensing region modulates the refractive index (RI) in response to environmental temperature variations, thereby altering the specklegram characteristics of the leaked modes. A convolutional vision transformer (ConViT)-based regression model was trained to establish quantitative mapping between speckle image features and temperature measurements. Comparative analysis demonstrated superior performance against convolutional neural network (CNN), vision transformer (Vit), and modified CNN architectures, achieving a median absolute error (MedAE) of 0.256 °C. This integrated approach effectively addresses the critical triad of cost reduction, miniaturization, and functional integration, potentially advancing the development of fiber-optic thermometry.
{"title":"Portable Integrated Transceiver Architecture for Low-Cost Temperature Sensing","authors":"Yin Liu;Man Yu;Kai Zhang;Yifan Men;Yuzhuo Li;Jia You;Xisheng Li;Hongbing Chen","doi":"10.1109/JLT.2025.3641889","DOIUrl":"https://doi.org/10.1109/JLT.2025.3641889","url":null,"abstract":"Temperature sensing has seen significant advancements across modern scientific applications. While fiber-optic temperature sensors (FOTS) offer multiple advantages, achieving a synergistic combination of cost-effectiveness, compact dimensions, and high integration remains a critical challenge for practical implementations. This work presents an artificial intelligence (AI)-driven solution featuring a miniaturized, cost-efficient fiber-optic leaky-mode temperature speckle sensor with integrated optoelectronic transceiver functionality. The system employs a fiber microsphere at the emission end for light source coupling and collection, while a fiber taper at the detection end facilitates modal leakage from the fiber core. Temperature-sensitive material integrated within the sensing region modulates the refractive index (RI) in response to environmental temperature variations, thereby altering the specklegram characteristics of the leaked modes. A convolutional vision transformer (ConViT)-based regression model was trained to establish quantitative mapping between speckle image features and temperature measurements. Comparative analysis demonstrated superior performance against convolutional neural network (CNN), vision transformer (Vit), and modified CNN architectures, achieving a median absolute error (MedAE) of 0.256 °C. This integrated approach effectively addresses the critical triad of cost reduction, miniaturization, and functional integration, potentially advancing the development of fiber-optic thermometry.","PeriodicalId":16144,"journal":{"name":"Journal of Lightwave Technology","volume":"44 4","pages":"1588-1595"},"PeriodicalIF":4.8,"publicationDate":"2025-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146116858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-08DOI: 10.1109/JLT.2025.3641699
Suh-young Kwon;Janghyun Ryu;Taeho Woo;Jaesun Kim;Ju Han Lee
This work systematically investigates the primary factors affecting birefringence in a 20/400 µm polarization-maintaining large-mode-area double clad fiber (PLMA DCF), which is extensively used in high-power laser applications. The fiber structure comprises a pure SiO2 cladding, a GeO2-doped core, and B2O3-doped stress-applying parts (SAPs). The finite element method (FEM) was utilized to analyze the complex relationships between material characteristics and geometric attributes. Initially, birefringence was evaluated by contrasting ideal circular cross-sections with those of elliptical geometry. The effects of SAP location and diameter on both the distribution of stress and resulting birefringence were quantitatively assessed. Furthermore, the influence of material variation was studied, focusing on the impact of SAP numerical aperture (NA) as it relates to B2O3 concentration. To mitigate deformation stemming from thermal expansion mismatch, the introduction of a Ge-Al-co-doped cap encasing the core was explored. This cap substantially lessened stress disparities between the core and adjacent materials, thereby enhancing mechanical reliability, while maintaining effective birefringence. The results offer actionable guidance for the design optimization of PLMA DCF systems.
{"title":"A Detailed Investigation Into Birefringence Characteristics of a 20/400-µm Polarization Maintaining Large Mode Area Double Clad Fiber Depending on Material and Geometric Properties","authors":"Suh-young Kwon;Janghyun Ryu;Taeho Woo;Jaesun Kim;Ju Han Lee","doi":"10.1109/JLT.2025.3641699","DOIUrl":"https://doi.org/10.1109/JLT.2025.3641699","url":null,"abstract":"This work systematically investigates the primary factors affecting birefringence in a 20/400 µm polarization-maintaining large-mode-area double clad fiber (PLMA DCF), which is extensively used in high-power laser applications. The fiber structure comprises a pure SiO<sub>2</sub> cladding, a GeO<sub>2</sub>-doped core, and B<sub>2</sub>O<sub>3</sub>-doped stress-applying parts (SAPs). The finite element method (FEM) was utilized to analyze the complex relationships between material characteristics and geometric attributes. Initially, birefringence was evaluated by contrasting ideal circular cross-sections with those of elliptical geometry. The effects of SAP location and diameter on both the distribution of stress and resulting birefringence were quantitatively assessed. Furthermore, the influence of material variation was studied, focusing on the impact of SAP numerical aperture (NA) as it relates to B<sub>2</sub>O<sub>3</sub> concentration. To mitigate deformation stemming from thermal expansion mismatch, the introduction of a Ge-Al-co-doped cap encasing the core was explored. This cap substantially lessened stress disparities between the core and adjacent materials, thereby enhancing mechanical reliability, while maintaining effective birefringence. The results offer actionable guidance for the design optimization of PLMA DCF systems.","PeriodicalId":16144,"journal":{"name":"Journal of Lightwave Technology","volume":"44 4","pages":"1512-1521"},"PeriodicalIF":4.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146116924","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-08DOI: 10.1109/JLT.2025.3641117
Ying Zhao;Christopher R. Doerr;Fengyu Liu;Sivagururaman Mahadevan;Fatemeh Ghaedi Vanani;Makoto Takeshita
We present a 425-Gbps/λ dual-polarization (DP) IMDD pluggable transceiver in an OSFP form factor for intra- data-center application scenario. Both DP transmitter (Tx) and receiver (Rx) are monolithically integrated in a silicon photonics (SiPh) chip. The Tx multiplexes two 212.5 Gbps polarization tributaries onto a single wavelength optical carrier, forming a 425-Gbps/λ data stream into the transmission link. The Rx performs a robust polarization tracking based on a proposed fast converging eigenvector-decomposition-based polarization recovery algorithm. Aided by off-the-shelf digital signal processing (DSP) and transimpedance amplifier (TIA) chips, the transceiver demonstrates a real-time 2 × 212.5 Gbps transmission over 1 km single mode fiber (SMF). A stable pre-FEC bit-error ratio (BER) floor of 2 × 10−7 level is obtained in both dynamic polarization scrambling and fiber handling cases. The experiment proves the feasibility that the DP solution is capable of doubling system capacity for short-reach transmission with robust polarization tracking.
{"title":"425-Gbps/λ Dual-polarization IMDD Transceiver","authors":"Ying Zhao;Christopher R. Doerr;Fengyu Liu;Sivagururaman Mahadevan;Fatemeh Ghaedi Vanani;Makoto Takeshita","doi":"10.1109/JLT.2025.3641117","DOIUrl":"https://doi.org/10.1109/JLT.2025.3641117","url":null,"abstract":"We present a 425-Gbps/λ dual-polarization (DP) IMDD pluggable transceiver in an OSFP form factor for intra- data-center application scenario. Both DP transmitter (Tx) and receiver (Rx) are monolithically integrated in a silicon photonics (SiPh) chip. The Tx multiplexes two 212.5 Gbps polarization tributaries onto a single wavelength optical carrier, forming a 425-Gbps/λ data stream into the transmission link. The Rx performs a robust polarization tracking based on a proposed fast converging eigenvector-decomposition-based polarization recovery algorithm. Aided by off-the-shelf digital signal processing (DSP) and transimpedance amplifier (TIA) chips, the transceiver demonstrates a real-time 2 × 212.5 Gbps transmission over 1 km single mode fiber (SMF). A stable pre-FEC bit-error ratio (BER) floor of 2 × 10<sup>−7</sup> level is obtained in both dynamic polarization scrambling and fiber handling cases. The experiment proves the feasibility that the DP solution is capable of doubling system capacity for short-reach transmission with robust polarization tracking.","PeriodicalId":16144,"journal":{"name":"Journal of Lightwave Technology","volume":"44 3","pages":"1133-1138"},"PeriodicalIF":4.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146071152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-08DOI: 10.1109/JLT.2025.3641313
Jing Zhang;Runnan Guan;Yifei Qi;Runhao Li;Wangyouyou Li;Han Wu;Yunru Fan;Qiang Zhou;Zinan Wang
Temporal ghost imaging (TGI) reconstructs ultrafast temporal signals by correlating the intensity fluctuations of a probe laser with the integrated intensity measured after its interaction with a temporal object. While most existing studies have focused on short-range scenarios, its implementation over long distances has been less explored. In this work, we propose a long-distance TGI system based on an ultra-long random fiber laser (RFL). We experimentally demonstrate, for the first time, that strong temporal intensity correlations exist between the pump-side and remote-side outputs of such an ultra-long RFL, making it highly suitable for long-range TGI. The pump-side output serves as the probe light, which is modulated by the temporal object and then transmitted over a 50-km fiber link before being detected by a slow photodetector. High-fidelity reconstruction of the temporal object is successfully achieved at the remote side by correlating the integrated signal from the slow detector with the random intensity fluctuations of the remote-side output. Moreover, by employing compressed sensing algorithms, the number of required realizations is substantially reduced while achieving a higher peak signal-to-noise ratio (PSNR). Our work leverages the unique properties of RFLs, including their long fiber length, inherent random intensity fluctuations, and intracavity temporal correlations—for TGI applications, thereby overcoming key challenges in long-distance TGI and providing a promising new approach for highly reliable long-range optical signal processing and communication.
{"title":"Long-Distance Temporal Ghost Imaging via Temporal Correlations of a Random Fiber Laser","authors":"Jing Zhang;Runnan Guan;Yifei Qi;Runhao Li;Wangyouyou Li;Han Wu;Yunru Fan;Qiang Zhou;Zinan Wang","doi":"10.1109/JLT.2025.3641313","DOIUrl":"https://doi.org/10.1109/JLT.2025.3641313","url":null,"abstract":"Temporal ghost imaging (TGI) reconstructs ultrafast temporal signals by correlating the intensity fluctuations of a probe laser with the integrated intensity measured after its interaction with a temporal object. While most existing studies have focused on short-range scenarios, its implementation over long distances has been less explored. In this work, we propose a long-distance TGI system based on an ultra-long random fiber laser (RFL). We experimentally demonstrate, for the first time, that strong temporal intensity correlations exist between the pump-side and remote-side outputs of such an ultra-long RFL, making it highly suitable for long-range TGI. The pump-side output serves as the probe light, which is modulated by the temporal object and then transmitted over a 50-km fiber link before being detected by a slow photodetector. High-fidelity reconstruction of the temporal object is successfully achieved at the remote side by correlating the integrated signal from the slow detector with the random intensity fluctuations of the remote-side output. Moreover, by employing compressed sensing algorithms, the number of required realizations is substantially reduced while achieving a higher peak signal-to-noise ratio (PSNR). Our work leverages the unique properties of RFLs, including their long fiber length, inherent random intensity fluctuations, and intracavity temporal correlations—for TGI applications, thereby overcoming key challenges in long-distance TGI and providing a promising new approach for highly reliable long-range optical signal processing and communication.","PeriodicalId":16144,"journal":{"name":"Journal of Lightwave Technology","volume":"44 4","pages":"1461-1467"},"PeriodicalIF":4.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146116909","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-08DOI: 10.1109/JLT.2025.3641159
Lei Zhang;Chen Zhang;Jinbiao Xiao;Zhenzhao Guo;Ting Feng;Shengbao Wu
Mode-division multiplexing (MDM) is a key strategy for boosting the capacity of optical interconnects, and its use in reconfigurable networks requires multimode optical switches with low loss, low crosstalk, and wide bandwidth. We propose and experimentally demonstrate a scalable, high-performance silicon multimode optical switch based on a robust Mach–Zehnder interferometer (MZI) architecture for arbitrary mode-to-dual-mode conversion. The switch integrates an arbitrary mode-to-single-mode power splitter, a passive pi phase shifter (for odd input modes), a thermo-optic phase shifter, and a single-mode-to-dual-mode combiner, enabling any guided mode in the multimode bus to be thermally switched to either the fundamental or first-order mode. A dual-mode demultiplexer then routes these modes to the desired output port. The design requires only a minimal set of fundamental building blocks, with identical intermediate component layouts for all input modes, eliminating the need for redesign when scaling to higher-order modes. By carefully engineering these components, all intermediate devices exhibit superior performance over a bandwidth exceeding 300 nm, ensuring robustness against fabrication variations and offering bandwidth advantages over existing devices. As a proof of concept, we fabricated a 1 × 2 multimode switch capable of independently routing four TE modes (TE0–TE3). Experiments show crosstalk below –18 dB across 1500–1600 nm for all modes, with a maximum modal loss of 3 dB and a switching power consumption of only 34.5 mW. Compared with existing approaches, the proposed device achieves low loss, reduced crosstalk, broader bandwidth, and improved scalability.
{"title":"Scalable, Low-Loss, Broadband Multimode Silicon Optical Switch Based on Robust MZI-Based Arbitrary-to-Dual-Mode Conversion","authors":"Lei Zhang;Chen Zhang;Jinbiao Xiao;Zhenzhao Guo;Ting Feng;Shengbao Wu","doi":"10.1109/JLT.2025.3641159","DOIUrl":"https://doi.org/10.1109/JLT.2025.3641159","url":null,"abstract":"Mode-division multiplexing (MDM) is a key strategy for boosting the capacity of optical interconnects, and its use in reconfigurable networks requires multimode optical switches with low loss, low crosstalk, and wide bandwidth. We propose and experimentally demonstrate a scalable, high-performance silicon multimode optical switch based on a robust Mach–Zehnder interferometer (MZI) architecture for arbitrary mode-to-dual-mode conversion. The switch integrates an arbitrary mode-to-single-mode power splitter, a passive pi phase shifter (for odd input modes), a thermo-optic phase shifter, and a single-mode-to-dual-mode combiner, enabling any guided mode in the multimode bus to be thermally switched to either the fundamental or first-order mode. A dual-mode demultiplexer then routes these modes to the desired output port. The design requires only a minimal set of fundamental building blocks, with identical intermediate component layouts for all input modes, eliminating the need for redesign when scaling to higher-order modes. By carefully engineering these components, all intermediate devices exhibit superior performance over a bandwidth exceeding 300 nm, ensuring robustness against fabrication variations and offering bandwidth advantages over existing devices. As a proof of concept, we fabricated a 1 × 2 multimode switch capable of independently routing four TE modes (TE0–TE3). Experiments show crosstalk below –18 dB across 1500–1600 nm for all modes, with a maximum modal loss of 3 dB and a switching power consumption of only 34.5 mW. Compared with existing approaches, the proposed device achieves low loss, reduced crosstalk, broader bandwidth, and improved scalability.","PeriodicalId":16144,"journal":{"name":"Journal of Lightwave Technology","volume":"44 4","pages":"1445-1453"},"PeriodicalIF":4.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146116810","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-05DOI: 10.1109/JLT.2025.3640654
Jian Fang;Ming-Fang Huang;Scott Kotrla;Tiejun J. Xia;Glenn A. Wellbrock;Jeffery A. Mundt;Ting Wang;Yoshiaki Aono
Vibration sensing based on forward transmission is an emerging topic for network protection and environmental monitoring, especially in long-haul submarine cables and urban fiber networks. However, previous field trials of this approach have mainly focused on localizing strong events under controlled or relatively quiet conditions. In this work, we investigate the capability of forward-transmission vibration sensing to detect weak signals in noisy environments. We demonstrate a high-sensitivity vibration sensing system operating over an 80-km deployed live urban fiber loop without optical amplifiers. The system is enhanced by adaptive time-frequency masking and in-band laser phase noise suppression techniques to improve sensitivity and noise robustness. It has successfully identified and localized weak real-world vibration events with peak-to-peak amplitude lower than 20 rad, such as construction activity near a manhole and even footsteps on handhole lids. Field trial results confirm its robust performance under dynamic environments, including road traffic-induced ground vibrations and aerial cable disturbances. To the best of our knowledge, this is the first demonstration of weak vibration event detection using forward transmission in urban fiber networks. It remarks a significant step towards practical distributed vibration sensing in smart city applications.
{"title":"Field Trial of High-Sensitivity Forward-Transmission Sensing for Real-World Event Detection Over Live Urban Fiber Networks","authors":"Jian Fang;Ming-Fang Huang;Scott Kotrla;Tiejun J. Xia;Glenn A. Wellbrock;Jeffery A. Mundt;Ting Wang;Yoshiaki Aono","doi":"10.1109/JLT.2025.3640654","DOIUrl":"https://doi.org/10.1109/JLT.2025.3640654","url":null,"abstract":"Vibration sensing based on forward transmission is an emerging topic for network protection and environmental monitoring, especially in long-haul submarine cables and urban fiber networks. However, previous field trials of this approach have mainly focused on localizing strong events under controlled or relatively quiet conditions. In this work, we investigate the capability of forward-transmission vibration sensing to detect weak signals in noisy environments. We demonstrate a high-sensitivity vibration sensing system operating over an 80-km deployed live urban fiber loop without optical amplifiers. The system is enhanced by adaptive time-frequency masking and in-band laser phase noise suppression techniques to improve sensitivity and noise robustness. It has successfully identified and localized weak real-world vibration events with peak-to-peak amplitude lower than 20 rad, such as construction activity near a manhole and even footsteps on handhole lids. Field trial results confirm its robust performance under dynamic environments, including road traffic-induced ground vibrations and aerial cable disturbances. To the best of our knowledge, this is the first demonstration of weak vibration event detection using forward transmission in urban fiber networks. It remarks a significant step towards practical distributed vibration sensing in smart city applications.","PeriodicalId":16144,"journal":{"name":"Journal of Lightwave Technology","volume":"44 3","pages":"1167-1177"},"PeriodicalIF":4.8,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146071180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-05DOI: 10.1109/JLT.2025.3640689
Jaehoon Jung;Chia-Chin Chiang;Yong Wook Lee
Polarization-diversified loop-based fiber comb filters have required at least two wave plates per birefringence element for polarization interference to achieve continuous wavelength tunability in high-order comb spectra, including flat-top or narrowband comb spectra. By incorporating variable wave plates (VWPs) whose orientation and retardance can be arbitrarily modified, we propose a continuously wavelength-tunable flat-top polarization-diversified fiber loop (PDFL) filter that utilizes one wave plate per polarization-maintaining fiber (PMF) segment used as a birefringence element to generate polarization interference. The proposed PDFL filter consists of a fiber-pigtailed polarizing beam splitter (PBS) to form the PDFL, two PMF segments, and two VWPs, each of which is located in front of each PMF segment. The slow-axis orientation of the PMF segment directly connected to the PBS is set at 22.5° with respect to the horizontal axis of the PBS to ensure optimal visibility of the comb spectrum. Based on the Jones calculus, we theoretically derived the filter transmittance, and the orientation angle (OA) and retardance sets of the two VWPs, which can introduce continuous extra phase shifts from 0° to 360° in the flat-top transmittance function, were found from the filter transmittance. The theoretical flat-top comb spectra calculated from these OA and retardance sets could corroborate the continuous wavelength tunability of the proposed filter. In particular, the wavelength tunability was also confirmed by experimental verification.
{"title":"Wavelength-Tunable Flat-Top Polarization-Diversified Fiber Loop Filter Using Variable Wave Plates","authors":"Jaehoon Jung;Chia-Chin Chiang;Yong Wook Lee","doi":"10.1109/JLT.2025.3640689","DOIUrl":"https://doi.org/10.1109/JLT.2025.3640689","url":null,"abstract":"Polarization-diversified loop-based fiber comb filters have required at least two wave plates per birefringence element for polarization interference to achieve continuous wavelength tunability in high-order comb spectra, including flat-top or narrowband comb spectra. By incorporating variable wave plates (VWPs) whose orientation and retardance can be arbitrarily modified, we propose a continuously wavelength-tunable flat-top polarization-diversified fiber loop (PDFL) filter that utilizes one wave plate per polarization-maintaining fiber (PMF) segment used as a birefringence element to generate polarization interference. The proposed PDFL filter consists of a fiber-pigtailed polarizing beam splitter (PBS) to form the PDFL, two PMF segments, and two VWPs, each of which is located in front of each PMF segment. The slow-axis orientation of the PMF segment directly connected to the PBS is set at 22.5° with respect to the horizontal axis of the PBS to ensure optimal visibility of the comb spectrum. Based on the Jones calculus, we theoretically derived the filter transmittance, and the orientation angle (OA) and retardance sets of the two VWPs, which can introduce continuous extra phase shifts from 0° to 360° in the flat-top transmittance function, were found from the filter transmittance. The theoretical flat-top comb spectra calculated from these OA and retardance sets could corroborate the continuous wavelength tunability of the proposed filter. In particular, the wavelength tunability was also confirmed by experimental verification.","PeriodicalId":16144,"journal":{"name":"Journal of Lightwave Technology","volume":"44 4","pages":"1485-1492"},"PeriodicalIF":4.8,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146116828","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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