Segment Of Polarization-maintaining Fiber Research Articles

1.94 & 2.04 µm dual-band four-wavelength-switchable single-frequency narrow linewidth fiber laser using a novel fs-laser direct-written polarization-dependent four-channel filter

We present a dual-band four-wavelength-switchable single-frequency thulium-holmium co-doped fiber laser (THDFL) utilizing a novel band-switchable polarization-dependent four-channel filter (BS-PDFCF). The filter incorporates two high-birefringence fiber Bragg gratings (HB-FBGs) and an electrical-controlled optical switch (EC-OS). Specifically designed for operation in the 1.94 μm and 2.04 μm bands, two HB-FBGs are fabricated using femtosecond (fs) laser direct-writing technology in two segments of polarization-maintaining fibers via a point-by-point method. Each HB-FBG features two narrow-band reflection channels with perpendicular polarization directions. The EC-OS switches the operation band of the BS-PDFCF. A 1.2 m long dynamic ultra-narrow-band filter is employed in the THDFL to achieve single-longitudinal-mode oscillation. The THDFL achieves exceptional output performance, including four single-wavelength and two dual-wavelength operations, spectral wavelength and power fluctuations of ≤0.012 nm and ≤0.386 dB, respectively, OSNRs of >76 dB, RINs of ≤−142.48 dB/Hz@≥5 MHz, linewidths of ≤3.59 kHz@1.94 μm band and ≤5.46 kHz@2.04 μm band, and output power fluctuations of ≤0.109 dB in a measurement time span of 30 min.

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.

All-polarization-maintaining divided pulse fiber oscillator mode-locked with the optical Kerr effect.

In this Letter, we investigate a Yb-doped mode-locked fiber oscillator that uses coherent pulse division and recombination to avoid excessive nonlinear phase shifts. The mode locking mechanism of the laser is based on the accumulation of a differential nonlinear phase between orthogonal polarization modes in the polarization-maintaining fiber segment. The inserted coherent pulse divider, based on YVO4 crystals rotated successively by 45°, enables stable and undistorted mode-locked steady states. The output pulse energy is increased from 89 pJ in the nondivided operation by ≈6.5 dB to more than 400 pJ with three divisions. A measurement of amplitude fluctuations reveals a simultaneous broadband noise suppression of up to ≈9 dB in the frequency range from 10 kHz to 2 MHz.

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.

All-fiber figure-eight wavelength-tunable noise-like pulse lasers

All-fiber wavelength-tunable fiber laser is a desirable light source architecture in many fields owing to their low cost, compactness and easy integration. However, most of them have independent filter elements and saturated absorption elements, which will undoubtedly increase the redundancy of laser. In this paper, we realize an all-fiber wavelength-tunable noise-like pulse (NLP) laser with the tunable central wavelength from 1547 nm to 1600 nm based on fiber loop mirror (FLM). The fiber loop (FLM) fused with two segments of polarization-maintaining fibers (PMF) acts as both a comb filter and a saturable absorber (SA). Such an all-fiber tunable NLP mode-locked laser wavelength at C-band (1530–1565 nm) and L-band (1565–1625 nm) is a potential choice for many practical applications.

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.

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.

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.

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.

Tunable multiwavelength erbium-doped fiber laser based on BPQDs packaged by poly tetra fluoroethylene and two segments of PMF

Two types of tunable and stable multiwavelength erbium-doped fiber lasers(MWEDFLs) are proposed and experimentally demonstrated, which are based on novel poly tetra fluoroethylene packaging device of black phosphorus quantum dots (PTFEPD-BPQDs) and two sections of polarization maintaining fiber(PMF) in cascade/in parallel. The novel fabrication process uses silica capillaries and PTFE to package BPQDs. The PTFEPD-BPQDs has the function of suppressing the mode competition and stabilizing the multiwavelength output. The channel space and wavelength number of the two types of tunable MWEDFLs can be tuned by adjusting polarization controllers(PCs). In the experiments, for the unpackaged BPQDs device, BPQDs will degrade and lose its function within 48 h, while for the PTFEPD-BPQDs, BPQDs can keep its function for more than 3 weeks. By adjusting the PC, in the cascaded structure, the multiwavelength channel spacing can be tuned among nearly 1.98, 0.67 and 0.43 nm, and the number of multiwavelength output is 4, 9 and 13, respectively.

Temperature- and strain- insensitive transverse load sensing based on optical fiber reflective Lyot filter

For the first time to our knowledge, we propose and experimentally demonstrate a transverse load sensor using an optical fiber reflective Lyot filter. Such an optical fiber reflective Lyot filter consist of a fiber polarizer, a segment of polarization-maintaining fiber and a single mode fiber based fiber reflector. By demodulating the wavelength of the interference dip, the proposed device exhibits a desirable high transverse load sensitivity of 64.72 nm/(N/mm) without temperature and strain confusion, which provides a new option for the transverse load measurement and further expands the application of the fiber Lyot filter.

All-polarization-maintaining dual-wavelength mode-locked fiber laser based on Sagnac loop filter.

We demonstrate an all polarization-maintaining (PM) fiber based dual-wavelength mode-locked Er-fiber laser. A nonlinear amplifying loop mirror (NALM) with an intracavity nonreciprocal phase shifter is used for self-started mode-locking. A short segment of PM fiber is angle-spliced to the NALM, functioning as a PM Sagnac loop filter, thus enabling dual-wavelength mode-locking. The wavelength separation is solely determined by the angle-spliced PM fiber length. Stable dual-wavelength mode-locking operation is switchable between 1570/1581 nm and 1581/1594 nm. The two-color pulse trains oscillating in the same cavity have an inherent offset repetition rate of ~1 kHz owing to cavity dispersion, allowing future high precision dual-comb applications with a simple and robust configuration.

Multimode interference-based fiber-optic strain and temperature sensor using polarization-maintaining fiber

A cost-efficient fiber-optic strain and temperature sensor has been proposed and demonstrated experimentally. The sensor consists of a segment of polarization-maintaining fiber (PMF) and two segments of multimode fiber (MMF). Two segments of MMF, which are used as beam splitter and combiner, are embedded on both ends of the PMF. The all-fiber sensor is put in the middle of the single-mode fiber. Due to the ratio of the strain and temperature responses of the sensor, the measurement of strain and temperature can be achieved by monitoring the transmission spectrum. The experimental result shows that the strain sensitivity is up to −3.16 pm / μϵ in the range of 0 to 1000 μϵ and the temperature sensitivity is 0.071 nm / ° C in the range from 10°C to 45°C. This sensor exhibits the advantages of low cost and high sensitivity and may have potential application in strain and temperature measurement.

Zeroth- and First-Order-Convertible Fiber Interleaving Filter

In this paper, we propose a zeroth- and first-order-convertible fiber interleaving filter that has a frequency-interleaving capability in the zeroth- or first-order multiwavelength transmission spectrum. The proposed interleaving filter is a kind of polarization-diversity-loop-based comb filter composed of a polarization beam splitter, three half-wave plates (HWPs), and two polarization-maintaining fiber (PMF) segments, each of which is located between two adjacent HWPs. The HWP inserted between two PMF segments enables the interleaving filter to operate in the zeroth- or first-order transmission mode by adjusting the relative angular difference between the principal axes of two PMF segments. With the orientation angles of the three HWPs set as specific angles, first-order flat-top and narrow-band transmission spectra with a channel spacing of ∼0.792 nm could be obtained and be interleaved by controlling only the HWP between the two PMF segments. In particular, at other specific angle sets of the three HWPs, the zeroth-order transmission spectrum with the same channel spacing could be obtained, and their multiwavelength channels could be interleaved by adjusting only the orientation angle of the intermediary HWP. That is, a first-order comb spectrum could be converted into a zeroth-order one with the same fringe period, and each one could be interleaved through the proper control of the three HWP angles.

Study on Transmission and Output Polarization Characteristics of a First-Order Lyot-Type Fiber Comb Filter Using Polarization-Diversity Loop

A first-order Lyot-type fiber comb filter was fabricated by incorporating a polarization-diversity loop structure composed of a polarization beam splitter, two half-wave plates (HWPs), and two polarization-maintaining fiber (PMF) segments. One of the two PMF segments was two times longer than the other, and they were concatenated with a 60 $^{\circ} $ offset between their principal axes. The transmission spectra and output polarization characteristics of the filter were theoretically predicted and experimentally verified. By proper control of the two HWPs, first-order transmission spectra could be obtained, including flat-top and lossy flat-top band modes, and the interleaving operation of the respective spectrum could be also achieved. This flat-top band mode spectrum showed a higher attenuation rate at the cutoff level, in comparison with that of the Solc-type filter. In particular, it was revealed that the output state of polarization of the filter was a periodical function of wavelength and that the evolution period was different, according to transmission band modes. With the help of a linear output polarizer, the specific portion of a passband could be passed or rejected by controlling input polarization. It was also theoretically predicted that the fine tuning of the passband center was possible within a specific wavelength range.

편광상이 고리 구조 기반 사냑 간섭계를 이용한 편광 간섭형 광섬유 압력 센서

In this paper, we demonstrated a polarimetric fiber pressure sensor using a polarization-diversity-loop-based Sagnac interferometer(PDLSI) composed of polarization-maintaining fiber(PMF) and a fiber Bragg grating(FBG). In order to compare the pressure sensitivity for various kinds of PMF, three kinds of bow-tie PMF were employed as sensor heads. The maximum pressure sensitivity was measured as approximately -15.07nm/MPa, and an R2 value to represent sensor linearity was measured as ~0.992 at the sensor system using corresponding PMF over a pressure range of 0-0.3MPa. An FBG was utilized and located adjacent to the PMF segment for compensating temperature-induced errors in the measurement of pressure. The pressure sensitivity of the proposed sensor was improved by approximately four times compared with the previously reported pressure sensor based on polarization-maintaining photonic crystal fiber.

Wavelength spacing tenable capability of optical comb filter using Polarization Maintaining Fiber

Abstract: In this paper, tuneable comb filter using single-mode fiber (SMF)has been proposed and theoretically studied its capability of tuning the output spectral spacing continuously by using the birefringence property of polarization maintaining fiber (PMF).The proposed filter consists of one QWP, one HWP, one SMF and one PMF segment . Depending on the dynamic settings of wavelength of the input signal, refractive index, and length of the fiber material the comb filter offers the continuous channel spacing tunability. Obtained output spectra are quite similar as calculated from equation. Channel spacing can be tuned at any desired value with the help of this comb filter. PMF based filter is very useful for long distance transmission.

A Stable and Tunable Linear-Polarization Fiber Ring Laser With a High SMSR by Using a Compounded Fiber Filter

A stable and tunable linear-polarization fiber ring laser with a high side-mode-suppression ratio (SMSR) is proposed and experimentally demonstrated by using a compounded fiber filter, which is composed of a dual-pass Mach-Zehnder interferometer filter incorporating one segment of polarization-maintaining fiber and a high finesse filter. By adjusting the polarization controllers, the output laser can be tuned from 1560.37 to 1568.56 nm and an SMSR as high as 72 dB is achieved. In addition, the peak power fluctuation and wavelength shift are monitored to be less than 0.08 dB and 0.02 nm over an hour. Due to the introduction of the compounded fiber filter as a wavelength selector, the side mode of lasing output can be effectively suppressed and mode competition can be weakened. As a result, the SMSR of lasing output is increased and power stability is improved.