Polarization-diversity Loop Configuration Research Articles

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.

Simplified tunable fiber comb filter based on polarization-diversity loop configuration

A simple tunable fiber comb filter composed of two quarter-wave plates and a section of polarization-maintaining fiber is proposed. The states of polarization are investigated through theoretical analysis, and we present the means for continuous wavelength tunability using analytic expression. The optimal angle combination of each birefringent device could be deduced so that an arbitrary wavelength could be a channel center of the comb filter without transmission loss, which is verified experimentally.

PDM Signal Amplification Using PPLN-Based Polarization-Independent Phase-Sensitive Amplifier

We demonstrate the first polarization-independent phase-sensitive amplification of a polarization-division multiplexing (PDM) signal. A novel polarization-diversity loop configuration using periodically poled LiNbO3 waveguides is proposed to achieve the polarization-independent amplification of both a single-polarized signal and a PDM signal. The proposed configuration provides two independent optical parametric amplification processes for two orthogonal polarization components in the loop, while preventing the amplification of the reflection noise by a counter-propagating pump. Polarization-independent error-free operation was confirmed with a bit-error-rate measurement for a 40-Gb/s quadrature phase-shift keying (QPSK) signal. We then demonstrated the phase regenerative amplification of an 80-Gb/s PDM-QPSK signal with artificial phase noise.

팔라듐 코팅된 편광 유지 광섬유를 이용한 편광 상이 배치 구조 기반 광섬유 수소 센서의 개발

In this study, we propose a fiber-optic hydrogen sensor using a polarization-diversity loop configuration composed of a polarization beam splitter, two quarter-wave plates, and a polarization-maintaining fiber coated with palladium whose thickness is ∼400nm. One transmission dip of the output interference spectrum of the proposed sensor, chosen as a sensor indicator, was observed to spectrally shift with the increase of the hydrogen concentration, and the sensing indicator showed a wavelength shift of ∼2.48nm at a hydrogen concentration of 4%. Except for a hydrogen concentration of 4%, the response time of the proposed sensor was measured as less than 12.5s and did not show significant dependence on the hydrogen concentration. In particular, the proposed fiber hydrogen sensor is more durable and highly resistant to external stress applied on a transverse axis of an optical fiber, compared with other hydrogen sensors based on side-polished fibers or fiber gratings.

Study on spectral deviations of high-order optical fiber comb filter based on polarization-diversity loop configuration

In this paper, we investigate optical factors that may cause deviations of experimentally observed output spectra from theoretically predicted ones in a high-order optical fiber comb filter based on a polarization-diversity loop configuration. They include the wavelength dependency of half-wave plates (HWPs) contained in the filter for wavelength switching and the weak birefringence of single-mode fibers (SMFs) that connect optical components comprising the filter. The wavelength dependence of the HWPs is considered using the phase difference curve of a commercial HWP, which is a function of the wavelength of an incident light. In order to examine the effect of the SMF birefringence on the spectral characteristics of the high-order comb filter, the SMF is modeled as a low birefringence fiber whose principal axes are arbitrarily oriented with a certain small birefringence value. It is concluded from the calculation results that the SMF birefringence rather than the wavelength dependency of HWPs strongly affects the spectral characteristics of the filter including an extinction ratio, wavelength location, and spectral shape of the filter channel.

Enhanced inline conversion of fiber Bragg grating spectra based on increased polarization controllability

We have demonstrated enhanced spectral conversion of a fiber Bragg grating (FBG) incorporating a polarization-diversity loop configuration (PDLC) with increased degree of freedom (DOF) in polarization control through the addition of wave plates. The proposed apparatus for spectral conversion consists of a four-port polarization beam splitter for constructing the PDLC, an FBG, and three wave plates including one half-wave and two quarter-wave plates. In the previous study using only two wave plates, slight birefringence of single-mode fibers connecting optical elements within the polarization-diversity loop induced random changes of states of polarization (SOPs), resulting in the spectral degradation. In this approach, the increased number of wave plates could complement it by providing a higher DOF in controlling SOPs and significantly improve spectral performances of the fabricated filter such as an insertion loss, side-mode suppression ratio, and band-rejection ratio.

단일 모드 광섬유의 복굴절이 편광상이 배치구조 기반 고차 광섬유 빗살 필터의 출력 스펙트럼에 미치는 영향에 대한 고찰

In this paper, we investigated possible optical parameters causing deviation of experimentally observed output spectra from theoretically predicted results in a high-order fiber comb filter based on a polarization-diversity loop configuration. They include wavelength dependency of half-wave plates (HWPs) inserted in the filter for wavelength switching and the modal birefringence of single-mode fibers (SMFs) with which optical components comprising the filter are connected. In order to consider the effect of the modal birefringence of the SMF on a filter performance, it is modeled as a low birefringence fiber with an arbitrary orientation angle and birefringence. It is found from the simulation results that the modal birefringence of SMFs strongly affects the spectral characteristics of the filter and decreases the extinction ratio of the filter, compared with the wavelength dependency of HWPs. In particular, it is also confirmed that the spectral deviation and asymmetric distortions of side-lobes in narrow band transmission spectra result mainly from the modal birefringence of SMFs.

광섬유 브래그 격자의 투과 및 반사 스펙트럼간 동일 선로상 변환이 가능한 편광상이 배치구조 기반 광섬유 필터

By incorporating a polarization-diversity loop configuration (PDLC), we have demonstrated inline conversion between transmission and reflection spectra of a fiber Bragg grating (FBG) without reconfiguration of the fiber filter structure. The proposed apparatus consists of a polarization beam splitter, an FBG, and two quarter-wave plates (QWP's). The inline conversion operation between transmission and reflection spectra of the FBG was performed by proper adjustment of QWP's within the proposed filter. The band rejection ratio and side-mode suppression ratio in transmission and reflection modes of the fabricated filter were measured as ∼17.0[㏈] and ∼16.4[㏈], respectively.

Simultaneous Polarization-Insensitive Wavelength Conversion of 80-Gb/s RZ-DQPSK Signal and 40-Gb/s RZ-OOK Signal in a Ti:PPLN Waveguide

Simultaneous all-optical wavelength conversion of an 80-Gb/s return-to-zero differential quadrature phase shift keying (RZ-DQPSK) data signal and a 40-Gb/s return-to-zero ON--OFF keying (RZ-OOK) data signal using a Ti:PPLN waveguide in a polarization-diversity loop configuration are demonstrated. The wavelength conversion is fully transparent to polarization, data rate, modulation format, and modulation level. The conversion efficiency for the signals was -21 dB, which includes 9.2-dB passive losses in the whole Ti:PPLN subsystem. Error-free performance for both wavelength-converted signals was achieved for polarization-scrambled input data signals without additional penalty caused by the polarization scrambling.

전류 조절로 파장 튜닝 가능한 편광상이 배치구조 기반 광섬유 빗살 필터

In this paper, we have demonstrated absolute wavelength tuning in an optical fiber comb filter based on a polarization-diversity loop configuration by controlling the current injected into enameled wires wound on polarization-maintaining fibers (PMF's), that is, adjusting Joule heat generated from enameled wires. The proposed fiber comb filter consists of a polarization beam splitter, a half-wave plate, a quarter-wave plate, and PMF's. And we observed wavelength change of spectral dips in transmission spectra of the fabricated filter by varying an input current applied to enameled wires. The absolute wavelength of the filter could be controlled in proportional to the square of the input current with good linearity, and the rate of the wavelength shift with respect to the input current was measured as 36.79[㎚/A²].

Second-order all-fiber comb filter based on polarization-diversity loop configuration

By concatenating three birefringence loops in series, a second-order all-fiber comb filter based on a polarization-diversity loop configuration is newly proposed. The proposed filter consists of one polarization beam splitter, polarization-maintaining fibers, and two halfwave plates. The effect of a second-order structure of polarization-maintaining fiber loops on a bandwidth of the filter passband was theoretically analyzed and experimentally demonstrated. Transmission output of the second-order filter (flat-top and narrow-band transmission spectra) could be obtained by adjusting two half-wave plates. 1 and 3 dB bandwidths of the proposed filter in flat-top and narrow-band operations were greater by approximately 102.9 and 44.3 % and smaller by approximately 47.9 and 47.1 % than those of a conventional Sagnac birefringence filter, respectively.

Tunable multiwavelength fiber laser employing a comb filter based on a polarization-diversity loop configuration

A tunable multiwavelength fiber laser based on a semiconductor optical amplifier (SOA) is newly proposed. The proposed fiber laser employs a fiber comb filter based on a polarization-diversity loop configuration (PDLC) for the multiwavelength selection. The spectral characteristic of the comb filter is graphically explained by tracing the state of polarization (SOP) of the light propagating through the filter on the Poincare sphere. Particularly, the method of adjusting the filter characteristics is established with the help of the Poincare-sphere representation. The experimental results show that 18 laser lines oscillate with the signal to amplified spontaneous emission noise ratio over 25 dB. Particularly, all of the laser lines with a fixed channel spacing of /spl sim/ 0.8 nm can be continuously shifted by adjusting only a wave plate contained within the filter.

Wavelength-switchable flat-top fiber comb filter based on a Solc type birefringence combination

In this paper a polarization-independent wavelength-switchable flat-top fiber comb filter is newly proposed, which is based on a Solc type birefringence combination and polarization-diversity loop configuration. The proposed filter consists of a polarization beam splitter, two concatenated polarization-maintaining fibers, and two half-wave plates. Our theoretical analysis shows that the proposed apparatus has a much flatter passband and sharper notch than the conventional Sagnac birefringence filter. Particularly, by interchanging the Solc type birefringence combination within the filter between the folded and fan designs, channel wavelength switching operation, more specifically channel interleaving operation, can be achieved through the proper adjustment of the half-wave plates contained within the apparatus. Theoretical prediction was verified by experimental demonstration.

Polarization-independent all-fiber multiwavelength-switchable filter based on a polarization-diversity loop configuration

In this paper a polarization-independent all-fiber multiwavelength-switchable filter based on a polarization-diversity loop configuration is newly proposed. The proposed apparatus consists of a polarization beam splitter, high birefringence fibers, and polarization controllers. Our theoretical analysis shows that the apparatus exhibits unique feature which allows it to operate as a polarization-independent multiwavelength periodic filter with a good channel isolation and to make its channel wavelength switchable by varying effective birefringence of the polarization-diversity loop through the proper adjustment of the polarization controllers contained within the loop. Theoretical prediction was experimentally verified.

Polarization-independent optical demultiplexing by conventional nonlinear optical loop mirror in a polarization-diversity loop configuration

All-optical demultiplexing schemes based on cross-phase modulation in a conventional nonlinear optical fiber loop mirror (NOLM) switch generally suffer from a polarization dependence. In this letter, we propose a polarization-diversity loop configuration that allows polarization-independent all-optical demultiplexing by a conventional NOLM switch. We demonstrate polarization-independent all-optical demultiplexing of 40 Gbit/s signal pulses using the proposed scheme.