Polarization-diversity Loop Research Articles

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.

Wavelength Conversion of RZ-OOK PDM Signals Based on XPM in Highly Nonlinear Fiber

Wavelength conversion of return-to-zero on-off keying (RZ-OOK) signals in polarization-division-multiplexing (PDM) systems based on cross-phase modulation (XPM) in highly nonlinear fiber (HNLF) using a polarization-diversified loop configuration is experimentally demonstrated. Eye-diagram-based signal-to-noise-ratio (SNR) results indicate that successful wavelength conversion can be achieved over the whole <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> -band.

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].

Inline Conversion Between Transmission and Reflection Spectra of Fiber Bragg Grating Using Polarization-Diversity Loop Structure

By incorporating a polarization-diversity loop structure, we have demonstrated an inline conversion between transmission and reflection spectra of a fiber Bragg grating (FBG) without reconfiguration of the filter structure containing the FBG. The proposed apparatus consists of a polarization beam splitter, an FBG, and two quarter-wave plates (QWPs). Without requiring rearrangement of input/output ports or additional optical switches, the spectral switching operation of the FBG was carried out through proper adjustment of the QWPs contained in the proposed filter.

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.

Polarization-insensitive all-optical NRZ-to-RZ format conversion by spectral filtering of a cross phase modulation broadened signal spectrum

All-optical modulation format conversion may be needed in future hybrid optical-time-division multiplexing (OTDM) and wavelength-division multiplexing (WDM) networks. This paper describes an approach for nonreturn-to-zero (NRZ) to return-to-zero (RZ) format conversion by spectral filtering of a cross phase modulation (XPM) broadened signal spectrum with a study of the polarization effect of XPM. Two configurations, single-pass and polarization diversified loop, are proposed to realize the all-optical format conversion, and to evaluate the polarization sensitivity of the proposed noninterferometric format conversion scheme by spectral filtering. Error-free operation is obtained for the format converted output.

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 Tunable Fiber Comb Filter

We have demonstrated a polarization-independent tunable fiber comb filter by using both polarization-diversity loop technique and birefringence tuning technique. The proposed apparatus consists of one polarization beam splitter, polarization-maintaining fibers, and three waveplates (one quarter-wave plate and two half-wave plates). The capability of continuously tuning the output spectrum was theoretically analyzed and then experimentally verified.

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.

All-optical time-division demultiplexing with polarization-diversity nonlinear loop interferometer

We demonstrate a polarization insensitive time-division demultiplexer using semiconductor optical amplifier based nonlinear interferometer in a polarization-diversity loop. The demultiplexer had a very low switching energy (<100 femtojoules) and error-free operation in demultiplexing a 40 Gb/s input was achieved. The residual polarization dependence of the incident signal was found to be only 0.3 dB. Capability of demultiplexing at higher bit rates was proved by the ultrafast switching of 160 Gb/s pulses.

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.