Faraday Rotator Mirror Research Articles

선체의 변형을 감지하기 위한 새로운 형태의 장주기 광섬유 격자 소자

We have developed novel optical-fiber sensors based on strain-induced long-period fiber gratings for monitoring the deformation of a hull. They have no external pressure for sustaining the mechanical formed gratings. The pressure, which provides a force to form the periodic grating along the single mode fiber, was realized by the bonding strength of a photopolymer. To reduce the polarization dependency of the sensors caused by the asymmetry structure of gratings, a Faraday Rotator Mirror (FRM) was utilized in this experiment. We have realized the polarization-insensitive function of the proposed sensors. The change of an external strain are measured by an optical spectrum analyzer. When the external stain increases. the attenuation at the resonant wavelength decreases and the loss peak was slightly shifted to the shorter wavelength.

Polarization fluctuation suppression and sensitivity enhancement of an optical correlation sensing system

Based on the optical pulse correlation measurement and differential detection technique, an optical fibre sensor with high time resolution has been developed. However, due to the birefringence in single mode fibre induced by the uneven thermal effect, polarization fluctuation in the correlation signal was observed. In order to suppress the polarization fluctuation in the correlation sensing system, a polarization-suppressed optical correlation sensing system is proposed by utilizing the birefringence compensation approach in a retraced fibre path using Faraday rotator mirror elements. The polarization fluctuation of the output correlation signals is suppressed by more than 15 dB. The results of temperature experiment indicate that the linearity between the temperature and differential signal is further improved. With the reflection of the mirror, a double-pass monitoring is established, which significantly enhances the sensitivities of the sensing system to temperature and strain.

A fiber depolarizer using polarization beam splitter loop structure for narrow linewidth light source

A new fiber depolarizer employing a polarization beam splitter loop structure is proposed and demonstrated. The depolarizer is devised for broad-band operation and the depolarization of narrow linewidth light source without any help of polarization controllers or Faraday rotator mirrors. A polarizing method is developed that shows good performance without polarization control unit. Therefore, the proposed depolarizer can be cost-effective and easily configured. From experiments, low output degree of polarization less than 10% is obtained for a narrow linewidth light source.

All silica S-band double-pass erbium-doped fiber amplifier

Double-pass (DP) and single-pass (SP) erbium-doped depressed cladding fiber amplifiers designed for S-band operation are evaluated under changes of the input optical power, pumping power, and fiber bending radius. The DP configuration employs the usual combination of a circulator and a Faraday rotator mirror while the SP is based on the copropagating scheme. The amplifiers were characterized in terms of gain and noise figure. It is demonstrated that the DP topology shows much improved gain performance compared to the SP configuration although the noise figure is slightly degraded by counterpropagating amplified spontaneous emission.

S-EDFA and R-EDFA polarization properties comparison

Experimental results on the behavior of the polarization state of the amplified optical signal for two configurations of erbium doped fiber amplifier: single pass erbium doped fiber amplifier (S-EDFA) and reflective erbium doped fiber amplifier (R-EDFA) employing a circulator and a faraday rotator mirror (FRM) are reported in this paper.

Polarization characteristics of a reflective erbium doped fiber amplifier with temperature changes at the Faraday rotator mirror

The temperature dependence of a Faraday rotator mirror (FRM) used in a reflective erbium doped fiber amplifier(R-EDFA) is reported in this paper. The influence of this dependence on the polarization state (PS) of amplified optical signals is also discussed.

Reflective type Raman amplification for loss compensation in dispersion compensating fiber

We demonstrate the characteristics of the reflective type discrete Raman amplifier in the dispersion compensating fiber which is composed of a circulator and a Faraday rotator mirror. With the same dispersion compensation, the gain of the reflective type is higher than that of the conventional single-pass type. Moreover, the forward pumping is better than the backward pumping in the reflective type dispersion compensating Raman amplifier. We also show that, by using the reflective type configuration, the polarization mode dispersion of the dispersion compensating fiber can be almost compensated.

Polarization-Insensitive All-Optical Wavelength Conversion Using Dispersion-Shifted Fiber With a Fiber Bragg Grating and a Faraday Rotator Mirror

We demonstrate a simple technique for polarization-insensitive all-optical wavelength conversion based on four-wave mixing in dispersion-shifted fiber (DSF) with a fiber Bragg grating and a Faraday rotator mirror. The experimental residual polarization sensitivity is reduced from more than 22-2 dB with 4 km of DSF, and the power penalty incurred in wavelength conversion for 10-Gb/s nonreturn-to-zero data is less than 1 dB for a 20-nm conversion distance. Theoretically, this technique will have negligible polarization sensitivity when the propagation loss of the pump through the DSF approaches zero.

Polarization Analysis in Double-Pass Erbium-Doped Fiber Amplifiers With an Embedded-DCF Module

Two configurations of double-pass erbium-doped fiber amplifiers with an embedded dispersion-compensating module are evaluated under changes of the input optical polarization. The first configuration employs the usual combination of a polarization-beam splitter and a Faraday rotator mirror (FRM), while the second is based on the use of two circulators. The amplifiers are characterized in terms of polarization-dependent gain, noise figure, and BER. It is demonstrated that the topology employing circulators show much improved performance compared to the configuration using the FRM.

Demonstration of a folded Sagnac sensor array immune to polarization-induced signal fading.

We demonstrate a new folded Sagnac sensor array design that combines a Faraday rotator mirror and a polarization beam splitter to eliminate the optical noise pulses otherwise generated in a folded Sagnac sensor array. A depolarization scheme compatible with this configuration is also proposed and demonstrated experimentally. It is shown that this new configuration passively eliminates polarization-induced signal fading on every sensor in the array. The minimum detectable phase was measured to be approximately 1.1 microrad/square root of Hz, in agreement with theory.

Er-doped superfluorescent fiber source with a //sup +/sub -//0.5-ppm long-term mean-wavelength stability

We report an Er-doped superfluorescent fiber source (SFS) with a record mean-wavelength stability of /spl plusmn/0.5 ppm over 17 h. This breakthrough was achieved in a double-pass SFS by implementing several improvements, namely 1) controlling all the parameters that affect its mean wavelength, including the pump diode temperature and current, 2) reducing polarization-induced drifts in mean wavelength with a Faraday rotator mirror and a long Er-doped fiber (EDF), and 3) getting rid of polarization controllers to eliminate polarization-dependent loss. The long-term mean-wavelength variations of this SFS were due almost entirely to variations in the EDF temperature. When the SFS temperature was allowed to vary, by calibrating its mean-wavelength dependence on temperature, it was possible to predict the mean wavelength to a /spl plusmn/2-ppm precision by simply measuring the EDF temperature. The same configuration was also implemented with a different Er-doped fiber to achieve an even lower dependence on EDF temperature. When controlling the temperature of this second SFS to about /spl plusmn/0.5/spl deg/C, it exhibited a stability of /spl plusmn/0.5 ppm over 17 h. These new developments constitute an important step toward a practical high-grade fiber-optic gyroscope.

Faraday 반사경을 이용한 광섬유형 전류센서의 안정화

편광분석법을 이용한 광섬유형 전류센서를 구성하여 다양한 전류측정 실험을 행하였다. 잔존 선형복굴절의 영향을 최소화하기 위하여 광섬유 센서 코일의 한쪽 끝에 Faraday 미러를 장착하였으며 일반적인 미러를 사용하는 경우와 출력의 안정성을 비교분석 하였다. 센서코일에 변형을 가하는 경우나 장시간에 걸친 안정성 실험에서도 Faraday 미러를 사용하는 경우에 출력의 안정성이 현저하게 증가함을 알 수 있었다.

Fiber optic microampere dc current sensor

A microampere dc current is measured by a fiber optic sen- sor. The phase change of the guided light induced by ohm's heat over a golden-coated fiber is detected by an interferometer. The thermal con- duction of the optical fiber and the relation of the temperature-induced phase change of the guided light are explored. A Michelson interferom- eter plus a Faraday rotator mirror enable system immunity from the polarization-induced signal fading due to the environmental disturbance, especially by vibration and temperature. A passive phase-generated car- rier (PGC) demodulation scheme enables the system to demodulate the interference signal stably by shifting the signal away from the high-noise, low-frequency band through a carrier. The sensitivity of the sensing sys- tem is improved by a biased method. The minimum measurable dc cur- rent is 3.416310 27 A with a dynamic range of 89.33 dB. © 2003 Society of

Characteristics of the erbium doped fiber amplifier with polarization mode dispersion compensation

We have experimentally demonstrated the characteristics of the reflective type erbium-doped fiber amplifier (R-EDFA) which is composed of a circulator and a Faraday rotator mirror. It is shown that the gain spectrum of the R-EDFA is shifted to longer wavelength when compared with that of the conventional single-pass EDFA. For the R-EDFA, the forward pumping is better than the backward pumping in gain and noise figure. Besides, the reflective structure can be used as a broad band light source because its ASE spectrum is wider and the output power is higher. We also show that, by using the reflective type configuration, the polarization dependent gain is reduced and the polarization mode dispersion of EDF can be completely compensated but the polarization mode dispersion from the circulator is still survived.

A polarization-stable Er-doped superfluorescent fiber source including a Faraday rotator mirror

We report a tenfold stability improvement in the mean wavelength variations induced by polarization fluctuations in an Er-doped superfluorescent fiber source. This was accomplished by replacing the mirror in a double-pass source with a Faraday rotator mirror, thereby nearly eliminating polarization dependent gain. The resulting mean wavelength variations of less than 3.5 parts-per-million (limited by the detection noise floor), approach the requirement for inertial-grade fiber optic gyroscopes.

Stable lightwave synthesized frequency sweeper using Fabry-Perot cavity composed of Faraday rotator mirrors

We describe a stable lightwave synthesized frequency sweeper (LSFS) using a Fabry-Perot (FP) cavity composed of two Faraday rotator mirrors (FRMs). In the former half of this paper, we numerically simulate the behavior of amplified spontaneous emission (ASE) noise accumulations, and show that angular deviations of the FRMs can cause instability in the frequency sweep span. We also show that the span is stabilized by placing a polarizer in one of the FRMs because the FP cavity then works as a single-polarization cavity with a small transmittance fluctuation. Experimental results confirming the stability of this LSFS are provided in the latter half of this paper.

Stable lightwave frequency synthesis over 1-THz span using Fabry-Perot cavity containing polarization-rotation elements and actively controlled tunable bandpass filter

We realized a lightwave synthesized frequency sweeper which has a >1-THz sweep span and operates stably. We employed an actively controlled tunable bandpass filter together with a Fabry-Perot cavity, which consisted of a Faraday rotator mirror and a polarization rotation mirror. We confirmed that the frequency information of an input pulse was preserved after 1000 round-trips in the cavity and that signal pulses could circulate stably for 12 h.

Polarization-stable and single-frequency fiber lasers

We propose a novel structure of fiber laser to achieve single-frequency and polarization-stable oscillation without using a polarization-maintaining (PM) active fiber. The proposed structure has two stabilization mechanisms. First, the laser has a Fabry-Perot cavity composed of Faraday-rotator mirrors (FRMs) to stabilize the polarization-mode competition. We make comparison of polarization-mode stability in various types of cavity structure, and confirm that the Fabry-Perot cavity composed of a non-PM fiber and FRMs has ideal stability similar to the ring cavity composed of a PM fiber and a polarizer. Second, in order to stabilize the longitudinal mode, the laser has an intracavity etalon specially designed to maximize its finesse by removing undesired reflections from the etalon. In the experiment, we construct a fiber laser composed of a non-PM erbium-doped fiber (EDF), FRMs, and an intracavity Fabry-Perot etalon. The polarization-stable and single-frequency operation of the laser is demonstrated.

Polarization-independent depolarizers for highly coherent light using Faraday rotator mirrors

We propose two novel polarization-independent optical depolarizers for highly coherent light using Faraday rotator mirrors (FRM). One uses delay fibers, and the other uses frequency shifters for depolarization. We demonstrate experimentally their polarization-independent depolarization. We also discuss the factors degrading the performance of these depolarizers.

Optical Fiber Amplifiers and Their Applications. Polarization Properties of Optical Fiber Amplifiers and Their Compensations.

Optical fiber amplifiers offeres basically polarization-indenpendent gain. However, they have polarization fluctuation and polarization mode dispersion (PMD) due to birefringnence in fibers, and still have small polarization-dependent properties such as polarization hole burning (PHB) and polarization dependent loss (PDL). In this paper, these properties are reviewed. Compensation of these properties are also reviewed, with emphasis on the reflective fiber amplifier using Faraday rotator mirror (FRM).