Faraday Rotator Mirror Research Articles

Frequency stabilization of two orthogonally polarized external cavity laser diodes using a novel γ-type optical configuration consist of a phase modulator and a Faraday rotator mirror

Frequency stabilization of two orthogonally polarized external cavity laser diodes using a novel γ-type optical configuration consist of a phase modulator and a Faraday rotator mirror

High Stability Er-Doped Superfluorescent Fiber Source Incorporating an Er-Doped Fiber Filter and a Faraday Rotator Mirror

An Er-doped fiber (EDF) filter and a Faraday rotator mirror (FRM) are used in an Er-doped superfluorescent fiber source (SFS) to improve its mean wavelength thermal stability. The thermal stabilities of mean wavelength for four configurations of SFS with or without the EDF filter and FRM are experimented. With an EDF filter and a FRM incorporated in an Er-doped SFS, the mean wavelength variation is measured to be 32.02 ppm from -40°C to 60°C. The mean wavelength is around 1561 nm and its bandwidth reaches 15.8 nm. The pump power is 55 mW at 974.2 nm and the output power reaches 7.8 mW with 5-m EDF.

Q-switched pulse generation from an all-f iber distributed Bragg reflector laser using graphene as saturable absorber

A Q-switched distributed Bragg reflector fiber laser using a graphene passive saturable absorber is proposed in a cavity consisting of a fiber Bragg grating and Faraday rotator mirror as end mirrors, together with a highly doped erbium-doped fiber as a gain source. The laser has a Q-switched threshold of about 28 mW and a tunable repetition rate of 10.4–18.0 kHz with varying pump power. The shortest pulse width obtained from the system is 3.7 μs, with a maximum pulse energy and peak power of 22.2 nJ and 3.4 mW, respectively.

Polarization in Retracing Circuits for WDM-PON

Reflective semiconductor optical amplifier (RSOA)-based network-embedded self-tuning solutions for colorless optical network unit in wavelength-division-multiplexed passive optical network architecture suffer the device polarization-dependent gain (PDG). The Faraday-mirror-based topology proposed in the literature for low PDG RSOA is not suitable for high PDG RSOA. A polarization retracing circuit is proposed and discussed to comply with the high PDG RSOA. The polarization evolution is theoretically and experimentally analyzed in the presence of a high PDG RSOA comparing three cases: standard topology with standard mirror, the retracing circuit proposed in the literature with a Faraday rotator mirror (FRM), and the proposed retracing circuit, which includes both an FRM and a Faraday rotator.

Robust and environmental insensitive fiber optic Sagnac interferometer for microwave photonic applications

A technique that allows a fiber optic Sagnac interferometer based microwave photonic device to be implemented using non-polarization maintaining components inside the Sagnac loop while still obtaining an output that is insensitive to changes in environmental conditions is presented. It is based on inserting the non-polarization maintaining components in between a polarization beam combiner and a Faraday rotator mirror inside the loop. The technique also introduces a phase bias to the light propagating inside the loop. Experimental results demonstrate that the discretely and continuously tunable Sagnac loop based signal processors implemented using non-polarization maintaining components have an environmentally insensitive frequency response.

Investigation of polarization-induced phase noise in interferometric optical fiber sensing system based on FRM

One of the key technologies of interferometric optical fiber sensing system is to overcome polarization-induced signal fading in interferometric fiber sensors. The theoretical and the experimental investigations of the residual polarization-induced phase noise (PIN) in single-mode optical fiber Michelson interferometer based on Faraday rotation mirror (FRM) are conducted in this paper. A theoretical model of the residual PIN based on Jones matrix is developed. Three leading influencing factors of the residual PIN are educed: the rotation deviation angle of FRM, the state of polarization of input light, and the birefrigent effect of the optical fiber. And three methods are proposed to overcome the residual PIN. The maximal PIN with its amplitude of 0.0815 rad possibly exists in the sensing system when the polarization modulation degree equals 1.84 rad. The correctness of the theoretical model is proved by the experimental results.

Linear-cavity fiber laser in nearly single-frequency operation using Faraday rotator mirror

A nearly single-frequency selection is realized in a linear-cavity fiber laser constructed using a Faraday rotator mirror (FRM) and a partial reflectance fiber Bragg grating (FBG) as the cavity ends. At 1552.46 nm wavelength, the measured optical signal-to-noise-ratio (OSNR) is 58.5 dB with a linewidth less than 400MHz obtained using a subring cavity and a polarization controller as the mode filters. The pumping efficiency is improved by 10% by recycling the residual pump power to the gain medium.

Polarization-maintaining amplification of phase modulated pulse employing ytterbium-doped single-mode fiber amplifier

Polarization-maintaining fiber amplifier using ytterbium-doped single-mode fiber (SMF) is proposed. A 45° Faraday rotator mirror (FRM) and a polarization independent fiber loop circulator (FLC) with polarization-maintaining fiber (PMF) pigtails are used to realize double-pass amplification and birefringence self-compensation. Arbitrary state of polarization (SOP) such as the linear polarization and elliptical polarization can be maintained. Polarization-maintaining amplification of phase modulated pulse with this amplifier is experimentally demonstrated while introducing little intensity modulation itself.

Distributed optical fiber vibration sensing system based on polarization detection

A novel distributed optical fiber vibration sensing system based on polarization detection is proposed and demonstrated. A Faraday rotator mirror is employed at the end of the system, which eliminates the slow polarization variation of signal light and only responses to rapid polarization change caused by external vibration interference. Based on the sensing signal characteristics, the location of polarization disturbance point can be detected accurately. Experiments on polarization controller simulation and actual vibration detection show that a higher localization accuracy better than 1% is successfully obtained in 13.8 km, 21.2 km and 35.8 km sensing fibers systems.

All-Fibered High-Quality Stable 20- and 40-GHz Picosecond Pulse Generators for 160-Gb/s OTDM Applications

In this work, we investigate the generation of stable 20- and 40-GHz pulse trains through the nonlinear compression of an initial beat-signal in a cavity-less optical-fiber-based device. Enhanced temporal stability is achieved by generating the sinusoidal beating thanks to a commercial LiNbO3 intensity modulator driven by a half repetition-rate external radio-frequency (RF) clock. We also show that the residual timing jitter induced by the RF phase modulation imposed to suppress Brillouin back-scattering can be reduced by managing the cumulated dispersion of the compression line, whereas complete polarization stabilization is obtained owing to a modified setup involving a Faraday rotator mirror. Finally, a high-quality 160-Gb/s signal is generated from our low duty-cycle 40-GHz pulse source through optical time-division multiplexing (OTDM).

A Comparison of Delayed Self-Heterodyne Interference Measurement of Laser Linewidth Using Mach-Zehnder and Michelson Interferometers

Linewidth measurements of a distributed feedback (DFB) fibre laser are made using delayed self heterodyne interferometry (DHSI) with both Mach-Zehnder and Michelson interferometer configurations. Voigt fitting is used to extract and compare the Lorentzian and Gaussian linewidths and associated sources of noise. The respective measurements are wL (MZI) = (1.6 ± 0.2) kHz and wL (MI) = (1.4 ± 0.1) kHz. The Michelson with Faraday rotator mirrors gives a slightly narrower linewidth with significantly reduced error. This is explained by the unscrambling of polarisation drift using the Faraday rotator mirrors, confirmed by comparing with non-rotating standard gold coated fibre end mirrors.

High sensitivity optical fiber current sensor based on polarization diversity and a Faraday rotation mirror cavity

A novel high sensitivity optical fiber current sensor (OFCS) based on polarization diversity and a Faraday rotation mirror cavity is proposed and demonstrated. Comparing with single-channel detection in a conventional OFCS, a signal power gain of 6 dB and a signal-to-noise ratio improvement of over 30 dB have been achieved in the new scheme. The cavity amplifies magnetic field-induced nonreciprocal phase modulation, while the Faraday rotation mirrors suppress the reciprocal birefringence. A linear response is obtained for current amplitude as low as several mA at an AC frequency of 1 kHz.

High Stability Er-Doped Superfluorescent Fiber Source Improved by Incorporating Bandpass Filter

A Faraday rotator mirror incorporating a Gaussian bandpass filter was used as the reflected end of an Er-doped superfluorescent fiber source to improve its mean wavelength thermal stability. Several different filters were modeled in this fiber source system, and the optimal central wavelength was chosen to be 1558 nm with the bandwidth of 15 nm. With a Faraday rotator mirror incorporating such a filter in an Er-doped fiber source, the mean wavelength variation was measured to be 8 ppm from -40°C to 60°C . The bandwidth reached 16 nm. The pump power was 70 mW at 974.2 nm and the output power reached 18 mW with 6-m Er-doped fiber.

Current-induced Phase Demodulation Using a PWM Sampling for a Fiber-optic CT

In this work, we used PWM sampling for demodulation of a fiber-optic interferometric current transformer. The interference signal from a fiber-optic CT is sampled with PWM triggers that produce a 90-degree phase difference between two consecutively sampled signals. The current-induced phase is extracted by applying an arctangent demodulation and a phase unwrapping algorithm to the sampled signals. From experiments using the proposed demodulation, we obtained phase measurement accuracy and a linearity error, in AC current measurements, of ~2.35 mrad and 0.18%, respectively. The accuracy of the proposed method was compared with that of a lock-in amplifier demodulation, which showed only 0.36% difference. To compare the birefringence effects of different fiber-optic sensor coils, a flint glass fiber and a standard single-mode fiber were used under the same conditions. The flint glass fiber coil with a Faraday rotator mirror showed the best performance. Because of the simple hardware structure and signal processing, the proposed demodulation would be suitable for low-cost over-current monitoring in high voltage power systems.

Single-Polarization Cladding-Pumped Optical Amplifier Without Polarization-Maintaining Gain Fiber

We demonstrate a single-polarization cladding-pumped Er : Yb optical amplifier using a dual-pass design with a Faraday rotator mirror and nonpolarization-maintaining gain fiber. Over a 25-nm range centered at 1562 nm, the amplifier output exceeds 1 W and maintains a polarization extinction ratio greater than 22 dB. We investigate enhanced relative intensity noise inherent in the dual-pass configuration and discuss scaling to higher powers.

A narrow-line Erbium-doped fiber laser and its application for testing fiber Bragg gratings

We inspect the spectral features of a diode-pumped Erbium-doped fiber laser (EDFL) with a Fabry-Perot cavity composed of a wavelength-selective coupler in the form of fiber Bragg grating (FBG) and wavelength-insensitive Faraday rotator mirror (FRM). High accuracy for the spectral measurements is provided with the use of an optical heterodyne scheme where the EDFL output is mixed with radiation from a narrow-line semiconductor laser, allowing the detection of the EDFL spectra with a sub-pm resolution. The heterodyne scheme permits precise measurements of the EDFL line-width as a function of the cavity length and pump power. It is worth noticing a narrow-line (a few pm) operation of the EDFL with a short length (<3 m) cavity and low (<5) excess of pump power over the laser threshold. The spectral response of the EDFL to a slow sinusoidal modulation of a physical length of the FBG coupler is analyzed and it is shown that as high as ∼1-nm modulation of the EDFL optical spectrum is attainable at maximal modulation amplitudes. The narrow-line EDFL with a modulated generation wavelength is hereby demonstrated to be a tool for high-resolution measurements of reflection spectra of FBGs, which is to the best of our knowledge a novel application of the EDFL.

Environmentally stable nonlinear optical polarization switching by using a nonreciprocal all‐optical circuit

AbstractWe proposed and demonstrated a stable nonlinear optical polarization self‐switching based on nonreciprocal nonlinear phase shift induced by self‐phase modulation in optical fiber. The polarization self‐switching was achieved at input power levels of around 10 mW in a nonreciprocal circuit using Faraday rotator mirrors. This nonlinear polarization switching is quite stable against polarization fluctuation caused by environmental perturbation. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2056–2059, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24548

Measurement of Differential Phasor Diagram of Multilevel DPSK Signals by Using an Adjustment-Free Delay Interferometer Composed of a 3$\,\times\,$3 Optical Coupler

We develop an adjustment-free differential-phase demodulator based on a delay-interferometer (DI) made of a 3 times 3 optical coupler, which is used as a 120-degree optical hybrid, and demonstrate the possibility of using it as a phasor monitor for the multilevel differential phase-shift keyed (DxPSK) signal. The key features of the proposed demodulator are twofold: (a) in-phase and quadrature (I-Q) components and the phasor diagram can be obtained only by using a single DI, and (b) the phase delay of the DI can be derived from the output power of the DI without the knowledge of the signal under test. These features enable us to demodulate the I-Q components of DxPSK signals without any adjustments. We formulate a theoretical model for deriving the differential phasor from the output signals of the 3 times 3 coupler regardless of unbalances in the phase retardations and the splitting ratios of the 3 times 3 coupler. Thus, the discrepancy from the ideal 120-degree optical hybrid is not a problem, and hence the requirements of the 3 times 3 couplers are greatly relaxed. For a demonstration, we implement the proposed demodulator by using a fiber Michelson interferometer with Faraday rotator mirrors and use it as a differential phasor monitor capable of the plug-and-play (wavelength- and polarization-independent) operation. We show that this phasor monitor can be used for diagnosis of differential phase-shift keyed (DPSK) and differential quadrature phase-shift keyed (DQPSK) transmitters by identifying the sources of impairments from the measured constellation diagram and phasor trajectories. The proposed phasor monitor can also be used for monitoring the optical signal-to-noise ratio (OSNR) of DPSK signal.

Stabilizing slow light delay in stimulated Brillouin scattering using a Faraday rotator mirror

The delay of the Stokes beam in stimulated Brillouin scattering (SBS) is sensitive to the polarization alignment between the pump and the Stokes. Typically, waveguides exhibit a birefringence that causes beams launched from opposite ends to have fluctuating and suboptimal alignment. We demonstrate in an optical fiber that using a Faraday rotator mirror not only overcomes this problem, but also enhances SBS slow light delay.

Novel distributed optical fiber acoustic sensor array for leak detection

We develop an in-line distributed optical fiber acoustic sensor array based on Sagnac interferometer use it to measure and locate leaks for the fluid-filled (or gas-filled) pipelines in real time. The advantage of the sensor array is that it can monitor two or many pipelines at the same time. The traditional loop Sagnac interferometer is changed into in-line structure by a Faraday rotator mirror. The representation of phase change caused by leakage is formulated for optic signal; the measuring principle and the leaking source location method for the sensor array are analyzed. An experiment is designed to detect and locate leaks. The results verify that the system can realize leak detection and locate leak accurately, and the error is less than 0.54%.