Faraday Rotator Mirror Research Articles

Effect of external magnetic fields on practical quantum random number generator

Quantum random number generator (QRNG) based on the inherent randomness of fundamental quantum processes can provide provable true random numbers which play an important role in many fields. However, the security of practical QRNGs is linked to the performance of realistic devices. In particular, devices based on the Faraday effect in a QRNG system may be affected by external magnetic fields, which will inevitably open a loophole that an eavesdropper can exploit to steal the information of generated random numbers. In this work, the effects of external magnetic fields on the security of practical QRNGs are analyzed. Taking the quantum phase fluctuation based QRNG with unbalanced Michelson interferometer as an example, we experimentally demonstrate the rotation angle of the Faraday rotation mirror (FRM) is influenced by external magnetic fields. Then, we develop a theoretical model between the rotation angle deviation of FRM and conditional min-entropy. Simulation results show that the imperfect FRM leads to a reduction in the variance of measured signal and extractable randomness. Furthermore, the impacts of practical sampling device on the extractable randomness are analyzed in the presence of imperfect FRM, which indicates suitable parameters of the sampling device can improve the security of practical QRNGs. Potential countermeasures are also proposed. Our work reveals that external magnetic fields should be carefully considered in the application of practical QRNGs.

Polarization-independent tilted fiber Bragg grating surface plasmon resonance sensor based on spectrum optimization.

We experimentally demonstrated polarization multiplexing schemes in a tilted fiber grating (TFBG) to achieve polarization-independent fiber-optic surface plasmon resonance (SPR) sensors. The first used two orthogonal polarized lights separated by a polarization beam splitter (PBS) that are p-polarized in polarization-maintaining fiber (PMF) and precisely aligned with the tilted grating plane, so as to achieve the transmission of p-polarized light in two opposite directions of the Au-coated TFBG to excite SPR. Alternatively, polarization multiplexing was also achieved by exploring two polarization components to achieve the SPR effect through a Faraday rotator mirror (FRM). The SPR reflection spectra are polarization-independent of the light source and any perturbations to fibers, which are explained by the superposition of p- and s-polarized transmission spectra in equal proportions. The spectrum optimization is presented to reduce the proportion of the s-polarization component. A polarization-independent TFBG-based SPR refractive index (RI) sensor with a wavelength sensitivity of 555.14 nm/RIU and an amplitude sensitivity of 1724.92 dB/RIU for small changes is obtained, exhibiting unique advantages of minimizing the polarization alterations by mechanical perturbations.

EDF laser displacement sensor based on bending characteristics of polarization-independent double-pass cascaded-chirped long-period fiber grating

In this study, we propose an Erbium-doped fiber (EDF) laser displacement sensor using bending characteristics of a cascaded-chirped long-period fiber grating (C-CLPG), in which the C-CLPG assisted by a Faraday rotator mirror (FRM), namely double-pass C-CLPG, shows a channeled spectrum and plays both the roles of wavelength tunable filter and sensor element. In the sensing scheme, the spectral shift of the channeled spectrum due to the displacement-induced bending deformation is utilized. Due to the FRM reflection, the double-pass C-CLPG has characteristics suitable for sensing: the polarization-independent channeled spectrum and the compensation effect for polarization variation in the sensor section. In the experiment, it is successfully demonstrated that the EDF laser in a sigma-type cavity configuration (EDFσL) using the double-pass C-CLPG enables precise displacement measurement based on the oscillation wavelength shift corresponding to the spectral shift of the double-pass C-CLPG. Further, the advantage of this EDFσL is confirmed by comparison with the conventional EDF ring laser using the single-pass C-CLPG.

Influence of Faraday Rotator Mirror on Measurement of Magneto-Optical Properties of Spun Fibers

Influence of Faraday Rotator Mirror on Measurement of Magneto-Optical Properties of Spun Fibers

Influence of Imperfect Faraday Rotation Mirror on All-Fiber Optic Current Sensor

The effects of the Faraday rotation mirror on the all-fiber optic current sensor (AFOCS) are studied in this paper. The reflectivity degradation of FRM with the long-term operation, the misalignment of the optical axis between FRM and the sensing fiber, and the influence of temperature fluctuation on FRM are modeled and simulated in this paper. The effect of temperature is the biggest obstacle to the application of the Faraday rotation mirror, while other factors can be easy to overcome by the data processing method. The experiments are designed and realized for verification. The temperature fluctuation range is related to the measured electric current to satisfy the required accuracy for IEC 60044-8 class 0.2S.

Research on All-Fiber Dual-Modulation Optic Current Sensor Based on Real-Time Temperature Compensation

We present a method to simultaneously measure the temperature and electric current, which can be applied for the all-fiber optic current sensor (AFOCS) temperature compensation. The Faraday rotation mirror is introduced as the temperature sensing unit based on the all-fiber dual-modulation optic current sensor. The temperature and electric current could be distinguished by the sequence of pulse light received by the photodetector. The working principle of temperature and electric current sensing are analyzed by modeling and simulation. The experiments are designed to confirm the temperature compensation scheme. The relative error of AFOCS decreases from 14% to 2% by temperature compensation, which meets the requirements of micro-current fiber sensing.

EDF laser temperature sensor using double-pass cascaded-chirped long-period fiber grating in sigma-cavity configuration

We propose a novel Erbium-doped fiber laser sensor in a sigma-cavity configuration (EDFσL) for temperature sensing. In this configuration, the sigma-branch of the EDFσL, or the double-pass cascaded-chirped long-period fiber grating (C-CLPG), consists of an optical circulator, a C-CLPG, and a Faraday rotator mirror (FRM), and works as a reflective sensor device as well as a wavelength selection element with a comb-like spectrum, namely a channeled spectrum. The double-pass C-CLPG has the advantage of not only a flexible sensor arrangement, especially for remote sensing, but also the compensation effect for the polarization fluctuations in the sigma-branch caused by the measurand. In the experiment, it is shown that the FRM reflection scheme can stabilize the output polarization state of the double-pass C-CLPG during the temperature change around the C-CLPG, and it is found that the EDFσL enables a more stable and precise measurement than the previous simple EDF ring laser using the C-CLPG. Furthermore, it is also demonstrated that the oscillation is stabilized by the polarization compensation effect of the double-pass C-CLPG even if the polarization state is intentionally changed by applying the mechanical deformation near the C-CLPG.

Polarization Stable Hollow Core Fiber Interferometer With Faraday Rotator Mirrors

Polarization Stable Hollow Core Fiber Interferometer With Faraday Rotator Mirrors

Polarization-insensitive interferometer based on a hybrid integrated planar light-wave circuit

Interferometers are essential elements in classical and quantum optical systems. The strictly required stability when extracting the phase of photons is vulnerable to polarization variation and phase shift induced by environment disturbance. Here, we implement polarization-insensitive interferometers by combining silica planar light-wave circuit chips and Faraday rotator mirrors. Two asymmetric interferometers with temperature controllers are connected in series to evaluate the single-photon interference. Average interference visibility over 12 h is above 99%, and the variations are less than 0.5%, even with active random polarization disturbance. The experiment results verify that the hybrid chip is available for high-demand applications like quantum key distribution and entanglement measurement.

A Polarization-Insensitive Recirculating Delayed Self-Heterodyne Method for Sub-Kilohertz Laser Linewidth Measurement

A polarization-insensitive recirculating delayed self-heterodyne method (PI-RDSHM) is proposed and demonstrated for the precise measurement of sub-kilohertz laser linewidths. By a unique combination of Faraday rotator mirrors (FRMs) in an interferometer, the polarization-induced fading is effectively reduced without any active polarization control. This passive polarization-insensitive operation is theoretically analyzed and experimentally verified. Benefited from the recirculating mechanism, a series of stable beat spectra with different delay times can be measured simultaneously without changing the length of delay fiber. Based on Voigt profile fitting of high-order beat spectra, the average Lorentzian linewidth of the laser is obtained. The PI-RDSHM has advantages of polarization insensitivity, high resolution, and less statistical error, providing an effective tool for accurate measurement of sub-kilohertz laser linewidth.

Simultaneous Measurement of Liquid Level and Temperature Using In-Fiber Grating-Based Mach-Zehnder Interferometer and Faraday Rotator Mirror.

Here we propose an optical fiber sensor capable of simultaneous measurement of liquid level and temperature by utilizing cascaded long-period fiber gratings (LPFGs) inscribed on high-birefringence fiber (HBF) and a Faraday rotator mirror (FRM). Due to the in-fiber Mach-Zehnder interference and birefringence of the HBF, these cascaded LPFGs have polarization-dependent discrete interference spectra, each of which is created within one of the two different attenuation bands obtained in the two orthogonal input polarization states, e.g., linear horizontal polarization (LHP) and linear vertical polarization (LVP). The minimum transmittance dip was selected as a sensor indicator for each interference spectrum obtained for LHP or LVP input signal. To monitor these indicator dips associated with LHP and LVP, referred to as the IDH and IDV, respectively, with one spectral scanning, an FRM was connected to the end of the cascaded LPFGs. Both the IDH and IDV spectrally shifted according to liquid-level or temperature changes and showed very linear responses to them with adjusted R₂ values greater than 0.997. The liquid-level sensitivities of the IDH and IDV were measured as approximately -37.29 and -121.08 pm/mm in a liquid-level range of 0 to 55 mm, respectively. The temperature sensitivities of the IDH and IDV were measured as ˜28.79 and ˜218.21 pm/°C in a temperature range of 30 to 60 °C, respectively. Owing to their linear and independent responses to liquid level and temperature, our sensor can perform temperature-independent liquid-level measurement using their pre-determined liquid-level and temperature sensitivities, even if both liquid level and temperature change simultaneously.

Phase-only modulation of light.

We disclose the method to obtain polarization insensitive phase-only modulation that preserves both the state and the degree of polarization of light modulated using a medium with controlled birefringence. We find that, in the double-pass configuration involving reflection from the Faraday rotator mirror, such a medium acts as the phase-only modulator. The experimental data measured in the Michelson-interferometer-based setup for deformed-helix ferroelectric liquid crystal cells are found to be in good agreement with the theoretical results. For such cells, we experimentally demonstrate high-frequency (4 kHz modulation rate) 2π phase-only light modulation governed by the average phase shift and solve the problem of optical axes switching.

Excess Relative-Intensity-Noise Reduction in a Fiber Optic Gyroscope Using a Faraday Rotator Mirror

The fiber optic gyroscope (FOG) suffers from the excess relative intensity noise (RIN) caused by the broadband light source, which significantly impacts the angular random walk (ARW) of the FOG. The existing suppression methods for the excess RIN usually require complex configuration or devices with big volume, and thus are not suitable for practical applications especially in small-sized FOGs. What is more, as the key parameters or components, that determine the practical suppression effects of the excess RIN, and the corresponding impacting mechanisms are not clarified, there is no efficient way in evaluating or optimizing the excess-RIN reduction configuration in practice. In this work, we propose a simple but effective method to achieve the reduction of the excess RIN at the demodulation frequency, in which a Faraday rotator mirror is inserted to the dead arm of the source coupler to realize the delay line filter for the excess RIN. Experimental results show that the ARW is improved from 1.70 mdeg/h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> to 0.58 mdeg/h <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> for a navigation-grade FOG. More importantly, this work provides a comprehensive understanding on how the main defects in the excess-RIN reduction scheme impact the practical excess-RIN suppression effects both theoretically and experimentally, which demonstrates the inherent robustness of the proposed scheme against internal and external influencing factors. This method is especially suitable for realizing the excess-RIN reduction in small-sized FOGs and upgrading the existing FOG products with minimal modifications, and is also potentially referable in evaluating and optimizing other similar excess-RIN reduction schemes.

High thermal-stability Er-doped superfluorescent fiber source with a vertical cleaved fiber tail

Abstract Mean wavelength stability, a key indicator for evaluating the dynamic performance of Er-doped superfluorescent fiber source (ED-SFS) and high-precision fiber optic gyroscope (FOG), shows high sensitivity to environmental temperature fluctuations. In this paper, a thermally-stable ED-SFS in a one-stage backward configuration is proposed by incorporating a vertical cleaved fiber tail which acts as a Fresnel reflector. Our proposed method demonstrates a mean wavelength stability of 150 ppm and a scale factor error of 702 ppm. Comparing with alternative techniques such as Faraday rotator mirror (FRM) or fiber mirror (FM) over a 100 °C range (−40 °C to +60 °C), the wavelength stability and scale factor error are 105~120 ppm and 230~400 ppm less, respectively. The proposed ED-SFS has a spectral width (FWHM) of 37.682 nm and 10.42 mW output power, which satisfies the requirements of high-precision FOG.

Trace Hydrogen Sulphide Gas Sensor Based on Cu/rGO Membrane-Coated Photonic Crystal Fibre Michelson Interferometer

Abstract A novel Michelson interferometric hydrogen sulphide sensor coated with copper/reduced graphene oxide (Cu/rGO) composite membrane is proposed and fabricated. A section of endlessly photonic crystal fibre (EPCF) was sandwiched in two single-mode fibres (SMFs). One SMF was spliced and tapered with EPCF; the other SMF was connected with the Faraday rotator mirror to construct the Michelson structure. The cladding of the EPCF was coated by the Cu/rGO-sensing membrane, which was prepared by the dip-coating method. The obtained Cu/rGO-sensing film has a length of 25.0 mm. The fabricated sensing membrane is characterised by the scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and so on. Experimental results demonstrated that the Cu/rGO-sensing film has a 24.56-nm thickness with a compact and uniform appearance. The XPS and Raman spectra indicate that there are three elements (C, O, and Cu), which are consistent with the expected compositions of the Cu/rGO membrane. With the increase of concentration of hydrogen sulphide, the interference spectra appear red-shifted. The linearity of 0.97662 and the sensitivity of 13.23 pm/ppm are achieved. In addition, the dynamic response and recovery time of the sensor are approximately 70 and 88 s, respectively. The surface adsorption energies of the film are calculated by the density functional theory. The theoretical results are in good agreement with the experimental findings. This sensor has some key advantages of small size, simple structure, easy fabrication, and great applicability for detecting the trace hydrogen sulphide.

Michelson Interferometric Hydrogen Sulfide Gas Sensor Based on NH2-rGO Sensitive Film

Abstract A highly sensitive hydrogen sulfide gas sensor based on NH2-rGO-coated thin-core-fibre (TCF) Michelson interferometer (MI) is proposed and evaluated. Two sections of TCFs are alternately sandwiched between three single-mode-fibres (SMFs). A Faraday rotator mirror (FRM) is fixed to the end of the last SMF to reflect the light signal and enhance the interference. Then the structure SMF-TCF-SMF-TCF-SMF-FRM (STSTS-F) is successfully constructed. NH2-rGO, as sensing film, is coated on two TCFs and is used to detect traces of hydrogen sulfide gas. Raman spectra and XPS analysis show that NH2-rGO has been successfully synthesised. The thickness of the NH2-rGO film coated on the TCF surface is about 500 nm. By introducing 0–60 ppm hydrogen sulfide gas into the chamber, with the increase in concentration of the gas, the monitoring trough exhibits a blue shift. Our experimental results show that the sensor has good linearity (R 2 = 0.98096) and selectivity for hydrogen sulfide gas. The sensitivity is 21.3 pm/ppm, and the response and recovery times are about 72 and 90 s, respectively. The sensor has the advantages of high sensitivity, high selectivity, and small size, enabling the detection of trace hydrogen sulfide in toxic gas environments.

Simultaneous measurement of strain and temperature based on a long-period fiber grating written on high birefringence photonic crystal fiber concatenated with a Faraday rotator mirror

Here we report simultaneous measurement of strain and temperature, carried out by incorporating a long-period fiber grating (LPFG) written on high birefringence photonic crystal fiber (HBPCF), referred to as an HBPC-LPFG, and a Faraday rotator mirror (FRM) concatenated in series with the LPFG. The HBPC-LPFG used as a sensor head was fabricated by irradiating CO2 laser pulses to unjacketed HBPCF with line-by-line technique. The HBPC-LPFG connected in series with the FRM exhibits a polarization-independent wavelength-dependent loss spectrum in its reflection spectrum, which has two resonance dips (RDs) with different cladding-mode orders, designated as RDs 1 and 2. As the two RDs in the fabricated HBPC-LPFG ended with the FRM have dissimilar cladding-mode orders, their strain sensitivities and their temperature sensitivities are different from each other. For the two RDs with resonance wavelengths of λ1 = ∼1470.5 nm and λ2 = ∼1495.1 nm, strain and temperature responses were investigated in an applied strain range from 0 to 1790 μe (step: 179 μe) and an ambient temperature range from 30°C to 95°C (step: 5°C), respectively. The strain sensitivities of the RDs 1 and 2 were measured to be approximately −0.77 and −1.07 pm / μe at room temperature, and the temperature sensitivities of the RDs 1 and 2 were measured as ∼10.44 and ∼8.56 pm / ° C without applied strain, respectively. Owing to their linear and independent responses to strain and temperature, strain and temperature changes applied to the HBPC-LPFG can be simultaneously estimated from the measured wavelength shifts of the RDs 1 and 2 using their predetermined strain and temperature sensitivities.

Polarization influence and its mitigation on laser frequency noise measurement by a short-delayed self-homodyne interference method.

This paper investigated how a polarization state influences frequency noise measurement accuracy of the short-delayed self-homodyne interference method. An autopolarization control method was demonstrated to mitigate polarization-induced fading (PIF) in a 120-deg phase difference Mach-Zehnder Interferometer (MZI). This method used a feedback adjustment with simulated annealing algorithm, which had the advantages of a short control period, high accuracy, and easy implementation. Frequency fluctuations' power spectral density and linewidth results measured by the improved MZI were consistent with the results of the Michelson interferometer, which used the Faraday rotator mirrors (FRMs) to overcome PIF. The novel MZI structure is unrestricted to FRMs and can extend the capability of the short-delayed self-homodyne interference technique for many special bands' laser frequency noise measurements such as visible bands.

Refractive index measurement using OTDR-based ring-down technique with S fiber taper

We proposed and demonstrated a fiber loop ring-down (FLRD) sensor based on S fiber taper (SFT) cascaded with a Faraday rotator mirror (FRM) for refractive index (RI) measurement. The FLRD cavity is established conveniently by an optical time domain reflectometry (OTDR). The net loss of the cavity is modulated by the RI-sensitive SFT. The surrounding refractive index (SRI) measurement can be realized by monitoring the slope of the ring-down pulses envelope. Owing to the compensation provided by the erbium-doped fiber amplifier (EDFA), the ring-down pulses signal of the OTDR-based FLRD cavity is improved effectively. Within the measurement range of 1.3330∼1.3518, the proposed sensor has a linear response to the SRI with a sensitivity of 2646.307 dB/(kmRIU) at the interrogating wavelength of 1550 nm. Compared with the conventional FLRD sensors, the proposed OTDR-based RI sensor has the advantages of simple design and reflective sensing structure, which is easily implementable and cost-effective.

Modeling and characterization of a dual-wavelength SOA-based single longitudinal mode random fiber laser with tunable separation

In this work, a novel Single longitudinal mode (SLM) dual-wavelength random fiber laser (DW-RFL) with narrow line-width and tunable separation between the two modes in the range 1.5 – 25 nm (187 GHz – 3.12 THz) is presented. The laser is based on Rayleigh backscattering in a standard single mode fiber of 2 km length acting as distributed mirrors and a semiconductor optical amplifier (SOA) acting as the optical amplifier. Two optical band pass filters are used for the wavelength selection, and two Faraday Rotator mirrors are used to sustain the stability of the two lasing wavelengths against fiber random birefringence. The measured line-width of each mode of the laser varies from 3 to 11.5 kHz with lasing wavelengths and SOA pump currents. The power and the wavelength stabilities at the peak power of each mode were also investigated.