Low-noise Fiber Research Articles

GA-BP-Based Low-Noise FBG Hydroacoustic Monitoring System with Reference Sensor.

To address the issue of harsh marine background noise impacting the monitoring signal of fiber-optic hydrophones, we propose a low-noise fiber Bragg grating (FBG) hydroacoustic monitoring system with a reference sensor based on genetic algorithm backpropagation (GA-BP). Through theoretical analysis, we deduce the noise suppression steps of the GA-BP algorithm based on the reference sensor and construct train and test sets based on the data from the reference sensor and monitoring sensor at different times, optimizing the GA-BP algorithm to find the best fitting results and thereby obtaining the low-noise monitoring signal. Experimental results from the anechoic tank show that the proposed method can suppress background noise interference on effective signals and that the suppression effect improves as the background noise increases. The sound pressure sensitivity ranges from -173.76 dB to -171.33 dB at frequencies of 8 kHz to 12 kHz, with a response flatness of less than 2.43 dB. The noise suppression effect is obvious under the condition of poor signal-to-noise ratio (SNR), which can reach more than 18.3 dB. The advantages of the proposed algorithm in array signal processing are further demonstrated by the directivity experiment, which proves that the algorithm has a great potential for engineering applications in harsh marine environment.

Phase noise suppression of optic flexural disk accelerometer by studying the thermal stability of optical fiber ring

As the core sensing elements of ultra-long fiber interferometer, the distributed thermal strain difference of the fiber rings can cause extra noise of the flexural disk, resulting in a penalty of the deterioration accuracy. In this paper, the thermal strain distribution characteristics of the fiber ring are firstly analyzed by the finite element method (FEM), and the distribution result is consistent with that demonstrated by the Rayleigh optical frequency-domain reflectometry (R-OFDR) strain measurement. The interferometer phase noise caused by the distributed strain difference is further studied by constructing a fully symmetric polarization-maintaining fiber-ring Mach-Zehnder interferometer (MZI) with an arm length of over 100 meters. The results show that the distributed thermal strain difference of two fiber rings will cause additional phase fluctuation, which leads to higher low-frequency noise. Therefore, a dual-fiber-ring MZI with matched distributed thermal strains is proposed to suppress the phase noise caused by the thermal strain, and the best suppression is as high as 45.6 dB. This is very important for the research and design of low noise fiber seismometer.

Focus on lasers, imaging, microscopy, and photonics

Focus on lasers, imaging, microscopy, and photonics

Real-time polarization compensation system for wavelength division multiplexing in low noise fiber channel based on single photon counting feedback

The physical effects such as random birefringence of fiber optic channels due to environmental influences make the optical signals transmitted in them have sensitive polarization variations, which seriously affects the performance of polarization biased code quantum key distribution systems. In this paper, a low-noise fiber channel wavelength division multiplexing real-time polarization compensation system is presented, where single photon counting is used as a feedback signal. The system can acquire the fiber channel polarization change information by detecting the photon counting of the conjugate reference light. In the system, the compensation algorithm is designed to control the electric polarization controller to calibrate the polarization state of the quantum signal light under the corresponding polarization base in real time, and the stable fiber channel polarization compensation is successfully achieved. In order to verify the effectiveness of the compensation system, a quantum key distribution test based on BB84 protocol with a transmission distance of 25.2 km is conducted, and stable test results of up to 8 hours are obtained in the laboratory environment and the simulated metropolitan area network buried fiber environment, with the average quantum bit error rate being 0.52% and 1.25%, respectively. The experimental results show that this system can guarantee the stable operation of polarization-encoded quantum key distribution in the buried fiber environment in urban areas.

Evolution of Relative Intensity Noise in High-Power Narrow-Linewidth Fiber Laser Systems

In this work, we carry out a systematic study on the evolution of relative intensity noise (RIN) in a high-power narrow-linewidth fiber laser system based on phase-modulated single-frequency seed laser. The experimental results clarify that enhancement of the RIN mainly occurs when the seed laser gets amplified from low power to medium power. In addition, further power scaling could lead to reduction of the RIN until it reaches saturation on the condition that the transverse mode instability (TMI) effect is effectively suppressed. Apart from the power scaling process, the phase-modulation would also lead to enhancement of the RIN at specific frequencies corresponded to the modulation frequency. More importantly, the contrast experiments reveal that the TMI effect could lead to obvious enhancement of the RIN of the signal laser during amplification well below the TMI threshold defined by the traditional method. Therefore, apart from degeneration of the RIN during amplification, potential enhancement of the RIN induced by the phase-modulation or the TMI effect below its traditional threshold should be carefully considered and controlled to achieve high-power low-noise fiber laser. Overall, our experimental results could provide a well reference for design of high-power low-noise fiber lasers and high-power narrow-linewidth fiber lasers.

Low-Noise Graded-Index Plastic Optical Fiber Achieved by Specific Copolymerization Process

Ultra-high-definition (UHD) technologies have recently received attention on account of their practical applications in consumer electronics. UHD devices require uncompressed video transmission at a data rate exceeding 100 Gb/s; thus, an optical fiber connection is essential. In consumer applications, optical fibers are very short. Moreover, their connections must permit variations in the fiber alignment, which accommodates rough handling by consumers. Under this condition, the transmitted signal quality is significantly degraded owing to noise and instabilities that strongly depend on the fiber alignment conditions in optical modules and connectors. Therefore, graded-index plastic optical fibers (GI POFs) are promising optical cables for consumer applications because of their flexibility, safety, and high bandwidth. Recently, the authors experimentally demonstrated that GI POFs can reduce interferometric noise, such as modal noise and multipath interference noise, in a multimode fiber link based on a vertical-cavity surface-emitting laser (VCSEL). This noise reduction effect results from strong mode coupling of GI POFs, which is closely related to microscopic heterogeneous structures of a core polymer matrix. In this paper, a control method of mode coupling using the copolymerization process for fiber core materials is proposed. The formation of composition fluctuations by copolymerization increases the mode coupling in the GI POF core. It thereby enables highly stable and robust data transmission with a large fiber misalignment tolerance in a VCSEL-based multimode fiber link. The proposed method for mode coupling control is expected to contribute to household optical communication systems in the upcoming UHD era.

Performance Enhancements of Femtosecond Fiber Amplifier by Pump Wavelength Optimization

We demonstrate an efficient scheme to accelerate the self-similar pulse evolution and reduce the intensity noise of a free-running femtosecond fiber amplifier based on the pump wavelength optimization. Experiments and simulations indicate the enhanced tolerances of the pulse self-similar amplification to the seed signal power and pump wavelength fluctuations, with the optimum 915 nm pump wavelength. ∼20% increase in the compressed pulse quality and ∼31% reduction in the amplifier root-mean-square (RMS) relative intensity noise (RIN) (1.5 kHz to 5 MHz) have been observed, even with a more than 4 times higher pump laser diode (LD) RIN than the case of 976 nm. ∼50 fs transform-limited pulses are generated with the ∼0.03% amplifier RMS RIN. The proposed scheme can lower the requirements of low-noise self-similar femtosecond fiber amplifiers on the power stability of the seed oscillator and the thermal control of the pump LD, thus denoting potentials for the various satellite-based high-precision applications of femtosecond laser in space.

Noise-sideband-free and narrow-linewidth photonic microwave generation based on anoptical heterodyne technique of low-noise fiber lasers.

Noise-sideband-free and narrow-linewidth photonic microwave generation based on an optical heterodyne technique is demonstrated experimentally. By beating a self-injection-locking low-noise single-frequency fiber laser and a Brillouin fiber laser, a 9.4 GHz microwave is produced, and its noise sidebands are completely suppressed. Additionally, the signal-to-noise ratio of the microwave signal is improved by 15 dB from 40 to 55 dB, and the linewidth is compressed from 1.6 to 0.53 kHz. The high-performance photonic microwave based on low-noise fiber lasers is a promising candidate in further applications such as wireless network, lidar, and satellite communication.

Ultra-low Brillouin scattering in anti-resonant hollow-core fibers

Sensitive optical experiments in fiber, including for applications in communications and quantum information, are limited by the noise generated when light scatters from thermally excited guided-acoustic phonons. Novel fibers, such as microstructured fibers, offer control over both optical and acoustic waveguide properties, which can be designed to mitigate optomechanical noise. Here, we investigate the optomechanical properties of microstructured anti-resonant hollow-core fibers and demonstrate their promise as a low-noise fiber platform. By developing an ultra-sensitive spectroscopy technique, a seven capillary anti-resonant hollow-core fiber is found to exhibit record low optomechanical coupling (<10−4 W−1 m−1), in agreement with comprehensive numerical calculations. The largest scattering occurs from a guided acoustic mode in the air confined in the core of the fiber. Acoustic resonances in the silica, due to minimal overlap with the optical mode in the core, scatter a hundred times less, resulting in negligible depolarization noise. The largest optomechanical interactions in anti-resonant hollow-core fibers are found to be at least three (five if evacuated) orders of magnitude weaker than those in conventional single-mode fibers, which makes this class of fibers a promising platform for low noise applications, including quantum information processing and optical communication.

WDM Transmission With In-Line Amplification at 1.3μm Using a Bi-Doped Fiber Amplifier

Extension in the reach of 1.3 μm optical communication systems has traditionally been restricted by the availability of suitable low-noise fiber amplifiers. Addressing this challenge, we present the first repeatered wavelength division multiplexing (WDM) experiments using a bismuth-doped exhibits 8.4 THz (50 nm) of gain bandwidth in the O-band. WDM signals arranged either with coarse or dense wavelength spacings are transmitted over lengths of single-mode fibre (SMF)-28e ranging between 100 and 140 km.

Low-noise femtosecond Cherenkov fiber laser, continuously tunable across the entire red-green-blue spectral range

Low-noise Cherenkov wave conversion in a tapered photonic crystal fiber turns a standard, fixed-wavelength femtosecond laser into an extremely widely-tunable source. Here we show the continuous laser tunability across the entire red-green-blue range.

Fiber-Wrapped Mandrel Microphone for Low-Noise Acoustic Measurements

A low-noise fiber optic microphone has been developed using a fiber-wrapped mandrel as the acoustic transducer. The microphone has an average sensitivity of 0.206 rad/Pa between acoustic frequencies of 50 Hz and 16 kHz and a minimum detectable pressure as low as 3 μPa/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> . The noise floor of the microphone approaches the thermal limit set by the length of fiber used in the system. Performance of the microphone is comparable to a current state-of-the-art condenser microphone. The design is small, lightweight, and readily packaged into multiplexed systems, making it an ideal candidate for use in acoustic sensor array systems.

25 W single-frequency, low noise fiber MOPA at 1120 nm.

This Letter reports on the development of a 25W single-frequency, all-fiber master oscillator power amplifier (MOPA) operating at 1120nm. By heating the gain fiber at 75°C, an output power of 25.3W is achieved with an optical-to-optical efficiency of 53.5%. The output shows no sign of stimulated Brillouin scattering and the signal to amplified spontaneous emission ratio is close to 40dB. A M2 value of 1.15 and a polarization extinction ratio of 17dB are measured. The relative intensity noise of the output is also characterized, reaching -155 dBc/Hz at 10MHz at the maximum output power. The study of the noise dynamics highlights, for the first time to the best of our knowledge, an unpredicted behavior due to the strong backward amplified spontaneous emission.

All-optical low noise fiber Bragg grating microphone.

We present an all-fiber design for a microphone using a fiber Bragg grating Fabry-Perot resonator attached to a diaphragm transducer. We analytically model and verify the fiber-diaphragm mechanical interaction, using the Hänsch-Couillaud readout technique to provide necessary sensitivity. We achieved a noise-equivalent strain sensitivity of 7.1×10-12 ϵ/Hz, which corresponds to a sound pressure of 74 μPa/Hz at 1kHz limited by laser frequency noise and yielding a signal-to-noise ratio of 47±2 dB with a 1Pa drive at 1kHz, in close agreement with modeled results.

High-Gain, Low-Noise-Figure, and High-Linearity Analog Photonic Link Based on a High-Performance Photodetector

We report a high-gain, low-noise-figure, and high-linearity analog photonic link. The link combines a high-power and low-noise fiber laser, a Mach-Zehnder modulator, a high-gain erbium-doped fiber amplifier (EDFA), and a high-performance charge-compensated modified unitraveling-carrier photodiode. The critical characteristics of the photodiode include 16-GHz bandwidth, 200-mA saturation current, and >35 dBm third-order intercept point. In the link, low biasing is utilized to reduce the noise and maximize the signal-to-noise ratio, and an EDFA is used to provide sufficient optical input to the MUTC photodiode to ensure that the link can achieve high gain and high output RF power. The combination of high-power low-noise fiber laser and high-bandwidth high-power photodiode, we have enabled high gain (27.8 dB at 6 GHz and 24.5 dB at 12 GHz), low noise figure (4.7 dB at 6 GHz and 6.9 dB at 12 GHz), and high spur free dynamic range (>120 dB · Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> ) in the frequency range 6-12 GHz.

Nonlinear fibre-optic devices pumped by semiconductor disk lasers

Semiconductor disk lasers offer a unique combination of characteristics that are particularly attractive for pumping Raman lasers and amplifiers. The advantages of disk lasers include a low relative noise intensity (-150 dB Hz-1), scalable (on the order of several watts) output power, and nearly diffraction-limited beam quality resulting in a high (∼70 % — 90 %) coupling efficiency into a single-mode fibre. Using this technology, low-noise fibre Raman amplifiers operating at 1.3 μm in co-propagation configuration are developed. A hybrid Raman-bismuth doped fibre amplifier is proposed to further increase the pump conversion efficiency. The possibility of fabricating mode-locked picosecond fibre lasers operating under both normal and anomalous dispersion is shown experimentally. We demonstrate the operation of 1.38-μm and 1.6-μm passively mode-locked Raman fibre lasers pumped by 1.29-μm and 1.48-μm semiconductor disk lasers and producing 1.97- and 2.7-ps pulses, respectively. Using a picosecond semiconductor disk laseramplified with an ytterbium-erbium fibre amplifier, the supercontinuum generation spanning from 1.35 μm to 2 μm is achieved with an average power of 3.5 W.

Full phase stabilization of a Yb:fiber femtosecond frequency comb via high-bandwidth transducers

We present full phase stabilization of an amplified Yb:fiber femtosecond frequency comb using an intracavity electro-optic modulator and an acousto-optic modulator. These transducers provide high servo bandwidths of 580 kHz and 250 kHz for f(rep) and f(ceo), producing a robust and low phase noise fiber frequency comb. The comb was self-referenced with an f-2f interferometer and phase locked to an ultrastable optical reference used for the JILA Sr optical clock at 698 nm, exhibiting 0.21 rad and 0.47 rad of integrated phase errors (over 1 mHz-1 MHz), respectively. Alternatively, the comb was locked to two optical references at 698 nm and 1064 nm, obtaining 0.43 rad and 0.14 rad of integrated phase errors, respectively.

Gain dynamics and refractive index changes in fiber amplifiers: a frequency domain approach

Gain dynamics and refractive index changes in fiber amplifiers are important in many areas. For example, the knowledge of the frequency responses for seed and pump power modulation are required to actively stabilize low noise fiber amplifiers. Slow and fast light via coherent population oscillations rely on the change of group index to delay or advance pulses, and refractive index changes in fiber amplifiers are a possible explanation for mode fluctuations in high power fiber amplifiers. Here, we analyze the frequency dependent influence of seed and pump power modulation on the fiber amplifier output power and the refractive index. We explain the observed power and refractive index modulation with an analytic model originally developed for telecom amplifiers and discuss a further simplification of the model.

Low-noise Raman fiber amplifier pumped by semiconductor disk laser

A 1.3 µm Raman fiber amplifier pumped by 1.22 µm semiconductor disk laser in co-propagation geometry is demonstrated. Measured relative intensity noise of -148 dB/Hz over frequency range up to 3.5 GHz was measured at 900 mW of pump power. 9 dB gain was achieved with co-propagating pumping geometry with less than 2 dB additional noise induced by amplifier to the signal. Nearly shot-noise-limited operation of semiconductor disk laser combined with the diffraction-limited beam allows for efficient core-pumping of the single-mode fiber Raman amplifiers and represents a highly practical approach which takes full advantage of co-propagating pumping.

Er-doped fiber frequency comb with mHz relative linewidth

A low-noise fiber frequency comb is demonstrated to improve the frequency accuracy and linewidth by suppressing the phase noise caused by the nonlinear self-phase modulation as well as the amplified spontaneous emission within the Er-doped fiber amplifier. The linewidth of the carrier-envelop- offset signal measures less than 1.9 mHz and the frequency stability well follows the reference Rb clock. This achievement will facilitate the use of the fiber frequency comb for industrial applications to precision near-infrared spectroscopy, frequency calibration, optical clocks and length metrology.