Seven-core Optical Fiber Research Articles

3D printing fiber-tip integrated Fabry-Perot interferometers for ultrasensitive RI sensing with an enhanced Vernier effect.

An ultrasensitive refractive index (RI) sensing technology based on an enhanced Vernier effect is proposed, which integrates a polymer Fabry-Perot interferometer (FPI) with an open cavity FPI on the tip of a seven-core optical fiber. Interference spectra of the polymer FPI and the open cavity FPI shift to opposite directions as the ambient RI changes, thus leading to the enhanced Vernier effect. Investigations of RI sensitivity and temperature dependence of the proposed fiber sensors are carried out. Taking advantage of the enhanced Vernier effect, we demonstrate a remarkable sensitivity of 19742.86 nm/RIU within the RI range from 1.39 to 1.395. The sensor exhibits substantial advantages such as ease of fabrication, compact structure, high sensitivity, and good repeatability, providing a practical and competitive solution for RI sensing.

Non-orthogonal multiple access scheme based on color-coded four-dimensional constellation pairing mapping

This paper proposes a short-range optical access method based on four-dimensional non-orthogonal multiple access (4D-NOMA), utilizing 4D constellation pairing mapping and two-dimensional inverse discrete Fresnel transform (2D-IDFnT) technology, achieving high compatibility with OFDM systems. An innovative color-coded 4D constellation pair mapping scheme was designed, introducing two types of four-dimensional spatial structures with 32 constellation points. By extending the three-dimensional constellation to four dimensions through color coding, the constellation figure of merit (CFM) increased by 22.2%. A 43.29 Gb/s 4D-NOMA transmission over a seven-core optical fiber was successfully demonstrated, verifying the feasibility and superiority of the proposed solution. Compared to conventional low-dimensional constellations, 4D-NOMA exhibits significant improvements in bit error rate and signal transmission sensitivity. Under the HD-FEC threshold, it provides approximately 0.9 dB and 1.3 dB sensitivity gains over traditional three-dimensional and two-dimensional constellations, respectively. This study indicates that the four-dimensional constellation structure and the 4D-NOMA scheme hold great potential for future short-range optical access systems.

Enhanced 4D-OFDM optical communication systems with color-coded constellations and probability constellation shaping.

The present work introduces a four-dimensional probability constellation mapping OFDM optical transmission system based on a two-dimensional inverse fast Fourier transform (2D-IFFT). A four-dimensional constellation structure employing color coding is designed, amalgamating geometric shaping with probability shaping to enhance the constellation figure of merit (CFM). Successful transmission of OFDM signals at 51.49 Gb/s is achieved over a 2 km seven-core optical fiber, validating the performance of the proposed constellation diagram. Under the conditions of multicore multiplexing and a bit error rate of 3.8 × 10-3, the receiver sensitivity of the OFDM signals mapped with the proposed color-coded four-dimensional constellation exhibits gains of 0.8 dB, 1.33 dB, and 1.83 dB compared to traditional four-dimensional constellations, 3D-OFDM, and 2D-OFDM modulation, respectively. Furthermore, under an entropy value of 4.4 bits/symbol, a receiver sensitivity gain of 1.36 dB is attained compared to a uniform distribution constellation, indicating the favorable error performance of this scheme with promising prospects for short-distance communication in the future.

Speckle wavemeter based on a multi-core fiber and compressive imaging.

Random speckle patterns contain valuable information about the incident light. Researchers have successfully constructed spectrometers and wavemeters by utilizing the speckles generated by inter-mode interferences of a multimode fiber (MMF). However, cameras were often employed to record the speckle data in previous reports. The camera's high cost (especially in the near-infrared range), large size, and low response speed limit the applications in optical communications, metrology, and optical sensing. A seven-core fiber (SCF) was fused with an MMF to capture the speckle pattern, where each core coupled part of the speckle field. Furthermore, we take advantage of the space division multiplexing capability of the SCF by incorporating an optical switch. This allows the variety of speckles generated by the incidence of different cores into the MMF. A convolutional neural network (CNN) regression algorithm was designed to analyze the complicated speckle data. The experimental results show that the proposed wavemeter can resolve adjacent wavelengths of 1pm with an error of about 0.2pm. We also discussed how different lengths of MMF influence the wavelength resolution. In conclusion, our research presents a robust and cost-effective approach to a wavelength measurement device by use of a seven-core optical fiber.

Research and assessment of high sensitivity intensity modulation vector curvature sensor based on cascaded bamboo-joint microcavity structure

This study presents the VC-BM, a novel vector bamboo joint cascaded microcavity curvature sensor, which utilizes light intensity correlation. The device is fabricated using arc fusion, connecting a tapered seven-core optical fiber with a multi-mode and hollow-core fiber. Meanwhile, mode-coupling theory optimizes its design for high-quality transmission spectra. The feasibility and sensitivity of vector curvature sensing via intensity modulation (VC-BM) have been demonstrated through theoretical simulations and experimental validation. Building upon this foundation, a novel envelope intensity differential modulation algorithm is proposed, which maintains curvature direction recognition and enhances sensitivity, reaching up to 243.57 ± 3.63 dB/m−1. Additionally, leveraging its advantages, the successful integration of a three-layer Backpropagation (BP) neural network has enabled predictive analysis of this curvature sensing device, thereby increasing its commercial value. Furthermore, the sensor's high stability and resistance to temperature interference make it an ideal solution for wearable micro-deformation monitoring.

Optical non-orthogonal multiple access based on amino acids and extended zigzag.

We propose a novel security-enhanced power division multiplexing (SPDM) optical non-orthogonal multiple access scheme in conjunction with seven-core optical fiber in this paper. This scheme could improve the security of data transmission at the physical layer and the split ratio of the access network, ensuring more users can be served at the same time. Additionally, multiple signals can be superimposed in the digital domain, leading to a significant improvement in spectral efficiency. We have further experimentally demonstrated the transmission of 47.25 Gb/s SPDM orthogonal frequency division multiplexing (OFDM) signals in a 2 km seven-core fiber system. The experimental results confirm that our scheme can increase the number of access users by 14 times without influencing the privacy of different users. It is worth mentioning the signal encryption method based on amino acids combine with extended zigzag is proposed for the first time as we know. Meanwhile, the key space reaches 10182, indicating that the data transmission process can be effectively protected from the attack of stealers. The proposed security-enhanced power division multiplexing space division multiplexing passive optical network (SPDM-SDM-PON) support multi-threading and multi-functions, showing a great potential to be applied in the future telecommunication systems.

Intelligent dynamic data perturbation OCDM encryption scheme based on cellular neural network and biological genetic encoding.

In this paper, an intelligent dynamic perturbation orthogonal chirp division multiplexing (OCDM) encryption scheme based on cellular neural network and biological genetic encoding for seven-core optical fiber is proposed for the first time to our knowledge. In this scheme, chaotic sequences generated by cellular neural network are employed to construct six masking vectors to achieve six dimensions of ultra-high security encryption. The transmitted bit data is interleaved according to the DNA operation rules. The subcarrier frequency, symbol matrix, and time are scrambled. Because the selected encoding rule, decoding rule, key base sequence, subcarrier frequency, symbol matrix, and scrambling position of time all change dynamically, the robustness against malicious attack is enhanced. Simultaneously, OCDM technology is employed to optimize the system, which effectively improves the anti-interference ability and bit error performance of the system. A 70 Gb /s (7×10 Gb /s) encrypted OCDM signal transmission experiment is carried out on a 2 km 7-core fiber, and an orthogonal frequency division multiplexing (OFDM) signal is transmitted under the same conditions for comparison and verification. The results show that the key space of the newly proposed encryption scheme can reach 101170, and the receiver sensitivity of OCDM is 1.2 dB greater than that of OFDM when the bit error rate is 10-3. The scheme can improve the security of encrypted information and the performance of the system, which is very promising in the optical access network of the future.

A multi-angle torsion sensor based on seven-core fiber microcavity structure

A multi-angle torsion sensor based on seven-core optical fiber(SCF) microcavity structure is proposed. An end of SCF is treated with microcavity processed and cascaded with single-mode fiber(SMF) and multi-mode fiber(MMF). Among them, the MMF1 and MMF2 at both ends of SCF realize the beam splitting and combining functions between SMF and SCF, and the microcavity structure mainly plays the role of beam splitting. Experiments results show that the intensity loss of the transmission spectrum changes significantly in the torsion range of 0°–360°, and the maximum torsion sensitivity is 0.04685 dB/°. The experimental results agree with the theoretical simulation. The sensor has simple structure and easy preparation, and can be widely used in the field of outdoor safety detection and bridge monitoring.

Polymer-coated polishing seven-core Mach-Zehnder interferometer for temperature sensitivity enhancement

A novel high sensitivity temperature sensor based on side-polished Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. The configuration of sensor is a section of side-polished seven-core optical fiber (SCF) structure sandwiched between two waist-enlarged tapers. In the proposed sensing structure, the temperature sensitivity can be improved theoretically by coating polymer on its polished part because of the different thermal expansion effects between polymer and fiber. The experimental results show that the temperature sensitivity of the polymer-coated sensor is 4.58 times as that of the sensor without polymer coating, and the maximum sensitivity is 336.67 pm/°C in the range of 30 °C to 65 °C. The improving time is not obviously changed before coating polymer, but affected by the polishing depth of SCF in the coated structure. The results show that the temperature sensitivity of sensor can be effectively improved, and it is easy to manufacture and operate.

Diagnosis of Oral Squamous Cell Carcinoma (OSCC) Using Laser Induced Fluorescence

Cancer is a dreaded disease; a large number of deaths occur every year due to this disease. Oral squamous cell carcinoma (OSCC) is the most common cancer of the head and neck, which is approximately 16% to 40% of all malignancies. In this study, Laser induced fluorescence (LIF) spectroscopy has been utilized to discriminate OSCC against healthy (normal) tissues and to investigate whether the LIF could provide information from formalin-fixed paraffin-embedded (FFPE) tissue samples similar to that reported using fresh tissues. Samples were prepared after biopsy from ten patients using standard FFPE tissues methods. LIF system consists of a continuous wave (CW) He–Cd laser at 325 nm, a seven-core optical fiber cable coupled to the laser, a spectrometer with cooled charge coupled device (CCD) detector, and a computer for acquisition of the LIF spectra. Spectra were decomposed using second derivative and curve fitting analysis to reveal the changes in molecular composition of the samples. Moreover, samples spectra were discriminated by hierarchical cluster analysis (HCA) and principal components analysis (PCA). Spectral results showed differences in peak areas and positions between normal and OSCC tissues. LIF spectroscopy revealed significant decrease in the peak area of collagen and decrease in peak area of coenzymes of OSCC tissues. In addition, significant shift in the peak position of coenzymes was recorded. HCA and PCA of LIF indicated a very clear discrimination of the normal and FFPE-OSCC tissues. The achieved discrimination between elliptic polygons of normal and OSCC tissues was 96.3% by PCA. This study confirms that the LIF spectroscopy is a good diagnostic tool for OSCC and it could be used with samples that are prepared using FFPE tissues methods.

Multicore optical fiber shape sensors suitable for use under gamma radiation.

We have designed and implemented a fiber optic shape sensor for high-energy ionizing environments based on multicore optical fibers. We inscribed two fiber Bragg gratings arrays in a seven-core optical fiber. One of the arrays has been inscribed in a hydrogen-loaded fiber and the other one in an unloaded fiber in order to have two samples with very different radiation sensitivity. The two samples were coiled in a metallic circular structure and were exposed to gamma radiation. We have analyzed the permanent radiation effects. The radiation-induced Bragg wavelength shift (RI-BWS) in the hydrogen-loaded fiber is near ten times higher than the one observed for the unloaded fiber, with a maximum wavelength shift of 415 pm. However, the use of the multiple cores permits to make these sensors immune to RI-BWS obtaining a similar curvature error in both samples of approximately 1 cm without modifying the composition of the fiber, pre-irradiation or thermal treatment.

Fiber-optic sensor implanted with seven-core helical structure for measurement of tensile strain and extrusion bending

We proposed a fiber-optic sensor implanted with helical seven-core structure based on Mach–Zehnder interference, which can be used for the measurement of tensile strain and extrusion bending. The sensor consisted of a section of seven-core optical fiber with helical structure, which can be described as the SMF-Taper-HSCF-Taper-SMF (HSCF, helical seven-core fiber) sensor. When stretching or bending is applied, the sensor will undergo certain deformation, which will lead to the changes of interference modes in the optical fiber. The tensile strain and extrusion bending can be measured accurately according to the response of transmission spectrum to mode change. The helical seven-core structure can effectively stimulate higher order modes and induced deformation changes. In the experiment, three sensors with different helical periods were fabricated and their spectral characteristics were analyzed. Finally, we selected the sensor with a helical period of 190 μm to conduct a strain and bending test. The results show that the strain sensitivity of the sensor is −21.31 pm / μe in the range of 0 to 500 μe, and the curvature sensitivity of the sensor is −6.36 nm / m − 1 in the range of 0.16 to 1.6 m − 1. This sensor can detect strain and bending and has stable sensing performance and high sensitivity.

Stack-and-Draw Manufacture Process of a Seven-Core Optical Fiber for Fluorescence Measurements

ABSTRACTMulti-core, optical-fiber technology is expected to be used in telecommunications and sensory systems in a relatively short amount of time. However, a successful transition from research laboratories to industry applications will only be possible with an optimized design and manufacturing process. The fabrication process is an important aspect in designing and developing new multi-applicable, multi-core fibers, where the best candidate is a seven-core fiber. Here, the basics for designing and manufacturing a single-mode, seven-core fiber using the stack-and-draw process is described for the example of a fluorescence sensory system.

Measuring the difference in group delays between the cores of a multicore optical fiber by means of time-domain interferometry

A way of measuring the difference in group delays between the cores of multi-core optical fiber is proposed. The method is based on a low-coherence Mach–Zehnder interferometer and a broadband radiation source. The corresponding experimental setup is constructed and a seven-core optical fiber with identical cores manufactured at the Fiber Optics Research Center, Russian Academy of Sciences, is studied.

Fiber-optic delay line using multicore fiber

A fiber-optic delay line based on a multicore optical fiber is fabricated for the first time. Due to the optical pulse sequential passage over all cores, the time delay of the optical signal of 45.0 μs is obtained at the optical fiber length of only 1300 m. The use of the seven-core optical fiber allows a sevenfold reduction in the used fiber length in comparison with single-core fibers, which is promising for developing lines with long signal delays.

Performance analysis of optical transmission based on seven cores fiber

This essay designed a kind of new seven-core fiber with lower crosstalk and loss, and made space division multiplexing transmission experiment based on this seven-core fiber. It is known that crosstalk has the most serious influence in multicore fiber transmission process. Before the experiment, the affecting factors of fiber crosstalk were analyzed through simulation, such as core space, bending radius, and fiber length. Combined with the simulation analysis, the design scheme of multicore fiber with low crosstalk was obtained. Before the fiber design, various factors of influence crosstalk such as the core-to-core distance, bending radius, fiber length and so on. Based on the simulation analysis, conclusion has made on the design scheme of multi-core optimal fiber with low crosstalk. The space division multiplexing and wavelength division multiplexing technology, was adopted to conduct seven-core optical fiber transmission of 58.7km. The crosstalk of adjacent core was suppressed to as low as 45dB/km, the attenuation of inner core was 0.24dB/km, the outer cores' 0.32dB/km. Different bit error rate (BER) performances were also studied under different conditions, through reasonably designing the system to reduce the error rate, improve the performance of the system, and realize long distance and large capacity transmission with fiber.

Silicon Photonics Core-, Wavelength-, and Polarization-Diversity Receiver

A seven-core optical fiber, each core carrying two wavelength channels, is coupled to a novel silicon photonic integrated circuit (PIC). The silicon PIC uses grating couplers, Mach-Zehnder interferometers, and photodiodes to demultiplex and receive all 14 signals. We demonstrate reception of polarization-scrambled 5-Gb/s on-off keyed signals.