Photonics

12 pages, 7080 KiB

Open AccessArticle

Design of Multi-Wavelength Diffractive Lenses Focusing Radiation of Different Wavelengths to Different Points

by Leonid L. Doskolovich, Roman V. Skidanov, Veronika A. Blank, Sofiya V. Ganchevskaya, Vladimir V. Podlipnov, Dmitry A. Bykov, Nikita V. Golovastikov and Evgeni A. Bezus

Photonics 2022, 9(10), 785; https://doi.org/10.3390/photonics9100785 - 21 Oct 2022

Viewed by 1322

Abstract

We propose a method for calculating the so-called multi-wavelength diffractive lenses (MWDLs) intended for separating and focusing the radiation of L given wavelengths to L given points located in a certain plane perpendicular to the optical axis. The method is based on minimizing [...] Read more.

We propose a method for calculating the so-called multi-wavelength diffractive lenses (MWDLs) intended for separating and focusing the radiation of L given wavelengths to L given points located in a certain plane perpendicular to the optical axis. The method is based on minimizing the objective function characterizing the deviation of the complex transmission functions of the MWDL from the complex transmission functions of diffractive lenses focusing the design wavelengths to the given points. In the method, the MWDL calculation is reduced to a set of independent pointwise optimization problems, each of which describes the calculation of the MWDL microrelief at one point. The presented results of the numerical simulation of the designed MWDLs confirm high performance of the proposed method. The numerical simulation results are confirmed by the results of experimental investigations, including the fabrication of MWDLs using the direct laser writing technique and the study of the MWDL operation in an optical experiment. Full article

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15 pages, 2833 KiB

Open AccessArticle

An Optical POCT Device for Colorimetric Detection of Urine Test Strips Based on Raspberry Pi Imaging

by Zixin Yang, Gaozhe Cai, Jianlong Zhao and Shilun Feng

Photonics 2022, 9(10), 784; https://doi.org/10.3390/photonics9100784 - 21 Oct 2022

Cited by 2 | Viewed by 2797

Abstract

Urine examinations are widely applied in hospitals using urine test strip analyzers or other sophisticated professional instruments. However, such methods are inconvenient health monitoring of patients at home. Herein, we construct an optical device for point-of-care testing (POCT) for urine analysis at home [...] Read more.

Urine examinations are widely applied in hospitals using urine test strip analyzers or other sophisticated professional instruments. However, such methods are inconvenient health monitoring of patients at home. Herein, we construct an optical device for point-of-care testing (POCT) for urine analysis at home or on the spot. A black box and color calibration curve are established to eliminate the influence of ambient light with an independent internal lighting system included in the device. A Raspberry Pi with a CSI camera is programmed to automatically collect the strip images and identify the HSV values of the image with an image processing algorithm. During this process, these corrected colors are converted to concentration values by preloaded standard curves. Under optimal conditions, the proposed POCT device can quantitatively and automatically detect glucose within 1 min, with linear detection ranging from 2 mM to 60 mM and a detection limit of 1.16 mM. In addition, the device demonstrates satisfactory accuracy and quantitative analysis of ketone bodies, glucose, protein, occult blood, pH, and leukocytes in human urine samples with high-resolution concentrations, achieving results similar to those obtained with hospital instruments. The proposed device is portable and user-friendly, providing convenient colorimetric analysis for urine. Furthermore, the proposed device also has considerable potential for the development of in vitro diagnosis methods through combination with other test strips. Full article

(This article belongs to the Special Issue Advances in Photonic Materials and Technologies)

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12 pages, 7419 KiB

Open AccessArticle

A Large Mode Area Parabolic-Profile Core Fiber with Modified Segmented in Cladding

by Song Yang, Wentao Zhang, Yulai She, Hao Du and San Tu

Photonics 2022, 9(10), 783; https://doi.org/10.3390/photonics9100783 - 21 Oct 2022

Cited by 3 | Viewed by 1229

Abstract

In this paper, a novel fiber with a parabolic-profile core and eight segmented trenches in cladding is designed. The designed fiber consists of the segmented trench of low refractive index in cladding and parabolic-profile of high refractive index in the core. The proposed [...] Read more.

In this paper, a novel fiber with a parabolic-profile core and eight segmented trenches in cladding is designed. The designed fiber consists of the segmented trench of low refractive index in cladding and parabolic-profile of high refractive index in the core. The proposed fiber has good bending resistance. The eight segmented trenches in the cladding can decrease the refractive index of cladding to increase the difference index between the core and cladding to limit fundamental mode (FM) loss. The proposed fiber can offer an effective single mode (SM) operation with a large mode area (LMA) of 952 µm² at the small bending radius (R = 10 cm). In addition, the fiber is also suitable under an 18 W/m heat load. The proposed fiber achieves good bending performance, which can be suitable for the compact high-power lasers. Full article

(This article belongs to the Special Issue Optical Fiber Lasers and Amplifiers. Practical Applications of Fiber-Based Laser Sources)

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18 pages, 3180 KiB

Open AccessArticle

Properties of Compacts from Mixtures of Calcium Fluoride Micro- and Nanopowders

by Vladislav G. Ilves, Sergey Yu. Sokovnin, Sergey V. Zayats and Mikhail G. Zuev

Photonics 2022, 9(10), 782; https://doi.org/10.3390/photonics9100782 - 21 Oct 2022

Viewed by 1103

Abstract

In this work, compacts from mechanical mixtures of CaF₂ micron powder (MCP) with CaF₂ nanopowder (NP) additives were produced, with mass ratios of the mixture components ranging from 10:0.125 to 10:1, respectively, using magnetic pulse (MP) and static pressing (SP) methods. [...] Read more.

In this work, compacts from mechanical mixtures of CaF₂ micron powder (MCP) with CaF₂ nanopowder (NP) additives were produced, with mass ratios of the mixture components ranging from 10:0.125 to 10:1, respectively, using magnetic pulse (MP) and static pressing (SP) methods. The effects of pressure (P_p) and pressing temperature (T_p), concentration and phase composition of the additive on the density and color of compacts were studied, taking into account the properties of the initial components of the mixtures. The evolution of pulsed cathodoluminescence (PCL) spectra and photoluminescence (PL) of compacts from pure powders and their mixtures depending on P_p, T_p and characteristics of initial CaF₂ NP was also studied. A new near-infrared (NIR) band associated with fluoride vacancies was discovered with a maximum at ~765 nm in PCL spectra of compacts produced by MP at a temperature of 425 °C. A blue band at 435 nm associated with impurity oxygen vacancies in the CaF₂ lattice was found in PL spectra compacts of pure NP and powder mixtures. The density of compacts of pure NP and MCP reached 89% of the theoretical density, and the density of compacts of mixtures did not exceed 78%. The defective structure and phase composition of the CaF₂ NP had a decisive effect on the luminescent properties of compacts from mixtures of micro- and nanopowders. Full article

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8 pages, 2189 KiB

Open AccessCommunication

Surface Curvature Sensor Based on Intracavity Sensing of Fiber Ring Laser

by Liang Yi, Zhifei Xue, Yiyun Ding, Min Wang, Zekang Guo and Jia Shi

Photonics 2022, 9(10), 781; https://doi.org/10.3390/photonics9100781 - 20 Oct 2022

Cited by 2 | Viewed by 1149

Abstract

The measurement of surface curvature is of great significance in aerospace, structural health monitoring, energy batteries, etc. In this paper, a fiber-optic surface curvature sensor, based on intracavity sensing of fiber ring laser (FRL), is experimentally demonstrated. A no-core fiber- based filter performs [...] Read more.

The measurement of surface curvature is of great significance in aerospace, structural health monitoring, energy batteries, etc. In this paper, a fiber-optic surface curvature sensor, based on intracavity sensing of fiber ring laser (FRL), is experimentally demonstrated. A no-core fiber- based filter performs as the sensing head of the FRL sensor. The response between the curvature of the NCF and the output wavelength of the FRL was investigated. In the measurement of curvature, the sensor system showed a narrow 3-dB bandwidth of 0.08 nm, with a high signal-to-noise ratio of about 60 dB. The curvature sensitivities were measured as −0.348 nm/m⁻¹ within 0.2 m⁻¹, and −3.185 nm/m⁻¹ from 0.2 m⁻¹ to 0.475 m⁻¹. The performance of the surface curvature sensor was characterized by parameters, including output stability, temperature cross-sensitivity, and detection limit. Full article

(This article belongs to the Special Issue Advanced Photonics Sensors, Sources, Systems and Applications)

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6 pages, 3255 KiB

Open AccessCommunication

50 Gb/s Electro-Absorption Modulator Integrated with a Distributed Feedback Laser for Passive Optical Network Systems

by Daibing Zhou, Song Liang, Ruikang Zhang, Qiulu Yang, Xuyuan Zhu, Dan Lu, Lingjuan Zhao and Wei Wang

Photonics 2022, 9(10), 780; https://doi.org/10.3390/photonics9100780 - 20 Oct 2022

Cited by 1 | Viewed by 2105

Abstract

We report an electro-absorption modulator integrated with a distributed feedback Bragg laser fabricated by butt-joint technology. The lasing wavelength of the EML laser was 1311.71 nm, the output power was 10.04 mW when the current of the DFB section was 100 mA, the [...] Read more.

We report an electro-absorption modulator integrated with a distributed feedback Bragg laser fabricated by butt-joint technology. The lasing wavelength of the EML laser was 1311.71 nm, the output power was 10.04 mW when the current of the DFB section was 100 mA, the side-mode suppression ratio was greater than 50 dB, and the small-signal bandwidth was 29.40 GHz when the bias voltage of the modulator was −2 V. A 50 Gb/s data transmission over a single-mode fiber of up to 10 km was realized, which could be used as a light source for 50 G passive optical network systems. Full article

(This article belongs to the Special Issue Chip-Scale Photonic Devices for Optical Communication and Information Processing)

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7 pages, 2084 KiB

Open AccessCommunication

Compact, High Extinction Ratio, and Low-Loss Polarization Beam Splitter on Lithium-Niobate-On-Insulator Using a Silicon Nitride Nanowire Assisted Waveguide and a Grooved Waveguide

by Jinming Tao, Xintong Li, Jinye Li, Shuangxing Dai, Yiru Zhao, Chuangchuang Wei and Jianguo Liu

Photonics 2022, 9(10), 779; https://doi.org/10.3390/photonics9100779 - 19 Oct 2022

Cited by 1 | Viewed by 1715

Abstract

We propose a compact, high extinction ratio, and low-loss polarization beam splitter (PBS) on a lithium-niobate-on-insulator (LNOI) platform, based on an asymmetrical directional coupler and using a silicon nitride nanowire assisted waveguide (WG) and a grooved WG. By properly designing [...] Read more.

We propose a compact, high extinction ratio, and low-loss polarization beam splitter (PBS) on a lithium-niobate-on-insulator (LNOI) platform, based on an asymmetrical directional coupler and using a silicon nitride nanowire assisted waveguide (WG) and a grooved WG. By properly designing

{Si}_{3} N_{4}

nanowires and grooved LN WGs, TE polarization meets the phase matching condition, while significant mismatching exists for TM polarization. Numerical simulations show that the PBS has an ultra-high extinction ratio (ER) of

{TE}_{0}

and

{TM}_{0}

(larger than 40 dB and 50 dB, respectively). The device extinction ratios are larger than 10 dB over 100 nm wavelength ranges. Moreover, the device has an ultra-low insertion loss (IL less than 0.05 dB) at the wavelength of 1550 nm and maintains ILs less than 0.4 dB over 100 nm wavelength ranges. Full article

(This article belongs to the Special Issue Chip-Scale Photonic Devices for Optical Communication and Information Processing)

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8 pages, 2230 KiB

Open AccessCommunication

All-Fiber Wavelength-Tunable Narrow-Linewidth Polarization-Maintaining Tm-Doped Fiber MOPA System

by Tianran Sun, Xinyang Su, Yunhong Zhang, Huaiwei Zhang, Tianjia Xu and Yi Zheng

Photonics 2022, 9(10), 778; https://doi.org/10.3390/photonics9100778 - 19 Oct 2022

Cited by 2 | Viewed by 1335

Abstract

An all-fiber wavelength-tunable narrow-linewidth polarization-maintaining (PM) Tm-doped fiber master oscillator power amplifier (MOPA) system is presented. We demonstrate an all-fiber ring cavity Tm-doped fiber master-oscillator (MO) with a tuning range of 110 nm (from 1925 to 2034 nm). The maximum output power of [...] Read more.

An all-fiber wavelength-tunable narrow-linewidth polarization-maintaining (PM) Tm-doped fiber master oscillator power amplifier (MOPA) system is presented. We demonstrate an all-fiber ring cavity Tm-doped fiber master-oscillator (MO) with a tuning range of 110 nm (from 1925 to 2034 nm). The maximum output power of 459 mW is obtained at 1992.9 nm for 16 W of launched pump power at 793 nm, corresponding to a slope efficiency of 5.6% concerning launched pump power. By using a one-stage Tm-doped fiber amplifier combined with a high gain of >10 dB, the maximum slope efficiency is 12.6% and the output power is 5.65 W at 1993 nm. The 3 dB linewidth is less than 0.5 nm, M² ≈ 1.25, and the polarization extinction ratio (PER) reaches 21.4 dB. The influence of different active fiber lengths on laser amplification is also studied. Full article

(This article belongs to the Special Issue Fiber Lasers and Amplifiers)

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11 pages, 4997 KiB

Open AccessArticle

Sensing Performance of Triple-Band Terahertz Metamaterial Absorber Based on Snowflake-Shaped Resonators

by Limin Ma, Yuhuang Liu, Yongkai Zhu and Wenhua Gu

Photonics 2022, 9(10), 777; https://doi.org/10.3390/photonics9100777 - 19 Oct 2022

Cited by 4 | Viewed by 1668

Abstract

Terahertz metamaterial absorbers are important functional devices for liquid analyte detection. In contrast to general metamaterial absorbers with single-layer metasurfaces that possess only one resonant mode, a triple-band terahertz metamaterial absorber formed by a single layer of symmetrically arrayed snowflake-shaped resonators was proposed [...] Read more.

Terahertz metamaterial absorbers are important functional devices for liquid analyte detection. In contrast to general metamaterial absorbers with single-layer metasurfaces that possess only one resonant mode, a triple-band terahertz metamaterial absorber formed by a single layer of symmetrically arrayed snowflake-shaped resonators was proposed in this study. The simulation results showed that the absorption of the metamaterial absorber reached 97.43% at 0.550 THz, 79.22% at 1.249 THz, and 99.02% at 1.867 THz with narrow resonant peaks. The resonant frequencies were sensitive to the refractive index of the surrounding medium at a fixed analyte thickness, which would play an important role in the performance of the sensor for detecting changes in the surrounding refractive index. The maximum value of the refractive index sensitivity was 137.70 GHz/RIU, 306.25 GHz/RIU, and 473.86 GHz/RIU, with a figure of merit (FoM) of 3.14, 2.33, and 6.46, respectively, for refractive index values ranging from 1.0 to 2.2 under three resonant modes. It is worth noting that most of the liquid samples showed a refractive index ranging from 1.0 to 2.0. Furthermore, the identification of peanut oil, carbon disulfide, and turpentine was considered to verify that the proposed terahertz sensor could be used for high-sensitivity liquid detection and has broad development prospects in the field of detecting and sensing. Full article

(This article belongs to the Special Issue Micro-Nano Optics and High-End Measurement Instruments)

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10 pages, 3126 KiB

Open AccessCommunication

UV-Induced Gold Nanoparticle Growth in Polystyrene Matrix with Soluble Precursor

by Andrey Kudryashov, Svetlana Baryshnikova, Sergey Gusev, Dmitry Tatarskiy, Ivan Lukichev, Nadezhda Agareva, Andrey Poddel’sky and Nikita Bityurin

Photonics 2022, 9(10), 776; https://doi.org/10.3390/photonics9100776 - 19 Oct 2022

Cited by 1 | Viewed by 1293

Abstract

It is demonstrated that UV (LED at 365 nm) irradiation with subsequent heating (90–110 °C) of the polystyrene matrix containing a soluble Au(I) compound ((Ph₃P)Au(n-Bu)) results in the growth of gold nanoparticles within the sample bulk, as confirmed by [...] Read more.

It is demonstrated that UV (LED at 365 nm) irradiation with subsequent heating (90–110 °C) of the polystyrene matrix containing a soluble Au(I) compound ((Ph₃P)Au(n-Bu)) results in the growth of gold nanoparticles within the sample bulk, as confirmed by UV-vis spectroscopy and TEM electron microscopy. Pure heating of the samples without previous UV irradiation does not provide gold nanoparticles, thereby facilitating optical image printing. Comparing the nanoparticles’ growth kinetics in samples with different precursor content suggests the nanoparticle growth mechanism through Au(I) autocatalytic reduction at the surface of a gold nanoparticle. Within the polymer matrix, this mechanism is suggested for the first time. Full article

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11 pages, 3917 KiB

Open AccessArticle

The Effect of the Spin and Orbital Parts of the Poynting Vector on Light Localization in Solid-Core Micro-Structured Optical Fibers

by Grigory Alagashev, Sergey Stafeev, Victor Kotlyar and Andrey Pryamikov

Photonics 2022, 9(10), 775; https://doi.org/10.3390/photonics9100775 - 18 Oct 2022

Cited by 4 | Viewed by 1285

Abstract

The optical properties of solid-core micro-structured optical fibers (SC MOFs) have been studied for a long time. The process of the energy outflow of the core modes has always been associated with the process of constructive interference of the core modes fields under [...] Read more.

The optical properties of solid-core micro-structured optical fibers (SC MOFs) have been studied for a long time. The process of the energy outflow of the core modes has always been associated with the process of constructive interference of the core modes fields under reflection from the photonic crystal cladding. In this paper, we want to offer a new look at the light localization in the core of SC MOFs related to the behavior of spin and orbital parts of the Poynting vector of these core modes and singularities arising in it. Such an approach can help in forming a better understanding of the process of the core modes energy leakage and also in the creation of SC MOFs with a simplified design and low losses. Full article

(This article belongs to the Special Issue Fiber Optics and Mainstream Areas of Photonics)

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13 pages, 6661 KiB

Open AccessArticle

Femtosecond Laser Direct Writing of Antireflection Microstructures on the Front and Back Sides of a GaSe Crystal

by Alexander Yelisseyev, Vladislav Fedyaj, Victor Simonov, Ludmila Isaenko, Sergey Lobanov, Alexander Shklyaev, Andrey Simanchuk, Sergey Babin and Alexander Dostovalov

Photonics 2022, 9(10), 774; https://doi.org/10.3390/photonics9100774 - 18 Oct 2022

Cited by 5 | Viewed by 1498

Abstract

The development of antireflection coatings is crucially important to improve the performance of various photonic devices, for example, to increase the efficiency of harmonic generators based on high-refractive index crystals with significant Fresnel losses. A promising technique for the reducing of radiation reflection [...] Read more.

The development of antireflection coatings is crucially important to improve the performance of various photonic devices, for example, to increase the efficiency of harmonic generators based on high-refractive index crystals with significant Fresnel losses. A promising technique for the reducing of radiation reflection is to change the refractive index by fabrication of antireflection microstructures (ARM) on the surface. This paper presents the results of ARM direct writing on the surfaces of a nonlinear GaSe crystal (of ε modification, according to Raman and photoluminescence spectroscopy data) using fs laser radiation and a multiples approach. An increase in transmission from 65% to 80% for an ARM fabricated on one side of the crystal and up to 94% for ARMs fabricated on both sides is demonstrated. The increase in transmission with the increasing pulse energy, as well as with an increase in the number of pulses used for the formation of a single crater, is shown. The experimental results of ARM transmission of GaSe are in qualitative agreement with the simulation results based on the measured profiles and morphology of the ARM structures. Full article

(This article belongs to the Special Issue Ultrafast Laser Written Photonic, Sensing and Microfluidic Circuits in Transparent Materials)

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12 pages, 3330 KiB

Open AccessArticle

Broadband Supercontinuum Generation in Dispersion Decreasing Fibers in the Spectral Range 900–2400 nm

by Irina V. Zhluktova, Vladimir A. Kamynin, Dmitry A. Korobko, Aleksei S. Abramov, Andrei A. Fotiadi, Alexej A. Sysoliatin and Vladimir B. Tsvetkov

Photonics 2022, 9(10), 773; https://doi.org/10.3390/photonics9100773 - 18 Oct 2022

Cited by 5 | Viewed by 1733

Abstract

The spectrally flat supercontinuum generation in the wavelength range of 900–2400 nm is demonstrated in silica-based fibers of variable core diameter and dispersion. It is shown that, in comparison with standard optical fibers of the same length, supercontinuum spectra 200 nm wider can [...] Read more.

The spectrally flat supercontinuum generation in the wavelength range of 900–2400 nm is demonstrated in silica-based fibers of variable core diameter and dispersion. It is shown that, in comparison with standard optical fibers of the same length, supercontinuum spectra 200 nm wider can be realized in the samples under study. The significant difference between the spectral and temporal transformations of radiation depending on the direction of propagation is demonstrated in the researched fiber samples. Full article

(This article belongs to the Section Lasers, Light Sources and Sensors)

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9 pages, 2634 KiB

Open AccessCommunication

Tunable Microwave Pulse Generation Based on an Actively Mode-Locked Optoelectronic Oscillator

by Jin Zhang, Depei Zhang, Maolong Zhang, Daikun Zheng, Anle Wang, Xiaotong Liu, Lei Hu, Xiaoniu Peng and Yalan Wang

Photonics 2022, 9(10), 772; https://doi.org/10.3390/photonics9100772 - 17 Oct 2022

Cited by 2 | Viewed by 1571

Abstract

A tunable microwave-pulse-generation scheme is proposed and demonstrated by employing an actively mode-locked optoelectronic oscillator (OEO) based on a microwave photonic filter (MPF). The MPF mainly consists of a phase-shifted fiber Bragg grating (PS-FBG) and a phase modulator. The microwave pulse trains with [...] Read more.

A tunable microwave-pulse-generation scheme is proposed and demonstrated by employing an actively mode-locked optoelectronic oscillator (OEO) based on a microwave photonic filter (MPF). The MPF mainly consists of a phase-shifted fiber Bragg grating (PS-FBG) and a phase modulator. The microwave pulse trains with variable repetition rates are achieved by injecting an external signal, of which the frequencies are equal to an integer multiple of the free spectrum range (FSR) of the OEO. The multi-mode oscillation mechanism is discussed in detail theoretically and experimentally. A microwave pulse train with a central frequency of 9.25 GHz and repetition rate of 1.68 MHz is demonstrated by setting the injecting signal frequency to be the same with the FSR of the OEO. A tunable center frequency of the microwave pulses from 5.47 GHz to 18.91 GHz can be easily generated by tuning the laser frequency benefit from adopting the MPF. Furthermore, the microwave pulses with different pulse periods of 297.62 ns, 198.69 ns, and 148.81 ns are also realized by harmonic mode-locking. The proposed tunable microwave-pulse-generation method has potential applications in the pulse Doppler radar and communications. Full article

(This article belongs to the Special Issue Microwave Photonic Techniques)

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10 pages, 5201 KiB

Open AccessCommunication

Monolithic Side-Pumped Amplifier Based on an Yb-Doped Tapered-Fiber and Yielding 0.53 MW 9.3 ps Pulses

by Konstantin Bobkov, Andrey Levchenko, Denis Lipatov, Alexey Guryanov, Mikhail Bubnov and Mikhail Likhachev

Photonics 2022, 9(10), 771; https://doi.org/10.3390/photonics9100771 - 15 Oct 2022

Viewed by 1259

Abstract

We demonstrated a simple design of a monolithic all-fiber side-coupled combiner for counter-pumped amplifiers that requires no special fiber processing systems for fabrication. The combiner based on a Yb-doped polarization-maintained tapered fiber with an output core diameter of 40 µm and a total [...] Read more.

We demonstrated a simple design of a monolithic all-fiber side-coupled combiner for counter-pumped amplifiers that requires no special fiber processing systems for fabrication. The combiner based on a Yb-doped polarization-maintained tapered fiber with an output core diameter of 40 µm and a total length of 1.8 m exhibiting over 60% coupling efficiency of 976 nm 0.10 NA pump power was demonstrated and utilized to amplify 1064 nm 9.3 ps 1.84 MHz pulses up to 9.1 W of average power and 0.53 MW of peak power with near diffraction-limited beam quality. The demonstrated approach seems promising for further power scaling, retaining good output beam characteristics via design optimization. Full article

(This article belongs to the Special Issue Fiber Lasers and Amplifiers)

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10 pages, 2851 KiB

Open AccessArticle

Thermal Sensor Based on Polydimethylsiloxane Polymer Deposited on Low-Index-Contrast Dielectric Photonic Crystal Structure

by Yousuf Khan, Muhammad A. Butt, Svetlana N. Khonina and Nikolay L. Kazanskiy

Photonics 2022, 9(10), 770; https://doi.org/10.3390/photonics9100770 - 14 Oct 2022

Cited by 7 | Viewed by 1672

Abstract

In this work, a dielectric photonic crystal-based thermal sensor is numerically investigated for the near-infrared spectral range. An easy-to-fabricate design is chosen with a waveguide layer deposited on a silicon dioxide substrate with air holes drilled across it. To sense the ambient temperature, [...] Read more.

In this work, a dielectric photonic crystal-based thermal sensor is numerically investigated for the near-infrared spectral range. An easy-to-fabricate design is chosen with a waveguide layer deposited on a silicon dioxide substrate with air holes drilled across it. To sense the ambient temperature, a functional layer of polydimethylsiloxane biguanide polymer is deposited on the top, the optical properties of which vary with changes in the temperature. An open-source finite-difference time-domain-based software, MEEP, is used for design and numerical simulation. The design of the sensor, spectral properties, and proposed fabrication method are part of the discussion. The performance of the sensor is investigated for an ambient temperature range of 10 to 90 °C, for which the device offers a sensitivity value in the range of 0.109 nm/°C and a figure-of-merit of 0.045 °C⁻¹. Keeping in mind the high-temperature tolerance, inert chemical properties, low material cost, and easy integration with optical fiber, the device can be proposed for a wide range of thermal sensing applications. Full article

(This article belongs to the Special Issue Recent Advances in Surface-Wave-Assisted Photonic-Crystal-Based Devices)

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9 pages, 3900 KiB

Open AccessArticle

Dual-Wavelength Continuous-Wave and Passively Q-Switched Alexandrite Laser at 736.7 nm and 752.8 nm

by Hongyi Lin, Shangfeng Bao, Xiao Liu, Shuo Song, Zhiwei Wen and Dong Sun

Photonics 2022, 9(10), 769; https://doi.org/10.3390/photonics9100769 - 14 Oct 2022

Cited by 1 | Viewed by 1391

Abstract

A dual-wavelength continuous-wave (CW) and passively Q-switched alexandrite laser based on a MoS₂ saturable absorber (SA) operating at 736.7 nm and 752.8 nm with a simple and compact 18 mm plano–plano resonator is reported. In the CW mode, the output power is [...] Read more.

A dual-wavelength continuous-wave (CW) and passively Q-switched alexandrite laser based on a MoS₂ saturable absorber (SA) operating at 736.7 nm and 752.8 nm with a simple and compact 18 mm plano–plano resonator is reported. In the CW mode, the output power is 1014 mW at the linear-polarized pump power of 5.44 W, with a slope efficiency of 28.7%. In the pulsed operation, the narrowest pulse width and the maximal peak power are 154 ns and 10.6 W, respectively. This laser can be used to generate 8.71 THz-wave light based on a suitable nonlinear optical crystal. Full article

(This article belongs to the Topic Applications of Photonics, Laser, Plasma and Radiation Physics)

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13 pages, 4281 KiB

Open AccessArticle

Tunable and Switchable Multi-Wavelength Erbium-Doped Fiber Laser Based on Composite Structure Filter

by Boya Shi, Chang Liu, Xinyan Lei, Junfa Zhao and Shuxia Yan

Photonics 2022, 9(10), 768; https://doi.org/10.3390/photonics9100768 - 14 Oct 2022

Cited by 1 | Viewed by 1359

Abstract

A multi-wavelength erbium-doped fiber laser (MW-EDFL) with wide tuning range, switching and adjustable wavelength interval is designed and tested, which is based on a composite filter. The filter consists of a tapered microfiber coupler loop (TMCL) with a nested single mode fiber (SMF)-two [...] Read more.

A multi-wavelength erbium-doped fiber laser (MW-EDFL) with wide tuning range, switching and adjustable wavelength interval is designed and tested, which is based on a composite filter. The filter consists of a tapered microfiber coupler loop (TMCL) with a nested single mode fiber (SMF)-two mode fiber (TMF)-SMF (STS) structure, which has a comb spectrum with obvious envelope and uniform fluctuation. Our experimental and theoretical results show that the laser can output thirteen wavelengths, when the angles of two polarization controllers (PCs) in the TMCL are accurately set. Moreover, by adjusting the PCs, the tuning range of single- to sextuple-wavelength can reach about 40 nm. Six non-adjacent multi-wavelength outputs can be observed in some specific polarization states. The maximum side-mode suppression ratio (SMSR) of the output laser is 40.6 dB. Compared with other multi-wavelength EDFL, the output characteristics of the laser, such as the adjustability and flexibility of wavelength spacing and the switch-ability of wavelength number, have been improved. Full article

(This article belongs to the Section Lasers, Light Sources and Sensors)

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12 pages, 3522 KiB

Open AccessArticle

Highly Efficient White Organic Light-Emitting Diodes Based on Phosphorescent Iridium Complexes with Multi-Light-Emitting Layers

by Ruixia Wu, Xiaokang Li, Weiqiang Liu and Liang Zhou

Photonics 2022, 9(10), 767; https://doi.org/10.3390/photonics9100767 - 13 Oct 2022

Viewed by 1303

Abstract

White organic light-emitting diodes (WOLEDs) incorporating a blend of blue, green and red phosphorescent small molecular materials are presented in this article. 4,4′,4″-Tris(carbazol-9-yl)triphenylamine (TcTa) and 9-(4-tert-Butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi) with different transmission characteristics were selected as hosts for different emitting layers aim to promote holes [...] Read more.

White organic light-emitting diodes (WOLEDs) incorporating a blend of blue, green and red phosphorescent small molecular materials are presented in this article. 4,4′,4″-Tris(carbazol-9-yl)triphenylamine (TcTa) and 9-(4-tert-Butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi) with different transmission characteristics were selected as hosts for different emitting layers aim to promote holes transport, which will reinforce carriers’ balance and broaden carrier composite. On account of adaptive energy levels of the utilized dopants and hosts, secured phosphorescent WOLED displayed high efficiencies, low operating voltage and slow efficiency roll-off. In addition, distribution of carriers’ recombination zone and spectral of change were studied in detail to further understand the light-emitting mechanisms of obtained WOLEDs. Finally, by majorizing the dosage concentration of (fbi)₂Ir(acac) (bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1H-benzoimidazol-N,C3)iridium(acetylacetonate)) and the architectures of WOLEDs, the optimal device exhibited the maximum efficiencies of 44.92 cd A⁻¹, 42.85 lm W⁻¹, 16.8%, respectively, turn on voltage of 2.6 V and Commission International de l’Eclairage coordinates of (0.337, 0.458) at the brightness level of 3000 cd m⁻². Full article

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11 pages, 3857 KiB

Open AccessEditor’s ChoiceArticle

Design and Characteristics of Diamond-Assisted Ring-Core Fiber for Space Division Multiplexing

by Yujing Song, Jingjing Zheng, Li Pei, Jing Huang, Tigang Ning, Jing Li, Jianshuai Wang and Bing Bai

Photonics 2022, 9(10), 766; https://doi.org/10.3390/photonics9100766 - 13 Oct 2022

Viewed by 1313

Abstract

In this paper, a novel diamond-assisted ring-core fiber (DRF) is proposed. With the introduction of a low-refractive-index diamond-shaped region located in the center of the core, the proposed fiber effectively eliminates spatial degeneracy of the LP_mn mode groups and maintains a low [...] Read more.

In this paper, a novel diamond-assisted ring-core fiber (DRF) is proposed. With the introduction of a low-refractive-index diamond-shaped region located in the center of the core, the proposed fiber effectively eliminates spatial degeneracy of the LP_mn mode groups and maintains a low level of birefringence. Under the fiber structure parameters proposed in this paper, the effective refractive index difference (Δn_eff) between the spatial modes supported by the fiber in the entire C-band is greater than 2.25 × 10⁻⁴, and the Δn_eff between adjacent modes falls within the scope of (2.11~9.41) × 10⁻⁴. The degree of degenerate separation between the two polarization modes of all modes is very low, which is 2~3 orders of magnitude lower than that of the spatial mode. By discussing the mode characteristics of DRF and several other center-assisted ring-core fibers, the method that can be used to manipulate the spatial mode degenerate separation with structural symmetry is obtained, which can be applied to provide guidance for similar fiber designs. The proposed fiber structure is a promising candidate in space division multiplexing systems. Full article

(This article belongs to the Special Issue Optical Fiber Communication Systems)

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11 pages, 3277 KiB

Open AccessArticle

Optical and Scintillation Properties of Tb-Doped Rare-Earth Pyrosilicate Single Crystals

by Prom Kantuptim, Takumi Kato, Daisuke Nakauchi, Noriaki Kawaguchi, Kenichi Watanabe and Takayuki Yanagida

Photonics 2022, 9(10), 765; https://doi.org/10.3390/photonics9100765 - 13 Oct 2022

Cited by 3 | Viewed by 1778

Abstract

Series of 1.0% Terbium (Tb)-doped rare-earth pyrosilicate single crystals including Lu₂Si₂O₇ (LPS), Y₂Si₂O₇ (YPS), Gd₂Si₂O₇ (GPS), and La₂Si₂O₇ (LaPS) have been prepared by [...] Read more.

Series of 1.0% Terbium (Tb)-doped rare-earth pyrosilicate single crystals including Lu₂Si₂O₇ (LPS), Y₂Si₂O₇ (YPS), Gd₂Si₂O₇ (GPS), and La₂Si₂O₇ (LaPS) have been prepared by the floating-zone method. After the phase confirmation by powder X-ray diffraction, the properties are measured on both photoluminescence and scintillation aspects, including the photoluminescence emission contour graph and decay times, X-ray induced scintillation spectra and decay times, afterglow profiles, and the recently developed pulse height spectra for scintillators with millisecond decay time. The results indicate the multiple emissions from Tb³⁺ 4f-4f transition with the dominant emission at 540 nm (⁵D₄ → ⁷F₅) on both ultraviolet and X-ray excitation with the decay time around 2.6–5.6 and 1.3–3.2 ms, respectively. Under the γ-ray irradiation from ¹³⁷Cs, the Tb-doped LPS, YPS, GPS, and LaPS have presented scintillation light yields of 20,700, 29,600, 95,600, and 47,700 ph/MeV with ±10%, respectively, which considerably very high among the oxide scintillators. Full article

(This article belongs to the Special Issue Advances in X-ray Optics)

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9 pages, 2968 KiB

Open AccessCommunication

Theoretical Development of Polymer-Based Integrated Lossy-Mode Resonance Sensor for Photonic Integrated Circuits

by Edvins Letko, Arturs Bundulis and Gatis Mozolevskis

Photonics 2022, 9(10), 764; https://doi.org/10.3390/photonics9100764 - 12 Oct 2022

Cited by 3 | Viewed by 2051

Abstract

A promising phenomenon such as lossy-mode resonance (LMR) is of great interest in sensor applications. Until now, this phenomenon has been shown only in fibers or planar waveguides; however, given the rapid development of such an important technological area as photonic integrated circuits [...] Read more.

A promising phenomenon such as lossy-mode resonance (LMR) is of great interest in sensor applications. Until now, this phenomenon has been shown only in fibers or planar waveguides; however, given the rapid development of such an important technological area as photonic integrated circuits (PICs), it is important to transfer LMR technology specifically to PICs. In this article, we propose the theoretical development of an integrated polymer-based LMR sensor that will also contribute to the development of hybrid organic–inorganic PICs. This work theoretically shows that LMR can be achieved using polymer SU-8 waveguides on a glass substrate, on top of which TiO₂ is deposited. In addition, the paper shows that multiple resonances can be achieved in the developed integrated sensor. The highest sensor sensitivity (about 1400 nm/RIU) was achieved with 40 nm of TiO₂. The effect of the waveguide and coating geometries, as well as the polarizations of propagating modes, is studied in this paper. Full article

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18 pages, 3095 KiB

Open AccessArticle

Design of High-Power Red VCSEL on a Removable Substrate

by Chun-Yen Peng, Wei-Ta Huang, Zhi-Kuang Lu, Shih-Chen Chen and Hao-Chung Kuo

Photonics 2022, 9(10), 763; https://doi.org/10.3390/photonics9100763 - 12 Oct 2022

Cited by 2 | Viewed by 2393

Abstract

In this work, the architecture of a high-power InAlGaP/InGaP vertical-cavity surface-emitting laser (VCSEL) with an emission wavelength of 680 nm was studied. The design of quantum well, including the well thickness, indium composition, and barrier aluminum composition targeting the emission wavelength, was elaborately [...] Read more.

In this work, the architecture of a high-power InAlGaP/InGaP vertical-cavity surface-emitting laser (VCSEL) with an emission wavelength of 680 nm was studied. The design of quantum well, including the well thickness, indium composition, and barrier aluminum composition targeting the emission wavelength, was elaborately optimized. Moreover, the influences of leakage current, temperature dependence of optical gain, and resonance mode gain to threshold current under different barrier aluminum compositions were investigated. Lastly, the temperature characteristics of InAlGaP/InGaP VCSEL with substrate removal have also been calculated with 24% and 40.6% improvement in thermal resistance and operating current range, respectively. It holds great promise for high-power red VCSEL application. Full article

(This article belongs to the Special Issue Vertical-Cavity Surface-Emitting Lasers (VCSELs))

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15 pages, 4382 KiB

Open AccessReview

Mesotronics: Some New, Unusual Optical Effects

by Igor V. Minin and Oleg V. Minin

Photonics 2022, 9(10), 762; https://doi.org/10.3390/photonics9100762 - 12 Oct 2022

Cited by 17 | Viewed by 2283

Abstract

The recently emerged field of Mesotronics provides novel opportunities for subwavelength magnetic and electric field localization and giant enhancement by mesoscale dielectric particles and structures from low-index to high-index materials, supported by novel optical phenomena. In this case, two regions: non-resonant and resonant, [...] Read more.

The recently emerged field of Mesotronics provides novel opportunities for subwavelength magnetic and electric field localization and giant enhancement by mesoscale dielectric particles and structures from low-index to high-index materials, supported by novel optical phenomena. In this case, two regions: non-resonant and resonant, can be distinguished. In this short review, which is a direct continuation of our recently published study, we continue to present the authors’ point of view on some new optical effects in dielectric mesotronics. Among them are anomalous apodization effect in phase mesoscale gratings, new effects on high order Fano-resonances and extreme effects in field localization, mesoscale particle-based super-resolution and high-speed communications, photonic hook-based high-contrast subwavelength imaging, and reverse optical energy flow in a perforated resonant spherical particle. Full article

(This article belongs to the Special Issue Extreme Photonics)

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8 pages, 2072 KiB

Open AccessCommunication

Suppression of Pulse Intensity Dependent Dispersion during Nonlinear Spectral Broadening with Intermediate Compression for Passive CEP Stable Pulse Generation

by Hushan Wang, Huabao Cao, Yishan Wang, Wei Zhao and Yuxi Fu

Photonics 2022, 9(10), 761; https://doi.org/10.3390/photonics9100761 - 12 Oct 2022

Viewed by 1212

Abstract

The intensity fluctuation induced spectral phase-change of the laser pulse during nonlinear spectral broadening is theoretically investigated. The oscillation of the phase-change curves at the central part of the spectra is explained by the two-wave interference model, while the bending of the phase-change [...] Read more.

The intensity fluctuation induced spectral phase-change of the laser pulse during nonlinear spectral broadening is theoretically investigated. The oscillation of the phase-change curves at the central part of the spectra is explained by the two-wave interference model, while the bending of the phase-change curves at the wings is considered to originate from the intensity dependent dispersion caused by the self-steepening (SST) effect. Both of them can degrade carrier envelop phase (CEP) stability after an intra-pulse difference frequency generation (IP-DFG) setup. We propose an effective approach to suppress the intensity dependent dispersion with intermediate compression. Verified by numerically simulations, well-phased spectral components at the wings can be obtained, which is highly beneficial for CEP stable pulse generation with noisy input. Full article

(This article belongs to the Special Issue Ultrafast Laser and Micro-Nano Machining)

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9 pages, 2496 KiB

Open AccessArticle

Narrow-Linewidth Single-Frequency Ytterbium Laser Based on a New Composite Yb³⁺-Doped Fiber

by Maksim Yu. Koptev, Olga N. Egorova, Oleg I. Medvedkov, Sergey L. Semjonov, Boris I. Galagan, Sergey E. Sverchkov, Boris I. Denker, Alexander E. Zapryalov and Arkady V. Kim

Photonics 2022, 9(10), 760; https://doi.org/10.3390/photonics9100760 - 12 Oct 2022

Cited by 2 | Viewed by 1567

Abstract

Fiber single-frequency lasers are currently being actively developed, primarily due to the growing number of applications that require compact and reliable narrow-band sources. However, the most developed single-frequency fiber lasers based on phosphate fibers have the disadvantages of low mechanical strength of both [...] Read more.

Fiber single-frequency lasers are currently being actively developed, primarily due to the growing number of applications that require compact and reliable narrow-band sources. However, the most developed single-frequency fiber lasers based on phosphate fibers have the disadvantages of low mechanical strength of both the phosphate fibers themselves and their splices. In this paper we demonstrate a single-frequency laser based on a new composite Yb³⁺-doped active fiber. The core of this fiber is made of phosphate glass with a high concentration of ytterbium ions and its cladding is made of standard silica glass. This structure ensures a higher splicing strength of the fiber compared to the phosphate fibers and provides high resistance to atmospheric moisture. Despite the multimode structure of this fiber, we achieved stable single-frequency lasing with an average power of 10 mW and a spectral contrast of more than 60 dB in the scheme with a short (1.1 cm) cavity formed by two fiber Bragg gratings. We believe that further optimization of this fiber will make it possible to create powerful and reliable single-frequency lasers in the one-micron wavelength range. Full article

(This article belongs to the Topic Optical and Optoelectronic Materials and Applications)

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2 pages, 404 KiB

Open AccessCorrection

Correction: Costanzo, V.; Costanzo, M. Intravital Imaging with Two-Photon Microscopy: A Look into the Kidney. Photonics 2022, 9, 294

by Vincenzo Costanzo and Michele Costanzo

Photonics 2022, 9(10), 759; https://doi.org/10.3390/photonics9100759 - 12 Oct 2022

Viewed by 765

Abstract

In the original publication [...] Full article

(This article belongs to the Special Issue Multiphoton Microscopy)

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8 pages, 7095 KiB

Open AccessCommunication

Broadband Polarization Rotator and Splitter Based on 70 nm-Etched Waveguides on SOI Platform

by Ye Tian, Zhe Kang, Tingge Dai, Peipeng Xu, Yan Li, Yegang Lv and Xiaowei Zhang

Photonics 2022, 9(10), 758; https://doi.org/10.3390/photonics9100758 - 12 Oct 2022

Cited by 2 | Viewed by 2012

Abstract

The standard silicon photonic platforms provide three-step silicon etching, i.e., 220 nm for full etching, 70 nm for shallow etching, and 130 nm (or 150 nm) for slab etching. Previously reported mode-evolution-based polarization rotators and splitters (PSRs) usually employ 130 nm-etched slab waveguides [...] Read more.

The standard silicon photonic platforms provide three-step silicon etching, i.e., 220 nm for full etching, 70 nm for shallow etching, and 130 nm (or 150 nm) for slab etching. Previously reported mode-evolution-based polarization rotators and splitters (PSRs) usually employ 130 nm-etched slab waveguides for adiabatic TM

_{0}

-to-TE

_{1}

conversion, however, they are not compatible with the platforms adopting 150 nm-etching techniques. In this paper, we demonstrate a broadband PSR based on 70 nm-etched slab waveguides, which is compatible with all the platforms. The PSR consists of a bi-level taper and an inverse-tapered coupler. The length of the polarization rotator shrinks from hundreds to only thirty microns by employing the 70 nm-etched slab waveguides, while a high efficiency of >95% is achieved, covering an ultra-wide bandwidth from 1250 nm to 1650 nm. The proposed PSR shows superior performance over S, C, and L bands. Low cross-talk of <−20 dB and a loss of <1.5 dB are experimentally confirmed over a wavelength range of 75 nm. Full article

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14 pages, 5971 KiB

Open AccessReview

Low- and High-Order Optical Nonlinearities of Quantum Dots

by Rashid A. Ganeev

Photonics 2022, 9(10), 757; https://doi.org/10.3390/photonics9100757 - 12 Oct 2022

Cited by 5 | Viewed by 1511

Abstract

Various potential applications of quantum dots (QDs) require knowledge of their optical nonlinearities. In this review, the third-order nonlinearities responsible for the saturable absorption, two-photon absorption, reverse saturable absorption, and nonlinear refraction in QDs, as well as the high-order harmonics generation in the [...] Read more.

Various potential applications of quantum dots (QDs) require knowledge of their optical nonlinearities. In this review, the third-order nonlinearities responsible for the saturable absorption, two-photon absorption, reverse saturable absorption, and nonlinear refraction in QDs, as well as the high-order harmonics generation in the laser-induced plasmas containing QDs, are analyzed. The methods of QD synthesis and preparation strongly affect their optical nonlinearities. Above-mentioned nonlinear optical studies in QDs are analyzed for various potential applications (sources of coherent extreme ultraviolet radiation, optical limiters, mode-lockers, etc.). Full article

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14 pages, 4039 KiB

Open AccessArticle

Tunable and Switchable Dual-Wavelength SLM Narrow-Linewidth Fiber Laser with a PMFBG-FP Filter Cascaded by Multi-Ring Cavity

by Mingquan Gao, Bin Yin, Yanzhi Lv, Guofeng Sang, Benran Hou, Haisu Li, Muguang Wang and Songhua Wu

Photonics 2022, 9(10), 756; https://doi.org/10.3390/photonics9100756 - 12 Oct 2022

Cited by 8 | Viewed by 1620

Abstract

A single longitudinal mode (SLM) dual-wavelength switchable erbium-doped fiber laser (DW-EDFL) based on polarization-maintaining fiber Bragg grating Fabry–Perot cavity (PMFBG-FP) cascaded multiple sub-ring cavities (MSCs) is proposed. A PMFBG-FP with a narrow-band transmission peak and MSCs was implemented as an optical filter to [...] Read more.

A single longitudinal mode (SLM) dual-wavelength switchable erbium-doped fiber laser (DW-EDFL) based on polarization-maintaining fiber Bragg grating Fabry–Perot cavity (PMFBG-FP) cascaded multiple sub-ring cavities (MSCs) is proposed. A PMFBG-FP with a narrow-band transmission peak and MSCs was implemented as an optical filter to achieve stable dual-wavelength laser output and guaranteed SLM status. By stretching the PMFBG, a highly stable dual-wavelength tunable output could be achieved with a maximum tuning interval of 0.17 nm. The optical signal-to-noise-ratio (OSNR) at dual-wavelength lasing was higher than 57 dB, and the optimal wavelength and power fluctuations within 0.5 h were 0.01 nm and 0.79 dB, respectively. Meanwhile, the measured linewidths of each wavelength were 1.55 kHz and 1.65 kHz, respectively. The measured polarization states of the two laser wavelengths were linear and orthogonal, with a degree of polarization (DOP) of nearly 100%. Full article

(This article belongs to the Section Lasers, Light Sources and Sensors)

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