All-fiber System Research Articles

Advances in mid-infrared spectroscopy enabled by supercontinuum laser sources.

Supercontinuum sources are all-fiber pulsed laser-driven systems that provide high power spectral densities within ultra-broadband spectral ranges. The tailored process of generating broadband, bright, and spectrally flat supercontinua-through a complex interplay of linear and non-linear processes-has been recently pushed further towards longer wavelengths and has evolved enough to enter the field of mid-infrared (mid-IR) spectroscopy. In this work, we review the current state and perspectives of this technology that offers laser-like emission properties and instantaneous broadband spectral coverage comparable to thermal emitters. We aim to go beyond a literature review. Thus, we first discuss the basic principles of supercontinuum sources and then provide an experimental part focusing on the quantification and analysis of intrinsic emission properties such as typical power spectral densities, brightness levels, spectral stability, and beam quality (to the best of the authors' knowledge, the M2 factor for a mid-IR supercontinuum source is characterized for the first time). On this basis, we identify key competitive advantages of these alternative emitters for mid-IR spectroscopy over state-of-the-art technologies such as thermal sources or quantum cascade lasers. The specific features of supercontinuum radiation open up prospects of improving well-established techniques in mid-IR spectroscopy and trigger developments of novel analytical methods and instrumentation. The review concludes with a structured summary of recent advances and applications in various routine mid-IR spectroscopy scenarios that have benefited from the use of supercontinuum sources.

Hectowatt-level GHz burst-mode all-fiber laser based on dissipative soliton resonance.

We demonstrate a high power Yb-doped burst-mode all-fiber laser system operating at GHz intra-burst repetition rate. To our knowledge, it is the first report utilizing dissipative soliton resonance (DSR) to generate tunable burst-mode rectangular pulses. Due to the tunable duration and the rapid rise/fall time for DSR pulses, a 1-10 ns adjustable burst pulse duration is achieved. The intra-burst with sinusoidal waveform can be tuned from 0.8 GHz to 1.5 GHz and actively modulated by an electro-optic modulator (EOM). Amplified by a three-stage Yb-doped fiber amplifier (YDFA), the output power achieves 304 W at 10 ns of burst duration, and the maximum peak power reaches over 50 kW at 2 ns of burst duration. This laser system is anticipated to be applied to generate high power arbitrary microwave signal.

Reusable smartphone-facilitated mobile fluorescence biosensor for rapid and sensitive on-site quantitative detection of trace pollutants

Increasing exposure to toxic pollutants highlights the need for their sensitive detection technologies that can be rapidly adapted and deployed in various settings. Optical biosensors are an excellent solution due to their outstanding features. However, the sophisticated and expensive optical design limits their scalability and actual application. Herein, an innovative reusable smartphone-facilitated mobile fluorescence biosensor (s-MFB) was built through integrating miniaturized all-fiber optical system and microfluidic system with smartphone. An asymmetric Y-shaped fiber optic coupler (Y-FOC) is constructed for simultaneous transmission of excitation light and the collected fluorescence. In particular, the incidence rays are introduced into the fiber bio-probe at a specific angle through the single-mode fiber of the Y-FOC, which enhances the evanescent wave field and the number of total internal reflections. The s-MBF showed a LOD for free Cy5.5 of 0.1 nM. Combining indirect competitive immunoassay with the s-MFB, this new assay, which achieve quantitative detection of bisphenol A and norfloxacin in 15 min with high sensitivity and reusability, substantially reduces the complexity and improves the scalability of trace pollutants detection. The adjunctive smartphone application allows on-site real-time quantitative detection, automated interpretation of reporting results, and early-warning of pollution accidents.

Laser Self-Mixing Sensor for Simultaneous Measurement of Young’s Modulus and Internal Friction

The Young’s modulus and internal friction are two important parameters of materials. Self-mixing interferometry (SMI) is an emerging non-destructive sensing method that has been employed for various applications because of its advantages of simple structure, ease of alignment and high resolution. Some recent works have proposed the use of SMI technology to measure the Young’s moduli and/or internal frictions by measuring the resonance frequencies and damping factors of specimen vibrations induced by impulse excitation. However, the measurement results may be affected by frequencies of SMI fringes, and the implementation requires extra signal processing on SMI fringes. In this work, we developed an all-fiber SMI system without SMI fringes to measure the Young’s modulus and internal friction simultaneously. Simulations and experiments were carried out to verify the feasibility of the proposed method. Two specimens of brass and aluminum were tested. The experimental results show that the standard deviations of Young’s moduli for brass and aluminum are 0.20 GPa and 0.14 GPa, and the standard deviations of internal frictions are 4.0×10−5 and 5.4×10−5, respectively. This method eliminates the influences of the SMI fringe frequency on the resonant frequency and requires no signal processing on SMI fringes, contributing to its simplicity as a method for the measurement of the Young’s modulus and internal friction.

Thermally Tunable Orbital Angular Momentum Mode Generator Based on Dual-Core Photonic Crystal Fibers.

The combination of mode division multiplexing (MDM) based on orbital angular momentum (OAM) modes with wavelength division multiplexing (WDM) has attracted considerable attention due to its ability to increase optical transmission capacity. However, the switching of the multi-wavelength and multi-order OAM mode in an all-fiber structure has always been a challenge. As a solution, a thermally tunable dual-core photonic crystal fiber (DC-PCF) is proposed to achieve multi-order and multi-wavelength switching of the OAM mode. The results show that the OAM mode with topological charge m = ±1 can be excited with the linear polarization fundamental mode (LPFM) and circular polarization fundamental mode (CPFM). In addition, the device can effectively excite a high-purity ±1st order OAM mode with wavelengths ranging from 1520 to 1575 nm by thermal tuning. The purity of the mode is in excess of 99%, and the energy conversion efficiency (ECE) is above 95%. The proposed design is expected to be applied in all-fiber communication systems combined with MDM and WDM.

Generation, Transmission and Application of Orbital Angular Momentum in Optical Fiber: A Review

Optical orbital angular momentum (OAM) has become a hot research topic because of its unique properties due to its spiral distribution of phases. The production and transmission of OAM has also become a necessary condition for effective use of OAM. As an optical waveguide with good propagation properties, optical fibers are used in optical systems supporting OAM. This paper introduces the OAM generation and transmission system based on fiber, summarizes the current photonic crystal fiber, ring core fiber, fiber grating and other all-fiber systems that can support OAM modes, and explains some experimental principles. Finally, an outlook on OAM generation or transmission devices for all-fiber systems is presented, providing a useful reference for future related research.

All-fiber beat-frequency laser heterodyne absolute distance measurement system

To realize precise absolute distance measurement, an all-fiber beat-frequency laser heterodyne distance measurement system based on a fiber-optic interferometric structure was proposed and demonstrated. An acousto-optic frequency shifter is introduced into one arm of a fiber-optic Mach–Zenhder interferormeter to generate the beat-frequency laser beams in two fiber-optic paths. By a ternary sinusoidal curve fitting method to extract the initial phases of the two beat-frequency laser signals and their phase difference, a distance measurement precision of several tens micrometers can be realized in a distance range of several meters. Experiments showed a maximum relative error of 0.0548% and a resolution of 83.333 μm in a distance range of 0 to 600 mm.

A large dispersion-managed monolithic all-fiber chirped pulse amplification system for high-energy femtosecond laser generation

A high energy monolithic all fiber chirped pulse amplification (CPA) system composed of fiber-silicate glass fiber is demonstrated in this work. In this compact system, the optical stretcher consists of two large dispersion chirped fiber Bragg gratings that offer a high stretch ratio to lower the nonlinearity that accumulates in the fiber amplifier. By employing high gain silicate glass fiber with a length of 20 cm as the main amplifier, an optimal balance of pulse energy and the B-integral is achieved. An amplified power of 42.6 W, corresponding to a pulse energy of 213 µJ, is obtained with an injection power of 100 mW. After compression, the laser pulses are compressed by a novel polarization-controlled double-pass configuration of a chirped volume Bragg grating (CVBG) to match the dispersion of the fiber stretcher. A total compression efficiency of 79.8% is obtained. The dispersion between the stretcher and the compressor is matched with the self-made temperature tuning device of the fiber grating. An optimized pulse width of 781 fs and a pulse energy of 170 µJ are obtained with the single-mode beam profile. To the best of our knowledge, this is the highest energy ever obtained with a single-mode beam profile for a spliced monolithic all-fiber CPA system. This compact high-energy fiber system will be useful in scientific research and industrial applications.

All-fiber hybrid displacement-sensing system based on self-mixing interference and intracavity spectroscopy

Micro-displacement is a classic application of laser self-mixing interference (SMI) measurement system, but most of the current researches are focused on single-channel measurement. In this paper, a dual-channel displacement-sensing system is proposed and demonstrated based on the SMI effect and intracavity spectroscopy. The 90.14-pm/μm sensitivity for the displacement sensing can be achieved when the intracavity spectroscopy is employed to monitoring the output spectra. For the SMI operation mode, the variational mode decomposition (VMD) is used to decompose and reduce the noise of the SMI signal, and the interference fringe counting method is used to reconstruct the displacement of the noise-reduced SMI signal to realize the displacement measurement of the target object. It is demonstrated that the displacement-reconstruction error is 110 nm when the frequency is 30 Hz and the peak-to-peak amplitude is 4 μm.

Simple structure dual-core photonic crystal fiber polarization beam splitter covering the O + E + S + C + L + U band based on the surface plasmon resonance effect

In this paper, a simple structure dual-core photonic crystal fiber (SS-DC-PCF) polarization beam splitter (PBS) based on the surface plasmon resonance (SPR) effect and symmetric dual-core coupling mode theory is proposed. For the proposed SS-DC-PCF-1 PBS, the coupling lengths (CLs) and coupling length ratio (CLR) are analyzed, and the variations of the normalized output powers with the propagation length are investigated for the chosen wavelengths 1.434, 1.451, and 1.469 µm. The extinction ratio in cores A and B are compared at the three splitting lengths (SLs) 170, 173, and 176 µm. When the optimal SL is 176 µm, the splitting bandwidth (SB) is 255 nm (1.437–1.692 µm), and the insertion loss (IL) is less than 0.043 dB. The regulations of the CLs and CLR with the change of the structure parameters are analyzed. For the proposed SS-DC-PCF-2 PBS, the optimal SL is 232 µm, the SB is 201 nm (1.249–1.450 µm), and the IL is less than 0.042 dB. Finally, it is demonstrated that the total SB of the proposed SS-DC-PCF-1 PBS and SS-DC-PCF-2 PBS is 443 nm (1.249–1.692 µm), which can cover theO+E+S+C+L+Uband, even if the gold film thickness changes by±1nm. The proposed SS-DC-PCF PBS has excellent performances, such as ultrashort SL, ultrawide SB, ultralow IL, and good error-tolerance rate. It will have important applications in all-fiber optical systems.

Ultralow-intensity noise, 10 W all-fiber single-frequency tunable laser system around 1550 nm.

We report herein on the development of a linearly polarized, single-frequency tunable laser system producing more than 10 W in the 1550 nm range, using a two-stage erbium/ytterbium co-doped fiber-based master oscillator power amplifier (MOPA) architecture. The all-fiber MOPA provides an ultralow intensity noise of -160dBc/Hz beyond 200 kHz between 1533 and 1571 nm (Δλ=38nm) at full output power and a minimum optical signal to noise ratio of 38 dB. A good stability is obtained over 4 h at maximum power for several wavelengths with peak-to-peak fluctuation less than 3% and rms below 0.5%.

Performance enhancement of an ultrafast all-fiber laser based on an InN saturable absorber using GRIN coupling

Indium nitride (InN)-based semiconductor saturable absorbers have previously shown advantages for application in near-IR fiber lasers due to their broad modulation depth, ultrafast nonlinear response and thermal stability. However, up to now all demonstrated saturable absorber elements based on InN (either transmissive or reflective) have shown limited performance due to poor coupling and insertion losses. We present here a simple mode-locking device based on a GRIN-rod lens in conjunction with an InN semiconductor saturable absorber mirror (SESAM) for its use in a passively mode-locked all-fiber laser system operating at telecom wavelengths. Our results demonstrate that this coupling element ensures not only a compact, turnkey and alignment-free design but also a highly-stable optical femtosecond pulse train. The reduction of insertion losses (3.5 dB) enables the generation of 90-fs ultrafast pulses with an average power of 40 mW and up to 7 nJ of pulse energy without the need for additional amplification.

All-fiber few-mode optical coherence tomography using a modally-specific photonic lantern.

Optical coherence tomography (OCT) was recently performed using a few-mode (FM) fiber to increase contrast or improve resolution using a sequential time-domain demultiplexing scheme isolating the different interferometric signals of the mode-coupled backscattered light. Here, we present an all-fiber FM-OCT system based on a parallel modal demultiplexing scheme exploiting a novel modally-specific photonic lantern (MSPL). The MSPL allows for maximal fringe visibility for each fiber propagation mode in an all-fiber assembly which provides the robustness required for clinical applications. The custom-built MSPL was designed for OCT at 930 nm and is wavelength-independent over the broad OCT spectrum. We further present a comprehensive coupling model for the interpretation of FM-OCT images using the first two propagation modes of a few-mode fiber, validate its predictions, and demonstrate the technique using in vitro microbead phantoms and ex vivo biological samples.

Multicore fiber integrated beam shaping devices for long-range plasmonic trapping.

The multicore fiber beam shaping devices based on surface plasmon polaritons (SPPs) have been proposed and demonstrated. The gold film is covered on the end face of the optical fiber. An air slit is perforated in the center of each core and the gratings with a fixed period are designed on the gold film on one side of the slit to obtain a deflected beam. Multiple deflected beams based on the multicore fiber interfere and form a periodic field, where the period of the interference field is determined by the deflection angle of the beams and the spacing between the cores. The interference field of the multiple deflected beams can be used to trap the nanosphere. The Maxwell stress tensor method is used to calculate the transverse and longitudinal trapping forces on a nanosphere. The nanosphere can be stably trapped at 45 μm away from the end face of the fiber. Such an all-fiber trapping system is compact and flexible integration, and is promising for long-working-distance and multiple-particle trapping.

Realization of carrier envelope phase control in an erbium-doped all-fiber comb via an intracavity electrical polarization controller.

We present an erbium-doped all-fiber comb that is realized via intracavity piezoelectric mechanical responses by inserting an electrical polarization controller (EPC) for carrier envelope phase offset (fceo) control and sticking a piezoelectric transducer (PZT) for repetition rate (fr) stabilization. With only three components inside the oscillator, it facilitates an all-fiber comb system with high integration and robustness. Besides fceo control, smart, recoverable, and precise searching of mode-locked states can also be achieved by finely tuning the EPC driving voltages. The fceo signal can be tightly phase-locked due to the 20 kHz 3 dB bandwidth of the EPC device. Compared with the traditional pump feedback mode, the EPC approach exhibits a larger and flatter gain in the near-zero-dispersion zone of the fiber comb, corresponding to less EPC induced intracavity fluctuations. It is also a benefit for reducing cross regulation between fr and fceo in long-term stabilization of the comb.

Development of a novel label-free all-fiber optofluidic biosensor based on Fresnel reflection and its applications

A novel, compact, cost-effective, and robust label-free all-fiber optofluidic biosensor (LF-AOB) based on Fresnel reflection mechanism was built through integrating single-multi mode fiber coupler and highly sensitive micro-photodetector. The Fresnel reflection light intensity detected by the LF-AOB greatly depended on the RI change on the end-surface of the fiber probe according to experimental and simulation results. The capability of the LF-AOB for real-time in situ detection in optofluidic system were verified by measuring salt and protein solution, and the lowest limit of detection was 1.0 × 10−6 RIU. Our proposed theory can effectively eliminate the influence of light intensity fluctuation, and one-point calibration method of sensor performance is conducive for rapid and convenient detection of targets. Label-free sensitive detection of SARS-Cov-2 Spike protein receptor-binding domain (S-RBD) and the binding kinetics assay between S-RBD and anti-S-RBD antibody were achieved using the LF-AOB. These contributed to the elegant design of all-fiber optical system with high efficiency, high resolution and sensitivity of micro-photodetector, and enhanced interaction between the light and the samples at the liquid-sensor interface because of the large surface area of the multi-mode fiber probe. The LF-AOB can be extended as a universal sensing platform to measure other factors associated with refractive index because its high sensitivity, low sample consumption (∼160 nL), and capability of real-time in situ detection.

Rapid, label-free, and sensitive point-of-care testing of anti-SARS-CoV-2 IgM/IgG using all-fiber Fresnel reflection microfluidic biosensor.

Graphical abstractThe ongoing global pandemic of SARS-CoV-2 has promoted to develop novel serological testing technologies since they can be effectively complementary to RT-PCR. Here, a new all-fiber Fresnel reflection microfluidic biosensor (FRMB) was constructed through combining all-fiber optical system, microfluidic chip, and multimode fiber bio-probe. The transmission of the incident light and the collection and transmission of Fresnel reflection light are achieved using a single-multi-mode fiber optic coupler (SMFC) without any other optical separation elements. This compact design greatly simplifies the whole system structure and improves light transmission efficiency, which makes it suitable for the label-free, sensitive, and easy-to-use point-of-care testing (POCT) of targets in nanoliter samples. Based on Fresnel reflection mechanism and immunoassay principle, both the SARS-CoV-2 IgM and IgG antibodies against the SARS-CoV-2 spike protein could be sensitively quantified in 7 min using the secondary antibodies-modified multimode fiber bio-probe. The FRMB performs in one-step, is accurate, label-free, and sensitive in situ/on-site detection of SARS-CoV-2 IgM or IgG in serum with simple dilution only. The limits of detection of SARS-CoV-2 IgM and SARS-CoV-2 IgG were 0.82 ng/mL and 0.45 ng/mL, respectively. Based on our proposed theory, the affinity constants of SARS-CoV-2 IgM or IgG antibody and their respective secondary antibodies were also determined. The FRMB can be readily extended as a universal platform for the label-free, rapid, and sensitive in situ/on-site measurement of other biomarkers and the investigation of biomolecular interaction. Supplementary InformationThe online version contains supplementary material available at 10.1007/s00604-021-04911-0.

A 1064 nm single-photon lidar for three-dimensional imaging

Single-photon light detection and ranging system has been widely used in three-dimensional (3D) imaging for its advantages in weak echo detection and high resolution. However, long-range imaging is a great challenge due to the device performance limits and strong solar irradiance. In this paper, we experimentally demonstrate a single-photon imaging system with an operation wavelength of 1064 nm in daytime. An all-fiber optical system with a two-dimensional rotation platform is designed to realize a wide scanning. And a sub-pixel scanning method is used to improve spatial resolution. Image reconstruction is based on the iterative shrinkage-threshold algorithm; herein the noise threshold is self-adaptive to the received photon-counting distribution. Multi-range information can be retrieved from each pixel and 3D point cloud is finally generated. Results show that the range resolution is 38 cm and the spatial resolution is about 7.4 cm at the distance of 2.13km, three times of the diffraction limit of the optical system.

Self-cleaning effect in an all-fiber spatiotemporal mode-locked laser based on graded-index multimode fiber

We demonstrate an all-fiber spatiotemporal mode-locked laser based on graded-index multimode fiber. Due to the high damage threshold of graded-index multimode fiber devices, the output single-pulse energy reach up to 11.67 nJ. The beam quality at mode-locked state is significantly improved compared with continuous wave state as a result of the self-cleaning effect. By amplifying the pulse in the multimode fiber amplifier, high power pulses with high beam quality can be obtained in the all-fiber system based on graded-index MMFs. We present an approach to get high single-pulse energy in the all-fiber multimode laser with a near single-mode output beam.

Intracavity second harmonic generation from a WSe2 monolayer in a passively mode-locked picosecond fiber laser

A single layer WSe2 crystal is transferred on the tip of a single mode fiber that is placed in the cavity of a Yb3+ doped picosecond fiber oscillator. This intracavity monolayer generates second harmonics without affecting the stable mode-locking and laser output of the fiber oscillator. This method utilizes the higher intracavity optical intensities to increase the SHG conversion efficiency, thus combining the high nonlinear susceptibility and the phase-matching independence of a monolayer with the versatility of a fiber laser in an all-fiber integrated system. We also demonstrated a procedure to verify the monolayer placement on the fiber core by hyperspectral mapping. This intracavity SHG has possible applications for self-referencing f-2f interferometry in fiber-laser frequency combs.