Polarization-maintaining Single-mode Fiber Research Articles

Metafiber transforming arbitrarily structured light

Structured light has proven useful for numerous photonic applications. However, the current use of structured light in optical fiber science and technology is severely limited by mode mixing or by the lack of optical elements that can be integrated onto fiber end-faces for wavefront engineering, and hence generation of structured light is still handled outside the fiber via bulky optics in free space. We report a metafiber platform capable of creating arbitrarily structured light on the hybrid-order Poincaré sphere. Polymeric metasurfaces, with unleashed height degree of freedom and a greatly expanded 3D meta-atom library, were 3D laser nanoprinted and interfaced with polarization-maintaining single-mode fibers. Multiple metasurfaces were interfaced on the fiber end-faces, transforming the fiber output into different structured-light fields, including cylindrical vector beams, circularly polarized vortex beams, and arbitrary vector field. Our work provides a paradigm for advancing optical fiber science and technology towards fiber-integrated light shaping, which may find important applications in fiber communications, fiber lasers and sensors, endoscopic imaging, fiber lithography, and lab-on-fiber technology.

Towards a Practical Implementation of a Single-Beam All-Optical Non-Zero-Field Magnetic Sensor for Magnetoencephalographic Complexes.

We present a single-beam all-optical two-channel magnetic sensor scheme developed for biological applications such as non-zero-field magnetoencephalography and magnetocardiography. The pumping, excitation and detection of magnetic resonance in two cells are performed using a single laser beam with time-modulated linear polarization: the linear polarization of the beam switches to orthogonal every half-cycle of the Larmor frequency. Light with such characteristics can be transmitted over a single-mode polarization-maintaining fiber without any loss in the quality of the polarization characteristics. We also present an algorithm for calculating optical elements in a sensor scheme, the results of measuring the parametric dependences of magnetic resonance in cells, and the results of direct testing of a sensor in a magnetic shield. We demonstrate sensitivity at the level of 20 fT/√Hz in one sensor channel in the frequency range of 80-200 Hz.

Regeneratively mode-locked optoelectronic oscillator.

A regeneratively mode-locked optoelectronic oscillator is proposed to realize multi-mode phase locking in optoelectronic oscillators by coupling a modulating signal generation loop. To verify the feasibility of the scheme, a numerical simulation model is established. In addition, a proof-of-concept experiment is demonstrated in a single-loop optoelectronic oscillator with a 2.2 km polarization-maintaining single-mode fiber, using an electric amplitude modulator/Mach-Zehnder modulator as an active mode-locking device. The generated microwave pulse signal has a center frequency of 10 GHz and a repetition rate of 95 kHz. We believe this scheme can provide a new approach to overcome the problem of detuning between the modulating frequency and the mode spacing during long-term operation.

Multi-parameter sensor with high sensitivity based on a long-period fiber grating prepared by a polarization-maintaining fiber.

We propose what we believe to be a novel long-period fiber grating (LPFG) based on a polarization-maintaining fiber (PMF) and single-mode fiber. Due to the principal axis of stress, the resonance peak is strongly dependent on the polarization state of the input light. Under different polarization states, the response of the resonance peak to the change of the external environment is different. A single resonance peak can measure several physical quantities without wavelength overlap using polarization multiplexing. The experimental results show that the PMF-LPFG realizes a high sensitivity torsion and bending measurement under different polarization states (-3.27 nm/rad*m and -13.38 nm/m) and can also measure the ambient temperature (84.10 pm/°C). The PMF-LPFG unit has the advantages of small size, high sensitivity, and multi-parameter measurement. The design scheme of the sensor provides a new idea for a multi-parameter sensor.

Compact, single-mode fiber-coupled, correlated photon pair source based on type-I beta-barium borate crystal

A small, portable, high-flux correlated photon-pair source has been designed and constructed from simple opto-mechanical parts. Unique to this device is its straightforward alignment process, together with the direct coupling of signal and idler photons into polarization-maintaining single-mode optical fibers. Spontaneous parametric down-conversion is used to produce photon pairs in β-barium borate (BBO) at a center wavelength of 810 nm. Owing to the applied type-I phase-matching, coincident photons have identical polarization. The estimated fiber-coupling efficiency is 51%, the measured photon and coincidence flux are 636 and 130 kHz/mW, respectively, normalized to pump power (44 mW). The source has an extremely wide wavelength spectrum of 202-nm FWHM, measured at the fiber output, which limits the actual heralding ratio to 20%.

All-solid polarization-maintaining silica fiber with birefringence induced by anisotropic metaglass.

We report the development of a silica glass single-mode polarization-maintaining fiber with birefringence induced by artificial anisotropic glass in the circular core without any external stress zones or structured cladding. The fiber core is composed of silica and germanium-doped silica nanorods ordered in submicrometer interleaved layers. The fiber has a measured cut-off wavelength at 1113 nm, phase birefringence of 0.3×10-4, and an effective mode diameter of 10.5 µm at the wavelength of 1550 nm. The polarization extinction ratio in the fiber is 20 dB at 1550 nm. The fiber is compatible with the standard SMF-28 fiber and can be easily integrated using standard fusion splicing with losses of 0.1 dB.

Electrically Sensing Characteristics of the Sagnac Interferometer Embedded With a Liquid Crystal-Infiltrated Photonic Crystal Fiber

The electrically sensing characteristics of a liquid-crystal (LC)-infiltrated polarization-maintaining photonic crystal fiber (PCF) have been studied. The small holes on the end face of the fiber collapse and two large holes remain open by controlling discharging-time, -current, and -position of a fiber splicer, then LC is selectively infiltrated into the two large holes, which can not only save LC but also make the welding between the LC-infiltrated polarization-maintaining PCF and single-mode fiber much easier. A new method to weld the two fibers is proposed by filling and volatilizing ethanol to make LC a few millimeters away from the end face which can improve the sensing system stability and prevent the discharge of a fiber splicer from destroying LC molecules. A Sagnac interferometer is set up by embedding the LC-infiltrated polarization-maintaining PCF in a fiber loop and then its electroresponse characteristics are studied. The refractive-index distribution of the LC-infiltrated polarization-maintaining PCF varies with electric voltage due to the variable index of LC, which makes it possible to detect voltage. Three voltage ranges are discussed by the different dips and the sensitivity is improved with voltage increasing. The high sensitivity is up to 3.49 nm/V with the tuning range of 7 nm as voltage changes from 149.67 to 151.61 V. The Sagnac interferometer embedded with an LC-infiltrated polarization-maintaining PCF can be utilized as a voltage sensor, electro-optical modulator, or filter.

1 μJ nanosecond low-coherent laser source with precise temporal shaping and spectral control

A μJ-level low-coherent pulse with dynamic and precise temporal shaping and spectral control is demonstrated. Low-coherent light delivered by a superluminescent diode is precisely shaped through a wave guide amplitude modulator driven by an arbitrary waveform generator. Utilizing a three-stage axial-alternating polarization-maintaining single-mode fiber amplifier, μJ-level low-coherent pulses with 3 ns durations and 20 nm instantaneous bandwidths at a 1 kHz repetition rate are obtained. In addition, a spectral control unit is used to adjust the spectrum shape. As a result, near flat-top, saddle-type, or other required special spectra can be produced. The low temporal coherence characteristics and output stability are characterized experimentally.

Real-time functional photoacoustic remote sensing microscopy.

A fiber-tetherable non-contact photoacoustic remote sensing microscopy system capable of multiplex functional imaging is reported. By utilizing stimulated Raman scattering within an over-pumped polarization-maintaining single-mode optical fiber, rapid pulse-to-pulse switching (500kHz) of excitation spectral content is demonstrated and utilized as a photoacoustic excitation source. These rapid acquisitions aim to reduce motion artifacts and facilitate high frame rates appropriate for real-time feedback to users. The system is characterized by estimating blood oxygen saturation in blood-flow phantoms and within a mouse ear in vivo.

Research Properties of the Mandelstam – Brillouin Scatter in the Polarization Maintaining Single-Mode Fibers

Results obtained in experimental studies of properties of the Mandelstam – Brillouin scatter in the polarization maintaining single-mode fibers are given in this paper. Experimental data for varieties of such fibers as “Panda” kind are analysed. Traces obtained by BOTDR are presented.Differences in traces when turning the axis of sections with optical fiber “Panda” at a certain angle are shown.Analysis of the experiment results revealed important dependence differences of the polarization maintaining fibers from the same dependences of others optical fiber kinds.

Broadband generation of the first-order OAM modes in two-mode fiber by offset splicing and fiber rotating technology

We demonstrate a simple, compact, and cost-effective all-fiber structure to generate the first-order orbital angular momentum (OAM) modes over a broad wavelength range. The offset splicing between a polarization-maintaining single mode fiber (PM-SMF) and a two-mode fiber (TMF) is adopted to excite LP11 mode in the TMF from LP01 mode in SMF. Then the OAM±1,1 modes are generated by rotating a customized fiber rotator, which can modulate the phase difference of the two degenerate LP11 modes (OAM±1,1 = LP11a ± i × LP11b). The interference phenomenon formed between OAM and Gaussian beams, which displays a fork-shape or spiral interference pattern, is used to confirm the generation of OAM modes. It should be noted that a PM fiber coupler and PM-SMFs are utilized in the experiment, which can avoid coupling of modes with orthogonal polarizations and then improves the OAM mode stability. Besides, the complexity of the OAM generation system is also reduced because the devices like polarization controller and half-wave plate are omitted by employing PM fibers. Based on this simple offset splicing and fiber rotating technology, the broadband generation of OAM±1,1 modes are experimentally demonstrated in wavelength range of 1530–1566 nm.

Sub-pm non-reciprocal noise in the LISA backlink fiber

The future space-based gravitational wave detector laser interferometer space antenna (LISA) requires bidirectional exchange of light between its two optical benches on board of each of its three satellites. The current baseline foresees a polarization-maintaining single-mode fiber for this backlink connection.Phase changes which are common in both directions do not enter the science measurement, but differential (‘non-reciprocal’) phase fluctuations directly do and must thus be guaranteed to be small enough.We have built a setup consisting of a Zerodur baseplate with fused silica components attached to it using hydroxide-catalysis bonding and demonstrated the reciprocity of a polarization-maintaining single-mode fiber at the 1 pm level as is required for LISA. We used balanced detection to reduce the influence of parasitic optical beams on the reciprocity measurement and a fiber length stabilization to avoid nonlinear effects in our phase measurement system (phase meter). For LISA, a different phase meter is planned to be used that does not show this nonlinearity. We corrected the influence of beam angle changes and temperature changes on the reciprocity measurement in post-processing.

A liquid lens switching-based motionless variable fiber-optic delay line

Abstract We present a Variable Fiber-Optic Delay Line (VFODL) module capable of imparting long variable delays by switching an input optical/RF signal between Single Mode Fiber (SMF) patch cords of different lengths through a pair of Electronically Controlled Tunable Lenses (ECTLs) resulting in a polarization-independent operation. Depending on intended application, the lengths of the SMFs can be chosen accordingly to achieve the desired VFODL operation dynamic range. If so desired, the state of the input signal polarization can be preserved with the use of commercially available polarization-independent ECTLs along with polarization-maintaining SMFs (PM-SMFs), resulting in an output polarization that is identical to the input. An ECTL-based design also improves power consumption and repeatability. The delay switching mechanism is electronically-controlled, involves no bulk moving parts, and can be fully-automated. The VFODL module is compact due to the use of small optical components and SMFs that can be packaged compactly.

Polarization-maintaining, large-effective-area, higher-order-mode fiber.

Higher-order-mode (HOM) fibers guiding light in large-effective-area (Aeff) Bessel-like modes have recently generated great interest for high-power laser applications. A polarization-maintaining (PM) version of HOM fibers can afford the added possibility of coherent beam combination, improved material processing, and polarization multiplexing of high-power fiber lasers. We report a PM-HOM fiber for guiding Bessel-like modes with Aeff ranging from 1200-2800 μm2. The fiber modes exhibit a birefringence value that compares well with that of a conventional single-mode PM fiber (2×10-4), and exhibit a polarization extinction ratio ranging from 13-23dB over meter-long fiber lengths, practical for amplifier systems. This fiber presents a unique platform for next-generation high-power fiber systems, as well as for the fundamental studies on deterministically polarized Bessel-like modes in fibers.

Impedance self-matching ultra-narrow linewidth fiber resonator by use of a tunable \u03c0-phase-shifted FBG

In this paper, we present a novel ultra-narrow linewidth fiber resonator formed by a tunable polarization maintaining (PM) π-phase-shifted fiber Bragg grating and a PM uniform fiber Bragg grating with a certain length of PM single mode fiber patch cable between them. Theoretical prediction shows that this resonator has ultra-narrow linewidth resonant peaks and is easy to realize impedance matching. We experimentally obtain 3 MHz narrow linewidth impedance matched resonant peak in a 7.3 m ultra-long passive fiber cavity. The impedance self-matching characteristic of this resonator also makes itself particularly suitable for use in ultra-sensitive sensors, ultra-narrow band rejection optical filters and fiber lasers applications.

Dissipative soliton resonance in a full polarization-maintaining fiber ring laser at different values of dispersion.

We investigated the dissipative solitons resonance in an ytterbium-doped fiber ring laser in which all the elements are polarization maintaining (PM). A semiconductor saturable absorber mirror was used as a mode-locker. The cavity included a normal dispersion single-mode fiber (SMF) and an anomalous dispersion photonic crystal fiber. The change of the length of the PM SMF allows the variation of the net-normal dispersion of the cavity in the range from 0.022 ps2 to 0.262 ps2. As the absolute value of the net-normal dispersion increases from 0.022 ps2 to 0.21 ps2, a square-shaped single pulse transformed to a single right-angle trapezoid-shaped pulse, and, at the dispersion of 0.262 ps2, to multiple right-angle trapezoid-shaped pulses, per round-trip.

High-power single-frequency 1014.8 nm Yb-doped fiber amplifier working at room temperature.

A single-frequency 1014.8 nm Yb-doped fiber amplifier working at room temperature was investigated in detail with respect to gain fiber length, fiber geometry, and fiber host material, which can be frequency quadrupled to 253.7 nm for laser cooling of mercury. After optimization, an up to 8.06 W laser was achieved with a single-stage amplifier, and 19.3 W power was obtained with another boost amplifier, using polarization-maintaining Yb-doped single-mode fiber with a 10 μm core and 125 μm inner clad. The amplified spontaneous emission was 25 dB lower than the signal in the final output of the laser system. The laser has a linewidth of ~24 kHz without noticeable broadening after amplification. Further power scaling is limited by stimulated Brillouin scattering.

Experimental demonstration of broadband Lorentz non-reciprocity in an integrable photonic architecture based on Mach-Zehnder modulators.

Lorentz reciprocity is a direct consequence of Maxwell equations governing the propagation of light in passive linear media with symmetric permittivity and permeability tensors. Here, we demonstrate the first active optical isolator and circulator implemented in a linear and reciprocal material platform using commercial Mach-Zehnder modulators. In a proof-of-principle experiment based on single-mode polarization-maintaining fibers, we achieve more than 12.5 dB isolation over an unprecedented 8.7 THz bandwidth at telecommunication wavelengths, with only 9.1 dB total insertion loss. Our architecture provides a practical answer to the challenge of non-reciprocal light routing in photonic integrated circuits.

Multifocus optical-resolution photoacoustic microscopy using stimulated Raman scattering and chromatic aberration

In this Letter, multifocus optical-resolution photoacoustic microscopy is demonstrated using wavelength tuning and chromatic aberration for depth scanning. Discrete focal zones at several depth locations were created by refocusing light from a polarization-maintaining single-mode fiber pumped by a nanosecond fiber laser. The fiber and laser parameters were chosen to take advantage of stimulated Raman scattering (SRS) in the fiber to create a multiwavelength output that could then be bandpass filtered. The collimator lens and objective lens are chosen to take advantage of chromatic aberration in which each generated SRS wavelength peak focuses at a slightly different depth. The maximum amplitude of photoacoustic signals is mapped to form C-scan images. Additionally, all wavelength peaks fired simultaneously offers improved depth-of-field structural imaging at the cost of slight degradation of mainlobe-to-sidelobe ratios. Wavelength-tuned depth scanning over more than 440 μm is demonstrated, significantly greater than the ~100 μm depth of field predicted from our focused Gaussian beams. The improved depth of focus could be valuable for structural imaging of microvascular morphology without the need for mechanical scanning in the depth direction.

Route of delivering 40-fs ultra-short laser pulses for gating photoconductive antenna in fiber-coupled terahertz time-domain spectroscopy

A route of delivering ultra-short laser pulses through a polarization-maintaining single-mode fiber has been investigated experimentally. The group velocity dispersion was well compensated, and the self-phase modulation was depressed in fiber. Finally, a 40-fs laser pulse with the energy of 70 pJ was obtained at the output of the transmitted fiber with the length up to 4 m in our fiber-delivery system. The route exhibits distinguishing features of compactness and flexibility, and this 40-fs laser pulse can be used not only to generate broadband terahertz (THz) radiation but also to detect broadband THz radiation, which is much better than the 150-fs laser pulse used previously.