In-line Polarization Research Articles

Ultrafast laser direct writing of in-line polarizers based on nano-gratings

Ultrafast laser direct writing of in-line polarizers based on nano-gratings

Impact Localization for Haptic Input Devices Using Hybrid Laminates with Sensoric Function

The required energy savings can be achieved in all automotive domains through weight savings and the merging of manufacturing processes in production. This fact is taken into account through functional integration in lightweight materials and manufacturing in a process close to large-scale production. In previous work, separate steps of a process chain for manufacturing a center console cover utilizing a sensoric hybrid laminate have been developed and evaluated. This includes the process steps of joining, forming and inline polarization as well as connecting to an embedded system. This work continues the research process by evaluating impact localization methods to use the center console as a haptic input device. For this purpose, different deep learning methods are derived from the state of the art and analyzed for their applicability in two consecutive studies. The results show that MLPs, LSTMs, GRUs and CNNs are suitable to localize impacts on the novel laminate with high localization rates of up to 99%, and thus the usability of the developed laminate as a haptic input device has been proven.

All-fiber Q-switched erbium-doped fiber laser generation with SMF-SIMF-SMF structure as artificial saturable absorber

A passively Q-switched Erbium-doped fiber laser (EDFL) was successfully demonstrated using SMF (single-mode fiber)-SIMF (step-index multimode fiber)-SMF or SMS structure as a saturable absorber (SA). The SMS structure operates on the Kerr-effect of multimode interference (MMI). To modulate the cavity loss, a 158 mm length of SIMF was fusion spliced into a ring cavity. By properly adjusting the in-line polarization controller (PC) that holds the SIMF, we were able to generate steady Q-switched pulses. As the input pump power increased from 115 to 343 mW, the repetition rate of the Q-switched laser increased from 87 to 158 kHz, while the corresponding pulse width decreased from 4.2 µs to 2.5 µs. The signal-to-noise ratio (SNR) of the fundamental mode for the pulsed laser was around 72 dB at a central wavelength of 1530 nm. Our results indicate that the SMS structure can be used as an SA to generate stable Q-switched EDFL with very simple cavity settings.

Fiber laser with dual-channel and a selectable comb filter based on Vernier effect of parallel-connected two Mach–Zehnder interferometers

We propose and demonstrate the implementation and application of a new configuration of an all-fiber comb filter based on the Vernier effect produced by parallel-connected two in-line Mach–Zehnder interferometers (MZIs). Each in-line MZI was fabricated by fusion splicing a section of panda-type polarization maintaining fiber (PMF) with peanut-shaped tapers between two single-mode fibers. These two in-line MZIs, respectively, form reference and sensing interferometers, which are parallel-connected by two 3-dB optical fiber couplers to realize the Vernier effect. By incorporating the proposed comb-filter into the erbium-doped fiber laser cavity, two output channels at 1533.2 and 1558.2 nm have been achieved. Further, the combination of the parallel-connected two in-line MZIs and polarization controllers (PC1 and PC2) promotes the lasing in a switchable and selective way. To the best of the authors’ knowledge, this is the first demonstration of a comb filter that employs paralleled two peanut-shaped MZIs in PMF. The experimental results indicate that the proposed filter has the potential to be used in communication systems.

Thulium-doped fiber laser with switchable single-wavelength output using polarization-dependent loss

A thulium-doped fiber laser (TDFL) with switchable single-wavelength output was proposed and experimentally constructed, and its output characteristics were investigated. The central wavelengths were 1940.52 nm and 2048.04 nm, defined by a superimposed uniform fiber Bragg grating (SI-UFBG) with reflectivity larger than 92%. Switchable output was successfully achieved by using polarization-dependent loss, with the help of a drop-in polarization controller and an in-line polarizer. For both output wavelengths, optical signal-to-noise ratios larger than 80 dB were achieved. Maximum fluctuations of the central wavelengths of 1940.52 nm and 2048.02 nm under 60 min were, respectively, 0.04 nm and 0.01 nm. Maximum fluctuations of output power for the same wavelengths over the same time period were, respectively, 1.09 dB and 0.12 dB. Maximum output powers of 215.12 mW and 155.53 mW were achieved for the respective output wavelengths of 1940.52 nm and 2048.02 nm. Moreover, a tuning range of ∼2 nm was realized by enforcing a strain on the SI-UFBG. The proposed TDFL may be applied in laser medicine and free-space-related applications.

Compact and high-reliability fiber-optic open-loop gyroscope enabled by an in-fiber polarizer.

The performance of an open-loop fiber-optic gyroscope is strongly dependent on the optical characteristics of its polarizer. Here we report the implementation of an in-house fabricated 45° tilted-fiber-grating-based polarizer, for the first time on an ultra-fine diameter polarization-maintaining fiber platform in an open-loop fiber-optic gyroscope. This special in-line polarizer is proven to have the merits of high extinction ratio, broad spectrum, bendability, stretchability, temperature insensitivity, and high reliability, all of which make it a perfect match for practical fiber optic gyros that need to be packaged compactly without affecting performance. Our prototype fiber optic gyroscope has a compact volume of only ϕ35 × 20 mm2, achieving a bias instability of less than 0.1 °/h, full temperature bias stability of less than 1 °/h, and scale factor linearity of better than 200 ppm. This compact and high-performance fiber gyro enabled by TFG polarizer may promise great potential in the field of automation and control.

Tilted fiber grating polarizer in a 40-µm polarization-maintaining fiber.

The optical polarizer is a crucial component widely used in many optical systems and applications. Fiber-optic polarizers have the merits of excellent compatibility and ease of integration with other fiber components. We report an in-line polarizer enabled by a 45° tilted fiber grating inscribed into a specialty fiber for the next generation fiber-optic gyroscope, i.e.,a 40-µm ultra-fine-diameter tiger-type polarization-maintaining fiber with which the size of fiber-optic sensors can be miniaturized. The results show that a 40-mm-long polarizer operates at a center wavelength of around 830nm with high-performance characteristics, such as a polarization extinction ratio exceeding 30dB, a low insertion loss of less than 1.5dB, and a large 3-dB optical bandwidth more than 60nm. This kind of fiber-optic polarizer may have a broad scope across applications and systems such as fiber lasers and sensors, especially high-precision fiber-optic gyroscopes.

Generation of different mode-locked states in a Yb-doped fiber laser based on nonlinear multimode interference.

We demonstrated an ultrafast Yb-doped fiber laser with a single mode fiber-graded index multimode fiber-single mode fiber (SMF-GIMF-SMF) structure based saturable absorber. The GIMF was placed in the groove of an in-line fiber polarization controller to adjust its birefringence, enabling the SMF-GIMF-SMF structure to realize efficient saturable absorption based on nonlinear multimode interference without strict length restriction. By adjusting two intra-cavity polarization controllers, stable dissipation solitons and noise-like pulses were achieved in the 1030 nm waveband with pulse durations of 10.67 ps and 276 fs, respectively. We also realized Q-switched mode-locked pulses in the same fiber laser cavity. By the dispersive Fourier transform method, the real-time spectral evolution in the buildup process of the Q-switched mode-locked state was captured, which showed that the continuous-wave in this laser could gradually evolved into the stable Q-switched mode-locked pulses through unstable self-pulsation, relaxation oscillation and rogue Q-switching stage. To the best of our knowledge, our work reveals the buildup dynamics of the Q-switched mode-locked operation in a fiber laser for the first time. And we also studied the real-time spectral evolution of the stable Q-switched mode-locked pulses, which exhibited periodic breathing property.

Linearly polarized ytterbium laser enabled by an antiresonant hollow-core fiber inline polarizer.

We report a linearly polarized ytterbium-doped fiber (YDF) laser cavity configured by integrating an antiresonant hollow-core fiber-based inline polarizer. The 5-cm-long compact fiber polarizer was fusion spliced to a commercial large-mode-area, polarization-maintaining YDF. Near-diffraction-limited linearly polarized signal output with a polarization extinction ratio of > 21 dB was achieved for up to 25 W of power that was limited only by the available pump power. The performance of the hollow-core fiber polarizer was found to be temperature insensitive, which obviates the need for the precise temperature control required in all-fiber, high-power polarized laser cavities employing crossed fiber Bragg gratings. We used the tapering technique to scale down the geometry of the polarizing fiber and shift its operating wavelength by ∼100 nm, which makes it an attractive candidate for a variety of fiber laser applications.

Numerical investigation of extra-cavity vector soliton molecules manipulation

We report on the numerical simulation results of vector soliton molecules (VSMs) manipulation based on the extra-cavity projected super-position technique. The VSMs are generated in a passively mode-locked fiber laser, and their time separations can be flexibly adjusted by applying different birefringence parameters. Moreover, along the laser output port, the generated VSMs can be flexibly manipulated by a projected module consisting of a polarization controller and an inline polarization beam splitter. Thus, a 2-2-2 and 2-2-4 type VSMs could be obtained separately. Moreover, we have verified that the vector soliton separation is the key parameter that determines the formation of obtained VSMs. These simulation results would greatly enrich the understanding of soliton dynamics and provide inspiration for experimental researches.

Manipulation of Kerr cavity solitons based on projected super-position technique

We report numerical simulation on the Kerr cavity solitons (CSs) manipulation based on projected super-position technique. The CSs are generated in a fiber-based Kerr resonator. The positions and amplitudes of these CSs can be adjusted by setting intra-cavity parameters. By introducing a polarization controller (PC) and an inline polarization beam splitter (PBS) into the system, the CSs can be projected, superposed, and manipulated flexibly to operate with controllable soliton positions and amplitudes. Moreover, depending on the time separation between two polarization components, the number of solitons after projection would change based on different type of CSs.

Highly stable multi-wavelength fiber laser based on hybrid enclosed two-armed fiber filter

A compact multi-wavelength fiber laser (MWFL) with high stability based on hybrid enclosed two-armed fiber filter (HETAFF) is demonstrated. The HETAFF composes of an enclosed Mach-Zehnder interferometer with an in-line polarization controller (PC) in one arm of optical couplers #1 (OC1) and a section of polarization maintaining fiber with two PCs in OC2 loop. By using the HETAFF in proposed fiber laser, a lasing state switchable and wavelength-interval adjustable MWFL is obtained. It can be switched in single-, dual-, triple-, quadruple- and quintuple-wavelength states. The wavelength-interval can be adjusted as it operates in dual-, triple- and quadruple-wavelength states. Its optical signal to noise ratio (OSNR) is more than 36.03 dB, and the lasing wavelength shift and power fluctuation are less than 0.08 nm and 0.94 dB, respectively. The output characteristics, such as abundant laser states and high stability, are inseparable from the unique performance of the HETAFF.

Plasmon-assisted fiber polarizers with high extinction ratio and low insertion loss

We propose a compact plasmon-assisted in-line fiber polarizer with metal films selectively coated on the lateral surface of the cladding in a conventional single mode fiber. The polarization-dependent loss mechanism intrinsically originates from the polarization-selective excitation of surface plasmon polaritons (SPPs) at both interfaces of metal films. Both the polarization extinction ratio (PER) and insertion loss (IL) of the plasmonic fiber polarizer strongly depend on the strength of the interaction between the polarized core modes and SPP modes. We numerically demonstrate the performances of an Au-coated and an Al-coated fiber polarizers, respectively. Both of them can achieve a PER at least higher than 10 dB/mm over the whole C- and L-bands. Notably, the PERs at 1550 nm in the Au-coated and Al-coated fiber polarizers can be up to 37.3 dB/mm and 29.4 dB/mm, respectively. The IL in the Al-coated fiber polarizer is about an order of magnitude higher than that in the Au-coated one, but it can still be lower than 0.1 dB/mm over the C- and L-bands. The achievable excellent performance shows that our proposed plasmonic fiber polarizer can provide a promising candidate for compact all-fiber polarizers with a high PER and a low IL.

Wavelength tunable Q-switched Er-doped fiber laser based on ZrSe2

We demonstrated a passively Q-switched Er-doped fiber laser based on the ZrSe2/PVA film. Here, the layer structure ZrSe2 platelets were produced by the liquid-phase exfoliation method. By means of nonlinear optical transmittance measurement, the modulation depth and saturation intensity of the ZrSe2/PVA SA were 31% and 4.75 MW/cm2, respectively. The Q-switched pulses revealed the highest repetition rate and pulse energy around 43.7 kHz and 139.8 nJ with the pump power at 346 mW. Based on the invisible filter, we produced the wavelength-tunable and dual-wavelength Q-switched pulses after insertion of the in-line polarizer inside the cavity. Through the proper adjustment of the polarization controller, a tuning wavelength of from 1544.3 to 1563.5 nm, a tuning range of around 19.2 nm, and the smallest tuning interval of around 1 nm have been achieved.

Ultra-broadband tunable and switchable multi-wavelength mode-locking Tm-doped all-fiber laser

Through regulating the in-band absorption of used gain fiber, we demonstrate an ultra-broadband tunable and switchable multi-wavelength mode-locking Tm-doped all-fiber laser. The tuning range can be enlarged as much as 153 nm (from 1828.45 to 1981.35 nm, the largest tuning range so far) by employing different lengths of used gain fiber with different in-band absorption and birefringent filtering mechanism. In addition, benefiting from four in-line polarization controllers and broadband gain profile of Tm-doped fiber, switchable quad-wavelength mode locking with part binary control can be observed clearly, even penta-wavelength. Such kind of ultra-broadband tunable and switchable mode-locking laser provide simpler and elastic way for practical application, such as optical signal processing, spectroscopy, optical communications, and so on.

Mode conversion from LP11 to LP02 based on in-line mode orientation control and antisymmetric refractive-index perturbation in a few-mode fibre

We present intra-fibre mode conversion from the antisymmetric LP11 mode to the circularly symmetric LP02 mode using a force-induced, long-period fibre grating accompanied by an in-line polarization controller. The field orientation of the incoming LP11 mode is aligned to the antisymmetric perturbation in the fibre grating to activate resonant mode coupling. Mode conversion is achieved by applying pressure with a spatial period of 430 μm along an interaction length of 50 mm. We verify the mode conversion process by observing the far-field patterns of the fibre output and comparing the transmission power with and without a high-numerical aperture, narrow-core fibre. The intra-fibre mode conversion system with erasable and reconfigurable natures exhibits an insertion loss of 0.48 dB and a 3-dB bandwidth of 52 nm.

Wavelength tunable passive-mode locked Er-doped fiber laser based on graphene oxide nano-platelet

The continuous wavelength tunable passively mode-locked Er-doped fiber laser (PML-EDFL) from C-band around 1544 nm to L-band around 1574 nm has been demonstrated in combination with graphene oxide (GO) nano-platelets and the nonlinear polarization rotation (NPR) mechanism. The preparation of GO nano-platelets was based on the liquid phase exfoliation and then mixed with a PVA solution to produce the GO/PVA film. The PML-EDFL was operated at the fundamental mode-locked state in the longer wavelength regime (>1565 nm) and was turned into the fourth harmonic mode-locked state in the shorter wavelength regime. The wavelength tuning mechanism is attributed to the invisible filter by means of the in-line polarizer inside laser cavity, which can be verified from the emission peaks of the dual wavelengths mode-locked state. The relatively stable operation of tunable PML-EDFL at certain wavelength, disregarding environmental perturbations, has been confirmed to reveal promising commercial applications in the near future.

Magnetically tunable hollow-core anti-resonant fiber polarizer

An in-line high efficient polarizer, composed of magnetic-ionic-liquid-adorned (MIL-adorned) hollow-core anti-resonant fiber (HARF), is theoretically proposed and experimentally demonstrated. The protocol is based on the selective conversion of polarization mode into leaky mode and attenuates quickly in MIL and the polarizer is featured by the magnetically tunable polarization extinction ratio (PER) and the thermally controllable operation bandwidth.

High-resolution wavemeter based on polarization modulation of fiber speckles

For speckle pattern-based wavemeters or spectrometers, the intermodal and the chromatic dispersion of the diffusion waveguide are key factors in determining the wavelength resolution. In this study, we propose a new mechanism to modulate the fiber speckles aside from the dispersion related effect. The polarization modulation is introduced in a rectangular core fiber (RCF) by using an in-line polarization rotator (IPR). The IPR can rotate the polarization angle at different wavelengths. Interestingly, it is observed that the modulated speckle patterns appear periodically similar, and they present more variations when compared to unmodulated ones. The theoretical simulation indicates that the polarization exerts an influence on the fiber speckles by modulating the mode coupling coefficients when light is coupled into the RCF. In the demonstration experiment, we first built a precise laser frequency tuning system based on an electro-optic modulator and a microwave source. By comparing the recorded speckles with and without polarization modulation, the former speckles have lower correlations, which are evaluated using the Arc Cosine Similarity algorithm. Reconstructing the spectrum of speckles, the smallest detectable wavelength that can be detected with polarization modulation is 0.2 fm. The experimental results prove that the polarization modulation is a convenient and effective method to enhance the speckle’s wavelength sensitivity. In addition, this study paves a new way to design high-resolution wavemeters with shorter, more compact optical waveguides.

In-line polarization controller for hollow core photonic bandgap fiber

We demonstrate an in-line polarization controller for hollow core photonic bandgap fiber made by inserting a length of the fiber into a standard, off-the-shelf, 3-paddle controller as widely used for polarization control using standard single mode fibers. Although the operational principle of this 3-paddle controller is very different when using hollow core photonic bandgap fiber rather than SMF effective polarization control is readily achieved.