dB Polarization Dependent Loss Research Articles

Orbital angular momentum mode femtosecond fiber laser with over 100 MHz repetition rate

Orbital angular momentum (OAM) lasers have potential applications in large capacity communication systems, laser processing, particle manipulation and quantum optics. OAM mode femtosecond fiber laser has become the research focus due to the advantages of simple structure, low cost and high peak power. At present, OAM mode femtosecond fiber lasers have made some breakthroughs in key parameters such as repetition frequency, pulse width, spectrum width, but it is difficult to achieve good overall performance. Besides, the repetition rate is tens of MHz at present. In this paper, a large-bandwidth mode coupler is made based on the mode phase matching principle. In coupler, the first order mode coupler with 3 dB polarization dependent loss is made by the technology of strong fused biconical taper, and the second order mode coupler with 0.3 dB polarization dependent loss is made by the technology of weak fused biconical taper. By combining the nonlinear polarization rotation mode-locking mechanism, OAM mode femtosecond fiber laser with over 100 MHz repetition rate is built. The achievement of the key parameters is attributed to the selection of dispersion shifted fibers that can accurately adjust intracavity dispersion. Comparing with traditional dispersion compensation fibers (DCF), the group velocity dispersion is reduced by an order of magnitude, so it can better adjust intracavity dispersion to achieve the indexes of large spectral bandwidth and narrow pulse width. In addition, the diameter of the fiber is 8 μm, which is the same as that of a single mode fiber. Comparing with DCF, the fusion loss can be ignored, so only a shorter gain Erbium-doped fiber is required, which ensures a shorter overall cavity length and achieves high repetition frequency. The experimental results show that the first order OAM mode fiber laser has 113.6 MHz repetition rate, 98 fs half-height full pulse width, and 101 nm 10 dB bandwidth. Second-order OAM mode fiber laser has 114.9 MHz repetition rate, 60 fs half-height full pulse width, and 100 nm 10 dB bandwidth. Compared with the reported schemes, our scheme has good performance in key parameters such as repetition rate, pulse width and spectral width. We believe that the OAM mode fiber laser with excellent performance is expected to be widely used in OAM communication, particle manipulation and other research fields.

Polarization-dependent covalent organic framework saturable absorber and application of femtosecond fiber laser therein

Covalent organic frameworks (COFs) are materials that can be used in a wide variety of applications because of the nature of their ordered, crystalline, low-density, and porous structures. This work demonstrates the use of a π-electron-extended porphyrin/pyrene-linked COF (PorPh-PyTA-COF) as a saturable absorber (SA) in the 1.5 μm spectral region. The nonlinear optical absorption properties of this COF SA were studied and demonstrated a modulation depth of 0.8 % and saturation intensity of 0.5 kW/cm2. Using the COF SA, the operation of a mode-locked erbium-doped fiber laser was realized with a pulse duration of 506 fs at 1570 nm. This is believed to be the first report of a COF-based mode-locked fiber laser operating in the near-infrared spectral range. Additionally, a 3.7 dB polarization-dependent loss was measured in the COF SA and its role in the mode-locking process was also discussed.

Orbital angular momentum mode femtosecond fiber laser with over 100 MHz repetition rate

Orbital Angular Momentum (OAM) lasers have potential demand in many applications such as large capacity communication systems, laser processing, particle manipulation and quantum optics. OAM mode femtosecond fiber laser has become the research focus with the advantages of simple structure, low cost and high peak power. The current OAM mode femtosecond fiber lasers have made breakthroughs in the repetition frequency, pulse width, spectrum width and other key parameters, but it is difficult to achieve good overall performance. Besides, the repetition rate is currently in tens of MHz. In this paper, a large-bandwidth mode coupler is made based on the mode phase matching principle. Among them, the first order mode coupler with 3dB polarization dependent loss is made by the technology of strong fused biconical taper, and the second order mode coupler with 0.3dB polarization dependent loss is made by the technology of weak fused biconical taper. Combined with the nonlinear polarization rotation mode-locking mechanism, OAM mode femtosecond fiber lasers with over 100 MHZ repetition rate are built. The achievement of the key parameters is attributed to the selection of dispersion shifted fibers that can accurately adjust intracavity dispersion. Compared to traditional dispersion compensation fibers (DCF), the group velocity dispersion is reduced by an order of magnitude, so it can better adjust intracavity dispersion to achieve the indicators of large spectral bandwidth and narrow pulse width. In addition, the diameter of the fiber is 8μm, which is the same as that of a single mode fiber. Compared to DCF, the fusion loss can be ignored, so only a shorter gain Erbium-doped fiber is required that ensure a shorter overall cavity length and achieve high repetition frequency. The experimental results show that the first order OAM mode fiber laser has 113.6 MHz repetition rate, 98 fs half-height full pulse width, and 101nm 10-dB bandwidth. Second-order OAM mode fiber laser has 114.9 MHz repetition rate, 60 fs half-height full pulse width, and 100nm 10-dB bandwidth. Compared with the reported schemes, our scheme has better performance in key parameters such as repetition rate, pulse width and spectral width. We believe that the OAM mode fiber laser with good over performance is expected to be more widely used in OAM communication, particle manipulation and other research fields.

Polarization-insensitive 40-channel 100-GHz spacing fold-back planar echelle grating Mux/Demux for photonic integrated wavelength-selective switches.

We present and numerically demonstrate a novel polarization-insensitive (PI) 40-channel 100-GHz spacing fold-back planar echelle grating (PEG) multiplexer/demultiplexer (Mux/Demux) to realize the compact 1 × 2 crossing-less photonic integrated wavelength-selective switch (PIC-WSS). The PI operation is achieved by a polarization splitter to feed the TE and TM mode into the PEG via two waveguides with different incidental angles so that the two diffracted modes combine at the same output waveguide. By optimizing the design of different input/output angle combinations and sharing the same blazed angle, a single compact PI PEG with fold-back configuration can simultaneously work as twice the Demux and Mux required. The footprint of the single fold-back PI PEG is only ∼40 mm2. The numerical results show that the 40-channel 100-GHz spaced PI fold-back PEG has < 2.4 dB insertion loss, < -60 dB cross talk, zero polarization-dependent wavelength shift (PDWS), 0.3 dB polarization-dependent loss (PDL), < 0.5 dB loss variation and < 0.01 nm wavelength shift between Mux and Demux.

Ultrawide-band Low Polarization Sensitivity 3-µm SOI Arrayed Waveguide Gratings

An ultrawide-band (UWB), O- to L- band, polarization insensitive (PI) 1 × 12 100 GHz channel spacing arrayed waveguide grating (AWG) is designed and realized in 3-μm Silicon-on-Insulator (SOI) platform. PI and UWB operations are achieved by directly exploiting the UWB 3-μm PI silicon waveguide as the arrayed waveguide. The PI AWG can be employed as demultiplexer and multiplexer in photonic integrated circuits (PIC)s, such as UWB wavelength selective switches (WSS)s. Experimental results demonstrate UWB (O- to L- band) and PI 1 × 12 AWG operation with −0.82 dB to −1.52 dB insertion losses, <−35 dB average cross-talk, 0.18 dB to 1.27 dB polarization dependent loss (PDL), and 0.006 nm to 0.041 nm polarization dependent wavelength shift (PDWS). Error-free operation at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−9</sup> BER were measured with power penalties <0.1 dB, <0.2 dB, and <0.8 dB for 10 Gb/s, 20 Gb/s and 35 Gb/s NRZ-OOK PRBS 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup> -1 multi-band data, respectively.

Polarization-independent fiber-chip grating couplers optimized by the adaptive genetic algorithm.

One-dimensional polarization-independent grating couplers are demonstrated with the aid of the adaptive genetic algorithm optimization. By adjusting the relative weight between the coupling efficiency and the bandwidth of the polarization-dependent loss (PDL), we control the evolution direction and customize the final performance of the device. Two specific designs are generated by giving more weight to the coupling efficiency and the PDL bandwidth, respectively. Coupling efficiencies of the first design are measured to be -7.6dB and -7.9dB at 1550 nm for TE and TM polarizations, respectively, while its 1.0 dB PDL bandwidth is 25.0 nm. In contrast, the second design presents higher coupling efficiencies of -7.6dB and -7.2dB at 1550 nm for TE and TM polarizations, respectively. However, its 1.0 dB PDL bandwidth is 22.0 nm.

Polarization Dependence of Optical Properties of Single-Mode Polymer Optical Waveguides Fabricated Under Different Processes at 1310/1550 nm

We experimentally investigate the polarization dependence of the optical properties of single-mode polymer optical waveguides. We compare two types of waveguides composed of the same polymer materials: step-index square-core waveguides fabricated using the direct curing method and graded-index (GI) circular-core waveguides fabricated using the Mosquito method. We demonstrate that the GI circular-core single-mode waveguides exhibit remarkably small dependence of optical loss on the polarization angle, which is less than 0.1 dB polarization dependent loss (PDL) at both 1310 and 1550 nm wavelengths. This steady polarization property is attributed to the material stress free to the composing polymers during the fabrication process of the Mosquito method and to parabolic GI profile formed in symmetric circular core.

Programmable spectral processor based on spatial polarization manipulation with liquid crystal on silicon.

We experimentally demonstrate a novel liquid crystal on silicon (LCoS)-based programmable spectral processor, including two cascaded photonic configurations, to realize the state of polarization (SOP) manipulation in the spatial and spectral domain. As the final SOP at each wavelength is linear polarization with a manageable polarization direction, a broadband linear polarizer is used to filter the undesired wavelengths. The polarization manipulation only needs to be implemented along the dispersion direction with a 1D-LCoS. The programmable spectral processor can experimentally reach an intensity modulation depth of 46.4 dB with less than 1 dB polarization-dependent loss (PDL). Moreover, arbitrary power spectral distribution can be obtained with around 40 dB channel isolation. In particular, our experimental results verify that the proposed setup can achieve the adjustable central wavelength and tunable filtering at a resolution of 0.08 nm.

Multi-layer silicon nitride-on-silicon polarization-independent grating couplers.

A polarization-independent grating coupler is proposed and demonstrated in a 3-layer silicon nitride-on-silicon photonic platform. Polarization independent coupling was made possible by the supermodes and added degrees of geometric freedom unique to the 3-layer photonic platform. The grating was designed via optimization algorithms, and the simulated peak coupling efficiency was -2.1 dB with a 1 dB polarization dependent loss (PDL) bandwidth of 69 nm. The fabricated grating couplers had a peak coupling efficiency of -4.8 dB with 1 dB PDL bandwidth of over 100 nm.

Mode-Locked Erbium-Doped Fiber Lasers Using 45° Tilted Fiber Grating

We have systematically studied the 45° tilted fiber grating (45TFG) as a functional device for erbium-doped fiber laser (EDFL) mode locking. A number of 45TFGs with different polarization-dependent loss (PDL) have been fabricated. Mode-locked (EDFL) using these devices have been characterized in terms of threshold, pulse duration, signal-to-noise ratio, and spectral width. Our results show that a 45TFG with higher PDL could achieve better laser results. By using a 45TFG with 24 dB PDL, the mode-locked laser has 8.1% conversion efficiency and a threshold of 200 mW.

Design and fabrication of polymer-based multimode interference optical splitters

A polymer-based multimode interference optical splitter chip has been designed and fabricated. Fiber-waveguide coupling loss as well as the structure of the multimode waveguide are optimized in the design to achieve higher performance. A simple UV-based soft nanoimprint lithography (Soft UV-NIL) technique is adopted in the fabrication. Fluorinated acrylate resins, LFR, with different refractive indices are used in this work. Both the residual layer and waveguide deformation are improved by controlling the fabrication processes. An average of 12.98 dB insertion loss is obtained from 1×4 splitters with 1.08 dB uniformity and 0.05 dB polarization-dependent loss. The validity of the polymer optical splitters fabricated through Soft UV-NIL technique is demonstrated by software simulation as well as experimental works.

Design and fabrication of polymer-based 1 × 4 Y-branch splitters

A polymer-based Y-branch splitter chip has been designed and fabricated in this work. Fiber-waveguide coupling loss, propagation loss as well as bending loss are considered in the design to optimize the overall performance. A simple UV-based soft nanoimprint lithography (Soft UV-NIL) technique is adopted in the fabrication. Fluorinated acrylate resins produced by ChemOptics with different refractive indices are used. Residual layer and waveguide deformation are improved via controlling fabrication processes. An average 11.28dB insertion loss is obtained for 1×4 splitters with a 1.73dB uniformity, 0.06dB polarization dependent loss (PDL). The validity of the polymer optical splitters fabricated through Soft UV-NIL technique is demonstrated by software simulation as well as experimental works.

Symmetrical polarization splitter/rotator design and application in a polarization insensitive WDM receiver.

In integrated photonics, the design goal of a polarization splitter/rotator (PSR) has been separating the TE0 and TM0 modes in a waveguide. This is a natural choice. But in theory, a PSR only needs to project the incoming State Of Polarization (SOP) orthogonally to its output ports, using any orthogonal mode basis set in the fiber. In this article, we introduce a novel PSR design that alternatively takes the linear combination of TE0 and TM0 (TE0 +/- TM0) as orthogonal bases. By contrast, existing approaches exclusively use TE0 and TM0 as their basis set. The design is based on two symmetric and robust structures: a bi-layer taper and a Y-junction, and involves no bends. To prove the concept, we incorporated it into a four-channel polarization insensitive wavelength division multiplexing (PI-WDM) receiver fabricated in a standard CMOS Si photonics process. 40 Gb/s data rate and 0.7 +/- 0.2 dB polarization dependent loss (PDL) is demonstrated on each channel. Lastly, we propose an improved PSR design with 12 μm device length, < 0.1 dB PDL, < 0.4 dB insertion loss and < 0.05 dB wavelength dependence across C-band for both polarizations. Overall, our PSR design concept is simple, easy to realize and presents a new perspective for future PSR designs.

A tunable polarization diversity silicon photonics filter

A tunable polarization diversity silicon waveguide based optical filter was demonstrated. With the polarization diversity scheme, less than 0.5dB polarization dependent loss of the silicon optical filter was achieved in the wavelength range from 1525nm to 1600nm. The insertion loss of the whole polarization diversity circuits is 6.3dB. The extinction ratio of the optical filter is more than 27dB.

Broadband 2 × 2 free-space optical switch using electronically controlled liquid lenses

To the best of our knowledge, proposed is the first liquid lens technology-based 2 × 2 free-space optical switch using a pair of Electronically Controlled Variable Focus Lenses (ECVFLs). By independently controlling the focal lengths of two cascaded liquid ECVFLs, the two input optical beams are spatially adjusted to couple to their respective output beam ports. At 633-nm, the experimental switch demonstrates 26.3 dB crosstalk, 23.0 dB within-channel isolation, 1.1 dB optical loss, and 0.2 dB Polarization Dependent Loss (PDL). A 0.2 dB Wavelength Dependent Loss (WDL) is measured over 633-nm and 514-nm wavelengths. A 1 × 2 optical-fiber coupled switch version is also tested. The proposed switch can be useful in free-space laser systems as well as fiber-based modules.

Demonstration of Coarse-Fine Grooming in Coarse-WDM-Routed PONs

A scalable access network architecture is implemented experimentally to demonstrate gradual deployment of time- and wavelength-division-multiplexed passive optical networks (PONs) in a single-platform with minor changes in fiber infrastructure. This is achieved by the application of dynamic coarse-fine grooming to route multiple reflective optical network units of either time- or wavelength-multiplexed PONs collectively through coarse passbands of an arrayed waveguide grating (AWG). To evaluate experimentally the contribution of the excessive properties of wider-than-dense-passband AWGs to network performance, a readily available 2.7 nm device is utilized to substitute for 7 nm coarse-AWG prototypes. Experimental results have confirmed 10−9 bidirectional transmission of data and continuous waves over 2.7-nm-wide passband windows of the AWG in the presence of 0.35 nm polarization-dependent wavelength shift and 1.5 dB polarization-dependent loss. In addition, Rayleigh backscattering is reported to be incapable of limiting the network performance.

An Encryption-Decryption Method Using XOR Gate Based on the XPM between O-Band and C-Band Light Waves

An all-optical encryption-decryption method using an exclusive-or gate based on the cross-phase modulation between O-band and C-band light waves is proposed. The feasibility of the encryption-decryption technique is verified by handling binary signals at 2.5 Gbps, with less than 3 dB penalty of extinction ratio and 1 dB polarization dependent loss.

A polarization-diversity wavelength duplexer circuit in silicon-on-insulator photonic wires

We present a wavelength duplexer based on a compact arrayed waveguide grating (AWG) in silicon-on-insulator photonic wire waveguides. Polarization insensitive operation is achieved through a special polarization diversity approach in which we use 2-D grating fiber couplers as integrated polarization splitters. To mitigate the effects of process variations, we propagated both polarizations in opposite directions through the same AWG with a mere 600x350microm(2) footprint. This resulted in an on-chip insertion loss between -2.1dB and -6.9dB, crosstalk of -15dB, and only 0.66dB polarization dependent loss. This is the first demonstration of a functional polarization-diversity circuit implemented in SOI nanophotonic waveguides, including interfaces to single-mode fiber.

A micro-machining-based digital variable optical attenuator

A micro-machining-based digital MOEMS variable optical attenuator is described. The device implements an electromagnetically actuated shutter interposed in a fiber collimator gap and is capable of digitally adjusting optical attenuation and latching during power-off. The device is fabricated using non-silicon micro-machining technology. The performance of the digital VOA is measured and compared with calculated results. The device has less than 0.3 dB insertion loss, greater than 40 dB dynamic range, less than 0.1 dB polarization-dependent loss and low wavelength-dependent loss with <0.2 dB over the C-band (1535–1565 nm).

Fiber-connectorized multiwavelength 2×2 switch structure using a fiber loop mirror

A fiber-connectorized multiwavelength 2×2 switch structure is introduced for the first time that deploys a fiber loop mirror (FLM) arrangement with polarization control. Switch operation is achieved via a programmable waveplate effect rather than an optical power consuming long fiber loop length non-linear optical effect. The results from an experimental four-wavelength (i.e., 1546.92 nm, 1548.52 nm, 1550.12 nm, and 1551.72 nm) proof of concept switch using two mechanical fiber-based polarization controllers embedded in a short 7 m fiber loop indicates an average optical coherent crosstalk of −31.2 dB. Presently, optical loss is mainly limited by the WDM devices used in our experimental setup. Hence, without the WDM multiplexers, an average optical loss of 2.22 dB is measured over a 50 nm optical bandwidth. Also, an average 0.08 dB polarization dependent loss is measured for this broadband switch.