Polarization-dependent Wavelength Shift Research Articles

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.

Asymmetric Phase-Tunable MZI Integrated by External Adjustor

A photonic waveguide asymmetric phase-tunable Mach-Zehnder interferometer (APT-MZI) integrated by the external adjustor is presented, in which the phase can be adjusted by changing the optical path of the adjustor. Using coupled mode theory and transfer matrix method, the characteristics of the APT-MZI chip with the linear adjustor are analyzed, and their optimization designs are also given. As an example, the APT-MZI chip is fabricated using silica-on-silicon technology. The experimental results show the chip with the insertion loss of less than 5.6 dB and the extinction ratio in output spectrum of 20 dB under the free spectral range of 0.05 and 0.02 nm. The polarization-dependent wavelength shift is 0.16 nm for 100-GHz channel spacing. The proposed APT-MZI chip can provide a cost-effective and easy-to-fabricate process for optical filter having precision phase adjustment.

Anisotropic effective permittivity of an ultrathin gold coating on optical fiber in air, water and saline solutions.

The optical properties of an ultrathin discontinuous gold film in different dielectric surroundings are investigated experimentally by measuring the polarization-dependent wavelength shifts and amplitudes of the cladding mode resonances of a tilted fiber Bragg grating. The gold film was prepared by electron-beam evaporation and had an average thickness of 5.5 nm ( ± 1 nm). Scanning electron imaging was used to determine that the film is actually formed of individual particles with average lateral dimensions of 28 nm ( ± 8 nm). The complex refractive indices of the equivalent uniform film in air at a wavelength of 1570 nm were calculated from the measurements to be 4.84-i0.74 and 3.97-i0.85 for TM and TE polarizations respectively (compared to the value for bulk gold: 0.54-i10.9). Additionally, changes in the birefringence and dichroism of the films were measured as a function of the surrounding medium, in air, water and a saturated NaCl (salt) solution. These results show that the film has stronger dielectric behavior for TM light than for TE, a trend that increases with increasing surrounding index. Finally, the experimental results are compared to predictions from two widely used effective medium approximations, the generalized Maxwell-Garnett and Bruggeman theories for gold particles in a surrounding matrix. It is found that both of these methods fail to predict the observed behavior for the film considered.

Birefringence compensated silicon nanowire arrayed waveguide grating for CWDM optical interconnects

We demonstrate an arrayed waveguide grating based on silicon nanowires with birefringence compensation for optical interconnects using coarse wavelength division multiplexing (CWDM). Angled star couplers are employed in combination with different diffraction orders for TM and TE polarizations. This device has a compact footprint of 0.36 mm×0.17 mm. Theoretical and experimental results show that the polarization-dependent wavelength shifts (PDλ) can be reduced from 380-420 to 0.5-3.5 nm, below 25% of the 3 dB bandwidth of channel response. The measured cross talk for TM polarization is better than -18 dB, and that for TE is better than -14 dB.

Ultra-Compact Birefringence-Compensated Arrayed Waveguide Grating Triplexer Based on Silicon-On-Insulator

We demonstrate an ultra-compact birefringence- compensated arrayed waveguide grating (AWG) triplexer for application in optical network units (ONUs) based on silicon nanowire waveguides. The cross-order design is employed to cover three operating wavelengths of 1310, 1490 and 1550 nm for the triplexer. The large birefringence of the silicon-on-insulator (SOI) waveguide is compensated by using angled star coupler design in combination with different diffraction orders for TE and TM modes. The device has a small footprint of only 0.18×0.12 mm2. The excess loss for TM polarization for three channels is 3 ~ 4 dB and the crosstalk is better than -18 dB. The polarization dependent wavelength shift (PDλ) is reduced from about 370 nm to less than 2.5 nm for wavelength channels at 1490-1550 nm.

Compact SOI-based polarization diversity wavelength de-multiplexer circuit using two symmetric AWGs

We demonstrate a compact 16-channel 200 GHz polarization diversity wavelength de-multiplexer circuit using two silicon AWGs and 2D grating couplers. Estimated fiber to fiber loss is better than -15.0 dB. Insertion loss and crosstalk induced by the AWGs are -2.6 dB and 21.5 dB, respectively. The maximum polarization dependent wavelength shift is 0.12 nm. The polarization dependent loss varies between 0.06 dB and 2.32 dB over the 16 channels. The total circuit footprint is 1400 × 850 μm(2).

Experimental Demonstration of Birefringence Compensation Using Angled Star Couplers in Silica-Based Arrayed Waveguide Grating

A birefringence compensation technique based on angled star couplers in arrayed waveguide grating (AWG) is experimentally investigated in silica-on-silicon waveguide with B–Ge codoped upper cladding. A 16-channel AWG with 100-GHz channel spacing is designed and fabricated. The star couplers are designed according to Rowland circle construction with an oblique incident/diffraction angle. Five different polarization compensation parameters corresponding to different incident/diffraction angles are employed to investigate the stress-induced birefringence. The experimental results confirm that the polarization-dependent wavelength shift <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $(\hbox{PD}\lambda)$</tex></formula> can be tuned by varying the incident/diffraction angle at the star couplers, and a birefringence-free AWG can be achieved without any additional fabrication process.

Uniform Polarization-Dispersion Compensation of All Channels in Highly Birefringent Silicon Nanowire-Based Arrayed Waveguide Grating

A design method for compensating polarization dispersion in arrayed waveguide gratings (AWGs) based on highly birefringent silicon nanowire waveguides is proposed by using angled star couplers in combination with different diffraction orders for TE and TM polarizations. Polarization-dispersion compensation for all output channels is achieved with the maximal polarization-dependent wavelength shift of 0.025 nm in an eight-channel AWG with 200-GHz spacing using 380 nm × 220 nm silicon waveguide with SU-8 upper-cladding.

Control of Linear Chirps in Waveguide Bragg Gratings by Applying Designed Core Profiles

Chirped gratings can be readily implemented in uniform-period waveguide Bragg gratings (WBGs) by adopting a tapered profile in the core patterning process. Based on our analysis, we have demonstrated that controlled linear chirps can be generated in WBGs with specifically designed core-taper profiles. By virtue of our established design and fabrication techniques, the measured center wavelengths, bandwidths, and dispersion coefficients of our fabricated straight and tapered polymeric WBGs agree very well with the designed values. We also obtained fairly low polarization-dependent wavelength shifts from the straight WBGs owing to the adopted low-birefringence polymeric materials.

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.

InP-Based Polarization-Insensitive Planar Waveguide Concave Grating Demultiplexer with Flattened Spectral Response

InP-based planar waveguide 48-channel concave grating demultiplexers with a channel spacing of 0.8 nm (100 GHz) are described and demonstrated. Polarization insensitivity and flattened spectral response are successfully achieved by the introduction of a polarization compensator and a two-focus grating, respectively. The fabricated device shows a polarization-dependent wavelength shift of less than 20 pm and a −3 dB spectral width of about 0.55 nm (68.75 GHz) over all channels.

InP-Based Polarization-Insensitive Planar Waveguide Concave Grating Demultiplexer with Flattened Spectral Response

ABSTRACT ⎯ InP-based planar waveguide 48-channel concave grating demultiplexers with a channel spacing of 0.8 nm (100 GHz) are described and demonstrated. Polarization insensitivity and flattened spectral response are successfully achieved by the introduction of a polarization compensator and a two-focus grating, respectively. The fabricated device shows a polarization-dependent wavelength shift of less than 20 pm and a -3 dB spectral width of about 0.55 nm (68.75 GHz) over all channels. Keywords ⎯ Planar waveguides, demultiplexer, concave grating, polarization, wavelength division multiplexing. Planar waveguide grating devices have been widely used for wavelength (de)multiplexing, switching, and optical add-drop applications in dense wavelength-division multiplexing optical communication systems. Among the various types of devices to implement a demultiplexer (demux) [1]-[4], the InP-based planar waveguide concave grating (CG) has shown great potential due to its compactness [2] and monolithic integration with laser diodes (LDs), photodetectors (PDs) [3], and semiconductor optical amplifiers [4]. However, compared to silica- or polymer-based CGs, it is difficult to achieve desirable performance in such areas as high channel-spacing accuracy, low polarization dependence, and flat-top spectral response over all channels due to its high refractive index dispersion,

Widely Tunable Wavelength-Selective Reflector Using Polymer Waveguide Double-Ring-Resonator Add/Drop Filter and Loop-back Mirror

A wavelength-selective reflector, composed of a double-ring-resonator add/drop filter and a loop-back mirror at the drop port to be used for a hybrid-integrated tunable laser is designed and fabricated. High-index-contrast polymer waveguide is used to realize a compact device as small as $2mm{\times}0.4mm$ . The radii of the rings are slightly different from each other to obtain a wide wavelength tuning via a vernier effect. Peak reflectivity is measured to be 52% for TE mode and polarization-dependent wavelength shift is 0.95 nm. The tuning range is measured to be about 42 nm for applied current as small as 46 mA.

Ultracompact AWG Using Air-Trench Bends With Perfluorocyclobutyl Polymer Waveguides

Using air-trench bends, an ultracompact 8 times 8 arrayed waveguide grating (AWG) demultiplexer (200-GHz channel spacing) for wavelength-division multiplexing (WDM) has been designed and fabricated with perfluorocyclobutyl (PFCB) core and clad co-polymers on a polyimide substrate. Compared to a conventional AWG in the same material system, the air-trench bend AWG shrinks the required chip area by a factor of 20. The decreased size is a factor in reducing the measured thermal shift to -0.012 nm/degC and decreasing the polarization-dependent wavelength shift to 1.3 nm.

Design of a Polarization-Insensitive Echelle Grating Demultiplexer Based on Silicon Nanophotonic Wires

A polarization-insensitive design of an echelle grating (or etched diffraction grating) demultiplexer based on silicon nanowires is proposed in the present letter, by introducing a polarization compensation area in its free propagation region. The polarization-dependent wavelength shift of the present device has been compensated at the whole spectral range. For a design with nine channels and 10-nm channel spacing, when the wavelength shift at the central channel 1550 nm is completely compensated, the wavelength shifts of the two edge channels are only 0.14 and 0.15 nm, which are acceptable.

Multi-PON access network using a coarse AWG for smooth migration from TDM to WDM PON

An interoperable access network architecture based on a coarse array waveguide grating (AWG) is described, displaying dynamic wavelength assignment to manage the network load across multiple PONs. The multi-PON architecture utilizes coarse Gaussian channels of an AWG to facilitate scalability and smooth migration path between TDM and WDM PONs. Network simulations of a cross-operational protocol platform confirmed successful routing of individual PON clusters through 7 nm-wide passband windows of the AWG. Furthermore, polarization-dependent wavelength shift and phase errors of the device proved not to impose restrain on the routing performance. Optical transmission tests at 2.5 Gbit/s for distances up to 20 km are demonstrated.

Silica-based 2.5%- arrayed waveguide grating using simple polarisation compensation method with core width adjustment

Silica-based 2.5%-Δ arrayed waveguide gratings using a polarisation compensation method with simple circuit design are demonstrated based on core width adjustment in the array. Experimental results show that the polarisation-dependent wavelength shift can be adjusted by optimising chirping parameters for core width.

Turning-Mirror-Integrated Arrayed-Waveguide Gratings on Silicon-on-Insulator

In this paper, optical demultiplexers (Demuxs) with the employment of the turning-mirror-integrated (TMI) arrayed-waveguide grating (AWG) are designed and fabricated on silicon-on-insulator (SOI) materials. The waveguide array in the conventional AWG configuration is replaced by a TMI waveguide array. The devices are more compact, while the performance is comparable to that of a conventional AWG fabricated on the same wafer. The adjacent and nonadjacent crosstalks are lower than -19 and -23 dB, respectively, and the typical on-chip loss is less than 8.8 dB. The polarization-dependent wavelength shifts are between 0.048 and 0.068 nm

Interleave filter based on coherent optical transversal filter

The principle of the transversal interleave filter previously proposed as a novel class of interleave filter is described. The principle of a conventional 1 /spl times/ 1 coherent optical transversal filter is reviewed. Then, the fundamental operating principle and the three design conditions required for the novel interleave filter are explained. As examples, three types of filter design, namely 1) a general/transposed design; 2) an asymmetric design; and 3) a symmetric design, are presented, and their interleave filter characteristics are discussed. The designed interleave filters with a free spectral range of 100 GHz was fabricated using silica-based planar lightwave circuit (PLC) technology. The asymmetric design achieved a wide 3-dB passband width of 55 GHz, whereas an ordinary lattice-form interleave filter could not realize a 3-dB passband width larger than 50 GHz because of the halfband property. A small polarization-dependent wavelength shift of 0.01 nm is demonstrated by inserting a single half waveplate in the middle of the circuit. The general/transposed and symmetric designs realized a practical interleave filter with a boxlike transmission spectrum and low chromatic dispersion. The two-stage interleave filter formed by cascading the general and transposed designs has the advantages of a low crosstalk of less than -46 dB and a wide 20-dB stopband width of 40 GHz, whereas the single-stage symmetric design has an extremely small chromatic dispersion of within /spl plusmn/5 ps/nm. In addition, the design concept to realize a 1/spl times/N transversal interleave filter is extended.