Full C-band Research Articles

Phase Noise Characterization and EEPN of a Full C-Band Tunable Laser in Coherent Optical Systems

We perform phase noise characterization of a tunable laser source that is capable of tuning to 103 channels between 1527.6-1568.36 nm with 50 GHz grid spacing between the channels. The measured frequency modulation (FM) noise power spectral density (PSD) is reproduced by simulations in order to investigate the impact of equalization-enhanced phase noise (EEPN) in a coherent transmission system. The simulations are performed on a 30 Gbaud channel with 16 quadrature amplitude modulation (16QAM) and using pilot-based carrier phase estimation with 3% overhead. By performing extensive system simulations, we show the impact of different accumulated dispersion. Furthermore, we show the possibility to overcome EEPN related penalties by using a local oscillator (LO) with reduced low frequency phase noise or flat FM-noise PSD profiles with lower linewidths.

Full C-Band 3060-km DMD-Unmanaged 3-Mode Transmission With 40.2-Tb/s Capacity Using Cyclic Mode Permutation

We have achieved the longest three mode-multiplexed full C-band transmission yet attained over 3060 km. In wideband mode-multiplexed transmission over weakly-coupled fewmode fibers (FMFs), the width of signal impulse responses is dependent on wavelength, and also exhibits a linear growth with increased transmission distance because of the presence of differential mode delay (DMD). Those properties are technically challenging issues for future deployable space division multiplexing (SDM) transport systems since they make a system design complicated, especially for terrestrial FMF transmission links. In this article, we describe how we applied a cyclic mode permutation (CMP) technique to achieve wideband long-haul FMF transmission where spatial channels are cyclically interchanged in each span to suppress DMD-induced pulse broadening. The CMP technique enabled DMD-unmanaged long-haul transmission across 4.4-THz optical bandwidth over two-mode FMF whose DMD varied in the range from 33.7-44.3 ps/km, resulting in 3060-km FMF transmission with a net capacity of 40.2 Tb/s.

Design and evaluation of quasi-Nyquist WDM networks utilizing widely deployed wavelength-selective switches.

Photonic networks based on wavelength-selective switches (WSSs) can transport wavelength-division-multiplexed (WDM) signals in a cost-effective manner. To accommodate the ever-increasing network traffic, the spectral efficiency should be maximized by minimizing the bandwidth of the guardbands inserted between WDM signals. Quasi-Nyquist WDM systems are seen as offering the highest spectral efficiency in a feasible way. However, highly dense WDM systems suffer from the signal-spectrum narrowing induced by the non-rectangular passbands of WSSs. Furthermore, widely deployed WSSs cannot process quasi-Nyquist WDM signals since the signal-alignment granularity does not match the passband resolution of the WSSs. This paper proposes a network architecture that enables quasi-Nyquist WDM networking with widely deployed WSSs. Through intensive network analyses based on computer simulations, we confirm that it has 30.8% higher spectral efficiency than conventional networks. Its feasibility is verified by transmission experiments on 72-channel 32-Gbaud/400-Gbps dual-carrier dual-polarization 16-ary quadrature-amplitude-modulation signals aligned with 66.6-GHz spacing in the full C-band. The net fiber capacity of 28.8 Tbps, the transmission distance of 900 km, and the hop count of 9 are attained by our proposed quasi-Nyquist WDM networking scheme.

An Integrated Few-Mode Power Splitter Based on Multimode Interference

A 1 × 2 integrated four-mode power splitter based on multimode interference is proposed and experimentally demonstrated for the first time. A three-dimensional simulation is used to optimize the core/cladding refractive index difference and the input waveguide position for the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> , and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> input waveguide modes. Minimum insertion loss (IL) and mode-dependent loss (MDL) of 0.1 and 0.2 dB are predicted, respectively. IL and MDL less than 1 dB can be maintained over a bandwidth of approximately 50 and 25 nm, respectively. The device was fabricated on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and experimentally characterized. The variation of the power splitting ratio for each mode is less than 0.4 dB over the full C-band, and the excess losses of the splitter for all four modes exceed the IL of a straight waveguide by less than 1.85 dB.

Amplification of orbital angular momentum modes in an erbium-doped solid-core photonic bandgap fiber

Abstract A new kind of erbium-doped solid-core photonic bandgap fiber (ED-SC-PBGF) for amplification of orbital angular momentum (OAM) modes is proposed and investigated. The configurations of annular erbium-doped profile with special design and multi pump modes are used to amplify the signal modes evenly. Using an optimized ED-SC-PBGF pumped with l = 1 and 2 modes, differential mode gains of 0.9 dB and gain of more than 20 dB can be achieved for l = 1 and 2 OAM signal modes across the full C-band. This OAM-in-fiber amplification techniques would have potential application in ultra-long distance and high capacity OAM optical communication systems and other systems that utilize high power OAM light.

Compact and low-crosstalk mode (de)multiplexer using a triple plasmonic-dielectric waveguide-based directional coupler

A compact and low-crosstalk mode (de)multiplexer [(De)MUX] is proposed based on a triple-waveguide coupler, consisting of a hybrid plasmonic waveguide in between two outer silicon waveguides. The proposed quasi-TM0 and quasi-TM1 mode (De)MUX is optimized by using the full vectorial finite element method and 3D full vectorial finite difference time domain method sequentially. The numerical results show that the proposed mode (De)MUX has a compact coupling length of 7.5 μm, an ultralow mode crosstalk of −30 dB, an insertion loss of 0.32 dB at 1550 nm, and an extinction ratio of >15 dB over the full C-band. The fabrication tolerance of the proposed mode (De)MUX is also investigated in detail. The effects of thermal tuning and absorption heating are studied to correct the fabrication errors and to evaluate the thermal effects on the performance, respectively.

Design and Verification of Large-Scale Optical Circuit Switch Using ULCF AWGs for Datacenter Application

The exponential increase in the volume of traffic being processed by datacenters demands massive electrical switches and complicated interconnections. The power consumption will soon become critical, and the problem is expected to be resolved by introducing large-port-count optical circuit switches that connect many server racks or pods. In this paper, we propose a novel optical-circuit-switch architecture that uses n × N uniformloss and cyclic-frequency (ULCF) arrayed-waveguide gratings (AWGs) as low-loss wavelength routers. To confirm the effectiveness of our proposal, a pair of 12 × 48 ULCF AWGs is fabricated using planar-lightwave-circuit technology. Part of a 1536 × 1536 optical circuit switch is constructed, and its good transmission performance is experimentally confirmed through 96-wavelength 100-Gbps signal transmission in the full C-band. The switch throughput reaches 153.6 Tbps.

8 kHz linewidth, 50 mW output, full C-band wavelength tunable DFB LD array with self-optical feedback

We describe a 1.5 μm, narrow linewidth, high output power wavelength tunable LD that employs a self-optical feedback circuit. By incorporating an optical circulator-based feedback circuit in a DFB LD array, we have successfully reduced the oscillation linewidth from several MHz to less than 8 kHz over the full C-band range. A high output power of approximately 50 mW and a low relative intensity noise of less than -130 dB/Hz were simultaneously achieved. Furthermore, by employing a partial reflection mirror as a self-optical feedback circuit, we have also realized a full C-band wavelength tunable LD with a linewidth of less than 11 kHz and a simple laser configuration.

Full C-Band Tunable V-Cavity-Laser based TOSA and SFP Transceiver Modules

&lt;span lang="EN-US"&gt;We report the latest development in tunable transmitter optical sub-assembly (TOSA) and small form-factor pluggable (SFP) transceivers based on simple and compact V-cavity laser (VCL), aiming for low-cost deployment in metro, access and data center networks. The VCL employs a half-wave coupler to achieve high side-mode suppression ratio (SMSR) and the Vernier effect to achieve a wide wavelength tuning range. Full C-band tuning from 1529.55-nm to 1566.31-nm with SMSR above 36 dB is demonstrated. Since the laser does not involve any grating or epitaxial regrowth, and has a simple tuning algorithm, it allows simpler processes for fabrication and testing as compared to other widely tunable laser structures. Compact TOSAs and SFP transceiver modules have been developed for full C-band tuning with up to 93 channels at 50 GHz spacing. Transmission experiments are carried out for direct modulation with data rates from 2.5 Gbps to 8.5 Gbps. The results of reliability tests of the modules are also presented.&lt;/span&gt;

Full C-band Si photonic crystal waveguide modulator.

The slow-light effect in silicon lattice-shifted photonic crystal waveguide (LSPCW) Mach-Zehnder modulators allows compact phase shifters, while limiting the working spectrum Δλ. We optimized the structural parameters of the LSPCW and extended Δλ to cover the full C-band in exchange for moderately decreasing the group index ng. We obtained Δλ=42 nm with ng=8-9 in a fabricated device and observed 25Gbps eye opening in the 200μm modulator in the full C-band.

42.3 Tbit/s, 18 Gbaud 64 QAM WDM coherent transmission over 160 km in the C-band using an injection-locked homodyne receiver with a spectral efficiency of 9 bit/s/Hz.

We demonstrate a 235-channel wavelength division multiplexing (WDM), polarization-multiplexed (pol-mux) 18-Gbaud 64 QAM coherent transmission of 160 km over the full C-band. By applying an injection-locked homodyne detection circuit to WDM coherent transmission, we have achieved low noise optical carrier-phase locking between transmitted data and a local oscillator over the full C-band range. As a result, a potential capacity of 42.3 Tbit/s data with a spectral efficiency of 9 bit/s/Hz was transmitted.

The Effect of PolSAR Image De-speckling on Wetland Classification: Introducing a New Adaptive Method

ABSTRACTSpeckle noise significantly degrades the radiometric quality of PolSAR image and, consequently, decreases the classification accuracy. This article proposes a new speckle reduction method for PolSAR imagery based on an adaptive Gaussian Markov Random Field model. We also introduce a new span image, called pseudo-span, obtained by the diagonal elements of the coherency matrix based on the least square analysis. The proposed de-speckling method was applied to full polarimetric C-band RADARSAT-2 data from the Avalon area, Newfoundland, Canada. The efficiency of the proposed method was evaluated in 2 different levels: de-speckled images and classified maps obtained by the Random Forest classifier. In terms of de-speckling, the proposed method illustrated approximately 19%, 43%, 46%, and 50% improvements in equivalent number of looks values, in comparison with SARBM3D, Enhanced Lee, Frost, and Kuan filter, respectively. Also, improvements of approximately 19%, 9%, 55%, and 32% were obtained in the overall classification accuracy using de-speckled PolSAR image by the proposed method compared with SARBM3D, Enhanced Lee, Frost, and Kuan filter, respectively. This new adaptive de-speckling method illustrates to be an efficient approach in terms of both speckle noise suppression and details/edges preservation, while having a great influence on the overall wetland classification accuracy.

1.5μm, mode-hop-free full C-band wavelength tunable laser diode with a linewidth of 8 kHz and a RIN of -130 dB/Hz and its extension to the L-band.

We demonstrate a narrow-linewidth, low-intensity noise, widely wavelength-tunable LD for which we adopted a long external cavity configuration (ECLD) with a tunable optical filter. By employing a simultaneous tuning circuit between the optical filter and the Fabry-Perot mode caused by the external cavity, the oscillation wavelength was successfully tuned over the full C-band without mode hopping. The tunable optical filter bandwidth was 0.55 nm (1530~1570 nm). We achieved a linewidth of less than 8 kHz obtained with a delayed self-heterodyne method. On the other hand, the linewidth estimated from the white noise level of the optical frequency modulation noise power spectrum of the laser output was as narrow as 314 Hz. A relative intensity noise (RIN) below -130 dB/Hz was simultaneously achieved over the C-band range. With the same configuration except for an optical filter with a filter bandwidth of 0.6 nm for L-band operation (1570~1610 nm), we also realized a full L-band wavelength tunable ECLD with a linewidth of less than 7.7 kHz and a RIN of below -126 dB/Hz.

Full C-Band Tunable V-Cavity-Laser Based TOSA and SFP Transceiver Modules

We report the latest development in tunable transmitter optical sub-assembly (TOSA) and small form-factor pluggable (SFP) transceivers based on simple and compact V-cavity laser (VCL), aiming for low-cost deployment in metro, access, and data center networks. The VCL employs a half-wave coupler to achieve high side-mode suppression ratio (SMSR) and the Vernier effect to achieve a wide wavelength tuning range. Full C-band tuning from 1529.55- to 1566.31-nm with SMSR above 36 dB is demonstrated. Since the laser does not involve any grating or epitaxial regrowth, and has a simple tuning algorithm, it allows simpler processes for fabrication and testing as compared with other widely tunable laser structures. Compact TOSAs and SFP transceiver modules have been developed for full C-band tuning with up to 93 channels at 50 GHz spacing. Transmission experiments are carried out for direct modulation with data rates from 2.5 to 8.5 Gbps. The results of reliability tests of the modules are also presented.

Demonstration of a 3 × 4 tunable bandwidth WSS with tunable attenuation using compact spatial light paths.

M × N wavelength selective switch (WSS) is a core component to address wavelength conflict in an optical switching node. In this paper, we design and experimentally demonstrate a performance enhanced 3 × 4 tunable bandwidth WSS (TBWSS) with tunable attenuation across the full C-band, and using compact spatial light paths. Wavelength channels from any input optical fiber port can be switched into any output optical fiber port with best insertion loss (IL) of 8.4 dB and worst IL of 12.5 dB. The attenuation tuning range can reach up to 35 dB. Compared to previous demonstrations, more than 2 dB IL improvement is achieved. Based on the proposed compact spatial light paths, the number of input and output ports can be easily extended to 10 and 20, respectively.

Non-duplicate polarization-diversity 8 × 8 Si-wire PILOSS switch integrated with polarization splitter-rotators

We demonstrate a fully integrated polarization-diversity 8 × 8 thermo-optic Si-wire switch that uses only a single path-independent insertion loss (PILOSS) switch matrix. All input/output ports of the PILOSS switch matrix are uniquely assigned for polarization diversity without switch duplication. To integrate polarization splitter-rotators on a chip, we propose a compact path-length-equalized polarization-diversity switch configuration. Polarization-dependent loss (PDL) and differential group delay (DGD) are minimized. The 8 × 8 switch is fabricated by the CMOS-compatible fabrication process on 300-mm diameter wafer and additional etching of upper cladding after dicing. The chip size is 7 × 10.5 mm2. A PDL of 2 dB and a DGD of 1.5 ps are achieved. The crosstalk in the worst-case scenario is -20 dB in the full C-band.

Highly fabrication tolerant InP based polarization beam splitter based on p-i-n structure.

In this work, a novel highly fabrication tolerant polarization beam splitter (PBS) is presented on an InP platform. To achieve the splitting, we combine the Pockels effect and the plasma dispersion effect in a symmetric 1x2 Mach-Zehnder interferometer (MZI). One p-i-n phase shifter of the MZI is driven in forward bias to exploit the plasma dispersion effect and modify the phase of both the TE and TM mode. The other arm of the MZI is driven in reverse bias to exploit the Pockels effect which affects only the TE mode. By adjusting the voltages of the two phase shifters, a different interference condition can be set for the TE and the TM modes thereby splitting them at the output of the MZI. By adjusting the voltages, the very tight fabrication tolerances known for fully passive PBS are eased. The experimental results show that an extinction ratio better than 15 dB and an on-chip loss of 3.5 dB over the full C-band (1530-1565nm) are achieved.

Ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser.

An ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser based on self-injection locking has been demonstrated. By the use of a tunable narrow-band fiber Fabry-Perot interferometer, the laser wavelength could be flexibly tuned from 1527 to 1563 nm with linewidths of < 700 Hz. The laser frequency noise is less than 40 dB re Hz/Hz1/2 at low frequencies (< 100 Hz) and reaches -5 dB re Hz/Hz1/2 at around 25 kHz. The measured relative intensity noise (RIN) is less than -130 dB/Hz with regard to frequencies of over 3 MHz, while the obtained linear polarization extinction ratio (LPER) is higher than 28 dB. This ultra-narrow linewidth low-noise tunable single-frequency linear-polarization fiber laser provides a promising candidate for high-order quadrature amplitude modulation (QAM) optical communication system.

UNSUPERVISED WISHART CLASSFICATION OF WETLANDS IN NEWFOUNDLAND, CANADA USING POLSAR DATA BASED ON FISHER LINEAR DISCRIMINANT ANALYSIS

Polarimetric Synthetic Aperture Radar (PolSAR) imagery is a complex multi-dimensional dataset, which is an important source of information for various natural resources and environmental classification and monitoring applications. PolSAR imagery produces valuable information by observing scattering mechanisms from different natural and man-made objects. Land cover mapping using PolSAR data classification is one of the most important applications of SAR remote sensing earth observations, which have gained increasing attention in the recent years. However, one of the most challenging aspects of classification is selecting features with maximum discrimination capability. To address this challenge, a statistical approach based on the Fisher Linear Discriminant Analysis (FLDA) and the incorporation of physical interpretation of PolSAR data into classification is proposed in this paper. After pre-processing of PolSAR data, including the speckle reduction, the H/α classification is used in order to classify the basic scattering mechanisms. Then, a new method for feature weighting, based on the fusion of FLDA and physical interpretation, is implemented. This method proves to increase the classification accuracy as well as increasing between-class discrimination in the final Wishart classification. The proposed method was applied to a full polarimetric C-band RADARSAT-2 data set from Avalon area, Newfoundland and Labrador, Canada. This imagery has been acquired in June 2015, and covers various types of wetlands including bogs, fens, marshes and shallow water. The results were compared with the standard Wishart classification, and an improvement of about 20% was achieved in the overall accuracy. This method provides an opportunity for operational wetland classification in northern latitude with high accuracy using only SAR polarimetric data.

Ultra-dense spatial-division-multiplexed optical fiber transmission over 6-mode 19-core fibers.

Ultra-dense spatial-division multiplexing (SDM) is achieved by mode multiplexed technique with multiple cores in a single fiber, namely few-mode multi-core fiber. Using a 9.8-km six-mode nineteen-core fiber, we demonstrate an ultra-dense SDM transmission of 16-channels wavelength-division-multiplexed (WDM) dual-polarization quadrature phase shift keying signals, achieving a record spatial multiplicity of 114. With the help of ultra-dense Super-Nyquist WDM techniques in the 4.5-THz bandwidth of the full C-band, we demonstrate 2.05 Pbit/s transmission over 9.8-km six-mode nineteen-core fibers. In this experiment, the highest aggregate spectral efficiency of 456 bit/s/Hz is achieved.