Statistical Modeling for Estimating Chromatic Dispersion in Filters Using Arrayed Waveguide Gratings With Random Phase Errors

Arrayed waveguide gratings (AWG) are widely used as wavelength division multiplexers (MUX) and demultiplexers (DEMUX) in optical networks. Here we propose and demonstrate that conventional AWGs can also be used as integrated spectral filters to realize a Fast Fourier transform (FFT) and its inverse form (IFFT). More specifically, we point out that the wavelength selection conditions of AWGs when used as wavelength MUX/DEMUX also enable them to perform FFT/IFFT functions. Therefore, previous research on AWGs can now be applied to optical FFT/IFFT circuit design. Compared with other FFT/IFFT optical circuits, AWGs have less structural complexity, especially for a large number of inputs and outputs. As an important application, AWGs can be used in optical OFDM systems. We propose an all-optical OFDM system with AWGs and demonstrate the simulation results. Overall, the AWG provides a feasible solution for all-optical OFDM systems, especially with a large number of optical subcarriers.

A conventional Arrayed Waveguide Grating (AWG) has been modified, without output receiver waveguides, for nonconventional applications such as Astrophotonics and spectroscopy sensing where the input signal can have information over the entire band and a continuum of light/spectrum. The material system chosen for the AWG design is siliconnitride/ SiO 2 /Si (Si 3 N 4 -SiO 2 -Si) for its relatively high refractive index, which for a given channel spacing allowing a more compact device than Silicon-on-Silica. Further, CMOS compatibility and the presence of high non-liner optical coefficient would be an added advantage to design and fabricate densely integrated photonic sub-systems, such as calibration source and AWG, for astrophotonics and spectroscopy. The proposed AWG utilizes a flat image plane optimized for minimal aberration. An analytical calculation, based on Gaussian beam approximation, was used to determine the optimal flat plane position where the non-uniformity in 1/e electric field widths is minimal. This plane can be used as the dicing plane to re-image the entire output of the AWG onto a detector array to sample the entire spectrum. Tailored AWG, with flat image-plane, designed to resolve 48 spectral channels with 0.4nm (50GHz) resolution and adjacent channel cross-talk level within a 0.2nm window (ITU-grid) ~ -28dB. Calculated insertion loss non-uniformity is close to 3dB. The foot-print of high index contrast (Δn=23%) IPS is ~ 12x8.5 mm 2 . The modelled mean spectral resolving power, R, at the flat image-plane is ~ 7,600. The design principle could be utilised for devices using other material systems with different parameters.

A silicon arrayed‐waveguide grating (AWG) with 1.6‐nm channel spacing is proposed and realized with high performances for dense wavelength‐division (de)multiplexing systems. For the present AWG, the arrayed waveguides are broadened uniformly to be far beyond the singlemode regime, so that random phase errors and propagation loss are minimized even without any additional requirement for the fabrication process. Particularly, Euler‐bends are introduced for the arrayed waveguides to shrink the device footprint and suppress any excitation of higher‐order modes. As an example, a 16 × 16 AWG (de)multiplexer is realized with a compact footprint of 600 × 800 µm2 by using single‐etched 220‐nm‐thick silicon photonic waveguides. When using the fabricated AWG to demultiplex the channels launched from the central input port, the excess loss and the adjacent‐channel crosstalk of the central output port are ≈2.2 and ≈−31.7 dB, respectively. Such an AWG is one of the best among silicon implementations.

We propose a new compensation technique for the second-order temperature dependence in a silica-based arrayed-waveguide grating (AWG) multi/demultiplexer with a resin-filled groove that realizes a wide operating temperature range. We newly employ an additional interferometer in the input port and control the optical field perturbation by using a first-mode lightwave at the entrance to the first slab waveguide. We employ the design to fabricate a 32-channel 100-GHz-spacing athermal AWG that is as compact as a conventional AWG, and demonstrate a reduction in the passband wavelength variation from 70 to 22 pm over an extended - 40degC to 80degC temperature range.

This paper proposes a cascade-connected arrayed-waveguide grating (AWG) as a solution to the problem of crosstalk accumulation in a large-scale AWG multiplexer/demultiplexer (MUX/DEMUX) and demonstrates a 64-channel cascaded AWG module with a very low background crosstalk of less than -80 dB and a total crosstalk of about -34 dB. In this paper, the authors densely integrate 64 additional compactly designed crosstalk-suppressing AWGs whose bandwidths were carefully optimized and directly attach them to a conventional 64-channel AWG. Consequently, in addition to a very low crosstalk, a low insertion loss and a compact size without passband shape distortion are achieved with this module. Based on the performance of the cascaded AWG module, it is then estimated that it is possible to realize a 1000-channel AWG MUX/DEMUX that is free from the problem of crosstalk accumulation.

This paper describes the performance improvement of 10-Gb/s four-channel WDM dispersion-supported transmission systems by using broadened passband arrayed-waveguide grating demultiplexers. Multimode interference couplers are assumed to be used to broaden the passaband of these demultiplexers. Performance Improvement of 40-Gb/s Capacity Four-Channel WDM Dispersion-Supported Transmission by Using Broadened Passband Arrayed-waveguide Grating Demultiplexers Mario M. Freire Department of Mathematics and Computer Science, University of Beira Interior Rua Marques d'Avila e Bolama, P-6200 Covilha, Portugal Telephone: +351 75 3101700, Fax: +351 75 26198, E-mail: mfreire@ alpha.ubi.pt Henrique J. A. da Silva Department of Electrical Engineering, Pole II of University of Coimbra Pinhal de Marrocos, P-3030 Coimbra, Portugal Telephone: +351 39 7006248, Fax: +351 39 7006247, E-mail: hjas@ci.uc.pt Summary Integrated N×N wavelength multiplexers based on arrayed-waveguide gratings (AWG) are being developed for wavelength division multiplexing (WDM) systems and networks, since they can offer four basic functions: multiplexing, demultiplexing, add/drop multiplexing, and N×N full-interconnection [1]. The use of this technology for demultiplexing in high density WDM systems may impose very stringent requirements on the alignment of signal wavelengths and demultiplexers due to their peaked (Gaussian-like) spectral passband. However, the passband of these demultiplexers may be broadened by the use of multimode interference couplers (MMI), as proposed and demonstrated in [2]. In this paper, we describe the performance improvement due to the use of broadened passband AWG demultiplexers in 40-Gb/s capacity four-channel WDM dispersion-supported transmission (DST) systems with 0.5 nm channel spacing. The block diagram of the simulated 10-Gb/s four-channel WDM-DST system is shown in Fig. 1. The system model is broadly similar to the one reported in [3] and includes a rate equation model for quantum-well lasers, and the frequency responses of a PIN photodiode and of a standard singlemode fiber (SMF) with chromatic dispersion of 17 ps/(nm.km) at 1532 nm. The frequency response of the AWG filter is assumed to be Gaussian and the frequency response of the broadened passband AWG filter is modeled by the double Gaussian approximation [2] with r = 2 , which is the ratio between the peak separation and the FWHM of each simple Gaussian profile. The optical amplifiers (EDFAs) have been considered as linear with a noise figure of 6 dB and an equivalent noise bandwidth of 1 THz. A RC lowpass filter was used to provide the 3-dB bandwidth required by the DST method [4]. The receiver sensitivity was estimated taking into account the signal-ASE and ASE-ASE beat noises, the thermal and shot noises, as well as the contribution due to frequency-to-intensity conversion of laser phase noise after propagation via dispersive fibers [5]. Fig. 2 shows the receiver sensitivity for channel 2 versus fiber length for single-channel DST, without optical filters, and for four-channel WDM-DST using an arrayed-waveguide grating demultiplexer with (BP-AWG) and without (AWG) broadened passband. For comparison purposes, the receiver sensitivity of four-channel WDM-DST using a three-mirror Fabry-Perot demultiplexer (TMF) is also shown. For distances larger than 80 km, the performance of four-channel WDM-DST systems using three-mirror Fabry-Perot demultiplexers is close to the performance of single-channel DST systems without optical filters. Compared with the performance of single-channel DST without optical filters, the use of conventional arrayed-waveguide grating filters as demultiplexers in four-channel WDMDST degrades the system performance at least 0.6 dB for link lengths larger than 11 km. However, the use of broadened passband AWG demultiplexers instead of the conventional AWG demultiplexers improves the performance of the four-channel WDM-DST system at least 1.5 dB, for link lengths larger than 11 km (see Fig. 2). Detailed BER characteristics for channel 2 are displayed in Fig. 3 for four-channel WDM-DST via 204 and 253 km SMF. For the 204 km transmission simulation, sensitivities of -23.886, -23.169 and -24.827 dBm have been estimated for TMF, AWG and BP-AWG demultiplexers, respectively. The BER curves for 253 km clearly indicate an error floor due to laser phase noise. In conclusion, the use of broadened passband AWG demultiplexers improves the performance of four-channel WDM-DST systems with 0.5 nm channel spacing, while conventional AWG demultiplexers are less suitable to operate at this channel spacing.

We propose a new type of arrayed waveguide grating (AWG) device that operates as a Fourier-transform (FT) spectrometer without the need of scanning elements. The large input aperture size typical of a FT spectrometer eliminates the requirement for a narrow single-mode input waveguide while still achieving high spectral resolution with a markedly increased light-gathering capability (etendue). An example of the device with a resolution of 0.07 nm (approximately 10 GHz) and designed for a silicon-on-insulator platform is presented. The calculated spectra show no noticeable deterioration for aperture widths as large as 40 microm, yielding more than a 50-fold increase in aperture size compared with conventional AWG or echelle grating based devices at the equivalent resolution.

Hypertensive disorders present significant morbidity and mortality during pregnancy. Although ambulatory blood pressure measurement remains the standard of care for normotensive women, self-monitoring at home is increasingly prevalent. The widespread use of smartphones worldwide has sparked interest in mobile applications that leverage the built-in hardware for blood pressure estimation, yet few trials have assessed their accuracy. This prospective, longitudinal and monocentric study evaluated the accuracy of the OptiBP algorithm against standard oscillometric blood pressure measurements in a sample of pregnant women. Patients scheduled for elective caesarean sections were enrolled during the preoperative anesthesia consultations. Paired blood pressure measurements using OptiBP and the reference method were obtained at multiple time-points in late pregnancy and the postpartum period. Agreement between methods was assessed using the AAMI/ESH/ISO 81060-2:2018 standard thresholds of 5 ± 8 mmHg for mean ± standard deviation of the error (criterion 1) and patient-specific standard deviation of the mean error (criterion 2) and represented graphically by Bland-Altman scatterplots. Forty-eight women were enrolled of which 32 completed the protocol, yielding 338 total valid measurement pairs. Mean and standard deviation of the error were -1.78 ± 7.94 and 1.19 ± 7.59, and the patient-specific standard deviation of the mean error was 4.68 and 4.52, for SBP and DBP, respectively. Compared with blood pressure measurements taken with an oscillometric device, OptiBP's blood pressure estimates meet the AAMI/ESH/ISO 81060-2:2018 criteria.

The crosstalk performance of an arrayed-waveguide grating (AWG) multiplexer or demultiplexer is primarily caused by random optical phase errors introduced in the arrayed waveguides. Because the layout of waveguides on a wafer is patterned via photomask through the photolithography process, the resolution of a photomask has a direct influence on the phase errors of an AWG. The paper presents a theoretical analysis on the phase error caused by photomask resolution and other basic design parameters. Both calculation and measurement results show that a high-resolution photomask (better than 25 nm) is a critical requirement to produce low-crosstalk (less than -30 dB) AWG demultiplexers. We also investigate the effect of nonideal power distribution in the arrayed waveguides because it contributes considerable phase errors when material impurity is not well controlled during wafer fabrication. Basic criteria of power profile truncation, number of grating waveguides, and material index variation are also summarized.

Fourier methods are widely used in optical information processing for time domain waveform synthesis and detection. In such approaches an input pulse is spectrally decomposed and modulated by an appropriately designed spectral filter. In general, various ultrafast applications may need either generation or characterization of waveforms depending whether their frequency response is or is not known a priori. Ultrafast pulses prove useful in driving or probing such systems because their broad, deterministic complex spectral amplitude “sees” a large continuous portion of the system transfer function. Traditionally, space domain spectral decomposition is used to perform optical Fourier processing, where pairs of gratings and lenses are used to decompose the spectral content of the pulsed, optical waveforms. Liquid crystal and acousto-optic (AO) modulators provide a means for introduction of somewhat arbitrary system transfer functions. More recently, compact waveguide-based approaches have used arrayed waveguide gratings (AWGs) to perform an analogous spectral decomposition to those achieved with traditional, free-space coupled gratings. Information processing arrangements using the space domain for transverse spectral decomposition benefit from the maturity of such techniques, with respect to basic understanding, component quality, and the excellent phase control that free-space manipulations provide. Component insensitivity to optical power permits the shaping and detecting of high peak power pulses used to drive nonlinear optical systems. Furthermore, nonlinear optical elements can be introduced directly into these processors to provide unique ultrafast waveform synthesis capabilities with response times in the range of femtoseconds. Drawbacks to free-space approaches include scaling in volume to achieve large time bandwidth products (TBWPs) and limiting the temporal extent of waveforms coupled back into a single-mode fiber (SMF). The origin of this last restraint is the time∕space interrelation inherent in traditional pulse shaping devices. AWG approaches rely on complex waveguide elements to circumvent large processor volumes and time∕space coupling issues, but they too are practically limited by fabrication requirements. The number of resolvable spots in the output waveform for both Fourier synthesis and direct space-to-time AWG approaches is equal to the number of waveguide channels. An alternative approach to Fourier processing relying on a single transverse spatial mode can better integrate with fiber systems and photonic lightwave circuits and will scale in length only for the achievement of large TBWPs. Fiber-based and fiber-integrated processors can manipulate optical waveforms in the time domain exploiting chromatic dispersion for longitudinal spectral decomposition and applying to it Fourier synthesis techniques. Drawing on the identical mathematical treatments of diffraction in space and dispersion in time, an approximate Fourier transform (FT) of an incident optical signal is achieved via chromatic dispersion after reaching the so-called “far-field approximation.” With such an amount of dispersion, the temporal waveform closely resembles the spectrum. Such a waveform is called a longitudinal spectral decomposition wave (SDW). A time-variant element (e.g., modulator) filters this SDW. And it is possible to recompose the pulse waveform through propagation in a conjugate dispersion source matched (i.e., of opposite sign but equal magnitude) to the first dispersive element. The number of resolvable spots that such a processor offers relies on a suitable modulation scheme and the experimental ability to disperse a sub-picosecond pulse using second-order dispersion.

Summary form only given. In optical burst switching (OBS) networks, a short switching time is very important for handling fine grain packets such as TCP ACK packets, which are only 40 bytes in length. At data rate of 10 Gbps, such a data burst will occupy a period of only 32 ns. Therefore OXC (optical cross connector) with fast switching speed, for example < 100 ns, are generally required for OBS networks. There are many methods to configure an OXC. Tunable optical filters may used to build large scale OXC. In an optical filter, the tuning ability is usually achieved by introducing extra phase shift via the electro optic, thermo optic, or piezoelectric effect, etc. Up to date, the most commonly used tunable filter structures are interferometric such as Fabry-Perot (FP) and Mach-Zehnder (MZ) interferometers. They are usually poor in the performance of passband flatness and the crosstalk, and require robust electronics to stabilize the central wavelength. Hence, they are rarely practically used as switching elements in the dense wavelength division multiplexing (DWDM) optical networks. In recent years, digitally tunable optical filter (DTOF) has received increasingly attention. Structures based on the arrayed waveguide grating (AWG) and on-off switches have been reported. DTOF based on AWG may require precision thermal control for AWG usually suffers the problem of temperature dependence. In this talk, we present a novel approach to realize the DTOF (digitally tunable optical filter) based on DWDM thin film filters (TTF) and semiconductor optical amplifier (SOA). Apart from the outstanding feature being consistent with the wavelength comb suggested by international telecommunication union-telecommunication (ITU-T), the proposed DTOF is very stable in temperature performance. Furthermore it requires less SOAs in comparison with the reported structures.

Chromatic dispersion from optical fiber is the most important problem that produces temporal skews and destroys the rectangular structure of code patterns in the spectra-amplitude-coding optical code-division multiple-access (SAC-OCDMA) system. Thus, the balance detection does not work perfectly and the system performance will be degraded. In order to improve the distortion, we apply cascaded Mach–Zehnder interferometers (MZIs) to design a dispersion slope equalizer for the SAC-OCDMA system integrated with arrayed-waveguide grating (AWG) router coder. The dispersion slopes of a cascaded MZI compensator could be adjusted by the arm length differences of MZIs and be complementary with the fiber links. In this study, we present a set of length differences for 10 km long single-mode fiber (SMF) and verify the compensation scheme by relative delay time slope and signal-to-interference ratio (SIR). The dispersion slope equalizer with perfect complementary slope successfully compensates the dispersion from SMF and the system performance with dispersion slope equalizer is highly improved.

High-speed fiber Bragg grating (FBG) interrogation based on arrayed waveguide gratings (AWGs) enables parallel, scan-free interrogation but is fundamentally limited by interrogation discontinuities when the FBG spectrum traverses adjacent AWG channels. This issue originates from insufficient spectral overlap at channel boundaries and leads to wavelength jumps during large or rapid spectral excursions. We report a compact AWG-based FBG interrogator that overcomes this limitation through a hardware-software co-design strategy. Contrary to conventional AWG designs that prioritize low crosstalk for optical communications, we deliberately utilize a high-crosstalk AWG to introduce substantial inter-channel spectral overlap, thereby ensuring a smooth and monotonic ratiometric response across channel boundaries. To further eliminate residual numerical discontinuities, a real-time wavelength jump suppression algorithm (WJSA) is developed to detect channel-switching events and apply adaptive reference-wavelength correction. Experimental results demonstrate a high interrogation linearity (R2=0.9992), even for narrowband FBGs with a bandwidth of 0.20 nm. The interrogator supports a sampling rate of up to 500 kS/s, enabling accurate dynamic strain measurements up to 50 kHz and resolving transient impact responses with microsecond-level temporal resolution. The proposed approach addresses a key limitation in AWG-based FBG interrogation and provides a scalable and cost-effective solution for high-speed structural health monitoring.

The authors have measured the phase and amplitude error distributions in an InP-based arrayed-waveguide grating (AWG) multi/demultiplexer using Fourier transform spectroscopy and signal data processing. The signal data processing technique was based on wavenumber scale transformation and was applied to reduce the effect of second-order dispersion in a measured interferogram. The results reveal that the main origins of the crosstalk and dispersion in an InP-based AWG are random and slowly-varying phase errors, respectively.

Convolutional neural networks are a powerful category of artificial neural networks that can extract features from raw data to provide greatly reduced parametric complexity and enhance pattern recognition and the accuracy of prediction. Optical neural networks offer the promise of dramatically accelerating computing speed while maintaining low power consumption even when using high‐speed data streams running at hundreds of gigabit/s. Here, we propose an optical convolutional processor (CP) that leverages the spectral response of an arrayed waveguide grating (AWG) to enhance convolution speed by eliminating the need for repetitive element‐wise multiplication. Our design features a balanced AWG configuration, enabling both positive and negative weightings essential for convolutional kernels. A proof‐of‐concept demonstration of an 8‐bit resolution processor is experimentally implemented using a pair of AWGs with a broadband Mach–Zehnder interferometer (MZI) designed to achieve uniform weighting across the whole spectrum. Experimental results demonstrate the CP's effectiveness in edge detection and achieved 96% accuracy in a convolutional neural network for MNIST recognition. This approach can be extended to other common operations, such as pooling and deconvolution in Generative Adversarial Networks. It is also scalable to more complex networks, making it suitable for applications like autonomous vehicles and real‐time video recognition.