Flat-top Arrayed Waveguide Gratings Research Articles

Group Delay-Based Wideband Photonic Receive-Mode Radio-Frequency Beamforming

A multi-channel wideband group delay-based photonic receive-mode beamformer implemented with bulk fiber-based true-time delays, discrete flat-top arrayed waveguide gratings (AWGs), and a linear receive antenna array is presented. The frequency-independent beam pointing angle is derived theoretically, along with the multi-channel RF gain and noise figure. Dependence of RF gain and noise figure on channel count is investigated experimentally and shown to agree with theoretical prediction. Flat-top and Gaussian AWG optical filter transmission and bandwidth are measured and their effects on RF gain and phase are compared. Effects of channel-to-channel RF amplitude and phase mismatch on the RF response are shown by comparison of measurement with theory. Finally, measured beamformer antenna patterns are provided to demonstrate the formation of four simultaneous beams.

Silicon Nitride (Si3N4) (De-)Multiplexers for 1-μm CWDM Optical Interconnects

We discuss the design and demonstration of 4-channel coarse wavelength-division (de-)multiplexers based on cascaded Mach-Zehnder interferometer (MZI) lattice filters and arrayed waveguide gratings (AWG) on a 150 nm silicon nitride (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) platform. The 1 × 4 (de-)multiplexers are designed for a channel separation of 25 nm and operate within 990-1065 nm for bottom emitting vertical cavity surface emitting lasers (VCSEL)-based optical links. For Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Gaussian AWGs, we demonstrate crosstalk <; -35 dB at the peak transmission band with insertion loss <; 0.5 dB. Measurements were performed over many dies, and pass-band standard deviations for channel 1-4 are 0.49, 0.66, 0.42, and 0.37 nm, respectively. Results for flat-top AWGs indicate crosstalk <; -20 dB, with insertion loss <; 3 dB for the best devices. Flat-top cascaded 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> order and 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> order MZI lattice filters show a minimum of crosstalk <; -15 dB and <; -20 dB, respectively. The pass-band temperature shift was determined to be 14.5 pm/°C, which is lower than reported values for silicon. The device footprint of the Gaussian and flat-top AWGs are both ~670 × 200 μm. The device footprint of the flat-top cascaded 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> order and 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> order lattice filters are 1160 × 470 μm and 1570 × 470 μm, respectively. We believe the Si3N4 platform has potential for its use in CWDM and possibly DWDM transceiver/optical-modules for data/computer communication in high temperature environments up to 80 °C.

O波段8通道硅基二氧化硅平坦化阵列波导光栅的设计及制备

O波段8通道硅基二氧化硅平坦化阵列波导光栅的设计及制备

Flat-top AWG based on InP deep ridge waveguide

To relax the requirements on wavelength control of arrayed waveguide grating (AWG) in InP-based photonic integrated circuits (PIC), two kinds of 10-channel InP-based AWGs with flat-top spectral response are designed and fabricated by introducing a rectangle multi-mode interference (MMI) or a parabolic MMI at the end of input waveguide. The test results demonstrate that these two kinds of flat-top AWGs have obtained flattened spectral response with 3dB-bandwidth of about 1.7nm, and the parabolic MMI-based flat-top AWG has 0.7dB superiority in on-chip loss.

Optimal Design of an Ultrasmall SOI-Based 1 × 8 Flat-Top AWG by Using an MMI

Four methods based on a multimode interference (MMI) structure are optimally designed to flatten the spectral response of silicon-on-insulator- (SOI-) based arrayed-waveguide grating (AWG) applied in a demodulation integration microsystem. In the design for each method, SOI is selected as the material, the beam propagation method is used, and the performances (including the 3 dB passband width, the crosstalk, and the insertion loss) of the flat-top AWG are studied. Moreover, the output spectrum responses of AWGs with or without a flattened structure are compared. The results show that low insertion loss, crosstalk, and a flat and efficient spectral response are simultaneously achieved for each kind of structure. By comparing the four designs, the design that combines a tapered MMI with tapered input/output waveguides, which has not been previously reported, was shown to yield better results than others. The optimized design reduced crosstalk to approximately −21.9 dB and had an insertion loss of −4.36 dB and a 3 dB passband width, that is, approximately 65% of the channel spacing.

Broad-spectral-range synchronized flat-top arrayed-waveguide grating applied in a 225-channel cascaded spectrometer

We present a new synchronized design for flattening the passband of an arrayed-waveguide grating (AWG) over a broad wavelength range of 90 nm. A wavelength-insensitive 3-dB balanced coupler is designed to be used in duplicate in a Mach-Zehnder interferometer (MZI); the phase deviation created by one of the balanced couplers is cancelled by flipping the other coupler around. This MZI is arranged in tandem with the AWG such that the output signal of the MZI is the input signal of the AWG. We demonstrate a 5-channel, 18-nm-spacing AWG with a 0.5-dB bandwidth of 12 nm over a 90-nm spectral range. A low-loss cascaded AWG system is demonstrated by using the MZI-synchronized flat-top AWG as a primary filter.

Three-dimensional hybrid modeling based on a beam propagation method and a diffraction formula for an AWG demultiplexer

An efficient and accurate three-dimensional (3D) hybrid modeling, which combines a 3D beam propagation method (BPM) and the two-dimensional (2D) Kirchhoff–Huygens diffraction formula, is developed to simulate the field propagation in an arrayed waveguide grating (AWG) demultiplexer. The 2D Kirchhoff–Huygens diffraction formula is used for the simulation of the light propagation in the free propagation regions (FPRs). A 3D BPM in a polar coordinate system is used to simulate the light propagation in the transition region between the input FPR and the arrayed waveguides so that the coupling coefficients for the arrayed waveguides are calculated conveniently and accurately. For the simulation in the transition region between the arrayed waveguides and the output FPR, only the central arrayed waveguide and several adjacent ones are needed in the computational window of a standard BPM and thus the computation efficiency is improved. Finally, a flat-top AWG is designed and fabricated to verify the reliability of the present simulation method. The calculated and measured spectral responses are in a good agreement.

AWG Model Validation Through Measurement of Fabricated Devices

In this paper, the validation of a previously published arrayed-waveguide grating (AWG) model is presented, using measures of fabricated devices. The measured spectrum, dispersion, and loss, along with Fourier spectroscopy (FS) measurements of the array errors, are used to verify the numerical simulations and analytical derivations for a Gaussian AWG device. The verified model is then used to investigate the relationship between the different fabrication errors and their impact on the response of flat-top AWG devices. Several conclusions are presented about the accuracy on the use of FS measurements in this modeling, since some discrepancies between the FS measurements and simulations are found and discussed and their motivations identified. Moreover, the ability and flexibility of this model to distinguish and clarify the source of each degradation in the performance of flat-top AWGs is proven.

Accurate two-dimensional model of an arrayed-waveguide grating demultiplexer and optimal design based on the reciprocity theory

An accurate two-dimensional (2D) model is introduced for the simulation of an arrayed-waveguide grating (AWG) demultiplexer by integrating the field distribution along the vertical direction. The equivalent 2D model has almost the same accuracy as the original three-dimensional model and is more accurate for the AWG considered here than the conventional 2D model based on the effective-index method. To further improve the computational efficiency, the reciprocity theory is applied to the optimal design of a flat-top AWG demultiplexer with a special input structure.

Geometrical optimization of the transmission and dispersion properties of arrayed waveguide gratings using two stigmatic point mountings

In this paper, the procedure to optimize flat-top Arrayed Waveguide Grating (AWG) devices in terms of transmission and dispersion properties is presented. The systematic procedure consists on the stigmatization and minimization of the Light Path Function (LPF) used in classic planar spectrograph theory. The resulting geometry arrangement for the Arrayed Waveguides (AW) and the Output Waveguides (OW) is not the classical Rowland mounting, but an arbitrary geometry arrangement. Simulation using previous published enhanced modeling show how this geometry reduces the passband ripple, asymmetry and dispersion, in a design example.

Using a tapered MMI to flatten the passband of an AWG

A tapered multimode interferometer (MMI) is used to flatten the passband of an arrayed-waveguide grating (AWG). The tapered MMI is connected at the end of the input waveguide of the AWG. The influences of the tapering angle to the performances (such as the 3 dB passband width, the ripple, the crosstalk and the insertion loss) of the flat-top AWG are studied. An AWG which has simultaneously a good flat spectral response and a good dispersion characteristic is designed by choosing appropriately the tapering angle and the length of the tapered MMI.

Low chromatic-dispersion flat-top arrayed waveguide grating filter

A low chromatic dispersion (CD) flat-top arrayed waveguide grating (AWG) filter with a novel parabolic waveguide horn is proposed, and a 100 GHz-spacing 16-channel flat-top AWG that reduces the CD from −20.9 to −3.2 ps/nm has been successfully fabricated.

A Flattened AWG Demultiplexer with Low Chromatic Dispersion

A design method is introduced to obtain a flat-top arrayed-waveguide grating (AWG) demultiplexer with low chromatic dispersion. A multimode interference (MMI) section is connected at the end of the input waveguide, and a tapered waveguide is connected at the entrance of each output waveguide of the AWG demultiplexer. The design procedure is presented. A design example is given and shown to have a much better performance than the conventional flat-top design using only an MMI section. The insertion loss of the designed AWG demultiplexer is also reduced.

Optimal design of an MMI coupler for broadening the spectral response of an AWG demultiplexer

Optimal design of a multimode interference (MMI) coupler for broadening the spectral response of an arrayed-waveguide grating (AWG) demultiplexer is considered. By using a Gaussian beam approximation, an analytical expression for the spectral response of an AWG demultiplexer (with an MMI section) is obtained. A simple analytical formula is derived to relate the optimal MMI length to the separation between the peaks of the twofold images in the MMI region. This peak separation is related to the width of the MMI section. In the proposed design method, a required 1-dB passband width determines the peak separation, which then determines the optimal value for the length of the MMI section according to the analytical formula. The designed flat-top AWG demultiplexer is verified by the beam propagation method.