Conventional Arrayed Waveguide Grating Research Articles

Conventional arrayed waveguide grating (CAWG) devices for high stability and low insertion loss in near infrared wavelength band

Abstract This study has presented the different suggested compounds based (CAWG) like silicon dioxide (SiO2), lithium niobate (LiNbO3) and gallium aluminum arsenide (Ga(1-x)Al(x)As) taking into consideration their operating wavelength range, their operating temperature range, their physical properties, and also their ability to be used in the manufacture of optical devices. The optimum performance was given in case of using the following materials such as SiO2, LiNbO3 and Ga(1-x)Al(x)As materials, so these materials have been used as a proposed materials based CAWG devices, which have been investigated for high stability and low insertion loss in near infrared wavelength band. The comparison between these proposed materials are clarified through the design parameters of CAWG device such as the order of diffraction (m), path length adjacent waveguides difference (ΔL), focal length (L f ), free spectral range (FSR), max no. of I/O wavelength channels (N max), and arrayed waveguides (P) number.

Theoretical investigation of compact high-resolution interleaved arrayed waveguide gratings with multi-layer structures

In this paper, a compact high-resolution two-stage interleaved arrayed waveguide grating (AWG) system with a 3D structure on a silicon nitride (Si3N4) platform is proposed. The device is comprised of a 7-channel primary AWG with a 0.4-nm resolution and seven 26-channel second-stage AWGs, each with a 2.8-nm resolution. Different arrayed waveguide widths are utilized to achieve the wavelength tuning of the second-stage AWGs. The AWGs have a greater fabrication tolerance than conventional AWGs. A taper-MMI input structure is utilized to make the -3 dB pass-band reach 0.4 nm, which is 100% of the channel spacing. Also, the horizontal slot arrayed waveguides are individually introduced into the AWG to reduce the inter-layer crossing and bending losses, which is also found to greatly reduce the footprint of the device. The proposed AWGs have an average crosstalk of about -24 dB in the 2-µm band, demonstrating the feasibility of the on-chip 3D optoelectronic integration design.

Superlattice Arrayed Waveguide Grating in Silicon Nitride

Emerging silicon nitride (SiN) nanophotonic circuits are an advantageous technology for dense wavelength division multiplexing systems but they have larger footprints than silicon-on-insulator devices due to the lower index contrast. We present an ultra-compact 100 GHz $1\times {8}$ SiN arrayed waveguide grating (AWG) enabled by the novel concept of the waveguide superlattice. A waveguide superlattice is a periodic structure consisting of alternate waveguide geometries with negligible parasitic couplings. Thanks to the densely arrayed waveguides, this superlattice AWG (SL-AWG) has a compact footprint of 4.3 mm $\times0.6$ mm, which is more than two times smaller than a conventional AWG with similar performance implemented previously on the same SiN platform. The SL-AWG also shows a low insertion loss of 3.4 dB and a low crosstalk of −18 dB.

Interleaved Silicon Nitride AWG Spectrometers

Interleaved arrayed waveguide gratings (AWGs) have a great potential in providing large channel counts and narrower channel spacings for many applications, including optical communication, spectroscopy, and imaging. Here, a 75-channel silicon nitride-based interleaved AWG was experimentally demonstrated. The design is comprised of a 3-channel primary AWG with 1 nm of resolution and three 25-channel secondary AWGs each with 3 nm of resolution. The final device has a spectral resolution of 1 nm over 75-nm bandwidth centered at 1550 nm. Its performance is compared with a conventional AWG spectrometer with 75 nm of bandwidth and 1 nm of resolution. The interleaved AWG demultiplexer showed lower crosstalk and better uniformity in addition to being two times smaller than the conventional design.

Investigation of AWG demultiplexer based SOI for CWDM application

9-channel Arrayed Waveguide Grating (AWG) demultiplexer for conventional and tapered structure were simulated using beam propagation method (BPM) with channel spacing of 20 nm. The AWG demultiplexer was design using high refractive index (n~3.47) material namely silicon-on-insulator (SOI) with rib waveguide structure. The characteristics of insertion loss, adjacent crosstalk and output spectrum response at central wavelength of 1.55 μm for both designs were compared and analyzed. The conventional AWG produced a minimum insertion loss of 6.64 dB whereas the tapered AWG design reduced the insertion loss by 2.66 dB. The lowest adjacent crosstalk value of -16.96 dB was obtained in the conventional AWG design and this was much smaller compared to the tapered AWG design where the lowest crosstalk value is -17.23 dB. Hence, a tapered AWG design significantly reduces the insertion loss but has a slightly higher adjacent crosstalk compared to the conventional AWG design. On the other hand, the output spectrum responses that are obtained from both designs were close to the Coarse Wavelength Division Multiplexing (CWDM) wavelength grid.

Comparison of AWGs and Echelle Gratings for Wavelength Division Multiplexing on Silicon-on-Insulator

We compare the performance (insertion loss and crosstalk) of silicon-based arrayed waveguide gratings (AWGs) and echelle gratings for different channel spacings. For high-resolution de/multiplexer (DWDM) applications, AWGs are the better choice, whereas echelle gratings perform well for low-resolution de/multiplexer (CWDM) applications. Alternatively, for low-resolution de/multiplexer applications, the conventional box-shaped silicon AWG can be modified by an S-shaped AWG. We report crosstalk as low as -27 dB for regular AWGs, whereas in the S-shaped AWGs, the crosstalk is better than -19 dB, with an insertion loss below -2 dB. The crosstalk of the echelle gratings varies between -19 and -23 dB, with insertion loss below -2 dB.

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

A statistical model is proposed for estimating the chromatic dispersion in the passband of a filter using an arrayed waveguide grating (AWG) with random phase errors. The model is derived without assuming the independence of random errors and can be applied to AWGs with frequency-dependent array amplitude coefficients as well as conventional AWGs. The average and variance of the chromatic dispersion in the passband can be calculated by using simple expressions without random computation once the standard deviation and correlation of random phase errors are given. The behavior of the chromatic dispersion in a synchronized-router-based flat-passband filter consisting of a multiple-input AWG and cascaded Mach-Zehnder interferometers (MZIs) was investigated. The standard deviation of the chromatic dispersion monotonically increases with the standard deviation of random phase errors, and has a distinctive dependence on frequency. The average and standard deviation of the chromatic dispersion in the passband obtained by the model are in good agreement with those obtained by random simulation for both a synchronized-router-based flat-passband filter and conventional AWGs.

Ultra Wide Wavelength Multiplexing/Demultiplexing Conventional Arrayed Waveguide Grating (AWG) Devices for Multi Band Applications

This paper has proposed new materials based conventional arrayed waveguide grating (AWG) devices such as pure silica glass (SiO 2), Lithium niobate (LiNbO 3), and gallium aluminum arsenide (Ga (1-x) Al (x) As) materials for multiplexing and demultiplexing applications in interval of 1.45 µm to 1.65 µm wavelength band, which including the short, conventional, long, and ultra long wavelength band. Moreover we have taken into account a comparison between these new materials within operating design parameters of conventional AWG devices such as diffraction order, length difference of adjacent waveguides, focal path length, free spectral range or region, maximum number of input/output wavelength channels, and maximum number of arrayed waveguides. As well as we have employed these materials based AWG to include Multi band applications under the effect of ambient temperature variations.

200-GHz spacing, 8ch, high-speed wavelength selective arrayed-waveguide grating using buried PLZT waveguides

A wavelength selective AWG (arrayed-waveguide grating) was fabricated using buried PLZT ((Pb, La)(Zr, Ti)O3) waveguides. It has 8 output channels with 200GHz spacing. The buried PLZT waveguides have lower propagation loss and higher optical confinement compared to the previously reported ridge PLZT waveguides. Therefore, using buried PLZT waveguides, an AWG with shorter channel spacing than a conventional AWG can be designed and fabricated. The 3-dB bandwidth was 110GHz, the maximum control voltage was 14V, and the tuning range was 1600GHz. Wavelength tuning was successfully demonstrated with a crosstalk of about -14dB for TE (transverse electric) polarized light and -13dB for TM (transverse magnetic) polarized light.

Performance Analysis of a Synchronized-Router-Based Flat-Passband Filter Using Multiple-Input Arrayed Waveguide Grating With Phase Errors

The filtering performance of a synchronized-router-based flat-passband filter with random phase errors is analyzed. For this purpose, an analytical model of a synchronized-router-based flat-passband filter using a multiple-input arrayed waveguide grating (AWG) with phase errors is derived without the assumption of the independence of random errors so that the model can treat general types of phase errors. For average transmittance, we proposed the analytical model for the variance of transmittance for a multiple-input AWG to predict the deviation of the transmittance. By using the proposed analytical model, device performance can be estimated once the spectral information of phase errors is given. The analysis clarifies that the frequency dependence of crosstalk reflects the spatial spectral distribution of phase errors. We also compared the transmittance characteristics of the synchronized-router-based flat-passband filter with conventional Gaussian and flat-type AWGs. We found that the crosstalk in the synchronized-router type has a different behavior from those in the conventional types, i.e., the crosstalk in the synchronized-router type has a periodic behavior according to the function of the input router. The probability distribution of the transmittance of the flat-passband filter is also calculated by random simulation and compared with the result from the analytical model. The agreement between the model and the random simulation confirms that the proposed model is effective for analytically estimating the performance of a synchronized-router-based flat-passband filter with phase errors.

Reduction of Second-Order Temperature Dependence of Silica-Based Athermal AWG by Using Two Resin-Filled Grooves

We devise a novel design for an athermal silica-based arrayed-waveguide grating (AWG) to reduce the residual second-order temperature dependence of conventional athermal AWGs with a silicone-filled groove. This athermal AWG has two grooves filled with silicone and polyolefin that compensate for the first- and second-order temperature dependence, respectively. The passband wavelength variation is successfully reduced from 80 to 16 pm in a -40°C ~ +80°C temperature range.

Improved arrayed-waveguide-grating layout avoiding systematic phase errors

We present a detailed description of an improved arrayed-waveguide-grating (AWG) layout for both, low and high diffraction orders. The novel layout presents identical bends across the entire array; in this way systematic phase errors arising from different bends that are inherent to conventional AWG designs are completely eliminated. In addition, for high-order AWGs our design results in more than 50% reduction of the occupied area on the wafer. We present an experimental characterization of a low-order device fabricated according to this geometry. The device has a resolution of 5.5 nm, low intrinsic losses (< 2 dB) in the wavelength region of interest for the application, and is polarization insensitive over a wide spectral range of 215 nm.

Optical FFT/IFFT circuit realization using arrayed waveguide gratings and the applications in all-optical OFDM system

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.

Compensation for Second-Order Temperature Dependence in Athermal Arrayed-Waveguide Grating Realizing Wide Temperature Range Operation

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.

$N \times N$ Cyclic-Frequency Router With Improved Performance Based on Arrayed-Waveguide Grating

We have developed an NxN cyclic-frequency router with improved performance by employing two types of modified configuration; a uniform-loss and cyclic-frequency (ULCF) arrayed-waveguide grating (AWG) and an interconnected multiple AWG. We have demonstrated a compact 50-GHz-spacing 64x64 ULCF-AWG router with low and uniform insertion losses of 5.4-6.8 dB and frequency deviations from the grid of less than plusmn8 GHz. We have also demonstrated a 100-GHz-spacing 8x8 interconnected multiple-AWG router with a practical configuration, very low and uniform insertion losses of 2.3-3.4 dB, and frequency deviations from the grid of less than plusmn6 GHz. We discuss the suitable or realizable scale N of the two types of routers by comparison with a conventional AWG router in terms of optical and dimensional performance and productivity.

Small Bend Structures Using Trenches Filled With Low-Refractive Index Material for Miniaturizing Silica Planar Lightwave Circuits

We have proposed the fabrication of small bend structures using trenches along both sides of the core, filled with low-refractive index material, in order to miniaturise silica planar lightwave circuits. The minimum bending radius of a silica waveguide was reduced from 2 mm to 200 mum by filling the trenches with low-refractive index material. The local lateral relative refractive index difference (Delta) was increased to 8.64%. We fabricated cascade S-shaped waveguides to estimate a bend loss of the proposed structure. Moreover, we applied those structures to arrayed-waveguide gratings (AWG)s. Both 8-channel, 100-GHz channel-spacing and 8-channel, 12.5-GHz channel-spacing AWGs were successfully fabricated. Compared with conventional AWGs, sizes of these devices were reduced by factors of about 2 and 4, respectively.

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.

Birefringence compensated AWG demultiplexer with angled star couplers

A new approach to birefringence compensation in arrayed waveguide gratings (AWG) is proposed. The star couplers are designed according to Rowland circle construction with an oblique incident/diffraction angle, similar to the case of an echelle grating. Such an AWG design is more general and flexible, and the conventional AWG becomes its special case when the grating angle is zero. By appropriately designing the star coupler shape, the birefringence of the arrayed waveguides can be compensated by that of the slab waveguides. The details of the design method and simulation results are presented.

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

A novel wavelength dispersive device with a dispersive element based on staircase-like straight and parallel arrayed waveguides

We propose a new type of arrayed waveguide grating (AWG) multiplexer/demultiplexer based on modified group refractive index. This device is composed by an array of straight and parallel waveguides of equal length and each waveguide consist of two sections with different width. The length of the two sections are changed from a waveguide to the adjacent one following a linear dependence resulting in a wavelength dispersive waveguide array. An example of the device design for silicon-on-insulator (SOI) platform is provided and numerical simulations have been carried out for various arrayed waveguide parameters. We demonstrate that the group index modification can be used for tailoring device dispersion properties, and that it can also result in new dispersion characteristics predicted numerically not observed in conventional AWGs. Additional advantages are that the demultiplexer does not necessarily require bending waveguide sections as in a conventional AWG (de)multiplexers, and thus yields highly compact devices with potentially very low insertion loss. Channel spacing of 1 nm have been predicted for sub-micron waveguides sizes. In this paper it is also proposed a novel wavefront converter based on waveguide array lens-like element with waveguides broadened sections. Numerical results for different input/output geometries are analized.