Etched Diffraction Grating Demultiplexer Research Articles

Polarization-insensitive EDG demultiplexer combined with a polarization beam splitter.

Polarization dependence is an inherent challenge for wavelength-division multiplexing transceivers on silicon photonic platforms, causing severe problems with polarization-dependent losses and hindering the implementation of monolithic integrated receivers. In this study, we developed a polarization-insensitive demultiplexer on a silicon nitride (Si3N4) platform, which provides a promising solution to the polarization challenge. Comprising an etched diffraction grating (EDG) and a polarization beam splitter (PBS), the demultiplexer can achieve polarization insensitivity by introducing an additional optical path difference for polarization compensation. The fabricated demultiplexers were experimentally measured to have minimum insertion losses of 1.5 dB, cross talks of better than -25 dB, and polarization-dependent losses of better than 0.7 dB. This is the first, to the best of our knowledge, proposed solution for a polarization-insensitive EDG demultiplexer combined with a PBS on a Si3N4 platform.

Demonstration of Distributed Etched Diffraction Grating Demultiplexer

The design principles and measurement results for a compact shallow etched distributed diffraction grating waveguide demultiplexer are presented. The deeply etched diffraction grating facets are replaced with a shallow etched odd-order quarter wavelength Bragg reflector to increase the Fresnel reflection coefficient. A prototype device was designed for coarse wavelength demultiplexing applications and was fabricated in nanophotonic silicon-on-insulator platform using deep ultraviolet (DUV) optical lithography. The demultiplexer, which supports four channels with 20-nm channel spacing, shows a crosstalk of -25 dB.

Distributed Etched Diffraction Grating Demultiplexer With Flat-Top Insertion Loss Envelope

It is numerically shown that incorporation of a distributed Bragg reflector at the facets of an etched diffraction grating (EDG) can be used to tailor the output spectral response of the device. This technique is used to optimize the overall insertion loss envelope of a distributed etched diffraction grating (DEDG) demultiplexer to improve the output channel uniformity. Numerical results are presented for the transverse electric (TE) polarization, where a channel uniformity of 0.45 dB over 43-nm bandwidth is achieved. A finite-difference time-domain (FDTD) method in combination with perfectly matched layers (PMLs) and periodic boundary condition (PBC) is used to calculate the insertion loss envelope of device.

Analytical Design of Total-Internal-Reflection Grating Demultiplexers With a Low Noise Floor

Etched diffraction grating (EDG) demultiplexers using total-internal-reflection (TIR) facets with a low noise floor have theoretically been designed based on silicon nanowire wafers. The transfer function (TF) of EDG demultiplexers is derived based on Fourier analysis. Since the Goos-Hänchen shift and the finite size of facets result in most of the loss of EDG demultiplexers with TIR facets, we can reshape the TF into an approximate Gaussian distribution by slightly adjusting each grating facet's size and structure. Thus, we design an EDG demultiplexer with a very low noise floor based on silicon waveguide.

Design and fabrication of compact etched diffraction grating demultiplexers based on -Si nanowire technology

Silicon nanowire waveguides and related etched diffraction grating (EDG) demultiplexers are studied by alpha-Si-on-SiO2 technology. Compact EDG demultiplexers with 10 nm spacing for both echelle and total-internal-reflection (TIR) facets have been fabricated and characterized.

Etched Diffraction Grating Demultiplexers With Large Free-Spectral Range and Large Grating Facets

A design for etched diffraction grating demultiplexers is presented to obtain both large grating facets and a larger free-spectral range (FSR) using the optimal chirped diffraction orders for different facets. The large grating facets by using a large diffraction order contribute to lowering the manufacturing difficulty, and can provide lower polarization-dependent loss. However, usually the large diffraction order must lower the FSR of the device by all means. Based on the present design, the FSR can overlay the whole diffraction envelop for a special order, but avoid the influence of the adjacent diffraction envelops. Calculations indicate that the extinction ratio between the operated order and adjacent orders can attain a 35 dB or so, which makes the crosstalk from channels in adjacent envelops to those in the operated diffraction envelop acceptable

Sidelobe suppression design of etched diffraction grating demultiplexers using optimized air trenches in front of each output waveguide

An etched diffraction grating (EDG) demultiplexer with high sidelobe suppression is designed. Sidelobes resulting from two adjacent wavelengths are suppressed by etching two optimized rectangular air trenches in front of each output waveguide that can induce large resonance loss in the adjacent wavelength but have little influence on the operational wavelength. The designed EDG demultiplexer can suppress crosstalk to less than 50 dB in theory.

A hybrid diffraction method for the design of etched diffraction grating demultiplexers

A novel hybrid diffraction method is proposed to simulate the demultiplexing of an etched diffraction grating (EDG). The scalar diffraction formula is adopted to simulate the propagation of the light field in the free propagation region (FPR), and a rigorous coupled-wave analysis (RCWA) is used to calculate the polarization-dependent diffraction near the grating. The hybrid diffraction method takes the advantages of both the conventional scalar diffraction method and the rigorous coupled-wave analysis and can simulate accurately the imaging property as well as the polarization-dependent efficiency of an EDG demultiplexer. Compared with the conventional scalar diffraction method, the proposed hybrid diffraction method reduces greatly the design error in, for example, the polarization-dependent insertion loss.

Reduction of multimode effects in a SOI-based etched diffraction grating demultiplexer

Multimode effects in the free propagation region (FPR) of a silicon-on-insulator (SOI)-based etched diffraction grating (EDG) demultiplexer are analyzed. In a conventional design, the power coupled to the higher order modes is considerable, which introduces a significant excess loss and crosstalk. It is shown that the multimode effects in an SOI EDG demultiplexer are much more detrimental than in an arrayed waveguide grating demultiplexer. Several methods for reducing the multimode effects are discussed. In particular, a laterally tapered structure between the FPR and the input/output waveguides is proposed as a simple and effective method for reducing the power coupled to the higher order modes and consequently reducing the multimode effects. The taper width is optimized to minimize the crosstalk.

The impact of phase and amplitude errors on an etched diffraction grating demultiplexer

The insertion loss and channel crosstalk of an etched diffraction grating (EDG) demultiplexer is significantly influenced by phase and amplitude errors. A statistical model to estimate the impact of phase and amplitude errors in an EDG is developed using scalar diffraction theory. The numerical results show that the influence of amplitude errors caused by nonuniformity in deposition and etching process is not distinct until the resolution of photomask is better than 40 nm. A basic requirement for an EDG demultiplexer with crosstalk less than −30 dB is given.

A MoM-based design and simulation method for an etched diffraction grating demultiplexer

A design and simulation method based on the method of moment (MoM) is proposed for an etched diffraction grating (EDG) demultiplexer. The method of moment is used to calculate the surface current, which produces the diffracted field at the image plane, for both polarizations. The present method can be used to design and simulate effectively and accurately an EDG demultiplexer with required specifications (such as the chromatic dispersion and loss variation) for both polarizations and the polarization-dependent loss.

A planar waveguide demultiplexer with a flat passband, sharp transitions and a low chromatic dispersion

A flat-topped planar waveguide demultiplexer with a low chromatic dispersion is designed. A parabolic multimode interference (MMI) section with a reshaping taper is connected at the end of the input waveguide. A 16-channel etched diffraction grating (EDG) demultiplexer with channel spacing of 100 GHz is considered as a design example. Wide-angle beam propagation method and the Kirchhoff diffraction theory are used in the simulation. The field distribution at the end of the taper is reshaped optimally to have sharp transitions. A genetic algorithm is used to optimize the parabolic MMI section. The designed EDG demultiplexer has an excellent flat-topped spectral response and a very low chromatic dispersion characteristic.