100-Gb/s dense wavelength division multiplexed (DWDM) transmitter and receiver photonic integrated circuits (PICs) are demonstrated. The transmitter is realized through the integration of over 50 discrete functions onto a single monolithic InP chip. The resultant DWDM PICs are capable of simultaneously transmitting and receiving ten wavelengths at 10 Gb/s on a DWDM wavelength grid. Optical system performance results across a representative DWDM long-haul link are presented for a next-generation optical transport system using these large-scale PICs. The large-scale PIC enables significant reductions in cost, packaging complexity, size, fiber coupling, and power consumption.

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Large-scale photonic integrated circuits

We present an overview of Infinera's current generation of 100 Gb/s transmitter and receiver PICs as well as results from the next-generation 500 Gb/s PM-QPSK PICs.

We studied the impact of the lithography mask discretization on silicon arrayed waveguide grating (AWG) performance. When we decreased the mask grid from 5 to 1 nm, we observed an experimental improvement in crosstalk of 2.7-6 dB and cumulative crosstalk improvement of 1.2-5 dB, depending on the wavelength channel spacing and the number of output channels. We demonstrate the effect for the AWGs with 200- and 400-GHz channel spacing, with 4, 8, and 16 output wavelength channels. With 1-nm mask grid, the average crosstalk is -26 and -23 dB for 400- and 200-GHz devices, respectively. This is the lowest crosstalk for silicon AWGs reported to the best of our knowledge. A simulation study is performed by looking specifically at phase errors due to mask grid snapping (ignoring other phase error sources), which shows an expected improvement in crosstalk of 12 dB.

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Effect of Mask Discretization on Performance of Silicon Arrayed Waveguide Gratings

A high-performance reflective arrayed waveguide grating multiplexer/demultiplexer designed for compatibility with silicon integrated circuit processing is described. The grating, folded by a flat reflecting surface, can be printed in a single-exposure field of a photolithographic stepper. Advanced plasma assisted deposition is used to prepare waveguides with very low loss and minimum birefringence. Multiplexers with 40 channels separated by 100 GHz show intrinsic insertion losses of -2.4 dB, channel uniformity less than 0.6 dB, and very low polarization dependent wavelength shift of 0.012 nm.

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Reflective arrayed waveguide grating multiplexer

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.

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Improved arrayed-waveguide-grating layout avoiding systematic phase errors.

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.

Qiang Wang

Papers

The role of photomask resolution on the performance of arrayed-waveguide grating devices