Eight-Channel Silicon-Photonic Wavelength Division Multiplexer With 17 GHz Spacing

Abstract

Dense wavelength division multiplexers are key components of data communication networks. This paper presents a silicon-photonic eight-channel multiplexer device with a channel spacing of only 0.133 nm (17 GHz). Devices were fabricated in a commercial silicon foundry, in 8" silicon-on-insulator wafers. The device layout consists of seven unbalanced Mach-Zehnder interferometers in a cascaded tree topology, and each interferometer unit also includes a nested ring resonator element. The transfer function of each unit is that of a maximally flat, autoregressive, moving-average filter. The devices are characterized by uniform passbands, sharp spectral transitions between pass and stop bands, and strong out-of-band rejection. The worst-case optical power crosstalk is −22 dB. The proper function of the device requires careful control of optical phase delays over 14 distinct optical paths. Post-fabrication trimming of phase delays was performed through local illumination of a photo-sensitive upper cladding layer of chalcogenide glass. The de-multiplexing of three adjacent QAM-16, 40 Gbit/s wavelength-division channels was successfully demonstrated. The devices are applicable in data communication and in integrated-photonic processing of radio-over-fiber waveforms.

Scaling capacity of fiber-optic transmission systems via silicon photonics

“…Due to the large channel count, the average delay length and phase errors rise up, leading to a relatively high crosstalk (∼−4 dB). Similar to the study by Munk et al [216], the performance can also be enhanced by phase error compensation. In the study by Gehl et al [214], a record resolution of 1 GHz is achieved by active phase correction using integrated thermo-optic PSs on the arrayed waveguides, at the cost of increased complexity and power consumption.…”

“…applications include arrayed waveguide gratings (AWGs) [211][212][213][214], echelle gratings (EGs) [215], cascaded MZIs [216], microring resonators (MRRs) [163,217,218], and Bragg grating filters such as contradirectional couplers [176,219]. AWGs, EGs, and cascaded MZIs are classified as finite impulse response (FIR) filters, which split input light to dispersive paths and recombine them at different outputs with regard to wavelength.…”

“…Therefore, postcorrection of phase errors is usually required. In the study by Munk et al [216], photosensitive As 2 Se 3 chalcogenide thin films deposited on top of silicon waveguides are used to compensate for fabrication errors in a cascaded MRR-assisted MZI filter; a narrow spacing of 17 GHz has been achieved. Postfabrication phase trimming using germanium implanted waveguides is another means for fine tuning [223,224].…”

Integrated High-Resolution Optical Spectrum Analyzer With Broad Operational Bandwidth

“…The eight-channel, dense wavelength-division de-multiplexer device separated the spectrum of incident light into eight output ports. The demultiplexer layout consisted of seven cascaded Mach-Zehnder interferometer stages, with ring resonators nested in the shorter arm of each interferometer [27]. The transfer functions of the device are characterized by uniform passbands, strong outof-band rejection, and sharp spectral transitions between pass and stop bands [27].…”

“…The change in the effective index of the guided mode, and the offset in resonance frequencies, are proportional to local temperature change [16], [21]. WDM devices are readily implemented in silicon as well [15], [22]- [27], in the forms of AWGs [15], [23], cascaded Mach-Zehnder interferometers (MZIs) [25], and more complex layout that combine MZIs and resonators [27].…”