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.

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Sampling is the first step to convert analogue into digital signals and one of the basic concepts for information handling. All practical sampling systems, however, are accompanied with errors. Bandwidth-limited signals can be seen as a superposition of time-shifted sinc pulses, weighted with the sampling values. Thus, due to orthogonality, bandlimited signals can be perfectly sampled by a corresponding sinc pulse with the correct time shift. But, sinc pulses are just a mathematical construct. Sinc pulse sequences, instead, can simply be generated by a rectangular, phase-locked frequency comb. For a high repetition-time to pulsewidth ratio, or a low duty cycle, the pulses of such a sequence come close to single sinc pulses, and thus, the sampling with them might lead to an almost ideal sampling. Here, we present the full-field optical sampling with a repetition-time to pulsewidth ratio of up to 153, or a duty cycle of around 0.65%. Since it enables amplitude and phase sampling, ultrahigh sampling rates should be possible.

Increasing demands for data centers, backbone, access, and wireless networks require inventive concepts to transmit and distribute digital or analog signal waveforms. We present a new, extremely simple transceiver concept, fundamentally different from conventional approaches. It does not rely on high-speed electronics and enables transmission of various time multiplexed analog waveforms or digital data signals with the maximum possible symbol rate in the same rectangular optical spectral band B. The aggregate symbol rate of N signal channels corresponds to B or twice the used modulator’s electro-optical bandwidth. By a modification of the system, it can be increased to three times the modulator bandwidth. The rectangular spectra can be further multiplexed into wavelength-superchannels without guardbands. To time demultiplex single signal channel, just another intensity modulator and a detector with an electrical bandwidth corresponding to the channel’s baseband width (B/(2N)) is required. No optical filter, high-speed signal processing, or unconventional photonic devices are needed; thus, it has the potential to be easily integrated into any platform and provides an economical and energy-efficient solution for future communication networks and microwave photonic links.

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