RESUMEN
We demonstrate for the first time, to the best of our knowledge, reconfigurable and real-time orthogonal time-domain detection of a high-bandwidth Nyquist signal with a low-bandwidth silicon photonics Mach-Zehnder modulator based receiver. As the Nyquist signal has a rectangular bandwidth, it can be multiplexed in the wavelength domain without any guardband as a part of a Nyquist-WDM superchannel. These superchannels can be additionally multiplexed in space and polarization. Thus, the presented demonstration can open a new possibility for the detection of multidimensional parallel data signals with silicon photonics. No external pulse source is needed for the receiver, and frequency-time coherence is used to sample the incoming Nyquist signal with orthogonal sinc-shaped Nyquist pulse sequences. All parameters are completely tunable in the electrical domain. The feasibility of the scheme is demonstrated through a proof-of-concept experiment over the entire C-band (1530 nm-1560 nm), employing a 24 Gbaud Nyquist QPSK signal due to experimental constraints on the transmitter side electronics. However, the silicon Mach-Zehnder modulator with a 3-dB bandwidth of only 16 GHz can process Nyquist signals of 90 GHz optical bandwidth, suggesting a possibility to detect symbol rates up to 90 GBd in an integrated Nyquist receiver.
RESUMEN
In this paper, the theory of phase-locking of a microwave oscillator on the interharmonics, i.e. non-integer harmonics, of the repetition rate of the optical pulse train of a mode-locked laser (MLL) is developed. A balanced optical microwave phase detector (BOMPD) is implemented using a balanced Mach-Zehnder modulator and is employed to discriminate the phase difference between the envelope of the optical pulses and the microwave oscillator. It is shown mathematically that the inherent nonlinear properties of BOMPD with respect to the microwave excitation amplitude can be used for interharmonic locking. The characteristic functions of the phase detector for interharmonic locking are derived analytically and are compared with the measurement results. An opto-electronic phase-locked loop (OEPLL) is demonstrated whose output frequency locks on interharmonics of the MLL repetition rate when an appropriate modulator bias and sufficient RF amplitude are applied. Thus, for the first time theory and experiment of reliable locking on interharmonics of the repetition rate of a MLL are presented.
RESUMEN
We present the design and experimental characterization of a silicon nitride pulse interleaver based on coupled resonator optical waveguide filters. In order to achieve a targeted free spectral range of 1.44 THz, which is large given the reduced optical confinement of the silicon nitride platform, individual ring resonators are designed with tapered waveguides. Its application to time-interleaved photonically-assisted ADCs is analyzed by combining experimental characterization of the photonic integrated circuit with a comprehensive model of the entire ADC. The impact of fundamental signal distortion and noise sources affecting the converter is investigated and suitable equalization techniques at the digital signal processing level are evaluated. The novel application of a simple but powerful equalization filter in the DSP domain allows for a significant improvement of the digitized signal SNR. An ENOB of 5 over a 75â GHz bandwidth (150 GS/s) and an ENOB of 4.3 over a 100â GHz bandwidth (200 GS/s) are expected to be achievable with compact and off-the-shelf single-section semiconductor mode locked lasers, that can be further improved with lower noise light sources.
RESUMEN
In this paper a novel opto-electronic Track-and-Hold Amplifier (OE-THA) is presented. The OE-THA can be used as a sampler in a photonic analog-to-digital-converter (ADC). It is fabricated in a silicon photonic 250 nm SiGe BiCMOS technology to allow for monolithic integration of photonic and electronic components. The OE-THA chip exhibits a small signal bandwidth of over 65 GHz, a total harmonic distortion below -34 dB up to 75 GHz and a signal-to-noise and distortion ratio (SINAD) of over 35 dB (5.5 effective bits, ENOB) up to 45 GHz. The measured resolution bandwidth products result in a corresponding equivalent jitter of below 80 fs rms from 20 to 70 GHz. The best equivalent jitter is achieved at 41 GHz with a value of 55.8 fs rms. This is enabled by using a low-jitter optical pulse train, generated by a Mode-Locked-Laser (MLL), as an optical sampling clock. The circuit integrates all optical and electronic components besides the MLL. It draws 110 mA operated from a supply voltage of -4.6 V and occupies a silicon area of only 0.59 mm2.
RESUMEN
The effect of phase noise introduced by optical sources in spectrally-sliced optically enabled DACs and ADCs is modeled and analyzed in detail. In both data converter architectures, a mode-locked laser is assumed to provide an optical comb whose lines are used to either synthesize or analyze individual spectral slices. While the optical phase noise of the central MLL line as well as of other optical carriers used in the analyzed system architectures have a minor impact on the system performance, the RF phase noise of the MLL fundamentally limits it. In particular, the corresponding jitter of the MLL pulse train is transferred almost one-to-one to the system-level timing jitter of the data converters. While MLL phase noise can in principle be tracked and removed by electronic signal processing, this results in electric oscillator phase noise replacing the MLL jitter and is not conducive in systems leveraging the ultra-low jitter of low-noise mode-locked lasers. Precise analytical models are derived and validated by detailed numerical simulations.