A new photonic RF instantaneous frequency measurement system is proposed and experimentally demonstrated. A frequency measurement independent of the optical input power and microwave modulation index is achieved by using the constructive and destructive ports of a polarization-domain interferometer. Experimental tests yield a peak-to-peak frequency error lower than 200 MHz for a frequency range of 1-18 GHz.
Ubiquitous satellite communications are in a leading position for bridging the digital divide. Fulfilling such a mission will require satellite services on par with fibre services, both in bandwidth and cost. Achieving such a performance requires a new generation of communications payloads powered by large-scale processors, enabling a dynamic allocation of hundreds of beams with a total capacity beyond 1 Tbit s −1 . The fact that the scale of the processor is proportional to the wavelength of its signals has made photonics a key technology for its implementation. However, one last challenge hinders the introduction of photonics: while large-scale processors demand a modular implementation, coherency among signals must be preserved using simple methods. Here, we demonstrate a coherent photonic-aided receiver meeting such demands. This work shows that a modular and coherent photonic-aided payload is feasible, making way to an extensive introduction of photonics in next generation communications satellites.
Optical wavelength conversion (OWC) is expected to be a desirable function in future optical transparent networks. Since high-order quadrature amplitude modulation (QAM) is more sensitive to the phase noise, in the OWC of high-order QAM signals, it is crucial to suppress the extra noise introduced in the OWC subsystem, especially for the scenario with multiple cascaded OWCs. Here, we propose and experimentally demonstrate a pump-linewidth-tolerant OWC scheme suitable for high-order QAM signals using coherent two-tone pumps. Using 3.5-MHz-linewidth distributed feedback (DFB) lasers as pump sources, our scheme enables wavelength conversion of both 16QAM and 64QAM signals with negligible power penalty, in a periodically-poled Lithium Niobate (PPLN) waveguide based OWC. We also demonstrate the performance of pump phase noise cancellation, showing that such coherent two-tone pump schemes can eliminate the need for ultra-narrow linewidth pump lasers and enable practical implementation of low-cost OWC in future dynamic optical networks.
The design and dimensioning of a photonic-aided payload for a multi-beam high-throughput communications satellite is a complex problem in which the antenna, RF and photonic subsystems must be considered as a whole for achieving best performance with lowest mass and power consumption. In this paper, we propose and dimension the receiving stage of a communications satellite comprising a phased array antenna (PAA) feeding a multibeam photonic beamforming system (PBS). The PBS uses a single wavelength and resorts to heterodyne detection such that the retrieved beams are frequency downconverted. End-to-end system modeling shows that the complexity of the PAA and PBS can be traded-off for signal-to-noise ratio (SNR) or power consumption without compromising the beam width. The dimensioning of a realistic scenario is presented, showing that an SNR and beam crosstalk on the order of 20 dB are achievable with a total power consumption below 1 kW for a typical number of 100 antenna elements (AEs).
In this Letter, we propose a monitoring and control system (MCS) for operating tunable optical delay lines (TODLs), regardless of their operation principle and implementation technology. The monitoring system resorts to two out-of-band pilot tones added to the input optical signal. The amplitude and phase difference between tones are retrieved to the control system, which calculates and applies the TODL control signals. The MCS was validated using a Mach-Zehnder delay interferometer-based TODL, implemented in three different silicon photonic integrated circuits (PICs). The three PICs resort to different kinds of phase shifters based on thermo-optic, carrier-injection, and carrier-depletion effects. The proposed MCS enabled tuning the delay within the entire range of the TODL in all tested PICs. The scalability of the MCS for large-scale photonic beamformers is discussed.
Tunable wavelength conversion of a 160 Gbit/s signal by means of cascaded sum frequency generation/difference frequency generation was performed on a periodically-poled lithium niobate waveguide. Operation at room temperature (258C) is demonstrated. A maximum power penalty of 2.1 dB for a bit error rate of 10 29 was achieved over a wavelength range of 29 nm.Introduction: Ultrafast all-optical signal processing has attracted significant interest as a potential enabler to increase the per-channel bit rate of optical communication systems well beyond the bit rates imposed by electronic bandwidth limitations. Recently, considerable attention has been given to ultrafast nonlinear signal processing in compact waveguides [1, 2], mainly because such devices are suitable for integration. Nonlinear signal processing techniques such as optical time division signal multiplexing [3], demultiplexing [2], add/drop [2] and wavelength conversion [4] have been reported using periodically-poled lithium niobate (PPLN) waveguides at bit rates up to 320 Gbit/s. These applications all take advantage of the ultrafast response and high efficiency offered by compact PPLN waveguides.In PPLN waveguides, tunable wavelength conversion is achieved through cascaded sum frequency generation/difference frequency generation (cSFG/DFG), enabled by the second-order nonlinearity of the material. The main limitation of PPLN waveguides is that SFG only occurs within a limited bandwidth, defined by the quasi-phase matching condition (QPM). There are two ways of increasing such bandwidth. The first is to trade maximum efficiency for bandwidth on the PPLN design. The second is to resort to pump depletion phenomena [2]. Although the latter approach has enabled operation at 320 Gbit/s, it presents additional complexity since it requires a clocked pump synchronised with the input signal. On the other hand, the problem of having a broad bandwidth and low efficiency is that high pump powers are required. Furthermore, in order to reduce photorefractive damage induced by high pump powers, operation temperatures higher than 1508C are usually required. This is a major drawback owing to the high power consumption needed to heat the device.In this Letter we demonstrate wavelength conversion of a 160 Gbit/s signal by means of cSFG/DFG on a 45 mm-long PPLN waveguide at 258C. The PPLN waveguide presents a broad bandwidth of about 5 nm in the C-band, and a low second harmonic generation (SHG) efficiency of 80%/W. Error-free operation was achieved with a maximum power penalty of 2.1 dB over a wavelength range of 29 nm, thus proving that photorefractive damage was effectively mitigated when using high pump powers.
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