We describe and compare in this paper two common methods to measure the half-wave voltage (Vpi) of an electro-optical modulator versus RF frequency of the driving electronic signal. We detail the required calibration procedures when necessary and demonstrate the methods experimentally from 100MHz up to 40GHz. Guidelines are finally given to select the most appropriate method depending on the application and modulator characteristics.

Optical satellite communications offer a viable path to meet the growing needs in transmission capacity of space communication networks, as well as the saturation of conventional RF bands. Yet long propagation distances and atmospheric turbulence limit coupled power, necessitating high-power amplification. To date, high-speed transmission at such power levels has not been demonstrated in a single system. Here, we report 1 Tbit/s data rates at 100 W optical power with a signal-to-noise ratio (SNR) advantage of up to 3.9 dB over a conventional single-amplifier system. The SNR advantage of 3.0 dB is obtained by mitigating amplifier-induced nonlinearities by an artificial neural network (ANN) equalizer, thereby outperforming conventional approaches by up to 2.3 dB. An additional SNR gain has been enabled by coherent beam combining of two 50 W amplifiers. The impact of beam combining is investigated, and an advantage of up to 0.9 dB SNR is shown. A system-level investigation into the SNR penalty due to high power amplification, the influence of the polarization multiplexing, and the best-case performance of the system is given. These findings provide critical insights for future high-capacity optical satellite links.

Time reversal of radio-frequency or microwave signals has important applications applications in telecommunications and electronic warfare. All-digital techniques are intrinsically limited in bandwidth by the speed of the converters, which necessitate the emergence of alternative analog techniques for future implementations. We demonstrate a new, to our knowledge, microwave-photonics architecture in this context, offering integration prospects. The system we propose is based on a pair of frequency-shifting loops, where the first loop transfers the input signal from the time domain into the frequency domain. In contrast, the second loop performs the opposite process, thus achieving the desired time-reversal process. The technique is particularly versatile, allowing the time reversal of signals with bandwidths of the order of tens of MHz, durations on the order of tens of microseconds, and with arbitrarily small latency. The system can also act as a temporal buffer for the reversed signal, a promising feature for photonic-based beamforming.

In this paper, we present a method based on a modal decomposition to quantify the efficiency of photonic lanterns (PLs) based free space optical (FSO) communication receivers. We fabricate a seven-port PL, and we evaluate numerically the free space to fiber coupling efficiency based on a reconstruction of the fields at the PL FSO multimode port. We validate the numerical approach with an experimental characterization of the PL. Then we compare the PL to a commercial multiplane light converter spatial demultiplexer. The PL shows better coupling efficiency for low-order spatial modes with orders of magnitude of demultiplexer size reduction. Finally, we evaluate the PL receiver with a simulation of received optical wavefront in a FSO communication.

We demonstrate an InP-on-Si3N4 widely tunable laser on imec's 200-mm low-loss Si3N4 platform through micro-transfer printing. The device shows a wavelength tuning range of 54 nm in C + L band with a side mode suppression ratio over 40 dB.

An optical coherent transmission link with 100Watt output power is tested for satellite communications. Modulation formats are tested for transmission of the highest data-rates despite of nonlinear amplifier impairments across a linear, low-SNR free-space link.

Leveraging its superior waveguide properties,silicon-nitride(Si3N4)photonics is emerging to expand the appli-cations of photonic integrated circuits to optical systems where bulk optics and fibers today still dominate.In order to fully leverage its advantages,heterogeneous integration of Ⅲ-Ⅴ gain elements on Si3N4 is one of the most critical steps.In this paper,we demonstrate a Ⅲ-Ⅴ-on-Si3N4 widely tunable narrow-linewidth laser based on micro-transfer printing.Detailed design considerations of the tolerant Ⅲ-Ⅴ-to-Si3N4 vertical coupler,Si3N4-based micro-ring resonators(MRRs),and micro-heaters are discussed.By introducing the dispersion of Si3N4 waveguide in the design,the proposed Vernier MRRs enable an extended tuning range over multiple Vernier periods.The laser shows a wavelength tuning range of 54 nm in C and L bands with intrinsic linewidth less than 25 kHz.Within the tuning range,the side mode suppression ratio is larger than 40 dB and the output power in the Si3N4 waveguide reaches 6.3 mW.The integration process allows for the fabrication and quality control of both the Si3N4 circuits and Ⅲ-Ⅴ devices in its own foundry,which greatly enhances the integration yield and paves the way for large-scale integration.

As part of the European Defense Agency-funded PICTURE project, we have investigated the potential of integrated photonics for radar systems, targeting a photonics-based architecture for electronically scanned active array antenna systems, including multifunctional signal generation and detection. In this context, we have developed integrated photonic transmit and receive modules with up- and down-conversion capability, powered by a mode-locked laser for frequency reference. Key elements such as narrowband optical bandpass filters are evaluated for different technology platforms (silicon-on-insulator and silicon nitride). Perspectives and lessons learned are presented, based on the evaluation of system performance with IF-to-RF and RF-to-IF conversion efficiencies.

We present advancements in free-space optical communication for satellite-ground networks. Using advanced atmospheric-turbulence-mitigation techniques, we tested new modulation formats at low-received optical powers at data rates of up to 1Tbit/s and transmitted output powers of up to 100 Watts across linear, free-space links of up to 53km.

Tunable lasers and photonic integrated circuits are a promising technology to provide compact and high performance solutions for coherent remote sensing applications such as Lidar, and distributed acoustic fiber sensing (DAS). A hybrid tunable laser was fabricated within the EU funded INSPIRE project, based on the micro-transfer printing of a pre-fabricated InP gain section on the IMEC low-loss silicon nitride platform. By simultaneously modulating the laser SOA current and Vernier ring resonators, we demonstrate a 20 GHz chirp amplitude, while maintaining a <5 kHz linewidth. DAS measurement with this laser are presented.

Coherent beam combination is one promising way to overcome the power limit of one single laser. In this paper, we use a Multi-Plane Light Converter to combine coherently 12 fibers at 1.03 µm with a phase locking setup. The overall loss measurement gives a combination efficiency in the fundamental Hermite-Gaussian mode as high as 70%. We demonstrate for the first time the beam steering capability of the system.

Highly efficient coherent beam combining (CBC) of two very-high-power optical amplifiers (VHPOA) with applications to long-range FSO communications such as ground-to-space feeder links is presented. The CBC setup is designed to minimize the telecom signal degradation, with a polarization beam splitter used to minimize the power fluctuations and to control the output polarization state of the beam. The system delivers 80 W output power and is proven to be compatible with 25 Gb/s telecom signals with a less than 1 dB power penalty.

Coherent combination of fiber lasers is a promising technique to overcome the power limitations of a single laser. The phase matching of a large number of fibers thus makes it possible to obtain high-energy lasers. Coherent beam combining has been the topic of tremendous works and can be achieved in either filled-aperture [1] or tiled-aperture [2] configuration. With the tiled-aperture configuration the maximum combination efficiency is limited to 66% due to the presence of grating lobes in far-field. With the filled-aperture configuration, it is possible to achieve one single output beam but the use of transmissive optics - such as diffractive optical elements - limits the scalability of the system, reducing the maximum achievable power. The Multi-Plane Light Conversion (MPLC) technology theoretically solves most of the problems inherent to previous techniques [3], [4]. The theoretical combination efficiency is 100%. The technology uses only phase plates in reflection and mirrors, compatible with high power. Finally, it allows the integration of a fine beam steering function.

Free space optical (FSO) links are considered as an essential part of future satellite communications as they benefit from wide optical bands, absence of frequency regulation, and synergy with terrestrial networks [1], [2]. Nevertheless, several challenges remain for enabling very high capacity optical links. For the optical feeder uplink, a major one is the generation of optical carriers strong enough to carry the communication signal from a ground station up to geostationary satellites. The output power of telecom optical amplifiers has been increased over the past decade, notably with the recent demonstration of very high power optical amplifier (VHPOA) capable of delivering up to 50 W [3]. However, the coherent beam combination (CBC) of several VHPOAs is a promising solution to meet the very demanding requirements of future optical ground-based terminals.

The use of millimeter-wave (mm-wave) frequencies is required in order to support the increasing number of connected devices expected from the fifth generation (5G) of mobile communications. Subsequently, the generation of radio-frequency (RF) carriers ranging from 10 GHz to 300 GHz and their transport through optical distribution network (ODN) is a key element of the future 5G fronthaul. Optically assisted RF carrier generation is one of the most promising solutions to tackle this issue, allowing a wide use of analog radio-over-fiber (ARoF) architectures. However the main limitation of these optical methods is related to the finite coherence of lasers sources, which can dramatically degrade data transmission in analog formats. To mitigate its impact, the use of orthogonal frequency-division multiplexing (OFDM) as the 5G standard allows employing efficient phase noise compensation algorithms. Therefore, in this study, we present an experimental demonstration of a mm-wave generation technique based on an optical phase-locked loop (OPLL) that fulfills the frequency specifications for 5G. Then, an algorithm is introduced that improves data recovery at reception and reduces the impact of a possible high phase noise carrier. Finally, a back-to-back data transmission experiment is performed, demonstrating the efficiency of the algorithm to reach the 5G requirements. These results emphasize the use of OPLLs as a viable solution to generate mm-wave carriers for 5G and beyond.

High power generation is an enabling technology for high capacity free space optical feeder links. We show the feasibility of optical transmission of WDM OOK / DPSK at high power based on 50 W amplifiers and their coherent combination to deliver up to 97 W power.

We demonstrate a narrow-linewidth tunable laser through micro-transfer printing a prefabricated III-V gain section on imec’s 200-mm Si/SiN platform. Lasing in distinct bands in the C+L band is demonstrated, with linewidth down to 2.87-kHz.

The experimental assessment of a novel all-optical FSO communication receive device based on a spatial mode demultiplexer and a photonic integrated coherent combiner, is reported. The device collects light from the spatial modes coupled into the input multimode fiber and coherently recombines these modes into an output single-mode fiber via a binary-tree integrated photonic circuit. It was evaluated in FSO transmission laboratory experiments featuring an atmospheric propagation channel emulator. The BER performance of a pre-amplified, OOK direct-detection receiver were measured at 10 Gbps, under various disturbance conditions and strengths. Efficient coupling into the receiver input was shown to be maintained resulting in almost constant BER. Low BER floors and limited detection sensitivity penalties were observed. The feasibility of the proposed FSO receiver is proven, together with its ability to provide higher collection efficiency and greater robustness to phase and intensity disturbances than standard SMF receivers.

Mitigation of atmospheric turbulence is a major challenge in optical wireless communication, especially for optical feeder links. In this paper, we present a free space optical (FSO) mode diversity receiver, based on a spatial demultiplexer and a silicon photonic coherent combiner to reduce the atmospheric turbulence deleterious effects. We simulate the spatial light distribution in the ground receiver aperture for a use case consisting of a FSO link from a GEO satellite. We then generate experimentally wavefronts corresponding to the spatial light distribution for that use case with a wavefront emulator, and we compare the collection efficiency of the proposed mode diversity receiver with a FSO single mode fiber (SMF) receiver. The proposed FSO receiver outputs a signal much more stable as the system is resilient to energy redistribution among higher order spatial modes.