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.

A laser source that is both narrow-linewidth and frequency-agile is essential for FMCW applications, such as LIDAR or distributed optical fiber sensing (DOFS). In this work, we present the design and characterization of a laser architecture based on the heterogeneous integration of III-V gain material on a SiN photonic circuit that meets these specifications. By incorporating a dual-ring resonator mirror in the cavity, we achieved a linewidth of 2.4 kHz and a large frequency excursion. We obtained chirps with an amplitude of 20 GHz, with residual nonlinearities of less than 1%. A preliminary DOFS measurement was carried out, demonstrating the excellent performance of the laser.

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.

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.

We present an experimental characterization of a thin film lithium niobate photonic integrated circuit (PIC) for a multimode free space optical communication receiver. The PIC coherently combines up to eight optical single mode signals with low insertion and propagation losses.

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.

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.

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.

Multimode receivers based on spatial or modal diversity are promising architectures to mitigate in real time the atmospheric turbulence effects for free space optical (FSO) communications. In this paper, we evaluate and comment on the dynamical communication performances of a FSO mode diversity receiver, based on a spatial demultiplexer and a silicon photonic coherent combiner, for an optical link from a GEO satellite to an optical ground station (OGS). We simulate time series of distorted wavefronts received by the OGS and we show numerically that the coherent combination of spatial modes mitigate the signal fading compared to a conventional single mode fiber (SMF) receiver. We verify this property in a laboratory environment by generating the wavefronts corresponding to the use case with an atmospheric propagation channel emulator. Then we modulate the optical carrier prior to the wavefront emulator with 10G OOK and DPSK data sequences to measure the BER performance of the proposed receiver during the time series emulation. Finally, we study and comment on the influence of the number of modes combined and the wavelength multiplexing on the BER performances. We prove that the mode diversity receiver provide a higher collection efficiency, has better BER performances and much less synchronization losses.

An optical fiber sensing system with a frequency shifting loop monitor phase perturbations applied to a transducer in an optical fiber. A sensitivity below 4 µrad/Hz^(1/2) in a 20 kHz – 2 MHz bandwidth is obtained.

We demonstrate a new and simple dynamic laser ranging platform based on analog all-optical coherent pulse compression of modulated optical waveforms. The technique employs a bidirectional acousto-optic frequency shifting loop, which provides a dual-comb photonic signal with an optical bandwidth in the microwave range. This architecture simply involves a CW laser, standard telecom components and low frequency electronics, both for the dual-comb generation and for the detection. As a laser ranging system, it offers a range resolution of a few millimeters, set by a dual-comb spectral bandwidth of 24 GHz, and a precision of 20 µm for an integration time of 20 ms. The system is also shown to provide dynamic measurements at scanning rates in the acoustic range, including phase-sensitive measurements and Doppler shift velocimetry. In addition, we show that the application of perfect correlation phase sequences to the transmitted waveforms allows the ambiguity range to be extended by a factor of 10 up to ∼20 m. The system generates quasi-continuous waveforms with low peak power, which makes it possible to envision long-range telemetry or reflectometry requiring highly amplified signals.

To concurrently cope with the scarcity of RF frequency bands, the growing capacity demand and the required lower cost of the ground segment, Very High Throughput Satellites systems must rely on new technical solutions. Optical feeder links are considered as a promising alternative to surpass classical RF technology, offering assets inherent to optical technologies (large bandwidth, no frequency regulation, low beam divergence, components availability). Nevertheless the potential of this technology shall not conceal the remaining challenges to be overcome to make it relevant for operational missions : clouds, turbulence, power generation and high efficiency modulations. VERTIGO (Very High Throughput Satellite Ground Optical Link) is a 3-year H2020 project funded by the European commission and started mid-2019 focusing on the optical link itself regardless of site diversity aspect and aiming at demonstrating in a ground demonstration required technologies to implement very high capacity optical feeder links. In particular, VERTIGO is built on 3 pillars each addressing a key issue for the implementation of optical feerder links: 1) Throughput increase through the use of advanced schemes with high spectral and power efficiency compared to current modulations used in space, as well as RF-over-Fiber approach. 2) High optical power generation to close the demanding link budgets by developing on-board and ground means to raise the transmitted optical power, not only based on amplifier power increase, but also on incoherent/coherent power combining. 3) Opto-mechanical and digital techniques for the mitigation of atmospheric propagation impairments, to make full use of throughput and power increases. Several demonstrations in-flight or on-ground already demonstrated separately key aspects (atmospheric propagation and impairments mitigation techniques, modulation format, high power…), for the implementation of optical (feeder) links. These aspects are closely linked since the solutions to each of them are necessary but not sufficient to allow for high throughput transmissions. VERTIGO concept is to address each key issue with at least one solution and to combine them in an unprecedented manner. To reach these objectives, VERTIGO will lean on a highly skilled consortium composed of : CREONIC, ETH Zürich, Fraunhofer HHI, Gooch and Housego, Leo Space Photonics RD, ONERA, Thales Research and Technology, Thales Alenia Space in France and Switzerland. This paper will present the VERTIGO project and its status.

We report on a detailed analysis of the effect of CW injection in an actively mode-locked laser at 780 nm, on the noise performances of the laser. The optical properties of the emitted pulse train, and the phase and amplitude noise of the RF pulse train generated after photodetection have been characterized with respect to the laser pumping rate, and to the injected power. We show that when injected, the laser exhibits a dramatic improvement of both RF phase noise and power spectrum, but at the expense of a degraded optical relative intensity noise.