The centrosymmetric structure of stoichiometric silicon nitride inhibits the realization of second-order nonlinear processes in this low-loss, complementary-metal-oxide-semiconductor fabrication-compatible platform. Nevertheless, linear electro-optic modulation is an essential functionality desired for implementation in photonic integrated circuits. This study presents the successful achievement of electro-optical modulation in a silicon nitride microring resonator, employing thermally assisted electric-field poling. With an inscribed electric field of 100 V/μm within the silicon nitride waveguide, an effective second-order susceptibility of 0.45 pm/V is induced. Leveraging silicon nitride as the active material for electro-optic modulation, we determined the operational bandwidth of the device, constrained by the electrode design, to be 78 MHz. Furthermore, we demonstrate the capability of the device to modulate data at bitrates of up to 75 Mb/s. Our findings highlight the potential of linear electro-optical modulation in the silicon nitride integrated platform.
We propose and demonstrate a feedback tunable self-injection locked (SIL) narrow linewidth laser, the feedback light intensity is dynamically adjusted to find the best locking state. The self-injection locked laser is composed of distributed feedback (DFB) semiconductor laser and high quality (Q) factor silicon nitride (SiN) external cavity, tunable sagnac loop reflector is used to achieve arbitrary ratio of feedback light and output light on the basis of add-drop type high Q microring resonator (MRR). The results show that the SIL state is closely related to the ratio of feedback light. When the optical feedback ratio is higher than -14 dB, a robust SIL state can be achieved, and the locking state is independent of the phase of the feedback light, the intrinsic linewidth is narrowed from 130 kHz to 1 kHz. By optimizing the ratio of feedback light to -9.3 dB, a narrow linewidth output of 345 Hz can be achieved. This work has important application value in the field of coherent laser communication and coherent detection.
Stoichiometric silicon nitride (Si3N4) constitutes a mature platform for integrated photonics. Its pertinent properties, including wide transparency window from the visible to the mid-IR, low propagation loss, and high third-order nonlinearity, are exploited in many linear and nonlinear applications. However, due to the centrosymmetric nature of the Si3N4, the absence of the second-order susceptibility (χ(2)) impedes a realization of three-wave mixing processes as well as the linear electro-optic effect, relevant for many applications on an optical chip. Here, we implement the electric-field poling technique to induce the effective χ(2) inside a Si3N4 waveguide, thus enabling the linear electro-optic modulation. Using numerical simulations, we estimated the concentration and the diffusion coefficient of the charges responsible for the space-charge electric field formation. In addition, the DC third-order susceptibility of Si3N4 previously unknown in the literature is measured using a free-space Mach-Zehnder interferometer.
Recent societal demands in climate awareness call for rapid launch of space optical spectrographs, such as to be capable of putting state-of-the-art technology in short timeframe into orbit. As a consequence, it is of paramount importance to compress instruments’ construction schedules down to the ultimately necessary need. Because calibration and characterization (C&C) partially takes place after full instrument assembly, it is de facto on the time-plan critical path, bearing antagonist requirements: measurement accuracy shall be guaranteed without jeopardizing the instrument delivery date. To solve this problem, Airbus has explored multiple paths in order to propose an instrument's "Design for Calibration": the method consists in integrating C&C at the very beginning of the instrument development in order to respond efficiently to the identified needs. First, all planned tests are exhaustively simulated and analyzed with tools validated before measurements, ensuring full control of the overall C&C throughout the entire lifecycle of the project. Next, Airbus strongly enforces its strategy of measuring relevant parameters as soon as they are accessible, hence providing early characterization out of the critical path. Then, the remaining parameters have been thoroughly analyzed to provide a lean optical ground support equipment (OGSE) architecture capable of responding to current challenges. Moreover, it enables full automation, enforcing its time-efficiency by minimizing overheads. Although rapidity is ensured, measurement accuracies are simultaneously kept compliant. Finally, this work presents also disruptive photonics hardware investigated by Airbus to provide calibration for relaxing design: optically filtered supercontinua and optical microcombs.
Mode-locked lasers, and in particular solid-state femtosecond lasers, are oscillators with a unique physics capable to exhibit extremely low-phase noise of the emitted pulse train. Here we report ultra-low phase noise microwave generation with a self-referenced, fully-stabilized mode-locked femtosecond laser. The system involves a 395-MHz repetition rate 1560nm laser which is self-referenced and whose repetition rate is locked to a cavity-stabilized continuous-wave laser. The selfreferencing is achieved with a f-3f nonlinear interferometer realized in a silicon nitride highly-nonlinear waveguide. Prior to optical-to-electrical conversion for X-band microwave generation, the 395-MHz repetition rate of the mode-locked laser pulse train is multiplied in a fiber interleaver to 3.16 GHz. A high-power handling photodiode converts the optical pulse train to an electrical frequency comb with 3.16 GHz frequency spacing. Finally, the 9.5-GHz harmonics is bandpassfiltered and phase noise measurements have shown a record-low phase noise floor of -175 dBc/Hz at 1-MHz offset frequency.
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