Thin-film lithium niobate circulator-free dispersion compensator in a time-lens system for femtosecond-pulse generation.

We demonstrate a circulator-free thin-film lithium niobate (TFLN) dispersion compensator based on the cascading 2 × 2 multimode interferometer (MMI) and two identical chirped Bragg gratings (CBGs). The cascaded MMI-CBG structure provides a dispersion value of 920 ps/nm/m over a 20 nm bandwidth covering 1537 to 1557 nm, featuring a compact footprint of 1 mm × 0.7 mm. Utilizing this device within a TFLN electro-optic time-lens system, we successfully generate 863-fs pulses at a 37 GHz repetition rate. Our compact, scalable, low-loss, and circulator-free dispersion compensator is the building block for the efficient generation of high-peak-power femtosecond laser pulses.

Bias-drift insensitive full-field frequency response characterization of a thin-film lithium niobate-based intensity modulator.

We propose a rapid and precise scheme for characterizing the full-field frequency response of a thin-film lithium niobate-based intensity modulator (TFLN-IM) via a specially designed multi-tone microwave signal. Our proposed scheme remains insensitive to the bias-drift of IM. Experimental verification is implemented with a self-packaged TFLN-IM with a 3 dB bandwidth of 30 GHz. In comparison with the vector network analyzer (VNA) characterization results, the deviation values of the amplitude-frequency response (AFR) and phase-frequency response (PFR) within the 50 GHz bandwidth are below 0.3 dB and 0.15 rad, respectively. When the bias is drifted within 90% of the Vπ range, the deviation fluctuation values of AFR and PFR are less than 0.3 dB and 0.05 rad, respectively. With the help of the full-field response results, we can pre-compensate the TFLN-IM for the 64 Gbaud PAM-4 signals under the back-to-back (B2B) transmission, achieving a received optical power (ROP) gain of 2.3 dB. The versatility of our proposed full-field response characterization scheme can extend to various optical transceivers, offering the advantage of low cost, robust operation, and flexible implementation.

Arbitrary-ratio 1 × 2 optical power splitter based on thin-film lithium niobate.

Optical power splitters (OPSs) have been widely used in photonic integrated circuits, but an OPS with a large fabrication tolerance and free choice of power splitting ratio (PSR) is still highly desired for thin-film lithium niobate (TFLN) platform. Here, we propose and experimentally demonstrate several 1 × 2 OPSs with PSRs from 50:50 to 5:95 using TFLN platform. The proposed devices are built by multimode interference structure to achieve a broad bandwidth and large fabrication tolerance. Various PSRs can be obtained by adjusting the geometry structure of the multimode interference region. All of our fabricated devices feature an insertion loss lower than 0.3 dB at the wavelength of 1550 nm, and a PSR variation less than 3% in the range of 1520 nm to 1590 nm.

C-Band optical 90-degree hybrid using thin film lithium niobate.

The integrated optical 90-degree hybrid is a crucial component for coherent receivers. Here, we simulate and fabricate a 4 × 4 multimode interference coupler as a 90-degree hybrid using thin film lithium niobate (TFLN). The device features low loss (0.37 dB), high common mode rejection ratio (over 22 dB), compact footprint, and small phase error (below 2°) within the whole C-band experimentally, which is promising for integration with coherent modulators and photodetectors for TFLN-based high-bandwidth optical coherent transceivers.

The effect of high-fructose corn syrup vs. sucrose on anthropometric and metabolic parameters: A systematic review and meta-analysis.

High-fructose corn syrup (HFCS) has been speculated to have stronger negative metabolic effects than sucrose. However, given the current equivocality in the field, the aim of the present study was to determine the impact of HFCS use compared to sucrose on anthropometric and metabolic parameters. We searched PubMed, Scopus, Cochrane Central and web of sciences, from database inception to May 2022. A random effects model and the generic inverse variance method were applied to assess the overall effect size. Heterogeneity analysis was performed using the Cochran Q test and the I2 index. Four articles, with 9 arms, containing 767 participants were included in this meta-analysis. Average HFCS and sucrose usage equated to 19% of daily caloric intake. Combined data from three studies indicated that HFCS intake does not significantly change the weight (weighted mean difference (WMD): -0.29 kg, 95% CI: -1.34, 0.77, I2 = 0%) when compared to the sucrose group. Concordant results were found for waist circumstance, body mass index, fat mass, total cholesterol (TC), high-density lipoprotein (HDL), low-density lipoprotein (LDL), triglyceride (TG), systolic blood pressure (SBP), and diastolic blood pressure (DBP). Moreover, overall results from three studies indicated a significant increase in CRP levels (WMD: 0.27 mg/l, 95% CI: 0.02, 0.52, I2 = 23%) in the HFCS group compared to sucrose. In conclusion, analysis of data from the literature suggests that HFCS consumption was associated with a higher level of CRP compared to sucrose, whilst no significant changes between the two sweeteners were evident in other anthropometric and metabolic parameters.

Widely tunable O-band lithium niobite/III-V transmitter.

The ever-increasing traffic has been driving the demand for compact, high-speed, and low-power-consumption optical transmitters. Thin-film lithium niobite (TFLN) platforms have emerged as promising photonic integrated solutions for next-generation optical transmitters. In this study, we demonstrated the first widely tunable optical transmitter based on a butt-coupling a TFLN modulator with an electrically pumped tunable laser. The tunable laser exhibited a side-mode suppression ratio of > 60 dB, linewidth of 475 kHz, and wavelength-tuning range of over 40 nm. The TFLN modulator presented a voltage-length product of 2.9 V·cm and an electro-optic response of 1.5 dB roll-off at 50 GHz. The optical transmitter support data rate was as high as 160 Gb/s.

Thermally tunable and efficient second-harmonic generation on thin-film lithium niobate with integrated micro-heater.

In this Letter, we report thermo-optic tunable and efficient second-harmonic generation (SHG) based on an X-cut periodically poled lithium niobate (PPLN) waveguide. By applying an on-chip heater with thermo-isolation trenches and combining a type-0 quasi-phase matching mechanism, we experimentally achieve a high on-chip SHG conversion efficiency of 2500-3000% W-1 cm-2 and a large tuning power efficiency of 94 pm/mW inside a single 5-mm-long straight PPLN waveguide. Our design is for energy-efficient, high-performance nonlinear applications, such as wavelength conversion, highly tunable coherent light sources, and photon-pair generation.

Heterogeneously integrated III-V-on-lithium niobate broadband light sources and photodetectors.

Heterogeneous integration of III-V active devices on lithium niobate-on-insulator (LNOI) photonic circuits enable fully integrated transceivers. Here we present the co-integration of InP-based light-emitting diodes (LEDs) and photodetectors on an LNOI photonics platform. Both devices are realized based on the same III-V epitaxial layers stack adhesively bonded on an LNOI waveguide circuit. The light is evanescently coupled between the LNOI and III-V waveguide via a multiple-section adiabatic taper. The waveguide-coupled LEDs have a 3-dB bandwidth of 40 nm. The photodetector features a responsivity of 0.38 A/W in the 1550-nm wavelength range and a dark current of 9 nA at -0.5 V at room temperature.

1-Pbps orbital angular momentum fibre-optic transmission.

Space-division multiplexing (SDM), as a main candidate for future ultra-high capacity fibre-optic communications, needs to address limitations to its scalability imposed by computation-intensive multi-input multi-output (MIMO) digital signal processing (DSP) required to eliminate the crosstalk caused by optical coupling between multiplexed spatial channels. By exploiting the unique propagation characteristics of orbital angular momentum (OAM) modes in ring core fibres (RCFs), a system that combines SDM and C + L band dense wavelength-division multiplexing (DWDM) in a 34 km 7-core RCF is demonstrated to transport a total of 24960 channels with a raw (net) capacity of 1.223 (1.02) Peta-bit s-1 (Pbps) and a spectral efficiency of 156.8 (130.7) bit s-1 Hz-1. Remarkably for such a high channel count, the system only uses fixed-size 4 × 4 MIMO DSP modules with no more than 25 time-domain taps. Such ultra-low MIMO complexity is enabled by the simultaneous weak coupling among fibre cores and amongst non-degenerate OAM mode groups within each core that have a fixed number of 4 modes. These results take the capacity of OAM-based fibre-optic communications links over the 1 Pbps milestone for the first time. They also simultaneously represent the lowest MIMO complexity and the 2nd smallest fibre cladding diameter amongst reported few-mode multicore-fibre (FM-MCF) SDM systems of >1 Pbps capacity. We believe these results represent a major step forward in SDM transmission, as they manifest the significant potentials for further up-scaling the capacity per optical fibre whilst keeping MIMO processing to an ultra-low complexity level and in a modularly expandable fashion.

Compact substrate-removed thin-film lithium niobate electro-optic modulator featuring polarization-insensitive operation.

A compact polarization-insensitive electro-optic (EO) modulator, which allows the laser and modulator to be located at different locations while using a standard single-mode fiber to interconnect them, is highly desirable for 5G or future 6G wireless networks. Herein, we propose a modulator based on substrate-removed thin-film lithium niobate. The proposed device exhibits a polarization-dependent loss of 0.35 dB and on-chip loss of approximately 2 dB. The polarization insensitivity of the proposed device was experimentally demonstrated using a four-level pulse-amplitude modulation format at 50 Gbaud (100 Gb/ s).

High-performance polarization management devices based on thin-film lithium niobate.

High-speed polarization management is highly desirable for many applications, such as remote sensing, telecommunication, and medical diagnosis. However, most of the approaches for polarization management rely on bulky optical components that are slow to respond, cumbersome to use, and sometimes with high drive voltages. Here, we overcome these limitations by harnessing photonic integrated circuits based on thin-film lithium niobate platform. We successfully realize a portfolio of thin-film lithium niobate devices for essential polarization management functionalities, including arbitrary polarization generation, fast polarization measurement, polarization scrambling, and automatic polarization control. The present devices feature ultra-fast control speeds, low drive voltages, low optical losses and compact footprints. Using these devices, we achieve high fidelity polarization generation with a polarization extinction ratio up to 41.9 dB and fast polarization scrambling with a scrambling rate up to 65 Mrad s-1, both of which are best results in integrated optics. We also demonstrate the endless polarization state tracking operation in our devices. The demonstrated devices unlock a drastically new level of performance and scales in polarization management devices, leading to a paradigm shift in polarization management.

Advances in integrated ultra-wideband electro-optic modulators [Invited].

Increasing data traffic and bandwidth-hungry applications require electro-optic modulators with ultra-wide modulation bandwidth for cost-efficient optical networks. Thus far, integrated solutions have emerged to provide high bandwidth and low energy consumption in compact sizes. Here, we review the design guidelines and delicate structures for higher bandwidth, applying them to lumped-element and traveling-wave electrodes. Additionally, we focus on candidate material platforms with the potential for ultra-wideband optical systems. By comparing the superiority and mechanism limitations of different integrated modulators, we design a future roadmap based on the recent advances.

Electrically pumped widely tunable O-band hybrid lithium niobite/III-V laser.

Significant improvements in the lithium niobate on insulator (LNOI) platform are pushing LNOI-based laser sources to the forefront of integrated photonics. Here, we report the first, to the best of our knowledge, electrically pumped hybrid lithium niobate/III-V laser by butt coupling an InP-based optical gain chip with a LNOI photonic integrated circuit (PIC). In the PIC, a Vernier filter consisting of two LNOI microring resonators is employed to select the lasing wavelength. A wavelength tuning range of more than 36 nm is achieved in the O band. The hybrid laser has a maximum on-chip optical power of 2.5 mW and threshold current density of 2.5kA/cm2. A side mode suppression ratio better than 60 dB is achieved.

Efficient four-way vertical coupler array for chip-scale space-division-multiplexing applications.

We propose and demonstrate a three-dimensional nano-printed four-channel vertical coupler array on the silicon-on-insulator platform for efficient chip-to-multicore fiber coupling. The proposed structure provides less than 1 dB loss in a single lane and around 2-4 dB loss in multicore fiber coupling, over 100 nm 1 dB bandwidth, and large 1 dB misalignment tolerances of more than 5 µm in the xy plane and 20 µm in the z direction. The device shows great promise for photonic integrated devices for space-division-multiplexing technology based on multicore fiber.

Folded Heterogeneous Silicon and Lithium Niobate Mach-Zehnder Modulators with Low Drive Voltage.

Optical modulators were, are, and will continue to be the underpinning devices for optical transceivers at all levels of the optical networks. Recently, heterogeneously integrated silicon and lithium niobate (Si/LN) optical modulators have demonstrated attractive overall performance in terms of optical loss, drive voltage, and modulation bandwidth. However, due to the moderate Pockels coefficient of lithium niobate, the device length of the Si/LN modulator is still relatively long for low-drive-voltage operation. Here, we report a folded Si/LN Mach-Zehnder modulator consisting of meandering optical waveguides and meandering microwave transmission lines, whose device length is approximately two-fifths of the unfolded counterpart while maintaining the overall performance. The present devices feature a low half-wave voltage of 1.24 V, support data rates up to 128 gigabits per second, and show a device length of less than 9 mm.

Low-loss edge-coupling thin-film lithium niobate modulator with an efficient phase shifter: publisher's note.

This publisher's note contains corrections to Opt. Lett.46, 1478 (2021)OPLEDP0146-959210.1364/OL.418996.

Low-loss edge-coupling thin-film lithium niobate modulator with an efficient phase shifter.

Thin-film lithium-niobate-on-insulator (LNOI) is a very attractive platform for optical interconnect and nonlinear optics. It is essential to enable lithium niobate photonic integrated circuits with low power consumption. Here we present an edge-coupling Mach-Zehnder modulator on the platform with low fiber-chip coupling loss of 0.5 dB/facet, half-wave voltage Vπ of 2.36 V, electro-optic (EO) bandwidth of 60 GHz and an efficient thermal-optic phase shifter with half-wave power of 6.24 mW. In addition, we experimentally demonstrate single-lane 200 Gbit/s data transmission utilizing a discrete multi-tone signal. The LNOI modulator demonstrated here shows great potential in energy-efficient large-capacity optical interconnects.

Implementing graph-theoretic quantum algorithms on a silicon photonic quantum walk processor.

Applications of quantum walks can depend on the number, exchange symmetry and indistinguishability of the particles involved, and the underlying graph structures where they move. Here, we show that silicon photonics, by exploiting an entanglement-driven scheme, can realize quantum walks with full control over all these properties in one device. The device we realize implements entangled two-photon quantum walks on any five-vertex graph, with continuously tunable particle exchange symmetry and indistinguishability. We show how this simulates single-particle walks on larger graphs, with size and geometry controlled by tuning the properties of the composite quantum walkers. We apply the device to quantum walk algorithms for searching vertices in graphs and testing for graph isomorphisms. In doing so, we implement up to 100 sampled time steps of quantum walk evolution on each of 292 different graphs. This opens the way to large-scale, programmable quantum walk processors for classically intractable applications.

Reconfigurable silicon bandpass filters based on cascaded Sagnac loop mirrors.

We demonstrate a high-performance reconfigurable bandpass filter implemented by cascaded Sagnac loop mirror (SLM)-based coupled resonator optical waveguides (CROWs) on the silicon-on-insulator platform. By dynamic thermal tuning of the reflectivity in each SLM, the proposed filter can achieve simultaneous 3 dB bandwidth tuning from 8.50 to 20.25 GHz and a central wavelength tuning range of 216.25 GHz. A box-like filtering response with an ultra-high extinction ratio up to 70 dB and an ultra-sharp roll-off of 0.61 are observed in a 6th-order SLM-coupled resonator optical waveguide (SLM-CROW). The proposed reconfigurable SLM-CROW filter can satisfy the demand for next-generation flexible-grid WDM networks.

Highly efficient thermo-optic tunable micro-ring resonator based on an LNOI platform: publisher's note.

This publisher's note contains corrections to Opt. Lett.45, 6318 (2020)OPLEDP0146-959210.1364/OL.410192.