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In this paper, we demonstrate up to 260-GBaud single-wavelength coherent transmission by employing an optical transmitter based on two wide-bandwidth devices: a novel 260-GS/s arbitrary waveform generator with a 10-dB bandwidth of 90-GHz and a thin-film Lithium Niobate I/Q modulator with a 3-dB bandwidth of 110-GHz. We first assess the performance of our high symbol rate transmitter for generating spectrally efficient Nyquist multilevel modulation format signals at symbol rates up to 210-GBaud with >1.4-Tbps achievable information rates and by using linear digital signal processing only. We achieve up to 1.84-Tbps at 185-GBaud using PCS-64QAM, highlighting the linear behavior of our transmitter for high symbol rate Nyquist signaling. We then switch to dual-polarization QPSK coherent transmission and further increase the symbol rate up to 260-GBaud. Without using nonlinear digital-signal-processing nor advanced inter-symbol-interference mitigation techniques, we successfully transmit 260-GBaud QPSK at 800-Gbps net rate over 100-km of standard single mode fiber.

As the broadband applications continue rising, the solutions of high-speed passive optical network (PON) with large power budget are highly desired. Direct detection scheme combined with digital signal procession (DSP) has been considered as a promising candidate due to its low cost, low power consumption and simple architecture. In this paper, we experimentally demonstrate 200 Gb/s/λ and 240 Gb/s/λ time division multiplexed passive optical network (TDM-PON) downstream transmissions based on four-level pulsed amplitude (PAM-4) modulation with direct detection in O-band. A high bandwidth thin film lithium niobate modulator is adopted to generate high Baudrate optical signal at the optical line terminal (OLT) side. A pre-amplified semiconductor optical amplifier SOA is employed at the optical network unit (ONU) side to improve the power budget. Several DSP algorithms are studied to compensate the linear and nonlinear distortions. We also propose a simplified Volterra nonlinear equalizer (S-VNLE) to reduce the computational complexity. Considering the soft-decision FEC (SD-FEC) threshold (1 × 10−2), over 29 dB and 28 dB power budgets are achieved respectively for 200 Gb/s/λ and 240 Gb/s/λ PON system after 20 km standard single mode fiber (SSMF) based on our proposed S-VNLE.

Optical vortices carrying orbital angular momentum (OAM) have recently attracted increasing interest for providing an additional degree of freedom for capacity scaling in optical communications. The optical vortex generator is an essential component to facilitate OAM-enabled optical communications. Traditional devices face challenges of limited compactness, narrow bandwidth, and first-order OAM modes. Here, using the direct-binary search (DBS) optimization algorithm, we design, fabricate, and demonstrate a digitized subwavelength surface structure on silicon platform for the generation of wavelength-/polarization-/charge-diverse optical vortices. It features an ultra-compact footprint (∼3.6 × 3.6 μm2) and ultra-wide bandwidth (1480–1630 nm), supporting two polarizations (x-pol., y-pol.) and high-order OAM modes (OAM+1, OAM−1, OAM+2, OAM−2) with high purity of larger than 84%. The mode crosstalk matrix is measured in the experiment with favorable performance. When generating x-pol. OAM+1, x-pol. OAM−1, y-pol. OAM+1, and y-pol. OAM−1mode, the crosstalk of the worst case is less than −14 dB. When generating OAM+1, OAM−1, OAM+2, and OAM−2mode, the crosstalk between any two OAM modes is less than −10 dB, and the lowest crosstalk is about −17 dB. In addition, we also show the possibility for generating much higher-order OAM modes (e.g. OAM+3, OAM−3, OAM+4, and OAM−4) with the digitized subwavelength surface structure. The wavelength-/polarization-/charge-diverse optical vortex generator enables the full access of multiple physical dimensions (wavelength, polarization, space) of lightwaves. The demonstrations may open up new perspectives for chip-scale solutions to multi-dimensional multiplexing optical communications.

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).

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/cm^2. A side mode suppression ratio better than 60 dB is achieved.

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.

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 V_π 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.

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.

We demonstrate a high-efficiency thermo-optic (TO) tunable micro-ring resonator in thin-film lithium niobate. Thermal insulation trenches around the heated micro-ring resonator and the underlying silicon substrate significantly reduce the heating power consumption and improve the tuning efficiency. Compared to conventional TO devices without thermal insulation trenches, the proposed device achieves a full free spectral range wavelength shift with a 14.9 mW heating power, corresponding to a thermal tuning efficiency of 53.7 pm/mW, a more than 20-fold improvement of tuning efficiency. The approach enables energy-efficient high-performance TO devices such as optical switches, wavelength routers, and other reconfigurable photonic devices.

In this study, we provide a theoretical overview for the potential of the integrated vortex beam emitter (IVBE) in optical tweezer applications. To the best of our knowledge, this is the first attempt in the literature to investigate the optical tweezing property of IVBE. The finite-difference time-domain numerical analysis technique has been utilized for the transverse optical trapping calculations. The results show that the basic IVBE device generates an optical force of an order of ${{10}^{ - 16}}\;{\rm N}$10^−16N, which can be increased up to ${{10}^{ - 15}}\;{\rm N}$10^−15N with the duty cycle adjustment. Therefore, this work emphasizes that the IVBE device can provide a compact, efficient, low-cost, and practical optical tweezing ability.

Vortex beams carrying orbital angular momentum have attracted a great deal of attention over the past few years. An integrated vortex beam generator with high efficiency is desirable for wide-ranging applications. Here we demonstrate a highly efficient silicon photonic integrated vortex beam generator based on superposed holographic fork gratings. A metal mirror is used to enhance emission efficiency by reflecting the power leaking down to the substrate back to air. Experimental characterization confirms that the emission efficiency of the generator increases by ${\sim} 5\,{\rm dB}$∼5dB. Moreover, the present device shows preferable features of broadband, polarization diversity, and compact footprint.

We propose and demonstrate a low-loss fiber-to-chip vertical coupler on the silicon photonic platform by using a 3D two-photon fabrication method. Such a coupler significantly reduces insertion loss, measured to be 1 dB, and provides a wide working wavelength range for both TE and TM polarizations over the entire C-band. Moreover, a large tolerance for misalignment of the coupling fiber, up to 4.5 µm for a 1 dB loss, enables the development of relaxed alignment techniques.

We experimentally demonstrate a high-spectral-purity photon source by designing a dual-Mach–Zehnder-interferometer-coupled silicon ring resonator, wherein the linewidths of pump and signal (idler) resonances can be engineered independently. A high spectral purity of $ 95\% \pm 1.5\% $95%±1.5% is obtained via a time-integrated $ {g^{(2)}} $g^(2) correlation measurement, which exceeds the theoretical 93% bound of a traditional ring’s spontaneous four-wave-mixing photon source. This source also possesses high performance in other metrics including a measured coincidence of 9599 pairs/s and a preparation heralding efficiency of 52.4% at a relatively low pump power of 61 µW as well as high drop-to-through suppression of 20.2 dB. By overcoming the trade-off between spectral purity and brightness in the post-filtering way, such a method guarantees bright pure photons and will pave the way for development of on-chip quantum information processing with improved operation fidelity and efficiency.

Optical modulators are at the heart of optical communication links. Ideally, they should feature low loss, low drive voltage, large bandwidth, high linearity, compact footprint and low manufacturing cost. Unfortunately, these criteria have been achieved only on separate occasions. Based on a silicon and lithium niobate hybrid integration platform, we demonstrate Mach–Zehnder modulators that simultaneously fulfil these criteria. The presented device exhibits an insertion loss of 2.5 dB, voltage–length product of 2.2 V cm in single-drive push–pull operation, high linearity, electro-optic bandwidth of at least 70 GHz and modulation rates up to 112 Gbit s−1. The high-performance modulator is realized by seamless integration of a high-contrast waveguide based on lithium niobate—a popular modulator material—with compact, low-loss silicon circuitry. The hybrid platform demonstrated here allows for the combination of ‘best-in-breed’ active and passive components, opening up new avenues for future high-speed, energy-efficient and cost-effective optical communication networks.

Compact and broadband manipulation of spatial modes is important in applications exploiting the space domain of light waves. Here, we demonstrate chip-scale generation and synthesization of ultrabroadband orbital angular momentum (OAM) modes (twisted light) on a silicon platform. By introducing a subwavelength holographic fork grating on top of a silicon waveguide, the in-plane guided mode is converted to the free-space OAM mode. Inputs from both sides of the waveguide enable the synthesization of OAM modes. We also characterize wavelength-dependent emission efficiency, offset angle, and purity with favorable performance. The chip-scale ultrabroadband OAM generator and synthesizer may find potential applications in multidimensional optical communications and quantum key distribution.

We design and fabricate a low-loss silicon photonic two-dimensional grating coupler that serves to couple light between standard single-mode fibers and single-mode waveguides in the silicon-on-insulator platform and to split both orthogonal polarization states. The efficiency of the fabricated device is enhanced by a backside metal mirror and reaches a record value of −1.8  dB with a 1 dB bandwidth of 32 nm around 1550 nm. The demonstrated coupling efficiency is 2.2 dB better than the conventional two-dimensional grating coupler without a metal mirror.

A novel concept to generate a linear chirped microwave signal is proposed and experimentally demonstrated. The frequency to time mapping method is employed, where the photonic crystal waveguide Mach–Zehnder interferometer structure acts as the spectral shaper thanks to the slow light effect. By optimizing the structural parameters of the photonic crystal waveguide, a linear chirped microwave signal with the time-bandwidth product of about 30 is experimentally obtained. The impact of the slow light photonic crystal waveguide on the generated linear chirped microwave signal is also investigated. The utilization of the slow light effect brings in significant advantages, including the ultra-small footprint of 0.096  mm^2 and simple structure to our scheme, which may be of great importance towards its potential applications.

Integrated devices that emit light beams with orbital angular momentum (OAM) are becoming key components for wide-ranging applications. Here we propose and demonstrate a highly directional silicon photonic vortex beam emitter based on a 3-turn Archimedean spiral adiabatic waveguide integrated with an angular grating. Such a compact emitter is capable of generating vortex beams with small divergence angles and high directivity. Various orders of OAM modes can be selectively generated by the emitter at different wavelengths with a side-mode suppression ratio as large as 13.6 dB.

We report, to our knowledge, the first dual-polarization thin-film lithium niobate coherent modulator for next-generation optical links with sub-1-V driving voltage and 110-GHz bandwidth, enabling a record single-wavelength 1.96-Tb/s net data rate with ultrahigh energy efficiency.

Emerging applications based on optical beams carrying orbital angular momentum (OAM) will likely require photonic integrated devices and circuits for miniaturization, improved performance and enhanced functionality. This paper reviews the state-of-the art in the field of OAM of light, reports recent developments in silicon integrated OAM emitters, and discusses the applications potentials and challenges in silicon integrated OAM devices which can be used in future OAM based optical communications systems.

In this paper, we proposed and experimentally demonstrated a route-asymmetrical light transmission scheme based on the thermal radiative effect, which means that forward and backward propagations of an optical device have different transmittances provided they are not present simultaneously. Employing a fiber-chip-fiber optomechanical system, our scheme has successfully achieved a broad operation bandwidth of at least 24 nm and an ultra-high route-asymmetrical transmission ratio (RATR) up to 63 dB. The route-asymmetrical device has been demonstrated effectively with not only the continuous- wave (CW) light but also 10 Gbit/s on-off-keying (OOK) digital signals. Above mentioned unique features can be mostly attributed to the significant characteristics of the thermal radiative effect, which could cause a fiber displacement up to tens of microns. The powerful and significant thermal radiative effect opens up a new opportunity and method for route-asymmetrical light transmission. Moreover, this research may have important applications in all-optical systems, such as the optical limiters and ultra-low loss switches.

Optical vortices (OVs) refer to a class of cylindrical optical modes with azimuthally varying phase terms arising either from polarization rotation or from the angular projection of the wave vector that at the quantum level corresponds to photon spin or orbital angular momenta. OVs have attracted the attention of researchers in many areas of optics and photonics, as their potential applications range from optical communications, optical manipulation, imaging, sensing, to quantum information. In recent years, integrated photonics has becomes an effective method of manipulating OVs. In this paper, the theoretical framework and experimental progress of integrated photonics for the manipulation of OVs were reviewed.

We experimentally demonstrate and evaluate the performance of an analog signal transmission system with photonic integrated optical vortex emitter and 3.6-km few-mode fiber (FMF) link using orbital angular momentum (OAM) modes. The fabricated photonic integrated device is capable of emitting vector optical vortices carrying well-defined and quantized OAM modes with topological charge l=−2 and 2. After propagating through 3.6-km FMF, we measure and assess the spurious free dynamic range of the second-order harmonic distortion. Moreover, we study the impact of nonlinearity-induced resonance wavelength shift of the optical vortex emitter on the analog link performance as increasing the input optical power.

The generation of light beams carrying orbital angular momentum (OAM) has been greatly advanced with the emergence of the recently reported integrated optical vortex emitters. Generally, optical vortices emitted by these devices possess cylindrically symmetric states of polarization and spiral phase fronts, and they can be defined as cylindrical vector vortices (CVVs). Using the radiation of angularly arranged dipoles to model the CVVs, these beams as hybrid modes of two circularly polarized scalar vortices are theoretically demonstrated to own well-defined total angular momentum. Moreover, the effect of spin–orbit interactions of angular momentum is identified in the CVVs when the size of the emitting structure varies. This effect results in the diminishing spin component of angular momentum and purer OAM states at large structure radii.

Emerging applications based on optical beams carrying orbital angular momentum will likely require photonic integrated devices and circuits for miniaturization, improved performance and enhanced functionality. This paper reviews the state-of-the-art in the field of orbital angular momentum of light, reports recent developments in silicon integrated orbital angular momentum emitters, and discusses the applications potentials and challenges in applying orbital angular momentum of light in optical communications, quantum information systems, and optical sensing, imaging, and manipulation systems.

Periodically poled lithium niobate on insulator (LNOI) ridge waveguides are desirable for high-efficiency nonlinear frequency conversions, and the fabrication process of such waveguides is crucial for device performance. In this work, we report fabrication and characterization of locally periodically poled ridge waveguides. Ridge waveguides were fabricated by dry etching, and then the high-voltage pulses were applied to locally poled ridge waveguides. Second harmonic generation with normalized conversion efficiency of 435.5% W^−1·cm^−2 was obtained in the periodically poled LNOI ridge waveguide, which was consistent with the triangular domain structure revealed by confocal microscopy.

We propose and demonstrate a polarization diversity two-dimensional grating coupler based on the lithium niobate on insulator platform, for the first time, to the best of our knowledge. The optimization design, performance characteristics, and fabrication tolerance of the two-dimensional grating coupler are thoroughly analyzed utilizing the three-dimensional finite-difference time-domain method. Experimentally, −7.2?dB of coupling efficiency is achieved with 1 dB bandwidth of 64 nm. The polarization-dependent loss is about 0.4 dB around 1550 nm. Our work provides new polarization multiplexing approaches for the lithium niobate on insulator platform, paving the way for critical applications such as high-speed polarization multiplexed electro-optical modulators.

We study the effect of dimension variation for second-harmonic generation (SHG) in lithium niobate on insulator (LNOI) waveguides. Non-trivial SHG profiles in both type-0 and type-I quasi-phase matching are observed during the wavelength tuning of the fundamental light. Theoretical modeling shows that the SHG profile and efficiency can be greatly affected by the waveguide cross-section dimension variations, especially the thickness variations. In particular, our analysis shows that a thickness variation of tens of nanometers is in good agreement with the experimental results. Such investigations could be used to evaluate fabrication performance of LNOI-based nonlinear optical devices.

Integrated traveling-wave lithium niobate modulators need relatively large device lengths to achieve low drive voltage. To increase modulation efficiency within a compact footprint, we report an integrated Fabry–Perot-type electro-optic thin film lithium niobate on insulator modulator comprising a phase modulation region sandwiched between two distributed Bragg reflectors. The device exhibits low optical loss and a high tuning efficiency of 15.7 pm/V. We also confirm the modulator’s high-speed modulation performance by non-return-to-zero modulation with a data rate up to 56 Gbit/s.

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

We develop a theoretical model for the recently reported integrated optical vortex beam emitters that incorporate angular gratings in microring resonators. Using azimuthally polarized dipole oscillators to represent emissions scattered from the grating elements that are located along the inner wall of the ring waveguide, we obtain expressions for far-field components under the paraxial approximation. The results show that the emission is of the form of cylindrical vector Bessel beams with exactly defined optical orbital angular momentum, and can have azimuthal, radial, and longitudinal field components after propagation. The calculation results for field distributions in both near and far zone agree well with the experimental results.

This publisher’s note contains corrections to Opt. Lett.45, 1607 (2020)OPLEDP0146-959210.1364/OL.385878.