High-speed Modulation Research Articles

Ghost imaging based on Fermat spiral laser array designed for remote sensing.

We propose a Fermat spiral laser array as illumination source in ghost imaging. Due to the aperiodic structure, the Fermat spiral laser array generates illuminating light field without spatial periodicity on the normalized second-order intensity correlation function. A single-pixel detector is used to receive the signal light from object for image reconstruction. The effects of laser array parameters on the quality of ghost imaging are analyzed comprehensively. Through experimental demonstration, the Fermat spiral laser array successfully achieves ghost imaging with high quality by combining with the compressive sensing reconstruction algorithm. This method is expected to be applied in remote sensing by combining with phased and collimated fiber laser array equipped with the high emitting power and high-speed modulation frequency.

Hybrid silicon-organic Huygens' metasurface for phase modulation.

Spatial light modulators have desirable applications in sensing and free space communication because they create an interface between the optical and electronic realms. Electro-optic modulators allow for high-speed intensity manipulation of an electromagnetic wavefront. However, most surfaces of this sort pose limitations due to their ability to modulate intensity rather than phase. Here we investigate an electro-optic modulator formed from a silicon-organic Huygens' metasurface. In a simulation-based study, we discover a metasurface design immersed in high-performance electro-optic molecules that can achieve near-full resonant transmission with phase coverage over the full 2π range. Through the electro-optic effect, we show 140 ∘ (0.79π) modulation over a range of -100 to 100 V at 1330 nm while maintaining near-constant transmitted field intensity (between 0.66 and 0.8). These results potentiate the fabrication of a high-speed spatial light modulator with the resolved parameters.

A Sub-Terahertz High-Speed Traveling-Wave Switch Modulator Based on Dynamically Tunable Double-Resonant Coupling Units

High-speed direct modulation devices are of great significance for the development of high-speed communication systems with large bandwidth, miniaturization, and low complexity. However, an increase in the carrier frequency in the sub-terahertz band and above will negatively impact high-performance direct modulation devices due to the large insertion loss and low on–off ratio. Based on the traveling-wave modulation mechanism, this article adopts the zero-phase-difference amplitude modulator design method. More specifically, a 1- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m small anode Schottky diode is combined with a Z-type matching structure to form a dual-resonant coupling dynamic tunable unit. Interunit coupling is found to further improve the on–off ratio. In this way, high-speed dynamic modulation is performed for the transmission traveling-wave amplitude with low insertion loss and a high on–off ratio. On this basis, a 0.14-THz on–off keying (OOK) high-speed traveling-wave modulator is proposed, and our results showed that a on–off ratio of 25.4 dB could be achieved at the zero-phase-difference point by only using two dynamic structural units. Meanwhile, the control voltage could be adjusted to achieve high-speed modulation with a phase difference of only 3.66 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^\circ$</tex-math> </inline-formula> during the entire control voltage transition, a data rate of 24 Gb/s, and 33.99% sidebands occupation.

Si3N4-plasmonic ferroelectric MZIR modulator for 112-Gbaud PAM-4 transmission in the O-band.

This paper presents a simulation-based analysis on the performance of plasmonic ferroelectric Mach-Zehnder in a ring (MZIR) versus symmetric Mach-Zehnder modulators (MZMs) on Si3N4 targeting O-band operation. The detailed investigation reveals the tradeoff between Au and Ag legacy noble metals providing lower modulator losses and CMOS compatible Cu featuring low cost. The numerical models also show that by opting for the MZIR layout there is a reduction in the Vπ x L product of 46% for Ag, 39% for Au and 30% for Cu versus MZMs. Time-domain simulations verify the successful generation of 112 Gbaud PAM-4 Signals from both MZIRs and MZMs for as low as 2 × 1.3 Vpp and 5µm long plasmonic phase shifters (PSs) with MZIRs providing a ΔQ signal improvement over MZMs of 2.9, 2.4, and 1.3 for Ag, Au, and Cu metals respectively. To the best of our knowledge, this is the first theoretical demonstration of such a low-loss, low-voltage, high-speed, and CMOS compatible plasmonic modulator on Si3N4, in the O-band.

High-speed electro-optic modulation in topological interface states of a one-dimensional lattice

Electro-optic modulators are key components in data communication, microwave photonics, and quantum photonics. Modulation bandwidth, energy efficiency, and device dimension are crucial metrics of modulators. Here, we provide an important direction for the miniaturization of electro-optic modulators by reporting on ultracompact topological modulators. A topological interface state in a one-dimensional lattice is implemented on a thin-film lithium-niobate integrated platform. Due to the strong optical confinement of the interface state and the peaking enhancement of the electro-optic response, a topological cavity with a size of 1.6 × 140 μm2 enables a large modulation bandwidth of 104 GHz. The first topological modulator exhibits the most compact device size compared to reported LN modulators with bandwidths above 28 GHz, to the best of our knowledge. 100 Gb/s non-return-to-zero and 100 Gb/s four-level pulse amplitude modulation signals are generated. The switching energy is 5.4 fJ/bit, owing to the small electro-optic mode volume and low capacitance. The topological modulator accelerates the response time of topological photonic devices from the microsecond order to the picosecond order and provides an essential foundation for the implementation of large-scale lithium-niobate photonic integrated circuits.

Tunable quasi-supercontinuum generation in a 1.7 µm spectral band for spectral domain optical coherence tomography

We present a system for generating a 1.7 µm quasi-supercontinuum (SC) as what we believe to be a new broadband light source for spectral domain (SD) optical coherence tomography (OCT). The quasi-SC source, whose spectral range and spectral shape can be arbitrarily changed, is based on wavelength-tunable soliton pulse generation and high-speed intensity modulation. A Gaussian-shaped quasi-SC was introduced into an SD-OCT system. A maximum axial resolution of 14 µm in air (corresponding to 10 µm in tissue) and an imaging sensitivity of 94 dB was obtained. We also demonstrated high-resolution imaging for tape stack, human nail and pig thyroid gland samples using a quasi-SC. From these results, we confirmed the usefulness of a quasi-SC for SD-OCT imaging.

Plasmonic metafibers electro-optic modulators

Digitalizing optical signals through electric driving signals, electro-optic modulators (EOMs) are one of the cardinal elements in modern optical communications. Most of current EOM devices are targeting on-chip integrations, which routinely suffer from high coupling losses, complex optical alignments and single-band operations. In this study, we for the first time integrate a lumped EOM device on the endfaces of a single-mode optical fiber jumper for fast amplitude modulations. Profiting from ultrathin and high quality-factor plasmonic metasurfaces, nanofabrication-friendly and highly efficient EO polymers and coupling-free connections with fiber networks, our EOM is demonstrated to allow dual-band operations (telecom O band and S band) and high-speed modulations (~1 GHz at a bias voltage of ±9 V). This work offers an avenue to ‘plug-and-play’ implementations of EO devices and ultracompact “all-in-fibers” optical systems for communications, imaging, sensing and many others.

High-speed mid-infrared graphene electro-optical modulator based on suspended germanium slot waveguides.

The mid-infrared (MIR) region is attracting increasing interest for on-chip synchronous detection and free-space optical (FSO) communications. For such applications, a high-performance electro-optical modulator is a crucial component. In this regard, we propose and investigate a graphene-based electro-absorption modulator (EAM) and microring modulator (MRM) using the suspended germanium waveguide platform. The modulators are designed for the second atmospheric window (8 to 12 µm). The incorporation of double-layer graphene on the suspended slot waveguide structure allows for the significant enhancement of light-graphene interaction, theoretically achieving a 3-dB bandwidth as high as 78 GHz. The EAM shows a calculated modulation depth of 0.022-0.045 dB/µm for the whole operation wavelength range. The MRM exhibits a calculated extinction ratio as high as 68.9 dB and a modulation efficiency of 0.59 V·cm around 9 µm. These modulators hold promise for constructing high-speed FSO communication and on-chip spectroscopic detection systems in the MIR atmospheric window.

Discovery of enhanced lattice dynamics in a single-layered hybrid perovskite.

Layered hybrid perovskites exhibit emergent physical properties and exceptional functional performances, but the coexistence of lattice order and structural disorder severely hinders our understanding of these materials. One unsolved problem regards how the lattice dynamics are affected by the dimensional engineering of the inorganic frameworks and their interaction with the molecular moieties. Here, we address this question by using a combination of spontaneous Raman scattering, terahertz spectroscopy, and molecular dynamics simulations. This approach reveals the structural dynamics in and out of equilibrium and provides unexpected observables that differentiate single- and double-layered perovskites. While no distinct vibrational coherence is observed in double-layered perovskites, an off-resonant terahertz pulse can drive a long-lived coherent phonon mode in the single-layered system. This difference highlights the dramatic change in the lattice environment as the dimension is reduced, and the findings pave the way for ultrafast structural engineering and high-speed optical modulators based on layered perovskites.

A Novel Silicon Forward-Biased PIN Mach-Zehnder Modulator with Two Operating States.

In this paper, we demonstrate a silicon forward-biased positive intrinsic negative (PIN) Mach-Zehnder modulator (MZM), which has two operating states of high efficiency and high speed. The two operating states are switched by changing the position where the electric signal is loaded. The modulator incorporates a PIN phase shifter integrated with the passive resistance and capacitance (RC) equalizer (PIN-RC), which expands the electro-optic (E-O) bandwidth by equalizing it with modulation efficiency. The fabricated modulator exhibits a low insertion loss of 1.29 dB in two operating states and a compact design with a phase shifter length of 500 μm. The modulation efficiencies are 0.0088 V·cm and 1.43 V·cm, and the corresponding 3 dB E-O bandwidths are 200 MHz and 7 GHz, respectively. The high-speed modulation performance of the modulator is confirmed by non-return-to-zero (NRZ) modulation with a data rate of 15 Gbps without any pre-emphasis or post-processing. The presented modulator shows functional flexibility, low insertion loss, and a compact footprint, and it can be suitable for applications like optical switch arrays and analog signal processing.

Heterogeneous integration of a high-speed lithium niobate modulator on silicon nitride using micro-transfer printing

Integrated photonic systems require fast modulators to keep up with demanding operation speeds and increasing data rates. The silicon nitride integrated photonic platform is of particular interest for applications such as datacom, light detection and ranging (LIDAR), quantum photonics, and computing owing to its low losses and CMOS compatibility. Yet, this platform inherently lacks high-speed modulators. Heterogeneous integration of lithium niobate on silicon nitride waveguides can address this drawback with its strong Pockels effect. We demonstrate the first high-speed lithium niobate modulator heterogeneously integrated on silicon nitride using micro-transfer printing. The device is 2 mm long with a half-wave voltage Vπ of 14.8 V. The insertion loss and extinction ratio are 3.3 and 39 dB, respectively. Operation beyond 50 GHz has been demonstrated with the generation of open eye diagrams up to 70 Gb/s. This proof-of-principle demonstration opens up possibilities for more scalable fabrication of these trusted and performant devices.

Simulating tunable coherence for scattered light suppression in laser-interferometric gravitational wave detectors

Ground-based gravitational wave detectors use laser interferometry to realize ultra-precise displacement measurements between free-floating test masses to detect signals in the frequency band of 10 Hz to 10 kHz. Light scattered out of and back into the main beam path creates noise in these detectors that non-linearly up-converts low-frequency, out-of-band signals into the measurement band. This scattered light induced noise becomes more relevant as the sensitivity at lower frequencies is improved in current and future detectors. To suppress this noise source, we study how the strong spatial coherence of the laser light can be reduced to a few centimeters by introducing high-speed pseudo-random noise phase modulations into the Michelson interferometer topology. We simulate the interferometer signals in the presence of scattered light in the time domain. Our simulations show that tuning of the coherence can reduce the coupling of scattered light by orders of magnitude, and that the phase modulations are, in principle, compatible with resonant cavities that are employed in the complex interferometer topologies of modern detectors to achieve ultra-low quantum noise levels. We outline the currently expected limitations of this approach and discuss the applicability to detectors.

High-Performance Monolithic Integration of III-V QD Lasers on Si Substrates

With the development of digital processes, the speed and efficiency of information exchange has increased to a great extent. Silicon-based photonics allows for large-scale photonic integration through CMOS manufacturing processes, the advantages of which lie in the low cost, low energy consumption and high quality of such processes. Currently, silicon-based monolithic integrated quantum dot lasers have achieved lifetimes comparable to those of heterogeneous integrated lasers and are even available for commercial applications. The silicon photonic platform also offers low-loss passive devices, as well as high-speed optical modulators and photodetectors. However, device performance suffers due to differences in physical properties between group III-V lasers and substrate materials, an important factor limiting the development of silicon-based monolithic integrated quantum dot lasers. This paper reviews the respective characteristics of silicon-based monolithic and heterogeneous integration. The advantages of monolithically integrated III-V quantum dot lasers over heterogeneous integration are highlighted, as well as the challenges, solutions and recent developments.

An Ultrabroadband and Cost-Effective Edge Coupler for Efficient Thin Film Lithium Niobate Photonics

Due to attractive material properties, thin film lithium niobate (TFLN) has emerged as a promising platform for advanced photonic functions such as high-speed electro-optical modulation, nonlinear frequency conversion, and frequency comb generation. The inevitable problems for the practical above-mentioned applications are the large coupling loss between the fiber and the TFLN waveguide and difficulty in achieving broadband coupling, especially covering the near-visible to near-infrared. Here, we theoretically propose a low-loss and ultrabroadband edge coupler with a six-layer structure. For transverse electric (TE) polarized light, the proposed coupler can achieve 0.62 dB, 0.38 dB, and 0.47 dB per facet at three common communication bands, 845 nm, 1310 nm, and 1550 nm, respectively. From 1200 nm to 2000 nm, the coupling loss is less than 1 dB/facet. Moreover, in the near-visible to near-infrared region ranging from 845 nm to 2000 nm, the coupling loss is lower than 2 dB/facet. The proposed coupler can avoid expensive electron beam lithography. Instead, it can be fabricated by i-line ultraviolet lithography, which is cost-effective and adaptable to wafer-scale fabrication. Also, simulated fabrication tolerances demonstrate the strong robustness of the proposed coupler. Our results pave a way towards practical TFLN photonic devices connected with optical fibers.

Integrated lithium niobate optical phased array for two-dimensional beam steering.

Optical phased arrays (OPAs) with high speed, low power consumption, and low insertion loss are appealing for various applications, including light detection and ranging, free-space communication, image projection, and imaging. These OPAs can be achieved by fully harnessing the advantages of integrated lithium niobate (LN) photonics, which include high electro-optical modulation speed, low driving voltage, and low optical loss. Here we present an integrated LN OPA that operates in the near-infrared regime. Our experimental results demonstrate 24 × 8° two-dimensional beam steering, a far-field beam spot with a full width at half maximum of 2 × 0.6°, and a sidelobe suppression level of 10 dB. Furthermore, the phase modulator of our OPA exhibits a half-wave voltage of 6 V. The low power consumption exhibited by our OPA makes it highly attractive for a wide range of applications. Beyond conventional applications, our OPA's high speed opens up the possibility of novel applications such as high-density point cloud generation and tomographic holography.

Reliable micro-transfer printing method for heterogeneous integration of lithium niobate and semiconductor thin films

High-speed Pockels modulation and second-order nonlinearities are key components in optical systems, but CMOS-compatible platforms like silicon and silicon nitride lack these capabilities. Micro-transfer printing of thin-film lithium niobate offers a solution, but suspending large areas of thin films for long interaction lengths and high-Q resonators is challenging, resulting in a low transfer yield. We present a new source preparation method that enables reliable transfer printing of thin-film lithium niobate. We demonstrate its versatility by successfully applying it to gallium phosphide and silicon, and provide an estimate of the transfer yield by subsequently printing 25 lithium niobate films without fail.

Plasmonic Ferroelectric Modulator Monolithically Integrated on SiN for 216 GBd Data Transmission

A high-speed plasmonic barium titanate (BTO, BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) Mach-Zehnder modulator is presented. We combine nanoscale plasmonics with BTO as solid-state active material and silicon nitride (SiN) for versatile and low loss waveguiding, and integrate them in a monolithic platform. We demonstrate a plasmonic BTO modulator processed onto foundry-produced SiN. The 15 µm long high-speed modulator features a flat electro-optic frequency response up to 70 GHz and is expected to be flat way beyond. A low V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> L product of 144 Vµm is shown. Data experiments reaching 216 Gbit/s with a 216 GBd 2PAM signal and 256 Gbit/s with a 128 GBd 4PAM signal are demonstrated. The merger of the versatile silicon nitride platform with high-speed plasmonics using the highly nonlinear ferroelectric BTO is an attractive solution as a future Tb/s optical interconnect platform.

Micro-Transfer-Printed Membrane Distributed Reflector Lasers on Si Waveguide Modulated With 50-Gbit/s NRZ Signal

In this work, we fabricate directly modulated membrane distributed reflector (DR) lasers on a Si waveguide by utilizing micro-transfer printing method. Micro-transfer printing enables low-loss coupling between the lasers and the silicon photonics circuit, and since it is a back-end process, we can test the lasers prior to integration. A membrane laser is as thick as the Si waveguides, which makes optical coupling between the two quite easy. In addition, membrane lasers with a lateral <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-i-n</i> diode structure have low capacitance and a large optical confinement factor, which means they can achieve a low threshold current and high-speed modulation operation with low energy consumption. The fabricated membrane DR laser integrated with a 220-nm-thick Si waveguide exhibits a low threshold current of 1.2 mA and single-mode operation at 1535 nm with a side-mode suppression ratio (SMSR) of about 40 dB at the bias current of 14 mA. It also achieves the E-O bandwidth of over 25 GHz and 50-Gbit/s non-return-to-zero (NRZ) signal modulation with an extinction ratio of 2.5 dB.

Efficient and Unidirectional Launching of Surface Plasmons from a Hyperbolic Meta‐Antenna

AbstractTunnel nanojunctions associated with inelastic electron tunneling have demonstrated crucial applications in on‐chip photonic and plasmonic circuitries due to their high photon modulation speed, large‐scale integration capability, and working‐wavelengths range tunability. However, because most electrons tunnel through a junction elastically, the external quantum efficiency of a nanojunction‐based plasmonic source tends to be around 10−4, severely limiting their applications to date. In this work, an integrated high‐efficiency unidirectional plasmonic source composed of an edge‐to‐edge thickness gradient hyperbolic meta‐antenna is proposed. By engineering the extra wavevector dimension, this study demonstrates a theoretical external quantum efficiency of up to 23% for this system. This is attributed to the large local density of optical states from hyperbolic dispersion and wavevector‐match conditions provided by the optical antennas. Furthermore, this study also demonstrates the tunability of this system across a range of wavelengths from 1300 to 1700 nm. The implementations of these metamaterial‐based tunneling structures enable fast and tunable on‐chip high‐efficiency sources for applications in high‐performance plasmonic circuitries.

Long-range high-spatial-resolution distributed Brillouin sensing enabled by correlation-domain encoding.

A hybrid aperiodic-coded Brillouin optical correlation domain analysis (HA-coded BOCDA) fiber sensor is proposed to achieve long-range high-spatial-resolution distributed measurement. It is found that high-speed phase modulation in the BOCDA actually forms a special energy transformation mode. This mode can be exploited to suppress all detrimental effects parasitized in a pulse coding-induced cascaded stimulated Brillouin scattering (SBS) process and thereby enable the HA-coding to reach its full potential to improve the BOCDA performance. As a result, under a low system complexity and an enhanced measurement speed, a 72.65-km sensing range and a 5-cm spatial resolution are achieved with a temperature/strain measurement accuracy of 2℃/40 με.