Octaves Of Bandwidth Research Articles

SiN waveguides for ultra-broadband visible-telecom photon pairs

We propose simple rectangular cross-section, few-cm long SiN waveguide designs capable of generating ultra-broadband frequency-correlated photon pairs via SFWM, exceeding an octave in bandwidth spanning the visible-to-telecom wavelengths ( $$\sim$$ 700–1700 nm for $$\sim$$ 1- $$\upmu$$ m pump) with a spectral brightness of $$>2.5\times 10^4$$ photon pairs/s/nm/mW $$^2$$ . Such compact sources, spanning the entire telecom spectrum (across O, E, S, C, L, and U bands) on one side and covering most of the major atomic transitions used in ultracold gases and solid-state based quantum memories on the other side, could potentially be employed in large-scale multi-channel hybrid (free space + fiber) quantum networking schemes in addition to the heralding of telecom single photons by utilizing high efficiency visible detectors.

Lossless Matching Layer for Silicon Lens Arrays at 500 GHz Using Laser Ablated Structures

We present the design, fabrication and characterization of a broadband lossless matching layer for silicon lens arrays. The proposed matching layer is based on silicon frusta (truncated pyramids) on top of the lens array fabricated by means of laser ablation. This matching layer is advantageous over quarter-wavelength dielectric matching layers since it covers more than an octave of bandwidth. We compare the performance of this matching layer with the commonly-used parylene-C matching layer at the center of the targetted band (500 GHz) in a lens-antenna integrated system. We measure a 1.6 dB higher transmission of the proposed silicon frusta matching compared to the parylene-C matching layer.

Current Sheet Antenna Array and 5G: Challenges, Recent Trends, Developments, and Future Directions.

Designing an ultra-wideband array antenna for fifth generation (5G) is challenging for the antenna designing community because of the highly fragmented electromagnetic spectrum. To overcome bandwidth limitations, several millimeter-wave bands for 5G and beyond applications are considered; as a result, many antenna arrays have been proposed during the past decades. This paper aims to explore recent developments and techniques regarding a specific type of phased array antenna used in 5G applications, called current sheet array (CSA). CSA consists of capacitively coupled elements placed over a ground plane, with mutual coupling intentionally introduced in a controlled manner between the elements. CSA concept evolved and led to the realization of new array antennas with multiple octaves of bandwidth. In this review article, we provide a comprehensive overview of the existing works in this line of research. We analyze and discuss various aspects of the proposed array antennas with the wideband and wide-scan operation. Additionally, we discuss the significance of the phased array antenna in 5G communication. Moreover, we describe the current research challenges and future directions for CSA-based phased array antennas.

Floquet-Mode Traveling-Wave Parametric Amplifiers

Simultaneous ideal quantum measurements of multiple single-photon-level signals would advance applications in quantum information processing, metrology, and astronomy, but require the first amplifier to be simultaneously broadband, quantum limited, and directional. However, conventional traveling-wave parametric amplifiers support broadband amplification at the cost of increased added noise and are not genuinely directional due to non-negligible nonlinear backward wave generation. In this work, we introduce a new class of amplifiers which encode the information in the Floquet modes of the system. Such Floquet mode amplifiers prevent information leakage and overcome the trade-off between quantum efficiency (QE) and bandwidth. Crucially, Floquet mode amplifiers strongly suppress the nonlinear forward-backward wave coupling and are therefore genuinely directional and readily integrable with qubits, clearing another major obstacle towards broadband ideal quantum measurements. Furthermore, Floquet mode amplifiers are insensitive to out-of-band impedance mismatch, which otherwise may lead to gain ripples, parametric oscillations, and instability in conventional traveling-wave parametric amplifiers. Finally, we show that a Floquet mode Josephson traveling-wave parametric amplifier implementation can simultaneously achieve $>\!20\,$dB gain and a QE of $\eta/\eta_{\mathrm{ideal}}\!> 99.9\%$ of the quantum limit over more than an octave of bandwidth. The proposed Floquet scheme is also widely applicable to other platforms, such as kinetic inductance traveling-wave amplifiers and optical parametric amplifiers.

Pairwise Mode Locking in Dynamically Coupled Parametric Oscillators.

Mode locking in lasers is a collective effect, where due to a weak coupling a large number of frequency modes lock their phases to oscillate in unison, forming an ultrashort pulse in time. We demonstrate an analogous collective effect in coupled parametric oscillators, which we term "pairwise mode locking," where many pairs of modes with twin frequencies (symmetric around the center carrier) oscillate simultaneously with a locked phase sum, while the phases of individual modes remain undefined. Thus, despite being broadband and multimode, the emission is not pulsed and lacks first-order coherence, while possessing a very high degree of second-order coherence. Our configuration comprises two coupled parametric oscillators within identical multimode cavities, where the coupling between the oscillators is modulated in time at the repetition rate of the cavity modes, with some analogy to active mode locking in lasers. We demonstrate pairwise mode locking in a radio-frequency experiment, covering over an octave of bandwidth with approximately 20 resonant mode-locked pairs, filling most of the available bandwidth between dc and the pump frequency. We accompany our experiment with an analytic model that accounts for the properties of the coupled parametric oscillators near threshold.

Generating few-cycle pulses with integrated nonlinear photonics

Ultrashort laser pulses that last only a few optical cycles have been transformative tools for studying and manipulating light-matter interactions. Few-cycle pulses are typically produced from high-peak-power lasers, either directly from a laser oscillator or through nonlinear effects in bulk or fiber materials. Now, an opportunity exists to explore the few-cycle regime with the emergence of fully integrated nonlinear photonics. Here, we experimentally and numerically demonstrate how lithographically patterned waveguides can be used to generate few-cycle laser pulses from an input seed pulse. Moreover, our work explores a design principle in which lithographically varying the group-velocity dispersion in a waveguide enables the creation of highly constant-intensity supercontinuum spectra across an octave of bandwidth. An integrated source of few-cycle pulses could broaden the range of applications for ultrafast light sources, including supporting new lab-on-a-chip systems in a scalable form factor.

Mode-crossing spectroscopy for photonic waveguide characterization

We report a novel spectroscopic technique to characterize photonic waveguides over more than an octave of wavelength. The technique, called mode-crossing spectroscopy, uses a broadband source and a spectrometer that are coupled to the input and output ends of a series of straight dielectric waveguides via single-mode optical fibers. Measurements of the wavelengths at which multiple modes are degenerate in a single waveguide enable the determination of the refractive index of the core, as well as the waveguide width variation. In addition, mode-dependent losses are reported from 700 nm to 1550 nm using waveguides of varying lengths. The core refractive indices are measured within an error of ±0.5%, waveguide width variation to an accuracy of less than 5 nm, and waveguide propagation losses within an error of ±0.5 dB/cm. Ultrabroadband in situ measurements of loss and index over an octave of bandwidth are crucial for the accurate characterization of photonic integrated circuits and devices, especially those based on precision broadband couplers, interferometers, and resonant cavities.

Theoretical design of eight‐band linear‐to‐circular converter in reflection and transmission modes based on self‐complementary metasurfaces

AbstractMultiband linear‐to‐circular (LTC) metamaterial converters have promising applications in modern optical system. However, it is challenging to design a converter with conversion bands of more than four and the axial ratio of less than 3 dB due to the coupling interaction of different resonant structures in a unit cell. In this article, we demonstrate a broad class of self‐complementary THz infinite thin metasurfaces composed of supercells of fractal metal rectangular patches and holes dimers of spanning 1 THz octave in bandwidth, while still being highly efficient. The advantages of this converter are as follows. The device is theoretically nonthickness; the LTC polarization conversion can be achieved in both the reflected and transmitted fields; the phase difference between two orthogonal linear polarization components is theoretically 90° in any frequency. Therefore, an eight‐band LTC converter is achieved in reflection and transmission modes. This new nonthickness multiband device will demonstrate a major advance toward an LTC synthetic metasurface in the THz band.

High-coherence mid-infrared dual-comb spectroscopy spanning 2.6 to 5.2 μm

Mid-infrared dual-comb spectroscopy has the potential to supplant conventional high-resolution Fourier transform spectroscopy in applications that require high resolution, accuracy, signal-to-noise ratio, and speed. Until now, dual-comb spectroscopy in the mid-infrared has been limited to narrow optical bandwidths or to low signal-to-noise ratios. Using a combination of digital signal processing and broadband frequency conversion in waveguides, we demonstrate a mid-infrared dual-comb spectrometer that can measure comb-tooth resolved spectra across an octave of bandwidth in the mid-infrared from 2.6-5.2 $\mu$m with sub-MHz frequency precision and accuracy and with a spectral signal-to-noise ratio as high as 6500. As a demonstration, we measure the highly structured, broadband cross-section of propane (C3H8) in the 2860-3020 cm-1 region, the complex phase/amplitude spectrum of carbonyl sulfide (COS) in the 2000 to 2100 cm-1 region, and the complex spectra of methane, acetylene, and ethane in the 2860-3400 cm-1 region.

Hollow Core Antiresonant Fiber With Radially Asymmetric Nodeless Claddings

We propose and numerically study a novel type of hollow core antiresonant fiber with a single layer of nodeless radially asymmetric cladding tubes, i.e., the cladding tube presents a bulb-like shape, that the local cladding curvature radius at the core/cladding boundary is larger than the other side. Compared with counterparts with conventionally used radially symmetric nodeless claddings, e.g., circular and elliptical tubes, numerical analysis shows that such structure can provide excellent broadband low-loss property and robust single-mode guidance. By tuning the local cladding tube curvature radius, the confinement loss characteristic can be less sensitive but the phase matching between core high-order modes (HOMs) and resonant cladding modes can be significantly enhanced than that of the elliptical structure. Since the cladding modal fields are moved closer to those of the core HOMs, the HOM extinction ratio can reach above 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> and maintain over an octave of bandwidth.

Octave-Spanning Broadband Absorption of Terahertz Light Using Metasurface Fractal-Cross Absorbers

Synthetic fractals inherently carry spatially encoded frequency information that renders them as an ideal candidate for broadband optical structures. Nowhere is this more true than in the terahertz (THz) band where there is a lack of naturally occurring materials with valuable optical properties. One example are perfect absorbers that are a direct step towards the development of highly sought after detectors and sensing devices. Metasurface absorbers that can be used to substitute for natural materials suffer from poor broadband performance, whilst those with high absorption and broadband capability typically involve complex fabrication and design and are multilayered. Here, we demonstrate a polarization-insensitive ultrathin (~λ/6) planar metasurface THz absorber composed of supercells of fractal crosses capable of spanning one optical octave in bandwidth, whilst still being highly-efficient. A sufficiently thick polyimide interlayer produces a unique absorption mechanism based on Salisbury screen and an...

Photonic-Chip Supercontinuum with Tailored Spectra for Counting Optical Frequencies

Supercontinuum generation using chip-integrated photonic waveguides is a powerful approach for spectrally broadening pulsed laser sources with very low pulse energies and compact form factors. When pumped with a mode-locked laser frequency comb, these waveguides can coherently expand the comb spectrum to more than an octave in bandwidth to enable self-referenced stabilization. However, for applications in frequency metrology and precision spectroscopy, it is desirable to not only support self-referencing, but also to generate low-noise combs with customizable broadband spectra. In this work, we demonstrate dispersion-engineered waveguides based on silicon nitride that are designed to meet these goals and enable precision optical metrology experiments across large wavelength spans. We perform a clock comparison measurement and report a clock-limited relative frequency instability of $3.8\times10^{-15}$ at $\tau = 2$ seconds between a 1550 nm cavity-stabilized reference laser and NIST's calcium atomic clock laser at 657 nm using a two-octave waveguide-supercontinuum comb.

Scanning Fourier transform spectrometer in the visible range based on birefringent wedges.

We introduce a spectrometer capable of measuring sample absorption spectra in the visible regime, based on a time-domain scanning Fourier transform (FT) approach. While infrared FT spectrometers typically employ a Michelson interferometer to create the two delayed light replicas, the proposed apparatus exploits a compact common-mode passive interferometer that relies on the use of birefringent wedges. This ensures excellent path-length stability (∼λ/300) and accuracy, with no need for active feedback or beam tracking. We demonstrate the robustness of the technique measuring the transmission spectrum of a colored bandpass filter over one octave of bandwidth and compare the results with those obtained with a commercial spectrophotometer.

Theoretical anisotropic transverse resonance technique for the design of low‐profile wideband antennas

The authors derive an anisotropic transverse resonance technique enabling the design of a low profile, wideband radiating rectangular cavity. They calculate a tapered geometry that preserves an effective half wavelength resonance within a cavity partially loaded with an anisotropic medium. This design results in an antenna profile of λ o/24, with 1.4 octaves of bandwidth, and a realised gain of 3.3–7.2 dB from 210 to 505 MHz. Using an adaption of a coaxial line to waveguide transition, which utilises two flat rectangular probes as a two-port matching network, as well as an external 180° hybrid coupler as a phase splitter, they achieve a voltage standing wave ratio of better than 2:1 across the whole band.

Frequency-division multiplexing in the terahertz range using a leaky-wave antenna

Using a leaky-wave antenna, free-space-to-waveguide frequency-division multiplexing and demultiplexing are demonstrated in the terahertz range. Both the frequency and the spectral bandwidth of multiplexed channels can be independently controlled. The idea of using radiation in the 0.1–1.0 THz range as carrier waves for free-space wireless communications has attracted growing interest in recent years, due to the promise of the large available bandwidth1,2. Recent research has focused on system demonstrations3,4, as well as the exploration of new components for modulation5, beam steering6 and polarization control7. However, the multiplexing and demultiplexing of terahertz signals remains an unaddressed challenge, despite the importance of such capabilities for broadband networks. Using a leaky-wave antenna based on a metal parallel-plate waveguide, we demonstrate frequency-division multiplexing and demultiplexing over more than one octave of bandwidth. We show that this device architecture offers a unique method for controlling the spectrum allocation, by variation of the waveguide plate separation. This strategy, which is distinct from those previously employed in either the microwave8 or optical9 regimes, enables independent control of both the centre frequency and bandwidth of multiplexed terahertz channels.

A wideband RF receiver with extended statistical element selection based harmonic rejection calibration

In this paper we present a wideband harmonic rejection (HR) RF receiver design. Both gain mismatch and phase mismatch of the HR mixer have been calibrated using a design and calibration method called extended statistical element selection to achieve best-in-class HR ratio (HRR) performance. The achieved concurrent 3rd order HRR and 5th order HRR are greater than 80dB and 70dB, respectively, after calibration. The even order HRR is also calibrated to greater than 80dB. A single calibration performed at 750MHz was further observed to be effective over more than two octaves of bandwidth with greater than 70dB HRR. The receiver was manufactured in 65nm CMOS technology. Input RF frequency range was 0.15–1GHz and the receiver consumes 64mW at 1GHz. Noise figure is 3.2dB and out-of-band IIP3 is −7dBm at a total gain of 48dB.

Extremely wideband in‐phase power divider using modified Wilkinson design

ABSTRACTA planar in‐phase power divider with extreme wideband behavior using modified Wilkinson design is presented. Instead of using T‐junction at the input port of the traditional design, the proposed divider uses broadside coupled microstrip to slotline configuration. Moreover, the impedance matching of the output ports is significantly improved across several octaves bandwidth using three binomial sections, whereas the isolation between those ports is enhanced across that band using three isolation resistors. The utilized structure is suitable for single layer integration as both the input and output ports are located at the same layer. A prototype of the presented device is designed using a proper theoretical approach, built, and tested. The developed device has a compact size with an overall dimension of 40 × 55 mm2 using the substrate Rogers RO4003 (dielectric constant = 3.38, thickness = 0.406 mm). While the device can be used for any wideband application, the developed prototype is designed to operate within the band 1–7 GHz, which is used in most microwave‐based medical imaging applications. The achieved simulated and measured results show that the proposed device has equal power division between the two output ports with less than 0.2‐dB amplitude imbalance, more than 10‐dB return loss and 15‐dB isolation, and less than 2° phase difference between the two output signals across the extremely wide frequency band 1.2–7 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1799–1802, 2015

Acousto-optics bandwidth broadening in a Bragg cell based on arbitrary synthesized signal methods.

In this work, we present the advantages of driving a multichannel acousto-optical deflector (AOD) with a digitally synthesized multifrequency RF signal. We demonstrate a significant bandwidth broadening of ∼40% by providing well-tuned phase control of the array transducers. Moreover, using a multifrequency, complex signal, we manage to suppress the harmonic deflections and return most of the spurious energy to the main beam. This method allows us to operate the AOD with more than an octave of bandwidth with negligible spurious energy going to the harmonic beams and a total bandwidth broadening of over 70%.

Role of adaptive beamforming with random and irregular arrays

When we design an array to accommodate as many as 4–5 octaves of bandwidth, the design must provide a variety of apertures and element spacings. Further, the concept of operations may be such that no structure is available for maintaining a regular array structure (even if we actually wanted one). One example of this is an array of freely drifting sonobuoys. Clearly, with a limited number of elements (far fewer than would be needed to provide half wavelength spacing for the highest frequency over the aperture needed at the lowest frequency), compromises must be made. Solutions include combinations of nested apertures, geometrically increasing spacings, and random spacings to varying degrees—in short irregular and random arrays. Such designs have very poor conventional beam response patterns, with very high sidelobes, compared to the fully populated arrays spaced at half wavelength. However, these objections are a red herring. We will show that adaptive beamforming produces beam responses with very low sidelobes. We will also show that irregular and random arrays indeed outperform regular arrays (of equivalent cost), if a wide bandwidth and range of interference directions are considered. We will also briefly review requirements for array calibration for adaptive beamforming.

Two octaves mid-infrared supercontinuum generation in As₂Se₃ microwires.

We report the first demonstration of mid-infrared supercontinuum generation in As₂Se₃ chalcogenide microwires with the added advantage of using low energy pulses. The generated SC covers two octaves of bandwidth from 1.1 μm to 4.4 μm at -30 dB. This exceeds the broadest reported SC bandwidth in As₂Se₃ microwires by a factor of 3.5. The microwire geometry and pumping conditions are the key parameters in generating the 3.3 μm bandwidth while using a low pump pulse energy of 500 pJ.