dB Extinction Ratio Research Articles

Aluminium nanoparticle-based ultra-wideband high-performance polarizer

The polarizer-based device industry is expanding quickly, requiring high-quality research on nanoscale wideband polarizers. Here, we investigated the possibility of utilizing Al dimer nanostructures on broad-band polarizers. Metals are always considered promising candidates for reflection-based polarizer development because of their high extinction ratio. This study proposes a novel nanoparticle polarizer comprised of semi-immersed Al nano-dimers with a 200 nm radius on a CaF2 substrate. Our proposed nano-dimer-based design demonstrated impressive polarization anisotropy in the near-infrared (NIR) and THz ranges than conventional wire-grid-based ones. This study includes calculating performance parameters for the extraction of the proposed polarizer, including insertion loss, extinction ratio (ER), Mueller matrix values, and polarization ellipse diagram. The finite-difference time-domain (FDTD) simulation-based results suggested obtaining more than 55 dB extinction ratio for the 0.2 to 9 THz range. In the THz region, simulation results suggest impressively better performance than conventional wire-grid polarizers. In THz frequency range, our proposed polarizer demonstrated its extinction ratio of up to 60 dB. The average extinction ratio and insertion loss over the 1–1665 μm wavelength were 29.01 dB and ∼1 dB, respectively. The idea of Al dimer and the insight gained from the results extracted from the rigorous simulation report suggested a great opportunity for developing micro-scale metallic wideband polarizers.

On-chip broadband Mach-Zehnder interferometer based on a broadband taper-section phase shifter

In this paper, we propose a new broadband nulling interferometer based on the Si3N4/SiO2 platform which utilizes a π-phase shifter. This π-phase shift multimode interference Mach-Zehnder interferometer (πPS MMI-MZI) leverages a novel low phase shift error (PSE) and broadband taper-section phase shifter (TSPS). For the TSPS, our simulation predicts an unprecedented PSE from 1450 nm to 1650 nm for the two- and three-section TSPS of 1 o and 0.02 o , respectively. Our experimental results demonstrate a PSE of 1 o within a 190 nm bandwidth for the two-section TSPS. A slightly adjusted TSPS gives an even lower PSE of 0.6 o within a narrower bandwidth of 90 nm. With the help of the TSPS, the πPS MMI-MZI shows a significant improvement in extinction ratio compared to the conventional MMI-MZI. Simulations predict an extinction ratio of 50 dB within a 150 nm bandwidth. Experimental measurements demonstrate a 40 dB extinction ratio within a 100 nm bandwidth. The broadband TSPS, as well as the broadband πPS MMI-MZI, pave the way for novel high performance photonic integrated circuits.

Birefringence-induced phase delay enables Brillouin mechanical imaging in turbid media

Acoustic vibrations of matter convey fundamental viscoelastic information that can be optically retrieved by hyperfine spectral analysis of the inelastic Brillouin scattered light. Increasing evidence of the central role of the viscoelastic properties in biological processes has stimulated the rise of non-contact Brillouin microscopy, yet this method faces challenges in turbid samples due to overwhelming elastic background light. Here, we introduce a common-path Birefringence-Induced Phase Delay (BIPD) filter to disentangle the polarization states of the Brillouin and Rayleigh signals, enabling the rejection of the background light using a polarizer. We demonstrate a 65 dB extinction ratio in a single optical pass collecting Brillouin spectra in extremely scattering environments and across highly reflective interfaces. We further employ the BIPD filter to image bone tissues from a mouse model of osteopetrosis, highlighting altered biomechanical properties compared to the healthy control. Results herald new opportunities in mechanobiology where turbid biological samples remain poorly characterized.

On-chip tunable quantum interference in a lithium niobate-on-insulator photonic integrated circuit

Programmable interferometric circuits are at the heart of integrated quantum photonic processors. While the lithium niobate-on-insulator platform has the potential to advance integrated quantum photonics due to its strong nonlinearity and tight mode confinement, the demonstration of reconfigurable two-photon interference has not yet been achieved. Here, we design, fabricate and characterize the building block of such interferometric networks in the form of a 2 × 2 Mach–Zehnder Interferometer. We use a thermo-optic phase shifter to achieve stable performance with a power consumption of Pπ=44.4 mW and sub-microsecond switching times. We demonstrate the effectiveness of our device for quantum applications by measuring single-photon routing with up to 34 dB extinction ratio. We show Hong-Ou-Mandel interference with fully tunable visibilities reaching a maximum value of 97.4±1.0% . As part of large scale quantum photonic circuits, this building block will facilitate reconfigurable and tunable photonic processing units integrated alongside non-classical light sources.

Multiphysics simulations of a cylindrical waveguide optical switch using phase change materials on silicon

This work presents the design and multiphysics simulation of a cylindrical waveguide-based optical switch using germanium-antimony-tellurium (GST) as an active phase change material. The innovative cylindrical architecture is theoretically analyzed and evaluated at 1550 nm wavelength for telecommunication applications. The dispersion relation is derived analytically for the first time to model the optical switch, while finite element method (FEM) and finite difference time domain (FDTD) techniques are utilized to simulate the optical modes, light propagation, and phase change dynamics. The fundamental TE01 and HE11 modes are studied in detail, enabling switching between low-loss amorphous and high-loss crystalline GST phases. Increasing the GST thickness is found to increase absorption loss in the crystalline state but also slows down phase transition kinetics, reducing switching speeds. A 10 nm GST layer results in competitive performance metrics of 0.79 dB insertion loss, 13.47 dB extinction ratio, 30 nJ average power consumption, and 3.5 Mb/s bit rate. The combined optical, thermal, and electrical simulation provides comprehensive insights towards developing integrated non-volatile photonic switches and modulators utilizing phase change materials.

Real-time and calibration-free generalized terahertz time-domain spectroscopic ellipsometry

Spectroscopic ellipsometry is a high-precision and powerful optical characterization technique, which can be categorized into two fundamental types of standard and generalized ellipsometry. The latter can obtain the complete Jones matrix to investigate various anisotropic samples. However, terahertz generalized ellipsometry has traditionally relied on frequency-domain instrumentation, which is limited in bandwidth, complicated in polarization manipulation, and slow in operation. In this study, we propose a highly accurate and efficient terahertz time-domain generalized ellipsometer based on a polarization beam coupler-splitter configuration. It measures four independent complex spectra in real-time without mechanical movement, providing ultrahigh data throughput. Each polarizer-antenna unit constructively superimposes their filtering effect, resulting in a 45–65 dB extinction ratio that approaches the system dynamic range. The superb illumination and detection linearity provides an outstanding polarization accuracy and eliminates the need for complicated calibration. Reflection characterization of the magneto-optical properties of an InAs wafer demonstrates the generalized ability to simultaneously obtain multiple dielectric functions. Transmission ellipsometric imaging of liquid crystals subjected to an inhomogeneous electric field further highlights the excellent efficiency. The proposed technique significantly expands the capabilities of terahertz spectroscopy, paving ways to anisotropic materials, in situ monitoring, and polarization-sensitive devices.

Integrated Broadband Filter with Sharp Transition Edges Based on SiN and SiON Composite Waveguide Coupler

Broadband filters with sharp transition edges are important elements in diverse applications, including Raman and fluorescence spectral analysis, wideband wavelength-division multiplexing (WDM), and multi-octave interferometry. While the multi-layer thin-film interference broadband filter has been widely applied in various free-space optical systems, its integrated counterpart is still far from mature, which is also highly desired for constructing chip-scale miniature optical modules. In this article, we design, fabricate, and characterize an integrated broadband filter with sharp transition edges. An adiabatic coupler based on silicon nitride (SiN) and silicon oxynitride (SiON) composite waveguide is employed here. Long-pass, short-pass, band-pass, and band-stop filters can be realized in a single design of the composite waveguide coupler for a specific wavelength range, with only a difference in the SiN taper waveguide width. Experimental results with a roll-off value of larger than 0.7 dB nm−1 and a 15 dB extinction ratio (ER) are presented.

Ultra-Broadband Integrated Optical Filters Based on Adiabatic Optimization of Coupled Waveguides

Broadband spectral filters are highly sought-after in many integrated photonics applications such as ultra-broadband wavelength division multiplexing, multi-band spectroscopy, and broadband sensing. In this study, we present the design, simulation, and experimental demonstration of compact and ultra-broadband silicon photonic filters with adiabatic waveguides. We first develop an optimization algorithm for coupled adiabatic waveguide structures, and use it to design individual, single-cutoff spectral filters. These single-cutoff filters are 1×2 port devices that optimally separate a broadband signal into short-pass and long-pass outputs, within a specified device length. We control the power roll-off and extinction ratio in these filters using the adiabaticity parameter. Both outputs of the filters operate in transmission, making it possible to cascade multiple filters in different configurations. Taking advantage of this flexibility, we cascade two filters with different cutoff wavelengths on-chip, and experimentally demonstrate band-pass operation. The independent and flexible design of these band edges enables filters with bandwidths well over 100 nm. Experimentally, we demonstrate band-pass filters with passbands ranging from 6.4 nm up to 96.6 nm. Our devices achieve flat-band transmission in all three of the short-pass, band-pass, and long-pass outputs with less than 1.5 dB insertion loss and extinction ratios of over 15 dB. These ultra-broadband filters can enable new capabilities for multi-band integrated photonics in communications, spectroscopy, and sensing applications.

Broadband, compact and reflection-less silicon polarizer and polarization beam splitter using chirped anti-symmetric multimode nanobeams.

We present chirped anti-symmetric multimode nanobeams (CAMNs) based on silicon-on-insulator platforms, and describe their applications as broadband, compact, reflection-less, and fabrication-tolerant TM-pass polarizers and polarization beam splitters (PBSs). The anti-symmetric structural perturbations of a CAMN ensure that only contradirectional coupling between symmetric and anti-symmetric modes is possible, which can be exploited to block the unwanted back reflection of the device. The new possibility of introducing a large chirp on an ultra-short nanobeam-based device to overcome the operation bandwidth limitation due to the coupling coefficient saturation effect is also shown. The simulation results show that an ultra-compact CAMN with a length of ∼4.68 um can be used to develop a TM-pass polarizer or a PBS with an ultra-broad 20 dB extinction ratio (ER) bandwidth of >300 nm and an average insertion loss of <1.3 dB. The CAMN-based polarizer and PBS were fabricated and experimentally characterized in a wavelength range from 1507 to 1575 nm. The measured ERs were >20 dB over the entire tested wavelength range and the average insertion losses were <0.5 dB for both devices. The mean reflection suppression ratio of the polarizer was ∼26.4 dB. Large fabrication tolerances of ±60 nm in the waveguide widths of the devices were also demonstrated.

Demonstration of a Plasmonic Nonlinear Pseudodiode.

We demonstrate a nonlinear plasmonic metasurface that exhibits strongly asymmetric second-harmonic generation: nonlinear scattering is efficient upon excitation in one direction, and it is substantially suppressed when the excitation direction is reversed, thus enabling a diode-like functionality. A significant (approximately 10 dB) extinction ratio of SHG upon opposite excitations is measured experimentally, and those findings are substantiated with full-wave simulations. This effect is achieved by employing a combination of two commonly used metals─aluminum and silver─producing a material composition asymmetry that results in a bianisotropic response of the system, as confirmed by performing homogenization analysis and extracting an effective susceptibility tensor. Finally, we discuss the implications of our results from the more fundamental perspectives of reciprocity and time-reversal asymmetry.

High-Performance All-Optical Hybrid Plasmonic Switch Using Zn-Doped Cadmium Oxide

In this article, a novel hybrid plasmonic waveguide (HPWG)-based all-optical switch (AOS) using zinc-doped cadmium oxide (ZnCdO) is reported and numerically investigated with the finite-element method. This oxide layer, which is a well-known transparent conductive oxide (TCO), can be switched from a dielectric to a metallic phase by electrical tuning the refractive index. The mobility of free-carrier concentration is highly magnified with a nonlinear optical effect induced by the epsilon-near-zero material near the telecommunication wavelength. We have simulated the plasmonic switch using the COMSOL Multiphysics simulator, predicting 13.75 dB extinction ratio (ER), 0.5 dB insertion loss (IL), and 27.5 figure-of-merit (FoM) at 1.55 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> wavelength. We also performed the reliability study by varying parameters, such as the width and height of the waveguide, which affect the performance of the on-chip switch design. In addition, the proposed AOS can be easily integrated with future silicon photonic circuits for ultrafast switching applications.

Tunable Metasurface Based on Plasmonic Quasi Bound State in the Continuum Driven by Metallic Quantum Wells

AbstractEffectual free‐space optical metasurface is essential for telecommunication and information processing. However, the lack of efficient optical nonlinearity is still an obstacle to empower its full capability and practical applications. Metallic quantum wells (MQWs) with large nonlinear susceptibility may pave a new way. Here, such MQWs are implemented into a resonance configuration of the quasi bound state in the continuum (BIC) and an efficient tunable plasmonic metasurface is proposed. Such metasurface is composed of MQWs‐based nanostructure, which supports the tunable plasmonic quasi‐BIC. The tunability is controlled through substantial change in refractive index of MQWs induced by Kerr‐type nonlinearity, which leads to around 9 dB extinction ratio and extremely high modulation speed up to terahertz level. The quasi‐BIC with narrow linewidth is obtained through symmetry‐breaking of nanoelliptical elements, further enhancing the modulation depth. This work satisfies the ultrafast‐speed and high‐efficiency requirement of free‐space all‐optical metasurfaces, including the spatial light modulators in optical computing field.

Meta‐Structured Silicon Nanophotonic Polarization Beam Splitter with an Optical Bandwidth of 415 nm

AbstractThe polarization beam splitter (PBS) is a pivotal element in the polarization management of free‐space optical instruments and systems. Photonic integrated circuits for sensing, imaging, communications, and quantum‐information processing also have needs for monolithically integrated PBSs with an ultra‐broad optical bandwidth. In this paper, a novel silicon nanophotonic PBS inspired by the crystalline Glan–Thompson prism but implemented with silicon subwavelength‐grating (SWG) metamaterials is presented. Due to the tailored artificial anisotropy of SWGs, the meta‐prism functions like a thin‐film reflector or a waveguide crossing for different polarizations. Thus, the incident light can be steered with strong polarization selectivity and negligible wavelength dependence. Unlike conventional PBS designs, the routing of polarized light is enabled by the wavelength‐independent total internal reflection in anisotropy‐engineered effective media, thereby breaking the bandwidth limit. The device footprint is as small as ≈15 × 7 µm2. Low insertion losses of 0.6–1.7 dB and high extinction ratios of 20–30 dB are experimentally achieved spanning a record broad bandwidth of over 415 nm, ranging from 1.26 to 1.675 µm wavelength. These results represent, to the best of their knowledge, the most broadband integrated PBS ever demonstrated to date.

Silicon–Organic Hybrid Tunable Fabry–Perot Filter for Electro-Optic Modulation

Recently, electro-optic integrated photonic elements have attracted considerable interest owing to their widespread application in optical communication and signal processing. The strong electro-optical properties and the complementary metal–oxide semiconductor (CMOS) technology compatibility of silicon–organic hybrid structures makes them promising photonic platforms. This study investigated a novel implementation of a high-speed electrically tuned bandpass optical filter using finite-difference time-domain and eigenmode expansion numerical methods. The proposed device was based on a Fabry–Perot cavity and was realized via an electro-optic organic molecular glass filled slot waveguide with Bragg gratings. Furthermore, the calculation considered the plasma dispersion effect, free-carrier absorption in the silicon component of the slot waveguide for different applied voltages, and doping profiles corresponding to ion implantation. It is shown that the spatial distribution of charge carrier density formed by the surface states accumulation/depletion layers has a significant effect on the optical properties of the slot waveguide. Lithographic distortions in the geometry of the proposed structures during fabrication were also considered. Therefore, this paper presents an optical filter designed for fabrication using CMOS-compatible processes on silicon-on-insulator wafers. The filter produced a 3 nm tunable range for a 10 V bias voltage swing, a 0.3 nm full width at half maximum (FWHM) passband with a center at 1550 nm at zero bias voltage, and a 12.5 nm free spectral range with a 27 dB extinction ratio. The proposed device outperforms many narrow passband analogs in terms of sensitivity (tunability: 0.3 nm/V) and can be applied extensively in the fields of optical communications and photonic spectral signal processing.

Fabrication tolerant and broadband polarization splitter-rotator based on adiabatic mode evolution on thin-film lithium niobate

A polarization splitter-rotator device can facilitate on-chip polarization-division multiplexing to enhance the transmission data rate. Here, we propose and experimentally demonstrate a polarization splitter-rotator based on adiabatic mode evolution on the thin-film lithium niobate platform. The measured results for a fabricated device show low insertion losses of <-0.5 dB and large extinction ratios of >20 dB over the 110-nm band. Large fabrication tolerance is also demonstrated with extinction ratios of >15 dB in the wavelength range of 1465-1630 nm for a waveguide width variation of 80 nm.

100 Gb/s NRZ OOK signal regeneration using four-wave mixing in a silicon waveguide with reverse-biased p-i-n junction.

A silicon waveguide with reverse-biased p-i-n junction is used to experimentally demonstrate all-optical regeneration of non-return-to-zero (NRZ) on-off keying (OOK) signal based on four-wave mixing. The silicon waveguide allows a high conversion efficiency of -12 dB. The 0.22 dB (1.1 dB) quality (Q) factor and 0.74 dB (6.3 dB) extinction ratio (ER) improvements on average are achieved for 100 Gb/s (50 Gb/s) NRZ OOK signal regeneration at different receiving powers via the optimal match between the input signal optical power and input-output transfer curve. To the best of our knowledge, this silicon-based all-optical regenerator exhibits superior regeneration performance, including large ER and Q factor improvements, and the highest regeneration speed of NRZ OOK signal, and it has wide applications in 5 G/6 G networks.

Silicon nitride stress-optic microresonator modulator for optical control applications.

Modulation-based control and locking of lasers, filters and other photonic components is a ubiquitous function across many applications that span the visible to infrared (IR), including atomic, molecular and optical (AMO), quantum sciences, fiber communications, metrology, and microwave photonics. Today, modulators used to realize these control functions consist of high-power bulk-optic components for tuning, sideband modulation, and phase and frequency shifting, while providing low optical insertion loss and operation from DC to 10s of MHz. In order to reduce the size, weight and cost of these applications and improve their scalability and reliability, modulation control functions need to be implemented in a low loss, wafer-scale CMOS-compatible photonic integration platform. The silicon nitride integration platform has been successful at realizing extremely low waveguide losses across the visible to infrared and components including high performance lasers, filters, resonators, stabilization cavities, and optical frequency combs. Yet, progress towards implementing low loss, low power modulators in the silicon nitride platform, while maintaining wafer-scale process compatibility has been limited. Here we report a significant advance in integration of a piezo-electric (PZT, lead zirconate titanate) actuated micro-ring modulation in a fully-planar, wafer-scale silicon nitride platform, that maintains low optical loss (0.03 dB/cm in a 625 µm resonator) at 1550 nm, with an order of magnitude increase in bandwidth (DC - 15 MHz 3-dB and DC - 25 MHz 6-dB) and order of magnitude lower power consumption of 20 nW improvement over prior PZT modulators. The modulator provides a >14 dB extinction ratio (ER) and 7.1 million quality-factor (Q) over the entire 4 GHz tuning range, a tuning efficiency of 162 MHz/V, and delivers the linearity required for control applications with 65.1 dB·Hz2/3 and 73.8 dB·Hz2/3 third-order intermodulation distortion (IMD3) spurious free dynamic range (SFDR) at 1 MHz and 10 MHz respectively. We demonstrate two control applications, laser stabilization in a Pound-Drever Hall (PDH) lock loop, reducing laser frequency noise by 40 dB, and as a laser carrier tracking filter. This PZT modulator design can be extended to the visible in the ultra-low loss silicon nitride platform with minor waveguide design changes. This integration of PZT modulation in the ultra-low loss silicon nitride waveguide platform enables modulator control functions in a wide range of visible to IR applications such as atomic and molecular transition locking for cooling, trapping and probing, controllable optical frequency combs, low-power external cavity tunable lasers, quantum computers, sensors and communications, atomic clocks, and tunable ultra-low linewidth lasers and ultra-low phase noise microwave synthesizers.

Ultra-broadband and high purity tapered mode converter for mode division multiplexing systems

This paper proposes a three-section tapered mode converter that can convert guided optical mode LP01 to LP02. The coupling section, the coupling enhancement section, and the undesired power reduction section are connected in sequence and shows operation with ultra-bandwidth of 178 nm with over 20 dB extinction ratio, the LP02 normalized power accounted for the high proportion. The proposed structure represents ultra-broadband and high purity component for use in mode division multiplexing systems.

50G-PON Downstream Link up to 40 km With a 1342 nm Integrated EML+SOA

A monolithically integrated EML+SOA delivering an output power of +13 dBm is demonstrated as a compact Tx for the 50G-PON downstream link. The device delivers +13 dBm of output power with 6 dB extinction ratio and 55 dB/0.1nm OSNR while also passing the 50G-PON eye mask. By exploiting SOA chirp reduction correlated to the gain saturation effects we demonstrate enhanced fiber transmission performance. Since 50G-PON is going to be the first PON technology to adopt digital signal processing (DSP), we use receiver side equalization (EQ) in a 20 km link to demonstrate a link budget of 35.8 dB. Furthermore, working in conjunction with the 50G-PON equalizer, a link up to 40 km SSMF at 1342 nm is realized.

On-Chip Notch Filter on a Silicon Nitride Ring Resonator for Brillouin Spectroscopy

Noncontact Brillouin spectroscopy is a purely optical and label-free method to retrieve fundamental material viscoelastic properties. Recently, the extension to a three-dimensional imaging modality has paved the way to novel exciting opportunities in the biomedical field, yet the detection of the Brillouin spectrum remains challenging as a consequence of the dominant elastic background light that typically overwhelms the inelastic Brillouin peaks. In this Letter, we demonstrate a fully integrated and ultra-compact Brillouin notch filter based on an optical ring resonator fabricated on a silicon nitride platform. Our on-chip ring resonator filter was measured to have a 10 dB extinction ratio and a Q factor of 1.9x10^5. The experimental results provide a proof-of-concept on the ability of the on-chip filter to attenuate the elastic background light, heralding future developments of fully integrated, ultra-compact and low-cost Brillouin spectrometers.