Minimum Insertion Loss Research Articles

Passive on-chip isolators based on the thin-film lithium niobate platform

Abstract Optical isolators, the photonic analogs of electronic diodes, are essential for ensuring the unidirectional flow of light in optical systems, thereby mitigating the destabilizing effects of back reflections. Thin-film lithium niobate (TFLN), hailed as "the silicon of photonics," has emerged as a pivotal material in the realm of chip-scale nonlinear optics, propelling the demand for compact optical isolators. We report a breakthrough in the development of a fully passive, integrated optical isolator on the TFLN platform, leveraging the Kerr effect to achieve an impressive 10.3 dB of isolation with a minimal insertion loss of 1.87 dB. Further theoretical simulations have demonstrated that our design, when applied to a microring resonator with a Q factor of 5×106, can achieve 20 dB of isolation with an input power of merely 8 mW. This advancement underscores the immense potential of lithium niobate-based Kerr-effect isolators in propelling the integration and application of high-performance on-chip lasers, heralding a new era in integrated photonics.

Design and optimization of a low-loss waveguide taper for a narrow-band O-band multiplexer

The fast deployment of high-performance data centers accelerates the development of O-band wavelength division multiplexing (WDM) and its devices. To minimize insertion loss in WDM devices, it is essential to maximize coupling efficiency between optical fibers and waveguides at micro- and nano-scale. In this paper, we propose a low-loss waveguide tapered coupler and its optimization around 1310 nm. The coupler has a vertically placed double-layer rib taper as an intermediate waveguide, and the inverted taper is in a tapered tandem structure. Rib tapers are introduced in the intermediate waveguide and the fiber is coupled to the rib tapers, which are adiabatically reduced in width along the direction of the coupler to vertically reduce the mode size. To minimize footprint, a cascaded inverted taper is introduced. The maximum taper angle per stage corresponding to the long adiabatic taper is first determined. Subsequently, the long tapers are replaced with new shorter tapers. Several parameters are optimized using frequency domain time division (FDTD), including the output waveguide and input surface dimension, the height ratio of rib tapers, the length of inverted tapers, the length of rib tapers, and the tapered profile of tandem structure. The optimization results show that the coupler has an insertion loss of only 0.06 dB at 1310 nm with a device length of 513.4 µm. The two-stage in-plane coupler operates in O-band narrow-band with low insertion loss, offering an efficient solution for coupling fiber to on-chip waveguides.

Compact, low-loss, and broadband 2 × 2 Si optical coupler designed by covariance matrix adaptation evolution strategy

Abstract We experimentally demonstrate compact, low-loss, and broadband 2 × 2 Si optical couplers on a Si photonic platform designed using the covariance matrix adaptation evolution strategy (CMA-ES). The measured minimum insertion losses (ILs) in the C-band were 0.071 dB, 0.016 dB, 0.016 dB, and 45%–55% optical bandwidth were 140 nm, 136 nm, and 139 nm for device lengths of 7.56 μm, 9.64 μm, and 12.32 μm, respectively. The ILs are smaller than ever reported in 2 × 2 optical couplers shorter than 10 μm, and the optical bandwidths are much larger than a conventional directional coupler. The results validate the effectiveness of the proposed CMA-ES-based design method, extending the scope of application of our design method to the design of passive devices on Si photonics platform.

A Broadband Coaxial‐to‐Elliptical Waveguide Transition Using Step‐Impedance Probe

ABSTRACTIn this letter, a broadband coaxial‐to‐elliptical waveguide (EWG) transition is proposed using the E‐plane stepped‐impedance probe (SIP). According to the E‐field distribution of the dominate TEc11 mode of the EWG, the SIP is arranged along the short axis of the EWG, and then the dominate TEc11 mode of the EWG can be excited well while its first two high‐order modes (TEc21 and TEs11) are suppressed. Accordingly, a wideband transition with single‐mode operation is achieved. To obtain good matching in the wideband, four‐step SIP is optimized. For verification, a back‐to‐back transition centered at 4.9 GHz is designed and measured. The measured impedance bandwidth with |S11| < −15 dB is over 58.4%. Within it, the minimum insertion loss is 0.03 dB. Good agreement between the simulated and measured results can be observed.

UWB bandpass filter with tilted square shape ring topology sandwiched in the middle of interdigital structure

ABSTRACT This paper consists of compact novel design and high-performance ultra-wide band (UWB) bandpass filter (BPF) employed with square ring resonator (SRR) sandwiched between an interdigital structure (IDS). The unique combination of these microstrip resonators achieves a good selectivity across the passband with good rejection performance. The proposed structure also achieves less complexity and ease of fabrication. The passband extends from 4.2 GHz to 10.9 GHz with a notch band of 3 dB fractional bandwidth 88% centred at 7.6 GHz. The first passband in UWB BPF has minimum insertion loss as 0.59 dB and maximum return loss as 40.1 dB, whereas second passband has minimum insertion loss as 1.33 dB and maximum return loss as 36.62 dB. The presented filter structure is designed using Keysight Advance Design System (ADS). The simulated s-parameter characteristics performance is found to be in good agreement with the measured result.

Twin cascaded-trisection coupling topology and its application to dielectric waveguide resonator diplexer

This article investigates the twin cascaded-trisection (TCT) coupling topology, based on which a dielectric waveguide resonator (DWR) diplexer is designed. The TCT topology is constructed by two traditional trisection structures with one coupling route being shared. By properly setting the polarities of the couplings, it can generate two transmission zeros (TZs) on one side of the passband, either the low side or the high side. In order to facilitate the TCT topology, a four-pole DWR unit is constructed by flexibly utilizing four hexagonal DWRs. A diplexer with two frequency bands of 3.4 GHz−3.5 GHz (Channel 1) and 3.6 GHz−3.7 GHz (Channel 2) is designed by using two four-pole DWR units. A printed circuit board (PCB) is employed to realize the feeding and matching network for the two units. Two TZs are generated on the high side of the Channel 1 and two TZs are generated on the low side of Channel 2, making the filtering selectivity improved. The designed diplexer is fabricated and measured. For the two measured channels, the minimum insertion losses are 0.85 dB and 0.94 dB, and the isolations are better than 44 dB and 31 dB.

A compact 5-Watt low-loss and low-leakage reflective limiter for C-band

This paper introduces a reflective, low insertion loss transistor-based limiter based on a new leakage reduction method. The effectiveness of the proposed limiter has been confirmed through simulation and measurement results. Due to its low insertion loss, the proposed limiter is suitable for low-noise receivers. It reflects approximately 70% of the input power, leading to lower temperature rise, when subjected to high incident power, compared to absorptive limiters. Fabricated using a low-noise 0.15-μm AlGaAs–InGaAs pseudomorphic HEMT (pHEMT) technology, this design allows for co-design with a low noise amplifier (LNA) on the same die. Measurement results have demonstrated that the proposed limiter can withstand up to 5-W continuous-wave (CW) input power without failure in a compact chip area of only 0.8 mm2. Additionally, measurements show a minimum insertion loss of 0.83 dB with 0.17 dB ripple over the frequency range of 4–6 GHz.

Single- and dual-band high-order polarization rotating frequency selective surface

Abstract This work presents the design and development of dual- and single-band polarization rotating frequency selective surfaces (PR-FSSs) based on aperture-coupled patch multimode resonators. Initially, an open-loop slot is incorporated into the patch of a second-order resonator to design a dual-band second-order PR-FSS (DPR-FSS), which enables effective polarization rotation and frequency selection across two distinct passbands. Then, to develop a single-band fourth-order PR-FSS (SPR-FSS), we introduce a metallic via into the DPR-FSS. This modification results in a single-band fourth-order response. The SPR-FSS offers a bandwidth of 41% with minimal insertion loss and high roll-off characteristics. Finally, experiments are conducted to verify the performance of the proposed structures. Good agreement can be observed between simulation and measurement.

A Miniaturized SISL Bandpass Filter Based on Deep Hole Drilling Capacitor

ABSTRACTIn this paper, a quasi‐lumped element‐based bandpass filter is implemented by substrate‐integrated suspended line (SISL) technology. To miniaturize the filter size, a deep hole drilling capacitor (DHDC) structure is proposed. The properties of DHDC are derived by parametric analysis and equivalent circuit analysis. Based on derived properties, a quasi‐lumped element bandpass filter using SISL technology is designed and fabricated. Experimental results demonstrate that the proposed bandpass filter achieves the center frequency of 1.48 GHz, with a fractional bandwidth of 50%. The minimum insertion loss within the passband is 0.96 dB, while the return loss exceeds 23.14 dB. The maximum out‐of‐band suppression is over −50 dB, and the filter size is only 0.172 λg × 0.062 λg.

In Situ Multiphysical Metrology for Photonic Wire Bonding by Two-Photon Polymerization.

Femtosecond laser two-photon polymerization (TPP) technology, known for its high precision and its ability to fabricate arbitrary 3D structures, has been widely applied in the production of various micro/nano optical devices, achieving significant advancements, particularly in the field of photonic wire bonding (PWB) for optical interconnects. Currently, research on optimizing both the optical loss and production reliability of polymeric photonic wires is still in its early stages. One of the key challenges is that inadequate metrology methods cannot meet the demand for multiphysical measurements in practical scenarios. This study utilizes novel in situ scanning electron microscopy (SEM) to monitor the working PWBs fabricated by TPP technology at the microscale. Optical and mechanical measurements are made simultaneously to evaluate the production qualities and to study the multiphysical coupling effects of PWBs. The results reveal that photonic wires with larger local curvature radii are more prone to plastic failure, while those with smaller local curvature radii recover elastically. Furthermore, larger cross-sectional dimensions contribute dominantly to the improved mechanical robustness. The optical-loss deterioration of the elastically deformed photonic wire is only temporary, and can be fully recovered when the load is removed. After further optimization based on the results of multiphysical metrology, the PWBs fabricated in this work achieve a minimum insertion loss of 0.6 dB. In this study, the multiphysical analysis of PWBs carried out by in situ SEM metrology offers a novel perspective for optimizing the design and performance of microscale polymeric waveguides, which could potentially promote the mass production reliability of TPP technology in the field of chip-level optical interconnection.

Graphene modulator and 2-bit encoder based on plasma induced transparency effect

Within this study, a periodic metasurface structure made up of two graphene strips, two fan-shaped graphene and a square ring graphene with notches is introduced to achieve plasma-induced transparency (PIT). The PIT effect is analyzed utilizing the Lorentz oscillatory coupling model, and it has been discovered that the theoretical values closely match the simulated values. The role of the Fermi level adjustments in graphene on the PIT effect was examined, and the PIT window was dynamically modified as the Fermi level changed, which was used to realize a 2-bit graphene encoder at 5.78 THz and 7.18 THz. The encoder boasts a greatest modulation depth of 80.9 % and exhibits a minimal insertion loss of 0.17 dB. By controlling the polarization direction of the incident photoelectric field, a high performance dual-channel switching modulator is successfully realized. Moreover, by increasing carrier mobility, the depth of modulation for the modulator at 11.22 THz is increased from 97.5 % to 99.5 %, and the insertion loss has dropped from 0.075 dB to 0.06 dB. In addition, the structure has superior sensing properties and slow light properties, featuring a sensitivity reaching up to 1.07 THz/RIU and a maximum group index of 293. The outcomes of our study contribute novel insights for the advancement of modulator, encoder, sensor technology and slow-light devices.

Compact THz Polarization Splitter with Large Bandwidth Based on Cascade Hexagonal Porous Two-Core PCF

ABSTRACT A novel cyclic olefin copolymer (COC)-based terahertz (THz) polarization beam splitter (PBS) employing photonic crystal fiber (PCF) with cascade hexagonal porous two-core structure is proposed. The porous two-core is achieved by replacing the original two large air holes with three layers of small air holes. The mode coupling characteristics between the even and odd modes in the x- and y-polarization directions for the proposed THz PBS are explored using the time-domain finite difference (FDTD) method. The influence of PBS structural parameters on its coupling length is investigated. Numerical analysis results indicate that the bandwidths of 227.8 GHz (ranging from 1.8970 to 2.1248 THz) and 147 GHz (ranging from 1.928 to 2.075 THz) are acquired for the x- and y-polarization fundamental modes, respectively. The highest extinction ratios (ERs) are 114.5 dB and 72.3 dB, and the minimum insertion losses (ILs) are 0.0142 dB and 0.0369 dB for the x- and y-polarization fundamental modes, respectively. Moreover, the length of the proposed PBS is merely 11.655 mm. The proposed PBS will find potential applications in polarization-diverse THz systems, including broadband line-of-sight communication, real-time security checks, and high-resolution imaging.

Silicon nitride directional coupler-based polarization beam splitter utilizing shallow ridge waveguides for improved fabrication tolerance

This study presents the design and fabrication of a silicon nitride (Si3N4) asymmetrical directional coupler (DC)-based polarization beam splitter (PBS) utilizing a shallow ridge waveguide structure. The use of Si3N4 with a moderate refractive index contrast and the design of a shallow ridge waveguide enables the DC structure to have a wider coupling gap of approximately 600 nm, which can be readily achieved with standard I-line lithography. The simulation results indicate that the polarization splitting is highly efficient with minimal insertion loss. This is corroborated by the experimental measurements, which show consistent broadband performance. The fabricated polarization beam splitter (PBS) exhibits a high polarization extinction ratio (PER) of over 20 dB for both transverse electric (TE) and transverse magnetic (TM) modes across a broad bandwidth of 120 nm (1500–1620 nm). This work demonstrates the potential of shallow ridge Si3N4 waveguides to enhance the fabrication tolerance and performance of integrated photonic devices.

Performance signature for angular misalignment measurement of fiber to fiber connectors with minimum insertion loss and low distortion in optical fiber transceiver systems

Performance signature for angular misalignment measurement of fiber to fiber connectors with minimum insertion loss and low distortion in optical fiber transceiver systems

Ionogels, Promising Exploration for Flexible Optically Transparent Tunable All‐Dielectric Electromagnetic Metamaterials

AbstractIonogels, as a novel class of environmentally friendly electronic materials, have received extensive attention. This study successfully prepared P(AM‐co‐AA) ionogel with optical transparency and flexibility via chemical polymerization. Experimental outcomes reveal that the dispersion of anions and cations within the ionogel is effectively controlled by the polymer network, resulting in distinct dispersive dielectric property, which is suitable for applications in electromagnetic metamaterials. Leveraging these properties, two distinct electromagnetic metamaterial devices are developed: An Ionogel‐based Broadband Absorber achieves over 90% absorption across 10.9–25.36 GHz, and An Ionogel‐based Frequency Selective Rasorber (FSR) transmits within 4.62–5.86 GHz, exhibiting minimal insertion loss −1.45 dB and achieves greater than 90% absorption from 13 to 17.8 GHz. High agreement between experimental results and simulations validates the feasibility of utilizing ionogel in electromagnetic metamaterial applications and introduces a novel paradigm and methodology for designing and fabricating flexible electromagnetic metamaterial devices.

A High Q Lamb Wave Resonator with Dummy Toes Based on 20% ScAlN Film

Abstract The lamb wave resonator (LWR) based on aluminum nitride (AlN) films are preferred strategy for high-frequency filters in 5G communication due to the tunable electromechanical coupling and high Q value. However, since the low electromechanical coupling and piezoelectric coefficient of AlN films, conventional lamb filters are difficult to meet the requirements of high bandwidth and low loss. This work proposes a lamb wave resonator with dummy toes (DT-LWR) based on scandium-doped aluminum nitride (ScAlN) film to improve the quality factor(Q) meanwhile suppress the spurious modes. The processed DT-LWR was tested using a vector network analyser (VNA, Keysight N5222B), and the MBVD model was used to fit the Z parameters. The Q value of DT-LWR is 1437.23, while that of LWR is 1250.09. It is increased by 14.97%. The enhancements make the DT-IWR as an ideal for filters with minimal insertion loss.

A miniaturized on‐chip BPF with low insertion loss and wide stopband based on integrated passive device technology

AbstractIn this study, a novel bandpass filter (BPF) characterized by low insertion loss (IL) and the presence of two transmission zeros (TZs) based on integrated passive device (IPD) technology is introduced. The design incorporates a low‐pass filter and a high‐pass filter which both exhibit strong out‐of‐band suppression performance. The control structure for TZs is constructed by cascading the inductance and capacitance components. The TZ controlling structure primarily generates TZs at high frequencies, resulting in a further bandwidth enhancement in the stopband. The lumped circuit of the proposed BPF is first constructed, and rigorous design formulas are provided to assist in constructing the proposed design. After schematic optimization, the second step involves layout optimization and simulation based on the specific IPD process. Experimental results mounted on a printed circuit board demonstrate that the bandwidth spans from 3.3 to 4.2 GHz with an IL of only 2.0 dB at the center frequency. Additionally, this BPF achieves impressive sideband suppression, exceeding 18 dB in the 0–1.7 GHz range and 30 dB in the 9–15 GHz range. Remarkably, the BPF is exceptionally compact with only 0.5 mm × 1.0 mm (0.006λc × 0.012λc). The proposed BPF exhibits outstanding performance with minimal IL and extensive sideband suppression at such a compact size based on the IPD technology.

Asymmetric CMOS switch for Dicke radiometer in millimeter-wave imaging system

An asymmetric Dicke switch implemented in bulk complementary metal-oxide-semiconductor (CMOS) technology is proposed to achieve high isolation and low insertion loss in the D-band. A Dicke switch eliminates the noise in the signal transmitted from the antenna, providing a high signal-to-noise ratio at the receiver front end. The proposed Dicke switch employs an asymmetric configuration for the signal transmission path and the reference noise incidence path, which overcomes the trade-off relationship between the insertion loss and isolation characteristics. The proposed asymmetric structure presents an optimum impedance in the reference component to achieve the same characteristics as those of the noise incident from the antenna port. The Dicke switch is fabricated using the 65-nm RFCMOS process with a chip size of 350 × 490 μm2, including all the pads. The measurement results in the D-band present an insertion loss below 2.8 dB in the on-state and isolation above 22 dB in the off-state. The minimum insertion loss and maximum isolation were measured to be 1.7 dB at 155 GHz and 29 dB at 122 GHz, respectively.

Filter cable design with defected conductor transmission structures

Electrical cables, as the industry’s blood vessels and nervous system, require evolving distributed filtering for complex electromagnetic environment adaptability. This article introduces a filter cable design featuring an insulated cylinder coated with a defected conductor transmission structure (DCTS). The DCTS, with a well-designed etched pattern, functions as a boundary condition for transmitting specific frequency electromagnetic waves, similar to a lumped filter circuit. To validate this method, a low-pass filter cable is proposed with six-slot-ring defected structures, utilizing polytetrafluoroethylene as the inner dielectric, encased within a flexible printed circuit board (FPCB)-manufactured DCTS. The proposed cable, with precise dimensions (2.4 mm diameter, 340 mm length), demonstrates minimal insertion loss ( < 0.38 dB below 6 GHz) in the passband and rejection exceeding 23 dB at 7.7-25 GHz in the stopband. Further enhancements achieve attenuation exceeding 50 dB in the stopband (7.1 GHz to 20 GHz). Compared to traditional cables, this filter cable addresses electromagnetic compatibility (EMC) by cutting off the interference coupling path.

Design of distributed impedance‐matching networks for ultra‐wideband low‐noise amplifiers

AbstractAn ultra‐wideband low‐noise amplifier (LNA) design was developed based on distributed network synthesis to achieve impedance matching of an active device by parasitic absorption. The equivalent device models of a low‐noise device were generated using negative‐image device modeling and traveling‐wave matching, and matching circuits were produced using the Chebyshev approximation. The minimum insertion loss and ripple of the matching networks were adjusted correctly to allow the parasitic absorption to match the device models. This paper describes the design methodology for distributed matching circuits and its application to the design of an ultra‐wideband LNA.