Search Results (60)

In this paper, an automatic phase-shifting interferometer has been developed using a homemade liquid-crystal phase shifter, which demonstrates a low-cost, fully automated technical solution for measuring the phase information of optical waves in devices. Conventional phase-shifting interferometers usually rely on PZT piezoelectric phase shifters, which are complex, require additional half-inverse and half-transparent optics to build the optical path, and are expensive. To overcome these limitations, we used a laboratory-made liquid-crystal waveplate as a phase shifter and integrated it into a Mach–Zehnder phase-shifting interferometer. The system is controlled by an STM32 microcontroller and self-developed measurement software, and it utilizes a four-step phase-shift interferometry algorithm and the CPULSI phase-unwrapping algorithm to achieve automatic phase measurements. Phase test experiments using a standard plano-convex lens and a homemade liquid-crystal grating as test objects demonstrate the feasibility and accuracy of the device by the fact that the measured focal lengths are in good agreement with the nominal values, and the phase distributions of the gratings are also in good agreement with the predefined values. This study validates the potential of liquid-crystal-based phase shifters for low-cost, fully automated optical phase measurements, providing a simpler and cheaper alternative to conventional methods. Full article

Photonic integrated circuits (PICs) are crucial for advanced applications in telecommunications, quantum computing, and biomedical fields. Silicon nitride (SiN)-based platforms are promising for PICs due to their transparency, low optical loss, and thermal stability. However, achieving efficient thermo-optic (TO) modulation on SiN remains challenging due to limited reconfigurability and high power requirements. This study aims to optimize TO phase shifters on SiN platforms to enhance power efficiency, reduce device footprint, and minimize insertion losses. We introduce a CMOS-compatible plasmo-photonic TO phase shifter using a SiOC material layer with a high TO coefficient combined with aluminum heaters on a SiN platform. We evaluate four interferometer architectures—symmetric and asymmetric Mach–Zehnder Interferometers (MZIs), an MZI with a ring resonator, and a single-arm design—through opto-thermal simulations to refine performance across power, losses, footprint, and switching speed metrics. The asymmetric MZI with ring resonator (A-MZI-RR) architecture demonstrated superior performance, with minimal power consumption (1.6 mW), low insertion loss (2.8 dB), and reduced length (14.4 μm), showing a favorable figure of merit compared to existing solutions. The optimized SiN-based TO switches show enhanced efficiency and compactness, supporting their potential for scalable, energy-efficient PICs suited to high-performance photonic applications. Full article

The polarization state of light is critical for biological imaging, acousto-optics, bio-navigation, and many other optical applications. Phase shifters are extensively researched for their applications in optics. The size of optical elements with phase delay that are made from natural birefringent materials is limited; however, fabricating waveplates from dielectric metamaterials is very complex and expensive. Here, we present an ultrathin (14 nm) metallic phase shifter developed using nanoimprinting technology and the oxygen plasma ashing technique for visible and near-infrared wavelengths. The fabrication process can produce desirable metallic phase shifters with high efficiency, large area, and low cost. We demonstrate through a numerical simulation and experiment that the metallic phase shifter exhibits phase delay performance. Our results highlight the simplicity of the fabrication process for a metallic phase shifter with phase delay performance and offer important opportunities for creating high-efficiency, ultrathin polarizing elements, which can be used in miniaturized devices, such as integrated circuits. Full article

In this study, the potential of employing SiN_x (silicon nitride) waveguide platforms to enable the use of liquid-crystal-based phase shifters for on-chip optical modulators was thoroughly investigated using 3D-FDTD (3D finite-difference time-domain) simulations. The entire structure of liquid-crystal-based Mach–Zehnder interferometer (MZI) optical modulators, consisting of multi-mode interferometer splitters, different tapering sections, and liquid-crystal-based phase shifters, was systematically and holistically investigated with a view to developing a compact, wideband, and CMOS-compatible (complementary metal-oxide semiconductor) bias voltage optical modulator with competitive modulation efficiency, good fabrication tolerance, and single-mode operation using the same SiN_x waveguide layer for the entire device. The trade-off between several important parameters is critically discussed in order to reach a conclusion on the possible optimized parameter sets. Contrary to previous demonstrations, this investigation focused on the potential of achieving such an optical device using the same SiN_x waveguide layer for the entire device, including both the passive and active regions. Significantly, we show that it is necessary to carefully select the phase shifter length of the LC-based (liquid crystal) MZI optical modulator, as the phase shifter length required to obtain a π phase shift could be as low as a few tens of microns; therefore, a phase shifter length that is too long can contradictorily worsen the optical modulation. Full article

Ultra-compact passive phase shifters are inversely designed by the multi-objective particle swarm optimization algorithm. The wavelength-dependent phase difference between two output beams originates from the different distances of the input light passing through the 4 μm × 3.2 μm rectangular waveguide with random-distributed air-hole arrays. As the wavelength changes from 1535 to 1565 nm, a phase difference tuning range of 6.26 rad and 6.95 rad is obtained for TE and TM modes, respectively. Compared with the array waveguide grating counterpart, the phase shifters exhibit higher transmission with a much smaller footprint. By combining the inverse-designed phase shifter and random-grating emitter together, integrated beam-steering structures are built, which show a large scanning range of ±25.47° and ±27.85° in the lateral direction for TE and TM mode, respectively. This work may pave the way for the development of ultra-compact high-performance optical phased array LiDARs. Full article

In this paper, a filterless 32-tupling millimeter wave generation scheme based on eight MZMs is proposed. The system has an upper and lower parallel two-branch structure. The upper branch consists of two subsystems Sub-A and Sub-B in cascade, each subsystem contains four MZMs, and the MZMs are all operating at maximum transfer point (MATP). Sub-A mainly generates ±8th order optical sideband signal as the incident light signal of Sub-B. After modulation of Sub−B, the output signal is mainly ±16th order optical sideband signal containing the central optical carrier component. The optical attenuator (OATT) and optical phase shifter (OPS) of the lower branch are used to regulate the phase and amplitude of the optical carrier. The upper and lower branches are coupled, and the central optical carrier component is superimposed and cancelled so only the ±16th order optical sideband signal is retained. Finally, the 32-tupling frequency millimeter is generated by the photodiode (PD) receiver after photoelectric detection which receives and generates a 32-tupling frequency millimeter wave signal. The simulation results show that the 160 GHz millimeter wave signal can be obtained by driving the MZM with a 5 GHz RF signal, and the optical sideband suppression ratio (OSSR) and the RF sideband suppression ratio (RFSSR) are 52.6 dB and 44.75 dB, respectively. Theoretical analysis and simulation experiments are carried out for the proposed scheme which proves the feasibility of the scheme. Full article

The paper presents a novel small-footprint varactor diode-based reconfigurable reflectarray (RRA) design and investigates its power reflection efficiency theoretically and experimentally in a real-life indoor environment. The surface is designed to operate at 865.5 MHz and is intended for simultaneous use with other wireless power transfer (WPT) efficiency-improving techniques that have been recently reported in the literature. To the best of the authors’ knowledge, no RRA intended to improve the performance of antenna-based WPT systems operating in the sub-GHz range has been designed and studied both theoretically and experimentally so far. The proposed RRA is a two-layer structure. The top layer contains electronically tunable phase shifters for the local phase control of an incoming electromagnetic wave, while the other one is fully covered by metal to reduce the phase shifter size and RRA’s backscattering. Each phase shifter is a pair of diode-loaded 8-shaped metallic patches. Extensive numerical studies are conducted to ascertain a suitable set of RRA unit cell parameters that ensure both adequate phase agility and reflection uniformity for a given varactor parameter. The RRA design parameter finding procedure followed in this paper comprises several steps. First, the phase and amplitude responses of a virtual infinite double periodic RRA are computed using full-wave solver Ansys HFSS. Once the design parameters are found for a given set of physical constraints, the phase curve of the corresponding finite array is retrieved to estimate the side lobe level due to the finiteness of the RRA aperture. Then, a diode reactance combination is found for several different RRA reflection angles, and the corresponding RRA radiation pattern is computed. The numerical results show that the side lobe level and the deviation of the peak reflected power angles from the desired ones are more sensitive to the reflection coefficient magnitude uniformity than to the phase agility. Furthermore, it is found that for scanning angles less than 50°, satisfactory reflection efficiency can be achieved by using the classical reactance profile synthesis approach employing the generalized geometrical optics (GGO) approximation, which is in accord with the findings of other studies. Additionally, for large reflection angles, an alternative synthesis approach relying on the Floquet mode amplitude optimization is utilized to verify the maximum achievable efficiency of the proposed RRA at large angles. A prototype consisting of 36 elements is fabricated and measured to verify the proposed reflectarray design experimentally. The initial diode voltage combination is found by applying the GGO-based phase profile synthesis method to the experimentally obtained phase curve. Then, the voltage combination is optimized in real time based on power measurement. Finally, the radiation pattern of the prototype is acquired using a pair of identical 4-director printed Yagi antennas with a gain of 9.17 dBi and compared with the simulated. The calculated results are consistent with the measured ones. However, some discrepancies attributed to the adverse effects of biasing lines are observed. Full article

A Silicon Photonics modulator is a high-speed photonic integrated circuit for optical data transmission in high-capacity optical networks. Silicon Photonics modulators in the configuration of a Mach–Zehnder interferometer, in which a PN-junction rib-waveguide phase shifter is inserted in each arm of the interferometer, are studied in this paper because of their superior performance of high-quality optical data generation in a wide range of spectral bands and their simplicity in fabrication processes suitable to production in foundries. Design, fabrication, and fundamental characteristics of Silicon Photonics Mach–Zehnder modulators are reviewed as an introduction to these high-speed PICs on the Silicon Photonics platform. Modulation speed, or modulation bandwidth, is a key performance item, as well as optical loss, in the application to high-speed optical transmitters. Limiting factors on modulation speed are addressed in equations. Electrical resistance–capacitance coupling, which causes optical modulation bandwidth–optical loss trade-off, is the most challenging limiting factor that limits high-speed modulation. Expansion of modulation bandwidth is not possible without increasing optical loss in the conventional approaches. A new idea including quantum-mechanical effect in the design of Silicon Photonics modulators is proposed and proved in computational analysis to resolve the bandwidth loss trade-off. By adding high-mobility quantum-well overlayers to the side slab wings of the rib-waveguide phase shifter, the modulation bandwidth is doubled without increasing optical loss to achieve a 200 Gbaud modulation rate. Full article

Micro-electromechanical systems (MEMS) have the potential to provide low-power phase shifting in silicon photonics, but techniques for designing low-loss devices are necessary for adoption of the technology. Based on coupled mode theory (CMT), we derive analytical expressions relating the loss and, in particular, the phase-dependent loss, to the geometry of the MEMS phase shifters. The analytical model explains the loss mechanisms of MEMS phase shifters and enables simple optimization procedures. Based on that insight, we propose phase shifter geometries that minimize coupling power out of the waveguide. Minimization of the loss is based on mode orthogonality of a waveguide and phase shifter modes. We numerically model such geometries for a silicon nitride MEMS phase shifter over a silicon nitride waveguide, predicting less than −1.08 dB loss over a $2\pi$ range and −0.026 dB loss when optimized for a $\pi$ range. We demonstrate this design framework with a custom silicon nitride process and achieve −0.48 dB insertion loss and less than 0.05 dB transmission variation over a $\pi$ phase shift. Our work demonstrates the strength of the coupled mode approach for the design and optimization of MEMS phase shifters. Full article

The demand on fast and high-bandwidth data transmission is in continuous increase. These demands are highly dependent on optical signal manipulation, including switching, modulation, and routing. We demonstrate a two-port silicon optical router based on the multimode interferometer (MMI) configuration. The same MMI structure was used for both inward and backward waveguiding to reduce the total length of the device. A phase shifter consisting of two ring-like waveguides made of silicon p-n junctions was used to introduce the phase shift needed for optical routing upon voltage application. Two designs for the MMI optical router were studied: Firstly, a conventional MMI with a crosstalk ratio of 15.1 dB was investigated. Finally, an angled MMI reaching a crosstalk ratio of 18.2 dB at a wavelength of 1.55 μm was investigated. Full article

This work serves as the first simulation investigation to tackle the liquid crystal (LC)-filled coaxially structured continuously variable phase shifter at 60 GHz, wherein the LCs act as single tunable dielectrics fully occupying the millimeter-wave (mmW) power transmitted (i.e., free of leakage or interference). Impedance and effective dielectric constant computations are settled, followed by the quantification of the interplay between the dielectric thickness and the dielectric constant (Dk) for a controlled 50 Ω impedance. Geometry’s aspect ratio (AR) effects are exploited for the coaxially accommodating topology filled with mmW-tailored LCs with an operatable Dk range of 2.754 (isotropic state) to 3.3 (saturated bias state). In addition to the proposed structure’s noise-free advantages, a novel figure of merit (FoM) enhancement method based on Dk-selection-based impedance matching is proposed. The optimum FoM design by simulation exhibits a 0–180.19° continuously variable phase shift with a maximum insertion loss of 1.75871 dB, i.e., a simulated FoM of 102.46°/dB when the LC-filled coaxial geometry is 50 Ω and matched with the Dk of 2.8, corresponding to the dielectric thickness of 0.34876 mm and line length of 15.92 mm. The envisioned device fabrication and assembly processes are free of the conventional polyimide alignment agent and the related thermal and electrical concerns. Significant cost reduction and yield improvement can hence be envisaged. The topology can also serve as a test structure for broadband characterizations of LC materials and new electro-optical effects. Full article

A microwave photonic frequency-doubling phase shifter with a broad bandwidth and large tuning range is proposed in this paper. Frequency doubling and phase shifting are realized by processing the input microwave signal in the optical domain at a dual-drive dual-parallel Mach–Zehnder modulator (DD-DPMZM) and a dual-parallel Mach–Zehnder modulator (DPMZM). The input signal is split into two branches through a 90-degree hybrid splitter. One signal is sent to the DD-DPMZM to achieve a phase-shifted carrier-suppressed up-sideband by tuning the bias voltage, and the other is sent to the DPMZM to realize a carrier-suppressed down-sideband. By beating the phase-shifted up-sideband and the down-sideband at a photodetector (PD), the input signal is frequency doubled and phase shifted. The proposed frequency-doubling phase shifter is simulated. The results show that the frequency-doubled signal has a phase-tuning range from 0 to 360 degrees. In addition, the influence of the amplitude and phase unbalance of the 90-degree hybrid splitter on the magnitude variation and phase deviation of the frequency-doubling phase shifter is studied. Full article

This work introduces a novel architecture for implementing a parallel coherent photonic digital-to-analog converter (PDAC), designed to transform parallel digital electrical signals into corresponding analog optical output, convertible to analog electrical signals using photodiodes. The proposed architecture incorporates microring resonator-based modulators (MRMs), phase shifters, and symmetric multimode interference couplers. Efficient modulation is achieved by MRMs utilizing carrier depletion-induced refractive index changes, while metal heaters facilitate tuning of the ring resonator resonance wavelength. The proposed architecture is scalable to higher bit resolutions and exhibits a dynamic range limited by MRM’s sensitivity to applied bias and noise levels. Experimental results of the fabricated chip in the silicon-on-insulator (SOI) platform showcase the successful realization of a 4 GSample/sec conversion rate in a 2-bit resolution operation, along with a stationary conversion of four parallel DC digital signals into 16 analog intensity levels in a 4-bit PDAC configuration. The study encompasses a proof-of-concept experimental demonstration of 8 Gbps data conversion, along with a 50 Gbps data conversion rate using the optimized design in the simulation, affirming the accuracy and quality of the PDAC architecture. These findings contribute to the advancement of PDAC technology, providing insights into performance characteristics, limitations, and potential applications. Full article

Electro-optic modulator (EOM) is one of the key devices of high-speed optical fiber communication systems and ultra-wideband microwave photonic systems. Silicon–organic hybrid (SOH) integration platform combines the advantages of silicon photonics and organic materials, providing a high electro-optic effect and compact structure for photonic integrated devices. In this paper, we present an SOH-integrated EOM with comprehensive investigation of EOM structure design, silicon waveguide fabrication with Slot structure, on-chip poling of organic electro-optic material, and characterization of EO modulation response. The SOH-integrated EOM is measured with 3 dB bandwidth of over 50 GHz and half-wave voltage length product of 0.26 V·cm. Furthermore, we demonstrate a microwave photonics phase shifter by using the fabricated SOH-integrated dual parallel Mach–Zehnder modulator. The phase shift range of 410° is completed from 8 GHz to 26 GHz with a power consumption of less than 38 mW. Full article

A commercial thermo-optic phase shifter (TOPS) is an efficient solution to the imbalance problem in the fabrication process of Mach–Zehnder modulator (MZM) arms. The TOPS consumes electrical power and transforms it into thermal energy, which changes the real part of the effective refractive index at the waveguide and adjusts the MZM transfer function to work in the linear region. The common model being used today is constructed with only one heater; however, this solution requires more electrical power, which can increase the transmitter system cost. To reduce the system energy cost, we propose a pioneering optimal double titanium nitride heater model under forward biasing at 1550 nm wavelength using the standard silicon-on-insulator technology. Numerical investigations were carried out on the key relative geometrical parameters, heat distribution at the silicon layer, thermal crosstalk, and laser wavelength drift. Results show that the optimal TOPS design can function with a low electrical power of 19.1 mW to achieve a π-phase shift, with a low thermal crosstalk of 0.404 and very low optical losses over 1 mm length. Thus, the proposed device can be used for improving the imbalance problem in MZMs with low electrical power consumption and low losses. This functionality can be utilized to obtain better performances in transmitter systems for data centers and long-range optical communication system applications. Full article