Tunable Power Splitter Research Articles

Tunable optical power splitter based on directional coupler structure with phase change material Sb2Se3

Traditional optical power splitters (OPSs) have fixed power split ratios, and although some can be tuned with an electro-optic polymer, continuous energy supply increases power consumption. Combining OPS with chalcogenide phase-change materials (PCMs) allows us to tune the power split ratio with a low power owing to the nonvolatility and contrasting optical properties of the PCM. In this paper, a compact 1 × 2 arbitrary ratio OPS with hybrid directional coupler structure with PCM Sb2Se3 is proposed for lower-power and reconfigurable PICs. It demonstrates a continuous change in the power split ratios by changing the crystalline fraction of the Sb2Se3 material covered on coupling waveguide. The non-volatile states of Sb2Se3 enables zero static power of the device. The splitting ratio can be tuned in a broad range from 1 % to 97 % with the excess loss of 0.11 dB at 1550 nm. Such device can be extended to perform a handwritten digit recognition task with the simulated properties to determine the performance of the OPS device in the neuromorphic network. Its recognition accuracy achieves as high as 95 % for the MNIST (Modified National Institute of Standard and Technology) handwritten digits, which is close to that of device with ideal characteristics based on the software computing. The results indicate that the proposed OPS can not only achieve large range tunable power allocation, but also be further applied to large-scale PICs and optical neuromorphic networks.

Compact Slow-Light Integrated Silicon Electro-Optic Modulators With Low Driving Voltage

In this work, we report two slow-light enhanced silicon optical modulators with electro-optic (EO) phase shifter lengths of 500 μm and 150 μm that were fabricated using the AIM Photonics foundry. Tunable power splitters give a threefold increase in the extinction ratio (ER). An eye diagram operating at 10 Gbps was achieved using a very low signal voltage of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> = 500mV. The energy per bit is 57.5 fJ/bit and 45 fJ/bit for the 500 μm and 150 μm modulators, respectively. The nonlinearity of the devices were measured yielding spur-free dynamic range of 113.2 dB/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> . The 150 μm length MZM is among the smallest optical modulators using Bragg gratings for slow light ever reported and results in an estimated modulation efficiency of 0.33 V·cm.

Design and simulation of a dynamically tunable 1× 2 power splitter using MZI configuration in the telecom regime

We propose an ultra-broadband, ultra-compact and a dynamically tunable power splitter on a silicon on Insulator (SOI) platform with a 220 nm thick silicon light-guiding layer, using two multimode interference (MMI) couplers connected with graphene-based waveguides as the phase-tuning section through a Mach-Zehnder Interferometer (MZI) configuration. First, we theoretically present and demonstrate a novel design for the MMI couplers by combining the plane wave expansion method (PWEM) and the mode expansion conjecture concept. To verify the proposed theory, a center-fed MMI coupler and a MMI coupler, respectively, as the input and output sections of our proposed device, are designed and simulated. The simulation results achieved by Lumerical FDTD show good agreement with the design theory. Then, a highly tunable graphene-embedded silicon waveguide, for the highly efficient modulation of the effective mod index (EMI), is duly designed using Lumerical Mode Solutions. As the two MZI arms, a pair of the proposed waveguides is introduced into the middle of the cascaded MMI couplers. Accordingly, the integration properties of the analytically designed MMI couplers and the numerically designed waveguide is demonstrated through our proposed device for the aim of achieving any wanted power splitting ratio. To this end, we consider the case that the real part of the EMI of the waveguide in the lower MZI arm is modulated by varying the graphene Fermi level values, being the same for all the layers belonging to the same waveguide, while that of the upper arm is constant. The corresponding power splitting ratio can be dynamically tuned in the range of All reported results assume TE polarization. The designed MZI-based splitter possesses a bandwidth of over the wavelength range from to for various power splitting ratios, maintaining the averaged insertion loss and the averaged power imbalance, respectively, below as low as and The overall footprint of the proposed device is also highly small, i.e., about

Unidirectional mode interference in magneto-optical photonic heterostructure

We investigate a unidirectional mode interference effect based on one-way coupled topological edge states (CTESs), which originate from the coupling of topological edge states (TESs) in magneto-optical photonic crystal (MOPC) heterostructure. By using the finite element method, the self-imaging phenomenon in the MOPC heterostructure is predicted. As an example of applications, a one-way tunable frequency and power splitter based on unidirectional mode interference is designed, which is reflectionless. Besides, the splitting ratio can be tuned by adjusting the external magnetic field. Moreover, the splitter is robust against common disorders, including the radius- and position-fluctuations of pillars and nonuniform magnetizations, which keep the bandgap open. Our findings provide a new, to the extent of our knowledge, way of designing integrated photonic circuit applications such as reflectionless filters, couplers, multiplexers, switches, or even nonreciprocal devices, and so on.

Ultra-compact In&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt; tunable power splitter based on direct binary search algorithm

Power splitter with multi-mode interference coupler structure has many advantages, such as large bandwidth and better manufacturing robustness, and has received much attention for a long time. Conventional power beam splitters usually use algorithms or numerical simulation to achieve a single beam splitting ratio; if the circuit has the requirement for power, the structural parameters of the device need changing and recalculating. In order to improve the utilization rate of power splitter in photonic integrated circuit and meet various demands for different optical paths, an ultra-compact tunable power splitter based on phase change material In&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt; with a 1×2 multimode interference coupler structure is proposed in this paper. The device consists of an input waveguide, a coupling region, and two output waveguides with a coupling region of only 2.4 μm× 3.6 μm in size, which contains several circular holes of the same size and is filled with SiO&lt;sub&gt;2&lt;/sub&gt;. The number and location of circular holes in the coupling region are optimized by direct binary search algorithm, making the device achieve different power splitting ratios by using only the high refractive index contrast variation between the two crystalline states (&lt;i&gt;α&lt;/i&gt; and &lt;i&gt;β&lt;/i&gt;) of In&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt; without changing any other structural parameter. In a wavelength range of 1540–1560 nm, three splitting ratios of 1∶1, 1∶1.5 and 1∶2 are achieved by this device, and the insertion losses of these three beam splitting ratios are less than 0.27, 0.13 and 0.17 dB, respectively. In addition, the robustness and balance of the device are analyzed and discussed, and compared with those of the power splitter of the same size designed by SOI platform and several power beam splitters reported in recent years, demonstrating the compact structure and simple regulation of this power splitter based on the phase change material In&lt;sub&gt;2&lt;/sub&gt;Se&lt;sub&gt;3&lt;/sub&gt;, its good robustness, and its possibility of application on photonic integrated circuits.

Interference at the single-photon level based on silica photonics robust against channel disturbance

Quantum key distribution (QKD) provides a solution for communication of unconditional security. However, the quantum channel disturbance in the field severely increases the quantum bit-error rate, degrading the performance of a QKD system. Here we present a setup comprising silica planar light wave circuits (PLCs), which is robust against the channel polarization disturbance. Our PLCs are based on the asymmetric Mach–Zehnder interferometer (AMZI), integrated with a tunable power splitter and thermo-optic phase modulators. The polarization characteristics of the AMZI PLC are investigated by a novel pulse self-interfering method to determine the operation temperature of implementing polarization insensitivity. Over a 20 km fiber channel with 30 Hz polarization scrambling, our time-bin phase-encoding QKD setup is characterized with an interference fringe visibility of 98.72%. The extinction ratio for the phase states is kept between 18 and 21 dB for 6 h without active phase correction.

Numerical simulations of tunable ultrashort power splitters based on slotted multimode interference couplers

This paper presents an ultracompact tunable device for power splitting and switching by tuning the Fermi energy level of monolayer patternless graphene underneath a slotted multimode interference (MMI) coupler operating in the mid-infrared, λ = 9–11 μm. By introducing a high-index silicon slot in the central region of the MMI structure, which can significantly shorten the beat length, the proposed device has an approximately 4.5-fold reduction in device length and a two-fold improvement in power transmission compared with conventional MMI couplers without slotting. The device has a footprint of only 0.30 × 0.65 μm2 (<λ/10), making it the smallest power splitter and switcher. Over the bandwidth of 2 μm, the power transmission of the proposed device is nearly uniform. Extending the operating bandwidth is limited only by the practically achievable Fermi energy of graphene. For the fabrication tolerance, the numerical results show that the relative power variations are lower than 5%, even though the dimension variations are greater than 15%. With its advantages of tunability, compact footprint, and broadband operation, the proposed device is suitable for highly dense photonic integrated circuits.

Polarization-resolved edge states in terahertz topological photonic crystal.

The discovery of topological photonic states has revolutionized our understanding of electromagnetic propagation and scattering. With the introduction of topology, some attractive properties such as unidirectional propagation and robustness against defects and impurities will be endowed to photonic edge modes. In this study, two-dimensionally confined topological edge states were achieved at terahertz (THz) frequency based on an all-dielectric photonic crystal structure. Trivial and nontrivial bandgaps of two deforming honeycomb lattices as well as unidirectional topological edge states were observed. Because the topological edge states with opposite helicity propagated in opposite directions at the interface, a polarization-resolved characteristic was demonstrated here, and thus a continuously tunable power splitter was achieved. This study provides some insights for further THz topological studies and possibilities for THz integrated platforms.

High-efficiency tunable T-shaped beam splitter based on one-way waveguide

Power splitters have been widely studied in the fields of radio frequency and integrated photonics, however, conventional splitters generally suffer from poor transmission and limited bandwidth. Here we propose a novel tunable T-shaped power splitter utilizing one-way waveguide that is composed by the yttrium–iron–garnet–air–metal configuration with one static magnetic field applied. We show that the transmission efficiency of such a splitter reaches 100% in the lossless case due to the suppression of reflection by the one-way waveguide. By introducing a defect in the junction area, the splitting ratio of the splitter can be gradually tuned by varying the external magnetic field, and large operation bandwidth can be achieved for a given splitting ratio. Our results presented here focus on the radio frequency, and the concept can easily be applied to the photonic area.

On the Use of Tunable Power Splitter for Simultaneous Wireless Information and Power Transfer Receivers

The use of a tunable power splitter (PS) as a constituent component of a simultaneous wireless information and power transfer (SWIPT) system is discussed. Two varactor diodes are used to achieve a tunable output power ratio P2 : P3 varying from 1 : 1 to 1 : 10 under good matching conditions. The SWIPT system that operates at 2.4 GHz consists of a typical patch antenna, cascaded with the tunable PS, and a voltage doubler rectifier. The constituent components were implemented and tested as stand-alone devices and were subsequently combined in a measurement system using interconnectors. The effect of the tunable PS was explored with respect to the SNR measurements on the port that is intended for the information decoding receiver and the DC voltage measurements on the termination load of the rectifier that is connected directly on the energy harvesting port of the tunable PS. A spectrum analyzer is used for the SNR measurements while the input power is controlled using a signal generator. Both wireless power transmission and on-board measurements verify that the harvested energy can be maximized by using the minimum SNR at the information decoding branch at the expense of DC power consumption required for the biasing of the varactor diodes.

All-optical tunable power splitter based on a surface plasmonic two-mode interference waveguide.

In this paper, we have introduced a surface plasmonic two-mode interference (SPTMI) coupler having a silicon core, GaAsInP side cladding, and silver top and bottom cladding as an optical power splitter. A wide range of tunability from the 50∶50 splitting ratio to 1∶99 is achieved by refractive index modulation of the GaAsInP cladding with application of varying optical pulse power. The coupling length of the SPTMI-based splitter is ∼11.5 times less than that of a previously reported optical power splitter based on multimode waveguide holograms. The proposed optical power splitter has potential in development of large-scale integrated circuits due to its compactness and high fabrication tolerance.

Polarization-Insensitive and Broadband Optical Power Splitter With a Tunable Power Splitting Ratio

In this paper, we propose a novel tunable power splitter based on symmetric Mach–Zehnder (MZ) structure to achieve the polarization-insensitive and broadband performance. This good performance is realized by utilizing two 3 dB broadband directional couplers and square waveguides in a conventional symmetric MZ structure. Based on thermo-optic effect, the power splitting ratio of our power splitter for the TE and TM modes can be equally controlled in a wide operating bandwidth of 63 nm. Our results show a low polarization-dependent loss of 0.001–0.089 dB over a wide wavelength range of 1541–1604 nm.

High-efficiency tunable Y-branch power splitters at terahertz frequencies

Terahertz Y-branch power splitters formed by one-way waveguide are investigated theoretically. For such splitters, there exists no backward reflection from the Y-junction region for incident waves because the input channel supports no backward-propagating mode, therefore the transmission efficiency is perfect in the lossless case. Moreover, by varying the applied external magnetic field, the power splitting ratio of the splitters can be tunable for a given frequency, and required (equal or unequal) splitting ratio can also be achieved over a wide frequency band.

Tunable power splitter based on MIM waveguide-rectangle cavity system with Kerr material

A tunable power splitter based on metal-dielectric metal (MDM) waveguide coupled with rectangle cavity with Kerr nonlinear material is proposed. The power splitter properties are simulated by the finite-difference time-domain (FDTD) method [Y. H. Guo et al., Opt. Express 19 (2011) 13831–13838]. Simple theoretically analysis and numerically calculation demonstrate that the waveguide-rectangle cavity coupled system performs a tunable plasmonic power splitter. Additionally, the output power ratio can be efficiency tuned by varying the control light intensity. Results obtained by the coupled mode theory are consistent with those from the FDTD simulation. The plasmonic splitter may become a choice for the highly integrated optical circuits.

Topological terahertz circuits using semiconductors

Topological insulator-based devices can transport electrons/photons at the surfaces of materials without any back reflections, even in the presence of obstacles. Topological properties have recently been investigated using non-reciprocal materials, such as gyromagnetics, or using bianisotropy. However, these effects usually saturate at the optical frequencies and limit our ability to scale down the devices. In order to implement topological devices that we introduce in this paper for the terahertz range, we show that the semiconductors can be utilized via their cyclotron resonance in combination with small magnetic fields. We propose two terahertz operating devices such as the topological tunable power splitter and the topological circulator. This work opens up the perspectives in designing the terahertz integrated devices and circuits with high functionality.

Low Loss and Dynamically Tunable Power Splitter Based on Circular-to-Rectangular POF Converter

A tunable power splitter based on the predefined end shape of polymer optical fiber (POF) is fabricated for an efficiently integrated optical device. We show that the reshaped end fiber from round to rectangle cross section greatly reduce the interstitial space between POFs and mold-insert's waveguide. Control of power splitting ratios is realized through varying the deflection of the input fiber toward fixed output fibers for 0:100 splitting ratios. A 5-μm resolution with 1% splitting ratio accuracy can be accomplished with greater uniform illumination efficiency. Lower excess loss of 0.7 dB and insertion loss of 3.7 dB for a 3-dB splitter is measured. The observational results obtained here are confirmed by theoretical investigation as well.

Multilayer Hybrid Waveguide Amplifier for Three-Dimension Photonic Integrated Circuit

In this letter, a multilayer hybrid waveguide that can be applied to compensate the loss of three-dimension photonic integrated circuit is designed. The multilayer waveguide structure consists of grade index ion-exchange Er3+–Yb3+ co-doped phosphate planar waveguide, step index polymer rectangular waveguide, and heating electrode. Er3+–Yb3+ co-doped phosphate layer is to provide stable amplification performance. Polymer waveguides are designed to control the optical field distribution. The operating temperature is adjusted using the heating electrode. The optical field of signal light and pump light of the hybrid structure is simulated by finite difference method. The six-level model is introduced to calculate the gain characteristic of the hybrid waveguide amplifier with different Er3+ concentrations and operating temperatures. The optimized gain of the hybrid structure can be up to 4 dB/cm with the signal power of 0.1 mW and pump power of 200 mW. This hybrid waveguide can be used in the loss compensation and tunable vertical power splitter area.

Active microring based tunable optical power splitters

In this paper we propose a set of novel tunable optical power splitters based on active microring resonators. They work by operating ring resonators in the transient zone between full resonance and off-resonance states for a specific wavelength. We can achieve different split ratios by either varying the bias voltage, or by selectively enabling a given resonator with a specific split ratio among an array of ring resonators. We take 500ps to tune the resonator, which is at least 10× better that competing designs. Its split ratio varies from 0.4 to 1.8 for an applied voltage range of 0–5V.

Integrated Reconfigurable Coherent Transmitter Driven by Binary Signals

A novel InP monolithically integrated transmitter composed of a tunable distributed Bragg reflector laser and a reconfigurable IQ modulator with tunable power splitters has been designed, fabricated and tested. The transmitter architecture allows, in principle, generation of offset-free phase-amplitude constellations such as QPSK and 16-QAM by employing simple binary signals with equal peak-to-peak amplitude. The adoption of tunable splitters enables reconfiguration of the output constellation and compensation for imperfections related to fabrication. The solution presented in this paper minimizes the complexity of the employed architecture together with the one of the driving signals. Numerical analysis has been conducted to predict system behavior and evaluate the impact of sub-optimum settings that might occur in a real implementation. Experimental results show the generation PM-QPSK signals at 10 Gbaud when using the integrated DBR laser and at 32 Gbaud when using an external low-phase-noise laser. Unfortunately, the generation of 16-QAM signals, which can be in principle realized with this novel PIC, was not possible in practice because of significant spurious amplitude modulation in the electro-optic phase modulators.

InP monolithically integrated coherent transmitter.

A novel InP monolithically integrated coherent transmitter has been designed, fabricated and tested. The photonic integrated circuit consists of a distributed Bragg reflector laser and a modified nested Mach-Zehnder modulator having tunable input power splitters. Back-to-back coherent transmission for PDM-QPSK signals is reported up to 10 Gbaud (40 Gb/s) using the integrated laser and up to 32Gbaud (128 Gb/s) using an external low phase noise laser.