Output Waveguide Research Articles

Ultra-Wide Modulation and Reversible Reconfiguration of a Flexible Organic Crystalline Optical Waveguide Between 645 and 731 nm.

Flexible organic crystalline optical waveguides, which deliver input or self-emit light through various dynamic organic crystals, have attracted increasing attention in the past decade. However, the modulation of the waveguide output relies on chemical design and substituent modification, being time-consuming and laborious. Here we report an elastic organic crystal that displays long-distance light transduction up to 2.0 cm and an ultra-wide modulation of crystalline optical waveguides between red (645 nm) and near infrared (731 nm) in both the pristine and the elastically bent states based on a pre-designed self-absorption effect. The flexible organic crystalline optical waveguides can be precisely and reversibly reconfigured by controlling the irradiation point. In addition, deep-red amplified spontaneous emission (ASE) that is able to transduce through a 5.0 mm bent crystal with an ultra-low optical loss coefficient of 0.093 dB/mm has been attained. To the best of our knowledge, this is the first report of flexible organic ASE waveguides. The present study not only provides a simple yet effective strategy to remarkably modulate flexible organic crystalline optical waveguides but also demonstrates the superiority of lasing over normal emission as flexible optical communication elements.

Ultra‐Wide Modulation and Reversible Reconfiguration of a Flexible Organic Crystalline Optical Waveguide Between 645 and 731 nm

AbstractFlexible organic crystalline optical waveguides, which deliver input or self‐emit light through various dynamic organic crystals, have attracted increasing attention in the past decade. However, the modulation of the waveguide output relies on chemical design and substituent modification, being time‐consuming and laborious. Here we report an elastic organic crystal that displays long‐distance light transduction up to 2.0 cm and an ultra‐wide modulation of crystalline optical waveguides between red (645 nm) and near infrared (731 nm) in both the pristine and the elastically bent states based on a pre‐designed self‐absorption effect. The flexible organic crystalline optical waveguides can be precisely and reversibly reconfigured by controlling the irradiation point. In addition, deep‐red amplified spontaneous emission (ASE) that is able to transduce through a 5.0 mm bent crystal with an ultra‐low optical loss coefficient of 0.093 dB/mm has been attained. To the best of our knowledge, this is the first report of flexible organic ASE waveguides. The present study not only provides a simple yet effective strategy to remarkably modulate flexible organic crystalline optical waveguides but also demonstrates the superiority of lasing over normal emission as flexible optical communication elements.

Integrating angled multimode interferometer with Bragg grating filters for coarse wavelength division (de)multiplexing with optimized shape factor

Abstract We propose and experimentally demonstrate an angled multimode interferometer (AMMI) integrated with cascaded phase-shifted Bragg gratings (PSBGs) for coarse wavelength division multiplexing, based on a 400 nm-thick silicon nitride waveguide platform. Due to the design constraints, the spectral response of a standard AMMI filter suffers from the drawbacks of limited optical bandwidth, high inter-channel crosstalk, and non-ideal shape factor. Two techniques were used to improve performance. Firstly, it was found that increasing the input waveguide width of the AMMI is beneficial for the optical bandwidth while maintaining good insertion loss and crosstalk performance. Experimental results show that the 1 dB bandwidth increases from 7.6 nm to 9.7 nm. To achieve an improved shape factor and decreased crosstalk, the PSBG filters were utilized as the second-stage filters by integrating them at the output waveguides of the AMMI. Simulation results demonstrate an average crosstalk reduction of approximately 15.1 dB at the center wavelengths of the four channels and shape factor improvement by about 0.29. However, measurement results show an average crosstalk decrease of only about 5.5 dB, which is possibly due to the fabrication imperfection of the PSBGs and the unsatisfactory film quality of the SiN wafers used. Despite deviations between measured and simulated performance, the shape factor is increased from 0.26 to 0.74 using these proposed techniques, showing the feasibility of such an integration method.

A tunable narrow single-mode bandpass filter using graphene nanoribbons for THz applications

This paper presents a tunable, single-mode narrowband optical filter designed for terahertz applications utilizing graphene nanoribbons. To attain optimal conditions, the filter was devised in three steps. It is composed of two input and output waveguides and a T-shaped resonator with nanoscale dimensions. The transmission spectrum analysis employs the three-dimensional finite difference time domain and coupled mode theory methods. Tunability is achieved through the adjustment of the nanoribbon size and the chemical potential of graphene. The filter demonstrates remarkable performance metrics, including a maximum transmission spectrum efficiency of 99%, a full width at half maximum (FWHM) of 0.115 THz, a quality factor (Q-factor) of 100, and a free spectral range (FSR) of 45 THz. The presented structure holds significant promise for integrated optical components and compact optical devices, showcasing its applicability in the terahertz frequency range. Furthermore, the inherent sensitivity of this structure to changes in the refractive index of the substrate positions it as a potential sensor.

All-optical NOT, OR, and XOR Logic Gates Using Silicon Slot Waveguides

All-optical NOT, OR, and Exclusive OR(XOR) logic gates utilizing silicon slot waveguides are proposed and numerically analyzed in this work. The structure has a silicon slab with slot regions such as two input waveguides and square cavity resonators and one output waveguide. The optical spectra of the designed structures are attained with the method of finite difference time domain. The all-optical logic gate features of the design are achieved by applying optical signals with 00 or 1800 phase differences from the input ports. Basic parameters such as transmission spectrum (T), modulation depth (MD), and contrast ratio (CR) are performed to show the optical features and ability of the proposed logic gates. The threshold transmission limit is 1.7% to define the status of the output ports as ON or OFF. At 689.5 nm, the maximum transmission, modulation depth, and contrast ratio are 149%, 97%, and 15.36 dB, respectively.

A magnetically switchable demultiplexer via Terfenol-D in phononic crystal

This study introduces a novel approach for developing a controllable demultiplexer by applying a magnetic field to Terfenol-D cylinders within a solid–solid phononic crystal structure. Dynamic controllable demultiplexers are essential devices in acoustic and optical communication networks, yet adjustable elastic demultiplexers are notably lacking in current sound systems and acoustic communication technologies. The proposed phononic crystal-based demultiplexer features a square lattice (12 × 19) composed of tungsten cylinders embedded in a poly methyl methacrylate (PMMA) substrate. The switchable design consists of two identical, symmetrical parts separated by an input waveguide. In addition, each unit includes an output channel, a common input channel, and a square ring resonator, with the output channel side-coupled to the input bus waveguide. Moreover, Terfenol-D, a magnetostrictive material, is utilized in the hollow cylinders of the output channels. Switchability of the elastic demultiplexer outputs is achieved by dynamically altering the Young’s modulus of the Terfenol-D cylinders through the application of a magnetic field. This magnetic influence modifies the Young’s modulus of the Terfenol-D material in the output waveguides, enabling controllability. By varying the magnetic field applied to the demultiplexer, we find two distinct values of Young’s modulus within the structure. These two values facilitate the high transmission of two desirable peaks with narrow bandwidth through the output channels, allowing for switchable functionality based on the magnetic field’s position. The proposed demultiplexer demonstrates an average crosstalk value of −25.34 dB, indicating strong performance, along with a high average quality factor (Q) of 1773.5 and low average insertion losses of 0.85 dB in the MHz frequency range. The solid–solid elastic controllable demultiplexer is simulated using the finite element method, showcasing its potential for practical applications.

Realization of all-optical logic gates using MIM waveguides and a rectangular ring resonator

In this study, all-optical OR, exclusive OR (XOR), NOR, XNOR, AND, NAND, and NOT logic gates using metal-insulator-metal (MIM) waveguides with a rectangular ring resonator are designed and analyzed. The structure has a silver plate with three input waveguides, one output waveguide, and a rectangular ring resonator. One of the input ports is used as a control port. The finite-difference time-domain (FDTD) method is utilized to obtain the optical spectrum of the proposed structures. To realize all-optical logic gate properties of the designed structures, optical signals with the same phase or different phases are passed through the waveguides. Transmission spectrum (T), contrast ratio (CR), and modulation depth (MD) parameters are obtained to determine the performances of all-optical logic gates. To determine the logic 1 (ON) and logic 0 (OFF) states of the output ports, the threshold transmission value is accepted as 0.23 for all-optical logic gates. For the proposed designs, the highest transmission, contrast ratio, and modulation depth values are 217%, 6.75 dB, and 100%, respectively. The structure also supports a data rate of 24 Tb/s. The designed optical logic gates have valuable features for developing high-performance optical devices.

Compact Silicon-Arrayed Waveguide Gratings with Low Nonuniformity.

Array waveguide gratings (AWGs) have been widely used in multi-purpose and multi-functional integrated photonic devices for Microwave photonics (MWP) systems. In this paper, we compare the effect of output waveguide configurations on the performance of AWGs. The AWG with an output waveguide converging on the grating circle had larger crosstalk and lower nonuniformity. We also fabricated a 1 × 8 AWG with an output waveguide converging onto the SOI's grating circle, whose central operation wavelength was around 1550 nm. The fabricated AWG has a chip size of 500 μm × 450 μm. Experimental results show that the adjacent channel crosstalk is -12.68 dB. The center channel insertion loss, as well as 3 dB bandwidth, are 4.18 dB and 1.22 nm at 1550 nm, respectively. The nonuniformity is about 0.494 dB, and the free spectral range is 19.4 nm. The proposed AWG is expected to play an important role in future MWP systems given its good nonuniformity and insertion loss level.

Hybrid WDM/MDM (De) multiplexer based on Fabry–Perot resonators with Bragg grating reflectors

The traveling-wave-like Fabry–Perot (TW-like F-P) resonators, utilizing transverse-mode conversion, have been thoroughly investigated as on-chip filters. However, the asymmetric directional coupling (ADC) between the phase shifter and the output waveguide in this structure is not fully utilized, resulting in a rare implementation of hybrid wavelength division multiplexing (WDM) and mode division multiplexing (MDM). In this paper, using the transfer matrix method (TMM), we investigate methods to effectively enhance the quality factor (Q-factor) of TW-like F-P resonators. This is achieved by increasing the phase shifter length and reducing the coupling coefficient between these waveguides, without significantly impacting the channel drop efficiency. MDM can be achieved by adjusting the width of the output waveguides, utilizing the ADC between the phase shifter and the output waveguide. We design nine-channel hybrid WDM-MDM multiplexers based on TW-like F-P resonators. The variational-finite-difference time-domain (varFDTD) method is utilized to analyze the device’s performance, and its single channel extinction ratio (ER) values can reach −20dB. This work paves the way for TW-like F-P-resonator-based large capacity optical communications and interconnections.

A gap waveguide-based mechanically reconfigurable phase shifter for high-power Ku-band applications

This paper presents a novel design of a low-loss, reconfigurable broadband phase shifter based on groove gap waveguide (GGW) technology. The proposed phase shifter consists of a folded GGW and three bends with a few pins forming the GGW and one bend attached to a movable plate. This movable plate allows for adjustments to the folded waveguide length, consequently altering the phase of electromagnetic waves. The advantage of GGW technology is that it does not require electrical contact between different parts of a structure. Therefore, it enables the moving parts to slide freely without electromagnetic energy leakage, resulting in improved insertion loss in high-power applications. In addition, in the proposed design, the position of the input and output waveguide ports of the phase shifter remains fixed, which is advantageous from a practical point of view. As shown by measurement and simulation results, there is nearly 37% impedance bandwidth with the highest insertion loss of 0.6 dB, and the developed device has a maximum phase shift of 770° at the center frequency of 13 GHz. The phase shifter can be used for various radar and satellite applications that require phase control, such as beamforming networks and phased array antennas.

Efficient single-photon directional transfer between waveguides via two giant atoms.

We investigate the single-photon transport properties in a double-waveguide quantum electrodynamic system. We force the energy degeneracy of the collective states by adjusting the direct coupling strength between the two giant atoms. Our results indicate that resonant photons can be completely transferred between the two waveguides owing to the scattering interference of eigenstates, which also results in the directional propagation of resonant photons in the output waveguide. Perfect transfer occurs when the two scattering states degenerate in the energy and decay rates. We further propose a simple scheme to realize the efficient photon transfer with directional control. This study has potential applications in quantum networks and integrated photonic circuits.

Polygon search algorithm for ultra-compact multifunctional integrated photonics design

Ultra-compact multifunctional integrated photonic modules have great practical significance to photonic integrated circuits (PICs). However, the design effect and efficiency of the existing mainstream inverse design algorithms are incompetent when designing these modules. We analyze their shortcomings in this task, and propose a new, to our knowledge, inverse design algorithm named polygon search (PS) algorithm to address these problems. We utilize the PS algorithm to design an integrated dual-channel mode-conversion-crossing waveguide module. This module integrates three functions: interconversion between TE0 and TE1, interconversion between TE0 and TE2, and channel crossing within only a 4 μm×4 μm footprint, and its performance is verified by experimental testing. It not only greatly reduces the total footprint of many PICs but also greatly improves their fabricating robustness. Furthermore, we propose a PS-designed mode mixer and a PS-designed bending waveguide, and connect them with the integrated modules to form a four-channel crossing-mode-division-multiplexing system. This system can provide multiple modes on the basis of channel crossing and transmit the output signal in the same direction in parallel within a single output waveguide, which significantly increases the communication bandwidth and decreases the footprint of PICs. At last, we demonstrate the effect and efficiency advantages of the PS algorithm over several mainstream inverse design algorithms by a comprehensive contrast experiment and explain these advantages in theory from several perspectives.

A Volumetric Waveguide-Type Rotman Lens Antenna for Three-Dimensional Millimeter-Wave Beamforming.

In this paper, a volumetric Rotman lens antenna operating at 28 GHz is proposed. The design formula and procedure were derived for the 3-D Rotman lens antenna. The number of tilted beams is 3 × 3. The six rectangular blocks are assembled using a metallic bolt. The input port consists of a waveguide, and the output port is made of an open-ended waveguide. The input and output waveguides are drilled in a flat conducting plate. The input and output port positions are optimized. Simulated and measured results show that the radiating beam is controlled almost exactly as calculated. Compared with the previous two-stage stacked Rotman lens antenna, the proposed Rotman lens antenna can dramatically decrease the antenna volume by approximately 75%.

Polymer-based three-waveguide polarization beam splitter with reduced crosstalk for optical circuitry

Polarization beam splitters are pivotal in manipulating polarized light within photonic integrated circuits for various optical applications. This study introduces a single-mode polarization beam splitter comprising three waveguides realized with polymer materials. The device optimization process employed the beam propagation method, explicitly using the RSoft CAD BeamProp solver. Our proposed beam splitter performs exceptionally well with 99% complete and null light transmission efficiency. In particular, it demonstrates minimal insertion loss (0.04 dB for complete transmission and 0.07 dB for null transmission) and low coupling loss (0.03 dB and 0.04 dB for complete transmission, 21.9 dB and 36.3 dB for null transmission from input to bridge and bridge to output waveguides, respectively). Additionally, the beam splitter showcases significantly reduced crosstalk: −27dB and −26.98dB for TE modes during complete light transfer, and −36.28dB and −33.61dB for TM modes during null light transfer. These results underscore its potential for advancing integrated optical systems.

WR‐3.4 multi‐mode waveguide module with single‐chip‐integrated array circuits

AbstractThis paper introduces a WR‐3.4 waveguide module that contains an array of circuits fabricated on a single chip with an area of 3 × 0.75 mm2. The array comprises ten elements, each containing a straight differential thru line connecting input and output waveguide transitions. Modifications to the edge element design are intended to produce perfect cell‐to‐cell symmetry by providing amplitude and phase balances for all array elements. The measurements show that the array module possesses an insertion loss of around 3.5 dB in the frequency range of 220–300 GHz. This result represents an increase of 2.5 dB compared to an empty waveguide module, displaying similarity to the performance of single‐element modules.

Hybrid Graphene–Silicon Arrayed Waveguide Gratings for On-Chip Signal–Frequency Conversion

We present the design and simulations of a novel integrated device concept enabling a frequency conversion of a broad signal. The solution is based on a hybrid silicon–graphene photonic chip, which could be used for controlled spectrometry in low-cost devices. The device is based on a silicon-on-insulator (SOI) platform on which an arrayed waveguide grating (AWG) is designed for operation at the center wavelength of λ = 1800 nm. The AWG is spectrally separating one broad input signal to thirty-two-output channels with a channel spacing of 2.72 nm. The output signals are well separated and uniform with the extinction ratio and the standard deviation of 10.00 dB and 0.04, respectively. The 3 dB channel width is 1.34 nm, which is suitable for sensing applications with significant accuracy. After spacial and spectral separation, each output signal is then converted to one signal at 1480 nm wavelength through a graphene-based saturable absorber scheme. Therefore, the device allows the detection of each separated signal with a simple near-infrared camera on which the outputs are imaged using conventional optics, leading to a classical pixel/wavelength correspondence. Crossed-waveguide couplers are designed to combine the controlling signal at 1480 nm to each channel waveguide of the AWG. The combination of the signals saturates the graphene layer at the output waveguides, allowing the pass of the controlling wavelength. This device can be applied as a spectrometer in environmental sensing and monitoring with high efficiency and low cost.

Picojoule-level supercontinuum generation in thin-film lithium niobate on sapphire.

We demonstrate ultraviolet-to-mid-infrared supercontinuum generation (SCG) inside thin-film lithium niobate (TFLN) on sapphire nanowaveguides. This platform combines wavelength-scale confinement and quasi-phasematched nonlinear interactions with a broad transparency window extending from 350 to 4500 nm. Our approach relies on group-velocity-matched second-harmonic generation, which uses an interplay between saturation and a small phase-mismatch to generate a spectrally broadened fundamental and second harmonic using only a few picojoules of in-coupled fundamental pulse energies. As the on-chip pulse energy is increased to tens of picojoules, these nanowaveguides generate harmonics up to the fifth order by a cascade of sum-frequency mixing processes. For in-coupled pulse energies in excess of 25 picojoules, these harmonics merge together to form a supercontinuum spanning 360-2660 nm. We use the overlap between the first two harmonic spectra to detect f-2f beatnotes of the driving laser directly at the waveguide output, which verifies the coherence of the generated harmonics. These results establish TFLN-on-sapphire as a viable platform for generating ultra-broadband coherent light spanning from the ultraviolet to mid-infrared spectral regions.

Near-infrared Y-branch polymer splitters realized with compact MMI structures for efficient power splitting

Optical splitters are promising photonic devices for next-generation photonic integrated circuits, which enable signal distribution and routing between the different components, facilitating complex optical functionalities on a single chip. This research introduces what we believe is a novel numerical technique for enhancing optical network efficiency by incorporating a taper-based step-index (SI) Y-branch multimode interference (MMI) splitter with organic-inorganic hybrid polymer materials. The proposed device comprises a core width of 5 µm for the input and output waveguides to satisfy the single-mode conditions. We designed and optimized the MMI splitter using the beam propagation method (BPM). The splitter demonstrates the power splitting property with an efficiency of 86%. The excess losses for the MMI splitter are 0.52 dB and 0.50 dB for TE and TM modes, respectively, at 1.55 µm. The polarization dependence loss (PDL) and propagation loss (PL) are 0.015 dB and 0.00019 dB/µm, respectively.

Data Center Four-Channel Multimode Interference Multiplexer Using Silicon Nitride Technology.

The operation of a four-channel multiplexer, utilizing multimode interference (MMI) wavelength division multiplexing (WDM) technology, can be designed through the cascading of MMI couplers or by employing angled MMI couplers. However, conventional designs often occupy a larger footprint, spanning a few millimeters, thereby escalating the energy power requirements for the photonic chip. In response to this challenge, we propose an innovative design for a four-channel silicon nitride (Si3N4) MMI coupler with a compact footprint. This design utilizes only a single MMI coupler unit, operating within the O-band spectrum. The resulting multiplexer device can efficiently transmit four channels with a wavelength spacing of 20 nm, covering the O-band spectrum from 1270 to 1330 nm, after a short light propagation of 22.8 µm. Notably, the multiplexer achieves a power efficiency of 70% from the total input energy derived from the four O-band signals. Power losses range from 1.24 to 1.67 dB, and the MMI coupler length and width exhibit a favorable tolerance range. Leveraging Si3N4 material and waveguide inputs and output tapers minimizes light reflection from the MMI coupler at the input channels. Consequently, this Si3N4-based MMI multiplexer proves suitable for deployment in O-band transceiver data centers employing WDM methodology. Its implementation offers the potential for higher data bitrates while maintaining an exemplary energy consumption profile for the chip footprint.

Study of Multi-Channel Mode-Division Multiplexing Based on a Chalcogenide-Lithium Niobate Platform

A multi-channel mode-division multiplexing based on a chalcogenide-lithium niobate platform using chalcogenide films with adjustable refractive index is proposed, with the aim of overcoming issues with narrow bandwidth and large crosstalk in conventional multiplexers. An asymmetric directional coupler, employing chalcogenide-based thin-film modulation, was designed to realize the multiplexing and separation of TE1, TE2, and TE3 modes. Simulations show that the device is capable of obtaining an insertion loss of between 0.03 dB and 0.7 dB and a crosstalk of between −21.66 dB and −28.71 dB at 1550 nm. The crosstalk of the TE1, TE2, and TE3 modes is below −20.1 dB when accessing the waveguide output port in the 1500–1600 nm band. The proposed multiplexer is a promising approach to enhance the transmission capability of thin-film lithium-niobate-integrated optical paths.