Wavelength Demultiplexer Research Articles

Integrated High-Repetition-Rate Optical Sampling Chip Exploiting Wavelength and Mode Multiplexing

We report a silicon-based integrated optical sampling chip. High-repetition-rate optical sampling pulses are generated by interleaving low-repetition-rate input optical pulses with the assistance of wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM). The WDM pulse interleaver is based on a loopback arrayed waveguide grating (AWG) with linearly increasing delays. The amplitude of the interleaved pulses can be adjusted by the attenuators in the loopback waveguides. Two high-order modes in a multimode waveguide are utilized to further increase the pulse repetition rate. With WDM and MDM, the optical pulse sampling rate is increased by 8 times. The optical sampling pulses are then modulated by a multimode Mach-Zehnder modulator with the active arms integrated with L-shaped PN junctions. The sampled pulses are finally separated by mode and wavelength demultiplexers for low-speed parallel processing. The wavelength demultiplexer is made of a dual-ring assisted Mach-Zehnder interferometer (DR-MZI) with high wavelength selectivity. This successful implementation of the high-speed sampling chip marks a significant step forward in the full integration of analog-to-digital converters on a single chip and opens up avenues toward real applications of microwave photonics.

Ultracompact 1310/1550 nm wavelength demultiplexer based on subwavelength grating-assisted multimode interference coupler

An ultra-compact 1310 / 1550 nm wavelength demultiplexer based on multimode interference (MMI) coupler assisted by subwavelength gratings (SWGs) is proposed. Two parallel SWG-based slots are inserted into the MMI section symmetrically. Equivalent refractive index and width of the SWG are designed properly to reduce the device length while keeping a low insertion loss (IL) and high extinction ratio (ER). In this way, the device length shrinks to 34.48 μm. The performance when the device working as a multiplexer and as a demultiplexer are both investigated. From the transmission spectrum, ILs of <0.24 dB, ERs of larger than 15.2 dB and broad 1-dB bandwidths of larger than 90 nm are obtained for the two wavelengths.

Reconfigurable and scalable 2,4-and 6-channel plasmonics demultiplexer utilizing symmetrical rectangular resonators containing silver nano-rod defects with FDTD method

Reconfigurable and scalable plasmonics demultiplexers have attracted increasing attention due to its potential applications in the nanophotonics. Therefore, here, a novel method to design compact plasmonic wavelength demultiplexers (DEMUXes) is proposed. The designed structures (two, four, and six-channel DEMUXes) consist of symmetrical rectangular resonators (RRs) incorporating metal nano-rod defects (NRDs). In the designed structures, the RRs are laterally coupled to metal–insulator-metal (MIM) waveguides. The wavelengths of the output channels depend on the numbers and radii of the metal NRDs in the RRs. The results obtained from various device geometries, with either a single or multiple output ports, are performed utilizing a single structure, showing real reconfigurability. The finite-difference time-domain (FDTD) method is used for the numerical investigation of the proposed structures. The metal and insulator used for the realization of the proposed DEMUXes are silver and air, respectively. The silver’s permittivity is characterized by the well-known Drude model. The basic plasmonic filter which is used to design plasmonic DEMUXes is a single-mode filter. A single-mode filter is easier to cope with in circuits with higher complexity such as DEMUXes. Also, different structural parameters of the basic filter are swept and their effects on the filter’s frequency response are presented, to provide a better physical insight. Taking into account the compact sizes of the proposed DEMUXes (considering the six-channel DEMUX), they can be used in integrated optical circuits for optical communication purposes.

Inverse-designed ultra-compact high efficiency and low crosstalk optical interconnect based on waveguide crossing and wavelength demultiplexer

In this paper, we use the inverse design method to design an optical interconnection system composed of wavelength demultiplexer and the same direction waveguide crossing on silicon-on-insulator (SOI) platform. A 2.4 μm × 3.6 μm wavelength demultiplexer with an input wavelength of 1.3–1.6 μm is designed. When the target wavelength of the device is 1.4 μm, the insertion loss of the output port is − 0.93 dB, and there is − 18.4 dB crosstalk, in TE0 mode. The insertion loss of the target wavelength of 1.6 μm in TE0 mode is − 0.88 dB, and the crosstalk is − 19.1 dB. Then, we designed a same direction waveguide crossing, the footprint is only 2.4 μm × 3.6 μm, the insertion loss of the wavelength 1.4 μm and 1.6 μm in TE0 mode is − 0.99 dB and − 1 dB, and the crosstalk is − 12.14 dB and − 14.34 dB, respectively. Finally, an optical interconnect structure composed of two devices is used, which can become the most basic component of the optical interconnect network. In TE0 mode, the insertion loss of the output wavelength of 1.4 μm at the output port is − 1.3 dB, and the crosstalk is − 29.36 dB. The insertion loss of the output wavelength of 1.6 μm is − 1.39 dB, and the crosstalk is − 38.99 dB.

Design and analysis of a compact subwavelength-grating-assisted 1.55/2 µm wavelength demultiplexer.

The wavelength demultiplexer (deWMUX) is an indispensable component for the wavelength diversity system. In this paper, we propose a subwavelength-grating-assisted ${{1}} \times {{2}}$ deWMUX based on the principle of multimode interference, which aims to output 1.55 and 2 µm wavelengths from two different channels. The simulation results show that the contrast of the designed deWMUX at both wavelengths is greater than 24 dB, the insertion loss is less than 0.5 dB, and the 1 dB bandwidth is wider than 100 nm. In addition, the manufacturing tolerances of the device are also studied.

Ultra-Compact Low Loss Polymer Wavelength (De)Multiplexer With Spot-Size Convertor Using Topology Optimization

Polymer waveguides are considered to be good candidates for optical interconnects application due to their advantages such as flexibility, good compatibility, and versatility for realizing 3D and micro structures. However, constrained by the limited degrees of freedom provided by template-based design approaches, there lacks a satisfying solution which achieves small footprint and low loss simultaneously. Inverse design has been proposed to improve the performance. However, most inverse design methods target at silicon-based optical devices optimization which has a relatively high refractive index difference. In this paper, we demonstrate an ultra-compact low loss polymer wavelength (de)multiplexer with spot-size conversion structure to interposing Si and optical fiber using gradient-based topology optimization and downhill simplex method. The 2-channel wavelength (de)multiplexer displays an excess propagation loss of 0.84 dB and 1.06 dB at 1310 nm and 1550 nm, respectively, with a total footprint of 245 × 35 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The 4-channel wavelength (de)multiplexer for coarse wavelength division multiplexing applications with 20 nm spacing (1270, 1290, 1310, and 1330 nm) with an excess waveguide propagation loss of 1.72 dB within 271 × 50 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> has also been demonstrated and all the output ports of the polymer wavelength demultiplexing structure achieved a conversion efficiency over 90%.

Topological inverse design of nanophotonic devices with energy constraint.

In this paper, we introduce an energy constraint to improve topology-based inverse design. Current methods typically place the constraints solely on the device geometry and require many optimization iterations to converge to a manufacturable solution. In our approach the energy constraint directs the optimization process to solutions that best contain the optical field inside the waveguide core medium, leading to more robust designs with relatively larger minimum feature size. To validate our method, we optimize two components: a mode converter (MC) and a wavelength demultiplexer. In the MC, the energy constraint leads to nearly binarized structures without applying independent binarization stage. In the demultiplexer, it also reduces the appearance of small features. Furthermore, the proposed constraint improves the robustness to fabrication imperfections as shown in demultiplexer design. With energy constraint optimization, the corresponding spectrum shifts under ±10 nm dimensional variations are reduced by 17% to 30%. The proposed constraint is unique in simultaneously taking both geometry and electric field into account, opening the door to new ideas and insights to further improve the computationally intensive topology-based optimization process of nanophotonic devices.

Triple-channel glasses-shape nanoplasmonic demultiplexer based on multi nanodisk resonators in MIM waveguide

In this paper a metal-insulator-metal (MIM) plasmonic waveguide is proposed. Based on the proposed MIM waeguide and nanodisk resonators a novel 1*3 wavelength demultiplexer (WDM) structure is designed. The proposed WDM structure is based on three plasmonic filters. Each of this plasmonic filters consists of two waveguides (input and drop), and a middle cavity that are coupled with nanodisk resonators horizontally. Using these proposed plasmonic filters a three channel plasmonic demultiplexer also designed and simulated in this paper. By seting suitable values for the designed structural parameters (refractive index and geometric parameters), the structure output can be modified and adjusted in a controlled. According to the simulation results of the plasmonic demultiplexer structure, the transmission efficiency of one of the channels reaches about 80 % and The effect of cross talk is less than -23 dB. There are three different wavelengths for each channel in this proposed WDM structure. It is also notable that, 2D Finite-Difference Time-Domain (FDTD) numerical method is imployed in this paper. Large-scale photonic integration, the ultra-compact demultiplexer devices, ultra-compact demultiplexer devices, the development of optical integrated circuits and integrated plasmonic devices are among of the application that the proposed structure can be used in them.

3D integrated wavelength demultiplexer based on a square-core fiber and dual-layer arrayed waveguide gratings.

We present a 3D integrated wavelength demultiplexer using a square-core fiber (SCF) and matched dual-layer arrayed waveguide gratings (AWGs). The SCF works as a 3D fiber multimode interference device, which splits the input light into symmetric four spots. The spots are then coupled to a pitch-matched 4-waveguide network, each connecting an AWG. Interface waveguides are designed to improve the coupling efficiency between the SCF and the dual-layer chip. The four AWGs are designed with different central wavelengths and a large free spectral range (FSR) of 120 nm. To reach a small and uniform insertion loss among different channels, only the central channels of each AWG are used for demultiplexing. The device is fabricated on a polymer platform. The upper and lower layers of the chip are fabricated using the same photolithography mask but rotated 180° so that 4 different AWG designs can be mapped to a single chip. The measured transmission spectra of the four AWGs cover a bandwidth of 112 nm. The insertion loss variation is smaller than 1.4 dB. The designed device can find applications in fiber optic sensing, communication, and astronomy.

Ultra-compact terahertz plasmonic wavelength diplexer.

Terahertz (THz) spoof surface plasmon polariton (SPP) waveguides can provide subwavelength confinement, which makes it possible for the THz waves to transmit at low loss over long distances along a metallic surface. This work reports on the design and actualization of an ultra-compact wavelength diplexer formed by THz spoof SPP waveguiding structures. By adding a certain number of periodic pillars in the coupling part of the directional coupler, the refractive index of the anti-symmetrically distributed odd modes can be engineered, thereby adjusting the coupling length. By adjusting the periodic pillar parameters properly, the SPP modes at two target frequencies will be coupled in the device for an odd or even number of times, so that the SPP modes at these two frequencies can be coupled out from different ports. The length of the wavelength diplexer is 1.6 mm, which is about 12.8% of its traditional counterpart. Minimum simulated transmittances of -24.34dB and -26.27dB can be obtained at 0.637 THz and 0.667 THz, respectively. The insertion losses at the two operating frequencies are less than 0.46 dB, and the extinction ratios are both better than 19 dB. By cascading the proposed diplexers, a compact wavelength demultiplexer with more channels can be obtained, which has important applications for future THz integrated communication systems.

A directional Gaussian smoothing optimization method for computational inverse design in nanophotonics

Local-gradient-based optimization approaches lack nonlocal exploration ability required for escaping from local minima in non-convex landscapes. A directional Gaussian smoothing (DGS) approach was proposed in our recent work and used to define a truly nonlocal gradient, referred to as the DGS gradient, in order to enable nonlocal exploration in high-dimensional black-box optimization. Promising results show that replacing the traditional local gradient with the nonlocal DGS gradient can significantly improve the performance of gradient-based methods in optimizing highly multi-modal loss functions. However, the current DGS method is designed for unbounded and unconstrained optimization problems, making it inapplicable to real-world engineering design optimization problems where the tuning parameters are often bounded and the loss function is usually constrained by physical processes. In this work, we propose to extend the DGS approach to the constrained inverse design framework in order to find a better design. The proposed framework has its advantages in portability and flexibility to naturally incorporate the parameterization, physics simulation, and objective formulation together to build up an effective inverse design workflow. A series of adaptive strategies for smoothing radius and learning rate updating are developed to improve the computational efficiency and robustness. To enable a clear binarized design, a dynamic growth mechanism is imposed on the projection strength in parameterization. The methodology is demonstrated by an example of wavelength demultiplexer. Our method shows superior performance compared to the state-of-the-art approaches. By incorporating volume constraints, the optimized design achieves an equivalently high performance but significantly reduces the amount of material usage.

Broadband detection of multiple spin and orbital angular momenta via dielectric metasurface.

Light beams carrying spin angular momentum (SAM) and orbital angular momentum (OAM) have created novel opportunities in the areas of optical communications, imaging, micromanipulation and quantum optics. However, complex optical setups are required to simultaneously manipulate, measure and analyze these states, which significantly limits system integration. Here, we introduce a novel detection approach for measuring multiple SAM and OAM modes simultaneously through a planar nanophotonic demultiplexer based on an all-dielectric metasurface. Coaxial light beams carrying multiple SAM and OAM states of light upon transmission through the demultiplexer are spatially separated into a range of vortex beams with different topological charge, each propagating along a specific wavevector. The broadband response, material dispersion and momentum conservation further enable the demultiplexer to achieve wavelength demultiplexing. We envision the ultracompact multifunctional architecture to enable simultaneous manipulation and measurement of polarization and spin encoded photon states with applications in integrated quantum optics and optical communications.

A Four Green TM/Red TE Demultiplexer Based on Multi Slot-Waveguide Structures.

A four green transverse magnetic (TM)/red transverse electric (TE) light wavelength demultiplexer device, based on multi slot-waveguide (SW) structures is demonstrated. The device aims to demultiplex wavelengths in the green/red light range with wavelengths of 530, 540, 550, and 560 nm; 630, 640, 650, and 660 nm. This means that the device functions as a 1 × 4 demultiplexer for each polarization mode (TE/TM). The controlling of the light switching between two closer segment SWs under the TM/TE polarization mode was studied by designing a suitable SW structure and setting the right segment length to fit the coupling lengths of the operating wavelengths. The device is composed of six-segment SW units and six S-bends (SB) SW. The key SW and SB parameters were optimized and determined by a full vectorial beam propagation method (FV-BPM). Results show power losses better than 0.138 dB, crosstalk better than −21.14 dB, and an optical spectrum smaller than 9.39 nm, with an overall compact size of 104.5 µm. The device can be integrated in wavelength division multiplexing (WDM) for increasing data bit rate in a visible light communication (VLC) system.

Polarization‐Enabled Steering of Surface Plasmons Using Crossed Reciprocal Nanoantennas

AbstractDirectional control over optical near‐fields using plasmonic structure is highly desirable for the realization of photonic nanocircuitry. A simple plasmonic nanostructure is designed to allow polarization‐sensitive directional launching and steering of surface plasmon polaritons (SPPs). In the past, polarization‐controlled SPP steering has been limited to wavelength demultiplexing that severely limits the realization of multiple output SPP‐based circuits excited by a monochromatic source. Based on crossed Babinet‐inverted nanoantennas, steering of SPPs in the first quadrant with very high sensitivity to the linear polarization of the exciting source is numerically and experimentally demonstrated. The same device also functions as a power‐splitter under a particular optical polarization. The results of this study can open up a new avenue towards full coherent control of SPPs and should accelerate the pace for the realization of highly functioning next‐generation optical nanocircuits.

Dual Ring Resonator Based 3D-Photonic Crystal For Add Drop Filter Using FDTD-Least Square Technique

The structure of an optical add-drop filter (ADF) which depends on a very-compact ring resonator made from a photonic crystal has been presented in the paper. An adequate structure of a three channel wavelength de-multiplexer along with a finite difference time domain is demonstrated in the visibility area. A 3D triangular lattice photonic crystal with 1.735 nm air pores in a silicon nitride planar waveguide provides a constraint for the light which can be detected. The double resonator has been simulated on a three-dimension photonic crystal and for the simulation of results, MATLAB has been used. The resultant structure consisting of three drops wavelengths at λ1 = 1555 nm, λ2 = 1579 nm, and λ3 = 1595 nm approximately. The average spacing between the adjacent channels is around 20 nm and the FSR obtained from numerical simulation is about 179 GHz. The output wavelength carries normalized transmissions of 0.97 having an inner rod radius for inner core 800. In addition to this, the Alternating Least Square—Add-Drop Filter (ADF)—Finite Difference Time Domain method has been used to achieve three various outputs such as transmitted intensity, reflectivity fineness, and constant factor. In future aspects, the simulation results can be further used in the fields of networks to design more accurate and efficient photonic crystals based on de-multiplexing devices.

Optical four-channel demultiplexer based on air-bridge structure and graphite-type ring resonators

A novel an optical four-channel demultiplexer based on a hexagonal lattice shape of embedded air holes in dielectric substrate (air-bridge type) is proposed. Demultiplexing for each channel is obtained by designing the graphite-type ring resonator which consists of small air hole defects in own unit cells. The physical parameters which govern the demultiplexer performance are investigated. It is observed that employing big air hole as a defect in the end of input waveguide enhanced the coupling efficiency between the rings and waveguides. By engineering the refractive index of substrate and size of air holes, the proposed demultiplexer is tuned. The demultiplexer has an average quality factor > 3000 and channel spacing $$\Delta \lambda \le 2\;{\text{nm}}$$ . We showed that big air hole defect in the end of input waveguide is an effective scheme for improving the transmission efficiency and cross talk between channels. The average transmission efficiency and cross talk value are above 98% and − 23 dB, respectively. The total size of proposed structure and its maximum delay time are 289 μm2 and 0.3 ps, respectively. Our demultiplexer has an easy fabrication structure, and it can find key applications for many cores CPU in an on-chip optical network and the dense wavelength demultiplexing in optical integrated circuits.

Femtosecond synchronization of multiple mode-locked lasers and a microwave oscillator by multicolor electro-optic sampling.

Simple multicolor electro-optic sampling-based femtosecond synchronization of multiple mode-locked lasers is demonstrated. Parallel timing error detection between each laser and a common microwave is achieved by wavelength division multiplexing and demultiplexing. The parallel timing error detection enables simultaneous femtosecond synchronization of more than two mode-locked lasers to the microwave oscillator, even when the lasers have different repetition rates. The residual root-mean-square (rms) timing jitter of laser-laser synchronization measured by an optical cross correlator is 2.6 fs (integration bandwidth, 100 Hz-1 MHz), which is limited by the actuator bandwidth in the laser oscillator. The long-term rms timing drift and frequency instability of laser-microwave synchronization are 7.1 fs (over 10,000 s) and 5.5×10-18 (over 2000 s averaging time), respectively. As a versatile and reconfigurable tool for laser-laser and laser-microwave synchronization, the demonstrated method can be used for various applications ranging from ultrafast x-ray and electron science facilities to dual- and triple-comb spectroscopy.

Graphene-based wavelength demultiplexing structure.

A wavelength demultiplexing (WDM) structure based on graphene nanoribbon resonators is proposed and simulated using the finite-difference time-domain (FDTD) method. Based on a simple structure, the demultiplexing wavelength and transmission characteristics of the WDM can be tuned by adjusting the length of the resonator, the nanoribbon width, or the chemical potential of graphene within a relative broadband frequency range. Moreover, the mechanism of the proposed WDM structure is analyzed in detail using the theory of Fabry-Perot (F-P) resonance and temporal coupled-mode theory. The proposed structure has promising potential in the field of ultracompact WDM systems in highly integrated optical circuits.

A Wavelength Demultiplexing Structure Based on the Multi-Teeth-Shaped Plasmonic Waveguide Structure

In this paper, a wavelength demultiplexing structure based on multi-teeth-shaped metal-insulator-metal (MIM) plasmonic waveguide is designed and numerically studied using the finite-difference time-domain (FDTD) method. Investigating the characteristics of a multi-teeth-shaped plasmonic waveguide structure reveals that with the design of the structure, it was possible to create a mode inside the bandgap of the filter. Based on the created mode inside the bandgap of the filter, the demultiplexer structure has been proposed and investigated. By changing the geometric parameters of the structure, the transmission wavelength of the demultiplexer channel can be adjusted. The proposed demultiplexer can be used in integrated optical circuits.

Rainbow trapping in a tapered photonic crystal waveguide and its application in wavelength demultiplexing effect

In this paper, we present the numerical and experimental demonstration of a wavelength demultiplexer (WDM) based on the photonic crystal (PC), in which the waveguide has a tapered width. Owing to the tapered waveguide, propagating light can be slowed down and be trapped by a local mode gap effect at certain distances from the entrance of the waveguide. The corresponding effect leads to the localization of four different wavelengths at different points inside the waveguide. The drop-channels are introduced at these specified locations to separate selected wavelengths. Here, we utilized an optimization algorithm to enhance the coupling efficiencies of the introduced drop-channels. The presented WDM PC separates the wavelengths of 22.29, 21.63, 20.80, and 19.87 mm (13.46, 13.87, 14.42, and 15.10 GHz, respectively) into different drop-channels with coupling efficiencies at around 80%. Experimental verifications of the numerically presented results are realized at the microwave frequency regime where the coupling efficiencies of each drop-channel are measured as around 75%. The designed WDM PC structure is all dielectric, compact, and efficient, and it exhibits low cross talk between drop-channels. Experimental measurements show a rainbow-trapping phenomenon and verify the simulation results of wavelength demultiplexing design with the margin of error between 0.8% and 1% frequency shifts in peak transmission values.