MEMS‐enabled Ultralow Power Consumption Programmable Arbitrary Order Mode Switch

Ultra-compact mode converter based on longitudinal refractive index modulation

Mode converters (MCs) play an essential role in mode-division multiplexing (MDM) systems. Numerous schemes have been developed on the silicon-on-insulator (SOI) platform, yet most of them focus solely on the conversion of fundamental mode to one or two specific higher-order modes. In this study, we introduce a hybrid shape optimization (HSO) method that combines particle swarm optimization (PSO) with adjoint methods to optimize the shape of the S-bend waveguide, facilitating the design of arbitrary-order MCs featuring compactness and high performance. Our approach was validated by designing a series of 13 μm-long MCs, enabling efficient conversion between various TE modes, ranging from TE0 to TE3. These devices can be fabricated in a single lithography step and exhibit robust fabrication tolerances. Experiment results indicate that these converters achieve low insertion losses under 1 dB and crosstalks below -15 dB across bandwidths of 80 nm (TE0-TE1), 62 nm (TE0-TE2), 70 nm (TE0-TE3), 80 nm (TE1-TE2), 55 nm (TE1-TE3), and 75 nm (TE2-TE3). This advancement paves the way for flexible mode conversion, significantly enhancing the versatility of on-chip MDM technologies.

The mode converter, as a passive mode conversion device in transmission lines, is well-investigated and widely implemented in various electromagnetic systems. However, most traditional mode converters can only realize a single conversion mode. Thus, a mode converter achieving multiple controllable output modes is urgently needed. In this paper, a reconfigurable mode converter operating in the microwave range is achieved by embedding a deformable all-dielectric material with quadrilateral shape into a rectangular waveguide based on coupled-mode theory. It can achieve different target modes with controllable output for the same input by exciting the deformable all-dielectric material. The design principle of the mode converter is expounded concretely and simulation is carried out using HFSS software 2022 R2. Experimental results, consisting of the simulation results, demonstrate that the proposed mode converter can achieve various mode conversions with mode purity higher than 95%. This article innovatively applies deformable materials to waveguide mode conversion, expanding the application of deformable memory materials in electromagnetic devices.

Two-mode converters at 1.3 μm, aiming at applications in mode-division multiplexing in Ethernet systems, are proposed and experimentally demonstrated. Based on multimode interference couplers, the two-mode converters with 50% and 66% mode conversion efficiencies are designed and fabricated on InP substrates. Mode conversion from the fundamental mode (TE0) to the first order mode (TE1) is successfully demonstrated within the wavelength range of 1280–1320 nm. The 1.3-μm mode converters should be important devices in mode-division multiplexing systems in Ethernet systems.

Recent progress in optical devices for mode division multiplex transmission system

Multicore fibers and few-mode fibers are potential candidates for achieving high-capacity space division multiplexing and mode division multiplexing (MDM) systems. Mode converters are an essential part of any MDM for effectively launching light into the desired mode. Fiber-based mode converters will be more useful than bulk converters because of their compatibility and ease of use. In this contribution, a two-core fiber-based mode converter design is proposed that can effectively convert the fundamental LP01 mode into the LP11 mode by mode coupling. This device can also be used as a demultiplexer in the reverse operation. Such a mode converter can be fabricated by heating a piece of two-core fiber with the thermally diffused core technique. This leads to the diffusion of dopants into the cladding, resulting in an expanded core giving power coupling between the cores. The conversion efficiency of this converter is −0.5  dB at the optimum value. This all-fiber mode converter ensures an extinction ratio of more than 30 dB over 45 nm wavelength, which covers the entire C band. The robustness of the proposed design is analyzed by evaluating the effect of changes in design parameters on the conversion efficiency and extinction ratios.

Dissipative solitons (DSs), which are pulses with high pulse energy and a broad rectangular output spectrum, have several applications. In a fiber system, the generation of higher-order DS requires a mode converter with a high and flat conversion efficiency that can cover the working waveband. The requirements on high and flat conversion efficiency as well as broadband working waveband is a great challenge for a traditional mode converter. This study presents an L-band mode-locked fiber laser with a 3-dB bandwidth of more than 47 nm and a first-order cylindrical vector (CV) mode DS output based on an ultra-broadband long-period fiber grating (LPFG). The fabricated mode converter is a novel cascading LPFG with an ultra-broadband working bandwidth and flat conversion efficiency which could meet the demand of DS mode conversion. The 15-dB bandwidth is 149.76 nm, from 1515.36 nm to 1665.12 nm. Furthermore, the conversion efficiency in the range of the output spectrum is 98.60 ± 0.23%. The single-, double-, and triple-soliton output characteristics and their real-time spectra are observed using time-stretched dispersion Fourier transformation (TS-DFT) technology. Experimental results demonstrate that the first-order CV mode DS laser can maintain its dynamics after mode conversion under the accuracy of detection system, implying that the LPFG works only as a mode converter. The broadband DS laser with CV mode output in the L-band has been presented for the first time in study, to the best of our knowledge. This study is also the first to detect real-time characteristics for a higher-order mode-locked fiber laser using the TS-DFT technology. The proposed type of LPFG is s good candidate for generating higher-order mode lasers with an all-fiber structure.

Small circular waveguide mode converters used in the 28 GHz, 200 kW ECH system for the Hitachi tokamak HT-1 have been developed. In order to convert from the TE02 to the TE11 mode, TE0202-to-TE01 and TE01-to-TE11 mode converters are used. Both converters use periodic waveguide wall perturbations, the case of the former, circularly symmetric perturbations, and in the case of the latter, curvature perturbations. The lengths of the mode converters were successfully shortened with high mode conversion efficiencies by decreasing the number of periods and then optimizing the periods using quite a small diameter for the converters. The 30ϕ TE02-to-TE01 mode converter is 103 · 34 mm long and its mode conversion efficiency measured by a scalar network analyser is 96% at 28GHz. The TE01-to-TE11 mode converter is 427 · 38 mm long and has an efficiency of 79%, which is 10% lower than the design value. This discrepancy resulted mainly from mode conversion from the TE11 to the TE12 mode, caused by the smaller number of...

In a waveguide‐based coupled‐mode system, various mode conversions are achieved by designing mode evolution procedures. However, the differences of refractive indices among modes exceed the capability of conventional tuning mechanism, so most reported mode manipulation devices can only realize fixed mode conversions. This paper introduces the cladding medium switching strategy to the subwavelength grating waveguide‐based coupled‐mode system, and proposes a reconfigurable mode converter on silicon nitride platform. This work systematically analyzes the phase matching conditions on a coupled‐mode system. Results show that for both whole and partial upper‐cladding switchable, it is possible to achieve reconfigurable mode conversions. For whole cladding switchable case, this work demonstrates a double‐state mode converter, which converts the input mode to TE2 and TE1 modes under cladding refractive indices of 1 and 1.7. This work expands it to triple‐state mode conversion with window‐style cladding, which converts the input to TE2, TE1, and TE0 modes under cladding of 1, 1.54, and 1.7. The optical bandwidths are relatively large, and the conversion efficiencies exceed 56% for all cases. The mechanism provides a non‐volatile and energy‐efficient way for tunable mode conversions, which is promising for applications in optical networks, communications, and sensors, etc.

We experimentally investigate the generation of high-order modes (HOMs) with flexible switchable output. Cascaded acoustically induced fiber gratings (AIFGs) act as mode converters. A periodic micro-bending in the AIFG is produced by travelling flexural acoustic wave, and two modes with adjacent azimuthal numbers can be coupled to each other. Different HOMs (LP21a/b and LP11a/b) could be obtained just by tuning the frequency of the radio frequency (RF) driving signal. The dependence of RF frequencies on the two acousto-optic (AO) coupling stages is theoretically analyzed and experimentally verified. Based on cascaded AIFGs mode converter, a multiple-level intensity modulator and an all-fiber Yb-doped laser with flexible mode switching output of HOMs (LP21a/b and LP11a/b) are demonstrated. Moreover, by optimizing the outer diameter of the second part of the AO coupling regions, the mode conversion between LP01 and LP21 can be realized by applying a single frequency on the piezoelectric transducer (PZT).

A mode conversion from the TE 10 in WR3 rectangular waveguide to the TE 53 in an oversized circular waveguide is required to perform the cold test of a Bragg resonator for a high power 250 GHz Cyclotron Auto-Resonance Maser (CARM) under development at the Frascati ENEA research centre. High operating frequency and oversized cylindrical cavity (exceeding any previous CARM experiment) make the design particularly challenging. An initial transition, aimed at transforming the TE 10 in WR3 rectangular waveguide into the TE 11 , in a circular waveguide, is performed using a linear taper, a well-assessed device. Then a serpentine mode converter in circular waveguide with average radius of 1.48 mm and appropriate length has been adopted for the conversion into the TE 01 mode. The subsequent transducers, for not-rotating (TE 0m ) and rotating (TE 53 ) modes, are provided by means of rippled wall mode converters with small periodic perturbations of waveguide radius. The ripple period corresponds approximately to the beat wavelength (X b = 2π/(β m − β n )) with β m and β n the wavenumbers of the two interacting modes. For not-rotating modes an efficient conversion has been obtained by cascading single step TE 01 to TE 02 , TE 02 to TE 03 and TE 03 to TE 04 mode converters. For each of them, profiles, radius and number of periods have been optimized in order to obtain low levels of unwanted spurious modes, low reflection and sufficient bandwidth. As the modes to convert (TE 04 to TE 53 ) present similar wavenumbers, the most appropriate method for the conversion consists in a three-periods rippled-wall mode converter made by a helically corrugated waveguide with an average radius of 4 mm and five azimuthal variations. The longitudinal profile of the ripples has been properly smoothed to avoid steps between the circular waveguide and the corrugated converter. In this paper the conversion chain will be described and the simulation results (S-parameters, efficiency and electric field) of each single converter will be reported. Finally some considerations about the high precision micromachining technique to be used, such as copper electroforming and Computer Numerically Controlled (CNC) milling, for the construction of these high frequency components, will be presented.

In this paper, a compact and broadband mode converter and demultiplexer based on multimode interference (MMI) is designed and experimentally demonstrated on silicon-on-insulator. We have designed a mode converter using cascaded MMI to convert the fundamental mode into a higher-order (first-order mode) and vice versa. Subsequently, we have demonstrated an on-chip two-mode demultiplexer with a compact footprint and low loss. The proposed mode demultiplexer shows low insertion loss (0.22 dB for ${{\rm TE}_0}$TE0 and 0.36 dB for ${{\rm TE}_1}$TE1 mode) and crosstalk (${-}{25.2}\;{\rm dB}$-25.2dB for ${{\rm TE}_0}$TE0 and ${-}{24.4}\;{\rm dB}$-24.4dB for ${{\rm TE}_1}$TE1 mode) at wavelength 1550 nm using the eigenmode expansion method. Moreover, the device supports a broad bandwidth having crosstalk ${ \lt } {-} {20}\;{\rm dB}$<-20dB over a wavelength range of 1520-1580 nm. The proposed device can be used in mode division multiplexing for photonic network-on-chip.

Background: Fast Fourier Transform (FFT) processor is the important method in Orthogonal Frequency Division Multiplexing (OFDM) communication systems. Split-Radix Fast Fourier Transform (SRFFT) estimates the least number of multiplications compared to other FFT algorithm; hence SRFFT is the best for the implementation of low power FFT processor. Methods: In this paper, the proposed “pipelined 32-point Split-Radix Multi-path Delay Commutator (SFMDC) FFT” architecture is designed. The MDC architecture has advantages in reducing the low chip area and lower power consumption. The SR-FFT algorithm has changing the numbers of butterfly elements in successive stages. The 32-point SR-MDC FFT architecture is to determine the frequency transformation techniques. The Split-Radix FFT algorithm is based on radix-2 and radix-4 algorithm and it is related to mixed radix FFT. Findings: The performance evaluation of proposed architecture is determined through VLSI System. Less area, low power consumption and high speed are the main parameters in this design. The proposed structure provides high throughput rate and low hardware complexity. Improvements: The goal of this proposed work is to reduce the slices and LUTs and power consumption and also to enhance the performances of the FFT processor than the existing method. The proposed method has been evaluated by using ModelSim 6.3C and synthesis results has been validated by using Xilinx Plan ahead 12.4.

We have proposed a memory based recursive FFT design which has much less gate counts, lower power consumption and higher speed. The proposed architecture has three main advantages (1) fewer butterfly iteration to reduce power consumption, (2) pipeline of radix-22 butterfly to speed up clock frequency, (3) even distribution of memory access to make utilization efficiency in SRAM ports. In summary, the speed performance of our design easily satisfies most application requirements of Fixed 802.16d and Mobile 802.16e WiMAX, which uses OFDMA modulated wireless communication system. Our design also occupies lesser area, hence lower cost and power consumption.

We present an iterative design method for the coupling and the mode conversion of arbitrary modes to focused surface plasmons using a large array of aperiodically randomly located slits in a thin metal lm. As the distance between the slits is small and the number of slits is large, significant mutual coupling occurs between the slits which makes an accurate computation of the field scattered by the slits difficult. We use an accurate modal source radiator model to efficiently compute the fields in a significantly shorter time compared with three-dimensional (3D) full-field rigorous simulations, so that iterative optimization is efficiently achieved. Since our model accounts for mutual coupling between the slits, the scattering by the slits of both the source wave and the focused surface plasmon can be incorporated in the optimization scheme. We apply this method to the design of various types of couplers for arbitrary fiber modes and a mode demultiplexer that focuses three orthogonal fiber modes to three different foci. Finally, we validate our design results using fully vectorial 3D nite-difference time-domain (FDTD) simulations.