Directional Coupler Switch Research Articles

Sensitivity analysis of a dielectric loaded 1 × 2 directional coupler switch based on foundry process optical waveguides

Sensitivity analysis of a dielectric loaded 1 × 2 directional coupler switch based on foundry process optical waveguides

Broadband Nonvolatile Electrically Controlled Programmable Units in Silicon Photonics

Programmable photonic integrated circuits (PICs) have recently gained significant interest due to their potential in creating next-generation technologies ranging from artificial neural networks and microwave photonics to quantum information processing. The fundamental building block of such programmable PICs is a tunable 2 x 2 switch, traditionally controlled by the thermo-optic or free-carrier dispersion. Yet, these implementations are power-hungry, volatile, and have a large footprint (typically > 100 um). Therefore, a truly 'set-and-forget' type 2 x 2 switch with zero static power consumption is highly desirable for large-scale PICs. Here, we report a broadband nonvolatile electrically programmable 2 x 2 silicon photonic switch based on the phase-change material Ge2Sb2Te5. The directional coupler switch exhibits a compact coupling length (64 um), small insertion loss (<2 dB), and minimal crosstalk (<-8 dB) across the entire telecommunication C-band while maintaining a record-high endurance of over 2,800 switching cycles. This demonstrated switch constitutes a critical component for realizing future generic programmable silicon photonic systems.

Ultralow-VπL Silicon Electro-Optic Directional Coupler Switch With a Liquid Crystal Cladding

An ultralow-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> L photonic switch device is demonstrated utilizing the high optical and electrical field confinement in silicon slot waveguides coupled with the strong electro-optic response of nematic liquid crystals. A silicon photonic directional coupler switch with a modulation efficiency of 0.0195 V·mm and a loss-efficiency product of 0.0624 V·dB is achieved. The 1.5 mm long device is based on two-mode interference within a single slot waveguide resulting in a V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> of 0.013 V and an extinction ratio of ~ 9dB at 1550 nm wavelength. The power consumption of the photonic switch is estimated to be below 0.6 nW and it possesses a response time of <; 1.5 ms. A comparative performance study between the directional coupler switch and a Mach-Zehnder Interferometer (MZI) switch is performed. The directional coupler switch is projected to have a smaller footprint and lower optical loss compared to a similar design MZI switch making it a strong candidate for switch matrix designs and applications.

Phase-change photonic crystal ring resonator for reconfigurable directional-coupler switching

A novel compact photonic crystal ring resonator is designed based on phase-change material (PCM) to realize reconfigurable directional-coupler switching for the two wavelengths of coarse wavelength division multiplexing (CWDM) system at 1530 nm and 1550 nm. The working mechanism of this PCM-based device is analyzed from the perspective of the coupled optical field in the inner and outer resonator rings during the phase transition of selected photonic crystal rods. This kind of PCM-based directional-coupler switches will play a strong role in the reconfigurable lattice mesh-based integrated intelligent photonic system.

LiTaO3 Directional Coupler Switch with Enhanced Extinction Ratio and Low Insertion Loss

A novel design of optical directional coupler switch with S-bend waveguides on LiTaO3 platform has been designed with R-Soft CAD tool and the same is simulated by Beam propagation method (BPM) for light propagation analysis. The simulation results of the optical directional coupler (ODC) switch is reported. We observed that the directional coupler (DC) switch has lower insertion losses and higher extinction ratios for a certain values that are discussed in the paper. This was studied by variation in waveguide parameters such as, wavelength, waveguide gap, and length of the device. Simulation results designate that the switching efficiency for TE and TM modes with extinction ratio about 3dB when the waveguide gap is 3.5μm for both the polarization modes and insertion loss is 13dB with same waveguide gap in TE mode and 16dB in TM mode at 1550nm wavelength.

Mid-infrared non-volatile silicon photonic switches using nanoscale Ge2Sb2Te5 embedded in silicon-on-insulator waveguides

We propose and numerically analyze hybrid Si-Ge2Sb2Te5 strip waveguide switches for the mid-infrared wavelength of 2.1 μm. The switches investigated are of one input-one output (on-off) and one input-two outputs (directional coupler) types. The reversible transition between the switch states is achieved by inducing phase transition from crystalline to amorphous and vice-versa by application of voltage pulses. The approach of embedding the nanoscale active material Ge2Sb2Te5 within the Si waveguide is taken to enhance the interaction of light with the active region of the switches. The dimensions of the active regions of the switches are optimized to achieve low insertion loss, low switching energy and high extinction ratio. In the case of the on-off switch, an extinction ratio of 33.79 dB along with an extremely low insertion loss of 0.52 dB is achieved using an optimum Ge2Sb2Te5 length of only 0.92 μm. For the directional coupler switch, an extinction ratio of 10.33 dB and 5.23 dB is obtained in the cross and bar states respectively using an active length of 52 μm. These values of extinction ratio, which are otherwise 18.59 dB and 8.33 dB respectively, are due to the necessity of doping the Si beneath the Ge2Sb2Te5 to facilitate the electrical conduction needed for Joule heating. A suitable gap of 100 nm is maintained between the active and passive arm of the directional coupler switch. Electro-thermal co-simulations confirm that phase change occurs in the whole of the Ge2Sb2Te5 region in both types of switches.

Low-Loss and Broadband Nonvolatile Phase-Change Directional Coupler Switches

An optical equivalent of the field-programmable gate array (FPGA) is of great interest to large-scale photonic integrated circuits. Previous programmable photonic devices relying on the weak, volatile thermo-optic or electro-optic effect usually suffer from a large footprint and high energy consumption. Phase change materials (PCMs) offer a promising solution due to the large non-volatile change in the refractive index upon phase transition. However, the large optical loss in PCMs poses a serious problem. Here, by exploiting an asymmetric directional coupler design, we demonstrate PCM-clad silicon photonic 1 \times 2 and 2 \times 2 switches with a low insertion loss of ~1 dB and a compact coupling length of ~30 {\mu}m while maintaining a small crosstalk less than ~10 dB over a bandwidth of 30 nm. The reported optical switches will function as the building blocks of the meshes in the optical FPGAs for applications such as optical interconnects, neuromorphic computing, quantum computing, and microwave photonics.

Evaluation of performance of a hybrid electro-optic directional coupler and a Mach–Zehnder switch

The efficiency of an electro-optic (EO) directional coupler (DC) and a Mach–Zehnder (MZ) switch is discussed. The specific designs employ a passive waveguide core and an EO cladding. The performance of a DC switch was evaluated by numerical methods, namely coupled mode theory (CMT), eigenmode expansion (EME) method, and beam envelope method. Using the CMT and EME methods, it is shown that in the DC with a passive waveguide core and EO cladding at certain waveguide parameters the switching effect does not take place. The effect is demonstrated for the first time and suggests that careful optimization of the DC switch should be done before experimental realization of the device. The efficiency of an optimized DC switch is shown to be of an order lower than that of an MZ switch.

Hybrid electro-optic plasmonic modulators based on directional coupler switches

By breaking the diffraction limit, plasmonics enable the miniaturization of integrated optical signal processing units in a platform compatible with traditional CMOS technology. In such architectures, modulators and switches are essential elements for fast and low-power optical signal processing. This work presents the design of a CMOS-compatible hybrid plasmonic modulator based on directional couplers enhanced with a layer of electro-optic polymer. The modulator shows very broad operating window with low crosstalk values and very small footprint with respect to similar couplers and switches of the silicon photonics platform.

Investigation and simulation of photonic crystal directional coupler switch

The photonic crystal optical switch is one of the most important applications of photonic crystals in telecommunication networks. Switching is a main process in digital computers and signal processing systems. The growth of optical signal processing systems draws particular attention to the design of ultra-fast optical switches. In this reported work, first a directional coupler switch based on photonic crystals is designed and the linear state has been analysed and simulated. Then, the principles of nonlinear optics are used to perform optical switching at a wavelength of 1550 nm by COMSOL Multiphysics in micron dimension. The dielectric rods of this photonic crystal lattice are made of AlGaAs. The central row is an important factor for attaining the required power in nonlinear switching performance. Finally, the radius of rods in the central nonlinear row is changed several times and the results are compared with each other. In this switch, the output power ratio, called the extinction ratio, and the required refractive index change for the nonlinear status are taken into account. The former is for the evaluation of directional coupler efficiency and the latter is generally an important factor in optical nonlinear switches.

Large-scale silicon photonic switches with movable directional couplers

Fast optical circuit switches (OCSs) with high port count offer reconfigurable bandwidth in optical networks and have the potential to significantly increase the performance and efficiency of modern datacenters. In this paper, we report on a new type of integrated OCS that combines silicon photonics with MEMS actuation. The switch is built on a 50×50 passive crossbar network with very low optical loss (0.04 dB/crossing). Efficient switching is achieved by a pair of directional couplers with moving waveguides and an actuation voltage of 14 V. 2500 MEMS-actuated directional coupler switches have been integrated with the crossbar network to form a strictly nonblocking 50×50 OCS on a 9 mm×9 mm chip. The measured switching time is 2.5 μs, and the extinction ratio is 26 dB. To our knowledge, this is the largest silicon photonic switch reported to date. The switch architecture is highly scalable because the light travels through only one active switching element, regardless of the size of the switch.

Electro-optical switching at 1550 nm using a two-state GeSe phase-change layer.

New designs for electro-optical free-space and waveguided 2 x 2 switches are presented and analyzed at the 1.55 μm telecoms wavelength. The proposed devices employ a ~10 nm film of GeSe that is electrically actuated to transition the layer forth-and-back from the amorphous to the crystal phase, yielding a switch with two self-sustaining states. This phase change material was selected for its very low absorption loss at the operation wavelength, along with its electro-refraction Δn ~0.6. All switches are cascadeable into N x M devices. The free-space prism-shaped structures use III-V prism material to match the GeSe crystal index. The Si/GeSe/Si "active waveguides" are quite suitable for directional-coupler switches as well as Mach-Zehnder devices-all of which have an active length 16x less than that in the free-carrier art.

Simulations of Silicon-on-Insulator Channel-Waveguide Electrooptical 2 × 2 Switches and 1 × 1 Modulators Using a ${\bf Ge_2}{\bf Sb_2}{\bf Te_5}$ Self-Holding Layer

This paper reports theoretical designs and simulations of electrooptical 2 × 2 switches and 1 × 1 loss modulators based upon GST-embedded SOI channel waveguides. It is assumed that the amorphous and crystalline phases of GST can be triggered electrically by Joule heating current applied to a 10-nm GST film sandwiched between doped-Si waveguide strips. TEo and TMo mode effective indices are calculated over 1.3 to 2.1-μm wavelength range. For 2 × 2 Mach–Zehnder and directional coupler switches, low insertion loss, low crosstalk, and short device lengths are predicted for 2.1 μm, although a decreased performance is projected for 1.55 μm. For 1.3–2.1 μm, the 1 × 1 EO waveguide has application as a variable optical attenuator and as a digital modulator, albeit with ≦100-ns state-transition time. Because the active material has two “stable” phases, the device holds itself in either state, and voltage needs to be applied only during transition.

Preparation of a main-chain azo polyurethane-urea and its application of Y-branch and Mach–Zehnder thermo-optic switch

A novel main-chain azo polyurethane-urea (MCAPUU) was prepared with chromophore molecule 1,1′-azobisformamide (ABFA), polyether polyol (NJ-220) and isophorone diisocyanate (IPDI). The chemical structures of ABFA monomer and MCAPUU were characterized by the FT-IR and UV–Visible spectroscopy. The thermal and mechanical properties of MCAPUU film were investigated. The refractive index and transmission loss of MCAPUU film were measured at different temperature and different laser wavelength by attenuated total reflection (ATR) technique and the CCD digital imaging devices. The thermo-optic coefficients (dn/dT) of MCAPUU are −4.5429 × 10−4 °C−1 (532 nm), −5.7943 × 10−4 °C−1 (650 nm) and −6.6057 × 10−4 °C−1 (850 nm), respectively. A Y-branch switch and Mach–Zehnder interferometer (MZI) thermo-optic switches based on thermo-optic effect were proposed and the performances of switches were simulated. The results showed that the power consumption of the Y-branch thermo-optic switch is only 0.74 mW. The rising and falling times of Y-branch and MZI switches are 12.0 and 1.8 ms, respectively. The results indicate that the prepared MCAPUU has high potential for the applications of the Y-branch digital optical switch (DOS), MZI thermo-optic switch, directional coupler (DC) switch and optical modulators.

Synthesis, physical properties and simulation of thermo-optic switch based on azo benzothiazole heterocyclic polymer

A chromophore molecule 4-[(benzothiazole-2-yl)diazenyl]phenyl-1,3-diamine (BTPD) was prepared with 2-amino benzothiazole and m-phenylenediamine by diazo-coupling reaction. Then, the BTPD was polymerized with polyether polyol (NJ-220) and isophorone diisocyanate (IPDI) to obtain novel azo benzothiazole polyurethane-urea (BTPUU). The chemical structures of BTPD and BTPUU were characterized by FT-IR and UV–visible spectroscopy. The thermal and mechanical properties of BTPUU film were investigated. The refractive index and transmission loss of BTPUU film were measured at different temperatures and different laser wavelengths (532nm, 650nm and 850nm) by an attenuated total reflection (ATR) technique and CCD digital imaging devices. The thermo-optic coefficients of BTPUU are −4.7086×10−4°C−1 (532nm), −6.5257×10−4°C−1 (650nm) and −5.1029×10−4°C−1 (850nm), respectively. A Y-branch switch and Mach–Zehnder interferometer (MZI) thermo-optic switches based on thermo-optic effect were proposed and the performances of the switches were simulated, respectively. The results show that the power consumption of the Y-branch thermo-optic switch is only 3.28mW. The response times of Y-branch and MZI switches are 8.0ms and 2.0ms, respectively. The results indicate that the prepared BTPUU has high potential for the applications of the Y-branch digital optical switch (DOS), MZI thermo-optic switch, directional coupler (DC) switch and optical modulators.

Dark soliton switching in nonlinear fiber couplers with gain

Abstract In this paper, we present a study of numerical simulations for all-optical dark soliton switching in nonlinear directional couplers with gain additions in two waveguides whilst considering intermodal dispersion and its higher-order effects. The effects of possible combinations of gain addition in the bar channel as well as in the cross channel of the nonlinear couplers are theoretically presented. In addition, the consequence of second-order coupling coefficient dispersion based on coupled mode theory for dark soliton switching is numerically depicted.

Nonlinear directional coupling between plasmonic slot waveguides

A numerical investigation of nonlinear switching in plasmonic directional couplers made of two dielectric slab waveguides with metallic claddings is presented. We assume Kerr-nonlinear dielectric and study the influence of geometrical parameters, metallic losses, and metal nonlinearities on coupler characteristics. We observe a general trade-off between losses and nonlinearity levels required for the switching operation. Underlying physical mechanisms that affect the coupler performance are discussed. The obtained results can be useful in design and optimization of the nonlinear plasmonic couplers.

Liquid-Crystal Tunable Long-Range Surface Plasmon Polariton Directional Coupler

A tunable plasmonic directional coupler is proposed based on the electro-optical control of a nematic liquid-crystal layer placed above two side-coupled gold stripe waveguides. It is shown that by proper adjustment of the structural parameters and the control voltage, the coupling length of the structure and the effective modal index of the individual waveguides can be tuned, allowing for the design of electro-optical liquid-crystal plasmonic directional coupler switches.

METHOD OF DEVELOPING ALL OPTICAL HALF-ADDER BASED ON NONLINEAR DIRECTIONAL COUPLER

The transfer of light energy from one wave guide to another due to direct coupling mechanism can be used as a directional coupler switch. Several all optical switching operations have already been proposed by scientists and technologists. In this paper we report the advantageous aspects of nonlinear coupling mechanisms for developing all optical half-adder systems. The basic principle behind this optical switch is the reduction of coupling length due to the nonlinear interaction of the wave guide with the intensity.

Preparation and thermo-optic switch properties based on chiral azobenzene-containing polyurethane

A chiral azo chromophore compound 4-(4′-nitro-phenyl-diazenyl)-phenyl-1,2-propanediol ether (NPDPPE) was prepared with p-nitroaniline, phenol and R(−)-3-chloro-1,2-propanediol by the diazo-coupling reaction. Then, the chromophore molecule NPDPPE was polymerized with isophorone diisocyanate (IPDI) to obtain novel chiral azobenzene-containing polyurethane (CACPU). The chemical structures of chromophore molecule and CACPU were characterized by the FT-IR and UV–visible spectroscopy. The physical properties (thermal conductivity, thermal diffusion coefficient, and specific heat capacity) and mechanical properties (tensile strength, elongation at break and hardness) of CACPU thin films were measured. The refractive index and thermo-optic (TO) coefficient (dn/dT) of CACPU thin film was investigated for TE (transversal electric) polarizations by using an attenuated total reflection (ATR) configuration at the wavelengths of 532, 650 and 850nm. The transmission loss of film was measured using the charge coupled device (CCD) digital imaging devices. A Y-branch switch and Mach–Zehnder interferometer (MZI) thermo-optic switches based on thermo-optic effect were proposed and the performances of switches were simulated. The results showed that the power consumption of the Y-branch thermo-optic switch was only 3.28mW. The rising and falling times of Y-branch and MZI switches were 12.0ms and 2.0ms, respectively. The conclusion has potential significance to improve and develop new Y-branch digital optical switch (DOS), MZI thermo-optic switch, directional coupler (DC) switch and optical modulators.