Mode-selective modulator and switch based on graphene-polymer hybrid waveguides.

The mode-division multiplexing (MDM) is an effective technology with huge development potential to improve the transmission capacity of optical communication system by transmitting multiple modes simultaneously in a few-mode fiber. In traditional MDM technology, the fundamental modes of multiple channels are usually modulated by external individual arranged electro-optic modulators, and then multiplexed into the few-mode fiber or waveguide by a mode multiplexer. However, this is usually limited by large device footprint and high power consumption. Here, we report a mode-selective modulator and switch to individually modulate or switch the TE11, TE12 and TE21 modes in a few-mode waveguide (FMW) to overcome this limitation. Our method is based on the graphene-polymer hybrid platform with four graphene capacitors buried in different locations of the polymer FMW by utilizing the coplanar interaction between the capacitors and spatial modes. The TE11, TE12 and TE21 modes in the FMW can be modulated and switched separately or simultaneously by applying independent gate voltage to different graphene capacitor of the device. Our study is expected to make the selective management of the spatial modes in MDM transmission systems more flexible.

Ultra-Broadband and Compact TM-Pass Polarizer Based on Graphene-Buried Polymer Waveguide.

We report an ultra-broadband and compact TM-pass polarizer based on graphene-buried polymer waveguides. The characteristic parameters of the polarizer were carefully designed and optimized. The standard microfabrication processes were employed to fabricate the device. The presented polarizers exhibit high polarization-dependent transmission imposing a TE mode cutoff while leaving the TM mode almost unaffected. We experimentally demonstrated the polarizer that has an ultra-high extinction ratio of more than 22.9 dB and 41.9 dB for the monolayer graphene film placed on the surface of core layer and buried in the center of core layer, respectively, and as low insertion loss as ~4.0 dB for the TM mode with the bandwidth over 110 nm. The presented polarizer has the advantages of high extinction ratio, ultra-broadband, low cost, and easy integration with other polymer-based planar lightwave devices.

Polymer/silica hybrid 3D waveguide thermo-optic mode switch based on cascaded asymmetric directional couplers.

A polymer/silica hybrid 3D waveguide thermo-optic (TO) mode switch based on cascaded asymmetric directional couplers (ADCs) is theoretically designed and simulated, where the spatial modes of a few-mode silica waveguide can be switched to various single-mode polymer waveguides placed above the few-mode silica waveguide. A beam propagation method is employed to optimize the dimensional parameters of the mode switch to convert the LP11a and LP11b modes of the few-mode silica waveguide to the LP01 mode of two single-mode polymer waveguides using the cascaded ADC 1 and ADC 2. The coupling ratios are higher than 96.4% (93.4%) and 95.1% (92.8%) for the ADC 1 and ADC 2, respectively, under the TE (TM) polarization within the wavelength range from 1530 to 1570 nm, which shows good wavelength independence. Furthermore, the monolayer graphene is introduced as the heating electrode and buried on the surface of the polymer core to increase the heating efficiency and reduce the power consumption. The power consumption for ADC 1 and ADC 2 is 16.69 mW and 17.35 mW, respectively. Compared to the traditional TO switch with an aluminum (Al) heating electrode, the heating efficiency of the presented device can be improved by ∼30%. Moreover, the response speed of the TO mode switch with a 3D waveguide structure was also significantly improved. Compared to the device with Al electrodes, the introduced graphene electrodes can improve the switching speed of the device by ∼60%. The presented TO mode switch with its small size and easy integration should find applications in reconfigurable mode division multiplexing systems.

Graphene-Assisted Polymer Waveguide Optically Controlled Switch Using First-Order Mode.

All-optical devices have a great potential in optical communication systems. As a new material, graphene has attracted great attention in the field of optics due to its unique properties. We propose a graphene-assisted polymer optically controlled thermo-optic switch, based on the Ex01 mode, which can reduce the absorption loss of graphene. Graphene absorbs 980 nm pump light, and uses the heat generated by ohmic heating to switch on and off the signal light at 1550 nm. The simulation results show that, when the graphene is in the right position, we can obtain the power consumption of 9.5 mW, the propagation loss of 0.01 dB/cm, and the switching time of 127 µs (rise)/125 µs (fall). The switching time can be improved to 106 µs (rise) and 102 µs (fall) with silicon substrate. Compared with an all-fiber switch, our model has lower power consumption and lower propagation loss. The proposed switch is suitable for optically controlled fields with low loss and full polarization. Due to the low cost and easy integration of polymer materials, the device will play an important role in the fields of all-optical signal processing and silicon-based hybrid integrated photonic devices.

Au Nanoparticles-Doped Polymer All-Optical Switches Based on Photothermal Effects.

This article demonstrated the Au nanoparticles-doped polymer all-optical switches based on photothermal effects. The Au nanoparticles have a strong photothermal effect, which would generate the inhomogeneous thermal field distributions in the waveguide under the laser irradiation. Meanwhile, the polymer materials have the characteristics of good compatibility with photothermal materials, low cost, high thermo-optical coefficient and flexibility. Therefore, the Au nanoparticles-doped polymer material can be applied in optically controlled optical switches with low power consumption, small device dimension and high integration. Moreover, the end-pumping method has a higher optical excitation efficiency, which can further reduce the power consumption of the device. Two kinds of all-optical switching devices have been designed including a base mode switch and a first-order mode switch. For the base mode switch, the power consumption and the rise/fall time were 2.05 mW and 17.3/106.9 µs, respectively at the wavelength of 650 nm. For the first-order mode switch, the power consumption and the rise/fall time were 0.5 mW and 10.2/74.9 µs, respectively at the wavelength of 532 nm. This all-optical switching device has the potential applications in all-optical networks, flexibility device and wearable technology fields.

Low-power-consumption polymer Mach-Zehnder interferometer thermo-optic switch at 532 nm based on a triangular waveguide.

We designed and fabricated a Mach-Zehnder interferometer (MZI) thermo-optic switch with an inverted triangular waveguide. The inverted triangular waveguide achieves a fundamental mode in a large waveguide dimension, which can reduce the coupling loss and increase the extinction ratio. The triangular waveguide-based switch was simulated and presented higher heating efficiency and lower power consumption than that of the traditional rectangular waveguide-based switch. Compared with the traditional rectangular waveguide-based device, the power consumption of the proposed device is reduced by 60%. Spacing photobleaching was introduced to fabricate the inverted triangular waveguide and adjust the refractive index to minimize the mode number. The insertion loss of the typical fabricated device with a 2 cm length is about 7.8 dB. The device shows an extinction ratio of ∼8.1dB at 532 nm with a very low power consumption of 2.2 mW, and the switching rise time and fall time are 110 and 130 µs, respectively. The proposed single-mode waveguide and low-power-consumption optical switch have great potential applications in visible optical communication fields such as wavelength division multiplexing and mode-division multiplexing.

Low Power Consumption 3D-Inverted Ridge Thermal Optical Switch of Graphene-Coated Polymer/Silica Hybrid Waveguide.

An inverted ridge 3D thermal optical (TO) switch of a graphene-coated polymer/silica hybrid waveguide is proposed. The side electrode structure is designed to reduce the mode loss induced by the graphene film and by heating the electrode. The graphene layer is designed to be located on the waveguide to assist in the conduction of heat produced by the electrode. The inverted ridge core is fabricated by etching and spin-coating processes, which can realize the flat surface waveguide. This core improves the transfer of the graphene layer and the compatibility of the fabrication processes. Because of the opposite thermal optical coefficient of polymer and silica and the high thermal conductivity of the graphene layer, the 3D hybrid TO switch with low power consumption and fast response time is obtained. Compared with the traditional TO switch without graphene film, the power consumption of the proposed TO switch is reduced by 41.43% at the wavelength of 1550 nm, width of the core layer (a) of 3 µm, and electrode distance (d) of 4 µm. The rise and fall times of the proposed TO switch are simulated to be 64.5 µs and 175 µs with a d of 4 µm, and a of 2 µm, respectively.

Dispersed-Monolayer Graphene-Doped Polymer/Silica Hybrid Mach-Zehnder interferometer (MZI) Thermal Optical Switch with Low-Power Consumption and Fast Response.

This article demonstrates a dispersed-monolayer graphene-doped polymer/silica hybrid Mach-Zehnder interferometer (MZI) thermal optical switch with low-power consumption and fast response. The polymer/silica hybrid MZI structure reduces the power consumption of the device as a result of the large thermal optical coefficient of the polymer material. To further decrease the response time of the thermal optical switch device, a polymethyl methacrylate, doped with monolayer graphene as a cladding material, has been synthesized. Our study theoretically analyzed the thermal conductivity of composites using the Lewis-Nielsen model. The predicted thermal conductivity of the composites increased by 133.16% at a graphene volume fraction of 0.263 vol %, due to the large thermal conductivity of graphene. Measurements taken of the fabricated thermal optical switch exhibited a power consumption of 7.68 mW, a rise time of 40 µs, and a fall time of 80 µs at a wavelength of 1550 nm.

Graphene-embedded first-order mode polymer Mach-Zender interferometer thermo-optic switch with low power consumption.

Two-dimensional-material integrated thermal optical switches have low power consumption; however, the devices are suffering from high propagation loss due to the two-dimensional material absorption. In this Letter, we present a graphene-embedded polymer Mach-Zender interferometer (MZI) thermo-optic switch, based on the E01x mode and designed to minimize both the loss and power consumption. Based on the symmetry of a three-dimensional structure and the E01x mode, the central embedded graphene electrode structure was simulated with an absorption loss of 0.06 dB/cm. Finite element method (FEM) simulations were run to find that the power consumption is 1.57 mW. Compared with the top heating electrode, the power consumption of the proposed graphene-embedded device is reduced by 74%. Further, the response speed of the graphene-embedded thermo-optic MZI switch is simulated to be 1.2 µs (rise) and 70.6 µs (down). This device may be applicable in the two-dimensional integrated low-power-consumption-mode division multiplexer field.

A Polymer Asymmetric Mach-Zehnder Interferometer Sensor Model Based on Electrode Thermal Writing Waveguide Technology.

This paper presents a novel electrode thermal writing waveguide based on a heating-induced refractive index change mechanism. The mode condition and the electrode thermal writing parameters were optimized, and the output patterns of the optical field were obtained in a series of simulations. Moreover, the effect of various adjustments on the sensing range of the nanoimprint M-Z temperature sensor was analyzed theoretically. A refractive index asymmetry Mach-Zehnder (M-Z) waveguide sensor with a tunable refractive index for a waveguide core layer was simulated with a length difference of 946.1 µm. The optimal width and height of the invert ridge waveguide were 2 µm and 2.8 µm, respectively, while the slab thickness was 1.2 µm. The sensing accuracy was calculated to range from 2.0896 × 104 to 5.1252 × 104 in the 1.51-1.54 region. The sensing fade issue can be resolved by changing the waveguide core refractive index to 0.001 via an electrode thermal writing method. Thermal writing a single M-Z waveguide arm changes its refractive index by 0.03. The sensor's accuracy can be improved 1.5 times by the proposed method. The sensor described in this paper shows great prospects in organism temperature detection, molecular analysis, and biotechnology applications.

Polymer M-Z Thermal Optical Switch at 532-nm Based on Wet Etching and UV-Writing Waveguide.

Polymer thermal optical switches have low power consumption and 532 nm is the communication window of polymer fiber. Polymer thermal optical switches at 532 nm are rarely reported, because of switching extinction ratio properties that are restricted by modes of the waveguide. Single mode waveguide at 532 nm is hard to fabricate due to the dissolution of core and cladding materials. A polymer M-Z thermal optical switch at 532 nm was first demonstrated based on the wet etching method. The proposed thermal optical switch was consisted of silica substrate, photosensitive polymer core, and cladding material. The device was fabricated and tested with the power consumption of 6.55mW, extinction of 4.8 dB, and switching time of 0.23 ms (rise)/0.28 ms (down). An optimized switch structure combining with the UV-writing technique and graphene thermal conduction layer was proposed based on the experiments above. A side electrode was designed to reduce the power consumption and the switching time. The optimized device was calculated to have a power consumption of 1.5 mW. The switching time of the UV-writing device was simulated to be 18.2 µs (rise) and 85 µs (down). The device is promising in the wearable device and laser radar area.

Polymer/glass hybrid DC-MZI thermal optical switch for 3D-integrated chips.

A directional coupler (DC) Mach-Zehnder interferometer (MZI) thermal optical switch based on a polymer and glass waveguide hybrid for three-dimensional (3D)-integrated chips is demonstrated. The proposed thermal optical switch consists of a polymer waveguide and glass waveguide prepared using an ion-exchange technique. The two waveguide cores can achieve coupling in the vertical direction, improving the integration level on 3D-integrated chips, realizing the complementary advantages of polymer and glass materials. Because of the opposite thermal optical coefficients of polymer and glass materials, and the good stability, low transmission loss and large thermal conductivity of glass material, the device with a low power consumption, small dimensions, fast response time and high extinction ratio can be easily obtained. The optical field coupling between the graded refractive index and step refractive index in 3D directions was simulated. The optimized coupling efficiency is 99.82% with an open-window dimension (w) of 3 µm. The refractive index difference between the diffusion surface center and cladding (Δn) is 0.022. The properties of the DC-MZI thermal optical switch were optimized, achieving a switch power consumption of 5.16 mW, a rising time of 128.8 µs, a falling time of 249.5 µs without an air trench structure, and a switch power consumption of 3.74 mW, a rising time of 140.7 µs, a falling time of 256.3 µs after the etching of an air trench structure with a heating electrode width of 8 µm.

Polymer-Silica Hybrid On-Chip Amplifier with Vertical Pumping Method.

This article demonstrates a multilayer polymer-silica hybrid on-chip amplifier combining mode division multiplexing method. The multilayer amplifier consists of a pumping silica waveguide and an amplifying polymer waveguide. The pumping waveguide possesses the stability and the high damage threshold. The amplifying waveguide takes the advantages of the high compatibility and the high doping rate. The vertical pump of mode division multiplexing method can introduce the pumping light into the amplifying waveguide at any desired position of the chip. By the isolation method between signal and pumping light, the pumping light can be coupled into the amplifying waveguide, while the signal light cannot be coupled into the pumping waveguide. The parameters of doping rates, waveguide lengths, overlap factors, coupling parameters are calculated to optimize the gain characteristics of the amplifier. The amplifier with three position-optimized pumping light was designed achieving a maximum gain of 33.89 dB/cm with a waveguide length of 6 cm, a signal power of 0.1 mW and a pumping power of 300 mW. This polymer-silica hybrid amplifier is promising for the on-chip loss compensation of the 3D photonic integrated circuits and all optical transistors.

Thermal tuning of graphene-embedded waveguide filters based on the polymer-silica hybrid structure.

Graphene-embedded waveguide filters have been widely used in the areas of polarization and mode filtering because of their characteristics of easy fabrication, high integration, and high extinction ratio. In this article, we propose thermal tuning filters based on a graphene-embedded polymer-silica hybrid waveguide. Compared to previously reported filters, this device can realize the efficient adjustment of the relative position between the optical field and graphene layer by thermal tuning. Consequently, the polarization and mode filtering properties of the filter can be adjusted by thermal tuning. This high-efficiency tuning characteristic is due to the opposite thermo-optic coefficient of the polymer and silica material. Furthermore, a layer with a low refractive index is embedded in the polymer-silica hybrid core to increase the tuning efficiency. The optical absorption, mode properties, and thermal field distributions were simulated. It was found that such single-mode filters could realize Ex 11-pass or Ex 11-stop selection, and the attenuation variation (Δα) was optimized to 32.20 dB cm-1 (Ex 11 mode) using the top electrode and air trench structure with ΔT = 10 K and P = 48.39 mW in the single-mode waveguide. For the multimode waveguide filters, the attenuation variation (Δα) of the Ex mn modes (Ex 11, Ex 12, and Ex 21) was also calculated. Such thermal tuning filters were found to be compatible with chemical potential regulation graphene modulators and filters, and they can be applied to broadband photonic integrated circuits and mode division multiplexing systems.