Electro-optic Polymer Modulators Research Articles

Synthesis, electro‐optic properties, and performance of novel fluorinated polyurethaneimide

AbstractUrethane imide anhydride oligomers with terminal groups as anhydride groups were designed and synthesized using second‐order nonlinear optical chromophore molecule, bisphenol AF‐type diethylidene dianhydride, and toluene diisocyanate as monomers. Polyurethaneimide (PUI) second‐order nonlinear optical polymers with the structure of imide and amino ester chain segments were then synthesized by the polycondensation reaction between urethane imide anhydride oligomers and aromatic diamine monomers. The glass transition temperature (Tg) of PUI reached 186°C, and the 5% heat‐loss decomposition temperature was 320°C. The corona‐polarized PUI had an electro‐optic (EO) coefficient (γ33) of 82 pm/V tested by the reflection method. The loss of light transmission of the polymer waveguide prepared with PUI as electro‐optical material was 1.13 dB/cm at 1550 nm. Mach–Zehnder type polymer waveguide electro‐optical modulators have been prepared based on the properties of the electro‐optic material PUI. The fabricated polymer EO modulators had favorable electro‐optic modulation response performance for low‐frequency electrical signals. The good modulation characteristics of the manufactured electro‐optical modulators proved that the synthesized PUI was a waveguide polymer material with good comprehensive performance.Highlights Electro‐optic fluorinated polyurethaneimide was synthesized. Polyurethaneimide as core material, polymer waveguide EO modulators were fabricated. The prepared modulators had good electro‐optic modulation performance.

Carrier conversion from terahertz wave to dual-wavelength near-infrared light for photonic terahertz detection in wireless communication.

THz waves are promising wireless carriers for next-generation wireless communications, where a seamless connection from wireless to optical communication is required. In this study, we demonstrate carrier conversion from THz waves to dual-wavelength NIR light injection-locking to an optical frequency comb using asynchronous nonpolarimetric electro-optic downconversion with an electro-optic polymer modulator. THz wave in the W band was detected as a stable photonic RF beat signal of 1 GHz with a signal-to-noise ratio of 20 dB via the proposed THz-to-NIR carrier conversion. In addition, the results imply the potential of the photonic detection of THz waves for wireless-to-optical seamless communication.

Low half-wave voltage polymeric electro-optic modulator using CLD-1/PMMA for electrocardiogram (ECG) signal acquisition.

Electro-optic (EO) modulators are typically made of inorganic materials such as lithium niobate; the replacement of these modulators with organic EO materials is a promising alternative due to their lower half-wave voltage (Vπ), ease of handling, and relatively low cost. We propose the design and fabrication of a push-pull polymer electro-optic modulator with voltage-length parameters (VπL) of 1.28 V·cm. The device uses a Mach-Zehnder structure and is made of a second-order nonlinear optical host-guest polymer composed of a CLD-1 chromophore and PMMA polymer. The experimental results show that the loss is 1.7 dB, Vπ drops to 1.6 V, and the modulation depth is 0.637 dB at 1550 nm. The results of a preliminary study show that the device is capable of efficiently detecting electrocardiogram (ECG) signals with performance on par with that of commercial ECG devices.

Enhanced poling and infiltration for highly efficient electro-optic polymer-based Mach-Zehnder modulators.

An ultra-narrow 40-nm slotted waveguide is fabricated to enable highly efficient, electro-optic polymer modulators. Our measurement results indicate that VπL's below ∼ 1.19 V.mm are possible for the balanced Mach-Zehnder modulators using this ultra-narrow slotted waveguide on a hybrid silicon-organic hybrid platform. Our simulations suggest that VπL's can be further reduced to ∼ 0.35 V.mm if appropriate doping is utilized. In addition to adapting standard recipes, we developed two novel fabrication processes to achieve miniaturized devices with high modulation sensitivity. To boost compactness and decrease the overall footprint, we use a fabrication approach based on air bridge interconnects on thick, thermally-reflowed, MaN 2410 E-beam resist protected by an alumina layer. To overcome the challenges of high currents and imperfect infiltration of polymers into ultra-narrow slots, we use a carefully designed, atomically-thin layer of TiO2 as a carrier barrier to enhance the efficiency of our electro-optic polymers. The anticipated increase in total capacitance due to the TiO2 layer is negligible. Applying our TiO2 surface treatment to the ultra-narrow slot allows us to obtain an improved index change efficiency (∂n/∂V) of ∼ 22% for a 5 nm TiO2 layer. Furthermore, compared to non-optimized cases, our peak measured current during poling is reduced by a factor of ∼ 3.

Superiorly low half-wave voltage electro-optic polymer modulator for visible photonics.

Chip-scale optical devices operated at wavelengths shorter than communication wavelengths, such as LiDAR for autonomous driving, bio-sensing, and quantum computation, have been developed in the field of photonics. In data processing involving optical devices, modulators are indispensable for the conversion of electronic signals into optical signals. However, existing modulators have a high half-wave voltage-length product (VπL) which is not sufficient at wavelengths below 1000 nm. Herein, we developed a significantly efficient optical modulator which has low VπL of 0.52 V·cm at λ = 640 nm using an electro-optic (EO) polymer, with a high glass transition temperature (Tg = 164 °C) and low optical absorption loss (2.6 dB/cm) at λ = 640 nm. This modulator is not only more efficient than any EO-polymer modulator reported thus far, but can also enable ultra-high-speed data communication and light manipulation for optical platforms operating in the ranges of visible and below 1000 nm infrared.

Demonstration of a flexible electro-optic polymer modulator with a low half-wave voltage for ECG signals acquisition

Polymer-based electro-optic (EO) modulators have the advantages of low half-wave voltages and a low-cost preparation process and thus have extensive application prospects. A flexible, low half-wave voltage SU-8 Mach–Zehnder (M-Z) EO polymer modulator was proposed for human electrocardiogram (ECG) signal detection; polydimethylsiloxane (PDMS) was used as the substrate, and crosslinked polymer disperse red 1 (DR1)/SU-8 was used as the waveguide core layer. PDMS surface modification and SU-8 polarization were achieved, and the device was prepared by spin coating, ultraviolet (UV) lithography, wet etching and low-temperature sputtering. The experimental results show that the modulator initially operates in a linear operating regime under unbiased voltage conditions, and direct linear modulation of the voltage can be realized. After the preparation process, the low half-wave voltage was measured to be 2 V with a core size of 4000 μm×22000 μm, and the loss of the device was −2.1 dB.

A 100 Gbaud On-off-Keying Silicon-Polymer Hybrid Modulator Operating at up to 110°C

We demonstrate 100-Gbaud on-off-keying (OOK) transmission driven at a low voltage using an electro-optic (EO) polymer modulator combined with a silicon Mach-Zehnder interferometer waveguide. Various types of organic- and polymer-based modulators have been reported to perform efficient EO modulation and high-speed data transmission at over 100 Gbaud. However, there are critical concerns regarding the practical application of polymer devices in terms of environmental stability. In particular, long-term thermal storage and stability during operation require improvements before EO polymer modulators can be applied in practical systems. We have developed an EO polymer with enhanced thermophysical stability and used it to fabricate an efficient EO polymer modulator. In this study we extend our earlier work on high-speed EO polymer modulators by performing fiber-link 100-Gbaud OOK transmission at various operating temperatures. A thermal stability test revealed that the EO polymer modulator can survive high-temperature exposure up to 110°C. Error-free signal transmissions over a distance of 2.0 km was successfully demonstrated with a driving voltage of 1.9 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> and a bit error rate below the 7% overhead forward error correction threshold. The driving voltage, bandwidth, bit error rate, and fiber-link performance of the device are presented.

Electro-optic polymer and silicon nitride hybrid spatial light modulators based on a metasurface.

Spatial light modulators (SLMs) are important for various applications in photonics, such as near-infrared imaging, beam steering and optical communication. After decades of advances, current commercial devices are typically limited to kilohertz modulating speeds. To realize higher operating speeds, an electro-optic (EO) polymer and silicon nitride hybrid SLM has been demonstrated in this work. We utilize a specially designed metasurface to support a relatively high quality resonance and simultaneously confine most of the incident light in the active EO polymer layer. Combing with the high EO coefficient of the polymer, a clear modulation at 10 MHz with a driving voltage of Vp-p=±10 V has been observed in the proof-of-concept device. Our first-generation device leaves vast room for further improvement and may open an attractive route towards compact SLM with an RF modulation higher than 100 GHz.

Coplanar Electrode Polymer Modulators Incorporating Fluorinated Polyimide Backbone Electro-Optic Polymer

High-speed coherent optical communication has been expanding to handle the ever-increasing data traffic, and the large modulation bandwidth of electro-optic (EO) polymer modulators has been especially appreciated. However, to be useful in optical communication, the EO polymer device should address several issues, such as thermal stability, photo-oxidation, and bias drift. In this work, as a part of the experiments to address these challenges, an EO polymer with a fluorinated polyimide backbone is utilized to create EO polymer modulators with improved thermal stability. A coplanar electrode structure is introduced to enhance the poling efficiency and reduce the bias drift.

Optical loss characterization of SEO100C electro-optic polymer within single mode rib waveguides

Designing high-performance electro-optic polymer modulators requires insight into device-specific waveguide losses. Losses for rib waveguiding structures fabricated using SE0100C core and NOA73 cladding layers are reported. The waveguide loss was measured at 4.2 dB/cm, which is high compared to losses for different electro-optic rib waveguides reported at 1.2-2.9 dB/cm. The refractive index of unpoled SEO100C was measured at 1.655, expanding on the manufacturer’s reported optical constants of 1.65 (TE) and 1.7 (TM) for poled SEO100C. Utilizing the reported specific structure loss in device design for minimal loss will facilitate high performance electro-optic polymer modulator applications.

Optical loss induced by metal electrodes in a polymer optical waveguide for optical sensor

Optical electric field sensors have received significant attention in recent years for their potential in a broad range of applications. There are many literatures about the optical electric field sensors, but only a few reports focus on the optical losses. In this paper, an analysis model is developed for the design of the electrode of a polymer electro-optic modulator in an optical electric field sensor. The optical losses due to the electrode are presented for different core waveguide thickness and cladding refractive indices. It also had been found that the optical loss due to electrode absorption will depend not only on the cladding layer but also on the core waveguide thickness. At the same time, the thickness of the cladding layer and core waveguide can be chosen freely by adjusting the refractive index of the polymer materials and keeping the optical losses to be less than 0·1 dB/cm. The results will be helpful for the design of a polymer electro-optic modulator in an optical electric field sensor.

High thermal stability 40 GHz electro-optic polymer modulators

As a consequence of the urgent demand for an electro-optic (EO) polymer modulator with an elevated temperature stability, we have prepared a selection of EO polymers having glass transition temperatures of up to 194°C. The measured half-wave voltage characteristics of the fabricated Mach-Zehnder interference modulators revealed an excellent thermal resistance at 105°C for approximately 2,000 hours. By utilizing traveling-wave electrodes on the modulator, the high-frequency response at 10-40 GHz was evaluated under ascending temperatures. The advantage of such high-temperature stability EO polymer modulators was clearly demonstrated by the continuous frequency response up to 130°C.

Compact Low Loss Vertical Coupling for Optical Transmitters With Polymer Modulators

Low-loss optical interconnects in hybrid integrated platforms for silicon photonics are likely to become increasingly important to overcome power consumption limitations in telecom packaging applications. Here, we show a short taper device that effectively interconnects electro-optic polymer modulators waveguides and silicon-on-insulator platforms without altering the polymer modulator fabrication process. We achieved power transmission better than $-\text{0.2}$ dB with very good alignment shift tolerance over the whole C -band, by using tapers as short as 179.5 $\mu$ m.

Polymer electro-optic modulator efficiency enhancement by the high permittivity dielectric strips

The performance improvement of rib-waveguide electro-optic (EO) polymer modulators resulting from the inclusion of high permittivity dielectric strips is considered. For this study, we take into account the heterogeneous nature of the poling of the electro-optic polymer by the electrode structure, the dispersion of the RF wave due to the material dispersion in the waveguide, and the finite conductivity of the electrodes. It is shown that the insertion of additional insulating strips with high dielectric permittivity (such as MgO) considerably enhances (from 120% to 280%) the efficiency of EO tuning. Furthermore, this efficiency grows with increasing modulation frequency, yielding a 2.0V half-wave voltage at 100GHz, when DH-80 EO polymer is used.

Optimizing low half-wave voltage electro-optic polymer modulator for optical waveguide sensor

Electro-optic (EO) modulator is used commonly in optical communication systems. Extensive research has being carried out to optimize the device by improving its design and making use of novel waveguide materials. For bio-sensing applications, optimizing the device to be able to operate in low frequency and low input voltage (half-wave voltage) are substantial. This paper discusses the ability of a selection of EO modulator materials and waveguide designs to increase the modulator's sensitivity by enhancing the value of the EO coefficient and reduce the half-wave voltage needed to modulate the input signal. EO phase modulator with a proper polymer material will produce better results compared to LiNbO3 in terms of length extension and low insertion loss. Furthermore, we show the performance study of a EO polymer phase modulator compared with the LiNbO3 waveguide to gain lower length extension as well low insertion loss. Those parameters are essential for bio-sensing applications like as biomedical tools to sense the response of human body. As well as these parameters are important to design an EO phase modulator that is feasible for measuring bio-potential signal of a human body in biomedical applications.

Efficiently poled electro-optic polymer modulators.

A titanium dioxide (TiO2) / electro-optic (EO) polymer hybrid waveguide modulator was designed and fabricated. This modulator possessed a significant advantage for realizing high poling efficiency regardless of the EO polymer resistivity. The in-device EO coefficient was measured to be 100 pm/V, which was 32% higher than that of the thin polymer film. As a result, the phase modulator displayed a VπL figure of merit of 3.5 V∙cm at 1550 nm, which can be reduced further in a push-pull Mach-Zehnder interferometer structure. Temporal stability test of the modulator at 85°C indicated only 8% change of Vπ over 500 hours. The propagation loss in the waveguide was measured as ~3 dB/cm.

Low half-wave voltage Y-branch electro-optic polymer modulator based on side-chain polyurethane-imide

A Y-branch electro-optic (EO) polymer modulator has been designed and fabricated. High performance side-chain polyurethane-imide (PUI) with a high EO coefficient of larger than 50 pm/V and a moderate glass-transition temperature [Formula: see text] of 206[Formula: see text]C is used as EO polymer core layer of the modulator. The fabricated phase modulator exhibits a low half-wave voltage of 1.94 V at 1550 nm in single arm modulation with 1 cm EO interaction length and 2 cm total length. The results show that the modulator fabricated by side-chain PUI EO materials possesses potential applications in low driving voltage and low cost optical systems.

Laser Ablation of a Polymer Electro-Optic Modulator

An electro-optic polymer-based Mach-Zehnder (M-Z) modulator is designed and fabricated for the 1550-nm telecom wavelength. The structures in the polymer films are patterned with micrometer resolution using a krypton fluoride excimer laser. This ensures that we can operate in the single-mode regime. We also present a new method for measuring the attenuation of the polymer waveguides by using waveguides of different lengths on the same substrate. While we have not optimized some parameters involved in the process, we have achieved a switching voltage $V_{\pi }$ of 80 V for a 20-mm long active region of the M-Z interferometer and a $r_{33}$ coefficient of 2.9 pm/V using 25% polycarbonate/DR1 chromophore.

An electro-optic polymer modulator for radio photonics

A method for developing an electro-optic polymer Mach‒Zehnder modulator based on polymethylmethacrylate- disperse red copolymer has been investigated. The inverse scheme is chosen as the basis for preparing a microstrip structure. This scheme entails the formation of microgrooves in the lower cladding layer by combining photolithography and reactive-ion etching (RIE), with subsequent deposition of an active electro-optic layer by centrifugation. The processes of forming layers and electrodes, the interaction between layers, the light transmission through the microstrip structure, and the modulator characteristics are considered.

The relationship of half-wave voltage and bandwidth in an electro-optic polymer modulator

In this paper, we present a detailed analysis about the relationship of half-wave voltage (Vπ) and bandwidth (Δf), based on a full vectorial finite difference (FVFD) mode solver for an optical waveguide and a finite-element method (FEM) for a microwave electrode, of an electro-optic (EO) polymer modulator. It has been found that we can get desirable VπL and ΔfL (L is EO interaction length) simultaneously. In other words, only the interaction length should be considered for a tradeoff of the Vπ and Δf in the design of a polymer EO modulator.