Electro-optic Polymer Waveguide Research Articles

D-band optical modulators using electro-optic polymer waveguides and non-coplanar patch antennas.

D-band (110-170 GHz) antenna-coupled optical modulators with electro-optic (EO) polymer waveguides and non-coplanar patch antennas were fabricated using a poled EO polymer film transfer method. A carrier-to-sideband ratio (CSR) of 42.3 dB corresponding to an optical phase shift of 15.3 mrad was obtained by irradiating 150 GHz electromagnetic waves with an irradiation power density of 34.3 W/m2. Our devices and fabrication method have great potential for achieving highly efficient wireless-to-optical signal conversion in radio-over-fiber (RoF) systems.

A Novel Millimeter Wave Receiver Enhanced by a Metallic Dipole Antenna and an Electro-Optic Polymer Waveguide Ring Resonator

The ever-demanding requirement for higher data transmission rate has pushed the carrier frequency in wireless communications from centimeter to millimeter waves (MMW) or even terahertz band. Hybrid integration between the wireless and fiber-optic systems can then help realize a seamless signal transition between the access and backbone networks. In this work, we propose a novel MMW receiver with a simple structure consisting of an electro-optic polymer racetrack waveguide ring resonator (WRR) and a metal dipole antenna. Due to Pockels effect within the polymer waveguide, the presence of the MMW electric field can introduce minor refractive index changes in the waveguide, which can affect light phase and the transmission through the WRR. This effect can be employed to effectively detect the presence of MMW based on the optical method. The phase changes can be highly improved by the dipole antenna resonating at the MMW frequency in order to achieve an enhanced detection of the MMWs. As a result, a low-cost, compact and reliable MMW receiver can be realized, which provides an effective functional interface between MMW and optical fiber-optic systems.

W-band optical modulators using electro-optic polymer waveguides and patch antenna arrays.

In this study, W-band (75-110 GHz) antenna-coupled optical modulators with a cyclo-olefin polymer (COP) lower cladding, an electro-optic (EO) polymer waveguide, and a gap-embedded patch antenna array were fabricated using a transfer and bonding method of a poled EO polymer film. A carrier-to-sideband ratio (CSR) of 56 dB corresponding to an optical phase shift of 3 mrad was obtained under irradiation with 100 GHz electromagnetic waves with a power of 12.8 W/m2. Our devices have the potential to achieve highly efficient wireless-optical signal conversion in radio-over-fiber (RoF) systems.

High-Speed Optical-Beam Scanning by an Optical Phased Array Using Electro-Optic Polymer Waveguides

Optical phased arrays (OPAs), which manipulate an optical beam by controlling the phase of light, are optical devices characterized by high speed, small size, light weight, and high reliability that make various applications possible. In this study, an eight-channel-waveguide OPA using an electro-optic (EO) polymer for phase control was fabricated. Very high-speed optical beam scanning with a frequency of 2 MHz was demonstrated by applying a driving waveform superimposing sinusoidal and rectangular-wave voltages. Furthermore, the EO polymer OPA can be operated with a low total-operation power consumption of 0.38 mW at a scanning speed of 500 kHz.

Synthesis and characterization of electro-optic waveguide material polyurethane-imides

The electro-optic (EO) polymers of Y-type polyurethane-imides (PUI-1 and PUI-2) were synthesized by reaction of monomer azo-based chromophores, phenyl diisocyanate and aromatic dianhydride, based on polycondensation mechanism. Molecular structure characteristics for the polymers were evidenced by 1HNMR, FTIR, elemental analysis and gel permeation chromatography. The polymers exhibited a glass transition temperature (Tg) of 185 °C and 192 °C and a temperature of 5% weight loss at 256 °C and 325 °C and showed EO coefficient, γ33, of 43 pm/V and 51 pm/V at 1550 nm wavelength. A type of single-mode embedded PUI polymeric inverted rib waveguide Mach-Zehnder (MZ) interferometer electro-optic modulators was fabricated and measured, and exhibiting favorable electro-optical modulation response and the average propagation loss of the waveguide was less than 2.0 dB/cm at 1550 nm. The experimental results indicated that the PUI were promising candidates for the preparation of comprehensive performance excellent EO polymer waveguide materials, due to their large nonlinear optic effects, thermal stability, good processability and low optical propagation loss.

Low driving voltage Mach-Zehnder interference modulator constructed from an electro-optic polymer on ultra-thin silicon with a broadband operation.

An electro-optic (EO) polymer waveguide using an ultra-thin silicon hybrid has been designed and fabricated. The silicon core has the thickness of 50 nm and a width of 5 μm. The waveguide was completed after covering the cladding with the high temperature stable EO polymer. We have demonstrated a low half-wavelength voltage of 0.9 V at the wavelength of 1.55 μm by using a Mach-Zehnder interference modulator with TM mode operation. The measured modulation corresponded to an effective in-device EO coefficient of 165 pm/V. By utilizing the traveling-wave electrode on the modulator the high-frequency response was tested up to 40 GHz. The 3 dB modulation bandwidth was measured to be 23 GHz. In addition, the high frequency sideband spectral measurement revealed that a linear response of the modulation index against the RF power was confirmed up to 40 GHz signal.

Hybrid and Etch-Less Electrooptic Waveguide Modulator Based on Photo-Bleaching and Strain Induced Optical Waveguide Technique in Polymer

A hybrid and etchless electrooptic (EO) polymer waveguide modulator based on both a photo-bleaching-induced optical waveguide (PBOW) and a strain-induced optical waveguide (SIOW) is described. The SIOW is defined by a metal strip line stressor deposited on top of the upper cladding that introduces the refractive index change within the core region. The PBOW technique is used to form an optical waveguide which is based on a photo-bleaching process, known as a photo-oxidation that is an irreversible decomposition of EO material, resulting in a permanent decrease in index of refraction. It is shown that this proposed fabrication idea combining two etchless techniques can be applicable to a wide range of polymer photonic integrated circuits. Preliminary results obtained from fabricated devices reveal that their half-wave voltage are ranging from 8 V to 10 V, their extinction ratio exhibits more than 15 dB, and the fiber-to-waveguide-to-lens loss is estimated to be ~9.5 dB for TM polarization at 1.55/m wavelength in the active interaction of ~1.5 cm long.

Electro-optic polymer waveguide modulator based on the Pockels and Kerr effects

An electro-optic polymer waveguide modulator based on both Pockels and Kerr effects has been demonstrated. A conjugated polymer, poly (9,9-dioctyl-2,7-fluorene-co-benzo [c][1,2,5]thiadiazole-co-9-hexyl-3,6-carbazole), which has the delocalization of p-electrons and a push-pull structure along the main conjugated chain, exhibits the Pockels effect and still maintains the Kerr effect after corona-poling. By applying a direct current (DC) bias, the optical output of the modulator is roughly linearly to a modulation voltage, and the modulation depth is improved with the DC bias at fixed modulation voltage. The proposed modulator achieves a 2.18% modulation depth with 5 V p-p modulation triangular voltage and 90 V DC bias at 100 kHz by employing both the Pockels effect and Kerr effect.

Linearized electro-optic modulators based on a two-section Y-fed directional coupler

We experimentally demonstrate a linearized Y-fed directional coupler (DC) modulator based on an electro-optic (EO) polymer waveguide. The spurious free dynamic range of 119 dB/Hz2/3, which is 11 dB higher than that of the conventional Mach-Zehnder modulator, is achieved by introducing the reversed Δβ technique in the two-section Y-fed DC. The in-device EO coefficient (r33) of the fabricated device is as high as 79 pm/V in 1.55 μm wavelength, which is 88% of a single film r33 of LPD-80/APC.

Alignment-free fabrication of a hybrid electro-optic polymer/ion-exchange glass coplanar modulator

A hybrid electro-optic (EO) polymer phase modulator with a 6 μm coplanar electrode gap was realized on ion exchange glass substrates. The critical alignment steps which may be required for hybrid optoelectronic devices were eliminated with a simple alignment-free fabrication technique. The low loss adiabatic transition from glass to EO polymer waveguide was enabled by gray scale patterning of novel EO polymer, AJLY. Total insertion loss of 5 dB and electrode gap of 8 μm was obtained for an optimized device design. EO polymer poling at 135 °C and 75 V/μm was demonstrated for the first time on a phosphate glass substrate and was enabled by the sol-gel buffer layer.

Design and Demonstration of Polarizing Polymer Waveguides Using Birefringent Polymers

TE-pass and TM-pass polarizing waveguides were fabricated by adjusting the birefringence properties of multi-layer stacks. The desired values of indices of refraction and birefringence were obtained by the proper selection and customization of core and cladding materials. The technique developed was used in the fabrication of waveguides in various design configurations such as etched ribs, backfilled trenches and photobleached channels. Both passive and active (electro-optic) core materials were successfully used in demonstrating the polarization extinction ratios as high as 61 dB. To our knowledge, this is the highest extinction ratio reported with polarizing polymer waveguides. In the case of electro-optic polymer waveguides, the designs were modified to enhance the electric field strength in the core without compromising the polarizing extinction ratios of the waveguides.

Optical Signal Processor Using Electro-Optic Polymer Waveguides

We have investigated an optical signal processor using electro-optic polymer waveguides operating at a wavelength of 1.55 mum. Due to recent developments, many useful optical devices have become available such as optical filters, modulators, switches, and multiplexers. It will be useful to have a single optical device, which is reconfigurable to implement all of these functions. We call such a device an ldquooptical signal processor,rdquo which will play a similar role to digital signal processors in electrical circuits. We realize such an optical device in a planar lightwave circuit. Since the planar lightwave circuits are based on the multiple interference of coherent light and can be integrated with significant complexity, they have been implemented for various purposes of optical processing such as optical filters. However, their guiding waveguides are mostly passive, and the only viable mechanism to reconfigure their functions is thermal effects, which is slow and cannot be used for high-speed applications such as optical modulators or optical packet switches. On the other hand, electro-optic polymer has a very high electro-optic coefficient and a good velocity match between electrical and optical signals, thus, permitting the creation of high-speed optical devices with high efficiency. Therefore, we have implemented a planar lightwave circuit using the electro-optic polymer waveguides. As a result, the structure is complex enough to generate arbitrary functions and fast enough to obtain high data rates. Using the optical signal processor, we investigate interesting applications including arbitrary waveform generators.

Development of an Electro-Optic Scanner for Potential Endoscope Application

Technological advancements in endoscopy design are in current development due to the increased demand for minimally invasive medical procedures. One such advancement is reducing the overall size of the endoscope system while maintaining the resolution and field-of-view (FOV). Reduction of size results in less tissue damage and trauma during operation as well as faster recovery times for patients. Additionally, areas that are inaccessible by today's endoscope designs will be possible to examine. Current endoscopes use either a bundle of optical fibers (optical waveguides) and/or one or more cameras having an array of detectors to capture an image. Thus, the diameter of these devices employed for remote imaging cannot be reduced to smaller than the image size. Even if one ignores additional optical fibers used for illumination of a region of interest, the scope diameter is therefore limited by the individual pixel size of a camera or by the diameter of optical fibers used to acquire the image. Therefore, it is apparent to achieve scopes with less than 3 mm overall diameter using current technologies, resolution and/or FOV must be sacrificed by having fewer pixel elements. All commercially available scopes suffer from this fundamental tradeoff between high image quality and small size. More recently, our research has been working on developing a 2-D electro-optic scanner potentially be implemented for clinical endoscopic imaging application. The proposed optical device has several unique advantages. Electro-optical scanning offers a sensitive, facile, accurate, and superb quality method to capture images of physical and biological tissues. In addition, the minute physical size of the imaging system has a much needed advantage over conventional imaging systems. The proposed design is based on the fact that the propagation direction of a light beam can be changed when the index of refraction of an electro-optic medium is altered by the application of an external electric field. The basic design of the system consists of a thin film electro-optic polymer waveguide with built-in cascaded prisms structure for horizontal beam deflection and an electro-optic grating structure for vertical beam deflection. The cascaded prisms are combined with the electro-optic polymer to create a voltage-controlled horizontal beam deflection. A grating coupler, a structure that is commonly used as light coupling device for dielectric waveguide, is combined with the EO polymer to create the vertical controlled beam deflection. A collimated light beam coupled into the waveguide by a mechanical coupler via an optical fiber cascaded down these two deflection stages. When the beam exits, the emitted light beam is displaced along two orthogonal directions in a raster pattern. A photodetector array integrated in the same substrate captured the reflected intensity. The scanned imaged is then analyzed and reconstruct based on the received signal.

High Δn strip-loaded electro-optic polymer waveguide modulator with low insertion loss

We demonstrate a novel electro-optic polymer modulator design which shows a record low optical insertion loss of 5.7 dB at 1550 nm. The modulator consists of a high numerical aperture passive waveguide which is converted to a strip-loaded electro-optic polymer waveguide through refractive index tapers. The device is fabricated using all wet-etch techniques which results in low excess loss from roughness created during fabrication and, employs new low loss passive sol-gel materials. The fabricated device also shows a low half-wave voltage of 2.8 V.

Investigation of drift in electro-optic polymer waveguides

The mechanism of the phase drift in electro-optic polymer waveguide devices is presented based on buildup of free ion charge at the electrode-clad interfaces. The difference of the electrode-clad interfaces at the top and bottom electrodes is shown to be important in reducing the drift and that doping of the core with macrocyclic polyethers can suppress this phenomenon. Arrhenius curves of long-term phase drifts using Mach–Zehnder modulators show the activation energies for symmetric electrode interfaces, asymmetric electrode interfaces, and macrocyclic polyether doped cores to be 0.30, 0.28, and 0.15 eV, respectively.

Polarization selective electro-optic polymer waveguide devices by direct electron beam writing

A novel technique for the fabrication of polarization selective electro-optic polymer waveguide devices with direct electron beam writing was described. Birefringence induced by the electric field poling in the electro-optic polymer film was erased in the electron beam exposed regions. The formed waveguides had stronger confinement for the light polarized along the poling direction. High fabrication resolution on the 100 nm scale or smaller could be achieved. Fabrication of polymer polarizer and polarization selective microring resonators with this technique was reported. The highest polarization extinction ratio was measured to be 21.4 dB.

Direct electron beam writing of electro-optic polymer microring resonators

Electro-optic polymer waveguides in electron beam sensitive polymethyl methacrylate (PMMA) polymer matrix doped with organic nonlinear chromophores could be directly patterned by electron beam exposure with high resolution and smoothness. The polymer in the exposed regions was removed with standard electron beam resist developer and without damaging the chromophore containing polymer waveguides. Feature sizes on the order of 100 nm could be clearly resolved. High quality microring resonators made of YL124/PMMA electro-optic polymer were successfully fabricated with this technique. The measured resonance extinction ratios were more than 16 dB and quality factors were in the range of 10(3) approximately 10(4).

Microring Resonators Made in Poled and Unpoled Chromophore-Containing Polymers for Optical Communication and Sensors

Poled and unpoled chromophore-containing polymers offer some unique advantages in device functionality and fabrication. UV light and electron beam (e-beam) can bleach out the color of chromophores and reduce the index of refraction of the polymer. The photobleaching and e-beam bleaching methods form optical waveguides in a single step and do not involve solvents or wet chemicals, and can be applied to polymers that are not compatible with other waveguide fabrication techniques. A variety of microring resonator devices for fiber-optic telecommunication and sensors have been realized with chromophore-containing polymers. A novel broadband fiber-optic electric field sensor is presented as an example. The sensor uses a polymer with chromophores preferentially aligned after electric poling, and the microring resonator is directly coupled to the core of optical fiber. The feasibility of vertical integration of a poled electrooptic polymer waveguide device interfaced with silicon microelectronic circuits is also demonstrated.

Multi-month thermal aging of electro-optic polymer waveguides: Synthesis, fabrication, and relaxation modeling

The preparation of polyimides containing side-chain chromophores and the long-term aging performance of poled films are described. These materials were compared to guest–host polycarbonate films. Mach–Zehnder optical interferometers were fabricated from these polymers that contained CLD- and FTC-type chromophores. Changes in optical properties were monitored for months at four temperatures ranging from ambient to 110°C. The isothermal relaxation data were modeled using both a stretched exponential equation and a power law in time equation. The temperature dependency of the time constants of these equations was modeled using a new activation-energy equation: ln(τ/τp)=ER(1+tanh[(Tc−T)/D])/2RT+Ep/RT where Tc is the central temperature of the transition zone, D is the breadth of the zone, and Es are the activation energies of rigid and pliable materials. Multi-year high-temperature stability of the poled guest–host and side-chain materials was predicted.

All-Dielectric Electrooptic Sensor Based on a Polymer Microresonator Coupled Side-Polished Optical Fiber

A novel electrooptic (EO) electric field (E-field) sensor based on side-polished fiber coupled with an EO polymer microring resonator is proposed and demonstrated. An EO polymer waveguide with a ring shape is fabricated on the polished flat of an optical fiber. Light in the fiber evanescently couples into the resonator and forms resonant modes for certain wavelengths and produces notches in the output intensity of the fiber. External electric fields change the index of refraction of the ring waveguide and therefore dither its resonant wavelengths. For light of wavelength on the slope of a resonance notch, a change in the output intensity can be detected. The sensor is all dielectric without metal layers to distort the measured E-field. The resonant structure allows the sensor to potentially have much higher sensitivity than other electrooptic sensors based on Mach-Zehnder or polarization modulation. Since electrooptic polymers have higher electrooptic coefficients, lower dielectric constants and faster electrooptic responses than inorganic crystals, higher sensitivity, lower invasiveness, and higher bandwidth of E-field sensing can be expected. This sensor eliminates unreliable fiber-to-waveguide butt coupling as well as the high propagation loss encountered in the long straight EO polymer waveguides of sensors based on Mach-Zehnder structures. By using the fiber itself as the supporting substrate of the ring waveguide, the sensor can have small size and low disturbance to the measured electric field. The concept is demonstrated using AJLS103 EO polymer. A sensitivity of 100 mV/m has been achieved at frequencies up to 550 MHz (limited by the measurement system)