Poly(methyl methacrylate-co-9-anthrylmethyl methacrylate) (PMMA-AMA) LP-136 with various AMA contents was
prepared. The polymer was modified via Diels-Alder (D-A) type "click chemistry". In one approach, the side-chain was
grafted stepwise with maleimide-containing chromophore AJL-04 followed with N-phenylmaleimide (PI) to form LP-160. LP-160 was doped with 30 wt % of chromophore AJLS-102 to give electro-optic (EO) core polymer AJ-415. In the
other approach, all the pending AMA groups were modified with PI in one step to yield LP-165. Doping 33.7 wt %
AJLS-102 in LP-165 gives another core polymer AJ-416. The EO and material properties of both polymers were
systematically studied. Via careful selection of bottom and top cladding materials with proper optical and electrical
properties, Mach-Zehnder type modulators were fabricated based on both core materials. At the operational wavelength
of 1550 nm, modulator with AJ-415 core has half-wave driving voltage (Vπ) of 0.95 V and insertion loss of 19.1 dB,
while the best results from modulators with AJ-416 core are 0.75 V of Vπ and 17.1 dB of insertion loss. AJ-416 also has
the advantage over AJ-415 for building EO modulator with better processibility and long-term stability.
The optical and material properties of AJ309 electro-optic (EO) polymer were systematically studied with the objective
to fabricate an optimized integrated device. Both bottom and top cladding materials were developed at Lumera to
match the processibility of AJ309, and sustain high poling voltage needed for an effective poling process. A device
fabrication process is developed. The degree of crosslinking of the EO polymer before poling is minimized by
processing the top clad polymer at room-temperature. The UV-curable top clad has shown no detectable chemical
damage to the EO polymer after the deposition process of the top clad, thus maintaining the integrity of the interface
between top clad and AJ309 core. A 2.1 cm long active length Mach-Zehnder modulator with low half-wave voltage
(Vπ) of 1.1 V @1550 nm was fabricated using the AJ309 EO polymer and in-house cladding materials. Other device
parameters are also reported.
Polymeric electro-optical modulators have the advantages in bandwidth, driving voltage, and cost over lithium niobate
modulator for potential industrial, military and space applications. There are strict requirements on electro-optical
polymer materials to be used for practical device fabrication: large EO response, high thermal and photochemical
stability, low optical loss, high long-term stability and good processibility. Lots of progress in material design,
modification and optimization has been made based on theoretical calculation and actual material processing. However it
is very challenging to put all good properties into one material. We report the development of a chromophore series
based on 3,4-ethylenedioxythiophene structure and two host polymers based on 4,4'-(3,3,5-trimethylcyclohexylidene)
diphenol monomer. EO activity and optical loss at different chromophore loadings were systematically studied and
compared on various guest/host combinations. Specifically, DH-52/APC system was compared with DH-6/APC system,
showing improved overall electrical and optical properties. LP-116, with higher glass transition temperature than that of
APC, exhibits excellent mechanical property and compatibility with various chromophore guests. Especially, DH-67/LP-
116 has optical loss of 0.87 dB/cm. This indicates that LP-116 can substitute APC as an improved host polymer and DH-
52/LP-116 is highly feasible for the fabrication of EO devices with enhanced performance.
Host polymers play an important role in determining the thermal, optical and electrical properties of guest-host electro-optic (EO) polymers. In this study, a series of novel polymers, polyaryletherketones (PEKs) and polyarylethersulfones (PES'), were synthesized. After an initial screening on EO modulator fabrication-related properties, a PEK, LP120, was identified as a good candidate to host the highly stable chromophores (DH6 and DH52) developed in the company. Further optimization indicated that solvents in chromophore/polymer solutions have a strong impact on the quality of spin-coated films. DH6/LP120 and DH52/LP120 films spun from cyclopentanone gave lower optical losses of 1.97 and 1.55 dB/cm, respectively, when compared with 2.84 dB/cm for DH6/APC and 1.96 dB/cm for DH52/APC. Moreover, poling efficiencies as being reflected by EO coefficient were also improved by using LP120 compared to APC.
Electro-optic (EO) polymer modulators have demonstrated high speed external modulation of optical signals. Additionally, EO polymers have closely matched refractive indices at optical and microwave wavelengths, which enables high bandwidth operation. An EO polymer includes a polymer matrix and an organic "push-pull" chromophore that can be modified to give poled polymers with high EO activity. This high EO activity and optical-microwave velocity match offer the promise of accomplishing broadband, high speed optical modulation with low drive voltage. Such optical signal modulation is critical for applications in phased array radar and RF photonics. Practical issues such as electrode design, optical fiber coupling, and hermetic packaging are critical in final device performance. Herein, we report on high-speed electrode parameters as well as electro-optic performance versus frequency of packaged modulators fabricated with novel, highly photostable chromophores.
Low Vπ modulators are desirable in RF photonic and phased array radar applications. In general, there is still a need for optical modulators that have lower drive voltage, lower loss, and large bandwidth to decrease complexity, expense, and size in other parts of the packaged transmission system. This is particularly important for space based applications where reducing launch weight is crucial. Polymer modulators potentially enable space-based RF photonics because low Vπ can be achieved by modifying the organic constituents of the material. Additionally, polymers tend to have relatively low loss tangent and good RF-optical velocity match, which enables broadband devices. One fundamental issue for polymer modulator usability in space is the resistance of the materials to radiation. Previous reports have shown a small but measurable change in modulator properties on irradiation with gamma-rays and protons. Herein we report on the fabrication of polymer modulators, the results of irradiation, and potential lifetimes in earth orbits.
Electro-optic (EO) polymer modulators have demonstrated high speed external modulation of optical signals. Additionally, EO polymers have closely matched refractive indices at optical and microwave wavelengths, which enables high bandwidth operation. An EO polymer includes a polymer matrix and an organic "push-pull" chromophore that can be modified to give poled polymers with high EO activity. This high EO activity and optical-microwave velocity match offer the promise of accomplishing broadband, high speed optical modulation with low drive voltage. Such optical signal modulation is critical for applications in phased array radar and RF photonics. However, practical fabrication of optical modulators that realize the potential of EO polymers requires clad materials with optimized properties such as conductivity, dielectric constant, optical loss, and refractive index. In addition, other practical issues such as electrode design, optical fiber coupling, and hermetic packaging are critical in final device performance. We report on high-speed electrode parameters as well as electro-optic performance versus frequency of modulators fabricated on 6" silicon wafers. The r33 values measured on single layer thin films are compared with those resulting from Vπ measurements on devices. We compare the effect of EO polymer morphology on device fabrication and optical loss for different EO polymers.
Polymeric electro-optic materials have made significant progress in increasing electro-optic co-efficient, enhancing temporal stability, and lower optical loss at operating wavelength. To fully realize the electro-optic activity in a waveguide device, appropriate cladding materials need to be designed carefully and a compatible fabrication process should be developed accordingly, which has been challenging and tedious. It would be desirable if glass-based optical fiber or silica substrate can be utilized as parts of device materials. The challenge is to match the relatively lower refractive index of fiber and silica substrates. Thus, a low refractive (~1.44) of electro-optic material was designed. The efforts include the synthesis and characterization of the low index host materials via sol-gel process and silanization of a chromophore with large hyperpolarizability. In this study, an electro-optic sol-gel material with a refractive index
~1.44 at the wavelength of 1.55 μm was developed. It was highly processible and compatible with glass-based fiber or silica-based materials. An interdigitated electrode configuration is designed and a substrate with such a configuration was fabricated. Combined with the in-situ SHG monitoring setup, poling process can be readily monitored and optimized. The r33 obtained at the wavelength of 1.3 μm is 19 pm/V. Thus, it becomes possible to design optical devices using glass-based fiber or silica substrate as part of the device structure, which could simplify the material and process development.
Polymeric electro-optic materials have many potential advantages over their inorganic counterparts in both industrial and military applications for the reason of bandwidth, driving voltage, and cost. To fulfill the device processing and performance requirements, electro-optic materials need to possess high electro-optic activity, low optical loss, adequate thermal and photochemical stability as well as long term alignment stability. In this work, first we have designed and synthesized a series of chromophores with various acceptors. Their thermal stability and electro-optic activity were
compared. Detailed chromophore loading studies were carried out. An electro-optic coefficient of 160 pm/V was achieved. Secondly we modified our chromophore bridge by adapting 3,4-ethylenedioythiophene moiety. Both thermal stability and electro-optic activity are improved. Finally, we synthesized two polycarbonates with higher glass transition temperatures and lower optical loss. Their guest-host systems show improved EO activity, optical loss and long term
alignment stability.
Low drive voltage Mach-Zehnder modulators were designed and fabricated using proprietary EO polymers with high electro-optic coefficients. We report on drive voltage and high-speed electrode parameters of modulators fabricated on silicon wafers with high yield. Special attention was paid to designing claddings to match the electro-optic core conductivity and dielectric constant. The r33 values measured on single layer thin films are compared with those resulting from drive voltage measurements on devices. Half-wave voltage measured on devices is compared with theoretical values derived from equations defined for poling of the core through bottom and top claddings. We compare results obtained from devices fabricated using commercially available UV-curable epoxies with devices fabricating using proprietary clad polymers developed at Lumera Corporation.
The electro-optic coefficient and long-term dipole alignment stability are two major factors in the development of high performance NLO materials for the application of high-speed EO devices. We have developed a high performance non-linear organic chromophore and incorporated it into a crosslinkable side-chain polyimide system. The polymer was synthesized through stepwise grafting of the crosslinker followed by the chromophore onto the polyimide backbone via esterification. Different chromophore loading levels were achieved by adjusting the crosslinker/chromophore feeding ratio. The polyimides films were contact-poled with second-harmonic generation monitoring. A large EO coefficient value was obtained and good long-term thermal stability at 85°C was observed.
Drawing on the success of the DH6-polycarbonate system, new derivatives based on the DH bridge structure, bis-1,2-(dibutoxythiophene)vinylene have been synthesized and tested. The property-structure function has been investigated, showing that location of the trifluorovinylether (TFVE) crosslinker on the chromophore has an impact on electro-optic (EO) activity as well as stability. A crosslinked polymer, IMOH_PCT-R and a linear high glass transition (Tg) analog, IMOH_HT, in combination with various DH derivatives are discussed. The temporal stability data of these systems show comparable results for both crosslinked and linear polymers, furthering the argument that the Tg of the EO material is the critical parameter in determining device lifetime.
New crosslinked clad polymers were developed for electro-optic polymer modulators with special attention paid to properties such as refractive index tunability, optical loss, and conductivity. These cured polymers showed relatively low optical loss at 1550 nm and desirable conductivity. The clads were used to fabricate electro-optic devices having mode profiles closely matched to that of optical fibers in order to reduce insertion loss. A new hardmasking technique was developed to define Mach-Zehnder rib waveguides by photolithography and dry etching with high reliability and surface smoothness. The hardmasking technique demonstrated flexibility in defining waveguides made with electro-optic polymers having different reactivity towards etchant gasses.
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