Photodefinable electro-optic polymer for high-speed modulators

Abstract

Direct waveguide definition of a negative photoresist (SU8) containing tricyanovinylidenediphenylaminobenzene (TCVDPA) as electro-optic (EO) chromophore, has been demonstrated for the first time. This was possible by utilising the chromophore low absorption window in the UV region allowing crosslinking of the host polymer by exposing to UV light followed by thermal curing. TCVDPA was modified by attachment of bulky side groups. This reduced the intermolecular interactions and resulted in an increased EO (r 33 ) coefficient.Introduction: Over the past decade the demand for telecommunication services and bandwidth has boomed. To handle this ever-increasing demand, high-speed electro-optic (EO) modulators operating over 100 GHz are required [1]. The currently used EO modulators based on LiNbO 3 are limited in bandwidth to 40 GHz, because at higher frequencies the velocity mismatch between the optical wave and the electrical travelling wave yields too large dephasing and consequently too short interaction lengths. To handle such high modulation frequencies a better performing material is required. Second-order nonlinear optical (NLO) polymers [2,3] were proposed two decades ago as useful candidates for this application. Though NLO polymers have the potential for high nonlinearity, the nonlinearity of the individual chromophores does not translate completely onto a macroscopic scale. This is because electrostatic intermolecular interactions lead to antiparallel clustering of the chromophores during electric field induced poling. These intermolecular interactions can be reduced by modifying the shape of the chromophore (making it more spherical) and thereby preventing their closer approach [4]. For long-term applications the chromophores should have a high photochemical stability at the operating wavelength and a high stability of the poling order at the operating temperature. TCVDPA has the highest reported photochemical stability [5]. In addition, its NLO figure of merit is higher than dimethylaminonitrostilbene (DANS) and disperse red (DR1). The difference between the glass transition temperature (T g ) of the polymer and the operating temperature, which determines the stability of the poling order, requires polymers with a high T g of about 200 C. When the NLO chromophores are incorporated in a photodefinable polymer, electro-optically active waveguides can be obtained by direct photodefinition. Compared with the reactive ion etching technique, this requires fewer processing steps and yields less sidewall roughness. In this Letter we report for the first time the direct photodefinition of an electro-optic polymer, i.e. TCVDPA in the SU8 host. Improvement of the poling efficiency by modifying TCVDPA with bulky side groups is also presented.

All-polymer Electro-optic switch

“…For long-term applications the EO chromophores must have a high photochemical stability at the operating temperature and a high stability of the poling order at the operating Temperature [8]. One such highly stable NLO chromophores is TCVDPA and direct photo-definition of TCVDPA in SU-8 host was reported first by Balakrishnan et.…”

Electro-optic effect of a soluble nonlinear optical polyimide containing two different chromophores with different sizes in the side chain

“…as active materials in photonic microdevices. [4][5][6][7] This interest has given rise to the need for materials with better electro-optic (EO) properties both at the molecular level and as elaborated materials. In order to design a highly active NLO chromophore, tricyanofuran (TCF)-and tricyanopyrroline (TCP)-based chromophores are employed; these are well known to have large permanent dipole moments and to exhibit electronic transitions at a higher wavelength.…”

The patent ductus arteriosus‐multiple defects and a moving target

“…Organic second‐order nonlinear optical (NLO) materials have strong potential for use in telecommunications, digital signal processing, optical modulator, THz generation, and many other applications as active materials in photonic microdevices 1–4…”