Rainbow Photonics (Switzerland)

We present THz time-domain spectroscopy and imaging covering a wide frequency range up to 20 THz. Our approach uses highly efficient organic nonlinear optical crystals (DSTMS, OH1) and a compact femtosecond pump laser (1560 nm) with MHz repetition rate and ultrashort pulse width (<40 fs). By optimizing the optical geometry, we achieve high SNR (>80 dB at 4 THz, >70 dB at 10 THz). Our theoretical model agrees well with experiments. We validate our system by obtaining high-resolution THz spectra of water vapor and various solid substances. Additionally, we present THz imaging with sub-50 μm spatial and sub-10 fs temporal resolution.

DSTMS organic electro-optic crystal is a very promising and efficient THz-wave generation material. It allows for both very high THz electric fields generation, exceeding several GV/m using optical rectification of femtosecond laser pulses, as well as the possibility for extremely broad bandwidth extending well beyond 10 THz [1]. However, the usual laboratory THz systems based on these crystals exploit very bulky and expensive fs laser systems [2], which are not desired for industrial THz imaging and spectroscopy applications [3,4]. Recently, some compact system employing organic crystals were demonstrated [5], however they use a conventional photoconductive antenna as a THz-wave detector. Here we present a compact THz time-domain spectroscopy system based on a relatively low-cost and small-size femtosecond fiber lasers operating at 1560 nm. As the THz generation and detection material, we choose the organic crystal DSTMS (4-N,N-dimethylamino-4‘-N‘-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate), since it reaches the highest overall efficiency and the flattest spectrum among the presently known state-of-the-art organic crystals (Figure 1).

In this chapter, an overview of applications of electro-optics is presented. Waveguide electro-optic devices are discussed in greater detail in Chapter 9 and applications involving second-order nonlinear optical effects other than electro-optic phenomena (e.g., frequency conversion) are discussed in Chapter 10. Photorefractivity phenomena, materials, and applications are discussed in Chapter 11. Some prototype devices, particularly silicon–organic hybrid (SOH) and plasmonic–organic hybrid (POH) devices, were briefly discussed in Chapter 7. Device parameters and materials requirements Applications of electro-optic materials include telecommunications, computing, defense, medical, and sensing technologies. A wide range of specific devices are critical for these technologies. Electro-optic devices can be divided into three general categories: (1) stripline devices such as Mach–Zehnder interferometers and directional couplers; (2) resonant devices such as ring microresonators, etalons, photonic crystal, and metamaterial devices; and (3) prism-based devices such as spatial light modulators. The relationships between device performance and material performance parameters vary with device type. Some properties, such as acceptable material optical loss, depend on system architectures, as well as individual device architectures. Material requirements, such as thermal and photochemical stability, will depend upon device and system operating conditions, e.g., temperature and optical power levels that are used. Telcordia standards define minimum thermal stability requirements, e.g., long-term operational stability at 85 °C (and 85% humidity). Optical power levels vary with application area, e.g., telecommunication applications currently utilize power levels of 10–20 mW at wavelengths centered around 1.3 or 1.55 μm. Clearly, material requirements and their relationship to device performance will depend upon application and upon device and system architectures, so general and simple requirements cannot be defined in a meaningful way. However, in the following, we provide insight into the relationship between device performance and materials characteristics for the simple general device structures noted above. A more in-depth discussion relevant to waveguide device architectures is presented in the next chapter. An even broader range of device architectures are relevant to the applications discussed in Chapters 10 and 11. Stripline devices . Representative stripline devices include Mach–Zehnder interferometers (amplitude modulators), birefringement or phase modulators, and directional couplers (see Figs. 9.6 and 9.8) [1,2].

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We design and synthesize various π-conjugated phenyltriene chromophores having different thiolated electron donor groups such as thiol, alkylthiol, and arylthiol groups to systematically investigate the electron-donating ability of sulfur analogues. For comparison, we also investigate the commonly used electron donor groups, oxygen-containing hydroxyl and alkoxy groups, as well as nitrogen-containing dialkylamino groups. Experimental and/or theoretical analysis of the nonlinear optical properties of these chromophores in gas, solution, and solid states suggest that the rotational isomerization of an arylthiolated group acting as electron donor in polyene chromophores induces a large variation of molecular optical nonlinearities. The first hyperpolarizabilities, calculated separately with finite-field (FF) and time-dependent density functional theory (TD-DFT) two-state model methods, indicate that this phenomenon is a consequence of the competitive electronic transitions from the ground state to the first and second excited states modulated by the rotation of thiophenyl group.

The combination of CMOS compatible Silicon-On-Insulator (SOI) fabrication technology with organic cover materials constitutes the Silicon-Organic Hybrid (SOH) fabrication platform, which shows innovative functionality for the making of integrated optical circuits. We report on experimental demonstrations of essential building blocks for transceivers, while relying only on well-known SOI processing steps and simple post processing of the organic materials.

We investigate new 4-nitophenylhydrazone crystals with thiolated electron donors for nonlinear optical applications. The methylthiolated (SM) electron donor and the biphenyl sulfane (SB) electron donor, which promotes a herringbone packing motif, are incorporated with an acentric nonlinear optical core, nitrophenylhydrazone (NPH), which promotes a λ-shaped packing motif in the crystalline state. SM-NPH (4-(methylthio)benzaldehyde-4-nitrophenylhydrazone) crystals show head-to-tail hydrogen-bonded chains, which outweigh the usual λ-shaped packing of the nitrophenylhydrazone group. SB-NPH crystals (4-(phenylthio)benzaldehyde-4-nitrophenylhydrazone) showsimultaneous λ-shaped packing, based on the hydrogen bonds of nitrophenylhydrazone with the nitro electron acceptor group, and the herringbone-shaped packing of biphenyl sulfane groups. Polar SM-NPH chains pack in a centrosymmetric crystal structure, while SB-NPH crystals exhibit a large macroscopic second-order nonlinearity resulting from an acentric molecular ordering of two rotational isomers. In addition, SB-NPH crystals undergo an irreversible phase transition before melting, with the second phase being also acentric with a strong second harmonic generation efficiency.