Mojca Jazbinsek

Silicon-Organic Hybrid Electro-Optical Devices

Organic materials combined with strongly guiding silicon waveguides open the route to highly efficient electro-optical devices. Modulators based on the so-called silicon-organic hybrid (SOH) platform have only recently shown frequency responses up to 100 GHz, high-speed operation beyond 112 Gbit/s with fJ/bit power consumption. In this paper, we review the SOH platform and discuss important devices such as Mach-Zehnder and IQ-modulators based on the linear electro-optic effect. We further show liquid-crystal phase-shifters with a voltage-length product as low as VπL = 0.06 V·mm and sub-μW power consumption as required for slow optical switching or tuning optical filters and devices.

Linear and nonlinear optical properties of the organic crystal DSTMS

We report on the linear and nonlinear optical properties of the novel organic crystal 4-N, N-dimethylamino-4′-N′-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS). The principal refractive indices n1, n2, and n3 have been determined by a direct measurement of the group index dispersion over a broad wavelength range from 0.6 to 1.6 μm. The linear absorption coefficients for light polarized along the dielectric axes have been measured in the transparency range from 600 to 2000 nm. DSTMS crystals show a large birefringence of Δn=0.5 and low absorption α<0.7 cm−1 in the telecommunication wavelength range at 1.55 μm. Furthermore, the nonlinear optical tensor elements d111, d122, and d212 have been determined by the Maker-fringe technique at the fundamental wavelength of 1.9 μm. DSTMS crystals exhibit a very large nonlinear activity with a nonlinear optical coefficient d111=214±20 pm/V. Phase-matching curves determined from our optical data showed that parametric oscillation can be achieved in the wavelength range from 1 to 2.2 μm with effective nonlinear optical coefficients larger than 25 pm/V.

High-power Broadband Organic THz Generator

The high-power broadband terahertz (THz) generator is an essential tool for a wide range of THz applications. Here, we present a novel highly efficient electro-optic quinolinium single crystal for THz wave generation. For obtaining intense and broadband THz waves by optical-to-THz frequency conversion, a quinolinium crystal was developed to fulfill all the requirements, which are in general extremely difficult to maintain simultaneously in a single medium, such as a large macroscopic electro-optic response and excellent crystal characteristics including a large crystal size with desired facets, good environmental stability, high optical quality, wide transparency range, and controllable crystal thickness. Compared to the benchmark inorganic and organic crystals, the new quinolinium crystal possesses excellent crystal properties and THz generation characteristics with broader THz spectral coverage and higher THz conversion efficiency at the technologically important pump wavelength of 800 nm. Therefore, the quinolinium crystal offers great potential for efficient and gap-free broadband THz wave generation.

Configurationally locked, phenolic polyene organic crystal 2-{3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene}malononitrile : linear and nonlinear optical properties

We show that the organic polyene crystal 2-{3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene}malononitrile (OH1) is a new material with excellent nonlinear optical and electro-optical properties. The principal refractive indices and the absorption constants have been determined over a broad wavelength range from 0.6to2.2 μm. OH1 shows a large birefringence of Δn>0.55 and a low absorption of α<1 cm−1 in a large wavelength range between 800 and 1400 nm. Furthermore, the nonlinear optical tensor elements d333=120 ± 10 pm/V, d223=13 ± 2 pm/V, and d322=8.5 ± 2 pm/V have been determined by the Maker-fringe technique at the fundamental wavelength of 1.9 μm. The electro-optic coefficients r333, r223, and r113 have been measured at the wavelengths of 633, 785, 1064, and 1319 nm, and it is shown that the dispersion can be described by a one-oscillator model. OH1 is a promising material for nonlinear optical and electro-optical applications due to the large nonlinear coefficient d333, the large electro-optic coefficient r333=109 ± 4 pm/V at 632.8 nm, the favorable crystal growth properties, as well as the orthorhombic crystal symmetry (point group mm2), which renders crystal preparation and orientation much simpler than in most organic nonlinear optical crystals.

Tailoring of infrared photorefractive properties of Sn 2 P 2 S 6 crystals by Te and Sb doping

The photorefractive properties of Sn2P2S6 crystals doped with Te and Sb in the near-infrared wavelength range up to 1064 nm are reported. The main photorefractive parameters, i.e., two-wave mixing gain, effective electro-optic coefficient, diffusion length, concentration of traps, and response time, are compared with conventional nominally pure Sn2P2S6. Te-doped Sn2P2S6 shows the fastest response with the smallest decrease of the photorefractive efficiency with increasing wavelength in the near infrared. Sb doping, on the other hand, inhibits photorefraction in the near infrared. Sn2P2S6:Te and Sn2P2S6:Sb crystals both show a high two-wave mixing gain Γ at 633 nm, and 10 and 20 cm−1. Te-doped Sn2P2S6 shows a photorefractive gain of 4.5 cm−1 at 1064 nm. Response times at 1064 nm of 20 ms have been measured for the intensity 6 W/cm2, which is 2 orders of magnitude shorter than in Rh-doped BaTiO3.

High efficiency THz generation in DSTMS, DAST and OH1 pumped by Cr:forsterite laser

We investigated Terahertz generation in organic crystals DSTMS, DAST and OH1 directly pumped by a Cr:forsterite laser at central wavelength of 1.25 μm. This pump laser technology provides a laser-to-THz energy conversion efficiency higher than 3 percent. Phase-matching is demonstrated over a broad 0.1-8 THz frequency range. In our simple setup we achieved hundred μJ pulses in tight focus resulting in electric and magnetic field larger than 10 MV/cm and 3 Tesla.

High-finesse laterally coupled organic-inorganic hybrid polymer microring resonators for VLSI photonics

We produced laterally coupled optical microring resonators having high finesse (F/spl sime/17 at 1.5-/spl mu/m wavelength) using a two-step patterning technique based on optical photolithography. The technique used allows us to separately control the height of both ring and port waveguides and structure submicrometer gaps. The resonance spectrum of microrings with radii of 50 /spl mu/m made of an organic-inorganic hybrid polymer have an extinction ratio of about 12 dB and a filter bandwidth /spl delta//spl lambda//spl sime/0.28 nm (full-width at half-maximum) at a wavelength /spl lambda/=1547.78 nm. We show that the resonances can be thermooptically tuned by 0.2 nm//spl deg/C, thus allowing us to modulate the transmission of the through port signal.

New acentric quinolinium crystal with high order parameter for nonlinear optical and electro-optic applications

We have designed and synthesized a new, highly efficient electro-optic vanillin-based quinolinium crystal. The HMQ-NS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium naphthalene-2-sulfonate) crystals exhibit an acentric monoclinic space group symmetry Pn with a large effective molecular hyperpolarizability in the crystal with the diagonal component βeff333 = 149 × 10−30 esu, which is comparable to that of benchmark ionic stilbazolium crystals, and a good thermal stability. Therefore, the newly developed HMQ-NS crystal is an attractive candidate for nonlinear optical and electro-optic applications.

Recent progress in acentric core structures for highly efficient nonlinear optical crystals and their supramolecular interactions and terahertz applications

During the past decade, various new types of organic nonlinear optical crystals have been developed to overcome the benchmark stilbazolium DAST (4-(4-(N,N-dimethylamino)styryl)-1-methylpyridinium 4-methylbenzenesulfonate) crystal. Here, we review the acentric core structures used in recently developed organic nonlinear optical crystals exhibiting high macroscopic second-order optical nonlinearity, along with their supramolecular interactions and THz applications. The nonlinear optical acentric core structures such as neutral CLP (configurationally locked polyene based on phenyltriene), ionic pyridinium-based N-alkyl DAS (4-(4-(N,N-dimethylamino)styryl)-1-alkylpyridinium benzenesulfonate) and N-phenyl DAP ((4-(N,N-dimethylamino)styryl)-1-phenylpyridinium hexafluorophosphate), ionic quinolinium-based HMQ (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium benzenesulfonate) and OHQ (2-(4-hydroxystyryl)-1-methylquinolinium benzenesulfonate) and benzoindolium-based DBI (2-(4-(dimethylamino)styryl)-1,3,3-trimethyl-3H-benzo[g]indolium iodide) exhibit comparable or enhanced physical properties compared to DAST crystals. Organic crystals introducing an identical acentric core structure often exhibit similar molecular alignment features with analogous supramolecular interactions. We also discuss the nonlinear optical properties and potential applications of these materials, in particular their very promising THz photonic applications.

Electro-optic tuning and modulation of single-crystalline organic microring resonators

We present, for the first time to our knowledge, the fabrication and electro-optic (EO) tuning of single-crystalline organic microring resonators. In recent years, optical microring resonators have proven to be highly suitable building blocks for the realization of very large-scale integrated photonic circuits. In particular, microresonators based on organic materials are very promising for ultrafast EO applications, due to the electronic nature of the EO response preserving the modulation performances beyond 100 GHz. In contrast to polymer waveguiding structures realized previously, our crystalline thin-film devices feature an excellent long-term stability of the chromophore orientation and superior photochemical stability, and they do not require high-field poling prior to operation. The introduced thin-film fabrication method significantly reduces fabrication complexity of organic crystalline EO waveguides, compared to previously developed techniques. We have fabricated crystalline COANP (2-cyclo-octylamino-5-nitropyridine) microring resonators with resonance contrast up to 10 dB, ring waveguide propagation losses of about 10 dB/cm, a free spectral range of 1.6 nm, a finesse of up to 20, and a corresponding Q-factor of about 20,000, measured in the telecom wavelength range around 1.55 μm. We have demonstrated resonance wavelength tuning at the rate of 0.13 GHz/V(1.1 pm/V).