Y. G. Zhao

Ultraviolet lasing in resonators formed by scattering in semiconductor polycrystalline films

A semiconductor laser whose cavities are “self-formed” due to strong optical scattering in highly disordered gain media is demonstrated. The lasers are made of zinc oxide polycrystalline films grown on amorphous fused silica substrates. Lasing occurs at an ultraviolet wavelength of ∼380 nm under optical pumping. Actual images of the microscopic laser cavities formed by multiple scattering have been captured. These results suggest the possibility of using disordered semiconductor microstructures as alternative sources of coherent light emission.

GaAs microcavity channel-dropping filter based on a race-track resonator

We have demonstrated add-drop filters using racetrack-shaped resonators coupled to straight waveguides across gaps which are larger compared with the conventional microcavity ring resonators. The finesse and the maximum transmission are characterized and are shown to be determined uniquely by the round-trip loss and the coupling factor of the resonator.

Polymer waveguides useful over a very wide wavelength range from the ultraviolet to infrared

We have designed and fabricated polymer waveguides using the glassy polymers Cytop™ (a fluorinated polyether), PMMA C6 [poly(methyl methacrylate)], and Cyclotene™ 3022-35 (bisbenzocyclobutane). Since these materials exhibit excellent transparency over a wide wavelength range, and since the refractive index difference of Cytop™ and Cyclotene™ or Cytop™ and PMMA is greater than 0.19, both Cytop™/Cyclotene™/Cytop™ and Cytop™/PMMA/Cytop™ waveguide structures can be employed over a very wide wavelength range from the ultraviolet to the infrared. Efficient waveguiding is achieved for different light sources with 390, 633, 1064, 1310, and 1550 nm wavelengths.

Effect of external feedback on lasing in random media

We have studied the effect of external feedback on random laser action in ZnO polycrystalline thin films. Reinjection of light into scattering-formed cavities strongly influences modes, intensity, and threshold of random lasers. We have compared the effect of external feedback from the side of the film and that from the film surface. Our study opens the possibility of controlling random laser frequencies by external feedback.

Traveling wave electro-optic phase modulators based on intrinsically polar self-assembled chromophoric superlattices

Traveling-wave electro-optic modulators based on chromophoric self-assembled superlattices (SASs) possessing intrinsically polar microstructures have been designed and fabricated. Although the thickness of the SAS layer is only ∼150 nm, a π-phase shift is clearly observed. From the measured Vπ value, the effective electro-optic coefficient of the SAS film is determined to be ∼21.8 pm/V at an input wavelength of 1064 nm.

Second-generation approach to all-organic modulators based on intrinsically polar self-assembled molecular superlattices

T. J. MarksNorthwestern UniversityDepartment of ChemistryandMaterials Research CenterEvanston, Illinois 60208-3113Abstract. Intrinsically acentric self-assembled superlattices(SASs) have been directly grown in a layer-by-layer processon the commercially available polymer Cyclotene™. Usingthe high-temperature/high-transparency fluoropolyether Cy-top™ as a cladding layer, the SAS films have been used tosuccessfully fabricate traveling-wave electro-optic (EO)modulators, demonstrating a straightforward approach to-ward ‘‘all-organic’’ modulators.

Waveguide electro-optic modulators based on intrinsically polar self-assembled superlattices (SASs)

In this paper we describe methods of fabricating and characterizing organic electro-optic modulators based on intrinsically polar self-assembled superlattices. These structures are intrinsically acentric, and exhibit large second harmonic generation and electro-optic responses without the requirement of poling by an external electric field. A novel wet chemical protection-deprotection approach for the growth of self-assembled superlattices have been developed, and the refractive indices of self-assembled organic electro-optic superlattices may be tuned during the self-assembly process. Prototype electro-optic modulators based on chromophoric self-assembled superlattices have been designed and fabricated. The effective electro-optic coefficient of the self-assembled superlattice film in a phase modulator is estimated as about 20 pm/V at a wavelength of 1064 nm.