Y.H. Shih

A new method for measuring the electro-optic coefficients with higher sensitivity and higher accuracy

Abstract A new method for measuring electrooptic coefficients of nonlinear crystals has been developed and used to obtain an accurate measurement of r33 and r13 for Strontium Barium Niobate (SBN). An electrooptic modulator was used with a Michelson interferometer for ac modulation (sub-Hz to MHz). By observing the appearance and symmetrical shape of the second harmonic of the ac modulation, the electrooptic coefficients r33 and r13 of SBN were measured with higher accuracy. The unclamped electrooptic coefficients of poled of SrxBa1-xNb2O6 single crystal are: r33=237±3 pm/V and r13=37±1 pm/V, at λ=632.8 nm and T=21°C. In addition the piezoelectric coefficient d23 has been measured with d23=25±5pm/V.

A novel supramolecular self-assembly thin film with spontaneous polar order

A novel supramolecular thin film in which a non-linear optical (NLO) chromophore is uniaxially included in the helical cavity of amylose, revealed a spontaneous self-assembly with a long-range polar order of the chromophores perpendicular to the film surface. This was manifested by a significantly large second harmonic generation (SHG) observed from solution-cast solid supramolecular thin films on a glass substrate without any external field. Such self-assembly/self-poling and the long-term polar stability of the supramolecular chromophores are thought to be due to the helical rigid-rod structure, their dipolar and/or chiral recognition in the ordering process following the polar initiation through the interface interaction of the chromophore with the glass substrate, and H-bonding among the ordered supramolecules.

Optical and nonlinear optical study of KTa 0.52 Nb 0.48 O 3 epitaxial film

The second-order nonlinear optical coefficients d(33) , d(31) , and d(15) of KTa(0.52) Nb(0.48) O(3) epitaxial thin films grown upon MgO were studied by the standard Maker fringe method of an anisotropic medium. The measured d(33)=-84pm/V is 2.8 times the d(33) of LiNbO(3). The refractive indices n(e) and n(o) at several wavelengths were determined by TE and TM waveguide mode measurements. The data presented here point out the excellent qualities of KTa(1-x) Nb(x)O (3) films for use in integrated optics applications.

Picosecond phase conjugation and two-wave coupling in strontium barium niobate

Abstract Picosecond phase conjugation and two-wave coupling in cerium-doped strontium barium niobate at 778 nm were studied. The phase conjugation reflectivity at 778 nm was measured to be R pc = 58%. It is close to that pumped by a continuous-wave pump source. The temporal width t pc and spectral width δγpc of the phase conjugate pulse were measured to be the same as that of the pump pulse. The intensity coupling gain of two-wave coupling as a function of time delay τD between two beams was also studied.

High Reflectivity Broad Band Self-pumped Phase Conjugator at Near Infrared Wavelengths Using SBN : Ce

Abstract A high reflectivity broad-band SBN : Ce phase conjugator with an external ring cavity in the near infrared wavelength region, 706 to 830 nm, is reported. Phase conjugation reflectivity was measured to be greater than 60% in the wavelength region, 706-820 nm, and as high as 67% at 716 nm. To our knowledge, this is the highest phase conjugation reflectivity by a SBN : Ce self-pumped phase conjugator. Both c.w. and square-wave pump sources were used. No significant changes of the phase conjugation reflectivity were observed when the pump source was changed from c.w. to a square wave at each different wavelength. The wave form of the phase conjugate wave follows the pump square wave. The build-up time of the phase conjugate wave under a square-wave pump was found to be twice that under a c.w. pump when the peak power of the square wave was the same as the power of the c.w. beam.

Quantum interference approach to two-photon correlation phenomena of chaotic light

We present a quantum two-photon interference approach to two-photon correlation phenomena of chaotic light, including the historical experiment of Hanbury Brown and Twiss. We argue against the interpretation of such phenomena in terms of a classical statistical correlation between intensity fluctuations. To support our view, we show a ‘ghost’ imaging experiment with chaotic light for which the classical understanding does not give a satisfactory interpretation. We also provide a two-photon optical picture of ghost imaging with chaotic light in terms of two-photon phase-conjugate mirrors which is very advantageous because it yields lensless two-photon imaging, suggesting imaging applications for radiations for which no effective lens is available.

Two-wave coupling and self-pumped phase conjugation at near infrared wavelengths in BaTiO3

Abstract Using an undoped BaTiO 3 crystal, the reflectivities of the self-pumped phase-conjugate mirror operated in total internal-reflection geometry (TIR) at near infrared wavelengths from 706 to 850 nm were measured. The phase conjugation reflectivities R pc > 50% at 706 to 760 nm, R pc =40% at 816 nm, and R pc =20% at 850 nm were observed. The two-wave coupling exponential gain coefficient Γ and the photorefractive index grating formation rate τ -1 PR as a function of wavelength from 706 to 850 nm were studied. The exponential gain coefficients Γ=11.1 cm -1 at 706 nm and Γ=7.6 cm -1 at 850 nm were obtained. It was also found that the absorption coefficient α in the near infrared wavelengths is much smaller than that in the visible region.

Two-wave coupling and self-pumped phase conjugation of SBN: Ce at near infrared wavelengths

Abstract Two-wave coupling and self-pumped phase conjugation with external ring cavity for SBN: Ce (Ce doped SBN:60) were studied at near infrared wavelengths from 710 nm to 850 nm. A gain coefficient Γ = 7.4 cm −1 around 800 nm was measured. The highest phase conjugate reflectivity was 48% around λ = 710 nm (uncorrected for Fresnel losses). The response time measurement showed a significant increase when the wavelength changed from 710 nm to 850 nm. The moving grating effect was also reported. Both reflectivity and stability of the phase conjugate wave were improved significantly once the moving grating was established inside the crystal.

Near‐infrared response of photorefractive crystals (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6:Cu and LiNbO3:Fe

Material response relevant to volume holographic storage for photorefractive crystals (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6:Cu (KNSBN:Cu) and LiNbO3:Fe was studied in the near‐infrared region. The dark decay time for KNSBN:Cu was measured to be on the order of 106 s. The light‐induced erasure time at the 1 mW/cm2 read beam intensity can be ≳1000 h for both KNSBN:Cu and LiNbO3:Fe. Read beam diffraction efficiencies of 28.7% for KNSBN:Cu and 50% for LiNbO3:Fe were obtained at 706 nm when the refractive index grating was written at 706 nm. The decay rate of the refractive index grating with an extraordinary‐wave read beam is about 3.6 times smaller than that with an ordinary‐wave read beam for KNSBN:Cu. The results show that near‐infrared light can be used to read holograms in the photorefractive volume holographic storage application.

High reflectivity broadband self‐pumped phase conjugator in near‐infrared wavelengths

A high reflectivity broadband BaTiO3 self‐pumped phase conjugator with external ring cavity in near‐infrared wavelengths (706–850 nm) is reported. Phase conjugate reflectivity as high as 77.5% was observed at 756 nm. The losses and the reflection grating are discussed in detail.