John D. Bierlein

Potassium titanyl phosphate: properties and new applications

Potassium titanyl phosphate (KTP) is a unique nonlinear-optical material that is being widely used for second-harmonic generation of Nd lasers emitting near 1 μm. KTP is also attractive for various sum- and difference-frequency and optical parametric applications over its entire transparency range from 0.35 to 4.5 μm. Its combination of large electro-optic coefficients and low dielectric constants makes KTP potentially useful for various electro-optic applications, and, in particular, it has a figure of merit for an optical waveguide modulator that is nearly a factor of 2 larger than that for any other inorganic material. Low-loss optical waveguides can be formed in KTP, and several electro-optic and nonlinear-optic devices have been fabricated that confirm that KTP is also a superior material for many optical waveguide applications.

Electro‐optic and dielectric properties of KTiOPO4

The electro‐optic and dielectric properties of potassium titanyl phosphate (KTP) have been measured from dc to 1 GHz and are compared with other electro‐optic materials. KTP is shown to possess a combination of properties that make it unique for a variety of electro‐optic modulator applications.

Fabrication and characterization of optical waveguides in KTiOPO4

Planar and channel optical waveguides have been fabricated in KTiOPO4 (KTP) using ion exchange processes. The exchange kinetics are diffusion limited and depend strongly on composition and surface orientation. Increases in surface refractive index of up to 0.23 and waveguide thicknesses of up to 15 μm have been observed. A simple waveguide modulator has been fabricated which shows electro‐optic r coefficients in the waveguide region to be similar to bulk KTP.

Magnitude of the nonlinear-optical coefficients of KTiOPO 4

The magnitude of the nonlinear-optical coefficients of KTiOPO4 are measured relative to those of quartz at 0.88 μm. When we use for quartz d11 = 0.308 pm/V at 0.88 μm (which corresponds to 0.30 pm/V at 1.06 μm), the following results (in pm/V) are obtained for KTiOPO4 (at 0.88 μm): d15 = 2.04, d24 = 3.92, d31 = 2.76, d32 = 4.74, and d33 = 18.5. The accuracy of the measurements is estimated to be ±10%. These results, if corrected for dispersion, predict an effective d coefficient for type II phase matching at 1.064 μm of 3.35 pm/V.

Balanced phase matching in segmented KTiOPO4 waveguides

A new phase matching technique is described which is based on phase mismatch balancing in crystal or waveguide segments that are short compared to their respective coherence lengths. The technique is demonstrated experimentally in a mixed bulk crystal/waveguide structure in KTiOPO4, resulting in a second‐harmonic generation conversion efficiency of 15%/W/cm2 at 1.064 μm, close to the theoretical maximum. We show that this technique can significantly broaden processing latitude for fabricating practical nonlinear optical waveguide devices.

Linear and nonlinear optical properties of flux‐grown KTiOAsO4

Single crystals of KTiOAsO4, a material which is isostructural with the well‐known nonlinear optical material KTiOPO4 (KTP), were grown by a flux process and its optical and dielectric properties characterized. Compared to KTP, KTiOAsO4 has a higher figure of merit for second‐harmonic generation, larger electro‐optic coefficients, and lower ionic conductivity. As a result, KTiOAsO4 should become a viable alternative for KTP.

Large nonlinear phase modulation in quasi-phase-matched KTP waveguides as a result of cascaded second-order processes

Nonlinear spectral modulation and broadening have been observed in quasi-phase-matched KTP waveguides near 850 nm, indicative of self-phase modulation that is due to cascaded second-order processes. Numerical beam-propagation simulations indicate nonlinear peak phase shifts larger than π for 600 W of peak power in a 2.8-mm-long guide.

Crystal growth and characterization of KTiOPO4 isomorphs from the self-fluxes

Abstract We report the crystal growth of KTiOPO 4 (KTP) and its isomorphs from the self-fluxes. Common features in the crystal growth properties of MTiOXO 4 within the M 2 O-TiO 2 -X 2 O 5 ternary, where M={K, Rb or Cs} and X={P or As (for M=Cs only)}, are noted. The solubility of these crystals in the M 5 X 3 O 10 and M 6 X 4 O 13 fluxes are presented. A previously unreported (00-1) growth face was observed in KTiOAsO 4 (KTA) and the morphological stability of this face in KTP is also discussed. Optimization of the crystal growth parameters allows us to grow inclusion-free crystals of up to 18×35×35 mm 3 from 250 ml charges. We discuss the domain characteristics of these crystals and present the optical, electro-optical and dielectric properties of these materials.

Reduction of the ionic conductivity of flux grown KTiOPO4 crystals

Abstract A mechanism and method for reducing the ionic conductivity of KTP crystals grown by the flux technique utilizing the doping of trivalent ions (Ga and A1) on the Ti site and tetravalent ions (Si) on the P site are described. Results are presented showing that, by using appropriate concentrations of these dopants added to the growth solutions, crystals can be grown over a range of growth temperatures which have ionic conductivities that are 1.5 to 3 orders of magnitude lower than undoped KTP crystals grown over similar temperatures. The dopant ion concentrations obtained in the crystals are consistent with the concentrations calculated, using the defect mechanism described, to achieve the observed ionic conductivity reductions. Distribution coefficients have been calculated for the dopants over a wide range of growth temperatures. The distribution coefficient for Ga in KTP appears to be relatively insensitive to concentration or temperature over a range of doping levels and growth temperatures. The use of doping is shown to also be effective in reducing the ionic conductivity of KTA crystals grown by the flux technique.

Linear and nonlinear optical properties of 3‐methyl‐4‐methoxy‐4’‐nitrostilbene single crystals

Single crystals of the new nonlinear optical material 3‐methyl‐4‐methoxy‐4’‐nitrostilbene (MMONS) have been grown by a seeded solution growth technique and the linear and nonlinear optic and electro‐optic properties determined. MMONS is highly birefringent with nz−nx =0.75 (0.532 μm), has large nonlinear optical coefficients with d33=184 pm/V and d24=71 pm/V (1.064 μm), has large electro‐optic coefficients with r33=39.9 pm/V (0.6328 μm), and can be efficiently type II phase matched for Nd lasers emitting ∼1 μm.