In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

Laser oscillation in Nd:MgO:LiNbO3 has been demonstrated. Thresholds as low as 3.6 mW and slope efficiencies up to 39% were achieved in a resonantly pumped miniature device. The electro-optical and nonlinear-optical properties of the host were also used to make active internal Q-switched and self-frequency-doubled lasers. Photorefractive damage is shown to be greatly suppressed compared with that for non-MgO-doped material. Absorption spectra, fluorescence spectra, and lifetime measurements are also reported.

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Nd:MgO:LiNbO 3 spectroscopy and laser devices

Z -cut X -propagating, LiNbO 3 :Ti planar waveguides have been characterized over a wide range of diffusion conditions. Measurements of Ti concentration and refractive indexes have revealed Gaussian profiles. Their dependence with diffusion conditions have been studied. The relation, established at several wavelengths ( \lambda = 0.6328 \mu m, 1.1523 μm, 1.523 μm), between extraordinary and ordinary refractive index change \Deltan_{e,0}(z) and titanium concentration C(z) is found to be nonlinear and of the form: \Deltan_{e,0}(z) = A_{e,0}(C_{0},\lambda) (C(z))^{\alpha_{e,0}} While \alpha_{e,0} is a constant, the proportionality coefficient A_{e,0} depends not only on the wavelength λ, but also on the diffusion conditions, characterized by C 0 , the Ti surface concentration of the diffused guide. Such a nonlinearity of Ti diffusion in LiNbO 3 has been revealed thanks to a complete and wide range investigation on both indiffused Ti and index profiles.

Wavelength dispersion of Ti induced refractive index change in LiNbO 3 as a function of diffusion parameters

Frontiers in Biosensorics II

The conventional rate equations for a Q-switched laser are augmented to explicitly include the effects of time- and level-dependent pumping, thermalization among the sublevels in the upper and lower multiplets, and multiplet relaxation in a homogeneously broadened four-level laser medium. To make the numerical computations more generally valid, we introduce a number of dimensionless variables. We show that the initial set of five coupled differential equations can be reduced to a simple set of two coupled equations for the inversion density and photon flux. Via numerical modeling, we have investigated the manner in which both thermalization and lower multiplet relaxation affect Nd:YAG laser characteristics such as output energy and temporal waveform. Our numerical results confirm earlier predictions that the Q-switched Nd:YAG laser output energy increases monotonically by a factor of 3.33 as one progresses from the assumption of slow to rapid thermalization and by an additional factor of 1.46 if one further assumes a terminal multiplet relaxation which is fast relative to the resonator photon decay time. We also find that the laser pulsewidth is substantially broadened when the resonator photon decay time is comparable to the thermalization, and to a lesser extent, the terminal multiplet relaxation times.

Effects of thermalization on Q-switched laser properties

The relaxation time of the transition from the lower laser level 4I11/2 to the ground state 4I9/2 of the Nd3+ ions was determined experimentally for a crystal of Y3Al5O12:Nd3+. The relaxation time was measured by two independent methods. The value obtained, τ21 ≤ 3·10–7 sec, was associated with the very broad (up to ~ 900 cm–1) phonon spectrum of the garnet crystal.

MEASUREMENT OF THE RELAXATION TIME τ21 OF A Y3Al5O12:Nd3+ CRYSTAL

A simple method is suggested for calculation of reflection, radiation and transmission coefficients for the distributed feedback structure in the second diffraction order. The method is based on a slight difference between coefficients of reflectionR and radiationI of the surface wave for λ=λ∞ (where λ∞ is the light wavelength corresponding to a precise resonance for the grating length I→∞) and those for λ=λl (where λl is the light wavelength corresponding to the resonance for the finite grating length). The simplicity of the method makes it possible to use it for optimization of the distributed feedback structure by a number of parameters. The technique can be used in the case of thin-film and diffused waveguides for both TE and TM modes.

Calculation and optimization of parameters of radiating distributed feedback structures

A simple method is suggested for measuring the parameters of waveguides prepared by diffusion. It is shown that glass stripe waveguides can be constructed and a report is given of tunnel pumping of light from one waveguide to another. Waveguide layers formed by the diffusion of titanium in a crystal of LiNbO3 are described.

Diffused waveguides in glasses and electro-optic crystals

An investigation was made of the linear and nonlinear optical properties of new neodymium yttrium aluminum borate crystals. These crystals were found to be suitable for use as multifunctional laser media and as nonlinear media capable of efficient frequency conversion of laser radiation.

http://iopscience.iop.org/article/10.1070/QE1983v013n07ABEH004544/pdf

Nonlinear optical properties of neodymium yttrium aluminum borate crystals

An experimental investigation was made of the dependence of the effective refractive indices of the TM and TE modes on the depth of waveguides fabricated in glass by ion exchange in an AgNO3 melt. It is shown that approximation of the refractive index profile by the function n(x)=n0–Δn[(x/d)+b(x/d)2] (d and b are the profile parameters) gives a high degree of accuracy and permits waveguides with the required parameters to be fabricated. The results of direct measurements of the profile n(x) are presented. A method is proposed for determining the effective thickness of diffused waveguides having an arbitrary profile n(x). This method is based on measurements of the effective refractive indices of only the TM or only the TE modes. It is shown that as a result of the anisotropy of diffused waveguides, the proposed method of determining the effective thickness from the difference n*TE – n*TM may be used for few-mode waveguides.

https://iopscience.iop.org/article/10.1070/QE1979v009n05ABEH009040/pdf

G P Shipulo

Papers

MEASUREMENT OF THE RELAXATION TIME τ21 OF A Y3Al5O12:Nd3+ CRYSTAL

Calculation and optimization of parameters of radiating distributed feedback structures

Diffused waveguides in glasses and electro-optic crystals

Nonlinear optical properties of neodymium yttrium aluminum borate crystals

Investigation of the parameters of planar optical waveguides fabricated by ion exchange in glass