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

Acoustic or mechanical resonators have emerged as a promising means to mediate efficient microwave-to-optical conversion. Here, we demonstrate conversion of microwaves up to 4.5 GHz in frequency to 1500 nm wavelength light using optomechanical interactions on suspended thin-film lithium niobate. Our method uses an interdigital transducer that drives a freestanding 100 μm-long thin-film acoustic resonator to modulate light traveling in a Mach–Zehnder interferometer or racetrack cavity. The strong microwave-to-acoustic coupling offered by the transducer in conjunction with the strong photoelastic, piezoelectric, and electro-optic effects of lithium niobate allows us to achieve a half-wave voltage of Vπ=4.6  V and Vπ=0.77  V for the Mach–Zehnder interferometer and racetrack resonator, respectively. The acousto-optic racetrack cavity exhibits an optomechanical single-photon coupling strength of 1.1 kHz. To highlight the versatility of our system, we also demonstrate a microwave photonic link with unitary gain, which refers to a 0 dB microwave power transmission over an optical channel. Our integrated nanophotonic platform, which leverages the compelling properties of lithium niobate, could help enable efficient conversion between microwave and optical fields.

/pdf/microwave-to-optical-conversion-using-lithium-niobate-thin-37ea4c5cwk.pdf

Microwave-to-optical conversion using lithium niobate thin-film acoustic resonators

We demonstrate conversion of up to 4.5 GHz-frequency microwaves to 1500 nm-wavelength light using optomechanical interactions on suspended thin-film lithium niobate. Our method utilizes an interdigital transducer that drives a free-standing 100 $\mu$m-long thin-film acoustic resonator to modulate light travelling in a Mach-Zehnder interferometer or racetrack cavity. Owing to the strong microwave-to-acoustic coupling offered by the transducer in conjunction with the strong photoelastic, piezoelectric, and electro-optic effects of lithium niobate, we achieve a half-wave voltage of $V_\pi$ = 4.6 V and $V_\pi$ = 0.77 V for the Mach-Zehnder interferometer and racetrack resonator, respectively. The acousto-optic racetrack cavity exhibits an optomechancial single-photon coupling strength of 1.1 kHz. Our integrated nanophotonic platform coherently leverages the compelling properties of lithium niobate to achieve microwave-to-optical transduction. To highlight the versatility of our system, we also demonstrate a lossless microwave photonic link, which refers to a 0 dB microwave power transmission over an optical channel.

An optical interconnecting device and method are disclosed for selectively directing signals from an array of optical inputs to an array of optical outputs through an optical medium. The input signals are angularly multiplexed and redirected by dynamic gratings of the appropriate spatial, or grating, frequency. Spatially periodic optical index perturbations propragated in the medium are utilized to achieve the dynamic gratings. The angles at which light is input to the gratings (input angles) and angles at which light is collected from the gratings (output angles) are selected to allow each grating frequency to connect signals at only one input angle to one output angle and thus only one optical output. The number of resolvable gratings required is the product of the number of inputs and the number of output. For the interconnection of an equal number of inputs and outputs connected in a one to one permutation, only a number of gratings equal to the number of inputs need be present simultaneously.

Optical interconnecting device and method

Employing absorption, excitation and luminescence spectroscopy in a wide spectral range, the upconversion processes are investigated in at low temperature. From the detailed analysis of the spectroscopic data and the power dependence of the upconverted intensity, excited state absorption and energy transfer between excited ions are found to be the important mechanisms. Structure in the Stark substate absorption suggests the ions occupy several different but well defined lattice sites for which the local symmetry is slightly perturbed, presumably by charge compensating defects. Site-selective measurements allow one to determine the ground state splittings for two of these sites. The observed energy transfer suggests the existence of interacting pairs of ions. .

http://iopscience.iop.org/article/10.1088/0022-3727/29/3/012/pdf

Upconversion and site-selective spectroscopy in erbium-doped

Chapter 2 has presented the basic principles and analytical techniques for bulk-wave Acousto-Optic (AO) interactions. In this chapter, a detailed treatment of wide-band AO Bragg diffraction in a planar LiNbO3 waveguide, the resulting devices, and some potential applications is given. The sequence of presentation for the content of the Chapter now follows. First, the basic configuration and mechanisms for planar guided-wave AO Bragg diffraction from a single Surface Acoustic Wave (SAW) in a LiNbO3 waveguide and the resulting diffraction efficiency and frequency response are analyzed in detail using the coupled-mode technique. As a comparison some calculated and measured performances with the other two potential materials, namely GaAs and nonpiezoelectrics such as thermally-oxidized Si or AS2S3, are also discussed. The key parameters of the resulting AO Bragg modulators and deflectors or cells and their inherent limitations are then identified and discussed. The coupled-mode technique is thereafter extended to analyze AO Bragg diffraction from multiple SAWs. The unified theory developed is applied to the two wide-band device configurations, namely, multiple tilted SAWs and phased SAWs. Subsequently, a number of SAW transducer configurations for realization of wide-band Bragg cells are described and compared. Design, fabrication, testing, and measured performance of wide-band AO Bragg cells in y-cut LiNbO3 substrates are also presented.

Chen S. Tsai

Papers

Wideband Acousto-Optic Bragg Diffraction in LiNbO 3 Waveguide and Applications