Artificially engineering ferroelectric and ferromagnetic oxide materials’ domain structures provide many potential opportunities to explore such materials’ extraordinary nonlinear optic, electrooptic (EO), and magnetooptic (MO) effects, to build unique photonic bandgap structures, and to generate phonon-photon-coupled polaritons. Domain engineering can be applied onto such materials, either one-dimensinally or two-dimensionally, can be patterned on the above materials periodically, quasiperiodically, or aperiodically, or can be aligned along different crystalline orientations or by using complicated cascaded structures. Those commonly involved photonic materials can be versatile including ferroelectric-ferromagnetic oxide crystals, semicondcutors, electrooptic polymers, and so on, in either bulk, thin film, or waveguide forms. Implementation of such domain engineering can be very versatile too, and it may follow direct crystal growth, superlattice growth, overgrowth on an already patterned structure, electrical field poling, E-beam writing, and so on. Potential applications of such domain-engineered materials for photonics are very widespread, including nonlinear frequency conversion, EO modulation, optical bistability, acoustics, ultrasonic transducers, terahertz (THz) generation, fiber optics, left-hand materials, and so on.
A remarkable example of past researches in this area is the realization of the quasi-phase-matched (QPM) nonlinear frequency conversions using periodically poled crystals. Recently, development of new photonic and optoelectronic components using such advanced domain-engineered materials, covering a broad range of operation frequencies and having unique optical functions, has become very attractive. However, the effort toward this direction has been crucially relying on the availability of new optical materials, new physical mechanisms, and new device designs. In this special issue focusing on exploring such new aspects, we invited a few papers that address the major issues in the area, summarized some of those recent progresses, and discussed those emerging opportunities of applications.
The first two papers of
this special issue are related to the realization of such domain-engineered
structures. The first article from M. Fujimura and T. Suhara is the specially
invited one, which reports a new formation method for making domain-inverted
gratings in MgO:LiNb
The following four papers
are discussing various issues in a few different nonlinear frequency conversion
processes including second harmonic generation (SHG)
and difference frequency generation (DFG). Among them is the fifth article by Y. Wong et al. which is also a specially invited one. The third paper by S. Chu et al. reports an ~1W continueous-wave green
light generation in a bulk periodically poled MgO:LiNb
The seventh and eighth articles in this special issue are directly focusing on EO modulators made from domain-engineered ferroelectric crystals. The seventh paper by H. V. Pham et al. discusses a new method to design traveling-wave EO modulators with fully controlled frequency responses, using nonperiodically domain-reversed structures. Frequency responses of both magnitude and phase of modulation index will be artificially controllable using such new nonperiodical designs. In this paper, several EO modulators for advanced modulation formats such as duobinary modulation and wideband single-sideband modulation are proposed. The eighth article actually discusses the estimation of the phase velocity of a modulation microwave in a quasi-velocity-matched (QVM) EO phase modulator, using the unique EO sampling method that should be very accurate and the most reliable for measuring voltage waveforms on modulator electrodes.
Moving forward from the above
discussions on frequency conversion and EO modulation, the last two papers of
this special issue actually touch the terahertz (THz) wave generation in a
specially designed nonlinear optical fiber, and, even further, the realization
of negative optical refraction in a multilayered structure that modulated both
tunable dielectric and magnetic behaviors. For avoiding the common absorption
problem in current nonlinear optical materials, a multicladding fiber design
having a periodically poled LiNb