75 research outputs found
Resonance enhancement of magnetic Faraday rotation
Magnetic Faraday rotation is widely used in optics. In natural transparent
materials, this effect is very weak. One way to enhance it is to incorporate
the magnetic material into a periodic layered structure displaying a high-Q
resonance. One problem with such magneto-optical resonators is that a
significant enhancement of Faraday rotation is inevitably accompanied by strong
ellipticity of the transmitted light. More importantly, along with the Faraday
rotation, the resonator also enhances linear birefringence and absorption
associated with the magnetic material. The latter side effect can put severe
limitations on the device performance. From this perspective, we carry out a
comparative analysis of optical microcavity and a slow wave resonator. We show
that slow wave resonator has a fundamental advantage when it comes to Faraday
rotation enhancement in lossy magnetic materials
Frozen light in periodic metamaterials
Wave propagation in spatially periodic media, such as photonic crystals, can
be qualitatively different from any uniform substance. The differences are
particularly pronounced when the electromagnetic wavelength is comparable to
the primitive translation of the periodic structure. In such a case, the
periodic medium cannot be assigned any meaningful refractive index. Still, such
features as negative refraction and/or opposite phase and group velocities for
certain directions of light propagation can be found in almost any photonic
crystal. The only reservation is that unlike hypothetical uniform left-handed
media, photonic crystals are essentially anisotropic at frequency range of
interest. Consider now a plane wave incident on a semi-infinite photonic
crystal. One can assume, for instance, that in the case of positive refraction,
the normal components of the group and the phase velocities of the transmitted
Bloch wave have the same sign, while in the case of negative refraction, those
components have opposite signs. What happens if the normal component of the
transmitted wave group velocity vanishes? Let us call it a "zero-refraction"
case. At first sight, zero normal component of the transmitted wave group
velocity implies total reflection of the incident wave. But we demonstrate that
total reflection is not the only possibility. Instead, the transmitted wave can
appear in the form of an abnormal grazing mode with huge amplitude and nearly
tangential group velocity. This spectacular phenomenon is extremely sensitive
to the frequency and direction of propagation of the incident plane wave. These
features can be very attractive in numerous applications, such as higher
harmonic generation and wave mixing, light amplification and lasing, highly
efficient superprizms, etc
Unidirectional Lasing Emerging from Frozen Light in Non-Reciprocal Cavities
We introduce a class of unidirectional lasing modes associated with the
frozen mode regime of non-reciprocal slow-wave structures. Such asymmetric
modes can only exist in cavities with broken time-reversal and space inversion
symmetries. Their lasing frequency coincides with a spectral stationary
inflection point of the underlying passive structure and is virtually
independent of its size. These unidirectional lasers can be indispensable
components of photonic integrated circuitry.Comment: 5 pages, 3 figure
Absorption suppression in photonic crystals
We study electromagnetic properties of periodic composite structures, such as
photonic crystals, involving lossy components. We show that in many cases a
properly designed periodic structure can dramatically suppress the losses
associated with the absorptive component, while preserving or even enhancing
its useful functionality. As an example, we consider magnetic photonic
crystals, in which the lossy magnetic component provides nonreciprocal Faraday
rotation. We show that the electromagnetic losses in the composite structure
can be reduced by up to two orders of magnitude, compared to those of the
uniform magnetic sample made of the same lossy magnetic material. Importantly,
the dramatic absorption reduction is not a resonance effect and occurs over a
broad frequency range covering a significant portion of photonic frequency
band
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