G. Q. Liang

Narrow frequency and sharp angular defect mode in one-dimensional photonic crystals from a photonic heterostructure.

By combining two one-dimensional defective photonic crystals (PCs), we obtained a photonic heterostructure with narrow frequency and a sharp angular defect mode. The key to obtaining such a structure is to design the two sub-PCs to make the frequencies of their defect modes the same at one incident angle and different at all other incident angles. Filters designed on the basis of this heterostructure possess not only a narrow-frequency passband but also a sharp angular pass breadth. Optimization of the practical design is also suggested.

Fabrication of two-dimensional coupled photonic crystal resonator arrays by holographic lithography

We demonstrate the holographic design and fabrication of two-dimensional coupled photonic crystal resonator arrays, which are composed of hexagonal cavities tiled together in a triangular lattice. Band structure analysis reveals that the inverse structure of the fabricated template supports monopole defect mode in a photonic band gap of TM polarization. Our results show the practical importance of holographic lithography in the fabrication of photonic component arrays.

Formation principles of two-dimensional compound photonic lattices by one-step holographic lithography

From the view of crystallography, a systematic theoretical study on one-step formation of two-dimensional compound photonic lattices by four noncoplanar elliptical waves is presented. A general formula for the interference intensity of N elliptically polarized waves, and relevant phase shifts that compensate for the initial phases and control the relative position and size of the motifs, have been deduced. Using appropriate polarization configurations, four kinds of beam geometries can be used to form various compound lattices. This provides an ideal new experimental platform for fabricating large-area compound photonic lattices.

Design and fabrication of two-dimensional holographic photonic quasi crystals with high-order symmetries

From group theory, we have deduced the minimum number of laser beams to create corresponding two-dimensional photonic quasilattices with high-order symmetries. One case is that a quasi-periodicity with eightfold, tenfold, or twelvefold symmetry can be formed by only five linearly polarized beams, which can reduce fabrication complexity and considerably improve feasibility. Accordingly, we have fabricated large-area eightfold and twelvefold photonic quasi crystals by use of a minimum beam single-exposure holographic lithography technique. The high-order symmetries of the fabricated microstructures are confirmed by scanning electron microscopy images and diffraction patterns.

Controllable fabrication of two-dimensional compound photonic crystals by single-exposure holographic lithography

We demonstrate an approach of single-exposure holographic lithography for controllable fabrication of large-scale two-dimensional square and hexagonal compound photonic crystals. In the sublattices, both circular and elliptical micropores on a 100 nm scale can be achieved. Theoretical analysis reveals that the inverse structure of a sample possesses a unique complete photonic bandgap pair in high frequency regions. This method is very robust for the general fabrication of complex periodic microstructures on the optical scale.

Robust absorption broadband in one-dimensional metallic-dielectric quasi-periodic structure

We demonstrated that a broad and robust absorption band for a wide range of incidence angles and for both polarizations can be realized using a one-dimensional metallic-dielectric quasi-periodic structure, when the thickness of the constituent metal is comparable to its skin depth. The absorptance in such peculiar structure can exceed 99% to meet different applications. Furthermore, employing the effective medium approach, a theoretical expression has been deduced to instruct the working frequency of the absorption band. By tuning the permittivity and thickness of the constituent layers, the robust absorption band can cover the wavelength from the visible to the near-infrared.

Efficient all-optical dual-channel switches, logic gates, half-adder, and half-subtracter in a one-dimensional photonic heterostructure

We have proposed a kind of one-dimensional photonic heterostructure for efficient all-optical dual-channel switches, logic gates, half-adder, and half-subtracter, based on the combined usage of two high-quality and one low-quality resonant modes with their electric fields strongly enhanced in the same defect regions. By exciting the low-quality modes with a low-intensity pump beam, one can efficiently shift the spectral positions of two high-quality modes and thus simultaneously control the propagation of signals at two frequency channels. For an AlGaAs/SiO2 heterostructure with two GaAs defect regions, the peak pump intensity can be lower than 6.2mW/mm2. When the frequency of the signal light is properly set relative to the two high-quality modes, its propagation can be logically controlled by pump beams with low intensity on the order of 10mW/mm2. Moreover, the frequency interval between the two high-quality modes and that between the high- and low-quality modes are adjustable in a wide range.

Complicated three-dimensional photonic crystals fabricated by holographic lithography

We have fabricated a kind of three-dimensional photonic crystal in a single exposure by two sets of conventional laser holographic configurations. Specific structural features, such as a kagomelike lattice with p6mm symmetry on the top surface and a chainlike lattice on a cleavage plane, are possessed in this large-area and high-quality complicated microstructure, and many interesting properties such as skyrocketlike diffraction pattern exist. This work demonstrates that holographic lithography is a good method for the fabrication of photonic materials with crystal structure differing from the electronic crystals.

Holographic formation of large area split-ring arrays for magnetic metamaterials

We theoretically demonstrate the formation of different kinds of two-dimensional split-ring arrays in both triangular and square lattices by one-step holographic interference. The slit width of the split-ring can be adjusted by proper polarization configurations. The dimension of the rings can be adjusted easily by using different wavelengths for interference, so the resonant frequency of the split-rings can be obtained in a wide range. Our theory is also proved in experiment. Our work would extend the application of holographic lithography to the fabrication of magnetic metamaterials.

Enhancing all-optical switching by localizing the control and signal light fields in the same defect region

We suggest an efficient mechanism for all-optical switching in one-dimensional photonic heterostructures based on the combined use of two resonant modes that have strong enhancement of their electric fields in the same defect region. By exciting the low-quality resonant mode with the low-intensity pump beam, one can very efficiently shift the spectral position of the high-quality resonant mode and thus control the propagation of a signal beam. For a AlGaAs/SiO2 heterostructure with two GaAs defect layers, we numerically demonstrate all-optical switching at a peak pumping intensity lower than 20 mW/mm2. Moreover, it is of great benefit to practical application that the frequency interval between the two resonant modes is adjustable in a wide range.