A new optical channel drop filter configuration was proposed based on two-dimensional (2D) square-lattice 45° photonic
crystal ring resonators (PCRRs). The ring was formed by removing the line defect along ΓM direction instead of
conventional ΓX direction. Its spectral information including transmission intensity, dropped efficiency and quality
factor affected by different configurations like single-ring PCRR and cascaded dual-ring PCRR was numerically
analyzed with 2D finite-difference time-domain technique. More than 830 spectral quality factor and 90% dropped
efficiency can be achieved at 1550-nm channel for one single-ring PCRR. Two different light wavelengths can be
dropped simultaneously for cascaded serial dual-ring PCRR. These findings make the 45° PCRR optical channel drop
filters as an alternative to current micro-ring resonators for ultra-compact WDM components and high density photonic
A Folded Mach-Zehnder interferometer (FMZI) in a two-dimensional photonic crystal is proposed. The FMZI consists
of one splitter and several mirrors. Light propagates between them employing self-collimation effect. Its two interfering
branches have different path lengths. The two complementary transmission spectra at two FMZI output ports are both in
the shape of sinusoidal curves and have a uniform peak spacing in the frequency range from 0.255c/a to 0.270c/a. The
peak spacing becomes smaller when the length difference between the two branches is increased. As self-collimation
light beams can cross each other without coupling, this FMZI is much smaller than non-folded interference-type filters in
photonic crystals. This FMZI may work as a wavelength division demultiplexer in high-density photonic integrated
The self-collimation frequencies (SCFs) in two-dimensional photonic crystals (2-D PhC) have been investigated
systematically by the plane-wave expansion method. In the wave-vector space, the square-lattice 2-D PhCs have some
square-shaped equifrequency contours (EFCs) both for TE modes and for TM modes. Narrow-beam lights with these
frequencies can propagate in the directions normal to the flat borders of the EFCs without any significant broadening,
which is known as self-collimation effect. We consider the 2-D PhCs consisting of a square lattice of air cylinders in a
dielectric material and the 2-D PhCs consisting of a square lattice of dielectric cylinders in air respectively. Calculation
results show how SCFs of TM and TE modes change with the radius of cylinders and the refractive index of the material.
These results can be applied to designing the PhC devices based on self-collimation effect.
A theoretical model of wavelength interleaver, which is based on an asymmetric Mach-Zehnder interferometer (AMZI) constructed in a two-dimensional photonic crystal (2D PhC), is proposed and numerically demonstrated. The 2D PhC consists of a square lattice of dielectric cylindrical rods in air. The AMZI includes two mirrors and two splitters. Light propagates between them employing self-collimation effect. The two interferometer branches have different path lengths. By using the finite-difference time-domain method, the calculation results show that the transmission spectra at two AMZI output ports are in the shape of sinusoidal curves and have a uniform peak spacing in the frequency range from 0.191<i>c/a</i> to 0.200<i>c/a</i>. When the path length of the longer branch is increased and the shorter one is fixed, the peaks shift to the lower frequencies and the peak spacing decreases nonlinearly. Consequently, the transmission can be designed to meet various application demands by changing the length difference between the two branches. For the dimensions of the wavelength interleaver are about tens of central wavelengths, it may be applied in future photonic integrated circuits.
A Fabry-Perot (FP) etalon constructed in a two-dimensional photonic crystal (2D PhC) utilizing self-collimation effect is
proposed and investigated. The 2D PhC consists of a square lattice of air holes in silicon. It has square-shaped equal
frequency contours (EFCs) in the frequency range of 0.275-0.295c/a for TE modes. The FP proposed consists of two
PhC reflectors and one cavity between them. Light propagates in the photonic crystal employing self-collimation effect.
The two reflectors have reflectivities of around 97.5% in the frequency range 0.275-0.295c/a. The FDTD calculation
results show that the transmission spectrum of the FP etalon has a uniform peak spacing between 0.275c/a and 0.295c/a.
The transmission spectrum shifts to the lower frequency as the refractive index of a fluid filling in the air holes in the FP
cavity is increased. Therefore this etalon can work as an optical sensor for a gas and a liquid. The fluids whose refractive
index vary within 1.0-1.5 can be sensed and detected. Its dimensions are only about tens of microns when the central
operating wavelength is equal to 1550nm. So it can be applied as a micro-scale sensor.
A Fabry-Perot interferometer (FPI) constructed in a two-dimensional photonic crystal (2D PhC) has been proposed and
demonstrated theoretically. The perfect 2D PhC consists of square-lattice cylindric air holes in silicon. Two same line
defects with spacing of <i>d</i> = 16<i>a</i>, which is the physical length of the FP resonant cavity, are introduced in the PhC to form
the FPI. The two line defects have high reflectivity and low transmission. Their transmission is between 4.81% and
11.1% for the self-collimated lights with frequencies from 0.275<i>c/a</i>to 0.295<i>c/a</i> and thus they form the two partial
reflectors. Lights propagate in the FPI employing self-collimation effect. The transmission spectrum of the FPI has been
investigated with the finite-difference time-domain method. The calculation results show that peaks have nearly equal
frequency spacing 0.0078<i>c/a</i>. Even slight increases of <i>d</i> can cause peaks shift left to lower frequencies. As a result, the
peak spacing decreases nonlinearly from 0.0142<i>c/a</i> to 0.0041<i>c/a </i>when <i>d</i>is increased from 9<i>a</i> to 30<i>a</i>. Through changing
the configuration of the reflectors which results in transmission between 4.18% and 7.73%, the varieties of the sharpness
of peaks and the degree of extinction of the frequencies between the peaks are obviously observed.
A Michelson interferometer (MI) constructed in a two-dimensional photonic crystal (2D PhC) utilizing self-collimation
effect is proposed and investigated theoretically. The 2D PhC consists of a square lattice of air holes in silicon. It has
square-shaped equal frequency contours (EFCs) in the frequency range of 0.26-0.275<i>c/a</i> for TE modes. The MI proposed
consists of two PhC mirrors and one defect-row splitter. Light propagates between them employing self-collimation
effect. The two interferometer branches have different path lengths L<sub>1</sub> and L<sub>2</sub>. The FDTD calculation results show that
the transmission spectrum from 0.26<i>c/a</i> to 0.275<i>c/a</i> at the MI output port is comb-shaped. The transmission peaks have a
uniform spacing. Moreover, the peaks shift to the lower frequencies and the peak spacing decreases when the difference
between L<sub>1</sub> and L<sub>2</sub> is increased. For the operating wavelength around 1550nm, the dimensions of this MI are only tens of
microns. So this PhC Michelson interferometer may be applied in future photonic integrated circuits.