Three-dimensional photonic crystals with face-centered cubic lattice structure, whose top plane is (111) plane, were
fabricated by triple exposure of two-beam interference fringes. The transmittance of photonic crystals with face-centered
cubic lattice structure fabricated by the holographic lithography mentioned above is analyzed by reducing the threedimensional
structure into multilayer thin films employing the effective medium theory (EMT) and matrix method. The
remarkable stop bands appeared at the Bragg wavelength calculated from the average of effective index. Relationships
between stop bands and effective refractive index on the reduced film or filling factor of photonic atoms for a facecentered
cubic lattice structure simulated by holographic lithography are shown. The validity of EMT result is also
discussed in comparison with that of plane wave expansion method for a face-centered cubic lattice structure with sphere
shape atoms. The stop bands were calculated by using the zero-th order, the second order and higher order EMT. The
stop bands calculated using higher order and second order EMT fairly well agreed with that of plane wave expansion
method, while the zero-th order result roughly agreed with that.
A simple method for fabricating three-dimensional photonic crystals with all fourteen Bravais lattice structures and
arbitrary lattice constant is proposed. The lattice structure is defined by three primitive translation vectors. The vectors
form three triangles on the non-parallel three planes, which shape a tetrahedron, and a united two tetrahedrons forms a
parallelepiped, which corresponds to a primitive cell of the lattice. All atoms lie at the vertexes of the parallelepiped
where these three planes intersect. This means that all crystal lattices can be described by three sets of periodically
aligned planes. The periodically aligned planes, or walls, can easily be fabricated by recording two-beam interference
fringes in the recording material with a recording threshold such as a photoresist. Therefore, triple exposure of the twobeam
interference fringes can create arbitrary crystal lattice structure. The optical arrangement of the practical
interferometer is simplified when the angles between the normal to the recording plane and the three planes are equal. In
this arrangement the triple exposure is followed subsequently by simply rotating the recording material around the
normal to the recording plane. To create a lattice with arbitrary lattice plane with respect to a recording plane, two axes
rotating stage must be used to rotate and tilt the recording plane. This method can create all fourteen Bravais lattices
with arbitrary lattice constant while the conventional four-beam interference method creates only a limited number of
lattice constants. Mathematical proof and numerical analysis results of this method are also shown.
The number of independent lattice constants of three-dimensional photonic crystals, which can be fabricated by four-beam interference, is analyzed for 14 Braivas lattices. The equation of maximum intensity point condition for interference fringe among four plane waves is the same as that between the lattice vector and the reciprocal lattice vector in the solid-state physics. This relation gives us the way to derive the wave number vectors for incident four plane waves to fabricate any desired three-dimensional photonic crystal structures. It is analyzed that the effective combination of incident wave number vectors is 16 for each of 14 Bravais lattices. Lattice constant is numerically analyzed for 16 combinations of wave number vectors for each 14 Bravais lattices. The resultant 16 lattice constants are not necessarily independent due to the symmetry of lattice. It is found that the maximum and minimum numbers for lattice constants are 16 for Triclinic and Face-centered orthorhombic lattices, and 1 for Primitive orthorhombic, Primitive tetragonal and Primitive cubic lattices. The others are 10 for Centered monoclinic, 9 for Body-centered orthorhombic, 6 for Body-centered tetragonal, 5 for Face-centered cubic, Body-centered cubic and Trigonal, and 2 for Primitive monoclinic, Centered orthorhombic and Hexagonal lattices. As a result, total number of 81 photonic crystals with different lattice structure or different lattice constant can be fabricated by using four-beam interference with a fixed wavelength.
This paper describes that arbitrary three-dimensional photonic crystals, so called fourteen Bravais lattices, and even a diamond structure can be fabricated by recording the four plane-waves interference fringe. It is derived that the equation of maximum intensity point condition for interference fringe among four plane waves is the same as that between the lattice vectors and the reciprocal lattice vectors in the solid-state physics. This relation gives us the way to calculate the incident directions for four plane waves to fabricate any desired three-dimensional photonic crystal structures. The diamond structure consists of two same face centered cubic lattices, which are shifted by a quarter of their lattice constant to each other. This shift can be introduced by shifting the phases of four plane waves for interference. Therefore, the diamond structure can be fabricated by double exposures without and with phase shifts. Experimentally, a face centered cubic lattice structure was fabricated in the positive photoresist layer by using a He-Cd laser. The polarization directions of four beams were adjusted to obtain a maximum interference modulation depth. The SEM observation and the diffraction pattern observation of the fabricated sample show that the fabricated structure has a face centered cubic periodic structure.
A digital video disk recorder which can record noncompressed NTSC digital video signal and 4 channel digital audio signals for 32 minutes has been developed. Using (phi) 30 cm magneto-optical (MO) double-sided disk, 23 GB recording data capacity and 123 Mbps high recording bit rate were performed. In order to realize high density and large capacity recording, we have improved optical heads, recording media and others, especially we have developed the new recording method called CWL_CAV (Constant minimum Wave Length - Constant Angular Velocity.
A compact optical head module for magneto-optical disks, combining a hybrid chip integration technology and a polarizing holographic optical element, has been developed. The module size is (phi) 10 mm X t11 mm. The validity of this optical head module has been demonstrated, by successful readout operation for a magneto-optical disk.
A compact optical head for CD-ROM drives, integrated with a laser diode chip, a photodiode chip, and a holographic optical element in a small optical module, using hybrid assembly technique, has been developed. The module size is 7.5 mm (W) X 8 mm (D) X 3 mm (H), and its weight is 0.6 g. The validity of this optical head design has been demonstrated by successful readout operation for a compact disc.
A new concept polarizer using a birefringent diffraction grating has been developed. The operating principles and fabricated polarizer characteristics are described. The fabricated element has more than 20 dB extinction ratios for both polarization lights which are sufficient for use in optical disk heads. The polarizer is easily mass manufactured by the planar batch process. A holographic optical element that is combined with this polarizer function is proposed. Applications of the holographic optical element for an optical disk read/write head are also described.
A compact magneto-optical disk head, integrated with chip elements and optical parts, using a hybrid assembly technique, has been developed. Optics and beam splitter characteristics were optimized so as to realize both compact size and sufficient read out characteristics. More than 46 dB C/N ratio and stable operation were achieved, while simple optics and an easy assembly method were used.
A compact magneto-optical disk head was constructed using a newly developed holographic optical element. The element has an analyzer function with more than 5dB extinction ratios for data signal detection1 in addition to focusing and tracking error signal detection functions . The element was fabricated in a birefringent LiNb0<sub>3</sub> substrate using the proton exchange method. which is a well known waveguide fabrication technique. In Read/Write experiments using the head, sufficient carrier-to-noise ratio values for practical use were obtained. As a typical result, a 47dB carrier-to-noise ratio was obtained for 3.7MHz pulse recorded signal.
A digital video recording system using a four-beam magneto-optical disk drive has been developed. In order to realize continuous parallel read/write operation on an ordinary single-spiral disk, periodic single track jumping during one disk rotation has been employed. Digital video signal recording has been carried out on the entire disk.