Using soft lithography technology, the 2D photonic crystal superprism structures
with a triangle array of air holes on the polymer slab were designed, simulated and
fabricated successfully. The profile of the molded structures with 450nm in diameter
and 900nm in lattice constant was obtained and observed by SEM. By means of
optical experiment and measurement, when the input incident angle varied from 15°
to 11°, we observed the beam propagation angle change from positive to negative and
the superprism effect was demonstrated effectively at near-infrared wavelength
1550nm.
An analysis of superprism effect in low index contrast polymer photonic crystal is presented. It
shows extremely sensitivity to the wavelength and angle of the incident light due to the strong
anisotropy of photonic band structures. Two-dimensional (2-D) polymer photonic crystals with
triangular lattice structure were fabricated by soft lithography using elastomeric
polydimethylsiloxane (PDMS) templates. Dense two dimensional photonic crystal superprism
structures with feature sizes of 150-500nm and aspect ratios of up to 1.25 were successfully
replicated by soft lithography. Large field size and easy fabrication are two major advantages when
compared with other imprint technology. Atomic Force Microscopy images showed that the molded
structures had high fidelity to the masters. Such an effective, low cost, and high throughput soft
lithography technique could find wide use in making photonic crystal based nanostructures.
An ultra-compact silicon Mach-Zehnder interferometer (MZI) modulator featuring p-i-n-diode-embedded photonic crystal
waveguides has been fabricated. As carrier injection is the only practical option for optical modulation in silicon, a lower limit of
current density (~104A/cm2) exists for achieving gigahertz modulation in the widely employed p-i-n diode configuration. Electrical
simulations have been performed to design and analyze the device. The device interaction length was reduced by one order of
magnitude compared to the conventional waveguide based MZI modulators by taking advantage of the slow group velocity exhibited
by photonic crystal waveguides (PCWs). A maximum modulation depth of 93% has been obtained under an injected current of 7.1
mA. High-speed optical modulation at 1 Gbit s-1 in the 1.55 micron wavelength region was experimentally demonstrated. To our
knowledge, this is the fastest speed ever achieved for a p-i-n diode based integrated silicon MZI modulator.
Photonic crystal based superprism offers a new way to design new optical components for beam steering and DWDM application. 3D photonic crystals are especially attractive as they could offer more control of the light beam based on the needs. A polygonal prism based holographic fabrication method has been demonstrated for a three-dimensional face-centered-cubic (FCC)-type submicron polymer photonic crystal using SU8 as the photo-sensitive material. Therefore antivibration equipment and complicated optical alignment system are not needed and the requirement for the coherence of the laser source is relaxed compared with the traditional holographic setup. By changing the top-cut prism structure, the polarization of the laser beam, the exposure and development conditions we can achieve different kinds of triclinic or orthorhombic photonic crystals on demand. Special fabrication treatments have been introduced to ensure the survivability of the fabricated large area (cm2) nano-structures. Scanning electron microscopy and diffraction results proved the good uniformity of the fabricated structures. With the proper design of the refraction prism we have achieved a partial bandgap for S+C band (1460-1565nm) in the [111] direction. The transmission and reflection spectra obtained by Fourier transform infrared spectroscopy (FTIR) are in good agreement with simulated band structure. The superprism effects around 1550nm wavelength for the fabricated 3D polymer photonic crystal have been theoretically calculated and such effects can be used for beam steering purpose.
Photonic crystals (PhCs) provide a promising nanophotonic platform for developing novel optoelectronic devices with significantly reduced device size and power consumption. Silicon nanophotonics is anticipated to play a pivotal role in the future nano-system integration owing to the maturity of sub-micron silicon complementary metal oxide semiconductor (CMOS) technology. An ultra-compact silicon modulator was experimentally demonstrated based on silicon photonic crystal waveguides. Modulation operation was achieved by carrier injection into an 80-micron-long silicon PhC waveguide of a Mach-Zehnder interferometer (MZI) structure. The driving current to obtain a phase shift of pi across the active region was as low as 0.15 mA, owing to slow light group velocity in PhC waveguides. The modulation depth was 92%. The electrode between the two waveguide arms of the MZI structure was routed to the space outside the MZI. In real devices, this planarized routing design would be essential to integrating the silicon modulator with electrical driving circuitry on a single silicon chip. For laboratory test, this routing scheme also eliminated the need of placing a bulky pad between the two arms and gave our modulator a distinctive slim profile and a much smaller footprint. Polymeric photonic crystals were designed for superprism based laser beam steering applications, and were fabricated by nano-imprint and other techniques.
A high performance polymer waveguide array with 45° micromirrors was fabricated by soft molding to achieve fully embedded board-level optoelectronic interconnects. One-step-transferring of a 3-D polymer structure is demonstrated. Low-loss and thermally stable UV curable polymers based on fluorinated acrylate are chosen as waveguide core and cladding materials. A 45° total interior reflection (TIR) micromirror was formed by two methods: blade cutting and mechanical polishing. And the surface roughnesses are further improved by using a focused ion beam (FIB) technique. The high-quality 45° micromirror was obtained to provide surface-normal light coupling between waveguide and the optoelectronic devices. The measured propagation loss of the multimode waveguide was 0.156dB/cm at 850nm wavelength. The excess loss of the mirror was less than 1.5dB.
We demonstrate a flexible optical waveguide film with integrated Vertical-cavity surface-emitting laser (VCSEL) and positive-intrinsic-negative (PIN) photodiode arrays for fully embedded board level optical interconnects. The optical waveguide circuits with 45° micro-mirror couplers are fabricated on a thin flexible polymeric substrate by soft molding. 45° micro-mirrors on waveguide array for fully embedded board level optical interconnections are investigated both theoretically and experimentally. Smooth mirror surface fabrication is demonstrated by using microtome blade. Thin film VCSEL arrays and PIN photodiode arrays are directly integrated on to the waveguide film. Measured propagation loss of the waveguide was 0.3dB/cm at 850nm.
Short-range optical interconnection is more emphasizing in high performance systems. Multimode waveguide array is considered as a major interconnection medium due to the relatively easy packaging with devices. The multimode fiber array conjunction with VCSEL and Pin photodiode array is widely used in board to board and/or system to system interconnection. We demonstrate a flexible optical waveguide film which was composed of VCSEL, photodiode array, multimode waveguide array and 45 degree micro mirror couplers. The flexible waveguide film has many potentials such as it can be integrated with typical rigid electronic board and free from geometrical constraint. The waveguide film with 45° mirror was fabricated on a flexible transparent substrate using soft molding technique and then thin film VCSEL and photo-detector array are integrated. Master structure of the waveguide, which has multimode waveguide array and 45° mirror structure was fabricated using conventional lithography and microtome technique.
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