Mark Tinker

Negative refraction in a Si-polymer photonic Crystal membrane

We have observed negative refraction in a photonic crystal (PC) membrane structure at near-infrared wavelengths. The device is fabricated on a silicon-on-insulator substrate and consists of a silicon rod matrix suspended in a polymer where optical energy is delivered by ridge waveguides with various incident angles. The propagation direction inside the PC shows extraordinary refraction with an angle consistent with our two-dimensional numerical simulations. To our knowledge, this is the first experimental observation of isotropic negative refraction in a Si-based planar PC structure at optical frequencies. The realization of negative refraction in a planar Si-based system enables applications in negative index imaging to be integrated into compact optical circuits.

Thermo-optic photonic crystal light modulator

A device concept is proposed for modulating light in silicon-based photonic crystal devices by using highly localized high-temperature modulation of a compact device to vary the position of the cutoff frequency in a photonic crystal waveguide and modulate light. The position of the cutoff frequency can be varied by up to 60nm at the telecommunication wavelength of 1550nm by locally increasing the temperature of the device. Modulators of a few to several micrometers in width can be designed that can modulate light with extinction ratios up to 50dB and low insertion loss.

Silicon-Based 2-D Slab Photonic Crystal TM Polarizer at Telecommunication Wavelength

We report an extremely compact (15.4 mum x 8 mum) silicon-based 2D slab nano photonic crystal (PC) transverse-magnetic (TM) polarizer which blocks propagation of the transverse-electric (TE) polarized light but passes TM polarized light around telecommunication wavelength (1550 nm). The TE polarized light totally vanishes but the TM polarized light propagates with some attenuation in a length of mere 4.9 mum and it has a great potential to be integrated in a complex photonic integrated circuits. To our knowledge, this is the first experimental demonstration of a silicon-based PC TM polarizer at 1.55-mum wavelength. The plane wave expansion method (PWEM) and 2-D and 3-D finite-difference time-domain (FDTD) simulation were utilized to design a periodic triangular array of air holes in 340-nm-thick silicon with a diameter of 170 nm and pitch distance of 347 nm for the TM polarizer and 371 nm for the input and output waveguide. Such a PC TM polarizer was fabricated in silicon-on-insulator wafer using focused ion beam and reactive ion etching. The device was characterized using tunable lasers in the wavelength range of 1528 nm~1604 nm. Transmitted light intensities of the TE and TM polarized lights were measured which clearly showed the TE polarized light is filtered out around 1.55-mum wavelength.

Silicon-Based Thermo-Optically Tunable Photonic Crystal Lens

We report an extremely compact (30 ¿m × 7 ¿m) silicon-based 2-D thermo-optically tunable photonic crystal (PhC) lens operated at around telecommunication wavelength (1.55 ¿m ) with transverse-magnetic-like polarization light. A honeycomb lattice array of high index silicon rods with 340 nm in thickness, 234 nm in diameter, and 338 nm in lattice constant were embedded in 3-¿m-thick low index silicon dioxide. A 150-nm-thick NiCr micro-heater was placed directly on top of the PhC structure to provide localized heating to the silicon rod array. The localized heating causes refractive index change in silicon due to thermo-optic effect which results in change of the focal length of the PhC lens. The device was characterized with a tunable laser light source in the wavelength range of 1500 ~ 1580 nm. Tuning of focal length in this device was experimentally demonstrated by applying different current through the heater. Such experimental results showed good agreement with the simulation results.

Electro-thermally tunable silicon photonic crystal lens

We report extremely compact (30 µm × 7 µm) silicon based two-dimensional (2D) thermo-optically tunable photonic crystal lens which operates at around telecommunication wavelength (1.55 µm) with transverse magnetic (TM) like polarized light. A 150 nm thick NiCr micro-heater was placed directly on top of the photonic crystal lens to provide localized heating. The focal length of the photonic crystal lens is modulated through refractive index change caused by thermo-optic effect of silicon. Tuning of the focal length was experimentally demonstrated by applying various current through the heater and the results showed good agreed with the simulation results.

Silicon-based 2D slab nano photonic crystal TM polarizer in telecommunication wavelength

We report an extremely compact (15.4 mum x 8 mum) silicon-based 2D slab nano photonic crystal transverse magnetic (TM) polarizer which blocks propagation of the transverse electric (TE) polarized light around telecommunication wavelength (1,550 nm). TM polarization occurs in a length of mere 4.9 mum and it has a great potential to be integrated in a complex photonic integrated circuits. To our knowledge, this is the first ever demonstration of silicon-based TM polarizer in telecommunication wavelength. 2D and 3D finite difference time domain (FDTD) simulation was utilized to design a triangular array of air holes in silicon. Such photonic crystal TM polarizer was fabricated in silicon-on-insulator wafer using focused ion beam and reactive ion etch with air hole diameter of 170 nm and pitch distance of 347 nm for the TM polarizer and 371 nm for the input and output waveguide. The device was fully characterized using tunable lasers in the wavelength range of 1,528 nm ~ 1,604 nm. Transmitted light intensities of the TE and TM polarized lights were measured which clearly showed the TE polarized light is filtered out around 1.55 mum wavelength.

Process integration and development of inverted photonic crystal arrays

A processing technology has been developed to produce inverted two-dimensional photonic crystal structures by embedding an array of silicon pillars inside a polyimide matrix and releasing this structure from the underlying substrate. The spatial distribution of the high dielectric and low dielectric regions of these structures is inverted compared to the spatial distribution of standard photonic crystal structures produced by etching air holes in a high dielectric slab. Consequently these structures are far more difficult to fabricate. The integration requirements required for developing this technology are discussed along with the processing technology developed to fabricate these devices. An inverted photonic crystal device based on the superprism effect was successfully demonstrated.

Tunable nanophotonic device based on flexible photonic crystal

We report a tunable nanophotonic device concept based on flexible photonic crystal, which is comprised of a periodic array of high index dielectric material and a low index flexible polymer. Tunability is achieved by applying mechanical force with nano-/micro-electron-mechanical system actuators. The mechanical stress induces changes in the periodicity of the photonic crystal and consequently modifies the photonic band structure. To demonstrate the concept, we theoretically investigated the effect of mechanical stress on the anomalous refraction behavior and observed a very wide tunability in the beam propagation direction. Extensive experimental studies on fabrication and characterizations of the flexible photonic crystal structures were also carried out. High quality nanostructures were fabricated by e-beam lithography. Efficient coupling of laser beam and negative refraction in the flexible PC structures have been demonstrated. The new concept of tunable nanophotonic device provides a means to achieve real-time, dynamic control of photonic band structure and will thus expand the utility of photonic crystal structures in advanced nanophotonic systems.

Corrections to “Silicon-Based 2-D Slab Photonic Crystal TM Polarizer at Telecommunication Wavelength” [15 Apr 08 641-643]

We report an extremely compact (15.4 mum x 8 mum) silicon-based 2D slab nano photonic crystal (PC) transverse-magnetic (TM) polarizer which blocks propagation of the transverse-electric (TE) polarized light but passes TM polarized light around telecommunication wavelength (1550 nm). The TE polarized light totally vanishes but the TM polarized light propagates with some attenuation in a length of mere 4.9 mum and it has a great potential to be integrated in a complex photonic integrated circuits. To our knowledge, this is the first experimental demonstration of a silicon-based PC TM polarizer at 1.55-mum wavelength. The plane wave expansion method (PWEM) and 2-D and 3-D finite-difference time-domain (FDTD) simulation were utilized to design a periodic triangular array of air holes in 340-nm-thick silicon with a diameter of 170 nm and pitch distance of 347 nm for the TM polarizer and 371 nm for the input and output waveguide. Such a PC TM polarizer was fabricated in silicon-on-insulator wafer using focused ion beam and reactive ion etching. The device was characterized using tunable lasers in the wavelength range of 1528 nm~1604 nm. Transmitted light intensities of the TE and TM polarized lights were measured which clearly showed the TE polarized light is filtered out around 1.55-mum wavelength.

Mechanically Tunable Nanophotonic Devices

We report a novel tunable nanophotonic device concept based on Mechanically Controlled Photonic Crystal (MCPC), which is comprised of a periodic array of high index dielectric material and a low index polymer. Tunability is achieved by applying mechanical force with nano-/micro-electron-mechanical system actuators. The mechanical stress induces changes in the periodicity of the photonic crystal, to which the photonic band structure is extremely sensitive. This consequently produces tunability much greater than that achievable by electro-optic materials such as liquid crystal. Our theoretical investigations revealed that we could achieve dynamic beam steering over a wide range of angles up to 75° with only 10% mechanical stretching. We also predicted tunable sub-wavelength imaging in which we could tune the frequency response and focal length of negative index PC lens. For experimental demonstration, we fabricated the PC structures on Si-on-insulator substrates. Optical characterizations clearly showed the anticipated negative refraction in which the incident beam was refracted back to the side it was incident. The experimental demonstration of negative refraction at optical frequencies in a Si-based photonic crystal structure is a significant step toward the next-generation nanophotonics.