Tunable Silicon Research Articles

Rigorous extraction tunability of Si-integrated Ba0.3Sr0.7TiO3 thin film up to 60 GHz

400-nm-thick Ba0.3Sr0.7TiO3 thin films are deposited on high resistivity silicon by in situ radio frequency magnetron sputtering. Coplanar waveguides with 1 μm slot width are designed, with accurate knowledge frequency losses behavior, to determine ferroelectric thin-films properties up to 60 GHz. Permittivity, loss tangent, and tunability are extracted through measurements and home made finite element analysis. Tunability of 33% and 29%, with 30 V maximum applied voltage (electric field of 300 kV/cm), are measured at 5 GHz and 60 GHz, respectively, while the dielectric losses evolve from 0.5% to 5%. A brief highlight is proposed about tunable silicon integrated quarter wavelength transformer potentialities for impedance matching.

Observation of the single-electron regime in a highly tunable silicon quantum dot

We report on low-temperature electronic transport measurements of a silicon metal-oxidesemiconductor quantum dot, with independent gate control of electron densities in the leads and the quantum dot island. This architecture allows the dot energy levels to be probed without affecting the electron density in the leads and vice versa. Appropriate gate biasing enables the dot occupancy to be reduced to the single-electron level, as evidenced by magnetospectroscopy measurements of the ground state of the first two charge transitions. Independent gate control of the electron reservoirs also enables discrimination between excited states of the dot and density of states modulations in the leads.

Preparation of tunable silicon q-dots through ultrasound

Silicon quantum dots (QDs) have been prepared through ultrasound treatments of light-emitting porous silicon layers (PSL) electrochemically etched from a p + type crystalline silicon (c-Si). The sonication treatments allowed separating the porous fraction from the bulk of c-Si as well as to mechanically reduce their dimensions. The ultrasounds processes have been carried out in two different organic solvents (toluene and tetrahydrofuran), and allowed obtaining silicon QDs emitting light in the blue–green part of the visible spectrum (estimated QDs diameter around 5 nm). Moreover, by adding the proper chemicals in the solvents, such as alkenes, or simply paraffin oil, we have stabilized the QDs achieving surface modification and observed an effect on size reduction. Photoluminescence spectra of the QDs, TEM images and a preliminary micro-FTIR investigation of functionalised QDs will be presented in this paper.

Tunable polymer/silicon over insulator ring resonators

A tunable ring resonator RR formed from Si/SiO2 waveguides with an electro-optic polymer cladding is proposed with em- phasis on the trade-off between the tuning voltage and ring radius. The ring resonator circuit combines the advantages of Si/SiO2 and polymer technologies. The advantages of this hybrid ring design over previously proposed tunable silicon rings include an increased switching speed, from 5 GHz to 20 to 100 GHz, single-polarity instead of dual-polarity voltage tuning and a voltage-independent quality factor. The hybrid de- sign also displays a greater free spectral range 1.85 nm instead of 0.1 nm and a wider tuning range 0.925 nm instead of 0.05 nm and is further compatible with silicon devices. Moreover, the device has a high quality factor of 3.410 4 . © 2008 Society of Photo-Optical Instrumentation

On-chip silicon photonic wavelength control of optical fiber lasers

Tunable silicon microring filters are used to demonstrate CMOS-compatible on-chip wavelength control of Er(+) doped fiber-lasers. An onchip Ni-Cr micro-heater consuming up to 20 mW is capable of tuning the Si microring filter by 1.3 nm with a lasing linewidths narrower than 0.02 nm. This approach enables arbitrary multiple wavelength generation on a silicon chip. Possible applications include on-chip and chip-to-chip dense-wavelength division multiplexed communications and sensor interrogation.

On-Chip NRZ-to-PRZ Format Conversion Using Narrow-Band Silicon Microring Resonator-Based Notch Filters

We report experimental demonstration and modeling of all-optical on-chip non-return-to-zero (NRZ) to pseudo-return-to-zero (PRZ) format conversion using narrow-band silicon microring resonator-based notch filters. Our proof-of-principle experiment using a carrier-injection-based tunable silicon microring resonator demonstrates NRZ-to-PRZ conversion at 3.6 Gbit/s. Our Fourier-transform-based modeling reveals in detail the format conversion dependence on the microring resonance Q factor, extinction ratio, phase response, and NRZ signal transition times, assuming signal format conversion of 40 Gbit/s.

Compact Thermally Tunable Silicon Wavelength Switch: Modeling and Characterization

A wavelength-selective photonic switch is developed based on a Si microring resonator using thermooptic effect. The 10-mum-diameter microring resonator uses single-mode strip Si waveguides of dimension 0.25 mum times 0.45 mum operating at 1.5 mum. Full-width at half-maximum are in the range 0.1-0.2 nm. The ultrawide tunable range (>6.4 nm) and wide free spectral range (~18 nm) of the switch element enables wavelength reconflgurable multichannel matrix switch by wavelength multiplexing/demultiplexing. Average rise delay time of 14 mus with low switching power of 3.15 mW has been achieved with 0.2-nm wavelength tuning and 78 mus, 104 mW for 6.4-nm tuning. Fall delay times are usually less than 10 mus. Thermal simulations show 10%-20% agreement with the measurements up to 3.2-nm tuning. The compact size of the switch shows its potential as an active element in photonic integrated circuits.

Microplasma synthesis of tunable photoluminescent silicon nanocrystals

An atmospheric-pressure microplasma reactor was developed for the fabricationof tunable photoluminescent silicon nanocrystals. A mixture of argon,hydrogen, and silicon tetrachloride was activated by a capacitively couplednon-equilibrium plasma generated in a capillary glass tube with a volume less than1 µl. The microplasma efficiently decomposes silicon tetrachloride intoatomic silicon even though the residence time is approximately100 µs. Supersaturated silicon vapour then leads to gas phase crystal nucleation viathree-body collision, followed by rapid termination of crystal growth due to the shortreactor residence time. Silicon nanocrystals are continuously synthesized in gasphase at room temperature. The room-temperature photoluminescence (PL) ofas-synthesized material with hydrogen concentration around 0.7–0.8% exhibitedintense visible light emission with peak intensity centred around 670 nm. The PLspectrum was blue-shifted to 520 nm with increasing hydrogen content, implyingthat partially oxidized nanocrystals of diameter less than 3 nm were synthesized.

Electrically tunable solid-state silicon nanopore ion filter

We show that a nanopore in a silicon membrane connected to a voltage source can be used as an electrically tunable ion filter. By applying a voltage between the heavily doped semiconductor and the electrolyte, it is possible to invert the ion population inside the nanopore and vary the conductance for both cations and anions in order to achieve selective conduction of ions even in the presence of significant surface charges in the membrane. Our model based on the solution of the Poisson equation and linear transport theory indicates that in narrow nanopores substantial gain can be achieved by controlling electrically the width of the charge double layer.

Electrically Tunable Silicon 2-D Photonic Bandgap Structures

Electrical tuning of high refractive index-contrast photonic bandgap (PBG) structures is required for a majority of PBG applications, particularly for integrated optics. When the host material is a semiconductor with poor electro-optical properties, tuning can be achieved by infiltrating the structure with an active optical material. In this paper we analyze the switching of electro-optic material in such structures, and suggest design rules to help achieve electrical tuning. In particular, a design concept that eliminates the electric field screening effects is proposed. The developed rules and concepts are demonstrated by the electrical tuning of liquid crystals inside two-dimensional porous silicon PBG structures. This approach can be generalized to different combinations of semiconductor PBG structures and active optical materials

Tunable silicon microring resonator with wide free spectral range

The authors present a silicon-on-insulator single ring resonator with a free spectral range equal to 47nm, which is the widest known value for this type of resonators. The ring radius is 2μm and is the smallest ring resonator ever reported, achieving experimentally such a wide spectral range. For this ring resonator, the authors demonstrate the quality factor to be equal to 6730±60. They thermally tune the resonant wavelength with 0.11nm∕°C, thus showing the ring resonator as an attractive component for on-chip ultracompact photonic add/drop filters and switches.

The effects of uniaxial compressive stress on the terahertz emission from phosphorus-doped silicon devices

The effects of uniaxial compressive stress on the terahertz electroluminescence from P-doped silicon devices have been studied. A shift by ∼0.5THz in the emission peaks of donor state transitions: 2p0→1s(E) and 3p+∕−→1s(E) has been observed for a stress of ∼0.1GPa along the [100] direction. Transitions from excited states to the strain split states of 1s(E) showed a pronounced polarization effect. Transitions involving the 1s(T1) ground state, however, showed no polarization effect. These results suggest that it may be possible to realize a tunable impurity-doped silicon terahertz emitter by externally applied stress.

Silicon-Based Micro-Fourier Spectrometer

A novel Fourier spectrometer based on a partly transparent thin-film detector in combination with a tunable silicon micromachined mirror was developed. The operation principle based on the detection of an intensity profile of a standing-wave by introducing a partly transparent detector in the standing-wave. Varying the position of the mirror results in a phase shift of the standing-wave and thus in a change of the optical intensity profile within the detector. The photoelectric active region of the sensor is thinner than the wavelength of the incoming light, so that the modulation of the intensity leads to the modulation of the photocurrent. The spectral information of the incoming light can be determined by the Fourier transform of the sensor signal. Based on the linear arrangement of the sensor and the mirror, the spectrometer facilitates the realization of one- and two-dimensional arrays of spectrometers combining spectral and spatial resolution. The operation principle of the spectrometer will be described and the influence of the detector design on the spectrometer performance will be discussed. A spectral resolution of down to 6 nm was achieved under real-time imaging conditions.

Tunable photonic bandgap structures for optical interconnects

As continued progress towards faster, low power consuming microelectronic devices becomes increasing difficult due to the scaling challenges of electrical interconnects, it becomes even more critical to explore alternative technologies. Tunable porous silicon photonic bandgap structures are viable building blocks for optical interconnects, which present a possible long term solution to the interconnect problem. Forming the structures on a silicon platform provides the advantage of easier integration with current semiconductor processing techniques. In this work, tuning of the optical properties is controlled by liquid crystals (LCs) that are infiltrated into the silicon matrix. Active tuning is demonstrated both out-of-plane, with one-dimensional porous silicon photonic bandgap microcavities, and in-plane, using two-dimensional porous silicon photonic bandgap structures.

Strain-tunable silicon photonic band gap microcavities in optical waveguides

We report the design, device fabrication, and measurements of tunable silicon photonic band gap microcavities in optical waveguides, using direct application of piezoelectric-induced strain to the photonic crystal. We show, through first-order perturbation computations and experimental measurements, a 1.54 nm shift in cavity resonances at 1.56 μm wavelengths for an applied strain of 0.04%. The strain is applied through integrated piezoelectric microactuators. For operation at infrared wavelengths, we combine x-ray and electron-beam lithography with thin-film piezoelectric processing. This level of integration permits realizable silicon-based photonic chip devices, such as high-density optical filters, with active reconfiguration.

Sensitive, Selective, & Tunable Porous Silicon Gas Sensor

ABSTRACTHybrid porous silicon, consisting of a microporous framework whose walls are covered with a thin nanoporous layer, proves to be an inexpensive and robust platform for fabrication of rapid, reversible, and sensitive semiconductor sensors. An extremely high surface area provides a mechanism for the detection of ppm and ppb levels of a range of gases including ammonia, NOx, and CO. A general method of coating electroless metal onto the surface provides a basis for nanostructure induced selectivity between these gases. Further, the introduction of FFT analysis to the rapidly reversible and linear response of the porous silicon gas sensor allows the gas response to be acquired and filtered on a drifting baseline.

Device for simultaneous monitoring of the channel wavelengths and power levels in a DWDM system

Feature Issue on Optical Performance Monitoring (OPM). A compact and cost-effective device for monitoring wavelengths and power levels of WDM channels labeled with pilot tones is presented. The device utilizes a tunable silicon etalon and a simple sampling scheme to identify and analyze the channels directly from the optical multiplex. The operation is demonstrated in a four-channel system. Extension to a large number of WDM channels is evaluated through simulations.

Tunable silicon etalon for simultaneous spectral filtering and wavelength monitoring of a DWDM transmitter

A temperature-tunable Fabry-Perot filter made of silicon has been developed and applied for simultaneous spectral filtering and wavelength monitoring of a directly modulated DFB laser. This novel device decreases the dispersion penalty of a cost-effective dense wavelength-division-multiplexing (DWDM) transmitter in a long-haul transmission link. Moreover, it allows the operating wavelength of the transmitter to be accurately monitored in real time.

Novel tunable laser diode arrangement with a micromachined silicon filter: feasibility

We demonstrate the workability of a new arrangement of a tunable high-power laser diode. This novel composite is realized with the use of a micro-optoelectro-mechanical system—a tunable silicon micromachined interferometric filter—a standard edge-emitting laser diode. In current extremely-short-external-cavity configuration, the quasi-continuous tuning over a 4-nm range with output power of tens of mW was obtained. Power and etalon characteristics of a considered hybrid laser are discussed. The advantage of proposed configuration is in its potentially low cost (due to the use of commercially available components) and loose alignment tolerances.