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Picosecond-pulse III-V-on-silicon mode-locked lasers based on linear and ring extended cavity geometries are presented. In passive mode-locked operation a 12 kHz -3dB linewidth of the fundamental RF tone at 4.7 GHz is obtained for the linear cavity geometry and 16 kHz for the ring cavity geometry. Stabilization of the repetition rate of these devices using hybrid mode-locking is also demonstrated.

We demonstrate low-voltage germanium waveguide avalanche photodetectors (APDs) with a gain × bandwidth product above 100GHz. A photonic receiver based on such a Ge APD, including a 0.13μm SiGe BiCMOS low-noise trans-impedance amplifier and a limiting amplifier, is realized. A 5.8dB sensitivity improvement is demonstrated at -5.9V bias at an avalanche gain of 6 through bit error ratio measurements. The absolute sensitivity in avalanche mode is -23.4dBm and -24.4dBm at a bit error ratio of 1 × 10(-12) and 1 × 10(-9) respectively.

Germanium-on-silicon thermo-optic phase shifters are demonstrated in the 5 μm wavelength range. Basic phase shifters require 700 mW of power for a 2π phase shift. The required power is brought down to 80 mW by complete undercut using focused ion beam. Finally an efficient thermo-optic phase shifter is demonstrated on the germanium on SOI platform. A tuning power (for a 2π phase shift) of 105 mW is achieved for a Ge-on-SOI structure which is lowered to 16 mW for a free standing phase shifter.

A silicon dual-ring modulator consisting of two serially cascaded rings with embedded PN junctions is driven by a differential signal pair. We show by simulation and experiment that the device has advantages over the single-ring modulator in terms of optical bandwidth, 3-dB modulation bandwidth and bit rate, at the expense of a 1.7-dB increase in the transmission penalty and a twofold increase of the RF power consumption. Driven by differential pseudo random binary sequence (PRBS) signals of 0.5-V peak-to-peak voltage (Vpp), the dual-ring modulator exhibits optical bandwidths of 66 pm and 40 pm at 12.5  Gb/s and 20  Gb/s, respectively. In contrast, the single-ring modulator has an optical bandwidth of 26 pm under a single-end PRBS signal of 0.5  Vpp at 12.5  Gb/s, and its eye diagram closes if the bit rate rises to 20  Gb/s.

The discovery of morphologically very similar but genetically distinct species complicates a proper understanding of the link between biodiversity and ecosystem functioning. Cryptic species have been frequently observed to co-occur and are thus expected to be ecological equivalent. The marine nematode Halomonhystera disjuncta contains five cryptic species (GD1-5) that co-occur in the Westerschelde estuary. In this study, we investigated the effect of three abiotic factors (salinity, temperature and sulphide) on life-history traits of three cryptic H. disjuncta species (GD1-3). Our results show that temperature had the most profound influence on all life-cycle parameters compared to a smaller effect of salinity. Life-history traits of closely related cryptic species were differentially affected by temperature, salinity and presence of sulphides which shows that cryptic H. disjuncta species are not ecologically equivalent. Our results further revealed that GD1 had the highest tolerance to a combination of sulphides, high salinities and low temperatures. The close phylogenetic position of GD1 to Halomonhystera hermesi, the dominant species in sulphidic sediments of the Håkon Mosby mud volcano (Barent Sea, 1280 m depth), indicates that both species share a recent common ancestor. Differential life-history responses to environmental changes among cryptic species may have crucial consequences for our perception on ecosystem functioning and coexistence of cryptic species.

An analytic model is developed to study the dynamic response of carrier-depletion silicon ring modulators. Its validity is confirmed by a detailed comparison between the modeled and the measured small signal frequency response of a practical device. The model is used to investigate how to maximize the optical modulation amplitude (OMA) and how the OMA could be traded for the bandwidth by tuning the coupling strength and the operation wavelength. Our calculation shows that for a ring modulator with equal RC time constant and photon lifetime, if its operation wavelength shifts from the position of the maximum OMA towards the direction that is away from the resonance, the 3dB modulation bandwidth increases ~2.1 times with a penalty of 3 dB to the OMA.

Mid-infrared light generation through four-wave mixing-based frequency down-conversion in a normal group velocity dispersion silicon waveguide is demonstrated. A telecom-wavelength signal is down-converted across more than 1.2 octaves using a pump at 2190 nm in a 1 cm-long waveguide. At the same time, a 13 dB on-chip parametric gain of the telecom signal is obtained.

On-chip optical interconnects still miss a high-performance laser monolithically integrated on silicon. Here, we demonstrate a silicon-integrated InP nanolaser that operates at room temperature with a low threshold of 1.69 pJ and a large spontaneous emission factor of 0.04. An epitaxial scheme to grow relatively thick InP nanowires on (001) silicon is developed. The zincblende/wurtzite crystal phase polytypism and the formed type II heterostructures are found to promote lasing over a wide wavelength range.

Advanced modulation formats call for suitable IQ modulators. Using the silicon-on-insulator (SOI) platform we exploit the linear electro-optic effect by functionalizing a photonic integrated circuit with an organic χ(2)-nonlinear cladding. We demonstrate that this silicon-organic hybrid (SOH) technology allows the fabrication of IQ modulators for generating 16QAM signals with data rates up to 112 Gbit/s. To the best of our knowledge, this is the highest single-polarization data rate achieved so far with a silicon-integrated modulator. We found an energy consumption of 640 fJ/bit.

The design and characterization of silicon-on-insulator mid-infrared spectrometers operating at 3.8 μm is reported. The devices are fabricated on 200 mm SOI wafers in a CMOS pilot line. Both arrayed waveguide grating structures and planar concave grating structures were designed and tested. Low insertion loss (1.5-2.5 dB) and good crosstalk characteristics (15-20 dB) are demonstrated, together with waveguide propagation losses in the range of 3 to 6 dB/cm.

A surface-illuminated photoconductive detector based on Ge0.91Sn0.09 quantum wells with Ge barriers grown on a silicon substrate is demonstrated. Photodetection up to 2.2µm is achieved with a responsivity of 0.1 A/W for 5V bias. The spectral absorption characteristics are analyzed as a function of the GeSn/Ge heterostructure parameters. This work demonstrates that GeSn/Ge heterostructures can be used to developed SOI waveguide integrated photodetectors for short-wave infrared applications.

Defect-mediated subbandgap absorption is observed in ion-implanted silicon-on-oxide waveguides that experience a rapid thermal annealing at 1075°C. With this effect, general carrier-depletion silicon modulators exhibit the capability of optical power monitoring. Responsivity is measured to be 22 mA/W for a 3 mm long Mach-Zehnder modulator of 2×10(18) cm(-3) doping concentration at -7.1 V bias voltage and 5.9 mA/W for a ring modulator of 1×10(18) cm(-3) doping concentration at -10 V bias voltage. The former is used to demonstrate data detection of up to 35 Gbits/s.

Carrier-depletion based silicon modulators with lateral and interdigitated PN junctions are compared systematically on the same fabrication platform. The interdigitated diode is shown to outperform the lateral diode in achieving a low VπLπ of 0.62 V∙cm with comparable propagation loss at the expense of a higher depletion capacitance. The low VπLπ of the interdigitated PN junction is employed to demonstrate 10 Gbit/s modulation with 7.5 dB extinction ration from a 500 µm long device whose static insertion loss is 2.8 dB. In addition, up to 40 Gbit/s modulation is demonstrated for a 3 mm long device comprising a lateral diode and a co-designed traveling wave electrode.

We report a broadband digital electro-optical switch, based upon a multi-stage Mach-Zehnder lattice design in silicon-on-insulator. A digital switching response is demonstrated, engineered through apodization of the coupling coefficients between stages. The digital switching behavior results in crosstalk lower than -15 dB for drive-voltage noise levels in excess of 300 mV(pp), which exceeds the noise tolerance of a conventional single-stage Mach-Zehnder switch by more than six-fold. In addition, the digital design enables a larger maximum 'on'-state extinction (below -26 dB) and lower 'on'-state free-carrier-induced insertion loss (less than 0.45 dB) than that of the single-stage switch. The noise-tolerant, low-crosstalk switch can thus play a key role within CMOS-integrated reconfigurable optical networks operating under noisy on-chip conditions.

We present a 4x4 spatially non-blocking Mach-Zehnder based silicon optical switch fabricated using processes fully compatible with standard CMOS. We successfully demonstrate operation in all 9 unique switch states and 12 possible I/O routing configurations, with worst-case cross-talk levels lower than -9 dB, and common spectral bandwidth of 7 nm. High-speed 40 Gbps data transmission experiments verify optical data integrity for all input-output channels.

Background: Lateral roots are formed at regular intervals along the main root by recurrent specification of founder cells. To date, the mechanism by which branching of the root system is controlled and founder cells become specified remains unknown., Results: Our study reports the identification of the auxin regulatory components and their target gene, GATA23, which control lateral root founder cell specification. Initially, a meta-analysis of lateral root-related transcriptomic data identified the GATA23 transcription factor. GATA23 is expressed specifically in xylem pole pericycle cells before the first asymmetric division and is correlated with oscillating auxin signaling maxima in the basal meristem. Also, functional studies revealed that GATA23 controls lateral root founder cell identity. Finally, we show that an Aux/IAA28-dependent auxin signaling mechanism in the basal meristem controls GATA23 expression., Conclusions: We have identified the first molecular components that control lateral root founder cell identity in the Arabidopsis root. These include an IAA28-dependent auxin signaling module in the basal meristem region that regulates GATA23 expression and thereby lateral root founder cell specification and root branching patterns., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

We report the performance of NiSi-based heaters integrated with submicrometer silicon waveguides. The heaters were fabricated using a standard complementary metal-oxide-semiconductor (CMOS) silicidation process on a thin silicon slab laterally connected with a silicon rib waveguide. The intrinsic properties of such NiSi waveguide heaters were characterized by using them as thermo-optic phase shifters in a Mach-Zehnder interferometer. The power consumption P(pi) for obtaining a pi phase shift was measured to be as low as 20 mW, using CMOS-compatible drive voltages. The time constant of the thermo-optic response was less than 2.8 mus. Simulations suggest that a further reduction in the power consumption P(pi) is feasible.

We review some opto-electronic devices based on the III-V/SOI heterogeneous integration platform, including lasers, modulators, wavelength converters, and photo-detectors. All of them are critical components for future on-chip interconnect and optical network-on-chip. The footprints of such devices are kept small by employing micro-cavity based structures. We give an overview of the device performances. The advantages over the all-silicon based devices are also discussed.

We present a novel design for a noise-tolerant, ultra-broadband electro-optic switch, based on a Mach-Zehnder lattice (MZL) interferometer. We analyze the switch performance through rigorous optical simulations, for devices implemented in silicon-on-insulator with carrier-injection-based phase shifters. We show that such a MZL switch can be designed to have a step-like switching response, resulting in improved tolerance to drive-voltage noise and temperature variations as compared to a single-stage Mach-Zehnder switch. Furthermore, we show that degradation in switching crosstalk and insertion loss due to free-carrier absorption can be largely overcome by a MZL switch design. Finally, MZL switches can be designed for having an ultra-wide, temperature-insensitive optical bandwidth of more than 250 nm. The proposed device shows good potential as a broadband optical switch in reconfigurable optical networks-on-chip.

We present an ultra-broadband Mach-Zehnder based optical switch in silicon, electrically driven through carrier injection. Crosstalk levels lower than -17 dB are obtained for both the 'on' and 'off' switching states over an optical bandwidth of 110 nm, owing to the implementation of broadband 50% couplers. Full 2 x 2 switching functionality is demonstrated, with low power consumption (approximately 3 mW) and a fast switching time (< 4 ns). The utilization of standard CMOS metallization results in a low drive voltage (approximately 1 V) and a record-low V(pi)L (approximately 0.06 V x mm). The wide optical bandwidth is maintained for temperature variations up to 30 K.

We report on a Si(3)N(4)-based surface-passivation technique for increasing free-carrier lifetimes in submicrometer silicon-on-insulator waveguides by up to 2 orders of magnitude. The carrier lifetime was measured by injecting free carriers into a critically coupled ring resonator through photoexcitation by short pump pulses and subsequently tracking the spectral detuning of the resonator during the carrier-recombination phase. Carrier lifetimes of up to 70 ns were obtained in waveguides passivated with a 45-nm-thick Si(3)N(4) coating. Such surface passivation is essential for low-power operation of optical switches based on carrier injection.

The simulation of spiking neural networks (SNNs) is known to be a very time-consuming task. This limits the size of SNN that can be simulated in reasonable time or forces users to overly limit the complexity of the neuron models. This is one of the driving forces behind much of the recent research on event-driven simulation strategies. Although event-driven simulation allows precise and efficient simulation of certain spiking neuron models, it is not straightforward to generalize the technique to more complex neuron models, mostly because the firing time of these neuron models is computationally expensive to evaluate. Most solutions proposed in literature concentrate on algorithms that can solve this problem efficiently. However, these solutions do not scale well when more state variables are involved in the neuron model, which is, for example, the case when multiple synaptic time constants for each neuron are used. In this letter, we show that an exact prediction of the firing time is not required in order to guarantee exact simulation results. Several techniques are presented that try to do the least possible amount of work to predict the firing times. We propose an elegant algorithm for the simulation of leaky integrate-and-fire (LIF) neurons with an arbitrary number of (unconstrained) synaptic time constants, which is able to combine these algorithmic techniques efficiently, resulting in very high simulation speed. Moreover, our algorithm is highly independent of the complexity (i.e., number of synaptic time constants) of the underlying neuron model.

A compact electro-optic modulator on silicon-on-insulator is presented. The structure consists of a III-V microdisk cavity heterogeneously integrated on a silicon-on-insulator wire waveguide. By modulating the loss of the active layer included in the cavity through carrier injection, the power of the transmitted light at the resonant wavelength is modulated; approximately 10 dB extinction ratio and 2.73 Gbps dynamic operation are demonstrated without using any special driving techniques.

We propose photonic reservoir computing as a new approach to optical signal processing in the context of large scale pattern recognition problems. Photonic reservoir computing is a photonic implementation of the recently proposed reservoir computing concept, where the dynamics of a network of nonlinear elements are exploited to perform general signal processing tasks. In our proposed photonic implementation, we employ a network of coupled Semiconductor Optical Amplifiers (SOA) as the basic building blocks for the reservoir. Although they differ in many key respects from traditional software-based hyperbolic tangent reservoirs, we show using simulations that such a photonic reservoir can outperform traditional reservoirs on a benchmark classification task. Moreover, a photonic implementation offers the promise of massively parallel information processing with low power and high speed.

For the compact integration of photonic circuits, wavelength-scale structures with a high index contrast are a key requirement. We developed a fabrication process for these nanophotonic structures in Silicon-on-insulator using CMOS processing techniques based on deep UV lithography. We have fabricated both photonic wires and photonic crystal waveguides and show that, with the same fabrication technique, photonic wires have much less propagation loss than photonic crystal waveguides. Measurements show losses of 0.24dB/mm for photonic wires, and 7.5dB/mm for photonic crystal waveguides. To tackle the coupling to fiber, we studied and fabricated vertical fiber couplers with coupling efficiencies of over 21%. In addition, we demonstrate integrated compact spot-size converters with a mode-to-mode coupling efficiency of over 70%.

The relevance of introducing optical interconnects (OI's) in monoprocessors and multiprocessors is studied from an architectural point of view. We show that perhaps the major explanation for why optical technologies have nearly been unable to penetrate into computers is that OI's generally do not shorten the memory-access time, which is the most critical issue for today's stored-program machines. In monoprocessors the memory-access time is dominated by the electronic latency of the memory itself. Thus implementing OI's inside the memory hierarchy without changing the memory architecture cannot dramatically improve the global performance. In strongly coupled multiprocessors the node-bypass latency dominates. Therefore the higher the connectivity (possibly with optics), the shorter the path to another node, but the more expensive the network and the more complex the structure of electronic nodes. This relation leaves the choice of the best network open in terms of simplicity and latency reduction. The bottlenecks resulting from and the benefits of implementing OI's are discussed with respect to symmetric multiprocessors, rings, and distributed shared-memory supercomputers.

On the basis of results obtained from an oral glucose tolerance test, (OGTT), twenty patients with gonadal dysgenesis were classified as normal (N = 8) and diabetic (N = 12). The two groups of patients were further tested by a rapid intravenous glucose injection, a tolbutamide test, an insulin sensitivity test and an oral amino acid load. Fasting levels of plasma growth hormone (GH) were normal in all subjects but one. Approximately 1/3 of the GH responses during testing periods were abnormal, being either absent during hypoglycaemia or following amino acid ingestion, or paradoxically increased during hyperglycaemia. No correlation was found between the degree of carbohydrate intolerance and the levels of plasma GH. There was no gross alteration of tissue sensitivity to exogenous insulin. The beta-cell response to tolbutamide, amino acid and intravenous glucose were comparable in patients with a normal or a diabetic OGTT. In both groups, the rates of decrease of blood glucose following tolbutamide or intravenous glucose were also similar and within the normal range. During OGTT, the diabetic group had a delayed insulin release and a low insulinogenic index. It is concluded that in gonadal dysgenesis the intolerance to an oral carbohydrate load is frequently associated with, but unrelated to, anomalies of the GH secretion. In diabetic subjects, the process of insulin secretion loses its normal sensitivity to the oral glucose stimulus while remaining unaltered and similiar to that of non-diabetic subjects in response to tolbutamide, amino acid and intravenous glucose.

The increase in the number of newly diagnosed cases of prolactinomas seems to coincide with the use of oral contraceptives during the past two decades. The following retrospective case-control study was undertaken in an attempt to disprove a null hypothesis of relationship between oral contraceptive use and prolactinomas. Each of 70 patients operated upon for removal of a prolactinoma was closely matched for age, gravidity, and year of final diagnosis with one patient in each of three control groups. The control groups selected were constituted, respectively, of patients with secondary amenorrhea and normal prolactin levels, patients with normal ovulatory cycles consulting for infertility, and subjects without medical or gynecologic problems. No statistically significative differences were found in the exposure rates to oral contraceptives among four groups. This study thus failed to reveal a significant association between prolactinomas and oral contraceptives but, given the sample size, a relative risk lower than 3.32 cannot be demonstrated or disproved.

The histologic pattern of the endometrium was studied in 38 patients, 19 to 44 years old, with primary hypoestrogenic amenorrhea treated by estrogen replacement therapy. At the time of endometrial biopsy 3 patients were receiving estrogens only and 35 patients were taking 1 of the following cyclic estrogen-progestogen combinations: 1) conjugated estrogens, 1.25 or 2.5 mg per day, combined with medroxyprogesterone, 5 or 10 mg for the last 5 to 10 days; 2) ethinyl estradiol, 50 microgram per day, combined with medroxyprogesterone, 5 mg per day for the last 5 days; or 3) mestranol, 40 microgram per day, in combination with norethindrone, 0.5 mg for the last 7 days. Evidence of endometrial hyperplasia was found in 3 patients. Two of them were taking unopposed estrogens and developed cystic hyperplasia; the other patient, treated with norethindrone in addition to mestranol, disclosed focal cystic glandular hyperplasia. This study and the review of the available data reported in the literature on the endometrial response to estrogen therapy in patients with gonadal dysgenesis stress the importance of appropriate estrogen and progestogen dosage to avoid the hazards of abnormal endometrial pattern in young patients receiving estrogen replacement therapy.

Clinical aspects and the incidence of the various underlying etiologic factors were studied in 86 patients with post-oral contraceptive amenorrhea. Patients were divided into two groups according to the presence or absence of detectable galactorrhea. Group I was composed of 55 amenorrheic patients without detectable galactorrhea and group II included 31 patients with amenorrhea associated with galactorrhea. Both groups were comparable for age, gravidity, duration of intake of oral contraceptives, and duration of amenorrhea. The incidence of previous oligomenorrhea and late menarche was high in both groups. The most striking difference between the two groups was in the incidence of pituitary prolactin-secreting tumor--32% among patients with galactorrhea and less than 2% among patients without galactorrhea. Identification of galactorrhea and accurate diagnosis of its causes are mandatory for successful management of postpill amenorrhea.

Among 42 patients with GD, one had clinical diabetes and 10 had chemical diabetes (26%) when tested by OGTT. The insulinogenic index was lower in patients with chemical diabetes than in patients with normal OGTT. Among 19 patients with isolated hypogonadotropic hypogonadism, similarly tested, three had chemical diabetes (15%). In a prospective study of 29 patients with GD tested repeatedly, the incidence of diabetic OGTT increased significantly with age. As glucose tolerance deteriorated, the plasma insulin response was delayed and the insulinogenic index decreased. The carbohydrate tolerance was unrelated to weight, estrogen replacement therapy, chromosomal pattern, and GH response. In six GD cases studied at a 6 year interval, the tolerance to oral glucose decreased with time whereas glucose utilization following its intravenous injection or tolbutamide administration was only slightly diminished; the plasma insulin was reduced by approximately 50% in response to each of these stimulations. These studies suggest that carbohydrate intolerance is frequently associated with GD and is due to a diminished beta-cell function.

We have given danazol to 25 women with mammary dysplasia. Clinical, cytologic and radiographic examinations were made before, during and after this treatment. In 23 patients breast pain disappeared completely. Danazol produced such a decrease in breast volume and density that on the mammogram the parenchyma was much more easily visualized. We suggest that danazol might be given before mammography to high risk women having dense dysplasic breasts, in order to ensure easier and more accurate interpretation.

The prognosis of unexplained infertility was studied for 47 couples. The cumulative rate of pregnancy was 65%, with 81% achieving a full-term pregnancy. The type and duration of infertility, the age of the woman, and the previous use of contraceptives did not significantly modify the results. This study indicates that a complete investigative protocol should include laparoscopy. It also suggests caution in the application of untried empirical treatments to normal infertile couples.