Chirp management in silicon-graphene electro absorption modulators.

We study the frequency chirp properties of graphene-on-silicon electro-absorption modulators (EAMs). By experimentally measuring the chirp of a 100 µm long single layer graphene EAM, we show that the optoelectronic properties of graphene induce a large positive linear chirp on the optical signal generated by the modulator, giving rise to a maximum shift of the instantaneous frequency up to 1.8 GHz. We exploit this peculiar feature for chromatic-dispersion compensation in fiber optic transmission thanks to the pulse temporal lensing effect. In particular, we show dispersion compensation in a 10Gb/s transmission experiment on standard single mode fiber with temporal focusing distance (0-dB optical-signal-to-noise ratio penalty) of 60 km, and also demonstrate 100 km transmission with a bit error rate largely lower than the conventional Reed-Solomon forward error correction threshold of 10-3.

Complex effective index in graphene-silicon waveguides.

We report for the first time and characterize experimentally the complex optical conductivity of graphene on silicon photonic waveguides. This permits us to predict accurately the behavior of photonic integrated devices encompassing graphene layers. Exploiting a Si microring add/drop resonator, we show the effect of electrical gating of graphene on the complex effective index of the waveguide by measuring both the wavelength shift of the resonance and the change in the drop peak transmission. Due to electro-refractive effect of graphene a giant (>10-3) change in the effective index is demonstrated for the first time on Si photonics waveguides and this large effect will crucially impact performances and consumption of Si photonics devices. We confirmed the results by two independent experiments involving two different gating schemes: Si gating through the ridge waveguide, and polymer-electrolyte gating. Both the experiments demonstrate a very large phase effect in good agreement with numerical calculations. The reported results validate the Kubo model for the case of graphene-Si photonics interfaces and for propagation in this type of waveguide. This is fundamental for the next design and fabrication of future graphene-silicon photonics devices.

-1 V bias 67 GHz bandwidth Si-contacted germanium waveguide p-i-n photodetector for optical links at 56 Gbps and beyond.

We demonstrate a 67 GHz bandwidth silicon-contacted germanium waveguide p-i-n photodetector operating at -1 V with 6.8 fF capacitance. The dark current is below 4 nA. The responsivity is 0.74 A/W at 1550 nm and 0.93 A/W at 1310 nm wavelength. 56 Gbps on-off-keying data reception is demonstrated with clear open eye diagrams in both the C-band and O-band.

III-V-on-silicon anti-colliding pulse-type mode-locked laser.

An anti-colliding pulse-type III-V-on-silicon passively mode-locked laser is presented for the first time based on a III-V-on-silicon distributed Bragg reflector as outcoupling mirror implemented partially underneath the III-V saturable absorber. Passive mode-locking at 4.83 GHz repetition rate generating 3 ps pulses is demonstrated. The generated fundamental RF tone shows a 1.7 kHz 3 dB linewidth. Over 9 mW waveguide coupled output power is demonstrated.

High sensitivity 10Gb/s Si photonic receiver based on a low-voltage waveguide-coupled Ge avalanche photodetector.

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.

Narrow-linewidth short-pulse III-V-on-silicon mode-locked lasers based on a linear and ring cavity geometry.

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.

Generation of 3.6 µm radiation and telecom-band amplification by four-wave mixing in a silicon waveguide with normal group velocity dispersion.

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.

Demonstration of Silicon-on-insulator mid-infrared spectrometers operating at 3.8 µm.

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.

GeSn/Ge heterostructure short-wave infrared photodetectors on silicon.

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.

Electrically pumped InP-based microdisk lasers integrated with a nanophotonic silicon-on-insulator waveguide circuit.

A compact, electrically driven light source integrated on silicon is a key component for large-scale integration of electronic and photonic integrated circuits. Here we demonstrate electrically injected continuous-wave lasing in InP-based microdisk lasers coupled to a sub-micron silicon wire waveguide, fabricated through heterogeneous integration of InP on silicon-on-insulator (SOI). The InP-based microdisk has a diameter of 7.5 mum and a thickness of 1 mum. A tunnel junction was incorporated to efficiently contact the p-side of the pn-junction. The laser emits at 1.6 mum, with a threshold current as low as 0.5 mA under continuous-wave operation at room temperature, and a threshold voltage of 1.65 V. The SOI-coupled laser slope efficiency was estimated to be 30 muW/mA, with a maximum unidirectional output power of 10 muW.

Heterogeneous integration of electrically driven microdisk based laser sources for optical interconnects and photonic ICs.

A new approach for an electrically driven microlaser based on a microdisk transferred onto Silicon is proposed. The structure is based on a quaternary InGaAsP p-i-n junction including three InAsP quantum wells, on a thin membrane transferred onto silicon by molecular bonding. A p++/n++ tunnel junction is used as the p-type contact. The technological procedure is described and first experimental results show a laser emission in pulsed regime at room temperature, with a threshold current near 1.5 mA.

Basic structures for photonic integrated circuits in Silicon-on-insulator.

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%.

Architectural approach to the role of optics in monoprocessor and multiprocessor machines.

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.

The concentrations of urinary prostaglandins E and plasma prostaglandins F2 alpha and E during induction of ovulation with human gonadotropins.

Plasma prostaglandins F2 alpha and E (PGF2 alpha, PGE) and urinary PGE were measured in 10 women treated with human gonadotropins (HMG) and subsequently with human chorionic gonadotropins (HCG). Five women became pregnant (6 pregnancies). There was no correlation between concentrations of plasma PGF2 alpha or PGE and plasma estradiol or progesterone. Urinary PGE concentrations showed a positive correlation with estradiol before HCG and a negative correlation with progesterone after HCG, only in women who subsequently became pregnant. Higher urinary PGE concentrations before HCG suggest that either HMG or rising estradiol levels stimulate PGE renal production. The significant negative correlation between urinary PGE and progesterone concentrations, after HCG, in those patients who became pregnant suggests that ovarian production of progesterone may decrease renal production of PGE.

The expectancy of pregnancy for "normal" infertile couples.

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.

Oral contraceptives and prolactinomas: a case-control study.

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.

PIP: The increase in the number of newly diagnosed cases of prolactinomas seems to coincide with the use of oral contraceptives (OCs) during the past 2 decades. The following retrospectives case-control study was undertaken in an attempt to disprove a null hypothesis of relationship between OC use and prolactinomas. Each of 70 patients operated upon for removal of a prolactinoma was closely matched for aged, gravidity, and year of final diagnosis with 1 patient in each of 3 control groups. The control groups selected were constituted 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 significant differences were found in the exposure rates to OCs among the 4 groups. Even the duration of OC use was not statistically significant in patients with prolactinoma and in patients with secondary amenorrhea and normal prolactin levels or patients with infertility. This study failed to reveal a significant association between prolactinomas and OCs but, given the sample size, a relative risk lower than 3.32 cannot be demonstrated or disproved. The results are reassuring and support the view that the increasing incidence of prolactinoma is probably due to advances in diagnostic technology rater than to OC exposure.

Effect of danazol on the radiographic density of breast parenchyma.

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.

Endometrial pattern in patients with primary hypoestrogenic amenorrhea receiving estrogen replacement therapy.

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.