Generation of tunable, high repetition rate optical frequency combs using on-chip silicon modulators

We experimentally demonstrate tunable, highly-stable frequency combs with high repetition-rates using a single, charge injection based silicon PN modulator. In this work, we demonstrate combs in the C-band with over 8 lines in a 20-dB bandwidth. We demonstrate continuous tuning of the center frequency in the C-band and tuning of the repetition-rate from 7.5GHz to 12.5GHz. We also demonstrate through simulations the potential for bandwidth scaling using an optimized silicon PIN modulator. We find that, the time varying free carrier absorption due to carrier injection, an undesirable effect in data modulators, assists here in enhancing flatness in the generated combs.Comment: 10 pages, 7 figure

Iron Oxide Nanoparticles: A Mighty Pioneering Diagnostic Tool But Is It Really Safe for Carcinoma and Neurodegenerative Diseases?

Iron oxide nanoparticles have been used in medicine for around 90 years, and this time has demonstrated their versatility, therapeutic efficacy, and safety. The primary constituents of iron oxide nanoparticles (IONs) are either magnetite (FeO Fe2O3) or maghemite (-Fe2O3). The most major clinical application of IONs is based on MRI. To detect cancers and age-related diseases, IONs are being used in medical diagnostic imaging. The two IONs with the best clinical repute are Resovist and Feridex IV. In addition to being used to detect cancers, IONs are also adapted as gastrointestinal negative contrast agents and as slow-release iron supplements to treat iron deficiency anemia. With IONs exposed to alternating magnetic fields, targeted imaging and thermal energy production are both feasible. Radiation therapy, immunotherapy, or chemotherapy be facilitated by the effects of heat. A growing number of IONs are being studied in therapeutic settings as nanotechnology develops swiftly. How IONs are used in biomedicine is determined by their interaction with the human immune system

Equilibirium studies of mixed ligand complexes fo uranyl ion with amino acids and carboxylic acids in aqueous solution

The stability constants of ternary uranyl ion complexes involving amino acids and carboxylic acids were determined by pH titrations at a temperature of 31 ± 0.1&#176;C and an ionic strength &#956;, of 0.1 mol dm<SUP>-3</SUP> (NaClO<SUB>4</SUB>). The stability values clearly show the discriminating qualities of the uranyl ion-amino acid 1:1 complex towards the secondary ligand to be coordinated. The values of log K<SUB>2YX</SUB> are linearly related to the product of the acid dissociation constants of the secondary ligands. The overall stability is found to be dependent on the binary stabilities. Preferential coordination by the uranyl-amino acid 1:1 complex towards O?O donors compared to O?S donors is observed

Broadband optical single sideband generation using an ultra high shape-factor self coupled ring resonator

In this study, we realize an integrated generation of optical Single SideBand with Carrier (SSB+C) signal for microwave photonics applications. It has been achieved using a Micro Ring Modulator (MRM) combined with a cavity based wavelength selective filter. MRM, when applied with an RF input, results in a Double SideBand with Carrier (DSB+C) signal where one sideband is suppressed by applying this signal to the filter. The filter has been created using a single resonance-split self-coupled cavity with an extremely high shape factor of 0.69. The sideband suppression ratio between DSB+C and SSB+C ranges from 16 dB to 55 dB for a frequency range of 4 GHz to 20 GHz. Tunable suppression ratio of 21 dB has been achieved at a fixed frequency of 15 GHz. Dynamic range performance of the generated signal has been evaluated at a noise floor of -156 dBm. The dynamic range remains stable in the range of 1 GHz - 5 GHz at � 80 dB.Hz2�3

Optical frequency comb based on nonlinear spectral broadening of a phase modulated comb source driven by dual offset locked carriers

We demonstrate a versatile technique to generate a broadband optical frequency comb source in the C-band. This is accomplished by nonlinear spectral broadening of a phase modulated comb source driven by dual frequency offset locked carriers. The locking is achieved by setting up a heterodyne optical frequency locked loop to lock two phase modulated electro-optic 25 GHz frequency combs sourced from individual seed carriers offset by 100 GHz, to within 6.7 MHz of each other.We realize spectral broadening in highly nonlinear fiber after suitable amplification to obtain an equalized, nonlinearly broadened frequency comb.We obtain ~86 lines in a 20 dB band spanning over 2 THz

Generation of a multi-wavelength source spanning the entire C-band by nonlinear spectral broadening of dual-carrier electro-optic frequency combs

We demonstrate a multi-wavelength source with a high repetition rate of 25 GHz, spanning the entire C-band, of which 124 lines lie within 10 dB bandwidth. We exploit the spectral and temporal properties of dual carrier electro-optic combs to simultaneously enhance self-phase modulation (SPM) based broadening and increase the stimulated Brillouin scattering (SBS) threshold. Dual carrier combs are generated through electro-optic modulation of spectrally separated narrow linewidth carriers. They are spectrally broadened in a highly nonlinear fiber after amplification with an in-house built erbium ytterbium co-doped fiber amplifier. The temporal profile of the dual carrier combs consists of significantly narrow pulses (1.4-1.9 ps FWHM) in comparison to the single laser comb (16.5 ps FWHM), increasing the peak power and enhancing the SPM effects. Further, the spectral power is distributed across the comb lines, increasing the SBS threshold and thus the power scalability of the system. These two factors together boost the bandwidth of the spectrally broadened multi-wavelength source

Frequency Offset Locked, Dual Carrier Excitation of Phase modulated, Electro-optic Frequency Combs for Bandwidth Scaling and Nonlinear Spectral Broadening

DWDM with/without superchannel based photonic networks require the use of optical carriers with equalised amplitudes and frequency stabilization of adjacent carriers to realise reliable high bandwidth optical communication systems with high spectral efficiency and long reach. Cascading of electro-optic (EO) modulators is a versatile method for generating tuneable, high repetition rate frequency combs which can be used as sources for the carriers. However, the number of lines produced with this technique is limited by the number of phase modulators. Nonlinear spectral broadening is an attractive option for bandwidth scaling; however, bandwidth scaling of single carrier combs through four wave mixing suffers from unequal comb lines or power limitations due to Brillouin scattering. A simpler technique to increase the number of comb lines would involve using multicarrier excitations for comb generation which would result in a proportional increase in the comb lines. Further, dual-carrier excitation enables an excellent temporal profile for nonlinear spectral broadening. However, since the two carriers have uncorrelated drifts, the resultant frequency combs would be unsuitable for most applications. This issue can be overcome by frequency offset locking the two lasers. Here, we demonstrate frequency offset locking (MHz accuracy) of two diode lasers spaced by 100GHz by using an optical phase locked loop which locks one laser to a RF harmonic of the other. This allows for the generation of frequency comb lines locked to each other even post nonlinear broadening. Using this technique, we demonstrate a 25GHz frequency comb with >90 lines (2THz) in the C-band