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Optical parametric amplifiers rely on the high Kerr nonlinearities and low two-photon absorption (TPA) to achieve large optical amplification. The high Kerr nonlinearity enables efficient energy transfer from the optical pump to the signal. On the other hand, the TPA process competes with the amplification process, and thus should be eliminated. Through Miller’s rule and Kramers-Kronig relations, it is known that the material’s Kerr nonlinearity scales inversely proportional to the band-gap, while the TPA process occurs when the photon energy is larger than the band-gap energy and Urbach tails, thus presenting a trade-off scenario. Based on these requirements, we have designed a CMOScompatible, band-gap engineered nitride platform with ultra-rich silicon content. The silicon nitride material is compositionally engineered to have a band-gap energy of 2.1 eV, which is low enough to confer a high Kerr nonlinearity, but still well above the energy required for the TPA process to occur. The new material, which we called ultra-silicon-rich nitride (USRN), has a material composition of Si7N3, a high Kerr nonlinearity of 2.8x10-13 cm2/W, and a negligible TPA coefficient. In optical amplification experiments, 500 fs pulses at 14 W peak power and centered around 1560 nm are combined with continuous wave signals. The maximum parametric gain of the signal could reach 42.5 dB, which is one of the largest gains demonstrated on CMOS platforms to date. Moreover, cascaded four-wave mixing down to the third idler, which was usually observed for mid-infrared silicon waveguides, is unprecedentedly observed at this spectrum.

CMOS-compatible nonlinear optics platforms with negligible nonlinear losses and high nonlinearity are of great merit. Silicon, silicon nitride and Hydex glass have made significant headway in nonlinear optical signal processing, though none of these platforms possesses the highly sought after combination of high nonlinearity and negligible nonlinear losses. In this manuscript, we present a nonlinear optics platform based on silicon-rich nitride, deposited at a low temperature of 250°C compatible with back-end CMOS processing. The silicon-rich nitride is designed and engineered in composition to have a bandgap of 2.05 eV, such that the two-photon absorption edge is well below 1.55 μm. The designed and developed waveguides have a nonlinear parameter of 550 W−1/m, 500 times larger than that in silicon nitride waveguides, while at the same time not possessing two-photon and free-carrier losses. Using 500-fs pulses, we generate supercontinuum exceeding 0.6 of an octave.

We experimentally demonstrate a CMOS compatible optical parametric amplifier based on Si 7 N 3 waveguides which are compositionally tailored that the 1550nm wavelength resides within the multi-photon regime, while possessing large nonlinear parameter of 550 W−1/m, 500 times larger than that in Si 3 N 4 .

CMOS platforms operating at the telecommunications wavelength either reside within the highly dissipative two-photon regime in silicon-based optical devices, or possess small nonlinearities. Bandgap engineering of non-stoichiometric silicon nitride using state-of-the-art fabrication techniques has led to our development of USRN (ultra-silicon-rich nitride) in the form of Si[subscript 7]N[subscript 3], that possesses a high Kerr nonlinearity (2.8 × 10[superscript −13] cm[superscript 2] W[superscript −1]), an order of magnitude larger than that in stoichiometric silicon nitride. Here we experimentally demonstrate high-gain optical parametric amplification using USRN, which is compositionally tailored such that the 1,550 nm wavelength resides above the two-photon absorption edge, while still possessing large nonlinearities. Optical parametric gain of 42.5 dB, as well as cascaded four-wave mixing with gain down to the third idler is observed and attributed to the high photon efficiency achieved through operating above the two-photon absorption edge, representing one of the largest optical parametric gains to date on a CMOS platform., Singapore Ministry of Education. Academic Research Fund (AcRF) Tier 2 grant, Singapore. Agency for Science, Technology and Research (PSF grant), SUTD-MIT International Design Centre (IDC), Temasek Laboratories, National Research Foundation of Singapore (Medium Sized Centre Program)

Multiplexing of optical modes in waveguides is demonstrated using coupled vertical gratings. The device utilizes sinusoidally corrugated waveguides of different widths with a period designed to multiplex information at 1.55 µm. The design, fabrication and characterization of devices is performed. Multiplexing of modes is demonstrated in optical structures which support 3 and 5 quasi-TE modes. The design utilizes counter-propagating modes in periodic structures, thus enabling the device to combine its mode division multiplexing capabilities with wavelength division multiplexing functionalities to further augment the multiplexing capacity of the device.

Supercontinuum generation over 0.6 of an octave is demonstrated at 1.55µm on silicon-rich nitride waveguides. The SRN films are engineered to have a band gap of 1.85eV, and do not suffer from two-photon absorption at 1.55µm. The SRN waveguides have a large nonlinear parameter of 550W-1/m, 500 times larger than that in silicon nitride waveguides.

Mode division multiplexing of modes in a silicon waveguide supporting three optical modes is demonstrated in the silicon on insulator platform. Cross-talk suppression of 17dB and 12dB are obtained for the zeroth and second order modes respectively. The extinction bandwidth is observed to increase with the mode order indicating a stronger cross coupling coefficient as the mode order is increased. The extinction ratio is also observed to increase from 5 dB to 15dB and >25dB as the mode order is increased, implying an increasing cross coupling coefficient.

We demonstrate low power four wave mixing using silicon rich nitride waveguides, engineered in bandgap to eliminate two photon absorption at 1.55µm, while preserving a high nonlinear parameter of 550 W−1/m. Broadband conversion over 170nm is demonstrated using a low pump power of 4.7 dBm.

Retinitis pigmentosa (RP) is a group of hereditary retinal diseases in which photoreceptor cells degenerate. It is both clinically and genetically heterogenous. Using a two-stage approach by combining linkage analysis with mutation detection, we have rapidly identified the gene locus and the mutation site of a Chinese Singaporean family with autosomal dominant RP.Three Chinese Singaporean families were tested. One family showed autosomal dominant inheritance pattern, while the other two could be recessive or sporadic. Twelve di-nucleotide markers tightly linked to 6 genes known to be responsible for either autosomal dominant or recessive RP were selected for linkage analysis. Cosegregation of marker and disease inheritance pattern permits identification of the target candidate gene. RFLP (restriction fragment length polymorphism) markers were added to confirm the linkage result prior to the detailed mutation detection study.With this two-stage strategy, the autosomal dominant RP family showed the rhodopsin locus segregating concordantly with the disease. Mutation screening later identified a nonsense mutation 5261CT in the last exon of rhodopsin gene. It predicted a Q344X changes at the C-terminus of the gene product, truncating it by 5 amino acids.This systematic approach facilitates molecular diagnosis of a genetically heterogenous disease like RP. This is the first report of an RP mutation in Singapore. This 5261CT mutation has been reported in the Caucasian, but not the Chinese population. The relatively milder phenotype in this family showed similarity to the reported US family, indicating the correlation of mutation site to severity of disease regardless of ethnicity.

The case records were reviewed of 27 patients with chronic glaucoma after vitreoretinal surgery who underwent 28 cyclocryotherapy procedures between March 1987 and March 1992. The average intraocular pressure after 3 months was between 11.0 and 13.3 mmHg with an average fall of 24-26 mmHg. More than 85% had intraocular pressures of less than 21 mmHg after 3 months; 28% were hypotonic (IOP6 mmHg). Six months postoperatively, 68% maintained or had improved vision. The hypotonic eyes were found to have deterioration in vision more frequently than those with an intraocular pressure5 mmHg (57% compared with 24%). The odds of a hypotonic eye losing vision were 4.27 times greater than for a non-hypotonic eye. Cyclocryotherapy was successful in relief of pain in all 4 eyes which were painful pre-operatively.

Thirty two eyes of 19 patients with capillary non-perfusion from preproliferative and early proliferative diabetic retinopathy underwent visual field testing on the 30-2 program of the Humphrey visual field analyser. The mean defect (MD) p value was < 5% in 30 (94%) eyes and the corrected pattern standard deviation (CPSD) was < 10% in 31 (97%) eyes. Areas of capillary non-perfusion demonstrated by fundal fluorescein angiography were closely associated with areas of reduced retinal sensitivity in these 31 eyes. More severe visual field defects were present in non-insulin dependent diabetics and in older patients. MD and CPSD p values of less than 0.5% and 1% respectively were found to be associated with non-insulin dependent diabetes (p < 0.05 and p < 0.01 respectively) and with the older age group (p < 0.05). There was no correlation between severity of field defects with hypertension and degree of retinopathy.

PurposeAlthough ocular manifestations are common among patients with Behcet's disease, corneal perforation has not been reported in the literature. We report an unusual case of Behcet's disease with corneal perforation as the main ocular involvement. Methods/resultsAn elderly Chinese patient was referred for eye examination because of clinical suspicion of Behcet's disease. Eye examination showed evidence of long-standing autoimmune disease of the eye, mild iritis and a corneal perforation in the left eye. Despite evidence of chronicity and corneal perforation, the patient was asymptomatic. The perforation was successfully treated with cyanoacrylate glue. ConclusionsWhile anterior segment involvement is common in Behcet's disease, this case highlights an unusual and hitherto unreported ocular involvement.

We fabricated highly-nonlinear (550W−1 m−1) and low loss ultra-rich silicon nitride waveguides that can achieve parametric wavelength conversion over 170nm and parametric amplification of 23dB.