Tunable dual optical frequency comb at 2 µm for CO2 sensing.

In this article, we demonstrate a dual frequency comb (DFC) based on the gain-switching of mutually injection-locked semiconductor lasers in the 2 µm wavelength region with a tunable free spectral range (FSR) between 500 MHz and 3 GHz. Through the down-conversion process enabled by DFCs, the beating spectra of the optical frequency combs were captured in a 15 MHz electrical bandwidth with high resolution and millisecond acquisition times. A first experimental demonstration of sensing CO2 with this architecture is also presented.

Gain-switched dual frequency comb at 2 µm.

This article shows a dual frequency comb in the 2 µm wavelength region using mutually injection locked gain-switched semiconductor lasers. Strained InGaAs multi-quantum-well discrete mode lasers and gain switching were used to generate two optical frequency combs with repetition rates of 2 GHz and 2.0001 GHz respectively, centred at 2.002 µm. Each optical comb spanned approximately 100 GHz. Through mutual injection locking to an edge comb line common in both combs, a phase locked dual frequency comb was demonstrated with 44 beating tones unique to single comb line pair interactions. This scheme allows for the comb information to be compressed into a 5 MHz detection bandwidth and captured with millisecond acquisition times, which could be of benefit to a number of sensing applications.

Key enabling technologies for optical communications at 2000 nm.

This paper discusses the potential for opening a new wavelength window at the 2 µm waveband for optical communications, showing current limitations of the system's performance. It focuses on novel results for key enabling technologies, including the analysis of laser injection locking at this waveband, an improved responsivity for bulk and strained InGaAs edge-couple detectors, and also an increased gain profile for thulium-doped fiber amplifiers.

10 Gb/s InP-based Mach-Zehnder modulator for operation at 2 µm wavelengths.

We report on the first InP-based Mach-Zehnder modulator (MZM) employing quantum-confined Stark effect (QCSE) for operation around 2000 nm. The polarization sensitive device is based on 15 compressively strained quantum wells and achieves an electro-optic (EO) bandwidth of at least 9 GHz, with a DC extinction ratio of ~9 dB, and a V(π)L ~9.6 V.mm. We demonstrate back-to-back communication with a 10 Gb/s pseudo-random bit sequence (PRBS) of length 2(7)-1 at a wavelength around 2000 nm.

100 Gbit/s WDM transmission at 2 µm: transmission studies in both low-loss hollow core photonic bandgap fiber and solid core fiber.

We show for the first time 100 Gbit/s total capacity at 2 µm waveband, using 4 × 9.3 Gbit/s 4-ASK Fast-OFDM direct modulation and 4 × 15.7 Gbit/s NRZ-OOK external modulation, spanning a 36.3 nm wide wavelength range. WDM transmission was successfully demonstrated over 1.15 km of low-loss hollow core photonic bandgap fiber (HC-PBGF) and over 1 km of solid core fiber (SCF). We conclude that the OSNR penalty associated with the SCF is minimal, while a ~1-2 dB penalty was observed after the HC-PBGF probably due to mode coupling to higher-order modes.

Dense WDM transmission at 2 µm enabled by an arrayed waveguide grating.

We show, for the first time, dense WDM (8×20 Gbit/s) transmission at 2 µm enabled by advanced modulation formats (4-ASK Fast-OFDM) and the development of key components, including a new arrayed waveguide grating (AWGr) at 2 µm. The AWGr shows -12.8±1.78 dB of excess loss with an 18-dB extinction ratio and a thermal tunability of 0.108 nm/°C.

Cognitive control, reward-related decision making and outcomes of late-life depression treated with an antidepressant.

BACKGROUND: Executive processes consist of at least two sets of functions: one concerned with cognitive control and the other with reward-related decision making. Abnormal performance in both sets occurs in late-life depression. This study tested the hypothesis that only abnormal performance in cognitive control tasks predicts poor outcomes of late-life depression treated with escitalopram. METHOD: We studied older subjects with major depression (N = 53) and non-depressed subjects (N = 30). Executive functions were tested with the Iowa Gambling Test (IGT), Stroop Color-Word Test, Tower of London (ToL), and Dementia Rating Scale - Initiation/Perseveration domain (DRS-IP). After a 2-week placebo washout, depressed subjects received escitalopram (target daily dose: 20 mg) for 12 weeks. RESULTS: There were no significant differences between depressed and non-depressed subjects on executive function tests. Hierarchical cluster analysis of depressed subjects identified a Cognitive Control cluster (abnormal Stroop, ToL, DRS-IP), a Reward-Related cluster (IGT), and an Executively Unimpaired cluster. Decline in depression was greater in the Executively Unimpaired (t = -2.09, df = 331, p = 0.0375) and the Reward-Related (t = -2.33, df = 331, p = 0.0202) clusters than the Cognitive Control cluster. The Executively Unimpaired cluster (t = 2.17, df = 331, p = 0.03) and the Reward-Related cluster (t = 2.03, df = 331, p = 0.0433) had a higher probability of remission than the Cognitive Control cluster. CONCLUSIONS: Dysfunction of cognitive control functions, but not reward-related decision making, may influence the decline of symptoms and the probability of remission of late-life depression treated with escitalopram. If replicated, simple to administer cognitive control tests may be used to select depressed older patients at risk for poor outcomes to selective serotonin reuptake inhibitors who may require structured psychotherapy.

Expressions for the nonlinear transmission performance of multi-mode optical fiber.

We develop an analytical theory which allows us to identify the information spectral density limits of multimode optical fiber transmission systems. Our approach takes into account the Kerr-effect induced interactions of the propagating spatial modes and derives closed-form expressions for the spectral density of the corresponding nonlinear distortion. Experimental characterization results have confirmed the accuracy of the proposed models. Application of our theory in different FMF transmission scenarios has predicted a ~10% variation in total system throughput due to changes associated with inter-mode nonlinear interactions, in agreement with an observed 3dB increase in nonlinear noise power spectral density for a graded index four LP mode fiber.

Demonstration of amplified data transmission at 2 µm in a low-loss wide bandwidth hollow core photonic bandgap fiber.

The first demonstration of a hollow core photonic bandgap fiber (HC-PBGF) suitable for high-rate data transmission in the 2 µm waveband is presented. The fiber has a record low loss for this wavelength region (4.5 dB/km at 1980 nm) and a >150 nm wide surface-mode-free transmission window at the center of the bandgap. Detailed analysis of the optical modes and their propagation along the fiber, carried out using a time-of-flight technique in conjunction with spatially and spectrally resolved (S2) imaging, provides clear evidence that the HC-PBGF can be operated as quasi-single mode even though it supports up to four mode groups. Through the use of a custom built Thulium doped fiber amplifier with gain bandwidth closely matched to the fiber's low loss window, error-free 8 Gbit/s transmission in an optically amplified data channel at 2008 nm over 290 m of 19 cell HC-PBGF is reported.

Hollow core photonic crystal fiber based viscometer with Raman spectroscopy.

The velocity of a liquid flowing through the core of a hollow core photonic crystal fiber (driven by capillary forces) is used for the determination of a liquid's viscosity, using volumes of less than 10 nl. The simple optical technique used is based on the change in propagation characteristics of the fiber as it fills with the liquid of interest via capillary action, monitored by a laser source. Furthermore, the liquid filled hollow core photonic crystal fiber is then used as a vessel to collect Raman scattering from the sample to determine the molecular fingerprint of the liquid under study. This approach has a wide variety of indicative uses in cases where nano-liter samples are necessary. We use 10-12 cm lengths of hollow core photonic crystal fibers to determine the viscosity and Raman spectra of small volumes of two types of monosaccharides diluted in a phosphate buffer solution to demonstrate the principle. The observed Raman signal is strongest when only the core of the hollow core photonic crystal fiber is filled, and gradually decays as the rest of the fiber fills with the sample.

Emotional processing subtypes in bipolar disorder: A cluster analysis.

BACKGROUND: Evidence regarding the performance of Bipolar Disorder patients (BD) on Emotional Processing (EP) is conflicting, suggesting that heterogeneity within this population may exist. It is not completely understood if this impacts on clinical presentation and functional outcomes. METHODS: A total of 212 BD patients were recruited. Patients underwent MATRICS Consensus Cognitive Battery as well as a clinical evaluation to detect premorbid traits, comorbidities and clinical features. Performance on each basic emotion on the Emotional Recognition Task (ERT) and Reading the Mind in the Eyes Test were entered into hierarchical cluster analyses in order to determine the number of clusters and to assign subjects to specific clusters. We then compared subgroups on clinical factors and real-world community functioning. RESULTS: No differences between BD patients as a group and controls were found in EP performance. Two clusters of BD patients were found, one with "intact" performance (71.2%) that performed as healthy controls (HC) and other with "impaired" performance (28.8%) performing worse than HC and schizophrenic patients on basic emotion recognition. Patients in the "impaired group" presented higher rates of childhood trauma, schizotypal traits, lower premorbid IQ and education, poor psychosocial functioning and cognitive performance. LIMITATIONS: Cross-sectional data which limits our ability to infer directionality of our findings. CONCLUSION: These results suggest the presence of two subgroups regarding EP performance with unique clinical and neurodevelopmental profiles associated. Next steps will include using these data to identify a homogeneous group of patients to target these disabling symptoms with treatment.

Selective neuroanatomic abnormalities in Down's syndrome and their cognitive correlates: evidence from MRI morphometry.

We examined the pattern of neuroanatomic abnormalities in adults with Down's syndrome (DS) and the cognitive correlates of these abnormalities. Specifically, we compared this pattern with what would be predicted by the hypotheses attributing DS pathology to either premature aging or Alzheimer's disease. We measured a number of brain regions on MRIs of 25 subjects: 13 persons with the DS phenotype and 12 age- and sex-matched healthy volunteers. Study participants had no history of cardiovascular disease, diabetes, thyroid dysfunction, or seizure disorder. After statistical adjustment for differences in body size, we found that, in comparison with controls, DS subjects had substantially smaller cerebral and cerebellar hemispheres, ventral pons, mammillary bodies, and hippocampal formations. In the cerebellar vermis of DS subjects, we observed smaller lobules VI to VIII without appreciable differences in other regions. In addition, we noted trends for shrinkage of the dorsolateral prefrontal cortex, anterior cingulate gyrus, inferior temporal and parietal cortices, parietal white matter, and pericalcarine cortex in DS subjects compared with normal controls. The parahippocampal gyrus was larger in DS subjects. We found no significant group differences in the volumes of the prefrontal white matter, the orbitofrontal cortex, the pre- and postcentral gyri, or the basal ganglia. We conclude that the pattern of selective cerebral damage in DS does not clearly fit the predictions of the premature aging or Alzheimer's disease hypotheses. To examine the relationship between brain abnormalities and cognitive deficits observed in DS, we correlated the size of brain regions that were significantly reduced in DS with performance on tests of intelligence and language. The correlation analysis suggested age-related decline in the DS subjects in general intelligence and basic linguistic skills. General intelligence and mastery of linguistic concepts correlated negatively with the volume of the parahippocampal gyrus. There was no relationship between total brain size and the cognitive variables.

Multiple-dose efficacy comparison of the two topical carbonic anhydrase inhibitors sezolamide and MK-927.

The multiple-dose twice-daily efficacy of the topical carbonic anhydrase inhibitor MK-927, a racemic compound, was compared with that of its pharmacologically more active S-enantiomer in a four-center, double-masked, randomized, placebo-controlled, parallel study of 1.8% sezolamide hydrochloride (MK-417), 2% MK-927, and placebo, given twice daily to 48 patients with bilateral primary open angle glaucoma or ocular hypertension and morning intraocular pressure greater than 24 mm Hg in both eyes following washout of ocular hypotensive medications. Parallel 10-hour modified diurnal curves were performed before the study and on day 14, with 4-hour curves on days 1 and 4. Both compounds demonstrated significant lowering of intraocular pressure at 8 AM, 12 hours following the evening dose, and through 10 and 6 hours following the 8 AM dose for sezolamide and MK-927, respectively. Morning trough (evening) activity as measured by mean percent change in intraocular pressure from prestudy was -9.2% for sezolamide and -11.1% for MK-927 (-13.5% and -9.6%); peak effect occurred 2 hours after dose administration and was -19.4% and -19.2% for sezolamide and MK-927, respectively. From 2 hours after dose administration, sezolamide consistently demonstrated a slightly greater decrease in intraocular pressure than MK-927; however, these differences were not statistically significant.

Results of cataract surgery and implantation of a compressible disc lens in patients with glaucoma.

We studied the efficacy and postoperative behavior of a compressible disc posterior chamber intraocular lens in 40 eyes of 33 glaucoma patients. They had a mean follow-up of 12.8 months. Postoperatively, 38 eyes (95%) had a best corrected visual acuity of 20/40 or better. Minor decentration occurred in one case. Early posterior capsule fibrosis (40%) was 50% less than in earlier reports on the rigid Galand disc IOL. Posterior synechias were present in 35% of eyes. Postoperative complications such as pupil capture (0%) and significant posterior capsule opacification (12.5%) were minimized by using this IOL. Closed-loop circular lenses are an attractive alternative to open-loop-supported IOLs in patients with glaucoma.

Lens extraction for uncontrolled angle-closure glaucoma: long-term follow-up.

PURPOSE: To evaluate the long-term effects of extraction of incipient cataracts or clear lenses on glaucoma control in patients with subacute or chronic angle-closure glaucoma. SETTING: Department of Ophthalmology, University of Amsterdam, The Netherlands. METHODS: This retrospective analysis comprised 22 extracapsular lens extractions with implantation of a posterior chamber intraocular lens in 18 patients with chronic or subacute angle-closure glaucoma (Group 1). The effect of glaucoma control was evaluated using visual field examination, diurnal intraocular pressure (IOP) curves, gonioscopic appearance, and number of antiglaucoma medications. The results were compared with those in 25 eyes of 19 patients with chronic angle-closure glaucoma in whom a filtering procedure was performed (Group 2). RESULTS: Glaucoma control was achieved in 15 eyes (68%) in Group 1 and in 17 eyes (68%) in Group 2. Mean preoperative IOP was 27.9 mm Hg +/- 8.1 (SD) and 29.0 +/- 7.7 mm Hg, respectively. Mean postoperative IOP was 17.1 +/- 2.9 mm Hg (Group 1) and 14.8 +/- 6.6 mm Hg (Group 2) after a mean follow-up of 52.6 and 58.9 months, respectively. Mean number of ocular hypotensive medications preoperatively was 2.3 +/- 0.8 in Group 1 and 2.2 +/- 0.8 in Group 2 and at last follow-up, 1.3 +/- 0.7 and 0.52 +/- 0.8, respectively. Twenty eyes (91%) in Group 1 had the same or better final visual acuity than before surgery. In Group 2, the final visual acuity was unchanged or better in 13 eyes (52%) and worse in 12 eyes (48%); subsequent cataract surgery was performed in 9 (75%) of these 12 eyes. Additional incisional surgery was done or recommended in 6 eyes (27%) in Group 1 and 20 eyes in Group 2 (80%). CONCLUSION: Drainage surgery in patients with angle-closure glaucoma proved to be associated with multiple surgical interventions and deterioration in visual function. The choice of first a cataract procedure with the option of a future trabeculectomy may be a more attractive approach in patients with subacute or chronic angle-closure glaucoma than trabeculectomy followed by an optional cataract procedure.

Early posterior capsular opacification after intercapsular cataract extraction and rigid Galand disc intraocular lens implantation.

From retrospective studies of implantation of the rigid Galand disc intraocular lens (IOL) and the Sinskey style J-loop IOL, we found that posterior capsular opacification was more common and developed faster in eyes implanted with a Galand disc IOL than in eyes implanted with a Sinskey style J-loop IOL. We investigated this further in a clinical study of 20 patients implanted with a Galand disc IOL. We found a specific type of posterior capsular haze, resembling a "moon landscape," in 10 (50%) of the 16 eyes (80%) with capsular fibrosis.

The surgical management of chronic hypotony due to uveitis.

PURPOSE: Evaluate surgery in chronic hypotony secondary to uveitis. METHOD: Retrospective analysis of six patients operated for chronic hypotony (< or =5 mmHg) of at least 1 month's duration. Surgery involved removal of all traction and membranes on the ciliary processes. Use of oil was limited to patients with atrophic ciliary processes. RESULTS: The average postoperative follow-up was 24 months (12-43). The average pressure increase was 7 mmHg at 6 months. Four of six uveitis patients had significantly increased vision. CONCLUSION: Improved vision, and a sustained pressure rise are possible in hypotonous uveitis. The presence of ciliary processes is necessary. However, they do not need to be intact.

Uncontrolled primary angle closure glaucoma: results of early intercapsular cataract extraction and posterior chamber lens implantation.

In this study we retrospectively evaluated the effect of intercapsular or extracapsular cataract extraction and posterior chamber lens implantation in 67 eyes of 57 patients with different types of primary angle closure glaucoma (PACG) in combination with cataract. We subdivided this patient population into three groups, based on the preoperative methods of intraocular pressure (IOP) control. The best results were obtained in patients with acute PACG (55% IOP reduction) and in patients with uncontrolled PACG (44% IOP reduction). In the other PACG groups an IOP reduction of between 20 and 33% was achieved. A long-term postoperative IOP of less than 21 mmHg was established in 63 eyes or 94%. In 91% the glaucoma medication was reduced, 65% of all eyes needed no glaucoma medication postoperatively. We conclude that an intercapsular cataract extraction with PC-IOL implantation should be considered in both controlled and uncontrolled PACG in patients with cataract, instead of filtering surgery or combined procedures. Even in eyes with relatively good visual acuity, cataract extraction might be considered as a means of achieving glaucoma control.

Intercapsular cataract extraction with implantation of the Galand disc lens: a retrospective analysis in patients with and without glaucoma.

We studied the results of intercapsular cataract extraction and implantation of the rigid Galand disc intraocular lens (IOL) in 164 cataract patients with and without glaucoma. Eighty-eight percent of the glaucomatous eyes and 98% of the eyes without glaucoma had a postoperative visual acuity of 20/40 or better after best-case analysis. Intercapsular bag placement appeared satisfactory in all but two cases, in which the IOL was slightly tilted. Cataract extraction favorably affected glaucoma control, especially in patients with angle-closure glaucoma (7.3 mm Hg intraocular pressure [IOP] reduction) and in those with primary open-angle glaucoma (2.6 mm Hg IOP reduction). The complications encountered, cystoid macular edema and hyphema, occurred in 1% and 0.5% respectively, and were not more frequent in the glaucoma subgroup. Posterior capsular opacification (30%) and inflammatory complications such as posterior synechiae (7.6%) and prepupillary fibrin (6%) were more often noted in the glaucomatous eyes. Pupillary capture or significant IOL decentration did not occur. We conclude that a circular type of IOL is the best currently available lens for use in glaucoma patients.

Astigmatism following cataract surgery: comparison of a scleral and a corneal incision in a mixed group of patients with and without glaucoma.

We retrospectively analysed the course of postoperative corneal astigmatism and corrected visual acuity after extracapsular cataract extraction and posterior chamber lens implantation with either a corneal or a scleral incision in 170 eyes of 155 patients with and without glaucoma. A continuous 10/0 nylon shoelace suture was used for wound closure in two groups. In a third group, corneal wound closure was performed with a shorter shoelace suture in combination with two vicryl wing sutures at 11 and 1 o'clock. Although early postoperative mean astigmatism in eyes operated through a corneal incision was high (range 2.92-6.67 diopters at 1 month postoperatively) and significantly different when compared to eyes operated through a scleral incision (1.96 diopters), final mean astigmatism did not differ significantly between those two groups. Moreover, in 27% of eyes operated through a corneal incision, mean astigmatism at 2 months postoperatively was not significantly different from the scleral group and suture removal was not necessary. There was no statistically significant difference in corrected visual acuity over the entire study period between groups. Since safety and functional results of the corneal incision were not different from the scleral incision, we prefer a corneal incision in cataract surgery because of its surgical advantages, especially in patients with cataract and coexisting glaucoma.