Severe outcomes following pediatric cannabis intoxication: a prospective cohort study of an international toxicology surveillance registry

INTRODUCTION

An increasing number of jurisdictions have legalized recreational cannabis for adult use. The subsequent availability and marketing of recreational cannabis has led to a parallel increase in rates and severity of pediatric cannabis intoxications. We explored predictors of severe outcomes in pediatric patients who presented to the emergency department with cannabis intoxication.

METHODS

In this prospective cohort study, we collected data on all pediatric patients (<18 years) who presented with cannabis intoxication from August 2017 through June 2020 to participating sites in the Toxicology Investigators Consortium. In cases that involved polysubstance exposure, patients were included if cannabis was a significant contributing agent. The primary outcome was a composite severe outcome endpoint, defined as an intensive care unit admission or in-hospital death. Covariates included relevant sociodemographic and exposure characteristics.

RESULTS

One hundred and thirty-eight pediatric patients (54% males, median age 14.0 years, interquartile range 3.7-16.0) presented to a participating emergency department with cannabis intoxication. Fifty-two patients (38%) were admitted to an intensive care unit, including one patient who died. In the multivariable logistic regression analysis, polysubstance ingestion (adjusted odds ratio = 16.3; 95% confidence interval: 4.6-58.3; P < 0.001)) and cannabis edibles ingestion (adjusted odds ratio = 5.5; 95% confidence interval: 1.9-15.9; P = 0.001) were strong independent predictors of severe outcome. In an age-stratified regression analysis, in children older than >10 years, only polysubstance abuse remained an independent predictor for the severe outcome (adjusted odds ratio 37.1; 95% confidence interval: 6.2-221.2; P < 0.001). As all children 10 years and younger ingested edibles, a dedicated multivariable analysis could not be performed (unadjusted odds ratio 3.3; 95% confidence interval: 1.6-6.7).

CONCLUSIONS

Severe outcomes occurred for different reasons and were largely associated with the patient's age. Young children, all of whom were exposed to edibles, were at higher risk of severe outcomes. Teenagers with severe outcomes were frequently involved in polysubstance exposure, while psychosocial factors may have played a role.

POS0576 ASSOCIATION BETWEEN POTENTIAL PROGNOSTIC FACTORS AND ADVERSE HEALTH OUTCOMES IN RHEUMATOID ARTHRITIS: A STUDY OF 5658 UK BIOBANK PARTICIPANTS

Background

There is a pressing need to identify simple prognostic factors, which are readily available in primary and secondary care settings, that can predict adverse health outcomes in people with rheumatoid arthritis (RA). Exploring various clinical, physiological and patient-reported measures as prognostic factors may enhance risk stratification and promote more personalised care for RA patients.

Objectives

To determine the association, if any, between selected prognostic factors and all-cause mortality and major adverse cardiovascular events (MACE; including myocardial infarction and stroke) in an RA population.

Methods

UK Biobank participants that self-reported RA were included in this study. Prognostic factors were selected from the literature based on relevance, predictive potential, simplicity and accessibility in a primary/secondary care setting. Those included were categorised into the following domains: anthropometric measures (body mass index (BMI), body fat percentage, waist circumference, waist-to-hip ratio), functional measures (hand grip strength (HGS), usual walking pace (UWP)), inflammatory markers (C-reactive protein (CRP)), patient-reported measures (pain), physiological measures (blood pressure (BP), heart rate (HR)) and serological markers (rheumatoid factor (RF)), with normal ranges used as reference categories. Associations between individual factors and outcomes were explored using Cox proportional hazards models. Models were adjusted for age, sex, socioeconomic status, number of additional long-term conditions and smoking status in the first instance to identify potential individual predictors. Models were then further adjusted for any identified individual predictors to determine the most important prognostic factors.

Results

5658 (1.1%) UK Biobank participants self-reported RA (mean age 59 (standard deviation 7.13); 69.8% female). 670 deaths (median 11 years) and 370 MACE (median 8 years) were recorded during the follow-up period. Several significant individual associations with all-cause mortality (Figure 1A) and MACE (Figure 1B) were found. After further adjustment for these significant individual predictors, the following factors demonstrated significant associations with risk of all-cause mortality, independent of the other significant predictors: underweight BMI (<18.5kg/m2) (hazard ratio (HR) 2.96 [95% confidence intervals (CI) 1.59-5.51]), obese BMI (≥30.0kg/m2) (HR 0.52 [95% CI 0.36-0.76]), 3-10mg/L CRP (HR 1.41 [95% CI 1.14-1.75]), >10mg/L CRP (HR 1.77 [95% CI 1.39-2.26]), low HGS (<16kg female or <27kg male) (HR 1.28 [95% CI 1.05-1.56]) and slow UWP (patient-reported) (HR 1.31 [95% CI 1.06-1.62]). Likewise, the following factors were found to be significantly associated with MACE, independent of other significant factors: >10mg/L CRP (HR 1.62 [95% CI 1.19-2.20]), low HGS (HR 1.61 [95% CI 1.26-2.07]) and slow UWP (HR 1.50 [95 % CI 1.15-1.97]).

Conclusion

In this RA population, the risk of all-cause mortality was approximately three-fold higher in those who have an underweight BMI when compared to those who have a BMI in the normal range, when adjusted for all other significant factors, while an obese BMI appeared to lower this risk, consistent with the “obesity paradox” reported in RA [1]. Increased levels of CRP, low HGS and slow UWP were also all independently associated with an increased risk of all-cause mortality and MACE. Our findings highlight the potential value of these factors for predicting adverse outcomes in RA populations. A simple, yet multidimensional approach to risk assessment, combining well-tolerated, easily repeatable measures such as those included here may provide important prognostic information at both primary and secondary care levels, while limiting excessive and overly invasive testing on RA patients.

References

[1]Wolfe F, Michaud K. Effect of body mass index on mortality and clinical status in rheumatoid arthritis. Arthritis Care Res (Hoboken). 2012; 64(10): 1471-1479. doi:10.1002/acr.21627

Acknowledgements

This work is supported by the Medical Research Council [grant number: MR/N013166/1].

Disclosure of Interests

Jordan Canning: None declared, Stefan Siebert Grant/research support from: Departmental research grants/support from: AbbVie, Amgen, Boehringer Ingelheim, Bristol Myers Squibb, GSK, Janssen, Novartis and UCB., Bhautesh Jani: None declared, Frances Mair: None declared, Barbara Nicholl: None declared.

Predictors of severe outcome following opioid intoxication in children

INTRODUCTION

While the opioid crisis has claimed the lives of nearly 500,000 in the U.S. over the past two decades, and pediatric cases of opioid intoxications are increasing, only sparse data exist regarding risk factors for severe outcome in children following an opioid intoxication. We explore predictors of severe outcome (i.e., intensive care unit [ICU] admission or in-hospital death) in children who presented to the Emergency Department with an opioid intoxication.

METHODS

In this prospective cohort study we collected data on all children (0-18 years) who presented with an opioid intoxication to the 50 medical centers in the US and two international centers affiliated with the Toxicology Investigators Consortium (ToxIC) of the American College of Medical Toxicology, from August 2017 through June 2020, and who received a bedside consultation by a medical toxicologist. We collected relevant demographic, clinical, management, disposition, and outcome data, and we conducted a multivariable logistic regression analysis to explore predictors of severe outcome. The primary outcome was a composite severe outcome endpoint, defined as ICU admission or in-hospital death. Covariates included sociodemographic, exposure and clinical characteristics.

RESULTS

Of the 165 (87 females, 52.7%) children with an opioid intoxication, 89 (53.9%) were admitted to ICU or died during hospitalization, and 76 did not meet these criteria. Seventy-four (44.8%) children were exposed to opioids prescribed to family members. Fentanyl exposure (adjusted OR [aOR] = 3.6, 95% CI: 1.0-11.6; p = 0.03) and age ≥10 years (aOR = 2.5, 95% CI: 1.2-4.8; p = 0.01) were independent predictors of severe outcome.

CONCLUSIONS

Children with an opioid toxicity that have been exposed to fentanyl and those aged ≥10 years had 3.6 and 2.5 higher odds of ICU admission or death, respectively, than those without these characteristics. Prevention efforts should target these risk factors to mitigate poor outcomes in children with an opioid intoxication.

Early Experience with Crotalidae Immune F(ab')2 Antivenom to Treat Arizona Rattlesnake Envenomations

INTRODUCTION

Crotalidae immune F(ab')₂ (Fab2AV) became available in the USA in 2019 for treatment of rattlesnake envenomation. In the clinical trial comparing Fab2AV to crotalidae immune polyvalent fab (FabAV), Fab2AV was associated with less late hemotoxicity. The purpose of this study was to describe outcomes following use of Fab2AV in patients with rattlesnake envenomation in Arizona.

METHODS

This is an observational study of patients admitted to a medical toxicology service at two hospitals in Arizona between January 1, 2019 and December 31, 2020. Patients with rattlesnake envenomation who received Fab2AV were included. Patients who received FabAV, alone or in combination with Fab2AV, were excluded. The main outcomes of interest were antivenom dose, adverse reactions, late hemotoxicity, and hospital readmission or retreatment.

RESULTS

Forty-six patients were included. The mean age was 40 years, with 15% under 12 years of age. All exhibited swelling, 20% thrombocytopenia, and 35% coagulopathy. Median time to treatment was 3 h and median total Fab2AV dose was 20 vials. Three patients had an acute reaction to Fab2AV which was non-life-threatening and resolved with antihistamines and/or steroids. In the follow-up period, one case of delayed thrombocytopenia (platelets = 108 K/mm³) and one case of recurrent thrombocytopenia (platelets = 111 K/mm³) were identified. There was no late coagulopathy. Five patients reported symptoms consistent with mild serum sickness.

CONCLUSIONS

In this series of patients with rattlesnake envenomation in Arizona who were treated with Fab2AV, there were no cases of clinically significant late hemotoxicity, and no patients required late retreatment with antivenom. Acute and delayed reactions did occur in some patients but were mild and easily treated.

AB0240 EXAMINING THE RELATIONSHIP BETWEEN RHEUMATOID ARTHRITIS, MULTIMORBIDITY AND ADVERSE HEALTH-RELATED OUTCOMES: A SYSTEMATIC REVIEW

Background:

Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterised by inflammation of the synovial joints causing pain, swelling and stiffness. Multimorbidity (the presence of two or more long-term conditions) affects approximately two thirds of people with RA. However, the relationship between RA and multimorbidity is poorly understand, as is the effect of this relationship on mortality and other health-related outcomes, particularly those relating to physical functioning and well-being.

Objectives:

To explore existing literature to determine what is known about the effect, if any, of multimorbidity on mortality and other health-related outcomes in people with RA.

Methods:

A systematic review was conducted following a protocol prepared using PRISMA-P 2015 reporting guidelines, ensuring the quality of the review. Studies were sourced from electronic medical databases, specifically MEDLINE, Embase, CINAHL, PsycINFO, The Cochrane Library and Scopus, using a pre-defined search strategy. Studies were selected based on specified eligibility criteria and quality appraised using the Cochrane Prognosis Methods Group-developed, Quality in Prognostic Studies (QUIPS) tool. A narrative synthesis of findings was conducted.

Results:

In total, 15 studies fulfilled our criteria for inclusion in our review. Of these, 7 studies had mortality as an outcome, with 6 reporting a significant association between multimorbidity and increased risk of all-cause mortality in people with RA. Nine studies had functional status/disability as an outcome, with 2 of these studies also including quality of life. All 9 studies reported significant associations between multimorbidity and the aforementioned health-related outcomes, demonstrating poorer functional status/increased disability and reduced quality of life in people with RA and multimorbidity.

Conclusion:

Multimorbidity in people with RA is significantly associated with increased mortality and poor health-related outcomes in current literature. A better understanding of this relationship will provide an important foundation of knowledge to guide future health service design.

Acknowledgments:

This work was supported by the Medical Research Council (MRC) [Grant Reference: MR/N013166/1].

Disclosure of Interests:

Jordan Canning: None declared, Stefan Siebert Grant/research support from: BMS, Boehringer Ingelheim, Celgene, GlaxoSmithKline, Janssen, Novartis, Pfizer, UCB, Consultant of: AbbVie, Boehringer Ingelheim, Janssen, Novartis, Pfizer, UCB, Speakers bureau: AbbVie, Celgene, Janssen, Novartis, Bhautesh Jani: None declared, Frances Mair: None declared, Barbara Nicholl: None declared

Correction: Water on Au sputtered films

Correction for ‘Water on Au sputtered films’ by J. Canning et al., Chem. Commun., 2014, 50, 9172–9175.

Picosecond 554 nm yellow-green fiber laser source with average power over 1 W

We demonstrate a source of 554 nm pulses with 2.7 ps pulse duration and 1.41 W average power, at a repetition rate of 300 MHz. The yellow-green pulse train is generated from the second harmonic of a 1.11 μm fiber laser source in periodically-poled stoichiometric LiTaO3. A total fundamental power of 2.52 W was used, giving a conversion efficiency of 56%.

Long-period gratings for selective monitoring of loads on a wind turbine blade

An optical fiber sensor based on long-period gratings (LPG) for selective measurements of flap- and edge-wise bending of a wind turbine blade is presented. Two consecutive LPGs separated by 40 mm interfere to improve resolution and reduce noise in a D-shaped fiber. The mode profile of the device was characterized experimentally to provide a model describing the mode couplings. The sensor was tested on a wind turbine blade.

Water on Au sputtered films

Transient changes in the contact angle, Δθ ∼ 10°, of water on gold (Au) reveal reversible wetting of near hydrophobic Au films.

Toxicology in the ICU: part 3: natural toxins

This is the third article of a three-part series that reviews the care of poisoned patients in the ICU. This article focuses on natural toxins, such as heavy metals and those produced by plants, mushrooms, arthropods, and snakes. The first article discussed the general approach to the patient, including laboratory testing; the second article focused on specific toxic agents, grouped into categories.

Characterization of nanoscale features in tapered fractal and photonic crystal fibers

The internal structure of nanostructured air-silica fiber probes have been characterized using a combined focused ion beam and scanning electron microscopy technique. The collapse rate of the air-holes is shown to differ substantially between a regular photonic crystal fiber (PCF) and the quasi-periodic Fractal fiber. The integrity of the Fractal fiber structure is maintained down to an outer diameter as small as 120 nm, whereas the air-holes of the regular PCF begin to collapse when the outer diameter is approximately 820 nm. The observed smallest hole diameter of 10 nm is suggested to be due to physical limits imposed by the molecular structure of silica. These results confirm structural inferences made in previous publications.

A study of regenerated gratings produced in germanosilicate fibers by high temperature annealing

In light of recent proposals linking structural change and stresses within regenerated gratings, the details of regeneration of a seed Type-I Bragg grating written in H2 loaded germanosilicate fiber annealed at high temperatures (~900°C) are systematically explored. In particular, the influence of the strength of the grating, the effect of GeO2 doping concentration and the annealing conditions on regeneration are studied. We show that the role of dopants such as Ge and F contribute nothing to the regeneration, consistent with previous results. Rather, they may potentially be detrimental. Strongest regenerated gratings with R ~35% from a 5mm seed grating could be obtained in fibres with the lowest GeO2 concentrations such as standard telecommunications-compatible grade fibre.

Mode-locked picosecond pulse generation from an octave-spanning supercontinuum

We generate mode-locked picosecond pulses near 1110 nm by spectrally slicing and reamplifying an octave-spanning supercontinuum source pumped at 1550 nm. The 1110 nm pulses are near transform-limited, with 1.7 ps duration over their 1.2 nm bandwidth, and exhibit high interpulse coherence. Both the supercontinuum source and the pulse synthesis system are implemented completely in fiber. The versatile source construction suggests that pulse synthesis from sliced supercontinuum may be a useful technique across the 1000 - 2000 nm wavelength range.

Metal-free scanning optical microscopy with a fractal fiber probe

Scanning Near-field Optical Microscopy (SNOM) is the leading instrument used to image optical fields on the nanometer scale. A metal-coating is typically applied to SNOM probes to define a subwavelength aperture and minimize optical leakage, but the presence of such coatings in the near field of the sample can often cause a substantial change in the sample emission properties. For the first time, the authors demonstrate near-field imaging on a metal substrate with a metal-free probe made from a novel structured optical fiber, designed to maximize optical throughput and potentially remove the need for the metal.

White light sources based on multiple precision selective micro-filling of structured optical waveguides

Multiple precision selective micro-filling of a structured optical fibre using three luminescent dyes enables the simultaneous capture of red, blue and green luminescence within the core to generate white light. The technology opens up a new approach to integration and superposition of the properties of multiple materials to create unique composite properties within structured waveguides.

A fractal-based fibre for ultra-high throughput optical probes

A core component of all scanning near-field optical microscopy (SNOM) systems is the optical probe, which has evolved greatly but still represents the limiting component for the system. Here, we introduce a new type of optical probe, based on a Fractal Fibre which is a special class of photonic crystal fibre (PCF), to directly address the issue of increasing the optical throughput in SNOM probes. Optical measurements through the Fractal Fibre probes have shown superior power levels to that of conventional SNOM probes. The results presented in this paper suggest that a novel fibre design is critical in order to maximize the potential of the SNOM.

Impact of water and ice 1h formation in a photonic crystal fiber grating

The impact of ice 1h formation inside the holes of a photonic crystal fiber Bragg grating was analyzed and discussed. As a result of the ice's expansion, a broadening of the grating spectrum was observed that corresponds to internal microbending of the fiber and after some temperature cycling leads to failure of the fiber. An analytical model with which to estimate the internal compression forces is proposed, and the calculated values are found to be in agreement with reported data.

Exposure and characterization of nano-structured hole arrays in tapered photonic crystal fibers using a combined FIB/SEM technique

This paper presents a technique to expose and characterize nano-structured hole arrays in tapered photonic crystal fibers. Hole array structures are examined with taper outer diameters ranging from 12.9 microm to 1.6 microm. A combined focused ion beam milling and scanning electron microscope system was used to expose and characterize the arrayed air-silica structures. Results from this combined technique are presented which resolve hole-to-hole pitch sizes and hole diameters in the order of 120 nm and 60 nm, respectively.

Diffraction in air-clad fibres

The angular transmissivity of high numerical aperture air-clad fibres is measured as a function of skewness of the launched light. Within the experimental limits the measured transmissivity of skew rays is significantly lower compared to theoretical predictions for air-clad fibres with uniform cladding surfaces. The discrepancy is attributed to diffractive losses of skew rays from the periodic corrugations at the pump core-cladding air interface.

Thermal hypersensitisation and grating evolution in Ge-doped optical fibre

Low temperature (sub 1000 degrees C) thermal hypersensitisation is reported in germanosilicate optical waveguides. Gratings are written using a CW 266nm laser source. In contrast to laser hypersensitisation, thermal excitation is generally dispersive involving a range of specific glass sites. More complex grating profiles presenting evidence of solid-state autocatalysis and bistability at increasingly high sensitisation temperatures are observed. More specifically, at 500 degrees C, a behaviour resembling type IIA grating response is observed.

Intermodal interference in a photonic crystal fibre

Intermodal interference in photonic crystal fibres, single mode over long lengths, is measured over a short length. Akin to conventional fibres, this poses a potential problem for practical device utilisation of photonic crystal fibres. We note that given the existing widespread fabrication capability of this fibre and indications that some commercial use in devices will come to fruition, the need for standardising measurement techniques, analogous to ITU standards for conventional fibre, specific to photonic crystal fibres will be required.

The characteristic curve and site-selective laser excitation of local relaxation in glass

The so-called characteristic curve describing photosensitivity change is elaborated and shown to be a powerful tool for understanding and characterizing photosensitive growth both at a fundamental and practical level. It has been used successfully to diagnose when optimal hypersensitization has been achieved and the physical basis for this is explained. By way of example, previous results using 355 nm hypersensitization are re-examined. Evidence of single site-selective glass relaxation through direct laser excitation offers a new approach to accessing and studying induced relaxations.

Hydrogen loading of optical waveguides by use of host diluent gases

Recent dramatic improvements in photosensitivity gas mixtures when very low hydrogen concentrations (as low as 0.1%) were used are shown to involve condensation of the host gas. The vapor pressure of the host determines the effective partial pressure of the hydrogen, and this accounts for the bulk of the observed enhancements.

All-fibre photonic crystal distributed Bragg reflector (PC-DBR) fibre laser

We describe an Er3+-doped aluminosilicate core photonic crystal fibre laser incorporating distributed Bragg reflectors written by two-photon 193nm irradiation through an optical phase mask as the feedback elements. The laser is diode pumped at 980nm and evidence of dual linewidth laser operation close to threshold is observed. However, at higher pumping levels gain competition preferentially selects one laser line.

Analysis and removal of fracture damage during and subsequent to holey fiber cleaving

The damage caused by cleaving holey fibers is investigated as a function of cleaving force. Comparisons are made with standard optical fibers and holey fibers. Optimum cleaving forces are determined for a number of holey fiber air fractions and fiber diameters. A simple technique for removing cleave damage is also presented.

Propagation in air by field superposition of scattered light within a Fresnel fiber

Propagation of light at 1.5 microm with peak intensity in an air hole is achieved within an air-silica-structured Fresnel waveguide. Thus a simpler fiber design alternative to photonic crystal fibers is possible for high-peak-power propagation with reduced nonlinear interactions. Multiple foci are observed in the far field.

Retaining and characterising nano-structure within tapered air-silica structured optical fibers

Air-silica fiber 125m in diameter has been tapered down to ~15m. At this diameter, it is commonly assumed that the nanostructured fiber holes have collapsed. Using an Atomic Force Microscope, we show this assumption to be in error, and demonstrate for the first time that structures several hundred nanometers in diameter are present, and that hole array structures are maintained. The use of Atomic Force Microscopy is shown to be an efficient way of characterising these structures.

Hypersensitization of rare-earth-doped waveguides for distributed-feedback amplifier and laser applications

Deterioration of the gain coefficient as a result of UV processing of hydrogen-loaded Er(3+) - and Er(3+)/Yb (3+) -doped silicate optical waveguides can be reduced by initial hypersensitization of the waveguide prior to bulk irradiation. This allows improved performance in active-grating devices such as distributed-feedback fiber amplifiers and lasers.

Stability of thermally hypersensitised phosphosilicate waveguides and the characteristic growth curve

Low temperature (80 0 C) hypersensitised hydrogen-loaded phosphosilicate optical fibre is found to be unstable, decaying progressively at room temperature. However, the hypersensitisation process linearises the grating growth characteristic curve. Further, a negative index contribution is inferred at low fluence in the presence of hydrogen.

Low-temperature hypersensitization of phosphosilicate waveguides in hydrogen

Conventional hydrogen loading of phosphosilicate optical fibers at relatively low temperatures (80 degrees C) is sufficient to enhance the fiber's photosensitivity after hydrogen outdiffusion, allowing permanent Bragg grating structures to be produced. Thermal sensitization is proposed to be a major contributor to stable index change.

Fabrication of long-period fiber gratings by use of focused ion-beam irradiation

Long-period gratings have been made in nonphotosensitive optical fibers by irradiation of the core of a fiber with a focused beam of high-energy protons. The irradiated fibers exhibit relatively low loss, even before thermal annealing, and possess strongly wavelength-dependent transmission. The absence of a mask provides the opportunity to tailor the grating to a desired profile, and a variety of grating profiles were explored. The profile most resembling a sinusoid was found to produce the cleanest transmission spectra.

Ultraviolet-induced absorption losses in hydrogen-loaded optical fibers and in presensitized optical fibers

Reduced hydroxyl formation in presensitized fibers exposed to cw 244-nm light after hydrogen outdiffusion is reported. The OH band in the presensitized fiber shifts toward 1390 nm. In the fully hydrogen-loaded fiber the OH band is centered at 1397 nm and does not shift with fluence.

Birefringence control in plasma-enhanced chemical vapor deposition planar waveguides by ultraviolet irradiation

Complete birefringence compensation is demonstrated in plasma-enhanced chemical vapor deposition waveguides by 193-nm postexposure. A single relaxation process dominates the decay in stress anisotropy, indicating that compressive stress from the substrate leads to an elastic stress anisotropy at the core.

Bending-induced colouring in a photonic crystal fibre

A photonic crystal fibre has been fabricated with a photonic crystal that is surrounded by a number of silica cores. Bending of the fibre induces an interaction between the core and photonic crystal areas, resulting in a highly wavelength-dependent loss of the core modes. White-light transmission experiments are presented which show that the colour of the transmitted light changes as a function of the fibre-bending radius. We compare the results to a simple model and find agreement.

Annealing properties of gratings written into UV-presensitized hydrogen-outdiffused optical fiber

Accelerated aging of gratings written in UV presensitized hydrogen outdiffused optical fibers show that these gratings are more stable than standard gratings written in hydrogen-loaded fibers. They are observed to grow initially by as much as 2%. The predicted decay after 25 years at 80 degrees C is ~0.1% . The results suggest that the index modulation decay is so slow that postfabrication annealing can be avoided.

Carbon dioxide laser-assisted poling of silicate-based optical fibers

A novel poling method, carbon dioxide laser-assisted poling (CLAP), is demonstrated. Localized heating during CLAP is achieved through silicate absorption of the CO>(2) laser radiation. Electro-optic coefficients of 0.2 pm/V are achieved within a 55-s scan of a twin-hole fiber. It is shown that there is a range of CO>(2) laser powers for which the residual electro-optic coefficient is maximized.

Engineering large anisotropy in amorphous glass

By exploiting the strain-related rollover thresholds that occur between UV-induced positive and negative index regimes in germanosilica glass it is possible to engineer large anisotropy into the structure. This is qualitatively analyzed for a planar waveguide and has been confirmed experimentally. However, the technique described here is not confined to waveguide devices and can in principle be applied to any glass structure that is capable of undergoing strain-sensitive transitions.

Locking in photosensitivity within optical fiber and planar waveguides by ultraviolet preexposure

Strong photosensitivity is locked in permanently after hydrogen outdiffusion of hydrogen-loaded waveguides presensitized with UV light by either pulsed 193-nm or cw 244-nm laser output.

Correlation of ultraviolet-induced stress changes and negative index growth in type IIa germanosilicate waveguide gratings

The stress anisotropy in planar germanosilicate waveguides is used to follow the changes in stress, measured as a birefringence, with UV irradiation. Compressive stress increases with the growth of the negative index grating, saturating when the grating modulation saturates.

High-temperature stable gratings in germanosilicate planar waveguides

Negative index gratings in planar germanosilicate waveguides were found to be stable up to 500 degrees C. The annealing properties are similar to those of negative index fiber gratings.

Grating-based transmission bandpass filters using dispersion-matched mode conversion

A narrow-bandpass filter with a 15-dB signal-to-noise level is demonstrated using Bragg-grating assisted mode conversion within a tapered waveguide. The potential effects of such filters in wavelength-division multiplexing systems are discussed.

Complex photosensitivity observed in germanosilica planar waveguides

Photosensitive effects distinguished as type I and type IIA photosensitivity within optical fibers were observed in a much more pronounced form within germanosilica waveguides deposited by hollow-cathode plasma-enhanced chemical-vapor deposition. With increasing exposure to 193-nm UV light, positive index changes greater than 2 x 10(-3) were observed, followed by negative index changes greater than -5 x 10(-3) . These behaviors are attributed to an increase in macroscopic polarizability and a reduction in material density, respectively. The negative index change is more temperature resistant and is fully annealed only at 900 degrees C, whereas the positive one is annealed at 500 degrees C.

Characterization of apodized fiber Bragg gratings for rejection filter applications

Apodized fiber Bragg gratings with > or = 30-dB sidelobe suppression +/-1 nm from the Bragg center wavelength are spatially characterized with side-scatter and side-diffraction techniques. Resonant side scatter is suppressed, indicating that little dispersion arises from reflections off the grating boundaries.

Modal interferometer for in situ measurements of induced core index change in optical fibers

A simple interferometer based on modal interference is described. Without compromising interferometer stability it is possible to measure index changes of less than 1 x 10(-6).

Incoherent scattering losses in optical fiber Bragg gratings

Scattered-light losses from UV-processed optical fibers and optical fiber Bragg gratings are investigated for wavelengths in the vicinity of the Bragg wavelength. Broadband incoherent scattering loss arising from nonuniform grating elements was measured ranging from 5 x 10(-5) to 0.2 dB/cm, depending on fiber type and (or) processing conditions. Asymmetry of the radially scattered-light profile is consistent with the grating elements' being localized to within a few micrometers of the core -cladding interface.

Rayleigh longitudinal profiling of optical resonances within waveguide grating structures using sidescattered light

The resonant characteristics of Bragg gratings in fibers are characterized by measurement of the wavelength dependence of the Rayleigh scattering of light propagating in the core along the grating length. This technique is found to give information on the standing-wave intensity profile in the grating that cannot be deduced from the standard transmission or reflection spectra.