Optical pulse generation and signal processing for the development of high-speed OTDM networks

Due to the continued growth of the Internet and the introduction of new broadband services, it is anticipated that individual channel data rates may exceed lOOGbit/s in the next 5-10 years. In order to operate at such high line rates new techniques for optical pulse generation and optical signal processing will have to be developed. As the overall data rate of an OTDM network is essentially determined by the temporal separation between data channels, an optical pulse source that is capable of producing ultra-short optical pulses at a high repetition rate and with wavelength tunability will be important, not only for OTDM, but for vanous applications in WDM and hybrid WDM/OTDM networks. This work demonstrates that by using the gain-switching technique, commercially available laser diodes can be used in the development of nearly transform-limited optical pulses that are wavelength tunable over nearly 65nm with durations ranging from 12-30ps and a Side-Mode Suppression Ratio (SMSR) exceeding 60dB. New optical signal processing techniques will also have to be developed in order to operate at individual data rates in excess of lOOGbit/s. Only nonlinear optical effects, present in fibres, semiconductors and optical crystals, can be employed as these occur on time scales in the order of a few-femtoseconds (10“15 5), with an example being Two-Photon Absorption (TPA) in semiconductors. This thesis describes a specially designed microcavity that can enhance the Two-Photon Absorption (TPA) response by over three orders of magnitude at specific wavelengths. A theoretical model demonstrating error-free demultiplexing of a 250Gbit/s OTDM signal via a TPA microcavity has been developed. Experimental work is also presented demonstrating the use of a TPA microcavity for optical sampling of 100GHz signals with a temporal resolution of 1 ps9 and system sensitivity of 0 009 (mW)2 This value for the sensitivity is the lowest ever reported for a TPA-based sampling system

Generation of wavelength tunable optical pulses with SMSR exceeding 50 dB by self-seeding a gain-switched source containing two FP lasers

In this letter, we show the generation of shorter pulses (∼20 ps) that exhibit side mode suppression ratios (SMSR's) greater than 50 dB and wider tuning range (48.91 nm). Our technique is based on the self-seeding of a gain-switched source containing two FP lasers

Simulation of all-optical demultiplexing utilizing two-photon absorption in semiconductor devices for high-speed OTDM networks

The performance of a two-photon absorption (TPA) based demultiplexer in an OTDM communication system is modeled. The demultiplexer is evaluated by comparing the electrical BER of the demultiplexed and detected channel to the optical BER of the signal before the demultiplexer. An error-free demultiplexing of a 250 Gbit/s signal (25 × 10 Gbit/s channels) is shown, using a 30:1 control-to-signal peak power ratio, with a TPA device with a bandwidth of 20 GHz should be possible. The device that is fabricated for TPA is a GaAs/AlAs PIN microcavity photodetector grown on a GaAs substrate

High-speed chromatic dispersion monitoring of a two-channel WDM system using a single TPA microcavity

Chromatic dispersion monitoring of two 160 Gb/s wavelength channels using a TPA Microcavity is presented. As the microcavity exhibits a wavelength resonance characteristic, a single device could monitor a number of different WDM-channels sequentially

High Morbidity during Treatment and Residual Pulmonary Disability in Pulmonary Tuberculosis: Under-Recognised Phenomena

BACKGROUND In pulmonary tuberculosis (PTB), morbidity during treatment and residual pulmonary disability can be under-estimated. METHODS Among adults with smear-positive PTB at an outpatient clinic in Papua, Indonesia, we assessed morbidity at baseline and during treatment, and 6-month residual disability, by measuring functional capacity (six-minute walk test [6MWT] and pulmonary function), quality of life (St George's Respiratory Questionnaire [SGRQ]) and Adverse Events ([AE]: new symptoms not present at outset). Results were compared with findings in locally-recruited volunteers. RESULTS 200 PTB patients and 40 volunteers were enrolled. 6WMT was 497m (interquartile range 460-529) in controls versus 408m (IQR 346-450) in PTB patients at baseline (p<0.0001) and 470m (IQR 418-515) in PTB patients after 6 months (p=0.02 versus controls). SGRQ total score was 0 units (IQR 0-2.9) in controls, versus 36.9 (27.4-52.8) in PTB patients at baseline (p<0.0001) and 4.3 (1.7-8.8) by 6 months (p<0.0001). Mean percentage of predicted FEV1 was 92% (standard deviation 19.9) in controls, versus 63% (19.4) in PTB patients at baseline (p<0.0001) and 71% (17.5) by 6 months (p<0.0001). After 6 months, 27% of TB patients still had at least moderate-severe pulmonary function impairment, and 57% still had respiratory symptoms, despite most achieving 'successful' treatment outcomes, and reporting good quality of life. More-advanced disease at baseline (longer illness duration, worse baseline X-ray) and HIV positivity predicted residual disability. AE at any time during treatment were common: itch 59%, arthralgia 58%, headache 40%, nausea 33%, vomiting 16%. CONCLUSION We found high 6-month residual pulmonary disability and high AE rates. Although PTB treatment is highly successful, the extent of morbidity during treatment and residual impairment could be overlooked if not specifically sought. Calculations of PTB-related burden of disease should acknowledge that TB-related morbidity does not stop at 6 months. Early case detection and treatment are key in minimising residual impairment.The study received funding from the Australian Respiratory Council, Royal Australasian College of Physicians (Covance Award to APR), National Health and Medical Research Council (NHMRC) of Australia (Grants 605806 and 496600, a scholarship to APR, and fellowships to APR, TWY, PMK, NMA). Graeme Maguire is supported by an NHMRC Practitioner Fellowship and the Margaret Ross Chair in Indigenous Health. Views expressed in this publication are those of the authors and do not reflect the views of NHMRC. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Wavelength tuneable pulse monitoring using a Two-Photon-Absorption microcavity

Two Photon Absorption (TPA) is a non-linear optical-to-electrical conversion process that can be significantly enhanced by placing the active region within a resonance microcavity. The experiment confirmed the potential use of the microcavity structure for monitoring a single channel in multi-wavelength systems. The cavity can be designed for different applications depending on desired resonance width or cavity life time allowing the contrast ratio to be further improved. Due to the possibility of tuning the resonance wavelength by cavity tilting, a single device can be used to monitor a number of WDM channels without the need for additional optical filters

Dispersion insensitive, high-speed optical clock recovery based on a mode-locked laser diode

An investigation into the effects of varying levels of chromatic dispersion on a mode- locked laser diode optical clock recovery process is presented. Results demonstrate that this technique is invariant to input dispersion varying between +75 ps/nm

Resonance tuning of two-photon absorption microcavities for wavelength-selective pulse monitoring

We show the potential use of a single photodetector for multichannel pulse monitoring. Two-photon absorption in a microcavity structure is used as the nonlinear optical technique for pulse monitoring. Angle tuning of the device allows the resonance to be tuned. For the device studied here that is optimized for 2-ps pulses, a possible tuning range of 55 nm is shown

Optical signal processing via two-photon absorption in a semiconductor microcavity for the next generation of high-speed optical communications network

Due to the introduction of new broadband services, individual line data rates are expected to exceed 100 Gb/s in the near future. To operate at these high speeds, new optical signal processing techniques will have to be developed. This paper will demonstrate that two-photon absorption in a specially designed semiconductor microcavity is an ideal candidate for optical signal processing applications such as autocorrelation, sampling, and demultiplexing in high-speed wavelength-division-multiplexed (WDM) and hybrid WDM/optical time-division-multiplexed networks

All-optical pulse processing for advanced photonic communication system

This paper investigates the use of a two-photon absorption photodetector for high speed processing of ultrashort optical pulses in advanced photonic communication systems. Specifically the paper describes how the two-photon absorption photodetector maybe employed for chromatic dispersion monitoring in high-speed, wavelength division multiplexed networks, and also for reducing multiple access interference noise in an optical code division multiplexed system