John O'Dowd

Chromatic Dispersion Monitoring of 80-Gb/s OTDM Data Signal via Two-Photon Absorption in a Semiconductor Microcavity

In this letter, a novel method of chromatic dispersion monitoring via two-photon absorption (TPA) is investigated. A specially designed semiconductor microcavity is employed as a TPA detector for monitoring data signals operating at rates up to 80Gb/s. As the microcavity has a wavelength-dependent response, a single device can be used to monitor multiple channels in a multiwavelength optical telecommunication system

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.

Demonstration of world-first experimental optical Fast OFDM system at 7.174Gbit/s and 14.348Gbit/s

We demonstrate the first experimental implementation of an optical Fast-OFDM (FOFDM) system with a reduced sub-carrier spacing equal to half of the symbol rate. The performance was evaluated in terms of BER for 7.174Gbit/s and 14.348Gbit/s BPSK-FOFDM signals.

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.

Two-Photon-Absorption-Based OSNR Monitor for NRZ-PSK Transmission Systems

A two-photon absorption microcavity-based technique for monitoring in-band optical signal-to-noise ratio (OSNR) in nonreturn-to-zero phase-shift-keying systems is presented. Experiments using a 10-Gb/s differential phase-shift-keying system showed that accurate measurements (±1 dB) were possible for OSNRs in excess of 20 dB.

Chromatic Dispersion Monitoring for High-Speed WDM Systems Using Two-Photon Absorption in a Semiconductor Microcavity

This paper presents a theoretical and experimental investigation into the use of a two-photon absorption (TPA) photodetector for use in chromatic dispersion (CD) monitoring in high-speed, wavelength division multiplexing network. In order to overcome the inefficiency associated with the nonlinear optical-to-electrical TPA process, a microcavity structure is employed. An interesting feature of such a solution is the fact that the microcavity enhances only a narrow wavelength range determined by device design and angle at which the signal enters the device. Thus, a single device can be used to monitor a number of different wavelength channels without the need for additional external filters. When using a nonlinear photodetector, the photocurrent generated for Gaussian pulses is inversely related to the pulse width. However, when using a microcavity structure, the cavity bandwidth also needs to be considered, as does the shape of the optical pulses incident on the device. Simulation results are presented for a variety of cavity bandwidths, pulse shapes and durations, and spacing between adjacent wavelength channels. These results are verified experimental using a microcavity with a bandwidth of 260 GHz (2.1 nm) at normal incident angle, with the incident signal comprising of two wavelength channels separated by 1.25 THz (10 nm), each operating at an aggregate data rate of 160 Gb/s. The results demonstrate the applicability of the presented technique to monitor accumulated dispersion fluctuations in a range of 3 ps/nm for 160 Gb/s return-to-zero data channel.

Influence of Cavity Lifetime on High-Finesse Microcavity Two-Photon Absorption Photodetectors

For optical pulse incidence as compared with continuous-wave incidence, the enhancement of two-photon absorption inside a high-finesse planar microcavity is reduced, the pulse inside the cavity and the cavity spectrum are broadened. The analysis shows that for transform-limited pulse incidence, the true pulsewidth and the cavity frequency resolution can be estimated if the cavity lifetime or the cavity bandwidth has been obtained from the reflection or transmission spectrum of the cavity

Novel synchronous DPSK optical regenerator based on a feed-forward based carrier extraction scheme

We experimentally demonstrate a novel synchronous 10.66 Gbit/s DPSK OEO regenerator which uses a feed-forward carrier extraction scheme with an injection-locked laser to synchronize the regenerated signal wavelength to the incoming signal wavelength. After injection-locking, a low-cost DFB laser used at the regenerator exhibited the same linewidth characteristics as the narrow line-width transmitter laser. The phase regeneration properties of the regenerator were evaluated by emulating random Gaussian phase noise applied to the DPSK signal before the regenerator using a phase modulator driven by an arbitrary waveform generator. The overall performance was evaluated in terms of electrical eye-diagrams, BER measurements, and constellation diagrams.

Interrogation and mitigation of polarization effects for standard and birefringent FBGs

Optical sensors based on Fiber Bragg Gratings (FBGs) are used in several applications and industries. Several inscription techniques and type of fibers can be used. However, depending on the writing process, type of fiber used and the packaging of the sensor a Polarization Dependent Frequency Shift (PDFS) can often be observed with polarized tunable laser based optical interrogators. Here we study the PDFS of the FBG peak for the different FBG types. A PDFS of <1pm up to >20pm was observed across the FBGs. To mitigate and reduce this effect we propose a polarization mitigation technique which relies on a synchronous polarization switch to reduce the effect typically by a factor greater than 4. In other scenarios the sensor itself is designed to be birefringent (Bi-FBG) to allow pressure and/or simultaneous temperature and strain measurements. Using the same polarization switch we demonstrate how we can interrogate the Bi-FBGs with high accuracy to enable high performance of such sensors to be achievable.

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.