Vahid G. Ta'eed

Ultrafast all-optical chalcogenide glass photonic circuits

Chalcogenide glasses offer large ultrafast third-order nonlinearities, combined with low two-photon absorption and absence of free carrier absorption in a photosensitivity medium. We review the key properties of these materials, including the strong photosensitivity and focus on several recent demonstrations of ultra-fast all-optical signal processing: optical time division multiplexing, all-optical signal regeneration and wavelength conversion.

Long, low loss etched As(2)S(3) chalcogenide waveguides for all-optical signal regeneration.

We report on the fabrication and optical properties of etched highly nonlinear As(2)S(3) chalcogenide planar rib waveguides with lengths up to 22.5 cm and optical losses as low as 0.05 dB/cm at 1550 nm - the lowest ever reported. We demonstrate strong spectral broadening of 1.2 ps pulses, in good agreement with simulations, and find that the ratio of nonlinearity and dispersion linearizes the pulse chirp, reducing the spectral oscillations caused by self-phase modulation alone. When combined with a spectrally offset band-pass filter, this gives rise to a nonlinear transfer function suitable for all-optical regeneration of high data rate signals.

Applications of Highly-Nonlinear Chalcogenide Glass Devices Tailored for High-Speed All-Optical Signal Processing

Ultrahigh nonlinear tapered fiber and planar rib Chalcogenide waveguides have been developed to enable highspeed all-optical signal processing in compact, low-loss optical devices through the use of four-wave mixing (FWM) and cross-phase modulation (XPM) via the ultra fast Kerr effect. Tapering a commercial As2Se3 fiber is shown to reduce its effective core area and enhance the Kerr nonlinearity thereby enabling XPM wavelength conversion of a 40 Gb/s signal in a shorter 16-cm length device that allows a broader wavelength tuning range due to its smaller net chromatic dispersion. Progress toward photonic chip-scale devices is shown by fabricating As2S3 planar rib waveguides exhibiting nonlinearity up to 2080 W-1ldr km-1 and losses as low as 0.05 dB/cm. The materials high refractive index, ensuring more robust confinement of the optical mode, permits a more compact serpentine-shaped rib waveguide of 22.5 cm length on a 7-cm- size chip, which is successfully applied to broadband wavelength conversion of 40-80 Gb/s signals by XPM. A shorter 5-cm length planar waveguide proves most effective for all-optical time-division demultiplexing of a 160 Gb/s signal by FWM and analysis shows its length is near optimum for maximizing FWM in consideration of its dispersion and loss.

Integrated all-optical pulse regenerator in chalcogenide waveguides

We report a fully integrated, passive, all-optical regenerator capable of terabit per second operation, based on a highly nonlinear chalcogenide (As2S3) glass rib waveguide followed by an integrated Bragg grating bandpass filter. We demonstrate a clear nonlinear power transfer curve with 1.4 ps optical pulses, capable of improving the signal-to-noise ratio and reducing the bit error rate for digital signals.

Ultra-High Nonlinear As

A low loss As2S3 planar waveguide with ultra-high optical Kerr nonlinearity ~2000 W-1 ldr km-1 and only 50-mm length demonstrates high-performance time-division demultiplexing of a 160-Gb/s signal into its tributary 10-Gb/s channels via four-wave mixing (FWM) with copropagating pump pulses. Although the waveguide has a high normal dispersion parameter, its combined high nonlinearity in such short length is shown to enable efficient FWM of high-speed optical signals for all-optical demultiplexing.

_2

We show both theoretically and experimentally that signal re-amplifying and reshaping (2R) optical regenerator based on self-phase-modulation (SPM)-induced spectral broadening followed by optical filtering has significant advantages over conventional 2R regenerators. By discriminating amplified spontaneous emission noise from a pulsed signal, the SPM-based regenerator is able to selectively attenuate noise more than the pulsed signal. This unique feature results in a direct improvement in bit-error ratio (BER) of a noisy pulsed signal, whereas conventional 2R regenerators can only prevent BER degradation-not actually improve it. We compare the two classes of regenerator and highlight their fundamental differences. We also demonstrate the BER improvement of a noisy signal filtered with an SPM-based regenerator that utilizes a highly nonlinear silica fiber, and present a compact version by exploiting a short length of As2Se3 chalcogenide glass fiber

S

We demonstrate integrated all-optical 2R regenerators based on Kerr optical nonlinearities (subpicosecond response) in chalcogenide glass waveguides with integrated Bragg grating filters. By combining a low loss As/sub 2/S/sub 3/ rib waveguide with an in-waveguide photo-written Bragg grating filter, we realize an integrated all-optical 2R signal regenerator with the potential to process bit rates in excess of 1 Tb/s. The device operates using a combination of self phase modulation induced spectral broadening followed by a linear filter offset from the input center wavelength. A nonlinear power transfer curve is demonstrated using 1.4 ps pulses, sufficient for suppressing noise in an amplified transmission link. We investigate the role of dispersion on the device transfer characteristics, and discuss future avenues to realizing a device capable of operation at subwatt peak power levels.

_3

We demonstrate all-optical wavelength conversion in As2S3 chalcogenide glass rib waveguides, with 6 ps pulses over a 10 nm wavelength range near 1550 nm. Frequency resolved optical gating (FROG) measurements show good converted pulse integrity in amplitude and phase in the frequency and time domains

Planar Waveguide for 160-Gb/s Optical Time-Division Demultiplexing by Four-Wave Mixing

We present the first demonstration of all optical wavelength conversion in chalcogenide glass fiber including system penalty measurements at 10 Gb/s. Our device is based on As2Se3 chalcogenide glass fiber which has the highest Kerr nonlinearity (n(2)) of any fiber to date for which either advanced all optical signal processing functions or system penalty measurements have been demonstrated. We achieve wavelength conversion via cross phase modulation over a 10 nm wavelength range near 1550 nm with 7 ps pulses at 2.1 W peak pump power in 1 meter of fiber, achieving only 1.4 dB excess system penalty. Analysis and comparison of the fundamental fiber parameters, including nonlinear coefficient, two-photon absorption coefficient and dispersion parameter with other nonlinear glasses shows that As(2)Se(3) based devices show considerable promise for radically integrated nonlinear signal processing devices.

2R optical regeneration: an all-optical solution for BER improvement

This work was produced with the assistance of the Australian Research Council (ARC). The Centre for Ultrahigh-bandwidth Devices for Optical Systems is an ARC Centre of Excellence. M. Shokooh-Saremi appreciates the partial support of the Iranian Ministry of Science, Research and Technology.