Shang-Da Yang

Four user, 2.5 Gb/s, spectrally coded O-CDMA system demonstration using low power nonlinear processing

This paper describes the demonstration of 2.5-Gb/s four-user optical-code-division-multiple-access (OCDMA) system operating at bit-error rate /spl les/10/sup -11/ utilizing programmable spectral phase encoding, an ultrasensitive (/spl sim/200 fJ/b) periodically poled lithium-niobate-waveguide nonlinear waveform discriminator and 10G Ethernet receiver. A comprehensive description of this ultra-short-pulse spectral phase-coded OCDMA system is presented. On the subsystem level, two key component technologies, namely, femtosecond encoding/decoding and low-power high-contrast nonlinear discrimination, have been developed and characterized. At the system level, data for the four-user OCDMA system operating at 2.5 Gb/s for binary as well as multilevel code families are described.We demonstrate for the first time 2.5 Gb/s four user O-CDMA operation at /spl les/10/sup -11/ BER utilizing programmable spectral phase encoding, an ultrasensitive (<0.4 pJ/bit) PPLN-waveguide nonlinear waveform discriminator and 10 G Ethernet receiver.

Four-user 10-Gb/s spectrally phase-coded O-CDMA system operating at /spl sim/30 fJ/bit

We demonstrate a four-user 10-Gb/s spectrally phase-coded optical code-division multiple-access system via nonlinear processing with ultralow power (/spl sim/30 fJ/bit). Full interference suppression is achieved in a time-slotted scheme without the need for chip-level coordination and synchronous detection. Performance degradation caused by pulse overlap between users is investigated.

Fully dispersion-compensated ?500?fs pulse transmission over 50?km single-mode fiber

We demonstrate essentially distortionless 50?km fiber transmission for ?500?fs pulses, using dispersion-compensating fiber and a programmable pulse shaper as a spectral phase equalizer. This distance is approximately five times longer than previously achieved at similar pulse widths.

Generation of intense supercontinuum in condensed media

Generation of supercontinuum in condensed media is a well-known approach to expand the spectrum of a femtosecond laser pulse. Yet large material dispersion and low optical damage threshold have limited input pulse energy to a few microjoules, making solids unattractive for high power applications [1]. Here we report the use of a multiple plates system that overcomes these problems to generate an intense supercontinuum (MPContinuum) that contains several hundred microjoules of energy and preserves the advantages of being compact, simple to operate, and highly reproducible [2]. With this multiple plates approach, we have obtained pulses that have an octave-spanning spectrum that covers from 450 nm to ~980 nm at the −20 dB intensity level while converting as much as 62 % of the input pulse energy to the MPContinuum. Frequency-resolved optical gating and spectral interferometric measurements indicate that the pulse is phase coherent so that it is compressible to a few femtoseconds.

400-photon-per-pulse ultrashort pulse autocorrelation measurement with aperiodically poled lithium niobate waveguides at 1.55 µm

We demonstrate accurate ultrashort pulse autocorrelation measurements for coupled energy of 52 aJ per pulse using aperiodically poled lithium niobate waveguides. The corresponding sensitivity is 3.2/spl times/10/sup -7/ mW/sup 2/, about 500 times better than the previous record.

Ultrasensitive second-harmonic generation frequency-resolved optical gating by aperiodically poled LiNbO 3 waveguides at 1.5??m

We retrieve intensity and phase profiles of 280 fs, 50 MHz optical pulses with 124 aJ coupled pulse energy (960 photons) by second-harmonic generation (SHG) frequency-resolved optical gating, using aperiodically poled LiNbO3 waveguides. The strong nonlinear interaction that is due to confinement within the micrometer-sized waveguide structure and the linearly chirped poling period contribute, respectively, to high SHG efficiency and broad phase-matching bandwidth. The achieved sensitivity is 2.7 x 10(-6) mW2, improving on the previous record for self-referenced complete pulse characterization by 5 orders of magnitude.

Low-power high-contrast coded waveform discrimination at 10 GHz via nonlinear processing

We demonstrate ultrafast optical code-division multiple-access nonlinear waveform discrimination at 10 GHz with less than 1 mW coupled into a nonlinear periodically poled lithium niobate waveguide and greater than 20-dB contrast ratio between coded and uncoded waveforms. Excellent signal-to-noise is observed at the system receiver, pointing toward the practicability of nonlinear waveform discrimination in a system environment.

Ultralow-power second-harmonic generation frequency-resolved optical gating using aperiodically poled lithium niobate waveguides [Invited]

We discuss ultralow-power second-harmonic generation (SHG) frequency-resolved optical gating (FROG) in the telecommunication C-band using aperiodically poled lithium niobate (A-PPLN) waveguides as the nonlinear medium. A key theme of this work is that the phase-matching curve of the nonlinear medium is engineered to obtain an optical bandwidth adequate for measurement of subpicosecond pulses while retaining the optimum nonlinear efficiency consistent with this constraint. Our experiments demonstrate measurement sensitivity (defined as the minimum product of the peak and average pulse powers at which a reliable nonlinear signal can be detected) of 2.0×10−6 mW2 in a collinear SHG FROG geometry, approximately 5 orders of magnitude better than previously reported for any FROG measurement modality. We also discuss asymmetric Y-junction A-PPLN waveguides that permit background-free SHG FROG and a polarization-insensitive SHG FROG technique that eliminates the impairment that frequency-independent random polarization fluctuations induce in the FROG measurement. Finally, we applied these SHG FROG techniques in chromatic dispersion and polarization mode dispersion compensation experiments. In these experiments the FROG data enabled complete correction of distortions incurred by subpicosecond pulses passing through optical fibers; these results also demonstrate the ability to retrieve extremely complex pulses with high accuracy.

Forty-photon-per-pulse spectral phase retrieval by shaper-assisted modified interferometric field autocorrelation

We report on spectral phase retrieval of 400 fs pulses using shaper-assisted modified interferometric field autocorrelation. The coupled energy is only 5.2 aJ per pulse, corresponding to an unprecedented sensitivity of 2.7 × 10⁻⁹ mW².

Ultrasensitive direct-field retrieval of femtosecond pulses by modified interferometric field autocorrelation.

We report on spectral phase retrieval of 50 MHz, 374 fs optical pulses at 1560 nm with 28 aJ coupled pulse energy by measuring two modified interferometric field autocorrelation traces using a 5-cm-long periodically poled lithium niobate waveguide. The corresponding sensitivity is 1.1x10(-7) mW(2), improving on the previous record by about 20 times. The same data traces can also be used to retrieve the power spectrum, given that the ratio of powers at two specific wavelengths is known.