Gordon K. P. Lei

Photonic crystal fiber based Mach-Zehnder interferometer for DPSK signal demodulation

We demonstrate a novel fiber-based in-line DPSK demodulator using an in-fiber Mach-Zehnder interferometer (MZI). The device is fabricated by mismatch splicing of a photonic crystal fiber (PCF) with standard single mode fibers. The spectral characteristics at different PCF lengths are analyzed. The envelope of the interference fringes show a period that is inversely proportional to the PCF length, and is attributed to the periodic coupling between the core mode and the cladding mode. Error free demodulations of 10-Gb/s RZ- and NRZ-DPSK signals have been demonstrated using the in-fiber PCF-MZI demodulator with only 3-m PCF to introduce 91-ps delay. Wideband DPSK demodulation has also been achieved.

All-Optical RZ-to-NRZ and NRZ-to-PRZ Format Conversions Based on Delay-Asymmetric Nonlinear Loop Mirror

We perform all-optical return-to-zero (RZ) to nonreturn-to-zero (NRZ) and NRZ to pseudoreturn-to-zero (PRZ) format conversions at tunable bit rates, both by using the same delay-asymmetric nonlinear loop mirror. The temporal and spectral characteristics of the input and output signals are analyzed. Bit-error-rate measurements of RZ-to-NRZ conversion at 10 and 12.5 Gb/s show error-free performance with power penalties less than 3 dB with reference to the input RZ signals.

Bit-Rate-Variable DPSK Demodulation Using Silicon Microring Resonators With Electro-Optic Wavelength Tuning

We demonstrate a bit-rate-variable differential phase-shift keying (DPSK) demodulator based on silicon microring resonators (MRRs) with an integrated diode for wavelength tuning. The resonance wavelength of the MRR may be tuned by carrier injection and depletion. Error-free operations (bit error rate <;10-9) have been achieved for all tuning wavelengths. In addition, the proposed scheme can demodulate DPSK signals over a wide range of bit rates from below 25 to 40 Gb/s.

Ultrawideband monocycle pulse generation based on delayed interference ofπ/2 phase-shift keying signal

We propose a scheme to generate ultrawideband (UWB) monocycle pulses using delayed interference of a π/2 phase-shift keying (PSK) signal. The PSK signal is generated with an optical phase modulator. A fiber-based delay interferometer is used to provide the delay together with a ±π/2 phase shift between the signals in its two arms before the interference. The two opposite phase shifts correspond to the generation of a pair of polarity-reversed UWB monocycle pulses. The full width at half maximum of the pulses is ~68 ps and the 10 dB fractional bandwidth is 168%.

Demodulation of 20 Gbaud/s differential quadrature phase-shift keying signals using wavelength-tunable silicon microring resonators

We experimentally demonstrate a demodulation scheme for 20 Gbaud/s nonreturn-to-zero differential quadrature phase-shift keying signals using a silicon microring resonator. Either the I or Q channel can be selected by electrical tuning using the carrier depletion effect. Error-free (bit error rate <10(-9)) operations can be achieved for both the I and Q channels with ~1.5 dB power penalty compared with a commercial 20 GHz Mach-Zehnder delay interferometer. The tuning range of the ring resonator can be up to 60 GHz, which enables operation over a wide range of data rates.

All-Optical OTDM-to-WDM Signal Conversion Using Cross-Absorption Modulation With Time- and Wavelength-Interleaved Short Pulses

Using two cascaded stages of cross-absorption modulation in electroabsorption modulators, we have successfully demonstrated the conversion of 40-Gb/s optical time-division- multiplexing to 4 × 10 Gb/s wavelength-division-multiplexing signals. Our approach exploits the generation of 40-GHz time- and wavelength-interleaved pulses that determines the wavelength assignment of the output. The setup is compact, potentially integrable, and operates at moderate optical power levels. Bit-error-rate measurement shows error-free operation of our conversion scheme with a 4- to 6-dB power penalty.

OSNR Monitoring for NRZ-PSK Signals Using Silicon Waveguide Two-Photon Absorption

We study the use of two-photon absorption (TPA) in a silicon optical waveguide for measuring the optical signal-to-noise ratio (OSNR) of a nonreturn to zero phase-shift keying (NRZ-PSK) signal. The average photocurrent generated in the silicon waveguide increased by 70 nA (from 375 to 445 nA) for a change in OSNR from 28 to 6 dB and a constant total input power of 10 dBm. The nonresonant nature of the silicon waveguide TPA detector enables the simple measurement of OSNR over a continuous wide (>; 10 nm) wavelength range. For a 10-Gb/s NRZ-PSK signal, we show that when the residual dispersion in the optical signal exceeds 425 ps/nm, further increases in dispersion have little effect on the photocurrent. Thus, this TPA-based OSNR monitor can be used in practical systems with large dispersion.

Reconfigurable two-channel demultiplexing using a single baseband control pulse train in a dispersion asymmetric NOLM.

We demonstrate a unique solution to use a one-pulse control to achieve simultaneous two-channel all-optical demultiplexing that usually requires a two-pulse control or a two-step operation based on the conventional approaches. By applying a dispersion asymmetric nonlinear optical loop mirror (DA-NOLM) to introduce cross phase modulation (XPM) in both the clockwise (CW) and the counter clockwise (CCW) propagating branches, we have demonstrated reconfigurable, error-free 40-to-10 Gb/s two-channel demultiplexing (DEMUX) for OTDM OOK signals. Switchable operation between two-channel and single-channel DEMUX is also realized based on the proposed all-optical DEMUX configuration.

40-GS/s all-optical sampling using four-wave mixing with a time- and wavelength-interleaved laser source

We demonstrate 40-GS/s all-optical wavelength division sampling using four-wave mixing in a dispersion-flattened photonic crystal fiber. Our 4x10-GHz time- and wavelength-interleaved sampling laser source is generated through multiwavelength cross-absorption modulation and optical dispersion management.

Polarization-Insensitive Phase-Preserving Regenerator Based on a Fiber Optical Parametric Amplifier With Dual Orthogonal Pumps

We investigate the gain-saturation characteristics of a dual-orthogonal-pump fiber optical parametric amplifier. Nearly uniform power transfer functions have been obtained for various input signal polarizations by adjusting the total pump power. Based on this physical behavior, we demonstrate polarization-insensitive phase-preserving amplitude regeneration of 40-Gb/s nonreturn-to-zero differential phase-shift keying signals. The receiver sensitivity has been improved by a maximum value of 4.7 dB.