Practical high-dimensional quantum key distribution protocol over deployed multicore fiber

Quantum key distribution (QKD) is a secure communication scheme for sharing symmetric cryptographic keys based on the laws of quantum physics, and is considered a key player in the realm of cyber-security. A critical challenge for QKD systems comes from the fact that the ever-increasing rates at which digital data are transmitted require more and more performing sources of quantum keys, primarily in terms of secret key generation rate. High-dimensional QKD based on path encoding has been proposed as a candidate approach to address this challenge. However, while proof-of-principle demonstrations based on lab experiments have been reported in the literature, demonstrations in realistic environments are still missing. Here we report the generation of secret keys in a 4-dimensional hybrid time-path-encoded QKD system over a 52-km deployed multicore fiber link forming by looping back two cores of a 26-km 4-core optical fiber. Our results indicate that robust high-dimensional QKD can be implemented in a realistic environment by combining standard telecom equipment with emerging multicore fiber technology.

Crosstalk-free all-optical switching enabled by Fano resonance in a multi-mode photonic crystal nanocavity

We demonstrate all-optical switching using a multi-mode membranized photonic crystal nanocavity exploiting the free-carrier induced dispersion in InP and the sharp asymmetric lineshape of Fano resonances. A multi-mode cavity is designed to sustain two spatially overlapping modes with a spectral spacing of 18 nm. The measured transmission spectrum of the fabricated device shows multiple asymmetric Fano resonances as predicted by optical simulations. The capabilities of the device are benchmarked by comparing a wavelength conversion from 1538.2 nm to 1565.2 nm with a single-mode wavelength conversion at 1566.2 nm on the same device. The results show an improvement in signal quality with a 5.6 dB power penalty reduction at the receiver as well as in energy efficiency with a reduction of the pump power from 534 fJ/bit to 445 fJ/bit.

744-nm wavelength conversion of PAM-4 signal using an AlGaAsOI nanowaveguide

Exploring new frequency bands for optical transmission is essential to overcome the capacity crunch. The 2-µm band is becoming a research spotlight due to available broadband thulium-doped fiber amplifiers as well as low-latency, low-loss hollow-core fibers. Yet most of the 2-µm band devices designed for optical communication are still in their infancy. In this Letter, we propose wavelength conversion based on four-wave mixing in a highly nonlinear AlGaAsOI nanowaveguide to bridge the 2-µm band and the conventional bands. Due to the strong light confinement of the AlGaAsOI nanowaveguide, high-order phase match is enabled by dispersion engineering to achieve a large synergetic conversion bandwidth with high conversion efficiency. Simulation results show a possible conversion bandwidth over an octave. An AlGaAsOI nanowaveguide with 3-mm length and a nominal cross-section dimension of $ 320\;{\rm nm} \times 680\;{\rm nm} $320nm×680nm is used for the wavelength conversion of a 10 Gbit/s non-return-to-zero on-off keying signal and a 10 Gbit/s Nyquist-shaped four-level pulse-amplitude modulation signal. A conversion efficiency of $ - {28}\;{\rm dB}$-28dB is achieved using a 17.5-dBm continuous-wave pump in the C band, with 744 nm conversion from 1999.65 to 1255.35 nm.

Air-cladded mode-group selective photonic lanterns for mode-division multiplexing

We have fabricated an air-cladded mode-group selective photonic lantern, which can (de)multiplex the first two mode groups of a standard two-mode step-index fiber. Instead of relying on a low-index capillary tube, our simple solution uses air to form the surrounding "cladding" and thereby enable guiding at the end of the taper. Characterization of a 25-mm long lantern taper results in multiplexing crosstalk values between -20 dB and -12 dB for both modal inputs. The de-multiplexing values were around -12 dB for the fundamental mode, and slightly higher for the first higher-order (LP₁₁) mode. Microscopic imaging of a taper cross section having a width of 30 μm reveals the presence of an uncollapsed airhole in the structure between the three fibers. The impact of such an airhole is numerically investigated using an eigenmode expansion method based on a full-vectorial mode solver, and is found to play an important role in assuring a more adiabatic mode conversion through the taper.

12 mode, WDM, MIMO-free orbital angular momentum transmission

Simultaneous MIMO-free transmission of 12 orbital angular momentum (OAM) modes over a 1.2 km air-core fiber is demonstrated. WDM compatibility of the system is shown by using 60, 25 GHz spaced WDM channels with 10 GBaud QPSK signals. System performance is evaluated by measuring bit error rates, which are found to be below the soft FEC limit, and limited by inter-modal crosstalk. The crosstalk in the system is analyzed, and it is concluded that it can be significantly reduced with an improved multiplexer and de-multiplexer.

Signal reshaping and noise suppression using photonic crystal Fano structures

We experimentally demonstrate the use of photonic crystal Fano resonances for reshaping optical data signals. We show that the combination of an asymmetric Fano resonance and carrier-induced nonlinear effects in a nanocavity can be used to realize a nonlinear power transfer function, which is a key functionality for optical signal regeneration, particularly for suppression of amplitude fluctuations of data signals. The experimental results are explained using simulations based on coupled-mode theory and also compared to the case of using conventional Lorentzian-shaped resonances. Using indium phosphide photonic crystal membrane structures, we demonstrate reshaping of 2 Gbit/s and 10 Gbit/s return-to-zero on-off keying (RZ-OOK) data signals at telecom wavelengths around 1550 nm. Eye diagrams of the reshaped signals show that amplitude noise fluctuations can be significantly suppressed. The reshaped signals are quantitatively analyzed using bit-error ratio (BER) measurements, which show up to 2 dB receiver sensitivity improvement at a BER of 10^-9 compared to a degraded input noisy signal. Due to efficient light-matter interaction in the high-quality factor and small mode-volume photonic crystal nanocavity, low energy consumption, down to 104 fJ/bit and 41 fJ/bit for 2 Gbit/s and 10 Gbit/s, respectively, has been achieved. Device perspectives and limitations are discussed.

Scalable WDM phase regeneration in a single phase-sensitive amplifier through optical time lenses

Optical data regeneration is attractive, due to its potential to increase transmission reach and data throughput in communication systems, and several interesting proposals have been made. However, efficient and scalable solutions for regeneration of multiple parallel wavelength channels have been elusive, constituting a key challenge, which must be overcome for optical regeneration to have any prospect of being adapted in actual communication systems. Here we report a scalable wavelength-division multiplexing (WDM) regeneration scheme for phase only regeneration, which satisfies the multichannel requirement, using a set of optical time-lens-based Fourier processors combined with a single phase-sensitive amplifier (PSA). We describe the concept theoretically, and experimentally demonstrate simultaneous regeneration of 16 WDM channels with 50-GHz spacing, each carrying 10-Gbit/s DPSK phase-modulated data. The proposed scheme relies on ultrafast broadband optical processing and is inherently scalable in modulation speed and channel number.

Scalable solutions for data regeneration of multiple parallel channels are elusive. Here the authors report a scalable wavelength-division multiplexing technique for phase regeneration and demonstrate the highest reported number of regenerated wavelength-division multiplexed channels in a single phase regenerator.

Pulse carving using nanocavity-enhanced nonlinear effects in photonic crystal Fano structures

We experimentally demonstrate the use of a photonic crystal Fano resonance for carving-out short pulses from long-duration input pulses. This is achieved by exploiting an asymmetric Fano resonance combined with carrier-induced nonlinear effects in a photonic crystal membrane structure. The use of a nanocavity concentrates the input field to a very small volume leading to an efficient nonlinear resonance shift that carves a short pulse out of the input pulse. Here, we demonstrate shortening of ∼500  ps and ∼100  ps long pulses to ∼30  ps and ∼20  ps pulses, respectively. Furthermore, we demonstrate error-free low duty cycle return-to-zero signal generation at 2 Gbit/s with energy consumption down to ∼1  pJ/bit and power penalty of ∼2  dB. The device physics and limitations are analyzed using nonlinear coupled-mode theory.

Optimization and characterization of highly nonlinear fiber for broadband optical time lens applications

We demonstrate simple and intuitive methods, for dispersion optimization and characterization of highly nonlinear fiber (HNLF) for use in four-wave-mixing (FWM) based time lens applications. A composite dispersion-flattened HNLF is optimized for high bandwidth time lens processing, by segmentation to mitigate FWM impairments due to dispersion fluctuations. The fiber is used for FWM conversion of 32 WDM-channels with 50 GHz spacing in a time lens, with -4.6 dB total efficiency, and <1 dB per-channel efficiency difference. The novel characterization method is based on two tunable continuous-wave lasers. The method is experimentally verified to predict the spectral output profile of time lenses for broadband multicarrier input, with detailed numerical simulations for support.

Reconfigurable SDM Switching Using Novel Silicon Photonic Integrated Circuit

Space division multiplexing using multicore fibers is becoming a more and more promising technology. In space-division multiplexing fiber network, the reconfigurable switch is one of the most critical components in network nodes. In this paper we for the first time demonstrate reconfigurable space-division multiplexing switching using silicon photonic integrated circuit, which is fabricated on a novel silicon-on-insulator platform with buried Al mirror. The silicon photonic integrated circuit is composed of a 7 × 7 switch and low loss grating coupler array based multicore fiber couplers. Thanks to the Al mirror, grating couplers with ultra-low coupling loss with optical multicore fibers is achieved. The lowest total insertion loss of the silicon integrated circuit is as low as 4.5 dB, with low crosstalk lower than −30 dB. Excellent performances in terms of low insertion loss and low crosstalk are obtained for the whole C-band. 1 Tb/s/core transmission over a 2-km 7-core fiber and space-division multiplexing switching is demonstrated successfully. Bit error rate performance below 10⁻⁹ is obtained for all spatial channels with low power penalty. The proposed design can be easily upgraded to reconfigurable optical add/drop multiplexer capable of switching several multicore fibers.

Detailed characterization of CW- and pulsed-pump four-wave mixing in highly nonlinear fibers

We present a quantitative comparison of continuous-wave- (CW) and pulsed-pump four-wave mixing (FWM) in commercially available highly nonlinear fibers (HNLFs), and suggest properties for which the CW- and pulsed-pump FWM bandwidths are limited in practice. The CW- and pulsed-pump parametric gain is characterized experimentally for several HNLFs with various dispersion properties, including zero-dispersion wavelength fluctuations, and the results are interpreted in conjunction with detailed numerical simulations. It is found that a low third-order dispersion (TOD) is essential for the pulsed-pump FWM bandwidth. However, an inverse scaling of the TOD with the dispersion fluctuations leads to different CW-optimized fibers, which depend only on the even dispersion orders.

THz photonic wireless links with 16-QAM modulation in the 375-450 GHz band

We propose and experimentally demonstrate THz photonic wireless communication systems with 16-QAM modulation in the 375-450 GHz band. The overall throughput reaches as high as 80 Gbit/s by exploiting four THz channels with 5 Gbaud 16-QAM baseband modulation per channel. We create a coherent optical frequency comb (OFC) for photonic generation of multiple THz carriers based on photo-mixing in a uni-travelling carrier photodiode (UTC-PD). The OFC configuration also allows us to generate reconfigurable THz carriers with low phase noise. The multiple-channel THz radiation is received by using a Schottky mixer based electrical receiver after 0.5 m free-space wireless propagation. 2-channel (40 Gbit/s) and 4-channel (80 Gbit/s) THz photonic wireless links with 16-QAM modulation are reported in this paper, and the bit error rate (BER) performance for all channels in both cases is below the hard decision forward error correction (HD-FEC) threshold of 3.8e-3 with 7% overhead. In addition, we also successfully demonstrate hybrid photonic wireless transmission of 40 Gbit/s 16-QAM signal at carrier frequencies of 400 GHz and 425 GHz over 30 km standard single mode fiber (SSMF) between the optical baseband signal transmitter and the THz wireless transmitter with negligible induced power penalty.

640 Gbit/s return-to-zero to non-return-to-zero format conversion based on optical linear spectral phase filtering

We propose a novel approach for all-optical return-to-zero (RZ) to non-return-to-zero (NRZ) telecommunication data format conversion based on linear spectral phase manipulation of an RZ data signal. The operation principle is numerically analyzed and experimentally validated through successful format conversion of a 640 Gbit/s coherent RZ signal into the equivalent NRZ time-domain data using a simple phase filter implemented by a commercial optical waveshaper.

4 × 160-Gbit/s multi-channel regeneration in a single fiber

Simultaneous regeneration of four high-speed (160 Gbit/s) wavelength-division multiplexed (WDM) and polarization-division multiplexed (PDM) signals in a single highly nonlinear fiber (HNLF) is demonstrated. The regeneration operation is based on four-wave mixing in HNLF, where the degraded data signals are applied as the pump. As a result, the noise on both '0' and '1' levels can be suppressed simultaneously in our scheme. The stimulated Brillouin scattering (SBS) from the continuous wave (CW) is suppressed by cross-phase modulation (XPM) from the data pump, relieving the requirement of external phase modulation of the CW light. Mitigation of the inter-channel nonlinearities is achieved mainly through an inter-channel 0.5 bit slot time delay. Bidirectional propagation is also applied to relieve the inter-channel four-wave mixing. The multi-channel regeneration performance is validated by bit-error rate (BER) measurements. The receiver powers at the BER of 10(-9) are improved by 1.9 dB, 1.8 dB, 1.6 dB and 1.5 dB for the four data channels, respectively.

Ultrafast all-optical clock recovery based on phase-only linear optical filtering

We report on a novel, efficient technique for all-optical clock recovery from RZ-OOK data signals based on spectral phase-only (all-pass) optical filtering. This technique significantly enhances both the recovered optical clock quality and energy efficiency in comparison with conventional amplitude optical filtering approaches using a Fabry-Perot filter. The proposed concept is validated through recovery of the optical clock from a 640 Gbit/s RZ-OOK data signal using a commercial linear optical waveshaper.

Compressive sensing in a photonic link with optical integration

In this Letter, we present a novel structure to realize photonics-assisted compressive sensing (CS) with optical integration. In the system, a spectrally sparse signal modulates a multiwavelength continuous-wave light and then is mixed with a random sequence in optical domain. The optical signal passes through a length of dispersive fiber, the dispersion amount of which is set to ensure that the group delay between the adjacent wavelength channels is equal to the bit duration of the applied random sequence. As a result, the detected signal is a delay-and-sum version of the randomly mixed signal, which is equivalent to the function of integration required in CS. A proof-of-concept experiment with four wavelengths, corresponding to a compression factor of 4, is demonstrated. More simulation results are also given to show the potential of the technique.

Phase regeneration of DPSK signals in a silicon waveguide with reverse-biased p-i-n junction

Phase regeneration of differential phase-shift keying (DPSK) signals is demonstrated using a silicon waveguide as nonlinear medium for the first time. A p-i-n junction across the waveguide enables decreasing the nonlinear losses introduced by free-carrier absorption (FCA), thus allowing phase-sensitive extinction ratios as high as 20 dB to be reached under continuous-wave (CW) pumping operation. Furthermore the regeneration properties are investigated under dynamic operation for a 10-Gb/s DPSK signal degraded by phase noise, showing receiver sensitivity improvements above 14 dB. Different phase noise frequencies and amplitudes are examined, resulting in an improvement of the performance of the regenerated signal in all the considered cases.

320 Gb/s Nyquist OTDM received by polarization-insensitive time-domain OFT

We have demonstrated the generation of a 320 Gb/s Nyquist-OTDM signal by rectangular filtering on an RZ-OTDM signal with the filter bandwidth (320 GHz) equal to the baud rate (320 Gbaud) and the reception of such a Nyquist-OTDM signal using polarization-insensitive time-domain optical Fourier transformation (TD-OFT) followed by passive filtering. After the time-to-frequency mapping in the TD-OFT, the Nyquist-OTDM signal with its characteristic sinc-shaped time-domain trace is converted into an orthogonal frequency division multiplexing (OFDM) signal with sinc-shaped spectra for each subcarrier. The subcarrier frequency spacing of the converted OFDM signal is designed to be larger than the transform-limited case, here 10 times greater than the symbol rate of each subcarrier. Therefore, only passive filtering is needed to extract the subcarriers of the converted OFDM signal. In addition, a polarization diversity scheme is used in the four-wave mixing (FWM) based TD-OFT, and less than 0.5 dB polarization sensitivity is demonstrated in the OTDM receiver.

All-optical OFDM demultiplexing by spectral magnification and band-pass filtering

We propose a simple OFDM receiver allowing for the use of standard WDM receivers to receive spectrally advanced OFDM signals. We propose to spectrally magnify the optical-OFDM super-channels using a spectral telescope consisting of two time-lenses, which enables reduced inter-carrier-interference in subcarrier detection by simple band-pass filtering. A demonstration on an emulated 100 Gbit/s DPSK optical-OFDM channel shows improved sensitivities after 4-times spectral magnification.

Dynamic characterization and amplification of sub-picosecond pulses in fiber optical parametric chirped pulse amplifiers

We show a first-time demonstration of amplification of 400 fs pulses in a fiber optical parametric amplifier. The 400 fs signal is stretched in time, amplified by 26 dB and compressed back to 500 fs. A significant broadening of the pulses is experimentally shown due to dispersion and limited gain bandwidth both in saturated and unsaturated gain regimes.

Parametric amplification and phase preserving amplitude regeneration of a 640 Gbit/s RZ-DPSK signal

We report the first experimental demonstration of parametric amplification and all-optical phase-preserving amplitude regeneration for a 640 Gbit/s return-to-zero (RZ) differential phase-shift keying (DPSK) optical time division multiplexed (OTDM) signal. In the designed gain-flattened single-pump fiber optical parametric amplifier (FOPA), 620 fs short optical pulses are successfully amplified with 15 dB gain with error-free performance and less than 1 dB power penalty. Phase-preserving amplitude regeneration based on gain saturation in the FOPA is carried out for optical signals with degraded optical signal-to-noise ratio. An improvement of 2.2 dB in receiver sensitivity at a bit-error-ratio of 10(-9) has been successfully achieved after regeneration, together with 13.3 dB net gain.

Forward error correction supported 150 Gbit/s error-free wavelength conversion based on cross phase modulation in silicon

We build a forward error correction (FEC) module and implement it in an optical signal processing experiment. The experiment consists of two cascaded nonlinear optical signal processes, 160 Gbit/s all optical wavelength conversion based on the cross phase modulation (XPM) in a silicon nanowire and subsequent 160 Gbit/s-to-10 Gbit/s demultiplexing in a highly nonlinear fiber (HNLF). The XPM based all optical wavelength conversion in silicon is achieved by off-center filtering the red shifted sideband on the CW probe. We thoroughly demonstrate and verify that the FEC code operates correctly after the optical signal processing, yielding truly error-free 150 Gbit/s (excl. overhead) optically signal processed data after the two cascaded nonlinear processes.

Simultaneous regeneration of two 160 Gbit/s WDM channels in a single highly nonlinear fiber

We experimentally demonstrate simultaneous all-optical regeneration of two 160-Gbit/s wavelength-division multiplexed (WDM) channels in a single highly nonlinear fiber (HNLF). The multi-channel regeneration performance is confirmed by bit-error rate (BER) measurements. The receiver powers at a BER of 10(-9) are improved by about 4.9 dB and 2.1 dB for the two channels, respectively. The BER performance is not degraded by the presence of a second channel. Mitigation of the inter-channel nonlinearities is achieved through bidirectional propagation.

Asymmetric gain-saturated spectrum in fiber optical parametric amplifiers

We demonstrate experimentally and numerically an unexpected spectral asymmetry in the saturated-gain spectrum of single-pump fiber optical parametric amplifiers. The interaction between higher-order four-wave mixing products and dispersive waves radiated as an effect of third-order dispersion influences the energy transfer to the signal, depending on its detuning with respect to the pump, and breaks the symmetry of the gain expected from phase-matching considerations in unsaturated amplifiers. The asymmetry feature of the saturated spectrum is shown to particularly depend on the dispersion characteristics of the amplifier and shows local maxima for specific dispersion values.

10 GHz pulse source for 640 Gbit/s OTDM based on phase modulator and self-phase modulation

We demonstrate a high-quality cavity-free 10 GHz 680 fs pulse source starting from a continuous wave (CW) laser. The pulse source is employed in a 640 Gbit/s on-off keying (OOK) OTDM data generation and demultiplexing experiment, where the error-free bit error rate (BER) performance confirms the high pulse quality. The pulse source is based on a linear pulse compression stage followed by two polarization-independent non-linear pulse compression stages. The linear pulse compression stage relies on a phase modulator, which is used to generate linear chirp and followed by a dispersive element to compensate the chirp. The non-linear pulse compression stages are based on self-phase modulation (SPM) in dispersion-flattened highly non-linear fibers (DF-HNLF). The pulse source is tunable over the C-band with negligible pedestal.

Synchronization, retiming and time-division multiplexing of an asynchronous 10 Gigabit NRZ Ethernet packet to terabit Ethernet

An asynchronous 10 Gb/s Ethernet packet with maximum packet size of 1518 bytes is synchronized and retimed to a master clock with 200 kHz frequency offset using a time lens. The NRZ packet is simultaneously converted into an RZ packet, then further pulse compressed to a FWHM of 400 fs and finally time-division multiplexed with a serial 1.28 Tb/s signal including a vacant time slot, thus forming a 1.29 Tb/s time-division multiplexed serial signal. Error-free performance of synchronizing, retiming, time-division multiplexing to a Terabit data stream and finally demultiplexing back to 10 Gb/s of the Ethernet packet is achieved.

Nonlinear properties of and nonlinear processing in hydrogenated amorphous silicon waveguides

We propose hydrogenated amorphous silicon nanowires as a platform for nonlinear optics in the telecommunication wavelength range. Extraction of the nonlinear parameter of these photonic nanowires reveals a figure of merit larger than 2. It is observed that the nonlinear optical properties of these waveguides degrade with time, but that this degradation can be reversed by annealing the samples. A four wave mixing conversion efficiency of + 12 dB is demonstrated in a 320 Gbit/s serial optical waveform data sampling experiment in a 4 mm long photonic nanowire.

Ultra-high-speed optical serial-to-parallel data conversion by time-domain optical Fourier transformation in a silicon nanowire

We demonstrate conversion from 64 × 10 Gbit/s optical time-division multiplexed (OTDM) data to dense wavelength division multiplexed (DWDM) data with 25 GHz spacing. The conversion is achieved by time-domain optical Fourier transformation (OFT) based on four-wave mixing (FWM) in a 3.6 mm long silicon nanowire. A total of 40 out of 64 tributaries of a 64 × 10 Gbit/s OTDM-DPSK data signal are simultaneously converted with a bit-error rate (BER) performance below the 2 × 10(-3) FEC limit. Using a 50 m long highly nonlinear fiber (HNLF) for higher FWM conversion efficiency, 43 tributaries of a 64 × 10 Gbit/s OTDM-OOK data signal are converted with error-free performance (BER<10(-9)).

One-to-six WDM multicasting of DPSK signals based on dual-pump four-wave mixing in a silicon waveguide

We present WDM multicasting based on dual-pump four-wave mixing in a 3-mm long dispersion engineered silicon waveguide. One-to-six phase-preserving WDM multicasting of 10-Gb/s differential phase-shift-keying (DPSK) data is experimentally demonstrated with bit-error rate measurements. All the six multicast signals show error-free performance with power penalty less than 3.8 dB.

Ultra-high-speed wavelength conversion in a silicon photonic chip

We have successfully demonstrated all-optical wavelength conversion of a 640-Gbit/s line-rate return-to-zero differential phase-shift keying (RZ-DPSK) signal based on low-power four wave mixing (FWM) in a silicon photonic chip with a switching energy of only ~110 fJ/bit. The waveguide dispersion of the silicon nanowire is nano-engineered to optimize phase matching for FWM and the switching power used for the signal processing is low enough to reduce nonlinear absorption from two-photon-absorption (TPA). These results demonstrate that high-speed wavelength conversion is achievable in silicon chips with high data integrity and indicate that high-speed operation can be obtained at moderate power levels where nonlinear absorption due to TPA and free-carrier absorption (FCA) is not detrimental. This demonstration can potentially enable high-speed optical networks on a silicon photonic chip.

Optical switching and detection of 640 Gbits/s optical time-division multiplexed data packets transmitted over 50 km of fiber

We demonstrate 1×4 optical-packet switching with error-free transmission of 640 Gbits/s single-wavelength optical time-division multiplexed data packets including clock distribution and short pulse generation for optical time demultiplexing based on a cavityless pulse source.

Demultiplexing of OTDM-DPSK signals based on a single semiconductor optical amplifier and optical filtering

We propose and demonstrate the use of a single semiconductor optical amplifier (SOA) and optical filtering to time demultiplex tributaries from an optical time division multiplexing-differential phase shift keying (OTDM-DPSK) signal. The scheme takes advantage of the fact that phase variations added to the target channel by cross-phase modulation from the control signal are effectively subtracted in the differential demodulation scheme employed for DPSK signals. Demultiplexing from 80 to 40 Gbit/s is demonstrated with moderate power penalty using an SOA with recovery time twice as long as the bit period at 80 Gbit/s. Large dynamic ranges for the input power and SOA current are experimentally demonstrated. The scheme is expected to be scalable toward higher bit rates.

Generation of a 640 Gbit/s NRZ OTDM signal using a silicon microring resonator

A 640 Gbit/s NRZ OTDM signal has been successfully generated for the first time by format conversion of a 640 Gbit/s OTDM signal from RZ to NRZ. First, a coherent 640 Gbit/s OTDM RZ signal is generated by wavelength conversion of the original incoherent OTDM signal utilizing Kerr switching in a highly nonlinear fiber. Second, RZ-to-NRZ format conversion is achieved in a specially designed silicon microring resonator with FSR of 1280 GHz, Q value of 638, high extinction ratio and low coupling loss to optical fiber. A 640 Gbit/s NRZ OTDM signal with very clear eye-diagram and narrower bandwidth than both the original incoherent 640 Gbit/s and the wavelength converted coherent 640 Gbit/s RZ OTDM signals has been obtained. Bit error ratio measurements show error free (<10(-9)) performance at a received power of -30 dBm for all the OTDM channels of the 640 Gbit/s NRZ signal, with very low power penalty (<0.5 dB) and improved dispersion tolerance compared to the wavelength converted RZ case.

Photonic chip based transmitter optimization and receiver demultiplexing of a 1.28 Tbit/s OTDM signal

We demonstrate chip-based Tbaud optical signal processing for all-optical performance monitoring, switching and demultiplexing based on the instantaneous Kerr nonlinearity in a dispersion-engineered As(2)S(3) planar waveguide. At the Tbaud transmitter, we use a THz bandwidth radio-frequency spectrum analyzer to perform all-optical performance monitoring and to optimize the optical time division multiplexing stages as well as mitigate impairments, for example, dispersion. At the Tbaud receiver, we demonstrate error-free demultiplexing of a 1.28 Tbit/s single wavelength, return-to-zero signal to 10 Gbit/s via four-wave mixing with negligible system penalty (< 0.5 dB). Excellent performance, including high four-wave mixing conversion efficiency and no indication of an error-floor, was achieved. Our results establish the feasibility of Tbaud signal processing using compact nonlinear planar waveguides for Tbit/s Ethernet applications.

640 Gbit/s and 1.28 Tbit/s polarisation insensitive all optical wavelength conversion

We report the first demonstration of polarisation insensitive all-optical wavelength conversion (AOWC) for single wavelength channel 640 Gbit/s return-to-zero differential-phase-shift-keying (RZ-DPSK) signal and 1.28 Tbit/s polarisation multiplexed (Pol-Mux) RZ-DPSK signals using a 100-m polarisation-maintaining highly nonlinear fiber (PM-HNLF) in a polarisation diversity loop configuration. The AOWC is based on four-wave mixing in PM-HNLF. Error free performance is achieved for the wavelength converted signals. Less than 0.5 dB polarisation sensitivity is obtained.

Demonstration of 5.1 Tbit/s data capacity on a single-wavelength channel

We have generated a single-wavelength data signal with a data capacity of 5.1 Tbit/s. The enabling techniques to generate the data signal are optical time-division multiplexing up to a symbol rate of 1.28 Tbaud, differential quadrature phase shift keying as data format, and polarisation-multiplexing. For the first time, error-free performance with a bit error rate less than 10(-9) is demonstrated for the 5.1 Tbit/s data signal. This is achieved in a back-to-back configuration using a direct detection receiver based on polarisation- and time-demultiplexing, delay-demodulation and balanced photo-detection.

Breakthrough switching speed with an all-optical chalcogenide glass chip: 640 Gbit/s demultiplexing

We report the first demonstration of error-free 640 Gbit/s demultiplexing using the Kerr non-linearity of an only 5 cm long chalcogenide glass waveguide chip. Our approach exploits four-wave mixing by the instantaneous nonlinear response of chalcogenide. Excellent performance is achieved with only 2 dB average power penalty and no indication of error-floor. Characterisation of the FWM efficiency for the chalcogenide waveguide is given and confirms the good performance of the device.

320 Gbps to 10 GHz sub-clock recovery using a PPLN-based opto-electronic phase-locked loop

We present successful extraction of a 10 GHz clock from single-wavelength 160 and 320 Gbps OTDM data streams, using an opto-electronic phase-locked loop based on three-wave mixing in periodically-poled lithium niobate as a phase comparator.