Open Eye Diagrams Research Articles

Silicon mode multiplexer processing dual-path mode-division multiplexing signals.

Great strides have been made in the optical interconnect for a mode-division multiplexing (MDM) system. The mode multiplexer/demultiplexer (MUX/DEMUX) is the crucial component for the MDM system. We propose and demonstrate a scheme that is different from the reported multiplexing schemes, mode MUX that tackles dual-path MDM signals simultaneously and avoids mode conflict. The performance is experimentally demonstrated by integrating the proposed MUX and DEMUX into a MDM link, with ∼1 dB of insertion loss and ∼18 dB extinction ratio over the C-band. Single-wavelength, non-return-to-zero on-off keying signals at 10Gb/s carried on dual-path different modes are successfully processed with open and clear eye diagrams, and <1 dB power penalty are obtained.

Silicon-on-Insulator RF Filter Based on Photonic Crystal Functions for Channel Equalization

A compact silicon-on-insulator two-tap interferometer is demonstrated as a channel equalizer. The radiofrequency filter is reconfigurable thanks to thermally controlled photonic crystal couplers and delay lines. The channel fading of a dispersive fiber link supporting a directly modulated telecommunication signal is successfully compensated for using the interferometer, leading to eye diagram opening and the possibility to recover the bit-error-rate of a reference signal with less than 1-dB power penalty.

Cost effective all-optical fractional OFDM receiver using an arrayed waveguide grating

Abstract We experimentally demonstrate the feasibility of implementing a cost effective all-optical fractional orthogonal frequency division multiplexing (AO-FrOFDM) receiver using an arrayed waveguide grating (AWG). The all-optical fractional Fourier transform at the receiver is implemented by modifying the second slab coupler from a conventional all-optical discrete Fourier transform AWG. The open eye diagrams obtained from the experimental results indicate that 12 × 10 Gbit/s DBPSK AO-FrOFDM signals were successfully demultiplexed.

Performance analysis of 112 Gb/s\xd74-channel WDM PDM-DQPSK optical label switching system with spectral amplitude code labels

We present the performance analysis of 112 Gb/s×4 wavelength division multiplexing (WDM) 100 GHz channel spacing polarization division multiplexed-differential quadrature phase shift keying (PDM-DQPSK) optical label switching system with frequency swept coherent detected spectral amplitude code labels. Direct detection is chosen to demodulate the payload by applying a polarization tracker, while 4-bits of 156 Mb/s spectral amplitude code label is coherently detected with a scheme of frequently-swept coherent detection. We optimize the payload laser linewidth as well as the frequency spacing between the payload and label. The label and payload signal performances are assessed by the eye-diagram opening factor (EOF) and bit-error rate (BER) at 10–9 as a function of the received optical power (ROP) and the optical signal to noise ratio (OSNR). The payload could well be demodulated after 900 km at a bit error rate of 10‒3 using forward error correction (FEC).

Simultaneous all-optical phase noise mitigation and automatically locked homodyne reception of an incoming QPSK data signal.

Simultaneous phase noise mitigation and automatic phase/frequency-locked homodyne reception is demonstrated for a 20-32 Gbaud QPSK signal. A phase quantization function is realized to squeeze the phase noise of the signal by optical wave mixing of the signal, its third-order harmonic, and their corresponding delayed variant conjugates, converting the noisy input into a noise-mitigated signal. In a simultaneous nonlinear process, the noise-mitigated signal is automatically phase- and frequency-locked with a "local" pump laser, avoiding the need for feedback or phase/frequency tracking for homodyne detection. Open eye-diagrams are obtained for in-phase and quadrature-phase components of the signal and ∼2 dB OSNR gain is achieved at BER 10-3.

On-chip switch for reconfigurable mode-multiplexing optical network.

The switching and routing is essential for an advanced and reconfigurable optical network, and great efforts have been done for traditional single-mode system. We propose and demonstrate an on-chip switch compatible with mode-division multiplexing system. By controlling the induced phase difference, the functionalities of dynamically routing data channels can be achieved. The proposed switch is experimentally demonstrated with low insertion loss of ~1 dB and high extinction ratio of ~20 dB over the C-band for OFF-ON switchover. For further demonstration, the non-return-to-zero on-off keying signals at 10 Gb/s carried on the two spatial modes are successfully processed. Open and clear eye diagrams can be observed and the bit error rate measurements indicate a good data routing performance.

Actively stabilized silicon microrings with integrated surface-state-absorption photodetectors using a slope-detection method.

We propose and experimentally demonstrate actively stabilized silicon microrings with integrated surface-state-absorption (SSA) photodetectors using a slope-detection method. Our proof-of-concept experiments reveal that the active stabilization using multiple discrete-step slope thresholds can effectively reduce the microring transmitted intensity variations upon various temperature modulation conditions. We demonstrate an actively stabilized microring transmission with intensity modulations within ~2.5 dB upon a 5mHz temperature modulation between 17 °C and 31 °C, which is ~7.5dB improved from without stabilization. The active alignment tolerance between the stabilized microring resonance wavelength and a carrier wavelength is ~0.16 nm over a 14°C temperature modulation. We observe open eye-diagrams at a data transmission rate of up to 30 Gb/s under temperature modulations with actively stabilized silicon microrings.

High performance waveguide-coupled Ge-on-Si linear mode avalanche photodiodes.

We present experimental results for a selective epitaxially grown Ge-on-Si separate absorption and charge multiplication (SACM) integrated waveguide coupled avalanche photodiode (APD) compatible with our silicon photonics platform. Epitaxially grown Ge-on-Si waveguide-coupled linear mode avalanche photodiodes with varying lateral multiplication regions and different charge implant dimensions are fabricated and their illuminated device characteristics and high-speed performance is measured. We report a record gain-bandwidth product of 432 GHz for our highest performing waveguide-coupled avalanche photodiode operating at 1510nm. Bit error rate measurements show operation with BER< 10-12, in the range from -18.3 dBm to -12 dBm received optical power into a 50 Ω load and open eye diagrams with 13 Gbps pseudo-random data at 1550 nm.

Wavelength Tunable V-Cavity Laser Employing Integrated Thin-Film Heaters

A wavelength tunable V-cavity laser (VCL) employing integrated thin-film heaters is reported. The laser is fabricated by a simple process with no grating or band-gap engineering. A single-electrode-controlled wavelength tuning of 32 channels is achieved by experiment, with a tuning efficiency of 0.13 nm/mW, which is about 1.5 times higher than that of the current injection based thermal tuning. By combining four single-electrode controlled tunings with different bias currents, we obtain 51 wavelength channels covering 43 nm. Well-open eye diagrams with extinction ratios above 6.6 dB are obtained in all channels under direct modulation at 2.5 Gbps. The power penalty over a 25-km fiber transmission is less than 0.3 dB. Clearly open eye diagrams with bit error rates (BERs) below $10^{-12}$ are also obtained at 5 and 8.5 Gbps after a 10-km single-mode fiber transmission.

Monolithically mode division multiplexing photonic integrated circuit for large-capacity optical interconnection.

We propose and fabricate an on-chip mode division multiplexed (MDM) photonic interconnection system. Such a monolithically photonic integrated circuit (PIC) is composed of a grating coupler, two micro-ring modulators, mode multiplexer/demultiplexer, and two germanium photodetectors. The signals' generation, multiplexing, transmission, demultiplexing, and detection are successfully demonstrated on the same chip. Twenty Gb/s MDM signals are successfully processed with clear and open eye diagrams, validating the feasibility of the proposed circuit. The measured power penalties show a good performance of the MDM link. The proposed on-chip MDM system can be potentially used for large-capacity optical interconnection in future high-performance computers and big data centers.

High-speed all-optical NAND/AND logic gates using four-wave mixing Bragg scattering.

A high-speed all-optical NAND logic gate is proposed and experimentally demonstrated using four-wave mixing Bragg scattering in highly nonlinear fiber. NAND/AND logic functions are implemented at two wavelengths by encoding logic inputs on two pumps via on-off keying. A 15.2-dB depletion of the signal is obtained for NAND operation, and time domain measurements show 10-Gb/s NAND/AND logic operations with open eye diagrams. The approach can be readily extended to higher data rates and transferred to on-chip waveguide platforms.

High-bandwidth uni-traveling carrier waveguide photodetector on an InP-membrane-on-silicon platform.

A uni-traveling carrier photodetector (UTC-PD), heterogeneously integrated on silicon, is demonstrated. It is fabricated in an InP-based photonic membrane bonded on a silicon wafer, using a novel double-sided processing scheme. A very high 3 dB bandwidth of beyond 67 GHz is obtained, together with a responsivity of 0.7 A/W at 1.55 μm wavelength. In addition, open eye diagrams at 54 Gb/s are observed. These results promise high speed applications using a novel full-functionality photonic platform on silicon.

Analysis and Execution of 80 Gb/s PDM-DQPSK Optical Label Switching System with SAC Labels

We present the performance of 80 Gb/s polarization division multiplexed-differential quadrature phase shift keying (PDM-DQPSK) optical label switching system with frequency swept coherent detected spectral amplitude code labels in simulation. 4 bits of 156 Mb/s spectral amplitude code (SAC) label are frequency-swept coherently detected. The label and payload signal performances are assessed by the eye diagram opening factor (EOF) and bit error rate (BER) as function of received optical power (ROP) and optical signal to noise ratio (OSNR). For back-to-back system and 138 km transmission, label eye opening factors are 0.94 and 0.86 respectively, while payload optical signal-to-noise ratio is 25.6 dB and the payload received optical power is -12.6 dBm for a bit error rate of 10 -9 . The payload could well be demodulated after 1,260 km transmission at a BER of 10 -3 using forward error correction (FEC).

Broad-Band All-Optical Wavelength Conversion of Differential Phase-Shift Keyed Signal Using an SOA-Based Nonlinear Polarization Switch

Broad-band all-optical wavelength conversion of differential phase-shift keyed (DPSK) signal is experimentally demonstrated. This scheme is composed of a one-bit delay interferometer demodulation stage followed by a semiconductor optical amplifier (SOA) based nonlinear polarization switch. A wavelength converter for the 10 Gb/s DPSK signal is presented, which has a wide wavelength range of more than 30 nm. The converted signals experience small power penalties less than 1.4 dB compared with the original signal, at a bit error rate of 10−9. Additionally, the optical spectra, the measured waveforms and the open eye diagrams of the converted signals show a high quality wavelength conversion performance.

-1 V bias 67 GHz bandwidth Si-contacted germanium waveguide p-i-n photodetector for optical links at 56 Gbps and beyond.

We demonstrate a 67 GHz bandwidth silicon-contacted germanium waveguide p-i-n photodetector operating at -1 V with 6.8 fF capacitance. The dark current is below 4 nA. The responsivity is 0.74 A/W at 1550 nm and 0.93 A/W at 1310 nm wavelength. 56 Gbps on-off-keying data reception is demonstrated with clear open eye diagrams in both the C-band and O-band.

Design and Analysis of Enhanced Modulation Response in Integrated Coupled Cavities DBR Lasers Using Photon-Photon Resonance

In the last few decades, various solutions have been proposed to increase the modulation bandwidth and, consequently, the transmission bit-rate of semiconductor lasers. In this manuscript, we discuss a design procedure for a recently proposed laser cavity realized with the monolithic integration of two distributed Bragg reflector (DBR) lasers allowing one to extend the modulation bandwidth. Such an extension is obtained introducing in the dynamic response a photon-photon resonance (PPR) at a frequency higher than the modulation bandwidth of the corresponding single-section laser. Design guidelines will be proposed, and dynamic small and large signal simulations results, calculated using a finite difference traveling wave (FDTW) numerical simulator, will be discussed to confirm the design results. The effectiveness of the design procedure is verified in a structure with PPR frequency at 35 GHz allowing one to obtain an open eye diagram for a non-return-to-zero (NRZ) digital signal up to 80 GHz . Furthermore, the investigation of the rich dynamics of this structure shows that with proper bias conditions, it is possible to obtain also a tunable self-pulsating signal in a frequency range related to the PPR design.

Error-free DWDM transmission and crosstalk analysis for a silicon photonics transmitter.

Individual channels of a five-channel microring silicon photonics transmitter are used for bit error ratio analysis and demonstrate error-free transmission at 10Gb/s. Two channels of the same transmitter are concurrently modulated using an 80GHz channel spacing comb laser and demonstrate open eye diagrams at 10Gb/s and 12.5Gb/s. Finally, concurrent modulation with tunable lasers is done to quantify optical power penalty for link bit error ratio versus channel spacing from +100GHz to -100GHz. When using a comb laser for concurrent modulation, no direct power penalty is observed for an 80GHz channel separation.

Microwave Photonic Mixer Based on Polarization Rotation and Polarization-Dependent Modulation

A microwave photonic mixer capable of both amplitude and phase modulation is proposed and experimentally demonstrated. This scheme utilizes single-sideband modulation in dual-drive Mach–Zehnder modulator and polarization rotation in semiconductor optical amplifier to generate a pair of phase coherent optical carriers with different polarizations, while a polarization sensitive Mach–Zehnder intensity modulator (MZM) is used for modulating the IF signal onto one of the generated carrier. Both the optical and the electrical spectra are measured and show successful frequency mixing. By setting the bias point of the MZM at slightly different voltages, our scheme supports binary-phase-shift keying, on–off keying, and amplitude-shift keying modulations. Widely opened eye diagrams and clear waveforms are experimentally obtained for all modulations. Moreover, the proposed scheme does not have a hard limit on the supported lowest local oscillator frequency and no reconfiguration is needed when a frequency change in the local oscillator is required.

Silicon-on-Insulator Modulators Using a Quarter-Wave Phase-Shifted Bragg Grating

We demonstrate, on the silicon-on-insulator platform, a modulator that uses a quarter-wave phase-shifted Bragg grating resonator. The modulator has open eye diagrams at data rates of up to 32 Gb/s. A bit error ratio of less than ${10}^{-10}$ is demonstrated using a $2^{31}-1$ pseudorandom binary sequence pattern at a data rate of 25 Gb/s.

Experimental Investigation of All-Optical NRZ-DPSK to RZ-DPSK Format Conversion Based on TOAD

We propose and experimentally demonstrate a novel all-optical non-return-to-zero differential-phase-shift-keying (NRZ-DPSK) to return-to-zero differential-phase-shift-keying (RZ-DPSK) format conversion scheme. This scheme is based on the terahertz optical asymmetric demultiplexer (TOAD). A 10 Gb/s converted RZ-DPSK signal is obtained with a wide duty cycle tuning range from 16% to 66%. For all converted RZ-DPSK signals, the receiver sensitivities at BER of 10−9 are 0.4 to 1.7 dB higher compared with the original NRZ-DPSK signal. The clear and open eye diagrams are presented to demonstrate the high quality format conversion performance. Moreover, the optical spectra show that this conversion is in a wavelength-preserving operation.