Optical Time-division Demultiplexing Research Articles

Characterization of the Frequency Response of Channel-Interleaved Photonic ADCs Based on the Optical Time-Division Demultiplexer

We characterize the frequency response of channel-interleaved photonic analog-to-digital converters (CI-PADCs) theoretically and experimentally. The CI-PADC is composed of a photonic frontend for photonic sampling and an electronic backend for quantization. The photonic frontend includes a photonic sampling pulse generator for directly high-speed sampling and an optical time-division demultiplexer (OTDM) for channel demultiplexing. It is found that the frequency response of the CI-PADC is influenced by both the photonic sampling pulses and the OTDM, of which the combined impact can be characterized through demultiplexed pulse trains. First, the frequency response can be divided into multiple frequency intervals and the range of the frequency interval equals the repetition rate of demultiplexed pulse trains. Second, the analog bandwidth of the CI-PADC is determined by the optical spectral bandwidth of demultiplexed pulse trains which is broadened in the OTDM. Further, the effect of the OTDM is essential for enlarging the analog bandwidth of the CI-PADC employing the photonic sampling pulses with limited optical spectral bandwidth.

Demonstration of an [formula omitted]-Gb/s optical time-division multiplexing system

An 8×25-Gb/s optical time-division multiplexing (OTDM) system is demonstrated experimentally. The optical pulse source is based on optical frequency comb (OFC) generation and pulse shaping, which can generate nearly chirp-free 25-GHz 1.6-ps optical Gaussian pulse. The eightfold optical time-division demultiplexer consists of a single-driven dual-parallel Mach–Zehnder modulator (DPMZM) and a Mamyshev reshaper. Error-free demultiplexing of 8×25-Gb/s back-to-back (B2B) signal with a power penalty of 4.1 dB to 4.4 dB at a bit error rate (BER) of 10−9 is achieved to confirm the performance of the proposed system.

Effective optical clock recovery and simultaneous fourfold demultiplexing of OTDM signal using an optoelectonic oscillator

We propose and demonstrate a novel scheme for clock recovery and simultaneous fourfold optical time-division demultiplexing using a dual-parallel Mach-Zehnder modulator based optoelectronic oscillator. 25-GHz prescaled optical clock with a 23% duty cycle and a 22-dB extinction ratio is successfully extracted from both 100-Gb/s on-off keying (OOK) and differential phase-shift keying (DPSK) optical time-division-multiplexing (OTDM) signal. The timing jitters (100 Hz to 10 MHz) are measured to be 195.9 fs and 125.6 fs for the optical clock extracted from the 100-Gb/s OOK and DPSK signal, respectively. Error-free optical time-division demultiplexing is also achieved simultaneously with clock recovery. By adjusting the phase shifter in the OEO loop, all four channels can be selectively demultiplexed. The power penalties at a bit error rate (BER) of 10⁻⁹ for the four demultiplexed channels are measured to be between 0.8 dB and 1.2 dB for the OOK signal and between 0.9 dB and 1.5 dB for the DPSK signal.

Simultaneous Clock Enhancing and Demultiplexing for 160-Gb/s OTDM Signal Using Two Bidirectionally Operated Electroabsorption Modulators

We demonstrate a technique for performing optical time-division simultaneous clock enhancing and demultiplexing using two bidirectionally operated electroabsorption modulators (EAMs). The performance of the proposed setup is verified experimentally in a 160-Gb/s 100-km transmission system. The 10-GHz clock component is enhanced before launching into the clock recovery module. The recovered 10-GHz clock signal is featured with low timing jitter ( <;300 fs) and error-free transmission is achieved with the power penalty of ~ 0.9 dB. The proposed setup has merits of simultaneously enhancing base clock component and demultiplexing.

Evaluate the Performance of Optical Time Division Demultiplexing with the Gain Saturation effect of Semiconductor Optical Amplifier

Optical Time Division Multiplexing (OTDM) system technique is the extend time division multiplexing by optically combining a number of lower speed electronic baseband digital channels. In addition, the Semiconductor Optical Amplifiers (SOA's) are important components for optical networks. In this paper, we propose a novel model for an OTDM demultiplexer based on Cross Gain Modulation in a SOA. Analysis are extended to find the output of an optical IM/DD receiver to receive the demultiplexed optical signal and to find the output signal to noise ratio (SNR) taking into account the amplified spontaneous emission (ASE) noise. The results are evaluated in terms of BER, SNR and pump power for various input signal power level. It is found that, at a given signal input power the BER can be reduced by increasing the pump power and the required pump power is higher at higher level of input power.

Turbo-switched Mach-Zehnder interferometer performance as all-optical signal processing element at 160 Gb/s

Two variations of the active Mach-Zehnder interferometer (MZI) that incorporate the recently proposed turbo-switch effect are introduced to carry out three key functionalities in forthcoming high-speed optical telecommunication networks, namely, all-optical wavelength conversion, photonic XOR gating and optical time-division demultiplexing. Their performance is numerically investigated at 160 Gb/s using a sophisticated semiconductor optical amplifier (SOA) model. The more practical of the two proposed geometries shows error-free operation as XOR Boolean gate, low patterning as wavelength converter, and poor performance as demultiplexer. For comparison, results derived from well-accepted (or typical) schemes are also presented, and the role of the required extra SOAs as distinguishing elements of the new architectures is investigated.

Subharmonic Optoelectronic Oscillator

I propose and demonstrate a subharmonic optoelectronic oscillator (SH-OEO), which contains a frequency divider in the feedback loop and performs optical clock division, prescaled optical clock recovery, and optical time-division demultiplexing in the absence of subharmonic tones in the input signals. Also, I propose a scheme that achieves divide-by-two optical clock recovery and serial-to-parallel conversion of optical data signals simultaneously using a polarization modulator-based SH-OEO.

160-Gb/s Optical Time-Division Demultiplexing Using a Mach–Zehnder Modulator in a Fiber Loop

Optical switching a 160-Gb/s signal using a LiNbO Mach-Zehnder modulator (MZM) is enabled by a novel method of connecting it within an optical fiber-loop mirror. The principle of operation exploits the unidirectional optical modulation of the MZM such that counterpropagating waves within the loop experience unequal amplitude modulation leading to output transmission of a high-quality 40-GHz pulse train of duration shorter than if using just the MZM alone. Measurements employing a commercially available MZM modulated at 40 GHz in a fiber-loop show generation of a 5.3- to 5.9-ps-wide gate pulse at a 40-GHz repetition rate with center wavelength tunable from 1535 to 1565 nm. Application to optical time-division demultiplexing of a 160-Gb/s return-to-zero format signal achieves less than 1-dB bit-error-rate power penalty for all four of its 40-Gb/s tributaries.

Kerr-type spatial optical solitons in planar waveguides with finite width and the design of all optical devices

The propagation of paraxial light beams injected at an inclined angle in a planar waveguide with finite width is studied by numerical method. The soliton beams with different wavelength and same width，if their incident point and incident slanting angle are the same，will propagate along the same periodic Z-type route in the planar waveguide. With the power of the beam increasing，the distance between two adjacent reflecting points will become longer and longer with the propagation distance and the Z-type route will lose its periodicity. When the power of a beam become fairly strong，the beam will propagate along z direction of the waveguide，and will no longer be reflected back and forth between the two boundaries of the planar waveguide. Using the characteristic that a beam injected at an inclined angle in the waveguide will propagate along different route with different power，a power switch and an optical time division demultiplexer are designed.

Optical Signal Processing by Phase Modulation and Subsequent Spectral Filtering Aiming at Applications to Ultrafast Optical Communication Systems

This paper describes optical signal processing based on optical phase modulation and subsequent optical filtering, which is applicable to 160-Gb/s optical time-division multiplexed (OTDM) subsystems. Ultrafast phase modulation of an optical signal is done by self-phase modulation (SPM) and cross-phase modulation (XPM) when an optical pulse passes through a nonlinear optical fiber. Such phase modulation induces the spectral shift of the optical signal. Various types of optical signal processing are realized simply by filtering out the spectral-shifted component. Using SPM-based pulse reshaping in a 500-m-long silica-based highly nonlinear fiber (HNLF), we demonstrate highly stable generation of a 10-GHz 2-ps optical pulse train tunable over the entire C band. A phase-locked loop (PLL) can suppress the slow phase drift of the output pulse train induced by fluctuations of the nonlinear fiber length, enabling the application of the pulse generator to a 160-Gb/s OTDM transmitter. Based on XPM in a 2-m-long photonic crystal fiber, optical time-division demultiplexing of 160-Gb/s optical signals is demonstrated. The long-term stability is drastically improved as compared with the device composed of a conventional silica-based HNLF, because the short fiber length reduces the phase fluctuation between the signal and control pulses. Instead of nonlinear fibers, an electrooptic modulator such as a (LN) modulator also performs the phase modulation in a more practical manner. We propose and demonstrate an optoelectronic time-division demultiplexing scheme for a 160-Gb/s OTDM signal, which consists of an LN phase modulator driven by a 40-GHz electrical clock and an optical bandpass filter (BPF). We also demonstrate base-clock recovery from a 160-Gb/s optical signal with an optoelectronic PLL. The phase comparator is simply composed of an LN phase modulator and an optical BPF, ensuring the stable and reliable operation in the 160-Gb/s receiver.

EA-Modulator-Based Optical Time Division Multiplexing/Demultiplexing Techniques for 160-Gb/s Optical Signal Transmission

In this paper, 160-Gb/s optical-time-division-multiplexing (OTDM) techniques employing electroabsorption (EA)-modulator-based optical multiplexer are described. The optical multiplexer integrates four EA modulators with free-space optics and enables, stably, to generate an authentic 160-Gb/s OTDM signal. The optical multiplexer possesses a switching capability of modulation format, which originates in the thermo-optic effect in EA waveguide, so that it is possible to generate various phase-coded OTDM signals such as carrier-suppressed return-to-zero (CS-RZ) signal by tuning operation temperatures of the EA modulators. By employing the novel 160-Gb/s optical multiplexer, prototypes of 160-Gb/s OTDM transmitter and receiver were developed. EA modulators are also adopted to optical short pulse source at transmitter side, optical time division demultiplexer, and phase-locked loop (PLL) circuit for clock recovery at the receiver side. The 160-Gb/s system prototype exhibited a superior performance maintaining high stability, and its applicability to practical use is discussed, showing experimental results of 160-Gb/s 635 km field trial on Japan Gigabit Network II (JGN II) optical testbed

Use of 1-mBi_2O_3 nonlinear fiber for 160-Gbit?s optical time-division demultiplexing based on polarization rotation and a wavelength shift induced by cross-phase modulation

We present, for the first time to our knowledge, experimental results of the use of a 1-m-long Bi2O3-based nonlinear fiber (Bi-NLF) with a nonlinear parameter gamma of approximately 1100 W(-1) km(-l) within an all-fiber-based 160Gbit/s optical time-division multiplexing (OTDM) data demultiplexer. Our demultiplexing switch basically uses the principle of the Kerr shutter, and its switching performance is further enhanced by the additional use of the wavelength blueshift of data pulses, which is induced by cross-phase modulation from the control pulse's trailing edge. The OTDM demultiplexer, composed of the 1-m Bi-NLF, readily achieves error-free demultiplexing operation of all 16 channels.

Polarization and wavelength-independent time-division demultiplexing based on copolarized-pumps FWM in an SOA

A novel optical time-division demultiplexer based on copolarized-pumps four-wave mixing in semiconductor optical amplifiers is presented. The scheme is polarization and wavelength independent. Effective 10-Gb/s channel extraction from an optical time-division multiplexed 40-Gb/s aggregate frame is experimentally demonstrated.

160-Gbit/s Full Channel Optical Time-Division Demultiplexer Based on SOA-Array Integrated PLC and Its Application to OTDM Transmission Experiment

This paper presents 160-Gbit/s full channel time-division demultiplexing using a semiconductor optical amplifier hybrid integrated demultiplexer on a planer lightwave circuit. Error-free demultiplexing from a 160-Gbit/s signal to 8 channel x 20Gbit/s signals is successfully demonstrated. Results of a 160-Gbit/s optical time-division-multiplexed full channel OTDM signal transmission experiment using the circuit and successful 80-km transmission are presented.

Noise and Intersymbol-Interference Properties of OTDM and ETDM Receivers

We experimentally and theoretically confirm the similar performance of optical time-division demultiplexing (OTDM) and electrical time-division demultiplexing (ETDM) receivers for beat-noise limited return-to-zero signal detection. OTDM receivers show a slight sensitivity advantage, largely independent of parameters like the receiver's optical filter bandwidth or center frequency. The OTDM sensitivity benefit is caused by reduced intersymbol-interference properties of the OTDM receiver, as well as by the suppression of beat noise by the temporal demultiplexing window. The latter effect can be captured by extended expressions for the beat-noise variances presented in this letter.

Ultrafast walk-off-free nonlinear optical loop mirror by a simplified configuration for 320-Gbit/s time-division multiplexing signal demultiplexing

We demonstrate a simplified configuration of an ultrafast walk-off-free nonlinear optical loop mirror (NOLM) for 320-10-Gbit/s optical time-division demultiplexing. The proposed NOLM consists of a short, 100-m length of highly nonlinear dispersion-shifted fiber, resulting in compact, highly stable, and ultrafast walk-off-free operation.

Optical signal processing using nonlinear semiconductor microring resonators

Recent fabrication advances have enabled compact semiconductor microring resonators to be fabricated with high-finesse values and picosecond cavity lifetimes. These devices have potential applications in optical signal processing as all-optical switches, multiplexers and logic gates. Theoretical analysis shows a maximum reduction in the switching power proportional to the fourth power of the field enhancement in the microring. An enhancement in the wavelength conversion efficiency by four-wave mixing which is proportional to the eighth power of the field enhancement is also predicted and experimentally confirmed. Experimental results demonstrating bistability, picosecond switching using pump and probe excitation, optical time-division demultiplexing, spatial pulse routing and four-wave mixing in GaAs-AlGaAs microring resonators are reported. Apart from the bistable response, which was thermally induced, the nonlinear effects observed in the microrings were caused by the two-photon absorption process. Applications of microrings to realize all-optical logic gates are also proposed.

Cross-talk analysis of optical time-division demultiplexer

We have developed a simulation model to investigate the demultiplexing of all-optical-time-division-multiplexed data, employing an optical time-division demultiplexer. Particular attention is paid to the cross-talk performance when selected parameters of the system are varied. The system used to demultiplex the data is the asymmetric semiconductor laser amplifier loop mirror (ASLALOM), which is capable of selecting high-speed optical pulses within a data train. The authors use a model of the ASLALOM that includes a time and space analysis of a traveling-wave semiconductor laser amplifier. Our investigation shows that this system produces cross talk that is dependent on the data rate, control pulse energy, and control pulse rate.

Novel scheme for optical time-division demultiplexing using a delayed interferometer

A novel cross-phase-modulation-based scheme to perform optical time-division demultiplexing using a delayed interferometer is put forward and its operational principles analysed. Simulations of 40:10 Gb/s demultiplexing show that, through operational parameter optimisation, suppression of the undesired channels can effectively be achieved. The simplicity and compactness of the device makes it suitable for practical applications.

Modeling of NOLM demultiplexers employing optical soliton control pulse

An optical soliton pulse may be used as a control signal in non-linear optical loop mirror demultiplexers in order to reduce timing-jitter noise and cross-talk. A mathematical model for calculating the width of the soliton switching window and optimizing critical parameters such as walk-off time and pulse width has been presented, and its accuracy is verified by solving the non- linear Schrodinger equation. Key word: Semiconductor laser amplifier, optical switching, soliton, optical time division demultiplexer, optical loop mirrors.