RZ Signals Research Articles

Prescaled clock recovery based on small timing misalignment of data pulses

A simple and robust prescaled clock recovery technique is analyzed and demonstrated. An electrical clock is extracted from an ultra-high-speed time-division multiplexed (TDM) RZ signal using a classic approach to clock recovery with a detector and a bandpass filter (BPF). A subharmonic tone at the base rate frequency is generated by inducing a small misalignment between adjacent pulses in the transmitted data. The subharmonic tone is recovered as a clock signal at the receiver. Numerical calculations clarify the effect of filter bandwidth, word length, and strength of timing shift on the received timing jitter. Furthermore, it is found numerically that correlated TDM channels will decrease the jitter of the recovered clock considerably. A clock recovery circuit is implemented into an experimental 40 Gb/s and 80 Gb/s optical TDM (O-TDM) system without any observed penalty. Measurements of the timing jitter of the recovered prescaled clock have been performed to verify the numerical results. A 10 GHz clock signal with subpicosecond root-mean-square timing jitter is recovered from a 40-Gb/s O-TDM sequence without a phase-locked loop (PLL) configuration. By using a PLL-configuration, the timing jitter is reduced further by 50%. A discussion on the influence on transmission capacity is performed in general and for nonlinear optical communication systems in particular.

Experimental comparison of transmission system penalty of 10 Gbit/s RZ and NRZ optical signals due to polarization-mode dispersion

Experimental comparison of transmission system penalty of 10 Gbit/s RZ and NRZ optical signals due to polarization-mode dispersion

Experimental comparison of transmission system penalty of 10 Gbit/s RZ and NRZ optical signals due to polarization-mode dispersion

Experimental comparison of transmission system penalty of 10 Gbit/s RZ and NRZ optical signals due to polarization-mode dispersion

Optical polarisation-mode dispersion compensationof 2.4 bit durations of differential group delay at 40 Gbit/s

A method for realising the optical polarisation-mode compensation of a differential group delay of 2.4 bit durations is demonstrated for the first time, using a distributed fibre optic equaliser. As a result, it is believed that much of the existing fibre network can be upgraded even to 40 Gbit/s and RZ signal format.

Polarisation mode dispersion compensation for 6ps,40 Gbit/s pulses using distributed equaliser in LiNbO 3

PMD compensation for RZ signals is demonstrated for the first time, using a distributed LiNbO/sub 3/:Ti PMD compensator. An electrical detection scheme allows the pulsewidth to be maintained at <6 ps.

340 Gbit/s (34 × 10 Gbit/s) WDM transmissionover 8,514 kmusing broadband gain equalisation technique for transoceanic systems

The authors successfully transmit 34 10 Gbit/s RZ signals over 8,514 km. The use of gain equalisation with a broad optical bandwidth of 23 nm and a higher-order dispersion-managed line are found to enable large capacity WDM transmission.

Transmission of 10 Gbit/s wavelength converted RZdataover 20 000 km in a dispersion-managed system

The first experimental demonstration of propagation of a wavelength converted RZ signal in a dispersion-managed system is described. An all-optical wavelength converter comprising a semiconductor optical amplifier and a fibre Bragg grating was used to generate the converted data. Error-free transmission of the 10 Gbit/s converted signal over 20 000 km was achieved.

10 Gbit/s RZ-signal transmission over 12960 kmin the anomalous regime with optimised in-line optical filters

An in-line filter arrangement is investigated experimentally for single-channel long-distance optical transmission in the anomalous region with periodic dispersion compensation. The optimal arrangement, along with the optimum compensation ratio and in-line amplifier output power, allows a 10 Gbit/s RZ signal to be successfully transmitted over 12960 km in a 720 km recirculating loop.

4 × 10 Gbit/s RZ-signal transmission over5040 kmin anomalous regime with optimallydispersion-compensated WDM channels

Allowable combinations of dispersion compensation period, compensation ratio, and line dispersion are investigated experimentally for WDM RZ-signal transmission in the anomalous dispersion region. One optimum combination enables 4 channel/spl times/10 Gbit/s RZ signals to be transmitted successfully over 5040 km in a recirculating loop.

80 Gbit/s-1200 km, 40 Gbit/s-based WDM transmissionexperiment using RZ pulse format

The successful two-channel WDM transmission of optically multiplexed 40 Gbit/s RZ signals with properly managed fibre dispersion is demonstrated. The dispersion dependence of the signal-to-noise-ratio for each signal channel is measured and it is found that the optimum total dispersion value, including dispersion compensation fibres, is not zero but is anomalous, which is slightly smaller than the value predicted by the soliton condition with uniform dispersion.

Optical RZ signal straight-line transmission experimentswith dispersion compensation over 5520 km at 20 Gbit/s and 2160 km at 2 ×20 Gbit/s

Through optimisation of a dispersion compensation ratio to balance the effects of timing jitter and waveform distortion, single-channel and two-WDM-channel 20 Gbit/s RZ signals are successfully transmitted over 5520 and 2160 km, respectively, in the anomalous dispersion region.

10 Gbit/s, 6000 km NRZ and 4400 km RZ signal transmissionexperiments at zero-dispersion wavelength

NRZ and RZ signals are compared in in-line amplifier transmission experiments conducted at a zero-dispersion wavelength. At 10 Gbit/s these two formats achieve transmission distances of 6000 and 4400 km, respectively. This difference is mainly attributed to their strength against the waveform distortion owing to the combined effect of higher-order group-velocity dispersion and self-phase modulation.

Four WDM channel NRZ to RZ format conversionusing a single semiconductor laser amplifier

Multiwavelength channel NRZ to RZ format conversion using a single semiconductor laser amplifier is proposed and experimentally demonstrated. Bit-error-rate measurement of four 10 Gbit/s converted RZ signal channels has confirmed that no noticeable error floor existed.

All-optical RZ-to-NRZ format conversionat 10 Gbit/s with nonlinear optical loop mirror

All-optical RZ-to-NRZ format conversion of a 10 Gbit/s RZ signal by a nonlinear optical loop mirror is demonstrated. The effect of walkoff, fibre loss and data mark ratio on resulting NRZ signals is analysed.

Bit-rate enhancement through optical NRZ-to-RZconversion and passive time-division multiplexingfor soliton transmission systems

A nonlinear optical loop mirror is used to convert an NRZ signal generated by a standard 2.5 Gbit/s transmitter into a near-transform-limited 2.5 Gbit/s RZ signal. Passive time-division multiplexing is then used to enhance the signal bit rate up to 10 Gbit/s. This experiment shows the potential of using NRZ transmitters for high bit rate soliton system applications.

A programmable optical demultiplexer using a 32–element photodiode array

AbstractThis paper describes the design and performance of a programmable optical demultiplexer which can compensate the influence of: (1) scattering in the wavelength of an optical source; and (2) wavelength fluctuation of the optical source caused by temperature change, by controlling the branching characteristics in accordance with the wavelength of the optical source. In this multiplexer, a 32‐element Si photodiode array was used to carry out programmable control of the branching characteristics. This optical demultiplexer has the following merits: (1) a wide channel passband is not needed; and (2) since the passband‐center wavelength of this multiplexer is adjusted to the wavelength of the optical sources, fine tuning of the branching characteristic in fabrication is not needed. The fabricated programmable optical demultiplexer has a channel wavelength spacing of 4.0 nm, an insertion loss of 8.0 dB which includes a loss of 3.9 dB due to the detection loss caused by the gap between two photodiodes composing the PD array, and a passband width of 2.8 nm. It was confirmed also by a digital transmission experiment (32 mB/s, RZ signal) that this demultiplexer can maintain its optimum branching characteristics for any wavelength deviation in the optical sources.

The instantaneous frequency of a sinewave squelched bandlimited signal.

We study the instantaneous frequency of a signal which is formed by the summation of a sinewave and a bandlimited signal. We refer to the composite signal as a sinewave squelched or simply a squelched signal. We study the behavior of the squelched signal at its real zeros and extrema. In particular when the sinewave frequency is equal to the largest frequency in the signal's spectrum and its amplitude is greater than the signal's maximum amplitude, the analytic signal corresponding to this resultant signal (hereafter abbreviated as RZ signal) has only real zeros which contain all of the bandlimited signal's information. FM systems often use zero crossing techniques in the demodulation process. For a process with a normal amplitude distribution, we derive a relationship between the zero crossing density of an RZ converted signal and that of the original signal. One application of these analyses is in ultrasonic FM imaging. We give an explanation for the behavior of the FM imaging system as a function of amplitude and frequency of the added cosine.

The instantaneous frequency of a sinewave squelched bandlimited signal

We study the instantaneous frequency of a signal which is formed by the summation of a sinewave and a bandlimited signal. We refer to the composite signal as a sinewave squelched or simply a squelched signal. We study the behavior of the squelched signal at its real zeros and extrema. In particular when the sinewave frequency is equal to the largest frequency in the signal's spectrum and its amplitude is greater than the signal's maximum amplitude, the analytic signal corresponding to this resultant signal (hereafter abbreviated as RZ signal) has only real zeros which contain all of the bandlimited signal's information. FM systems often use zero crossing techniques in the demodulation process. For a process with a normal amplitude distrubution, we derive a relationship between the zero crossing density of an RZ converted signal and that of the original signal. One application of these analyses is in ultrasonic FM imaging. We give an explanation for the behavior of the FM imaging system as a function of amplitude and frequency of the added cosine.

Injection-locking technique applied to a 170 km transmission experiment at 445.8 Mbit/s

Transmission with a BER less than 10−11 has been achieved using an injection-locking technique with a 445.8 Mbit/s RZ signal over a 170 km single-mode fibre. The injection-locking technique provides a single-longitudinal-mode optical source with a 35 dB main/side-mode power ratio and a 1.5 GHz spectral width.

4 Gbit/s pseudo-noise generator using GaAs MESFETs

A multiplexing gate using GaAs MESFETs is described and operation up to 4 Gbit/s is demonstrated. A 2 Gbit/s pseudo-noise generator which can deliver NRZ or RZ signals has been implemented with this circuit; the corresponding output sequences are shown.