We demonstrate novel optical signal processing functions based on self-induced nonlinear polarization rotation in a semiconductor optical amplifier (SOA). Numerical and experimental results are presented, which demonstrate that a nonlinear polarization switch can be employed to achieve all-optical logic. We demonstrate an all-optical header processing system, an all-optical seed pulse generator for packet synchronization, and an all-optical arbiter that can be employed for optical buffering at a bit rate of 10 Gb/s. Experimental results indicate that optical signal processing functions based on self-polarization rotation have a higher extinction ratio and a lower power operation compared with similar functions based on self-phase modulation.

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Optical signal processing based on self-induced polarization rotation in a semiconductor optical amplifier

This paper describes the demonstration of a simple all-optical data format conversion scheme between return-to-zero (RZ) and nonreturn-to-zero (NRZ) that employs a semiconductor optical amplifier (SOA) in a nonlinear optical loop mirror. The format conversion has been performed between the most widely used data formats-NRZ and RZ formats. The format conversion scheme is based on gain variation by an intensity-dependent phase change in an SOA-loop mirror. The input data stream acts as a control signal that induces the phase differences between clockwise- and counterclockwise-propagating data inside an SOA-loop mirror. It is possible to change the data format of the output data stream by controlling the phase differences of the clockwise and counterclockwise pulse in an SOA-loop mirror appropriately. For the converted NRZ data from RZ data, 10-Gb/s error-free transmission up to 78 km over standard single-mode fiber has been obtained. By comparing the conventional NRZ transmission with the Mach-Zehnder modulation scheme, the proposed RZ-to-NRZ conversion shows an improved transmission performance. The NRZ-to-RZ conversion has clear eye openings up to 78 km. On the contrary, the conventional RZ binary data from a mode-locked laser has a nearly closed eye even at 52 km. The converted RZ data has a 2-dB conversion power margin to the injected NRZ data, which indicates an increase in the receiver sensitivity due to the signal format conversion. The improved transmission distance of the converted RZ signal is due to the duobinary coding effect of the SOA-loop mirror. The SOA has the possibility of high-speed operation over 40 Gb/s, and the SOA-loop mirror has the capabilities of format and wavelength conversions. Therefore, the SOA-loop mirror can be a universal building block in future all-optical networks. In addition, the proposed format conversion scheme can serve as an important format converter between the ultrafast optical-time-division-multiplexed networks and the lower line-rate wavelength-division-multiplexed networks.

Experimental demonstration of 10-gb/s data format conversions between NRZ and RZ using SOA-loop-mirror

A simple technique, based on nonlinear polarization rotation, for the amplitude equalization of high repetition rate pulses generated from a rational harmonic mode-locked fiber ring laser was demonstrated. Amplitude equalized pulses at 10 GHz (the fourth rational harmonic) were obtained with a harmonic component suppression ratio up to 30 dB. A theoretical explanation was given in detail, which indicates that, after pulse amplitude equalization, the situation of unequal pulse spacing can be improved to a certain extend.

Theoretical and experimental study of pulse-amplitude-equalization in a rational harmonic mode-locked fiber ring laser

The present invention consists of a system and method for regenerating and converting optical signals. The invention provides both “2R (i.e. reamplification and reshaping) and “3R” (i.e. reamplification, reshaping, and resynchronization (or retiming)) regeneration. The components of the inventive system include a tunable continuous wave (CW) laser source, an optical circulator, an semiconductor optical amplifier (SOA), and a spectral filter that has a very sharp cutoff frequency. In alternative embodiments, the filter may be replaced with an interleaver that passes several wavelengths. A single interleaver may be used by several of the optical regenerators/converters described herein. Each regenerator uses a separate wavelength that is associated with a passband frequency of the single interleaver. During counter-propagation in the SOA, a CW signal from the CW laser is chirped by bits in an input signal. The chirped signal is then output to the filter, which blocks the original CW signal.

All-optical, tunable regenerator, reshaper and wavelength converter

Nonlinear dynamics of semiconductor lasers is applied for microwave frequency division. Optical injection is used to drive a slave laser into the dynamical period-two state. A fundamental microwave frequency and its subharmonic are generated in the power spectrum. Both frequencies will be simultaneously locked when an external microwave near either frequency is applied on the bias. In our experiment, precise microwave frequency division is demonstrated by modulating the laser at the fundamental of 18.56 GHz. A locked subharmonic at 9.28 GHz with a low phase variance of 0.007 rad/sup 2/ is obtained from a 10-dBm input. A large locking range of 0.61 GHz is measured under a 4-dBm modulation. Similarly, precise frequency multiplication is demonstrated by modulating at 9.65 GHz. At an input power of -5 dBm, a multiplied signal at 19.30 GHz is obtained with a phase variance of 0.027 rad/sup 2/ and a locking range of 0.22 GHz.

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Microwave frequency division and multiplication using an optically injected semiconductor laser

The feasibility of all-optical clock recovery (CR) from non-return-to-zero (NRZ) data with a simple NRZ-to-pseudo-RZ (PRZ) converter based on the self-phase modulation (SPM) of a semiconductor optical amplifier (SOA) is empirically presented The SPM induces a frequency chirp at every leading edge of the NRZ data passing through the SOA The SPM-induced chirp component is extracted by an optical grating bandpass filter and then transformed to PRZ data with a low polarisation dependency of ~07 dB By transmitting the PRZ data into a mode-locked Er-doped fibre laser, all-optical CR has been achieved at 25 Gbit/s

All-optical clock recovery from NRZ data with simple NRZ-to-PRZ converter based on self-phase modulation of semiconductor optical amplifier

Pulse-amplitude equalization of rational harmonic mode-locked fiber laser using a semiconductor optical amplifier loop mirror

The authors experimentally demonstrate simple packet-level clock extraction using a modified terahertz optical asymmetric demultiplexer without wavelength-division-multiplexed couplers in the loop mirror. For a 10-Gb/s optical packet composed of identical pulses, we have obtained more than 10-dB contrast ratio between the packet-level clock pulse and the other pulses.

A simple packet-level clock extraction scheme using a terahertz optical asymmetric demultiplexer

By exploiting pump-induced birefringence in addition to cross-gain modulation, we have obtained improved extinction ratio and reduced optical power penalties for a wavelength converter using a semiconductor optical amplifier. In the probe beam wavelength range of 1528-1566 nm, while extinction ratios and power penalties of a conventional wavelength converter are found to be 4.5-9.2 dB and -0.5-2.1 dB, those of the proposed converter are 6.6-10 dB and -0.7-1.0 dB, respectively. The proposed converter shows better performance for all wavelengths in the range examined for both extinction ratio and power penalty. Especially, more improvements have been obtained in the longer wavelength.

Wavelength dependent performance of a wavelength converter based on cross-gain modulation and birefringence of a semiconductor optical amplifier

We propose and experimentally demonstrate, for the first time to our knowledge, polarization-independent all-optical clock division (CD) of an optical pulse train at 2.88 GHz. This is achieved using a semiconductor-optical amplifier (SOA)/grating-filter switch, where the SOA acts as a spectral shifter by a self-phase modulation (SPM) and the grating filter acts as a spectral shutter. The proposed scheme is very insensitive to the polarization of input pulses and requires very low switching energy (/spl sim/102 fJ). After the all-optical CD operation, we have obtained the output pulse train at 1.44 GHz, which is half the input repetition rate, with high extinction ratio (>20 dB).

Hae Geun Kim

Papers

All-optical clock recovery from NRZ data with simple NRZ-to-PRZ converter based on self-phase modulation of semiconductor optical amplifier

Pulse-amplitude equalization of rational harmonic mode-locked fiber laser using a semiconductor optical amplifier loop mirror

A simple packet-level clock extraction scheme using a terahertz optical asymmetric demultiplexer

Wavelength dependent performance of a wavelength converter based on cross-gain modulation and birefringence of a semiconductor optical amplifier

Polarization-independent all-optical clock division using a semiconductor optical amplifier/grating filter switch