Extinction Ratio Improvement Research Articles

All-Optical Wavelength Conversion Using SOA at Nearly Symmetric Position in a Fiber-Based Sagnac Interferometric Loop

We report an experimental analysis of the wavelength conversion operation of a fiber-based Sagnac interferometric loop with a semiconductor optical amplifier (SOA) at nearly symmetric position. Improved extinction ratio is obtained due to the complementary operation of cross-polarization modulation and cross-gain modulation effects. Power penalty of 2.4 dB was obtained when the SOA offset is 17% of the bit period, which enables the use of the Sagnac interferometer with asymmetrically placed SOA-the terahertz optical asymmetric demultiplexer (TOAD)-as a multiple-functionality all-optical signal processing network element.

Wavelength Conversion Using an Integrated DFB Laser–Phase Shifter

A method of wavelength conversion with signal reshaping (2R regeneration) is proposed based on injection of probe light into an integrated distributed feedback laser-phase shifter. The conversion is based on optically induced mode hopping between the two dominant modes of the laser. The wavelength hop is extremely discrete, leading to a significant improvement in extinction ratio of greater than 25 dB under static conditions. This gives rise to excellent signal reshaping potential. The mode hop can be induced by probe light varying from 1480 to 1580 nm, showing the large conversion bandwidth of this scheme. We also observe optical bistability in our experiment.

Extinction ratio improvement by strong external light injection and SPM in an SOA for OTDM pulse source using a DBR laser diode

We demonstrate above 6-dB extinction ratio (ER) improvement by strong external light injection for 20-GHz optical pulses generated from a gain-switched high-speed distributed Bragg reflector (DBR) laser diode. The pulses also exhibit a reduced chirp accompanied with a reduced total root-mean square noise. Above 12-dB pulse ER improvement was further obtained with self-phase modulation (SPM) effect in a semiconductor optical amplifier (SOA) followed by an optical bandpass filter. Stable 40-GHz pulses were demonstrated through passively multiplexing the pulses with 6-ps pulsewidth.

Extinction ratio improvement of an electroabsorption modulator by using Be as a p-type dopant with small diffusion coefficient

Beryllium (Be) has been applied as an acceptor in the p-type cladding layer and the contact layer of an InGaAsP-based electroabsorption modulator (EAM) fabricated by metalorganic chemical vapor deposition (MOCVD). The concentration of diffused dopants in the absorption layer of the EAM was significantly reduced by employing Be instead of zinc (Zn) which has been conventionally used as an acceptor for MOCVD-grown III–V semiconductors. Numerical simulation of the diffusion of Be and Zn in the EAM device structure showed that the diffusion of Be was dominated by interstitials with small diffusion coefficient, while the diffusion of Zn was dominated by a fast diffusion mechanism of a divacancy-related complex which was not observed in the Be-doped EAM. The measured extinction ratio of the Be-doped EAM was higher by approximately 40% than that of the Zn-doped counterpart. The improvement of the extinction ratio is due to improved uniformity of the electric field applied to the absorption layer of the EAM.

All-optical 2R regeneration based on polarization rotation in a linear optical amplifier

All-optical 2R-regeneration based on polarization rotation in a single semiconductor linear optical amplifier is experimentally demonstrated. An extinction ratio (ER) improvement of 15 dB has been obtained for an input ER of 5 dB under static operation. With a degraded input signal, a receiver-sensitivity improvement of >3 dB at a bit error rate of 10/sup -9/ was found for 2.5 Gb/s. Regenerative capability for 10 Gb/s has also been verified.

Extinction ratio improvement by four-wave mixing in dispersion-shifted fibre

The regenerative properties of four-wave mixing (FWM) in a dispersion-shifted fibre have been experimentally investigated through a pump-modulated FWM scheme. An improvement of more than 6 dB in the extinction ratio of the FWM product relative to that of the input signal is experimentally demonstrated, in satisfactory agreement with the theoretical predictions.

Dynamic birefringence of the linear optical amplifier and application in optical regeneration

Dynamic birefringence of the linear optical amplifier (LOA) is theoretically and experimentally investigated. Significant nonlinear variations of the state of polarization with the input power and bias current of the LOA have been found. Based on this nonlinear change of the state of polarization, an all-optical 2R regenerator is demonstrated. Under static operation, an extinction ratio (ER) improvement of 15 dB has been obtained for an input ER of 5 dB. With a degraded input signal, a receiver sensitivity improvement of over 3 dB at a bit-error rate (BER) of 10/sup -9/ has been found for 2.5 Gb/s. For 10 Gb/s, zero power penalty is observed. Significant improvements of ER for both 2.5 and 10 Gb/s are obtained.

Demonstration of extinction ratio improvement from 2 to 9 dB and intensity noise reduction with the MZI-GCSOA all-optical 2R regenerator

In this letter, we experimentally demonstrate improved static and dynamic characteristics of the all-optical 2R regenerator based on a Mach-Zehnder interferometer with gain-clamped semiconductor optical amplifiers. A true digital-like optical decision characteristic with an adjustable decision threshold has been found. A tremendous noise suppression at the logic 0 and a large improvement in the extinction ratio have been obtained even for a very deteriorated input signal with small extinction ratio at a bit rate of 2.488 Gb/s. An 8-dB improvement in extinction ratio can be achieved for an input extinction ratio of 5- and 7-dB improvement for an input extinction ratio of 2 dB. Furthermore, a good regeneration is achieved over a broad wavelength range of 20 nm.

Waveform restoration in semiconductor optical amplifier using fiber loop mirror

In this letter, we present a simple and effective interferometric approach for waveform restoration in a semiconductor optical amplifier (SOA) using a fiber loop mirror. Pattern-dependent distortion caused by gain dynamics of the SOA can be compensated. With our scheme, an enhanced input power dynamic range of 7 dB was achieved. For data sequences with different pattern lengths, both significant waveform and extinction ratio improvement were obtained.

Pulse extinction ratio improvement using SPM in an SOA for OTDM systems applications

Improvement of pulse extinction ratio from 15-20 dB to approximately 40 dB of a 10-GHz pulse train is demonstrated using the self-phase modulation-induced spectral shift caused by a semiconductor optical amplifier (SOA). The improvement permits penalty-free optical time-division multiplexing to 40 Gb/s, and demultiplexing back to 10 Gb/s of an intentionally distorted signal. Without using the SOA the 40-Gb/s signal is not receivable.

All-optical 2R regeneration based on integrated asymmetric Mach-Zehnder interferometer incorporating MMI-SOA

2R regeneration is proposed with an integrated Mach-Zehnder interferometer containing a monomodal semiconductor optical amplifier (SOA) and an SOA with a 1 /spl times/ 1 multimode interference (MMI) coupler-SOA in the arms. Simulations and measurement of the static transfer function show a digital shape with a high extinction ratio improvement.

Distributed effects model for cascaded traveling-wave electroabsorption modulator

A distributed model based on the large-signal electrooptic conversion is proposed to analyze cascaded traveling-wave electroabsorption modulators (TWEAMs) for high-speed optical switching applications. The microwave propagation loss, velocity mismatch, as well as frequency chirping are included. The model predicts that a cascaded TWEAM structure has the advantage of a high design tolerance to various distributed effects and an improved extinction ratio and optical loss in comparison to a single device of same total length. The agreement between experimental and calculated results indicates that the cascaded structures can be implemented for efficient TWEAM design.

Suppression of level fluctuation without extinction ratio degradation based on output saturation in higher order optical parametric interaction in fiber

Optical limiting operation based on output saturation in higher order parametric interaction in dispersion-shifted fiber is reported. The output powers in a parametric amplifier configuration were measured as a function of the signal input power, with the result that new-wavelength light is efficiently generated in addition to the pump, signal, and idler, resulting from a higher order parametric process, and its output power initially increases quadratically and then saturates as the input power increases. By utilizing this output property of the higher order parametric light, suppression of level fluctuation with an improved extinction ratio was demonstrated.

All-Optical OTDM Add/Drop Multiplexing using Semiconductor Optical Amplifier based Mach-Zehnder Interferometer with improved Extinction Ratio

Article All-Optical OTDM Add/Drop Multiplexing using Semiconductor Optical Amplifier based Mach-Zehnder Interferometer with improved Extinction Ratio was published on August 1, 2001 in the journal Journal of Optical Communications (volume 22, issue 4).

Extinction ratio improvement and wavelength conversion based on four-wave mixing in a semiconductor optical amplifier

We have demonstrated an extinction ratio improvement of more than 3 dB at 2.5 Gb/s with a method based on four-wave mixing in a semiconductor optical amplifier. A wavelength conversion and a data format conversion from nonreturn-to-zero (NRZ) to return-to-zero (RZ) have been simultaneously achieved.

40 Gbit/s wavelength conversion in cascade of SOA and NOLM and demonstration of extinction ratio improvement

The authors demonstrate that the extinction ratio (ER) can be improved when a nonlinear optical loop mirror (NOLM) is used as a wavelength conversion medium. At 4O Gbit/s. An extinction ratio (ER) of 7 dB for a converted signal generated by cross-gain modulation in a semiconductor optical amplifier is improved to an ER of 10 dB after wavelength conversion in an NOLM.

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

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.

Extinction ratio of cross-gain modulated multistage wavelength converters: model and experiments

Extinction ratio conservation, wide dynamic range, and large operating wavelength window are important features for all-optical wavelength converters. Practical converters may probably be multistage devices and have to be precisely modeled. We present an experimental analysis and phenomenological modeling of single- and multistage wavelength converters using cross-gain modulation in polarization insensitive multiquantum-well optical amplifiers. One of the studied double-stage converters is able to produce a large extinction ratio improvement with a regeneration factor higher than 1.5 for any conversion in the 1.53-1.56-μm window. The phenomenological model yields a very good agreement with the experimental results.

The effect of carrier transport on the dynamic performance of gain-saturation wavelength conversion in MQW semiconductor optical amplifiers

This paper investigates the effect of carrier transport on the dynamic properties of wavelength conversion using gain-saturation in semiconductor optical amplifiers (SOAs). It is shown that the carrier transport slows the rise time of the probe optical power by about 10 ps, but the fall time of the probe power is not significantly slowed. However, the dynamics of the probe chirp are slowed by as much as 30-50 ps when operating at 5 Gb/s. The effect of the modified chirp dynamics due to transport is shown to give an additional dispersion penalty, but this is always less than 1 dB. Electrical feedforward of the optical signal input into the SOA is shown to improve extinction ratio of the conversion process. Carrier transport degrades performance of this scheme by up to 3 dB at high data rates. These results show that it is important to take the chirp performance of SOAs into account when designing them for long-haul communications.

Extinction ratio improvement using the nonlinear optical loop mirror

We have investigated the nonlinear optical loop mirror operating as an extinction ratio (ER) improvement device. ER improvement and bit-error-rate measurements were made in a polarization insensitive mode. An ER of 3.8 dB can be improved to 10.8 dB with an improvement of the receiver power penalty from 4.1 dB to 1.6 dB. >