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We simulate supercontinuum generation for various shapes of a dispersion varying As2S3 waveguides on MgF2 substrate with air cladding. The supercontinuum generation is simulated for pulses of 2000 W peak power and 50 fs pulse width centered at 1.55 μm wavelength. For a uniform waveguide the generated spectrum is considerably narrower than that for a non-uniform waveguide. This is because the non-uniform waveguide allows a continuous phase matching of the generated waves through nonlinear interaction. We have demonstrated that a high coefficient of nonlinear refractive index is necessary for generating supercontinuum with large bandwidths. Larger supercontinuum bandwidth is predicted for waveguides with increasing As2S3 thickness along the propagation direction.

A scheme to generate 50 GHz pulse train using rational harmonic mode locking technique is proposed and studied experimentally. The modulation frequency is adjusted to achieve a 50 GHz pulse train which has a pulse width of 5.25 ps. Numerical simulation results show good agreement with the experimental results.

The effect of two-photon absorption (TPA) on all-optical logic operation in quantum-dot semiconductor optical amplifier (QD-SOA) has been carried out. The rate equation was modeled with the TPA effect for the logic XOR gate, AND gate, and, for pseudo-random bit sequence (PRBS) generation. The output Q-factor (quality) has increased due to the implementation of TPA induced pumping. The results show that the quality of the output depends on the input pulse width and the speed of operation. The PRBS system has been shown to operate at 250 Gb/s and 320 Gb/s and the Q-factor decreases with an increase in pulse width.

A fiber ring laser which implements hybrid mode locking technique has been proposed and experimentally demonstrated to generate pulse train at 20 GHz repetition rate with ultrashort pulse width. Graphene and charcoal nano-particles acting as passive mode lockers are inserted into a rational harmonic mode-locked fiber laser to improve the performance. With graphene saturable absorbers, the pulse duration is shortened from 5.3 ps to 2.8 ps, and with charcoal nano-particles, it is shortened to 3.2 ps. The RF spectra show that supermode noise can be removed in the presence of the saturable absorbers. Numerical simulation of the pulse transmission has also been carried out, which shows good agreement with the experimental results.

An axially non-uniform tapered As 2 S 3 planar waveguide has been designed for mid-IR supercontinuum generation. The dispersion profile is varying along the propagation distance. Numerical results show this scheme significantly broadens the generated continuum, extending from ~1 μm to ~7 μm.

We numerically study the broadband mid-infrared supercontinuum generation in a non-uniform SF57 microstructured fiber. The dispersion of the fiber is tailored by linearly varying the air hole diameters along the propagation distance. The fiber has zero dispersion at two wavelengths. This allows a continuous shift of the higher zero dispersion wavelength to a longer wavelength. Results show this scheme can significantly broaden the generated spectrum.

We have studied high speed optical logic utilizing ultrafast two-photon absorption (TPA) induced phase change in semiconductor optical amplifiers (SOA). Results show that this scheme can realize all-optical logic and encryption at data speeds to 250 Gb/s.

A scheme to generate return-to-zero on-off keying (RZ-OOK) high speed all-optical pseudo random bit sequence (PRBS) using binary phase shift keyed (BPSK) signal based on quantum-dot semiconductor optical amplifiers (QD-SOA) has been designed and studied. The PRBS is generated by a linear feedback shift register (LFSR) composed of all-optical logic XOR and AND gates. The XOR gate is composed of a pair of QD SOA Mach-Zehnder interferometers, which can generate BSPK signal to realize all-optical logic XOR gate. Results show that this scheme can mitigate the patterning effects and increase the operation speed to ~250Gb/s.

We have studied the broadband mid-IR supercontinuum generation in a lead-silicate tapered microstructured fiber for femto-second input pulses at 1550 nm. The supercontinuum generated extends from ~1000 to ~ 5000 nm for a suitably designed tapered fiber. The coherence properties of the supercontinuum depends on the input pulse parameters. It is possible to generate perfectly coherent supercontinuum with a flat broadened spectrum extending to ~5000 nm in this fiber taper.

In this paper we numerically study the coherence properties of the supercontinuum generated in a lead-silicate microstructured fiber taper, with an increasing core radius along the propagation distance which tailors the dispersion property. Simulations are conducted by adding quantum noise into the input pulse at 1.55 μm, and the complex degree of first-order coherence function and the overall spectral coherence degree are both calculated. Although the spectral broadening is comparable, the coherence degree is shown to vary with different pumping conditions. It decreases with higher peak power and longer duration due to the significant competition between the soliton-fission process and the noise-seeded modulation instability. By controlling the input pulse parameters, it is possible to generate perfectly coherent supercontinuum with a flat broadened spectrum extending to ~5μm in this fiber taper.

A fiber ring laser which generates ~ 570 ps wide pulse train at 40 GHz has been demonstrated using a photonic crystal fiber as a nonlinear optical loop mirror (NOLM). Theoretical simulation of the NOLM transmission has been carried out using the split-step Fourier method.

Semiconductor optical amplifiers are important for wide range of applications in optical networks, optical tomography and optical logic systems. For many of these applications particularly for optical networks and optical logic, high speed performance of the SOA is important. All optical Boolean operations such as XOR, OR, AND and NOR has been demonstrated using SOA based Mach-Zhender interferometers (SOA-MZI). A rate equation model for SOA-MZI has been developed. The model has been used to analyze the Set-Reset (S-R) latch, the gated S-R latch and the D-Flip-Flop devices. The modeling results suggest that the Flip-Flop circuits should work at high speeds. An optical pseudo-random bit stream (PRBS) generator is important for all-optical encryption circuits. A model of a PRBS generator using SOAMZI based devices has been developed. We show that a PRBS generator can work @ 80 Gb/s using regular SOAs and @ ~ 250 Gb/s or at higher speeds using two-photon absorption based processes in SOAs.

When the two-photon absorption of a high intensity pump beam takes place in a semiconductor optical amplifier there is an associated fast phase change of a weak probe signal. A scheme to realize fast all-optical NAND logic function using two-photon absorption induced phase change has been analyzed. NAND gate is important because other Boolean logic elements and circuits can be demonstrated using NAND gates as a basic building block. Rate equations for semiconductor optical amplifiers (for input data signals with high intensity) configured in the form of a Mach-Zehnder interferometer has been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The model shows that both AND and NAND operation at 250 Gb/s with good signal to noise ratio is feasible.

Semiconductor optical amplifiers are important for wide range of applications in optical networks, optical tomography and optical logic systems. For many of these applications particularly for optical networks and optical logic, high speed performance of the SOA is important. All optical Boolean operations such as XOR, OR, AND and NOR has been demonstrated using SOA based Mach-Zhender interferometers (SOA-MZI). A rate equation model for SOA-MZI has been developed. The model has been used to analyze the Set-Reset (S-R) latch, the gated S-R latch and the D-Flip-Flop devices. The modeling results suggest that the Flip-Flop circuits should work at high speeds.

When the two-photon absorption of a high intensity pump beam takes place in a semi conductor optical amplifier there is an associated fast phase change of a weak probe signal. A scheme to realize fast all-optical XOR logic function using two-photon absorption induced phase change has been analyzed. Rate equations for semiconductor optical amplifiers, for input data signals with high intensity, configured in the form of a Mach-Zehnder interferometer has been solved. The input intensities are high enough so that the two-photon induced phase change is larger than the regular gain induced phase change. The model shows that both XOR operation and pseudorandom binary sequence generation at 250 Gb/s with good signal to noise ratio is feasible. Keywords: semiconductor optical amplifier, two-photon absorption, optical logic INTRODUCTION In future high-speed communication systems, optical logic gates are expected to play an important role in switching, signal regeneration, addressing, header recognition, data encoding and encryption, etc.[1]. In recent years, optical logic based on several different schemes have been demonstrated and reported, including that based on dual semiconductor optical amplifier (SOA) Mach-Zehnder interferometer (MZI)[2-3], semiconductor laser amplifier (SLA) loop mirror [4], ultrafast nonlinear interferometers [5], four-wave mixing process in SOA[6] or cross gain (XGM) or cross phase (XPM) modulation in nonlinear devices[7]. Among these schemes, the SOA based MZI has the advantage of being relatively stable, simple and compact. However, to the author’s knowledge, all these schemes have a lim itation of signal bit rate of up to 40 or 80 Gb/s. A scheme for higher data rate logic using quantum dot (QD) based optical amplifier[8,9] has been analyzed[10]. Another process that can result in a fast phase change of a probe signal is two-photon absorption of a pump beam[11-15]. Pump-probe experiments have shown that phase changes take place in a duration ~ 1 ps or less when the pump and probe signals are injected into a semiconductor optical amplifier[11-14]. In this work, we present a model of XOR and a pseudorandom binary sequence (PRBS) generator based on two-photon absorption (TPA) of pump beams. The proposed device is a Mach-Zehnder interferometer (MZI) each arm of which has a semiconductor optical amplifier (SOA). Th e pump beams are the data signals which are injected into each arm. The probe beam is a weaker signal injected into the middle arm. The pump and probe beams have single pulse durations ~ 0.5 ps. The concept of XOR using SOA based MZI is the same as has been described and demonstrated earlier for XOR[1-6]. The principal new element of the current an alysis is that the phase change ( GI ) due to the pump beam has a fast component, the magnitude of which is given by[11-13] GI = -(1/2) ED

Semiconductor optical amplifiers are important for wide range of applications including optical networks, optical tomography and optical logic systems. For many of these applications particularly for optical networks and optical logic high speed performance of the SOA is important. The speed of operation of SOA is limited by the gain and phase recovery times in the SOA. We have demonstrated higher speed operation (i) for SOAs with a carrier reservoir layer, (ii) for SOAs with a multi-quantum well modulation doped active region, and, (iii) for SOAs with a quantum dot (QD) active region. The multi-quantum well SOA has been integrated with InGaAsP/InP based waveguides to build Mach- Zehnder interferometers (MZI). XOR optical logic has been demonstrated at 80 Gb/s using these SOA-MZI structures. XOR operation has been analyzed by solving the rate equation of the SOA, for SOAs with both regular and QD active region. Mach-Zehnder interferometers fabricated using SOA with quantum dot active region (QD-SOA) can be used for XOR operation at 250 Gb/s. Pseudo random bit stream (PRBS) generation using both regular and QD-SOA have been studied and their performance modeled. The model shows QD-SOA based devices can be used to produce PRBS generators that operate near 250 Gb/s.

We simulated the evolution of self-similar parabolic pulses (similaritons) in a normally dispersive fiber amplifier. The rate of development of a Gaussian pulse into the asymptotic parabolic regime has been studied. The model has been applied to an optical transmission system with a fiber amplifier. By calculating the Q-factor, we numerically determined the signal to noise performance of the pulse train along fiber length. For the parameters we used, a 6m long fiber amplifier with 20 dB gain is capable of amplifying 200Gb/s initial chirp-free Gaussian pulses of duration 0.4ps with no distortion and additional noise. The trade-off between pulse width and amplifier length has been studied.

A scheme to realize fiber-based all-optical Boolean logic functions including XOR, AND, OR and NOT based on a semiconductor optical amplifier with a closely stacked Stranski-Krastanow InAs/GaAs quantum dot layers is proposed. Rate equations is given to describe the population dynamics of the carrier in the device, as well as the nonlinear dynamics including carrier heating and spectral hole-burning. The model is used to simulated the cross gain and cross phase modulation in the device that are related to the logic processes. Results show with QD excited state serving as a carrier reservoir, this type of QD device is suitable for high speed operations with ultra fast carrier and phase relaxation. All optical logic operation can be carried out at up to 250 Gb/s.

A model to study four-wave mixing (FWM) wavelength conversion in InAs-GaAs quantum-dot semiconductor optical amplifier is proposed. Rate equations involving two QD states are solved to simulate the carrier density modulation in the system, results show that the existence of QD excited state contributes to the ultra fast recover time for single pulse response by serving as a carrier reservoir for the QD ground state, its speed limitations are also studied. Nondegenerate four-wave mixing process with small intensity modulation probe signal injected is simulated using this model, a set of coupled wave equations describing the evolution of all frequency components in the active region of QD-SOA are derived and solved numerically. Results show that better FWM conversion efficiency can be obtained compared with the regular bulk SOA, and the four-wave mixing bandwidth can exceed 1.5 THz when the detuning between pump and probe lights is 0.5 nm.

A scheme for high speed clock and data recovery using an electroabsorption modulated laser and a semiconductor optical amplifiers arranged in an optical-electrical-optical (OEO) loop has been demonstrated. By injecting the 80Gb/s optical data into the OEO ring, the 10GHz clock tone is traced and amplified in the loop. A 10GHz electrical clock and, a 10 GHz optical clock are recovered simultaneously.

Multi-stripe laser diodes are important for a wide range of applications including pump sources for high power fiber amplifiers and industrial applications. It is now believed that multimode single stripe laser diodes with high reliability have been designed and fabricated by several manufacturers. We have data which show FIT (failure in 109 hours) rates of ~ 12 FIT for 100 μm wide multimode emitters at power levels 2.5 W for a 15 year operation at 20 C. We have developed a method for calculating the survival probability of such multimode lasers when they are assembled in the form of a multi-stripe array. For a demanding application, a multi-stripe array can be considered a failure if one emitter in the array fails whereas for some other applications higher number of emitter failures is acceptable. The survival probability of the entire ensemble of lasers in the array as a function of number of stripes, number of failures, operating power level, and, near neighbor thermal interaction has been studied.

We present model calculations of gain at 1550 nm for Er-Yb double clad amplifiers as a function of pump power, pump wavelength, signal input power, and fiber length. The absorption coefficient of Yb varies ( by a factor of ~ 5) with the pump wavelength in the range of 910 to 990 nm. However, semiconductor lasers may be available only at certain wavelengths. Thus it is important to calculate optical gain and amplified output power as a function of pump wavelength. The calculation shows that significant optical gain and amplified output power can be obtained even if the pump laser wavelength is not at the peak absorption wavelength. The gain decreases with increasing input signal. We show that a high power Er-Yb co-doped double-clad fiber amplifier also exhibits high gain for Yb transition near 1060 nm. This is not unexpected since the input pump causes population inversion in Yb. More than 100 W of amplified power can be obtained using 24m long fiber with 300 W of total pump power by using side-pumping method. Side pumping increases the efficiency over end pumping for high output power.

An all-optical logic NOR gate operating at 40 Gb/s has been demonstrated using an SOA-based Mach-Zehnder interferometer (MZI). An optical loop mirror is used as a delayed interferometer to reshape the return-to-zero (RZ) NOR sequence from the MZI output port. The performance of the NOR operation is numerically analyzed by solving the rate equation of an SOA. An increase in signal output power enhances the Q factor and extinction ratio. Faster SOAs such as quantum-dot SOAs can achieve higher Q value. The demonstrated technique has potential for optical logic operation at ultrahigh speed

80Gb/s All-optical Boolean function XNOR has been demonstrated using a dual four wave mixing scheme in two identical highly nonlinear fibers. A numerical model based on nonlinear Schrodinger equation (NLS) in fiber has been employed to simulate the wave mixing process. The NLS equations have been solved using the split-step Fourier method. From the numerical model, system transmission rate is predicted to be as high as 250Gb/s.

All-optical XOR operation has been demonstrated using a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) and delayed interferometer (DI) at 80 Gb/s. The DI is based on a polarization maintaining loop mirror (PML). The results show using the PML-DI to perform differential scheme can improve the pulse quality of the XOR result.

All optical XOR, AND, OR, and, NOR functionality has been demonstrated experimentally using semiconductor optical amplifier (SOA) based devices at 40 Gb/s, 80 Gb/s. The performance of the optical logic operations has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the gain and phase recovery times in the SOA. In order to solve these limitations, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to > 100 Gb/s.

In this paper, detailed analyses of the conversion efficiency in high-speed clock recovery based on Mach-Zehnder (MZ) modulator has been carried out. The theoretical results show the conversion efficiency changes with RF driving power and the mixing order. For high order clock recovery, the cascaded MZ modulator provides higher conversion efficiency. A study of clock recovery at 160 Gb/s using the cascaded MZ modulator has been carried out. The experimental results agree with the results of the analysis.

Mode locked fiber lasers are important for generation of short pulses for future high speed optical time division multiplexed (OTDM) transmission systems. The design and performance of mode locked fiber lasers are described in this talk.

The performances of all-optical logic gates AND, OR, XOR, and NOT, based on quantum-dot semiconductor optical amplifier (QD-SOA) devices, are simulated. The saturation power, optical gain, and optical phase response of a QD-SOA is analyzed numerically using a rate-equation model of quantum dots embedded in a wetting layer. The calculated response is used to model the performance of the logic gates. The impact of the injection current and the input-signal power on the system's quality factor are studied. For the parameters used in this paper, all-optical logic gates using QD-SOA are capable of operating at speeds of ∼250 Gb/s. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 29–35, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21252

In this work, an optical short pulse generator is designed consisting of a pulse compressor and cascaded notch filter type repetition rate doublers. The performance characteristics such as pulse width and peak power as a function of design parameters are studied. The pulse compressor is optimized based on the simulation results. The 6ps wide pulses at 20 GHz repetition rate directly generated from mode-locked fiber laser (MLL) are compressed to 1.25ps wide pulses. Using a set of polarization maintaining fiber (PMF) loop mirrors the repetition rate is quadrupled and stable 1.45 ps wide pulse train at 80GHz is achieved.

In this work, we demonstrate clock recovery from a patterned 160Gb/s optical-time-division-multiplexed (OTDM) return-to-zero (RZ) data stream. A cascaded LiNbO 3 Mach-Zehnder modulator is employed as an efficient optical-electrical mixer. A phase-locked-loop (PLL) is used to lock the cross-correlation component between the optical signal and a local oscillating signal. As a result, clock signal at 10GHz is extracted from the 160Gb/s optic al TDM signal. The measured root-mean-square (RMS) timing jitter of the 10GHz clock signal is ~ 130 fs. Keywords : Clock Recovery, Cascaded Modulator INTRODUCTION In ultra high speed optical communication networks, clock recovery is an essential element for any optical access node because it synchronizes the receiver decision circuitry with the incoming data stream 1 . Therefore, a stable clock source with low jitter characteristic 2 at the receiver end is required. However, due to the speed limitation of electrical circuits, at data rates beyond ~ 40 Gb/s, it becomes increasingly difficult to perform the stable clock recovery electronically. Optical clock recovery techniques that can be scaled to data rates of many tens of Gb/s to > 100 Gb/s will be a prerequisite to high data rate communication links of the future. For the optical clock recovery systems, the key steps are Optical-Electric (OE) mixing and cross-correlation detection. One approach to high-speed clock extraction is the injection mode locking technique, in which optical clock signal is obtained by launching the pulse trains into the cavity of a self-pulsating laser

All optical Boolean logic functionality has been demonstrated experimentally using integrated semiconductor optical amplifier (SOA) based interferometry at 40 Gb/s. The demonstrated functions are XOR, AND, and OR. The performance of the operations has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the carrier lifetime in the SOA. In order to solve the limitations imposed by carrier lifetime, a differential scheme for the XOR operation has been experimentally investigated.

All optical XOR, AND, and, OR functionality has been demonstrated experimentally using semiconductor optical amplifier (SOA) based devices at 40 Gb/s, 80 Gb/s. The performance of the optical logic operations has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the gain and phase recovery times in the SOA. In order to solve these limitations, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to > 100 Gb/s.

In this paper, we demonstrate clock recovery from a patterned 160Gb/s optical-time-division-multiplexed (OTDM) return-to-zero (RZ) data stream. A cascaded LiNbO3 Mach-Zehnder modulator is employed as an efficient optical-electrical mixer. A phase-locked-loop (PLL) is used to lock the cross-correlation component between the optical signal and a local oscillating signal. As a result, clock signal at 10GHz is extracted from the 160Gb/s optical TDM signal. The measured root-mean-square (RMS) timing jitter of the 10GHz clock signal is ~ 130fs.

All-optical OR operation has been demonstrated using a semiconductor optical amplifier (SOA) and delayed interferometer (DI) at 20 Gb/s and 40 Gb/s. The DI is based on a polarization maintaining loop mirror. Q-factor of the operation is discussed through the numerical simulations. The results show the OR gate operation rate is limited by the carrier lifetime and the input pulse energy.

Gain and output power as a function of pump power has been calculated for short Er/Yb doped single mode fibers for various fiber parameters. The calculation shows (i) small signal gain increases with increasing Er concentration, (ii) long fiber lengths provide both higher gain and higher output, (iii) calculated gain is larger for higher Er emission cross section, and, (iv) > 25 dB gain is feasible for 5 cm long fiber for Er and Yb concentrations of 3 X 10 26 m -3 and 1.2 X 10 27 m -3 . Gain of 14 dB has been observed in a 30 mm long fiber at 400 mW. The observed gain is found to be linearly proportional to the length of the fiber with a slope of 0.44 dB/mm at 400 mW of pump power.

All optical XOR functionality has been demonstrated experimentally using an integrated SOA-based Mach-Zehnder interferometer (SOA-MZI) at 20 and 40 Gb/s. The performance of the XOR results has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the carrier lifetime in the SOA. In order to solve the limitations imposed by carrier lifetime, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to > 100 Gb/s.

We present two methods for timing jitter measurement. The first method uses the spectral content of the noise, and, the second method uses autocorrelation and cross correlation of the pulsed output. For a distributed feedback (DFB) laser gain switched at 1 GHz, the timing jitter is about 3-4 ps. When an external CW laser injected into the DFB laser, the timing jitter can be reduced to 1-1.5 ps.

We demonstrate simultaneous stabilized operation of a mode locked ring fiber laser at two wavelengths. At one of the wavelengths the mode locked operation is at 10 GHz and it is at 40 GHz at the second wavelength. The laser has an intracavity LiNbO 3 modulator driven at 10 GHz. The 40 GHz pulses are obtained by rational harmonic mode locking. Pulses with widths in 5 to 8 ps range are obtained.

Gain and output power as a function of pump power has been calculated for short Er/Yb doped single mode fibers for various fiber parameters. The calculation shows (i) small signal gain increases with increasing Er concentration, (ii) long fiber lengths provide both higher gain and higher output, (iii) calculated gain is larger for higher Er emission cross section, and, (iv) >25 dB gain is feasible for 5 cm long fiber for Er and Yb concentrations of 3 X 10 26 m -3 and 1.2 X 10 27 m -3 .

An number of parameters, such as gain, modulation response, linewidth enhancement factor and relative intensity noise in modulation-doped InGaAsP quantum well (QW) laser emitting at 1.55 μm have been theoretically investigated. The results indicate that the relaxation oscillation frequency for p-type modulation doped QW laser is enhanced by a factor of more than 2 compared to that for undoped MQW lasers. The linewidth enhancement factor of p-type modulation doped QW laser is reduced to ½ of that of undoped MQW laser and the relative intensity noise (RIN) is reduced by a factor of > 10 dB compared to that for undoped MQW lasers.

We present model calculations of gain at 1550 nm for Er-Yb double clad amplifiers as a function of pump power, signal input power, fiber length and temperature. The calculated gain is ~20 dB for 6W pump for 20 mW input signal at 25 C. More than 10 W of amplified power can be obtained using 8m long fiber with ~25 W of pump power. The gain decreases with increasing input signal. We show that a high power Er-Yb co-doped double-clad fiber amplifier also exhibits high gain for Yb transition near 1060 nm. This is not unexpected since the input pump causes population inversion in Yb also. The high gain can lead to high peak power pulses at 1060 nm in the presence of small reflections.

In this paper, we present a scheme for recovering 1 0GHz clock from 40Gb/s and 80 Gb/s time division multiplexed (TDM) return to zero (RZ) data stream. Theproposed clock recovery is successfully demonstrated using an electrical phase locked ioop (PLL). The jitter of the recovered clock is estimated to be around 5Ofs. The key part in the proposed clock recovery circuit is a LiNbO3 Mach-Zehndermodulator which is shown to be highly effective in optical to electrical down conversion. Keywords: High speed transmission, LiNbO3 modulator, Clock recovery IntroductionThe continuing demand for higher data transmission capacity will fuel the need for higher speed optical transmission system than that installed today. Systems operating at single channel speeds of 1 0Gb/s are currently being deployed. For time division multiplexed (TDM) systems, signals at low data rate are multiplexed tocreate data at a higher rate. At the receiver end, the received optical TDM pulsetrain is then demultiplexed into each lower data rate channel using varioustechniques like nonlinear optical loop mirror (NOLM) [1] and semiconductoroptical amplifier (SOA) [2] .

Pulses with - 200 fs pulse width were generated by using a two stage pulse compression mechanism of gain-switched DFB laser pulses which were originally — 1 0 ps long. The pulse compression mechanism utilizes fiber nonlinearities and it involves propagation through specific lengths of various types of fiber and a nonlinear ioop mirror. Simulation of the whole compression scheme by solving the nonlinear Schrodinger equation using the split step method shows good agreement with the experiment results. Keywords: Pulse compression, Gain switch, semiconductor laser 1. Introduction Generation of ultrashort optical pulses at 1 .55 m has attracted considerable attention for high data rate transmission systems. The combination of a gain-switched DFB laser diode and the soliton-effect compression technique1'2 has been shown to be one of the promising ways to generate compact and stable femtosecond pulse sources. The pulse widths of the gain-switched

A tunable laser operating near 944 nm is important for micro LIDAR systems. The high power laser would consist of a tunable (and possibly Q-switched) low power fiber laser, the output of which would be amplified using a double clad fiber amplifier. A model of a Nd doped laser using a Gaussian beam approximation for both the propagating pump and the laser mode has been developed. The threshold power and output power for various parameters such as pump absorption and reflectivity have been calculated. The spectral width (linewidth) of a fiber laser under CW operation has been calculated. The laser linewidth varies inversely as the square of the fiber length and inversely as the output power. Shorter pulse width and higher peak power is obtained using a small fiber core under Q-switched operation.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The variational method is a useful tool that can be used for design and optimization of dispersion-managed communication systems. Using this powerful tool, we evaluate the characteristics of a carrier signal for certain system parameters and describe several features of a dispersion-managed soliton.

The operation of a semiconductor colliding pulse mode locked (CPM) laser has been analyzed using the time domain approach. In this approach the re-circulating transmission of a pulse through the various elements of the optical cavity such as the gain medium, the waveguide, and, the saturable absorber is carried out with the condition that the pulse must remain unchanged after one round trip. The pulse width of a CPM laser as a function of gain section current, saturable absorber current, and, modulation frequency has been measured. The laser is ∼ 8.5 mm long and operates at a pulse repetition rate of ∼ 10 GHz. The measurements and modeling results agree well. Both measured and calculated minimum pulse width is ∼ 1 ps.

All optical XOR functionality has been demonstrated experimentally using an integrated SOA-based Mach-Zehnder interferometer (SOA-MZI) at 20 Gb/s. The performance of the XOR results has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the carrier lifetime in the SOA. In order to solve the limitations imposed by carrier lifetime, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to > 100 Gb/s.

We have experimentally demonstrated that the stability of CW and mode-locked erbium doped fiber ring laser can be significantly improved with a semiconductor optical amplifier (SOA) inside the cavity. The fast saturable gain of the SOA suppresses significantly the self-pulsing due to ion pairs in the erbium-doped fiber, which acts as a saturable absorber. A linear stabilization analysis of the laser system agrees with out experiment results.