ICOP 2009-International Conference on Optics and Photonics CSIO, Chandigarh, India, 30 Oct.-1 Nov. 2009 Effect of Intraband effects on wavelength conversion of high-speed signals using cross-gain modulation in SOA K. Hussain 1 , S. K. Varshney 1,2 , and P. K. Datta 1 1 Department of Physics and Meteorology, I I T Kharagpur, Kharagpur-721302, India 2 Department of Electronics and Electrical Communication Engineering, I I T Kharagpur, Kharagpur- 721302, India E-mail: kamalhussain123@gmail.com Abstract: Wavelength conversion is very essential in wavelength division multiplexing (WDM) networks where blocking due to wavelength contention can be reduced to a good extent. We present a theoretical model to analyze the effect of intraband effects like spectral hole burning and carrier heating on wavelength conversion exploiting the cross-gain modulation (XGM) technique in a bulk semiconductor optical amplifier (SOA). Though XGM technique have the shortcomings like large chirping in the converted signal and degradation of extinction ratio in wavelength up-conversion, but still it is favored due to its simple to implementation and good performance at high signal-rates. It is also polarization independent provided the SOA used is also polarization independent. Using our model, we show the effect of these intraband effects on the output converted pulse, chirping of the output signal and on the efficiency of conversion. Besides, an overall gain compression, there is a fast recovery of the gain due to the intraband effects. 1. INTRODUCTION Semiconductor optical amplifiers (SOAs), due to their high saturation nonlinearity property show the potentiality to be used as indispensible components for the next generation all-optical communication devices. Many recent experiments have shown their potentiality in various applications in optical communication like in-line amplifiers, demultiplexers, wavelength converter, and optical switches. High gain, electrical pumping requirement and very small size, which make it favorable to be integrated on chips, are some of its advantages over fiber amplifiers. Besides, SOA exhibits nonlinear properties in the saturation regime, which is exploited in all-optical switching and all-optical wavelength generation. It can become an important constituent of wavelength-division-multiplexing (WDM) systems and in signal regeneration where wavelength conversion is an integral part [1]. The different nonlinear techniques employed for wavelength conversion in SOA are cross gain modulation (XGM), cross phase modulation (XPM, and four wave mixing (FWM) [2]. XGM is easier to implement, polarization maintaining and applicable at high signal rates. Performance analysis of XGM-based wavelength converters has been shown for both large and small- signal amplitude approximations [3]. But this model does not take into consideration the effect of fast- pulse propagation in SOA. When the signal rate is high (>10 Gb/s), intraband effects creeps in. Generally, at lower bit-rates the gain variation of the pulses inside the amplifier is mostly governed only by the interband carreir recombination lifetime τ s . But, for higher signal rates when the input pulses becomes very short (pulsewidth are in the order of the intraband relaxation times), than the gain of the amplifier gets modulated also by the intraband effects. The intraband band effects that affects the gain of the amplifier are the carrier heating (CH), spectral hole burning (SHB) and two-photon absorption (TPA). A detailed experimental investigation had been carried out by Hall et al. [4] in InGaAsP diode lasers for propagation of subpicosecond pulses. The pump-probe experimental curves for the three regimes of absorption, transparency and gain shows the existence of gain compression with recovery time on the order of 600 fs in the three regimes, besides the prolonged effect of carrier recombination. This effect is attributed to CH. Another transient variation of gain is observed, with a recovery time of 100-300 fs and is quite distinct in the absorption regime but its contribution decreases in the other regimes of operation and this effect is attributed to SHB. Agrawal and Olsson [5] studied the propagation of short Gaussian and super-Gaussian pulses by assuming approximate solutions of the integrated gain within the amplifier for different cases. They studied the output pulse profile, spectra and chirping for all the different cases but neglected the effect of intraband effects which arises when the pulsewidth of the input signal becomes of the order of the intraband transition relaxation times. Uskov et al. [6] have presented theoretical results on wave-mixing in traveling wave semiconductor laser amplifiers in presence of intraband effects like carrier-density pulsations, carrier heating, and spectral hole burning. A detailed model was given by Mecozzi and Mork [7, 8] to analyze the saturation effects in short pulse amplification and nondegenerate four- wave mixing, incorporating the effects of CH and SHB.