We propose, analyze and simulate a microwave photonic system for generation of damped sinusoidal and ultra- wideband (UWB) microwave waveforms based on an optoelectronic approach. In the proposed system, a pulsed laser source (PLS) of 1 fs pulse width generates pulses at a repetition rate of 1 Tbps. These train of pulses are fed as input to a silicon-on-insulator microring resonator of radius 10µm. . The wavelength of the pulsed laser source is tuned to the resonance wavelength (1555.8 nm) of microring resonator (MRR) due to which the pulses are coupled into the ring cavity and emerge at the drop port of MRR. In order to compensate for the propagation losses within the cavity, an Erbium doped fiber amplifier (EDFA) is used to amplify the signal appearing at the drop port of the MRR. This amplified signal is then detected by an InGaAs photodetector of bandwidth 40 GHz and responsivity 0.85 A/W. The generated signal at the photodetector is reshaped by a bandpass Butterworth filter. In other words, the generated photocurrent acts as an impulse to the filter, the response to which results in different shapes of microwave waveforms for different characteristics of the filter. In this paper, a bandwidth of 6 GHz and order 34 results in a damped sinusoidal waveform when the repetition rate of PLS is 1 Tbps. Variations in repetition rate of PLS results in delayed damped sinusoidal waveforms. Maintaining the bandwidth to be 6 GHz and decreasing the order of the filter results in suppression of the damped oscillations of the damped sinusoidal waveform. When the order of the filter is reduced to 4, the resultant waveform at the filter is reshaped to an ultra-wideband waveform. The frequency spectra of the generated UWB waveform covers half of the UWB frequency band spanning from 3.2 to 6 GHz. The repetition rate of the generated microwave waveforms is found to be 1 GHz. The generated damped sinusoidal waveforms and UWB waveforms will be suitable for medical imaging and high data rate, short range indoor wireless communication applications respectively.
Optical 4-bit binary to gray and gray to binary code conversion has been demonstrated. The encoders are designed by implementing XOR gates in optical domain. Phase modulation in Mach–Zehnder interferometer has been exploited to achieve results at considerably high data rates of up to 60 Gbps. Also, the designs, being reversible in nature, will amount to less power consumption when embedded in an optical network. Performance parameters of the design, such as Q factor and extinction ratio, are analyzed based on simulation results carried out using comprehensive design suite OptiSystem-13.
In this paper a study on modulation formats like non return to zero (NRZ), return to zero (RZ) and carrier suppressed
return to zero (CSRZ) in terms of generation, dispersion analysis and performance at the receiver end has been done for a standard single mode fiber (SMF) of fixed length and data rate. The principle of external modulation through a Mach Zehnder Modulator (MZM) is been employed for the generation of the various formats. Linear effect or dispersion performance of formats alone is considered here. A dispersion compensation technique based on dispersion compensation fibers (DCF) that improves the performance of the optical link is also studied. The performances have been analyzed in terms of bit error rate (BER) and quality factor (Q-factor). The study reveals that RZ exhibits superior performance over the other formats in terms of dispersion tolerance, BER and Q-factor values. It is also shown that by introducing a DCF module system performance can be improved.