Georgios Kalogerakis

Homodyne Phase-Shift-Keying Systems: Past Challenges and Future Opportunities

Homodyne phase-shift-keying systems can achieve the best receiver sensitivity and the longest transmission distance among all optical communication systems. This paper reviews recent research efforts in the field and examines future possibilities that might lead toward potential practical use of these systems. Additionally, phase estimation techniques based on feed-forward phase recovery and digital delay-lock loop approaches are examined, simulated, and compared

Continuous-wave fiber optical parametric wavelength converter with +40-dB conversion efficiency and a 3.8-dB noise figure

We have obtained 40 dB of internal (on-off) conversion gain and a sub-4-dB noise figure (NF) with a continuous-wave (cw) fiber optical parametric wavelength converter. To our knowledge, this is the lowest NF reported for any cw wavelength converter. We have also investigated the properties of NF versus signal input power and pump power.

Continuous-wave fiber optical parametric amplifier with 60-dB gain using a novel two-segment design

We have obtained 60 dB of internal (ON-OFF) gain with a continuous-wave fiber optical parametric amplifier by using an isolator between two fiber segments to increase the pump stimulated Brillouin scattering threshold. Subdecibel penalties were measured for transmission of 10-Gb/s signals, with 35 dB of gain.We have obtained 60 dB of internal (ON-OFF) gain with a continuous-wave fiber optical parametric amplifier by using an isolator between two fiber segments to increase the pump stimulated Brillouin scattering threshold. Subdecibel penalties were measured for transmission of 10-Gb/s signals, with 35 dB of gain.

Pump-to-signal transfer of low-frequency intensity modulation in fiber optical parametric amplifiers

This paper describes the theoretical and experimental investigation of the transfer of low-frequency intensity modulation (IM) from pump to signal in fiber optical parametric amplifiers (OPAs). It is first established that low-frequency IM of the pump remains unchanged over the length of the amplifier in spite of the presence of parametric gain. The pump-power dependence of the OPA gain is then used to calculate the instantaneous effect of pump IM on the signal and idler output powers. These calculations are performed for both one- and two-pump OPAs. The main predictions are that 1) the ratio /spl rho/ of the signal intensity modulation depth to that of the pump varies across the OPA gain spectrum and 2) for a 20-dB gain, /spl rho/ can exceed 10 at some wavelengths, which indicates that this effect can be detrimental. Experiments have been performed to verify these predictions. Using sinusoidal IM of the pump, the resulting amplified signal IM was measured, and the experimental results were found to be in good agreement with the theoretical predictions.

Multiple-wavelength conversion with gain by a high-repetition-rate pulsed-pump fiber OPA

We propose and demonstrate a novel multiple wavelength converter with gain based on a pulsed-pump fiber optical parametric device. Penalties ranging from 0.26 to 1.24 dB for /spl plusmn/k /spl times/100 GHz (k= 1,2,3,4) wavelength conversion were measured.

High-repetition-rate pulsed-pump fiber OPA for amplification of communication signals

The use of a high-repetition-rate pulsed-pumped fiber optical parametric amplifier (OPA), followed by a narrow optical filter for transparent signal amplification, was proposed. Theory and simulations predict larger gain and gain bandwidth compared to a continuous-wave pump with the same average power. Experimentally, when using a pump with 0.63 W of average power in a 500-m-long highly nonlinear fiber, the gain increased from 19.7 to 29.2 dB, and the bandwidth increased when a CW pump was changed to one that is modulated by a 20-GHz cosine-squared function. Clear eye openings were demonstrated for the amplification of a 10-Gb/s NRZ signal, with a power penalty of 1.5 dB

Multiple wavelength conversion with gain by high repetition-rate pulsed-pump fiber OPA

The authors propose and demonstrate a novel multiple-wavelength converter with gain, based on a pulsed-pump fiber optical parametric amplifier (OPA). It generates multiple replicas of the signal, as well as spectrally inverted versions. The device is modeled by using quasi-steady-state OPA gain equations, as well as by the split-step Fourier method. Predicted conversion gains of up to 20 dB have been confirmed by experiments. A 10-Gb/s nonreturn-to-zero (NRZ) input signal was converted into several replicas, with penalties ranging from 0.26 to 1.24 dB for frequency shifts of /spl plusmn/k/spl times/100 GHz (k=1, 2, 3, 4).

Timing jitter and amplitude noise reduction by a chirped pulsed-pump fiber OPA

A novel optical pulse reshaping scheme is proposed to reduce timing jitter and amplitude noise. Sensitivity improvement of 2.6 dB was demonstrated by the temporal lens effect realized by a linearly-chirped pulsed-pump optical parametric amplifier followed by optimum dispersion.

Accurate numerical simulation of short fiber optical parametric amplifiers

We improve the accuracy of numerical simulations for short fiber optical parametric amplifiers (OPAs). Instead of using the usual coarse-step method, we adopt a model for birefringence and dispersion which uses fine-step variations of the parameters. We also improve the split-step Fourier method by exactly treating the nonlinear ellipse rotation terms. We find that results obtained this way for two-pump OPAs can be significantly different from those obtained by using the usual coarse-step fiber model, and/or neglecting ellipse rotation terms.

Methods for full utilization of the bandwidth of fiber optical parametric amplifiers and wavelength converters

In fiber optical parametric amplifiers (OPAs), idlers are generated during the amplification process. For very wide and dense signal input spectra, idlers may overlap with signals, thereby interfering with proper operation as an amplifier. In this paper, filter-based methods to fully utilize the bandwidth of OPAs and wavelength converters in the presence of very broad signal spectra are investigated. In the basic filter setup, two parallel OPAs and two filters are used; alternatively, one can use a single OPA bidirectionally and a single filter. An interleaver-based arrangement, separating signals from idlers at the system output, with a crosstalk of below -20 dB and subdecibel bit-error-rate penalty, is experimentally demonstrated