Optical Communications

To reduce the non-linearities in the fiber it is possible to increase the effective area of the fiber by increasing the fiber core radius a. True. False.

To reduce the non-linearities in the fiber it is possible to reduce the effective length by increasing the fiber length L. True. False.

To reduce the XPM induced by the channel at λ1 to the channel at λ2, it is possible to decrease the power of the channel at λ2. True. False.

To reduce the SPM induced to the channel at λ2, it is possible to decrease the power of the channel at λ1. True. False.

To reduce the XPM induced by the channel at λ1 to the channel at λ2, it is possible to increase the dispersion slope of the fiber. True. False.

The Raman gain coefficient shows a maximum at 13.2 GHz. True. False.

The Stimulated Raman Scattering can limit the performance of a multichannel WDM system by transferring energy from the shorter-wavelength channels to the higher-wavelength channels. True. False.

The Brillouin gain coefficient depends by λ and is considerably lower than the Raman gain coefficient. True. False.

To reduce the stimulated Brillouin scattering it is possible to superimpose a soft phase modulation to the signal. True. False.

Consider a frequency chirp. In case of operation in the normal dispersion region of the fiber, the higher wavelength components of the pulse are delayed. True. False.

Consider a frequency chirp. In case of operation in the anomalous dispersion region of the fiber, the lower frequency components of the pulse are delayed. True. False.

Consider a frequency chirp. Owing to the FWM induced in the fiber, a Gaussian pulse can experiment a frequency chirp with blue shift. True. False.

Consider a frequency chirp. In case of optical amplification by an EDFA operating in the saturation regime, the amplified pulse is affected by frequency chirp. True. False.

Consider a frequency chirp. In case of direct modulation of the laser source, the emitted pulse is affected by frequency chirp. True. False.

Consider a frequency chirp. Owing to the SPM induced in the fiber, a Gaussian pulse can experiment a frequency chirp with red shift. True. False.

Consider a frequency chirp. In case of fiber propagation in the normal dispersion regime, the positive frequency chirp (red shift) induced by to nonlinearities can be useful to compensate the pulse broadening due to chromatic dispersion. True. False.

Let’s consider the SNR of an optical signal after the receiver. In coherent detection, considering heterodyne case, the SNR improvement is lower by 3 dB compared with the homodyne case. True. False.

Let’s consider the SNR of an optical signal after the receiver. SNR improves by decreasing the load resistance of the receiver. True. False.

Let’s consider the SNR of an optical signal after the receiver. The NEP is the maximum optical power per unit bandwidth required to produce SNR = 1. True. False.

Let’s consider the SNR of an optical signal after the receiver. Optical preamplification of the signal helps to achieve the quantum limit, resulting in an improved SNR. True. False.

Let’s consider the SNR of an optical signal after the receiver. By using an APD, additional noise is added both to the thermal noise and the shot noise. True. False.

Let’s consider the SNR of an optical signal after the receiver. In coherent detection, quantum limit can be achieved thanks to the local oscillator, without adding any excess shot noise, as in case of direct detection with the APD. True. False.

Let’s consider the SNR of an optical signal after the receiver. NEC stands for NET EQUIVALENT CURRENT. True. False.

Let’s consider the OSNR in multi-span amplified system. Conventionally the optical band chosen to measure the received OSNR corresponds to 1 nm and 2 nm. True. False.

Let’s consider the OSNR in multi-span amplified system. The OSNR at the end of the multi-span amplified system depends by the ASE introduced by the final EDFA only, because the ASE added by the previous amplifiers is attenuated in succeeding fiber spans. True. False.

Let’s consider the OSNR in multi-span amplified system. To increase the OSNR at the end of the multi-span amplified system is possible to increase the optical power at the output of each amplifier. True. False.

Let’s consider the OSNR in multi-span amplified system. To increase the OSNR at the end of the multi-span amplified system is possible to decrease the number of spans, by increasing the length of each span, to maintain the system length constant. True. False.

Let’s consider the OSNR in multi-span amplified system. To increase the OSNR at the end of the multi-span amplified system is possible to increase the spontaneous inversion factor of the amplifiers. True. False.

Let’s consider the OSNR in multi-span amplified system. To reduce the NF of the system, amplification supported by distributed Raman amplification can be used. True. False.

Let’s consider the OSNR in multi-span amplified system. Target OSNR at the receiver can be reduced by the employment of FEC codes. True. False.

Let’s consider the OSNR in multi-span amplified system. To compensate the losses accumulated during the propagation in the span, the gain of the EDFA in dB at the end of the span must be equal to ten times the base-10 logarithm of the product between the attenuation coefficient of the span fiber at the span length. True. False.

Let’s consider the OSNR in multi-span amplified system. In case of WDM transmission, the non-flat gain of the EDFA across the wavelengths leads to a non-uniformity in the OSNR accumulated by the different WDM channels in the system. True. False.