| Triangular optical pulse with a special time-domain waveform whose change of pulse intensity in front and back edges has constant rate and opposite sign.When pulses with a certain power are transmitted in optical fiber,the frequency chirp generated by SPM(self-phase modulation)and XPM(cross-phase modulation)around the front and back edges of the pulse will be constant,that is,SPM and XPM will only introduce the frequency shift,without generating new frequency components,it is possible to achieve the transfer of two new pulse energy at a frequency to realize wavelength conversion.Therefore,the generation and application of triangular optical pulse has also become a hot research.In this paper,the theoretical research and simulation analysis of the occurrence of triangular optical pulse are carried out.The main research work is as follows:(1)The application of triangular optical pulse in the field of microwave photonics is introduced.The performance advantages of triangular pulse compared with Gaussian pulse in wavelength conversion is analyzed.The two schemes of generating triangular pulses by time-domain waveform superposition are introduced.Their structures are theoretically deduced and the strengths and weaknesses are analyzed.The structure and principle of the Mach-Zehnder modulator involved in this scheme and the characteristics of the three bias points are presented.Based on this,a scheme in time-domain to generate full-duty-cycle triangular optical pulses based on orthogonal polarizes is proposed.Two similar sinusoidal signals are superimposed with the state of orthogonal polarization,and a certain delay is introduced before the superimposition.By adjusting the delay,an ideal triangular optical pulse can be obtained.The modulation index in this scheme is no longer to be fixed at one point,but can be aligned within a proper range(0.92???1.57).This scheme adopts the time-domain waveform superposition,which avoids the traditional method of operation for the spectrum lines and achieves more flexible and stable operation.(2)The scheme of this paper is verified by simulation.Firstly,the output of triangular optical pulse is obtained through the simulation,and the triangle optical pulse of various frequencies is also acquired,including the pulse signal with the highest frequency of 40GHz,which proves the feasibility of the scheme and the tuning flexibility.Then,the affection of these parameters drift on the final waveform are analyzed,which contained modulation index,bias voltage and time mismatching.The fitting error is introduced to quantitatively measure the fitting degree of the waveform,and the effect of the parameters drift on the waveform can be judged more intuitively.When the fitting error is less than 3%,the waveform obtained can be regarded as the ideal waveform.Under this condition,an acceptable drift range relative optimal value of modulation index,bias voltage difference and time mismatching are-10%?5%,-3%?3%and-14%?16%.(3)The designed scheme is compared with the similar time-domain waveform generation scheme.The principles of the two schemes are identical,by combining two similar waveforms to construct a triangle.One scheme is utilizing two similar square waves and another one is using two similar sinusoidal waves.On the one hand,due to the experiment of the scheme,the paper verifies the two schemes in the same simulation environment,which can indirectly verifies the experimental feasibility of the scheme.On the other hand,the advantages of this scheme,for example,simpler tuning,flexible selection for modulation index,can be get through comparative analysis.The scheme in this paper can get the triangular pulse directly in the optical domain,which makes its application in the field of all-optical more extensive. |
PDF Full Text Request