No abstract

A photonics-assisted scheme for generating various microwave waveforms has been investigated in this paper. In the proposed scheme, two phase modulation to intensity modulation (PM-IM) conversions are realized using two cascaded Sagnac interferometers (SIs) to manipulate light in the optical domain. From the first SI, by adjusting the amplitude of the microwave signal and time delay of the tunable optical delay line (TODL), both half duty cycle square and full duty cycle triangular waveforms can be generated from the photodetector (PD) and balanced photodetection (BPD). Using the second SI and applying microwave signals with appropriate amplitudes and phases, as well as the BPD process, results in full duty cycle sawtooth and reversed sawtooth waveforms. Detailed theoretical analyses are presented and results are verified by simulations. In the simulations, square-, triangular-and sawtooth-shaped (or reversed sawtooth-shaped) waveforms are obtained successfully. To complete the simulation results, the effects of non-ideal microwave hybrid coupler and optical couplers on the performances of the proposed scheme have been studied and no destructive effects were observed. The proposed structure does not include any optical or electrical filters which result in a wide operational bandwidth.

No abstract

In this paper, we report and theoretically investigate an optical single-sideband suppressed-carrier (OSSB-SC) modulator/frequency shifter with ultralow spurious sidebands. The novel, to the best of our knowledge, structure is based on three Sagnac interferometers (SIs) and two bidirectional phase modulators (PMs). The two bidirectional PMs are driven by four radio frequency (RF) signals with equal powers and appropriate phases. An OSSB-SC signal with only ( 4 n + 1 ) th-order sidebands, where n is an integer number, is generated. Besides, by applying appropriate RF phase shifts, an OSSB with carrier ( O S S B + C ) modulator can be obtained whose optical carrier-to-sideband ratio (OCSR) can be tuned by controlling the PMs modulation indices. Also, by using the proposed OSSB-SC modulator in another SI, its OCSR can be tuned by controlling the state of polarization in addition to the modulation indices of the PMs. Since the proposed structure is based on SI and no direct current (DC) bias is required for the PMs, it is robust against environmental perturbations and decreases problems associated with DC bias-drift. In addition, performance of the proposed structure under the power and phase imbalances due to the external non-ideal RF hybrid couplers and the phase imbalance of practical non-ideal nonreciprocal optical phase shifters are investigated. Simulation results using commercial software are also presented which are in good agreement with analytical results.

A novel scheme to implement an optical single-sideband (OSSB) polarization modulator (PolM) is proposed and theoretically demonstrated in this paper. The proposed OSSB-PolM is based on the phase modulation technique in two consecutive Sagnac interferometers (SIs). It is shown that by applying four equal-power radio frequency (RF) signals with appropriate phases to electro-optic modulators and aligning the polarization state of the modulated signal in the proper direction, an OSSB-PolM signal will be generated. The proposed scheme can find many microwave photonic (MWP) applications. To show this, an OSSB modulator with tunable optical carrier-to-sideband ratio, an OSSB-suppressed carrier modulator/optical frequency shifter, and a full-ranged MWP phase shifter are proposed and demonstrated. The proposed structure includes several important advantages. For instance, the system is free from the limitations caused by optical/electrical filters. Since the propagating lights in an SI traverse the identical optical path in clockwise and counterclockwise directions, the system is immune to environmental perturbations. Furthermore, there is no need for a bias control circuit, so the system has a stable operation. In addition, the proposed scheme can be extended to multichannel applications in array antennas. Theoretically, calculations have been verified by simulation results.