Aijun Wen

Microwave Generation With Photonic Frequency Sextupling Based on Cascaded Modulators

A novel scheme to optically generate a microwave signal with frequency sextupling is proposed. The proposed scheme is based on cascading an intensity modulator (IM) and a dual-parallel Mach-Zehnder modulator (DPMZM), without any optical or electrical filter. The low frequency local oscillator signal is divided into two paths, with one path driving the IM at the minimum transmission point and the other path driving the upper arm of the DPMZM. By controlling the three dc biases of the DPMZM, the third-order sidebands are generated, with other sidebands well suppressed. A 20-dB electrical spurious suppression ratio is demonstrated in the experiment. The phase noise measurements show that the phase noise performance of the generated microwave signal is not deteriorated by the optical system. The proposed scheme has no strict requirements for the modulation indexes and the generated signal exhibits advantages of high frequency tunability and purity.

Studies in an optical millimeter-wave generation scheme via two parallel dual-parallel Mach–Zehnder modulators

A novel filterless optical millimeter-wave generation scheme via two parallel dual-parallel Mach–Zehnder modulators (MZMs) is proposed. Theoretical analysis suggests that it can be used for the generation of millimeter-wave signal with octupling or 16-tupling of the local oscillator. An 80 GHz millimeter-wave is generated by octupling of a 10 GHz RF oscillator, or 16-tupling of a 5 GHz RF oscillator. Several influence factors on the performance of the optical sideband suppression ratio (OSSR) and the radio frequency spurious suppression ratio (RFSSR) are numerically studied. Simulation results show that the generated millimeter-wave can keep good performance, especially for octupling millimeter-wave generation; its performance is stable and insensitive to the extinction ratio of MZMs and the DC bias drift.

Frequency-Multiplying Optoelectronic Oscillator With a Tunable Multiplication Factor

A frequency-multiplying optoelectronic oscillator (OEO) with a tunable multiplication factor to generate a frequency-quadrupled, sextupled, or octupled microwave signal without using an optical filter is proposed and experimentally demonstrated, for the first time to the best of our knowledge. In the proposed OEO, a polarization modulator (PolM), a polarization controller (PC), and an optical polarizer (Pol) function jointly as a Mach-Zehnder modulator (MZM). Microwave oscillation is achieved in the OEO by feedbacking the intensity-modulated signal to the PolM after photodetection, and the oscillation frequency is determined by the center frequency of an electrical bandpass filter (EBPF) in the loop. A frequency-multiplied microwave signal is generated by a joint use of the PolM and a second modulator to generate two sidebands at the ±second, ±third, or ±fourth orders with the sidebands at other orders fully suppressed. By beating the two sidebands at a second photodetector (PD), a frequency-quadrupled, sextupled, or octupled microwave signal is generated. An experiment is performed. A fundamental microwave signal at 9.957 GHz is generated in the OEO loop, which is multiplied to generate a frequency-quadrupled, sextupled, or octupled microwave signal at 39.828, 59.742, or 79.656 GHz, respectively. The phase-noise performance of the frequency-multiplying microwave signal is also investigated.

Compensation of the Dispersion-Induced Power Fading in an Analog Photonic Link Based on PM–IM Conversion in a Sagnac Loop

An analog photonic link with the compensation of the dispersion-induced power fading is proposed and demonstrated based on phase modulation to intensity modulation conversion in a Sagnac loop. Due to the velocity mismatch of the modulator, only the incident light wave along the clockwise direction is effectively modulated by the radio frequency signals, while the counterclockwise light wave is not modulated. After combining the two light waves in a polarizer, an intensity modulated optical signal is generated, which can be directly detected. In addition, the phase difference between the two light waves can be adjusted through the polarization controller before the polarizer. This feature is used to shift the frequency response of a dispersive link to compensate the dispersion-induced power fading at any working frequency. Experimental results show that the power fading after transmission over both 25 and 50 km lengths of fiber in a conventional intensity modulated link can be successfully compensated in the proposed link, and thus, a high and constant link gain over a large frequency range is achieved. The spur-free dynamic ranges of the link before and after fiber transmission are also measured.

Photonic generation of binary and quaternary phase-coded microwave waveforms with an ultra-wide frequency tunable range

A novel photonic approach to generating binary and quaternary phase-coded microwave waveforms with an ultra-wide frequency tunable range is proposed and experimentally demonstrated. In the proposed system, a dual-parallel Mach-Zehnder modulator (DP-MZM) is used as an optical wavelength shifter. To generate a phase-coded microwave waveform, the coding signal is modulated on the original wavelength using a phase modulator (PM). Combining the shifted wavelength and the original wavelength, two wavelengths with a frequency space determined by the input microwave signal are obtained. Applying them to a photodetector (PD), a phase-coded microwave waveform is generated. The key significance of the approach is that both binary and quaternary phase-coded microwave waveforms can be generated with an ultra-wide frequency tunable range. An experiment is performed. The generation of binary and quaternary microwave waveforms with a microwave carrier frequency at 10 and 20 GHz is demonstrated.

Photonic Microwave Generation With Frequency Octupling Based on a DP-QPSK Modulator

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated using a dual-polarization quadrature phase shift keying modulator. By properly setting the phase difference between the two drive signals, the working points of the modulator, and the polarization state of the light wave after the modulator, an optical signal with only ±4th order sidebands is generated. A pure 24-GHz microwave signal with low-phase noise is experimentally obtained using a 3-GHz local oscillator signal. The proposed photonic frequency octupling system also exhibits good frequency tunability as no electrical or optical filter is used.

Simultaneously photonic frequency downconversion, multichannel phase shifting, and IQ demodulation for wideband microwave signals

A single photonic system that can simultaneously perform frequency downconversion, multichannel phase shifting, and in-phase (I) and quadrature (Q) demodulation for microwave signals is proposed and experimentally demonstrated. Using an integrated polarization-division multiplexing Mach-Zehnder modulator, radio frequency (RF) signals can be frequency downconverted to multichannel intermediate frequency (IF) signals and the phase of each IF signal can be independently and arbitrarily tuned. Using two quadrature channels, the RF signal can be IQ demodulated. In the experiment, high and flat conversion gains from 8 to 40 GHz and continuously tunable phase shifts over the 360-deg range are demonstrated. In addition, vector signals with various modulation formats at 40 GHz are frequency downconverted to baseband and the IQ data are successfully extracted.

Photonic Generation of Frequency Tunable Binary Phase-Coded Microwave Waveforms

A novel photonic approach to generating a precisely π phase-shifted binary phase-coded microwave waveform with ultra-wide frequency tunable range is proposed and experimentally demonstrated. In the proposed system, a polarization modulator (PolM) functions in conjunction with a polarization controller (PC) and an optical polarizer (Pol) as an equivalent Mach-Zehnder modulator (MZM) with the bias point switchable by applying a binary-coding signal to the PolM. To generate a phase-coded microwave signal at a specific microwave frequency, the binary-coding signal is combined with a microwave signal at that frequency and applied to the PolM. By switching between the two quadrature transmission points or the maximum and the minimum transmission points, a phase-coded microwave waveform at the fundamental or doubled frequency is generated. The proposed technique is experimentally evaluated. A phase-coded microwave waveform at the fundamental and doubled frequency is generated. The tunability of the approach is also experimentally demonstrated.

Photonic microwave waveform generation based on phase modulation and tunable dispersion

Photonic generation of microwave waveforms is currently an interesting topic due to the advantages of large bandwidth and immunity to electromagnetic interference. In this paper, a photonic microwave waveform generator with tunable waveforms and repetition rates is proposed and experimentally demonstrated. A continuous-wave (CW) light is phase modulated by a local oscillator (LO) signal to generate optical sidebands. By locating the phase modulator (PM) in a Sagnac loop, we can control the intensity and phase of the carrier of the phase modulated signal. Then a compact tunable dispersion compensation module is used to introduce phase shifts to the optical sidebands. Thanks to the flexible controlling of the optical signal, the generation of microwave waveforms with tunable shapes and repetition rates can be realized. In the demonstration experiment, full-duty-cycle triangular and square waveforms with repetition rates of 5 and 10 GHz (bandwidths of 15 and 30 GHz) are successfully generated, respectively. The bandwidths are expected to be improved to above 120 GHz if larger-bandwidth measurement instruments are used. In addition to the flexible tunability, the proposed scheme also features the advantages of easy implementation and free from bias drift.

Microwave Photonic Frequency Conversion With High Conversion Efficiency and Elimination of Dispersion-Induced Power Fading

In this paper, a novel microwave photonic mixer based on a single integrated dual-drive dual-parallel Mach-Zehnder modulator (DD-DPMZM) is proposed. One submodulator is used to generate a single sideband (SSB) signal of the local oscillator, whereas the other submodulator is used to generate a double sideband signal of the radio-frequency signal. By adjusting the main dc bias of DD-DPMZM, we can suppress the optical carrier at the output of the DD-DPMZM. Mixed signals can be obtained after a photodiode. The structure features the advantages of high conversion efficiency and the elimination of dispersion-induced power fading. An experiment is carried out to verify the effectiveness of the scheme, and a significant improvement of 15.5 dB in conversion efficiency compared with the conventional photonic mixer is achieved. In addition, it avoids the influence of fiber dispersion. The proposed mixer is promising to find applications in future wideband wireless communication systems.