Generation Of Phase-coded Microwave Signals Research Articles

A Photonics-Assisted Binary/Quaternary Phase-Coded Microwave Signal Generator Applicable to Digital I/O Interfaces.

A photonics-assisted binary/quaternary phase-coded microwave signal generator with fundamental/doubling reconfigurable carrier frequency applicable to digital I/O interfaces is proposed and has been verified by experiments. This scheme is based on a cascade modulation scheme, which is used to reconfigure fundamental/doubling carrier frequency and load the phase-coded signal, respectively. By controlling the radio frequency (RF) switch and the bias voltages of the modulator, the switching of the fundamental or doubling carrier frequency can be realized. When the amplitudes and sequence pattern of the two independent coding signals are set reasonably, binary or quaternary phase-coded signals can be realized. The sequence pattern of coding signals is applicable to digital I/O interfaces and can be directly generated through the IO interfaces of FPGA instead of an expensive high-speed arbitrary waveform generator (AWG) or other digital-to-analog conversion (DAC) systems. A proof-of-concept experiment is carried out, and the performance of the proposed system is evaluated from the aspects of phase recovery accuracy and pulse compression capability. In addition, the influence of residual carrier suppression and polarization crosstalk in non-ideal states on phase shifting based on polarization adjustment has also been analyzed.

Switchable Dual-Band Binary and Single-Band Quaternary Phase-Coded Microwave Signal Generation Using a Dual-Polarization Dual-Drive Mach–Zehnder Modulator

A switchable dual-band binary and single-band quaternary phase-coded microwave signal generator based on a single dual-polarization dual-drive Mach–Zehnder modulator (DP-DDMZM) is proposed. Two radio frequency (RF) signals are first coupled with two bipolar coded signals and then used to drive the DP-DDMZM. When the frequencies of the two RF signals are different, the generator will be in dual-band binary phase-coded mode and a dual-band binary phase-coded signal can be generated. When the frequencies of the two RF signals are the same but their phase difference is adjusted to be 90°, the generator will be in single-band quaternary phase-coded mode and a single-band quaternary phase-coded signal can be obtained. Detailed analysis is carried out to illustrate the mechanism and a proof-of-concept experiment is also performed to demonstrate the feasibility. The dual-band binary and single-band quaternary phase-coded microwave signal are both experimentally generated and their performance is evaluated. The proposed generator features the advantages of simple structure, high flexibility and stable performance, which is promising in the future multifunctional radar systems.

Photonic Generation and Antidispersion Transmission of Background-Free Multiband Arbitrarily Phase-Coded Microwave Signals

A novel type of photonic background-free multiband arbitrarily phase-coded microwave signal generator with power fading elimination capability is reported. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -polarized phase modulated optical signal and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y$ </tex-math></inline-formula> -polarized radio frequency (RF) modulated harmonic single-sideband (HSSB) optical signal are produced based on a dual-polarization quadrature phase shift-keying modulator (DP-QPSKM). After polarization modulation to intensity modulation conversion, a microwave signal with arbitrarily phase encoding in multiple frequency bands is generated. Benefiting from the phase modulation state of the driven electrical coded signal, the generated arbitrarily phase-coded signal has no baseband components. Moreover, the equivalent HSSB modulation ensures the system can realize antidispersion transmission of one-to-multi base stations (BSs). The main distinct highlights of our generator are multifunction. The proposed single-modulator-based photonic scheme can achieve phase encoding in arbitrary format over multiple frequency bands and transmit over long-distance single-mode fiber with the elimination of power fading simultaneously. This work is pretty promising in multiband radar systems for one-to-multi BSs transmission and can increase the detection range, range resolution, Doppler tolerance, and sensitivity of objective recognition of radars.

Phase-coded microwave signal generation with a built-in optoelectronic oscillator based on a dual-parallel Mach-Zehnder modulator.

A scheme for binary phase-coded microwave signal generation is proposed and experimentally demonstrated with a dual-parallel Mach-Zehnder modulator (DPMZM). The carrier of the generated phase-coded signal is provided by the built-in dual-loop optoelectronic oscillator (OEO) based on the DPMZM. The principle of this signal generator and the oscillating condition of the OEO is theoretically described in detail. It is found that phase-coded signals can be produced by setting the three working points and the modulation depth of the DPMZM. In the proving experiment, a 10-GHz oscillating signal with a side mode suppression ratio of 49 dB is generated. The phase noise of this carrier wave is measured to be -80dBc/Hz at 10 kHz offset with a 100-m and 1-km optical fiber used in the two oscillation loops. When 1-Gbit/s and 2-Gbit/s coding signals are, respectively, applied to the DPMZM, two 10-GHz self-oscillating phase-coded signals are eventually produced, and the π phase shift in the signals is successfully confirmed with the phase information extracted from the phase-coded signals.

Reconfigurable photonic binary phase-coded microwave signal generator with fundamental/subharmonic carrier frequency.

A reconfigurable photonic binary phase-coded microwave signal generator with fundamental/subharmonic carrier frequency is proposed and experimentally investigated based on a dual-electrode dual parallel Mach-Zehnder modulator (DE-DPMZM). The local oscillator (LO) signal and coding signal are intensity modulated and phase modulated, respectively, on the two arms of the DE-DPMZM. The bias voltage of the intensity modulator is set to the quadrature or maximum working points to produce fundamental or subharmonic frequency, respectively. By precisely adjusting the amplitude of the LO signal and the bias voltage of the parent modulator, the light carriers of both arms of the DE-DPMZM can be eliminated. After detection, binary phase-coded microwave signal with frequency equal to or twice the frequency of the LO signal can be generated. The proposed system has a simple structure, high reconfigurability, and good frequency tunability due to its avoidance of using optical filters. In the experiment, phase-coded microwave waveforms at 6 GHz and 11 GHz are generated by using 6 GHz and 11 GHz LO signals or 3 GHz and 5.5 GHz LO signals, respectively. Meanwhile, the performance is evaluated in terms of phase recovery accuracy and pulse compression capability. The experimental results show that the proposed generator has high peak-to-sidelobe ratio, which has practical significance for radar detection of weak targets.

Multi-Frequency Phase-Coded Microwave Signal Generation With an Increased Number of Frequencies

A photonics-based approach to multi-frequency phase-coded microwave signal generation is proposed with an increased number of frequencies. Two microwave reference signals are sent to one arm of a dual-drive Mach-Zehnder modulator (DD-MZM), whereas the binary coding signal is sent to the other arm of the DD-MZM. The optical output of the DD-MZM is detected in a photodetector. Due to the nonlinearity in the electro-optic modulation, the generated photocurrent contains the nonlinear intermodulation products of the two reference signals, which are all modulated by the coding signal. An experiment is performed. Multi-frequency phase-coded microwave signals from 1 to 24 GHz with more than twelve different frequency components are generated. The performance of the generated signal including phase recovery accuracy and pulse compression capability is also verified.

Phase-Coded Microwave Signal Generation Based on a Segmented Silicon Mach–Zehnder Modulator

We demonstrate novel phase-coded microwave signal generation based on a two-segment single-drive push–pull silicon Mach–Zehnder modulator. The coding signal and the microwave frequency are each applied to one of the separate segments. The phase-coded microwave signal is generated by properly setting the working point of the modulator. The precise π phase shift is determined by the sign of the coding signal. Both theoretical analysis and experimental demonstration are performed to verify the concept. The modulator successfully generates a 10-GHz (20-GHz) phase-coded microwave signal with a 5-Gb/s (10-Gb/s) coding data rate and the measured pulse compression ratio is 133.0 (156.8).

Photonic generation of binary and quaternary phase-coded microwave signals by utilizing a dual-polarization dual-parallel Mach-Zehnder modulator.

A photonic method to generate binary and quaternary phase-coded microwave signals using a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM) is proposed and experimentally demonstrated. The upper DPMZM driven by a radio frequency (RF) signal acts as an optical wavelength shifter, while the lower DPMZM is used to generate a binary phase shift key (BPSK) or quadrature phase shift key (QPSK) signal. By combining the wavelength-shifted optical sideband and phase-modulated optical carrier, both binary and quaternary phase-coded microwave signals can be generated. Such signals with the carrier frequency of 10 GHz and 15 GHz are demonstrated. The pulse compression performance is also investigated.

Phase-coded microwave signals generation using a dual parallel construction including two phase modulators

A photonic approach to realizing binary phase-coded microwave signal generation using a dual parallel construction including two phase modulators (PMs) was proposed and demonstrated. A beam CW is split into two beams light wave with equal power in the dual parallel construction, one beam is modulated in a PM driven by a radio frequency (RF) microwave signal in the upper arm, and the other beam is modulated by another PM driven by a binary coding electrical pulse sequence in the under arm, then the two phase-modulated beams combine and interfere. When the interference light field is send to a high-speed photodetector (PD) for beating, 2 Gbit/s binary phase-coded 10 GHz and 2.5 Gbit/s phase-coded 20 GHz microwave waveform with a π phase shift was respectively achieved, and corresponding pulse compression ratio is 20 and 16.5, respectively. The obtained phase-coded microwave signals exhibit a good pulse compression performance, which can find potential applications in modern radar systems and wireless communications.

Multi-format signal generation using a frequency-tunable optoelectronic oscillator.

A novel photonic approach for multi-format signal generation based on a frequency-tunable optoelectronic oscillator (OEO) is proposed using a dual-polarization quadrature phase shift-keying (DP-QPSK) modulator. The upper dual-parallel Mach-Zehnder modulator (DP-MZM) integrated in the DP-QPSK modulator is properly biased to serve as an equivalent phase modulator, which functions in conjunction with a phase-shifted fiber Bragg grating (PS-FBG) in the OEO loop as a high-Q microwave photonic band-pass filter. The lower DP-MZM in the DP-QPSK modulator injected by the oscillation signal functions as a frequency multiplier, a phase-coded microwave signal generator or an optical frequency comb generator, respectively, with different signal injection methods. An experiment is performed. When the lower DP-MZM serves as a frequency multiplier, tunable frequency-doubled and quadrupled microwave signals up to 40 GHz are generated without using an optical notch filter; and if it functions as a phase-coded microwave signal generator, fundamental and frequency-doubled binary phase-coded microwave signals are generated with a tunable frequency. Furthermore, tunable five-line optical frequency combs are also generated using the compact system without an external RF source. The performance of the generated signals is also investigated.

A Frequency-Tunable Binary Phase-Coded Microwave Signal Generator With a Tunable Frequency Multiplication Factor

A novel frequency-tunable binary phase-coded microwave signal generator with a tunable frequency multiplication factor is proposed. The key component of the proposed system is a dual-polarization quadrature phase-shift-keying (DP-QPSK) modulator, which is driven by the microwave reference signal and the coding signal. By properly controlling the bias points of the DP-QPSK modulator and the amplitudes of the microwave reference signal and the coding signal, a fundamental, frequency-doubled, frequency-tripled or frequency-quadrupled binary phase-coded microwave signal can be generated when two orthogonally polarized optical signals at the output of the DP-QPSK modulator are combined and then detected in a photodetector. The proposed system is experimentally evaluated. A binary phase-coded microwave signal is generated at the fundamental, doubled, tripled, or quadrupled frequency. The frequency tunability and the pulse compression performance of the generated phase-coded microwave signals are also experimentally studied.

Multi-frequency phase-coded microwave signal generation based on polarization modulation and balanced detection.

Photonic multi-frequency phase-coded microwave signal generation is proposed and demonstrated based on polarization modulation and balanced detection. Consisting of only a polarization modulator (PolM) driven by an electrical coding data, a polarization beam splitter (PBS) and a balanced photodetector (BPD), the proposed microwave phase coder has no requirement on the wavelength, intensity modulation format, or modulation index of the input optical microwave signal, and allows phase coding of arbitrary-format RF signals, which enables multi-frequency phase coding with compact structure, simple operation, and high flexibility. A proof-of-concept experiment is performed, achieving simultaneous phase coding of 15 and 30GHz, or 10 and 20GHz RF signals with a coding rate of 5 Gb/s.

Phase-coded microwave signal generation based on a single electro-optical modulator and its application in accurate distance measurement.

A novel scheme for photonic generation of a phase-coded microwave signal is proposed and its application in one-dimension distance measurement is demonstrated. The proposed signal generator has a simple and compact structure based on a single dual-polarization modulator. Besides, the generated phase-coded signal is stable and free from the DC and low-frequency backgrounds. An experiment is carried out. A 2 Gb/s phase-coded signal at 20 GHz is successfully generated, and the recovered phase information agrees well with the input 13-bit Barker code. To further investigate the performance of the proposed signal generator, its application in one-dimension distance measurement is demonstrated. The measurement accuracy is less than 1.7 centimeters within a measurement range of ~2 meters. The experimental results can verify the feasibility of the proposed phase-coded microwave signal generator and also provide strong evidence to support its practical applications.

Single Phase Modulator for Binary Phase-Coded Microwave Signals Generation

We report a new approach to photonic generation of binary phase-coded microwave signals based on the asymmetric phase modulation indexes of a phase modulator in the TE and TM polarization states. The proposed system is extremely simplified compared with any other techniques reported in the previous literature since we only use one phase modulator. The microwave carrier frequency is widely tunable, and the π phase shift of the microwave signal is independent of the amplitude of the electrical driving signal. The proposed technique is theoretically analyzed and experimentally verified at carrier frequencies of 10 and 25 GHz, respectively.

Photonic Generation of Binary Phase-Coded Microwave Signals With Large Frequency Tunability Using a Dual-Parallel Mach–Zehnder Modulator

We present a photonic approach to generating binary phase-coded microwave signals with large frequency tunability using a dual-parallel Mach-Zehnder modulator (DPMZM). The DPMZM consists of a pair of sub-MZMs embedded in the two arms of a parent MZM. In our scheme, one of the sub-MZMs is fed by a sinusoidal microwave signal to be phase-coded, and the other sub-MZM is driven by a rectangular coding signal. The optical signals from the two sub-MZMs are destructively interfered by adjusting the dc bias of the parent MZM. As a result, the optical carrier is binary phase coded. A binary phase-coded microwave signal is generated by beating between the optical carrier and the sidebands. The carrier frequency of the phase-coded microwave signal is widely tunable. Phase-coded microwave signals with two different frequencies at 10 and 20 GHz are experimentally generated, respectively.

Photonic generation of phase-coded microwave signals with tunable carrier frequency

A photonic scheme to generate a phase-coded microwave signal with tunable carrier frequency based on a simple single-trip and two-pass structure is proposed. Facilitated by the fiber Bragg grating and phase modulator along the trip, both frequency doubling and signal phase coding could be achieved simultaneously. Phase-coded microwave signals at 20 and 22 GHz are experimentally generated.

Photonic Generation of Chirp-Free Phase-Coded Microwave With Accurate $\pi$ Phase Shift and Large Continuous Operating Bandwidth

This paper presents a novel approach to generate a binary phase-coded microwave signal with accurate π phase shift and large continuous operating bandwidth. In the system, the phase-coding modulation with an accurate π phase shift has been realized by the joint use of two cascaded polarization modulators (PolMs). The generation of phase-coded microwave signals at 10 GHz, 18 GHz, and 28 GHz has been experimentally demonstrated, which verifies the proposed technique positively. Since there is no use of any optical filters and fiber Bragg gratings (FBGs), this system is rather simple and free from the optical bandwidth limitation problem with operating in a continuous microwave bandwidth as large as limited only by the PolMs (from dc to 40 GHz).

Generation of phase-coded microwave signals using a polarization-modulator-based photonic microwave phase shifter

A scheme for the generation of phase-coded microwave signals using an electrically tunable photonic microwave phase shifter is proposed and demonstrated. The photonic phase shifter is based on a single-sideband polarization modulator (PolM), and the tuning of the phase shifter is implemented by a second PolM. By introducing an RF signal to the first PolM and an electrical coding signal to the second PolM, a phase-coded microwave signal with binary phase codes or polyphase codes is achieved. An experiment is performed. The simple and flexible operation, high coding rate, large frequency range, excellent transmission performance, and high stability of the system is confirmed.

Photonic Generation of Phase-Coded Microwave Signal With Large Frequency Tunability

A photonic approach to realizing phase-coded microwave signal generation with large frequency tunability is proposed and demonstrated. Two coherent optical wavelengths are generated based on external modulation by biasing a Mach-Zehnder modulator (MZM) at the minimum transmission point to generate ±1 -order sidebands while suppressing the optical carrier. The two ±1-order sidebands are then sent to a fiber Sagnac interferometer (SI) incorporating an optical phase modulator (PM) and a broadband flat-top fiber Bragg grating (FBG), with one of the sidebands being phase modulated at the PM. A frequency tunable phase-coded microwave signal is generated by beating the two sidebands at a photodetector (PD). The proposed technique is experimentally investigated. The generation of a frequency tunable phase-coded microwave signal at 22 and 27 GHz is demonstrated.