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A high-accuracy photonics-assisted frequency measurement with rough-accurate compensation based on Mach-Zehnder interfering and power cancellation is proposed. A polarization division multiplexing dual-parallel Mach–Zehnder modulator (PDM-DPMZM) is employed to mix the unknown RF signal and sweep signal to optical field. The rough measurement is firstly performed by the interference of a Mach-Zehnder interferometer (MZI) to realize fast frequency estimation. Then, based on the rough measurement result, the accurate measurement based on power cancellation is implemented in a much narrower range, which greatly improves the efficiency of frequency measurement. The simulation results show that the amplitude comparison function (ACF) established by interference can achieve a measurement error of less than 0.3 GHz over 0.5 ~39 GHz. Moreover, thanks to the rough-accurate compensation, the accuracy can be further improved to 4 MHz. Additionally, the multiple frequency identification with a resolution of 10 MHz can also be achieved based on this system.

A novel photonic approach to generate frequency and bandwidth multiplying dual-chirp microwave for application in dual-band radar system is proposed using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator. The proposed approach is based on optical frequency multiplying and polarization selection. In the approach, the baseband signal and RF signal are injected into the DP-QPSK modulator to generate optical broad spectra and sidebands respectively. By adjusting the bias points of the DP-QPSK modulator, after polarization selection and optical to electrical conversion, frequency-quadrupling bandwidth-octupling and frequency-double bandwidth-quadrupling or frequency-tripling bandwidth-sextupling and frequency-fundamental bandwidth-doubling dual-chirp signals can be generated in the single structure respectively. The proposed approach is verified by simulations. Dual-chirp microwaves with central frequency–bandwidth of 32 GHz-8 GHz, 16 GHz-4 GHz or 24 GHz-6 GHz, 8 GHz-2 GHz are generated in the two ports respectively. Their autocorrelation results manifest good pulse compression capabilities. The central frequency, bandwidth, chirp rate and time duration can be tuned independently. The generated dual-chirp signals show good performance on the range-Doppler coupling and can significantly improve the range-Doppler resolution in dual-band radar system.

A method for photonic generation of arbitrary microwave binary digital modulation signal based on polarization switch is proposed and investigated. A polarization modulator is utilized to switch the direction of a linearly-polarized optical signal between two orthogonal axes. Then, a polarization-dependent modulation structure is employed to modulate an external RF signal to the two optical carriers with different polarization directions respectively. The modulation structure consists of a polarization beam splitter, two parallel placed dual-drive Mach–Zehnder modulators and an optical combiner. By adjusting the parameters of the two modulators, different optical sidebands can be obtained in two polarization directions. After optical-to-electrical conversion, a microwave amplitude shift keying (ASK), frequency shift keying (FSK) or phase shift keying (PSK) signal can be achieved. The modulation format, bit-rate and carrier frequency of the generated signal can be tuned independently and flexibly. A simulation is demonstrated to verify the proposed scheme, a 2-Gbit/s 40-GHz ASK signal, a 2-Gbit/s FSK signal with carrier frequencies of 20 and 40 GHz, and a 2-Gbit/s 20-GHz PSK signal are obtained. The scheme has good tunability.

A photonic microwave hybrid frequency and phase shift keying (FPSK) signal generator is proposed and demonstrated. In the scheme, a parallel structure is constructed to functions as an optical sidebands selector, in which a single-drive Mach-Zehnder modulator (MZM) is placed in parallel with another MZM and a phase modulator (PM). After the parallel structure, a following PM is employed to realize phase modulation. The output signal of the PM is combined with a local oscillator at the receiver after 6-km fiber transmission, and then a hybrid FPSK signal can be obtained after photodetection. The feasibility of the proposed scheme is verified by simulation through a transmission test in a radio over fiber (ROF) system, and a hybrid FPSK signal with frequencies of 5/15 GHz and phase shift of 𝜋 is successfully generated. The scheme features the advantages of polarization independence and good frequency tunability since no polarization multiplexing devices or frequency-dependent devices are applied.

A photonic approach for the generation of microwave hybrid frequency/phase shift keying (FSK/PSK) signal based on an integrated polarization division multiplexing dual-parallel Mach–Zehnder modulator (PDM-DPMZM) is proposed and demonstrated. In the scheme, the polarization modulator is employed to modulate the linearly polarized lightwave to generate an optical polarization-shift keying (PolSK) signal. Then the PolSK signal is sent to the PDM-DPMZM via a polarization controller to generate optical PSK signal. After photo-detection, a microwave hybrid FSK/PSK signal can be obtained. Simulations are conducted to verify the proposed scheme. As bit rate is set to 1 Gbit/s, a hybrid FSK/PSK signal with frequency of 10/15 GHz and phase shift of $$\pi$$ is successfully demonstrated. Hybrid signals with 2-Git/s frequency shift and 1-Git/s phase shift are also implemented. The compression ratio of the generated signal is 25.5 and the main-to-sidelobe ratio is 11.2 dB. The generations of ASK, PSK and FSK signals are discussed, and the impact of the polarization extinction ratio is also analyzed.

Photonic microwave frequency down-conversion based on carrier suppression single sideband (CS-SSB) modulation via an integrated dual-drive dual-parallel Mach-Zehnder modulator (DP-MZM) is proposed....

A method for photonic generation of a linearly chirped microwave waveform using a frequency-sweeping laser and a dual-polarization modulator is proposed and investigated. A frequency-sweeping continuous-wave light is generated from the laser and then sent to the modulator. In the modulator, one part of the light is modulated with an RF signal to generate a frequency-shifting optical signal, while another part of the light is passed through a polarization rotator to rotate the polarization to an orthogonal direction. At the output of the modulator, the two optical signals are combined with orthogonal polarizations, and then injected into a polarization delay device to introduce a time delay. After combining the two optical signals for heterodyning, a linearly chirped waveform can be generated. The bandwidth, time duration, chirp rate and sign, central frequency of the generated waveform can be tuned independently and flexibly, furthermore, frequency doubling for the central frequency can be achieved in the waveform generation. A simulation is demonstrated to verify the proposed scheme, a linearly chirped microwave pulse with up or down chirp, central frequency of 20 or 40 GHz, bandwidth of 20 GHz, time duration of 500 ns, time-bandwidth product (TBWP) of 10000 is obtained.

Photonic microwave frequency down-conversion with independent multichannel phase shifting and zero-intermediate frequency (IF) receiving is proposed and demonstrated by simulation. By combined use of a phase modulator (PM) in a sagnac loop and an optical bandpass filter (OBPF), orthogonal polarized carrier suppression single sideband (CS-SSB) signals are obtained. By adjusting the polarization controllers (PCs) to introduce the phase difference in the optical domain and using balanced detection to eliminate the direct current components, the phase of the generated IF signal can be arbitrarily tuned. Besides, the radio frequency (RF) vector signal can be also frequency down-converted to baseband directly by choosing two quadrature channels. In the simulation, high gain and continuously tunable phase shifts over the 360 degree range are verified. Furthermore, 2.5 Gbit/s RF vector signals centered at 10 GHz with different modulation formats are successfully demodulated.

A novel scheme for the generation of ultraflat and broadband optical frequency comb (OFC) is proposed based on cascaded two dual-electrode Mach–Zehnder modulators (DE-MZM). The first DE-MZM can generate a four-comb-line OFC, then the OFC is injected into the second DE-MZM as a carrier, which can increase the number of comb lines. Our modified scheme finally can generate a broadband OFC with high flatness by simply modifying the electrical power and the bias voltage of the DE-MZM. Theoretical analysis and simulation results reveal that a 16-comb-line OFC with a frequency spacing that two times the frequency of the RF signal can be obtained. The power fluctuation of the OFC lines is 0.48 dB and the unwanted-mode suppression ratio (UMSR) can reach 16.5 dB. Additionally, whether the bias drift of the DE-MZMs has little influence on the power fluctuation is also analyzed. These results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness.

A novel photonic dual-frequency phase-coded signals generator based on the optical carrier phase shifting and polarisation selection techniques is proposed by using an integrated dual-polarisation quadrature phase shift keying (DP-QPSK) modulator. The key feature of the scheme is the capability to generate dual-frequency phase-coded signals with reconfigurable frequency multiplication factors. In the upper QPSK modulator, an optical binary phase shift keying (BPSK) signal and a carrier-suppressed double-sideband optical signal are generated, while in the bottom QPSK modulator, another carrier-suppressed double-sideband optical signal is generated. Thanks to the dual-polarisation property of the integrated modulator, the optical BPSK signal and different optical sidebands can be selected by using polarisation selection. As a result, two phase-coded signals with different frequencies can be achieved simultaneously. By adjusting the bias phases of the submodulators, dual-frequency phase-coded signals with frequencies of one and three, or two and four times the frequency of the RF carrier can be generated. The generation of 2.5 Gbps dual-frequency phase-coded signals with frequencies of 20 and 40 GHz, or 10 and 30 GHz are verified. The proposed scheme is simple, compact, and promising to find applications in future multi-band and multi-functional radars.

A photonic approach to generate frequency-doubled microwave waveforms using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator driven by a sinusoidal radio frequency (RF) signal is proposed. By adjusting the dc bias points of the DP-QPSK modulator, the obtained second-order and six-order harmonics are in phase while the fourth-order harmonics are complementary when the orthogonal polarized outputs of the modulator are photodetected. After properly setting the modulation indices of the modulator, the amplitude of the second-order harmonic is 9 times of that of the six-order harmonic, indicating a frequency-doubled triangular waveform is generated. If a broadband 90° microwave phase shifter is attached after the photodetector (PD) to introduce a 90° phase shift, a frequency-doubled square waveform can be obtained after adjusting the amplitude of the second-order harmonic 3 times of that of the six-order harmonic. The proposal is first theoretically analyzed and then validated by simulation. Simulation results show that a 10 GHz triangular and square waveform sequences are successfully generated from a 5 GHz sinusoidal RF drive signal.

A simple photonic microwave image-reject mixer (IRM) using two parallel phase modulators is proposed. First, a photonic microwave mixer with phase shift ability is achieved using two parallel phase modulators (PMs), an optical bandpass filter, three polarization controllers, three polarization beam splitters and two balanced photodetectors. At the output of the mixer, two frequency downconverted signals with tunable frequency difference can be obtained. By adjusting the phase difference as 90° and utilizing an electrical 90° hybrid, the useless components can be eliminated, and the image reject operation is realized. The key advantage of the proposed scheme is the usage of PM, which avoid the DC bias shifting problem and make the system simple and stable. A simulation is performed to verify the proposed scheme, a relative − 90° or 90° phase shift can be obtained between the two output ports of the photonic microwave mixer, at the output of the IRM, 60 dB image-reject ratio is obtained.

We propose and demonstrate a simple, flexible and stably operated multi-band frequency conversion approach based on a dual-polarization quadrature phase shift keying modulator (DP-QPSK). The modulator incorporating two dual parallel Mach–Zehnder modulators (DPMZMs) which perform as OFC generator and +1st carrier suppressed single sideband generator, respectively, to achieve the purpose of frequency conversion. The theoretical analysis indicates that by properly adjusting six DC bias points in the integrated modulator and two modulation indices, a frequency of received RF signal can be directly converted into different frequencies that cover different bands simultaneously. The simulation results verified the possibility. For example, the received C band frequency of 3.8 GHz can be converted into X, Ku, K and Ka bands. An X band frequency of 9.6 GHz can be down-converted to C band and up-converted to Ku, K, Ka band. In addition, the simulation also focuses on how the adjustable parameters (such as DC bias points and modulation index) influence the conversion results. It demonstrates stable conversion efficiency against the DC drafting.

A simple image rejection mixer based on a dual-polarization quadrature phase shift keying modulator is presented without a 90° hybrid coupler in electrical field. By properly adjusting DC bias points in the integrated modulator and performing balanced photo-detection, the influence of image components can be well rejected. The simulation results show that a 52.24 dB image suppression ratio (ISR) and a conversion efficiency (CE) of −9.17 dB can be achieved by the proposed mixer. Besides, another research on the ISR and CE against non-ideal parameters is carried out. According to the simulation results, it can be figured that the main factor to influence the ISR and CE is the DC drifting which results both of them changed rapidly as the DC bias points deviate from the settled values. On the other hand, with different extinction ratios and LO signal powers and RF signal powers, the mixer still performs good ISR and CE.

We report a photonic approach to generate frequency-doubled microwave waveforms using an integrated electro-optic dual-polarization modulator driven by a sinusoidal radio frequency (RF) signal. With active bias control, two MZMs of the dual-polarization modulator operate at minimum transmission points, a triangular waveform can be generated by a parameter setting of modulation index. After introducing a broadband 90° microwave phase shifter, a square waveform can be obtained by readjusting the power relationship of harmonics. The proposal is first theoretically analyzed and then validated by simulation. Simulation results show that a 10 GHz triangular and square waveform sequences are successfully generated from a 5 GHz sinusoidal RF drive signal, and the performance of the microwave waveforms are not influenced by the finite extinction ratio of modulator.

An ultra-flat and broadband optical frequency comb (OFC) generator is proposed and experimentally demonstrated by directly modulating a dual-driven Mach–Zehnder Modulator (MZM) with only one RF signal. The proposed scheme can generate two forms of OFCs by simply adjusting the bias voltages of the MZM and the power of the RF signal. One form is a 20-line OFC with a frequency spacing equals the frequency of the RF signal, the other form is a 16-line OFC with a frequency spacing of two times the frequency of the RF signal. The generated OFCs have low power variation and broad bandwidth. The proposed scheme is verified by an experiment. A 20-line OFC with a frequency spacing of 10 GHz and flatness of 0.7 dB, and a 16-line OFC with a frequency spacing of 20 GHz and flatness of 0.3 dB are experimentally demonstrated.

A photonic approach to generate a frequency and bandwidth multiplying dual-chirp microwave waveform using a single dual-polarization quadrature phase shift keying (DP-QPSK) modulator is proposed and demonstrated. In the proposed scheme, an RF carrier is applied to one QPSK modulator and a baseband single-chirp waveform is applied to another. By setting the driving signals applied to the modulator and adjusting the dc bias phases in the modulator, high-order optical sidebands can be obtained with the optical carrier suppressed. After optical to electrical conversion, a frequency-doubling and bandwidth-quadrupling, or frequency-quadrupling and bandwidth-octupling dual-chirp microwave can be generated. The approach is verified by simulation. Dual-chirp microwave waveforms with 16-GHz central frequency, 2048-MHz bandwidth and 32-GHz central frequency, 4096-MHz bandwidth are generated through an 8-GHz RF carrier and 512-MHz bandwidth baseband signal. The generated dual-chirp microwave waveform can be used in a radar system to improve its range-Doppler resolution.

An approach to generate flat optical frequency comb (OFC) is proposed and experimentally demonstrated using a single integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator. By adjusting six dc bias points and two modulation indices of the modulator, the OFC with adjustable comb number and exactly the same intensity can be theoretically generated according to the equations derived from the DP-QPSK modulation model. Experimental results show that the proposed OFC generator can produce 7, 9, 11, and 13 lines with a spectral flatness of 0.96, 1.13, 2.01, and 1.17 dB, respectively. The unwanted-mode suppression ratio of the generated 7, 9, 11, and 13 lines OFCs are 10.33, 9.54, 6.79, and 10.45 dB, respectively. In addition, the generated OFC exhibits good frequency tunability. The nine-lines OFCs with frequency spacing of 6.02, 7.02, 8.02, and 9.02 GHz are experimentally generated.

Detection and frequency estimation of radio frequency (RF) signals are critical in modern RF systems, including wireless communication and radar. Photonic techniques have made huge progress in solving the problem imposed by the fundamental trade-off between detection range and accuracy. However, neither fiber-based nor integrated photonic RF signal detection and frequency estimation systems have achieved wide range and low error with high sensitivity simultaneously in a single system. In this paper, we demonstrate the first Brillouin opto-electronic oscillator (B-OEO) based on on-chip stimulated Brillouin scattering (SBS) to achieve RF signal detection. The broad tunability and narrowband amplification of on-chip SBS allow for the wide-range and high-accuracy detection. Feeding the unknown RF signal into the B-OEO cavity amplifies the signal which is matched with the oscillation mode to detect low-power RF signals. We are able to detect RF signals from 1.5 to 40 GHz with power levels as low as -67 dBm and a frequency accuracy of ± 3.4 MHz. This result paves the way to compact, fully integrated RF detection and channelization.

We propose and experimentally demonstrate a novel electro-optic frequency shifter with frequency multiplication operation based on high-order optical single-sideband (SSB) modulation and polarization multiplexing using an integrated dual-polarization quadrature phase shift keying (DP-QPSK) modulator. By changing the dc bias phases of the modulator and the phase difference between the input RF signals, two-high-order SSB modulation signals are generated from the two QPSK modulators. After that, the two optical signals are polarization multiplexed and then projected to one direction to remove the low-order sidebands while only the high-order sideband is reserved. The scheme is numerically analyzed with the modulation indices of the modulator for optimal operation. A distinct advantage of this approach is the capability to generate a frequency shifting with a continuous and ultrawide tunable range (more than ±100 GHz), and the tuning operation is accurate, simple, and flexible. An experiment is carried out to achieve a frequency-doubled optical frequency shifter. A continuous frequency shifting ranged from −36 to 36 GHz is experimentally verified.

Filterless photonic generation of microwave signals with various frequency multiplication factors via series connected polarization modulators is proposed and demonstrated experimentally. Frequency octupling, sextupling, or quadrupling microwave signal can be obtained when the polarization state of the light wave, the modulation indices of the modulators, and the phase of the radio frequency (RF) driving signal are suitably set. The optical sideband suppression ratios and RF spurious suppression ratios of the generated frequency multiplication signals are measured. Besides, the frequency-tunable ability and phase noise are analyzed.

A novel scheme for generation of an optical frequency comb (OFC) based on the chirping of two cascaded modulators is proposed. The first modulator is a dual-electrode Mach–Zehnder modulator (MZM), while the other modulator is an integrated MZM composed of two parallel MZMs that increases the number of comb lines. Our modified scheme can generate a large number of frequency lines with excellent flatness by simply modifying the chirp factor, and it is shown that up to 54 frequency lines could be observed. Theoretical analysis and simulation results show that under the variety of conditions that can be used in this scheme, the power fluctuations of the OFC lines are less than 0.5 dB in all cases; these results demonstrate the robustness of our scheme and verify its good accuracy and high stability with perfect flatness. Additionally, our modified scheme has the merit of tunable frequency spacing, which is practical for experimental realization of the OFC.

A novel analog photonic link with enhanced spurious-free dynamic range (SFDR) based on an integrated electro-optic dual-polarization modulator is presented and demonstrated. The dual-polarization modulator, which consists of a polarization beam splitter, a polarization beam combiner, and two z-cut LiNbO3 MZMs, can achieve complementary intensity modulation along the orthogonal polarization directions with different modulation indexes. By properly adjusting the power relationship of the orthogonal polarization directions, two third-order intermodulation distortions (IMD3) have equal intensity and opposite phase and cancel each other out. Combined with a low-biasing technique to reduce the noise power, the SFDR of the link can be further improved. A theoretical analysis is presented and validated by a simulation. The IMD3 can be suppressed by 30.6 dB, giving an improvement in SFDR of about 22 dB compared with a conventional optical double-sideband modulation link.

A polarization-dependent optical frequency comb (OFC) generation scheme based on recirculating frequency shift (RFS) is proposed and demonstrated. A dual-parallel Mach-Zehnder modulator (DPMZM) is employed to perform the carrier suppressed single sideband (CS-SSB) modulation and a polarization modulator (PolM) is adopted to generate a 5-line OFC. They are working in two orthogonal polarizations, respectively. The simulation results show that the proposed scheme can generate a 120-line OFC with flatness of 3.91 dB.

A novel approach to photonic generation of Microwave hybrid frequency/phase shift keying (FSK/PSK) signal is proposed and demonstrated. In the proposed method, an electrical signal with different direct currents for bit ‘0’ and bit ‘1’ is generated. The signal is fed into a Mach-Zehnder modulator which is biased at minimum and maximum transmission point corresponding to bit ‘0’ and bit ‘1’ respectively. Then the optical signals are fed into a Sagnac loop incorporating a fiber Bragg grating and modulated by a coding signal through a phase modulator. After photo-detection, a hybrid FSK/PSK signal can be obtained. Simulations are conducted to verify the proposed scheme. A hybrid FSK/PSK signal with frequency shift of 20/40GHz and phase shift of π is successfully demonstrated. The compression ratio of the generated FSK/PSK signal is 16, the main-to sidelobe ratio is 7.5 dB.

Photonic frequency-quadrupling millimeter-wave (mm-wave) vector signal generation is proposed by balanced detection without precoding. A dual-polarization quadrature phase shift keying (DP-QPSK) modulator is the main component of the scheme. In the DP-QPSK modulator, An optical carrier and ± 4st-order optical sidebands can be obtained in one QPSK modulator, while the other QPSK modulator driven by 16QAM baseband electrical I/Q data. After balanced detection, a 16QAM vector signal can be obtained by frequency-quadrupling. The proposed scheme can reduce the complexity of transmitter digital signal processing. By adjusting the sub modulators of the DP-QPSK modulator, a 4 Gbaud baseband 16QAM vector signal can be generated at 40 GHz by frequency-quadrupling. In addition, after 20 km single-mode fiber (SMF) transmission, the constellation, eye diagrams and the BER curves of the frequency-quadrupling mm-wave vector signal perform well.

A multi-band frequency conversion scheme with multi-phase shift is proposed. The dual polarization quadrature phase shift keying (DP-QPSK) modulator is employed to realize multi-band frequency conversion with multi-phase shift.

A reconfigurable and stable mixer is proposed and demonstrated in this paper. It mainly consists of a dual-driven Mach–Zehnder modulator and a polarization modulator with several polarization controllers (PC) and polarizers (Pol). According to the theoretical analysis, different functions (such as single ended mixer, balanced mixer, I/Q mixer and image rejection mixer) can be realized by adjusting the PCs and Pols. The simulation results verify the possibility of multi-functions that realized by the reconfigurable mixer. In addition, another research on how the non-ideal parameters affect the image rejection ratio (ISR) and conversion efficiency of the mixer is also carried. The results show that both of them perform better as the extinction ratio gets higher. However, they are incurring a sharp decrease if the DC bias points deviate from the settled values. In the meantime, the results also indicate that the higher modulation indices lead to a better ISR. A 57.12 dB ISR can be achieved with conversion efficiency of − 9.53 dB.

Microwave frequency multiplication using two cascaded dual-parallel Mach–Zehnder modulators (DP-MZMs) to generate an optical millimeter-wave (mm-wave) with 16-tupling of the radio frequency (RF) driving signal frequency is proposed. A theoretical analysis leading to the optimum operating conditions including the direct current (dc) bias points, the modulation index, and the phase difference between RF driving signals is developed and demonstrated. A 160 GHz mm-wave with an optical sideband suppression ratio (OSSR) of 21.5 dB and a radio frequency spurious suppression ratio (RFSSR) of 38 dB is generated from a 10 GHz RF driving signal, which largely reduce the frequency of electrical driving signal and electrooptic devices. Since no optical filter is employed to suppress the undesired optical sidebands, the system exhibits the advantage of large frequency tunable range.

A novel linearized single-sideband modulator is proposed and demonstrated to generate optical single-sideband (OSSB) signal and improve the dynamic range of microwave photonic links. The modulator is composed of a dual-electrode Mach–Zehnder modulator (DEMZM) lying on the top branch and a phase shifter (PS) lying on the bottom branch. By optimizing the optical power split ratio of the linearized modulator and the phase shift of the PS, the third-order inter-modulation distortion (IMD3) can be efficiently suppressed while the second-order distortion components are eliminated simultaneously. It is a multi-octave linearization technique which can be applied for broadband systems. Simulation results show that, the linearized modulator can provide a spurious-free dynamic range (SFDR) of 130 dB for a bandwidth of 1 Hz at the received optical power of 2 dBm assuming shot noise is the dominant noise contribution, which is 22 dB higher than the conventional DEMZM. The effects of the finite extinction ratio of modulator, the phase deviation of PS and the dispersion of fiber on the linearization performance are also investigated.

A novel filterless optical millimeter-wave signal generation scheme is proposed. In the scheme, the undesired sidebands are suppressed using two parallel dual-parallel Mach–Zehnder modulators (MZMs) with different modulation indexes and polarization multiplexing, and frequency multiplication factor as high as 16 can be achieved. Simulation results show that 80, 120, and 160 GHz signals are generated through a 10 GHz RF signal using the proposed method, and the performance of the generated signals is good when commercially available MZMs with extinction ratio of 20–30 dB are used. The scheme has large tunability of modulation index for frequency octupling and 12-tupling signals generation and high stability against the RF driving voltage deviation for frequency 16-tupling generation.

The performance of optical inter-satellite communications using microwave photonics technologies employing intensity modulation with direct detection (IMDD) and phase modulation (PM) with interferometric detection are investigated and demonstrated with a numerical example. The theoretical model considering the saturated gain and amplifier spontaneous emission noise of optical booster amplifier and optical preamplifier is constructed for both architectures. Furthermore, the authors compare the performance of PM with interferometric detection to optimum biased IMDD in terms of radio frequency (RF) gain, RF noise figure and compression dynamic range (CDR). The numerical results show that the PM with interferometric detection can achieve better RF gain, RF noise figure and CDR than the optimum biased IMDD link as the laser output power is lower than 14.34, 12.45 and 4.2 dBm, respectively.

A novel scheme to generate 120 GHz millimeter (mm)-wave from 10 GHz radio frequency (RF) local oscillator (LO) with an integrated nested Mach–Zehnder modulator (MZM) is proposed and demonstrated. By properly adjusting the modulator dc bias voltages and the LO voltages and phases, a frequency of 12-tupling optical mm-wave with an optical sideband suppression ratio (OSSR) higher than 37 dB can be generated without optical filter. This scheme largely reduces the response frequency of the modulator and the LO frequency. Furthermore, the non-ideal nested MZM parameters are analyzed theoretically, and we find that both the imperfect extinction ratio of the MZM and the phase imbalance between two arms of optical coupler have an influence on the performance of the generated optical mm-wave.

A highly linear transmitter that consists of a dual-drive Mach–Zehnder modulator (DD-MZM), an optical gain, and an optical phase shifter in radio-over-fiber links is proposed and demonstrated by simulation. The optical carrier is split equally with one part driving the DD-MZM, while the other part remaining unmodulated. By properly adjusting the magnitude and phase shift of unmodulated optical carrier, two kinds of main origins of third-order IMD (IMD3) have equal intensity and opposite phase, and cancel each other out. The comparison of the proposed technique and double-sideband modulation by MZM is presented. Simulation results shown that the spurious-free dynamic range of 125.3 dB Hz2/3 is achieved, which is about 26 dB more than a quadrature biased MZM.

A tunable orthogonally polarized dual-wavelength optical signal generator is proposed based on an integrated dual-polarization quadrature phase shift keying modulator, a polarizer and a Sagnac loop. By driving the integrated modulator with an RF signal, an optical signal with two orthogonal polarization states is generated. Leading the polarization multiplexing optical signal to a polarizer with a specific principal axis, the low-order optical components of the signal are cancelled each other, while two high-order sidebands with a wavelength spacing of eight, twelve or sixteen times the frequency of the RF signal reserved. After that, a Sagnac loop is used to make the two sidebands separated and combined with orthogonal polarization states. The proposed approach features large wavelength spacing and good tunability for the generated optical signal. An experiment is performed. The generation of an orthogonally polarized dual-wavelength optical signal with wavelength spacing at 32, 80 and 91.2 GHz is verified by using an RF signal with frequency at 4, 10 and 11.4 GHz.

A novel reconfigurable photonic microwave mixer using an integrated dual-polarization binary phase shift keying modulator is proposed. In the modulator, one dual-drive Mach–Zehnder modulator (DMZM) is driven by an RF signal to perform optical single sideband modulation, while another DMZM is driven by a local oscillator (LO) signal. Thanks to the orthogonal-polarization property of the integrated modulator, the optical carriers from the two DMZMs can be cancelled out each other. By adjusting the phase difference of the two LO signals applied to the modulator and the bias phase of the DMZM, the photonic microwave mixer can be worked as a single sideband mixer or harmonic mixer. The scheme is simple, compact and filter-free. The reconfigurable photonic microwave mixer is verified by simulation. The results show that the electrical spurs suppression ratios for both the single sideband mixer and the harmonic mixer are 31 dB.

Aiming at the characteristics of distributed satellites system that the information exchanging and wavelength conversion are frequent but the payload is limited, a wavelength conversion scheme based on the self-phase modulation (SPM) and the four-wave mixing (FWM) is put forward, which can substitute several pump lasers in case of multiple wavelength channels. By utilizing the SPM in high nonlinear fiber to broaden the spectrum of initial signal, a pre-conversion signal is obtained as the pump light for wavelength conversion through an offset filtering. Then the wavelength conversion is realized based on the FWM in semiconductor optical amplifier. The principle of the scheme is deduced theoretically, and the relationship between conversion properties and structural parameters is analyzed. The simulation results show that the scheme can improve the quality of signal to some extent when completing a wavelength conversion, the Q factor improvement can be of 3 dB at most, while the conversion efficiency can reach to 20 dB.

A simple approach for high loss intersatellite microwave photonic link with intensity modulation and coherent balanced detection is proposed. In the transmitter, the double sideband-suppressed carrier (DSB-SC) modulated optical signal and optical carrier (OC) are combined by employing a polarization combiner to chose and control the signals polarization directions, while in the receiver, they are selected respectively by using a polarization splitter for they have orthogonal polarization directions. The separated DSB-SC signal and OC put into balanced detectors and the coherent detection is realized without a local oscillator (LO). At the output, the fundamental signal is augmented and the third-order distortion is suppressed for the DSB-SC modulation, the second-order distortion is removed for the balanced detection and the noise is reduced for the polarization direction control. The signal to noise and distortion ratio (SNDR) can be optimized by adjusting the power of OC and modulation index. The simulation results show that, a SNDR higher than 30 dB can be obtained for the proposed method, which is in agreement with the theoretical analysis.

A radio-over-fiber system with frequency 12-tupling optical millimeter-wave (mm-wave) generation using an integrated nested Mach-Zehnder modulator (MZM) is proposed and demonstrated by simulation. Through properly adjusting the direct current bias voltages of two sub-MZMs, the RF local oscillator (LO) voltages and phases, and the gain of base-band signal, the frequency 12-tupling optical mm-wave with data only carried by one sixth-order sideband is generated. As the signal is transmitted along the fiber, there is no periodical fading and bit walk-off effect caused by chromatic dispersion. The eye diagrams stay open even when the signal is transmitted over 60 km and the power penalty is 0.67 dB at a BER of 10-10. Furthermore, it is also proved to be valid that the BER is insensitive to the deviation of modulator extinction ratio and RF LO voltage.

To verify the potential space radiation-induced degradation of optical satellite communication system, the γ ray radiation experiments of its key components have been developed. No obvious performance degradations of the DFB laser and photo detector module were found at the total dose less than 150 krad. The EDFA seems to be the most radiation sensitive, and it comes to its malfunction through the radiation of 16.2 krad. It is believed that the high energy particles’ radiation effect should be first considered when it refers to the optical terminals’ applications in the space.

A generalized time-domain model is presented for the evaluation of nonlinear distortion effects in inter-satellite microwave photonics links using a dual-drive Mach-Zehnder modulator (DD-MZM) under dual-tone modulation. The model results in simple exact expressions for any harmonic and inter-modulation components at the output of the detector which can be applied to almost all operating conditions of DD-MZM, providing useful information to select system parameters for the performance optimization. Two special cases, double sideband and single sideband modulation, are studied in detail. Numerical results for the third-order inter-modulation distortion ratio (IMR3) are well matched with the analysis ones.

An exact analytical expression of signal-to-noise ratio (SNR) for inter-satellite microwave photonics links using a low-biased Mach-Zehnder modulator, and with both an optical booster amplifier and a preamplifier, is derived with the method of Bessel expansion and Graf's addition theorem. It is observed that the most limitative noise is changed from the thermal noise to the signal-amplifier spontaneous emission beating noise that arises from the optical preamplifier, and the signal power is seen to increase more compared with the power of noise because of optical preamplifier. Thus, the SNR of system configurations with both an optical booster amplifier and an optical preamplifier can be improved compared with the SNR of system configurations with only an optical booster amplifier. For the preamplifier gain of 20 dB and noise figure of 3 dB, an increase of about 19.7 dB in optimum SNR is accessible. In addition, the effect of optical booster amplifier and preamplifier parameters on the optimum DC bias phase shift and SNR is also investigated.

A generalized intersatellite microwave photonics links model to study the influence of the modulation index of Mach–Zehnder modulator on the receiver sensitivity with multiple radio frequency (RF) signals is presented. An exact analytical solution of signal-to-noise and distortion ratio (SNDR) for optical double-sideband (ODSB) and optical single-sideband (OSSB) modulation is deduced with Bessel expansion and Graf's addition theorem. Numerical results show that the receiver sensitivity increases and then decreases as the increase in modulation index, there is an optimum modulation index that maximizes the receiver sensitivity and the larger channel numbers lead to lower receiver sensitivity for maintaining the SNDR at the desired level. In addition, ODSB modulation can be more attractive than OSSB modulation in intersatellite microwave photonics links, since the maximum receiver sensitivity for ODSB modulation is better than that for OSSB modulation.

An optical preamplifier is applied to increase the signal-to-noise ratio (SNR) of inter-satellite microwave photonics links considering the large signal loss in distant propagation. An optically preamplified intersatellite microwave photonics links model is established and an analytical expression of SNR is derived with the method of expanding Bessel series and Graf addition theorem. The dominant noise components influence the link performance is confirmed, given the desired SNR, the direct current (DC) bias phase shift of modulator can be optimized so as to minimize the output power of laser diode (LD) under different gain of optical preamplifier, and the effects of the optical preamplifier gain on the minimum output power of LD and optimal DC bias phase shift is also examined. According to the numerical results, the output power of LD needed to achieve the required SNR decreases while increasing the gain of preamplifier, and the corresponding optimal DC bias phase shift decreases first and then increases. For QPSK modulation signal, the output power of LD needed to achieve the SNR of 15.56 dB (BER=10-9) is at least 45 dBm without an optical preamplifier, while the output power of LD is required only 22.57 dBm as the gain of preamplifier is 15 dB.

An approach to generate microwave signal with tunable frequency multiplication factor (FMF) is presented based on an integratable electro-optic dual-parallel polarization modulator (DPPolM), which consists of a polarization beam splitter, two polarization modulators, and a polarization beam combiner. From a theoretical analysis, the frequency-octupled and frequency-quadrupled microwave signal can be generated respectively depending on the polarization direction of the polarizer after the DPPolM. Simulation results show that the frequency-octupled microwave signal with an optical sideband suppression ratio (OSSR) of 56.36 dB and a radio frequency spurious suppression ratio (RFSSR) of 49.24 dB, the frequency-quadrupled microwave signal with an OSSR of 41.15 dB and a RFSSR of 35.95 dB can be obtained, which match well with the theoretical analysis. The DPPolM based system is simple, compact, and able to generate high FMF microwave signal without an optical filter.

A novel orthogonal polarization optical carrier suppression with carrier (OCS+C) modulation and a coherent balanced detection intersatellite microwave photonic link with improved signal-to-noise and distortion ratio (SNDR) is proposed. By bidirectional use of a polarization modulator in a Sagnac loop in conjunction with a polarization beam splitter and two polarization controllers, only the light wave along the clockwise direction is effectively modulated while the counterclockwise light wave is not modulated due to the velocity mismatch, which generates the orthogonal polarization OCS+C modulation signal to mitigate the third-order intermodulation distortion (IMD3) and the signal-amplifier spontaneous emission beating noise. By demultiplexing and adjusting the polarization of the orthogonal polarization OCS+C modulation signal, coherent balanced detection can be realized without a local oscillator signal in the receiver, which suppresses the second-order distortions. Thus, a broadband linearized intersatellite microwave photonic link with high SNDR is achieved. Simulation results show that the maximum SNDR of 36.2 dB can be obtained when the optimum modulation index is 0.26, which is 8 dB higher than our previously proposed intersatellite microwave photonic link with an optical preamplifier.

For the scheme of 80 GHz optical millimeter-wave (mm-wave) generation using two cascaded Mach-Zehnder modulators (MZMs), an exact analytical solution for the optical mm-wave affected by phase shift drift and splitting ratio is derived with the method of expanding Bessel series. The results show that for the carrier and the fourth-order sideband, the influence caused by phase shift drift is dominant, while the first-order, the second-order and the third-order sidebands are influenced by both phase shift drift and splitting ratio. It follows that the undesired sideband suppression ratio is at least 35.9 dB when the splitting ratio deviation is 0.001, and the phase shift drift is 1°. The performance of the system is perfect if the accuracy is achieved.

We propose a novel approach to generate quadrupling-frequency optical millimeter-wave using a dual-drive Mach–Zehnder modulator (MZM) in radio-over-fiber system. By properly adjusting the phase difference in the two modulation arms of MZM, the direct current (DC) bias, the modulation index and the gain of base-band signal, the quadrupling-frequency optical millimeter-wave with signal only carried by one second-order sideband is generated. As the signal is transmitted along the fiber, there is no time shift of the codes caused by chromatic dispersion. Theoretical analysis and simulation results show that the eye diagram keeps open and clear even when the quadrupling-frequency optical millimeter-wave are transmitted over 110 km and the power penalty is about 0.45 dB after fiber transmission distance of 60 km. Furthermore, due to another second-order sideband carrying no signals, a full duplex radio-over-fiber link based on wavelength reuse is also built to simplify the base station. The bidirectional 2.5 Gbit/s data is successfully transmitted over 40 km standard single mode fiber with less than 0.6 dB power penalty in the simulation.