Photonic generation of microwave signals using dual-wavelength single-longitudinal-mode fiber lasers

Photonic generation of microwave signals is demonstrated with a dual-wavelength single-longitudinal-mode erbium-doped fiber ring laser. Microwave signal with a frequency of 21.07 GHz is obtained by aligning the reflection band of a uniform fiber Bragg grating to the two transmission peaks within a fiber Bragg grating-based Fabry-Perot filter. Stable dual-wavelength single-longitudinal-mode operation is guaranteed by means of the combined filtering effect of a saturable absorber and the Fabry-Perot filter. This approach provides an effective solution to the photonic generation of high-frequency microwave signals.     

Photonic generation of microwave frequency shift keying signals using a dual-polarization quadrature phase shift keying modulator

Optical Review - A novel method to generate microwave frequency shift keying (FSK) signals based on a dual-polarization quadrature phase shift-keying (DP-QPSK) modulator is proposed and verified by...     

Sensitive amplitude-and phase-modulated absorption-spectroscopy with a continuously tunable diode laser

The output beam of a continuously tunable GaA1As-diode laser with external cavity is phase-modulated at 800 MHz in an electrooptic LiTaO₃ crystal. The amplitude of the rf voltage applied to the EOM is modulated at 80 kHz in order to allow lock-in detection. Using a multipass absorption cell the detection limit of the absorption coefficient α could be pushed down to α_min ≧2 × 10^?10 cm^2212;1. The sensitivity of the techique is demonstrated by examples of overtone transitions in C₂H₂ and H₂O vapor.     

Photonic approach to microwave frequency measurement with extended range based on phase modulation

We propose and demonstrate a photonic approach to instantaneous frequency measurement with an extended range based on phase modulation.In the measurement system,two optical wavelengths and two dispersion fiber segments are used to construct the frequency-dependent amplitude comparison functions(ACFs).Several ACFs can be utilized jointly to determine the microwave frequency without ambiguities beyond a monotonic region of the lone conventional ACF.The measurable range of microwave frequency can be extended and the accuracy can be improved by selecting an ACF with a large slope.The experimental results show that the errors are limited within ±140 MHz of a frequency measuremental range from 8 to 20 GHz.     

Photonic generation of microwave signals using a dual-transmission-band FBG filter with controllable wavelength spacing

Two π-phase shifts are introduced in a uniform fiber Bragg grating (FBG) structure and a dual-transmission-band opens in the stopband of FBG. When incorporating this kind of FBG filter in a fiber ring cavity with a semiconductor optical amplifier (SOA) acted as gain medium, a stable dual-wavelength lasing with wavelength spacing of 0.032, 0.052 and 0.068 nm is achieved, respectively. Therefore, the laser output is heterodyned on a photodetector and desired microwave frequencies of 3.15, 6.16 and 8.08 GHz are generated. PACS 41.20.-q; 42.55.Wd; 42.81.-i     

Photonic microwave generation and transmission using direct modulation of stably injection-locked semiconductor lasers

Direct modulation of a semiconductor laser subject to stable injection locking is capable of generating microwave subcarriers that are broadly frequency-tunable, more than 4 times its free-running relaxation resonance frequency, and are highly sideband-asymmetric, more than 22 dB. The latter characteristic makes the laser system particularly attractive for radio-over-fiber applications. Therefore, such modulation sideband asymmetry, its underlying mechanism, and its effect on chromatic dispersion-induced microwave power variation are extensively studied, in particular, over a broad range of injection conditions. Mappings showing integrated and global understandings of the modulation sideband asymmetry together with the modulation frequency enhancement are obtained accordingly. Interestingly, it is found that the microwave frequency can be tuned over a broad range while keeping a similar level of modulation sideband asymmetry and vice versa, either of which is achieved by simply changing the injection condition. This, therefore, considerably adds the flexibility and re-configurability to the laser system. The cavity resonance shift due to injection locking is responsible for not only the enhanced modulation frequency but also the modulation sideband asymmetry, where a modification in its previous interpretation is obtained for explanation. The modified modulation characteristics are strong functions of the linewidth enhancement factor, making it possible to choose lasers with proper values of the factor for different photonic microwave characteristics.     

High frequency microwave signal generation using dual-wavelength emission of cascaded DFB fiber lasers with wavelength spacing tunability

A dual-wavelength fiber laser source based on two cascaded phase-shifted fiber Bragg gratings is presented. The gratings are written in an erbium-doped fiber, each configuring the cavity of a distributed feedback fiber laser. The spacing between lasing modes is controlled dynamically by the use of piezoelectric actuators. A continuous tuning range of 5-724 pm of the wavelength difference, which is equivalent to a photodetected 0.72-92 GHz range, is obtained. Efficient generation from the L to the W microwave and millimeter bands has been achieved by heterodyne photodetection of the dual-wavelength optical signal.     

Photonic instantaneous microwave frequency measurement based on two different phase modulation to intensity modulation conversions

A novel photonic technique for instantaneous frequency measurement of microwave signal based on phase modulation to intensity modulation conversion is proposed and demonstrated. In the proposed system, an optical carrier is modulated by a microwave signal with its frequency to be measured through a phase modulator. The phase-modulated optical signal is then converted to intensity-modulated signals in two independent paths using a dispersive media and a frequency discriminator respectively. Since the dependence of the received microwave power on the input microwave frequency in the two paths differs, the microwave power ratio between the two paths can be used to uniquely determine the microwave frequency. The major advantages of the approach lie in that only one laser source and the bias-free phase modulator is employed in the system, which improves the stability of the system. Experimental demonstrations of the frequency measurement based on the proposed approach are presented.     

Photonic generation of millimeter-wave ultra-wideband signal using phase modulation to intensity modulation conversion and frequency up-conversion

We propose and experimentally demonstrate the generation of a pair of polarity-reversed 24 GHz millimeter-wave (MMW) ultra-wideband (UWB) monocycles. The scheme is realized by using delay interferometer (DI) based phase modulation to intensity modulation (PM–IM) conversion and carrier suppression modulation (CSM) based frequency up-conversion. The phase modulation is realized by using either electro-optic phase modulator (EOPM) or cross phase modulation (XPM) in semiconductor optical amplifier (SOA), which is an all-optical approach to obtaining baseband UWB signals, respectively. After frequency up-converted by using CSM in a Mach–Zehnder modulator (MZM), a pair of polarity-reversed 24 GHz MMW-UWB signals complying with the Federal Communication Committee (FCC) requirements is generated. The bi-phase modulation (BPM) of 24 GHz MMW-UWB signals can also be realized by electrically switching the bias voltage of delay interferometer.     

Broadband optical frequency comb generation with a phase-modulated parametric oscillator

We introduce a novel broadband optical frequency comb generator consisting of a parametric oscillator with an intracavity electro-optic phase modulator. The parametric oscillator is pumped by 532-nm light and produces near-degenerate signal and idler fields. The modulator generates a comb structure about both the signal and the idler. Coupling between the two families of modes results in a dispersion-limited comb that spans 20 nm (5.3 THz). A signal-to-noise ratio of >30 dB in a 300-kHz bandwidth is observed in the beat frequency between individual comb elements and a reference laser.     

Photonic generation of microwave arbitrary waveforms

In this paper, techniques to generate microwave arbitrary waveforms based on all-fiber solutions are reviewed, with an emphasis on the system architectures based on direct space-to-time pulse shaping, spectral-shaping and wavelength-to-time mapping, temporal pulse shaping, and photonic microwave delay-line filtering. The generation of phase-coded and frequency-chirped microwave waveforms is discussed. The challenges in the implementation of the systems for practical applications are also discussed.     

Reconfigurable photonic generation of microwave hybrid frequency/phase shift keying signals

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 generation of background-free millimeter-wave ultra-wideband signals

We review the recent progress of photonic generation of millimeter wave(MMW)-ultra-wideband(UWB) signals. To fully satisfy the standard defined by the Federal Communications Commission(FCC), the baseband signal(background signal) and the residual local oscillator(LO) signal should be well controlled. We discuss several schemes in this work for generating background-free MMW-UWB signals that are fully compliant with the FCC requirement.     

Photonic generation of frequency-switchable microwave signals exploiting polarization-induced spectrum splitting in fiber grating-based Fabry-Perot filters

Frequency-switchable microwave signals are optically generated using a dual-wavelength single-longitudinal-mode erbium-doped fiber ring laser. The splitting of the resonance peak is observed in fiber grating-based Fabry-Perot (F-P) filters depending on the injected light polarization states. Choosing two different resonance peaks of the grating-based F-P filter and using a variable saturable absorber formed by a section of incompletely transparent erbium-doped fiber, wavelength-switchable dual-wavelength single longitudinal-mode operation is achieved in the fiber ring laser. Microwave frequency switched among 8.75, 21.25 and 25.4 GHz is implemented by feeding the output laser to a high-speed photodetector.     

Photonic generation of RF and microwave signal with relative frequency instability of 10~(-15)

We demonstrate the ultra-stable frequency sources aiming to improve the short-time instability of primary frequency standards. These sources are realized by using photonic generation approach, and composed of ultra-stable lasers, opticalfrequency-combs, optical signal detecting parts, and synthesizers. Preliminary evaluation shows that the sources produce fixed-frequency at 9.54(/9.63) GHz, 10 MHz, and tunable-frequency around 9.192 GHz with relative frequency instability of 10~(-15) for short terms.     

Photonic generation of tunable microwave signals by beating a dual-wavelength single longitudinal mode fiber ring laser

A novel method of generating tunable microwave signals in the photonic domain is proposed. Eighteen pairs of stable dual-wavelength single longitudinal mode lasings are achieved by incorporating a fiber Bragg grating based Fabry–Pérot filter and a tunable fiber grating into a fiber ring cavity. The frequency of the generated microwave signal obtained by beating the dual-wavelength laser with a photodetector can be tuned simply through configuring the working wavelength of the laser. A series of microwave frequencies of 9.4885, 9.572, 9.7111, 9.8498, 9.9598 and 10.0712 GHz are generated experimentally. The proposed method is useful in applications such as wireless access networks, sensor networks, radio-over-fiber systems and software-defined radio. PACS 41.20.-q; 42.55.Wd; 41.81.-i     

混沌超宽带信号的光学产生及其链路传输

用光反馈半导体激光器产生混沌超宽带(UWB)信号, 搭建了混沌UWB光载无线通信链路, 实现了360, 720 Mbit/s和1.44 Gbit/s三种不同传输速率下混沌UWB脉冲信号的生成和传输. 在未经任何色散补偿处理的情况下, 1.44 Gbit/s的混沌UWB信号在经过10 km单模光纤和0.6 m无线链路传输后, 在天线接收端被成功解调. 由于混沌UWB信号输出的随机性, 对应的UWB信号频谱中未出现任何离散的谱线. 这意味着利用混沌UWB信号实现的光载无线通信链路, 可以完全避免离散谱线对系统传输性能的劣化.     

Photonic generation of switchable multi-format linearly chirped signals

A compact and cost-effective photonic approach for generating switchable multi-format linearly chirped signals is proposed and experimentally demonstrated. The core component is a dual-drive Mach–Zehnder modulator driven by a coding sequence and a linearly chirped waveform. By properly setting the amplitudes of the coding sequence, a linearly chirped signal with different formats, including the frequency shift keying [FSK), phase shift keying [PSK), dual-band PSK, and FSK/PSK modulation formats,...     

Photonic RF frequency measurement combining SSB-SC modulation and birefringence

A new technique to instantaneously measure microwave frequency and amplitude is presented and experimentally demonstrated. The architecture described is based on a single sideband modulation with suppressed carrier (SSB-SC) and the measurement of the Stokes parameters at the output of a birefringent medium. The results show errors below 50 MHz in the 59% of measurements carried out in a range from 1 to 11 GHz and an average power error of 0.34 dB. The technique shows the potential to increase the resolution and the range by increasing the differential time delay of the birefringent medium.