Frequency-doubled Microwave Signal Research Articles

Widely tunable frequency-doubling optoelectronic oscillator using a polarization modulator and a phase-shifted fiber Bragg grating

A frequency-doubling optoelectronic oscillator with wideband frequency tunability implemented using a polarization modulator (PolM) and a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. In the proposed structure, the output from the PolM is divided into two branches by an optical coupler. In the lower branch, an optoelectronic feedback loop is formed in which a tunable microwave photonic filter (MPF) is constructed by the joint operation of the PolM, the PS-FBG, a tunable laser source (TLS), a polarization controller (PC), and a polarizer, the MPF serves as an oscillation mode selector that its central frequency is a function of the frequency difference between the TLS and the notch of the PS-FBG. In the upper branch, an equivalent Mach–Zehnder modulator (MZM) is performed by the joint use of the PolM, a second PC, and a second polarizer, the second PC is adjusted to let the bias point of the MZM located at the minimum transmission point (MITP), which generates an optical signal with two sidebands at the ±first orders. By beating the two sidebands at a second photodetector (PD), a frequency-doubled microwave signal is generated. By simply adjusting the wavelength of the TLS, the central frequency of the MPF is shifted, and the fundamental oscillation and its frequency-doubled signals can be tuned. The detailed theoretical study is achieved, and a verified experiment is established. A fundamental oscillation signal with a frequency tuning range from 9.39 to 15.4 GHz is generated in the OEO loop, which is multiplied to generate a tunable frequency-doubled signal. Their overall performances are also investigated.

Tunable frequency-multiplying optoelectronic oscillator based on a dual-parallel Mach-Zehnder modulator incorporating a phase-shifted fiber Bragg grating

A tunable frequency-multiplying optoelectronic oscillator (OEO) based on a dual-parallel Mach-Zehnder modulator (DPMZM) is proposed and experimentally demonstrated. In the proposed system, the tunable fundamental microware signal is generated by a tunable optoelectronic oscillator incorporating a phase-shifted fiber Bragg grating (PS-FBG). By adjusting the DC bias of the DPMZM, the frequency-doubled microwave signal with a tunable frequency range from 11 GHz to 20 GHz and the frequency-quadrupled microwave signal with a tunable frequency range from 22.5 GHz to 26 GHz are generated. The phase noises of the fundamental, frequency-doubled and frequency-quadrupled signals at 10 kHz offset frequency are −105.9 dBc/Hz, −103.3 dBc/Hz and −86.2 dBc/Hz, respectively.

Optoelectronic oscillation of the second harmonic of a period-one oscillating distributed feedback laser

The optoelectronic oscillation using the second harmonic of a period-one (P1) oscillation as the oscillation seed is proposed and experimentally demonstrated. The P1 oscillation was generated by a distributed feedback (DFB) laser subject to optical feedback. By using a bandpass electrical amplifier to provide sufficient gain for the second harmonic frequency of the P1 oscillation, frequency-doubled microwave signal was generated with the single sideband phase noise below -114.2 dBc/Hz at a 10-kHz frequency offset from the carrier.

Frequency-Doubled Microwave Signal Generation and Phase Shifting With Arbitrary Signal Amplitude

A photonic-assisted frequency-doubled microwave signal generation and phase shifting approach with arbitrary signal amplitude is proposed. The key device in the proposed technique is a dual-polarization quadrature phase-shift keying modulator, whose two sub-dual-parallel Mach-Zehnder modulators are both biased as a carrier-suppressed single-sideband modulator but generating two opposite first-order optical sidebands. The phase difference between the orthogonally polarized two first-order optical sidebands and the polarization state of the optical signal are tuned independently by a polarization controller. After the optical signal from the polarization controller is combined via a polarizer and detected at a photodetector, a frequency-doubled microwave signal is generated, whose phase and amplitude can be independently controlled by tuning the polarization controller. An experiment is performed. Frequency-doubled microwave signals with carrier frequencies from 10 to 40 GHz are generated and phase shifted over 360° phase range with arbitrary signal amplitude. The proposed technique can not only be operated as a phase and amplitude tunable frequency-doubled microwave source, but also find applications in phased array radar systems as a wideband frequency-doubled multichannel phase shifter.

Microwave frequency upconversion employing a coupling-modulated ring resonator

We present a method to generate a frequency-doubled microwave signal by employing a coupling-modulated ring resonator. Critical coupling is achieved when the resonator intrinsic loss is perfectly balanced by the external coupling enabled by a Mach–Zehnder interferometer coupler. The high suppression of the carrier leads to a clean two-tone optical signal with the frequency interval two times larger than that of the input microwave frequency. The beating of the two-tone signal at a photodiode generates the frequency upconverted microwave signal. A theoretical model is established to analyze the modulation process and the microwave signal generation. Experimental results show that the electrical harmonic suppression ratio is around ∼20 dB (29 dB) for an input microwave signal with 5 dBm (10 dBm) power.

Multifold clock recovery and demultiplexing based on a polarization-dependent phase modulator incorporated frequency-doubling optoelectronic oscillator

A novel multifold clock recovery structure with demultiplexing function based on a frequency-doubling optoelectronic oscillator (FD-OEO) incorporating a common commercial phase modulator (PM) is proposed and experimentally demonstrated. A special phase modulation is obtained thanks to polarization-sensitive feature of LiNbO3 crystal of the PM. The special phase modulated signal is then split two parts connected by two pairs of polarization controllers (PCs) and polarizers to perform polarization interference and phase modulation to intensity modulation conversion. By controlling the PCs, the joint use of PC and polarizer in the loop is to guarantee an OEO with fundamental frequency self-oscillation, while the other outside of the OEO obtains frequency-doubled microwave signal at the output of the photodetector. Additionally, an optical filter can be inserted into the outside branch to only allow ±2nd-order sidebands pass through and realize frequency quadrupling after beating at the PD. Therefore, a prescaled clock at 10 GHz, a line-rate clock at 20 GHz and a 40 GHz frequency-doubled clock can be extracted from the injection-locked OEO respectively when a 2×10Gb∕s optical time division multiplexing (OTDM) data signal is injected. A twofold time division demultiplexing is demonstrated. Theoretical analysis is developed, which is validated by an experiment.

Frequency-multiplying optoelectronic oscillator with a tunable frequency multiplication technique

An optoelectronic oscillator (OEO) for the generation of a frequency-doubled or -quadrupled microwave signal with a tunable frequency multiplication technique is proposed and demonstrated. In the proposed OEO, a modulated signal is generated by a Mach–Zehnder modulator (MZM). The modulated signal is then divided into two parts. One part is sent to a photodetector (PD1) via an optical domain dual-loop composite cavity and then fed back to the MZM to form the OEO loop that can generate an oscillation signal with the frequency determined by the center frequency of an electrical bandpass filter used in the loop and the length difference of the dual-loop composite cavity. The other part is sent to a fiber-optic recirculating delay line (RDL) structure and then applied to another PD (PD2) for the formation of a microwave photonic (MWP) notch filter. Through using the cascade characteristics of the RDL loop in the fiber-optic RDL structure and the notch response of the MWP notch filter, a frequency-doubled or -quadrupled microwave signal is generated. A detailed theoretical analysis is provided and the results are verified by an experiment. A fundamental oscillation signal at 5.592 GHz is generated in the OEO loop, which is multiplied to generate a frequency-doubled microwave signal at 11.184 GHz or a frequency-quadrupled microwave signal at 22.368 GHz, respectively. The performance of the generated microwave signals is also investigated.

Optical spectral response measurement based on optical single‐sideband modulation with doubled measurement range

Accurate measurement of the optical magnitude and phase responses based on optical single-sideband (OSSB) modulation with doubled measurement range is proposed and demonstrated. In the scheme, an optical carrier and a second-order sideband are generated by an RF signal at an OSSB modulator consisting of a Mach–Zehnder modulator and an optical bandpass filter. After the optical device under test, the signal is sent to a photodetector, generating a frequency-doubled microwave signal, which is mixed with the RF signal from the transmitter to generate another fundamental frequency signal for phase and magnitude extraction. As a result, the measurement range of the OSSB-based optical vector analysers is doubled. In a proof-of-concept experiment, the magnitude and phase responses of a fibre Bragg grating are accurately measured.

Filter-less frequency-doubling microwave signal generator with tunable phase shift

A prototype for frequency-doubling microwave signal generator with tunable phase shift based on a filter-less architecture is proposed and analyzed. In the proposal, one dual parallel polarization modulator is used as the key component to generate two ±1st order sidebands along the orthogonal polarization directions with suppressed carrier. Then the polarization states of the two sidebands are aligned with the principal axes of an electro-optical phase modulator (EOPM). Tunable phase shift is implemented by controlling the direct current voltage applied to the EOPM. Without using any filters or wavelength-dependent components, the system possesses good frequency tunability and it can be applied to multi-wavelength operation. Taking advantage of the ability of frequency multiplication, the frequency tuning range can be wider than the operation bandwidth of the modulator. By theoretical analyses and simulated verifications, a frequency-doubling microwave signal ranging from 22 to 40GHz with full range phase shift is achieved.

Photonic-assisted microwave signal multiplication and modulation using a silicon Mach-Zehnder modulator.

Photonic generation of microwave signal is obviously attractive for many prominent advantages, such as large bandwidth, low loss, and immunity to electromagnetic interference. Based on a single integrated silicon Mach–Zehnder modulator (MZM), we propose and experimentally demonstrate a simple and compact photonic scheme to enable frequency-multiplicated microwave signal. Using the fabricated integrated MZM, we also demonstrate the feasibility of microwave amplitude-shift keying (ASK) modulation based on integrated photonic approach. In proof-of-concept experiments, 2-GHz frequency-doubled microwave signal is generated using a 1-GHz driving signal. 750-MHz/1-GHz frequency-tripled/quadrupled microwave signals are obtained with a driving signal of 250 MHz. In addition, a 50-Mb/s binary amplitude coded 1-GHz microwave signal is also successfully generated.

Frequency-doubling optoelectronic oscillator based on destructive interference

A frequency-doubling optoelectronic oscillator (OEO) using two cascaded modulators based on destructive interference is proposed and experimentally demonstrated. In the proposed system, we utilize a cascaded modulator including a phase modulator and an intensity modulator, which implements a carrier-suppressed double-sideband modulation based on destructive interference to generate a frequency-doubled microwave signal. Meanwhile, the phase modulator is connected by a chirp fiber Bragg grating in the loop, which forms a microwave photonic filter to select the fundamental frequency signal in the OEO loop. As a result, a frequency-doubled microwave signal at 17.9 and 20.5 GHz is generated, respectively. The phase noises and the long-term stability of the generated microwave signals are also investigated.

Photonic-assisted microwave frequency multiplier based on nonlinear polarization rotation

A photonic-assisted microwave frequency multiplier (MFM) based on the Kerr shutter is proposed and demonstrated. In this MFM, the nonlinear polarization rotation in the high nonlinear optical fiber is used for the first time to implement the light-controlled optical-carrier-suppressed modulation. The frequency-doubled microwave signal with the frequency up to 144GHz is generated. The results of the experiment are in accordance with the theoretical prediction.

Multichannel Continuously Tunable Microwave Phase Shifter With Capability of Frequency Doubling

A photonic generation of tunable microwave phase shifter with capability of frequency doubling is proposed and experimentally demonstrated using optical spectral shaping technique. Our proposed configuration only consists of a phase modulator (PM), a programmable optical filter, and one photodetector (PD). The phase modulated optical signal is fed into the programmable optical filter, where two specific harmonic sidebands of the modulated signal are chosen in order to apply a tunable phase shift to one of the selected sidebands. After optical amplification and beating at the PD, a frequency doubling microwave signal with continuously tunable phase shifter from 0° to 360° is obtained with less than 2.5 dB power fluctuation over a frequency range from 20 GHz to 33 GHz. Moreover, simultaneous four-channel microwave signals with independent phase shift setting are achieved, due to that the proposed configuration is compatible with wavelength division multiplexing (WDM) operation.

Widely tunable frequency-doubling microwaves generated using Brillouin-assisted carrier phase shift

An optically tunable frequency-doubling microwave generation technique based on stimulated Brillouin scattering (SBS) in optical fibers is proposed and experimentally demonstrated. Due to the strong dispersion characteristics in SBS, when a up/2 phase shift is imposed on the optical carrier of an amplitude-modulated signal by SBS, only a frequency-doubling microwave signal from the beating between the optical carrier and the 1st sidebands is generated. Due to the inherent narrowband character of SBS and the phase shift being only imported on to the optical carrier while the sidebands are kept unchanged, the frequency-doubling with large frequency tunability is realized, the operational bandwidth is just limited by other optical device deployed. In addition, all the required optical signals and pumps can be generated from the same laser source, the influence from the wavelength drifting is eliminated, so the stability of the system is established.

An electrically tunable frequency-doubling optoelectronic oscillator with operation based on stimulated Brillouin scattering

An electrically tunable frequency-doubling optoelectronic oscillator (OEO) with operation based on stimulated Brillouin scattering (SBS) and phase modulation is proposed and experimentally demonstrated. In this OEO configuration, the phase modulator in combination with an optical filter is employed to produce a frequency-doubling microwave signal, while the SBS effect provides the narrowband filtering and ensures the oscillation of the feedback driving signal at the fundamental frequency. By varying the Brillouin pump signal obtained from double-sideband–carrier-suppression modulation, the frequency tunability is realized. In our experiment, a continuous tunable frequency-doubling signal from 21.4 to 25 GHz is generated when the tuning signal applied to the intensity modulator is tuned from 200 MHz to 2 GHz.

Coupled frequency-doubling optoelectronic oscillator based on polarization modulation and polarization multiplexing

A coupled frequency-doubling optoelectronic oscillator (OEO) is proposed and experimentally demonstrated, which is constructed based on the perfect combination of polarization modulation and polarization multiplexing. A fundamental microwave signal at 9.95 GHz or a frequency-doubled microwave signal at 19.9 GHz is generated with a wavelength-independent sidemode-suppression ratio (SMSR) as high as 78 dB obtained. The phase noise of the generated 19.9-GHz signal is − 103.45 dBc/Hz at 10-kHz frequency offset, indicating a good short-term stability. The proposed scheme is simple and flexible, which can find applications in radars and wireless communications.

A Frequency-Doubling Optoelectronic Oscillator Using a Polarization Modulator

A novel realization of a frequency-doubling optoelectronic oscillator (OEO) using a polarization modulator (PolM) is proposed and experimentally demonstrated. In the proposed system, the PolM in combination with two optical polarizers connected via two polarization controllers (PCs) is operating as a two-output intensity modulator. One output of the intensity modulator is connected to the radio-frequency port of the PolM, to form an optoelectronic loop for the generation of a microwave signal with the fundamental frequency determined by the center frequency of a narrowband electronic filter. The other output of the intensity modulator provides a fundamental or frequency-doubled optically modulated microwave signal depending on the static phase term introduced by the PC before the polarizer. The proposed OEO is experimentally demonstrated. A fundamental microwave signal at 10 GHz or a frequency-doubled microwave signal at 20 GHz is generated. The phase noise performance of the generated microwave signal is also investigated.