Optical RF Signal Research Articles

Low-power, chip-based stimulated Brillouin scattering microwave photonic filter with ultrahigh selectivity

Highly selective and reconfigurable microwave filters are of great importance in radio-frequency signal processing. Microwave photonic (MWP) filters are of particular interest, as they offer flexible reconfiguration and an order of magnitude higher frequency tuning range than electronic filters. However, all MWP filters to date have been limited by trade-offs between key parameters such as tuning range, resolution, and suppression. This problem is exacerbated in the case of integrated MWP filters, blocking the path to compact, high-performance filters. Here we show the first chip-based MWP bandstop filter with ultrahigh suppression, high resolution in the megahertz range, and 0–30 GHz frequency tuning. This record performance was achieved using an ultralow Brillouin gain from a compact photonic chip and a novel approach of optical resonance-assisted RF signal cancellation. The results point to new ways of creating energy-efficient and reconfigurable integrated MWP signal processors for wireless communications and defence applications.

Photonic microwave downconverter based on an optoelectronic oscillator using a single dual-drive Mach-Zehnder modulator

A novel and compact photonic microwave downconverter is proposed and experimentally demonstrated based on an optoelectronic oscillator (OEO) using a single dual-drive Mach-Zehnder modulator (DMZM). The DMZM is used to simultaneously convert the input RF signal into an optical signal, form an OEO for RF carrier extraction, and downconvert the optical RF signal to the baseband. In the experiment, a 2-Gb/s NRZ coded 10.66-GHz RF signal is successfully downconverted to the baseband. In addition, a microwave receiver for wireless high-definition (HD) video transmission is built and verified based on the proposed downconverter. The experiment results confirm that the proposed downconverter has simple configuration, good downconversion performance and very stable operation.

All-Optical Frequency Up-Converter Utilizing Cross Polarization Modulation in an SOA for 60-GHz-Band Radio-Over-Fiber Systems

A broadband all-optical frequency up-converter using cross polarization modulation in a semiconductor optical amplifier is proposed and experimentally demonstrated. Error-free transmission of 1.25 Gb/s pseudorandom bit sequence data with an optical RF signal (fRF=60 GHz) was achieved. The receiver sensitivities at a bit error rate of 10-9 were -12.16 and -9.6 dBm in the inverted and noninverted modes, respectively. This all-optical frequency up-conversion technique showed negligible power penalties for fiber length up to 29.6 km.

Electro-optical radiofrequency mixer based on semiconductor optical amplifier

Presented is an electro-optical radiofrequency mixer based on a semiconductor optical amplifier directly modulated by an electrical local oscillator in the presence of an optical RF signal. A good conversion gain of about 5.7 dB and a low error vector magnitude below 3.8% were obtained for this mixer, proving its ability to achieve a frequency downconversion from 2.4 GHz to 100 MHz for an optical complex-modulated RF signal: QPSK, 16QAM and 64QAM.

Full-Duplex WDM-Based RoF System Using All-Optical SSB Frequency Upconversion and Wavelength Re-Use Techniques

We have experimentally demonstrated a full-duplex wavelength division-multiplexing-based radio-over-fiber system using all-optical single-sideband (SSB) frequency upconversion and wavelength re-use techniques for broadband optical-wireless access networks. The optical SSB RF signal having the RF frequency of 62.5 GHz is generated by using this all-optical frequency upconverter that consists of an arrayed waveguide grating for optical demultiplexing and a semiconductor optical amplifier for wavelength conversion based on the cross-gain modulation effect. The receiver sensitivity at the bit error rate of is 11.5 and for downlink (including air transmission of 1.5 m) and uplink, respectively. The power penalties originating from the fiber chromatic dispersion are negligible after transmission over 25-km standard mode fibers (SMFs) for both downlink and uplink. For the IF wavelengths from 1530 to 1580 nm (covering -band), the variation of the receiver sensitivity is less than 2.5 dB.

Loop-mirror filters based on saturable-gain or -absorber gratings

We present a novel all-fiber narrow-band filter based on pump-induced saturable-gain or-absorber gratings in a loop mirror. Our design provides built-in interferometric phase alignment of the signal to the grating for optimal filtering. Notch or bandpass functionality is determined by the choice of gain or absorption and the input ports selected for the pump and signal. The loop-mirror filter has potential bandwidths from the submegahertz to beyond the gigahertz regimes, and one can tune it optically by changing the wavelength of the pump light that establishes the grating. Such filters have potential applications to wavelength-division-multiplexed optical networks and optical rf signal processing.

A photonic-link millimeter-wave mixer using cascaded optical modulators and harmonic carrier generation

Efficient frequency conversion into and out of the millimeter wave frequency band has been demonstrated using photonic link signal mixing with cascaded optical modulators. By adjusting the modulator bias point and RF drive power to the modulator introducing the local oscillator signal at f/sub LO/=8.8 GHz, frequency conversions from f/sub s/ to f/sub LO//spl plusmn/f/sub s/, sf/sub LO//spl plusmn/f/sub s/, and 4f/sub LO//spl plusmn/f/sub s/ with respective losses of 4.8, 6.3, and 7.5 dB have been demonstrated. The direct phase noise measurement of the optical RF signal at 2f/sub LO/=17.6 GHz with 1 kHz offset shows -89 dBc/Hz, limited by the RF drive source.

Guided-wave acoustooptic Bragg modulators for wide-band integrated optic communications and signal processing (Invited Paper)

This paper presents a selective review of planar guided-wave acoustooptics, including some of the most recent results. The emphasis is on those aspects which relate to wide-band multichannel optical communications and real-time signal processing. First to be discussed are the analytical and numerical techniques required for the treatment of a Bragg modulator which uses a single aperture SAW transducer. The frequency responses generated for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</tex> -cut <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LiNbO_3</tex> waveguides using a digital computer serve as the basic data for the design of such a basic modulator. Next the key device parameters relevant to modulation and signal processing are discussed. The design parameters and procedures for wide-band Bragg modulators and deflectors are then established. Finally, some potential applications of such wide-band modulators and deflectors in optical communications and RF signal processing together with the best measured performance figures are described.