Down-converted Signal Research Articles

Electromagnetically Induced Transparency and Wideband Wavelength Conversion in Silicon Nitride Microdisk Optomechanical Resonators

We demonstrate optomechanically mediated electromagnetically induced transparency and wavelength conversion in silicon nitride (Si3N4) microdisk resonators. Fabricated devices support whispering gallery optical modes with a quality factor (Q) of 10(6), and radial breathing mechanical modes with a Q=10(4) and a resonance frequency of 625 MHz, so that the system is in the resolved sideband regime. Placing a strong optical control field on the red (blue) detuned sideband of the optical mode produces coherent interference with a resonant probe beam, inducing a transparency (absorption) window for the probe. This is observed for multiple optical modes of the device, all of which couple to the same mechanical mode, and which can be widely separated in wavelength due to the large band gap of Si3N4. These properties are exploited to demonstrate frequency up-conversion and down-conversion of optical signals between the 1300 and 980 nm bands with a frequency span of 69.4 THz.

Flexible receiver for multiband orthogonal frequency division multiplexing signals at the millimeter waveband based on optical downconversion

A novel (to our knowledge) and flexible photonics-based downconversion scheme is proposed for wireless receivers in base stations. It allows simultaneous detection of multiple signals at carriers up to tens of gigahertz, enabling communications at millimeter waves. Experiments demonstrate the effective downconversion of Wi-Fi signals at 2.4 and 39.8 GHz with the error vector magniture <-43 dB.

Double-slit implementation of the minimal Deutsch algorithm

We report an experimental implementation of the minimal Deutsch algorithm in an optical setting. In this version, a redundancy is removed from the most famous form of the algorithm. The original version involves manipulation of two qubits, while in its minimal version, only one qubit is used. Our qubit is encoded in the transversal spatial modes of a spontaneous parametric down-converted signal photon, with the aid of a double slit, with the idler photon playing a crucial role in creating a heralded single-photon source. A spatial light modulator (SLM) is programmed to physically generate one-bit functions necessary to implement the algorithm's minimal version, which shows that the SLM can be used in future implementations of quantum protocols.

A 186 to 212 GHz Downconverter in 90 nm CMOS

The design and measurements of a 200 GHz downconverter in 90 nm standard CMOS are presented. A positive conversion gain of +6.6 dB, a noise figure of 29.9 dB and an output bandwidth of 3 GHz are measured for an LO power of −14.9 dBm. The conversion gain remains within 3 dB for an RF frequency between 186 and 212 GHz. Downconversion of BPSK and QPSK signals is demonstrated with eye diagrams and constellation plots with data rates over 4 Gbit/s. A mathematical analysis is made of the MOSFETs in the triode region and a new small-signal parameter κ is introduced, which enables the design of the mixing transistors for minimum conversion loss.

Dynamic tracking down-conversion signal processing method based on reference signal for grating heterodyne interferometer

Traditional displacement measurement systems by grating, which purely make use of fringe intensity to implement fringe count and subdivision, have rigid demands for signal quality and measurement condition, so they are not easy to realize measurement with nanometer precision. Displacement measurement with the dual-wavelength and single-grating design takes advantage of the single grating diffraction theory and the heterodyne interference theory, solving quite well the contradiction between large range and high precision in grating displacement measurement. To obtain nanometer resolution and nanometer precision, high-power subdivision of interference fringes must be realized accurately. A dynamic tracking down-conversion signal processing method based on the reference signal is proposed. Accordingly, a digital phase measurement module to realize high-power subdivision on field programmable gate array (FPGA) was designed, as well as a dynamic tracking down-conversion module using phase-locked loop (PLL). Experiments validated that a carrier signal after down-conversion can constantly maintain close to 100 kHz, and the phase-measurement resolution and phase precision are more than 0.05 and 0.2 deg, respectively. The displacement resolution and the displacement precision, corresponding to the phase results, are 0.139 and 0.556 nm, respectively.

Millimeter-Wave Optoelectronic Mixers Based on Uni-Traveling Carrier Photodiodes

We present a novel technique for optoelectronic frequency down-conversion of millimeter-wave signals generated from photomixers. The mixing element proposed here is a uni-traveling carrier (UTC) photodiode employing a traveling wave design, originally fabricated for the generation of millimeter-wave signals. For fundamental mixing at a frequency of 100 GHz, a conversion gain of was measured, representing a significant improvement on previously published results. When the device was operated as a subharmonic mixer, an additional loss of 20, 27, and 39 dB was measured for second-, third- and fourth-harmonic mixing, respectively, for the same level of RF input power (0 dBm). A nonlinear dependence of the IF signal on the optically generated signal was measured. From subharmonic mixing measurements, a flat intermediate frequency (IF) response was found over a wide range of frequencies, limited mainly by the IF electronic components.

Multiheterodyne Detection for Spectral Compression and Downconversion of Arbitrary Periodic Optical Signals

Optical frequency combs are used as local oscillators for the measurement and analysis of unknown optical waveforms with periodic time domain structures. Experimental results obtained by heterodyning pulsed and phase-modulated laser sources are presented. The analysis is then extended to the heterodyning and sampling of bandlimited incoherent light sources. It is shown theoretically and experimentally that the correlations between photodetected white light at different times can generate RF interference that is sensitive to the optical phase.

Photonic generation of 60 GHz-band vector signals for RoF systems based on optical vector signal down-conversion

A novel photonic method of 60 GHz-band vector signal generation for RoF systems based on optical vector signal down-conversion is proposed and experimentally demonstrated in this paper. In the proposed method, the target vector signals are first generated in the optical domain with the help of mature commercial optical devices and then directly distributed to the base stations (BSs) through the fiber link. The generated vector signals can be automatically down-converted to the 60 GHz band in the BSs after O/E conversion, and then directly transmitted to the users without any further processing. With the proposed method, higher spectrum efficiency and system capacity will be obtained compared with the traditional OOK RoF systems while almost no extra system complexity and cost is brought in. According to the characteristics of different types of vector signals, two particular modulation schemes are provided, which are then verified by corresponding simulations and experiments. In the experimental 60 GHz RoF system, the 622 MSym/s 60 GHz-band 8-QAM and 4-QAM signals generated with two different schemes respectively are successfully transmitted over 50 km SMF and 5 m wireless channel without any compensation, and the power penalty are both about 1.7 dB at the BER of 10 − 9 .

Multi-band radio over fiber system with all-optical halfwave rectification, transmission and frequency down-conversion

We introduce a novel application of all-optical half-wave rectification in the transportation and delivery of multi-frequency radio-over fiber signals. System evaluation was performed of transmission over various optical fiber types and all-optical envelope detection was implemented to achieve error-free frequency down-conversion of ASK signals modulated on 10 GHz, 16 GHz and 40 GHz carriers. Transmission power penalty of less than 1.5 dB was observed after 25 km SMF and 80 km NZDSF.

Re-configurable digital receiver for optically envelope detected half cycle BPSK and MSK radio-on-fiber signals

We present the first known integration of a digital receiver into optically envelope detection radio-on-fiber systems. We also present a re-configurable scheme for two different types of optically envelope detected wireless signals while keeping the complexity of used optical components low. Our novel digital receiver consists of a digital signal processing unit integrating functions such as filtering, peak-powers detection, symbol synchronization and signal demodulation for optically envelope detected half-cycle binary phase-shift-keying and minimum-shift-keying signals. Furthermore, radio-frequency signal down-conversion is not required in our proposed approach; simplifying evens more the optical receiver front-end. We experimentally demonstrate error-free optical transmission (bit-error rate corresponding to 10 −3 related to FEC-compatible levels) for both 416.6 Mbit/s half-cycle binary phase-shift-keying and 104.17 Mbit/s minimum-shift-keying radio-frequency modulated signals after 30 km of fiber transmission.

High-Speed Photonic Power-Efficient Ultra-Wideband Transceiver Based on Multiple PM-IM Conversions

We experimentally demonstrate a novel photonic ultra-wideband (UWB) transceiver with pulse spectral efficiency of 50.97% and transmission speed up to 3.125 Gb/s. The UWB generator only consists of a highly nonlinear fiber (HNLF) and a commercial arrayed-waveguide grating (AWG). By using the concept of multiple cross-phase modulation in the HNLF and multiple phase modulation to intensity modulation conversions in the AWG, a power-efficient UWB pulse is combined with incoherent summation of two asymmetric monocycle pulses with inverted polarities. Benefiting from the ultra-fast response of fiber nonlinearities in the HNLF, on-off keying encoded UWB signals generated at 781.25 Mb/s, 1.5625 Gb/s, and 3.125 Gb/s are all error-free transmitted through a 22.5-km single-mode fiber (SMF) with power penalties lower than 1 dB. The bit-error rate is directly measured on down-converted baseband signals by using optical full rectification and electrical low-pass filtering technologies. The measured electrical spectra before and after 22.5-km SMF link transmission both fully comply with the spectral mask specified by the U.S. Federal Communications Commission (FCC) without power attenuation.

A Novel UWB Sampling Receiver and Its Applications for Impulse GPR Systems

A novel ultrawideband (UWB) synchronous receiver for a UWB radar system is presented. The developed receiver is the first to employ a sampling phase detector, which integrates a step recovery diode and a pair of Schottky diodes, to sample the UWB signal of a radar, enabling the miniaturization of the design. It achieves a 6-GHz sampling bandwidth, a dynamic range of more than 50 dB, and low harmonic distortion of the output baseband signal. The receiver's down-converted IF signals closely match with their original shape, demonstrating its good performance to reconstruct the microwave signals from a receiving antenna. These IF signals can be converted to digital signals by a low-cost A/D. For verification, the performance of the UWB receiver is tested through the experiments of buried steels at different thicknesses in the sand when it is applied to the ground-penetrating radar (GPR). The results show that the GPR system has good horizontal resolution and large detection depth. Therefore, this GPR system is very attractive and effective for applications of short-range and high-resolution detection.

Polarization-insensitive and widely tunable wavelength conversion for polarization shift keying signal based on four wave mixing in highly non-linear fiber

A fiber-based polarization-insensitive and widely tunable all-optical wavelength conversion for polarization shift keying (PolSK) signal is experimentally demonstrated by means of four-wave-mixing (FWM) in highly non-linear fiber. Polarization sensitivity of our scheme is compared with the conventional one and the conversion performance of the PolSK signal is investigated. In our scheme, preservation of state of polarization (SOP) of input PolSK signal is possible on both of the converted spectral components in FWM spectrum. In addition, over 23 nm of wavelength tunable operation with high conversion performance is achieved and detailed bit-error-rate (BER) characteristics are measured for both the up- and down-converted signal.

Acquisition of satellite navigation signals using dynamically chosen measurements

A new approach to sequential acquisition of satellite navigation signals is presented where the collection of measurement statistics is steered dynamically during the acquisition process. The process consists of a fixed number of operation cycles during which the state of the receiver is maintained as a vector of conditional probabilities of acquisition hypotheses, each hypothesis being associated with a code delay and a Doppler frequency. During each operation cycle, one hypothesis is singled out by applying a suitable policy on the state vector. The down-converted satellite signal is then despread and frequency shifted according to the hypothesis. The resulting signal is integrated and squared to form a statistic that is used to update the state vector according to Bayes' theorem. After completing the cycles, a decision is made in favour of the hypothesis corresponding to the highest posterior probability. Two policies are investigated, one based on the maximisation of one-step posterior probability and the other based on the maximisation of information gain. Simulation results are presented indicating that the proposed approach provides a significant performance advantage over standard techniques for a wide range of signal-to-noise ratios.

Bandwidth enhancement of electro-optic sensing using high-even-order harmonic sidebands

We demonstrate that the bandwidth of an electro-optic sensing system can be significantly enhanced by the use of even-order harmonic sidebands (order > 2) produced on an optical-carrier probe beam with two cascaded electro-optic modulators. The sensing frequency range may be routinely expanded by at least four times, with respect to the use of fundamental-harmonic sidebands, by enhancing the nonlinearity of high-order-harmonic electro-optic modulation. The creation of harmonic modulation sidebands up to the sixth order of the drive frequency on a laser-diode output is described analytically, as is photonic heterodyne down-conversion of microwave signals using these high-order even harmonics within an electro-optic sensor crystal. The nonlinear harmonics serve as beneficial local-oscillator modulations for broadband electro-optic detection of microwave fields without nonlinear distortion. Transverse near-field distributions from an 18.5 GHz patch antenna are extracted using the fourth- (sixth-) order-harmonic sidebands at the output of the cascaded electro-optic modulators driven with a 4.6- (3.1-) GHz continuous-wave input.

Complex bandpass sampling and direct downconversion of multiband analytic signals

The kernel concept of the software defined radio architecture is to eliminate the analogue mixers and to place analogue-to-digital converters as near the antenna as possible. Bandpass sampling can be used for direct downconversion without analogue mixers. In this paper, we report an efficient method to find the ranges of valid bandpass sampling frequency for direct downconverting multiple bandpass analytic signals (single-sideband RF signals). The algorithm results in the ranges of valid bandpass sampling frequency for the complex signals in terms of bandwidths and band positions of the single-sideband RF signals. Compared to real bandpass sampling, the valid sampling frequency ranges are easier to find and the ranges thus obtained having much wider interval than those of real sampling. As a consequence, the complex sampling scheme is more flexible in choosing sampling frequency and more robust to the sampling frequency variation. Furthermore, if spectral inversion is not permitted, then in some cases there will have no applicable sampling frequency under Nyquist rate for real sampling.

Sub-Millimeter-Wave Imaging Array at 500 GHz Based on 3-D Electromagnetic-Bandgap Material

The design, fabrication, and characterization of a 500-GHz electromagnetic bandgap (EBG) based heterodyne receiver array is presented. The array contained seven planar dipole antennas that were photolithographically defined on a common 20-mum-thick quartz substrate. Each antenna incorporated a Schottky diode and was connected to coplanar transmission lines that conveyed the down-converted 500-GHz signals to detectors. The quartz substrate was backed by a silicon EBG woodpile structure, which reduced antenna crosstalk and increased directivity. An off-axis parabolic mirror completed the beam-forming network.

Bandwidth enhancement of electro-optic field sensing using photonic down-mixing with harmonic sidebands

We demonstrate that harmonic sidebands of an electro-optic modulator's driving frequency can be used as the local oscillator in a photonic down-mixing process in order to significantly enhance the bandwidth of near-field, electro-optic, microwave measurements. The creation of second- and third-order-harmonic modulation sidebands on a laser-diode output are described, with heterodyne down-conversion of microwave signals taking place within an electro-optic sensor crystal. The measurement bandwidth of an electro-optic microwave probe can thus be enhanced by as much as a factor of three with respect to the use of conventional, fundamental-harmonic sidebands. Carrier-sideband analysis from the measured optical spectrum indicates that millimeter-wave-frequency local-oscillator sidebands can be created using a Ku-band electro-optic modulator and that the electro-optic-signal-modulation depth can be enhanced by suppressing the light-beam carrier component. Transverse near-field distributions from high frequency patch antennas are extracted using both second- and third-order-harmonic sidebands.

A searching algorithm for minimum bandpass sampling frequency in simultaneous down-conversion of multiple RF signals

Bandpass sampling (BPS) techniques for the direct down-conversion of RF bandpass signals have become an essential technique for software defined radio (SDR), due to their advantage of minimizing the radio frequency (RF) front-end hardware dependency. This paper proposes an algorithm for finding the minimum BPS frequency for simultaneously down-converting multiple RF signals through full permutation over all the valid sampling ranges found for the multiple RF signals. We also present a scheme for reducing the computational complexity resulting from the large scale of the purmutation calculation involved in searching for the minimum BPS frequency. In addition, we investigate the BPS frequency allowing for the guard-band between adajacent down-converted signals, which help lessen the severe requirements in practical implementations. The performance of the proposed method is compared with those of other pre-reported methods to prove its effectiveness.

ULTRASENSITIVE WIDEBAND INTEGRATED SPECTROMETER FOR CHEMICAL AND BIOLOGICAL AGENT DETECTION

A novel concept of a compact mm/submm integrated spectrometers for environmental monitoring for hazardous materials of chemical and biological origin as well as for remote monitoring of the Earth atmosphere is discussed. The agents will be exactly identified by their unique spectral signatures. The assembled on a multi-chip module, cryocooler-mounted Superconducting Integrated SPectromer (SISP) exploits the superior performance of superconducting Josephson junction technology and unique on-chip integration of analog components, analog-to-digital converter, and digital components. Analog components include a superconductor-insulator-superconductor (SIS) mixer with integrated quasioptical antenna, mm-wave local oscillator, and SQUID amplifier for the down-converted (IF) signals. Upon amplification, the IF signal is digitized using a bandpass delta-sigma modulator, followed by real time processing with rapid single flux quantum (RSFQ) circuitry. Experimental results showing both operation of spectrometer components and the way to their successful integration are presented.