Phase Coherent Detection Research Articles

A portable NMR platform with arbitrary phase control and temperature compensation.

In this paper, we present a custom-designed nuclear magnetic resonance (NMR) platform based on a broadband complementary metal-oxide-semiconductor (CMOS) NMR-on-a-chip transceiver and a synchronous reference signal generator, which features arbitrary phase control of the excitation pulse in combination with phase-coherent detection at a non-zero intermediate frequency (IF). Moreover, the presented direct digital synthesis (DDS)-based frequency generator enables a digital temperature compensation scheme similar to classical fieldlocking without the need for additional hardware. NMR spectroscopy and relaxometry measurements verify the functionality of the proposed frequency reference and temperature compensation scheme as well as the overall state-of-the-art performance of the presented system.

High-SFDR 100.8km ROF link with optical homodyne detection and genetic-algorithm-assisted digital demodulation.

Radio-over-fiber (ROF) link based on phase modulation and coherent detection has been widely proposed for linear transmission. Nowadays, there are increasing demands for long-distance analog radio-frequency (RF) signal transmission, as radars and broadcast systems. In this paper, a high spurious-free-dynamic-range (SFDR) analog coherent ROF link based on optical homodyne detection and genetic-algorithm-assisted digital demodulation is proposed and experimentally investigated. The ROF link is designed for transmitting RF signals ranging from 500 kHz to 100 MHz over a long-distance fiber under the environment of wide temperature. We test the link performance by transmitting different groups of two-tone signals (580 kHz and 600 kHz, 9 MHz and 10 MHz, 49 MHz and 50 MHz, 99 MHz and 100 MHz) over a 100.8-km single-mode fiber (SMF) under the temperature varying from -40°C to 70°C, the shot-noise-limited SFDR of the link are measured to be greater than 122 dB·Hz2/3.

A General Relation Between Frequency Noise and Lineshape of Laser Light

Lasers and especially semiconductor lasers (SCLs) are playing a major role in advanced technological and scientific tasks ranging from sensing, fundamental investigations in quantum optics and communications. The demand for ever-increasing accuracy and communication rates has driven these applications to employ phase modulation and coherent detection. The main laser attribute that comes into play is its coherence which is usually quantified by either the Schawlow-Townes (S-T) linewidth, the spectral width of the laser field, or the power spectral density (PSD) function of the laser frequency fluctuation. In this paper, we present a derivation of a general and direct relationship between these two coherence measures. We refer to the result as the Central Relation. The relation applies independently of the physical origin of the noise. Experiments are described which demonstrate the validity of the Central Relation and at the same time suggest new methods of controlling frequency noise at base band by optical filtering.

A modified 160 Gbit/s OTDM system based on QPSK Nyquist pulses and coherent detection

In this paper, we design and implement a 160 Gbit/s orthogonal time division multiplexing (OTDM) transmission system based on quadrature phase shift keying (QPSK) Nyquist pulses and coherent detection. We proposed an optimized Nyquist pulses generation scheme, which produce ultra-flat frequency combs with near-perfect rectangular spectrum and high suppression of out-of-band components by two cascaded Lithium Niobate Mach Zehnder modulators (LN-MZMs). Divided by variable length of optical delay line (Odl), 10GBaud QPSK Nyquist pulses are multiplexed to 80GBaud in a single wavelength. A set of training sequence (TS) which are inserted in front of data are employed to realize the inclusion of optical phase-locking and estimate channel transmission function. In this scheme, we make use of the TS overhead to achieve homodyne detection synchronization between local advanced receiver and Nyquist-pulses generator which is controlled by loop digital signal processing (DSP) module via an optical phase-locking loop. Meanwhile, for the advantage of the TS scheme and DSP, the Nyquist system compensates the residual physical dispersion and improves the transmission quality after 150 km transmission.

基于伪随机码相位调制和相干探测的激光测距技术研究

基于伪随机码相位调制和相干探测的激光测距技术研究

4 m/100 Gb/s Optical Wireless Communication Based on Far L–Band Injection Locked Quantum-Dash Laser

An indoor 100 Gb/s free space optical communication link using an injection locked ∼1621 nm quantum-dash laser has been experimentally demonstrated. The results are achieved using dual-polarization quadrature phase shift keying (DP-QPSK) and coherent detection over a 4 m indoor free space link. The system exhibited a receiver sensitivity of –17.5 dBm to achieve the bit error rate forward error correction (BER FEC) threshold of 3.8 × 10–3. This displays the potential of tunable injection locked far L -band quantum-dash lasers, with less scattering loss compared to C -band counterpart, as promising light sources in both indoor and outdoor future high speed free space optical information and communication technology.

System Performance and Limits of Optical Modulation Formats in Dense Wavelength Division Multiplexing Systems

In this paper we investigate in OptSim software environment the system performance of intensity and phase modulation formats for different network scenarios and dense wavelength division multiplexing grids. OptSim employs the Time Domain Split Step method to implement the signal distribution equation in a fiber. We investigate intensity formats, such as Non Return to Zero, Return to Zero, Carrier-Suppressed Return to Zero and DuoBinary, and phase modulation formats like Differential Phase-Shift Keying and Differential Quadrature Phase-Shift Keying. The main goal is to compare these formats in terms of bit error rate, Q-factor, optical reach and grid limitations for transmission rates 10, 40 and 100 Gbps per channel and discuss the possibilities of increasing their spectral efficiency. We also focus on other advanced solutions such as the polarization division multiplexing combined with phase modulations, coherent detection and advanced digital signal processing which mainly benefits in spectral efficiency, optical signal to noise ratio and chromatic dispersion tolerances. DOI: http://dx.doi.org/10.5755/j01.eie.22.2.9599

Wavefront twisting by rotating black holes: Orbital angular momentum generation and phase coherent detection

In this paper we study wave propagation and scattering near a rotating black hole. In particular, we assume a coherent emission source near the black hole and investigate the wavefront distortion as seen by a distant observer. Near the observer, the propagating wave can be decomposed using the Laguerre-Gaussian mode basis and its wavefront distortion can be characterized by the decomposition coefficient. We find that this decomposition spectrum is symmetric for wave sources located near a Schwarzschild black hole, but is generically asymmetric if the host black hole is rotating. The spectrum asymmetry, or the net orbital angular momentum carried by the wave, is intimately related to the black hole spin and mass, the wave frequency and the locations of the source and the observer. We present semi-analytical expressions and numerical results for these parameter-dependences. If the radiation is temporally coherent, our results show that the secondary images of the source can be almost as bright as its primary image. In the case of temporally-incoherent radiation, we show that the non-fundamental spectrum components could be resolved by spatially-separated telescopes, although that would be degenerate with the telescope direction. Finally, our results suggest that the black-hole-induced spectrum asymmetry is generally too weak to be observed in radio astronomy, even if the observer were located near a caustic point.

Wavefront twisting by rotating back holes: orbital angular momentum generation and phase coherent detection

Wavefront twisting by rotating back holes: orbital angular momentum generation and phase coherent detection

Phase-coherent detection of an optical dipole force by Doppler velocimetry

We report phase-coherent Doppler detection of optical dipole forces using large ion crystals in a Penning trap. The technique is based on laser Doppler velocimetry using a cycling transition in 9Be+ near 313 nm and the center-of-mass (COM) ion motional mode. The optical dipole force is tuned to excite the COM mode, and measurements of photon arrival times synchronized with the excitation potential show oscillations with a period commensurate with the COM motional frequency. Experimental results compare well with a quantitative model for a driven harmonic oscillator. This technique permits characterization of motional modes in ion crystals; the measurement of both frequency and phase information relative to the driving force is a key enabling capability--comparable to lockin detection - providing access to a parameter that is typically not available in time-averaged measurements. This additional information facilitates discrimination of nearly degenerate motional modes.

Analytical estimation of laser phase noise induced BER floor in coherent receiver with digital signal processing

The Bit-Error-Ratio (BER) floor caused by the laser phase noise in the optical fiber communication system with differential quadrature phase shift keying (DQPSK) and coherent detection followed by digital signal processing (DSP) is analytically evaluated. An in-phase and quadrature (I&Q) receiver with a carrier phase recovery using DSP is considered. The carrier phase recovery is based on a phase estimation of a finite sum (block) of the signal samples raised to the power of four and the phase unwrapping at transitions between blocks. It is demonstrated that errors generated at block transitions cause the dominating contribution to the system BER floor when the impact of the additive noise is negligibly small in comparison with the effect of the laser phase noise. Even the BER floor in the case when the phase unwrapping is omitted is analytically derived and applied to emphasize the crucial importance of this signal processing operation. The analytical results are verified by full Monte Carlo simulations. The BER for another type of DQPSK receiver operation, which is based on differential phase detection, is also obtained in the analytical form using the principle of conditional probability. The principle of conditional probability is justified in the case of differential phase detection due to statistical independency of the laser phase noise induced signal phase error and the additive noise contributions. Based on the achieved analytical results the laser linewidth tolerance is calculated for different system cases.

Analytical expression for large signal transfer function of an optically filtered analog link

We present an analytical expression for the transfer function of an optically-filtered radio frequency photonic link using phase modulation and coherent detection. This solution is applicable to quadrature passband signals and is significant for evaluating the distortion and consequently improving the linearity of such electrical-optical-electrical links. We show that the nonlinearity appears as an envelope distortion and discuss linearization techniques along with experimental validation.

Planar chirality of plasmonic multi-split rings

We develop an analytical framework for the analysis of planar chiral multi-split rings, based on a Fourier series expansion of the induced current. The number, width, and location of each split (gap) is arbitrary. Provision is made for the possibility of inserting lumped active or passive impedance loads in the gaps. The model demonstrates the hallmark of planar chirality and its consequent magneto-electric coupling as a function of the parameters of the splits and impedance loads. It is demonstrated that impedance loads sequenced in a clockwise or anti-clockwise fashion allow for generation of dissymetric current distributions in the plane, like for geometric (structural) chirality. We also determine the effect of planar chirality on the relevant dyadic polarizability components of a split ring. Reflection and transmission coefficient characteristics of regular arrays of such rings are determined with the aid of the periodic method of moments. Phase-coherent detection of the sense of handedness and incoherent detection of planar chirality per se by measurement of the field intensity are shown to be possible, in both the reflection and transmission characteristics. These results are relevant to both coherent and incoherent detection at optical and suboptical wavelengths.

Mode-Selective Dynamic Light Scattering Spectroscopy: Application to the Isotropic Phase of Liquid Crystals

We have developed a new method of "mode-selective" dynamic light scattering spectroscopy. This method allows us to study dynamic modes usually hidden behind large fluctuations of a critical mode. Here we apply this method to measurements of three dynamic modes of the isotropic phase of liquid crystals near the isotropic-nematic transition. In conventional methods detecting thermally excited modes, the thermal diffusion and sound modes are usually overwhelmed by the orientational relaxation mode since the intensity of the last mode diverges toward the isotropic-nematic critical point. Thanks to the phase-coherent detection ability of our method, we have successfully observed the thermal diffusion and sound modes without the interference of incoherent critical orientational fluctuations.

Measuring optical phase singularities at subwavelength resolution

We will present experimental and theoretical studies of optical fields with subwavelength structures, in particular phase singularities and coherent detection methods with nanometric resolution. An electromagnetic field is characterized by an amplitude, a phase and a polarization state. Therefore, experimental studies require coherent detection methods, which allow one to measure the amplitude and phase of the optical field with subwavelength resolution. We will present two instruments, a heterodyne scanning probe microscope (heterodyne SNOM) and a high resolution interference microscope (HRIM). We will review some earlier work using the heterodyne SNOM, in particular the measurement of phase singularities produced by a 1 μm pitch grating with 10 nm spatial sampling. Using the HRIM we have investigated the intensity and phase distributions (with singularities) in the focal region of microlenses. The measurements are compared with the results calculated by rigorous diffraction theory.

Quantitative Millimetre Wavelength Spectrometry

Quantitative Millimetre Wavelength Spectrometry

A novel CDMA multiuser interference cancellation receiver with reference symbol aided estimation of channel parameters

A novel multistage successive interference cancellation scheme is proposed which operates on the reverse code-division multiple-access (CDMA) link using binary phase shift keying (BPSK) modulation, coherent detection and reference symbols to obtain channel estimates. The results of a single cell multiuser investigation demonstrate increased traffic capacity. However, this increase is initially very moderate due to corruption of the channel estimates by interference from symbols not yet demodulated and cancelled. A modification in the transmitted signal structure addressing this problem is proposed. The results of a single cell analysis of the modified cancellation scheme demonstrate that the system's traffic capacity reaches approximately 80% of that of a multistage successive interference cancelling receiver operating with the perfect knowledge of channel parameters. A subsequent multicell investigation shows that for a hexagonal cell geometry with a path loss exponent of four and without any forward error correction (FEC) coding or cell sectorization, the system capacity compares very favorably with that of the IS-95 system, which employs powerful error control coding. Capacities with other path loss exponents and cell geometries are also investigated. The results show a substantial traffic capacity increase over that of a comparable receiver without interference cancellation.

Error rate analysis of MDPSK/CPSK with diversity reception under very slow Rayleigh fading and cochannel interference

The distribution of the phase noise due to additive white Gaussian noise (AWGN) and cochannel interference (CCI) is analyzed for differential phase detection (DPD) and coherent phase detection (CPD) in a very slow nonfrequency selective Rayleigh fading environment. The effects of modulation timing offset between the desired signal and the CCI and of the overall channel filter response are considered. Simple closed-form expressions are derived for ideal selection diversity reception. The derived phase noise distributions are used for evaluating the bit error rate (BER) performance of 2-16DPSK/CPSK assuming square-root raised cosine Nyquist transmit/receive filters. It is found that the BER performance of CPSK is less sensitive to CCI modulation timing offset than DPSK, and that increasing the filter rolloff factor can improve the BER performance due to CCI. Finally, the accuracy of the BER approximation that uses the symbol error rate is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurements of electron parallel-momentum distributions using cyclotron wave transmission*

Practical aspects of the implementation of cyclotron wave transmission diagnostics are considered in three specific areas. Questions raised by the calculation of the diagnostic resolution and sensitivity, elimination of reflections through swept frequency and phase-coherent detection, and correcting for the effects of wave refraction through the use of equivalent rays are addressed. Results of preliminary tests and experiments as well as comments on future implementations are used to illustrate the discussion.

Time spread modulation system for digital land mobile radio communication

AbstractThis paper proposes an improvement of the time‐spread modulation/demodulation system in land mobile radio communications. The following elaborations are employed in the proposed system. The quadrature modulation with fading compensation is employed to improve the spectral efficiency. The interleaving is employed to enhance the time‐spreading effect. The maximum‐likelihood estimation is employed to improve the error rate.To demonstrate the usefulness of the proposed method, the bit‐error rate is examined by computer simulation. It is seen as a result for the four‐symbol time‐spread that Eb/N0 is approximately 12 dB and 18 dB for the bit‐error rate (BER) of 10‐2 and 10‐3, respectively. The foregoing performance is better compared to the theoretical performance for the absolute phase coherent detection QSK, with Eb/N0 being better by 2.5 dB for BER = 10‐2. It is seen also that the performance is improved by increasing the number of time‐spread symbols to 6 and 8. The proposed system also is compared to the case of the Reed‐Solomon code applied to the multivalued QAM modulation system. The difference of performances is discussed from the theoretical viewpoint.