Submillimeter wave generation through optical four-wave mixing using injection-locked semiconductor lasers

A nonlinear circuit with periodic operation, such as a mixer and oscillator, can be modeled as a linear periodic time‐varying circuit by assuming a small‐signal input and output. This paper presents a method by which the transfer function of such a periodic time‐varying circuit can be decomposed into phase and amplitude modulation components. Assuming a small input, the phase modulation component can be interpreted as a result of narrow‐band phase modulation with a small modulation index. Thus, it suffices to consider only the first sideband. As regards the spectrum of the amplitude modulated signal, it suffices to consider only the first sideband, regardless of the modulation index. Thus, the two spectra corresponding to the upper and lower sidebands around the carrier are decomposed into narrow‐band phase and amplitude modulation components, and the transfer function can be decomposed into phase and amplitude modulation components. By this method, it becomes possible to decompose the noise of the mixer and the oscillator into the amplitude noise and the phase, or to simulate AM‐PM conversion. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 85(7): 29–37, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.1105

A theoretical investigation of the second- and third-order intermodulation distortions (IMDs) in an injection-locked semiconductor laser under small-signal modulation is presented. The results show that a substantial reduction of the laser nonlinearity can be obtained, depending on both the injection level and frequency detuning between the master and slave lasers. The intensity modulation frequency response is also reported and shows that the injection-locked laser may also have a significantly improved behavior over the same free-running laser, revealed mostly in the reduced resonance peak and the broadening of the modulation bandwidth available.

As a high-frequency carrier, the terahertz (THz) wave is essential for achieving high-data-rate wireless transmission due to its ultra-wide bandwidth. Phase stabilization becomes crucial to enable phase-shift-based multilevel modulation for high-speed data transmission. We developed a Mach–Zehnder interferometric phase stabilization technique for photomixing, which has proved a promising method for phase-stable continuous THz-wave generation. However, this method faced inefficiencies in generating phase-modulated THz waves due to the impact of the phase modulator on the phase stabilization system. By photomixing, which is one of the promising methods for generating THz waves, the phase of the generated THz waves can be controlled in the optical domain so that the stability of the generated THz wave can be controlled by photonics technologies. Thus, we devised a new phase stabilization approach using backward-directional lightwave, which is overlapped with the THz wave generation system. This study presented a conceptual and experimental framework for stabilizing the phase differences of optical carrier signals. We compared the optical domain and transmission performances between forward-directional and backward-directional phase stabilization methods. Remarkably, our results demonstrated error-free transmission at a modulation frequency of 3 Gbit/s and higher.

In this paper we report the results of extensive research on phase modulation (PM) and amplitude modulation (AM) noise in linear bipolar junction transistor (BJT) amplifiers. BJT amplifiers exhibit 1/f PM and AM noise about a carrier signal that is much larger than the amplifier's thermal noise at those frequencies in the absence of the carrier signal. Our work shows that the 1/f PM noise of a BJT based amplifier is accompanied by 1/f AM noise which can be higher, lower, or nearly equal depending on the circuit implementation. The 1/f AM and PM noise in BJTs is primarily the result of 1/f fluctuations in transistor current, transistor capacitance, circuit supply voltages, circuit impedances, and circuit configuration. We discuss the theory and present experimental data in reference to common emitter amplifiers, but the analysis can be applied to other configurations as well. This study provides the functional dependence of 1/f AM and PM noise on transistor parameters, circuit parameters, and signal frequency, thereby laying the groundwork for a comprehensive theory of 1/f AM and PM noise in BJT amplifiers. We show that in many cases the 1/f PM and AM noise can be reduced below the thermal noise of the amplifier.

We demonstrate experimentally that optical four-wave mixing can be used to study surface polaritons in solids. The dispersion characteristics of surface polaritons in GaP are measured and compared with theoretical calculations.

Acoustic holography underpins the number of modern acoustics applications. The usage of multi-focal acoustic holograms with phased array transducers (PATs) in ultrasonic tactile displays and acoustic levitation are increasing, and achieving a high-quality hologram are of significant interest. Inspired by the latest optical hologram optimizer, we developed a novel acoustic hologram optimizer for PATs called Diff-PAT [T. Fushimi, K. Yamamoto, and Y. Ochiai, “Acoustic hologram optimisation using automatic differentiation”]. Diff-PAT is based on a gradient-descent algorithm and automatic differentiation. The performance of Diff-PAT was numerically evaluated using three array configurations and it achieved superior accuracy over the conventional optimizers. For example, when two focal points are generated with 196 ultrasonic (40 kHz) transducers; the state of art optimizer (with phase and amplitude modulation) based on Eigensolver has an average error of 4.07 % where Diff-PAT (with only phase modulation) achieve average error of 0.0174%. These results show that amplitude and phase modulation may not be necessary for PATs to be successful. Furthermore, we demonstrate the versatility of Diff-PAT by applying it to binary acoustic holograms, simultaneous modulation of acoustic amplitude and phase at the target plane, and phase plates. [Work supported by Pixie Dust Technologies, Inc., Diff-PAT is patent pending (JP2020-167367A).]

This paper deals with mechanical fault monitoring in induction machines from stator current measurements. The considered faults lead to amplitude and/or phase modulations of the measured stator current. The different faults can be characterized by their time-frequency signatures via the Wigner distribution. The time-frequency representations apply to complex signals that may be obtained through the Hubert transform of the real measured signal. In case of high frequency modulations, it can not be taken advantage of the time frequency signatures. This study proposes an alternative complex signal representation for modulated stator currents. The so-called space vector is obtained through the Concordia transform. From three stator current measurements, the Concordia transform builds a complex vector which conveniently carries the information about phase and amplitude modulations. This paper applies and compares the Wigner distribution computed with the Hilbert and Concordia transforms in case of simulated and experimental signals with various modulation frequency ranges.

A portable amplitude-modulation (AM) and phase-modulation (PM) noise standard has been developed for carrier frequencies of 10.6, 21.2 and 42.4 GHz. The noise level from the carrier 1/2 S/sub /spl phi//(f) (phase noise) or 1/2 S/sub a/(f) (amplitude noise) is -122.6 dBc/Hz at 10.6 GHz, -119.6 dBc/Hz at 21.2 GHz and -116.3 dBc/Hz at 42.4 GHz. For Fourier frequencies of 1 kHz to 10 MHz the added noise is flat with an uncertainty of /spl plusmn/0.25 dB. The uncertainty of the noise level for Fourier frequencies of 1 kHz to 100 MHz is /spl plusmn/0.5 dB. The residual PM noise floor between the signal and reference outputs at 100 MHz is less than -182 dBc/Hz.

We generate the phase-modulated signal by utilizing the chirp characteristics of the directly-modulated reflective semiconductor optical amplifier (RSOA) for the cost-effective realization of a long-reach wavelength-division-multiplexed passive optical network (WDM PON). We first investigate the relation between the amplitude and phase modulation indices in a directly-modulated RSOA and optimize these modulation indices to maximize the symbol distance on the constellation diagram. The results show that, by operating the RSOA under this optimum condition, we can achieve the excellent receiver sensitivity of -49.8 dBm at 1.25 Gb/s. We implement a long-reach WDM PON by using the phase-modulated RSOAs and self-homodyne receivers, and demonstrate the error-free transmission of 1.25-Gb/s signal over a 110-km long link without using any optical amplifiers.

Natural auditory scenes such as frog choruses consist of multiple sound sources (i.e., individual vocalizing males) producing sounds that overlap extensively in time and spectrum, often in the presence of other biotic and abiotic background noise. Detection of a signal in such environments is challenging, but it is facilitated when the noise shares common amplitude modulations across a wide frequency range, due to a phenomenon called comodulation masking release (CMR). Here, we examined how properties of the background noise, such as its bandwidth and amplitude modulation, influence the detection threshold of a target sound (pulsed amplitude modulated tones) by single neurons in the frog auditory midbrain. We found that for both modulated and unmodulated masking noise, masking was generally stronger with increasing bandwidth, but it was weakened for the widest bandwidths. Masking was less for modulated noise than for unmodulated noise for all bandwidths. However, responses were heterogeneous, and only for a subpopulation of neurons the detection of the probe was facilitated when the bandwidth of the modulated masker was increased beyond a certain bandwidth – such neurons might contribute to CMR. We observed evidence that suggests that the dips in the noise amplitude are exploited by TS neurons, and observed strong responses to target signals occurring during such dips. However, the interactions between the probe and masker responses were nonlinear, and other mechanisms, e.g., selective suppression of the response to the noise, may also be involved in the masking release.

Designs of optical lenses based on metallic nanoslits are carried out based on the phase and amplitude modulation by tuning the slit widths. The slits are perforated on thin metallic film, and the width of each slit is achieved by simulated annealing algorithms, which is connected with both the amplitude and phase modulation. Two kinds of focal lenses, which can realize one or two focus points, have been designed. The finite-difference time-domain method is employed to check the performance of the designed lenses. Simulation results show that the designed lenses can perform the preset functions well. Using this method, multiple optical elements with different functions can be conveniently achieved in subwavelength scale.

A series of experiments investigated the interaction of phase and amplitude modulation in the auditory perception of movement of a fused, lateralized sound image. A technique was developed whereby the perception of periodic motion in the coronal plane of the head could be produced either by sinusoidal modulation of the amplitude or phase relation of a pure tone carrier presented to each ear. At a given modulation frequency the observer set the amplitude of either the phase shift or the differential amplitude change in order to just detect motion in the sound image. The threshold amount of each measure was defined as unity and the observer was then presented with various ratios of the two mixed in two ways: (1) Phase lead to one ear with amplitude increase to the same ear or (2) phase lead to one ear with amplitude increase to the other ear. Evidence for super additivity of amplitude and phase modulation was found for condition I while evidence for subadditivity for am and pm was found in condition number 2. Both these results suggest that, although both time and intensity differences are used by the human auditory mechanisms involved in the perception of movement, they have at least some different neural substrates.

A practical implementation of a portable secondary standard for phase modulation (PM) and amplitude modulation (AM) noise at 5, 10, and 100 MHz is described. The accuracy of the standard for both PM and AM noise is +or-0.14 dB, and the temperature coefficient is less than 0.02 dB/K. The noise floor of the standard for PM noise measurements is less than -190 dBC rel to 1 rad/sup 2//Hz at 5, 10, and 100 MHz. The noise floor for AM measurements depends on the configuration. A calibrated level of PM and AM noise of approximately-130+or-0.2 dB rel to 1 rad/sup 2//Hz is used to evaluate the accuracy versus Fourier frequency. This standard can also be used as an alternative to the normal method of the PM/AM detector for PM/AM measurements. >

Electrical control of amplitude and phase of terahertz radiation (THz) is the key technological challenge for high resolution and noninvasive THz imaging. The lack of active materials and devices hinders the realization of these imaging systems. Here, we demonstrate an efficient terahertz phase and amplitude modulation using electrically tunable graphene devices. Our device structure consists of electrolyte-gated graphene placed at quarter wavelength distance from a reflecting metallic surface. In this geometry, graphene operates as a tunable impedance surface which yields electrically controlled reflection phase. Terahertz time domain reflection spectroscopy reveals the voltage controlled phase modulation of π and the reflection modulation of 50 dB. To show the promises of our approach, we demonstrate a multipixel phase modulator array which operates as a gradient impedance surface.

This paper concerns an optical millimeter-wave signal generator for fiber-based millimeter-wave systems. The millimeter-wave signal generator is based on two-mode injection locking of a Fabry-Perot (F-P) laser. The millimeter-wave signal can be induced by self-heterodyne detection of the locked two modes in a high-speed photodetector (PD). The locking characteristics of the F-P slave laser and the tunability for the millimeter-wave carrier frequency are demonstrated. When the F-P laser is directly modulated by data signals, the locked two modes are modulated simultaneously. The data signals can then be up-converted to the millimeter-wave band at the PD output. By this direct modulation method, the effect of fiber chromatic dispersion on the millimeter-wave signal components at the PD output can be moderate according to mixing of amplitude and phase modulation on the locked two modes. In virtue of the wide response of the F-P laser, relatively high-speed data (2.5 Gbit/s nonreturn to zero (NRZ)-ASK or 622 Mbit/s NRZ-BPSK) on the millimeter-wave band (52 or 60 GHz) can be transmitted on a 32-km single-mode fiber without bit error. A wide tunable range (56-63 GHz) for the central frequency of the millimeter-wave signals and a wide optical bandwidth (1530-60 nm) of the F-P slave laser are also confirmed by the bit-error measurements of the transmitted data signals.