Electrooptic Modulators with Controlled Frequency Responses by Using Nonperiodically Polarization‐Reversed Structure

The effects of electrical vestibular stimulation upon movement and perception suggest two evoked sensations: head roll and inter-aural linear acceleration. The head roll vector causes walking subjects to turn in a direction dependent on head pitch, requiring generation of torque around a vertical axis. Here the effect of vestibular stimulation upon vertical torque (T(z)) was investigated during quiet stance. With the head tilted forward, square-wave stimuli applied to the mastoid processes evoked a polarity-specific T(z) response accompanied by trunk yaw. Stochastic vestibular stimulation (SVS) was used to investigate the effect of head pitch with greater precision; the SVS–T(z) cross-correlation displayed a modulation pattern consistent with the head roll vector and this was also reflected by changes in coherence at 2–3 Hz. However, a separate response at 7–8 Hz was unaffected by head pitch. Head translation (rather than rotation) had no effect upon this high frequency response either, suggesting it is not caused by a sense of body rotation induced by an inter-aural acceleration vector offset from the body. Instead, high coherence between medio-lateral shear force and T(z) at the same frequency range suggests it is caused by mechanical coupling to evoked medio-lateral sway. Consistent with this explanation, the 7–8 Hz response was attenuated by 90 deg head roll or yaw, both of which uncouple the inter-aural axis from the medio-lateral sway axis. These results demonstrate two vertical torque responses to electrical vestibular stimulation in standing subjects. The high frequency response can be attributed to mechanical coupling to evoked medio-lateral sway. The low frequency response is consistent with a reaction to a sensation of head roll, and provides a novel method for investigating proprioceptive-vestibular interactions during stance.

An approach to measuring frequency response of high-speed electro-optic phase modulators via a single scan is proposed and experimentally demonstrated. This method employs low-speed photonic sampling to transfer the response information at any high frequency to a fixed low-frequency duplicate in the first Nyquist frequency range by setting the microwave frequency sweeping step equal to the repetition rate of the mode-locked laser. Through low-frequency detection and analysis in the electrical domain, the relative frequency response can be directly calculated from the relative intensity between the low-frequency duplicate and the direct current component without calibration of the photodetector response. In the experiment, the relative frequency responses (i.e., the S21 curve) of two 20 Gb/s LiNbO3-based electro-optic phase modulators and two 40 Gb/s samples are measured with a resolution of 96.9 MHz by using the proposed method, where the measurement results fit in with those obtained by using the conventional optical spectrum analysis method. The frequency measurement resolution can be further improved by using a mode-locked laser with a lower repetition rate.

Recent efforts in our group towards the fabrication of sensors capable of detecting passive levels of millimeter-wave radiation have led to the development of an optically-based detector with sub-picowatt noise equivalent powers. This sensor is based on upconverting the received radiation into sidebands on an optical carrier using electro-optic modulation techniques and, subsequently, suppressing the remaining carrier energy. The noise equivalent power of such detectors is critically dependent on the ability of the electro-optic modulator to efficiently convert frequencies up to and exceeding 95 GHz onto the optical carrier while suppressing potential noise sources. In this paper, we discuss the specific device requirements generated by this unique potential application of high-frequency optical modulators. The effects of various modulator properties, such as half-wave voltage, frequency response, and maximum optical power density are discussed in the context of millimeter-wave detection capability. In addition, we present experimental efforts towards fabricating a passive millimeter-wave detector based on this approach, including efforts to develop an optimized optical modulator technology.

Several new nonperiodic spatial codes for phase-reversal coplanar waveguides (CPWs) used in the framework of the quasi-phase match technique (QPM) for broadening the optical response of z-cut LiNbO/sub 3/ electrooptic modulators (EOMs) are presented. The peculiarity of the codes is that they open the possibility for time-domain applications of EOMs based on nonperiodic QPM structures. They were obtained by using a specialized version of the genetic algorithm that generates an optimal length and number of the phase-reversal sections. The codes provide both flat amplitude and nearly linear phase frequency responses of the EOM within several frequency ranges important for fiber-optical/radio systems: from dc to 25, 40, and 90 GHz. The phase-reversal structures described here were optimized taking into account the CPW electrode losses and under the matching condition with 50 /spl Omega/-sources. They possess as low value of the drive voltage (V/sub /spl pi//, required for realization of 100% EO modulation efficiency) as possible for EOMs based on QPM, under the above conditions.

We present a novel near-infrared spectroscopy technique based on Dual-Comb optical interrogation (DC-NIRS) applied to dispersive media. The technique recovers the frequency response of the medium under investigation by sampling its spectral response in amplitude and phase. The DC-NIRS reference and sample signals are generated using electro-optic modulation which offers a cost-effective, integrable solution while providing high adaptability to the interrogated medium. A careful choice of both line spacing and optical span of the frequency comb ensures that the retrieved information enables the reconstruction of the temporal impulse response of the medium, known as the diffuse-time-of-flight (DTOF), to obtain its optical properties with a 70 µs temporal resolution and 32 ps photon propagation delay resolution. Furthermore, the DC-NIRS technique also offers enhanced penetration due to noiseless optical amplification (interferometric detection). The presented technique was demonstrated on a static bio-mimetic phantom of known optical properties reproducing a typical brain’s optical response. The DTOF and optical properties of the phantom were measured, showing the capabilities of this new technique on the estimation of absolute optical properties with a deviation under 3%. Compared to current technologies, our DC-NIRS technique provides enhanced temporal resolution, spatial location capabilities, and penetration depth, with an integrable and configurable cost-effective architecture, paving the way to next-generation, non-invasive and portable systems for functional brain imaging, and brain-computer interfaces, among other. The system is patent pending PCT/ES2022/070176.

An optoelectronic oscillator implemented in a 250 nm SiGe BiCMOS Silicon photonic technology is presented. It features a monolithic integration of the electronic amplifier components, the electro-optical modulator and the photodiode to achieve a low-parasitics and compact solution on a single chip. A phase noise of −115 dBc/Hz at a frequency offset of 100 kHz from the fundamental frequency of 750 MHz was measured. The phase noise is among the lowest for monolithically integrated optoelectronic oscillators. The frequency response gives a promising outlook to future fully monolithic integrated optoelectronic oscillators when a low loss micro-resonator is utilized to simultaneously act as an optical delay element and filter at frequencies above 20 GHz.

Frequency responses are frequently referred to in the stability analysis of fractional order control systems. Frequency response-based methods have been introduced in the literature to reduce complex fractional order systems. However, the magnitude and phase response improvement is not handled by these techniques. The optimization methods are utilized to improve the approximation of fractional order filters in the desired frequency range. The article discusses the ideal Fractional-Order Butterworth Filter (FOBF) configuration by utilizing integer-order rational approximations to achieve a precise magnitude and phase response. Additionally, this study utilizes optimal FOBF magnitude and phase characteristics to minimize errors and expands the approximation bandwidth to cover multiple decades in both pass and stop bands. Optimized fractional order Butterworth filter designs have been implemented in biomedical signal processing, audio engineering, telecommunications, and control systems, enhancing performance in noise reduction and signal fidelity across these applications. It is essential to precisely determine these transfer functions regarding frequency and time responses. Therefore, there is room for further enhancements in these approximation methods to reduce errors and enhance the accuracy of real-world implementations. In pursuit of this goal, the study introduced a powerful metaheuristic optimization technique called Enhanced Colliding Bodies Optimization (ECBO), which not only showcases better precision in modelling but also exhibits a higher level of stability when compared to existing methods. This process guides all entities towards an optimal solution in each successive round, boosting the likelihood of finding a superior solution and thoroughly examining the full range of potential solutions. This technique better fits the BF filter function to a fractional-order continuous filter. The digital integrator is optimized in the frequency domain using the Coyote Optimization Algorithm (COA) because of its effectiveness, ease of use, and strength in tackling various complex optimization challenges. This optimizes the magnitude and phase reaction of the low-pass BF filter depending on the Minimum Square Error (MSE). Expanding the scope of the ECBO’s search range allows the enhanced filter to closely replicate the frequency behaviour of fractional order continuous filter functions.

The work is devoted to the study of the frequency response (phase response) of combined UWB antennas. Some researchers determine the bandwidth of single UWB antennas basing on these parameters. In this work, the fact of the existence of identical frequency (phase) response of combined antennas in the transmitting and receiving mode and, consequently, the possibility of determining these parameters for a single antenna by previously proposed methods is questioned.

This paper presents the magnitude and phase characteristics of a Room Impulse Response (RIR) for various sampling frequencies and obtains its response on the application of ramp signals of different widths. Furthermore, it is shown that the originating point of it remains the same, while its notch shifts as the sampling frequency increased. The magnitude response of it for different width of the ramp signals is obtained as a low–pass filter and the phase responses as piece–wise linear and minimum phase for the lower range of frequencies. It is also observed that the shape of the various phase characteristics is identical for all the widths of input signal.

We report anomalous sub-MHz frequency response of electro-optic (EO) phase modulators in X-cut lithium niobate on insulator (LNOI) and demonstrate improved response via careful preparation of the LiNbO3/metal interface and high temperature annealing in forming gas.

A speaker system is disclosed which is capable of supplying reproduced sounds vibrating in substantially the same manner as in the respiratory sphere to human's sense of hearing by using conventional unidirectional speaker units in combination in a contrived arrangement, and by applying real time digital signal processing by means of a digital signal processor to the speaker units to cancel a peak and a dip in frequency response and in phase response through inverse correction which cannot be canceled only by improving the arrangement of the speaker units, thereby forming a sound emitter capable of providing ideal reproduced sounds. The speaker system comprises an enclosure EC having a basic structure of a hollow 32-hedron composed of 12 pentagonal flat surfaces and 20 hexagonal flat surfaces, speaker units 7 or 8 mounted in all or 25-31 of the 32 surfaces, and a real time digital signal processing system inserted in a input line of each of the speaker units 7 or 8. The digital signal processing system inverse-characteristically filtering driving signals of the speaker units to evenly correcting a peak 4 and a dip 5 caused in frequency response and in phase response of each of the speaker units 7 or 8.

This study presents a novel high-efficiency electro-optic (EO) light modulator whose operation is based on the attenuated total reflec- tion effect, in which the surface plasmon wave is excited by an incident waveguide light wave. The EO light modulator is fabricated using a non- linear optical polymer material that is a side-chain EO polyimide with 2-(N-ethyl-4-(tricyanovinyl)anilino)ethanol chromophore. The modulator is characterized, and its performance tested, in terms of the thickness and dielectric constant of the polymer thin film, the EO coefficient, the insertion loss, and the modulation index. Additionally, the dynamic re- sponse of the EO light modulator is fully investigated and discussed. © 2005 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1868775) Subject terms: surface plasmon resonance; attenuated total reflection; electro- optic polymer; waveguide-coupled; nonlinear optical.

Two-tone frequency modulation saturation spectroscopy for tunable frequency offset locking of a single laser

Graphene's featureless optical absorption, ultrahigh carrier mobility, and variable optical absorption by an applied gate voltage enable a new breed of optical modulators with broad optical and electrical bandwidths. Here we report on an electro-optic modulator that integrates single-layer graphene in a sub-wavelength thick, reflective modulator structure. These modulators provide a large degree of design freedom, which allows tailoring of their optical properties to specific needs. Current devices feature an active aperture ~100 µm, and provide uniform modulation with flat frequency response from 1 Hz to >100 MHz. These novel, low insertion-loss graphene-based modulators offer solutions to a variety of high-speed amplitude modulation tasks that require optical amplitude modulation without phase distortions, a flat frequency response, or ultra-thin geometries, such as for controlling monolithic, high-repetition rate mode-locked lasers or active interferometers.

The synthesis of photonic microwave filters employing optical sources with modulation side-bands, as multimode optical sources, and chirped fiber gratings is addressed. A single wavelength laser externally modulated using electrooptical Mach-Zehnder modulators and electroabsorption modulators have been proved as optical sources with modulation sidebands. Microwave filter features such as wide range tunability, compactness, readily reconfigurable frequency responses and flexibility have been achieved and demonstrated for the proposed structure. Experimental results using both a dual-electrode Mach-Zehnder electrooptical modulator and an electroabsorption modulator as optical sources with modulation sidebands are provided to demonstrate the feasibility of this technique.