Electro-optic Amplitude Modulator Research Articles

Bound-state-in-continuum guided modes in a multilayer electro-optically active photonic integrated circuit platform.

In many physical systems, the interaction with an open environment leads to energy dissipation and reduced coherence, making it challenging to control these systems effectively. In the context of wave phenomena, such lossy interactions can be specifically controlled to isolate the system, a condition known as a bound-state-in-continuum (BIC). Despite the recent advances in engineered BICs for photonic waveguiding, practical implementations are still largely polarization- and geometry-specific, and the underlying principles remain to be systematically explored. Here, we theoretically and experimentally study low loss BIC photonic waveguiding within a two-layer heterogeneous electro-optically active integrated photonic platform. We show that coupling to the slab wave continuum can be selectively suppressed for guided modes with different polarizations and spatial structure. We demonstrate a low-loss same-polarization quasi-BIC guided mode enabling a high extinction Mach-Zehnder electro-optic amplitude modulator within a single Si3N4 ridge waveguide integrated with an extended LiNbO3 slab layer. By elucidating the broad BIC waveguiding principles and demonstrating them in an industry-relevant photonic configuration, this work may inspire innovative approaches to photonic applications such as switching and filtering. The broader impact of this work extends beyond photonics, influencing research in other wave dynamics disciplines, including microwave and acoustics.

Integrated femtosecond pulse generator on thin-film lithium niobate.

Integrated femtosecond pulse and frequency comb sources are critical components for a wide range of applications, including optical atomic clocks1, microwave photonics2, spectroscopy3, optical wave synthesis4, frequency conversion5, communications6, lidar7, optical computing8 and astronomy9. The leading approaches for on-chip pulse generation rely on mode-locking inside microresonators with either third-order nonlinearity10 or with semiconductor gain11,12. These approaches, however, are limited in noise performance, wavelength and repetition ratetunability10,13. Alternatively, subpicosecond pulses can be synthesized without mode-locking, by modulating a continuous-wave single-frequency laser using electro-optic modulators1,14-17. Here we demonstrate a chip-scale femtosecond pulse source implemented on an integrated lithium niobate photonic platform18, using cascaded low-loss electro-optic amplitude and phase modulators and chirped Bragg grating, forming a time-lens system19. The device is driven by a continuous-wave distributed feedback laser chipand controlled by a single continuous-wave microwave source without the need for any stabilization or locking. We measure femtosecond pulse trains (520-femtosecond duration) with a 30-gigahertz repetition rate, flat-top optical spectra with a 10-decibel optical bandwidth of 12.6 nanometres, individual comb-line powers above 0.1 milliwatts, and pulse energies of 0.54 picojoules. Our results represent a tunable, robust and low-cost integrated pulsed light source with continuous-wave-to-pulse conversion efficiencies an order of magnitude higher than those achieved with previous integrated sources. Our pulse generator may find applications in fields such as ultrafast optical measurement19,20 or networks of distributed quantum computers21,22.

Time-resolved dual-comb spectroscopy with a single electro-optic modulator.

Time-resolved near-infrared absorption spectroscopy of single non-repeatable transient events is performed at high spectral resolution with a dual-comb interferometer using a continuous-wave laser followed by a single electro-optic amplitude modulator. By sharing high-speed electrical/optical components, our spectrometer greatly simplifies the implementation of dual-comb spectroscopy and offers a high mutual coherence time, measured up to 50 s, without any active stabilization system and/or data processing. The time resolution is as short as 100 µs in our experimental demonstration. For a span of 36 GHz, the mean signal-to-noise ratio of 80, at 100-MHz spectral resolution and 100-µs measurement time, enables precise determination of the parameters of rovibrational lines, including intensity or concentration.

Real Time PC-Based Flow Measurement Technique Using Optical Channel as a Signal Transmitting Media

A PC based cost effective electro-optic type flow measurement technique is designed and developed. The anemometric principle i.e. the effect of heat loss on a heating element due to flowing fluid is utilized for the measurement of flow rate of liquid in the process industry. A constant voltage p-n junction diode is used as a basic sensing element and the output of the sensing element is amplified and conditioned with the help of the instrumentation amplifier and signal conditioning circuit. Transmission of electrical signals in remote locations suffers from measurement errors due to electromagnetic induction effect, stray capacitance effect etc. The transmission of electrical signal is also not safe for the industries where an inflammable area is present between fields to remote locations and optical transmission is preferred in such areas. To overcome these, an electro-optical system has been developed. The process variable is first sensed electrically. This electrical signal of the transducer is converted into an optical signal using an electro-optic amplitude modulator and then it is transmitted in the form of an optical signal from field to control room through inflammable areas. The modulated signals are demodulated in the control room or remote location and then send to the PC through an optoisolator circuit and DAS card. The experiment has been performed and the theory as well as the mathematical equation has been derived to explain the operation of the proposed system. The overall PC based flow indicator system is also found to have linear characteristics with very good repeatability within tolerable percentage error.The experimental result is reported in the paper.

Pulse doublets generated by a frequency-shifting loop containing an electro-optic amplitude modulator.

We investigate theoretically and experimentally an all-fibered frequency-shifting loop which includes an electro-optic amplitude modulator (EOM) and an optical amplifier, and is seeded by a continuous-wave laser. At variance with frequency-shifted feedback lasers, or Talbot lasers, that contain an acousto-optic frequency shifter, the EOM creates at each round-trip two side-bands that recirculate inside the loop. Benefiting from the high modulation frequency of the EOM, a wide optical frequency comb up to 40 GHz is generated. We demonstrate an original double-pulse regime when the loop length is a multiple of the RF modulation wavelength applied to the modulator. The inter-pulse interval is governed by both the bias voltage and modulation depth of the EOM. Besides, some typical waveforms such as saw-tooth and rectangle are experimentally obtained by properly setting operating frequency, bias voltage and the RF power. The system is modeled by a linear interference model that takes the amplitude modulation function and loop delay into account. The model explains the formation of pulse doublets and reproduces well all the experimental waveforms. Furthermore, the un-seeded loop driven above threshold also generates mode-locked picosecond pulse doublets with a continuously adjustable delay up to the modulation period.

Fourier-domain mode-locked laser combined with a master-oscillator power amplifier architecture

Originally introduced in 2005 for high-speed optical coherence tomography, the rapidly wavelength-swept Fourier-domain mode-locked (FDML) laser still, to this day, enables highest imaging speeds through a very high-speed spectral tuning capability. The FDML laser achieves a tuning bandwidth of over 1/10th of its center wavelength and can sweep this entire bandwidth in less than a microsecond. Interestingly, even though it covers a very broad spectral range, instantaneously it has a narrow spectral linewidth that puts it in a unique space compared to other high-speed broadband laser sources, e.g., mode-locked lasers or supercontinuum sources. Although it has been applied for nonlinear Raman spectroscopy and imaging, a current drawback of this continuous wave laser is the relatively low instantaneous power of 10-100mW. Here, we report the combination of an FDML laser with a master oscillator power amplifier (MOPA) architecture to increase the instantaneous power of the FDML for nonlinear optical interactions. The output of an FDML laser around 1060nm is modulated to short pulses by using an electro-optic amplitude modulator and subsequently amplified using ytterbium-doped fiber amplifiers (YDFAs). This generates a spectral rainbow of 65 picosecond pulses, where each pulse has a distinct, monochromatic wavelength. The instantaneous power can be adjusted by the YDFAs to reach nonlinear optical excitation regimes. This wavelength-swept FDML-MOPA laser will have a vast range of applications in, e.g., nonlinear optics, spectroscopy, imaging, and sensing.

Low-drift AM–PM based optical single-sideband modulator without 2nd-order sideband with adjustable optical carrier-to-sideband ratio

We propose and theoretically investigated a novel scheme to implement optical single-sideband (OSSB) modulator without 2nd-order sideband with adjustable optical carrier-to-sideband ratio (OCSR). The proposed structure is based on a hybrid concatenated electro-optic amplitude (or intensity) modulator (AM) and phase modulator (PM). The AM consists of a bidirectional PM inside a Sagnac loop (SL). Bias-drift associated problems do not present in the proposed structure because it uses PMs which are bias-free. Furthermore, clockwise (CW) and counter clockwise (CCW) optical signals propagate in the same optical fiber inside the SL, so its robustness against environmental changes increases. The structure is fed by three microwave signals with equal amplitudes and proper phases. The OCSR of the generated OSSB modulated signal can be adjusted by tuning the optical and/or microwave phase shifters and/or the PM modulation indices. The 3rd-order sidebands can also be suppressed by setting the proper optical and microwave phase shifts and adjusting the PM modulation indices.

A Real-Time Feedback System to Stabilize Laser Intensity on Wavelength Modulation Interferometer

The phase of an interferogram carries the desired information for various applications such as 3-D profilometry. It can be obtained with a wavelength tuning interferometer by acquiring a series of interferograms while changing the laser wavelength. The phase achieved by the interferometer, however, has severe error due to the laser output power change, which is produced inherently from changing the laser wavelength. To eliminate such phase error, we propose a real-time closed-loop feedback control system to keep the laser output power stable during the wavelength tuning. The control system integrates a photodetector, a data acquisition card, and an electro-optic amplitude modulator with our software to achieve the purpose. The experimental result of the system can steadily output a desired intensity value and the measurement speed is up to 600 KHz. Both its control principles as well as its experimental validation are depicted in this letter.

Intensity and Phase Modulators at 1.55 μm in GaAs/AlGaAs Layers Directly Grown on Silicon

We report for the first-time electro-optic phase and amplitude modulators in GaAs/AlGaAs epitaxial layers grown on misaligned silicon substrates containing germanium buffer layers. Epilayer has a npin doping profile and is equivalent to a pin diode. The 4-mm long electrode Mach–Zehnder modulators have 7.4- and 3.6-V Vπ under single-arm and push–pull drive conditions corresponding to 1.5 ± 0.1 V-cm modulation efficiency. Data on 7-mm long electrode Fabry–Perot phase modulators indicate 2.3-V Mach–Zehnder modulators are possible. These data also indicate less than 1-dB/cm on-chip propagation loss under 5-V reverse bias.

Wave coupling theory of nonlocal linear electro-optic effect in a linear absorbent medium

Being an important optical phenomenon, the linear electro-optic effect has diverse applications in the optical modulation and optical switching. The refractive index ellipsoid theory has been widely used to study the linear electro-optic effect for a long time. Despite of its visualization such a theory has limitations and cannot deal with a lot of cases in which the linear absorption cannot be neglected, or the electric displacement vector has a nonlocal response to electric field, etc. To overcome such shortcomings, in 2001 a wave coupling theory of linear electro-optic effect was developed by She and Lee (She W, Lee W 2001 Opt. Commun. 195 303). And in 2016 we generalized this wave coupling theory to the treatment of nonlocal linear electro-optic effect in which the displacement vector has a nonlocal response to electric field. In this paper, we use this wave-coupling theory to investigate how the linear absorption influences the linear electro-optic effect in a nonlocal medium. Starting from Maxwell's equations and considering the linear absorption and the nonlocality of the susceptibility tensors, we obtain two coupling equations for two orthogonal linear polarized waves and also analytical solutions of the resulting equations, which can be used to describe the nonlocal linear electro-optic effect for a light beam propagating along any direction, with an external direct current electric field applied along an arbitrary direction in a linear absorbent crystal. With such solutions, we study the influences of the linear absorption on the phase, amplitude, shape of the output beam, as well as the half-wave voltage and the extinction ratio of electro-optic modulation. The results show that no matter whether there exists linear absorption, the Rayleigh distance of the Gaussian beam in the crystal will be shortened as a result of the nonlocality of (1). When linear-absorption coefficients 11 and 22 are equal, the linear absorption damps equally the amplitudes of the two polarized output beams with keeping their phases and shapes unchanged. So in the case of 11=22, just as in a lossless medium, the phenomenon that the output beam is no longer a Gaussian beam in an electro-optic amplitude modulation scheme can be considered as a possible signal of the nonlocal response of (2). More interestingly, when 1122, the linear absorption not only reduces the amplitudes of output beams, but also changes their phases and shapes. In such a case one need to measure the nonlocal characteristic length of (2) to judge whether (2) has a nonlocal response. Finally, in the case of 1122, as a result of linear absorption, the extinction ratio is reduced, but the half-wave voltage keeps nearly unchanged in an electro-optic amplitude modulation scheme. Besides the discussion on the influence of the linear absorption, we also make suggestions of how to measure the nonlocal characteristic lengths of (1) and (2) and the absorption coefficients 11 and 22.

Implementation of electro-optic amplitude modulator in the external cavity of semiconductor laser for generation of periodic sates and chaos control

در این مقاله با قرار دادن مدولاتور الکترو اپتیکی در کاواک خارجی یک لیزر نیمرسانا و مدوله کردن پسخوراند اپتیکی، تغییرات دینامیک شدت خروجی لیزر مورد مطالعه قرار گرفته است. این امر به وسیله نمودارهای دوشاخه شدگی و تحول زمانی نسبت به پارامترهای ضریب دامنه مدولاسیون اعمال شده و فرکانس ولتاژ مدولاسیون مربوط به مدولاتور الکترو اپتیکی به صورت عددی مورد آنالیز قرار گرفته است. در این مطالعه نشان دادیم که با مدولاسیون دامنه پرتوی اپتیکی پسخوراند یافته، تغییرات متنوعی در نوع دینامیک قابل مشاهده بوده و می‌توان حالت‌های پریودیک متنوعی را تولید نمود. این امر، این امکان را فراهم می‌آورد تا بدون تغییر در پارامترهای اصلی لیزر نیمرسانا، دینامیک مورد نظر را از لیزر دریافت نمود. همچنین روشی برای کنترل ناپایداری بر اساس مدولاسیون الکترو اپتیکی در کاواک خارجی لیزر ارائه کرده‌ایم. نتایج به دست آمده تایید می‌کند که بر اساس این روش دینامیک آشوبناک می‌تواند به دینامیک پریود اول کنترل گردد.

A stabilized laser continuously tunable over a range of 1.5 GHz.

We demonstrate a method to stabilize laser frequency which can be continuously tuned over a range of 1.5 GHz. It is based on saturated absorption spectroscopy (SAS) generated by an external-cavity diode laser (ECDL) which is modulated by an electro-optic amplitude modulator (EO-AM). The spectra consist of not only the original peaks corresponding to resonant and crossover lines of 133Cs D2 line, but also signals introduced by sidebands from an EO-AM. Thus, the laser frequency can be locked to any point within the range of the spectra. Furthermore, the tuning range of the laser can be doubled compared to the coverage of common SAS by fixing the frequency of the pumping laser. The best stability of the locked laser induced by the EO-AM is 1.27 × 10-11 over an integrating time of 125 s. This method may be applied for more precise and flexible manipulation of atoms and molecules.

Remote picometer fiber Bragg grating demodulation using a dual-wavelength source.

We report on the self-referenced, intensity-based, remote and passive interrogation of a fiber Bragg grating (FBG) for point sensing, by use of a reconfigurable dual-wavelength source composed of a tunable wavelength and subsequent suppressed-carrier, electro-optic amplitude modulation. The demodulation procedure is based on the measurement of the reflected power at two different wavelengths within the FBG spectral response. The grating was interrogated by use of conventional spectral analysis, and also after 32.9 km of single-mode fiber using a dispersive incoherent optical Fourier-domain reflectometry technique. Both procedures provide picometer resolution in the determination of Bragg wavelength shifts at a comparatively similar scan time (∼1 s) and received power (-16 dBm). The main limitations in each interrogation scheme have been identified. These results show the feasibility of interrogation systems incorporating relatively simple frequency combs at a calibrated, and eventually reconfigurable, wavelength grid with an, at least, similar performance to that of commercial FBG interrogators.

Multipoint sensing with a low-coherence source using single-arm frequency-shifted interferometry.

We demonstrate that multiple-site sensing along an optical fiber can be done with incoherent continuous-wave light. Using a broadband low-coherence noise source, a slow detector, and an optical modulator, we construct a single-arm frequency-shifted interferometer (SA-FSI) capable of simultaneously sensing multiple weak-reflection sites distributed either in parallel or in series along fiber links. By scanning the driving frequency of an electro-optic amplitude modulator in the range of 2.7-3.2GHz at steps of 41.7KHz, we demonstrate a spatial resolution of 0.3m and a measurement range of over 1km.

Wave coupling theory of nonlocal linear electro-optic effect.

We derive a wave coupling theory of nonlocal linear electro-optic effect, and the analytical solutions of the resultant equations are provided. With the solutions we study the nonlocal linear electro-optic effect in crystals of different symmetry groups. It shows that the nonlocality of χ̄(2) plays a non-negligible role on the linear electro-optic effect only when the nonlocal characteristic length of χ̄(2) is comparable with the beam width, and the output beam is no longer Gaussian shape as the input beam in an electro-optic amplitude modulation when nonlocality of χ̄(2) is non-negligible. Methods to measure the nonlocal characteristic lengths of of χ̄(1) and χ̄(2) are also discussed.

Point-by-point inscription of phase-shifted fiber Bragg gratings with electro-optic amplitude modulated femtosecond laser pulses

Femtosecond laser pulses were used for the direct point-by-point inscription of phase-shifted fiber Bragg gratings (FBGs) in a single fabrication step without postprocessing. An electro-optic amplitude modulator is used in the setup to generate a defined delay between two identical laser pulse trains for the grating inscription. The grating structure with a central phase shift is formed by focusing the modulated laser pulses into the core of a fiber, while the fiber is translated with a constant velocity. The induced phase shift leads to a narrow transmission band with a bandwidth considerably below 10 pm within the stop band of the FBG. The inscribed FBGs show a birefringence of 3.9×10(-5) whereas their temperature and strain sensitivities are 10.4 pm/K and 1.4 pm/μstrain, respectively. The fabrication process is fast and offers a high grade of flexibility for the control of all grating parameters.

Long-term and wideband laser intensity stabilization with an electro-optic amplitude modulator

This paper aims at two practical design issues encountered with electro-optic amplitude modulators, namely (1) the long-term optical power drift when a single electro-optic crystal is used and (2) the mechanical resonances of the crystal that limit the control bandwidth. We investigated an active control scheme using a single crystal to offset the drifts of different origins such as polarization, crystal birefringence, and electronics. The control system worked continuously for at least 15h without interruption and a power instability of 8×10−4 was achieved in a 3-h measurement. This technique can be employed in electro-optic applications where two matched crystals are usually used to compensate the birefringence-related drifts. Meanwhile, mechanical resonances in two crystals (LiNbO3 and KTiOPO4) were mapped out and their influences on the control bandwidth were quantitatively investigated. Residual noises of two intensity-stabilized lasers (a Helium–Neon laser and a dye laser) were analyzed in detail.

Radio frequency interrogated actively mode-locked fiber ring laser for sensing application

This paper proposes an actively mode-locked fiber ring laser for sensing applications. Mode-locking of the laser is achieved by driving an electro-optic amplitude modulator at an RF corresponding to the fundamental beat frequency between the longitudinal modes. The change of the cavity length produces a frequency comb around the beat frequencies. The frequency separation of the comb is found to be linearly proportional to the cavity length change. The sensing mechanism of the device is shown. Temperature measurement is demonstrated using the proposed actively mode-locked fiber ring laser.

The Principle of the Electro-Optic System in Passive Synthetic Aperture Lmging

As the synthetic aperture has been widely used in remote sensing and imaging system. Various methods have been used to enhance the imgaing speed of the system. Optical method has been proved to have the high imaging speed in processing microwave signals. The received signal can be modulated in optical carrier by the electro-optic amplitude modulation. The optical signal is processed by relevant optical instruments. The article compares the new electro-optic imaging system with the original system. The principle of the new system has been proved to be similar with the original system. The structure of the new system has been verified to have the possibility to realize real-time imaging. The key point of the new system has been analysed and the main challenge in the new system has been checked in the article.

Application of Difference Frequency Laser in Trace Gas Measurement System

Based on Nd:YAG laser, tunable diode laser, electro-optic amplitude modulator and the difference frequency generator, a servo scanning laser source is designed, and the principle of trace gas concentration measurement model is introduced as well, which can realize the gas concentration measurement in the band of mid-infrared and far-infrared. Based on the theory of electromagnetic field, mutual coupling equation about laser transmission in nonlinear crystal and the optical frequency conversion characteristics are analyzed theoretically. As a result, in the range of far-field, electric field intensity of coupled wave increases approximatively exponentially,then tends to be stable.