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A Traceable High-Accuracy Velocity Measurement by Electro-Optic Dual-Comb Interferometry
摘要： An electro-optic dual-comb Doppler velocimeter for high-accuracy velocity measurement is presented in this paper. The velocity information of the object can be accurately extracted from the change of repetition frequency, which is in the microwave frequency domain and can be locked to an atomic clock. We generate two optical combs by electro-optic phase modulators and trace their repetition frequencies to the rubidium clock. One functions as the measurement laser and the other the reference. Experimentally, we verify its high accuracy in the range of 100–300 mm/s with a maximum deviation of 0.44 mm/s. The proposed velocimeter combines the merits of high accuracy and wide range. In addition, since the repetition frequency used for the measurement is traceable to the rubidium clock, its potential superiority in traceability can be utilized in velocity metrology.
关键词： electro-optic dual-comb interferometry,Traceability,laser Doppler velocimetry
更新于2025-09-12 10:27:22
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Comparative Study of Silicon Photonic Modulators based on Transparent Conducting Oxide and Graphene
摘要： Transparent conducting oxides (TCOs) and graphene have been extensively investigated as promising materials for electro-optic modulation applications due to their dynamically configurable near-infrared properties. In this study, a detailed comparison between modulators comprising either a TCO film or a graphene-insulator-graphene structure is presented, considering a conventional silicon photonic waveguide as the underlying physical system. Both in-line and resonant configurations are investigated, integrating an electro-optic switching mechanism that changes the free-carrier concentration in the configurable material by means of electrical gating. The carrier-concentration change effect is rigorously modeled using solid-state physics principles, providing a physically consistent and straightforward comparison between the investigated material platforms. The performance of the designed modulators is thoroughly evaluated in terms of the extinction ratio, insertion loss, energy consumption, and bandwidth in both TE and TM operation. On the whole, both technologies support high-performance optical modulation, with TCO designs exhibiting an up to 40% smaller footprint, with their graphene counterparts standing out for their subpicojoule-per-bit performance on a physical system as simple as the employed silicon-wire waveguide. The low insertion losses as well as the impressive over-100-GHz switching speeds suggest both TCOs and graphene as very promising material candidates for future on-chip modulation applications.
关键词： silicon photonic modulators,transparent conducting oxide,near-infrared properties,electro-optic modulation,graphene
更新于2025-09-12 10:27:22
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Nd <sup>3+</sup> :YAG laser based on the <sup>4</sup> F <sub/>3/2</sub> → <sup>4</sup> I <sub/>13/2</sub> secondary transition with a phase-conjugate electro-optically Q-switched open multiloop cavity
摘要： Lasing on the 4F3/2 → 4I13/2 secondary transition (λ = 1.34 μm) in a Nd3+ : YAG laser with phase conjugation by four-wave mixing directly in the active laser medium was experimentally studied in the regime of electro-optic Q-switching of an open multiloop cavity. The use of an electro-optic Q-switch with a controllable delay of its opening made it possible to increase the amplitude and temporal stabilities of the output laser parameters. The maximum laser pulse energy was 100 mJ at a pulse duration of 120 ns. The phase-conjugate radiation divergence was 0.8 mrad at beam quality Mx2 = My2 = 1.3. Nonlinear optical conversion of 1.34 μm laser radiation to visible radiation was achieved experimentally. Second and third harmonic generation at wavelengths of 0.67 and 0.446 μm with conversion efficiencies of 25 % and 8 %, respectively, was demonstrated.
关键词： phase conjugation,secondary transition,stability of laser parameters,Nd3+ : YAG laser,electro-optic Q-switching
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Effect of Polarization Modulation on the Stability of a 1.5 μm Laser Locked to a Libre Cavity
摘要： We analyse limitations introduced by a fibre connectorised Lithium-Niobate electro-optic modulator which modulates the beam of a1.5 μm laser for frequency lock onto one mode of a fibre cavity. It is shown that the ellipticity and/or misalignment of the input polarization with the main axes of the modulator leads to a modulation of the output polarization. This results in two effects on the signal detected at the cavity output: an offset due to residual amplitude modulation (RAM) and a distortion due to the slight birefringence presented by the cavity. Both effects limit the stability of the frequency lock.
关键词： laser stability,electro-optic modulator,fibre cavity,polarization modulation,birefringence
更新于2025-09-12 10:27:22
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Fast electro-optic switching for coherent laser ranging and velocimetry
摘要： The growth of 3D imaging across a range of sectors has driven a demand for beam steering technology. Fields as diverse as autonomous vehicles and medical imaging can benefit from a high speed, adaptable method of beam steering. We present a monolithic, submicrosecond electro-optic switch as a solution toward the need for reliability, speed, dynamic addressability, and compactness. Here, we demonstrate a laboratory-scale, solid-state light detection and ranging system, using the electro-optic switch to launch modulated coherent light into free space and then to collect the reflected signal. We use coherent detection of the reflected light to simultaneously extract the range and axial velocity of targets at each of the several electronically addressable output ports.
关键词： electro-optic switching,beam steering,coherent laser ranging,velocimetry,LIDAR
更新于2025-09-12 10:27:22
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Failure Analysis of Metallic Armoured Electro-Optic Mechanical Cables in Underwater Towed Sonar Systems
摘要： In towed sonar systems generally, the array is towed behind a ship using a combination of electro-optic mechanical (EOM) tow cables - negatively buoyant metallic armoured Heavy Cable and neutrally buoyant fibre armoured Light Cable- the former for depth control and latter for depth maintenance. Any failure in these cables can affect the performance of the sensor array and can even result in loss of the towed system to sea. During a series of towed array trials, it was observed that the metallic armoured cable had lost its circularity and became flattened during deployment and retrieval from ship. This may be due to the extreme radial forces acting on the cable while passing through a) rollers located at winch spooler and b) main fairlead comprising of 5 rollers located at aft end of ship, which causes permanent changes in cable’s internal configuration. To verify the cause and study the effects of such flattening on functionality and life of the cable, cyclic load testing studies were carried out after simulating the actual deployment-retrieval conditions as that in the ship. Both indigenously developed and imported cable samples were chosen as test samples for performance comparison. During the tests, it was observed that severe flattening of armour and core cable resulting in failure of electrical & optical lines had occurred in indigenous cable samples. The imported cable samples showed no flatness or failure of lines. Based on the results, steps were taken to improve the radial load bearing capacity of the indigenous cable. Modifications were made in a) core cable sheath material b) core cable sheath thickness & c) armour wire material and an improved indigenous cable was developed, which has withstood all the above tests and is now ready to be inducted to the system for sea trials.
关键词： Towed array sonar,Metallic armored cable,Electro-Optic Mechanical (EOM) tow cables,Cyclic load testing
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Atlanta, GA, USA (2019.7.7-2019.7.12)] 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Optimization of Coplanar Waveguide Structure for Ultra Wideband Integrated Electro-optic Mach Zehnder Modulator
摘要： Using numerical tools, coplanar waveguide (CPW) transmition line is optimized to be utilized in ultra-compact traveling wave electro-optic modulators (EOMs). Important factors such as minimization of the radio frequency (RF) loss, impedance mismatch, and velocity mismatch are investigated. Our results reveal that coplanar waveguide can provide conditions for ultra compact Mach-Zehnder modulators (MZM) to operate at frequencies up to terahertz range.
关键词： velocity mismatch,electro-optic modulators,impedance mismatch,RF loss,coplanar waveguide
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Field-Resolved Infrared Transmission Spectroscopy of Strongly Absorbing Samples
摘要： Molecular vibrational spectroscopies provide chemically-specific information on complex samples. The label-free nature of these techniques renders them highly attractive for studies of biological processes and medical diagnosis. Among these methods, the direct, broadband interrogation of molecular vibrations at their fundamental frequencies in the infrared (IR) molecular fingerprint region, profits from large interaction cross-sections, potentially affording a unique combination of detection sensitivity and molecular coverage. However, the strong absorption of (liquid) water in this spectral range has so far severely limited the applicability of IR vibrational spectroscopy (and microscopy) in transmission geometry. In this contribution, we demonstrate the potential of field-resolved infrared spectroscopy (FRS) to overcome these long-standing limitations. FRS relies on the excitation of resonant molecular vibrations with waveform-stable, broadband IR pulses, and electric-field-resolved detection of the emerging fingerprint waveforms via electro-optic sampling, bringing about two major advantages over other IR spectroscopies. Firstly, it directly measures the electric field, resulting in a square root scaling of the signal with the intensity attenuation. Together with quantum-efficiency maximised electro-optic sampling and sensitive photodiodes in the near-infrared, this offers an unprecedented intensity dynamic range. Secondly, the nature of time-domain measurements enables recording resonant fingerprints trailing an impulsive excitation in a background-free manner, rendering FRS mostly immune to intensity noise of the excitation. Assuming a detection immune to intensity noise, and with the DR shown in Fig. 1.a, for our system we model the curve in Fig. 1b for the limit of detection (LOD) of a test molecule, DMSO2, solved in water. For an aqueous layer of 33 μm, we experimentally obtain an LOD of 200 ng/ml (for 45 seconds of measurement time), which validates this model and our assumption. These results predict fast, broadband measurements of aqueous samples as thick as 0.1 mm, with sub-μg/ml detection sensitivities, opening the door to a new realm of applications of vibrational spectroscopy to biological samples such as tissue and live cells.
关键词： detection sensitivity,infrared (IR) molecular fingerprint region,molecular vibrational spectroscopies,electro-optic sampling,field-resolved infrared spectroscopy
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Electro-Optic Frequency Comb Generation in Lithium Niobate Whispering Gallery Mode Resonators
摘要： Optical frequency combs (OFCs) are light sources whose spectra consists of equally spaced frequency lines in the optical domain [1]. They have great potential for improving high-capacity data transfer, all-optical atomic clocks, spectroscopy, and high-precision measurements [2]. In contrast to the traditional third-order nonlinearity based OFC generation methods, we present a new approach which is based on second-order non-linear effects in a whispering gallery mode (WGM) resonator made of lithium niobate (LN) [3,4]. Our system is composed of a resonant hybrid structure comprising an optical LN disk resonator and a microwave copper cavity. The hybrid structure enables highly efficient nonlinear mixing of photons. In this scheme, two continuous waves, one in the optical domain ((cid:2033) = 193 THz) and another in the microwave region (Ω = 8.9 GHz) couple within a LN WGM resonator [5]. The second-order non-linearity of LN leads to frequency comb generation via cascaded symmetric sum and difference frequency generation [6]. In our experiment, the optical pump power is coupled into the WGM by using a standard prism coupling method that is based on frustrated total internal reflection (Fig. 1 (a)). The microwave power is coupled using a coaxial probe coupled attached to the 3-D copper cavity specifically designed to have the microwave cavity resonance to be equal to the optical free spectral range of the LN resonator, required for efficient phase matching. In addition, the cavity design also provides a very good spatial overlap between the microwave and optical modes by confining the microwave field to the rim of the LN disk. In our proof-of-concept experimental demonstration we observe a 1.6 THz long frequency comb centred around 193.5 THz more than180 comb lines by using only 20 dBm of microwave power. Compared to previously reported OFCs generation schemes, this method has two major advantages: inherent phase stability, and better power efficiency. The power efficiency when measured in terms of pi-voltage of the modulator is 25 times better than a commercial Thorlabs modulator.
关键词： second-order non-linearity,whispering gallery mode resonators,electro-optic frequency comb generation,Optical frequency combs,lithium niobate
更新于2025-09-12 10:27:22
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Enhanced Terahertz Detection Efficiency via Grating-Assisted Noncollinear Electro-Optic Sampling
摘要： Sensitive detection of phase-locked terahertz (THz) pulses is routinely achieved using electro-optic sampling (EOS), a technique that harnesses second-order optical nonlinearities in a crystalline semiconductor. The thickness and electro-optic coefficient of such a crystal set the detection sensitivity in EOS, while its linear optical properties often determine the accessible detection bandwidth through the phase-matching conditions. Here, we demonstrate how a periodically patterned structure on the incident surface of an EOS crystal can be used to overcome bandwidth limitations by enabling noncollinear propagation between the THz waves and a near-infrared (NIR) gating pulse. The concept is demonstrated with phase gratings etched on a 1-mm-thick gallium phosphide (GaP) semiconductor. The use of a diffracted NIR gating pulse to retrieve the THz waveform results in a sensitivity enhancement of a factor of approximately 2 with regard to the spectral maximum at 2 THz and exceeding an order of magnitude at 5 THz. This extends the spectral detection bandwidth up to 5 THz, which is twice as large as that achievable in a similar configuration with collinear THz and NIR pulses, facilitating the broadband detection of weak signals in THz spectroscopy.
关键词： electro-optic sampling,phase grating,gallium phosphide,noncollinear propagation,terahertz
更新于2025-09-12 10:27:22