Resonant Electro-optic Modulator Research Articles

Resonant electro-optic phase modulator and photodetector for stabilizing laser frequency and quantum optics

Photoelectric functional device with specific optical, electrical and photoelectric conversion effects is one of the most important resources of modern information science and technology. Electro-optic modulator and photodetector are very important photoelectric functional devices, which are key devices in the fields of frequency locking, feedback control, photoelectric information conversion, optical communication, photoelectric information modulation, etc., and play an irreplaceable role in frequency stabilization locking technology of PDH (Pound-Drever-Hall, simply referred to as PDH). The PDH technology is widely used in researches of large scientific devices, quantum optics, optical communication and other fields. Using electro-optical phase modulator to carry out laser phase modulation is the primary process to realize frequency stabilization locking of standard PDH. Photoelectric detection can implement the photoelectric conversion of the carried weak modulation signal and spectral peak signal into electrical signal, and then feedback control through proportional integral and differential circuits, so as to achieve stable locking and frequency stabilization. The resonant electro-optical phase modulation (RPM) with high modulation depth, low power consumption and low half-wave voltage and microwatt resonant photoelectric detection (RPD) functional device with high signal-to-noise (SNR) ratio are invented to meet the demand for extraction and detection of extremely weak signals. The resonant circuit is composed of the single-end wedge-angle lithium niobate crystal, low noise photodiode and low-loss and high-Q electronic components. Low power consumption, high modulation depth electro-optic modulation, and high gain photoelectric detection are realized by the principle of resonant enhancement. When the optimal modulation frequency point is 10 MHz, the bandwidth of RPM is 225 kHz with <i>Q</i> of 44.4, when the modulation depth is 1.435, the RPM requires RF drive voltage of RPM to be 4 V. When the optimal modulation frequency point is 20 MHz, the bandwidth of RPM is 460 kHz with <i>Q</i> of 43.5, the required RF drive voltage of RPM is 6.5 V when the modulation depth is 1.435. The optimal detection frequency point of the self-invent RPD is 20.00 MHz, with a bandwidth of 1 MHz, Q of 20, the gain of 80 dB at 100 μW. With the home-made RPM and RPD in the extraction loop for extremely weak signal, the SNR of error signal is as high as 5.088 at 10 μW, 34.933 at 50 μW and 58.7 at 100 μW. Such a loop improves the performance and stability of the entire feedback control loop by optimizing parameters of proportional integral differential, which provides key devices and technological approaches for preparing a highly stable quantum light source and ultra-stable laser.

Compact single-seed, module-based laser system on a transportable high-precision atomic gravimeter

A single-seed, module-based compact laser system is demonstrated on a transportable 87Rb-based high-precision atomic gravimeter. All the required laser frequencies for the atom interferometry are provided by free-space acousto-optic modulators (AOMs) and resonant electro-optic phase modulators (EOMs). The optical phase-locked loop between the two optical paths derived from the same laser provides an easy frequency manipulation between two laser frequencies separated by the hyperfine frequency of 6.835 GHz using an AOM and an EOM, respectively. Our scheme avoids parasite Raman transitions present in the direct EOM modulation scheme (modulating directly at the frequency of the hyperfine splitting), which have detrimental effects on the accuracy of the gravity measurements. The optical phase-locked loop also provides a convenient way for vibration compensation through the Raman lasers' phase offset. Furthermore, the modular design approach allows plug-and-play nature on each individual optic module and also increases the mechanical stability of the optical systems. We demonstrate high-precision gravity measurements with 17.8 μGal stability over 250 s averaging time and 2.5 μGal stability over 2 h averaging time.

Frequency-multiplexed hybrid optical entangled source based on the Pockels effect

In the recent years important experimental advances in resonant electro-optic modulators as high-efficiency sources for coherent frequency combs and as devices for quantum information transfer have been realized, where strong optical and microwave mode coupling were achieved. These features suggest electro-optic-based devices as candidates for entangled optical frequency comb sources. In the present work, I study the generation of entangled optical frequency combs in millimeter-sized resonant electro-optic modulators. These devices profit from the experimentally proven advantages such as nearly constant optical free spectral ranges over several gigahertz, and high optical and microwave quality factors. The generation of frequency multiplexed quantum channels with spectral bandwidth in the MHz range for conservative parameter values paves the way towards novel uses in long-distance hybrid quantum networks, quantum key distribution, enhanced optical metrology, and quantum computing.

Sensitivity and noise in THz electro-optic upconversion radiometers

This paper presents a study of noise in room-temperature THz radiometers that use THz-to-optical upconversion followed by optical detection of thermal radiation. Despite some undesired upconverted thermal noise, no noise is intrinsically introduced by efficient electro-optic modulation via a sum-frequency-generation process in high quality factor (Q) whispering-gallery mode (WGM) resonators. However, coherent and incoherent optical detection results in fundamentally different noise characteristics. The analysis shows that the upconversion receiver is quantum limited like conventional amplifiers and mixers, only when optical homodyne or heterodyne detection is performed. However, this type of receiver shows advantages as a THz photon counter, where counting is in the optical domain. Theoretical predictions show that upconversion-based room-temperature receivers can outperform state-of-the-art cooled and room-temperature THz receivers based on low-noise amplifiers and mixers, provided that a photon conversion efficiency greater than 1% is realized. Although the detection bandwidth is naturally narrow due to the highly resonant electro-optic modulator, it is not fundamentally limited and can be broadened by engineering selective optical coupling mechanisms to the resonator.

Triply resonant coupled-cavity electro-optic modulators for RF to optical signal conversion.

We propose an on-chip triply resonant electro-optic modulator architecture for RF-to-optical signal conversion and provide a detailed theoretical analysis of the optimal "circuit-level" device geometries and their performance limits. The designs maximize the RF-optical conversion efficiency through simultaneous resonant enhancement of the RF drive signal, a continuous-wave (CW) optical pump, and the generated optical sideband. The optical pump and sideband are resonantly enhanced in respective supermodes of a two-coupled-cavity optical resonator system, while the RF signal can be enhanced in addition by an LC circuit formed by capacitances of the optical resonator active regions and (integrated) matching inductors. We show that such designs can offer 15-50 dB improvement in conversion efficiency over conventional microring modulators. In the proposed configurations, the photon lifetime (resonance linewidth) limits the instantaneous RF bandwidth of the electro-optic response but does not limit its central RF frequency. The latter is set by the coupling strength between the two coupled cavities and is not subject to the photon lifetime constraint inherent to conventional singly resonant microring modulators. This feature enables efficient operation at high RF carrier frequencies without a reduction in efficiency commonly associated with the photon lifetime limit and accounts for 10-30 dB of the total improvement. Two optical configurations of the modulator are proposed: a "basic" configuration with equal Q-factors in both supermodes, most suitable for narrowband RF signals, and a "generalized" configuration with independently tailored supermode Q-factors that supports a wider instantaneous bandwidth. A second significant 5-20 dB gain in modulation efficiency is expected from RF drive signal enhancement by integrated LC resonant matching, leading to the total expected improvement of 15-50 dB. Previously studied triply-resonant modulators, with coupled longitudinal [across the free spectral range (FSR)] modes, have large resonant mode volume for typical RF frequencies, which limits the interaction between the optical and RF fields. In contrast, the proposed modulators support maximally tightly confined resonant modes, with strong coupling between the mode fields, which increases and maintains high device efficiency across a range of RF frequencies. The proposed modulator architecture is compact, efficient, capable of modulation at high RF carrier frequencies and can be applied to any cavity design or modulation mechanism. It is also well suited to moderate Q, including silicon, implementations, and may be enabling for future CMOS RF-electronic-photonic systems on chip.

Athermal Hybrid Silicon/Polymer Ring Resonator Electro-optic Modulator

In this work, we have demonstrated a hybrid silicon/polymer ring resonator electro-optic (EO) modulator with a temperature-independent modulation. The waveguide consisted of an ultrathin silicon core with an EO polymer cladding. Using ultrathin silicon is advantageous, as it allows a reduction in the side-wall scattering loss and also offers excellent light distribution to enable athermal operation. With a radius of 60 μm, the ring exhibited a 9.7 dB extinction depth and a Q value of 1.25 × 104. After poling of the EO polymer, the ring resonator functioned well as an EO modulator and operated in a stable manner between 25 and 55 °C.

Compact optoelectronic oscillator based on a Fabry–Perot resonant electro-optic modulator

A novel compact optoelectronic oscillator (OEO) employing a Fabry–Perot (FP) resonant electro-optic (EO) modulator is proposed and experimentally demonstrated. The resonant modulator is used as the optical storage element as well as the mode selection element, which can greatly reduce the system complexity and make the system more portable. Moreover, the optical resonance and electrical transmission response for the FP resonant EO modulator are theoretically and experimentally studied. The proposed OEO oscillates at 10 and 20 GHz in the proof-of-concept experiment, and the corresponding single-sideband phase noise can reach below −118 and −108 dBc/Hz at 1 MHz offset frequency, respectively.

First demonstration of long-haul transmission using silicon microring modulators

We report error-free long-haul transmission of optical data modulated using a silicon microring resonator electro-optic modulator with modulation rates up to 12.5 Gb/s. Using bit-error-rate and power penalty characterizations, we evaluate the performance of this device with varying modulation rates, and perform a comparative analysis using a commercial electro-optic modulator. We then experimentally measure the signal integrity degradation of the high-speed optical data with increasing propagation distances, induced chromatic dispersions, and bandwidth-distance products, showing error-free transmission for propagation distances up to 80 km. These results confirm the functional ubiquity of this silicon modulator, establishing the potential role of silicon photonic interconnects for chip-scale high-performance computing systems and memory access networks, optically-interconnected data centers, as well as high-performance telecommunication networks spanning large distances.

Polarization-sensitive swept-source optical coherence tomography with continuous source polarization modulation

We present fiber-based polarization-sensitive swept-source optical coherence tomography (SS-OCT) based on continuous source polarization modulation. The light source is a frequency swept laser centered at 1.31 microm with a scanning rate of 20 kHz. The incident polarization is modulated by a resonant electro-optic modulator at 33.3 MHz, which is one-third of the data acquisition frequency. The zeroth- and first-order harmonic components of the OCT signals with respect to the polarization modulation frequency have the polarimetric information of the sample. By algebraic and matrix calculations of the signals, this system can measure the depth-resolved Jones matrices of the sample with a single wavelength scan. The phase fluctuations of the starting trigger of wavelength scan and the polarization modulation are cancelled by monitoring the OCT phase of a calibration mirror inserted into the sample arm. We demonstrate the potential of the system by the measurement of chicken breast muscle and the volumetric measurement of an in vivo human anterior eye segment. The phase retardation image shows an additional contrast in the fibrous tissue such as the collagen fiber in the trabecular meshwork and sclera.

General equations for the induced phase shift in resonant electrooptic modulators

We derive general equations to calculate the electrooptically induced optical phase shift in resonantly enhanced modulators. The equations are useful in designing modulator electrodes with optimal length and optimal mismatch between electrical and optical velocities. We demonstrate the existence of an optimal velocity mismatch depending on the resonant mode used.

Whispering-gallery-mode electro-optic modulator and photonic microwave receiver

We report on the experimental observation of efficient all-resonant three-wave mixing using high-Q whispering-gallery modes. The modes were excited in a millimeter size toroidal cavity fabricated from LiNbO3. We implemented a low-noise resonant electro-optic modulator based on this wave mixing process. We observe an efficient modulation of light with coherent microwave pumping at 9 GHz with applied power of approximately 10 mW. Used as a receiver, the modulator allows us to detect nanowatt microwave radiation. Preliminary results with a 33-GHz modulator prototype are also reported. We present a theoretical interpretation of the experimental results and discuss possible applications of the device.

Highly selective terahertz optical frequency comb generator

Using a 10.5-GHz resonant electro-optic modulator placed inside a resonant optical cavity, we generated an optical frequency comb with a span wider than 3 THz. The optical resonator consists of three mirrors, with the output coupler being a thin Fabry-Perot cavity with a free spectral range of 2 THz and a finesse of 400. Tuning this filter cavity onto resonance with a particular high-order sideband permits efficient output coupling of the desired sideband power from the comb generator, while keeping all other sidebands inside for continued comb generation. This spectrally pure output light was then heterodyne detected by another laser with a frequency offset of the order of 1 THz.

Enhanced loading of a magneto-optic trap from an atomic beam.

We demonstrate enhanced loading of a $^{7}\mathrm{Li}$ magneto-optic trap by broadening the frequency spectrum of the laser trapping light with a resonant electro-optic modulator. We achieve an \ensuremath{\sim}20-fold improvement in the loading rate over that obtained without a broadened spectrum when directly capturing atoms from a divergent atomic beam.

Resonantly enhanced radio frequency electrooptic phase modulator

We have designed and fabricated a new type of resonant electrooptic phase modulator. With this device, the rf power required to produce the same modulation index as that obtained from the conventional traveling wave design can be reduced by as much as 3 dB. The peak modulation response can be controlled from ~150 to 350 MHz by varying the value of an externally loaded surface mount inductor. The resonant device may be modeled as a lumped-element bandpass filter. Results of the experimental characterization show excellent agreement with the model.