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1.
Nature ; 627(8004): 534-539, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-38448599

RESUMO

Numerous modern technologies are reliant on the low-phase noise and exquisite timing stability of microwave signals. Substantial progress has been made in the field of microwave photonics, whereby low-noise microwave signals are generated by the down-conversion of ultrastable optical references using a frequency comb1-3. Such systems, however, are constructed with bulk or fibre optics and are difficult to further reduce in size and power consumption. In this work we address this challenge by leveraging advances in integrated photonics to demonstrate low-noise microwave generation via two-point optical frequency division4,5. Narrow-linewidth self-injection-locked integrated lasers6,7 are stabilized to a miniature Fabry-Pérot cavity8, and the frequency gap between the lasers is divided with an efficient dark soliton frequency comb9. The stabilized output of the microcomb is photodetected to produce a microwave signal at 20 GHz with phase noise of -96 dBc Hz-1 at 100 Hz offset frequency that decreases to -135 dBc Hz-1 at 10 kHz offset-values that are unprecedented for an integrated photonic system. All photonic components can be heterogeneously integrated on a single chip, providing a significant advance for the application of photonics to high-precision navigation, communication and timing systems.

2.
Opt Lett ; 49(6): 1520-1523, 2024 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-38489440

RESUMO

We demonstrate an efficient simultaneous self-injection locking of two semiconductor lasers to high-order modes of a standalone monolithic non-confocal Fabry-Perot cavity. The lasers are used to generate a low-noise microwave signal on a fast photodiode. The overall improvement of the laser spectral purity exceeds 80 dB. The observed single-sideband phase noise of X- to W-band signals is at the -110 dBc/Hz level and is limited by the fundamental thermorefractive noise of the cavity. The demonstrated cavity-laser configuration can be tightly packaged and is promising for the generation of high-frequency RF signals as well as for referencing optical frequency combs.

3.
Opt Lett ; 48(3): 715-718, 2023 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-36723571

RESUMO

Pumping a nonlinear optical cavity with continuous wave coherent light can result in generation of a stable train of short optical pulses. Pumping the cavity with a non-degenerate resonant coherent dichromatic pump usually does not produce a stable mode-locked regime due to competition of the oscillations at the pump frequencies. We show that generation of stable optical pulses is feasible in a dichromatically pumped cavity characterized with group velocity dispersion optimized in a way that the group velocity value becomes identical for the generated pulses and the beat note of the pump harmonics. The power threshold of the process drops nearly four times in this case and the produced pulses become sub-harmonically locked to the dichromatic pump harmonics. The process is useful for generation of broadband optical frequency combs and optical time crystals.

4.
Sensors (Basel) ; 22(3)2022 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-35161549

RESUMO

We introduce an RF-photonics receiver concept enabling the next generation of ultra-compact millimeter wave radars suitable for cloud and precipitation profiling, planetary boundary layer observations, altimetry and surface scattering measurements. The RF-photonics receiver architecture offers some compelling advantages over traditional electronic implementations, including a reduced number of components and interfaces, leading to reduced size, weight and power (SWaP), as well as lower system noise, leading to improved sensitivity. Low instrument SWaP with increased sensitivity makes this approach particularly attractive for compact space-borne radars. We study the photonic receiver front-end both analytically and numerically and predict the feasibility of the greater than unity photonic gain and lower than ambient effective noise temperature of the device. The receiver design is optimized for W-band (94 GHz) radars, which are generally assessed to be the primary means for observing clouds in the free troposphere as well as planetary boundary layer from space.

5.
Appl Opt ; 60(12): 3487-3491, 2021 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-33983256

RESUMO

We describe basic principles of operation and report on implementation of a standalone photonic link stabilized using the electronic phase conjugation technique. This method has been demonstrated to improve link stability by more than 2 orders while reducing its size and power consumption compared to other systems. We have demonstrated packaged robust links that achieve a relative frequency instability of 2×10-17 (5×10-17) at 10 h averaging while the temperature of the fiber was varied with 2°C (15°C) magnitude.

6.
Opt Lett ; 45(13): 3609-3612, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32630911

RESUMO

We show that an evanescent field coupler can break the symmetry of a high quality factor monolithic ring microcavity, enabling generation of strongly nondegenerate frequency harmonics involving a few mode families that are orthogonal in an unperturbed microcavity. Using this property, we explain observed experimental generation of frequency combs in magnesium fluoride whispering gallery mode resonators characterized with strong normal group velocity dispersion.

7.
Opt Lett ; 44(12): 3086-3089, 2019 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-31199387

RESUMO

Solitons, ubiquitous in nonlinear sciences, are wavepackets which maintain their characteristic shape upon propagation. In optics, they have been observed and extensively studied in optical fibers. The spontaneous generation of a dissipative Kerr soliton (DKS) train in an optical microresonator pumped with continuous wave (CW) coherent light has placed solitons at the heart of optical frequency comb research in recent years. The commonly observed soliton has a "sech"-shaped envelope resulting from resonator cubic nonlinearity balanced by its quadratic anomalous group velocity dispersion (GVD). Here we exploit the Lagrangian variational method to show that CW pumping of a Kerr resonator featuring quartic GVD forms a pure quartic soliton (PQS) with Gaussian envelope. We find analytical expressions for pulse parameters in terms of experimentally relevant quantities and derive an area theorem. Analytical predictions are validated with extensive numerical simulations and apply also to fiber-based and spatial Kerr resonators. Broader bandwidth with flatter spectral envelope of a PQS, compared to a DKS of the same pulse width and peak power, make it superior for applications requiring small frequency comb line-to-line power variation.

8.
Opt Lett ; 44(17): 4175-4178, 2019 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-31465356

RESUMO

In this Letter, we have studied the performance of a gallium nitride 370 nm Fabry-Perot laser diode self-injection locked via a high quality (Q-) factor magnesium fluoride whispering gallery mode (WGM) resonator and show that the state of locking strongly depends on frequency detuning between the internal laser cavity and the resonator modes. Optimizing the detuning, we were able to observe monochromatic laser emission with a sub-100 kHz linewidth. The Q-factor of the resonator measured in this regime exceeded 109.

9.
Opt Lett ; 44(6): 1472-1475, 2019 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-30874679

RESUMO

We experimentally demonstrate that a single microresonator can emit two orthogonally polarized individually coherent combs: (i) a strong polarized soliton comb and (ii) an orthogonally polarized continuous wave seeded weaker comb, generated from the first one via cross-phase modulation, sharing the repetition rate of the soliton comb. Experimental results show that the power of the transverse electric-polarized seed can be well below the threshold of comb generation (e.g., 0.1 mW). In addition, simulations show that a dark pulse could be generated in the anomalous dispersion regime by a bright soliton when the two orthogonally polarized modes have the same group velocity in the microresonator.

10.
Appl Opt ; 58(9): 2138-2145, 2019 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-31044910

RESUMO

While whispering gallery mode resonators are well known for their low acceleration sensitivity, there has not been much published experimental research on the subject. We performed environmental sensitivity tests of a 2 µm semiconductor distributed feedback (DFB) laser, self-injection locked to a high-Q crystalline whispering gallery mode resonator. Measured acceleration sensitivity of the laser is below 5×10-11 g-1 in the 1-200 Hz frequency bandwidth and thermal sensitivity does not exceed 12 MHz/°C. The laser's frequency noise is below 50 Hz/Hz1/2 at 10 Hz, reaching 0.4 Hz/Hz1/2 at 400 kHz. The instantaneous linewidth of the laser is improved by nearly 4 orders of magnitude compared to the free-running DFB laser and is measured to be 50 Hz at 0.1 ms measurement time. The Allan deviation of the laser frequency is on the order of 10-9 from 1 to 1000 s. All these features make the laser attractive for metrology applications involving low-noise 2 µm seed lasers.

11.
Opt Express ; 25(2): 681-695, 2017 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-28157957

RESUMO

An integrated heterodyne optical phase-locked loop was designed and demonstrated with an indium phosphide based photonic integrated circuit and commercial off-the-shelf electronic components. As an input reference, a stable microresonator-based optical frequency comb with a 50-dB span of 25 nm (~3 THz) around 1550 nm, having a spacing of ~26 GHz, was used. A widely-tunable on-chip sampled-grating distributed-Bragg-reflector laser is offset locked across multiple comb lines. An arbitrary frequency synthesis between the comb lines is demonstrated by tuning the RF offset source, and better than 100Hz tuning resolution with ± 5 Hz accuracy is obtained. Frequency switching of the on-chip laser to a point more than two dozen comb lines away (~5.6 nm) and simultaneous locking to the corresponding nearest comb line is also achieved in a time ~200 ns. A low residual phase noise of the optical phase-locking system is successfully achieved, as experimentally verified by the value of -80 dBc/Hz at an offset of as low as 200 Hz.

12.
Opt Lett ; 42(22): 4764-4767, 2017 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-29140364

RESUMO

We show theoretically that dynamic behavior of light confined in the modes of a nonlinear optical ring cavity characterized by resonant Rayleigh scattering can be described using the Bose-Hubbard model. Nonlinear interaction between clockwise and counterclockwise optical modes results in instability and intermode hopping occurring at a rate defined by the frequency separation of the Rayleigh doublet harmonics. Hopping may lead to an instability and breathing behavior of a Kerr frequency comb observed in the cavity.

13.
Opt Lett ; 42(22): 4736-4739, 2017 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-29140356

RESUMO

We report on an accurate measurement of the frequency splitting of an optical rotating ring microcavity made out of calcium fluoride. By measuring the frequencies of the clockwise and counter-clockwise coherent Raman emissions confined in the cavity modes, we show that the frequency splitting is inversely proportional to the refractive index of the cavity host material. The measurement has an accuracy of 1% and unambiguously confirms the classical theoretical prediction based on special theory of relativity. This Letter also demonstrates the usefulness of the ring Raman microlaser for rotation measurements.

14.
Opt Lett ; 42(7): 1249-1252, 2017 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-28362741

RESUMO

We demonstrate a simple, compact, and cost-effective laser noise reduction method for stabilizing an extended-cavity diode laser to a 3×105 finesse mirror Fabry-Perot (F-P) cavity, corresponding to a resonance linewidth of 10 kHz, by using a crystalline MgF2 whispering gallery mode microresonator. The laser linewidth is reduced to sub-kilohertz such that a stable Pound-Drever-Hall error signal is built up. The wavelength of the pre-stabilized laser is tunable within a large bandwidth covering the high-reflection mirror coating of an F-P supercavity.

15.
Opt Lett ; 41(13): 2907-10, 2016 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-27367062

RESUMO

We show that an optical analog of Cherenkov radiation (dispersive wave) is observable in a nonlinear microring resonator generating Kerr frequency comb and containing linearly interacting families of equidistant modes. The radiation results from disruptions in the frequency dependent group velocity dispersion of the pumped cavity modes and is emitted into different mode families of the resonator. This effect reveals itself as a dispersive shaped structure in the spectral envelope of the frequency comb. We found that the dips in the comb spectrum correspond to peaks of the emission of the power in the other mode families of the resonator. The spectrum of the combs that includes both mode families does not have any dips, but peaks and resembles the Cherenkov radiation spectra frequently observed in Kerr comb systems. This Letter shows that a correct description of the Kerr comb in presence of mode anti-crossings should take into account not only the pumped mode family with modified dispersion parameter, but also the modes of the interacting families.

16.
Opt Lett ; 41(21): 5102-5105, 2016 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-27805695

RESUMO

We show theoretically that it is feasible to generate a spectrally broad Kerr frequency comb consisting of several spectral clusters phase matched due to interplay among second- and higher-order group velocity dispersion contributions. We validate the theoretical analysis experimentally by driving a magnesium fluoride resonator, characterized with 110 GHz free spectral range, with a continuous wave light at 1.55 µm and observing two comb clusters separated by nearly two-thirds of an octave.

17.
Opt Lett ; 41(18): 4375-8, 2016 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-27628401

RESUMO

Crystalline whispering gallery mode (WGM) electro-optic resonators made of LiNbO3 and LiTaO3 are critical for a wide range of applications in nonlinear and quantum optics, as well as RF photonics, due to their remarkably ultrahigh Q(>108) and large electro-optic coefficient. Achieving efficient coupling of these resonators to planar on-chip optical waveguides is essential for any high-yield and robust practical applications. However, it has been very challenging to demonstrate such coupling while preserving the ultrahigh Q properties of the resonators. Here, we show how the silicon photonic platform can overcome this long-standing challenge. Silicon waveguides with appropriate designs enable efficient and strong coupling to these WGM electro-optic resonators. We discuss various integration architectures of these resonators onto a silicon chip and experimentally demonstrate critical coupling of a planar Si waveguide and an ultrahigh QLiTaO3 resonator (Q∼108). Our results show a promising path for widespread and practical applications of these resonators on a silicon photonic platform.

18.
Opt Lett ; 41(23): 5559-5562, 2016 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-27906238

RESUMO

We report on the stabilization of a high-power distributed feedback (DFB) semiconductor laser operating at 2.05 µm wavelength, using a crystalline whispering gallery mode microresonator. The laser's frequency noise is measured to be below 100 Hz/Hz1/2 at Fourier frequencies ranging from 10 Hz to 1 MHz. The instantaneous linewidth of the laser is improved by four orders of magnitude compared with the free-running DFB laser, and is measured to be 15 Hz at 0.1 ms measurement time. The integral linewidth approaches 100 Hz. The stabilized DFB laser is integrated with a polarization maintaining output fiber and an integrated optical isolator.

19.
Opt Lett ; 41(16): 3706-9, 2016 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-27519068

RESUMO

We stabilize a chip-scale Si3N4 phase-locked Kerr frequency comb via locking the pump laser to an independent stable high-Q reference microresonator and locking the comb spacing to an external microwave oscillator. In this comb, the pump laser shift induces negligible impact on the comb spacing change. This scheme is a step toward miniaturization of the stabilized Kerr comb system as the microresonator reference can potentially be integrated on-chip. Fractional instability of the optical harmonics of the stabilized comb is limited by the microwave oscillator used for a comb spacing lock below 1 s averaging time and coincides with the pump laser drift in the long term.

20.
Sensors (Basel) ; 16(2): 238, 2016 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-26901199

RESUMO

The need for highly performing and stable methods for mid-IR molecular sensing and metrology pushes towards the development of more and more compact and robust systems. Among the innovative solutions aimed at answering the need for stable mid-IR references are crystalline microresonators, which have recently shown excellent capabilities for frequency stabilization and linewidth narrowing of quantum cascade lasers with compact setups. In this work, we report on the first system for mid-IR high-resolution spectroscopy based on a quantum cascade laser locked to a CaF2 microresonator. Electronic locking narrows the laser linewidth by one order of magnitude and guarantees good stability over long timescales, allowing, at the same time, an easy way for finely tuning the laser frequency over the molecular absorption line. Improvements in terms of resolution and frequency stability of the source are demonstrated by direct sub-Doppler recording of a molecular line.

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