Brillouin Laser Research Articles

Forward stimulated Brillouin scattering and opto-mechanical non-reciprocity in standard polarization maintaining fibres

Opto-mechanical interactions in guided wave media are drawing great interest in fundamental research and applications. Forward stimulated Brillouin scattering, in particular, is widely investigated in optical fibres and photonic integrated circuits. In this work, we report a comprehensive study of forward stimulated Brillouin scattering over standard, panda-type polarization maintaining fibres. We distinguish between intra-polarization scattering, in which two pump tones are co-polarized along one principal axis, and inter-polarization processes driven by orthogonally polarized pump waves. Both processes are quantified in analysis, calculations and experiment. Inter-modal scattering, in particular, introduces cross-polarization switching of probe waves that is non-reciprocal. Switching takes place in multiple wavelength windows. The results provide a first demonstration of opto-mechanical non-reciprocity of forward scatter in standard fibre. The inter-polarization process is applicable to distributed sensors of media outside the cladding and coating boundaries, where light cannot reach. The process may be scaled towards forward Brillouin lasers, optical isolators and circulators and narrowband microwave-photonic filters over longer sections of off-the-shelf polarization maintaining fibres.

Demonstration of enhanced four-wave mixing by harnessing stimulated Brillouin scattering within a suspended cascaded microring resonator

We experimentally demonstrate the enhanced four-wave mixing (FWM) by harnessing the forward stimulated Brillouin scattering (FSBS) within a silicon-based cascaded racetrack microring resonator (MRR). The frequency spacing of the split resonant peaks is precisely designed to match the Brillouin frequency shift (BFS). The cooperative interaction of the FSBS resonance and cascaded MRR resonance achieves an FWM enhancement of 2.97 and 2.43 dB for anti-Stokes and Stokes sidebands under the launched pump power of 35.48 mW and probe power of 17.78 mW. The BFS from 3.34 to 7.13 GHz is demonstrated by changing the waveguide width. Moreover, we show that this same system behaves as a single-sideband modulator, providing more than the 17 dB single-sideband rejection ratio under the condition that the probe light and Stokes are resonant in the cascaded MRR. Building on these results, this device opens the door to new types of all-silicon Brillouin laser, amplifier, isolator, and single-sideband modulator.

Research progress of stimulated Brillouin scattering pulse compression technique

Stimulated Brillouin scattering (SBS) as a third-order optical effect is widely used in laser beam combination, distributed fiber sensing, Brillouin lasers and other fields. In recent years, SBS pulse compression has also received special attention. Based on the energy transfer characteristics of the Brillouin amplification process, SBS pulse compression technology can compress nanosecond pulses to sub-nanosecond levels, and the peak power can be increased by 1-2 orders of magnitude. This paper systematically introduces the basic theory of SBS pulse compression, comprehensively discusses the influence of SBS compressor structure, gain medium, pump pulse and other factors on pulse compression characteristics, and looks forward to the development trends of SBS pulse compression. It provides a useful reference for the future study of SBS characteristics and a feasible scheme for the acquisition of high repetition frequency and high energy laser.

Sub-kilohertz Brillouin fiber laser with stabilized self-injection locked DFB pump laser

We report on experimental demonstration of a low-cost sub-kilohertz Brillouin fiber ring laser pumped from an actively stabilized self-injection locked distributed feedback (DFB) laser diode. Locking of the commercial DFB laser to a ~11-m-length high-Q-factor fiber-optic ring cavity leads to ~10,000-fold narrowing of the laser Lorentzian linewidth down to 400 Hz. Such pump laser operation inside the ring cavity forces the cavity to host Brillouin lasing enabling the laser threshold power as low as ~1.5 mW. The laser operation is perfectly stabilized by active optoelectronic feedback driven by a simple microcontroller. The laser delivers radiation at Stokes frequency with the Lorentzian linewidth reduced down to ~75 Hz and a phase noise less than –100 dBc/Hz (>30 kHz). The reported laser configuration is of great interest for many laser applications where a narrow sub-kHz linewidth, simple design and low cost are important.

Analysis of giant forward Brillouin gain enhancement in double-disk microcavities by tailoring optical forces

Stimulated Brillouin scattering in whispering gallery resonators has numerous potential applications. However, previously reported approaches are difficult to integrate and the Brillouin gain coefficient is small. We propose here a new approach to achieve giant forward stimulated Brillouin scattering (FSBS) and lasing on chip with double-disk microcavities made of silica glass. By considering the thickness of air gap to tailor optical forces especially radiation pressure in these double-disk microcavities, giant Brillouin gain enhancement can be realized in the intermode FSBS. The numerical simulation results indicate that for double-disk microcavity within the radius range of 50 μm, stimulated Brillouin scattering gain is ten times larger than that of single-disk microcavity up to 74.3 m−1W−1 with Rayleigh acoustic mode and 102 to 103 times larger up to 6361.19 m−1W−1 with symmetric Lamb acoustic mode. Correspondingly, the on-chip pump power threshold of Brillouin lasing can be reduced to 55 μW with the slope efficiency of 8.0%. Our proposed double-disk microcavities offer an effective and simple method to implement Brillouin lasing and can find versatile applications of acousto-optic interaction on all-integrated CMOS compatible chip.

Dry-etched ultrahigh-Q silica microdisk resonators on a silicon chip

We demonstrate the fabrication of ultrahigh quality (Q) factor silica microdisk resonators on a silicon chip by inductively coupled plasma (ICP) etching. We achieve a dry-etched optical microresonator with an intrinsic Q factor as high as 1.94 × 10 8 from a 1-mm-diameter silica microdisk with a thickness of 4 μm. Our work provides a chip-based microresonator platform operating in the ultrahigh-Q region that will be useful in nonlinear photonics such as Brillouin lasers and Kerr microcombs.

Stable self-pulsing regime in a Brillouin ring fiber laser cavity

This study reports that when solving by full integration a set of coupled ordinary differential equations that describe the spatial evolution of the guided pump and Stokes powers caused by stimulated Brillouin scattering in the regime of pump depletion, a structure of regular pulses emerge from the output of a Brillouin laser cavity characterized as a stable self-pulsing regime. The dependence of this self-pulsing mechanism on the laser cavity length, the coupling factor, and the pump power is investigated revealing the existence of three regimes: no lasing, continuous, and self-pulsing. When compared to records in the scientific literature, this is the first time, to the best of the author’s knowledge, that a stable self-pulsing regime is reported theoretically. Furthermore, we also demonstrated the pumping depletion during the formation of the self-pulsing regime. These results provide not only a better understanding of the dynamics of self-pulsing regimes in a fiber laser cavity but also the possibility of unlocking the mechanisms responsible for the formation of stable pulse trains in a Brillouin fiber-ring laser.

Self-stabilized soliton generation in a microresonator through mode-pulled Brillouin lasing.

Reducing the complexity required for starting and maintaining a soliton state has been a major task to fully miniaturize soliton microcombs including the accompanying external operating systems. Here we experimentally examine the generative process of a self-stabilized soliton in which a continuous-wave pump detuned on the thermally stable blue side of a resonance generates a Brillouin lasing signal that relays the pump power to the soliton pulses via intracavity mode-coupling without breaking thermal self-stability. Based on a simple setup consisting of a free-running laser and a microcavity without any external feedback systems by virtue of internal thermal locking, single-soliton pulses of 11 GHz repetition rate were deterministically generated. We demonstrate that the single-soliton pulses can be passively maintained over several days in a laboratory environment with a phase noise performance of -137dBc/Hz at 100 kHz.

Brillouin-Kerr Soliton Frequency Combs in an Optical Microresonator.

By generating a Brillouin laser in an optical microresonator, we realize a soliton Kerr microcomb through exciting the Kerr frequency comb using the generated Brillouin laser in the same cavity. The intracavity Brillouin laser pumping scheme enables us to access the soliton states with a blue-detuned input pump. Because of the ultranarrow linewidth and the low-noise properties of the generated Brillouin laser, the observed soliton microcomb exhibits narrow-linewidth comb lines and stable repetition rate. Also, we demonstrate a low-noise microwave signal with phase noise of -49 dBc/Hz at 10Hz, -130 dBc/Hz at 10kHz, and -149 dBc/Hz at 1MHz offsets for a 10.43GHz carrier with only a free-running input pump. The easy operation of the Brillouin-Kerr soliton microcomb with excellent performance makes our scheme promising for practical applications.

Dynamic vortex mode-switchable erbium-doped Brillouin laser pumped by high-order mode.

We experimentally demonstrated that the transversal vortex modes of an all-fiber erbium-doped Brillouin laser can be dynamically switched by using the high-order mode (HOM) of Brillouin pump (BP), which is used to achieve the oscillation of HOM inside the ring cavity. Core-mode conversion in a few-mode fiber (FMF) between the fundamental mode and HOM is obtained by cascading an acoustically induced fiber grating (AIFG) and a mode selection coupler (MSC) operating at the same wavelength region. Through frequency shift keying (FSK) modulation of the AIFG signal, the output transversal modes can be switched dynamically between LP01 and vortex modes, and the measured purities of output HOM are more than 82%. Moreover, the output Brillouin wavelength can also be tuned via altering the input wavelength of BP and the resonant response of AIFG. We have achieved HOM Brillouin-shifted laser output within the wavelength band from 1545-1560 nm. The output linewidth of the proposed Brillouin laser is less than 4 kHz.

All-optical carrier recovery for self-homodyne detection via injection locked Brillouin laser in whispering-gallery-mode microcavity

We demonstrate comprehensive investigation of the injection locking dynamics of a backscattered Brillouin laser in silica whispering-gallery-mode microcavity. Via injection locking, the Brillouin laser acquires highly correlated phase with the seed laser, enabling ultra-narrow bandwidth, high gain, and coherent optical amplification. Also, for the first time, to the best of our knowledge, the injection locked Brillouin laser is utilized to implement all-optical carrier recovery from coherent optical data signals. We show that by using the injection locked Brillouin laser as a local oscillator for self-homodyne detection, high-quality data receiving can be realized, even without traditional electrical compensations for carrier frequency and phase drifts.

Operation of an optical atomic clock with a Brillouin laser subsystem

Microwave atomic clocks have traditionally served as the 'gold standard' for precision measurements of time and frequency. However, over the past decade, optical atomic clocks1-6 have surpassed the precision of their microwave counterparts by two orders of magnitude or more. Extant optical clocks occupy volumes of more than one cubic metre, and it is a substantial challenge to enable these clocks to operate in field environments, which requires the ruggedization and miniaturization of the atomic reference and clock laser along with their supporting lasers and electronics4,7,8,9. In terms of the clock laser, prior laboratory demonstrations of optical clocks have relied on the exceptional performance gained through stabilization using bulk cavities, which unfortunately necessitates the use of vacuum and also renders the laser susceptible to vibration-induced noise. Here, using a stimulated Brillouin scattering laser subsystem that has a reduced cavity volume and operates without vacuum, we demonstrate a promising component of a portable optical atomic clock architecture. We interrogate a 88Sr+ ion with our stimulated Brillouin scattering laser and achieve a clock exhibiting short-term stability of 3.9×10-14 over one second-an improvement of an order of magnitude over state-of-the-art microwave clocks. This performance increase within a potentially portable system presents a compelling avenue for substantially improving existing technology, such as the global positioning system, and also for enabling the exploration of topics such as geodetic measurements of the Earth, searches for dark matter and investigations into possible long-term variations of fundamental physics constants10-12.

Power threshold reduction and laser efficiency improvement of Brillouin fiber laser based on an As[formula omitted]S[formula omitted] Chalcogenide fiber via a mode field adaptor

A Brillouin fiber laser with low power threshold and high laser efficiency based on a 4.2-m-long As2S3 chalcogenide step-index fiber is presented in this work. Due to the free-space system between the As2S3 and single mode fiber (SMF), a high coupling efficiency is required to reduce the ring cavity loss and laser threshold, and hence improve the laser conversion efficiency. Compared with the lensed fiber and ultrahigh numerical aperture (UHNA) fiber which are commonly used as butt-coupling devices, the mode field adaptor (MFA) employed in this work can better match the mode field diameter and numerical aperture of the As2S3 and SMF, exhibiting a total coupling loss of only 1 dB. A low Brillouin laser threshold of 14 mW is achieved benefiting from the high cavity feedback of 16%. A Stokes power of ∼50 mW is generated for an injected pump power of 120 mW, showing a high laser efficiency of 42%. Furthermore, the Brillouin laser with the MFA butt-coupling exhibits lower relative intensity noise and phase noise and hence narrower laser linewidth than that with the lensed fiber and UHNA fiber butt-coupling. These results suggest the significance of the MFA which can reduce the cavity loss for a Brillouin laser with good performance based on As2S3 chalcogenide fiber.

Dual-frequency laser comprising a single fiber ring cavity for self-injection locking of DFB laser diode and Brillouin lasing.

Low-noise lasers are a powerful tool in precision spectroscopy, displacement measurements, and development of advanced optical atomic clocks. While all applications benefit from lower frequency noise and robust design, some of them also require lasing at two frequencies. Here, we introduce a simple dual-frequency laser leveraging a ring fiber cavity exploited both for self-injection locking of a standard semiconductor distributed feedback (DFB) laser and for generation of Stokes light via stimulated Brillouin scattering. In contrast to the previous laser configurations, the system is supplied by a low-bandwidth active optoelectronic feedback. Importantly, continuous operation of two mutually locked frequencies is provided by self-injection locking, while the active feedback loop is used just to support this regime. The fiber configuration reduces the natural Lorentzian linewidth of light emitted by the laser at pump and Stokes frequencies down to 270 Hz and 110 Hz, respectively, and features a stable 300-Hz-width RF spectrum recorded with beating of two laser outputs. Translating the proposed laser design to integrated photonics will dramatically reduce cost and footprint for many laser applications such as ultra-high capacity fiber and data center networks, atomic clocks, and microwave photonics.

Correlation between Color and Elasticity in Anomia ephippium Shells: Biological Design to Enhance the Mechanical Properties.

Anomia ephippium (Oyster) shell has an inorganic "pseudo nacre" microstructure that is colored (white, yellow, orange, and red) with varying concentrations of organic polyene pigments. Using Brillouin laser light scattering, we measured the elastic constants of A. ephippium and Abalone prismatic and nacre microstructures. We find a direct correlation between the polyene concentration and the measured elastic stiffnesses of A. ephippium shells, suggesting that polyene pigment enhances the shell's primary function of mechanical protection. Further, Young's, bulk, and shear moduli of A. ephippium shells are found to surpass that of ultrastrong Abalone nacre. By studying both microstructures, we demonstrate that pseudo nacre is stiffer than nacre. This work sheds light on the structure-property relation of pseudo nacre and organic constituents that may potentially be a paradigm shift for the future mimicry of super strong biomaterials.

Backscatter-Immune Injection-Locked Brillouin Laser in Silicon

As self-sustained oscillators, lasers possess the unusual ability to spontaneously synchronize. These nonlinear dynamics are the basis for a simple yet powerful stabilization technique known as injection locking, in which a laser's frequency and phase can be controlled by an injected signal. Due to its inherent simplicity and favorable noise characteristics, injection locking has become a workhorse for coherent amplification and high-fidelity signal synthesis in applications ranging from precision atomic spectroscopy to distributed sensing. Within integrated photonics, however, these injection locking dynamics remain relatively untapped--despite significant potential for technological and scientific impact. Here, we demonstrate injection locking in a silicon photonic Brillouin laser for the first time. Injection locking of this monolithic device is remarkably robust, allowing us to tune the laser emission by a significant fraction of the Brillouin gain bandwidth. Harnessing these dynamics, we demonstrate amplification of small signals by more than 23 dB. Moreover, we demonstrate that the injection locking dynamics of this system are inherently nonreciprocal, yielding unidirectional control and back-scatter immunity in an all-silicon system. This device physics opens the door to new strategies for phase noise reduction, low-noise amplification, and back-scatter immunity in silicon photonics.

Photonic Flywheel in a Monolithic Fiber Resonator.

We demonstrate the first compact photonic flywheel with sub-fs time jitter (averaging times up to 10 μs) at the quantum-noise limit of a monolithic fiber resonator. Such quantum-limited performance is accessed through novel two-step pumping scheme for dissipative Kerr soliton generation. Controllable interaction between stimulated Brillouin lasing and Kerr nonlinearity enhances the DKS coherence and mitigates the thermal instability challenge, achieving a remarkable 22-Hz intrinsic comb linewidth and an unprecedented phase noise of -180 dBc/Hz at 945-MHz carrier at free running. The scheme can be generalized to various device platforms for field-deployable precision metrology.

New Stimulated Brillouin Laser with an Induced Cavity

A paradoxical decrease in the generation threshold of high Stokes and anti-Stokes components of stimulated Brillouin scattering in water has been detected for the first time to our knowledge upon the displacement of the caustic of a focused laser beam from the bulk of water to air. The mechanism of generation of components caused by the four-wave mixing on counterpropagating beams when the water surface serves as the mirror of an induced cavity of a stimulated Brillouin laser is discussed. An upper bound R ≪ 0.02 has been obtained for the reflection coefficient R of distributed feedback at stimulated Brillouin scattering in water.

Linewidth enhancement factor in a microcavity Brillouin laser

The linewidth of regenerative oscillators is enhanced by amplitude–phase coupling of the oscillator field [Phys. Rev. 160, 290 (1967)]. In laser oscillators, this effect is well known for its impact on semiconductor laser performance. Here, this coupling is studied in Brillouin lasers. Because their gain is parametric, the coupling and linewidth enhancement are shown to originate from phase mismatch. The theory is confirmed by measurement of linewidth in a microcavity Brillouin laser, and enhancements as large as 50 × are measured. The results show that pump wavelength and device temperature should be carefully selected and controlled to minimize linewidth. More generally, this work provides a new perspective on the linewidth enhancement effect.

Multiwavelength Brillouin Generation in Bismuth-Doped Fiber Laser With Single- and Double-Frequency Spacing

Multiwavelength fiber lasers operating in the 1.3 μm wavelength region are of great interest as they complement existing systems in the conventional optical communication band of 1.55 μm. In this work, a multiwavelength Brillouin fiber laser with single- and double-Brillouin frequency spacings operating in 1.3 μm is proposed and demonstrated using a dispersion compensating fiber (DCF) as the Brillouin gain medium. A bismuth-doped fiber serves as the laser gain medium. At the maximum pump power of 1021 mW and with the Brillouin pump set at 11 dBm, up to 7 Brillouin Stokes lines with a wavelength spacing of 0.074 nm are obtained in the single-spaced configuration. In the case of the double-spaced configuration, 14 Stokes lines are generated with a wavelength spacing of 0.15 nm between the even Stokes lines. By tuning the central wavelength of the Brillouin pump, both laser configurations are wavelength-tunable with a range of 93 nm and 19 nm for the single-spaced and double-spaced Brillouin lasers respectively. This is, to the best of the author's knowledge, the first demonstration of a multiwavelength/Brillouin laser using a bismuth-doped fiber as the laser gain medium.