Laser Noise Research Articles

Optical frequency comb generation using cascaded injection of semiconductor lasers

We study optical frequency comb (OFC) generation using cascaded injection of semiconductor lasers in this work. The OFC generation system is operated in two cascaded optical injection stages. When a master laser optically injects into the first stage with proper injection power and frequency, period-one (P1) dynamics are invoked in an optically injected semiconductor laser of the first stage. Another semiconductor laser in the second stage is then optically injected by the P1 dynamics. With proper injection power adjusted in the second stage, the P1 dynamics are regenerated, and the semiconductor laser relaxation oscillations (ROs) become undamped so that subharmonic oscillations appear. Because a subharmonic oscillation frequency is half of an oscillation frequency of the P1 dynamics, extra optical frequency components appear in the middle of the adjacent optical frequency components of the P1 dynamics, thus signaling OFC generation. The OFC signals exhibit at least 15 comb lines, resulting in a bandwidth greater than 140 GHz. Microwave comb signals are obtained after photodetection, although the microwave linewidth is on the order of a few megahertz because of the semiconductor laser noise. Thus, we propose a cascaded injection-locking scheme to stabilize the P1 dynamics and OFC signals. We have demonstrated pure microwave generations with a linewidth of less than 3 Hz and low phase noise.

High-power quantum-limited 35 MHz photodiode and classical laser noise suppression

To benefit high-power interferometry and the creation of low-noise light sources, we develop a simple lead-compensated photodetector enabling quantum-limited readout from 0.3 to 10 mW and 10 kΩ gain from 85 Hz to 35 MHz, with a noise equivalent power of 9 pW/Hz. Feeding the detector output back to an intensity modulator, we suppress the classical amplitude noise of a commercial 1550 nm fiber laser to the shot noise limit over a bandwidth of 700 Hz–200 kHz, observing no degradation to its (nominally ∼100 Hz) linewidth.

Theoretical Analysis of Phase Noise in Laser With ${1}/{{{f}^{\alpha }}}$ FM Noise for Self-Homodyne Coherent System

Theoretical Analysis of Phase Noise in Laser With ${1}/{{{f}^{\alpha }}}$ FM Noise for Self-Homodyne Coherent System

On prediction of chaotic dynamics in semiconductor lasers by reservoir computing.

Studying the chaotic dynamics of semiconductor lasers is of great importance for their applications in random bit generation and secure communication. While considerable effort has been expended towards investigating these chaotic behaviors through numerical simulations and experiments, the accurate prediction of chaotic dynamics from limited observational data remains a challenge. Recent advancements in machine learning, particularly in reservoir computing, have shown promise in capturing and predicting the complex dynamics of semiconductor lasers. However, existing works on laser chaos predictions often suffer from the need for manual parameter optimization. Moreover, the generalizability of the approach remains to be investigated, i.e., concerning the influences of practical laser inherent noise and measurement noise. To address these challenges, we employ an automated optimization approach, i.e., a genetic algorithm, to select optimal reservoir parameters. This allows efficient training of the reservoir network, enabling the prediction of continuous intensity time series and reconstruction of laser dynamics. Furthermore, the impact of inherent laser noise and measurement noise on the prediction of chaotic dynamics is systematically examined through numerical analysis. Simulation results demonstrate the effectiveness and generalizability of the proposed approach in achieving accurate predictions of chaotic dynamics in semiconductor lasers.

Amplitude noise suppression in Yb:doped NALM oscillators utilizing saturable absorber settings.

Optical frequency combs based on fiber lasers mode-locked (ML) with a nonlinear amplifying loop mirror (NALM) have become the backbone of many cutting-edge applications, ranging from precision spectroscopy to quantum physics. Being extremely precise measurement tools, understanding their passive stability and low-noise operation regimes is vital. While several influences on the laser noise have been studied, many parameters remain poorly understood. Here, we systematically analyze under which preconditions the artificial saturable absorber settings of the laser can be modified during operation without losing mode-locking and the effects on laser noise, the spectrum and the output power. Our results show that it is possible to decrease the amplitude noise (AM noise) of the laser by more than 50 % by simply rotating a wave plate within the laser cavity. Additionally, we discuss differences to a similar effect observed in a NALM-alike laser amplifier and of changing the output coupling. These findings deepen our understanding and capabilities of optimizing the noise performance of ML fiber lasers, enable us to investigate new parameter spaces, and can be used to further optimize the noise performance of the NALM laser design, making it an ideal light source for advanced setups both in research and industry.

Differential phase-diversity electrooptic modulator for cancellation of fiber dispersion and laser noise

Bandwidth and noise are fundamental considerations in all communication and signal processing systems. The group-velocity dispersion of optical fibers creates nulls in their frequency response, limiting the bandwidth and hence the temporal response of communication and signal processing systems. Intensity noise is often the dominant optical noise source for semiconductor lasers in data communication. In this paper, we propose and demonstrate a class of electrooptic modulators that is capable of mitigating both of these problems. The modulator, fabricated in thin-film lithium niobate, simultaneously achieves phase diversity and differential operations. The former compensates for the fiber’s dispersion penalty, while the latter overcomes intensity noise and other common mode fluctuations. Applications of the so-called four-phase electrooptic modulator in time-stretch data acquisition and in optical communication are demonstrated.

Noise Suppression of Nitrogen-Vacancy Magnetometer in Lock-In Detection Method by Using Common Mode Rejection.

Nitrogen-vacancy (NV) centers in diamonds are promising solid-state magnetic sensors with potential applications in power systems, geomagnetic navigation, and diamond NV color center current transformers, in which both high bandwidth and high magnetic field resolution are required. The wide bandwidth requirement often necessitates high laser power, but this induces significant laser fluctuation noise that affects the detection magnetic field resolution severely. Therefore, enhancement of the magnetic field resolution of wide-bandwidth NV center magnetic sensors is highly important because of the reciprocal effects of the bandwidth and magnetic field resolution. In this article, we develop a common mode rejection (CMR) model to eliminate the laser noise effectively. The simulation results show that the noise level of the light-detected magnetic resonance signal is significantly reduced by a factor of 6.2 after applying the CMR technique. After optimization of the laser power and modulation frequency parameters, the optimal system bandwidth was found to be 75 Hz. Simultaneously, the system's detection magnetic field resolution was enhanced significantly, increasing from 4.49 nT/Hz1/2 to 790.8 pT/Hz1/2, which represents an improvement of nearly 5.7 times. This wide-bandwidth, high-magnetic field resolution NV color center magnetic sensor will have applications including power systems, geomagnetic navigation, and diamond NV color center current transformers.

Graphene-Based Hyperbolic Metamaterial Acting as Tunable THz Power Limiter

In this paper, we investigate the possibility of employing a graphene-based hyperbolic metamaterial as a tunable optical power limiter and/or controllable laser noise suppressor for terahertz frequency range. This is the first time that the mentioned functionalities are obtained with a voltage-controlled nonlinear hyperbolic metamaterial utilizing graphene. We believe that such structures, feasible by means of planar deposition techniques, will find practical applications in THz systems requiring optical power limiting.

High stability and low noise laser-diode end-pumped Nd: YAG ceramic passively Q-switched laser at 1123 nm based on a Ti3C2T x -PVA saturable absorber

We report a high repetition frequency, high power stability and low laser noise laser-diode (LD) end-pumped Nd: YAG ceramic passively Q-switched laser at 1123 nm based on a Ti3C2T x -polyvinyl alcohol (PVA) film as a saturable absorber (SA). A Brewster polarizer (BP) and a birefringent crystal (BC) are incorporated to enable frequency selection and filtering for the passively Q-switched 1123 nm pulsed laser to improve the power stability and reduce the noise. When the pump power is 5.1 W, an average output power of 457.9 mW is obtained, corresponding to a repetition frequency of 1.09 MHz, a pulse width of 56 ns, a spectral line width of 0.65 nm, a power instability of ±0.92%, and a laser noise of 0.89%. The successful implementation of the “Ti3C2T x -PVA film passively Q-switching” combined with “frequency selection and filtering of BP + BC” technology path provides a valuable reference for developing pulsed laser with high repetition frequency, high stability and low noise.

MEMS Sensor-Glasses Pair for Real-Time Monitoring of Intraocular Pressure

We present a novel implantable MEMS sensor – readout glasses pair towards the real-time monitoring of intraocular pressure. The overall system comprises i) a diffraction grating interferometric MEMS sensor to be embedded in the cornea and ii) readout glasses embedded with a laser diode, miniaturized aspheric lenses, and a CMOS camera. Owing to the abundance of diffracted orders, the proposed intraocular pressure measuring system offers ±8 degrees of eye tilt tolerance during monitoring via the camera. Furthermore, the use of one or multiple reference gratings adjacent to the sensor mitigates the effects of altering optical power (due to eye motion or laser noise) on the sensor. The design of the proposed device is justified with the analytical modeling of diffracted orders from the pressure sensor and ray-tracing simulations of the readout glasses. Through in-vitro measurements, we demonstrated a measurement range of ΔP = 40 mmHg pressure, with an average deflection sensitivity of 4.06 nm/mmHg and a resolution of 2.5 mmHg. With further development, the proposed system can be used for personalized real-time glaucoma monitoring.

Robust atom optics for Bragg atom interferometry

Multi-photon Bragg diffraction is a powerful method for fast, coherent momentum transfer of atom waves. However, laser noise, Doppler detunings, and cloud expansion limit its efficiency in large momentum transfer (LMT) pulse sequences. We present simulation studies of robust Bragg pulses developed through numerical quantum optimal control. Optimized pulse performance under noise and cloud inhomogeneities is analyzed and compared to analogous Gaussian and adiabatic rapid passage pulses in simulated LMT Mach–Zehnder interferometry sequences. The optimized pulses maintain robust population transfer and phase response over a broader range of noise, resulting in superior contrast in LMT sequences with thermal atom clouds and intensity inhomogeneities. Large optimized LMT sequences use lower pulse area than Gaussian pulses, making them less susceptible to spontaneous emission loss. The optimized sequences maintain over five times better contrast with tens of momentum separation and offer more improvement with greater LMT. Such pulses could allow operation of Bragg atom interferometers with unprecedented sensitivity, improved contrast, and hotter atom sources.

Amplitude and phase noise in two-membrane cavity optomechanics

Cavity optomechanics is a suitable field to explore quantum effects on macroscopic objects and develop quantum technology applications. A perfect control of the laser noise is required to operate the system in such extreme conditions necessary to reach the quantum regime. In this paper, we consider a Fabry–Perót cavity, driven by two laser fields, with two partially reflective SiN membranes inside it. We describe the effects of amplitude and phase noise on the laser introducing two additional noise terms in the Langevin equations of the system’s dynamics. Experimentally, we add an artificial source of noise on the laser. We calibrate the intensity of the noise, inject it into the system, and check the validity of the theoretical model. This procedure provides an accurate description of the effects of a noisy laser in the optomechanical setup and allows for quantifying the amount of noise.

Non-Hermitian optics and photonics: from classical to quantum

Non-Hermitian optics is a burgeoning field at the intersection of quantum physics, electrodynamics, and nanophotonics. It provides a new perspective of the role of gain and loss in optical systems. Leveraging the advanced designs inspired by non-Hermitian physics, classical optical platforms have been widely investigated to unveil novel physical concepts, such as parity-time symmetry and exceptional points, which have no counterparts in the conventional Hermitian settings. These investigations have yielded a plethora of new phenomena in optical wave scattering, optical sensing, and nonlinear optical processes. Non-Hermitian effects also have a profound impact on the lasing behaviors in the semiclassical framework of lasers, allowing for novel ways to engineer single-mode lasers, chiral laser emission, laser noise, linewidth, etc. Furthermore, over recent years, there has been increasing interest in the explorations of non-Hermitian physics in quantum optics, which addresses photon statistics, entanglement, decoherence, and quantum sensing in non-Hermitian systems. In this review, we review the most recent theoretical and experimental advances in non-Hermitian optics and photonics, covering the significant progress in both classical and quantum optics regimes.

Stochastic Approach to the Quantum Noise of a Single-Emitter Nanolaser.

It is shown that the quantum intensity noise of a single-emitter nanolaser can be accurately computed by adopting a stochastic interpretation of the standard rate equation model. The only assumption made is that the emitter excitation and photon number are stochastic variables with integer values. This extends the validity of rate equations beyond the mean-field limit and avoids using the standard Langevin approach, which is shown to fail for few emitters. The model is validated by comparison to full quantum simulations of the relative intensity noise and second-order intensity correlation function, g^{(2)}(0). Surprisingly, even when the full quantum model displays vacuum Rabi oscillations, which are not accounted for by rate equations, the intensity quantum noise is correctly predicted by the stochastic approach. Adopting a simple discretization of the emitter and photon populations, thus, goes a long way in describing quantum noise in lasers. Besides providing a versatile and easy-to-use tool for modeling emerging nanolasers, these results provide insight into the fundamental nature of quantum noise in lasers.

Revisiting time delay interferometry for unequal-arm LISA and TAIJI

Three spacecraft of LISA/TAIJI mission follow their respective geodesic trajectories, and their interferometric arms are unequal and time-varying due to orbital dynamics. Time-delay interferometry (TDI) is proposed to suppress the laser frequency noise caused by the unequal-arm. By employing the numerical orbit, we investigate the sensitivity of the first-generation TDI configurations and their corresponding optimal A, E, and T channels. The sensitivities of T channels from Michelson and Monitor/Beacon configurations diverge from the equal-arm case in frequencies lower than 10 mHz, and their performances vary with the inequality of the arm lengths. The mismatches of the laser beam paths are evaluated in a dynamic case, and the residual laser noise in the first-generation TDI could not satisfy the mission requirement.

Theoretical analysis of relative intensity noise in semiconductor QD lasers

Theoretical analysis of relative intensity noise in semiconductor QD lasers

140-Hz Narrow-Linewidth Brillouin/Erbium- Ytterbium Fiber Laser

We demonstrate an ultra-narrow-linewidth Brillouin/Erbium-Ytterbium co-doped fiber ring laser, which uses a length of 80-cm Erbium-Ytterbium co-doped fiber as both the Brillouin gain and linear gain media. The 976-nm pump threshold is only 80 mW when the Brillouin pump power is 20 mW. The output power of this laser reaches about 200 mW. The laser linewidth is as narrow as 140 Hz. The relative intensity noise of the fiber laser is -145 dB/Hz. The phase noise at 1 kHz is as low as to -107 dB re rad/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> (1-m optical path difference). Moreover, the 140-Hz-linewidth Brillouin laser light is transferred from a 2-MHz-linewidth Brillouin pump light. This fiber laser presents outstanding linewidth-narrowing characteristic. It presents many potential applications in coherent communications, optical fiber sensors, and etc.

Internal temperature determination for laser noise cancellers

Noise cancellers of the type described by Hobbs [Appl. Opt. 36, 903 (1997)], used in dual-beam laser spectroscopy, provide an analog logarithmic output that is monotonic in, but not linearly related to, the sample absorbance. If the goal of a spectroscopic experiment is to determine an absolute absorbance or a spectral lineshape, rather than simply a line location, the conversion function between detector output and absorbance needs to be known. That function depends on the internal temperature of the transistors used in the device’s current splitter, and an incorrect assumption about the temperature leads to errors in absorbance or distortions in the extracted lineshape. Neither the original design nor a commercial implementation (Newport Nirvana) gives a direct indication of the temperature. A simple laboratory procedure for determining the transistor temperature is described.

Impact of combinations of time-delay interferometry channels on stochastic gravitational wave background detection

The method of time-delay interferometry (TDI) is proposed to cancel the laser noise in space-borne gravitational-wave detectors. Among all different TDI combinations, the most commonly used ones are the orthogonal channels A, E, and T, where A and E are signal-sensitive and T is signal-insensitive. Meanwhile, for the detection of stochastic gravitational-wave background, one needs to introduce the overlap reduction function to characterize the correlation between channels. For the calculation of overlap reduction function, it is often convenient to work in the low-frequency approximation, and assuming the equal-arm Michelson channels. However, if one wishes to work on the overlap reduction function of $\mathrm{A}/\mathrm{E}$ channels, then the low-frequency approximation fails. We derive the exact form of overlap reduction function for $\mathrm{A}/\mathrm{E}$ channels. Based on the overlap reduction function, we calculate the sensitivity curves of TianQin, TianQin $\mathrm{I}+\mathrm{II}$, and $\mathrm{TianQin}+\text{LISA}$. We conclude that the detection sensitivity calculated with $\mathrm{A}/\mathrm{E}$ channels is mostly consistent with that obtained from the equal-arm Michelson channels.

Self-Injection Locked Silica External Cavity Narrow Linewidth Laser

A silica-based external cavity narrow linewidth laser is fabricated and experimentally demonstrated based on a commercial silica platform. An add-drop microring resonator and a 2×2 directional coupler in the silica chip form a wavelength-dependent and self-injection-locked external cavity. The linewidth-suppressing effect of the external cavity is theoretically calculated based on the chirp reduction theory, which shows that a long external cavity length at the resonant wavelength can be used to suppress the noise of a free-running laser. In the self-injection locked state, the measured intrinsic linewidth of the fabricated external cavity laser is 27 Hz, which is greatly reduced compared to the 49.7-kHz linewidth of the free-running state. The frequency stability is also measured to be improved by an order of magnitude from 4.52 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−8</sup> to 9.07 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−10</sup> at 1 s averaging time. The proposed narrow-linewidth laser shows the potential for massive production and can be used in various applications such as integrated microwave photonics, LIDAR, high-resolution metrology, and satellite communications.