Narrow-linewidth Light Source Research Articles

Precision spectroscopic measurements of few-electron atomic systems in extreme ultraviolet region

<sec>Precision spectroscopic measurements on the few-electron atomic systems have attracted much attention because they shed light on important topics such as the “proton radius puzzle” and testing quantum electrodynamics (QED). However, many important transitions of few-electron atomic systems are located in the vacuum/extreme ultraviolet region. Lack of a suitable narrow linewidth light source is one of the main reasons that hinder the further improvement of the spectral resolution.</sec><sec>Recently, narrow linewidth extreme ultraviolet (XUV) light sources based on high harmonic processes in rare gases have opened up new opportunities for precision measurements of these transitions. The recently implemented XUV comb has a shortest wavelength of about 12 nm, a maximum power of milliwatts, and a linewidth of about 0.3 MHz, making it an ideal tool for precision measurements in the XUV band. At the same time, the Ramsey comb in the XUV band can achieve a spectral resolution of the kHz range, and may operate throughout the entire XUV band.</sec><sec>With these useful tools, direct frequency spectroscopy and Ramsey comb spectroscopy in the XUV region are developed, and precision spectroscopic measurements of few-electron atomic systems with these methods are becoming a hot topic in cutting-edge science. In this paper, we provide an overview of the current status and the progress of relevant researches, both experimentally and theoretically, and discuss the opportunities for relevant important transitions in the extreme ultraviolet band.</sec>

Intra-cavity frequency-doubled VECSEL system for narrow linewidth Rydberg EIT spectroscopy.

High-power, narrow-linewidth light sources in the visible and UV spectra are in growing demand, particularly as quantum information and sensing research proliferates. Vertical external-cavity surface-emitting lasers (VECSELs) with intra-cavity frequency conversion are emerging as an attractive platform to fill these needs. Using such a device, we demonstrate 3.5 MHz full-width half-maximum Rydberg-state spectroscopy via electromagnetically induced transparency (EIT). The laser's 690 mW of output power at a wavelength of 475 nm enables large Rabi frequencies and strong signal-to-noise ratio in shorter measurement times. In addition, we characterize the frequency stability of the VECSEL using the delayed self-heterodyne technique and direct comparison with a commercial external-cavity diode laser (ECDL). We measure the pre-doubled light's Lorentzian linewidth to be 2π × 5.3(2) kHz, and the total linewidth to be 2π × 23(2) kHz. These measurements provide evidence that intra-cavity frequency-doubled VECSELs can perform precision spectroscopy at and below the MHz level, and are a promising tool for contemporary, and future, quantum technologies.

Single-frequency fiber Fabry-Perot Brillouin laser.

We demonstrate single-frequency stimulated Brillouin lasing in short fiber Fabry-Perot resonators. A sub-milliwatt threshold for lasing is observed in resonators with high quality factors of ∼1.5 × 108 and effective resonator lengths as short as ∼5 mm. The strong dispersion of fiber Bragg gratings results in unequal frequency separations for neighboring pairs of longitudinal modes with separation differences larger than the Brillouin gain bandwidth, thereby avoiding cascaded lasing. Our achievement will enable compact, robust, efficient narrow-linewidth light sources.

Spectral synthesis of multimode lasers to the Fourier limit in integrated Fabry–Perot diamond resonators

Fourier-limited nanosecond pulses featuring narrow spectral bandwidths are required for applications in spectroscopy, sensing, and quantum optics. Here, we demonstrate a direct and simple route for the generation of single-frequency light relying on phonon-resonant Raman interactions within a monolithic diamond resonator. The technique enables the production of nearly Fourier-limited nanosecond optical pulses (15 ns), with an overall spectral bandwidth of down to 180 MHz, which is nearly two orders of magnitude narrower than the pump laser linewidth used (12 GHz). The power conversion efficiency was 47%, yielding a power spectral brightness enhancement of > --> 50 × compared to the pump. Our results pave the way to the integration of pulsed widely tunable, power scalable, narrow linewidth light sources into integrated photonic platforms. Furthermore, the device does not need elaborate mechanical feedback loops for cavity length or frequency stabilization, or any additional optical components.

Large dynamic-range fiber Bragg grating sensor system for acoustic emission detection.

A distributed feedback (DFB) fiber laser and fiber Bragg gratings (FBGs) are configured to demodulate the wavelength shifts of FBG dynamic strain sensors. The FBG sensors act as sensing units to detect the dynamic strain and the demodulators while the DFB fiber laser only acts as a narrow-linewidth light source. As the reflective spectrum of the FBG sensor changes due to dynamic strains, the output is subsequently converted into a corresponding intensity change and detected directly by a photodetector. The 0.2 nm linewidth FBG sensor can detect the impact signal with a frequency of up to 300 kHz with a maximum of 29.17 µɛ, which is comparable with the detecting result of the piezoelectric transducer sensor. Moreover, the directional response of the FBG sensor is maximized when the direction of acoustic wave propagation is parallel to the optical fiber. The relation between the sensitivity and the FBG spectrum linewidth is presented, and the detectable strain range versus different FBG linewidths is also discussed.

Waveguide external cavity narrow linewidth semiconductor lasers

Narrow linewidth light source is a prerequisite for high-performance coherent optical communication and sensing. Waveguide-based external cavity narrow linewidth semiconductor lasers (WEC-NLSLs) have become a competitive and attractive candidate for many coherent applications due to their small size, volume, low energy consumption, low cost and the ability to integrate with other optical components. In this paper, we present an overview of WEC-NLSLs from their required technologies to the state-of-the-art progress. Moreover, we highlight the common problems occurring to current WEC-NLSLs and show the possible approaches to resolving the issues. Finally, we present the possible development directions for the next phase and hope this review will be beneficial to the advancements of WEC-NLSLs.

Nanophotonic phase noise filter in silicon

Narrow-linewidth light sources have far-reaching applications from communication1 to metrology2–4. Benchtop linewidth reduction methods such as feedback5,6 and feed-forward7,8 schemes have been used to reduce the linewidth of lasers. The feedback scheme typically has a limited bandwidth and depends on the laser characteristics and the feed-forward scheme is highly sensitive to gain and delay mismatches. Here, we report the demonstration of an integrated nanophotonic phase noise filter, which can be placed after a low-cost laser to significantly suppress its phase noise independent of the light source. The hybrid-integrated electronic–photonic system measures and suppresses the phase noise of the input light using an electronic–photonic loop without interacting with the light source. Using the integrated phase noise filter, laser linewidth reduction from 2.55 MHz to 4 kHz and from 200 kHz to 320 Hz is demonstrated. The silicon photonic and complementary metal–oxide–semiconductor (CMOS) electronic chips were hybrid-integrated within a footprint of 3 mm2. An optoelectronic device that measures and suppresses the phase noise of a source has been realized in an integrated silicon platform.

Widely tunable narrow-linewidth 1.5 μm light source based on a monolithically integrated quantum dot laser array

A monolithically integrated widely tunable narrow-linewidth light source was realized on an InP-based quantum dot (QD) gain material. The quasi zero-dimensional nature of QDs and the resulting low linewidth enhancement factor enabled standalone distributed feedback (DFB) lasers with intrinsic linewidths as low as 110 kHz. An integrated device comprising four DFB lasers with on-chip micro-heaters, a 3 dB-coupler network, and a semiconductor optical amplifier (SOA), which covers the entire C+ telecom band, exhibits a linewidth of below 200 kHz independent of the SOA operation current.

基于MgO∶PPLN晶体差频产生的宽调谐中红外连续激光光源

the continuous;wave mid;infrared radiation (mid;ir) was experimentally obtained by difference frequency quasi;phase;matching in a mgo;doped periodically poled linbo3crystal (mgo:ppln), which the narrow linewidth light sources with 1083 nm and 1550 nm were used as pump light and signal light, respectively. moreover, the multiple mid;ir wavelengths were realized by adjusting the signal wavelength and using the temperature controlling on a mgo:ppln. the wavelength tuning region is around 3547.6 nm to 3629.1 nm. a maximum mid;infrared radiation power of 3.2 mw at 3597.0 nm is generated when the optical power of signal and pump lights are amplified to 3.5 w and 2.8 w respectively. the power jitter of mid;infrared output is less than ±1.6% after along time test recording. this study can be used as a reference for the design and development of narrow line width multi;wavelength continuous;wave infrared light source. © 2016, science press. all right reserved.

Enhancement for Φ-OTDR performance by using narrow linewidth light source and signal processing

In order to enhance the signal-to-noise-ratio of a distributed acoustic sensing system based on phase-sensitive optical time-domain reflectometry (Φ-OTDR), we have proposed a combination of segmented unwrapping algorithm, averaging estimation of phase difference, and infinite impulse response (IIR) filtering method. The enhancement of signal quality is numerically demonstrated. Moreover, we have studied the influence resulted from the light source noise on the Φ-OTDR performance. The result has shown that when the linewidth of light source used in the Φ-OTDR system is narrower, the performance of the system is better. In a word, such a Φ-OTDR system could obtain higher quality demodulated signals when the narrower linewidth light source is chosen and the method of averaging estimation phase difference is used.

Narrow-linewidth light source for a coherent Raman transfer of ultracold molecules

We describe a tunable two-color CW light source sufficient for realizing a coherent Raman transfer between two molecular states that are more than 0.5 eV (120 THz) apart. The simultaneous frequency stabilization of 901 nm and 655 nm light was achieved by locking diode lasers to a single ultralow expansion cavity with dual wavelengths coating. By utilizing offset-locking and optical phase-locked loop (OPLL), we ensured a large mode-hop free tuning range (> 2 GHz). The obtained short term linewidth (<10 Hz) and the linear drift of frequency (65 mHz/s) were both sufficient to eliminate the influence of laser linewidths on the efficiency of coherent Raman transition.

Dual-wavelength narrow-linewidth light source with ultranarrow wavelength spacing based on the pump-induced thermal effects in an Er-Yb-codoped distributed-Bragg-reflector fiber laser

A dual-wavelength narrow-linewidth laser system, with ultranarrow wavelength spacing, is proposed and demonstrated. The operation principle of the laser system is based on the pump-induced thermal effects of the Er-Yb-doped fiber distributed Bragg reflector (DBR) laser. We designed and constructed a common Er-Yb-doped DBR fiber laser with proper parameters. With the pump power of the DBR laser increasing, the Bragg wavelengths and the bandwidths of the two gratings will change unequally. When the laser is pumped with 45 mW, we obtain stable dual-wavelength lasing with a 3-dB bandwidth of 0.014 nm and a wavelength spacing of 0.055 nm.

A fiber depolarizer using polarization beam splitter loop structure for narrow linewidth light source

A new fiber depolarizer employing a polarization beam splitter loop structure is proposed and demonstrated. The depolarizer is devised for broad-band operation and the depolarization of narrow linewidth light source without any help of polarization controllers or Faraday rotator mirrors. A polarizing method is developed that shows good performance without polarization control unit. Therefore, the proposed depolarizer can be cost-effective and easily configured. From experiments, low output degree of polarization less than 10% is obtained for a narrow linewidth light source.

Microring and microdisk optical resonators using silicon nanocrystals and erbium prepared using silicon technology

A methodology for the integration of narrow-linewidth light sources monolithically onto silicon using silicon process technology is presented. Microcavity resonator based narrow-linewidth light sources were designed and modeled using the 3-D full-wave finite-difference time-domain (FDTD) method of solving Maxwell’s equations. The microcavity confines light to a small modal volume by resonant recirculation in a structure with low roundtrip optical loss. The resonators were formed in close proximity to waveguides used for evanescent-wave coupling of light out of the microcavity. Waveguides using Si-nanocrystals in SiO 2 are difficult to couple to planar microdisks because the mode extends deep into the oxide, whereas simulations show that microresonators using SiN x can. The coupling efficiency between the resonator and the single-mode waveguides was optimized by varying the gap size and the waveguide width and thickness. Luminescence from silicon nanoparticles in both SiO 2 and SiN x films was studied. Process optimization for forming Si nanoparticles in SiO 2 or SiN x including the effects of hydrogen annealing and the preparation of SiN x films with excess Si by various techniques (CVD and Si ion implantation) was performed. High-index-contrast microcavity resonators were fabricated using SiN x on SiO 2 with silicon nanoparticles and imaged using atomic force microscopy. The structures include microdisk and microring cavities doped with silicon nanoparticles with and without erbium.

A finesse-enhanced Er-doped-fiber ring resonator

A two-coupler-type Er-doped-fiber ring resonator that compensates for the round-trip optical loss by optical amplification is proposed. Also proposed is a mode-filtered heterodyne method for resonant-linewidth measurements which does not demand narrow-linewidth light sources, but uses the beat noise between two uncorrelated lights filtered by the resonator passband. With this method, a finesse >or=500 and a resonant linewidth >

High-power pulsed dye laser with Fourier-limited bandwidth

A high-peak-power, narrow-linewidth light source with a homogeneous beam profile has been constructed by modifications to a commercially available pulsed-dye-laser system. Output pulses of up to 10 mJ were generated with linewidths of about 50 MHz for 12-nsec pulses. The pulse-to-pulse frequency stability was better than the linewidth, and the center frequency could be scanned over a frequency range of 142.5 GHz at a wavelength of 600 nm. The performance of the system was demonstrated by observing the 6s2 1S0–6s7s1S0 transition in atomic mercury at 2λ = 312.8 nm and the 6s2S1/2–8s2S1/2 transition in atomic gold at 2λ = 308.9 nm using up to 1 mJ of frequency-doubled output for two-photon nonlinear absorption spectroscopy. The lifetimes of both excited states, the magnetic hyperfine splitting of the 8s2S1/2 state in gold, and the isotope shift of the 6s7s1S0 state of mercury were determined.