Showing papers on "Laser linewidth published in 2021"
TL;DR: In this article, a high Q factor of 260 million was achieved in an electrically pumped integrated laser with a corresponding short-term linewidth of 12'Hz and the same configuration was shown to relieve the dispersion requirements for microcomb generation that have handicapped certain nonlinear platforms.
Abstract: Driven by narrow-linewidth bench-top lasers, coherent optical systems spanning optical communications, metrology and sensing provide unrivalled performance To transfer these capabilities from the laboratory to the real world, a key missing ingredient is a mass-produced integrated laser with superior coherence Here, we bridge conventional semiconductor lasers and coherent optical systems using CMOS-foundry-fabricated microresonators with a high Q factor of over 260 million and finesse over 42,000 A five-orders-of-magnitude noise reduction in the pump laser is demonstrated, enabling a frequency noise of 02 Hz2 Hz−1 to be achieved in an electrically pumped integrated laser, with a corresponding short-term linewidth of 12 Hz Moreover, the same configuration is shown to relieve the dispersion requirements for microcomb generation that have handicapped certain nonlinear platforms The simultaneous realization of this high Q factor, highly coherent lasers and frequency combs using foundry-based technologies paves the way for volume manufacturing of a wide range of coherent optical systems Using CMOS-ready ultra-high-Q microresonators, a highly coherent electrically pumped integrated laser with frequency noise of 02 Hz2 Hz−1, corresponding to a short-term linewidth of 12 Hz, is demonstrated The device configuration is also found to relieve the dispersion requirements for microcomb generation that have limited certain nonlinear platforms
235 citations
TL;DR: In this article, the authors developed an original theoretical model of the laser self-injection locking to a nonlinear microresonator, and constructed state-of-the-art hybrid integrated soliton microcombs with electronically detectable repetition rate of 30 GHz and 35 GHz.
Abstract: Soliton microcombs constitute chip-scale optical frequency combs, and have the potential to impact a myriad of applications from frequency synthesis and telecommunications to astronomy. The demonstration of soliton formation via self-injection locking of the pump laser to the microresonator has significantly relaxed the requirement on the external driving lasers. Yet to date, the nonlinear dynamics of this process has not been fully understood. Here, we develop an original theoretical model of the laser self-injection locking to a nonlinear microresonator, i.e., nonlinear self-injection locking, and construct state-of-the-art hybrid integrated soliton microcombs with electronically detectable repetition rate of 30 GHz and 35 GHz, consisting of a DFB laser butt-coupled to a silicon nitride microresonator chip. We reveal that the microresonator's Kerr nonlinearity significantly modifies the laser diode behavior and the locking dynamics, forcing laser emission frequency to be red-detuned. A novel technique to study the soliton formation dynamics as well as the repetition rate evolution in real-time uncover non-trivial features of the soliton self-injection locking, including soliton generation at both directions of the diode current sweep. Our findings provide the guidelines to build electrically driven integrated microcomb devices that employ full control of the rich dynamics of laser self-injection locking, key for future deployment of microcombs for system applications.
61 citations
TL;DR: In this article, a bound state in the continuum based on Fano interference is proposed to quench quantum fluctuations, which can effectively quench the effect of spontaneous emission in a small laser.
Abstract: It is an important challenge to reduce the power consumption and size of lasers, but progress has been impeded by quantum noise overwhelming the coherent radiation at reduced power levels. Thus, despite considerable progress in microscale and nanoscale lasers, such as photonic crystal lasers, metallic lasers and plasmonic lasers, the coherence length remains very limited. Here we show that a bound state in the continuum based on Fano interference can effectively quench quantum fluctuations. Although fragile in nature, this unusual state redistributes photons such that the effect of spontaneous emission is suppressed. Based on this concept, we experimentally demonstrate a microscopic laser with a linewidth that is more than 20 times smaller than existing microscopic lasers and show that further reduction by several orders of magnitude is feasible. These findings pave the way for numerous applications of microscopic lasers and point to new opportunities beyond photonics. Quantum noise is suppressed by a bound state in the continuum (BIC) approach, enabling a microlaser with narrow linewidth compared to other small lasers.
56 citations
TL;DR: In this article, the authors self-injection-lock a diode laser to a 1.41 m long, ultra-high Q integrated resonator, achieving a Lorentzian linewidth below 40 mHz.
Abstract: We self-injection-lock a diode laser to a 1.41 m long, ultra-high Q integrated resonator. The hybrid integrated laser reaches a frequency noise floor of 0.006Hz2/Hz at 4 MHz offset, corresponding to a Lorentzian linewidth below 40 mHz-a record among semiconductor lasers. It also exhibits exceptional stability at low-offset frequencies, with frequency noise of 200Hz2/Hz at 100 Hz offset. Such performance, realized in a system comprised entirely of integrated photonic chips, marks a milestone in the development of integrated photonics; and, for the first time, to the best of our knowledge, exceeds the frequency noise performance of commercially available, high-performance fiber lasers.
56 citations
TL;DR: In this article, a 1-mol% erbium-doped lithium niobate crystal and its LNOI on a silicon substrate was developed and a 1.05×105-nm laser emission at ∼1530 and ∼1560 nm (linewidth 0.12 nm) was demonstrated with 974- and 1460-nm pumping, with the latter having better thermal stability.
Abstract: The commercialization of lithium niobate on insulator (LNOI) wafer has resulted in significant on-chip photonic integration application owing to its remarkable photonic, acousto-optic, electro-optic, and piezoelectric nature. In recent years, a variety of high-performance on-chip LNOI-based photonic devices have been realized. In this study, we developed a 1-mol% erbium-doped lithium niobate crystal and its LNOI on a silicon substrate and fabricated an erbium-doped LNOI microdisk with high quality factor (∼ 1.05×105). C-band laser emission at ∼1530 and ∼1560 nm (linewidth 0.12 nm) from the high-Q erbium-doped LNOI microdisk was demonstrated with 974- and 1460-nm pumping, with the latter having better thermal stability. This microlaser would play an important role in the photonic integrated circuits of the lithium niobate platform.
44 citations
TL;DR: In this article, the authors report high performance laser on SiN with tens of milliwatts output power through the SiN waveguide and sub-kHz fundamental linewidth, addressing all the aforementioned issues.
Abstract: Silicon nitride (SiN) waveguides with ultra-low optical loss enable integrated photonic applications including low noise, narrow linewidth lasers, chip-scale nonlinear photonics, and microwave photonics. Lasers are key components to SiN photonic integrated circuits (PICs), but are difficult to fully integrate with low-index SiN waveguides due to their large mismatch with the high-index III-V gain materials. The recent demonstration of multilayer heterogeneous integration provides a practical solution and enabled the first-generation of lasers fully integrated with SiN waveguides. However, a laser with high device yield and high output power at telecommunication wavelengths, where photonics applications are clustered, is still missing, hindered by large mode transition loss, non-optimized cavity design, and a complicated fabrication process. Here, we report high-performance lasers on SiN with tens of milliwatts output power through the SiN waveguide and sub-kHz fundamental linewidth, addressing all the aforementioned issues. We also show Hertz-level fundamental linewidth lasers are achievable with the developed integration techniques. These lasers, together with high-Q SiN resonators, mark a milestone towards a fully integrated low-noise silicon nitride photonics platform. This laser should find potential applications in LIDAR, microwave photonics and coherent optical communications.
42 citations
TL;DR: In this paper, a planar microcavity with only one resonant mode, which fitted with the CDs' ASE peak, was constructed, which produced a solid state laser with a single longitudinal mode, a linewidth of 0.14 nm and a signal-to-noise ratio of 14.8 dB (Q∼4600).
Abstract: Miniaturized solid-state lasers with a single longitudinal mode are vital for various photonic applications. Here we prepare red-emissive carbon dots (CDs) with a photoluminescence quantum yield (PLQY) of 65.5 % by combining graphitic nitrogen doping and surface modification. High-concentration doping alters the CDs' emission from blue to red, while the electron-donating groups and polymer coating on their surfaces improve the PLQY and photostability. The CDs exhibit excellent stimulated emission characteristics, with a low threshold of amplified spontaneous emission (ASE) and long gain lifetime. A planar microcavity with only one resonant mode, which fitted with the CDs' ASE peak, was constructed. Combining the CDs and microcavity produced a solid-state laser with a single longitudinal mode, a linewidth of 0.14 nm and a signal-to-noise ratio of 14.8 dB (Q∼4600). Our results will aid the development of colorful solid-state micro/nano lasers with potential use in practical photonics.
41 citations
Posted Content•
TL;DR: In this article, a high-power transmitter consisting of an electrically-pumped laser integrated with a 50 GHz modulator is demonstrated on a TFLN platform with up to 60 mW of optical power in the waveguide.
Abstract: Integrated thin-film lithium niobate (TFLN) photonics has emerged as a promising platform for realization of high-performance chip-scale optical systems. Of particular importance are TFLN electro-optic modulators featuring high-linearity, low driving voltage and lowpropagation loss. However, fully integrated system requires integration of high power, low noise, and narrow linewidth lasers on TFLN chip. Here we achieve this goal, and demonstrate integrated high-power lasers on TFLN platform with up to 60 mW of optical power in the waveguides. We use this platform to realize a highpower transmitter consisting an electrically-pumped laser integrated with a 50 GHz modulator.
40 citations
TL;DR: In this paper, an on-chip single-mode microlaser with a low threshold fabricated on erbium doped lithium-niobate-on-insulator (LNOI) was reported.
Abstract: We report an on-chip single-mode microlaser with a low threshold fabricated on erbium doped lithium-niobate-on-insulator (LNOI). The single-mode laser emission at 1550.5 nm wavelength is generated in a coupled microdisk via the inverse Vernier effect at room temperature, when pumping the resonator at 977.7 nm wavelength. A threshold pump power as low as 200 μW is demonstrated due to the high quality factor above 106. Moreover, the measured linewidth of the microlaser reaches 348 kHz without discounting the broadening caused by the utilization of optical amplifiers, which is, to our knowledge, the best result in LNOI microlasers. Such a single-mode microlaser lithographically fabricated on chip is in high demand by the photonics community.
39 citations
TL;DR: In this paper, a light trap design for non-resonant laser based on a spherical scattering cavity with a small entrance was proposed to achieve efficient and directional laser emission using a porous Nd3+:YAG ceramic.
Abstract: Non-resonant lasers exhibit the potential for stable and consistent narrowband light sources. Furthermore, non-resonant lasers do not require well-defined optics, and thus has considerably diversified the available types of laser gain materials including powders, films, and turbid ceramics. Despite these intrinsic advantages, the practical applications of non-resonant lasers have been limited so far, mainly because of their low power efficiency and omnidirectional emission. To overcome these limitations, here we propose a light trap design for non-resonant lasers based on a spherical scattering cavity with a small entrance. Using a porous Nd3+:YAG ceramic, directional laser emission could be observed with significant enhancements in the slope efficiency and linewidth (down to 32 pm). A theoretical model is also developed to describe and predict the operation characteristics of proposed non-resonant laser. Non-resonant lasers have many advantages since the allow for a diverse set of architectures and gain media, but their application is limited due to their low directionality and efficiency. Here, the authors present a scattering cavity laser with a single hole to achieve efficient and directional emission.
37 citations
TL;DR: In this paper, the first visible light photonic integrated Stimulated Brillouin scattering (SBS) laser was demonstrated at 674 nm to address the 88Sr+ optical clock transition.
Abstract: Narrow linewidth visible light lasers are critical for atomic, molecular and optical (AMO) applications including atomic clocks, quantum computing, atomic and molecular spectroscopy, and sensing. Historically, such lasers are implemented at the tabletop scale, using semiconductor lasers stabilized to large optical reference cavities. Photonic integration of high spectral-purity visible light sources will enable experiments to increase in complexity and scale. Stimulated Brillouin scattering (SBS) is a promising approach to realize highly coherent on-chip visible light laser emission. While progress has been made on integrated SBS lasers at telecommunications wavelengths, barriers have existed to translate this performance to the visible, namely the realization of Brillouin-active waveguides in ultra-low optical loss photonics. We have overcome this barrier, demonstrating the first visible light photonic integrated SBS laser, which operates at 674 nm to address the 88Sr+ optical clock transition. To guide the laser design, we use a combination of multi-physics simulation and Brillouin spectroscopy in a 2 meter spiral waveguide to identify the 25.110 GHz first order Stokes frequency shift and 290 MHz gain bandwidth. The laser is implemented in an 8.9 mm radius silicon nitride all-waveguide resonator with 1.09 dB per meter loss and Q of 55.4 Million. Lasing is demonstrated, with an on-chip 14.7 mW threshold, a 45% slope efficiency, and linewidth narrowing as the pump is increased from below threshold to 269 Hz. To illustrate the wavelength flexibility of this design, we also demonstrate lasing at 698 nm, the wavelength for the optical clock transition in neutral strontium. This demonstration of a waveguide-based, photonic integrated SBS laser that operates in the visible, and the reduced size and sensitivity to environmental disturbances, shows promise for diverse AMO applications.
TL;DR: In this paper, the authors leverage the ultra-low losses of silicon-nitride waveguides to demonstrate a heterogeneously integrated III-V-on-silicon-nitrite passively mode-locked laser with a narrow 755 MHz line spacing, a radio frequency linewidth of 1 Hz and an optical linearewidth below 200 kHz.
Abstract: Generating optical combs in a small form factor is of utmost importance for a wide range of applications such as datacom, LIDAR, and spectroscopy. Electrically powered mode-locked diode lasers provide combs with a high conversion efficiency, while simultaneously allowing for a dense spectrum of lines. In recent years, a number of integrated chip scale mode-locked lasers have been demonstrated. However, thus far these devices suffer from significant linear and nonlinear losses in the passive cavity, limiting the attainable cavity size and noise performance, eventually inhibiting their application scope. Here, we leverage the ultra-low losses of silicon-nitride waveguides to demonstrate a heterogeneously integrated III-V-on-silicon-nitride passively mode-locked laser with a narrow 755 MHz line spacing, a radio frequency linewidth of 1 Hz and an optical linewidth below 200 kHz. Moreover, these comb sources are fabricated with wafer scale technology, hence enabling low-cost and high volume manufacturable devices.
TL;DR: In this article, a compound-cavity-based six-wavelength-switchable single-longitudinal-mode (SLM) thulium-doped fiber laser (TDFL) with a homemade polarization-maintaining sampled fiber Bragg grating (PM-SFBG) is proposed and demonstrated.
Abstract: A compound-cavity-based six-wavelength-switchable single-longitudinal-mode (SLM) thulium-doped fiber laser (TDFL) with a homemade polarization-maintaining sampled fiber Bragg grating (PM-SFBG) is proposed and demonstrated. The PM-SFBG in the 2 μm band is studied theoretically and experimentally, and is utilized as a polarization-dependent multi-channel reflecting filter in a multi-wavelength-switchable fiber laser, both for the first time. The SLM lasing in each channel is guaranteed by using a tri-ring sub-cavity. 6 single-wavelength operations are easily obtained and switched each other, and the maximum power and wavelength fluctuations are as low as 0.71 dB and 0.02 nm, respectively. The frequency noise of each lasing wavelength is measured through an unbalanced Michelson interferometry system, and the linewidths for all six lasing wavelengths are among 0.60–1.08 kHz, calculated by the β-separation line method on the basis of the measured frequency noise spectra. Benefiting from the enhanced polarization hole burning effect formed in the gain fiber, 9 switchable dual-wavelength operations with different wavelength intervals and orthogonal polarizations at two lasing wavelengths are obtained with the maximum power and wavelength fluctuations of only 0.95 dB and 0.03 nm, respectively. We believe the proposed TDFL will find great applications as an ideal light source in free space optical communication and optical sensing.
TL;DR: In this paper, a high-power monolithic continuous wave (CW) Yb doped fiber amplifier at 1064 nm has been demonstrated based on traditional large mode area step-index fiber, which generated 5.07 kW narrow line-width laser with near diffraction-limited beam quality.
Abstract: A high-power monolithic continuous wave (CW) Yb doped fiber amplifier at 1064 nm has been demonstrated based on traditional large mode area step-index fiber, which generated 5.07 kW narrow line-width laser with near diffraction-limited beam quality. At the maximal output power, >35dB OSNR has been achieved with line-width being 370pm, and the measured beam quality is M2x = 1.252, M2y = 1.322. The influence of cooling temperature on SRS has been investigated in high power fiber lasers, which shows that the SRS at 4kW has been suppressed 24 dB by lowering the temperature from 20°C to 8°C. To the best of our knowledge, this is the highest narrow line-width laser power generated from the traditional large mode area step-index monolithic fiber amplifier.
01 Oct 2021
TL;DR: In this article, the authors demonstrate that single-frequency and single-mode operation can be achieved even in a single multi-mode Er:LNOI microring by introducing mode-dependent loss and gain competition.
Abstract: Erbium-doped lithium niobate on insulator (Er:LNOI) is a promising platform for photonic integrated circuits as it adds gain to the LNOI system and enables on-chip lasers and amplifiers. A challenge for the Er:LNOI laser is to increase its output power while maintaining single-frequency and single (-transverse)-mode operation. In this work, we demonstrate that single-frequency and single-mode operation can be achieved even in a single multi-mode Er:LNOI microring by introducing mode-dependent loss and gain competition. In a single microring with a free spectral range of 192 GHz, we have achieved single-mode lasing with an output power of 2.1 µW, a side-mode suppression of 35.5 dB, and a linewidth of 0.9 MHz.
TL;DR: This paper demonstrates a high-power, narrow-linewidth, polarization-maintaining fiber amplifier with near-diffraction-limited beam quality and achieves double the self-pulsing threshold from conventional white noise signal phase modulation with the same optical linewidth.
Abstract: In this paper, we demonstrate a high-power, narrow-linewidth, polarization-maintaining fiber amplifier with near-diffraction-limited beam quality. By optimizing the phase modulation signal, a nearly top-hat-shaped spectrum was generated for self-pulsing suppressing. That results in doubling the self-pulsing threshold we got from conventional white noise signal phase modulation with the same optical linewidth. Based on an optimized signal and a high power, polarization-maintaining, counter-pumped fiber amplifier, we obtain a 3.25 kW narrow-linewidth linearly polarized laser output with a linewidth of ∼20GHz, the polarization extinction ratio is about 15 dB, and the M2 is less than 1.22 at the maximum output power. To the best of our knowledge, this is the first demonstration of a narrow-linewidth, linear polarization, all-fiber amplifier with 3.25 kW laser output.
TL;DR: In this article, the advantages of single-mode VCSELs lie primarily on the narrower linewidth, lower numerical aperture, and smaller spot size compared to multimode VCSels.
Abstract: Single-mode VCSEL technology has advanced significantly in the past few years. The advantages of single-mode VCSELs lie primarily on the narrower linewidth, lower numerical aperture, and smaller spot size compared to multimode VCSELs. They are suitable for transmitting over both multimode fibers and few-mode fibers. For multimode fiber systems, the narrow linewidth can reduce the chromatic dispersion penalty and increase the system reach. A single-mode VCSEL also allows the coupling into graded-index single-mode fiber, which is few-mode around 850 nm with high bandwidth, for few-mode transmission. We review recent progress and present new experimental results and modeling analyses of single-mode VCSEL transmission over both types of fibers. The experiments and analyses shed new light on how single-mode VCSELs can be used with multimode fibers and graded-index single-mode fibers and relative merits between 850 nm single-mode VCSELs versus 980 nm and 1060 nm single-mode VCSELs to address the needs of various applications.
TL;DR: In this paper, an all-fiberized and narrow-linewidth 5 kW power-level fiber amplifier is presented based on the master oscillator power amplification configuration, in which the phase-modulated single-frequency laser is applied as the seed laser and a bidirectional pumping configuration is applied in the power amplifier.
Abstract: In this paper, an all-fiberized and narrow-linewidth 5 kW power-level fiber amplifier is presented. The laser is achieved based on the master oscillator power amplification configuration, in which the phase-modulated single-frequency laser is applied as the seed laser and a bidirectional pumping configuration is applied in the power amplifier. The stimulated Brillouin scattering, stimulated Raman scattering, and transverse mode instability effects are all effectively suppressed in the experiment. Consequently, the output power is scaled up to 4.92 kW with a slope efficiency of as high as approximately 80%. The 3-dB spectral width is about 0.59 nm, and the beam quality is measured to be M2∼1.22 at maximum output power. Furthermore, we have also conducted a detailed spectral analysis on the spectral width of the signal laser, which reveals that the spectral wing broadening phenomenon could lead to the obvious decrease of the spectral purity at certain output power. Overall, this work could provide a reference for obtaining and optimizing high-power narrow-linewidth fiber lasers.
TL;DR: An efficient high-power single-frequency thulium-doped fiber ring laser operating at 1720 nm is demonstrated by incorporating a fiber Bragg grating and potential power scaling of the single- frequencies with different quantity and lengths of the sub-rings was theoretically investigated.
Abstract: Here we demonstrated an efficient high-power single-frequency thulium-doped fiber ring laser operating at 1720 nm. Three cascaded sub-rings were inserted into the main cavity to significantly enlarge the effective free spectral range. By incorporating a fiber Bragg grating, the single longitudinal mode operation was achieved. The maximum single-frequency output power reached up to 1.11 W under 3.75-W launched pump power, while the slope efficiency with respect to the absorbed pump power was 46.4%. The laser linewidth at maximum single-frequency power was measured of 1.9 kHz. Potential power scaling of the single-frequency output power with different quantity and lengths of the sub-rings was also theoretically investigated.
TL;DR: In this paper, the influence of phase noise on the performance of self-homodyne coherent (SHC) systems is thoroughly analyzed by studying the PN probability distribution characteristic and bit error rate performance in theory.
Abstract: The intra- and inter- data center links face continuously increasing pressure on the transmission capacity while having to meet strict constraints in cost and power consumption. For such cost-sensitive data center applications, self-homodyne coherent (SHC) system as a promising solution has attracted increasing attention. In this article, the influence of phase noise (PN) for the SHC system is thoroughly analyzed by studying the PN probability distribution characteristic and bit-error rate (BER) performance in theory. The correctness of the theorical PN analysis is also verified by simulation. Further, the PN characteristics in SHC systems are investigated and discussed with and without the implementation of carrier phase recovery (CPR). A unique property is found for SHC systems that the system performance is only related to the product of linewidth and mismatch length, independent of the symbol rate in the absence of CPR. For SHC-16QAM systems, in order to limit the OSNR penalty to below 1-dB, the product of laser linewidth and delay mismatch should be kept below 0.18 ${\bf{MHz}} \cdot {\bf{m}}$ . Under such a conduciton, no CPR algorithm is reuiqred. Alternatively, in presence of CPR, the phase noise tolerance of SHC and conventional coherent systems are similar.
TL;DR: In this paper, a pulsed-laser induced generation of nitrogen-vacancy (NV) centers in diamond facilitated by a solid-immersion lens (SIL) was reported.
Abstract: We report on pulsed-laser induced generation of nitrogen-vacancy (NV) centers in diamond facilitated by a solid-immersion lens (SIL). The SIL enables laser writing at energies as low as 5.8 nJ per pulse and allows vacancies to be formed close to a diamond surface without inducing surface graphitization. We operate in the previously unexplored regime where lattice vacancies are created following tunneling breakdown rather than multiphoton ionization. We present three samples in which NV-center arrays were laser-written at distances between ~1 $\mu$m and 40 $\mu$m from a diamond surface, all presenting narrow distributions of optical linewidths with means between 62.1 MHz and 74.5 MHz. The linewidths include the effect of long-term spectral diffusion induced by a 532 nm repump laser for charge-state stabilization, thereby emphasizing the particularly low charge-noise environment of the created color centers. Such high-quality NV centers are excellent candidates for practical applications employing two-photon quantum interference with separate NV centers. Finally, we propose a model for disentangling power broadening from inhomogeneous broadening in the NV center optical linewidth.
TL;DR: By introducing self-injection feedback locking at a feedback strength of -24dB, the RF linewidth of the QD-MLL was significantly narrowed by two orders of magnitude from 900kHz to 8kHz.
Abstract: Silicon based InAs quantum dot mode locked lasers (QD-MLLs) are promising to be integrated with silicon photonic integrated circuits (PICs) for optical time division multiplexing (OTDM), wavelength division multiplexing (WDM) and optical clocks. Single section QD-MLL can provide high-frequency optical pulses with low power consumption and low-cost production possibilities. However, the linewidths of the QD-MLLs are larger than quantum well lasers, which generally introduce additional phase noise during optical transmission. Here, we demonstrated a single section MLL monolithically grown on Si (001) substrate with a repetition rate of 23.5 GHz. The 3-dB Radio Frequency (RF) linewidth of the QD-MLL was stabilized at optimized injection current under free running mode. By introducing self-injection feedback locking at a feedback strength of -24dB, the RF linewidth of MLL was significantly narrowed by two orders of magnitude from 900kHz to 8kHz.
TL;DR: In this article, a four-wavelength erbium-doped fiber laser (EDFL) was proposed and demonstrated using a figure-8 compound-ring-cavity (F8-CRC) filter for single-longitudinal-mode (SLM) selection and a polarization-managed four-channel filter (PM-FCF) for defining four lasing wavelengths.
Abstract: We propose and demonstrate a high performance four-wavelength erbium-doped fiber laser (EDFL), enabled by a figure-8 compound-ring-cavity (F8-CRC) filter for single-longitudinal-mode (SLM) selection and a polarization-managed four-channel filter (PM-FCF) for defining four lasing wavelengths. We introduce a novel methodology utilizing signal-flow graph combined with Mason's rule to analyze a CRC filter in general and apply it to obtain the important design parameters for the F8-CRC filter used in this paper. By combining the functions of the F8-CRC filter and the PM-FCF filter assisted by the enhanced polarization hole-burning and polarization dependent loss, we achieve the EDFL with fifteen lasing states, including four single-, six dual-, four tri- and one quad-wavelength lasing operations. In particular, all the four single-wavelength operations are in stable SLM oscillation, typically with a linewidth of =3 MHz and an output power fluctuation of <=+/-3.45%. In addition, all the six dual-wavelength operations have very similar performances, with the performance parameters close to those of the single-wavelength lasing operations. Finally, we achieve the wavelength spacing tuning of the dual-wavelength operations for the photonic generation of tunable microwave signals, and successfully obtain a signal at 23.10 GHz as a demonstration.
TL;DR: In this paper, a reduction in the linewidth and suppression of spectral diffusion of quantum emitters in hexagonal boron nitride supported on a conductive substrate was reported.
Abstract: We report a reduction in the linewidth and suppression of spectral diffusion of quantum emitters in hexagonal boron nitride supported on a conductive substrate. We observe a temperature-dependent reduction in the spectral emission linewidth for CVD-grown and exfoliated crystals on conductive ITO relative to those seen on silicon dioxide (${\mathrm{Si}\mathrm{O}}_{2}$) substrates. We show that the inhomogeneous linewidth can be suppressed by 45% as a result of using a conductive substrate. We investigate the zero-phonon line profile at temperatures ranging from 4 to 300 K and decompose the effects of thermal broadening and spectral diffusion at each temperature by Voigt fitting. The temperature dependence of homogeneous and inhomogeneous components of the broadening is discussed.
TL;DR: In this article, a low-cost sub-kilohertz Brillouin fiber-optic ring laser was demonstrated using an active optoelectronic feedback driven by a simple microcontroller.
Abstract: 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.
TL;DR: In this paper, a Si3N4 resonator with an ultra-high quality factor (Q) of almost half a billion and a narrow sub-MHz linewidth was reported.
Abstract: High quality-factor (Q) optical resonators are a key component for ultra-narrow linewidth lasers, frequency stabilization, precision spectroscopy and quantum applications Integration in a photonic waveguide platform is key to reducing cost, size, power and sensitivity to environmental disturbances However, to date, the Q of all-waveguide resonators has been relegated to below 260 Million Here, we report a Si3N4 resonator with 422 Million intrinsic and 34 Billion absorption-limited Qs The resonator has 453 kHz intrinsic, 906 kHz loaded, and 57 kHz absorption-limited linewidths and the corresponding 0060 dB m−1 loss is the lowest reported to date for waveguides with deposited oxide upper cladding These results are achieved through a careful reduction of scattering and absorption losses that we simulate, quantify and correlate to measurements This advancement in waveguide resonator technology paves the way to all-waveguide Billion Q cavities for applications including nonlinear optics, atomic clocks, quantum photonics and high-capacity fiber communications Integrated photonic all-waveguide resonators are a critical component in many future applications Here the authors develop an optimized photonic all-waveguide resonator with an ultra-high quality factor, Q, of almost half a billion, and a narrow sub-MHz linewidth
TL;DR: In this article, a single-frequency operation of a thulium-doped fiber laser at a short wavelength of 1720 nm is investigated in a ring resonator.
Abstract: The single-frequency operation of a thulium fiber laser at a short wavelength of 1720 nm is investigated in a ring resonator. Powerful single-longitudinal-mode operation was realized by utilizing an unpumped thulium-doped fiber as the saturable absorber. The fiber laser delivered 407 mW single-frequency output with a spectral linewidth of 4.4 kHz under 2.7-W launched pump power at 1570 nm, which turned to multi-longitudinal-mode operation at higher pump powers. Additionally, optical bistability of both output power and longitudinal mode behavior, originating from the saturable absorption effect, were observed and discussed. To the best of our knowledge, this is the first efficient 1.7-μm single-frequency fiber laser as well as the first demonstration of optical bistability in thulium-doped fiber lasers.
TL;DR: In this paper, the design, growth, and fabrication of InAs/InP quantum dash (QD) gain materials and their use in lasers for optical network applications are reported. But the authors focus on the C-band coherent comb laser (CCL) modules with an electrical fast feedback loop control system to ensure a targeted mode frequency spacing.
Abstract: We report on the design, growth, and fabrication of InAs/InP quantum dash (QD) gain materials and their use in lasers for optical network applications. A noise performance comparison between QD and quantum well (QW) Fabry–Perot (F-P) lasers has been made. By using the QD gain material we have successfully developed and assembled C-band coherent comb laser (CCL) modules with an electrical fast feedback loop control system to ensure a targeted mode frequency spacing. The frequency spacing was maintained within ±100 ppm and the operation wavelengths locked on the desired ITU grid within 0.01 nm over a period of several months. We also investigated a 25-GHz C-band QD CCL with an external cavity self-injection feedback locking (SIFL) system to reduce the optical linewidth of each individual channel to below 200 kHz in the wavelength range from 1537.55 nm to 1545.14 nm. The RF mode beating signal 3-dB bandwidth was also reduced from 9 kHz to approximately 500 Hz with this SIFL system. These QD CCLs with ultra-low relative intensity noise (RIN), ultra-narrow optical linewidth, and ultra-low timing jitter are excellent laser sources for multi-terabit optical networks. Using a 34.2 GHz QD CCL we demonstrate 10.8 Tbit/s (16QAM 48 × 28 GBaud PDM) coherent data transmission over 100 km of standard single mode fiber (SSMF) and 5.4 Tbit/s (PAM-4 48 × 28 GBaud PDM) aggregate data transmission capacity over 25 km of SSMF with error-free operation.
TL;DR: In this paper, a sub-kHz-linewidth wavelength-tunable single-frequency ring-cavity fiber laser operating in C- and L-band is demonstrated experimentally.
Abstract: In this paper, a sub-kHz-linewidth wavelength-tunable single-frequency ring-cavity fiber laser operating in C- and L-band is demonstrated experimentally. In our design, a single-longitudinal mode is achieved in a wide tuning range by a narrow-band filtering device composed of a fiber Fabry-Perot interferometer and a 1.6-m-long un-pumped Er3+-doped fiber as a dynamic grating. Under the control of a fiber Fabry-Perot tunable filter, a wavelength tuning range of 76.69 nm from 1535.50 to 1612.19 nm with a tuning interval of about 0.2 nm is finally achieved. In the entire tuning range of the fiber laser, the laser linewidth is less than 310 Hz. The measured optical signal-to-noise ratio is over 40 dB and the relative intensity noise is lower than -143 dB/Hz at frequencies above 1 MHz. Our results suggest that such fiber laser with narrow-linewidth and superior wavelength tunability can serve as a promising candidate applied in optical communication system.
TL;DR: In this paper, dual-channel phase-shifted Bragg grating filters in the telecom band on thin-film lithium niobate are demonstrated, with an extinction ratio of 27 dB and two channels with close linewidths of about 19 pm.
Abstract: We demonstrate dual-channel phase-shifted Bragg grating filters in the telecom band on thin-film lithium niobate. These integrated tunable ultra-narrow linewidth filters are crucial components for optical communication and sensing systems, as well as future quantum-photonic applications. Thin-film lithium niobate is an emerging platform suitable for these applications and has been exploited in this Letter. The demonstrated device has an extinction ratio of 27 dB and two channels with close linewidths of about 19 pm (quality factor of ${8} \times {{10}^4}$), separated by 19 GHz. The central wavelength could be efficiently tuned using the high electro-optic effect in lithium niobate with a tuning factor of 3.83 pm/V. This demonstration can be extended to tunable filters with multiple channels, along with desired frequency separations and optimized tunability, which would be useful for a variety of complex photonic integrated circuits.