Narrow-linewidth Diode Laser Research Articles

Hybrid integrated Si3N4 external cavity laser with high power and narrow linewidth.

We have designed and fabricated a hybrid integrated laser source with full C-band wavelength tunability and high-power output. The external cavity laser is composed of a gain chip and a dual micro-ring narrowband filter integrated on the silicon nitride photonic chip to achieve a wavelength tuning range of 55 nm and a SMSR higher than 50 dB. Through the integration of the semiconductor optical amplifier in the miniaturized package, the laser exhibits an output power of 220 mW and linewidth narrower than 8 kHz over the full C-band. Such a high-power, narrow-linewidth laser diode with a compact and low-cost design could be applied whenever coherence and interferometric resolutions are needed, such as silicon optical coherent transceiver module for space laser communication, light detection and ranging (LiDAR).

Hybrid integrated narrow-linewidth semiconductor lasers.

Integrated narrow-linewidth lasers are the key devices in compact coherent optical systems of metrology, sensing, and optical microwave generation. Here, we demonstrate a hybrid integrated laser based on an optical negative feedback scheme. The laser is composed of a commercial distributed feedback (DFB) laser diode and an on-chip micro-resonator with a Q-factor of 0.815 million. The feedback optical field is coupled back to the laser cavity through the back facet. Therefore, the laser can maintain the lasing efficiency of the DFB laser diode. The linewidth of the DFB laser diode is compressed from 2MHz to 6kHz, corresponding to the linewidth reduction factor of 25.2dB. The theoretical result shows that the laser performance still has a huge improvement margin through precise control of the detuning between laser frequency and the micro-resonator, as well as the phase delay of the feedback optical field. The hybrid narrow-linewidth laser diode has wide application prospects in coherent optical systems benefitting from the low cost and volume productivity.

High resolution laser spectroscopy of iodine molecule in the 14400–14600 cm−1 range

We have extended our previous work (Torres et al., 2022) by performing absorption laser spectroscopy of I2 in the 14400–14600 cm−1 range, using a narrow linewidth diode laser, whose frequency is actively measured using a calibrated wavelength meter. In this range, we have observed 1204 reference lines, 417 more lines than Salami and Ross (2005). The remaining lines are in good agreement with the works carried out by Gerstenkorn and Luc (1979) and by Salami and Ross (2005). The spectrum predicted by the software Iodine Spec5 reproduced our results very accurately.

A Compact Self-Injection-Locked Narrow-Linewidth Diode Laser with Narrowband Dielectric Filter

The self-injection-locked diode laser can significantly reduce the linewidth down to a sub-100 kHz level but requires optical filtering that is much narrower than the laser cavity linewidth. Such optical filtering is usually sophisticated and beyond the capability of the normal dielectric coating approach. Here we develop a 0.16 nm narrowband dielectric coating using a Fabry–Perot dielectric filter (HFFPF) for the narrow linewidth self-injection-locked laser demonstration using a cost-effective Fabry–Perot laser diode. Single-longitude-mode output is achieved, with beat linewidth down to ~66 kHz and a high side mode suppression ratio over 60 dB. This setup of self-injection-locked laser is cost-effective for mass production and thus is suitable for various applications such as laser ranging, LIDAR, optical communication, and holographic.

Wavelength-Tunable Narrow-Linewidth Laser Diode Based on Self-Injection Locking with a High-Q Lithium Niobate Microring Resonator.

We demonstrate a narrow linewidth 980 nm laser by self-injection locking of an electrically pumped distributed-feedback (DFB) laser diode to a high quality (Q) factor (>105) lithium niobate (LN) microring resonator. The lithium niobate microring resonator is fabricated by photolithography-assisted chemo-mechanical etching (PLACE) technique, and the Q factor of lithium niobate microring is measured as high as 6.91 × 105. The linewidth of the multimode 980 nm laser diode, which is ~2 nm measured from its output end, is narrowed down to 35 pm with a single-mode characteristic after coupling with the high-Q LN microring resonator. The output power of the narrow-linewidth microlaser is about 4.27 mW, and the wavelength tuning range reaches 2.57 nm. This work explores a hybrid integrated narrow linewidth 980 nm laser that has potential applications in high-efficient pump laser, optical tweezers, quantum information, as well as chip-based precision spectroscopy and metrology.

High-power narrow-linewidth diode laser based on external cavity feedback technology for Yb: YAG pumping

An external cavity feedback structure based on volume Bragg grating is introduced to realize the spectral stabilization and linewidth narrowing of a diode laser with a central wavelength of 968.668 nm and a spectral linewidth of 0.405 nm. A diode laser source producing 1.443 kW power from an output fiber with a core diameter of 1000 μm is achieved by using a spatial beam, combining, and polarization multiplexing technologies. The external cavity feedback and fiber coupling efficiencies exceed 93% and 90%, respectively. Such a high-power narrow-linewidth diode laser can be applied in Yb: YAG pumping efficiently and stably.

Hybrid silicon photonics DBR laser based on flip-chip integration of GaSb amplifiers and µm-scale SOI waveguides.

The development of integrated photonics experiences an unprecedented growth dynamic, owing to accelerated penetration to new applications. This leads to new requirements in terms of functionality, with the most obvious feature being the increased need for wavelength versatility. To this end, we demonstrate for the first time the flip-chip integration of a GaSb semiconductor optical amplifier with a silicon photonic circuit, addressing the transition of photonic integration technology towards mid-IR wavelengths. In particular, an on-chip hybrid DBR laser emitting in the 2 µm region with an output power of 6 mW at room temperature is demonstrated. Wavelength locking was achieved employing a grating realized using 3 µm thick silicon-on-insulator (SOI) technology. The SOI waveguides exhibit strong mode confinement and low losses, as well as excellent mode matching with GaSb optoelectronic chips ensuring low loss coupling. These narrow line-width laser diodes with an on-chip extended cavity can generate a continuous-wave output power of more than 1 mW even when operated at an elevated temperature of 45°C. The demonstration opens an attractive perspective for the on-chip silicon photonics integration of GaSb gain chips, enabling the development of PICs in a broad spectral range extending from 1.8 µm to beyond 3 µm.

High-power narrow-linewidth 780 nm diode laser based on external cavity feedback technology of volume Bragg grating

A diode-pumped alkali metal vapor laser (DPAL) combines the advantages of a solid laser and a gas laser. DPAL is useful in the industrial, medical, aerospace and military fields and can yield high output power while maintaining excellent beam quality. However, applications in many fields are limited due to the narrow absorption spectrum of the alkali metal vapor laser. In this study, a novel linewidth narrowing structure of the high-power diode laser based on volume Bragg gratings (VBGs) is proposed to match the absorption spectrum of the alkali metal vapor laser. With the combination of fast-axis collimating lens, beam transformation systems, slow-axis collimating lens, VBGs and metal ceramic heaters, the divergence angles of both fast and slow axis are compressed within 10 mrad. A high-power narrow linewidth diode laser source with a central wavelength of 780.044 nm, a spectral width of 0.138 nm, and an output power of 1090 W is achieved at an operating current of 50 A. Experimental results show that the effect of external cavity feedback based on VBG is improved and the multi-channel spectral linewidth is narrowed effectively by such a structure. The diode laser source based on this structure can be applied for pumping the rubidium alkali metal vapor laser.

High resolution laser spectroscopy of iodine molecule in the [formula omitted] range

In this work, we report the absorption laser spectroscopy of iodine molecule in the 14600–14710cm−1 range, which was performed using a narrow linewidth diode laser, whose frequency is actively measured using a calibrated wavelength meter. Our signal-to-noise ratio is about three times greater than Salami and Ross (2005), allowing us to observe a total of 648 reference lines, 238 of which are new. The previous reported lines are in good agreement with the works carried out by Gerstenkorn and Luc (1979) and by Salami and Ross (2005). Our results also suggest that reference cells of more modest dimension should provide a viable signal for wavelength calibration and laser stabilization in this range.

High-power narrow-linewidth diode laser pump source based on high-efficiency external cavity feedback technology

High-power narrow-linewidth diode laser pump source based on high-efficiency external cavity feedback technology

All-fiber gas Raman laser oscillator.

Here, we report the first, to the best of our knowledge, all-fiber gas Raman laser oscillator (AFGRLO), which is formed by fusion splicing solid-core fibers and a hydrogen-filled hollow-core photonic crystal fiber, and further introducing fiber Bragg gratings at a Stokes wavelength. Pumping with a homemade 1.54 µm fiber amplifier seeded by a narrow linewidth diode laser, we obtain the maximum output Stokes power of 1.8 W at 1693 nm by rotational stimulated Raman scattering of hydrogen molecules. Due to the involvement of the resonant cavity, the measured Raman threshold is as low as 0.98 W, which has been reduced nearly 20 times, compared with that of the single-pass structure. Moreover, a numerical model of an AFGRLO is established for the first time, to the best of our knowledge, and the simulations agree well with the experimental results. This Letter is significant for the development of fiber gas Raman lasers (FGRLs), particularly for achieving compact CW FGRLs towards the mid-infrared.

18.4 GHz evenly spaced flat multi-wavelength Brillouin–Raman comb fiber laser in the U-band region

We report on a double spaced Brillouin–Raman comb fiber laser covering the spectral range of 1654–1677 nm. A 3 W fiber laser source with center wavelength at 1545 nm is used as the Raman pump for a 2.6 km dispersion compensation fiber to generate peak Raman gain at 13.2 THz away from the Brillouin pump (BP) which is around 1655 nm. A 5 mW narrow linewidth laser diode is utilized as the BP to generate multiwavelength Brillouin–Raman comb fiber laser (MBRCFL). A stable MBRCFL is generated with maximum bandwidth of 23 nm which contains 136 Brillouin Stokes with 0.168 nm spacing between BP and first Stoke corresponding to 18.4 GHz frequency spacing, an average power of 340 mW and optical signal to noise ratio of 26 dB. The output power fluctuation of less than 4% is measured over a period of 4 h. Moreover, the slope efficiency of 34% is achieved while the flat-amplitude bandwidth of about 17 nm is observed.

Hyperfine structure of molecular iodine measured using a light source with a laser linewidth at the megahertz level

The hyperfine structure of the absorption lines of molecular iodine at 531 nm was measured using a low-cost, coin-sized light source with a laser linewidth at the megahertz level. The measured hyperfine splittings were found to be systematically smaller than those measured using a narrow-linewidth diode laser. The theoretical fit of the measured hyperfine splittings to a four-term Hamiltonian, including the electric quadrupole, spin-rotation, tensor spin-spin, and scalar spin-spin interactions, does not clarify the observed systematic deviation in the measurement, but instead results in deviated hyperfine constants from reliable literature values beyond the uncertainties. Therefore, the theoretical fit, which is usually used to validate the measurement, does not provide the validation function in the case of megahertz level laser linewidths.

Narrow linewidth near-UV InGaN laser diode based on external cavity fiber Bragg grating

We realize a fiber Bragg grating InGaN-based laser diode emitting at 400 nm and demonstrate its high coherency. Thanks to the fabrication of a narrowband fiber Bragg grating in the near-UV, we can reach single-mode and single-frequency regimes for the self-injection locked diode. The device exhibits 44 dB side-mode suppression ratio and mW output power. Detailed frequency noise analysis reveals sub-MHz integrated linewidth and 16 kHz intrinsic linewidth. Such a narrow linewidth laser diode in the near-UV domain with a compact and low-cost design could find applications whenever coherency and interferometric resolutions are needed.

All-fiberized very-large-mode-area Yb-doped fiber based high-peak-power narrow-linewidth nanosecond amplifier with tunable pulse width and repetition rate* *Project supported by the National Natural Science Foundation of China (Grant No. 61675009) and the Beijing Natural Science Foundation Program, China, and Scientific Research Key Program of Beijing Municipal Education Commission, China (Grant No. KZ201910005006).

We demonstrate an all-fiberized narrow-linewidth nanosecond amplifier with high peak power, tunable pulse width, and repetition rate. A fiber-coupled narrow-linewidth laser diode operating at 1064.1 nm is employed as the seed source, which is gain-switched to generate nanosecond pulses with tunable pulse widths of 1–200 ns and tunable repetition rates of 10 Hz–100 kHz. By utilizing a very-large-mode-area Yb-doped fiber with a core diameter of 50 μm in the power amplifier, thresholds of the stimulated Brillouin scattering at different pulse widths and repetition rates are increased. The maximum average power reaches 30.8 W at the pulse width of 4 ns and a repetition rate of 100 kHz, corresponding to an optical-to-optical conversion efficiency of ∼55.2%. Pulse energy and peak power are calculated to be 0.2 mJ and 50 kW, respectively, which are limited by stimulated Brillouin scattering. The 3-dB spectral linewidth remains around 0.05 nm during the power scaling process. The stimulated Brillouin scattering limited output powers at different pulse widths and repetition rates are investigated. Peak power of 47.5 kW (0.19 mJ) is obtained for the 4 ns pulses at a repetition rate of 50 kHz, which is nearly the same as that of 4 ns pulses at 100 kHz. When the pulse width of the seed source is increased to 8 ns, peak powers/pulse energies are decreased to 19.6 kW/0.11 mJ and 13.3 kW/0.08 mJ at repetition rates of 50 kHz and 100 kHz, respectively.

638 nm narrow linewidth diode laser with a grating external cavity

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Advances in narrow linewidth diode lasers

The era of smart travel has arrived, and the need for high precision lidar detection technology is increasing. With the advantages of high resolution, a strong anti-active jamming ability, small volume, light weight, and low cost, new solid-state lidars can meet the requirements of intelligent cars in the future. A narrow linewidth diode laser is an ideal light source of solid-state lidars. The progress and development of narrow linewidth diode laser techniques can greatly improve the application of solid-state lidars. In this paper, the technology and development is described in detail. In addition, the design ideas, key fabrication technologies, and optical characteristics of various narrow linewidth diode lasers are analyzed and discussed. Finally, the developments of narrow linewidth diode lasers are proposed.

Narrow-linewidth, tunable external cavity dual-band diode lasers through InP/GaAs-Si3N4 hybrid integration.

We demonstrate hybridly integrated narrow-linewidth, tunable diode lasers in the InP/GaAs-Si3N4 platform. Silicon nitride photonic integrated circuits, instead of silicon waveguides that suffer from high optical loss near 1 µm, are chosen to build a tunable external cavity for both InP and GaAs gain chips at the same time. Single frequency lasing at 1.55 µm and 1 µm is simultaneously obtained on a single chip with spectral linewidths of 18-kHz and 70-kHz, a side mode suppression ratio of 52 dB and 46 dB, and tuning range of 46 nm and 38 nm, respectively. The resulting dual-band narrow-linewidth diode lasers have potential for use in a variety of novel applications such as integrated difference-frequency generation, quantum photonics, and nonlinear optics.

Investigation of pernicious oscillation inside a LD-pumped cesium vapor cell

After finding some unbelievable laser radiation emitted from a cesium cell end-pumped by a narrow-linewidth laser diode (LD) without any additional oscillator mirrors, we established a kinetic model to theoretically investigate the lasing oscillation inside an alkali vapor cell. Then, we demonstrated that some pernicious oscillation could be generated by three possible oscillators formed by our alkali vapor cell. Afterward, we built the system mentioned above to experimentally evaluate this undesired lasing oscillation. We also compared the theoretical results with experimental ones of output laser power from both sides of the Cs cell changing with cell temperature. It has been found that the experimental output power from the pump side of the Cs cell was basically greater than the theoretical result. The conclusions could be helpful for the structural design in a high-powered alkali vapor laser system in the near future.

In situ laser measurement of oxygen concentration and flue gas temperature utilizing chemical reaction kinetics

Combustion research requires detailed localized information on the dynamic combustion conditions to improve the accuracy of the simulations and, hence, improve the performance of the combustion processes. We have applied chemical reaction kinetics of potassium to measure the local temperature and O2 concentration in flue gas. An excess of free atomic potassium is created in the measurement volume by a photofragmenting precursor molecule such as potassium chloride or KOH which are widely released from solid fuels. The decay of the induced potassium concentration is followed with an absorption measurement using a narrow-linewidth diode laser. The temperature and O2 concentration are solved from the decay curve features using equations obtained from calibration measurements in a temperature range of 800°C-1000°C and in O2 concentrations of 0.1%-21%. The local flue gas temperature and O2 concentration were recorded in real time during devolatilization, char burning, and ash cooking phases of combustion in a single-particle reactor with a 5Hz repetition rate. The method can be further extended to other target species and applications where the chemical dynamics can be disturbed with photofragmentation.