Longitudinal Mode Laser Research Articles

Continuous-wave operation of InGaN tunable single-mode laser with periodically slotted structure

By introducing wavelength tunability, InGaN single longitudinal mode lasers can be used for pumping wavelength conversion devices with a small pump wavelength tolerance. A 405 nm InGaN tunable slotted laser was designed and fabricated by a simple process without high-resolution lithography and epitaxial regrowth. Continuous-wave single-mode oscillation was obtained. By current injection to active and slotted channels separately, a wavelength tuning range of 0.55 nm was successfully demonstrated for the first time in InGaN in-plane single-mode lasers.

Twist sensor based on fiber Bragg grating fiber laser frequency splitting effect

AbstractA twist sensor based on the frequency splitting effect of fiber Bragg grating laser is proposed and experimentally demonstrated. Laser longitudinal mode was split into two frequencies under the action of birefringence induced by fiber twist and by monitoring the periodical beat frequency response, the twist angle could be deduced. The experimental results show that the relationship between the fiber twist angle and the beat frequency is linear (linearity is more than 99%) when the twist angle is in the range of 10°–55°. Moreover, the wavelength drift caused by the temperature does not affect this linearity. Since the sensor is based on frequency rather than on the wavelength, its sensitivity is not limited to the resolution of the spectrometer, and has been improved to 31.59 MHz/rad (0.55 M/degree).

Interference filter based external-cavity diode laser with combined dual interference filters and largely adjustable feedback range

External-cavity diode lasers (ECDL) are widely used as light sources in laser spectroscopy, atomic physics, and quantum optics. This study demonstrated a home-made 852–nm ECDL with variable feedback, using the combined dual narrow-band interference filters (IFs) as the laser longitudinal mode selection element. The combination of narrow-band IFs, mainly for the current commercially available narrow-band IFs with the full width at half maximum (FWHM) of approximately 0.5 nm for 780-895 nm. We designed different narrow-band IFs combinations to achieve a narrower FWHM, and applied them in the ECDL. The combination of the dual narrow-band IFs further reduces the laser linewidth. We measured the laser linewidth using a high-finesse Fabry-Perot cavity with a linewidth of approximately 10 kHz. The laser linewidth is approximately 176 kHz for the Single-IF-ECDL and 96 kHz for the Dual-IF-ECDL with the same feedback. In addition, we have experimentally verified the results of narrower laser linewidth and larger tuning range with increase in the feedback. The developed Dual-IF-ECDL has the capability of narrow linewidth and wavelength tunability and can be applied to precision spectroscopy, cooling and trapping of neutral atoms.

High-repetition-rate pulse generation via self-sustaining cross-gain modulation in a semiconductor-based laser.

We present a simple and efficient method for generating regular pulse trains with GHz pulse repetition rates in lasers based on semiconductor optical amplifiers (SOAs). This method enables pulse formation without active modulation or saturable absorption of the generated radiation. The method relies upon the self-sustaining cross-gain modulation which is achieved by adding the negative optical feedback (NOF) to a ring laser configuration. The resulting modulation of laser gain is shown to be restricted to the frequencies which match both the spacing of longitudinal laser modes and the highest peaks in the NOF-induced instability gain spectrum. This enables the reproducible stationary pulse generation at the strictly defined repetition rates. The feasibility of the method was confirmed by the stable generation of sub-nanosecond pulses at repetition rates up to 1.79 GHz in a SOA-based laser with a simple fiber cavity.

UV generation via periodically poled MgO:LiTaO3 circular waveguide crystal and diode-based master oscillator power amplifier.

Lasers with emission wavelengths in the near-ultraviolet (UV) spectral range have been used in many applications across various fields, and the demand for these lasers has been on the rise. For example, in medicine, near-UV light has been used for fluorophore excitation. Although laser diodes emitting in this region exist, single longitudinal mode lasers emitting at 380nm with high optical power are limited. One of the solutions to this problem is the use of second harmonic generation by a non-linear crystal. In this work, single-longitudinal-mode laser emission at 380.5nm with an optical power of up to 13mW has been achieved. The emission was realized by frequency doubling using a periodically poled circular waveguide crystal of stoichiometric L i T a O 3 doped with MgO (PPMgSLT) pumped by a master oscillator power amplifier with optical power up to 5W. A distributed Bragg reflector ridge waveguide laser diode at 761nm was used as the master oscillator and a tapered amplifier as the power amplifier.

Polarimetric parity-time symmetry fiber laser with switchable and tunable orthogonal single-polarization narrow-linewidth output

Parity-time (PT) symmetry has garnered significant attention in the field of photonics owing to its remarkable properties. High-performance lasers, which require simultaneous gain and loss, serve as an ideal platform for harnessing the exceptional properties of PT symmetry. In this study, we present and experimentally verify a polarimetric PT-symmetry fiber laser that uses a polarization-maintaining fiber Bragg grating (PM-FBG). This design allows for tunable, switchable dual-wavelength operation with narrow linewidth and orthogonal single-polarization characteristics. By converting two equal-length yet distinct polarization states into two spatial subspaces sharing a common wavelength space, we can achieve PT symmetry. Regulating the polarization controllers (PCs) enables interconversion between PT-symmetry phases. During the PT-symmetric phase (or PT exact phase), a dual-wavelength laser is realized with wavelength fluctuations below 0.098 nm and power fluctuations below 2.175 dB. At this stage, light propagates through both ordinary and extraordinary wavelength-spaces. During the PT-broken phase, one waveguide has a net gain and the other incurs a net loss, leading to a single longitudinal mode (SLM) laser output. The wavelength and power fluctuations of left-wavelength λ1 and right-wavelength λ2 remain below 0.002 nm and 0.770 dB over a 20-minute period, during single-wavelength operation. By adjusting the axial strain on the PM-FBG, the laser output can be tuned within the wavelength range of 1549.754 nm to 1551.690 nm, while maintaining a linewidth variation of less than 0.130 kHz. As the wavelength is adjusted, the azimuth sum of λ1 and λ2 consistently remains close to 90 degrees, accompanied by degrees of polarizations exceeding 99%.

Model of multiple mode gain competition in self-mixing laser diode

Multiple mode gain competition in self-mixing laser diode has been investigated assisted by output optical spectrum. Experimental results show that multi-peaks appear in self-mixing signals depending on the length of the external cavity. The numbers of self-mixing peak signals are the same as that of the output optical spectrum. Laser multi-mode gain competition model has been established to analyze the multiple mode competition in self-mixing laser diode. Numerical analysis demonstrates that the sub-peak in self-mixing signals is attributed to mode gain competition between different longitudinal laser modes.

Locked-energy at first-order Stokes stimulated Raman scattering for an aqueous sulfuric acid solution

We introduced a locked-energy coherent Stokes radiation scheme based on multi-mode stimulated Raman scattering (SRS) of aqueous sulfuric acid solutions. SRS of pure sulfuric acid has only one vibrational characteristic peak. Mixing sulfuric acid with water leads to the appearance of bisulfate, and the energy transfer between adjacent vibrational energy levels in a 17.0 mol/l aqueous sulfuric acid solution leads to generation of five different vibrational modes in a solution. The competition between these five SRS modes prevents the vibrational energy from being transferred to high-order Stokes waves, thereby locking most of the energy in the first-order Stokes SRS and outputting a very strong, broadband, and coherent Raman radiation ranging from 555 to 570 nm. This study demonstrates the possibility of producing an intense single longitudinal mode laser.

Coherent control of transverse modes in semiconductor laser frequency combs via radio-frequency injection

Increasing the output power of semiconductor laser frequency combs, while maintaining a single-lobe far-field characteristic is of great interest for mid-infrared sensing applications. Broadening of the ridge waveguide represents the most common approach for power scaling, however, the excitement of higher-order transverse modes often limits general applicability. Here, we demonstrate that the coherent control of the longitudinal laser modes enables control over the transverse modes of a quantum cascade laser. Modulating the laser in a frequency range 60 ± 3 MHz above the free-running laser beatnote and applying modulation powers above 25 dBm provides reliable fundamental transverse mode operation, observable as single-lobe, Gaussian-like characteristic in the recorded far-field. Furthermore, coherent comb operation for both fundamental and higher-order transverse mode states is demonstrated.

Microwave photonic filter with a sub-kHz bandwidth based on a double ring Brillouin fiber laser

A scheme to achieve a sub-kHz bandwidth microwave photonic filter (MPF) based on a double-ring Brillouin fiber laser (DR-BFL) is proposed and experimentally verified in this study. The stimulated Brillouin scattering gain spectrum can be efficiently narrowed by the DR-BFL, which comprises a main-ring cavity with a 100-m single-mode fiber (SMF) and a sub-ring cavity with a 10-m SMF. A single passband narrow bandwidth MPF is accomplished by the DR-BFL with a single longitudinal mode laser output using the Vernier effect. The bandwidth of the MPF at the center frequency of 10.735 GHz is 114 Hz, and the corresponding Q-factor is 9.42 × 107, which is the highest Q value to the best of our knowledge. Since the measured linewidth of the DR-BFL is 1.2 Hz at the −20-dB power point, the theoretical bandwidth of the DR-BFL-based MPF is 0.16 Hz. This design provides a new idea for realizing high-precision signal extraction in future communication or sensing systems.

2 μm Laser generation and amplification based on dual Tm3+-doped high-Q silica microsphere using an ASE light source for pumping

A dual Tm3+-doped silica microsphere-tapered optical fiber (TDSM-TOF) structure was proposed to excite 2 μm whispering gallery mode (WGM) laser generation and amplification. A C-band amplified spontaneous emission (ASE) light source was employed as the pumping source of TDSMs. The absorption spectra and the laser spectra of TDSM1 and TDSM2 and their concatenations were measured respectively. The ASE source has polarized light in any direction to satisfy the resonance of the microsphere cavity, the laser longitudinal mode distributions can counteract the influence of polarization variation because of environmental vibration. Meanwhile, six photons up-conversion fluorescence could also be observed.

Michelson interferometry with a diode laser

A typical Fabry–Pérot diode laser is used to study the relationship between the laser spectrum and the interference signal obtained from a Michelson interferometer. The interference signal is measured over a range of path length differences of a few centimeters, and the laser spectrum is obtained with a spectrometer of a high resolution of 0.005 nm. Contrary to the laser datasheet, the laser is found to have several longitudinal modes even at high injection currents well above the threshold current. A simple model based on treating the laser's longitudinal modes as pure sinusoidal waves is derived and successfully used in modeling the complex and repetitive interference signal. The spectral spacing and the laser cavity length can be found from the interference signal without the need to use a spectrometer, provided that the interference signal is measured over a long enough range of path length differences.

Single longitudinal mode lasing near the exceptional point in a fiber laser using a tunable isolator.

Parity time symmetry breaking was obtained in a specially designed fiber ring laser with a homemade tunable isolator in the cavity. The dynamic evolution of the cavity eigenmodes around the exceptional point (EP) was further experimentally studied. We showed that operating the laser near the EP can facilitate single longitudinal mode lasing. A single-frequency fiber laser with a linewidth of 163 Hz was first, to the best of our knowledge, demonstrated near the EP of the cavity without using any filter with a narrow bandwidth.

Research on multi-wavelength single-longitudinal mode optical fiber laser with FBG and FBG based Fabry-Perot filter

A multi-wavelength single-longitudinal-mode optical fiber laser using fiber Bragg grating (FBG) as wavelength selector and FBG based Fabry-Perot filters as frequency selector is studied. The optical fiber laser includes several fiber laser resonators and there is a length of erbium-doped fiber used as gain medium in each resonator. Each of the laser resonators uses a FBG as wavelength selector and there are two FBG based Fabry-Perot filters used as frequency selectors in each resonator and thus each resonator can emit single longitudinal mode laser. Experiments show that the fiber laser can emit multiple wavelengths simultaneously, and each wavelength is single longitudinal mode. The stability of each wavelength can reach 10−6.

The performance optimization of Pr:YLF single longitudinal mode laser under the pre-lase technology

The performance optimization of Pr:YLF single longitudinal mode laser under the pre-lase technology

Signatures of a frequency-modulated comb in a VECSEL

Optical frequency combs based on mode-locked lasers have revolutionized many areas of science and technology, such as precision metrology, optical frequency synthesis, and telecommunications. In recent years, a particular kind of frequency comb has been observed in edge-emitting semiconductor lasers where the phase difference between longitudinal laser modes is fixed but not zero. This results in a linearly chirped output in the time domain with nearly constant intensity. Here, by using coherent beatnote spectroscopy, we show that such a comb regime can also exist in vertical-external-cavity surface-emitting lasers, as evidenced for a specific part of the laser spectrum. Our findings may not only lead to a better understanding of the physics of frequency-modulated combs but also enable comb applications with high optical power per comb line and flexible emission wavelengths.

High‐resolution continuous‐wave coherent anti‐Stokes Raman spectroscopy in a CO2‐filled hollow‐core photonic crystal fiber

AbstractWe demonstrated high‐resolution continuous‐wave (CW) coherent anti‐Stokes Raman spectroscopy of gaseous samples in a single ring hollow‐core photonic crystal fiber. Pump beam and Stokes beam were provided by CW single longitudinal mode lasers. These narrow linewidth lasers brought the benefit of a spectral resolution of 99 MHz. The high resolution allowed a measurement of a linewidth 0.3 GHz of the ν1 transition of CO2 in a gas mixture with partial pressure of 0.15 MPa and total pressure of 0.9 MPa. Pump beam from a tunable dye laser and Stokes beam from an external cavity diode laser were coupled into the fiber containing gaseous CO2. Fundamental mode phase matching was achieved by tuning gas pressure. The long interaction length provided by the hollow fiber yielded a 60‐dB increase in the anti‐Stoke signal. The attained signal to noise ratio of the spectrum of ν1 component of 0.6‐MPa CO2 was ~25,000 with 152‐mW pump power and 1.4‐mW Stokes power.

Fabry-Perot Lasers as Enablers for Parallel Reservoir Computing

We introduce the use of Fabry-Perot (FP) lasers as potential neuromorphic computing machines with parallel processing capabilities. With the use of optical injection between a master FP laser and a slave FP laser under feedback we demonstrate the potential for scaling up the processing power at longitudinal mode granularity and perform real-time processing for signal equalization in 25 Gbaud intensity modulation direct detection optical communication systems. We demonstrate the improvement of classification performance as the number of nodes increases and the capability of simultaneous processing of arbitrary data streams. Extensive numerical simulations show that up to 8 longitudinal modes in typical Fabry-Perot lasers can be leveraged so as to enhance classification performance.

A 795 nm gain coupled distributed feedback semiconductor laser based on tilted waveguides* *Project supported by the National Science and Technology Major Project of China (Grant Nos. 2017YFB0503100, 2018YFB0504600, 2018YFB2200300, and 2020YFB2205902), Frontier Science Key Program of the President of the Chinese Academy of Sciences (Grant No. QYZDY-SSW-JSC006), the National Natural Science Foundation of China (Grant Nos. 62090051, 62090052, 62090054,

The 795 nm distributed feedback lasers have great application in pumping the Rb D1 transition. In this paper, in order to realize specific 795 nm lasing, we designed tilted ridge distributed feedback lasers based on purely gain coupled effect induced by periodic current injection windows through changing the angle of the tilted ridge. The fabricated devices were cleaved into 2 mm-cavity-length, including 5 tilted angles. The peak output powers of all devices were above 30 mW. Single longitudinal mode lasing was realized in all tilted Fabry–Perot cavities using periodic current injection windows, with side mode suppression ratio over 30 dB. The total wavelength range covered 8.656 nm at 20 °C. It was disclosed theoretically and experimentally that the output powers, threshold currents, and central wavelengths of the tilted ridge purely gain coupled DFB lasers were relevant to the tilted angles. The results will be instructive for future design of DFB laser arrays with different central wavelengths.

Single Longitudinal Mode Lasers by Using Artificially Controlled Backscattering Erbium Doped Fibers

In this work, we propose and experimentally demonstrate a new distributed short linear cavity fiber laser. At one of the cavity ends, fabricated by a commercial femtosecond fiber laser chirped pulse amplifier, an artificially controlled backscattering erbium doped fiber section has been connected. This distributed reflector acts also as a saturable absorber, leading to the generation of tunable and switchable single longitudinal-mode laser emissions. The distributed reflector consists of 9 micro-drilled sections of about 1cm each one and randomly spread throughout 2 meters of highly doped erbium fiber. The total length of the fiber laser is 9.5 m and the laser shows a single mode behavior at all the emitted wavelengths. Using this new kind of reflecting saturable absorber, single and multiple single-mode emissions can be obtained. The achieved laser presents a pump threshold as low as 45 mW and shows up to 8 different single-mode emission lines with an optical signal to noise ratio of 45dB.