Dual-Wavelength Bad Cavity Laser as Potential Active Optical Frequency Standard

We experimentally realize the dual-wavelength bad cavity laser for the first time. As the Cs cell temperature is kept between 118℃ and 144℃, both the 1359nm and 147Ohm lasing outputs of dual-wavelength bad cavity laser are detected. The laser output power of dual-wavelength bad cavity laser is measured when changing the 455 nm pumping laser frequency and power at 127℃ Cs cell temperature. Both the 1359 nm laser and the 1470 nm laser are working at the deep bad cavity regime, and the ratio between the linewidth of cavity mode and the laser gain bandwidth a ≈ 40 for 1359nm and 1470nm lasers. The 147Ohm laser linewidth is measured to be 407.3Hz. The dual-wavelength bad cavity laser operating on atomic transitions demonstrated here has a potential in the application as a stable optical local oscillator, even an active optical frequency standard directly in the future.

Optomagnonically tunable whispering gallery cavity laser wavelength conversion

We achieve laser wavelength conversion in an optomagnonical whispering gallery cavity by adjusting the strength of the applied static magnetic field. Numerical simulations are carried out on a yttrium iron garnet(YIG) sphere under different cavity quality factors or coupling strength. It is found that a high cavity quality factor will not always mean a high cavity excitation field for Gaussian lasers with finite linewidth. On state of the art, the high cavity quality factor will always mean the higher lightwave conversion rate. In addition, we also find that increasing the mode coupling strength is beneficial to the conversion of the laser. Our study provides new insights into generation of highly precise tunable coherent light.

Green Vertical‑Cavity Surface‑Emitting Lasers Based on InGaN Quantum Dots and Short Cavity

Room temperature low threshold lasing of green GaNbased vertical cavity surface emitting laser(VCSEL)was demonstrated under continuous wave(CW)operation.By using self-formed InGaN quantum dots(QDs)as the active region,the VCSEL emitting at 524.0 nm has a threshold current density of 51.97 A cm^(-2),the lowest ever reported.The QD epitaxial wafer featured with a high IQE of 69.94%and theδ-function-like density of states plays an important role in achieving low threshold current.Besides,a short cavity of the device(~4.0λ)is vital to enhance the spontaneous emission coupling factor to 0.094,increase the gain coefficient factor,and decrease the optical loss.To improve heat dissipation,AlN layer was used as the current confinement layer and electroplated copper plate was used to replace metal bonding.The results provide important guidance to achieving high performance GaN-based VCSELs.

Numerical Simulation of External-Cavity Distributed Feedback Semiconductor Laser

We propose a theoretical model to describe external-cavity distributed feedback semiconductor lasers and investigate the impact of the number of external feedback points on linewidth and side-mode suppression ratio through numerical simulation. The simulation results demonstrate that the linewidth of external-cavity semiconductor lasers can be reduced by increasing the external cavity length and feedback ratio, and adding more external feedback points can further narrow the linewidth and enhance the side mode suppression ratio. This research provides insight into the external cavity distributed feedback mechanism and can guide the design of high-performance external cavity semiconductor lasers. .

Two-hertz-linewidth Nd:YAG lasers at 1064 nm stabilized to vertically mounted ultra-stable cavities

Two Nd：YAG lasers operating at 1064 nm are separately servo-locked to two vertically mounted ultra-stable cavities. The optical heterodyne beat between two cavity-stabilized lasers shows that the linewidth of each laser reaches 2 Hz and the average frequency drift reduces to less than 1 Hz/s.

Broad bandwidth interference filter-stabilized external cavity diode laser with narrow linewidth below 100kHz

Interference filter-stabilized external cavity diode lasers （ECDLs） have properties of simple configurations, high sta- bilities, and narrow linewidths. However, the interference filter used in common ECDL designs requires an ultra-narrow bandwidth （about 0.3 nm） to achieve mode selection, that is considerably expensive and not yet available for a wide range of wavelengths. In this paper, a robust ECDL using an available broad bandwidth （about 4 nm） interference filter as the wavelength discriminator is constructed and tested. The ECDL demonstrated a narrow Lorentzian fitted linewidth of 95 kHz and a spectral purity of 2.9 MHz. The long-term frequency stability of the ECDL reaches 5.59 x 10 12.

Stable single longitudinal mode erbium-doped silica fiber laser based on an asymmetric linear three-cavity structure

We present a stable linear-cavity single longitudinal mode （SLM） erbium-doped silica fiber laser. It consists of four fiber Bragg gratings （FBGs） directly written in a section of photosensitive erbium-doped fiber （EDF） to form an asymmetric three-cavity structure. The stable SLM operation at a wavelength of 1545.112 nm with a 3-dB bandwidth of 0.012 nm and an optical signal-to-noise ratio （OSNR） of about 60 dB is verified experimentally. Under laboratory conditions, the performance of a power fluctuation of less than 0.05 dB observed from the power meter for 6 h and a wavelength variation of less than 0.01 nm obtained from the optical spectrum analyzer （OSA） for about 1.5 h are demonstrated. The gain fiber length is no longer limited to only several centimeters for SLM operation because of the excellent mode-selecting ability of the asymmetric three-cavity structure. The proposed scheme provides a simple and cost-effective approach to realizing a stable SLM fiber laser.

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.

Frequency doubled femtosecond Ti:sapphire laser with an assisted enhancement cavity

We report an enhancement cavity for femtosecond Ti：sapphire laser at the repetition rate of 170 MHz. An enhancement factor of 24 is obtained when the injecting pulses have an average power of 1 W and a pulse duration of 80 fs. By placing a BBO crystal at the focus of the cavity, we obtain a 392-mW intracavity doubled-frequency laser, corresponding to a conversion efficiency of 43%. The output power has a long-term stability with a root mean square （RMS） of 0.036%.

A broadband external cavity tunable InAs/GaAs quantum dot laser by utilizing only the ground state emission

A broadband external cavity tunable laser is realized by using a broad-emitting spectral InAs/GaAs quantum dot （QD） gain device. A tuning range of 69 nm with a central wavelength of 1056 nm, is achieved at a bias of 1.25 kA/cm^2only by utilizing the light emission from the ground state of QDs. This large tunable range only covers the QD ground-state emission and is related to the inhomogeneous size distribution of QDs. No excited state contributes to the tuning bandwidth. The application of the QD gain device to the external cavity tunable laser shows its immense potential in broadening the tuning bandwidth. By the external cavity feedback, the threshold current densitycan be reduced remarkably compared with the free-running QD gain device.

Broadband tunable external cavity laser using a bent-waveguide quantum-dot superluminescent diode as gain device

A broadband tunable grating-coupled external cavity laser is realized by employing a self-assembled InAs/GaAs quantum-dot （QD） superluminescent diode （SLD） as the gain device. The SLD device is processed with a bent-waveguide structure and facet antireflection （AR） coating. Tuning bandwidths of 106 nm and 117 nm are achieved under a-A and 3.5-A injection currents, respectively. The large tuning range originates essentially from the broad gain spectrum of self-assembled QDs. The bent waveguide structure combined with the facet AR coating plays a role in suppressing the inner-cavity lasing under a large injection current.

3D cavity detection technique and its application based on cavity auto scanning laser system

Ground constructions and mines are severely threatened by underground cavities especially those unsafe or inaccessible ones.Safe and precise cavity detection is vital for reasonable cavity evaluation and disposal.The conventional cavity detection methods and their limitation were analyzed.Those methods cannot form 3D model of underground cavity which is used for instructing the cavity disposal;and their precisions in detection are always greatly affected by the geological circumstance.The importance of 3D cavity detection in metal mine for safe exploitation was pointed out;and the 3D cavity laser detection method and its principle were introduced.A cavity auto scanning laser system was recommended to actualize the cavity 3D detection after comparing with the other laser detection systems.Four boreholes were chosen to verify the validity of the cavity auto scanning laser system.The results show that the cavity auto scanning laser system is very suitable for underground 3D cavity detection,especially for those inaccessible ones.

High-performance frequency stabilization of ultraviolet diode lasers by using dichroic atomic vapor spectroscopy and transfer cavity

We develop a high-performance ultraviolet(UV)frequency stabilization technique implemented directly on UV diode lasers by combining the dichroic atomic vapor laser lock and the resonant transfer cavity lock.As an example,we demonstrate a stable locking with measured frequency standard deviations of approximately 200 kHz and 300 kHz for 399 nm and 370 nm diode lasers in 20 min.We achieve a long-term frequency drift of no more than 1 MHz for the target 370 nm laser within an hour,which is further verified with fluorescence count rates of a single trapped ^171Yb+ion.We also find strong linear correlations between lock points and environmental factors such as temperature and atmospheric pressure.Our approach provides a simple and stable solution at a relatively low cost,and features flexible control,high feedback bandwidth and minimal power consumption of the target UV laser.

Thermal Analysis of Implant-Defined Vertical Cavity Surface Emitting Laser Array

A three-dimensional electrical-thermal coupling model based on the finite element method is applied to study thermal properties of implant-defined vertical cavity surface emitting laser （VCSEL） arrays. Several parameters including inter-element spacing, scales, injected current density and substrate temperature are considered. The actual temperatures obtained through experiment are in excellent agreement with the calculated results, which proves the accuracy of the model. Due to the serious thermal problem, it is essential to design arrays of low self-heating. The analysis can provide a foundation for designing VCSEL arrays in the future.

A High-Pulse-Energy High-Beam-Quality Tunable Ti:Sapphire Laser Using a Prism-Dispersion Cavity

A high-pulse-energy high-beam-quality tunable Ti：sapphire laser pumped by a frequency-doubled Nd：YAG laser is demonstrated. Using a fused-silica prism as the dispersion element, a tuning range of 740-855 nm is obtained. At an incident pump energy of 774mJ, the maximum output energy of 104mJ at 790nm with a pulse width of 100μs is achieved at a repetition rate of 5 Hz. To the best of our knowledge, it is the highest pulse energy at 790 nm with pulse width of hundred micro-seconds for an all-solid-state laser. The linewidth of output is 0.5 nm, and the beam quality factor M2 is 1.16. The high-pulse-energy high-beam-quality tunable Ti：sapphire laser in the range of 740-855 nm can be used to establish a more accurate and consistent absolute scale of second-order optical-nonlinear coefficients for KBe2BO3F2 measured in a wider wavelength range and to assess Miller＇s rule quantitatively.

External-cavity birefringence feedback effects of microchip Nd:YAG laser and its application in angle measurement

External-cavity birefringence feedback effects of the microchip Nd：YAG laser are presented. When a birefringence element is placed in the external feedback cavity of the laser, two orthogonally polarized laser beams with a phase difference are output. The phase difference is twice as large as the phase retardation in the external cavity along the two orthogonal directions. The variable extra-cavity birefringence, caused by rotation of the external-cavity birefringenee element, results in tunable phase difference between the two orthogonally polarized beams. This means that the roll angle information has been translated to phase difference of two output laser beams. A theoretical analysis based on the Fabry-Perot cavity equivalent model and refractive index ellipsoid is presented, which is in good agreement with the experimental results. This phenomenon has potential applications for roll angle measurement.

Power dissipation in oxide-confined 980-nm vertical-cavity surface-emitting lasers

We presented 980-nm oxide-confined vertical-cavity surface-emitting lasers （VCSELs） with a 16 -um oxide aperture. Optical power, voltage, and emission wavelength are measured in an ambient temperature range of 5 ℃-80 ℃. Measurements combined with an empirical model are used to analyse the power dissipation in the device and the physical mechanism contributing to the thermal rollover phenomenon in VCSEL. It is found that the carrier leakage induced selfheating in the active region and the Joule heating caused by the series resistance are the main sources of power dissipation. In addition, carrier leakage induced self-heating increases as the injection current increases, resulting in a rapid decrease of the internal quantum efficiency, which is a dominant contribution to the thermal rollover of the VCSEL at a larger current. Our study provides useful guidelines to design a 980-nm oxide-confined VCSEL for thermal performance enhancement.

Absolute density measurement of nitrogen dioxide with cavity-enhanced laser-induced fluorescence

The absolute number density of nitrogen dioxide（NO2） seeded in argon is measured with cavity-enhanced laserinduced fluorescence（CELIF） through using a pulsed laser beam for the first time. The cavity ring down（CRD） signal is acquired simultaneously and used for normalizing the LIF signal and determining the relationship between the measured CELIF signal and the NO2 number density. The minimum detectable NO2 density down to（3.6±0.1）10^8 cm^-3 is measured in 60 s of acquisition time by the CELIF method. The minimum absorption coefficient is measured to be（2.0±0.1）10^-9 cm^-1, corresponding to a noise equivalent absorption sensitivity of（2.2±0.1）10^9 cm.^-1Hz^-1/2. The experimental system demonstrated here can be further improved in its sensitivity and used for environmental monitoring of outdoor NO2 pollution.

Simulation of High Power Er/Yb Codoped Fiber Linear Cavity Lasers

The performances of high power Er/Yb codoped fiber linear cavity lasers are investigated numerically. The numerical analysis is based on the iterative solution of rate equations for population density of the Er/Yb ions. The behaviors of co-pump and counter-pump methods are contrasted. Dependence of output power on input pump power, output reflectivity, operating wavelength and active fiber length is simulated, respectively. High conversion efficiency Er/Yb laser output is obtained in simulations and experiments.

Polarization switching and synchronization of mutually coupled vertical-cavity surface-emitting semiconductor lasers

Polarization switching （PS） dynamics and synchronization performances of two mutually coupled vertical-cavity surface-emitting lasers （VCSELs） are studied theoretically in this paper. A group of dimensionless rate equations is derived to describe our model. While analysing the PS characteristics, we focus on the effects of coupling rate and frequency detuning regarding different mutual injection types. The results indicate that the x-mode injection defers the occurrence of PS, while the y-mode injection leads the PS to occur at a lower current. Strong enough polarization-selective injection can suppress the PS. Moreover, if frequency detuning is considered, the effects of polarization-selective mutual injection will be weakened. To evaluate the synchronization performance, the correlation coefficients and output dynamics of VCSELs with both pure mode and mixed mode polarizations are given. It is found that performance of complete synchronization is sensitive to the frequency mismatch but it is little affected by mixed mode polarizations, which is opposite to the case of injection-locking synchronization.