Wavelength-tunable Single-frequency Research Articles

Nitrogen Dioxide Detection in Hollow Core Fiber With Long Dynamic Range

We present a compact nitrogen dioxide (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) detection system using a wavelength-tunable single-frequency blue laser in hollow core fiber with absorption dips and photoacoustic (PA) signals. The molecular NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has a harmful impact on human health, such as lung function and visibility decreasing. It even inhibits plant growth. How to detect NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with low detection limit and long dynamic range is a vital issue. However, an ultralow detection limit sometimes means these devices cannot work well under high concentration level. Compared with ultralow detection limits, long dynamic range was considered more important for the fields of agricultural and environmental engineering. So, we combined two detection methods in one optomechanical design: PA and direct absorption spectroscopies. The interaction between the NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> molecules and lights in hollow core fiber can be effectively increased. High light absorption induced fast heating process. The ppb detection limit can be realized by the PA signals. But due to the mechanic design, the nonlinearity of PA signals can be found at high concentration level. Compared with PA, the direct absorption spectroscopy can be extended to high concentration level. Long dynamic range, i.e., 57 dB, can be achieved with this one optomechanical design. The ppb detection limit of PA signals can also be realized. The work range for NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> concentration can be from 2 ppb to 1000 ppm. The long-term instability was estimated as 0.11%.

Broadband high-gain Yb: YAG crystal-derived silica fiber for low noise tunable single-frequency fiber laser

An over 75 nm broadband spectrum with a gain per unit length of >2 dB/cm was obtained from a homemade Yb: YAG crystal-derived silica fiber (YCDSF) with Yb-doping concertation of 6.57 wt.%. Using a 13-cm-long YCDSF, a low-noise wavelength-tunable single-frequency fiber laser has been constructed, enabling a single longitudinal mode oscillation from 1009 to 1070 nm. In particular, in the 1023-1056 nm waveband, the laser operating at any wavelength exhibited a maximum output power over 37 mW with power fluctuations below 0.38%, a slope efficiency >8%, and an optical signal-to-noise ratio higher than 60 dB. A linewidth of less than 2.8 kHz was also observed at the maximum pump powers, and relative intensity noise was as low as -155 dB/Hz at frequencies above 1.0 MHz. These results indicate that the YCDSFs with broadband high-gain characteristics are promising for wavelength-tunable fiber lasers in applications such as optical coherence tomography, precision metrology, nonlinear frequency conversion, and so on.

Sub-kHz-Linewidth Wavelength-Tunable Single-Frequency Ring-Cavity Fiber Laser for C- and L-Band Operation

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-Pérot interferometer and a 1.6-m-long un-pumped Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped fiber as a dynamic grating. Under the control of a fiber Fabry-Pérot 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.

Wavelength-tunable single-frequency ytterbium-doped fiber laser based on a double-circulator interferometer

We reported a novel type of wavelength-tunable single-frequency ytterbium-doped fiber laser based on a double-circulator compound cavity and a section of unpumped ytterbium-doped fiber. The multi-longitudinal-mode oscillations are suppressed by the double-circulator structure and the single frequency operation is obtained finally by the standing wave grating in the unpumped ytterbium-doped fiber. The central wavelength of the laser beam is selected by a tunable filter ranging from 1040 nm to 1080 nm. The results show that the side mode suppression ratio in this range is greater than 47 dB and the maximum value is 58 dB at 1070.06 nm. The observed maximum wavelength fluctuation and power variation at 1060 nm are 0.012 nm and 0.22 dB during 1 h, respectively. The mean value of the linewidth in this range is 2.82 kHz and the minimum value of the linewidth at 1060 nm is 2.38 kHz. The relaxation oscillation frequency is right on 94 kHz.

Continuous-Wave 3.1–3.6 μm Difference-Frequency Generation of Dual Wavelength-Tunable Fiber Sources in PPMgLN-Based Rapid-Tuning Design

We report on a single-frequency continuous wave (CW) difference-frequency generation (DFG) source based on single-frequency wavelength-tunable polarization-maintaining ytterbium- and erbium-doped fiber master oscillator–power amplifiers (MOPAs), acting as the pump and signal source, respectively, and a 40-mm long periodically poled MgO-doped LiNbO3 (PPMgLN) crystal. Owing to the dual wavelength-tuning of the MOPAs, the generated idler light reaches a wavelength-tuning range of close to 500 nm, from ∼3117.2 to ∼3598.8 nm, only by tuning the launched pump and signal wavelengths from 1040 to 1084.6 nm and from 1545.2 to 1561.4 nm, respectively, without any change of temperature or grating period of the PPMgLN. Compared to temperature-based idler-wavelength-tuning, this method is potentially faster in speed. The maximum idler power exceeds 60 mW, which is the highest reported power for a wavelength-tunable single-frequency CW DFG source. A rapidly wideband-tunable DFG source with tens of milliwatts of output power in a narrow line can be a practical tool for mid-infrared molecular spectroscopy, detection, and sensing at high measurement rates.

High-Stability Broadband Wavelength-Tunable Single-Frequency Ytterbium-Doped All-Fiber Compound Ring Cavity

A high-stability wavelength-tunable single-frequency (SF) ytterbium-doped all-fiber compound ring laser has been demonstrated experimentally. The compound ring cavity is composed of a fiber optical tunable filter, a high-finesse ring filter, and a loop mirror filter. Three segments of ytterbium-doped fibers are employed as the gain medium or saturable absorber, respectively. The SF operation is observed to be stable during 1 h without mode hopping. The SF fiber laser achieves a wide-band tunability from 1030 to 1090 nm with maximum output slope efficiency of 7.95%. The power instability over 2 h gives standard deviation value of 1.34%. The average linewidth is 8.8 kHz and the relaxation oscillation frequency is at 62 kHz.

Tunable single-frequency fiber laser based on the spectral narrowing effect in a nonlinear semiconductor optical amplifier.

A wavelength-tunable single-frequency fiber laser based on the spectral narrowing effect in a nonlinear semiconductor optical amplifier (NL-SOA) is proposed and experimentally demonstrated. The single-frequency operation is achieved based on the spectral narrowing effect resulted from the inverse four-wave mixing in a NL-SOA. By incorporating the NL-SOA in the fiber laser cavity, single-frequency lasing is achieved. The lasing frequency can be tuned by tuning the center wavelength of a tunable filter (TF) incorporated in the laser cavity. The proposed wavelength-tunable single-frequency fiber laser is experimentally evaluated. Stable single-frequency oscillation with a side-mode suppression ratio (SMSR) as high as 55 dB and a spectral linewidth of less than 10.1 kHz over a wavelength tuning range of as wide as 48 nm is demonstrated.

Wavelength-Tunable Single Frequency Ytterbium-Doped Fiber Laser with Loop Mirror Filter**Supported by the International Cooperation Projects of Ministry of Science and Technology under Grant No 2012DFB10120, and the National Natural Science Foundation of China under Grant No 61177059.

By using a loop mirror filter, a novel wavelength-tunable single-frequency ytterbium-doped fiber laser is developed to select single longitudinal modes in a linear cavity. The output wavelength could be tuned 2.4nm intervals range from 1063.3 to 1065.7nm with the temperature change of the fiber Bragg grating. The maximum output power could reach 32mW while the pump power increases to 120mW. The corresponding optical-to-optical conversion efficiency is 26.7% and the slope efficiency is 33.9%, respectively. The output power fluctuation is below 2%, and its highest signal-to-noise ratio is 60 dB.

Characterization of wavelength-tunable single-frequency fiber laser employing acoustooptic tunable filter

This paper demonstrates and characterizes a novel wavelength-tunable single-frequency erbium-doped fiber ring laser incorporating an all-fiber acoustooptic tunable bandpass filter and a self-constructed saturable absorption grating (SAG). Stable single-longitudinal-mode operation was achieved over the wavelength range of 48 nm with a sidemode suppression ratio higher than 50 dB. The wavelength tuning characteristics, and the laser dynamics in wavelength switching and sweeping are analyzed in detail. A theoretical analysis on the effect of the SAG is also described.

Wavelength-tunable single-frequency and single-polarisation er-doped fibre ring-laser with 1.4 kHz linewidth

A narrow linewidth of 1.4 kHz with single frequency operation is demonstrated in an Er-doped fibre ring-laser. A stable lasing spectrum can be achieved using a single polarisation fibre-cavity. An optical bandpass filter incorporated in the ring-cavity makes the lasing wavelength tunable, and a 2.8 nm tuning range is demonstrated.

Continuously tunable single-frequency laser diode utilising transverse tuning scheme

A new wavelength-tunable single-frequency laser diode has been developed using a tunable twin-guide structure. The applied transverse tuning scheme provides a basically continuous tuning behaviour with only a single wavelength control current. The first 400μm-long, λ = 1.56μm devices are tunable over a range of 1.5 nm and show the expected continuous tuning behaviour.