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Mini Palm Fiber Femtosecond Laser

        The ultra-fast laser source has the characteristics of narrow pulse width, high peak power and high pulse energy, and has extensive application value in precision measurement and detection, communication and information processing, 3D printing, and ultra-fast optical diagnosis. In the past ten years, the ultrashort pulsed laser dominated the market of ultrafast laser sources, but the titanium-gemstone laser is large, expensive, difficult to maintain and sensitive to the environment.Titanium gemstone femtosecond laser system from Coherent,USA, for example, has a volume of about 3000 x 1500 x 500 mm3(as shown in figure 1) and costs hundreds of thousands to millions of dollars.It requires a high working environment and is complex to debug and maintain. Compared with the ultrashort pulsed laser of titanium gemstone, the fiber ultrashort pulsed laser has many advantages, such as compact structure, high reliability, good beam quality, low price and low energy consumption.At present, several companies have launched ultra-fast fiber laser products on the market, but they generally include two parts: laser head and controller.The whole laser system is large in size and high in cost.For example, the Genki HP ultrafast fiber laser from Switzerland's Onefive company has a laser head size of 420 x 260 x 125 mm3 and a controller size of 483 x 400 x 133 mm3 (as shown in figure 2(a)).C-fiber ultra-fast optical Fiber laser from Menlo Systems, Germany: the laser head size is 413 x 178 x 90 mm3, and the controller size is 448 x 437 x 132 mm3 (as shown in figure 2(b)).

Figure 1. Physical map of the titanium gemstone femtosecond laser system from Coherent, USA.
(including controllers, lasers, amplifiers)

Figure 2. (a) Physical picture of the Genki HP ultrafast fiber laser from Onefive, Switzerland
(including laser head and controller);
(b) Physical picture of C-Fiber ultrafast fiber laser from Menlo Systems, Germany (laser head only)

        The research group of professor Liu from zhejiang university has carried out an in-depth research on the high-stability miniaturized fiber femtosecond laser, and developed a series of practical fiber ultrafast laser products with strong practicability by using integrated optical devices, superior mode-locking devices, and reasonably designed driving circuits.This series of products not only have small geometric size, but also have stable performance and great potential in practical application.Recently, the ultra-fast optical fiber laser developed by the research group has exceeded one third of the size of a 6-inch mobile phone, and its geometric size is 75 * 55 * 15 mm3, as shown in figure 3.At the same time, the laser product has high stability, is not sensitive to the environment, and has strong anti-interference ability. It can work stably for a long time without maintenance.It only needs to plug in 220V power supply to use, one key type of open work, and easy to carry.

Figure 3. Physical picture of the microfiber-optic femtosecond laser product.
(a) compared with huawei Mate 7 mobile phone size, (b) the whole laser

       So far, the research group has developed three kinds of ultra-fast fiber laser products: traditional soliton, dissipative soliton, and high repetition frequency ultra-fast fiber laser.
        (1)Traditional soliton ultra-fast fiber laser: the central wavelength is ~1560 nm, the spectral width is 6~10 nm adjustable, the repetition frequency is ~30 MHz, and the pulse width is 0.1~1 ps. Figure 4 shows the output characteristics of a typical laser, with a central wavelength of 1565.7 nm, a spectral width of 6.5 nm, a pulse width of 810 fs, and a weight frequency of 32.7 MHz.

Figure 4. Output characteristics of traditional soliton ultra-fast fiber laser :
(a) spectrum, (b) autocorrelation curve

        (2) Dissipated soliton ultra-fast fiber laser: the central wavelength is ~1560 nm, the spectral width is adjustable from 10 nm to 20 nm, the frequency is ~20 MHz, and the pulse width can be compressed below 200 fs.As shown in figure 5, typical laser output features are: 1561 nm central wavelength, 17.5 nm spectral width, 4.59 ps pulse width (180 fs after compression), and 17.2 MHz heavy frequency.

Figure 5. Output characteristics of dissipative soliton ultra-fast fiber laser :
(a) spectrum, (b) autocorrelation curve

        (3) High repetition rate ultra-fast fiber laser: the central wavelength is ~1570 nm, the spectral width is ~8.5 nm, the pulse width is 760 fs, the double frequency is ~110 MHz, and the signal-to-noise ratio is ~60 dB. Typical features are shown in figure 6.

Figure 6. output spectrum of high repetition rate ultra-fast fiber laser :
(a) fundamental frequency, (b) large range