Some Wavelength-Spacing Continuously Tunable Multi-wavelength Fiber Lasers Based on Four-Wave-Mixing Effect

We have developed a tunable multi-wavelength semiconductor fiber laser (SFL) for chromatic dispersion measurements of optical fiber based on the time-of flight method. The SFL incorporates a programmable high-birefringence fiber loop mirror to select the separation of the lasing wavelengths between 3.2nm and 1.6nm. The SFL emits 5 wavelengths with an average power of 11.96dBm per wavelength and 11 wavelengths with an average power of 18.35dBm per wavelength, for separations of 3.2nm and 1.6nm respectively, all within the C-band. The linewidth of each oscillating wavelength resides in the 0.16nm - 0.28nm range, the signal-to-noise ratio varies between 33.5dB and 39.2dB, and the uniformity of the output power is within 3.2dB. Stability measurements for each lasing peak show a wavelength deviation of +/-0.09nm/hour and a power variation of +/-0.90dB/hour. Results from time-of-flight measurements are compared with standard phase-shift techniques and the differences analyzed. The percent error between the two methods is better than -0.73 to 1.13% for measurements on various standard optical fiber lengths. The time-of-flight method is easier and faster to use for the characterization of sufficiently dispersive media such as deployed fiber spools. Our tunable laser provides a simple low cost solution for such measurement applications. The tunable nature of our SFL source also provides the following advantages for chromatic dispersion measurements: (1) greater precision can be obtained since two independent measurements (one at each wavelength separation) can be performed using a single optical source and (2) there is increased flexibility since the wavelength spacing can be tailored for a specific situation; shorter lengths benefiting from larger wavelength separations.

A tunable Brillouin multi-wavelength mode-locked fiber laser (BMMFL) is proposed, predominantly based on a nonlinear optical loop mirror (NOLM) and assisted by nonlinear polarization rotation (NPR). The system employs 10 km of dispersion-shifted fiber (DSF) as the Brillouin gain medium to generate multiple wavelengths. The DSF, together with the polarization controller (PC1) and the optical coupler (OC1), forms the NOLM; the combined NOLM-NPR action functions as an equivalent saturable absorber (SA) to enable mode-locked pulse generation. By adjusting the PCs, the BMMFL generated 69 Brillouin multi-wavelength lines (BMLs) with a 10.9 GHz Brillouin frequency shift, when the pump power, Brillouin pump (BP) power, and BP central wavelength were fixed at 250 mW, 6 dBm, and 1546.5 nm, respectively. Under these conditions, no stably repeating mode-locked pulses were observed. A multi-wavelength tuning range of 30 nm was also obtained at different BP central wavelengths. Subsequently, by further adjusting the PCs, the BMMFL achieved a mode-locked pulse train with a pulse width of 236 ns and a fundamental frequency repetition rate of 19.92 kHz, with only 13 BMLs retained. At a pump power of 350 mW, the maximum average output power of the mode-locked pulse reached 1.29 mW. Moreover, harmonic mode locking up to the fifth order was achieved. This BMMFL offers broad application prospects in dense wavelength division multiplexing (DWDM) systems, laser processing and optical fiber communications.

A tunable multi-wavelength erbium-doped fiber laser (MEDFL) based on a nonlinear optical loop mirror (NOLM) was proposed and experimentally demonstrated by cascading a standard Mach–Zehnder interferometer (MZI) and a twin-core fiber (TCF)-based filter. Due to the ‘blue shift’ of the transmission band of the TCF-based filter when the TCF was bent, a tunable lasing waveband was realized by moving the transmission band of the TCF-based filter to cover different channels provided by the standard MZI. Experimental results showed that the lasing waveband can be linearly tuned over a range of 24 nm from 1542 to 1566 nm with a channel spacing of 0.4 nm, a maximum lasing line amount of 19, and an optical signal to noise ratio (OSNR) of 39 dB. The stability of the laser spectra was verified with a wavelength drift of 0.04 nm and a power fluctuation of ±0.3 dB.

Based on a piece of highly-nonlinear near-zero-dispersion-flattened photonic crystal fiber (PCF), a broadly tunable multiwavelength erbium-doped fiber laser is proposed by using a bi-directionally pumping scheme. This kind of PCF induces the modulation-instability-assisted four-wave mixing to generate new wavelengths. The proposed laser with excellent stability is tunable and switchable by adjusting the fiber Bragg gratings and the variable optical attenuators. The outstanding merits of the proposed multiwavelength laser are the flexible tuning and the ultrabroad spectral range over 150 nm. Especially, the proposed laser source can work at the wavelength of less than 1460 nm, overcoming the limit of gain bandwidth of erbium-doped fiber.

We propose and demonstrate a tunable self-excited multiwavelength Brillouin-erbium fiber laser based on a novel in-line Mach–Zehnder interferometer sensor (NMZIS) with variable temperature. The configuration of the NMZIS is a section of uncoated single-mode fiber sandwiched between an up-taper and multimode fiber. With the temperature changing from 30 °C to 90 °C, the transmission spectrum of the NMZIS shifts towards longer wavelengths. By embedding the NMZIS to act as a fiber filter in the ring cavity, the wavelength of the output multiwavelength comb is tuned from 1552.35 to 1564.48 nm. The corresponding generation of 21 Brillouin–Stokes lines with 25 dB optical signal-to-noise ratio is achieved.

Multi-wavelength fiber lasers are under intense research due to their potential in many application fields like wavelength-division-multiplexing communication, fiber-based sensing, ranging, microwave photonics and terahertz generation, etc. In this manuscript, we will present our detailed investigation on tunable high power multi-wavelength double-clad fiber laser pumped by high-power multimode laser diode. The fiber laser is constructed in a ring-cavity. By adjusting the polarization-controller inside the cavity, the laser can operate at single-wavelength, dual-wavelength and triple-wavelength regime. The maximal output power is 5.5 watt and the conversion efficiency is 68.8%.

A tunable multi-wavelength narrow-linewidth thulium-doped fiber laser employing two-stage cascaded Sagnac loop mirrors is proposed and experimentally demonstrated. The designed fiber laser is composed of a pump source, wavelength division multiplex, circulator, thulium-doped fiber, polarization controllers (PCs), couplers and polarization-maintaining fibers (PMFs). Two cascaded Sagnac loops are used as the cavity reflector and filter, and the proposed filter is fabricated using two sections of PMFs with 2-m and 1-m lengths, respectively. In the experiment, the laser threshold is 110 mW, and laser can emit single, double, triple, quadruple and quintuple wavelengths in the spectral range of 1873–1901 nm through the simultaneous adjustment of the two PCs. The power fluctuations and 3-dB linewidth are less than 2.1 dB and 0.2 nm, respectively, over 10 min at room temperature, and the side-mode suppression ratio is greater than 20 dB. The proposed laser will be useful in various fields, such as spectral analysis, fiber sensing and optical communication.

Tunable and switchable multiwavelength fiber laser incorporating tapered few-mode fiber Bragg gratings

Tunable multiwavelength erbium-doped fiber laser incorporating single-core comb filter at room temperature

A practically tunable multiwavelength Raman fiber laser based on few-mode fiber Bragg gratings with dynamic range of more than 15 nm is investigated. We achieved a high extinction ratio of more than 45 dB.

In this paper, we propose a scheme on precisely tunable L-band multi-wavelength fiber laser. This fiber laser has two main characteristics namely broad wavelength band, uniform power spectrum and precise electronic tunability. About 65 wavelengths output within ± 1.5dB power variation with 50GHz channel spacing in broad spectrum range can be obtained at room temperature. The measured optical signal noise ratio (OSNR) and line width of each wavelength are about 20dB and 345.5MHz respectively. Theses 65 wavelengths are able to be tuned simultaneously up or down in frequency domain with a tuning step ranging from 10 MHz to 14 GHz. The tuning resolution can potentially be as low as 1 Hz in our experiment.

Gain enhanced L-band optical fiber amplifiers and tunable fiber lasers with erbium-doped fibers

Wavelength spacing tunable multiwavelength fiber laser with lasing wavelength selectivity

A novel concept of individually switchable and widely tunable erbium-doped multiwavelength fiber laser (MWFL) is proposed and experimentally demonstrated. The key component of the laser is a channel transmissivity individually variable comb filter composed of two cascaded different-length long-period fiber gratings (LPFGs), named cascaded mismatching LPFGs. When inserted into the laser cavity, this polarization-dependent comb filter functions as the wavelength selector and switching filter simultaneously. By properly adjusting the polarization controllers (PCs) in the laser cavity and in the high birefringence Sagnac loop mirror (HiBi-SLM), eleven individually switchable wavelengths with different flexible lasing states, including successively tunable adjacent single-, dual- and triple-wavelength outputs, nonadjacent dual- and triple-wavelength outputs, as well as quadruple- and quintuple-wavelength outputs, have been achieved. This MWFL may be useful in optical fiber sensing or other fields desiring very flexible optical source.

In this paper, a stable highly tunable and switchable multi-wavelength fiber laser is presented. It is based on the filtering characteristics of the Sagnac loop mirror and the polarization-dependent devices, the polarization hole burning effect is induced to generate multi-wavelength output with high optical signal-to-noise ratio and narrow 3 dB linewidth, optical signal-to-noise ratio is about 50 dB and linewidth is less than 0.02 nm. The tunable bandwidth is about 30 nm, which covers almost the entire C-band. By the adjusting polarization controller, the number and wavelength spacing of laser emissions can be controlled and switched. The single-wavelength exhibits good power and wavelength stability, the peak power fluctuation is less than 0.04 dB and the wavelength drift is less than 0.04 nm, and the wavelength spacing of the dual-wavelength can be tuned from 0.67 to 27.4 nm. In the proposed structure, multi-wavelength up to 6 laser emissions can be obtained span from 1528 to 1562 nm.