Tunable Wavelength Spacing Research Articles

Tunable wide spacing all-fiber dual-wavelength holmium-doped fiber laser using a Lyot filter operating above 2 µm

In this work, we successfully demonstrated an all-fiber, dual-wavelength holmium-doped fiber laser (HDFL) with a tunable wavelength spacing range of 8 nm to 24 nm. The HDFL utilizes a Lyot filter to obtain a stable dual wavelength output, with the Lyot filter being constructed from a polarizer, a 20 m polarizing maintaining fiber (PMF) and two polarization controllers (PCs). The dual-wavelength HDFL has an operating wavelength range from 2072.1 nm to 2097.2 nm and a maximum spacing of 24 nm between the lasing wavelengths as well as a signal-to-noise ratio of up to 45 dB and a side mode suppression ratio as low as 0.15 dB. The HDFL is highly stable, with the lasing output have a low power fluctuation of only 2.3 dB over a continuous operation period of 75 min. The proposed HDFL would have substantial applications as a low cost laser source for sensing applications beyond the 2 µm region, particularly those that require a control signal.

Tunable Brillouin-erbium fiber laser producing multiwavelength cylindrical vector beams

A multiwavelength Brillouin-erbium fiber laser producing cylindrical vector beams with tunable central wavelength and wavelength spacing is presented and experimentally investigated. Owing to the inhomogeneous broadening characteristic of the Brillouin gain, stable multiwavelength lasing is achieved by combination of the cascaded stimulated Brillouin scattering in the ultra-long single mode fiber and the wavelength selection of the fiber Mach-Zehnder interferometer. Multiwavelength lasing with tunable wavelength spacing of about 0.09, 0.11, 0.17, 0.24 and 0.3 nm is achieved by adjusting the optical delay line in the Mach-Zehnder comb filter. With the sufficient pump power, multiwavelength lasing with more than 10 channels is obtained when the wavelength spacing is tuned to be about 0.09 nm. Through adjusting the flat-top tunable bandpass filter, the central lasing wavelength can be tuned from 1534.37 nm to 1570.06 nm continuously. Cylindrical vector beams with purity higher than 93% are produced through regulating polarization controllers on either side of the two-mode long-period grating serving as the mode convertor. Multiwavelength cylindrical vector beams with the largest number of channels and tuning range are obtained to the best of our knowledge.

Tunable Multiwavelength Thulium-Doped Fiber Laser Based on Parallel Lyot Filter

This paper demonstrates a tunable wavelength spacing of thulium-doped fiber laser (TDFL) based on a parallel Lyot filter. An intensity-dependent loss (IDL) mechanism acts as an amplitude equalizer to flatten and stabilize the multiwavelength spectrum. The IDL mechanism is obtained at a certain polarization state from the combination of highly nonlinear fiber and polarizer. The wavelength spacing of the TDFL can be tuned to either 0.9 nm or 1.8 nm when the polarization controllers (PCs) in each branch of the parallel Lyot filter are adjusted. The wavelength spacing is tuned by adjusting both PC2 and PC3 to suppress or transmit the light at each branch. Up to 4 and 9 lasing lines are generated based on wavelength spacing of 0.9 nm and 1.8 nm, respectively. Lower pump power has disappeared lasing lines, while different half-wave plate angle of PC has shown variation the laser performances.

Dual-wavelength Brillouin-erbium fiber laser with tunable wavelength spacing

Abstract A novel wavelength-spacing tunable dual-wavelength Brillouin-erbium fiber laser is proposed and demonstrated experimentally. The dual-wavelength lasing is achieved by combining the erbium-doped fiber laser (EDFL) and the first-order Brillouin laser using a 4 m high nonlinear fiber (HNLF) as Brillouin gain medium. The evolutionary power spectrum of the EDFL and the first-order Brillouin laser are investigated through adjusting the output power of tunable laser source (TLS) and 980 nm pump. The high stability of the single-and dual-wavelength operation are experimentally verified by the measured wavelength variation of ≤0.01 nm and power fluctuation of ≤1.6 dB within 100 min. With the good tunability of the TLS, the wavelength spacing of a dual-wavelength operation could be achieved in the pass band of the FBG. The fiber laser will find potential applications in fiber sensing and microwave photonics areas.

Switchable dual-wavelength fiber laser based on a phase-shifted fiber Bragg grating combined with Mach-Zehnder interferometer and Sagnac loop

Abstract A switchable dual-wavelength erbium-doped fiber laser is proposed and demonstrated. It is based on the finer filter effect of phase-shifted fiber Bragg grating (PSFBG), combining with the compound interference filtering effect of Mach-Zehnder interferometer (MZI) and Sagnac loop. By adjusting the polarization controller (PC) and tuning the delay, the switchable single- and dual-wavelength fiber laser with tunable wavelength spacing can be obtained. As a result, the dual-wavelength spacing as small as 0.04 nm is achieved, the output wavelength is from 1555.580 nm to 1559.928 nm, and the side mode suppression ratio (SMSR) is larger than 40 dB. The maximum wavelength drift of single-wavelength is less than 0.033 nm, and the maximum fluctuation of dual-wavelength is less than 0.02 nm. The experimental results show that the proposed fiber laser has important applications, such as in high fineness dense wavelength division multiplexing (DWDM) systems and other similar fields.

Switchable multi-wavelength and tunable wavelength spacing erbium-doped fiber laser based on a phase-shifted fiber Bragg grating combined with a Mach-Zehnder interferometer

A switchable multi-wavelength fiber laser with tunable wavelength spacing is proposed. It is based on a structure filter composed of a phase-shifted fiber Bragg grating (PSFBG) and a Mach-Zehnder interferometer (MZI), and the MZI is fabricated by splicing a section of polarization-maintaining fiber with two segments of multi-mode fibers. By adjusting the variable optical attenuator in the cavity and slightly changing the temperature, stable single-, dual-, triple- and quadruple-wavelength emissions can be obtained. The minimum wavelength spacing of adjacent peaks is 0.176 nm, and the maximum is 17.86 nm. The laser line emissions can be switched from 1527.684 nm to 1550.224 nm with optical signal to noise ratio of more than 50 dB. The maximum wavelength fluctuation of the fiber laser is less than 0.025 nm over 50 min. When the strain applied to the filter is changed, the tunable wavelength spacing can be achieved. The wavelength spacing of dual-wavelength laser can be continuously tuned from 21.82 nm to 22.69 nm by applying strain of 0–258 με to the filter.

Tunable dual-wavelength Er3+-doped fibre laser based on a single multimode interference filter

We report a dual-wavelength erbium-doped fiber laser (EDFL) with a tunable wavelength spacing from ~9 to 58 nm based on a single multimode interference filter (MMIF). The MMIF has a simple structure of single mode fiber (SMF)-multimode fiber-SMF and two main transmission peaks at 1537 and 1565 nm, which are located in the gain spectrum of the EDF. The wavelength spacings of these two transmission peaks were tuned from 7.8 to 58.5 nm, owing to the multimode interference effect by mechanically bending the MMIF. By adding the MMIF into the EDFL cavity, dual-wavelength lasers were obtained and the corresponding wavelength spacing was tuned from 9 to 58 nm by adjusting the MMIF. To the best of our knowledge, this is the first time an all fiber dual-wavelength EDFL with a tunable wavelength spacing using a curved MMIF has been reported.

Spacing-adjustable multi-wavelength erbium-doped fiber laser using a fiber Michelson interferometer

We demonstrate a stable spacing-adjustable multi-wavelength erbium-doped fiber laser by employing an adjustable fiber Michelson interferometer. The central wavelength of the multi-wavelength laser can be tuned by adjusting the polarization controllers, while the wavelength spacing can be continuously tuned by adjusting the optical delay line in the Michelson interferometer. Tunable wavelength spacing is achieved in the range of 0.045 to 0.7 nm. More than 60 wavelengths within a flatness of 3 dB and wavelength spacing of 0.0474 nm can be achieved.

A stable wavelength-spacing-tunable dual-wavelength single-longitudinal-mode fiber ring laser based on a DMD filter

A stable single-longitudinal-mode dual-wavelength( SLM-DW) multiple ring fiber laser with a tunable wavelength spacing was proposed and demonstrated. In the multiple ring cavities,the mode selection is made by the tunable digital micro-mirror device( DMD) filter and two different length passive sub-ring cavities. The DMD filter can select and couple any two wavelengths from the gain spectrum of the erbium-doped fiber( EDF). The SLM lasing is guaranteed by the two sub-ring cavities which serve as a mode filter. The stable and uniform dualwavelength oscillation is obtained by the highly-nonlinear photonic crystal fiber( HN-PCF),which can generate the four-wave-mixing( FWM) effective. By loading different gratings on the DMD filter without any mechanically shift,the tunable wavelength spacing from appropriately 0. 165 nm to 1. 08 nm within a tuning accuracy of 0. 055 nm is achieved at room temperature.

Generation of stable and narrow spacing dual-wavelength ytterbium-doped fiber laser using a photonic crystal fiber

We demonstrate the design and operation of novel narrow spacing and stable dual-wavelength fiber laser (DWFL). A 70-cm ytterbium-doped fiber has been chosen as the gain medium in a ring cavity arrangement. Our design includes a short length photonic crystal fiber, acting as a dual-wavelength stabilizer based on its birefringence coefficient and nonlinear behavior and tunable band pass filter (TBPF) to achieve narrow spacing spectrum lasing. Our laser output is considered to be highly stable, with power fluctuation less than 0.8 dB over a period of 15 min. The flexibility and tunability of TBPF, together with polarization controller enable the spacing tuning of the DWFL from 0.03 nm up to 0.07 nm for 1040 nm region, and 0.10 nm up to 0.40 nm for 1060 nm region. The tunable wavelength spacing shows the flexibility of the DWFL in addition to stable and reliable properties of fiber laser in 1-μm region.

Stable Dual-Wavelength Coherent Source With Tunable Wavelength Spacing Generated By Spectral Slicing a Mode-Locked Laser Using Microring Resonator

We demonstrate a stable tunable dual-wavelength erbium-doped fiber laser generated by launching a mode-locked laser into an add–drop microring resonator. Two silicon-based high-index-contrast microring resonators with $Q$ -factors of 1.2 × 10 5 and 0.6 × 10 5 have been used as add–drop filters independently. As a result, multiwavelength generation was achieved and demonstrated both theoretically and experimentally with free spectral range (FSR) of 0.202 and 0.404 nm corresponding to the microrings' diameter of $\textrm{D}=2.54$ and $\textrm{D}=1.27\,\mbox{mm}$ . A high-resolution tunable bandpass filter and fiber Bragg gratings (FBGs) are then used to extract a tunable and switchable dual-wavelength coherent source from the generated multiwavelength coherent source. Subsequently, the dual-wavelength coherent source with tunable FSRs from 0.404 to 3.232 nm is achieved and presented. The obtained dual-wavelength output has a side-mode suppression ratio of more than 30 dB.

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

The generation of tunable multiwavelength erbium-doped fiber laser based on an integrated structure of a single-core comb filter and nonlinear polarization rotation (NPR) is proposed and successfully demonstrated at room temperature. The NPR effect effectively induced intensity and wavelength-dependent loss to alleviate mode competition caused by homogeneous gain broadening in erbium-doped fibers. Thirty-two lasing wavelengths in a 3dB flattened spectrum with a tunable wavelength spacing of 0.9nm–1.8nm have been achieved. Good stability of the laser operating at room temperature has been verified by using an optical spectrum analyzer to measure every 10min for an hour.

Photonic generation of tunable microwave signal using a passively Q‐switched dual‐wavelength fiber laser

ABSTRACTA novel photonic tunable microwave generation based on a dual‐wavelength Q‐switched Er‐doped fiber laser is proposed and experimental demonstrated. In the proposed configuration, two cascaded fiber Bragg gratings (FBG) are used as a cavity mirror, and a semiconductor saturable absorber mirror as another one. By changing the operation temperature of the FBG, stable dual‐wavelength Q‐switched pulses with tunable wavelength spacing are achieved, and wavelength spacing of 0.24–0.66 nm, corresponding to microwave signals of 30–82.5 GHz can be obtained. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:166–168, 2015

Thermal effect on the output transmission of single-core fiber Comb filter

We propose and experimentally demonstrate switchable and tunable transmission characteristics of a single-core comb filter based on thermal operation. Its temperature characteristics are investigated to reveal a shift in the peak wavelength position from 0.15 to 0.41 nm/°C and a tunable range of wavelength spacing of 1.18–1.38 nm for maximum and minimum effective lengths, respectively. This configuration provides the unique advantages of an all-fiber structure, tunable wavelength spacing, switchable spectral peaks, independent tuning of the center wavelength and wavelength spacing of the spectral peaks, and low polarization sensitivity. It is relatively simple to fabricate and is expected to have applications in temperature fiber optic sensors and multiwavelength fiber laser sources.

Transmission characteristics of Mach–Zehnder interferometer comb filter based on thermal operation

We propose and experimentally demonstrate switchable and tunable transmission characteristics of a Mach–Zehnder interferometer comb filter based on thermal operation. Its temperature characteristics are investigated to reveal a shift in the peak wavelength position from 0.003 to 0.004 nm/°C and a tunable range of wavelength spacing of 0.76–0.90 nm for maximum and minimum effective lengths, respectively. This configuration provides the unique advantages of an all-fiber structure, tunable wavelength spacing, switchable spectral peaks, independent tuning of the center wavelength and wavelength spacing of the spectral peaks, and low polarization sensitivity. It is relatively simple to fabricate and expected to have applications in temperature fiber optic sensors and multiwavelength fiber laser sources.

Dual-wavelength erbium-doped fiber laser with tunable wavelength spacing using a twin core fiber-based filter

A dual-wavelength erbium-doped fiber laser with tunable wavelength spacing was proposed and experimentally demonstrated by using a twin core fiber (TCF)–based filter. Benefiting from the polarization dependence of the TCF-based filter, the laser operated in dual-wavelength oscillation with two orthogonal polarization states. By adjusting the polarization controller, the wavelength spacing was tuned from 0.1 nm to 1.2 nm without shifting the centre position of the two wavelengths. By stretching the TCF, the two wavelengths were simultaneously tuned with fixed wavelength spacing. Such a dual-wavelength fiber laser could find applications in optical fiber sensors and microwave photonics generation.

A wavelength spacing switchable and TUNABLE high‐birefringence fiber loop mirror filter

ABSTRACTWe demonstrated an all‐fiber birefringent comb filter with tunable and switchable wavelength spacing. The comb filter is based on a fiber loop mirror (FLM) with three sections of high‐birefringence (HB) fibers and polarization controllers (PCs). The transmission characteristics of the birefringent FLM are dependent of the relative phase difference of the two orthogonal polarization modes and the rotational angles of the different HB fibers. By adjusting the PCs, four different wavelength spacings can be obtained; particularly, interleaving operation—halved and quartered wavelength spacing—can be effectively realized. By using a Jones matrix method, the transmission of the birefringent comb filter is analyzed. The theoretical analysis agrees with the experimental results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1666–1670, 2014

Stable, uniform, approximately linearly polarized dual-wavelength PM-EDF laser with tunable wide wavelength spacing using a compound filter

A stable uniformity approximately linearly polarized dual-wavelength polarization-maintaining erbium-doped fiber (PM-EDF) laser obtained by using a compound filter is proposed and experimentally demonstrated. By adjusting the polarization controllers (PCs), the output laser can not only be switched between single-wavelength and dual-wavelength operation, but is also tunable. Dual-wavelength lasing has the performance characteristics of uniformity, tunable wavelength spacing, tunable wavelength position, and the same approximately linear polarization. Besides, the peak power fluctuation and wavelength shift are monitored to be less than 0.2 dB and 0.02 nm during an hour, respectively. The characteristics of the two compound filters measured in the experiment are in accord with those of a theoretical analysis.

Widely tunable wavelength spacing dual-wavelength single longitudinal mode erbium doped fiber laser

A simple widely tunable wavelength spacing dual-wavelength single longitudinal mode (SLM) erbium doped fiber laser (EDFL) based on cascaded fiber Bragg gratings (FBGs) and birefringent fiber filter is proposed and demonstrated. Experimental results show that the lasing wavelength spacing is widely tunable in a range from 2nm to 18nm, which has potential to generate frequency tunable terahertz (THz) waves by beating the lasing dual-wavelength in a high speed photodetector. The birefringent fiber filter acts as an ultra-narrow bandpass filter and benefits the simultaneous oscillation of dual-wavelength in a single laser cavity. The output peak power of the lasing dual-wavelength is approximately equalized at room temperature, and a high optical signal-to-noise ratio (OSNR) is realized in the whole tuning range. The SLM operation of dual-wavelength fiber laser is verified by Fabry–Perot (F–P) scanning interferometer, and the clear eye diagram proves that the proposed fiber laser is effective in the application of fiber optic communication system.

A dual-wavelength erbium-doped fiber laser with widely tunable wavelength spacing

A stable dual-wavelength erbium-doped fiber laser (EDFL) with tunable wavelength spacing and equalized output power is proposed and experimentally demonstrated. The fiber laser uses two fiber Fabry-Perot tunable filters (FFPTFs) as the wavelength filter. The main cavity is divided into two sub-cavities with imbalance cavity losses through a 30/70 optical coupler. The tunable wavelength spacing can be achieved by changing the center wavelength of the filters and the equalized dual-wavelength output power can be achieved by properly controlling the variable optical attenuator (VOA) inserted in the lower-loss cavity.