Lyot-Sagnac Filter Research Articles

Wavelength-spacing-controllable multi-wavelength fiber laser based on a Lyot-Sagnac filter.

A wavelength-spacing-controllable multi-wavelength polarization-maintaining erbium-doped fiber laser (MW-PM-EDFL) in a linear cavity configuration is presented based on a Lyot-Sagnac filter and a nonlinear optical loop mirror (NOLM). Using a Lyot-Sagnac filter as the wavelength selective filter makes the wavelength spacing controllable by adjusting the effective length of polarization-maintained fiber (PMF) segments. An NOLM inducing wavelength-dependent cavity loss can be used as an amplitude equalizer, which is employed to suppress the mode competition resulting from the homogeneous line broadening effect of the erbium-doped fiber in the cavity. Thus, a stable wavelength-spacing-controllable MW-PM-EDFL is realized. In this experiment, 20 stable lasing wavelengths are obtained with a pump power of 170mW at 980nm when the length of the PMF is 13m. When the length of the PMF is 8m, 10 stable lasing wavelengths are obtained at 185mW pump power. The power fluctuations and wavelength shifts are less than 2dB and 0.02nm in 1h at room temperature. The demonstrated multi-wavelength fiber laser has great potential for applications in optical communications and optical sensing systems.

Channel‐spacing tunable multiwavelength thulium‐doped fiber laser based on four‐wave mixing effect in a high nonlinear fiber

ABSTRACTWe propose a channel‐spacing tunable multiwavelength thulium‐doped fiber laser in the 2‐μm waveband. Stable multiwavelength operation at room temperature is achieved using four‐wave mixing effect in a high nonlinear fiber. The wavelength spacing and number of channels of the multiwavelength fiber laser are adjustable by controlling the effective length of polarization‐maintaining fiber in the intracavity Lyot–Sagnac filter. Four channels with 3.0‐nm spacing, eight channels with 1.5‐nm spacing, and 11 channels with 1.0‐nm spacing are experimentally demonstrated. Characteristics of output stability and extinction ratio are also evaluated. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:337–340, 2016

Tunable passively harmonic mode-locked Yb-doped fiber laser with Lyot-Sagnac filter.

A novel passively harmonic mode-locked dissipative soliton Yb-doped fiber laser with all normal dispersion is proposed and experimentally demonstrated based on a semiconductor saturable absorption mirror and tunable Lyot-Sagnac filter. By only tuning the bandwidth of the filter at fixed pump power, the repetition rate of 9.87 to 167.8MHz (corresponding to 17th-order harmonic) is obtained. This is the highest repetition rate and harmonic order for a passively harmonic mode-locked dissipative soliton Yb-doped fiber laser with all-normal dispersion to the best of our knowledge. The signal-to-noise ratio and super-mode suppression ratio for all harmonic orders are higher than 65 and 35dB, respectively, which shows the high stability of the fiber laser.

Lyot‐type flat‐top fibre multiwavelength filter based on polarisation‐diversity loop structure

Proposed is a Lyot-type flat-top fibre multiwavelength filter based on a polarisation-diversity loop structure, which has flat-top and lossy flat-top passbands and multiwavelength switching capability. The proposed filter is composed of a polarisation beam splitter, two half-wave plates (HWPs) and two polarisation-maintaining fibre (PMF) loops concatenated with a 60° offset between their principal axes. One of the two PMF loops is two times longer than the other. It is able to operate in a flat-top or a lossy flat-top band mode at the selected combination of the azimuthal orientation angles of two HWPs. In particular, through the adjustment of the orientation angles of the two HWPs, its multiwavelength channels can be interleaved in each mode, which cannot be realised in a previously reported Lyot-Sagnac comb filter based on a fibre coupler. In addition to the channel interleaving capability, it provides narrower passbands compared with previous fibre multiwavelength filters with the same order. To make a quantitative comparison between the passband bandwidths of the proposed filter and other filters, both −1 and −3 dB passband bandwidths of a conventional zeroth-order, a Solc-type first-order and the proposed multiwavelength filters were considered and compared with each other.

A variable coefficient microwave photonic filter based on multi-wavelength fiber laser and Mach-Zehnder interferometer

A microwave photonic filter (MPF) with variable coefficient is proposed and demonstrated, which is constructed by a multi-wavelength fiber laser and Mach-Zehnder interferometer (MZI). Through changing the slope characteristics of Mach-Zehnder interference spectrum adjusted by optical variable delay line (OVDL), the conversion from phase modulation (PM) to intensity modulation (IM) is realized. The multi-wavelength fiber laser with Lyot-Sagnac optical filter has variable wavelength spacing. So the designed filter has a variable number of taps and tap weights. As a result, the tunable range of passband center frequency is 2.6 GHz. The reconfigurability of MPF can be also realized by adjusting the output of fiber laser.

A band-pass microwave photonic filter based on Lyot-Sagnac filter and cascaded optical structures

A band-pass microwave photonic filter (MPF) based on Lyot-Sagnac filter and two cascaded optical structures is demonstrated. In the experiment, a stabilized and tunable multi-wavelength optical source is obtained by slicing the broadband optical source (BOS) with a Lyot-Sagnac filter. A standard single-mode fiber (SMF) and a fiber ring resonator are cascaded to improve the mainlobe-to-sidelobe suppression ratio (MSSR) and Q-factor of the filter. The analysis shows that MSSR and Q-factor are improved by reducing the split ratio of the coupler or increasing the length of fiber in fiber ring resonator. The results have significant guidance for MPF design by choosing appropriate devices and parameters. Based on the analyses, a band-pass filter with MSSR of 53.54 dB and Q-factor of 4048 is achieved by choosing the split ratio of 0.01, the length of SMF of 30 km and the length of fiber in fiber ring resonator of 152.27 cm.

Multiwavelength erbium-doped fiber laser based on a nonlinear amplified loop mirror with a highly-nonlinear photonic crystal fiber

A multiwavelength erbium-doped fiber laser based on a nonlinear amplified loop mirror with a highly-nonlinear photonic crystal fiber was proposed and experimentally investigated. The performance of the nonlinear amplified loop mirror was improved by using a single 3-dB coupler and a highly-nonlinear photonic crystal fiber with a length of 100 m. The extinction ratio of the proposed multiwavelength erbium-doped fiber laser was measured to be more than 50 dB. The output power fluctuation was measured to be less than 0.5 dB. The output power difference among multiple peaks was measured to be less than 0.3 dB. A Lyot-Sagnac filter with two segments of polarizationmaintaining photonic-crystal fibers was employed as a multichannel filter, and the wavelength spacing was controlled by changing the polarization states within the Lyot-Sagnac filter. Two different wavelength spacings, 0.6 nm and 0.8 nm, were obtained. The number of channels was also changed: 20 for Δλ = 0.6 nm and 16 for Δλ = 0.8 nm. In addition, a precisely-interleaved switching based on the proposed multiwavelength erbium-doped fiber laser was realized by changing the polarization states.

Flexibly switchable multi-wavelength fiber optical parametric oscillator based on a Lyot-Sagnac filter

We experimentally demonstrate a flexibly switchable multi-wavelength fiber optical parametric oscillator (MW-FOPO) by employing a highly nonlinear dispersion-shifted fiber (HNL-DSF) as the gain medium and a Lyot-Sagnac fiber ring as the comb filter. The wavelength spacing and the number of channels in the switchable MW-FOPO are adjustable by controlling the effective length of polarization maintaining fiber (PMF) segments in the intracavity Lyot-Sagnac filter. We achieve 36 lasing channels with 0.5 nm-spacing and 22 lasing channels with 0.8 nm-spacing in a wavelength range from 1541 to 1559 nm at room temperature. A comparison of the output spectra between the dual-pump MW-FOPO and single-pump MW-FOPO is presented as well.

Switchable quadruple-wavelength erbium-doped fiber ring laser based on two-segment Lyot–Sagnac filter

We propose and demonstrate a novel switchable quadruple-wavelength erbium-doped fiber ring laser (EDFL) based on two-segment Lyot–Sagnac filter which is used as the wavelength-selective filter. Due to the deeply saturated spectral hole-burning (SHB) effect in an ordinary erbium-doped fiber, the laser realizes stable single-wavelength, dual-wavelength, triple-wavelength, and quadruple-wavelength output by controlling two polarization controllers (PCs) appropriately. The optical signal-to-noise ratio (OSNR) is over 30 dB. The peak fluctuation is less than ~2 dB over 1.5 h at room temperature.

Switchable multiwavelength erbium-doped fiber laser with cascaded fiber Bragg gratings and dual-section Lyot–Sagnac filter

We propose and demonstrate a novel switchable multiwavelength erbium-doped fiber laser with a overlapping linear cavity, which is formed by a dual-section Lyot–Sagnac filter and three fiber Bragg gratings (FBGs). Taking advantage of the high extinction of the Lyot–Sagnac filter, independent controlling of the different wavelength losses and the spatial hole burning in the overlapping linear cavities, with this structure we realize stable switchable multiwavelength laser emission at room temperature. An output signal to background noise ratio of ∼43 dB and less than 3 dB fluctuation on output power were observed for all wavelength switching cases.

Room-temperature multiwavelength erbium-doped fiber ring laser based on phase modulation of semiconductor optical amplifier with lasing-wavelength and spacing tunability

We have experimentally investigated a stably tunable multiwavelength erbium-doped fiber ring laser based on phase modulation of a semiconductor optical amplifier with lasing wavelength and spacing tunability at room temperature. Stable multiwavelength operation is obtained by direct modulation of the bias current in the amplifier. We demonstrate such a laser incorporating a tunable Lyot-Sagnac filter with two segments of polarization-maintaining fibers with wavelength-spacing and lasing wavelength tunability. We successfully achieved 1.0-nm-spacing eight-channel and 0.8-nm-spacing ten-channel lasing wavelengths at room temperature. The lasing wavelength of the laser can be also controlled by a polarization controller.

Wavelength spacing tunable multiwavelength fiber laser with lasing wavelength selectivity

We experimentally demonstrate a wavelength spacing tunable multiwavelength fiber laser with lasing wavelength controllability based on a hybrid gain medium. The wavelength spacing can be readily controlled by the effective length of PMF segments in an intracavity PMF Lyot–Sagnac filter. The lasing wavelength can be also controlled in a range from 1510 to 1560nm by the effect of non-linear gain compression effect of a semiconductor optical amplifier incorporated with a C-band erbium doped fiber amplifier. The interleaved optical switching performance based on the proposed multiwavelength fiber laser was achieved depending on the relative phase difference between the two orthogonal modes.

Lasing wavelength and spacing switchable multiwavelength fiber laser from 1510 to 1620 nm

We experimentally demonstrate a flexibly switchable multiwavelength fiber laser with multiple functionalities like a wide tuning range of lasing wavelength, wavelength spacing, and the number of channels simultaneously. The lasing wavelength is controlled in the range from 1510 to 1620 nm based on the effect of nonlinear gain compression of a semiconductor optical amplifier incorporated with an erbium-doped fiber amplifier. The wavelength spacing and the number of channels in the multiwavelength fiber laser are readily controlled by the effective length of polarization-maintaining fiber (PMF) segments in the intracavity PMF Lyot-Sagnac filter.

Multiwavelength erbium-doped fiber Fabry-Pe/spl acute/rot laser and its uniform spectral lines power operation

Multiwavelength erbium-doped fiber laser by means of phase modulation in a linear cavity configuration is presented. Stable multiwavelength lasing is achieved by applying any one of the waveforms of sine, square, sawtoothed, and triangular at a suitable frequency between 500 Hz to a few tens of kilohertz to the phase modulator. The output spectral lines power equalization is performed by adjusting the frequency to drive the all-fiber phase modulator and the polarization controller or dc offset voltage of a LiNbO/sub 3/ amplitude modulator, which is incorporated in a polarization-maintaining fiber Lyot-Sagnac filter.

Flexibly tunable multiwavelength erbium-doped fiber laser based on four-wave mixing effect in dispersion-shifted fibers

We experimentally demonstrate a flexibly tunable multiwavelength erbium-doped fiber laser based on degenerate four-wave mixing in a dispersion-shifted fiber. We successfully achieve the stable operation of the multiwavelength erbium-doped fiber laser at room temperature. The number of channels and wavelength spacing of the proposed multiwavelength laser can be controlled by the combination of two polarization maintaining fiber segments in the intracavity Lyot-Sagnac filter. We achieve 1.0 nm-spacing eleven channel and 0.8 nm-spacing seventeen channel lasing wavelengths at room temperature. The lasing wavelength of multiwavelength fiber laser can be also controlled by the polarization controller.

Tunable multi-wavelength Raman fibre laser based on fibre Bragg grating cavity with PMF Lyot-Sagnac filter

A flexibly-tunable multi-wavelength Raman fibre laser based on the polarisation maintaining fibre (PMF) Lyot-Sagnac filter after composing fibre Bragg grating cavity is demonstrated experimentally. The number of channels and wavelength spacing of the Raman laser can be controlled readily by Δn · L products of PMF segments in the intracavity PMF Lyot-Sagnac filter.

Single-longitudinal-mode multiwavelength fiber ring laser

A single-longitudinal-mode multiwavelength fiber ring laser is proposed and demonstrated. The single-longitudinal-mode operation is realized using a fiber loop mirror with a saturable absorber. The fiber loop mirror acts as a passive self-tracking narrow multiband optical filter. Single-longitudinal-mode multiwavelength lasing is generated by using either a Lyot-Sagnac filter or a fiber grating array.

Label erasing technique employing Lyot-Sagnac filter

A novel label erasing technique employing a Lyot-Sagnac filter with a flat top and a sharp notch is proposed and experimentally demonstrated in all-optical label swapping systems. It is shown that the performance of this eraser is superior to the traditional fibre loop mirror eraser.