Intensity-dependent Loss Research Articles

Sagnac-interferometer-based multiwavelength SOA fiber laser assisted by an intensity-dependent loss mechanism.

We demonstrate a Sagnac-interferometer-based multiwavelength fiber laser with an intensity-dependent loss (IDL) mechanism in the L-band region using a semiconductor optical amplifier (SOA) as the gain medium. The IDL mechanism flattens and stabilizes the multiwavelength spectrum. We also investigate the effect of rotation angles of polarization controllers (PCs) at different polarization devices on multiwavelength performance. At best settings, 31 lasing lines within 3dB uniformity were generated with an extinction ratio (ER) of 17dB. Adjusting the half-wave plate of PC1 and PC2 from 0° to 90° shifted the multiwavelength output by 0.01nm and 0.072nm, respectively. PC2 adjustment also affects the multiwavelength flatness as compared to PC1. Furthermore, the number of lasing lines and the ER were directly influenced by the SOA current.

Switchable and tunable multi-wavelength random distributed feedback fiber laser based on parallel Lyot filter

A switchable and tunable multi-wavelength random distributed feedback fiber laser based on a parallel Lyot filter is designed, and the transmission characteristics of the filter are deduced in detail by using the transmission matrix theory. The randomly distributed backward Rayleigh scattering generated in single-mode fiber (SMF) serves as a feedback mechanism. The number of output wavelength increases linearly with the increase of pump power. By adjusting the polarization controller (PC) to control the polarization state of the beam into the polarization maintaining fiber (PMF), laser channels with wavelength interval of 0.88 nm or 0.46 nm can be output. Where the wavelength interval depends on the wavelength phase difference caused by the corresponding branch PMF. The intensity-dependent loss (IDL) caused by the nonlinear optical loop mirror (NOLM) in the experimental structure is not only used to suppress the intense mode competition caused by EDF, but also to control the spectral range of the output wavelength to achieve tunable laser output. When the wavelength interval is 0.88 nm, the wavelength tuning ranges of the three and four laser channels are 4.4 nm and 3.7 nm, respectively. When the wavelength interval is 0.46 nm, the wavelength tuning ranges of the three and four laser channels are 3.7 nm and 4 nm, respectively. Subsequently, the influence of using different lengths of SMF on the output wavelength is analyzed. It is found that longer SMF can increase the linewidth of the laser channel, and the side mode suppression ratio (SMSR) will be improved to 39 dB. In addition, the output power fluctuation of the laser is less than 0.32 dB within 30 min, and the power amplitude and SMSR are stable at −4.47dBm and 34.5 dB, respectively, indicating that the laser can achieve flat and stable multi-wavelength output at room temperature.

Switchable multi-wavelength actively Q-switched erbium-doped fiber laser based on nonlinear polarization rotation and Sagnac filter

This letter describes a switchable multi-wavelength actively Q-switched erbium-doped fiber (EDF) ring laser based on nonlinear polarization rotation (NPR) structure with Sagnac filter and electro-optic modulator (EOM). The intensity-dependent loss (IDL) generated by the constructed NPR structure can suppress the mode competition caused by EDF, combined with a comb filter Sagnac loop which composed of only 2-m-long polarization maintaining fiber (PMF), the constructed laser generates nine-wavelengths laser output with a constant wavelength interval of 3 nm. When the NPR structure is removed, the constructed laser generates quadruple-wavelengths laser output with 3 nm constant wavelength interval. It is proved that the effect of the NPR can suppress mode competition to achieve multi-wavelength laser output. In the laser with the constructed NPR structure, the nine-wavelengths laser output has a maximum wavelength shift of 0.21 nm and a maximum power fluctuation of 0.69 dB, while when the NPR structure is removed from the constructed laser, for the quadruple-wavelengths laser output, the maximum wavelength shift is 0.16 nm and the maximum power fluctuation is 0.29 dB. When the constructed laser with or without NPR structure, the minimum Q-switched pulse width and maximum average output power are 1.42 μs, 1.24 μs and 3.2μW, 10.2μW, respectively.

Effect of hybrid optical amplifier in multiwavelength fiber laser utilizing Sagnac loop mirror interferometer

This paper presents a multiwavelength fiber laser (MWFL) utilizing a Sagnac loop mirror (SLM) interferometer with a hybrid optical amplifier comprising a semiconductor optical amplifier (SOA) and an erbium-doped fiber amplifier (EDFA). Previously, no research reported MWFL based on SOA and EDFA combination utilizing SLM interferometer. The combination of a polarizer and SOA induces intensity-dependent loss mechanism at a certain polarization state. It is utilized to flatten and stabilize the multiwavelength spectrum. The laser produces maximum lasing lines of 65 channels within 5 dB uniformity and with 10 dB of extinction ratio. The removal of EDFA from the cavity reduces the peak power by 11 dB with the output spectrum shifted to shorter wavelength by 6 nm. Furthermore, the laser shows a significantly stable output with peak power fluctuation lower than 0.8 dB within 100 min of observation time.

Selectable multiwavelength thulium-doped fiber laser based on parallel Lyot filter

This paper demonstrates a selectable 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 specific polarization state from the combination of highly nonlinear fiber and polarizer. The wavelength spacing of the TDFL can be selected 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 selected by adjusting 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 in the laser performances.

Nonlinearity Effect on Multiwavelength fiber laser based on Sagnac loop mirror interferometer

This paper demonstrates a multiwavelength fiber laser (MWFL) with erbiumdoped fiber amplifier (EDFA) as gain medium and Sagnac loop mirror interferometer as filter. Stable and flat lasing spectrum was achieved when highly nonlinear fiber (HNLF) was inserted into the laser cavity. The number of lasing lines and extinction ratio (ER) was directly influenced by EDFA gain where at maximum setting, 14 lasing lines with ER of 19 dB were generated. The stable and flat spectrum achieved spanned about 1.6 nm. This is due to the induced intensity dependent loss mechanism in the cavity by adjusting the half-wave plate of the polarization controller in combination with the HNLF. The MWFL output showed peak power variation of about 2.1 dB within 100 minutes of observation time.

Nonlinear control of topology

Topological Optics Controlling the topological properties of physical systems provides a platform for developing devices and technology that are robust to defects. Xia et al. present a photonic platform in which the underlying dynamics are driven and tuned by the interplay among topology, non-Hermiticity, and nonlinearity (see the Perspective by Roztocki and Morandotti). Using photonic lattices consisting of laser-written waveguides that are continuous (“gain”) and sectioned (“loss”) and coupled to an interface defect, they demonstrate the nonlinear control of parity-time symmetry and nonlinearity-induced restoration and/or destruction of non-Hermitian topological states. Such concepts are applicable to a broad spectrum of non-Hermitian systems that have intensity-dependent gain or loss and may enable new approaches for light manipulation. Science , this issue p. [72][1]; see also p. [32][2] [1]: /lookup/doi/10.1126/science.abf6873 [2]: /lookup/doi/10.1126/science.abg5441

Nonlinear tuning of PT symmetry and non-Hermitian topological states.

Topology, parity-time (PT) symmetry, and nonlinearity are at the origin of many fundamental phenomena in complex systems across the natural sciences, but their mutual interplay remains unexplored. We established a nonlinear non-Hermitian topological platform for active tuning of PT symmetry and topological states. We found that the loss in a topological defect potential in a non-Hermitian photonic lattice can be tuned solely by nonlinearity, enabling the transition between PT-symmetric and non-PT-symmetric regimes and the maneuvering of topological zero modes. The interaction between two apparently antagonistic effects is revealed: the sensitivity close to exceptional points and the robustness of non-Hermitian topological states. Our scheme using single-channel control of global PT symmetry and topology via local nonlinearity may provide opportunities for unconventional light manipulation and device applications.

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.

Investigation on factors influencing flatness of a bidirectional SOA-based multiwavelength fiber laser

We investigate the flatness of the output spectrum in two multiwavelength fiber lasers (MWFLs) using two different configurations, unidirectional and bidirectional semiconductor optical amplifiers (SOAs). The most significant finding is the large variance in flatness values between the configurations where the unidirectional SOA is at 6.54 dB and the bidirectional SOA is at 1.45 dB. This is due to the lower total power and incomplete counter propagation in the cavity. The best SOA-based MWFL using a bidirectional SOA can generate 215 spectral lines within 5 dB uniformity. The multiwavelength spectrum is flat with a broad range, about 20 nm, owing to the property of spectral reshaping by the bidirectional amplification process in the SOA as well as complete counter propagation. Apart from the bidirectional SOA, the intensity-dependent loss (IDL) mechanism also contributes to the multiwavelength spectrum flatness. The adjustment of the half-wave plate (HWP) in the polarization controller (PC) affects the wavelength range and optical signal-to-noise ratio (OSNR). The MWFL shows excellent power stability, with the highest power deviation being only 0.95 dB.

The method of single expression (MSE) as a prospective modeling tool for boundary value problems: an extension from nano-optics to quantum mechanics

Mathematical description of the wave phenomena in nano-optics and quantum mechanics is similar and requires wavelength-scale analysis of wave interaction with nano-layers in optics and micro-particle interaction with potential barriers or wells in quantum mechanics. Traditionally, when dealing with boundary problems in nano-optics and quantum mechanics, the same fundamental approach of counter-propagating waves is often being used, when general solutions of the wave equations are presented as a sum of counter-propagating waves. This type of solution presentation relies on the superposition principle restricting correct description of strong intensity-dependent nonlinear wave-matter interaction. The non-traditional method of single expression (MSE) does not exploit the superposition principle, but rather uses resulting field representation and backward-propagation algorithm allowing to obtain correct steady-state solutions of boundary value problems without approximations and at any value of wave intensity by taking into account correctly intensity-dependent nonlinearity, loss or gain in a medium. In the present work a detailed description of the MSE approach extended for one dimensional quantum mechanical boundary value problems is presented. Results of numerical simulations by the MSE of electron tunneling through rectangular single and double potential barriers are presented and discussed.

Stable and Broad Multiwavelength Generation with the Assistance of Intensity Dependent Loss Mechanism based on Bidirectional SOA

Multiwavelength fiber laser is based on bidirectional semiconductor optical amplifier (SOA) is demonstrated. The multiwavelength spectrum from this setup produces 143 lasing lines within 5 dB uniformity. This bidirectional setup can maintain a flat multiwavelength lines with high peak power since both lights from SOA are fully utilized. The combination of polarization controllers (PCs), SOA and polarization beam combiner (PBC) induces an intensity dependent loss (IDL) mechanism which acts as the flatness element. The multiwavelength performance is investigated at different SOA current and PCs setting. Lower SOA current and different PC adjustment deteriorate multiwavelength performance. The laser is greatly stable since no laser fluctuation is found within 100 minutes of stability test.

Wavelength-number-tunable multi-wavelength SOA fiber laser based on NPR effect

Abstract A wavelength-number-tunable multi-wavelength SOA fiber laser incorporating a double pass Mach–Zehnder interferometer (MZI) is experimentally demonstrated in this paper. Due to the nonlinear polarization rotation (NPR) effect of SOA, the intensity-dependent loss (IDL) is induced by the combination consisting of SOA and polarization devices to achieve stable multiwavelength output with ultra-narrow wavelength spacing. In addition, the degree of IDL can be controlled by adjusting PCs for the purpose of tuning the number of wavelengths. Stable multiwavelength output with power equality have been achieved at room temperature, which have no obvious power fluctuation. The wavelength spacing is ultra-narrow, which is as small as 0.081 nm, and the number of lasing lines is tuned from 168 to 250. However, due to the high noise figure of SOA, the optical signal-to-noise ratios (OSNR) is less than 8.85 dB.

Tm-doped fiber laser with multiwavelength output and switchable wavelength difference based on nonlinear polarization rotation effect

In this paper, we report on the characteristics of multiwavelength output and wavelength difference switching in a Tm-doped fiber laser based on the nonlinear polarization rotation effect. The multiwavelength output and wavelength difference switching were realized through joint action of nonuniform intensity-dependent loss caused by the nonlinear polarization rotation effect and the polarization controller intertwined with Tm-doped fiber. Under dual-wavelength state, one wavelength could be switched within wavelength intervals of 44.7, 58.0, 68.2, and 73.1 nm, and the position of the other wavelength nearly remained unchanged in the switching process. The fiber laser with switchable wavelength difference has a broad application prospect in laser space communication and optical fiber sensing.

Recent progress in multi-wavelength fiber lasers: principles, status, and challenges

In recent years, multi-wavelength fiber lasers play a significant role in plenty of fields, ranging from optical communications to mechanical processing and laser biomedicine, owing to their high beam quality, low cost, and excellent heat dissipation properties. Benefitting from increasing maturity of optical elements, the multi-wavelength fiber laser has made rapid developments. In this review, we summarize and analyze diverse implementation methods covering continuous wave and pulsed fiber lasers at room temperature conditions: inserting an optical filter device and intensity-dependent loss structure in the resonant cavity, and applying ultrafast nonlinear optical response of materials and a dual-cavity structure. Finally, future challenges and perspectives of the multi-wavelength fiber laser are discussed and addressed.

Generation of sub-nanosecond pulse in dual-wavelength praseodymium fluoride fibre laser

In this paper, we demonstrate a stable dual-wavelength pulsed output from a praseodymium doped fluoride fiber laser. These dual functions are induced by intensity-dependent transmission and loss due to the cavity birefringence. The two lasing wavelengths centered at 1298.26 nm and 1299.91 nm with a spacing of 1.65 nm and a 3 dB bandwidth of 0.11 nm and 0.13 nm respectively are obtained. The pulse width induced by the dual-wavelength laser falls within the picosecond region, with a repetition rate of 389 KHz and a maximum average pulse energy of 5.4 nJ.

结构紧凑的双波长连续波掺铒光纤激光器

Multiwavelength erbium-doped fiber lasers can be applied to many fields, such as wavelength division multiplexing optical communication and others attracting considerable attention. To meet the requirements of different applications, we propose a compact dual-wavelength continuous-wave erbium-doped fiber laser based on nonlinear amplifying loop mirror. An all-polarization-maintaining fiber cavity is adopted in which there are only three intracavity devices besides fiber itself:a wavelength division multiplexer, a 2×2 fiber coupler and a fiber reflector. The intensity-dependent loss effect induced by the nonlinear amplifying loop mirror is used to equalize the intensity in the cavity. The input laser with higher power suffers a higher loss than the one with lower power. This feature can be used to suppress mode competition and achieve stable multiwavelength oscillation. With a pump power of 260 mW, dual-wavelength erbium-doped fiber laser can be achieved, with wavelengths of 1 560.5 nm and 1 563.2 nm, respectively. The side-mode suppression ratio is 46.8 dB. As pump power increases, the laser can operate in single-, dual-and triple-wavelength regions in proper order. As the multi-wavelength lasing oscillation is a balance between intensity-dependent loss and mode competition, the intensity change breaks the original balance state, resulting in the change in number and wavelength of lasing lines. This laser is simply structured and easy to operate. It can have applications in many fields.

Wavelength-tunable Q-switched fiber laser based on a 45° tilted fiber grating

A continuously tunable Q-switched all-fiber Er-doped laser based on a 45° tilted fiber grating and tunable bandpass filter is demonstrated. The 45° tilted fiber grating is used to achieve the nonlinear polarization rotation (NPR) along with two polarization controllers (PCs), Q-switching is realized due to the fact that the NPR effect induced intensity-dependent loss. Under the pump power of 655 mW, the Q-switched optical spectrum can be continuously tuned from 1512 nm to 1552 nm by simply rotating the tunable bandpass filter. During the wavelength tuning process, the average output power increases from 0.282 mW to 4.884 mW while the repetition rate enhances from 27.3 kHz to 119 kHz. To the best of our knowledge, this is the widest continuously tunable range of Q-switched fiber Lasers based on nonlinear polarization rotation effect and spectral bandpass filter.

Multiwavelength Fiber Laser based on Bidirectional Lyot Filter in Conjunction with Intensity Dependent Loss Mechanism

<span>We experimentally demonstrate a multiwavelength fiber laser (MWFL) based on bidirectional Lyot filter. A semiconductor optical amplifier (SOA) is used as the gain medium, while its combination with polarization controllers (PCs) and polarization beam combiner (PBC) induces intensity dependent loss (IDL) mechanism. The IDL mechanism acts as an intensity equalizer to flatten the multiwavelength spectrum, which can be obtained at a certain polarization state. Using different ratio of optical splitter has affected to multiwavelength flatness degradation. Subsequently, when we removed a polarizer in the setup, the extinction ratio (ER) is decreased. Ultimately, with two segments of polarization maintaining fiber (PMF), two channel spacings can be achieved due to splicing shift of 0° and 90°.</span>

Broad bandwidth SOA-based multiwavelength laser incorporating a bidirectional Lyot filter

We demonstrate a broad bandwidth multiwavelength laser based on a bidirectional Lyot filter and a semiconductor optical amplifier with a mechanism of intensity-dependent loss as the flatness agent. A wide bandwidth of a multiwavelength spectrum of 32.9 nm within a 5 dB uniformity is obtained under optimized polarization parameters. For this case, the number of generated lasing lines is 329 with a fixed wavelength separation of 0.1 nm. The power stability of this multiwavelength laser is less than 1.35 dB within 200 min time frame. This shows that the bidirectional Lyot filter provides an alternative option for multiwavelength generation in laser systems.