Multimode Interference Filter Research Articles

Buildup of multiple spatiotemporal nonlinear dynamics in an all-fiber multimode laser

Ultrafast lasers based on multimode fibers have attracted extensive attention owing to the large mode-field area and nonlinear tolerance. The high spatial degree of freedom of multimode fibers is significant for spatiotemporal pulses locked both in transverse and longitudinal modes, where the energy of output pulses can be remarkably improved. Herein, the 1.5-μm all-fiber spatiotemporal mode-locked laser was realized based on carbon nanotubes as a saturable absorber. Moreover, by tuning the polarization controller and the pump power carefully, the output wavelengths can be ranged from 1529 to 1565 nm based on the multimode interference filter. In addition, Q-switched mode-locking and spatiotemporal mode-locked dual combs were also observed by further adjusting the polarization controller. Such a kind of an all-fiber multimode laser offers a crucial insight into the spatiotemporal nonlinear dynamics, which is of great significance in scientific research and practical applications.

Research Progress in Tunable Fiber Lasers Based on Multimode Interference Filters.

Tunable fiber lasers have the advantages of good beam quality, high integration, and adjustable output wavelength, and they are widely used in fields such as optical fiber communication and optical fiber sensing. The fiber filter is one of the key components of tunable fiber lasers. Among the various filters currently used, multimode interference filters have the advantages of simple structure, convenient implementation, flexible tuning methods, and convenient spectral range design. The structures of multimode interference filters based on multimode fibers, no-core fibers, multi-core fibers, tapered fibers, and other special fibers are introduced in this paper. The working principles and tuning methods are analyzed and the research progress of tunable fiber lasers based on these filters is summarized. Finally, the development trend of tunable fiber lasers based on multimode interference filters is discussed. The rapid development and applications of multimode interference filters can help improve the performance of continuous and pulse lasers as well as promote the practicality of tunable fiber lasers.

Effect of graphite oxide electrochemically exfoliated over a multimode interference filter.

In this work, we study multimodal interference filters with a graphite oxide coating. Use of the multimodal interference filter shows a distinctive peak in the signal spectrum, and when using the exfoliated graphite coated multimodal interference filter, the signal shows different spectral changes, such as the full width at half maximum of the curve, the maximum power, and central wavelength, which indicates that graphite oxide absorbs part of the energy. In addition, microscope observations when a He-Ne laser is passed through the filter confirm that graphite oxide is adhered to the filter.

Tunable and interval-adjustable multiwavelength Erbium-doped fiber laser based on a compound filter

We propose and experimentally demonstrate a multiwavelength erbium-doped fiber laser (EDFL) based on a compound filter. The compound filter is composed of polarization controllers (PCs), polarizers and a piece of home-made polarization-maintaining photonic crystal fiber (PM-PCF). Due to the high birefringence and few-mode properties of the PM-PCF, Lyot filter and multimode interference filter can be realized simultaneously in the compact structure. Hence, the EDFL can achieve flexible lasing output. By adjusting PCs, the lasing can obtain single-, dual-, triple- and quad-wavelength output, respectively. The tuning range of single-wavelength lasing output can exceed 20 nm with side-mode suppression ratio (SMSR) above 40 dB. For dual-wavelength lasing output, the tuning range with fixed interval can reach 16 nm. Besides, the wavelength interval can be adjusted from 2.5 nm to 17.4 nm. The great interval adjustability is also observed in triple-wavelength output. The wavelength interval can be adjusted from 8.2 nm to 14.7 nm. Compact structure, flexible lasing output, and good stability make our proposed EDFL more convenient and practical to the applications such as sensing and wavelength division multiplexing.

Wavelength Tuning of Multimode Interference Fiber Lasers: A Review

Herein, the main aspects of fiber lasers are summarized where multimode interference (MMI) is the underlying phenomenon for the wavelength tuning mechanism. Also, 15 years of work in the field are covered, from its first report, in 2005, to the most recent publications, in 2020. In addition to the historical perspective, insights into the different mechanisms are also provided that are exploited to tune the spectral response of the MMI filters used in fiber lasers, among which are free space, optofluidic, stress optic, thermo optic, and nonlinear mechanisms.

Fiber laser refractometer operating in the 2 μm spectral region based on the MMI effect

We experimentally demonstrate a fiber laser refractometer based on the use of a multimode interference (MMI) fiber structure. The MMI filter is constructed with an uncladded fiber segment which acts as sensing element to determine the refractive index (RI) of liquid solutions. The laser emission, generated at the 2 μm waveband, is wavelength shifted in linear proportion to the RI of the liquid. The proposed fiber laser refractometer exhibits high sensibility of 937.81 nm/RIU.

基于MMI滤波器的可调谐连续光全光纤OPO

基于MMI滤波器的可调谐连续光全光纤OPO

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.

Dual-wavelength thulium-doped fiber laser with separate wavelengths selection based on a two mmi filters configuration

Dual-wavelength laser emission of a ring cavity Tm-doped fiber laser with a separate wavelength selection of the simultaneously generated laser lines is experimentally demonstrated. A dual-wavelength laser operation is obtained by using two homemade multimode interference (MMI) filters with transmission peaks at the wavelengths of 1814.23 and 1872.15 nm, which are placed in a Mach Zehnder interferometer configuration for independent selection of the dual-wavelength generated laser lines. The selection of the shorter laser wavelength is achieved by submerging the MMI filter in different ethylene glycol/water mixtures, reaching a wavelength selection in the broad range of ~24 nm. The stability results of the simultaneously generated laser lines are also shown. The use of the proposed MMI filters as reliable spectral filters for dual-wavelength generation in all-fiber Tm-doped fiber laser systems is experimentally demonstrated.

Passively Q-switched dual-wavelength thulium-doped fiber laser based on a multimode interference filter and a semiconductor saturable absorber

In this paper, we have demonstrated a theta cavity passively Q-switched dual-wavelength fiber laser based on a multimode interference filter and a semiconductor saturable absorber. Relying on the properties of the fiber theta cavity, the laser can operate unidirectionally without an optical isolator. A semiconductor saturable absorber played the role of passive Q-switch while a section of single-mode-multimode-single-mode fiber structure served as an multimode interference filter and was used for selecting the lasing wavelengths. By suitably manipulating the polarization controller, stable dual-wavelength Q-switched operation was obtained at ~1946.8 nm and ~1983.8 nm with maximum output power and minimum pulse duration of ~47 mW and ~762.5 ns, respectively. The pulse repetition rate can be tuned from ~20.2 kHz to ~79.7 kHz by increasing the pump power from ~2.12 W to ~5.4 W.

Liquid level and temperature sensing by using dual-wavelength fiber laser based on multimode interferometer and FBG in parallel

Abstract The detection of liquid level and temperature based on a fiber ring cavity laser sensing configuration is presented and demonstrated experimentally. The sensing head contains a fiber Bragg grating (FBG) and a single-mode–cladding-less–single-mode multimode interferometer, which also functions as wavelength-selective components of the fiber laser. When the liquid level or temperature is applied on the sensing head, the pass-band peaks of both multimode interference (MMI) filter and FBG filter vary and the two output wavelengths of the laser shift correspondingly. In the experiment, the corresponding sensitivities of the liquid level with four different refractive indices (RI) in the deep range from 0 mm to 40 mm are obtained and the sensitivity enhances with the RI of the liquid being measured. The maximum sensitivity of interferometer is 106.3 pm/mm with the RI of 1.391. For the temperature measurement, a sensitivity of 10.3 pm/°C and 13.8 pm/°C are achieved with the temperature ranging from 0 °C to 90 °C corresponding to the two lasing wavelengths selective by the MMI filter and FBG, respectively. In addition, the average RI sensitivity of 155.77 pm/mm/RIU is also obtained in the RI range of 1.333–1.391.

Spectral Tailoring of Random Fiber Laser Based on the Multimode Interference Filter

In this paper, we propose and experimentally demonstrate a novel scheme to tailor the spectrum of random fiber laser (RFL) based on the multimode interference effect. A fiber loop mirror (FLM) incorporating multimode interference filter (MMIF) with single mode fiber (SMF)-MMF-SMF structure acts as a wavelength-dependent point reflector in half-opened RFL. By varying the length of MMF, either single wavelength random lasing with specific wavelength or multiwavelength random lasing with selective wavelength spacing can be generated in MMIF-FLM-based RFL. Due to the wide wavelength range of the MMIF, cascaded multiwavelength random lasing can also be realized. The spectrum adjustable all fiberized RFL based on the MMIF shows distinct advantages, such as easy fabrication, wide operating wavelength range, and low-cost. Besides, the MMIF-FLM can has good power handling ability, by combining the MMIF-FLM and the short-length cavity, the proposed MMIF-based forward-pumping RFL also has a great potential to generate high power, high efficiency random lasing with the adjustable spectral property.

Isolator-Free Unidirectional Multiwavelength Tm-Doped Double-Clad Fiber Laser Based on Multimode Interference Effect

In this paper, an isolator-free unidirectional multiwavelength Tm-doped fiber laser is experimentally investigated. The isolator-free unidirectional operation of the laser is realized by the construction of a type of theta cavity. A single-mode-multimode-single-mode fiber structure served as a multimode interference filter is employed for implementing multiwavelength operation. Wavelength numbers from one to three can be obtained by increasing the pump power and properly adjusting the polarization controller. Besides the single wavelength emission at ∼2002.6 nm, dual-wavelength operations (∼1952.6 nm, ∼1954.7 and ∼1954.8 nm, ∼2002.7 nm) with signal-to-noise ratios larger than ∼46 dB and three-wavelength operation (∼1952.8, ∼1954.5, and ∼2002.9 nm) with signal-to-noise ratios larger than ∼50 dB have also been obtained, respectively. The maximum output power of ∼545 mW was obtained at pump power of ∼7.3 W, when the laser operates at three-wavelength oscillation and the slope efficiency is ∼10%. Our demonstrated fiber laser source represents a type of all-fiberized solution for the realization of high-power, unidirectional and controllable multiwavelength operations, simultaneously.

Narrow-linewidth broadly tunable Yb-doped Q-switched fiber laser using multimode interference filter.

A narrow-linewidth broadly tunable Yb-doped Q-switched fiber laser using an acousto-optic modulator and multimode interference filter (MMIF) in the linear bulk cavity resonator and an all-fiber ring cavity resonator has been demonstrated. Insertion of an MMIF in the linear cavity resonator using bulk components decreased the spectral bandwidth of the Q-switched signal by two orders of magnitude from 11 to less than 0.1 nm. Spectral tunability of more than 16 nm in the range from 1057 to 1073 nm has also been achieved by the combination of MMIF and a standard polarization controller (SPC). A decrease in the pulse duration with a decrease in the spectral bandwidth of the output signal has also been recorded. The pulse duration of the Q-switched signal was reduced from ∼305 to ∼240 ns by the introduction of the MMIF in the resonator at the same value of the input pump power. In the case of the all-fiber Q-switched ring cavity resonator, the spectral bandwidth of the Q-switched signal was reduced by two orders of magnitude from ∼17 to less than 0.1 nm due to the introduction of the MMIF in the resonator. The spectral tunability of more than 12 nm in the range from 1038 to 1050 nm was achieved by an MMIF and an SPC.

Wavelength-Spacing Switchable Dual-Wavelength Single Longitudinal Mode Thulium-Doped Fiber Laser at 1.9 μm

We propose and demonstrate a spacing switchable dual-wavelength single longitudinal mode thulium-doped fiber laser at 1.9 μm. The fiber laser employs a ring cavity and a segment of 4-m thulium-doped fiber pumped by a 1563 nm laser. A fiber Sagnac loop is used as a comb filter to generate a stable dual-wavelength laser. A multimode interference filter consisting of a single-mode–multimode–single-mode fiber and a rotary fiber squeezer is used to adjust the wavelength spacing. When pump power is fixed at 260 mW, a stable dual-wavelength laser at 1.9 μm is obtained by adjusting the polarization controller in the Sagnac filter, and the wavelength spacing can be tuned from 6.7 to 26.7 nm by adjusting the rotary fiber squeezer in the multimode interference filter. Each wavelength of the dual-wavelength laser operates at a single longitudinal mode state, and the maximum linewidth is 7.5 MHz analyzed by a Fabry–Perot scanning interferometer.

MMI filters configuration for dual-wavelength generation in a ring cavity erbium-doped fibre laser

Dual wavelength laser generation has been of constant interest due to their applications in optical communications and teraheartz generation. A novel configuration for Dual-wavelength laser generation based on the use of a couple of multimode interference (MMI) filters is demonstrated in a ring cavity Erbium-doped fibre laser. The MMI filters consist of a segment of no-core fibre spliced between two SMF-28 single mode fibre segments. The MMI filters configured as a Mach-Zehnder interferometer, are used as transmission spectral filters for simultaneous generation of two laser wavelengths. An optical attenuator is used to adjust the intra-cavity losses for dual-wavelength laser generation. Laser emission at 1540.4 and 1554 nm for a wavelength separation of ~13.6 nm is obtained. The laser wavelengths output power stability variations with the applied pump power is also experimentally discussed. The use of MMI filters in the proposed dual-wavelength laser filter is experimentally demonstrated as a reliable device for dual-wavelength generation in fibre lasers.

All-fiber widely tunable mode-locked thulium-doped laser using a curvature multimode interference filter

We demonstrated a widely tunable mode-locked thulium doped fiber laser (TDFL) by using a homemade multimode interference filter (MMIF). The MMIF had a structure of single mode fiber (SMF)—multimode fiber (MMF)—SMF and three main transmission peaks at 1901.2, 1957.2 and 2043.2 nm. By mechanically bending the MMIF, the three main transmission peaks were tuned in the range of 1860–2024 nm due to multimode interference effect. By inserting the MMIF into a passively mode-locked TDFL cavity pumped by a 1570 nm fiber laser, a tunable mode-locked TDFL with a tuning range of 1919.6–2014.9 nm was achieved by adjusting the MMIF. To the best of our knowledge, such a tunable range is the largest among all-fiber tunable mode-locked TDFLs.

Tunable multiwavelength Tm-doped fiber laser based on the multimode interference effect.

A simple multiwavelength Tm-doped fiber laser at the 2μm band based on multimode interference (MMI) is proposed and experimentally demonstrated. In this scheme, a 4m Tm-doped single-mode fiber is pumped by a 1568nm laser, and a single-mode-multimode-single-mode (SMS) fiber structure is used as an MMI filter in which the multimode fiber is used to tune the laser. Laser operation of up to three wavelengths is obtained based on the MMI filter. The wavelengths can be tuned by adjusting the polarization controller and rotating the multimode fiber in the SMS structure, and the tuning region is about 24nm, i.e., 1892-1916nm. The side-mode suppression ratio of the laser is about 54dB. The 3dB linewidth is less than 0.04nm. Peak fluctuation at each wavelength is analyzed, and the results show that the power fluctuation is less than 3dB around the average power.

Wide range optofluidically tunable multimode interference fiber laser

An optofluidically tunable fiber laser based on multimode interference (MMI) effects with a wide tuning range is proposed and demonstrated. The tunable mechanism is based on an MMI fiber filter fabricated using a special fiber known as no-core fiber, which is a multimode fiber (MMF) without cladding. Therefore, when the MMI filter is covered by liquid the optical properties of the no-core fiber are modified, which allow us to tune the peak wavelength response of the MMI filter. Rather than applying the liquid on the entire no-core fiber, we change the liquid level along the no-core fiber, which provides a highly linear tuning response. In addition, by selecting the adequate refractive index of the liquid we can also choose the tuning range. We demonstrate the versatility of the optofluidically tunable MMI filter by wavelength tuning two different gain media, erbium doped fiber and a semiconductor optical amplifier, achieving tuning ranges of 55 and 90 nm respectively. In both cases, we achieve side-mode suppression ratios (SMSR) better than 50 dBm with output power variations of less than 0.76 dBm over the whole tuning range.

Note: Broadly tunable all-fiber ytterbium laser with 0.05 nm spectral width based on multimode interference filter.

A multimode interference filter with narrow transmission bandwidth and large self-imaging wavelength interval is constructed and implemented in an ytterbium doped fiber laser in all-fiber format for broad wavelength tunability as well as narrow spectral width of the output beam. The peak transmission wavelength of the multimode interference filter was tuned with the help of a standard in-fiber polarization controller. With this simple mechanism more than 30 nm (1038 nm-1070 nm) tuning range is demonstrated. The spectral width of the output beam from the laser was measured to be 0.05 nm.