Dual-wavelength Single-longitudinal-mode Research Articles

Tunable and switchable dual-wavelength SLM narrow-linewidth fiber laser with Lyot filter cascaded by double-ring cavity

An erbium-doped fiber (EDF) laser with single longitudinal mode (SLM), narrow linewidth, and switchable dual-wavelength based on a Lyot filter cascaded dual-ring cavity structure (DRCs) has been designed and constructed. In the experimental system, an Employed passive DRCs enhances the longitudinal mode spacing, while the Lyot filter effectively mitigates mode competition within the laser cavity. The composite filter structure facilitates stable dual-wavelength output while ensuring a consistent SLM output. Then, experimental results reveal optical signal-to-noise ratios (OSNR) with 62 dB for single-wavelength and 55 dB for dual-wavelength. Additionally, the power and wavelength fluctuations for both single-wavelength and dual-wavelength remained stable throughout monitoring periods of 20 min and 1 h, respectively. Meanwhile, a maximum tuning range of 2 nm is achieved by stretching a polarization-maintaining fiber Bragg grating (PM-FBG) using a fiber displacement stage. The linewidths of each wavelength are 2.8 kHz and 2.6 kHz, respectively. During the process of wavelength tuning, the fluctuations of linewidth do not exceed 0.3 kHz and 0.45 kHz, respectively. Simultaneously, the polarization states of each wavelength are measured, which reveals orthogonal single polarization. The relative intensity noise (RIN) is measured below −133 dB/Hz at frequencies above 1 MHz.

Switchable and tunable orthogonal single-polarization dual wavelength SLM fiber laser based on parity-time symmetric system and PM-FBG

A dual-wavelength narrow linewidth orthogonal single polarization fiber laser based on a parity-time (PT) symmetric system is proposed and demonstrated, which achieves the function of tunable and switchable wavelength, and single longitudinal mode (SLM) operation. The PT symmetric system composes of a single physical loop, which includes two polarization controllers (PCs) and a polarization beam splitter (PBS). By modulating PCs to match gain, loss and coupling coefficient, the switchable wavelength and stable SLM laser output have been achieved. Through stretching the polarization maintaining fiber Bragg grating (PM-FBG), the wavelength adjustment range from 1549 nm to 1551 nm is obtained. In the process of tuning, the full width at half maxima (FWHM) linewidths and polarization states at each wavelength have been measured and keep basically stable. The measured FWHM linewidths are less than 13.66 kHz and 11.89 kHz. Further, the stable orthogonal single polarization state has been realized. The degree of polarization (DOP) at each wavelength exceeds 97% and basically remains unchanged during 20 min.

Tunable and switchable dual-wavelength SLM narrow-linewidth fiber laser with cascaded passive double-ring cavity narrowband filters

In this article, we have proposed and demonstrated a tunable, switchable dual-wavelength linear cavity fiber laser, which has a passive dual ring cavity structures (DRCs) and polarization-maintaining fiber Bragg grating (PM-FBG), and can be used for the operation of single-longitudinal mode(SLM), narrow-linewidth, and orthogonal single polarization. The passive DRCs, consisted of four 2 × 2 optical couplers (OCs), work as the narrow-band filter and mirror. The tunable and switchable wavelength of the fiber laser is realized by stretching PM-FBG and adjusting the polarization controller (PC). The optical signal-to-noise ratio (OSNR) at the dual-wavelength operating state can be more than 45 dB in the tunable range. While the OSNR of fiber laser at the each-wavelength operating state can reach 50 dB with the maximum wavelength and power fluctuation of 0.01 nm and 1.2 dB, during the monitoring time of 40 min. In addition, the measured laser linewidths are 375 Hz and 420 Hz, respectively. Meanwhile, the states of polarization are orthogonal single polarization, and the degree of polarization (DOP) is close to 100 %.

Orthogonally polarized dual-wavelength single longitudinal mode Pr:YLF laser at 607 nm and 604 nm

We demonstrate a diode-pumped orthogonally polarized dual-wavelength single-longitudinal-mode Pr:YLF laser output at 607 nm and 604 nm by using combined F-P etalons. The experimental results show that switchable single and dual-wavelength single-longitudinal-mode laser output can be realized by selectively combining the F-P etalons with 0.3 mm and 1 mm thickness. We obtained the maximum output power of the orthogonally polarized dual-wavelength single-longitudinal-mode laser at π-polarized 607 nm and σ-polarized 604 nm is reaches 79 mW, corresponding to a slope efficiency of 6.2%. The measured spectral line-widths are 115.4 MHz and 133.3 MHz respectively. The maximum output power of the single wavelength single-longitudinal-mode laser at 607 nm and 604 nm are 201 mW and 81 mW respectively, corresponding to a slope efficiency of 11.5% and 6%. The measured spectral line-widths are 52.3 MHz and 111.3 MHz respectively. To the best of our knowledge, it is the first time to investigate the orthogonally polarized dual-wavelength single-longitudinal-mode CW Pr:YLF laser.

Tunable and Switchable Dual-Wavelength SLM Narrow-Linewidth Fiber Laser with a PMFBG-FP Filter Cascaded by Multi-Ring Cavity

A single longitudinal mode (SLM) dual-wavelength switchable erbium-doped fiber laser (DW-EDFL) based on polarization-maintaining fiber Bragg grating Fabry–Perot cavity (PMFBG-FP) cascaded multiple sub-ring cavities (MSCs) is proposed. A PMFBG-FP with a narrow-band transmission peak and MSCs was implemented as an optical filter to achieve stable dual-wavelength laser output and guaranteed SLM status. By stretching the PMFBG, a highly stable dual-wavelength tunable output could be achieved with a maximum tuning interval of 0.17 nm. The optical signal-to-noise-ratio (OSNR) at dual-wavelength lasing was higher than 57 dB, and the optimal wavelength and power fluctuations within 0.5 h were 0.01 nm and 0.79 dB, respectively. Meanwhile, the measured linewidths of each wavelength were 1.55 kHz and 1.65 kHz, respectively. The measured polarization states of the two laser wavelengths were linear and orthogonal, with a degree of polarization (DOP) of nearly 100%.

Switchable dual-wavelength SLM narrow linewidth fiber laser based on nonlinear amplifying loop mirror

We demonstrate a stable switchable dual-wavelength single longitudinal mode (SLM) narrow linewidth ytterbium-doped fiber (YDF) laser using a nonlinear amplifying fiber loop mirror (NALM) at 1064nm. The NALM of intensity-dependent transmission acts as a saturable absorber filter and an amplitude equalizer to suppress mode competition and the fiber Bragg grating (FBG) pair is used as one wavelength selection component. By properly adjusting the polarization controllers (PCs), the switchable dual-wavelength SLM fiber laser can be operated steadily at room temperature. The optical signal-to-noise ratio (OSNR) is better than 50dB for both lasing wavelengths. Meanwhile, the linewidth of the fiber laser for each wavelength is approximate 17.07kHz and 18.64kHz with a 20dB linewidth, which means the laser linewidth is approximate 853Hz and 932Hz FWHM. Correspondingly, the measured relative intensity noise (RIN) is less than −120dB/Hz at frequencies over 5.0MHz.

Tunable dual-wavelength single-longitudinal-mode fiber laser based on spectral narrowing effect in a nonlinear semiconductor optical amplifier

A tunable dual-wavelength single-longitudinal-mode (SLM) fiber laser based on a nonlinear semiconductor optical amplifier (NL-SOA) and an optical comb filter is proposed and demonstrated successfully. The SLM operation principle is based on the spectral narrowing effect resulting from the inverse four-wave mixing (FWM) in a NL-SOA. By inserting the NL-SOA inside the fiber laser cavity, SLM lasing can be possibly achieved when stable laser oscillation is established after many roundtrips through the NL-SOA. Further, tunable dual-wavelength SLM output can be obtained by incorporating a tunable optical filter (TOF) and a comb filter inside the laser cavity to perform dual-wavelength selection function. As a result, tunable dual-wavelength SLM oscillation with a wavelength spacing of 0.4nm and a wavelength tuning range of about 56nm has been achieved. Each wavelength has a linewidth less than 8kHz and a side-mode suppression ratio (SMSR) larger than 40dB.

Stability wavelength-spacing-tunable single-longitudinal-mode dual-wavelength erbium-doped fiber laser based on nonlinear amplifying loop mirror

A simple linear cavity configuration for a stability wavelength-spacing-tunable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber laser based on a nonlinear amplifying loop mirror (NALM) is proposed. The gain competition in the erbium-doped fiber (EDF) has been suppressed by the intensity dependent loss introduced by the NALM. The SLM operation is guaranteed by a section of unpumped EDF as saturable absorber. A stable dual-wavelength SLM fiber laser with a wavelength-spacing of 11.35 nm is experimentally realized. The optical signal-to-noise ratio is over 47 dB and the linewidths of two wavelengths measured by delayed self-heterodyne method are 1.1 and 1.0125 kHz, respectively. The tuning range of wavelength-spacing is 9.09–11.35 nm, correspondingly, and the THz signal is from 1.235 to 1.416 THz.

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.

Switchable 10 nm-spaced dual-wavelength SLM fiber laser with sub-kHz linewidth and high OSNR using a novel multiple-ring configuration

A switchable dual-wavelength (10 nm spacing) single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) that uses a multiple-ring configuration was demonstrated experimentally. A novel theoretically lossless triple-ring passive secondary cavity composed of three optical couplers was utilized to select the SLM from the dense main cavity longitudinal modes for the first time. Using two superimposed fiber Bragg gratings as one compact mode-restricting element and introducing the nonlinear polarization rotation effect to alleviate the strong mode competition for the fiber laser, a highly stable dual-wavelength mode-hop-free SLM operation with sub-kHz linewidths and optical signal to noise ratios (OSNRs) of >69 dB was achieved for both lasing wavelengths. By adjusting the polarization controllers, the dual-wavelength operation could be easily switched to single-wavelength lasing with a linewidth of <1 kHz and an OSNR of >72 dB. The proposed EDFL may find many important applications, such as the generation of very pure terahertz waves.

Dual wavelength single longitudinal mode Ytterbium-doped fiber laser using a dual-tapered Mach-Zehnder interferometer

This paper describes a dual wavelength single longitudinal mode (SLM) demonstration for a proposed ytterbium-doped fiber laser. A dualtapered Mach-Zehnder interferometer (MZI) was inserted into the laser ring cavity setup to ensure a stable dual wavelength and SLM operation. The consequent dual wavelength lasing operation had a wavelength spacing of 0.94 nm and a side mode suppression ratio (SMSR) of 50 dB, with the linewidth of this setup measured as 294.15 kHz. A stability test allowed for a measurement of max power fluctuation as less than 0.8 dB for each wavelength and which was indicative of a stable dual wavelength operation.

Dual-wavelength single longitudinal mode fiber laser for microwave generation

Abstract A simple dual-wavelength single longitudinal mode (DW SLM) fiber laser for microwave generation is proposed and demonstrated. Simultaneous oscillation of dual-wavelength with a wavelength spacing of 0.2124 nm is realized, the output peak power of the lasing dual-wavelength is equalized by adjusting polarization controller at room temperature. Birefringent fiber filter and saturable absorber are utilized to guarantee the SLM operation of dual-wavelength fiber laser. A microwave signal at 26.49 GHz is successfully obtained in the experiment, the laser is proved to be effective in the application of microwave generation.

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.

Photonic generation of microwave signal by beating a dual-wavelength single longitudinal mode erbium-doped fiber ring laser based on the polarization maintaining fiber bragg grating

A single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber (EDF) ring laser based on one polarization maintaining fiber Bragg grating (PMFBG) is demonstrated.Due to the polarization hole burning enhanced by the PMFBG, the laser can be designed to operate in stable dual-wavelength oscillation with a wavelength spacing of 0.182 nm at room temperature by adjusting a polarization controller. A section of unpumped EDF acting as a saturable absorber and a feedback fiber loop is used to ensure SLM operation in each of the two lasing lines. A microwave signal at 22.807 GHz is obtained by beating the dual-wavelength fiber laser at a photodetector. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:347–351, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27280

Photonic generation of microwave signal using a dual-wavelength erbium-doped fiber ring laser with CMFBG filter and saturable absorber

A simple approach for photonic generation of microwave signal using a dual-wavelength single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser is proposed and demonstrated. For the first time as we know, a chirped moiré fiber Bragg grating (CMFBG) filter with ultra-narrow transmission band and a chirped fiber Bragg grating (FBG) are used to select the laser longitudinal mode. The stable SLM operation of the fiber laser is guaranteed by the combination of the CMFBG filter and 3m unpumped EDF acting as a saturable absorber. Stable dual-wavelength SLM fiber laser with a wavelength spacing of approximately 0.140nm is experimentally realized. By beating the dual-wavelength fiber laser at a photodetector, photonic generation of microwave signal at 17.682GHz is successfully obtained.

Channel-switchable single-/dual-wavelength single-longitudinal-mode laser and THz beat frequency generation up to 3.6 THz

We propose and demonstrate a simple approach to realize channel-switchable single-/dual-wavelength single-longitudinal-mode (SLM) lasers and switchable beat frequency generation in the THz frequency regime. It is a compact fiber-ring laser incorporating a Fabry–Perot etalon, tunable filters, and a piece of unpumped polarization maintaining erbium-doped fiber (PM-EDF) as the saturable absorber. Two parallel-arranged tunable filters are configured inside the ring cavity to support switchable dual-wavelength SLM operation and consequent THz beat frequency generation. Switchable 19-channel 200-GHz ITU-grid-compatible single-wavelength SLM operation is implemented. Moreover, the channel-switchable dual-wavelength SLM laser and switchable THz beat frequency generation ranging from 0.2 to 3.6 THz with a tuning step of 0.2 THz are demonstrated in the experiment.

Dual-Wavelength Single-Longitudinal-Mode Polarization-Maintaining Fiber Laser and Its Application in Microwave Generation

A novel approach for generating high-frequency microwave signals is proposed and experimentally demonstrated. With a pair of wavelength matched fiber Bragg gratings written directly in a polarization-maintaining erbium-doped fiber, a stable short cavity dual-wavelength single-longitudinal-mode (DW-SLM) distributed-Bragg-reflector fiber laser with orthogonal oscillation modes is realized at room temperature. The wavelength spacing between the two lasing modes is 0.374 nm. By heterodyning the two wavelengths of the DW-SLM fiber laser at a photodetector, microwave signal at over 46 GHz is achieved.

Photonic generation of microwave signal using a dual-wavelength single-longitudinal-mode distributed Bragg reflector fiber laser

In this paper, a novel all-optical microwave generation technique based on a dual-wavelength single-longitudinal-mode (SLM) distributed Bragg reflector (DBR) fiber laser is proposed and demonstrated. By exploiting spatial hole burning (SHB) effect, this laser could provide stable dual-wavelength SLM operation with a wavelength separation of ∼0.088 nm corresponding to the microwave signal at ∼10.484 GHz with a 3 dB bandwidth of ∼28 kHz. By appropriately adjusting the pump power, dual-wavelength oscillation could be maintained at different temperatures. We have theoretically analyzed the mechanism for microwave generation of the proposed DBR laser, and the calculated microwave frequency is in good agreement with our experimental results. Furthermore, experimental observation shows both of the laser wavelengths and generated microwave signals have good stability at room temperature.

A Proposal and Demonstration for Photonic Generation of a Microwave Signal by Incorporating a Microring Resonator

A proposal for photonic generation of a microwave signal is presented by employing a dual wavelength erbium-doped fibre ring laser. In the laser, a microring resonator is cascaded with a tunable bandpass filter to serve as a dual-wavelength selector, an unpumped polarization maintaining erbium-doped fibre is used as a saturable absorber. By replacing the microring resonator with a delay interferometer to verify the proposal, a wavelength-tunable dual wavelength single longitudinal mode laser is demonstrated, and a microwave signal at 10.01 GHz with a linewidth of less than 25 kHz is obtained by beating the two wavelengths at a photodetector.

Photonic generation of tunable microwave signals by beating a dual-wavelength single longitudinal mode fiber ring laser

A novel method of generating tunable microwave signals in the photonic domain is proposed. Eighteen pairs of stable dual-wavelength single longitudinal mode lasings are achieved by incorporating a fiber Bragg grating based Fabry–Perot filter and a tunable fiber grating into a fiber ring cavity. The frequency of the generated microwave signal obtained by beating the dual-wavelength laser with a photodetector can be tuned simply through configuring the working wavelength of the laser. A series of microwave frequencies of 9.4885, 9.572, 9.7111, 9.8498, 9.9598 and 10.0712 GHz are generated experimentally. The proposed method is useful in applications such as wireless access networks, sensor networks, radio-over-fiber systems and software-defined radio.