Stable Single Longitudinal Mode Research Articles

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.

Single longitudinal mode diamond Raman laser in the eye-safe spectral region for water vapor detection.

We report a narrowband and tunable diamond Raman laser generating eye-safe radiation suitable for water vapor detection. Frequency conversion of a tunable pump laser operating from 1063 to 1066 nm to the second order Stokes component in an external standing-wave cavity yielded 7 W of multimode output power in the wavelength range from 1483 to 1488 nm at a conversion efficiency of 21%. Stable single longitudinal mode operation was achieved over the whole tuning range at low power (0.1 W), whereas incorporation of a volume Bragg grating as an output coupler enabled much higher stable power to be attained (0.5 W). A frequency stability of 40 MHz was obtained over a minute without active cavity stabilization. It was found that mode stability is aided via seeding of the second Stokes by four-wave mixing, which leads to a doubling of the mode-hopping interval. The laser was employed for the detection of water vapor in ambient air, demonstrating its potential for remote sensing applications.

A Single Longitudinal Mode Fiber Ring Laser Based on Cascaded Microfiber Knots Filter

A single longitudinal mode (SLM) fiber ring laser based on a cascaded microfiber knots filter (CMKF) is proposed and demonstrated. The CMKF is consists of two microfiber knot resonators, which can cause a spatial mode beating interference deriving from high proportional evanescent field of microfiber and spectrum magnification function of Vernier effect, resulting in a passive narrow-band filter with the ability to generate stable SLM. Theoretical analysis and simulation are carried out to investigate the Vernier transmission spectrum of the CMKF and then the SLM principle. A narrow linewidth, high stability, and low-noise SLM lasing with a central wavelength of 1560.6 nm, a 3-dB bandwidth of less than 0.016 nm, and side mode suppression ratio better than 55 dB is achieved experimentally.

Intrinsically stable high-power single longitudinal mode laser using spatial hole burning free gain

A fundamental advantage of lasers is their ability to produce a large number of photons in a single optical mode, yet this is achieved in only a minor fraction of devices due to the instability mechanism called spatial hole burning. Here, we exploit the spatial hole burning free nature of a stimulated scattering gain medium to demonstrate single longitudinal mode (SLM) operation in a generic standing wave cavity. A continuous wave diamond Raman oscillator with multi-Watt-level output power and a frequency stability of 80 MHz is demonstrated without use of additional mode-selective elements. Mode stability is addressed by considering the coupling of the Stokes power with thermally induced optical path length changes in the gain medium. The results foreshadow a novel approach for greatly extending the power and wavelength range of SLM laser sources, and with potential advantages for achieving sub-Poissonian intensity noise and sub-Schawlow–Townes linewidths.

A Single -Longitudinal-Mode Nd:Ce:YAG Q-Switched Laser Based on a Three-Plan Resonant Reflector

We present an efficient and compact passively Q-switched flash-lamp-pumped Nd:Ce:YAG singlelongitudinal-mode (SLM) laser system. With Cr4+:YAG as a saturable absorber, we design a three-plan resonant reflector for generating smooth SLM Q-switched pulses. We provide a theoretical calculation and optimization of the resonant reflector for improving the longitudinal-mode selection ability. We obtain a stable SLM output with a single-pulse energy of 10 mJ and a pulse width of 10.7 ns at 10 Hz. The near-diffraction-limited beam-quality parameter M2 is less than 1.5. The system can operate with a repetition rate from 1 to 10 Hz. We achieve the stable laser operation with less than 3% fluctuation of the pulse energy within 10,000 shots.

A Novel Switchable and Tunable Dual-Wavelength Single-Longitudinal-Mode Fiber Laser at 2

A switchable and tunable dual-wavelength single-longitudinal-mode (SLM) fiber laser in a 2- $\mu \text{m}$ region based on saturable absorber and self-injection locking is proposed and experimentally demonstrated. The laser topology is based on the parallel connection of fiber Bragg gratings (FBGs) using a coupler to realize switchability and tunability by adjusting the cavity losses and the center wavelengths of FBGs, respectively. The saturable absorber and the self-injection locking ensure the stable operation of the laser at SLM. Dual-wavelength with the power-instability of $\sim 0.7$ dB, the wavelength drift of ±0.08 nm, and a tuning range of 6.7 and 2.7 nm is obtained. Stable SLM operation with linewidths of <9.1 MHz analyzed by the self-homodyne method is obtained. The proposed configuration has ingenious and compact structure and reliable performance, and will have promising applications in the fields of multi-parameter detection in gas sensing or new wavelength-division-multiplexing (WDM) communication systems.

Selectable dual-wavelength erbium-doped fiber laser with stable single-longitudinal-mode utilizing eye-type compound-ring configuration

In this paper, a tunable dual-wavelength erbium-doped fiber (EDF) ring laser with stable single-longitudinal-mode (SLM) under a tuning range of 1530.0–1560.0nm is proposed and demonstrated. Here, the mode spacing of lasing dual-wavelength from 1.0 to 30.0nm can be selected arbitrarily in any wavelength position. To accomplish the SLM output, the eye-type compound-ring scheme is proposed inside ring cavity for suppressing the multi-longitudinal-mode (MLM) highly. The entire measured output power and optical signal to noise ratio (OSNR) of each dual-wavelength are larger than −13.3dBm and 60dB respectively. In addition, the output stability measurement of proposed EDF laser is also performed and analyzed.

Stabilized dual-wavelength erbium-doped fiber laser with a single-longitudinal mode by utilizing fiber Bragg grating and a compound-ring filter

In this investigation, a stable single-longitudinal-mode (SLM) dual-wavelength erbium-doped fiber (EDF) multiring laser by utilizing fiber Bragg grating is proposed and investigated. Here, to accomplish a SLM output, the multiring cavity of the proposed EDF laser is employed for suppressing the densely multilongitudinal mode. Hence, the output powers and wavelengths of the proposed dual-wavelength EDF laser are 7.0 and 6.7 dBm and 1531.72 and 1537.32 nm, respectively. In addition, the maximum output stabilities of the power and wavelength in the proposed laser are also executed and discussed.

Narrow line-width single-longitudinal-mode fiber laser using silicon-on-insulator based micro-ring-resonator

In this work, we propose and demonstrate a stable single-longitudinal-mode (SLM) fiber laser with narrow line-width by using an integrated silicon-on-insulator micro-ring resonator (SOI MRR) and two subsidiary fiber rings for the first time, to the best of our knowledge. The laser is tunable over the wavelength range from 1546 to 1570 nm, with only step tuning of 2 nm steps. A maximum 49 dB side mode suppression ratio (SMSR) can be achieved. The compact SOI MRR provides a large free-spectral-range (FSR), while the subsidiary rings provide Vernier effect producing a single lasing mode. The FSR of the SOI MRR can be very large and controllable (since it is easy to fabricate small SOI MRR when compared with making small fiber-rings) using the complementary-metal–oxide–semiconductor (CMOS) compactable SOI fabrication processes. In our proposed laser, the measured single sideband (SSB) spectrum shows that the densely spaced longitudinal modes can be significantly suppressed to achieve SLM. The laser linewidth is only 3.5 kHz measured by using the self-heterodyne method. 30 min stability evaluation in terms of lasing wavelength and optical power is performed; showing the optical wavelength and power are both very stable, with fluctuations of only 0.02 nm and 0.8 dB, respectively.

Broad-stripe single longitudinal mode laser based on metal slots

Single-longitudinal-mode end-emitting laser with 10 periods of metal slots at around 956nm has been fabricated. 100μm wide broad-stripe and ten periods of 9.5μm periodicity metal slots are defined by i-line lithography and dry etching. Experimentally, continuous-wave power of 213mW has achieved, at a slope efficiency of 520mW/A, having a 3dB spectrum width of less than 0.04nm at 900mA, and operating in a stable single longitudinal mode with the side-mode suppression ratio (SMSR) of 42dB. We prove that metal slots introduce sufficient loss into the cavity to filter out the wanted mode, and is more efficient on our chip structure than traditional slot laser. This paper provides a new method for the realizing high power broad-stripe (~100μm) laser and array with single longitudinal mode operation.

Transient mode competition in directly modulated DFB semiconductor laser

A new effect of transient mode competition in directly modulated DFB laser based on equivalent phase-shift (EPS) technique is presented and studied. Since there are multi-order reflections in EPS structure and if the 0th order subgrating is properly designed, the transient lasing of 0th order will occur during the rising time of the injection current. As a result, transient mode competition between -1st order (main mode) and 0th order will occur accordingly. This can consume redundant carrier and suppress the transient relaxation oscillation, which may be applied in some areas like on-off switching modulation of DFB semiconductor lasers. As an example, an equivalent π phase shift (π-EPS) is carefully designed to realize the effect. In such a laser the 0th order wavelength is in the margin of the material gain region and the -1st order wavelength is around the gain peak, while the stable single longitudinal mode (SLM) operation of the -1st order is guaranteed. The simulation investigation is performed. Good results with suppressed relaxation oscillation and 1.25 Gb/s directly on-off modulation (32 dB extinction ratio) are demonstrated. We believe it provides a new kind of method for on-off switching with high extinction ratio and weak relaxation oscillation.

1.3-μm-Wavelength AlGaInAs Multiple-Quantum-Well Semi-Insulating Buried-Heterostructure Distributed-Reflector Laser Arrays on Semi-Insulating InP Substrate

1.3-μm-wavelength AlGaInAs distributed-reflector laser arrays on semi-insulating InP substrate for high-speed direct modulation are investigated to realize compact and low-power-consumptive optical modules. Combination of AlGaInAs quantum wells with large differential gain and semi-insulating buried-heterostructure for reduction of the volume in active region achieved high-speed direct modulation. The fabricated lasers in the array lase with different wavelengths with stable single-longitudinal mode. Clear eye-opening and large mask margin were obtained in push-pull driving at 25.8 Gb/s direct modulation with coplanar electrode and semi-insulating InP substrate. Comparison of modulation waveform under simultaneous operation of neighbor lasers shows that crosstalk between lasers in the array is small. Clear eye-openings, large mask margins, and 10-km fiber transmission of four different wavelength lasers on LAN-WDM grid are demonstrated under 28-Gb/s operation at 50 °C. For further high-speed operation, 43-Gb/s direct modulation were performed. These results indicate that the 1.3-μm AlGaInAs DR laser arrays are promising as light sources for 100-Gb/s Ethernet and higher speed transmission.

A Single-Frequency Linearly Polarized Fiber Laser Using a Newly Developed Heavily Tm3+-Doped Germanate Glass Fiber at 1.95 μm**Supported by the National High-Technology Research and Development Program of China under Grant Nos 2013AA031502 and 2014AA041902, the National Natural Science Foundation of China under Grant Nos 11174085, 51132004, and 51302086, the Natural Science Foundation of Guangdong Province under Grant Nos S2011030001349 and

A compact linearly polarized, low-noise, narrow-linewidth, single-frequency fiber laser at 1950 nm is demonstrated. This compact fiber laser is based on a 21-mm-long homemade Tm3+-doped germanate glass fiber. Over 100-mW stable continuous-wave single transverse and longitudinal mode lasing at 1950 nm are achieved. The measured relative intensity noise is less than −135 dB/Hz at frequencies over 5 MHz. The signal-to-noise ratio of the laser is larger than 72 dB, and the laser linewidth is less than 6 kHz, while the obtained linear polarization extinction ratio is higher than 22 dB.

Experimental Demonstration of a Multicorrugation-Pitch-Modulated (MCPM) DFB Semiconductor Laser Based on Reconstruction-Equivalent-Chirp Technology

A multicorrugation-pitch-modulated (MCPM) distributed-feedback semiconductor laser is experimentally demonstrated for the first time to achieve stable single longitudinal mode (SLM) performance. The MCPM structure was equivalently realized based on a sampled grating using reconstruction equivalent chirp (REC) technology. The proposed REC-MCPM structure can effectively flatten the optical intensity distribution along the laser cavity, leading to the strong suppression in spatial hole burning. In addition, the REC-MCPM grating structures can be readily fabricated using conventional holographic lithography combined with low-cost standard micrometer-level photolithography. A proof-of-principle study both in a simulation and an experiment is presented in this paper. The fabricated 400- $\mu\hbox{m} $-long REC-MCPM semiconductor laser shows very good SLM performance with SMSRs being more than 42 dB under test conditions of a large injection current range (up to 300 mA) and different ambient temperatures.

Coupled ridge waveguide distributed feedback quantum cascade laser arrays

A coupled ridge waveguide quantum cascade laser (QCL) array consisting of fifteen elements with parallel integration was presented. In-phase fundamental mode operation in each element is secured by both the index-guided nature of the ridge and delicate loss management by properly designed geometries of the ridges and interspaces. Single-lobe lateral far-field with a nearly diffraction limited beam pattern was obtained. By incorporating a one-dimensional buried distributed feedback grating, the in-phase-operating coupled ridge waveguide QCL design provides an efficient solution to obtaining high output power and stable single longitudinal mode emission. The simplicity of this structure and fabrication process makes this approach attractive to many practical applications.

Stable multiwavelength single longitudinal mode dual ring Brillouin fiber laser

A novel stable multiwavelength single longitudinal mode (SLM) dual ring Brillouin fiber laser is proposed and demonstrated. Dual ring configuration with 100 and 10 m length of single mode fiber guarantees each Stokes and anti-Stokes waves in SLM status. Linewidth of the first Stokes wave is below 4 kHz with 60 dB sidemode suppression value. 7 stable SLM lasing wavelengths including the pump with a 5 dB bandwidth of 0.5, 0.084 nm wavelength spacing and 15 dB average optical signal-to-noise ratio are generated through the cascaded SBS and degenerate FWM process. The laser can freely be tuned 30 nm range from 1535 to 1565 nm. The power fluctuation of the first Stokes wave is about 8 % measured by Data Acquisition System in 1 h.

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.

Stabilized single longitudinal mode fibre ring laser based on an inline dual taper Mach Zehnder interferometer filter coated with graphene oxide

This paper describes a proposal and experimental demonstration of a narrow single longitudinal mode fibre ring laser with high power efficiency and a simple setup. A single longitudinal mode filter was realized by depositing graphene oxide flakes on a dual fibre taper Mach Zehnder interferometer in a loop mirror, wherein the loop structure acted as a passive narrowband reflector with the ability to generate a stable single longitudinal mode. This filter incorporation allowed for the generation of a single longitudinal mode having a side mode suppression ratio of 75dB at 60mW pump power and a 3dB line width of 0.16nm which is limited by the optical spectrum analyzer resolution.

An Equivalent-Asymmetric Coupling Coefficient DFB Laser With High Output Efficiency and Stable Single Longitudinal Mode Operation

An equivalent-asymmetric coupling coefficient (EACC) distributed feedback laser (DFB) semiconductor laser with equivalent-half apodization grating (EHAG) structure is proposed and experimentally demonstrated for the first time; the EHAG profile is equivalently realized by linearly changing the duty cycle of a sampled Bragg grating along the one half cavity, while that of the other half cavity is kept uniform. Compared with the equivalent-symmetric coupling coefficient DFB laser, the simulated intensity distribution of the EACC DFB laser shows that the light power is concentrated not only on near the phase-shift region and that the power at the front end is enlarged. Therefore, the longitudinal spatial hole burning may be reduced; the output efficiency and the single-mode stability may be improved. The experimental results show that the output power ratio between the front and rear facets is about 2.17 and the side-mode suppression ratios are over 50 dB when the injection current is in the range from 60 to 200 mA.

Parity-time-symmetric microring lasers.

The ability to control the modes oscillating within a laser resonator is of fundamental importance. In general, the presence of competing modes can be detrimental to beam quality and spectral purity, thus leading to spatial as well as temporal fluctuations in the emitted radiation. We show that by harnessing notions from parity-time (PT) symmetry, stable single-longitudinal mode operation can be readily achieved in a system of coupled microring lasers. The selective breaking of PT symmetry can be used to systematically enhance the maximum attainable output power in the desired mode. This versatile concept is inherently self-adapting and facilitates mode selectivity over a broad bandwidth without the need for other additional intricate components. Our experimental findings provide the possibility to develop synthetic optical devices and structures with enhanced functionality.