Single-mode DFB Research Articles

Gain-Coupled High-Power Low-RIN 1.55 μm Single-Mode DFB Lasers With Wide Ridge Waveguide

Gain-Coupled High-Power Low-RIN 1.55 μm Single-Mode DFB Lasers With Wide Ridge Waveguide

Development of a Single-Mode DFB Heterolaser with Inclined Radiation Output

Development of a Single-Mode DFB Heterolaser with Inclined Radiation Output

Разработка одномодового РОС-гетеролазера с выводом излучения под углом к поверхности структуры

We study a possibility of implementing a single-mode DFB heterolaser with inclined (with respect to the surface of the structure) output of the generated radiation. We find the periodic dielectric structure shape that makes it possible to realize the distributed feedback for wavebeams propagating along the structure and, at the same time, to ensure the output of up to 70% of the generated radiation power in the inclined direction. Within the framework of the semiclassical quasi-optical model, the possibility of stationary lasing regimes is shown for finite lateral dimensions of the Bragg structure.

Wide-waveguide high-power low-RIN single-mode distributed feedback laser diodes for optical communication.

We present an 8-µm-wide 800-µm-long high-power, single-mode and low RIN DFB laser using a dual-waveguide structure. The introduced passive lower waveguide has weakenes the lateral optical confinement for the ridge waveguide, and thus reduces losses caused by the p-doped layers and maintains single mode stability of the laser. The fabricated laser exhibited an output power higher than 170 mW and a relative intensity noise (RIN) below -157 dB/Hz along with a side-mode suppression-ratio (SMSR) over 55 dB. The temperature tuning from -10°C to 60°C allows an 8.6 nm wavelength tunability with a variation coefficient of 0.12 nm/K. The relaxation oscillation frequency is around 8 GHz, and the linewidth is about 250 kHz at 100 mW output power for the fabricated laser. The characteristics of the proposed high-power laser, including high slope efficiency, single mode stability and low noise, make it a suitable candidate for optical communication.

On The Technology of the Bragg Grating for the Laterally Coupled Single-Mode Distributed Feedback Laser Diodes

The paper presents the results of the successful development and application of the diffractive Bragg grating fabrication technology for the single-mode ridge-type DFB laser realization. The single-mode 1550 nm laser transmitters with SMSR not less than 50 dB were first made in Russia. The developed technology is capable of making a dielectric hard mask for etching the laterally coupled grating with periods in the range of 0.19—0.25 um, which corresponds to a wavelength range 1.3—1.6 um, and has been easily incorporated into the conventional route of the DFB-laser manufacturing process of the JSC "NII "Polyus" by M. F. Stelmakh".

Physics and technology of Terahertz quantum cascade lasers

ABSTRACT Even though already in the seventies, right after the invention of the quantum cascade laser (QCL) concept, it was argued that this device could be operated in the THz (far-infrared) range of the electromagnetic spectrum, it was only in 2002 that the first working THz QCL was demonstrated. Soon afterwards, the progress was very rapid; in the space of 2–3 years, operating temperatures were raised, single-mode DFB devices were produced, applications as local oscillators in heterodyne transceivers were implemented, frequency coverage was extended to the whole 1–5 THz region. In the last few years, technological advancement has continued to improve performances: the maximum operating temperature has now reached about 250 K and about 1 W peak output power has been demonstrated. Several beam engineering techniques have been implemented, with the scope of enhancing spectral purity, improving beam quality and achieving vertical emission. In parallel, various approaches have been devised that allow frequency tunability of the emitted light, with the most efficient schemes achieving a tuning range of about 10% of the central emission frequency. Even the generation of frequency combs directly from THz QCLs has been obtained, by employing dispersion compensated waveguides and an intrinsic material non-linearity. This manuscript reviews the physics underlying the operation of THz QCLs, the technology developed to advance laser performances, and highlights the latest most promising progresses in this fascinating area of opto-electronics.

Gratings with longitudinal variations in coupling coefficients: super-efficiency and unidirectionality in distributed feedback Raman fiber lasers

We propose a technique to design highly-efficient and -unidirectional DFB Raman fiber lasers based on the engineering of the grating’s coupling coefficient including a π-phase shift position in the fiber. For this purpose, first the ideal intra-cavity signal powers for different pump power levels are determined for given fiber lengths. Then, the sum and difference between the counter-propagating wave intensities at each small segment within fiber lengths are calculated resulting in determining the ideal grating’s coupling functions for co- and contra-directional-pumping. The steady-state behavior of the laser using realistic parameters is finally simulated for modified coupling functions considering the Kerr nonlinearity. For a 10 W co-directional-pumped, ∼1 m long single-mode super-efficient DFB, a ∼50% increase in the laser efficiency, more than 44 dB reduction in contra-directional lasing power, ∼15 times drop in the peak power of intra-cavity signal and ∼38% decrease in the unused-pump power are found, compared to those in a standard DFB with the same coupling-length product. Although an enhanced nonlinear refractive index due to thermal gradient reduces the output power of such lasers, it is shown that the super-efficient laser presents a better performance than the standard one, under such conditions.

Single-mode surface-emitting DFB lasers with a large-area oxidized aperture based on the surface grating.

We propose and experimentally demonstrate an 850 nm single-mode surface-emitting distributed feedback laser based on the surface grating. The laser composes a second-order grating section sandwiched by two first-order grating sections. The second-order grating provides not only surface emission, but also phase shift to remove the emission degeneracy. A high side-mode suppression ratio of 47 dB has been achieved. By employing a large-area rectangle-shaped oxidized aperture, a low threshold current of 1.8 mA and a low differential resistance of 59 Ω are successfully achieved in a horizontal-cavity surface-emitting laser.

Electrically and Optically Bistable Operation in an Integration of a 1310nm DFB Laser and a Tunneling Diode**Supported by the National Key Research and Development Program of China under Grant No 2017YFB0405301, and the National Natural Science Foundation of China under Grant Nos 61604144 and 61504137.

We experimentally demonstrate an InP-based hybrid integration of a single-mode DFB laser emitting at around 1310nm and a tunneling diode. The evident negative differential resistance regions are obtained in both electrical and optical output characteristics. The electrical and optical bistabilities controlled by the voltage through the tunneling diode are also measured. When the voltage changes between 1.46V and 1.66 V, a 200-mV-wide hysteresis loop and an optical power ON/OFF ratio of 17 dB are obtained. A side-mode suppression ratio of the integrated device in the ON state is up to 43 dB. The tunneling diode can switch on/off the laser within a very small voltage range compared with that directly controlled by a voltage source.

A Biochemical Sensor Based on a Sensing Waveguide With Efficient Analyte Overlap and a Single-Mode DFB Laser

A biochemical sensor based on the combination of a complex coupled distributed feedback laser with a sensing waveguide is presented. The sensing waveguide was realized by etching a deep trench into the middle of a ridge waveguide to increase the analyte overlap. These devices were investigated with respect to their sensitivity to refractive index changes of a surrounding analyte. A wavelength shift of about 12nm was observed applying an index change of $\Delta n= {{0.48}}$ . The analyte overlap was calculated to be 5.6. Using this kind of monolithic, active, and single-frequency device could be an easy approach to sensitive affinity arrays.

Monolithically integrated chirp-managed laser based on a resonant tunneling filter

We have proposed a monolithically integrated chirp-managed laser (CML) that consists of a directly modulated single-mode DFB laser and an optical spectrum reshaper (OSR) filter based on a double-slanted-trench resonant tunneling structure (DST-RTS). Slanted trenches facilitates the occurrence of resonant tunneling effect, which produces a steep-edge narrow-band OSR filter, and meanwhile directing most of the reflected waves out of the laser cavity, consequently eliminating the need of an isolator. Characteristics of the DST-RTS filter have been investigated and simulation results show that the proposed 25 Gbps 1.55 μm CML can send signal over 22 km standard single-mode fiber for bit error rate of 10−12.

Improvement of Buried Grating DFB Quantum Cascade Lasers by Small-Angle Tapered Structure

Small-angle tapered waveguide structure combining with the sampled grating was adopted to improve the output power and achieve room temperature continuous-wave (CW) operation of buried grating distributed feedback quantum cascade lasers (DFB QCLs). By utilizing the first-order channel of sampled grating, single-mode DFB QCLs at four different wavelengths were fabricated simultaneously. At 298 K, all four devices can emit more than 130 mW optical power in CW operation. Fundamental transverse mode operation with excellent beam quality was preserved.

Enhanced Optical Comb Generation by Gain-Switching a Single-Mode Semiconductor Laser Close to Its Relaxation Oscillation Frequency

We demonstrate, through experimental results and supporting numerical simulations, the optimum conditions to generate an optical comb via gain-switching of a single-mode DFB semiconductor laser. The DFB laser is biased appropriately and gain-switched with a large amplitude sinusoidal current, modulating the gain that is sufficient to turn the laser ON and OFF. This results in the generation of a train of short optical pulses albeit with a relatively large amount of temporal jitter. The jitter is a result of the varying turn on time delay, which breaks the periodicity of the pulses leading to an optical spectrum with no discernible tones. However, we find that the conditions for creating an optical frequency comb exist when the modulation frequency is greater than or equal to the relaxation oscillation frequency of the laser. Corresponding optical pulses are shown to exhibit lower levels of temporal jitter at these optimum points of operation. The spectral purity of the comb tones is analyzed, and we show that the FM-noise of the comb tones decreases with increasing modulation frequency with the lower limit set by operating the laser in CW conditions. All of the simulation results were obtained using standard laser rate equations.

Characterization and optimization of 2-step MOVPE growth for single-mode DFB or DBR laser diodes

We have studied the MOVPE regrowth of AlGaAs over a grating for GaAs-based laser diodes with an internal wavelength stabilisation. Growth temperature and aluminium concentration in the regrown layers considerably affect the oxygen incorporation. Structural characterisation by transmission electron microscopy of the grating after regrowth shows the formation of quaternary InGaAsP regions due to the diffusion of indium atoms from the top InGaP layer and As–P exchange processes during the heating-up procedure. Additionally, the growth over such gratings with different facets leads to self-organisation of the aluminium content in the regrown AlGaAs layer, resulting in an additional AlGaAs grating, which has to be taken into account for the estimation of the coupling coefficient. With optimized growth conditions complete distributed feedback laser structures have been grown for different emission wavelengths. At 1062 nm a very high single-frequency output power of nearly 400 mW with a slope efficiency of 0.95 W/A for a 4 μm ridge-waveguide was obtained.

Experimental evidence for the thermal origin of1/ffrequency noise in erbium-doped fiber lasers

We present experimental evidence in support of the recent theoretical proposal that intrinsic $1/f$ frequency noise in short cavity erbium-doped fiber lasers is of thermal origin. We demonstrate that the power spectral density of frequency noise in distributed-feedback fiber lasers (DFB FL) exhibits predicted ${T}^{2}$ temperature dependence across all frequencies over a temperature range of almost 200 K. This temperature dependence is observed both in direct interferometric measurements of frequency noise in a single mode DFB FL and noninterferometric measurements of polarization-beat-frequency noise in a dual frequency DFB FL. It is also shown that frequency noise of orthogonal polarization modes in the dual frequency DFB FL is substantially correlated providing a strong indication of a common origin.

Experimental and theoretical characterization of the mode profile of single-mode DFB fiber lasers

The characterization of the spatial mode profile of distributed feedback fiber lasers (DFB-FLs) is discussed. A new approximate solution for the mode profile of single longitudinal mode DFB-FLs with nonuniform phase and grating profiles is derived. An enhanced high resolution heat perturbation method for mode shape characterization is described. Experimental mode shape profiles are compared with theoretical predictions with good agreement.

Low threshold distribution feedback quantum cascade lasers at 7.6 μm grown by gas source molecular beam epitaxy

We have demonstrated the first Gas source molecular beam epitaxy (GSMBE) grown distributed feedback quantum cascade laser (DFB QC-laser) laser with low threshold current density operation at 7.6 μm. High quality DFB QC-laser heterostructures were grown by an one step GSMBE growth procedure. The first-order grating was defined by a holographic technology. A tunable single mode DFB QC-laser operation in pulsed mode with a low threshold current density of 574 A/cm 2 and a peak optical power of 50 mW at 70 K and 7.6 μm have been obtained. The side mode suppression ratio and the maximum single mode wavelength tuning range by changing their heat sink temperature are 23 dB and 20 nm, respectively.

Fiber-optic evanescent-field laser sensor for in-situ gas diagnostics

A compact, rugged and portable fiber-optic evanescent-field laser sensor is developed for the detection of gaseous species in harsh environments such as volcano fumaroles or industrial combustion of glass furnaces. The sensor consists of an optical multi-mode fused silica fiber with jacket and cladding removed and the bare fiber core in direct contact with the surrounding molecules. The beam of a single-mode DFB diode laser with an emission wavelength centered at 1.5705 μm is coupled into the fiber. At the other end of the fiber an infrared detector is used to record the transmitted infrared laser light intensity. Due to the frustrated total reflection (FTR) and the attenuated total reflection (ATR) the laser intensity is attenuated when passing through the fiber. The FTR is related to a change of the index of refraction while the latter one is related to a change of the absorption coefficient. While tuning the DFB laser wavelength across absorption lines of molecules surrounding the fiber a spectral intensity profile is measured. Voigt functions are fitted to the recorded intensity profiles to estimate relative molecule concentrations. In this paper results from first field measurements at the volcano site ‘Solfatara’ in Italy are reported that use such a sensor device for simultaneous detection of H 2S, CO 2 and H 2O directly in the gas stream of a volcano fumarole.

High-power, single-mode, Al-free InGaAs(P)/InGaP/GaAs distributed feedback diode lasers

The selective etching and oxide-free regrowth properties of the Al-free InGaAs(P)/InGaP/GaAs material system have been exploited at λ=968 nm to demonstrate a novel single-spatial-mode diode laser: the simplified antiresonant reflecting optical waveguide (S-ARROW) laser structure, and also to achieve single-mode DFB operation to record-high power levels. The device is fabricated using a three-step MOCVD growth process, incorporating a lower (i.e. below the active layer) grating for single-frequency operation, and an S-ARROW structure (above the active region) for spatial mode selectivity and stability. Devices with 6.5 μm wide emitting apertures operate single-frequency and single-spatial mode to 157 mW under CW operation.

Linewidth rebroadening due to nonlinear gain and index induced by carrier heating in strained quantum-well lasers

The carrier heating has been recently recognized as one of the main origins of nonlinear gain, in particular in strained quantum-well lasers. The asymmetry of this effect introduces a nonlinear refractive index. The joint effects of nonlinear gain and nonlinear refractive index that are both due to carrier heating together with the spatial-hole-burning give rise to an increase in the carrier density and in the linewidth enhancement factor. These effects can explain the linewidth rebroadening at high power in phase-shifted single-mode DFB lasers.