Laterally Coupled Distributed Feedback Research Articles

Single-mode GaSb-based laterally coupled distributed-feedback laser for CO2 gas detection

We report on a GaSb-based laterally coupled distributed feedback (LC-DFB) laser with Cr gratings operating at 2004 nm for CO2 detection application. Butterfly packaged with single-mode fiber pigtailed, the laser diode operates in the continuous-wave mode in a temperature range from −10 °C to 60 °C, with a maximum output power of 2 mW and a maximum side-mode suppression ratio over 30 dB. Wavelength-modulated absorption spectroscopy of CO2 demonstrates the applicability of the LC-DFB laser to tunable diode laser absorption spectroscopy. Furthermore, the diode junction temperature, which is measured by using the wavelength shift method, exhibits a maximum value of 17 °C in the single-mode operation range.

InAs/GaAs quantum dot laterally coupled distributed feedback lasers at 1.3 μm

We report the InAs/GaAs quantum dot laterally coupled distributed feedback (LC-DFB) lasers operating at room temperature in the wavelength range of 1.31 µm. First-order chromium Bragg gratings were fabricated alongside the ridge waveguide to obtain the maximum coupling coefficient with the optical field. Stable continuous-wave single-frequency operation has been achieved with output power above 5 mW/facet and side mode suppression ratio exceeding 52 dB. Moreover, a single chip integrating three LC-DFB lasers was tentatively explored. The three LC-DFB lasers on the chip can operate in single mode at room temperature, covering the wavelength span of 35.6 nm.

Enhanced Carrier Confinement and Mode Discrimination for Laterally-Coupled DFB Lasers

Reducing carrier leakage is the key to obtain laterally coupled distributed feedback (DFB) lasers with high injection efficiency. We proposed a device structure with slots fabricated between the ridge and gratings to form a good confinement on carriers. The incorporation of slots also makes the grating morphology easier to fabricate. To evaluate the dependence of coupling efficient on main structural parameters, four grating samples with different sizes are studied with FDTD Solutions. Calculation results indicate that slots with a width of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.1\!-\!0.3\;\mu{m}$</tex-math></inline-formula> is suitable for the device. And, changing the lateral width of the grating can be used as a direct method to adjust the coupling strength. In addition, the carrier distribution and optical field distribution of the device were simulated with Crosslight PICS3D, and the results show that compared with the traditional laterally-coupled gratings, this structure can strengthen the competitive advantage of fundamental mode and enhance the mode discrimination of the device. This structural design provides ideas and references for improving the injection efficiency and mode stability of laterally-coupled DFB lasers.

A Directly Modulated Laterally Coupled Distributed Feedback Laser Array Based on SiO2 Planarization Process

Low-cost and high-speed single-mode semiconductor lasers are increasingly required as wide-band access fiber communication expands in recent years. Here, a high-speed laterally coupled distributed feedback (LC-DFB) laser array is achieved based on a SiO2 planarization process. The device exhibits low threshold currents of about 12 mA and high slope efficiencies over 0.26 W/A. Stable single mode operation and high-speed performance are realized with side mode suppression ratios (SMSR) over 45 dB, and 3-dBe bandwidths exceed 14 GHz for all four channels. Such a high-speed and process simple LC-DFB laser array shows great potential to the low-cost fiber communication networks.

High-power, high-spectral-purity GaSb-based laterally coupled distributed feedback lasers with metal gratings emitting at 2 μ m

We report on the fabrication of high-power, high-spectral-purity GaSb-based laterally coupled distributed feedback (LC-DFB) lasers emitting at 2 μm. Second-order Chromium-Bragg-gratings are fabricated alongside the ridge waveguide by lift off. Due to the introduction of gain coupling, the lasers exhibit a stable single mode operation [side-mode suppression ratio (SMSR) &amp;gt;40 dB] from 10 °C to 50 °C and the maximum SMSR is as high as 53 dB. At a heat-sink temperature of 10 °C, the lasers emit more than 40 mW continuous-wave in a single longitudinal mode. A high external quantum efficiency of 48% is obtained, resulting in a notable increase in power conversion efficiency peaking at 13%. The lasers achieve a comparable output power with that of the index-coupled LC-DFB lasers, while maintaining a better single mode performance. Thus, we prove the feasibility of the metal-grating LC-DFB structure to achieve high-power, frequency-stable semiconductor lasers through a simpler and much more convenient way.

DFB Laser Diodes Based on GaN Using 10th Order Laterally Coupled Surface Gratings

Single longitudinal mode emission of laterally coupled distributed-feedback (LC-DFB) laser diodes (LDs) based on InGaN/GaN multiquantum-well structures containing 10th-order surface Bragg gratings with V-shaped grooves is demonstrated. The gratings were fabricated alongside a 2-μm-wide contact stripe by i-line stepper lithography and inductively coupled plasma etching. A single peak emission at 404.6 nm with a fullwidth at half-maximum of 0.04 nm was achieved at an output power of about 46 mW under pulsed laser operation. The shift of the lasing wavelength of LC-DFB LDs in the temperature range from 22 °C to 45 °C was around three times smaller than that of comparable ridge waveguide Fabry-Perot LDs.

Laterally coupled distributed feedback type-I quantum well cascade diode lasers emitting near 322 μm

The laterally coupled distributed feedback (LC-DFB) GaSb-based type-I quantum well cascade diode lasers using the second- and the sixth-order gratings to stabilize the output spectrum near 3.22μm were designed and fabricated. The laser heterostructure contained three cascades. The devices were manufactured using a single dry etching step defining the ∼5-μm-wide ridge with ∼5-μm-wide gratings sections adjacent to the ridge sides. The grating coupling coefficients were estimated to be about 1 cm-1. The stability of the single-frequency operation was ensured by alignment of the DFB mode to the relatively wide gain peak. The 2-mm-long second-order LC-DFB lasers generated above 10mW of continuous-wave (CW) output power at 20°C in epi-side-up configuration and demonstrated power conversion efficiency above 2%. The sixth-order LC-DFB lasers showed lower efficiency but still generated several milliwatts of CW output power. The devices demonstrated a CW current tuning range of about 3.5nm at the temperature of 20°C.

Laterally coupled distributed feedback lasers emitting at 2 μm with quantum dash active region and high-duty-cycle etched semiconductor gratings

Single-mode diode lasers on an InP(001) substrate have been developed using InAs/In0.53Ga0.47As quantum dash (Qdash) active regions and etched lateral Bragg gratings. The lasers have been designed to operate at wavelengths near 2 μm and exhibit a threshold current of 65 mA for a 600 μm long cavity, and a room temperature continuous wave output power per facet &amp;gt;5 mW. Using our novel growth approach based on the low ternary In0.53Ga0.47As barriers, we also demonstrate ridge-waveguide lasers emitting up to 2.1 μm and underline the possibilities for further pushing the emission wavelength out towards longer wavelengths with this material system. By introducing experimentally the concept of high-duty-cycle lateral Bragg gratings, a side mode suppression ratio of &amp;gt;37 dB has been achieved, owing to an appreciably increased grating coupling coefficient of κ ∼ 40 cm−1. These laterally coupled distributed feedback (LC-DFB) lasers combine the advantage of high and well-controlled coupling coefficients achieved in conventional DFB lasers, with the regrowth-free fabrication process of lateral gratings, and exhibit substantially lower optical losses compared to the conventional metal-based LC-DFB lasers.

Optically Pumped DFB Lasers Based on GaN Using 10th-Order Laterally Coupled Surface Gratings

An optically pumped GaN-based laser structure with 10th-order laterally coupled surface grating is demonstrated. The fabrication involved i-line photolithography and dry etching, avoiding more complex technologies such as multiple epitaxy steps. The lasing threshold of the laterally coupled distributed-feedback (LC-DFB) laser was similar to that of a ridge waveguide Fabry–Perot (RW-FP) laser. Single-peak emission with a full width at half maximum of 0.06 nm at 404.2 nm was achieved for LC-DFB lasers. In contrast to the RW-FP lasers, the LC-DFB laser is shown to exhibit a smaller shift of the emission wavelength with temperature.

2-μm single longitudinal mode GaSb-based laterally coupled distributed feedback laser with regrowth-free shallow-etched gratings by interference lithography**Project supported by the National Key Basic Research Program of China (Grant Nos. 2014CB643903 and 2013CB932904), the National Special Funds for the Development of Major Research Equipment and Instruments, China (Grant No. 2012YQ140005), the National Natural Science Foundation of China (Grant Nos. 61435012, 61274013,

We report a type-I GaSb-based laterally coupled distributed-feedback (LC-DFB) laser with shallow-etched gratings operating a continuous wave at room temperature without re-growth process. Second-order Bragg gratings are fabricated alongside the ridge waveguide by interference lithography. Index-coupled LC-DFB laser with a cavity of 1500 μm achieves single longitudinal mode continuous-wave operation at 20 °C with side mode suppression ratio (SMSR) as high as 24 dB. The maximum single mode continuous-wave output power is about 10 mW at room temperature (uncoated facet). A low threshold current density of 230 A/cm2 is achieved with differential quantum efficiency estimated to be 93 mW/A. The laser shows a good wavelength stability against drive current and working temperature.

Narrow linewidth two-electrode 1560 nm laterally coupled distributed feedback lasers with third-order surface etched gratings.

We report on the design and characterization of a re-growth free InGaAsP/InP multiple quantum well two-electrode laterally coupled distributed feedback (LC-DFB) lasers. Third-order surface etched gratings have been defined on the ridge sidewalls along the laser cavity by means of stepper lithography. The lasers oscillate in single-mode around 1560 nm with high side mode suppression ratios (>52 dB), a wavelength tuning (≥ 3nm), an output power (≥ 6 mW), and narrow linewidth (<170 kHz) under various current injection ranges at room temperature. A minimum linewidth of 94 kHz has been recorded for 1500 µm-long two-electrode LC-DFB laser while providing non-uniform current injection through the two electrodes. The effect of the width of the inter-electrode gap on these different performance measures is also studied.

A laterally-coupled distributed feedback laser with equivalent quarter-wave phase shift

We report the first laterally-coupled distributed feedback (LC-DFB) laser with a quarter-wave equivalent phase shift (EPS) realized by interference lithography (IL) and conventional photolithography. A specially designed sampled grating is fabricated on both sidewalls of a ridge waveguide to provide a quarter-wave EPS at the center of the cavity. The resulting laser exhibits stable single-mode lasing operation over a wide range of injection currents, with a side mode suppression ratio (SMSR) of 41.1 dB. This provides a practical, low-cost method to fabricate quarter-wave phase shifted DFB lasers with high performance without any epitaxial regrowth or the use of electron-beam lithography, thereby simplifying the fabrication of DFB lasers with stable and precise wavelengths, as single devices or as arrays in photonic integrated circuits.

Simulation of the Optimized Structure of a Laterally Coupled Distributed Feedback (LC-DFB) Semiconductor Laser Above Threshold

In this paper, the laterally coupled distributed feedback semiconductor laser is studied. In the simulations performed, variations of structural parameters such as the grating amplitude a, the ridge width W, the thickness of the active region d, and other structural properties are considered. It is concluded that for certain values ​​of structural parameters, the laser maintains the highest output power, the lowest distortion Bragg frequency δL and the smallest changes in the wavelength λ. Above threshold, output power more than 40mW and SMSR values greater than 50 dB were achieved.

Numerical Study of Dual Mode Generation Using a Sampled-Grating High-Order Quantum-Dot Based Laterally-Coupled DFB Laser

We propose a fabrication-friendly dual-mode laser source based on a sampled surface-grating, quantum-dot (QD), third-order, and laterally-coupled distributed feedback (LC-DFB) laser composed of alternating grating and Fabry-Perot sections. The dynamic behavior of this device is investigated through numerical modelling, and mode spacing in the millimeter-wave domain (60 GHz) was achieved. We extended a time-domain travelling-wave algorithm, including Streifer's terms, to numerically study the dynamic behavior of the modified high-order LC-DFB lasers. We also incorporated an active QD region via a set of rate equations that considers both in homogeneous broadening because of spatial distribution of QD and homogeneous broadening because of the scattering or polarization dephasing rate. It was found that stable dual mode operation in the millimeter-wave range can be achieved with a dual-side-mode-suppression-ratio as high as ~ 50 dB.

Time-Domain Analysis of Third-Order Quantum-Dot-Based Laterally-Coupled Distributed Feedback Lasers Using Travelling-Wave Approach

In this paper, we present a time-domain (TD) coupled model suitable to investigate high-order $\lambda/4$ phase-shift grating quantum-dot (QD) based laterally-coupled distributed feedback (LC-DFB) laser. First, by integrating the Streifer's coefficients, we include the effects of radiation and evanescent modes into the TD coupled wave equations, and hence we investigate the effect of the radiation modes. Then, via a well-established set of rate equations coupled with the travelling field propagation equations, population dynamics in the QD region are modeled and the homogeneous and inhomogeneous broadening of, respectively, the whole QD ensemble and each QD inter-band transition are properly taken into account in the model. Finally, we consider the coupling between forward and backward electric fields due to the grating via the travelling-wave approach. This approach advances the impact of radiating partial waves in high-order QD-LC-DFB lasers. It is shown that, in particular for third-order rectangular grating, longitudinal spatial hole-burning is highly reduced, high single mode suppression ration (60 dB) is obtained and larger frequency modulation is achieved thanks to the fine engineering of the grating features and the particular properties of QD. Eventually, such results highlight the beneficial effect of considering high-order grating QD-LC-DFB lasers for better longitudinal-mode discrimination and high device performances.

Coupling coefficient calculation for GaSb-based quantum well distributed feedback lasers with laterally coupled gratings

We calculated the coupling coefficient of different types of laterally coupled distributed feedback (LC-DFB) structures with coupled-wave theory and the two-dimensional semivectorial finite difference method. Effects neglected in previous studies such as other partial waves, the ohmic contact and metal contact layers are taken into account in this calculation. The LC-DFB structure with metal gratings is especially studied due to its advantage over index-coupled structures. The dependence of coupling coefficient on structure parameters is theoretically calculated such as grating order, ridge width, thickness of the residual cladding layer, grating depth and lateral proximity of gratings to the ridge waveguide. A complex-coupled GaSb-based 2 µm LC-DFB structure is optimized to achieve a high coupling coefficient of 14.5 cm−1.

Numerical Analysis of SHB Effects in Laterally-Coupled Distributed Feedback (LC-DFB) Lasers

In this paper the stability of Laterally-Coupled Distributed Feedback (LC-DFB) Lasers against the Spatial Hole Burning (SHB) effect is analyzed theoretically. The stability of the laser structure is evaluated using the flatness parameter F. It is shown that the LC-DFB lasers are stable in a wide range of different values ​​of ridge width and amplitude grating. The stability is sustained with increasing injection current. The results show that the flatness parameter is minimal for certain values ​​of the amplitude grating. The numerical calculations have been done by coupled wave and carrier rate equations on the basis of the transfer matrix method (TMM)

Dynamic Analysis of High-Order Laterally Coupled DFB Lasers Using Time-Domain Traveling-Wave Model

This paper describes the application of a time-domain modeling approach for a laterally coupled distributed feedback (LC-DFB) semiconductor laser for the first time. We numerically study the effect of the radiation modes on LC-DFB laser properties. We integrate the Streifer's coefficients, which represent the effects of radiation and evanescent modes into the time-domain coupled-wave equations. High-order corrugated gratings with λ/4 phase-shift are analyzed, where the degree of longitudinal spatial hole burning can be effectively reduced by means of fine tuning of the grating duty cycle. Additionally, we show a remarkably enhanced side-mode suppression ratio (SMSR). For example, for the third-order gratings with a 50% duty cycle, an SMSR as high as 45 dB can be predicted.

Fabrication-tolerant 1310 nm laterally coupled distributed feedback lasers with high side mode suppression ratios

1310 nm laterally coupled distributed feedback (LC-DFB) laser was designed and fabricated using stepper lithography. LC-DFB lasers, unlike conventional DFB lasers, do not require a regrowth step during the fabrication process. The lateral grating of the LC-DFB lasers can be patterned along both sidewalls of the ridge waveguide. Gratings with higher order can enhance the lithographic tolerance for lower resolution patterning, yielding lasers more amenable to mass-manufacturing. Excellent side mode suppression ratio over 53 dB has been measured with a single mode lasing around 1310 nm.

Simulation Analysis of Higher Order Laterally-Coupled Distributed Feedback Lasers

Laterally-coupled distributed feedback (LC-DFB) lasers use a lithographic fabrication step to define the distributed feedback grating, avoiding subsequent regrowth. Using higher order gratings can enhance the lithographic tolerance for lower resolution patterning, yielding lasers more amenable to fabrication. We show that LC-DFB lasers with higher order gratings, although requiring a higher threshold gain than those of first-order, provide a degree of longitudinal mode discrimination. Incorporating radiating partial waves, we have calculated modified coupled-mode coefficients for various duty cycles, grating orders, and grating geometries using a two-dimensional finite-element method. The modified coupled-mode equations were solved with and without a lambda/4 phase shift. The phase shift, while beneficial for first-order gratings, was found to generally diminish laser performance for lasers with higher order gratings.