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Parity-Time Symmetry in Laterally Coupled Bragg Waveguides
摘要： We investigate theoretically, in the frame of Coupled-Mode Theory (CMT), a system made of two laterally coupled, index-coupled Bragg waveguides, the modal gain of the amplifying one compensating exactly the modal losses of the other. Reverting to the supermode eigenbasis of the underlying “naked” (non-periodic) Parity-Time Symmetric (PTS) directional coupler, we derive analytically the scattering parameters of the whole structure. We also consider a system made of two purely gain-coupled Bragg waveguides, either in phase or in anti-phase. In each case, we comment upon the gain requirement for achieving a laser oscillation.
关键词： Parity-Time Symmetry (PTS),Coupled-Mode Theory (CMT),Distributed Feedback (DFB),Distributed Bragg Reflector (DBR)
更新于2025-09-12 10:27:22
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InP-based surface-emitting distributed feedback lasers operating at 2004 nm
摘要： We demonstrate InP-based buried grating coupled surface-emitting distributed feedback (DFB) lasers designed to operate at a wavelength of 2004 nm. The laser structure consists of three InGaAsSb/InGaAs QWs, with a 5 μm-wide double-channel ridge waveguide. A second-order semiconductor/semiconductor grating is used for in-plane feedback and vertical out-coupling. The single longitudinal mode emission wavelength of the fabricated laser can be adjusted from 2002.7 to 2006 nm without any mode hopping. High side-mode suppression ratio (SMSR) of at least 35 dB is achieved under all injection currents and temperature conditions. The edge output power reaches 19 mW, measured in continuous-wave (CW) mode at 10 °C. Simultaneously, the output power of surface emission reaches 8 mW.
关键词： distributed feedback,InP-based,surface emission,quantum well lasers
更新于2025-09-12 10:27:22
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Slot-Waveguide Silicon Nitride Organic Hybrid Distributed Feedback Laser
摘要： one of the major barriers for a widespread commercial uptake of silicon nitride photonic integrated circuits for cost-sensitive applications is the lack of low-cost monolithically integrated laser light sources directly emitting into single-mode waveguides. In this work, we demonstrate an optically pumped organic solid-state slot-waveguide distributed feedback laser designed for a silicon nitride organic hybrid photonic platform. Pulsed optical excitation of the gain medium is achieved by a 450 nm laser diode. the optical feedback for lasing is based on a second-order laterally coupled Bragg grating with a slot-waveguide core. Optimized material gain properties of the organic dye together with the increased modal gain of the laser mode arising from the improved overlap of the slot-waveguide geometry with the gain material enable single-mode lasing at a wavelength of 600 nm. The straightforward integration and operation with a blue laser diode leads to a cost-effective coherent light source for photonic integrated devices.
关键词： photonic integrated circuits,silicon nitride,slot-waveguide,distributed feedback laser,organic hybrid
更新于2025-09-12 10:27:22
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[IEEE 2019 Compound Semiconductor Week (CSW) - Nara, Japan (2019.5.19-2019.5.23)] 2019 Compound Semiconductor Week (CSW) - Thermal dependence of the emission linewidth of $1.52-\mu \mathrm{m}$ single mode InAs/InP quantum dot lasers
摘要： This paper experimentally investigates the thermal dependence of the emission linewidth of 1.52-μm single mode InAs/InP quantum dot lasers. Using a distributed feedback cavity made with symmetric antireflection coatings, a minimum linewidth of 300 kHz is unveiled. This narrow line is found rather constant with the injection current and the temperature range (293 K - 313 K). However, under certain operating conditions, a linewidth rebroadening is also observed, which may be attributed to the spectral hole burning and to the variations of the alpha-factor with the temperature and bias current. Nevertheless, these results confirm the potential of this technology for manufacturing low-phase noise oscillators for coherent optical communications.
关键词： Quantum dots,Distributed feedback lasers,spectral linewidth,rebroadening
更新于2025-09-12 10:27:22
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The effect of detuned wavelength in the dynamic performance of distributed feedback lasers operating at O band and C band
摘要： A comparison is presented between the experimental dynamic behavior of detuned AlInGaAs ridge waveguide distributed feedback lasers operating at O band and C band at two different temperatures. The nominal center wavelengths at 25(cid:1)C for the set of devices studied were 1270, 1310, and 1550 nm. Preliminary static characterization of the samples showed consistent trends between wavelength detuning, characteristic temperature, and power output. For all set of samples, the characteristic temperature was substantially higher for the samples detuned to longer wavelengths (red) at room temperature. At the temperature of 85(cid:1)C, a higher power efficiency was observed for those samples that thermally shifted nearer the peak optical gain. Resonance frequencies were extracted at 25(cid:1)C and 85(cid:1)C by means of electro-optical transmission measurements and relative intensity noise measurements. The extracted values confirmed that at room temperature the samples detuned to shorter wavelengths (blue) showed the highest modulation efficiencies. At the temperature of 85(cid:1)C, however, the wavelength and optical gain thermal shift makes those same samples to have the lowest resonant frequencies. The dynamic trends over temperature were clearer for the O band set of samples, while the detuning had a less pronounced effect at C band. The range of maximum resonance frequencies studied was from 12 to 14 GHz, which makes the devices suitable for uncooled communication applications at multi-gigabit data rates.
关键词： dynamics,wavelength detuning,distributed feedback laser
更新于2025-09-12 10:27:22
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Low Power Consumption Distributed-Feedback Quantum Cascade Lasers Operating in Continuous-Wave Mode above 90°C at λ ～ 7.2 μm
摘要： We report on the design and fabrication of ?? ～ 7.2 ??m distributed feedback quantum cascade lasers for very high temperature cw operation and low electrical power consumption. The cw operation is reported above 90°C. For a 2-mm-long and 10-??m-wide laser coated with high-reflectivity on the rear facet, more than 170 mW of output power is obtained at 20°C with a threshold power consumption of 2.4 W, corresponding to 30 mW with a threshold power consumption of 3.9 W at 90°C. Robust single-mode emission with a side-mode suppression ratio above 25 dB is continuously tunable by the heat sink temperature or injection current.
关键词： high temperature operation,Distributed feedback quantum cascade lasers,low power consumption,continuous-wave mode
更新于2025-09-12 10:27:22
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Influence of structural parameters on organic semiconducting polymer lasers with an external holographic grating as feedback layer
摘要： We report on the fabrication and characterization of an organic distributed feedback laser excited from a semiconducting polymer gain layer, poly(2-methoxy-5-(20-ethyl-hexyloxy)-p-phenyl-envinylene) (MEH-PPV). A holographic polymer dispersed liquid crystal grating is fabricated on top of the homogeneous MEH-PPV layer as an external cavity. We established a model to calculate the con?nement factor Γ. With the change of laser structural parameters (the refractive index of the grating layer, the ?lm thickness of the MEH-PPV layer, etc.), the con?nement factor Γ changes accordingly. It was found that a single longitudinal lasing mode could be observed only when the con?nement factor Γ was in a speci?c range. Choosing a reasonable thickness of gain ?lm and prepolymer with higher refractive index can obtain a lower threshold emission laser.
关键词： organic distributed feedback laser,lasing mode,semiconducting polymer,holographic polymer dispersed liquid crystal grating,con?nement factor
更新于2025-09-12 10:27:22
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Properties of self-mixing interference in terahertz distributed feedback quantum cascade lasers
摘要： The properties of self-mixing interference in terahertz distributed feedback quantum cascade lasers (THz DFB-QCLs) were studied by coupled wave theory and the multimode rate equation method. Under weak self-mixing optical feedback, the response behaviors of the DFB-QCLs are similar to those of Fabry–P(cid:2)erot lasers and can be described by the Lang–Kobayashi equations with a modi?ed feedback parameter. The amplitudes of the self-mixing power and frequency signals decrease with the increasing DFB coupling factor. Under strong feedback, new side modes arise, which broaden the laser linewidth. The number of side modes decreases with the increasing DFB coupling factor. The simulation also demonstrates that the maximum power mode of a THz DFB-QCL under strong self-mixing feedback is the minimum linewidth mode. These results support the development of self-mixing interferometers based on DFB-QCLs.
关键词： DFB-QCLs,Lang–Kobayashi equations,self-mixing interference,distributed feedback quantum cascade lasers,terahertz
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Ring Interband Cascade Lasers for Environmental Monitoring
摘要： Interband cascade lasers (ICLs) combine the concept of quantum cascade lasers (QCLs) and conventional photodiodes, because they rely on the voltage-efficient in-series connection of multiple active regions as in QCLs as well as the long upper-level recombination lifetimes of photodiodes. The distinctive low power consumption of ICLs makes them especially attractive for mobile applications in the mid-infrared, such as process control, medical applications and spectroscopy. As a first proof of principle we present ICLs fabricated into ring-shaped cavities. A second order distributed feedback (DFB) grating is used for the light outcoupling of our ring ICLs, in vertical direction through the GaSb substrate. The first demonstrated devices with a waveguide width of 10 μm and 400 μm outer diameter show light emission at a wavelength of ~3.7 μm. A pulsed threshold current density <1 kA/cm2 is measured at 20°C. We are currently working on the second generation of such ring ICLs with smaller waveguides for better suppression of higher order lateral modes and larger outer diameter (e.g. 800 μm) for increased optical output power. The newly developed devices are used in a project for trace gas sensing via the principle of photothermal interferometry.
关键词： Interband cascade lasers,trace gas sensing,distributed feedback grating,photothermal interferometry,ring-shaped cavities
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - A Simple Approach, Based on Coupled Mode Theory, to Study PhC Lasers
摘要： PhC lasers have attracted large interest as efficient light-sources in on-chip and chip-to-chip interconnections. They allow for scaling the active volume while maintaining the high cavity Q-factor, thus exhibiting low threshold current and operating energy [1,2]. Methods for studying these laser cavities are typically based on FDTD simulations, which are often time-consuming and do not allow to catch the most relevant physics of these devices. We propose here an alternative and simple approach to analyze active PhC waveguides and lasers. Our approach is based on coupled-mode theory, which has proved to be an effective tool to study lasers with periodic gain and/or refractive index perturbation, as standard DFB lasers. We apply this method to PhC line-defect waveguides and lasers with a small complex refractive index perturbation (to account for gain and refractive index variation) with respect to a reference, unpumped PhC line-defect waveguide [3]. The optical electric field of the TE-like guided mode is expanded as sum of the forward- and backward-propagating Bloch modes of the passive waveguide; the equation governing the evolution (cid:549)+,-(z) of the Bloch modes along the perturbed waveguide are: (cid:2034)(cid:1878)(cid:2032)+ = (cid:1861)(cid:2018)11,(cid:1869)=0((cid:2033)) (cid:2032)++ (cid:1861)(cid:2018)12,(cid:1869)=1((cid:2033)) (cid:1857)+2(cid:1861)(cid:2012)((cid:2033))(cid:1878)(cid:2032)(cid:3398) (cid:3398)(cid:2034)(cid:1878)(cid:2032)(cid:3398) = (cid:1861)(cid:2018)21,(cid:1869)=(cid:3398)1((cid:2033))(cid:1857)(cid:3398)2(cid:1861)(cid:2012)((cid:2033))(cid:1878)(cid:2032)++ (cid:1861)(cid:2018)11,(cid:1869)=0((cid:2033)) (cid:2032)(cid:3398) (1) where k11,q=0 and k12,q=1;21q=-1 are the self- and cross- coupling coefficients calculated as in [3]. An example is in Fig. 1 for refractive index perturbation ((cid:507)(cid:81)s(cid:143)(cid:19)) and positive gain g0. This figure proves that, differently from standard DFB lasers, the cross-coupling coefficient is always comparable to the self-coupling coefficient. This is because of the strong z-component of the TE-like electric field of the fundamental guided mode. The coupling coefficients are gain-dependent since gain, not present in the holes, is also a periodic perturbation; k11,q=0 and k12,q=1;21q=-1 are also frequency-dependent because of the slow-light effect and they significantly increase as frequency approaches the band edge. Therefore, Bloch modes at shorter frequency and/or with higher gain of the active waveguide will go through a stronger distributed feedback effect with respect to longer frequency Bloch modes and/or lower active waveguide gain. Based on this model, we have simulated a laser cavity with the geometry as in Fig. 2a, consisting of a pumped active section, a rear passive mirror with material refractive index smaller than the active section and a front passive buffer with material refractive index equal (Type A) , slightly larger (Type B) or smaller (Type C) than the active region. Based on the model of eq. (1), we have calculated the rear and buffer mirror reflection coefficients (S11) (Fig.2a). Threshold condition, found searching for frequency and gain g0 satisfying rL(cid:11)(cid:550)(cid:12)(cid:194) rR(cid:11)(cid:550)(cid:15)(cid:74)0)=1, is in Fig.2b as function of the front buffer number of cells. The different trends of the threshold gain with the number of buffer cells can be explained by the interplay, in determining rR(cid:11)(cid:550)(cid:15)(cid:74)0), between the distributed feedback in both the active region and the front buffer. In Type C, the latter is dominant (nearly doubled with respect to the active region feedback); therefore, threshold gain diminishes as the front buffer reflection increases (similar to a FP laser with increase of the front mirror reflection). On the contrary, in Type A and Type B the role of distributed feedback in the active region plays a major role and the threshold depends on the interference between the active region distributed feedback and the front buffer back reflection. For this reason, Type B shows an optimum number of cells minimizing threshold gain.
关键词： coupled-mode theory,FDTD simulations,PhC lasers,distributed feedback,Bloch modes
更新于2025-09-12 10:27:22