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In this letter, we report a distributed feedback (DFB) laser having a dielectric grating formed by SiO and InP to explore both the large refractive index difference and the partial gain coupling. Epitaxy lateral overgrowth by metal-organic chemical vapor deposition is conducted to grow the top p-type InP waveguide layer in the dielectric grating template. An index coupling coefficient of about 250 cm is estimated on the laser vertical waveguide structure. The insulating nature of the dielectric grating also partially blocks the injection current flow and modulates the optical gain of the active quantum-well region underneath it. A prototype DFB laser was fabricated and showed a stable single-mode operation with a sidemode suppression ratio larger than 47 dB measured at room temperature and continuous-wave operation. The technology developed can also be used for other applications that require high efficiency grating structures. [ABSTRACT FROM PUBLISHER]

A novel 1.55-μm AlGaInAs-InP laterally coupled (LC) distributed feedback (DFB) semiconductor laser is presented. Longitudinal feedback and lateral optical confinement are realized simultaneously by incorporating deep gratings etched with inductively coupled plasma technique. Stable single-mode operation with a sidemode suppression ratio over 45 dB has been demonstrated for the fabricated LC-DFB laser. [ABSTRACT FROM PUBLISHER]

Semiconductor lasers with surface high-order gratings have been fabricated and measured. $31^{\mathrm {st}}$ -order gratings were defined by the standard contact-type i-line photolithography near the front facet and subsequently etched into the ridges of the semiconductor lasers by the inductively coupled plasma. Both the static and dynamic characteristics were investigated. The threshold current and maximum output power are 22 mA and 12 mW, respectively. Side-mode suppression ratios are larger than 35 dB at bias currents except approximately 145 mA due to mode hopping. −3 dB bandwidth of the small signal response is 13.8 GHz at 130 mA. The eye diagram at a bit rate of 30 Gbps is clearly open. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We propose a robust way of advancement of the gyrotrons into the region of terahertz frequencies and MW-level power of radiation while retaining high efficiency and high stability of the frequency. These gyrotrons may be used for electron cyclotron resonance heating and current drive systems (ECRH&CD) in future fusion setups, in large complexes of coherently radiating gyrotrons for THz data and energy transmission, for THz particles acceleration. We at first demonstrate the advantages of this way at the example of the gyrotron with very-high-order operating mode TE56.24, driven by a relatively weak external monochromatic signal, and show that in the phase- and frequency-locking mode a significant enhancement of radiation parameters – frequency, power and efficiency – can be achieved. [ABSTRACT FROM AUTHOR]

We demonstrate a 750-Hz linewidth single-mode erbium-doped fiber (EDF) ring laser with wide tunability using a widely tunable fiber Bragg grating (FBG). The stable single-mode operation is realized by using the FBG as a narrow wavelength-selective element and 4 m of unpumped EDF as a saturable absorber in the cavity. The 40-nm continuous tuning range of 1522-1562 nm is achieved using a highly stretchable FBG that exhibits a filter tuning range of over 52 nm. The grating is prepared with chemically stripped deuterium-loaded fiber to eliminate degrading factors for the grating strength, thereby achieving the wide tunability. The tuning range represents a 3.5-fold increase in wavelength tuning over previous use of FBGs [ABSTRACT FROM PUBLISHER]

1300-nm vertical-cavity surface-emitting lasers (VCSELs) were fabricated by wafer fusion (WF) technique and studied. The active region based on InGaAs/InAlGaAs superlattice was grown by molecular-beam epitaxy (MBE). Current and optical confinement was provided by composite n ++ -InGaAs / p ++ -InGaAs / p ++ -InAlGaAs buried tunnel junction (BTJ) realized by selective etching and overgrowth by n-InP. AlGaAs/GaAs distributed Bragg reflectors grown by MBE were applied on both sides of the cavity by WF and substrate removal techniques. The devices with BTJ diameter of 5 μm demonstrated a stable single-mode lasing with threshold current <1.3 mA and output optical power >6 mW and operation in a wide temperature range. The measured −3 dB bandwidth was more than 8 GHz at 20°C and about 5.5 GHz at 85°C, the eye diagrams were open with a bit rate up to 20 Gbps using nonreturn-to-zero (NRZ) modulation standard at 20°C. Using 5-tap feedforward equalizer, the NRZ transmission at 25 Gbps was demonstrated up to 5 km single-mode fiber at 20°C. The developed VCSELs represent a platform for further significant performance improvement. [ABSTRACT FROM AUTHOR]

An external cavity wavelength-fiber ring laser (ECWTFL) based on a semiconductor optical amplifier and a combined wavelength scanning filter in the Littrow configuration is proposed and experimentally demonstrated. With the benefit of the combination of an external cavity wavelength filter and a Lyot filter, the laser achieves a single-mode narrow linewidth output with a linewidth of 1.75 kHz. The wavelength tuning range reaches 133 nm, covering the entire S + C band. The proposed ECWTFL is used for demodulation of a fiber EFPI sensor; the result shows that the proposed ECWTFL has the ability to demodulate the small cavity-length FPI sensor. [ABSTRACT FROM AUTHOR]

In this paper we present a comprehensive overview of the theoretical and experimental studies on gyrotrons operating at harmonics of the electron cyclotron frequency. Besides the conventional (small-orbit) gyrotrons, three other types of such devices are considered, namely large-orbit gyrotrons (LOG), double-beam gyrotrons, and gyro-devices with a frequency multiplication. Based on a comparison between them and the devices that work on the fundamental resonances, both the advantages and disadvantages of the harmonic gyrotrons are critically examined. Such an analysis is helpful for choosing between different alternative concepts in the design process of appropriate radiation sources for various applications. [ABSTRACT FROM AUTHOR]

Semiconductor lasers, characterized by their high efficiency, small size, low weight, rich wavelength options, and direct electrical drive, have found widespread application in many fields, including military defense, medical aesthetics, industrial processing, and aerospace. The mode characteristics of lasers directly affect their output performance, including output power, beam quality, and spectral linewidth. Therefore, semiconductor lasers with high output power and beam quality are at the forefront of international research in semiconductor laser science. The novel parity–time (PT) symmetry mode-control method provides the ability to selectively modulate longitudinal modes to improve the spectral characteristics of lasers. Recently, it has gathered much attention for transverse modulation, enabling the output of fundamental transverse modes and improving the beam quality of lasers. This study begins with the basic principles of PT symmetry and provides a detailed introduction to the technical solutions and recent developments in single-mode semiconductor lasers based on PT symmetry. We categorize the different modulation methods, analyze their structures, and highlight their performance characteristics. Finally, this paper summarizes the research progress in PT-symmetric lasers and provides prospects for future development. [ABSTRACT FROM AUTHOR]

This article mainly focuses on the side mode injection locking phenomena when a single-loop optoelectronic oscillator (OEO) is under RF signal injection. The analyses are made regarding lock range, phase noise and locking time. Also, a comparative study has been prepared when the OEO is injection-locked in the first side and the main mode. We show that the lock range is smaller for injection-locked OEO in the first side mode than in the main mode. The phase noise performance of the OEO for both cases is also demonstrated. It is exhibited that the phase noise performance is better in the case of injection-locked OEO at first side mode, particularly in a strong injection regime. The transient behaviour is also approximated by measuring locking time in both cases. The lock range, phase noise and locking time dependency on optical fibre length have also been studied. Finally, we perform experiments to support our analytical findings developed earlier. [ABSTRACT FROM AUTHOR]

With the growing trend in the information industry, silicon photonics technology has been explored in both academia and industry and utilized for high-bandwidth data transmission. Thanks to the benefits of silicon, such as high refractive index contrast with its oxides, low loss, substantial thermal–optical effect, and compatibility with CMOS, a range of passive and active photonic devices have been demonstrated, including waveguides, modulators, photodetectors, and lasers. The most challenging aspect remains to be the on-chip laser source, whose performance is constrained by the indirect bandgap of silicon. This review paper highlights the advancements made in the field of integrated laser sources on the silicon photonics platform. These on-chip lasers are classified according to their gain media, including V semiconductors, III–V semiconductors, two-dimensional materials, and colloidal quantum dots. The methods of integrating these lasers onto silicon are also detailed in this review. [ABSTRACT FROM AUTHOR]

Abstract Whispering gallery mode (WGM) laser with single‐mode is important for optoelectronic applications because of the higher stability during the light signal transmission. But till now, for InGaN‐based WGM laser, most reports of lasing behavior are multimode lasing. To achieve single‐mode WGM laser, an InGaN‐based micro‐ring laser is proposed and demonstrated with lateral nanoporous distributed Bragg reflector (DBR), where the high‐order lasing modes are strongly suppressed. The side mode suppression ratio (SMSR) is more than 9 times larger than that of the micro‐disk laser with the same radius. Combined with FDTD simulation, the results show that the enhancements are originated from the suppression of the high‐order resonant mode because of the inner boundary of micro‐ring. This work provides a new solution to achieve stable single‐mode WGM laser for future photonic integration.

Single-mode, wide wavelength range, high output power and low threshold current density DFB QCLs emitting around 4.7 $$\upmu $$ m were presented. The multi-wavelength lasers were fabricated simultaneously on a single wafer by different sampled gratings. Instead of electron beam lithography, conventional holographic exposure combined with the optical photolithography was used to fabricate the sampled grating. Single-mode lasing at different wavelengths with a mean side mode suppression ratio above 20 dB was obtained. A wide wavelength range of 238 nm ( $$\sim $$ 106 cm $$^{-1}$$ ) was achieved in pulsed mode at room temperature with different sampling periods. All the DFB-QCLs showed a stable single-mode operation with threshold current density in the range from 1.067 to 1.3 kA/cm $$^{2}$$ , and output power from a single facet in the range from 666.7 to 944.4 mW at 293 K. [ABSTRACT FROM AUTHOR]

This paper analyzes the relative intensity noise (RIN) associated with intensity modulation (IM) of multilongitudinal mode semiconductor lasers. We considered two states of operation; namely, stable single-mode and multimode hopping that correspond to weak and strong asymmetric gain suppression. The former is typically considered by AlGaAs lasers, whereas the latter is considered by InGaAsP lasers. We introduce comparison of the influence of the modulation parameters on both the total and modal RIN between both lasers. We show that the IM response and 2HD display a peak at the relaxation frequency. The multimode hopping in the InGaAsP laser induces levels of signal distortion much higher than those in the AlGaAs laser in the regime of low modulation frequencies. Under weak modulation, the total and modal RINs of both the lasers vary little from those of the non-modulated lasers. The deep modulation releases the multimode hopping phenomenon in the InGaAsP laser and suppresses the mode-hopping peak in the RIN spectrum. [ABSTRACT FROM AUTHOR]

We demonstrate the operation of coupled-cavity terahertz frequency quantum-cascade lasers composed of two sub-cavities separated by an air gap realized by optical lithography and dry etching. This geometry allows stable, single mode operation with typical side mode suppression ratios in the 30-40 dB range. We employ a transfer matrix method to model the mode selection mechanism. The obtained results are in good agreement with the measurements and allow prediction of the operating frequency. [ABSTRACT FROM AUTHOR]

Single-mode operation from an index-guided vertical-cavity surface-emitting laser (VCSEL) has been achieved by using a fiber Bragg grating (FBG) as an external selective wavelength reflector. The spectral characteristics of the external cavity controlled VCSEL under static and dynamic conditions have been studied. The FBG provided stable single mode operation under pseudorandom modulation with a sidemode suppression ratio of ~30 dB from 500 Mb/s up to 4 Gb/s at room temperature [ABSTRACT FROM PUBLISHER]

We achieved 2.5-Gb/s-1200-km transmission in standard optical fiber using an electroabsorption modulator integrated with a distributed feedback laser diode having quarter-wavelength shifted corrugation and optimized coupling in the laser section. Several devices from on wafer showed high optical output power and stable single mode operation. These results showed that our electroabsorption-modulator-integrated distributed-feedback laser diodes with quarter-wavelength-shifted corrugation are cost effective and have very long-haul transmission capability [ABSTRACT FROM PUBLISHER]

Single-spatial-mode semiconductor vertical-cavity surface-emitting lasers (VCSELs) with a non-planar upper (output) dielectric distributed Bragg reflector (DBR) for the 850 nm spectral region are fabricated. The suggested design provides stable single-mode generation in the entire range of working currents, limited by overheating of the active region. Devices with intracavity contacts and a comparatively large current-aperture diameter (5-6 μm) exhibit single-mode lasing at a wavelength of 840-845 nm in the continuous-wave mode at room temperature with threshold currents of 1.2-1.3 mA, a differential efficiency of 0.5-0.55 mW mA, and anoutput power of up to 2 mW. [ABSTRACT FROM AUTHOR]

Gyrotron oscillators are millimeter wave sources, capable of reaching megawatt power levels. Such high RF power is required for electron cyclotron resonance heating and current drive systems for current and future nuclear fusion facilities. With total heating system powers in the range up to about 100 MW, these installations call for unit powers above 1 M W, to reduce cost and complexity of the complete heating system. In this paper, a mode selection process for a 4-MW 170-GHz coaxial-cavity gyrotron is presented and stable operating parameters are elaborated. The employed formalism, based on normalized variables, suggests one mode, namely the TE{-52,31}, which is sufficiently separated from its competitors and supports an advanced two-beam quasi-optical mode converter refid="ref1"/. Through the utilization of time-dependent and self-consistent approaches, a coaxial cavity is optimized and stable single-mode operation at 4.35 MW of generated output power with an interaction efficiency of 33% is predicted. This paper discusses the mode selection process under consideration of realistic technical limitations, optimization of the cavity for stable operation with a pure output mode, and finally thermo-mechanical calculations on cavity cooling and surface temperature. [ABSTRACT FROM PUBLISHER]

To suppress spatial hole burning, a direction related polarizer is adopted in Er-doped fiber ring laser gyroscope. To decrease the frequency drift caused by fluctuation of environment temperature, the polarization maintaining (PM) fiber is substituted for single mode fiber in the ring cavity. To obtain better reciprocity, two 90-deg rotations of PM fiber are introduced. Through the manners, the stable single-mode continuous wave lasers are observed simultaneously in both output directions. At last, better performance of the ring laser gyroscope based on Er-doped fiber is achieved. [ABSTRACT FROM AUTHOR]

This study was motivated by the desire to increase the power, which can be delivered by gyrotrons in long pulse and continuous regimes. Since the admissible power level is determined by the density of ohmic losses in resonator walls, to increase the radiated power a gyrotron should operate in higher order modes. Using an existing gyrotron developed for plasma experiments in the International Thermonuclear Experimental Reactor as a base model, the stability of operation of such a gyrotron in modes with larger number of radial variations was studied. It is shown that the power level achievable in such gyrotrons in stable single mode regimes is close to 1.5 MW. The power level 1.7-1.8 MW can be realized in regimes where the oscillations of the desired mode are accompanied by excitation of distant sidebands whose power is about 1% level of the power of the operating mode. Finally, in the case of operation at the 2-MW level, either the desired mode loses its stability and is replaced by less efficient oscillations of a mode with a smaller azimuthal index or oscillations of the operating mode are accompanied by excitation of sidebands with equally spaced frequencies. [ABSTRACT FROM AUTHOR]

A multi-hole vertical-cavity surface-emitting laser (VCSEL) operating in stable single mode with a low threshold current was produced by introducing multi-leaf scallop holes on the top distributed Bragg-reflector of an oxidationconfined 850 nm VCSEL. The single-mode output power of 2.6 mW, threshold current of 0.6 mA, full width of half maximum lasing spectrum of less than 0.1 nm, side mode suppression ratio of 28.4 dB, and far-field divergence angle of about 10° are obtained. The effects of different hole depths on the optical characteristics are simulated and analysed, including far-field divergence, spectrum and lateral cavity mode. The single-mode performance of this multi-hole device is attributed to the large radiation loss from the inter-hole spacing and the scattering loss at the bottom of the holes, particularly for higher order modes. [ABSTRACT FROM AUTHOR]

We demonstrate room temperature, continuous wave lasing of laser diodes based on AlGaAs whispering gallery mode (WGM) resonators (microcylinder and microring) embedding a quantum dot (QD) active layer. Using InGaAlAs QDs, high-Q (>60 000) lasing modes are observed around 910 nm, up to 50 °C. Lasing with similar performance is obtained around 1230 nm, using InAs QDs. Furthermore, we show that the current injection in the active part of the device is improved in ring resonators, leading to threshold currents of approximately 4 mA for a device with 80 μm diameter. This geometry also suppresses WGMs with a high radial order, thus simplifying the lasing spectra. In these conditions, stable single-mode and two-color lasing can be obtained. [ABSTRACT FROM AUTHOR]

We describe the main stages of the development of a gyrotron in the sub-terahertz band with a power of several hundreds of kilowatts, a duration of the output radiation pulses of about 10 μs, and the generation frequency corresponding to an atmospheric transparency window. The gyrotron having a working frequency of 0.67 THz, a power of 200-300 kW, and the focal diameter of the output beam 1-2 mm can be used to detect sources of ionizing radiation from a distance of several tens of meters. The detection principle is based on the appearance of a microwave frequency discharge in the focal spot if the number of free electrons exceeds the natural background by 1-2 orders of magnitude. The electron-optical system of such a gyrotron has been calculated and optimized. The scenario of the gyrotron switch-on has been analyzed for the electron beam formed in such a system, and the possibility of stable single-mode generation on the TE mode is demonstrated. The results of analysis of thermal loads, which demonstrate their acceptable level in the cavity and the tube cavity for pulse durations of about 10 μs are presented. [ABSTRACT FROM AUTHOR]

Two multichannel 1.3-\mum lens integrated surface-emitting laser arrays for massive data links were fabricated. The basic structure of the lasers consists of a short InGaAlAs multiple-quantum-well distributed-feedback (DFB) active-stripe array monolithically integrated with both a 45^\circ total reflection mirror and an aspheric collimation lens. One of them, a four-channel laser array based on this structure, exhibited clear 25-Gb/s eye openings up to 50 ^\circC over all four channels and achieved a total output of 100 Gb/s. The other laser, a multiple-wavelength array for wavelength-division-multiplexing applications, produces multiple-wavelength emission thanks to precisely modified DFB gratings by electron beam lithography. It exhibited nine-wavelength stable single-mode operation (side-mode suppression ratio >40 dB) between 1260 and 1290 nm at 3.7-nm intervals, and a clear 25-Gb/s eye opening for each wavelength. These two surface-emitting laser arrays have demonstrated their suitability for next-generation multichannel data links (including 100-Gb Ethernet and optical interconnects). [ABSTRACT FROM PUBLISHER]

We report on the design of the \lambda/4-shifted DFB laser that can provide the high output efficiency as well as the stable single-mode operation. In particular, we investigate the effects of the asymmetry in the grating structure on the lasing characteristics of the \lambda/4-shifted DFB laser theoretically and experimentally. The steady-state and mode-stability analyses are performed for the \lambda/4-shifted DFB lasers having the asymmetric phase shift (APS) and asymmetric coupling coefficient (ACC) grating structures by numerical simulations. Although the \lambda/4-shifted DFB laser fabricated with APS structure is found to be capable of providing high output efficiency, its lasing mode is relatively unstable due to the increased longitudinal spatial hole-burning. On the other hand, by using the ACC grating structure, we can significantly improve both the output efficiency and single-mode stability. To verify these simulation results, we fabricate both types of \lambda/4-shifted DFB lasers having APS and ACC grating structures. The measured data agree well with the simulated results. For example, when we fabricate the DFB laser with the ACC structure and coupling coefficient ratio of 0.55, the output power ratio between the front and rear facets of \sim2.5 and the side-mode suppression ratio (SMSR) of >50~dB can be achieved as long as the operating current is in the range of 60 mA \sim200~mA. [ABSTRACT FROM PUBLISHER]

We introduce and demonstrate experimentally that 2-D photonic crystals (PhC) allow the integration of single-mode distributed-feedback (DFB) lasers with both a precise control of the emission wavelength and a high robustness toward optical feedback. This work is based on double deformation , a novel approach, offering theoretical Q-factors above 6\times 10^5 for high volume guided mode. Experimentally, DFB lasers on a GaAs membrane, lasing around 1 \,\mum, show stable single-mode emission with unaltered performances under high optical feedback of around 15% in energy. [ABSTRACT FROM PUBLISHER]

The latest advances in \1550-nm high-speed short-cavity vertical-cavity surface-emitting lasers (VCSELs) are presented. The electrical, optical, and thermal design of these devices is discussed with respect to their high-speed modulation behavior. The implemented design improvements allow high output powers for ambient temperatures up to \90\,^\circ \C, high differential quantum efficiencies up to 40%, temperature-stable single-mode emission, low thermal resistances down to 1.6 K/mW, small-signal modulation bandwidths in excess of 17 GHz, and error-free data transmission at room temperature at data rates of 35 Gb/s in back-to-back configuration and up to 25 Gb/s over 4.2 km of single-mode fiber. [ABSTRACT FROM PUBLISHER]

Effect of optical properties of a planar texture and its thickness on lasing spectrums and thresholds in dye-doped cholesteric liquid crystal (CLC) of steroid type is explored. Transition from the qualitative planar texture to the poor texture quality is accompanied by change of characteristic mode structures and by shift of barycentre in the long-wave side and the considerable growth of the lasing threshold. It is found that in the CLC texture created by substrates with perpendicular directions of orientation the stable single-mode lasing takes place. The obtained results show that in steroid CLC, unlike induced one, lasing spectrums could be described by the coupled wave model. [ABSTRACT FROM AUTHOR]

Semiconductor lasers with stable longitudinal single-mode operation are essential for optical fiber communication systems. Distributed feedback (DFB) lasers are effective to obtain a stable longitudinal single-mode operation; however, stability is not enough mainly because of the spatial hole-burning effect. A corrugation-pitch-modulated (CPM) structure was proposed to improve the stability of longitudinal single-mode operation in distributed feedback lasers. CPM-DFB lasers have a unique corrugation structure to suppress the spatial hole-burning effect. This structure was obtained by a newly developed corrugation fabrication method, a photomask self-interference method. It is confirmed that the CPM-DFB lasers operate in a stable longitudinal single-mode by suppressing the spatial hole-burning effect. This structure is also suitable for narrowing the spectral linewidth for use in coherent optical fiber communication systems. Narrow spectral linewidth lasers with a CPM structure have achieved the narrowest spectral linewidth reported to date. [ABSTRACT FROM AUTHOR]

The results of numerical simulation and study of lasing characteristics of semiconductor verticalcavity surface-emitting lasers based on AlGaAs alloys are presented. Lasers exhibit stable single-mode lasing at a wavelength of 795 nm at low operating currents ∼1.5 mA and an output power of 350 μW, which offers prospects of their applications in next-generation chip-scale atomic clocks [ABSTRACT FROM AUTHOR]

We report the device characteristics of the metal–dielectric high-reflectivity (HR) coated 1.55 μm laterally coupled distributed feedback (DFB) laser with metal surface gratings by using holographic lithography. The HR coating films are composed of Au/Ti/SiO2. It provides a variety of advantages compared to the uncoated DFB laser on the same processed wafer while there is no degradation on current–voltage characteristics. For 3 μm wide and 300 μm long HR coated DFB laser, it exhibits a maximum output power of ∼17 mW and a threshold current of 14.2 mA at 20°C under continuous-wave mode. It is clear that the threshold current and slope efficiency are improved by 36% and 96%, respectively, due to the reduction of mirror loss. The metal–dielectric HR coating on one facet of DFB laser is found to have significantly increased characteristic temperature (i.e., T0∼88 K). Furthermore, the stable single-mode operation with an increased single-mode suppression ratio was achieved. [ABSTRACT FROM AUTHOR]

Carefully designed distributed feedback terahertz quantum cascade lasers based on surface metallic‐stripe grating structure are presented. Stable single‐mode emission with a side‐mode suppression ratio of >20 dB is obtained under all injection currents and operating temperatures. Maximum edge‐emitting power of 58 mW is realised in continuous‐wave mode. In pulsed mode, record output powers of 286 mW at 10 K and 82 mW at 77 K are achieved at 97.1 μm with a well‐shaped beam pattern. [ABSTRACT FROM AUTHOR]

We present a single mode intra-cavity spectroscopy system in which the test laser is locked to a narrow band external single mode laser. This technique solves many problems typically encountered in single mode intra-cavity spectroscopy: it results in good tuning properties, a stable single mode operation close to the lasing threshold, a high side-mode suppression and a reduction of spontaneous emission without the use of any frequency selective element. Measurements of broadband absorptions as well as measurements of a narrow band absorption line of the oxygen A-band are presented and compared with theoretical model predictions. The prototype described in this work provides an enhancement in sensitivity of approximately a factor of 12, and it demonstrates the influence of optical injection to single mode intra-cavity spectroscopy. As there is no need for any frequency selective element inside the cavity, the sensitivity can be massively enhanced by optimizing the laser cavity. [ABSTRACT FROM AUTHOR]

The paper presents a simulation-based analysis of laterally-corrugated ridge-waveguide distributed feedback semiconductor lasers emitting at 980 nm. The simulations were performed using software developed in-house and the PICS3D software package from Crosslight Software Inc. The effects of the corrugation geometry, phase-shift section, and mirror reflectivities on single longitudinal mode operation are discussed. The lasers, designed along the guidelines derived from the simulation results, were fabricated by using molecular beam epitaxy for wafer growth and low-cost nano-imprint lithography. They exhibited stable single-mode operation with up to 50 dB side-mode suppression ratio. [ABSTRACT FROM AUTHOR]

Multimode characteristics of circular-grating-coupled distributed feedback (CGC DFB) lasers are studied theoretically. A modified time-domain finite-difference method is used to solve the time-dependent coupled-mode equations and carrier rate-equation in a self-consistent manner. It is found that, at a moderate injection current density (les 4 times its threshold), the high-order radial modes with fundamental azimuthal profile can be excited when either (1) the grating duty cycle is in the range between 0.35 and 0.5, (2) the phase shift of the grating center is greater than pi, or (3) the facet reflectivity is greater than 0.2. On the other hand, switching between the modes with fundamental and first-order azimuthal profiles is observed when the grating duty cycle is either ~ 0.08 or ~ 0.45 . Switching of azimuthal modes is also observed if facet reflectivity is greater than 0.02. Outside these conditions or the lasers with duty cycle greater than 0.5, stable single-mode operation is observed. Therefore, the design of single-radial and azimuthal mode CGC DFB lasers can be realized. [ABSTRACT FROM PUBLISHER]

We realized strongly index-coupled membrane buried-heterostructure (BH) distributed-feedback (DFB) lasers fabricated by electron-beam lithography, CH4/H2 reactive-ion etching, and regrowth by organometallic vapor-phase epitaxy, using surface corrugation DFB. First, we fabricated narrow stripe membrane BH-DFB lasers with surface corrugation for stable single-mode operation. Under optically pumped room-temperature continuous-wave (RT-CW) operation, a wide stopband width of 68 nm was observed in spite of the narrow stripe width of 0.6 mum. The corresponding index-coupling coefficient of 2950 cm-1 is over two times larger than that of a flat-surface (conventional) membrane BH-DFB laser with a stripe width of 2.0 mum. In addition, we fabricated a short-cavity membrane DFB laser with a surface corrugation structure. A threshold optical pump power of as low as 0.34 mW was realized for a 2.0-mum-wide and 80-mum-long device under RT-CW conditions. [ABSTRACT FROM PUBLISHER]

A wavelength-tunable distributed feedback (DFB) laser array integrated with a funnel combiner is described. Two types of optical combiner, namely a multimode interferometer (MMI) combiner and a funnel combiner, are compared theoretically and experimentally. It is shown that the funnel combiner is superior in terms of wavelength dependence and fabrication tolerance. The laser module covers the full C-band wavelength range ( ~38 nm), and a high fiber output power of 40 mW (16 dBm) is obtained with stable single-mode operation. [ABSTRACT FROM PUBLISHER]

We report on the emission characteristics of micro-cavity quantum-cascade lasers emitting in the terahertz frequency range based on circular-shaped microresonators. Strong mode confinement in the growth and in-plane directions are provided by a double-plasmon waveguide and due to the strong impedance mismatch between the gain material and air. This allows laser emission from devices with overall dimensions much smaller than the free-air emission wavelength (λ > 100 μm). Hence, for the smallest microdisks we achieved a threshold current as low as 13.5 mA (350 A/cm²) in pulsed-mode operation at 5 K and stable single-mode emission up to 95 K in continuous-wave mode operation. We have observed dynamical frequency pulling of the resonator mode on the gigahertz scale, as a consequence of the gain shift due to the quantum-confined Stark effect. Thus, we were able to estimate the peak gain of the material to 27 cm-1. The smallest microcavities exhibited a strong dependence on the exact placement of the bond wire which resulted in single- as well as double-mode emission. Finite-difference time-domain simulations were performed in order to identify the modes of the recorded spectra. They confirm that most of the observed spectral features can be attributed to the lasing emission of whispering-gallery modes. [ABSTRACT FROM AUTHOR]

In the paper, a comparison between results of the optical scalar and vectorial optical methods, using the scalar effective frequency method and the vectorial method of lines, respectively, as their typical examples, applied for simulating an operation of vertical-cavity surface-emitting diode lasers (VCSELs) is presented. Both optical approaches has been applied to simulate an operation of the standard 1.3-μm GaAs-based oxide-confined GaInAsN double quantum-well VCSEL, but comparison conclusions seem to be more general and concerns all VCSELs. Validity limits of the simplified scalar approach have been determined by comparing its approximate results with more exact ones obtained with the aid of the accurate vectorial model. The scalar model has been found to be quite exact in the case of a determination of the wavelength of emitted radiation, whereas its exactness in the lasing threshold analysis is much worse, especially in the case of higher order modes, smaller aperture diameters and/or weak radial optical guidance. Our analysis leads also to more general designing conclusions concerning the optimal position and the thickness of the oxide layer assuring, respectively, the stable single mode operation and the lowest threshold gain. [ABSTRACT FROM AUTHOR]

With the aim of developing a fast wavelength-tunable laser for advanced dynamic network reconfigurations or optical burst switching, a short-cavity (SC) distributed-Bragg-reflector (DBR) laser array with an active-DBR (ADBR) structure (SC-ADBR laser) was fabricated. First, it was experimentally confirmed that the ADBR structure compensates for optical loss and achieves stable single-mode operation during wavelength tuning. An artificial-laser-phase-adjustment technique in the SC-ADBR laser by precise adjustment of a DBR mirror was then proposed. By applying this technique to a six-channel SC-ADBR laser array, perfect wavelength accessibility across a 21-nm range was attained [ABSTRACT FROM PUBLISHER]