This PDF file contains the front matter associated with SPIE Proceedings Volume 12141, including the Title Page, Copyright Information, Table of Contents and Committee list.

We propose and explore a stabilization mechanism of a semiconductor laser array based on asymmetric coupling between neighboring lasers. The stabilization scheme takes advantage of the symmetry breaking of non-Hermitian potentials. We perform a comprehensive numerical analysis in terms of the design parameters, namely the distance between lasers and spatial shift between the individual laser stripe and corresponding electrode. In turn, a mirror symmetric architecture is intended to lead to a light redistribution within the array which is expected to facilitate direct coupling efficiency to optical fibers.

Optical square waves (SWs) have been extensively investigated in semiconductor laser diodes (LDs) like VCSELs or EELs under optical feedback and/or optical injection. In this abstract, we discuss optical SW generation in a delay-driven optoelectronic (OE) feedback system. We have found that at high J, the SWs originate from the same branches of the dynamical regime as the gain-switched pulsing found close to the injection threshold (J_th) of a positive optoelectronic feedback system. A single-mode DFB multi-quantum-well (MQW) InGaAsP LD (3SP Technologies-1953LCV1) with J_th of 20 mA is used for this experiment. The origin of the feedback signal is the photodetector output, which is appropriately boosted in the amplifiers/attenuator cascade before feeding it to the radio frequency input arm of the Bias Tee. An oscilloscope measures the optical intensity after the PD. The delay in the feedback loop is τ=10.64 ns. The first appearance of the SW for this particular configuration is recorded at 48.20 mA. The SW appears with a repetition rate of f_τ=τ^(-1)=(10.64 ns)^(-1)=94 MHz. The optical spectrum shows two peaks separated by a frequency related to the duty cycle of the SWs. At higher feedback delay, the SWs appear at harmonics of the fundamental delay frequency. Theoretical analysis based on a delay-differential model and accounting for the multilevel amplification, multistage filtering, and saturable nonlinearity attributes the origin of the SWs to the same branches of dynamical regimes as those observed for the gain-switched pulse-train generation near the J_th and confirms the experimental observation of SW harmonics for higher feedback delays. In conclusion, we experimentally demonstrate SWG in a laser diode subjected to OE delayed feedback on its injection current.

Catastrophic optical mirror damage (COMD) limits the output power and reliability of lasers diodes (LDs). Laser self heating together with facet absorption of output power cause the facet to reach a critical temperature (Tc), resulting in COMD and irreversible device failure. The self-heating of the laser contributes significantly to the facet temperature, but it has not been addressed so far. We implement a multi-section waveguide method where the heat is separated from reaching the output facet by exploiting an electrically isolated window. The laser waveguide is divided into two electrically isolated laser and transparent window sections. The laser section is pumped at high current levels to achieve laser output, and the passive waveguide is biased at low injection currents to obtain a transparent waveguide with negligible heat generation. Using this design, we demonstrate facet temperatures lower than the junction temperature of the laser even at high output power operation. While standard LDs show COMD failures, the multi-section waveguide LDs are COMD-free. Our technique and results provide a pathway for high-reliability LDs, which would find diverse applications in semiconductor lasers

Fiber Bragg Grating (FBG) sensors offer multiple benefits in comparison with electronic sensors due to their compactness, electromagnetic immunity as well as their resistance to harsh environments and their multiplexing capabilities. Structural Health Monitoring (SHM) is one of the various potential industrial applications that could take full advantage of those sensors. However, there is a need for a low size, weight, power and cost interrogation unit for certain application areas such as aerospace or aeronautics. That is the reason why recent efforts have been made to use integrated components and circuits for interrogation of FBGs. Among different techniques, interrogation with a swept laser source is of high interest since it has a high multiplexing capability and could reach a high level of integration using other integrated components such as photodetectors, grating couplers or directional couplers to form a compact interrogation unit. In this paper, we present characterization results of a fully-packaged hybrid III-V on silicon tunable laser diode operating in the C and L bands. Wavelength maps are produced and analyzed and modulation of emitted wavelength is discussed. Preliminary results corresponding to a moderate frequency (10-Hz sweep rate) were obtained and FBG reflection spectra acquired with a broadband source (BBS) and a swept laser diode are compared. Finally, we discuss potential design improvements in order to reach high scan rates (< 10 kHz) and a large tuning range

We present our patented extended-cavity diode laser (ECDL) based on a modified Littrow configuration. Here, the coarse wavelength adjustment via the rotation of a diffraction grating is decoupled from the fine tuning of the external cavity modes by positioning a piezoelectric transducer behind the diode laser. As a result, the fine adjustment of the laser frequency with the piezo does not affect neither the optical feedback alignment nor the broader grating frequency selection curve, resulting in a better mode-hop stable performance compared to the one of standard Littrow ECDLs without optimized pivotal point. We characterize the design and show that it is well suited to atomic and molecular experiments demanding a high level of stability over time and for long cavities ECDLs.

As a potential high-energy laser, diode pumped metastable rare gas laser (DPRGL) and diode pumped alkali metal vapor laser (DPAL) have drawn attention worldwide. By using chemically inert metastable rare gas instead of aggressive alkali metal vapor as the active medium, DPRGL has overcome a major problem in DPAL that active medium would react with hydrocarbons and chamber windows. Though one of the advantages of DPRGL is that it can convert diode laser (pumping laser) into laser with high output power and excellent beam quality, efficient pumping of DPRGL requires high pumping intensity and narrow linewidth. By applying narrow bandwidth filters and external optical reflectors, the broad spectra linewidth of diode lasers can be narrowed. Development of volume Bragg grating provides a more convenient and efficient way of linewidth narrowing where VBG is applied as both optical filter and output coupler. In this program, an external cavity diode laser stack (ECDL) coupled with a reflective volume Bragg grating for metastable rare gas laser pumping is presented. The maximum output power of 130 W with 78 pm (FWHM) linewidth was realized. Higher output power can be achieved by vertically increasing the number of laser bars in the diode laser stack. A tuning range of 230 pm was measured which is sufficient for DPRGL pumping. The stability of output wavelength in long-time operation was evaluated by a 5-h test run where wavelength shifted ±7 nm. Total losses caused by passive optical elements, absorptions, etc. do not exceed 14 %. Performance of this narrow-linewidth diode laser stack as pumping source of DPRGL was furtherly examined by transverse pumping of metastable argon laser where the oscillation of metastable argon laser and absorption of pumping laser were detected by photon diode and spectrometer respectively

This work investigates the effects of the confinement factor on the linewidth enhancement factor in hybrid silicon quantum dot comb lasers, which is a key parameter involved in frequency comb generation. Experiments are performed on two laser devices sharing the same gain material with slightly different cavity designs resulting in different confinement factors. The results highlight that a lower confinement factor leads to a smaller carrier-induced refractive index variation and a larger differential gain, together resulting in a smaller linewidth enhancement factor, which in turn translates into different sets of performance regarding the feedback applications. This paper brings novel insights on the fundamental aspects of quantum dot comb lasers and provides new guidelines of future on-chip light sources for integrated wavelength-division multiplexing applications.

We report a continuous wave room temperature quantum cascade laser operating in an external cavity in the Littrow configuration with a 10-facet polygon mirror rotating at 24,000 RPM. The quantum cascade laser emission is swept across ∼1520 – 1625 cm-1 wavenumber range in less than ~45 µs with a sweep repetition rate of 4 kHz. The measured maximum output power at the laser gain maximum, 15°C and 0.86 A driving current is ~90 mW; the estimated average output power across the 45 µs wavenumber sweep is ~50 mW. Through its sweep, the laser emits on the sequential Fabry-Perot longitudinal modes of the laser chip cavity with the mode separation of ~0.5 cm-1 . The linewidth of the emitting modes is less than ~0.15 cm-1 . Spectral measurements of the infrared absorption features of a 10 µm thick layer of acetophenone and water vapor in the air have demonstrated the capability of obtaining spectral data in less than 45 μs.

Semiconductor lasers subject to optical feedback usually produce rich nonlinear dynamics, including periodic oscillations, quasi-periodic oscillations, and chaotic oscillations. However, quantum cascade lasers (QCLs) are highly stable against normal optical feedback, owing to the intersubband transition with ultrashort carrier lifetime and the near zero linewidth broadening factor. This work numerically shows that tilted optical feedback from a misaligned reflection mirror triggers the generation of nonlinear dynamics from QCLs, which is in good agreement with our previous experimental observations. The physical mechanism is attributed to the non-degeneration of the odd-order round-trip feedback path with the even-order ones.

Lead sulfide (PbS) colloidal quantum dots (CQDs) are a novel infrared gain medium, which can exhibit tunable gain across the short-wave infrared (SWIR); lasing in this material however, remained undemonstrated until recent. Here we present a random-like laser emission from PbS CQDs at 1607 nm using a silica based distributed-feedback structure. We determined this random lasing behavior to arise via heating of the CQDs from the intense pulsed laser source, causing a drift in gain. The effects of the thermal conductivity of the substrate were then explored and were seen to be a critical factor in forming stable DFB lasing. By using an alumina based grating, DFB lasing was demonstrated between 1.55 μm – 1.65 μm with linewidths as low as ~0.9 meV.

Fiber Bragg grating (FBG) feedback has initially been investigated as a promising approach to conceal the time-delay signature in optical chaos generation. It has been shown that the laser dynamics vary greatly with respect to the FBG properties, especially to the frequency detuning between the laser emission and the Bragg wavelength. As a result, adjusting the FBG features will lead to significantly different behaviour. Here, we theoretically study the response of FBGs with different lengths but with similar reflectivity: this way, the impulse response is stretched over a longer period of time while its overall shape is maintained. This leads to a broadening of the FBG bandwidth and, thus, to a longer distribution of the feedback over time. In this work, we analyse the effects of the time-distribution variations for long gratings by simply tracking the first Hopf bifurcation and the feedback rate needed to destabilize the laser. The numerical results are generated using a modified version of the well-known Lang and Kobayashi equations. Our results show that the time-distribution of the feedback seem to have little effect in itself on the overall dynamics though it obviously affects the FBG spectra properties. We report stability oscillations of the laser behavior when long, narrow-bandwidth gratings are considered. The influence of the grating length on the specific dynamic details is investigated through the time delay signature (TDS) focusing especially on the implication of the stability oscillations on the TDS. We report that although variation of the TDS for long grating are observed the better TDS suppression is achieved with relatively short gratings.

The development of precision laser spectroscopy around 420 nm for gas sensing, atomic clocks and laser cooling is slowed down by the lack of compact narrow linewidth laser sources allowing lab-to-market technology transfer. In the infrared (IR) part of the spectrum, the laser diode technology is mature to address those kind of specifications but for shorter wavelengths there are still technological issues. Commercial blue laser diodes have a wide multimode optical spectrum. To improve the frequency noise performances, the use of an external cavity has been proven to favor single mode behavior. Nevertheless, opto-mechanical instabilities of the external cavity limit the laser linewidth to a few MHz. To overcome this issue, we propose a compact and low-cost all-fiber-based locking setup for frequency noise suppression of a 420 nm external-cavity diode laser. This versatile and compact optical reference allows to reduce the laser frequency noise up to 40 dB associated with a linewidth reduction from 850 kHz to 20 kHz. To our knowledge this is the first demonstration of such a stabilization scheme in this wavelength range. The originality of our work is to point out that actual performances of fiber based photonic components around 420 nm, limit the noise reduction efficiency of such optoelectronic feedback loop scheme. This simple locking scheme might be implemented for a large range of wavelengths and can be integrated on a small footprint for embedded applications requiring narrow linewidth blue laser diodes.

The recent advancements of swept-source optical coherence tomography (SS-OCT) calls for a compact widely tunable swept-source that can emit single mode, and narrow linewidth radiation over a 70-100 nm wavelength tuning range. However, the gain bandwidth of the laser material critically limits the wider tuning range of the device. Moreover, to ensure the single-mode operation, the mirror sections of the laser should be designed with a specific free spectral range (FSR) which further limits achieving wider tuning range of the device. These limitations drive the laser manufacturer to opt for external filters which restricts the speed of operation of the device. In this work, we have discussed an alternative approach of increasing the tuning range of the device without adding further complexities in the laser design by employing the method of electro-optic synchronization. Two tunable semiconductor lasers with different epitaxial structures and central wavelengths have been electrically synchronized and their outputs have been coupled optically. The tuning range of these lasers partially overlaps with each other for a smooth transition of the laser emission. Two multi-section semiconductor lasers with a central wavelength of 830 nm and 862 nm respectively, and with a tuning range of 40 nm, have been fabricated using standard UV optical lithography to be utilized in this approach. Initial electro-optic characterization of the lasers shows single mode emission with high SMSR throughout the tuning range.

Laser designed to emit at multiple and controllable modes, or multi-wavelength lasers, have the potential to become key building blocks in future compact THz or mm-wave transceivers. Combined with optical injection, these lasers can function as low-noise THz sources or even enable all-optical THz signal processing. Among the various multi-wavelength laser concepts, DBR-based lasers stand out because of their simplicity principle to control and switch the output wavelength of the laser. The extra wavelengths also add new degrees of freedom and interesting new features for laser dynamics. Yet, the coupling between the different laser modes has not been carefully considered so far. Here, we experimentally and numerically analyze the effect of nonlinear mode coupling and interactions in a dual-wavelength laser under optical injection. We focus particularly on the evolution of the locking bandwidth for different gain coefficients between the injected and non-injected modes. In addition, we report a wavelength shift of the non-injected mode which follows the evolution of the detuning in the other mode. Our work brings a new important insight into the mode competition taking place in multi-wavelength lasers, pushing them forward towards novel applications.

In this work, we experimentally and theoretically report on optical comb dynamics in VCSELs induced by optical injection. We show that injection of a narrow comb with parallel, orthogonal or arbitrary polarization can sustain two polarization comb dynamics in single-mode VCSELs. More specifically, we show that the two polarization comb dynamics can be observed whatever the injected comb’s polarization. The appearance of the comb can be controlled with the linewidth enhancement factor for fixed injected comb spacing and detuning frequency. Also, we show that the harmonics comb in the two orthogonal polarization modes can be suppressed with the linewidth enhancement factor in the cases of parallel and orthogonal optical injection.

The transverse modes in microchip lasers (MCL) appear different from the classical mode theory, as the resonator consists of a set of plane mirrors (similar to semiconductor edge-emitting lasers and VCSELs). Then the parabolic potential is absent, and the electromagnetic radiation is confined in the transverse space of the resonator by other mechanisms, essentially by gain guiding. Thermal lensing also can play some role in confining the radiation. Laser engineers use several intuitive assumptions about the number of supported modes in the resonator, relating with the Fresnel number of the resonator. However, despite some attempts to calculate the modes in such resonators and investigate combined gain with index guiding, no clear and straightforward methods were provided to calculate the beam radiation profiles. We aim to fill this gap by providing analytical and numerical treatment of MCL modes in two dimensions. We analyze the transverse modes in microchip laser formed due to both gain guiding and thermal lensing. Analytical and numerical results are compared with the results of experimental measurements. Using the cylindrical pumping profile approach, we provide a simple 2D theory of the gain-guided and thermal-lens induced modes in such plane-mirror resonators. We estimate the mode beam quality factor dependency on pumping strength. The model is versatile and applicable to wider range of optical resonators consisting of plane mirrors with longitudinal pumping. Finally, we compare the experimental measurements of beam quality factor with our theoretical model.

We present a classification of the transverse light states observed in a 3D degenerated optical system using a specially design VECSEL based on III-V semiconductor nanotechnology with weak light confinement in matter. A broad transverse area system with low but tunable diffraction combine with saturable absorption is used for light confinement. These light states include CW paraxial spherical coherent beams linearly polarized, conical waves and spatially degenerate coherent light. A first result of a non-linear structuration is also shown

We report on a low-cost Brillouin fiber ring laser pumped from an actively stabilized self-injection locked distributed feedback (DFB) laser diode. Locking of the commercial DFB laser to a ~11-m-length high-Q-factor fiber-optic ring cavity leads to ~10,000-fold narrowing of the laser Lorentzian linewidth down to 400 Hz. Such pump laser operation inside the ring cavity forces the cavity to host Brillouin lasing enabling the laser threshold power as low as ~1.5 mW. The laser operation is perfectly stabilized by active optoelectronic feedback driven by a simple microcontroller. The laser delivers radiation at Stokes frequency with the Lorentzian linewidth reduced down to ~75 Hz and a phase noise less than –100 dBc/Hz (<30 kHz). The reported laser configuration is of great interest for many laser applications where a narrow sub-kHz linewidth, simple design and low cost are important.

Realization of the coupling of the laser diode to an external reflector may provide efficient suppression of the phase noises and significant stabilization of the laser source. Locking a semiconductor laser to high-quality-factor microresonator was shown to result in a laser linewidth narrowing to sub-Hz level. The straightforward way to get better stabilization and wider locking band is to increase the feedback level. However, most of the theories used to describe the self-injection locking effect assume the weak feedback from the external reflector. Here we develop the more complete theory of the laser -- resonant reflector interaction that allows to describe this effect for the high feedback level as well. We define different possible regimes taking place at different feedback levels (including the so-called external cavity laser regime) and study applicability domains of the previous and proposed models. We show that existing model of the self-injection locking to whispering-gallery mode resonator is a consequence of the considered model in the low-feedback regime. Finally, we check the model in high-feedback limit experimentally and show a good correspondence with the theory.

Optical Coherence Tomography (OCT) is a technique used to create 2D and 3D images of biological samples. OCT can be performed using multi-section swept source lasers. We discus the challenges associated with such devices that operate near 850nm, which are of interest in ophthalmology as they have a low absorption rate in water and the short wavelength leads to good spatial resolution. In a typical multi-section swept source laser there is a Gain Section bounded by two Mirror Sections. The Mirror Sections have slots etched into them and act like Bragg Reflectors. The reflected wavelengths can be tuned by changing the refractive index of each Mirror Section, achieved by changing the temperature through the applied current. To ensure single mode operation, longitudinal modes must be sufficiently spaced so that only one mode lies beneath the overlapping mirror reflection peaks. A laser operating near 850 nm must be approximately a third of the size of a similar 1550 nm laser in order to achieve similar mode spacing. A shorter device has less gain available to compensate for lossy slots and since the Mirror Sections will be closer to each other there can be an increase in thermal cross talk. Stronger slot reflectivity reduces losses and reduces the width of mirror reflectivity peaks which defines the minimum cavity length required for single mode lasing. Different cavity lengths are investigated and the widths of the reflectively peaks are found.