This PDF file contains the front matter associated with SPIE Proceedings Volume 11263 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

TVertical cavity surface emitting laser (VCSEL) is brightening in everybody’s mobile device, every car, and every home. Industrially, we are in a period of rapid growth. Attention is drawn to the trend as a light source supporting the physical layer of AI and IoT technology. This is a talk from the invention of the surface emitting laser by the author to research, peening development, and recent strides toward expansion of applications. New technical and business areas have been now generated in the area of such as high-speed LANs, parallel optical interconnects, computer mice, laser printers, face recognition systems, LiDARs, and various optical sensors. The total sales are reaching over 2000 M$ headed by data-coms, recognition sensors, and power applications.

Mode-locked vertical external-cavity surface emitting lasers are promising compact sources for high-power, ultrafast pulses with excellent beam quality and the flexibility offered by an external cavity. Classical models of these lasers use either phenomenological approaches, which rely heavily on experimentally observed macroscopic parameters, or are based on quasi-equilibrium conditions. Although these models enjoy widespread success, they cannot capture the underlying charge carrier dynamics, shown to be critical components of pulse formation and propagation. The Maxwell Semiconductor Bloch Equations capture these dynamics through a coupling of pulse propagation to the field induced polarization within an active semiconductor quantum well. We utilize a transverse implementation of this model to microscopically investigate fundamental Gaussian pulse formation as well as destabilizing effects of pump parameters. These behaviors are directly linked to the underlying charge carrier dynamics. Excess carriers around the pulse's spatial or spectral centers destabilizes the pulse and are shown to lead to the formation of higher order transverse modes and secondary pulses within the cavity.

Today the generation of femtosecond laser pulses nearly exclusively relies on passive mode-locking, which requires a phase lock between the longitudinal modes of a laser. In order to overcome the non-equidistance of the cold cavity modes, it is generally considered necessary to include an effective saturable absorption mechanism in the laser cavity. However, there exists a number of experimental demonstrations of mode-locking in which saturable absorption was clearly absent. Here we show that four-wave mixing may equally well lead to a mode-locking effect. However, the resulting pulse trains are only partially coherent, and the comb structures lack perfect equidistance. Operation of lasers in the pseudo mode-locked regime can easily be confused with traditional mode-locking. We discuss indications and characterization approaches for unveiling pseudo mode-locking.

We show the characterisation of spectral broadening in the Tantalum Pentoxide waveguide system as a function of pump wavelength, showing spectra for central pump wavelengths of 0.9 to 1.5 um (150 fs, 80 MHz). We have achieved octave spanning spectra with approximately 5 mW of laser power coupled in the waveguide at 1 um pumping wavelength for a linear buried waveguide using a commercial source.

We present a laser system for the generation and stabilization of continuous wave emission at 1.9 THz. The system is based on difference frequency generation (DFG) from a bi-color vertical external cavity surface emitting laser (VECSEL). The intracavity DFG process enables THz generation with milliwatt power level at room temperature with a clear quadratic dependence on the intracavity power. The two colors are spectrally selected via an intracavity etalon while the laser cavity geometry is engineered to minimize mode competition between the two colors via spatial hole burning, improving the stability of the THz emission. The intensity noise of the THz output is further reduced by 16 dB/Hz with an active stabilization scheme. The origin of residual fluctuations is discussed and we found that the asymmetrical amplification of one color reduced the RIN even further, down to 21 dB/Hz, comparing to the free-running symmetrical lasing.

Output power of VECSELs had been scaled by lateral scaling to tens of watts and beyond. Longitudinal scaling, employing multiple VECSEL devices in a single resonator, has the potential to scale up the power as well. However, some of the devices need to be placed at a fold of the resonator and inherently suffers from the spectral instability. The standing wave pattern created at a fold of a standing wave cavity exhibits that of 4-wave interference, and the resulting pattern shows high contrast modulation in the plane of the quantum well. The phase of that modulation depends on the phase relationship between the forward and backward beams, which differs for different longitudinal modes. This results in a situation similar to the special hole burning effect in solid-state lasers in which case the standing wave pattern is in the longitudinal direction. Because of the resonant periodic gain structure, VECSELs do not suffer from spatial hole burning if the device is placed at the end of the standing-wave cavity and single-frequency operation can be obtained relatively simply. This no longer holds when the VECSEL device is placed at the fold of a standing wave cavity. Twisted-mode configuration addresses this and allows narrow-linewidth or single-frequency operation of multidevice VECSELs. By having forward and backward modes in oppositely rotating circular polarization, the standing wave pattern does not show modulation in the planes of quantum wells, recovering the advantage of resonant periodic gain.

Over the last 30 years, Sodium Guidestar Lasers (SGLs) have proved to be an important element of adaptive-optics (AO) image correction techniques for astronomical observatories. In recent years, the astronomy community has employed Raman shifted fiber lasers to meet the need. However, emerging applications would greatly benefit by a reduction in the cost per Watt of on-sky power and the Size Weight and Power (SWAP) required by the laser. Small (meter-class) observatories seek to incorporate AO systems to meet space situational awareness and free space laser communication applications. Simultaneously, large (10 meter class) observatories require larger numbers of lasers on-sky to implement multi-conjugate AO systems, Further, techniques such as re-pumping and frequency-chirping are being developed to increase returns from the sky for a given laser power. The next generation of SGLs (Sodium Guidestar Lasers) must be suited for such modes of operation while reducing cost and SWAP. Optically pumped semiconductor lasers (OPSLs), also referred to as Vertical External Cavity Surface Emitting Lasers (VECSELs), represent a technology pathway to realizing SGLs with high performance, compact size, high reliability, and low acquisition and maintenance costs. In pursuit of the next generation of SGL, we demonstrate 8W of single-frequency power at 589 nm based on in intracavity frequency doubling of 1178 nm fundamental wavelength VECSEL. Our work investigates the key challenges of the laser design; especially frequency selection, tuning, and locking the laser to sodium resonance, laser power, and gain-mirror lifetime.

We report recent progress in sub-kHz-linewidth operation of AlGaInP-based SDL systems designed for neutral Strontium optical clocks. Overall system performance is presented, including intensity, frequency and phase noise characterisation. Two almost identical SDLs, each with >150 mW output at 689 nm, were frequency locked and an optical beat note measurement produced a linewidth of 160 Hz with fractional frequency stability reaching below 2×〖10〗^(-15) for averaging times from 60-400 s. Spectroscopic measurements of a blue magneto-optical trap (MOT) of Strontium with one SDL resulted in a reduction of the atomic sample fluorescence and revealed Zeeman splitting of the 3P1 electronic level.

This Conference Presentation, “Engineering SDL systems for single-frequency applications” was recorded at Photonics West LASE 2020, held in San Francisco, California, United States of America

A MECSEL emitting around 825nm is reported. With a tuning range from 807nm to 840 nm, the MECSEL extends the coverage of high beam quality semiconductor based lasers in the short 8XXnm region and opens new perspectives for scanning ground-based water-vapor differential absorption lidar. 1.4W maximum output power has been achieved at room temperature operation and at 12.5W absorbed power using a 532 nm emitting pump laser. The beam quality has been investigated by M² measurements at different pump power. The effect from a growing pump mode and thermal lensing has been observed as the beam divergence angle decreases and the beam waist radius enlargens with increasing pump power.

We demonstrate the operation of two optically pumped high-power membrane external-cavity surface-emitting lasers (MECSELs) that emit in 1600–1800 nm spectral region. The region of the MECSEL consisted of eight strained InGaAs quantum wells (QWs) that are enclosed by InGaAlAs barriers. The heterostructures were deposited on InP substrates by molecular beam epitaxy. In order to efficiently dissipate heat, the developed MECSEL technology requires etching-off the epitaxial substrate and bonding two diamond heat spreaders on both sides of membrane. Maximum output powers of 1.6 W at 1640 nm and 2.1 W at 1760 nm were achieved. The mount temperatures were -6°C in both cases. The introduction of a birefringent filter into the resonator of the 1760 nm emitting laser produced a 133-nm wavelength tuning range, from 1695 nm to 1828 nm.

Vertical-external-cavity surface-emitting lasers employing QDs as gain media in comparison to QW-based VECSELs can offer beneficial lasing features, such as, temperature resilience, broadband gain and wider wavelength tunability. We demonstrate the first QD-based VECSEL providing 2 W emission at 1.5 µm and a tuning range of 60 nm. This achievement paves the way to multi-Watt VECSELs with extended wavelength tunability.

Spatially Localized States are individually addressable structures that may appear in large aspect-ratio optical resonators. They can be used as bits of information for all-optical buffering. We design and operate a modeless laser cavity based on a 1/2 VCSEL coupled to a distant mirror in self-imaging condition. Our study indicates how a VeCSEL can be specially designed to provide a robust system potentially capable of emitting Spatially Localized States and paves the way towards the observation of three dimensional - in space and time - confined states, the so-called light bullets.

Mid infrared frequency combs allow for high resolution absorption spectroscopy of molecular species, which have strong signatures in this spectral region. Dual comb spectroscopy can provide broadband and high-resolution capability, but requires two fully stabilized frequency combs which adds complexity to the system.

Previous work has demonstrated that frequency combs coupled with a high resolution spectrometer, consisting of a virtually imaged phased array (VIPA) along with a grating, can perform time-resolved, broadband and high- resolution absorption spectroscopy with a single frequency comb. The VIPA spectrometer disperses the spectrum in two dimensions and images it onto a focal plane detector array. If the comb teeth can be resolved, the VIPA is easily calibrated and provides comb-tooth resolved resolution and accuracy. However, in previous work, the repetition rate of the laser sources used was too low to be resolved directly, and additional passive "filter cavities" had to be employed to increase the effective repetition rate of the frequency comb. In this work we use a fully stabilized mid infrared frequency comb based on a 1.6 GHz repetition rate modelocked vertical external cavity surface emitting laser (VECSEL) and difference frequency generation to produce an off set free comb in the 3- 4 micron wavelength range. The source is directly coupled to the VIPA spectrometer to provide comb-tooth resolved absorption spectroscopy. We discuss the system's performance in gas absorption spectroscopy and its time resolving capabilities, which are limited only by the speed of the detector system.