Methods, devices and systems for improving single-frequency operation of diode lasers are described. One such method includes ramping up an operational current of a diode laser for a first predetermined number of steps, and measuring an associated current value indicative of optical power within the laser diode for each of the first predetermined number of steps. Next, operational current of the diode laser is ramped down for a second predetermined number of steps, and an associated current value indicative of optical power within the laser diode is measured for each of the second predetermined number of steps. Using the measured data current values at which a mode hop or a multimode operation is likely to occur are identified, and a contiguous range of operating currents that is devoid of identified likely mode hops or multimode regions of operation is determined as the operating current range of the diode laser.

Low phase noise signal generated in a small structure is required for communication and high-resolution imaging. A DBR based multi-mode laser is combined with mode-locking method to build frequency stabilized and tunable RF signal generator. The number of the output modes from each laser is adjusted using reflecting bandwidth of distributed Bragg reflector and electro-absorption (EA) modulator for amplitude control, while the phase section in integrated laser system provides frequency tuning. Mode-locking of 60 laser modes results in a highly frequency stable 10 GHz RF beat-notes with a calculated phase noise of −150 dBc/Hz at 10 kHz offset frequency.

The present disclosure relates to a diode laser having reduced beam divergence. Some implementations reduce a beam divergence in the far field by means of a deliberate modulation of the real refractive index of the diode laser. An area of the diode laser (e.g., the injection zone), may be structured with different materials having different refractive indices. In some implementations, the modulation of the refractive index makes it possible to excite a supermode, the field of which has the same phase (in-phase mode) under the contacts. Light, which propagates under the areas of a lower refractive index, obtains a phase shift of π after passing through the index-guiding trenches. Consequently, the in-phase mode is supported and the formation of the out-of-phase mode is prevented. Consequently, the laser field can, in this way, be stabilized even at high powers such that only a central beam lobe remains in the far field.

A semiconductor laser source including a Mach-Zehnder interferometer, this interferometer including first and second arms. Each of the arms is divided into a plurality of consecutive sections, the effective index of each section located immediately after a preceding section being different from the effective index of this preceding section. The lengths of the various sections meet the following condition: $\underset{n=1}{\overset{N_2}{.Math.}}{L}_{2,n}{\mathrm{neff}}_{2,n}-\underset{n=1}{\overset{N_1}{.Math.}}{L}_{1,n}{\mathrm{neff}}_{1,n}=k_f{\lambda }_{\mathrm{Si}}$
where: k.sub.f is a preset integer number higher than or equal to 1, N.sub.1 and N.sub.2 are the numbers of sections in the first and second arms, respectively, L.sub.1,n and L.sub.2,n are the lengths of the nth sections of the first and second arms, respectively, neff.sub.1,n and neff.sub.2,n are the effective indices of the nth sections of the first and second arms, respectively. The first and second arms each comprise a gain-generating section.

A monolithic integrated semiconductor random laser comprising substrate, lower confinement layer on the substrate, active layer on the lower confinement layer, upper confinement layer on the active layer, strip-shaped waveguide layer longitudinally made in middle of the upper confinement layer, P.sup.+ electrode layer divided into two segments and made on the waveguide layer and N.sup.+ electrode layer on a back face of the lower confinement layer, wherein the two segments correspond respectively to gain region and random feedback region. The random feedback region uses a doped waveguide to randomly feedback light emitted by the gain region and then generates random laser which is random in frequency and intensity. Further, the semiconductor laser is light, small, stable in performance and strong in integration.

A method or apparatus for narrowing the linewidth of a single mode laser is provided. The linewidth of a single mode laser is narrowed by injecting an optical feedback simultaneously into the first laser cavity mirror and the second laser cavity mirror of the single mode laser.

Disclosed are embodiments of bidirectionally emitting semiconductor (BEST) laser architectures including higher order mode suppression structures. The higher order mode suppression structures are centrally located and extend from an inner transition boundary, which may be established by confronting high reflector (HR) facets in some embodiments or a central plane defining two sides of a unitary, bidirectional optical cavity in other embodiments. Examples of the higher order mode suppression structures include narrow regions of bidirectional flared laser oscillator waveguide (FLOW) devices, which are also referred to as reduced mode diode (REM) devices; high-index regions of bidirectional higher-order mode suppressed laser (HOMSL) devices; and non- or less-etched gain-guided lateral waveguides of bidirectional low divergence semiconductor laser (LODSL) devices. The aforementioned devices may also include scattering features, distributed feedback (DFB) gratings, distributed Bragg reflection (DBR) gratings, and combination thereof that also act as supplemental higher order mode suppression structures.

A laser arrangement including a laser element; a volume Bragg grating, VBG, for providing optical feedback to the laser element along a beam path; a polarizing beam splitter, PBS, arranged in the beam path between the laser element and the VBG; and a polarization-modifying element arranged in the beam path between the PBS and the VBG element; wherein the polarization-modifying element is structured and arranged to alter a polarization state of light reflected from the VBG such that the PBS is operative to divide said light reflected from the VBG into a first portion that provides the optical feedback to the laser element and a second portion that provides an output beam from the laser arrangement. Embodiments may be useful for low wavenumber Raman spectroscopy.

A segmented VCSEL array having a plurality of individually addressable segments, each segment comprising one or more VCSELs. In some cases, at least two of the plurality of individually addressable segments may be driven in combination. The plurality of individually addressable segments, in some embodiments, may be centered around the same central point. An optical element may be used in conjunction with the segmented VCSEL array, and in some cases may be aligned to the central point. The optical element may be configured such that light passing therethrough may be directed according to which of the plurality of individually addressable segments is activated. In some embodiments, the optical element is a grating or diffractive optical element. The grating or diffractive optical element could be patterned with optical segments that each correspond to at least one the plurality of individually addressable segments.

Examples herein relate to optical systems. In particular, implementations herein relate to an optical system including a bidirectional optical link such as an optical fiber. The optical system includes a resonator tuned to filter a resonant wavelength of light emitted by an optical source. The optical source may be configured to emit light having multiple wavelengths, and the resonator may be configured to receive light emitted by the optical source. The optical system may further include a photodetector to receive the resonant wavelength and measure a power of the resonant wavelength. The optical system may further include a controller coupled to the optical source. The controller may receive the measured first power of the resonant wavelength and change the state of the optical source when the measured power of the resonant wavelength is outside a per-wavelength threshold range.