External cavity laser systems are described that can operate with essentially no mode hopping. One example configuration of the laser system includes a semiconductor laser device, a folded cavity external to the semiconductor laser device, where at the semiconductor laser device is positioned at a fold in the folded cavity. In this configuration, at least one mirror is positioned in the folded cavity to enable sustained propagation of light within the folded cavity, and at least two polarization elements are positioned in the folded external cavity. The polarization elements cause a polarization state of the light that impinges in different directions on each semiconductor laser device that is positioned at a fold to be orthogonal to one another, thus eliminating or substantially reducing mode hopping in the laser output.

Multi-stage fiber amplifiers can amplify signals from a few Watts to several kilowatts. These amplifiers are limited in power by intensity instabilities resulting from a sequence of nonlinear optical effects. These nonlinear optical effects include stimulated Brillouin scattering (SBS), with produces a high-intensity pulse close to the signal wavelength that propagates backward up the amplifier chain, causing permanent damage to the upstream components. This SBS pulse can be blocked by an optical isolator that blocks backward-propagating light at or near the signal wavelength. At high enough power levels, the SBS pulse can also induce backward-propagating light at wavelengths tens to hundreds of nanometers away from the signal wavelength. This SBS-Pulse Induced Non-linear Spectrum light is outside the isolator's reject band, so it can propagate upstream and de-stabilize the upstream amplifier stages. It can be suppressed using a filter with a broad reject band and a suppression ratio of 30 dB, enabling higher power operation.

A laser light source unit for vehicles is provided, having a resonator containing a first end mirror and a second end mirror. Between the two, an active laser medium is arranged. The laser light source unit further has a pump device for generating a pump radiation which can be introduced via the first end mirror into the resonator. The pump radiation corresponds to a first wavelength and the active laser medium is configured such that laser light of the first wavelength and/or of a second wavelength and/or of a third wavelength can be radiated. An intermediate mirror and a third end mirror assigned to the same are provided. The intermediate mirror is configured in such a way that the radiation of the second wavelength is reflected, and the radiation of the third wavelength is transmitted, by means of said intermediate mirror. The third end mirror is configured in such a way that the radiation of the second wavelength is reflected, a color control module is provided, which acts on the radiation of the second wavelength and/or the radiation of the third wavelength in such a way that an intensity of the stimulated emission of the radiation of the second wavelength is adjusted to the radiation of the third wavelength, or vice versa.

An external-cavity semiconductor laser includes a semiconductor laser element containing a gallium nitride material, a first lens disposed in an optical path of light emitted from the semiconductor laser element, a wavelength selective element disposed in an optical path of light transmitted through the first lens and configured to selectively transmit light having a predetermined wavelength, a second lens disposed in an optical path of light transmitted through the wavelength selective element, an output coupler disposed in an optical path of light condensed through the second lens, and a light-transmissive protective member bonded to at least one surface of the output coupler. The second lens is configured to cause light transmitted through the second lens and incident on the output coupler to form an image on a surface of the output coupler. The protective member covers the surface of the output coupler on which the image is formed.

A laser for high power applications. The laser is a lamp driven slab design with a face to face beam propagation scheme and an end reflection that redirects the amplified radiation back out the same input surface. Also presented is a side to side larger amplifier configuration, permitting very high average and peak powers due to the electrical efficiency of absorbing energy into the crystal, optical extraction efficiency, and scalability of device architecture. Cavity filters adjacent to pump lamps convert the unusable UV portion of the pump lamp spectrum into light in the absorption band of the slab laser thereby increasing the overall pump efficiency. The angle of the end reflecting surface is changed to cause the exit beam to be at a different angle than the inlet beam, thereby eliminating the costly need to separate the beams external to the laser with the subsequent loss of power.

A narrow-linewidth tunable external cavity laser includes, sequentially arranged along an optical path, a laser gain chip, a collimating lens, a bandpass filter, a tunable filter, and an output cavity surface. The laser gain chip includes a first end surface and a second end surface positioned along the optical path. The first end surface is further away from the collimating lens and is coated with a highly reflective film to form an external cavity with the output cavity surface.

The invention relates to a MOPA laser system having at least one laser oscillator (MO), which generates laser radiation at an emission wavelength (.sub.0), and having an optical amplifier (PA) downstream the laser oscillator (MO) in the propagation direction of the laser radiation, which optical amplifier amplifies the laser radiation and thereby spectrally broadens it to a useful bandwidth (). It is an object of the invention to provide an improved MOPA laser system which is designed for a high power of the amplified laser radiation and which is insensitive to back-reflection. Unavoidable back-reflections should neither affect the output power of the optical amplifier (PA), nor lead to the destruction of the laser oscillator (MO) or other components of the system. This object is achieved by the invention in that an optical bandpass filter (BPF) is arranged between laser oscillator (MO) and amplifier (PA), which optical bandpass filter is transparent to laser radiation at the emission wavelength (.sub.0), wherein those spectral components of the returning, that is, counter to the propagation direction, laser radiation impinging on the bandpass filter (BPF), which, in terms of wavelength, lie outside the passband (4), are reflected at the bandpass filter (BPF) in the propagation direction.

A measurement system for performing measurement by Brillouin scattering analysis, the system comprising a laser emitter device (10) configured to emit an incident wave (0) and a reference wave (0B), the incident wave presenting an incident frequency (0) and the reference wave presenting a reference frequency (0B), the reference frequency (0B) being shifted from the incident frequency (0) by a predetermined value (B). The system is configured to: project the incident wave (0) into the optical fiber (25); receive in return a backscattered wave (0S); generate a composite wave (0-S, 0-B) combining the backscattered wave (0S) and the reference wave (S0B); and determine at least one property relating to the fiber by analyzing a Brillouin spectrum of the composite wave (0-S, 0-B). Advantageously, the incident wave and the reference wave come from a dual-frequency vertical-cavity surface-emitting laser source (12) forming part of the laser emitter device.

A multi-wavelength single-frequency optical fiber laser source for a laser radar system includes a resonant cavity composed of a high-reflectivity chirped optical fiber grating, a high gain optical fiber and a low-reflectivity chirped optical fiber grating, a single-mode semiconductor pump laser served as a pump light source, an optical wavelength division multiplexer, an optical coupler, an optical isolator, an optical circulator, an optical filter module, and a semiconductor optical amplifier. The pump light source performs optical fiber core pumping with respect to the high gain optical fiber. A portion of the wide-spectrum laser is filtered by the optical filter module to obtain a wavelength corresponding to a specific central frequency. Multi-wavelength laser lasing with a narrow linewidth and single longitudinal mode is implemented by combining a short linear resonant cavity structure and the optical filter module.

An optical system can lock a wavelength of a tunable laser to a specified wavelength of a temperature-insensitive spectral profile of a spectral filter. In some examples, the spectral filter, such as a Fabry-Perot filter, can have a temperature-insensitive peak wavelength and increasing attenuation at wavelengths away from the peak wavelength. The spectral filter can spectrally filter the laser light to form filtered laser light. A detector can detect at least a fraction of the filtered laser light. Circuitry coupled to the detector and the laser can tune the tunable laser to set a signal from the detector to a specified value corresponding to a specified wavelength in the spectral profile, and thereby adjust the selectable wavelength of the tunable laser to match the specified wavelength. In some examples, the optical system can include a polarization rotator, and can use polarization to separate incident light from return light.