A device includes a first excitation light source that emits first excitation light, a second excitation light source that emits second excitation light, a wavelength converter that converts signal light of a first wavelength into signal light of a second wavelength according to the first excitation light, and a measurer that measures a frequency difference between the first excitation light and the second excitation light, wherein when an abnormality of the first excitation light is detected, the second excitation light source is adjusted so that a frequency of the second excitation light is aligned with a frequency of the first excitation light before the abnormality detection, based on the frequency difference before the abnormality detection, and the wavelength converter converts the signal light of the first wavelength into the signal light of the second wavelength according to the second excitation light, after adjusting the frequency of the second excitation light.

Operating an optical frequency comb assembly includes operating an optical frequency comb source to generate laser light constituting an optical frequency comb and introducing the laser light into a common light path and seeding at least one branch light path by the laser light from the common light path, the branch light path comprising at least one optical element. For the branch light path, a phase difference of a first frequency mode ν.sub.1 of the optical frequency comb is determined between laser light coupled out at a reference point within the frequency comb assembly upstream of the at least one optical element and laser light coupled out at a measurement point provided in the branch light path downstream of the at least one optical element. Phase correction for the laser light from the branch light path is based on a deviation of the determined phase difference from a target value.

Methods and apparatuses for determining the polarization state and for providing polarization control in optical fiber lasers and amplifiers. One embodiment of the invention is an optical fiber amplifying system including a circulator (260) having a first optical port (260a), a second optical port (260b) that is configured to output radiation received from the first optical port, and a third optical port (260c) that is configured to output radiation received from the second optical port; one or more amplifier stages (216) connected in series, together having an optical input (216a) optically coupled to the second port of the circulator, and an optical output (216b); and a polarization detector (240) having an optical input optically coupled to the third port of the circulator. Thereby the polarization state of the amplified radiation can be determined using radiation backscattered from the amplifying stage.

The present disclosure relates to a technical field of optical communication, and provides a method and an apparatus for determining maximum gain of Raman fiber amplifier. Wherein the method includes obtaining transmission performance parameters of a current optical fiber transmission line; respectively obtaining impact factors A.sub.1, A.sub.2, A.sub.4 according to a distance between a joint and a pump source, a fiber loss coefficient, and a fiber length included in the transmission performance parameters; calculating a joint loss value Att.sub.Aeff according to a distance between a joint and a pump source, a fiber loss coefficient, and looking up impact factor A.sub.3 according to Att.sub.Aeff; determining an actual maximum gain which may actually be achieved by the Raman fiber amplifier according to A.sub.1, A.sub.2, A.sub.3, A.sub.4. The actual maximum gain obtained in the present disclosure is the maximum gain that may be achieved over all input power ranges, and the original signal in system is kept to operate at a fixed gain, such that a gain locking effect is realized, and fluctuation of existing transmission signal power caused by signal change in transmission fiber link is avoided.

There is provided a laser system that may include a Raman cell, a pumping light generator, and a Raman cell laser unit. The pumping light generator may include one or more optical parametric amplifiers (OPAs), and may be configured to output first Raman-cell pumping light and second Raman-cell pumping light to the Raman cell. The Raman cell laser unit may be configured to output probing light as a target of wavelength conversion to the Raman cell.

Example fiber amplifiers and gain adjustment methods for the fiber amplifiers are described. One example fiber amplifier includes a first power amplifier, a wavelength level adjuster, and a controller, where the first power amplifier is connected to the wavelength level adjuster. The controller includes a first input end and a control output end. The first input end is configured to receive an input optical signal, and the control output end is configured to output a first amplification control signal to the first power amplifier, and output an adjustment control signal to the wavelength level adjuster. The wavelength level adjuster is configured to perform power adjustment on each wavelength in a separate manner based on the adjustment control signal.

A laser processing method of performing laser processing on a transparent material that is transparent to ultraviolet light by using a laser processing system includes: performing relative positioning of a transfer position of a transfer image and the transparent material in an optical axis direction of a pulse laser beam so that the transfer position is set at a position inside the transparent material at a predetermined depth ΔZsf from a surface of the transparent material in the optical axis direction; and irradiating the transparent material with the pulse laser beam having a pulse width of 1 ns to 100 ns inclusive and a beam diameter of 10 μm to 150 μm inclusive at the transfer position.

Multi-Channels coherent beam combining (CBC) using a mechanism for phase and/or polarization locking that uses a reference optical beam and an array of optical detectors each detector being configured and located to detect overall intensity of an optical interference signal caused by interfering of the reference beam and a beam of the respective channel, where the fast intensity per-channel detection allows simultaneous and quick phase/polarization locking of all channels for improving beam combining system performances.

Provided are a method and system for controlling a Raman fiber amplifier. The method comprises: according to a target gain and a tilt, calculating an expected output power of a pump by using a feedforward formula, and obtaining an actual output power of the pump through detection (201); locking the actual output power of the pump to the expected output power through first-stage feedback control (202); according to the target gain and the tilt, calculating an expected ASE power of the pump by using an ASE formula, and obtaining an actual out-of-band ASE power of the pump through detection (203); if the out-of-band ASE is not locked, determining gain compensation and tilt compensation of the pump through second-stage feedback control, and feeding the compensation back to the feedforward formula and the ASE formula for recalculation (204); and repeatedly performing the first-stage feedback control and the second-stage feedback control until the gain and the tilt are locked (205). In the system, a combination of feedforward and multi-closed loop feedback control is used to realize rapid locking of a pump power and locking of the gain and the tilt compensation, which improves the control precision of the gain and the tilt and accelerates a response speed.

An optical system element includes a first enclosure designed for receiving in circulation a functional fluid and at least one inlet and/or outlet window located on the first enclosure and through which a light beam can pass. The inlet and/or outlet window includes two viewports which delimit a spacer cavity adjacent to the first enclosure. The spacer cavity is designed to receive a second fluid with a predetermined optical index and is equipped with a device for adjusting the pressure therein. Degradation of a beam during its passage through the inlet and/or outlet window can be limited by careful selection of the optical index of the second fluid and the pressure in the spacer cavity.