Apparatuses, methods, and systems for detecting a substance are disclosed. One system includes a light source, an optical cavity, a cavity detector, and a processor. The light source generates a beam of electro-magnetic radiation, wherein a wavelength of the beam of electro-magnetic radiation is tuned to operate at multiple wavelengths. The optical cavity receives the beam of electro-magnetic radiation, wherein the physical characteristics of the cavity define a plurality of allowed axial-plus-transverse electro-magnetic radiation modes, wherein only a subset of the allowed axial-plus-transverse electro-magnetic radiation modes are excited when the optical cavity receives the beam of electro-magnetic radiation. The cavity detector senses electro-magnetic radiation emanating from the optical cavity. The processor operates to receive information relating to the sensed electro-magnetic radiation, and detects the substance within the optical cavity based on amplitude and/or phase of the sensed electro-magnetic radiation emanating from the optical cavity.

A novel narrow linewidth laser device is disclosed that includes a gain element, such as a quantum well, quantum dot or bulk waveguide laser chip and a fiber Bragg grating formed in an optical fiber positioned to receive the output from a first end of the gain element and return a portion of said output back into the gain element. The fiber Bragg grating is constructed so that its power reflectivity profile has a ratio of reflectivity slope over reflectivity at the 3 dB point below the reflectivity peak on the red side (longer wavelength side) of the grating larger than a value of 2/nm. The operating wavelength of the device may be tuned thermally, electrically, or thermo-electrically to be on the red side of the fiber Bragg grating reflectivity profile, preferably, but not necessarily, at the 3 dB point below the reflectivity peak or lower. In another embodiment, a second grating is optically coupled to a second end of the gain element and has a reflectivity profile that overlaps at least a portion of the reflectivity profile of the front end fiber Bragg grating.

A low noise, single mode laser includes a semiconductor gain element generating light and having a highly reflective first end forming a first end of a laser cavity. The gain element may be monolithically or discretely integrated with, or distinct from, and coupled to a waveguide comprised of a low loss material with a refractive index ‘n’ greater than 3. The waveguide includes a Bragg grating forming the second end of the laser cavity. A cavity phase control section may be provided between the gain element and the Bragg grating. Two photodetector monitors provide a feedback signal for locking the light from the gain element to a specific wavelength on the Bragg grating reflection spectrum by varying at least one of the cavity phase control section and the gain element bias current. The Bragg grating may have a physical length larger than 10 mm and that occupies at least 50% of the optical length of the external cavity.

An optical power transmission apparatus includes: a light emitting unit including a first optical gain generating means and a first light reflecting means; an optical fiber; a second light reflecting means; and a light receiving means. Further, the second light reflecting means is arranged nearer to the light receiving means than the optical fiber is, a first laser resonator is formed, between the first light reflecting means and the second light reflecting means, by optical connection between the first optical gain generating means and the optical fiber, and first laser light generated by the first laser resonator is configured to be incident on the light receiving means.

A diagnostic system is provided with a plurality of semiconductor light emitters, each configured to generate an optical beam, and a beam combiner to generate a multiplexed optical beam. An optical fiber or waveguide communicates at least a portion of the multiplexed optical beam to form an output beam, wherein the output beam is pulsed. A filter, coupled to at least one of a lens and a mirror to receive at least a portion of the output beam, forms an output light. A beam splitter splits the light into a sample arm and a reference arm and directs at least a portion of the sample arm light to a sample. A detection system is configured to receive from the sample at least a portion of reflected sample light, to generate a sample detector output, and to use a lock-in technique with the pulsed output beam.

A distributed feedback (DFB) laser outputting a predetermined wavelength of laser light includes a quantum well active layer positioned between a p-type cladding layer and an n-type cladding layer in thickness direction. The DFB laser includes a separate confinement heterostructure layer positioned between the quantum well active layer and then-type cladding layer. The DFB laser includes an electric-field-distribution-control layer positioned between the separate confinement heterostructure layer and then-type cladding layer and configured by at least two semiconductor layers having band gap energy greater than band gap energy of a barrier layer constituting the quantum well active layer. The DFB laser has a function to select a specific wavelength by returning a specific wavelength in the wavelength-variable laser.

A continuous optical beat laser element for generating terahertz (THz) waves and a laser source using same includes periodically poled lithium niobate (ppLN) crystals arranged along a predetermined direction forming a surface generally parallel to the predetermined direction. A Ti diffused region is applied on the surface and an array of gold nanowires are applied on the Ti diffused region to form a gold metal-insulator-metal (MIM) element that optimizes coupling and channeling of THz radiation from the crystals into the gold nanowires. The system provides a simple, stable, compact and cost-effective THz source using a widely tunable C-band SOA-based laser to excite a non-linear photo-mixer to produce terahertz radiation that ranges from 0.8 to 2.51 THz at room temperature. This laser source can be modified into an all fiber-based THz generator by embedding ppLN crystals in a fiber filament configuration resulting in less absorption and producing high output power.

An optical semiconductor device outputting a predetermined wavelength of laser light includes a quantum well active layer positioned between a p-type cladding layer and an n-type cladding layer in thickness direction. The optical semiconductor device includes a separate confinement heterostructure layer positioned between the quantum well active layer and the n-type cladding layer. The optical semiconductor device further includes an electric-field-distribution-control layer positioned between the separate confinement heterostructure layer and the n-type cladding layer and configured by at least two semiconductor layers having band gap energy greater than band gap energy of a barrier layer constituting the quantum well active layer. The optical semiconductor device is applied to a ridge-stripe type laser.

A laser machining device includes a plurality of oscillators to emit laser beams having different wavelengths from each other; a machining head to emit laser beams emitted from the respective oscillators to a machining object; a plurality of transmission fibers to transmit the laser beams to the machining head; a wavelength dispersion element; and a focusing lens to superpose the laser beams emitted from the transmission fibers, wherein the wavelength dispersion element is arranged at a position at which the laser beams are superposed by the focusing lens.

An optical amplifier according to an embodiment includes a pump laser that emits a pumping light beam, and an external resonator that is provided on the outside of the pump laser. In the inside of the external resonator, an optical waveguide that is doped with a rare earth element which absorbs the pumping light beam and that amplifies a signal light beam is disposed, and residual pumping light beams and which are emitted from the optical waveguide are confined.