In one embodiment of the invention, a semiconductor optical amplifier (SOA) in a laser ring is chosen to provide low polarization-dependent gain (PDG) and a booster semiconductor optical amplifier, outside of the ring, is chosen to provide high polarization-dependent gain. The use of a semiconductor optical amplifier with low polarization-dependent gain nearly eliminates variations in the polarization state of the light at the output of the laser, but does not eliminate the intra-sweep variations in the polarization state at the output of the laser, which can degrade the performance of the SS-OCT system.

Integrated wavelength selectors are described. The wavelength selector may include silicon nitride ring resonator disposed vertically between a heater and a temperature sensor. The temperature sensor may be formed of silicon in some embodiments. The wavelength selector may be coupled to the output port of a tunable laser, or may be disposed within a laser cavity.

A gain medium is pumped by a source. An optical wave passes through a photonic integrated circuit (PIC) that comprises: a substrate comprising Silicon, a plurality of photonic structures, an input port coupling an optical wave into a waveguide formed in the PIC, and an output port coupling an optical wave out of a waveguide formed in the PIC. Propagation of an optical wave circulating around a closed path of a laser ring cavity is limited using an optical isolator such that, when the pump source exceeds a lasing threshold, the optical wave propagates in a single direction through the gain medium and the PIC. From output coupler, an output that is provided that comprises a fraction of the power of an optical wave that is incident upon the output coupler, and remaining power of the optical wave is redirected around the closed path of the laser ring cavity. The fraction can be greater than 0.5.

A laser light source includes an inner ring and an outer ring. The inner ring includes a semiconductor optical amplifier (SOA), a pair of optical circulators, a first optical filter, and a first optical waveguide connecting those in series. The outer ring includes the SOA, a pair of optical circulators, a second optical filter, an output port, and a second optical waveguide connecting those in series except for a portion shared. The inner ring operates as a gain-clamped SOA with a feedback control light defined by the first optical filter. The outer ring generates a laser output in a gain region of the clamped SOA, and with multiple peak wavelengths defined by the second optical filter, in a range from L Band to U band, applicable to WDM network systems. A WDM network system and a method of controlling the laser light source are also disclosed.

An apparatus includes an optical splitter configured to receive an optical signal and to split the input optical signal to provide a first and a second optical signal. The apparatus further includes an interferometer comprising a first arm and a second arm, with the first arm being configured to receive the first optical signal, and the second arm being configured to receive the second optical signal. Notably a portion of the first arm is exposed to a reference gas that attenuates light of a characteristic wavelength. The apparatus further includes an optical coupler configured to receive an output optical signal from the first arm, and an output optical signal from the second arm and to provide a third optical signal; and a photodetector configured to receive the third optical signal, and to provide a photocurrent. The photocurrent increases when the difference between the characteristic wavelength and the wavelength of the optical signals increases. The apparatus also comprises a feedback control circuit configured to change the properties of the laser to be locked until an error signal indicative of the difference between the characteristic wavelength and the wavelength of the laser is substantially zero.

A passively, Q-switched laser operating at an eye safe wavelength of between 1.2 and 1.4 microns is described. The laser may operate at a lasing wavelength of 1.34 microns and use a gain element of Nd:YVO.sub.4 and a saturable absorber element of V:YAG. The systems and methods to produce short pulses having a pulse duration less than 1 ns and high energy pulses having pulse energies greater than 2 μJ are described.

Systems and methods here may include improved tunable lasers having a tunable filter and a tunable channel selector that can control precisely the wavelength and the bandwidth of the light emitted by the laser, while suppressing light that may otherwise be emitted by the laser outside the desired wavelength and bandwidth with unidirectional ring lasers having a resonator of which forms a ring and where light propagates only in one of the two possible directions.

A Lidar system includes a tunable laser configured to generate an output light signal and a photodiode array for receiving light from the tunable laser reflected from a target object. The tunable laser includes a feedback loop including a Mach-Zender interferometer, MZI, receiving the output light signal from the tunable laser, in which the MZI includes two optical paths receiving the output light signal. A phase shifter is provided in one optical path that is operable to produce a pre-determined shift in the phase angle of the light signal passing through the one optical path relative to the phase angle of the light signal passing through the other optical path. A photodiode configured to detect the interference signal generated by the MZI is operable to generate a photodiode current in response thereto. Circuitry converts the photodiode current to a control signal for controlling the tunable laser.

A measurement device includes: an optical gain unit for generating and amplifying light; a transmission optical band variation unit for selecting a specific optical frequency band from the light generated by the optical gain unit, and varying the selected specific optical frequency band to transmit light; a resonant optical frequency variation unit for performing a frequency variation so that multiple resonant optical frequency orders within the specific optical frequency band vary over a variation range narrower than intervals between the respective orders; resonance induction units forming an optical resonance unit which includes the optical gain unit, the transmission optical band variation unit, and the resonant optical frequency variation unit and causes selective oscillation of light having a specific resonant optical frequency within a specific transmission optical band; and a control signal unit for varying each of the transmission optical band variation unit and the resonant optical frequency variation unit.

An apparatus includes a wavelength-tunable laser and an electronic controller. The electronic controller is configured to control the wavelength-tunable laser such that an output wavelength of the wavelength-tunable laser performs a zigzag in time. The wavelength-tunable laser is capable of rapidly and densely scanning wavelengths across a broad spectral range.