A wavelength monitor includes: a wavelength tunable laser (1) having a plurality of emitting ports (10, 11), from which laser beams of the same wavelength are emitted; collimating lenses (20, 21) , which are configured to collimate the laser beams emitted from the emitting ports (10, 11) to emit the collimated laser beams; an optical filter (4) having a periodic transmittance with respect to a frequency, on which the laser beams emitted from the collimating lenses (20, 21) are incident; and an optical detector (5) configured to receive the laser beams that have passed through the optical filter (4) to detect light intensities of the laser beams. In the wavelength monitor, the collimating lenses (20, 21) and the optical filter (4) are disposed so that the laser beams are incident on the optical filter (4) while a condition expressed as Equation (1) is satisfied.

A wavelength monitor includes: a wavelength tunable laser (1) having a plurality of emitting ports (10, 11), from which laser beams of the same wavelength are emitted; collimating lenses (20, 21), which are configured to collimate the laser beams emitted from the emitting ports (10, 11) to emit the collimated laser beams; an optical filter (4) having a periodic transmittance with respect to a frequency, on which the laser beams emitted from the collimating lenses (20, 21) are incident; and an optical detector (5) configured to receive the laser beams that have passed through the optical filter (4) to detect light intensities of the laser beams. In the wavelength monitor, the collimating lenses (20, 21) and the optical filter (4) are disposed so that the laser beams are incident on the optical filter (4) while a condition expressed as Equation (1) is satisfied.

There is described an interferometer for use in an optical locker. The interferometer comprises at least two transparent materials having different thermal path length sensitivities. The interferometer is configured such that an input beam is split by the interferometer into first and second intermediate beams, which recombine to form an output beam, the first and second intermediate beams travelling along respective first and second intermediate beam paths which do not overlap. At least one of the intermediate beam paths passes through at least two of the transparent materials. A length of each intermediate beam path which passes through each transparent material is selected such that an optical path difference between the first and second intermediate beam path is substantially independent of temperature.

A tunable laser system includes a tunable laser to be scanned over a range of frequencies and an interferometer having a plurality of interferometer outputs. At least two interferometer outputs of the plurality of interferometer outputs have a phase difference. A wavelength reference has a spectral feature within the range of frequencies, and the spectral feature does not change in an expected operating environment of the tunable laser. Processing circuitry uses the spectral feature and the plurality of interferometer outputs to produce an absolute measurement of a wavelength of the tunable laser and controls the tunable laser based on a comparison of the absolute measurement of the wavelength of the tunable laser with a setpoint wavelength.

A wavefront sensor measures the phase distribution of a beam of light perpendicular to its axis of propagation. The Shack-Hartmann (S-H) wavefront sensor is based on segmentation of the incident light beam into small, spatially distributed, parts. Each of these parts is then incident on a lens, and the deviation of the focal spot from the lens optical axis is measured in two dimensions, usually by a camera or detector array. An array of lenses is used to characterize the wavefront of the entire beam.

Conventionally, wavelength locking and monitoring has been achieved used various components, including calibrated etalon filters, gratings, and arrays of color filters, which offer fairly bulky solutions that require complicated controls. An improved on-chip wavelength monitor comprises: a combination comb filter comprising a plurality of comb filters, each for receiving a test beams, and each comb filter including a substantially different FSR, e.g. 10 to 20 the next closest FSR. A controller dithers a phase tuning section of each comb filter to generate a maximum or minimum output in a corresponding photodetector indicative of the wavelength of the test signal.

A three-dimensional interferometer for measuring a light field produced by an object, comprising a first interferometer arm, a second interferometer arm, a beam splitter arranged between an object point of the object and the first interferometer arm and the second interferometer arm, and is set up to split a beam coming from the object point at the beam splitter into the first beam and the second beam, a detection plane or a detection surface which is arranged downstream of the first interferometer arm and the second interferometer arm and is set up in such a manner that the first beam and the second beam are made to interfere in an interference region on said plane or surface, and an overlapping device which is arranged between the detection plane and the first interferometer arm and the second interferometer arm.

There is described an interferometer for use in an optical locker. The interferometer comprises at least two transparent materials having different thermal path length sensitivities. The interferometer is configured such that an input beam is split by the interferometer into first and second intermediate beams, which recombine to form an output beam, the first and second intermediate beams travelling along respective first and second intermediate beam paths which do not overlap. At least one of the intermediate beam paths passes through at least two of the transparent materials. A length of each intermediate beam path which passes through each transparent material is selected such that an optical path difference between the first and second intermediate beam path is substantially independent of temperature.

An apparatus includes a photonic integrated circuit (PIC) to measure an optical wavelength of a light source. The PIC includes an optical splitter, a plurality of tunable interferometers and one or more detectors. The optical splitter is coupled to the light source, and the interferometers are coupled to the optical splitter. Each interferometer receives a portion of an optical signal of the light source. One or more detectors are coupled to each interferometer, and the interferometers have different free spectral ranges (FSRs). A largest FSR value of the different FSRs is greater than an entire intended wavelength measurement range of the PIC.

A method for determining spectral calibration data (.sub.cal(S.sub.d), S.sub.d,cal()) of a Fabry-Perot interferometer (100) comprises: forming a spectral notch (NC2) by filtering input light (LB1) with a notch filter (60) such that the spectral notch (NC2) corresponds to a transmittance notch (NC1) of the notch filter (60), measuring a spectral intensity distribution (M(S.sub.d)) of the spectral notch (NC2) by varying the mirror gap (d.sub.FP) of the Fabry-Perot interferometer (100), and by providing a control signal (S.sub.d) indicative of the mirror gap (d.sub.FP), and determining the spectral calibration data (.sub.cal(S.sub.d), S.sub.d,cal()) by matching the measured spectral intensity distribution (M(S.sub.d)) with the spectral transmittance (T.sub.N()) of the notch filter (60).