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 device may include a first waveguide with an optical input at a first port. A device may include a second waveguide. A device may include a first coupler that optically couples the first waveguide to the second waveguide at a first position. A device may include a waveguide delay arm. A device may include a second coupler that optically couples the first waveguide to the second waveguide at a second position, the second position different from the first position.

A birefringent Mach-Zehnder interferometer (MZI) is provided for optically sensing a small fluctuation from an un-polarized light beam. The birefringent MZI includes first and second birefringent crystals arranged coaxially, the first crystal to receive the beam; and first and second 45 polarizers positioned behind respective the first and second crystals. The first crystal divides the beam into first ordinary and extraordinary rays. The first polarizer converts the first rays into first 45 rays. The second crystal divides the first 45 rays into second ordinary, extraordinary and recombination rays. The second polarizer converts the second rays into second 45 rays.

According to an aspect there is provided an optical monitoring device comprising: a first input for receiving a portion of a first optical signal coupled from a first waveguide into the first input; a second input for receiving at least a portion of a second optical signal coupled into the second input; a mixing unit for controlling combining of the portion of the first optical signal with the at least a portion of the second optical signal into a combined signal at an output from the mixing unit; and at least one photodetector for detecting the combined signal.

The optical monitoring device is configured to apply a modulation signal to modulate at least one of a phase of the portion of the first and/or second optical signal, a coupling of the portion of the first and/or second optical signal into the respective input, or an amplitude of the portion of the first and/or second optical signal being transferred into the combined signal.

An optical sensor module includes an interferometric sensor and a set of one or more optical elements. The interferometric sensor includes a coherent light source and at least one detector configured to generate an interferometric signal. The set of one or more optical elements is configured to simultaneously direct a first portion of light emitted by the coherent light source toward a first focus area within a first depth of focus; direct a second portion of the light emitted by the coherent light source toward a second focus area within a second depth of focus; and direct portions of the emitted light that are returned from one or more objects within the first depth of focus or the second depth of focus toward the interferometric sensor.

Provided is an optical pulse-generator and an optical pulse-generating method which are capable of generating an optical pulse train with an arbitrary pattern. An optical pulse-generator 1 includes a first optical modulator 21 configured to modulate input light using a first modulation signal SIG1 to generate optical pulses, a second optical modulator 41 configured to perform a modulation operation using a second modulation signal SIG2 synchronizing with the first modulation signal SIG1 and having a signal pattern that is set to output only specific part of the optical pulses, and a dispersion compensator 30 configured to compensate a chirp of the optical pulse output from the first optical modulator 21.

A Mach-Zehnder interferometer (MZI) structure based on a doubly-corrugated spoofed surface plasmon polariton (DC-SSPP) waveguide is presented. The dependence of phase change on the dielectric loading of the DC-SSPP structure causes the output from both arms to interfere and enhance features on the transmission spectrum of the MZI. The proposed MZI structure can be used for tag-free bio-molecular sensing. The highly localized electro-magnetic field at frequencies close to SSPP resonance is shown to reduce the sample amount needed to produce interference patterns without affecting the selectivity of the sensing structure.

A tri-mask optical polarization diversity receiver with a single input terminal and three output terminals prevents polarization induced signal fade, and may be used in an optical interferometry system for coherent detection. The device is composed of optical collimators, non-polarizing beam splitters, linear polarizers and photodetectors. In addition, the structural design incorporates two mechanically identical modulets, as well as a beam displacement compensation mechanism for ease of alignment and assembly. Compared to fiber-based design, the free-space configuration gets rid of inevitable birefringence in fused fiber couplers which detrimentally alter the polarization state received by the polarizers. As a result, it facilitates effective and precise measurements of optical interference with optimized visibility.

Disclosed is an illumination arrangement for providing at least one radiation beam for use as an illumination beam and/or reference beam in a metrology device. The illumination arrangement comprises at least one radiation beam modifier module operable to receive source illumination and output a modified radiation beam comprising a first beam component and a second beam component. Each radiation beam modifier module comprises at least one path length varying arrangement for controllably varying the optical path length of at least one of said first beam component and said second beam component, such that said first beam component and second beam component of said modified radiation beam comprise a respective different optical path length.

A laser source may include a laser diode, a modulation device, and a feedback device. The modulation device may include an electric power source and may be suitable for modifying a current intensity applied to the laser diode, which may modify an emission frequency of the laser diode. The feedback device may be suitable for modifying a current intensity applied to the laser diode by the electric power source as a function of the electromagnetic radiation emitted by the laser diode.