A tunable solid state laser device are described comprising a semiconductor based gain chip and a silicon photonic filter chip with tuning capability. The silicon photonic filter chip can comprises an input-output silicon waveguide, at least two ring resonators formed with silicon waveguides, one or more connecting silicon waveguides interfacing with the ring resonators, a separate heater associated with each ring resonator, a temperature sensor configured to measure the chip temperature, and a controller connected to the temperature sensor and the separate heaters and programmed with a feedback loop to maintain the filter temperature to provide the tuned frequency. The one or more connecting silicon waveguides are configured to redirect light resonant with each of the at least two ring resonators back through the input-output silicon waveguide. Corresponding methods are described for the control of the laser frequency. Improved structures of the SiPho multiple filter chip involve a Zagnac interferometer.

A tunable solid state laser device are described comprising a semiconductor based gain chip and a silicon photonic filter chip with tuning capability. The silicon photonic filter chip can comprises an input-output silicon waveguide, at least two ring resonators formed with silicon waveguides, one or more connecting silicon waveguides interfacing with the ring resonators, a separate heater associated with each ring resonator, a temperature sensor configured to measure the chip temperature, and a controller connected to the temperature sensor and the separate heaters and programmed with a feedback loop to maintain the filter temperature to provide the tuned frequency. The one or more connecting silicon waveguides are configured to redirect light resonant with each of the at least two ring resonators back through the input-output silicon waveguide. Corresponding methods are described for the control of the laser frequency. Improved structures of the SiPho multiple filter chip involve a Zagnac interferometer.

A sensor degradation evaluation method according to an aspect of the present disclosure includes an evaluation step of evaluating degradation of at least one of a sensor for coarse measurement that receives interference fringes produced by a spectrometer for coarse measurement and a sensor for fine measurement that receives interference fringes produced by a spectrometer for fine measurement, and the evaluation step includes causing a plurality of kinds of laser light having wavelengths different from one another to be sequentially incident on the spectrometer for coarse measurement and the spectrometer for fine measurement and acquiring a coarse-measurement wavelength and a fine-measurement wavelength on a wavelength basis from a plurality of the received interference fringes, acquiring a degradation parameter on a wavelength basis from the coarse-measurement wavelength and the fine-measurement wavelength on a wavelength basis, and comparing the degradation parameter on a wavelength basis with a threshold.

A gain medium is pumped by a source. An optical wave passes through a photonic integrated circuit (PIC) that comprises: a substrate comprising silicon, multiple 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 PIC. From an output coupler, an output is provided that comprises a fraction (e.g., >0.5) 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.

A gain medium is pumped by a source. An optical wave passes through a photonic integrated circuit (PIC) that comprises: a substrate comprising silicon, multiple 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 PIC. From an output coupler, an output is provided that comprises a fraction (e.g., >0.5) 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.

In a tunable transmission-grating laser, alignment of the lasing cavity mode with the grating filter spectrum of the laser can be achieved using the position of the intracavity beam relative to the gain medium as feedback. In various embodiments, the displacements of the intracavity beam from the gain medium are monitored indirectly, using an image of the intracavity beam created outside the cavity with an additional transmission grating. Various means for measuring the position of that monitoring beam and for adjusting the tunable components of the laser based thereon are described.

In a tunable transmission-grating laser, alignment of the lasing cavity mode with the grating filter spectrum of the laser can be achieved using the position of the intracavity beam relative to the gain medium as feedback. In various embodiments, the displacements of the intracavity beam from the gain medium are monitored indirectly, using an image of the intracavity beam created outside the cavity with an additional transmission grating. Various means for measuring the position of that monitoring beam and for adjusting the tunable components of the laser based thereon are described.

A line narrowing module includes a prism including an entrance side surface that light enters, an exit side surface from which the light is emitted, and a bottom surface, and configured to wavelength-disperse the light having entered the entrance side surface and to emit the light from the exit side surface; a holder portion having a stationary surface on which the bottom surface of the prism is secured; a rotary mechanism portion including a rotary stage on which the holder portion is secured, the rotary stage being configured to rotate the prism around an axis perpendicular to a dispersion plane of the light emitted from the prism; a drive unit configured to rotate the rotary stage; and a grating configured to reflect the light emitted from the prism, centroids of the prism, the holder portion, and the rotary stage being located on the axis.

A line narrowing module includes a prism including an entrance side surface that light enters, an exit side surface from which the light is emitted, and a bottom surface, and configured to wavelength-disperse the light having entered the entrance side surface and to emit the light from the exit side surface; a holder portion having a stationary surface on which the bottom surface of the prism is secured; a rotary mechanism portion including a rotary stage on which the holder portion is secured, the rotary stage being configured to rotate the prism around an axis perpendicular to a dispersion plane of the light emitted from the prism; a drive unit configured to rotate the rotary stage; and a grating configured to reflect the light emitted from the prism, centroids of the prism, the holder portion, and the rotary stage being located on the axis.

An optical system can lock a wavelength of a tunable laser to a specified wavelength of a temperature-insensitive spectral profile of a spectral filter. In some examples, the spectral filter, such as a Fabry-Perot filter, can have a temperature-insensitive peak wavelength and increasing attenuation at wavelengths away from the peak wavelength. The spectral filter can spectrally filter the laser light to form filtered laser light. A detector can detect at least a fraction of the filtered laser light. Circuitry coupled to the detector and the laser can tune the tunable laser to set a signal from the detector to a specified value corresponding to a specified wavelength in the spectral profile, and thereby adjust the selectable wavelength of the tunable laser to match the specified wavelength. In some examples, the optical system can include a polarization rotator, and can use polarization to separate incident light from return light.