An atomic oscillator includes a gas cell, a semiconductor laser, and a frequency modulation signal generation section (such as a frequency transform circuit) which generates a frequency modulation signal for causing the semiconductor laser to generate frequency-modulated light including a resonance light pair (first-order sideband light pair) that causes an electromagnetically induced transparency phenomenon in metal atoms. When a modulation index of the frequency modulation signal, by which a first-order differential value of oscillation frequency deviation of the atomic oscillator becomes 0, is regarded as a first modulation index, the modulation index is within a range between a second modulation index, which is smaller than the first modulation index, with which the oscillation frequency deviation is 0 and a third modulation index, which is greater than the first modulation index, with which the oscillation frequency deviation is 0.

A stabilized laser source includes a fiber-ring Brillouin laser that incorporates a circulator for non-reciprocal operation and for launching of a pump optical signal. Most of the pump optical signal is launched in a forward direction and drives Brillouin laser oscillation in the backward direction, a portion of which exits via an optical coupler as the optical output of the laser source. A small fraction of the pump optical signal is launched in the backward direction via the optical coupler, and a fraction of that backward-propagating pump optical signal exits via the optical coupler as an optical feedback signal. A frequency-locking mechanism receives the optical feedback signal and controls the pump optical frequency to maintain resonant propagation of the backward-propagating pump optical signal. A second pump optical signal can be launched in the forward direction to generate a second Brillouin laser oscillation.

A quantum interference device includes an atomic cell, a light source, a light detector, a package, and a reflective portion. The atomic cell has alkali metal atoms disposed within, and the light source emits light to excite the alkali metal atoms in the atomic cell. The light detector detects light transmitted through the atomic cell. The package defines an internal space and houses at least the light source. The reflective portion is provided between an inner surface of the package and the light source, and has reflectance to an electromagnetic wave having a wavelength of 4 μm, where the reflectance is greater than or equal to 50%.

A quantum interference device includes an atom cell, a light source emits light to the alkali metal atoms, a photodetector that detects the light transmitted through the atom cell, a thermal conductor, which is disposed so as to straddle the light source side and the photodetector side of the atom cell, and the thermal conductor having higher thermal conductively than the atom cell, and a support, which is disposed so as to be separated from the thermal conductor, and supports the atom cell, the light source, the photodetector, and the thermal conductor in a lump, the support having lower thermal conductivity than the thermal conductor.

A quantum interference device (atomic oscillator) includes a light source unit as a coherent light source, a unit that superimposes microwave on the light source unit to generate a side band, an atom cell in which an alkali metal gas is enclosed, and a light receiving unit that detects light transmitted through the atom cell, wherein the light source unit is a surface-emitting laser that outputs a zero-order mode light and a plurality of higher-order mode lights, and a mode filter that cuts the higher-order mode lights is placed between the light source unit and the atom cell.

A quantum interference device includes a base having a mounting surface, an atom cell in which alkali metal atoms are encapsulated, a light source adapted to emit light adapted to excite the alkali metal atoms, a photodetector adapted to detect the light having been transmitted through the atom cell, and a support adapted to support the atom cell, the light source, and the photodetector in a lump with respect to the mounting surface in a state in which the atom cell, the light source, and the photodetector are arranged in a direction along the mounting surface.

A quantum interference device has an atomic cell which has alkali metal atoms disposed within. A light source emits light to excite the alkali metal atoms in the atomic cell. An optical element is disposed between the light source and the atomic cell, and enlarges the radiation angle of light emitted from the light source. A light detector detects light transmitted through the atomic cell.

An oscillator circuit includes an oscillating circuit coupled to a vibrator, and a control circuit that controls the oscillating circuit. The oscillator circuit has a normal operation mode in which the oscillating circuit oscillates in a state where a negative resistance value is a first value, and a start mode in which the oscillator circuit shifts from a state where oscillation is stopped to the normal operation mode. In the start mode, the control circuit controls the negative resistance value to increase from a second value which is smaller than the first value.

An oscillator circuit includes an oscillating circuit coupled to a vibrator, and a control circuit that controls the oscillating circuit. The oscillator circuit has a normal operation mode in which the oscillating circuit oscillates in a state where a negative resistance value is a first value, and a start mode in which the oscillator circuit shifts from a state where oscillation is stopped to the normal operation mode. In the start mode, the control circuit controls the negative resistance value to increase from a second value which is smaller than the first value.

In some embodiments, a molecular clock includes a waveguide gas cell containing gas molecules having a rotational spectral line with a first frequency a voltage-controlled oscillator (VCO) to generate a clock signal, a transmitter referenced to the clock signal to generate a probing signal for transmission through the waveguide gas cell, and a receiver to receive the probing signal transmitted through the waveguide gas cell and interacting with gas molecules. The receiver can include a filter circuit configured to filter out even harmonic components from the received signal and can further include a lock-in detector to generate an error signal indicating an offset between the first frequency and the second frequency. The error signal is fed back to control generation of the VCO clock signal.