Laser interferometer
A laser interferometer that includes a light source which emits laser light, an optical divider that divides the laser light into a first optical path and a second optical path, an optical modulator being provided on the first optical path or the second optical path, including an oscillator that oscillates when a current is applied, and modulate the laser light by using the oscillator, a photoreceptor that receives the laser light and output a photoreception signal, the laser light being reflected by an object to be measured that is provided on the first optical path or the second optical path, and a demodulation circuit that demodulates, from the photoreception signal, a Doppler signal derived from the object to be measured, based on a reference signal and a modulation signal derived from the optical modulator.
1 . A laser interferometer, comprising:
a light source configured to emit laser light;
an optical divider configured to divide the laser light into a first optical path and a second optical path;
an optical modulator on the first optical path;
an oscillation circuit configured to output a reference signal and a drive signal wherein
the optical modulator includes an oscillator that oscillates in a case where the drive signal is supplied to the oscillator,
the optical modulator includes a container that accommodates the oscillator and the oscillation circuit,
the optical modulator is configured to modulate the laser light by making the laser light enter the oscillator, and
the oscillator is a signal source of the oscillation circuit;
a photoreceptor configured to receive the laser light and output a photoreception signal, wherein the laser light is reflected by an object to be measured that is provided on the second optical path; and
a demodulation circuit configured to demodulate, from the photoreception signal, a Doppler signal derived from the object to be measured, wherein
the demodulation is based on the reference signal output from the oscillator and a modulation signal derived from the optical modulator,
the reference signal is changed according to an angular frequency of the modulation signal,
the modulation signal is different from the Doppler signal, and
Iq/f≤1×10 −7 is satisfied, where an amplitude value of the current applied to the oscillator that is oscillating is Iq and an oscillation frequency of the oscillator is f.
2 . The laser interferometer according to claim 1 , wherein
the oscillator is a crystal oscillator, and
2×10 −10 ≤Iq/f≤1×10 −7 is satisfied, where the amplitude value of the current applied to the crystal oscillator is Iq and the oscillation frequency of the crystal oscillator is f.
3 . The laser interferometer according to claim 2 , wherein
the oscillation circuit is a circuit including an inverter, a feedback resistor, a limit resistor, a first capacitor, and a second capacitor,
a load capacitance Ct of the oscillation circuit is indicated in Expression (a)
[
Mathematical
Equation
1
]
C
L
=
C
d
C
g
C
d
+
C
g
(
a
)
a capacitance of the first capacitor is C g ,
a capacitance of the second capacitor is C d , and
the load capacitance C L is from 50 pF to 150 pF.
4 . The laser interferometer according to claim 3 , wherein a resistance value of the limit resistor is from 30Ω to 200Ω.
5 . The laser interferometer according to claim 1 , wherein
the oscillator is a Si oscillator, and
4×10 −10 ≤Iq/f≤5×10 −8 is satisfied, where the amplitude value of the current applied to the Si oscillator is Iq and the oscillation frequency of the Si oscillator is f.
6 . The laser interferometer according to claim 5 , wherein
the oscillation circuit is a circuit including an inverter, a feedback resistor, a limit resistor, a first capacitor, and a second capacitor,
a load capacitance C L of the oscillation circuit is indicated in Expression (a)
[
Mathematical
Equation
1
]
C
L
=
C
d
C
g
C
d
+
C
g
(
a
)
a capacitance of the first capacitor is C g ,
a capacitance of the second capacitor is C d , and
the load capacitance C L is from 50 pF to 150 pF.
7 . The laser interferometer according to claim 6 , wherein a resistance value of the limit resistor is from 30Ω to 200Ω.
8 . The laser interferometer according to claim 1 , wherein
the container includes:
a container main body having an opening; and
a lid that closes the opening, and
the oscillator and the oscillation circuit are arranged inside the container main body.
9 . The laser interferometer according to claim 8 , wherein
the container main body includes a first recess that is inside the opening of the container main body, and
the oscillator is arranged on a bottom surface of the first recess.
10 . The laser interferometer according to claim 9 , wherein
the container main body includes a second recess that is on an inner side of the first recess and is deeper than the first recess, and
the oscillation circuit is arranged on a bottom surface of the second recess.
11 . The laser interferometer according to claim 10 , wherein the oscillator and the oscillation circuit are arranged such that the oscillator overlaps the oscillation circuit.