Optical phase shifter and demodulator

1. A optical phase shifter comprising:

a thermo-optical element where a refractive index of the thermo-optical element with respect to an input optical signal is temperature dependent;

a temperature change section contacting one end of the thermo-optical element, and a temperature of the temperature change section changes a temperature of the thermo-optical element to a desired temperature;

a heat dissipation section disposed on an opposite side of the thermo-optical element than the temperature change section and which enters a state of thermal equilibrium at a different temperature than the temperature of the temperature change section; and

a temperature buffer section disposed between and contacting the temperature change section and the heat dissipation section where the temperature buffer section has a heat resistance greater than the heat dissipation section,

wherein the thermo-optical element is surrounded by an ambient gas, and

wherein a product R 1 ×S×h of a heat resistance R 1 of the thermo-optical element, an area S of a surface of the thermo-optical element surrounded by the ambient gas, and a heat transfer ratio h of the ambient gas is less than a desired refractive index distribution ratio δ of the thermo-optical element.

2. The optical phase shifter according to claim 1 , wherein the ambient gas is a gas which contains nitrogen as a main component.

3. An optical phase shifter comprising:

a thermo-optical element where a refractive index of the thermo-optical element with respect to an input optical signal is temperature dependent;

a temperature change section contacting one end of the thermo-optical element, and a temperature of the temperature change section changes a temperature of the thermo-optical element to a desired temperature;

a heat dissipation section disposed on an opposite side of the thermo-optical element than the temperature change section and which enters a state of thermal equilibrium at a different temperature than the temperature of the temperature change section; and

a temperature buffer section disposed between and contacting the temperature change section and the heat dissipation section where the temperature buffer section has a heat resistance greater than the heat dissipation section,

wherein the thermo-optical element is surrounded by a vacuum, and

wherein a product R 1 ×S×T o 3 of a heat resistance R 1 of the thermo-optical element, an area S of a surface of the thermo-optical element surrounded by the vacuum, and a cubed absolute temperature T o of the thermo-optical element is less than a product 4000000×δ of a desired refractive index distribution ratio δ of the thermo-optical element and a constant 4000000.

4. An optical phase shifter comprising:

a thermo-optical element where a refractive index of the thermo-optical element with respect to an input optical signal is temperature dependent;

a temperature change section contacting one end of the thermo-optical element, and a temperature of the temperature change section changes a temperature of the thermo-optical element to a desired temperature;

a heat dissipation section disposed on an opposite side of the thermo-optical element than the temperature change section and which enters a state of thermal equilibrium at a different temperature than the temperature of the temperature change section; and

a temperature buffer section disposed between and contacting the temperature change section and the heat dissipation section where the temperature buffer section has a heat resistance greater than the heat dissipation section,

wherein a product C 2 ×R 2 of a heat capacity C 2 of the temperature buffer section and a heat resistance R 2 of the temperature buffer section is in the range of half to double of a product C 1 ×R 1 of a heat capacitor C 1 of the thermo-optical element and a heat resistance R 1 of the thermo-optical element.

5. The optical phase shifter according to claim 1 , wherein the thermo-optical element has a pair of surfaces parallel to each other in a region through which the input optical signal passes and the pair of surfaces are substantially perpendicular to a surface of the thermo-optical element contacting the temperature change section.

6. The optical phase shifter according to claim 1 , wherein an edge of a surface of the thermo-optical element contacting the temperature change section is surrounded by the temperature change section.

7. The optical phase shifter according to claim 1 , wherein the temperature change section is a thin film resistor formed on the temperature buffer section and the thermo-optical element is adhered with an insulating adhesive to contact the temperature change section.

8. The optical phase shifter according to claim 1 , wherein the thermo-optical element contains silicon as a main component.

9. A demodulator comprising one or a plurality of the optical phase shifters according to claim 1 .

10. The demodulator according to claim 9 , wherein when the input optical signal is branched into two optical signals, the single or each of the plurality of optical phase shifters shifts a phase of one of the two optical signals.

11. The demodulator according to claim 9 , further comprising:

a Mach-Zehnder interferometer,

wherein the single or the plurality of optical phase shifters are disposed in the Mach-Zehnder interferometer.

12. The demodulator according to claim 9 , further comprising:

a Michelson interferometer,

wherein the single or the plurality of optical phase shifters are disposed in the Michelson interferometer.