Tunable optical filter

• US 20030016432A1
• Filed: 09/13/2002
• Published: 01/23/2003
• Est. Priority Date: 01/23/1998
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Fukushima, Nobuhiro, Terahara, Takafumi
• Granted Patent: US 6,717,730 B2
• Time in Patent Office: Days
• US Class Current: 359/256
• CPC Class Codes: G02F 1/0121 Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
• CPC Class Codes: G02F 1/09 based on magneto-optical elements, e.g. exhibiting Faraday effect
• CPC Class Codes: G02F 2203/05 wavelength dependent
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: H01S 2301/04 Gain spectral shaping, flattening
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence

Abstract

The present invention relates to a tunable optical filter having a variable wavelength characteristic of transmittance. The tunable optical filter includes first and second polarizers each having a transmission axis determining a polarization axis of transmitted polarized light, a birefringent element having an optic axis determining a phase difference given between two orthogonal components of transmitted polarized light, and a Faraday rotator for giving a variable Faraday rotation angle to transmitted polarized light. The birefringent element and the Faraday rotator are provided between the first and second polarizers. The order of arrangement of the birefringent element and the Faraday rotator, and the relative positional relation between the optic axis of the birefringent element and the transmission axis of each polarizer are set so that the shape of a characteristic curve giving a wavelength characteristic of transmittance changes along a transmittance axis according to a change in the Faraday rotation angle.

Claims

1. An optical filter comprising:

a filter filtering a light and having a controllable optical transmittance; and

a controller controlling the optical transmittance of the filter to have a fixed amount of transmittance at a specific wavelength.

2. An optical filter comprising:

a filter filtering a light and having a controllable optical transmittance; and

a controller controlling the optical transmittance of the filter to have a minimum optical transmittance and a maximum optical transmittance at the same specific wavelength.

3. An optical filter comprising:

a filter filtering a light and having a controlling optical transmittance;

a controller controlling the optical transmittance of the filter to have a constant center of gravity wavelength.

4. A method comprising:

controlling an amount of optical transmittance in accordance with a cyclical optical transmittance curve; and

controlling a fixed amount of optical transmittance at a specific wavelength in accordance with the curve.

5. A method of controlling a cyclical optical transmittance curve comprising:

controlling an amount of optical transmittance in accordance with the curve; and

controlling a minimum optical transmittance and a maximum optical transmittance to be at the same specific wavelength in accordance with the curve.

6. A method of controlling a cyclical optical transmittance curve comprising:

controlling an amount of optical transmittance in accordance with the curve; and

controlling a center of gravity wavelength to be constant in accordance with the curve.