JPH10227942A - High-speed continuously variable wavelength filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-speed continuously variable wavelength filter which is variable over a wide wavelength range at a high speed with low loss. SOLUTION: This high-speed continuously variable wavelength filter 8 is composed of band-pass filters 1-1, 1-2...1-8 of different passing-range wavelengths λ1, λ2...λ8 formed of a dielectric multi-layered film on a glass substrate. The respective band-pass filters 1-1, 1-2...1-8 are fixed to respective side wall surfaces of a regular prism provided on the top surface of a turntable 2 by using an adhesive, etc. A 1st collimator 9 consisting of a single-mode optical fiber 4 and a 1st lens 5 and a 2nd collimator 10 consisting of a 2nd lens 6 and a single- mode optical fiber 7 are arranged opposite each other. When the turntable 2 is rotated fast, the respective band-pass filters cross parallel luminous flux propagated between the 1st and 2nd collimators 9 and 10 while continuously varying the angle to the parallel luminous flux.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical filter which is suitably used in the field of optical communication systems and optical measurement, and which can change the wavelength at high speed and continuously.

[0002]

2. Description of the Related Art An interference film (dielectric multilayer film) filter is
It refers to an optical filter formed by alternately depositing several or several tens of two dielectric thin films having a different refractive index having a thickness of λ / 4 on a glass substrate. Physically, the light wave propagating through the filter partially reflects the light wave for each film, and the light waves interfere with each other. As a result, only the wavelength determined by the product of the thickness of the dielectric thin film and the effective refractive index of the film with respect to the guided light is selectively transmitted. Further, the center transmission wavelength of this filter has an angle dependence with respect to the incident beam. Therefore, the transmission wavelength can be changed by changing the incident angle.

In the prior art, a filter provided with a gradient in which the wavelength is varied by mechanically changing the angle of the filter by a fine-movement tilting mechanism or the film thickness is changed in one direction in a plane is introduced into a light beam. The wavelength was tuned by the method. The former has a disadvantage that the insertion loss increases when the angle is increased to increase the wavelength variable amount. In the latter case, although there is no increase in loss, it is extremely difficult to manufacture a continuous gradation, and the yield is significantly reduced.

In any method, it is impossible in principle to continuously vary a wide wavelength range at high speed while maintaining low loss.

[0005]

As described above, in the conventional wavelength tunable filter, the wavelength can be varied by mechanically changing the angle of the filter by a fine movement tilt mechanism, or the gradient can be changed in one direction in the plane. The wavelength is varied by a method in which a filter provided with an emission is put out into the light beam, but in any case, there is a problem that a wide wavelength range cannot be continuously varied at high speed while maintaining low loss.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a high-speed continuous wavelength tunable filter capable of continuously changing a wide wavelength range at a high speed with low loss. Is to do.

[0007]

The present invention comprises a first collimator comprising an input optical fiber and a first lens;
A second collimator comprising a lens and an output optical fiber and arranged opposite to the first collimator; and at least one optical filter provided vertically on the upper surface near the outer periphery of the rotating disk which is rotated at a high speed The optical filter includes a parallel light beam propagating between the first and second collimators.
It is characterized by crossing while continuously changing the angle with respect to the parallel light beam. Also, the present invention is characterized in that, in the above invention, a plane mirror is provided instead of the second collimator, and an optical circulator is provided in the input optical fiber.

According to the first aspect of the present invention, as means for continuously changing the transmission wavelength at a high speed, a plurality of optical filters having different pass bands provided vertically on a rotating disk are guided by an optical fiber and a lens. The laser beam is configured to continuously traverse the collimated parallel beam while gradually changing the angle, so that the wavelength can be continuously varied at high speed. According to the second aspect of the present invention, since a reflecting mirror is used instead of the second collimator and the optical circulator is provided in the input fiber, it is possible to prevent a beam axis shift caused by the inclination of the filter. Further, the number of components is reduced because the input and output collimators are shared.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a diagram showing a high-speed continuous wavelength tunable filter according to a first embodiment of the present invention. Reference numeral 8 denotes a high-speed continuous wavelength tunable filter which is formed by a dielectric multilayer film such as TiO ₂ / SiO ₂ on a glass substrate and has a plurality of band-pass filters 1-1, λ 8,. 1-2,... 1-8, for example, A
1 is fixed to the side wall surface of a regular polygonal prism which is processed with high precision perpendicularly to the upper surface of the metal turntable 2 using, for example, a synthetic resin-based adhesive or a holding metal.
High speed rotation in one direction (direction of arrow) by the servo motor 3 attached to the center axis of the motor (eg, 500 to 10000 rp)
m).

Here, each pass band wavelength filter 1-1, 1-
2,... 1-8 have the same pass bandwidth and the center wavelengths are equally spaced. Further, since the incident angle of the beam to the filter with a small increase in loss is about 5 to 10 degrees at the maximum, the component arrangement and the device configuration in consideration of this are adopted.

Further, pass band wavelength filters 1-1, 1-2,
... Arranged as closely as possible so that there is no gap between 1-8. The reason for this is that if there is a small gap, a part of the unnecessary wavelength component will pass through and the blocking band characteristic will be degraded. For example, a countermeasure such as filling an appropriate amount of an absorbent for blocking the unnecessary wavelength component into the gap of the filter within a range in which the increase in loss is allowed is considered. Alternatively, it is conceivable to perform processing such as arranging adjacent filters so as to slightly overlap each other. Alternatively, a measure such as eliminating a gap by arranging the surface of the multilayer thin film of the filter so as to be on the back side with respect to the beam incidence can be considered.

Reference numeral 4 denotes a single mode fiber constituting an input optical fiber, and reference numeral 5 denotes a first lens. These constitute a first collimator 9. Reference numeral 6 denotes a lens, and reference numeral 7 denotes a single mode fiber constituting an output optical fiber, and these constitute a second collimator 10. The first collimator 9 and the second collimator 10 are arranged to face each other so that the optical axes coincide. When the turntable 2 is rotated, the passband wavelength filters 1-1, 1-2,.
A parallel light beam propagating between the first and second collimators 9 and 10 crosses while continuously changing the angle with respect to the parallel light beam.

Next, the operation of the high-speed continuous wavelength tunable filter 8 having the above configuration will be described. First, focusing on the first band-pass filter 1-1 having the center wavelength of the wavelength λl, this band-pass filter 1-1 is composed of the first and second collimators 9,
It crosses the parallel beam between 10 while gradually changing the incident angle. As a result, the incident angle of the beam becomes smaller, and the passing wavelength shifts to the longer wavelength side. Bandpass filter 1-1
Is large when the first half of the beam crosses a part of the parallel beam, but the loss is minimized when it moves to a position crossing the whole beam. Roughly, bandpass filter 1-1
The loss increases as the second half of the beam travels over the lower half of the beam. However, at this time, as shown in FIG. 2, the first half of the second band-pass filter 1-2 having the center wavelength of the wavelength .lambda.2 is applied to the upper half of the beam, so that the second band-pass filter 1-2 occupies. If the pass wavelength range is set to be the same as the pass wavelength range occupied by the first band pass filter 1-1, it is possible to suppress a decrease in transmittance as a whole.

By sequentially performing such operations, a wide wavelength range from the wavelength λ1 to the wavelength λ8 can be continuously changed at high speed without an instantaneous interruption, and can be repeated periodically. For example, when the beam diameter is relatively large, eg, 2 to 5 mm, when the boundary between the band-pass filters 1-1, 1-2,... A valley can be hardly generated in the wavelength characteristic. That is, there is an effect that the transmittance of the variable peak wavelength becomes uniform over a wide wavelength range that is swept.

Further, in the high-speed continuous wavelength tunable filter according to the present invention, a wide wavelength range can be covered with a small number of filters (the number of filters) without increasing loss without using many filters as in the prior art. For example, if it is possible to change the wavelength by 5 to 10 nm per filter, it is estimated to be 40 to 80 nm with eight filters (types).

FIG. 3 is a diagram showing another embodiment of the present invention. The basic configuration and operation are the same as in the above embodiment. The difference from the above-described embodiment is that a plane reflecting mirror 11 and an optical circulator 12 are provided instead of the second collimator 10 described above. The optical circulator 11 is provided in the input optical fiber 4. In this way, signal light can be input and output with one collimator 9, which contributes to a reduction in the number of components. The signal light passing through each of the band-pass filters 1-1, 1-2,..., 1-8 returns through the original optical path by the reflection mirror 9, so that the light generated by passing through the inclined filter is returned. Loss due to displacement of the parallel beam perpendicular to the axis can be prevented. Further, since the light passes through the band-pass filter twice, the filter characteristic becomes narrower, and there is an advantage that unnecessary noise light can be reduced.

In the above-described embodiment, an example is shown in which the regular octagonal high-speed continuous wavelength tunable filter 8 is constituted by eight band-pass filters, but the present invention is not limited to this. The number of band-pass filters is arbitrary. For example, it may be constituted by one band pass filter, and in that case, it may be arranged near the outer periphery of the turntable 2.

[0018]

As described above, according to the high-speed continuous wavelength tunable filter according to the present invention, the first collimator including the input optical fiber and the first lens, the second lens and the output optical fiber, A second collimator, which is disposed opposite to the first collimator, and at least one optical filter vertically provided on an upper surface near an outer periphery of a rotating disk that is rotated at a high speed. Adopts a structure that crosses a parallel light beam propagating between the first and second collimators while continuously changing the angle with respect to the parallel light beam, whereby a wide wavelength range can be continuously varied at high speed. Also, there is no large fluctuation of the insertion loss and no interruption of the passing optical signal. Further, the type (number of sheets) of required filters can be greatly reduced.

Further, according to the present invention, since a plane mirror is provided in place of the second collimator and an optical circulator is provided in the input optical fiber, the beam axis deviation caused by the inclination of the filter can be prevented. Can be used to reduce the number of parts.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a high-speed continuous wavelength tunable filter according to the present invention.

FIG. 2 is a diagram showing a relationship between wavelength and transmittance.

FIG. 3 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

1-1, 1-2, 1-8 band-pass filter, 2 turntable (rotary disk), 3 servo motor, 4 single-mode optical fiber, 5 lens, 6 lens, 7 single Mode fiber, 8 high-speed tunable filter, 9 first collimator, 10 second collimator, 11 reflecting mirror, 12 optical circulator.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshio Suzuki 3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A first collimator comprising an input optical fiber and a first lens, and a second collimator comprising a second lens and an output optical fiber and arranged opposite to the first collimator. At least one optical filter vertically provided on the upper surface near the outer periphery of the rotating disk that is rotated at a high speed. The optical filter converts a parallel light beam propagating between the first and second collimators into a parallel light beam. A high-speed continuous wavelength tunable filter characterized by crossing while continuously changing the angle with respect to. 2. The high-speed continuous wavelength tunable filter according to claim 1, wherein a plane mirror is provided in place of the second collimator, and an optical circulator is provided in the input optical fiber.