JP3394637B2 - Optical bandpass filter device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical bandpass filter device, and particularly to an optical bandpass filter suitable for use in the case of selecting only a specific optical signal from wavelength multiplexed signals in optical wavelength multiplexed communication. The present invention relates to a filter device.

[0002]

2. Description of the Related Art An optical bandpass filter chip is considered to be one of the core optical components in future optical fiber communications because it can be used for limiting the optical amplifier noise band, selecting optical wavelength division multiplexing signals, etc., and is a commercial product. Already exists. In this commercial product, a dielectric multilayer film is used to realize the optical bandpass characteristic as shown in FIG. In this example, the 3 dB bandwidth is about 1 nm as shown in the figure, but the 20 dB bandwidth is important for the future separation of the high-density optical wavelength division multiplexed signal. In this example, the 20 dB bandwidth is about 9
Since the optical bandpass filter chip has one stage, it is impossible to separate the high-density optical wavelength division multiplexed signal.

As an example of the high-density optical wavelength division multiplexed signal, when the wavelength interval is set to be extremely narrow at 0.53 nm, FIG.
It has been proposed in the past to use several optical bandpass filters having such characteristics in cascade connection (reference document: NS Bergano et al., OFC'95, PD19).

[0004]

However, when a plurality of optical band pass filter devices are cascade-connected, it is necessary to make the transmission center wavelengths of the optical band pass filters identical to each other with extremely high precision. Therefore, when the center wavelength is deviated, the insertion loss is significantly increased, and the transmission characteristics are not smooth as shown in FIG. Therefore, the conventional device may cause deterioration of the optical signal waveform. There is also a problem that a large space is required as the number of optical bandpass filter devices increases.

Also, in order to narrow the 20 dB bandwidth and save space, an optical band pass filter device such as a so-called double cavity or triple cavity in which a multilayer film has two stages and three stages into one filter. Is also commercially available. However, in this type of optical bandpass filter, since it is necessary to make the characteristics of the multilayer films of each stage completely the same, there is a possibility that the same problem as in the case of the cascade connection may occur due to a manufacturing error. It was

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide an optical bandpass filter device capable of narrowing the 20 dB bandwidth without causing problems due to manufacturing errors and the like. It is what

[0007]

In order to achieve the above object, the present invention provides a reflection plate such as a mirror in an optical path passing through an optical bandpass filter chip, and the same optical bandpass filter chip is provided at the same point. It is characterized by making two round trips and a total of four or more passes. According to the invention, the passing filter chips are the same and the passing points are the same.
In Since point, it is not necessary to cascade a plurality of optical band-pass filter apparatus as in the conventional apparatus, such not shift or the like of the transmission center wavelength of the optical band-pass filter apparatus due to a manufacturing error is a problem Kunar.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory diagram of an embodiment of the optical bandpass filter device of the present invention. In the figure, 1 is an optical bandpass filter chip composed of a dielectric multilayer film, 2
Is a mirror (reflector), 3 is an optical bandpass filter chip 1
An optical fiber 4 for injecting light into the lens, 4 is a lens for collimating the light from the optical fiber 3 and guiding it to the optical bandpass filter chip 1, 5 is an optical fiber for outputting the light transmitted through the optical bandpass filter chip 1, 6 Is a lens for collimating the light passing through the optical bandpass filter chip 1 to the optical fiber 5. The arrow in the figure indicates the optical path of the light input to the optical bandpass filter chip 1.

Since the light input to this optical bandpass filter device is transmitted through the same optical bandpass filter chip 2 twice, the 20 dB bandwidth can be narrowed. As an example, FIG. 2 shows the result of calculation of the transmission characteristics when the optical bandpass filter chip 1 having the characteristics shown in FIG. 9 is used and the configuration shown in FIG. 1 is used. In FIG. 2, a shows the characteristics when one stage of the optical bandpass filter chip 1 is used, and b shows the characteristics of this embodiment.
As is clear from the figure, according to this embodiment, 20 dB
It can be seen that the bandwidth can be significantly reduced from the conventional 9 nm to 2.8 nm.

Next, a second embodiment of the present invention will be described with reference to FIG. In the figure, 7 is an optical fiber that inputs and outputs light to and from the optical bandpass filter chip 1, 8 is a lens that collimates the light from the optical fiber 7 to the optical bandpass filter chip 1, 9 is a three-terminal optical circulator, and 10 is An optical fiber that inputs light to the optical circulator 9 and an optical fiber 11 that outputs light from the optical circulator 9. Reference numerals other than the above indicate the same as or equivalent to the same reference numerals in FIG. 1, and solid line arrows in the drawing indicate the optical paths of the light input to the optical bandpass filter chip 1. The inclination of the optical bandpass filter chip 1 with respect to the optical path can be selected as an appropriate value between several degrees and several tens of degrees. As an example, it is preferable to set it to 8 degrees.

In the optical bandpass filter device having such a configuration, the optical circulator 9 is passed through the optical fiber 10.
The light input to is guided to the optical fiber 7, passes through the lens 8, and is emitted to the optical bandpass filter chip 1. next,
The light passes through an optical bandpass filter chip 1 and a mirror 2
Is reflected by the optical band pass filter chip 1 again and is guided to the optical fiber 7 through the lens 8. Next, it enters the optical circulator 9 and proceeds to the optical fiber 11. As a result, according to the optical bandpass filter device of the present embodiment, the light input to the optical bandpass filter device is the same as the optical bandpass filter chip 1 as in the first embodiment.
Since it is transmitted twice, the 20 dB bandwidth can be narrowed.

Since the optical circulator 9 advances the light entering from the optical fiber 10 to the optical fiber 7 and advances the light entering from the optical fiber 7 to the optical fiber 11,
Even if the optical path across the optical bandpass filter chip 1 is exactly the same, the light before passing through the optical bandpass filter chip 1 and the light after passing through it can be separated. The light that does not pass through the optical bandpass filter chip 1 is reflected on the surface of the optical bandpass filter chip 1 as shown by the dotted arrow, but the optical bandpass filter chip 1 tilts with respect to the optical path. Since it is inserted, it does not enter the lens 8.

Next, a third embodiment of the present invention will be described with reference to FIG. In the figure, reference numerals 2a and 2b denote mirrors that reflect light, and other reference numerals are the same as or equivalent to the same reference numerals in FIG. In this embodiment, the light traveling through the optical fiber 3 is collimated by the lens 4 and is emitted toward the optical bandpass filter chip 1. Then, the light passes through the optical bandpass filter chip 1, is reflected by the mirror 2a, passes through the optical bandpass filter chip 1 again, is reflected by the mirror 2b, and again passes through the optical bandpass filter chip 1.
And enters lens 6. Then, it is collimated by the lens 6 and travels through the optical fiber 5.

According to this embodiment, since the light input to this optical bandpass filter is transmitted through the same optical bandpass filter chip 3 three times, a bandwidth of 20 dB is further increased as compared with the first embodiment. Can be narrowed.

Next, a fourth embodiment of the present invention will be described with reference to FIG. In the figure, 13 is an optical fiber, and 14
Is a second three-terminal optical circulator, 15 is an optical fiber,
Reference numeral 16 denotes a lens, and other reference numerals are the same as or equivalent to the same reference numerals in FIG. The first and second three-terminal optical circulators 9 and 14 are connected in series via an optical fiber 13. According to this embodiment, the light that has entered through the optical fiber 10 is the optical circulator 9 → optical fiber 7 → lens 8 → optical bandpass filter chip 1 → mirror 2
→ Optical band pass filter chip 1 → Lens 8 → Optical fiber 7 → Optical circulator 9 → Optical fiber 13 → Optical circulator 14 → Optical fiber 15 → Lens 16 → Optical band pass filter chip 1 → Mirror 2 → Optical band pass filter chip 1 → Lens 16 → optical fiber 15 → optical circulator 14 → optical fiber 11

As a result, according to the present embodiment, the light passes through the same optical bandpass filter chip 1 four times, and therefore has better characteristics than the third embodiment.
That is, it is possible to obtain an optical bandpass filter having a narrower bandwidth of 20 dB than that of the third embodiment. In this embodiment, a three-terminal optical circulator is used, but instead of the optical circulators 9 and 14, one four-terminal circulator 17 is used as shown in FIG. May be. Further, it is needless to say that the same optical bandpass filter chip 1 can be passed six times or more by connecting two or more three-terminal optical circulators in series instead of two. Is.

Next, a fifth embodiment of the present invention will be described with reference to FIG. The feature of this embodiment is that the optical band pass filter chip 1 made of a dielectric multilayer film is made variable in angle formed with the optical path (solid line) as shown by d.
The point is that the center wavelength of the light passing through the optical bandpass filter chip 1 is variable. Reference numeral 18 in the figure denotes an obstacle plate for preventing stray light reflected by the optical bandpass filter chip 1 from entering the lens 6, and other reference numerals are the same as or equivalent to those in FIG.

In this embodiment, when the angle between the optical bandpass filter chip 1 and the optical path (solid line) is changed back and forth around 8 degrees as shown by d, the optical bandpass filter chip 1 is changed. The central wavelength of the light passing through can be changed within the range of 1520 to 1570 nm, for example. Therefore, when the angle formed by the optical bandpass filter chip 1 and the optical path is set to a desired angle and then the light is guided to the optical fiber 3, this light is collimated by the lens 4 and is emitted to the optical bandpass filter chip 1. It The optical bandpass filter chip 1 transmits light having a central wavelength corresponding to the angle, is reflected by the mirror 2, passes through the optical bandpass filter chip 1 again, and enters the lens 6. Therefore, according to this embodiment, 20 dB of the optical bandpass filter device
There is an advantage that the bandwidth can be narrowed and the central wavelength of the light transmitted through the optical bandpass filter device can be changed. The optical bandpass filter chip 1
When the angle is changed, stray light reflected by the optical bandpass filter chip 1 is incident on the lens 6 at a certain angle. However, in this embodiment, the obstacle plate 18 is provided. The plate 18 reflects or absorbs this stray light. Therefore, stray light can be prevented from being output from the optical fiber 5 through the lens 6.

Next, a sixth embodiment of the present invention is shown in FIG.
It will be explained with reference to (b) and. 1A is a top view of the optical bandpass filter device, and FIG. 1B is a front view thereof. The feature of this embodiment is that the optical bandpass filter chip 21 is x
This is because the transmission center wavelength is continuously variable in the axial direction and is uniform in the z-axis direction. The other reference numerals are the same as or equivalent to the same reference numerals in FIG.

In this embodiment, when the optical bandpass filter chip 21 shown in FIG. 8A is moved in the x-axis direction, the transmission center wavelength of the light collimated by the lens 4 becomes
For example, it can be arbitrarily selected in the range of 1520 to 1570 nm. Therefore, the optical bandpass filter chip 2
When the position of 1 in the x-axis direction is fixed to a position where a desired transmission center wavelength is obtained and light is introduced from the optical fiber 3, this light is collimated by the lens 4 and is emitted toward the optical bandpass filter chip 21. It Subsequently, the light of the selected transmission center wavelength passes through the optical bandpass filter chip 21,
It is reflected by the mirror 2 and again the optical band pass filter chip 2
It is incident on the lens 6 through 1. Therefore, according to this embodiment, similar to the fifth embodiment, the 20 dB bandwidth of the optical bandpass filter device can be narrowed and the optical bandpass filter chip 21 is moved in the x-axis direction. , The central wavelength of the light passing through the optical bandpass filter device can be changed.

[0021]

As is apparent from the above description, according to the present invention, optical wavelength-multiplexed signal light passes through the same optical bandpass filter chip a plurality of times and is output from the output optical fiber. become. Therefore, it is possible to connect a plurality of optical bandpass filter chips in cascade,
There is no need to use so-called double cavities or triple cavities with one filter as three stages,
There is no fear of causing deterioration of the optical signal waveform due to manufacturing error. Further, it becomes possible to obtain an optical bandpass filter having a narrow 20 dB bandwidth and good characteristics such as insertion loss, so that the effect is great. For example, when the optical bandpass filter device of the present invention is used for demultiplexing a high-density optical wavelength division multiplexed signal, the effect is large.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a first embodiment of an optical bandpass filter device of the present invention.

FIG. 2 is a characteristic diagram illustrating reduction of 20 dB bandwidth according to the first embodiment.

FIG. 3 is a diagram illustrating a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a third embodiment of the present invention.

FIG. 5 is a diagram illustrating a fourth embodiment of the present invention.

FIG. 6 is a diagram illustrating a modified example of the fourth embodiment.

FIG. 7 is a diagram illustrating a fifth embodiment of the present invention.

FIG. 8 is a diagram illustrating a sixth embodiment of the present invention.

FIG. 9 is a characteristic diagram of a conventional optical bandpass filter device.

[Explanation of symbols]

1 ... Optical bandpass filter chip, 2, 2a, 2b ... Mirror, 3, 5, 7, 10, 11, 13, 15 ... Optical fiber, 4, 6, 8, 16 ... Lens, 9, 14 ... 3 terminal light Circulator, 17 ... 4-terminal optical circulator, 21 ...
Optical bandpass filter chip.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-7-198937 (JP, A) JP-A-5-82882 (JP, A) JP-A-6-26931 (JP, A) JP-A-4- 213403 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 27/00 G02B 5/20 G01J 3/12

Claims (3)

(57) [Claims] 1. A first optical circulator and an optical signal input / output connected to the first optical circulator.
And a second optical fiber connected in series with the first optical circulator.
Connected to the optical circulator and the second optical circulator, input and output optical signals
Output from each of the second optical fiber and the first and second optical fibers
An optical bandpass filter chip on which an optical signal is incident and a reflection of the optical signal that has passed through the optical bandpass filter chip
And a reflector that guides the optical bandpass filter chip again.
And the optical signal output from the first optical fiber is
Passes through the band pass filter chip and is reflected by the reflector.
And pass through the same position of the optical bandpass filter chip again
And enters the first optical fiber, and the first optical circuit
Circulator, second optical circulator, second optical fiber
The optical signal output from the second optical fiber via
It passes through the optical bandpass filter chip and is reflected by the reflector.
The same position of the optical bandpass filter chip.
Passes through the second optical fiber and enters the second optical fiber.
An optical bandpass filter device characterized by being output from a curator . 2. The first and second optical circulators are
Each is a 3-terminal optical circulator
The optical bandpass filter device according to claim 1 . 3. A four-terminal optical circulator and two terminals of the four-terminal optical circulator.
And output from each of the first and second optical fibers that input and output the optical signal and the first and second optical fibers .
An optical bandpass filter chip on which an optical signal is incident and a reflection of the optical signal that has passed through the optical bandpass filter chip
And a reflector that guides the optical bandpass filter chip again.
And the optical signal output from the first optical fiber is
Passes through the band pass filter chip and is reflected by the reflector.
And pass through the same position of the optical bandpass filter chip again
And then enters the first optical fiber, and the 4-terminal optical circuit
And a second optical fiber via a second optical fiber
The optical signal output from the optical bandpass filter chip
And then is reflected by the reflector and passes through the optical band again.
Pass through the same position of the filter chip and
Iber enters and is output from the 4-terminal optical circulator
An optical bandpass filter device characterized by the above .