JPH04291203A - Optical attenuator - Google Patents

Abstract

PURPOSE:To accurately set an attenuating amount with a desired arbitrary wavelength by reducing the storage capacity of data and only measuring relation between the attenuating amount of two wavelengths and the rotational angle of a continuous attenuation filter. CONSTITUTION:An optical power meter measuring means 1 measures the rotational angle of the filter to the attenuatmng amount of two wavelengths in the range of use. This measured data is stored in a data storage part (storing means) 4 and when a wavelength/attenuating amount set part (setting means) 2 sets the wavelength and the attenuating amount, a linear approximating means 3a reads the measured data from the storing means 4 and linearly approximates it for each same attenuating amount. A calculating means 3b calculates the rotational angle of a continuous attenuation filter (filter) 7 to the attenuating amount of the set wavelength based on the linearly approximated data.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical attenuator used in optical communications, and more particularly to an optical attenuator that can be used at a desired wavelength.

0002

[Prior Art] Measuring equipment used in optical communications uses a metal plate on a glass plate so that the transmittance changes continuously along the same circumference when the incident light is attenuated by a desired amount and output. A film-formed optical attenuator is used.

By the way, when using this type of optical attenuator, the data of the rotation angle with respect to the attenuation amount is stored and set in advance. Conventionally, this data is stored and set by using a continuous filter at a certain wavelength λ1. The relationship between attenuation and rotation angle is measured and written into ROM, and then a different wavelength λ2 is measured.
Measure the relationship between the attenuation amount and rotation angle of the continuous filter with R
I was writing to OM.

When actually using an optical attenuator, one of the two wavelengths λ1 and λ2 is selected, and the relationship between the amount of attenuation at one wavelength and the rotation angle of the continuous attenuation filter is calculated. The desired amount of attenuation was obtained by reading from the ROM and controlling the rotation angle of the continuous attenuation filter.

[0005]

[Problem to be Solved by the Invention] However, in the conventional setting method described above, when the relationship between attenuation and rotation angle is written in the ROM for two wavelengths, it can only be used for one of the wavelengths. , could not be used at any many wavelengths.

[0006] Therefore, when using many wavelengths,
RO the relationship between attenuation and rotation angle for all wavelengths used.
This can be solved by writing to M, but there are the following problems. 1) Since the ROM has a limited capacity, it is not possible to store ROM data at many wavelengths, for example, from 1100 nm to 1650 nm in 1 nm increments. 2) Measure the relationship between attenuation amount and rotation angle and store the data in ROM
It takes about 1 hour per wavelength to write to
Creating and storing ROM data at many wavelengths, for example, every 1 nm from 1100 nm to 1650 nm, requires as much time as about 551 hours, which is inefficient. 3) In order to write the relationship between attenuation and rotation angle at all wavelengths used, for example, to write the relationship between attenuation and rotation angle at wavelength λ3 into ROM, a light source with wavelength λ3 must be used. . At this time, the wavelength is 1100n
There are two ways to prepare a light source with a wavelength of 1 nm from m to 1650 nm, one method is to separate white light with a spectrometer and extract one wavelength, and the other is to prepare a high output light source with a wavelength of every 1 nm from 1100 nm to 1650 nm. However, in the former method, only a low output light amount of -60 dBm can be obtained, and for example, the light amount -120 dBm after passing through a 60 dB attenuation filter cannot be accurately measured with an optical power meter. Furthermore, in the latter method, as many as 551 types of light sources must be prepared.

By the way, the attenuation amount of the continuous attenuation filter is
It has been found that even if the rotation angle position of the continuous attenuation filter is the same, the attenuation amount changes as the wavelength changes, as shown in FIG. 5. This is because the metal deposited on the continuous attenuation filter has wavelength dependence, and can be explained using the formula: (attenuation) = (absorption of deposited metal) + (reflection of deposited metal)
Since most of the attenuation is due to absorption, when considering absorption, (absorption of deposited metal) = (absorption coefficient) times (thickness of deposited metal) (absorption coefficient) = (transition probability of absorption) × (number of electrons present)
× (Number of holes existing) × (Probability of electron existence) × (Speed of light)
There is a relationship as follows: ÷ (refractive index of deposited metal), and (transition probability of absorption) and (refractive index of deposited metal) have wavelength dependence, so differences in attenuation occur depending on the wavelength. Therefore, when changing the wavelength to obtain the same amount of attenuation, it is necessary to change the rotation angle of the continuous attenuation filter as shown in the relationship between wavelength and rotation angle in FIG.

By the way, the wavelength and rotation angle in FIG. 6 have a curvilinear relationship, and the unit of attenuation is expressed in dB, but the relationship between the wavelength and absorption coefficient in FIG. Wavelength band from 1100nm to 1650n
The unit of attenuation in the linear part of the range of m is expressed by the formula Y = 10 (
x/10)...It was found that if converted to a linear display based on (1), it becomes almost a straight line.

The present invention has been made in view of the above problems, and is capable of reducing data storage capacity, and measures the relationship between the amount of attenuation of two wavelengths and the amount of movement (rotation angle) of a continuous attenuation filter. The object of the present invention is to provide an optical attenuator that allows the attenuation amount to be set with high precision at any desired wavelength by simply using the following method.

0010

[Means for Solving the Problems] In order to achieve the above object, an optical attenuator according to the present invention includes a setting means 2 for setting a wavelength and an attenuation amount, and a filter for attenuation amounts of at least two wavelengths within a usage range. 7, a storage means 4 for storing data of two wavelengths among the data obtained by the measurement means, and a linear approximation of the data stored in the storage means for each same amount of attenuation. Straight line approximation means 3
a, and calculation means 3b for determining the amount of movement of the filter with respect to the amount of attenuation of the set wavelength based on the data linearly approximated by the linear approximation means.

[0011]

[Operation] When the measuring means 1 determines the amount of movement of the filter 7 with respect to the amount of attenuation of at least two wavelengths within the usage range, the data of two wavelengths of this data are stored in the storage means 4.
is memorized. Then, when the wavelength and attenuation amount are set by the setting means 2, the data stored in the storage means 4 is linearly approximated for each same attenuation amount by the linear approximation means 3a,
The calculation means 3b calculates the amount of movement of the filter 7 with respect to the amount of attenuation of the set wavelength based on the linearly approximated data.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of an optical attenuator according to the present invention. The optical attenuator according to this embodiment sets an attenuation amount at an arbitrary wavelength and attenuates input light by a desired amount to obtain output light.
, wavelength/attenuation setting section (setting means) 2, calculation processing section 3,
It comprises a data storage section (storage means) 4, a light source section 5, a driving section 6, a continuous attenuation filter (filter) 7, and an optical section 8.

The optical power meter 1 shown by the dashed line in the figure is within the usable wavelength range, for example, one of the wavelength bands used for optical communication.
It is connected only when measuring the rotation angle (travel amount) for the attenuation of two wavelengths from 100 nm to 1650 nm. The wavelength/attenuation amount setting section 2 sets the wavelength and attenuation amount in order to obtain the desired output light, and this information is output to the calculation processing section 3. With the optical power meter 1 connected, the calculation processing unit 3 takes in the rotation angle for each of the two wavelengths measured by the optical power meter, and stores each data in the data storage unit 4 for each wavelength. . The calculation processing section 3 also includes a linear approximation means 3a that reads data stored in the data storage section 4 and performs linear approximation for each same attenuation amount, and a wavelength and attenuation amount set and inputted by the wavelength/attenuation amount setting section 2. It is provided with calculation means 3b for calculating the rotation angle corresponding to from the linearly approximated data. Further, the calculation processing section 3 outputs a control signal for controlling the light source section 5 and the driving section 6 so that the output light set and inputted in the wavelength/attenuation amount setting section 2 can be obtained based on the calculation result. There is. The data storage section 4 stores data on rotation angles for the attenuation amounts of the two selected wavelengths for each wavelength, and data is read and written in accordance with control signals from the calculation processing section 3. The light source unit 5 is previously equipped with two types of light sources depending on the wavelength range to be used, and switching is controlled by a control signal from the calculation processing unit 3. The drive section 6 rotates the continuous attenuation filter 7 based on the control signal from the calculation processing section 3 . The continuous attenuation filter 7 is composed of, for example, a circular glass plate, and a metal film is formed on this glass plate so that the transmittance changes continuously along the same circumference. The continuous attenuation filter 7 is rotationally driven by the driving section 6 under the control of the calculation processing section 3 to a predetermined position calculated by the calculation processing section 3. The optical section 8 is disposed on both sides of the continuous attenuation filter 7, and focuses the parallel light incident from the light source section 5 through an incident-side connector (not shown) onto one point on the surface of the continuous attenuation filter 7, so that the light passes through the continuous attenuation filter 7. The emitted light is returned to parallel light and guided to an output side connector (not shown).

Next, the operation of the optical attenuator constructed as described above will be explained. With the optical power meter 1 connected, first, the relationship between the amount of attenuation of the continuous attenuation filter 7 and the rotation angle at the wavelength λ1 (for example, 1.3 μm) is measured. Then, the data at this time (see FIG. 2) is stored in the data storage section 4. Next, the wavelength λ2 (for example, 1.55 μm)
The relationship between the attenuation amount and the rotation angle of the continuous attenuation filter 7 is measured, and the data at this time (see FIG. 3) is stored in the data storage unit 4 in the same manner as the data for the wavelength λ1. Then, when the desired wavelength and attenuation amount are set by the wavelength/attenuation amount setting section 2, the linear approximation means 3a of the calculation processing section 3 reads out the data of the wavelength λ1 and the wavelength λ2 stored in the data storage section 4. A linear approximation is performed by connecting the data of wavelength λ1 and wavelength λ2 for each same amount of attenuation (see FIG. 4). Furthermore, calculation processing unit 3
The calculation means 3b calculates the rotation angle of the continuous attenuation filter 7 for the wavelength and attenuation of the wavelength/attenuation amount setting section 2 based on equation (2), and based on the calculation result, switches the wavelength of the light source section 5 and Controls the rotation of the continuous attenuation filter 7.

The equation (formula (2)) for linear approximation is shown below. (Rotation angle) = θ1 + (λ-1.3) x (θ2-θ1
)/(1.55-1.3) θ1: Rotation angle of the continuous attenuation filter at a desired attenuation amount at a wavelength of 1.3 μm θ2: Rotation angle of the continuous attenuation filter at a desired attenuation amount at a wavelength of 1.55 μm λ: Desired arbitrary wavelength For example, when setting the wavelength to 1.48 μm and the attenuation amount to 20 dB, if the rotation angle of the continuous attenuation filter is θ, then θ=
7/25θλ120+8/25θλ220θλ120:
Rotation angle θλ220 of a continuous attenuation filter with an attenuation amount of 20 dB at a wavelength of 1.3 μm: It can be expressed as a rotation angle of a continuous attenuation filter with an attenuation amount of 20 dB at a wavelength of 1.55 μm.

Therefore, in the embodiment described above, 1.3 μm
and the attenuation amount and rotation angle of the continuous attenuation filter 7 for only two types of wavelengths, 1.55 μm, are stored in the data storage unit 4,
The data read from the data storage unit 4 is linearly approximated for each same attenuation amount, and the rotation angle of the continuous attenuation filter 7 at a desired wavelength is determined from equation (2). A desired damping output can be obtained by setting with high precision.

Furthermore, since the data stored in the data storage section 4 is only two types of wavelength data, it can be configured with a small capacity storage section.

By the way, in the above embodiment, the wavelength range used is from 1100 nm to 1650 nm, which is used for optical communication. However, if the linear portion of each curve in FIG. 7 is selected as the wavelength range, other wavelength ranges can be used. The same effects as in the above-mentioned embodiments can also be obtained in the wavelength band.

Furthermore, although the data stored in the data storage unit 4 has been described as having two types of wavelengths, data on rotation angles for attenuation amounts of a plurality of wavelengths is stored, and data between the most adjacent wavelengths is linearly approximated. If the rotation angle of the continuous attenuation filter 7 is calculated and controlled based on Equation (2), the attenuation amount can be set with higher accuracy. Furthermore, although the continuous attenuation filter 7 has been explained by taking as an example a case where the rotation is controlled, the same effect can be obtained even if the continuous attenuation filter 7 is controlled to move in a predetermined direction including parallel movement.

[0020]

As explained above, the optical attenuator according to the present invention stores data on the amount of attenuation due to two types of wavelengths and the amount of movement of the continuous attenuation filter in the storage section, and the data stored in the storage section Since the configuration uses a linear approximation for each same attenuation amount and calculates the amount of movement of the continuous attenuation filter at a desired wavelength, the storage unit for storing data can be configured with a small capacity, allowing accurate attenuation at any wavelength within the usage range. You can set the amount.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an optical attenuator according to the present invention.

[Figure 2] Diagram showing measurement data of rotation angle versus attenuation of wavelength λ1 in the same optical attenuator.

[Figure 3] Diagram showing measurement data of rotation angle versus attenuation amount of wavelength λ2 in the same optical attenuator.

[Figure 4] Data of wavelength λ1 and wavelength λ in the same optical attenuator
A diagram showing the data when the data in 2 is linearly approximated for each same attenuation amount.

[Figure 5] Diagram showing the relationship between wavelength and attenuation amount

[Figure 6] Diagram showing the relationship between wavelength and rotation angle of continuous attenuation filter

[Figure 7] Diagram showing the relationship between wavelength and absorption coefficient

[Explanation of symbols] 1 Optical power meter (measuring means) 2 Wavelength/attenuation setting section (setting means) 3 Calculation processing section 3a Linear approximation means 3b Calculation means 4 Data storage section (storage means) 7 Continuous attenuation filter (filter)

Claims (1)

[Claims] 1. Setting means (2) for setting the wavelength and attenuation, and measuring means (1) for determining the amount of movement of the filter (7) with respect to the attenuation of at least two wavelengths within the usage range.
), storage means (4) for storing data of two wavelengths among the data obtained by the measurement means, and linear approximation means (3a) for linearly approximating the data stored in the storage means for each same attenuation amount. and calculation means (3b) for determining the amount of movement of the filter with respect to the amount of attenuation of the set wavelength based on the data linearly approximated by the linear approximation means.