KR20210085383A - Appratus of Measuring Wavelength of Optical Signal Using Edge Filter - Google Patents

Abstract

An optical wavelength measuring device using an edge filter in accordance with the present invention comprises: an optical coupler (10) for receiving an optical signal to be measured and branching the optical signal into two output optical signals; a first edge filter (21) having a first slope (S1) in a characteristic of a change in transmittance in accordance with a wavelength in a predetermined wavelength range and receiving one of the output optical signals output from the optical coupler (10); a second edge filter (22) having a second slope (S2) in a characteristic of a change in transmittance in accordance with a wavelength in the same wavelength range as the predetermined wavelength range, and receiving the other one of the output optical signal output from the optical coupler (10); and a comparator (30) for obtaining a wavelength of the optical signal to be measured by using an optical power ratio between the optical signal output from the first edge filter (21) and the optical signal output from the second edge filter (22). The first slope and the second slope have inclinations in opposite directions to each other. The optical wavelength measuring device can be implemented at low cost and can operate robustly.

Description

Appratus of Measuring Wavelength of Optical Signal Using Edge Filter

The present invention relates to an apparatus for measuring an optical wavelength of an optical signal, and more particularly, to an optical wavelength measurement that can be implemented at a low cost and configured in a compact size to have portability.

An optical spectrum analyzer (OSA) is well known as a measuring instrument for measuring an optical wavelength. For example, an optical spectrum analyzer such as Patent Document 1 is known, in which an optical tuning member such as a diffraction grating is disposed, and a driving motor is connected to the optical tuning member to adjust the optical system. Such a conventional optical spectrum analyzer requires very precise optical alignment, and the elements constituting the device are expensive, so the manufacturing cost is very high.

Although the optical spectrum analyzer is a device that can measure the wavelength of light very precisely, it is mainly used as a fixed type because it is heavy and very expensive.

However, if high wavelength measurement precision is not required depending on the field of application to measure the optical wavelength, it is inefficient to use an expensive and difficult optical spectrum analyzer.

Republic of Korea Patent 10-0803237, registered on February 04, 2008, "Optical system for simultaneously detecting correction signal and test signal in optical spectrum analyzer, optical spectrum analyzer and its detection method"

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical wavelength measuring apparatus capable of being implemented at a lower cost and capable of robust operation.

Another object of the present invention is to provide an optical wavelength measuring device that can be implemented in a compact size.

An optical wavelength measuring apparatus using an edge filter according to an aspect of the present invention comprises: an optical coupler 10 for receiving an optical signal to be measured and branching it into two output optical signals; a first edge filter 21 having a first slope S1 in a characteristic of a change in transmittance according to wavelength in a predetermined wavelength range and receiving one of the output optical signals output from the optocoupler 10; The second edge filter 22 has a second slope S2 in the characteristic of a change in transmittance according to wavelength in the same wavelength range as the predetermined wavelength range, and receives the other one of the output optical signal output from the optocoupler 10 . ); A comparator 30 for obtaining the wavelength of the optical signal to be measured using the optical power ratio between the optical signal output from the first edge filter 21 and the optical signal output from the second edge filter 22; and wherein the first slope and the second slope have inclinations in opposite directions to each other.

In the optical wavelength measuring apparatus using the edge filter, the optical coupler 10 may be a 3dB coupler.

In the optical wavelength measuring apparatus using the edge filter, the optical power ratio is the optical power (log scale) of the optical signal output from the first edge filter 21 and the second edge filter 22 It can be obtained by subtracting the optical power (log scale) of the optical signal.

In the optical wavelength measuring apparatus using the edge filter, the comparator 30 includes a table in which a one-to-one correspondence between a plurality of optical power ratios and a plurality of wavelengths is defined and stored in advance, and using the table , the wavelength of the corresponding optical signal to be measured may be obtained from the optical power ratio between the optical signal output from the first edge filter 21 and the optical signal output from the second edge filter 22 .

In the optical wavelength measuring apparatus using the above-described edge filter, the table measures the optical power ratio in the comparator 30 while providing test light by sequentially inputting a single wavelength light source whose wavelength is known in advance during the production process. may have been created.

In the optical wavelength measuring apparatus using the edge filter, the comparator 30 includes two photodiodes for sensing the optical signals output from the first edge filter 21 and the second edge filter 22, respectively. 31,32) and; two driving and signal processing circuits (33, 34) for driving the photodiodes (31,32) and outputting analog-digital converted values from the electrical signals output by the photodiodes (31,32), respectively; and a processing unit 35 for deriving the wavelength of the optical signal to be measured using the analog-to-digital converted value and the table.

An optical wavelength measuring apparatus using an edge filter according to an aspect of the present invention has a first slope (S1) in a characteristic of a change in transmittance according to a wavelength in a predetermined wavelength range and a second slope (S2) in a characteristic of a change in reflectivity according to a wavelength. an edge filter 20 for receiving an optical signal to be measured and outputting a transmitted optical signal and a reflected optical signal, respectively; and a comparator (30) for obtaining the wavelength of the optical signal to be measured by using the optical power ratio of the transmitted optical signal and the reflected optical signal output from the edge filter (20).

In the optical wavelength measuring apparatus using the edge filter, the optical power ratio is the optical power (log scale) of the transmitted optical signal output from the edge filter 22 and the reflected optical signal output from the edge filter 20 It can be obtained by subtracting the optical power (log scale) of .

In the optical wavelength measuring apparatus using the edge filter, the comparator 30 includes a table in which a one-to-one correspondence between a plurality of optical power ratios and a plurality of wavelengths is defined and stored in advance, and using the table The wavelength of the corresponding optical signal to be measured may be obtained from the optical power ratio of the transmitted optical signal and the reflected optical signal.

In the optical wavelength measuring apparatus using the edge filter, the comparator (30) comprises: two photodiodes (31, 32) for sensing the transmitted optical signal and the reflected optical signal, respectively; two driving and signal processing circuits (33, 34) for driving the photodiodes (31,32) and outputting analog-digital converted values from the electrical signals output by the photodiodes (31,32), respectively; and a processing unit 35 for deriving the wavelength of the optical signal to be measured using the analog-to-digital converted value and the table.

The optical wavelength measuring apparatus using the edge filter according to the present invention is composed of a coupler, an edge filter, and a photodiode, so that the device configuration is very simple, and there is no need for fine optical alignment, so it can be easily implemented.

The optical wavelength measuring device using the edge filter according to the present invention cannot measure the optical wavelength with very high precision like an optical spectrum analyzer, but it can be implemented as a low-cost portable type, so that high precision is not required, such as wavelength analysis of WDM channels. It has the advantage that it can be applied very effectively in

1 is a graph showing transmission characteristics according to wavelength of a typical edge filter.
FIG. 2 is a graph showing transmission characteristics according to wavelengths of the edge filter, and illustrates the correspondence between the degree of attenuation of an optical signal and the wavelength.
3 is a block diagram showing the configuration of an optical wavelength measuring apparatus according to a first embodiment of the present invention.
4 is a block diagram showing a detailed configuration of a comparator in the optical wavelength measuring apparatus according to the first embodiment of the present invention.
5 is a graph showing the characteristics of an edge filter used in the optical wavelength measuring apparatus according to the first embodiment of the present invention.
6 is a block diagram illustrating an optical wavelength measuring apparatus according to a second embodiment of the present invention.
7 is a schematic diagram illustrating an edge filter in more detail in the optical wavelength measuring apparatus according to the second embodiment of the present invention.
8 is a graph illustrating transmission characteristics and reflection characteristics of an edge filter used in an optical wavelength measuring apparatus according to a second embodiment of the present invention.

With reference to the accompanying drawings, the embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar names and reference numerals are used for similar parts throughout the specification.

First, before explaining the optical wavelength measuring device according to the present invention, for the convenience of understanding, the invention of the intermediate stage in the process leading to the present invention (hereinafter referred to as 'invention of comparative example') will be first described, and the The invention uses an optical edge filter.

1 is a graph showing transmission characteristics according to wavelength of a typical edge filter.

Optical filters are used to selectively transmit or block wavelengths or wavelength ranges, and there are various optical filters according to transmission characteristics such as bandpass, notch, and edge. Bandpass filter transmits part of spectrum and blocks all other wavelengths, notch filter blocks part of spectrum and transmits all other wavelengths. Edge filter filters wavelengths larger than the cut-on wavelength or smaller than the cut-off wavelength. It is a permeable filter. In the invention of the comparative example, a device capable of measuring the optical wavelength and power of an optical signal is proposed by using an optical edge filter (hereinafter also referred to as an 'edge filter') and a photodiode whose transmittance is linearly changed according to wavelength.

FIG. 2 is a graph showing transmission characteristics according to wavelengths of the edge filter, and illustrates the correspondence between the degree of attenuation of an optical signal and the wavelength.

As shown in FIG. 2 , the edge filter may be designed so that the transmittance of the optical signal according to the wavelength changes almost linearly on a log scale basis. After passing through the edge filter, the output optical power shows a characteristic that the magnitude varies according to the optical wavelength. Therefore, if the optical power of the input optical signal is constant, the wavelength of the optical signal can be found by measuring the optical power of the output optical signal. For example, when an optical signal whose optical power of the input optical signal is 0 dBm is input in the edge filter having the characteristics shown in FIG. 2, the optical power value of the output optical signal is measured as -10 dBm, which is 10% of the input optical power. The wavelength of the input optical signal becomes ?3.

However, in order to measure the wavelength of the optical signal in the same way as above, it is necessary to assume that the optical power of the input optical signal is always kept constant. If the optical power of the input optical signal is not constant and varies, even if the wavelength of the optical signal is the same, the measured value of the output optical power also changes after passing through the edge filter, thereby causing an error in the optical wavelength measurement.

For example, in FIG. 2 above, measurements were made on the assumption that the optical power of the input optical signal of the λ3 wavelength was 0 dBm. If the actual input optical power was -10 dBm, the output optical power would be measured as -20 dBm. A measurement error will occur. After all, in order to measure the wavelength of an optical signal using an edge filter, the system must be configured to keep the optical power of the optical signal to be measured constant, or the process of measuring the optical power of the input optical signal before measuring the optical wavelength is required. There is a problem to go through. Hereinafter, embodiments of the present invention that solve the above problems will be described.

3 is a block diagram showing the configuration of an optical wavelength measuring device according to a first embodiment of the present invention, and FIG. 4 is a block diagram showing a detailed configuration of a comparator in the optical wavelength measuring device according to the first embodiment of the present invention. . 5 is a graph showing the characteristics of an edge filter used in the optical wavelength measuring apparatus according to the first embodiment of the present invention.

The optical wavelength measuring apparatus according to the first embodiment of the present invention includes a 50:50 optocoupler 10 , two edge filters 21 and 22 , and a comparator 30 .

The 50:50 optocoupler 10 is an optical element that receives an optical signal to be measured and branches it into two output optical signals having the same or similar optical power ratio, and a 3dB optocoupler is preferred.

The two edge filters are those that transmit wavelengths greater than the cut-on wavelength or less than the cut-off wavelength. One of the first edge filter 21 and the second edge filter 22 is a filter that transmits a wavelength greater than the cut-on wavelength, and the other is a filter that transmits a wavelength smaller than the cut-on wavelength.

The first edge filter 21 receives one of the output optical signals output from the optocoupler 10 and has a first slope S1 in a characteristic of a change in transmittance according to wavelength in a predetermined wavelength range (see FIG. 5 ). . The second edge filter 22 receives the other one of the output optical signal output from the optocoupler 10, and provides a second slope S2 in the transmittance change characteristic according to wavelength in the same wavelength range as the predetermined wavelength range. have One of the first slopes S1 and the second slope S2 has a positive slope and the other has a negative slope, in a dual relationship with each other, and the first slope S1 and the second slope S2 have inclinations in opposite directions.

The first edge filter 21 and the second edge filter 22 have a wavelength range to be measured inside the range in which the first slope S1 and the second slope S2 exist. The wavelength range to be measured has, for example, a wavelength range of 20 nm or 35 nm. In FIG. 5 and the like, although it is shown as if there is a discontinuous point of change rate (slope) between a section with a slope and a section with a flat section, it may be a smooth curved section having a continuous rate of change. Also, the first slope and the second slope may not be a perfect straight line having a constant inclination. For example, the first slope may be a slope having a positive slope but gradually changing within a certain range, and the second slope may be a slope having a negative slope but gradually changing within a certain range. can

The two edge filters 21 and 22 have opposite transmittance characteristics according to wavelength, and the optical power value in the input optical signal cancels each other out by utilizing the difference in transmittance between the two edge filters, so that the optical power value of the input optical signal Make it possible to measure the wavelength even if (P _{in ) changes.}

The comparator 30 receives the optical signal output from the first edge filter 21 and the optical signal output from the second edge filter 22, and uses the optical power ratio of the two optical signals to determine the wavelength of the optical signal to be measured. to acquire The comparator 30 may include two photodiodes 31 and 32 , two driving and signal processing circuits 33 and 34 , and a processing unit 35 (see FIG. 4 ).

The two photodiodes 31 and 32 respectively sense the optical signals output from the first edge filter 21 and the second edge filter 22 to output an electrical signal. The two driving and signal processing circuits 33 and 34 are The photodiodes 31 and 32 are driven, respectively, and analog-digital converted values are respectively output from the electrical signals output by the photodiodes 31 and 32 and provided to the processing unit 35, and some or all of these functions are processed. It may be configured inside the unit 35 . The processing unit 35 generally controls each component of the optical wavelength measuring device, and may be implemented as an MPU, CPU, microcontroller, application processor, or the like, or implemented as an FPGA or ASIC. In particular, the processing unit 35 derives the wavelength of the optical signal to be measured using the analog-to-digital converted values in the two driving and signal processing circuits 33 and 34 and the following table.

The comparator 30 stores therein a table in which a one-to-one correspondence relationship between a plurality of optical power ratios and a plurality of wavelengths is predefined and stored, and as an equivalent alternative, it is provided in the form of an equation in an execution program or an execution program It may be provided in the form of an algorithm within.

For example, the table may configure the table as shown in Table 1 below, such as matching the wavelength of λ1 to -30db and the wavelength of λ2 to -20dB.

light power ratio -30dB -20dB -10dB 10dB 20dB 30dB wavelength
λ1 λ2 λ3 λ4 λ5 λ6

In this table, the optical power ratio and the number of wavelengths may be sufficiently larger, and when the measured optical power ratio is located between specific optical power ratios in the table, the wavelength may be calculated using an interpolation method or the like.

Meanwhile, such a table may be generated or corrected during the production process of the optical wavelength measuring device and stored. By sequentially inputting a known light source of a single wavelength, the comparator measures the optical power ratio while providing the test light, and the correspondence between the optical power ratio and the wavelength can be set according to the actual edge filter characteristics. In this way, there is an effect of increasing the degree of freedom in managing the tolerance during the production process of the edge filter, such as perfectly aligning the characteristics of the two edge filters used.

The comparator obtains the wavelength of the corresponding optical signal to be measured from the optical power ratio of the optical signal output from the first edge filter 21 to the optical signal output from the second edge filter 22 using this table.

In a logarithmic scale, the optical power ratio ( _{Po_ratio ) (dB) is the difference between the optical power (Po_1} ) (dBm) of the optical signal output from the first edge filter 21 and the optical signal output from the second edge filter 22 . It can be obtained by subtracting the optical power (P _{o_2 ) (dBm).} The optical power ratio on the non-log scale may be obtained by dividing the optical power of the optical signal output from the first edge filter 21 and the optical power of the optical signal output from the second edge filter 22 .

In the optical wavelength measuring apparatus according to the first embodiment of the present invention, the input optical signal is output through the edge filters 1 and 2 having opposite transmission characteristics after being branched through a 50:50 coupler, and Ratio P _{o_ratio} (dB) = P _{o_1} - P _{o_2} can be measured and calculated. Since P _{o_ratio} has a constant value according to the wavelength of the input optical signal, the wavelength of the input optical signal can be obtained by measuring the _{P o_ratio value.}

6 is a block diagram illustrating an optical wavelength measuring apparatus according to a second embodiment of the present invention, and FIG. 7 is a schematic diagram showing the edge filter 20 in more detail in the optical wavelength measuring apparatus according to the second embodiment of the present invention. to be. 8 is a graph illustrating transmission characteristics and reflection characteristics of an edge filter used in an optical wavelength measuring apparatus according to a second embodiment of the present invention.

In the optical wavelength measuring apparatus according to the second embodiment of the present invention, a single edge filter 20 is used to achieve the same effect as using two edge filters.

The single optical edge filter 20 receives an optical signal to be measured and outputs a transmitted optical signal and a reflected optical signal, respectively, having a first slope S1 in the characteristic of change in transmittance according to wavelength in a predetermined wavelength range, It has a second slope S2 in the characteristic of change of reflectivity according to wavelength. In the edge filter, the transmitted optical signal and the reflected optical signal are divided and output. All or most of the optical signals other than the transmitted optical signal can be reflected without loss. The edge filter 20 exhibits transmission and reflection characteristics as shown in FIG. 8 , and the optical wavelength can be measured even with the structure of FIG. 6 including only a single edge filter.

Since the structure and function of the comparator 30 are the same as or similar to those of the optical wavelength measuring apparatus according to the first embodiment, only the photodiodes 31 and 32 will be shown and briefly described below, without specific illustration.

The comparator 30 includes two photodiodes 31 and 32 (hereinafter, referring to FIG. 4) for sensing a transmitted optical signal and a reflected optical signal, respectively; two driving and signal processing circuits 33 and 34 for driving the photodiodes 31 and 32 and outputting analog-digital converted values from the electrical signals output from the photodiodes 31 and 32, respectively; The analog-to-digital converted value and the above table may be used to derive the wavelength of the optical signal to be measured, the processing unit 35 may be configured to include.

The comparator 30 obtains the wavelength of the optical signal to be measured using the optical power ratio of the transmitted optical signal and the reflected optical signal output from the edge filter 20, and the optical power ratio is output from the edge filter 22 It can be obtained by subtracting the optical power (log scale) of the transmitted optical signal and the optical power (log scale) of the reflected optical signal output from the edge filter 20 . The comparator 30 includes a table in which a one-to-one correspondence relationship between a plurality of optical power ratios and a plurality of wavelengths is defined and stored in advance. Using this table, a corresponding table is provided from the optical power ratio of the transmitted optical signal and the reflected optical signal. Obtain the wavelength of the optical signal to be measured.

Conventional optical spectrum analyzers, spectral measuring devices using diffraction gratings and linear image sensors, etc. require very precise optical alignment, and have a disadvantage in that the manufacturing cost is very high because the elements constituting the device are expensive.

On the other hand, in the optical wavelength measuring device according to the present invention, the configuration of the device such as a 50:50 coupler, an edge filter, and a photodiode is very simple, and there is no need for fine optical alignment, so it can be easily implemented. Although the optical wavelength measuring device according to the present invention cannot measure the optical wavelength with very high precision like an optical spectrum analyzer, it can be implemented as a low-cost portable device, so it is very effectively applied in applications that do not require high precision, such as wavelength analysis of WDM channels. It is possible.

10: optocoupler 20, 21, 22: optical edge filter
30: comparator 31, 32: photodiode
33, 34: driving and signal processing circuit
35 processing unit

Claims (10)

an optical coupler 10 for receiving an optical signal to be measured and branching it into two output optical signals;
a first edge filter 21 having a first slope S1 in a characteristic of a change in transmittance according to wavelength in a predetermined wavelength range and receiving one of the output optical signals output from the optocoupler 10;
The second edge filter 22 has a second slope S2 in the characteristic of a change in transmittance according to wavelength in the same wavelength range as the predetermined wavelength range, and receives the other one of the output optical signal output from the optocoupler 10 . );
A comparator 30 for obtaining the wavelength of the optical signal to be measured using the optical power ratio between the optical signal output from the first edge filter 21 and the optical signal output from the second edge filter 22; includes,
The first slope and the second slope, characterized in that having a slope in opposite directions to each other,
Optical wavelength measuring device using edge filter. The method according to claim 1,
The optocoupler 10 is a 3dB coupler,
Optical wavelength measuring device using edge filter. The method according to claim 1,
The optical power ratio,
Obtained by subtracting the optical power (log scale) of the optical signal output from the first edge filter 21 and the optical power (log scale) of the optical signal output from the second edge filter 22,
Optical wavelength measuring device using edge filter. The method according to claim 1,
The comparator 30 is
and a table in which a one-to-one correspondence relationship between a plurality of optical power ratios and a plurality of wavelengths is predefined and stored,
Obtaining the wavelength of the corresponding optical signal to be measured from the optical power ratio of the optical signal output from the first edge filter 21 and the optical signal output from the second edge filter 22 using the table ,
Optical wavelength measuring device using edge filter. 5. The method according to claim 4,
The table is generated by measuring the optical power ratio in the comparator 30 while providing test light in a manner of sequentially inputting a single wavelength light source whose wavelength is known in advance during production
Optical wavelength measuring device using edge filter. 5. The method according to claim 4,
The comparator 30 is
two photodiodes (31 and 32) for sensing optical signals output from the first edge filter (21) and the second edge filter (22), respectively; two driving and signal processing circuits (33, 34) for driving the photodiodes (31,32) and outputting analog-digital converted values from the electrical signals output by the photodiodes (31,32), respectively; and a processing unit (35) for deriving the wavelength of the optical signal to be measured using the analog-to-digital converted value and the table;
Optical wavelength measuring device using edge filter. In a predetermined wavelength range, it has a first slope (S1) in the characteristics of change in transmittance according to wavelength and a second slope (S2) in characteristics of change in reflectivity according to wavelength, and receives an optical signal to be measured and transmits a transmitted light signal and reflected light. an edge filter 20 for outputting a signal, respectively;
and a comparator (30) for obtaining the wavelength of the optical signal to be measured by using the optical power ratio of the transmitted optical signal and the reflected optical signal output from the edge filter (20);
Optical wavelength measuring device using edge filter. 8. The method of claim 7,
The optical power ratio,
Obtained by subtracting the optical power (log scale) of the transmitted optical signal output from the edge filter 22 and the optical power (log scale) of the reflected optical signal output from the edge filter 20,
Optical wavelength measuring device using edge filter. 8. The method of claim 7,
The comparator 30 is
and a table in which a one-to-one correspondence relationship between a plurality of optical power ratios and a plurality of wavelengths is predefined and stored,
obtaining the corresponding wavelength of the optical signal to be measured from the optical power ratio of the transmitted optical signal and the reflected optical signal using the table;
Optical wavelength measuring device using edge filter. 10. The method of claim 9,
The comparator 30,
two photodiodes (31 and 32) for sensing the transmitted light signal and the reflected light signal, respectively; two driving and signal processing circuits (33,34) for driving the photodiodes (31,32) and outputting analog-digital converted values from the electrical signals output by the photodiodes (31,32), respectively; and a processing unit (35) for deriving the wavelength of the optical signal to be measured using the analog-to-digital converted value and the table;
Optical wavelength measuring device using edge filter.

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