JPH045575A - Optical spectrum analyzer - Google Patents

Abstract

PURPOSE:To continuously and accurately calculate the frequency of an input signal by interpolating the signal of a detecting element which adjoins to a detecting element indicating the peak signal of a photodetector and finding an offset frequency, and correcting the frequency indicating the peak signal. CONSTITUTION:Light emitted by a light source 1 is diffracted according to the frequency of an RF signal inputted to an optical modulator 3 and focused on a corresponding detecting element of the linear photodetector 6. Then a peak detecting circuit 11 determines the detecting element which indicates the peak signal and a frequency calculating circuit 12 calculates the frequency of the RF signal which varies continuously. A sum circuit 14 corrects the offset frequency based upon the interpolation of the output signals of adjacent detecting elements on both sides of the detecting element indicating the peak signal from the circuit 11 by an interpolating circuit 11 to continuously and accurately calculate and output the input signal frequency having no offset error.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical spectrum analyzer, and more particularly to an optical spectrum analyzer that can accurately detect the frequency or input level of an input RF signal.

[Conventional technology]

FIG. 6 shows, for example, a microwave journal (Mic
rowave Journal, March 198
6+ p141-157), this optical spectrum analyzer detects the frequency of an input RF signal. In the figure, 1 is a light source, 2 is a collimating lens that converts the incident light 7 from the light source 1 into parallel light, 3 is an optical modulator that diffracts the light according to the input RF signal IO, and 4 is the light that has passed through the optical modulator 3. 5 is an absorber that absorbs undiffracted light 8 of the light that has passed through the optical modulator 3; 6 is a linear light detector that detects the diffracted light 9 of the light that has passed through the optical modulator 3; vessel, 1
1 is a peak detection circuit that detects a peak signal from the output signal from the photodetector 6, and 12 is a frequency calculation circuit that calculates and outputs a frequency corresponding to the element of the photodetector that outputs the peak signal.

Next, the operation will be explained.

Light emitted from a light source 1 is turned into parallel light by a collimating lens 2, and enters an optical modulator 3. Optical modulator 3 is input RF
A portion of the input light 7 is diffracted by an angle proportional to the frequency f in of the signal 10Si, . The diffracted light 9 and the undiffracted light 8 pass through the condensing lens 4 and are condensed onto the focal plane. this house,
The undiffracted light 8 is absorbed by the absorber 5. On the other hand, the diffracted light 9 is detected by a linear photodetector 6 placed on the focal plane. Output signal S from photodetector 6. , , , are the detection outputs of the respective elements of the photodetector arranged in series as shown in FIG. In the figure, 0...k...n-1 are numbers indicating the order of the elements of the photodetector. The peak detection circuit 11 determines the peak position from this S out and determines the element that outputs it. As mentioned above, the diffraction angle of the diffracted light is proportional to the input RF signal frequency f = n, so the input frequency f
, A, the element position of the detector 6 on which the diffracted light is focused also differs. From the above, the frequency calculation circuit 12 calculates the frequency r in of the input RF signal inversely from the photodetector element position indicating the peak value of 5out determined by the peak detection circuit.

Figure 8 shows the same (micro unit journal (Mic)
rowave Journal, March 198
6. This shows the conventional optical spectrum analyzer shown on pages 141 to 157), and this optical spectrum analyzer detects the input RF multiplied signal signal level.

In the figure, the same reference numerals as in FIG. 6 indicate the same or corresponding parts, and 120 is a circuit that calculates the input signal level from the peak signal value and outputs it.

Next, the operation will be explained.

Light emitted from a light source 1 is turned into parallel light by a collimating lens 2, and enters an optical modulator 3. Optical modulator 3 has input R
A portion of the incident light 7 is diffracted by an amount proportional to the input RF power P87 in an angular direction proportional to the frequency f in of the F signal 10Si. The diffracted light 9 and the undiffracted light 8 pass through the condensing lens 4 and are condensed onto the focal plane. Of these, 8 undiffracted lights
is absorbed by the absorber 5. On the other hand, the diffracted light 9 is detected by a linear photodetector 6 placed on the focal plane. Output signal S from photodetector 6. U, is the detection output of each element of the photodetector arranged in series as shown in FIG.

In the figure, 0...k...n-1 are numbers indicating the order of the elements of the photodetector. The peak detection circuit 11 is this S. ut
The peak position is then determined and the element that outputs it is determined. As mentioned above, since the intensity of the diffracted light is proportional to the input RF power, the photodetector 60 level is also proportional to the input RF signal power. From the above, S determined by the peak detection circuit in the input level calculation circuit 120. ut
The level of the input RF signal can be determined conversely from the peak value of .

By the way, when the frequency f in of the RF input signal S in is continuously changed with the same power, the focal position of the diffracted light 9 changes continuously, so when focusing on a certain element of the photodetector 6, its output When the signal level is plotted with f87 on the horizontal axis and the level on the vertical axis, a curve shown in FIG. 10(a) is drawn. When this is determined for all elements of the photodetector 6, it is shown in Fig. 10 (
A group of curves shown in b) is obtained. A curve connecting these individual peaks shows the frequency characteristics of the output level. One peak is the band covered by one element of the photodetector 6, and if the frequency band of the input signal is 8 and the number of elements of the photodetector is n, then B/
It becomes n.

[Problem to be solved by the invention]

Since the conventional optical spectrum analyzer is configured as described above, if the frequency band of the input signal Si, , is B and the number of elements of the photodetector is n, the frequency corresponding to each element is fo + -B /n (however, k=o~n1.fo
is the frequency corresponding to the element with element number 0), and B /
This means that they are discretely arranged every n, and the frequency is the detection frequency f. There is a problem in that the detection frequency fout is accompanied by an uncertainty of B/2n.

Furthermore, since the conventional optical spectrum analyzer is constructed as described above, ripples occur in the photodetector output level, as shown in FIG. 10, regardless of the RF signal input at the same level. Therefore, due to the proportional relationship, the input R
There is also a problem in that an error occurs due to this ripple when calculating the F signal level.

This invention was made to solve the above-mentioned problems, and the detection frequency f. An object of the present invention is to obtain an optical spectrum analyzer that can continuously determine ut with high accuracy.

Moreover, this invention was made to solve the above-mentioned problems, and the detection level is P. An object of the present invention is to obtain an optical spectrum analyzer that can accurately determine ut.

[Means to solve the problem]

The optical spectrum analyzer according to the present invention calculates the offset frequency from the frequency corresponding to the element exhibiting the peak signal by performing interpolation processing using the signals of the elements adjacent to the element exhibiting the peak signal, and uses the offset frequency to obtain the peak signal. It is equipped with means for correcting the frequency corresponding to the element indicating the signal.

Further, the optical spectrum analyzer according to the present invention calculates a correction value for the peak signal value of the photodetector by performing interpolation processing using the signal of the element adjacent to the element showing the peak signal, and uses the correction value to detect the photodetector. The device is equipped with means for correcting the peak signal value of the device.

[Effect]

In this invention, an offset frequency from the frequency corresponding to the element exhibiting the peak signal is obtained by interpolation processing using the signal of the element adjacent to the element exhibiting the peak signal, and the offset frequency of the element exhibiting the peak signal is determined by the offset frequency. Since the frequency corresponding to f is corrected, the detected frequency f. uL can be determined continuously and accurately.

Further, in the present invention, a correction value for the peak signal value of the photodetector is obtained by performing interpolation processing using the signal of the element adjacent to the element showing the peak signal, and the correction value is used to generate the peak signal of the photodetector. Since the value is corrected, the detection level is P. This is to obtain uL with high accuracy.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an optical spectrum analyzer according to a first embodiment of the present invention. In the figure, 1 is a light source, 2 is a collimating lens that converts incident light 7 from the light source 1 into parallel light, and 3 is a collimating lens. An optical modulator that diffracts light according to the RF input signal 10; 4 a condensing lens that condenses the light that has passed through the optical modulator; 5 an absorber that absorbs non-diffracted light 8 of the light that has passed through the optical modulator 3; 6 is a linear photodetector that detects the diffracted light 9 out of the light that has passed through the optical modulator 3; 11 is a peak detection circuit that detects a peak signal from the output signal from the photodetector 6;
12 is a frequency calculation circuit that calculates and outputs a frequency corresponding to the element of the photodetector that outputs the peak signal; 13 is a frequency calculation circuit that calculates and outputs an offset frequency by interpolation processing from the signal level of an element adjacent to the element exhibiting the peak signal; The interpolation processing circuit 14 is an addition circuit that calculates the sum of the frequency obtained by the frequency calculation circuit 12 and the frequency obtained by the interpolation processing circuit 13 and outputs the sum.

Next, the operation will be explained.

The diffracted light 9 focused by the condensing lens 4 is transmitted to the photodetector 6
Focus on the top. RF input signal S8. , the frequency f, ,
, the focal position of this diffracted light changes continuously. Therefore, when focusing on a certain element of the photodetector 6, its output signal level is expressed by fkn on the horizontal axis and level on the vertical axis. When taken, a curve as shown in FIG. 2(a) is drawn.

When this is determined for all elements of the photodetector 6, it is shown in Figure 2 (
A group of curves shown in b) is obtained. In the figure, 0...n-1 are element numbers of the photodetector, and fo...f, -1 are frequencies assigned to each element, which are discrete as shown in the figure. Conventionally, the frequency corresponding to the element exhibiting the peak signal was used as the detection frequency, so discrete values were calculated.

Now, when the curve group shown in FIG. 2(b) is approximated by a straight line, it becomes as shown in FIG. 2(C). Frequency fifi (fk-
When a signal of +<f, -<fk-+) is input, as shown in FIG. 2(C), the element numbered indicates a peak level 1. At this time, the adjacent number is -1,k+
Element 1 has two signals vk-□ and V whose level corresponds to the deviation of fin from fk. 1 is output, but the level difference δV =Vs=-+Vk-+ is proportional to the offset frequency δf=fi-fk, as is clear from the figure. That is, conversely, the offset frequency δf is determined from the level difference δ■, and the input frequency is determined from the sum of this and the frequency fk corresponding to the element exhibiting the peak level.

In the above embodiment, a case has been described in which the output signal from the photodetector 6 is directly processed, but as in a modification of this embodiment shown in FIG. When the curves shown in FIG. 2(b) are outputted through
It may be approximated by a Gaussian function + k −B / n (k = O to n −1). Then, in the logarithmic amplifier output, the level difference δ■ after the logarithmic amplifier 15 output of the element adjacent to the element indicated by the peak signal is δV = V
k++ Vm-+ = 4 b-B/nδf, which is proportional to the offset frequency δf.

Next, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a diagram showing the configuration of an optical spectrum analyzer according to a second embodiment of the present invention. In the figure, 1 is a light source, 2 is a collimating lens that converts the incident light 7 from the light source 1 into parallel light, and 3 is a collimating lens. An optical modulator that diffracts light according to the RF input signal 10; 4 a condenser lens that condenses the light that has passed through the optical modulator; 5 that absorbs non-diffracted light 8 of the light that has passed through the optical modulator 3; Absorber 6 is the light that has passed through the optical modulator 3.
A linear photodetector detects the diffracted light 9, 11 is a photodetector 6
a circuit for detecting a peak signal from an output signal from 120;
130 is a circuit that calculates and outputs the input signal level from the correction value of the peak signal value, and 130 is a circuit that calculates and outputs the correction value of the peak signal value by interpolation processing from the signal level of the element adjacent to the element showing the peak signal. be.

Next, the operation will be explained.

If the group of curves shown in FIG. 10(b) shown in the description of the conventional example is approximated by straight polygonal lines, the result will be as shown in FIG. 10(c). -1, ni and +1 in the figure are the element numbers of the photodetector, fk-0+ fk+ rk++ are the input signal frequencies corresponding to the peak values of each approximation function, and correspond to the cross points Ok of adjacent approximation functions. frequency. Also, F (r-rk-,), F (ffk), F
(f−fk,,) indicates an approximation function assigned to each element characteristic. Frequency fin (fk-1<r6,<fm-+
) When a signal of ) is input, as shown in FIG. 10(C), the element numbered indicates a peak level ①A. At this time, flFl is f for the adjacent numbered elements -1 and k+1,
The level of the signal Vm-+ corresponds to the deviation from Vi
=. 1 is output, and the level difference δV=V. l
As is clear from the figure, Vk-1 is proportional to the offset frequency δf=f i++-r k. In other words, on the contrary, the offset frequency δf is greater than the level difference δ■.
is determined, and the input frequency f in is determined from the sum of this and the frequency fk corresponding to the element exhibiting the peak level. Furthermore, from this f in and the above approximation function F (f-fk), the ratio of V, (fmf, .) to the peak value (fmfk) (this becomes a correction coefficient) is determined. According to this ratio■
and calculate the input signal level after correction.

In the above embodiment, a case has been described in which the output signal from the photodetector 6 is directly processed, but as in a modification of this embodiment shown in FIG. In the case of output through the curve group shown in FIG. 10(b), -b (f-fklfk=f0+
can be approximated by a Gaussian function -B/n (k=o to n-1). Then, in the logarithmic amplifier output, the logarithmic amplifier 14 of the element adjacent to the element exhibiting the peak signal
The level difference δ■ after output is δV"'Vh, + ¥ - +
=4b-B/n·δf, which is proportional to the offset frequency δf.

〔Effect of the invention〕

As described above, according to the present invention, the offset frequency is determined by interpolation using the signal of the element adjacent to the element showing the peak signal of the photodetector, and the frequency corresponding to the element showing the peak signal is corrected. This has the effect that the input signal frequency can be calculated continuously and accurately.

Further, as described above, according to the present invention, the offset frequency is determined by interpolation using the signal of the element adjacent to the element indicating the peak signal of the photodetector, and the peak signal value is corrected. Therefore, there is an effect that the input signal level can be calculated with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an optical spectrum analyzer according to a first embodiment of the present invention, FIG. 2 is a diagram showing output characteristics of a photodetector for explaining the principle of the first embodiment of the present invention, and FIG. 3 shows a modification of the first embodiment, FIG. 4 shows an optical spectrum analyzer according to the second embodiment of the invention, and FIG. 5 shows a modification of the second embodiment. Figure 6 shows an example of a conventional optical spectrum analyzer, Figure 7 shows an example of a conventional optical spectrum analyzer.
The figure shows the output of a photodetector to explain the principle of the conventional example shown in Fig. 6, Fig. 8 shows another example of the conventional optical spectrum analyzer, and Fig. 9 shows the conventional example shown in Fig. 8. FIG. 10 is a diagram showing the output of the photodetector for explaining the principle of the example, and FIG. 10 is a diagram showing the output characteristics of the photodetector for explaining the conventional example and the second embodiment of FIG. 1 is a light source, 2 is a collimating lens, 3 is a light modulator, 4 is a condensing lens, 5 is a light absorber, 6 is a linear photodetector, 7 is incident light, 8 is non-diffracted light, 9 is diffracted light, 10 is an input signal,
11 is a peak detection circuit, 12 is a frequency calculation circuit, 13 is an interpolation circuit, 14 is a summation circuit, 15 is a logarithmic amplifier, 120 is an input signal level calculation circuit, and 130 is an interpolation circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) It has an optical modulator that diffracts the light emitted from the light source according to the input RF signal, and a plurality of linearly arranged photodetecting elements, and the light is diffracted by the optical modulator and guided by the optical system. a photodetector that detects the light detected by the light; a peak detection circuit that detects an element exhibiting a peak signal among the plurality of photodetection elements; and a frequency calculation that outputs a frequency corresponding to the element detected by the peak detection circuit. The output of the frequency calculation circuit is corrected by interpolation processing using the circuit and the signal of the element adjacent to the element indicating the peak signal of the photodetector, and the input R
An optical spectrum analyzer comprising: interpolation processing means for determining the frequency of the F signal. (2) It has an optical modulator that diffracts the light emitted from the light source according to the input RF signal, and a plurality of linearly arranged photodetecting elements, and the light is diffracted by the optical modulator and guided by the optical system. a photodetector that detects the light detected by the photodetector, a peak detection circuit that detects an element exhibiting a peak signal among the plurality of photodetection elements, and an input level calculator that outputs a signal level of the element detected by the peak detection circuit. interpolation processing using a circuit and a signal of an element adjacent to the element indicating the peak signal of the photodetector, correcting the output of the input level calculation circuit, and determining the signal level of the input RF signal; An optical spectrum analyzer characterized by comprising means.