Optical spectrum analyzer

Abstract

To provide an optical spectrum analyzer with high resolving power.SOLUTION: An optical spectrum analyzer comprises: generation means that generates continuous light, in which the generation means is configured to enable changing a frequency of the continuous light; multiplex means that multiplexes observation object light and the continuous light in a frequency band to thereby output multiplex light including the observation object light and the continuous light; a nonlinear medium that allows the multiplex light to pass; filter means that allows a component of a band of the observation object light of the multiplex light passing through the nonlinear medium to pass; and measurement means that measures power of light the filter means outputs.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to an optical spectrum analyzer. [Background Art]

[0002] In recent years, many reports have been made on optical parametric oscillation in integrated devices such as silicon and silicon nitride. Non-Patent Document 1 and Non-Patent Document 2 disclose a configuration that generates signal light and idler light separated by hundreds of THz from pump light through optical parametric oscillation. [Prior Art Documents] [Non-Patent Documents]

[0003] [Non-Patent Document 1] Xiyuan Lu, et.al., "Milliwatt-threshold visible-telecom optical parametric oscillation using silicon nanophotonics", Optica 6, 1535-1541, 2019 [Non-Patent Document 2] Renato R. Domeneguetti, et.al., "Parametric sideband generation in CMOS-compatible oscillators from visible to telecom wavelengths", Optica 8, 316-322, 2021 [Summary of Invention] [Problem to be Solved by Invention]

[0004] Currently, the frequency resolution of optical spectrum analyzers is on the order of several GHz, and an optical spectrum analyzer with higher resolution is desired.

[0005] The present disclosure provides a high-resolution optical spectrum analyzer. [Means for solving the problem]

[0006] According to one aspect of the present disclosure, an optical spectrum analyzer includes a generating means for generating continuous light, configured to change the frequency of the continuous light; a multiplexing means for multiplexing the observed light and the continuous light in the frequency domain to output multiplexed light including the observed light and the continuous light; a nonlinear medium through which the multiplexed light passes; and the observed light among the multiplexed light that has passed through the nonlinear medium. all The system includes a filtering means for passing components of a certain frequency band, and a measuring means for measuring the power of the light output by the filtering means. [Effects of the Invention]

[0007] According to this disclosure, a high-resolution optical spectrum analyzer is provided. [Brief explanation of the drawing]

[0008] [Figure 1] A diagram showing an example of how the amount of phase mismatch changes with frequency. [Figure 2] This diagram shows the relationship between the frequency of the pump light and the frequency at which the phase mismatch is zero. [Figure 3] Configuration diagram of an optical spectrum analyzer. [Figure 4] A diagram showing multiplexed light before and after a nonlinear medium. [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more features from the multiple features described in the embodiments may be combined arbitrarily. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted.

[0010] Before describing the embodiments, an overview of optical parametric oscillation will be provided.

[0011] Optical parametric oscillation is a method of generating a signal light of frequency fs and an idler light of frequency fi by injecting a pump light of frequency fp into a nonlinear medium such as an optical integrated device using silicon (Si) or silicon nitride (Si3N4). Optical parametric oscillation occurs in the frequency (wavelength) region where the phase mismatch of the three lights—the pump light, the signal light, and the idler light—is close to zero. The sum of the frequencies of the signal light and the idler light (fs + fi) is twice the frequency fp of the pump light. The amount of phase mismatch is determined by the transmission parameters of the nonlinear medium used for optical parametric oscillation, such as the dispersion value. In other words, the frequency fs of the signal light and the frequency fi of the idler light generated in optical parametric oscillation are determined by the nonlinear medium used for optical parametric oscillation and the frequency fp of the pump light. Optical parametric oscillation can also be generated by utilizing the nonlinearity of optical fibers, in addition to optical integrated devices.

[0012] For example, as shown in Figure 1, if a pump light of a fixed frequency fp is input to a predetermined nonlinear medium, the phase mismatch amount moves away from 0 as the frequency difference with frequency fp increases, but then approaches 0. In the first frequency region, where the phase mismatch amounts on both sides of frequency fp are far from 0, optical parametric oscillation does not occur, and therefore, signal light / idler light of frequencies within the first frequency region is not generated. However, in the second frequency region, where the frequency difference with frequency fp is larger than in the first frequency region and the phase mismatch amount is close to 0, optical parametric oscillation occurs, and therefore, signal light / idler light of frequencies within the second frequency region can be generated. The reason why the phase mismatch amount approaches 0 in the second frequency region is due to dispersion of order 4 or higher in the nonlinear medium. Non-patent documents 1 and 2 disclose that optical parametric oscillation due to this dispersion of order 4 or higher generates signal light of frequency fs and idler light of frequency fi, which are several hundred THz apart from the pump light frequency fp.

[0013] Furthermore, the frequency range of the second frequency domain is extremely narrow, and therefore the signal light (idler light) is extremely narrowband, for example, on the order of several hundred MHz. Also, when calculating the relationship between the frequency fp of the pump light and the frequency at which the phase mismatch becomes zero due to dispersion of the fourth order or higher, the slope is greater than 1, as shown in Figure 2. This means that if the frequency of the pump light is changed by Δf, the frequency of the signal light (idler light) changes by αΔf (α corresponds to the slope in Figure 2 and is greater than 1). In other words, if the frequency of the pump light is changed by Δf, the change in the frequency of the signal light (idler light) is greater than Δf.

[0014] Based on the above findings, the inventors have completed the present invention. The details of this embodiment are described below.

[0015] Figure 3 is a diagram of the configuration of an optical spectrum analyzer according to this embodiment. The variable light source 10 generates continuous light of frequency fp and outputs it to the multiplexer 20 as pump light. The variable light source 10 can change the frequency fp of the continuous light it generates. In other words, the frequency fp is not a fixed value, but a changeable value. The light observed by the optical spectrum analyzer (hereinafter referred to as the observed light) is input to the multiplexer 20 via the polarization control unit 60. The polarization control unit 60 is provided to match the polarization plane of the observed light to the polarization plane of the pump light. Alternatively, the polarization control unit 60 may be placed between the variable light source 10 and the multiplexer 20, and the polarization plane of the pump light may be adjusted to match the polarization plane of the pump light and the polarization plane of the observed light. Alternatively, the arrangement of the variable light source 10 may be adjusted to match the polarization plane of the pump light and the polarization plane of the observed light, in which case the polarization control unit 60 may be omitted.

[0016] The multiplexing unit 20 combines the pump light and the observed light to output the first multiplexed light to the nonlinear medium 30. Figure 4(A) shows the first multiplexed light output by the multiplexing unit 20 to the nonlinear medium 30. The first multiplexed light includes the pump light 80 and the observed light 90. In Figure 4(A), reference numeral 81 indicates the signal light generated by optical parametric oscillation in the nonlinear medium 30 using the pump light with frequency fp.

[0017] Due to the optical parametric oscillation in the nonlinear medium 30, components of the observed light 90 other than the band in which the signal light 81 is generated are attenuated, so that only the component corresponding to the band in which the signal light 81 is generated is output from the nonlinear medium 30. Therefore, the second multiplexed light output from the nonlinear medium 30 is as shown in Figure 4(B). In Figure 4(B), reference numeral 82 denotes the filtered light, which is the portion of the observed light 90 in which the signal light 81 is generated. As described above, the bandwidth of the signal light 81 is on the order of several hundred MHz, and therefore the bandwidth of the filtered light 82 is also on the order of several hundred MHz. The power of the filtered light 82 depends on the power of the component in the band in which the signal light 81 is generated within the observed light 90 and the gain of the optical parametric oscillation. Note that in Figure 4, the power of the pump light 80 for the first multiplexed light (Figure 4(A)) and the power of the pump light 80 for the second multiplexed light (Figure 4(B)) are shown in the same way, but the power of the pump light 80 can also fluctuate in the nonlinear medium 30.

[0018] The separation unit 40 is configured to extract a component of the second multiplexed light within a predetermined band, including at least the band of the observed light 90, and output it to the power measurement unit 50. The predetermined band is set so as not to include the pump light 80 and the idler light (not shown in Figure 4). In other words, the separation unit 40 performs filtering to attenuate (remove) the pump light 80 and the idler light (not shown in Figure 4) included in the second multiplexed light, and outputs the filtered second multiplexed light to the power measurement unit 50. The filtered second multiplexed light contains only the filtered light 82. Therefore, the power measurement unit 50 measures the power of the component in the band where the signal light 81 of the observed light 90 is generated.

[0019] As described above, changing the frequency of the pump light 80 also changes the frequency fs of the signal light 81. Therefore, changing the frequency of the pump light 80 also changes the frequency of the filtered light 82. This allows sweeping of the observation target light 90 and analysis of the frequency components of the observation target light 90 with high resolution. Note that, as described above, when the frequency of the pump light 80 is changed by Δf, the frequency of the signal light 81, that is, the frequency of the filtered light 82, is changed by αΔf (where α is greater than 1). Therefore, even if the bandwidth of the observation target light 90 is larger than the range in which the frequency can be changed in the variable light source 10, frequency analysis of the observation target light 90 can be performed.

[0020] Note that, as described above, the power of the filtered light 82 depends on the power of the component in the band where the signal light 81 is generated among the observation target light 90, and the gain of optical parametric oscillation. Therefore, by obtaining the gain of optical parametric oscillation in advance, the power for each frequency component (depending on the bandwidth of the signal light 81) of the observation target light 90 can be measured.

[0021] Note that in the present embodiment, the frequency fs of the signal light 81 is swept in the band of the observation target light 90, but a configuration in which the frequency fi of idler light is swept in the band of the observation target light 90 may also be adopted.

[0022] As described above, a high-resolution optical spectrum analyzer is realized by utilizing optical parametric oscillation in the nonlinear medium 30. The nonlinear medium 30 is configured to generate optical parametric oscillation based on the pump light 80 included in the first multiplexed light. Preferably, the nonlinear medium 30 is configured to generate optical parametric oscillation based on dispersion of the fourth order or higher. The variable light source 10 is configured to be able to change the frequency of the continuous light within the range from the first frequency to the second frequency. When the variable light source 10 changes the frequency of the continuous light within the range from the first frequency to the second frequency, the nonlinear medium 30 is configured such that the range in which the frequency of the signal light or idler light generated by the optical parametric oscillation based on the pump light 80 changes includes the bandwidth of the observed light 90. Alternatively, the variable range of the frequency in the variable light source 10 is set so that the frequency of the signal light or idler light generated by the optical parametric oscillation based on the pump light 80 can be changed within a range that includes the bandwidth of the observed light 90.

[0023] With the above configuration, a high-resolution optical spectrum analyzer can be provided. Therefore, it will be possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0024] The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention. [Explanation of Symbols]

[0025] 10: Variable light source, 20: Multiplexing unit, 30: Nonlinear medium, 40: Separation unit, 50: Power measurement unit

Claims

1. A generating means for generating continuous light, the generating means configured to be capable of changing the frequency of the continuous light, Multiplexing means that outputs multiplexed light including the observed light and the continuous light by multiplexing the observed light and the continuous light in the frequency domain, A nonlinear medium through which the multiple light beams pass, A filter means that allows the entire bandwidth component of the observed light among the multiplexed light that has passed through the nonlinear medium to pass through, A measuring means for measuring the power of light output by the aforementioned filter means, An optical spectrum analyzer equipped with [this feature].

2. The optical spectrum analyzer according to claim 1, wherein the nonlinear medium is configured to generate optical parametric oscillations based on the continuous light contained in the multiplexed light.

3. The optical spectrum analyzer according to claim 2, wherein the nonlinear medium is configured such that the optical parametric oscillation based on the continuous light occurs based on a dispersion of the fourth order or higher.

4. The generating means is capable of changing the frequency of the continuous light within a range from a first frequency to a second frequency. The optical spectrum analyzer according to claim 2, wherein when the frequency of the continuous light is varied within the range from the first frequency to the second frequency, the nonlinear medium is configured such that the range in which the frequency of the signal light or idler light generated by the optical parametric oscillation based on the continuous light changes includes the bandwidth of the light to be observed.

5. The optical spectrum analyzer according to claim 1, wherein the nonlinear medium is an optical integrated device or an optical fiber.

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