Self-heterodyne detection system including optical frequency comb light source

Abstract

This invention provides a self-heterodyne detection system capable of stably and over long periods of time measuring broadband laser linewidths. [Solution] The present invention discloses a self-heterodyne detection system. The system may include a frequency comb light source that generates light, a photodetector that detects the light, an electrical spectrum analyzer connected to the photodetector that analyzes the frequency and wavelength of the light using the detection signal of the photodetector, an interferometer including an input coupler provided between the frequency comb light source and the photodetector to receive the light, a branch waveguide branched by the input coupler, and an output coupler connected to the branch waveguide, and a programmable filter provided in the branch waveguide to select the peak wavelength of the light.

Description

Technical Field

[0001] The present invention relates to an optical detection system, and more particularly to a self-heterodyne detection system including an optical frequency comb light source.

Background Art

[0002] Generally, light sources having excellent spectral stability and narrow linewidth characteristics are usefully used in fields such as coherent optical communication systems, coherent detection, microwave photonics, precision spectroscopy, etc. Requirements for light sources may vary in various application fields. In order to determine the practicality of a light source, a solution that can accurately measure and characterize the light source is essentially required.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The problem to be solved by the present invention is to provide a self-heterodyne detection system capable of stably and long-term measuring a broadband laser linewidth.

Means for Solving the Problems

[0004] The present invention discloses a self-heterodyne detection system. The system includes a light source that generates light, a photodetector that detects the light, a programmable filter provided between the photodetector and the light source, and an electrical spectrum analyzer connected to the photodetector and analyzing the frequency and wavelength of the light using the detection signal of the photodetector. Here, the light source can include an optical frequency comb light source.

[0005] For example, the programmable filter may include a pulse shaping machine.

[0006] For example, the system may further include interferometers provided before and after the programmable filter.

[0007] For example, the interferometer may include a Mach-Zehnder interferometer.

[0008] For example, the interferometer may include an input coupler provided between the light source and the programmable filter, an output coupler provided between the programmable filter and the photodetector, and branch waveguides branched at the input coupler and connected to the output coupler.

[0009] For example, the branch waveguide may include a first branch waveguide and a second branch waveguide parallel to the first branch waveguide.

[0010] For example, the programmable filter may include a first programmable filter provided in the first branch waveguide and a second programmable filter provided in the second branch waveguide.

[0011] For example, each of the first programmable filter and the second programmable filter may include a pulse shaping machine.

[0012] For example, each of the first programmable filter and the second programmable filter may include an optical bandpass filter.

[0013] For example, the photodetector may include a photodiode.

[0014] An example of a self-heterodyne detection system according to the present invention includes a frequency comb light source that generates light, a photodetector that detects the light, an electrical spectrum analyzer connected to the photodetector that analyzes the frequency and wavelength of the light using the detection signal of the photodetector, an input coupler provided between the frequency comb light source and the photodetector to receive the light, an interferometer including a branch waveguide branched by the input coupler and an output coupler connected to the branch waveguide, and a programmable filter provided in the branch waveguide that selects the peak wavelength of the light.

[0015] For example, each of the programmable filters may include a pulse shaper or an optical bandpass filter.

[0016] For example, the branch waveguide may include a first branch waveguide and a second branch waveguide parallel to the first branch waveguide.

[0017] For example, the programmable filter may include a first programmable filter connected to the first branch waveguide and a second programmable filter connected to the second branch waveguide.

[0018] For example, the system may further include a polarization tuner connected to the second branch waveguide between the second programmable filter and the output coupler.

[0019] An example of a self-heterodyne detection system according to the present invention includes a frequency comb light source that generates light, a photodetector that detects the light, an electrical spectrum analyzer connected to the photodetector that analyzes the frequency and wavelength of the light using the detection signal of the photodetector, an input coupler provided between the frequency comb light source and the photodetector to receive the light, an interferometer including a first branch waveguide and a second branch waveguide branched by the input coupler, and an output coupler connected to the first branch waveguide and the second branch waveguide, a first programmable filter and a second programmable filter provided in the first branch waveguide and the second branch waveguide to select the peak wavelength of the light, and a first nonlinear crystal plate provided between the frequency comb light source and the input coupler.

[0020] In one example, a second nonlinear crystal plate may be further included between the programmable filter and the output coupler.

[0021] For example, the first nonlinear crystal plate and the second nonlinear crystal plate may include BBO (Beta Barium Borate), PPKTP (Periodically Poled Potassium Titanyl Phosphate), and PPLN (Periodically Poled Lithium Niobate).

[0022] For example, the first nonlinear crystal plate and the second nonlinear crystal plate may include silicon (Si), silicon nitride (SiN), aluminum gallium arsenide (AlGaAs), or silicon carbide (SiC).

[0023] For example, the system may further include a third programmable filter provided between the output coupler and the photodetector. [Effects of the Invention]

[0024] As described above, the self-heterodyne detection system according to the embodiment of the present invention can stably measure the broadband laser linewidth for a long time by using an optical frequency comb light source.

Brief Description of Drawings

[0025] [Figure 1] It is a drawing showing an example of a general heterodyne detection system. [Figure 2] It is a drawing showing an example of a self-heterodyne detection system according to the concept of the present invention. [Figure 3] It is a drawing showing an example of a self-heterodyne detection system according to the concept of the present invention. [Figure 4] It is a graph showing the frequency comb spectrum of the light, reference light, and measurement light in FIG. 3, the first peak wavelength, the second peak wavelength, and the beating frequency signal. [Figure 5] It is a drawing showing an example of a self-heterodyne detection system according to the concept of the present invention. [Figure 6] It is a drawing showing an example of a self-heterodyne detection system according to the concept of the present invention. [Figure 7] It is a drawing showing an example of a self-heterodyne detection system according to the concept of the present invention.

Embodiments for Carrying Out the Invention

[0026] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The advantages and / or features of the present invention, and the method for achieving them, will become clear by referring to the embodiments described in detail later together with the accompanying drawings. However, the invention is not limited to the embodiments described here and may be embodied in different forms. Rather, the embodiments introduced here are provided so that the disclosed content is thorough, complete, and the idea of the present invention is sufficiently conveyed to those skilled in the art, and the invention is only defined by the scope of the claims. The same reference numerals refer to the same components throughout the specification.

[0027] The terms used herein are for illustrative purposes only and are not intended to limit the invention. In this specification, singular terms include plural terms unless otherwise specified. The terms “comprises” and / or “comprising” as used in this specification do not preclude the presence or addition of one or more other components, operations, and / or elements. Furthermore, as preferred embodiments exist, the reference numerals presented in the order of description are not necessarily limited to that order.

[0028] Furthermore, the embodiments described herein are explained with reference to the cross-sectional and / or plan views, which are ideal illustrative diagrams of the present invention. In the drawings, the thicknesses of the films and regions are exaggerated for the efficient explanation of the technical content. Therefore, the form shown in the illustrative diagrams may be altered due to manufacturing techniques and / or tolerances. Accordingly, the embodiments of the present invention are not limited to the specific forms shown, but also include variations in form brought about by the manufacturing process.

[0029] Figure 1 shows an example of a typical heterodyne detection system 200.

[0030] Referring to Figure 1, a typical heterodyne detection system 200 may include a light source 10, a photodetector 30, an electrical spectrum analyzer 40, an interferometer 50, a polarization tuner 60, a high-frequency oscillator 12, an optical fiber delay 14, and a frequency transition 16. The light source 10 can generate light 11. The light source 10 can generate continuous wave laser light 11. The photodetector 30 can detect light 11. The electrical spectrum analyzer 40 can measure the wavelength components of light 11 using the detected signal of light 11. The interferometer 50 is placed between the light source 10 and the photodetector 30 and can modulate light 11. Light 11 can be isolated by the input coupler 52 of the interferometer 50 and interfered with by the output coupler 54. The polarization tuner 60 and the optical fiber delay 14 can be connected in series to the first branch waveguide 55. The polarization modulator 60 and the optical fiber delay unit 14 can polarize and delay the reference light 13 of the light 11. The frequency transition unit 16 can be connected to the second branch waveguide 57. The frequency transition unit 16 can be connected to the high-frequency oscillator 12. The frequency transition unit 16 can modulate the light 11 to generate modulated light. The high-frequency oscillator 12 can provide a pulse signal to the frequency transition unit 16. The measurement light 15 can be pulsed by the pulse signal. The reference light 13 and the measurement light 15 can be interfered with by the output coupler 54 to generate a beating frequency signal 19.

[0031] Therefore, a typical heterodyne detection system 200 may necessarily include an external pulsed light source for the high-frequency oscillator 12.

[0032] Figure 2 shows an example of a self-heterodyne detection system 100 based on the concept of the present invention.

[0033] Referring to Figure 2, the self-heterodyne detection system 100 of the present invention not only does not use an external reference light 13 signal from a high-frequency oscillator 12, as in a typical heterodyne detection system 200, but can also have a simple structure without a frequency transition unit 16. The self-heterodyne detection system 100 of the present invention can have a very simple in-line self-heterodyne direct detection configuration. The self-heterodyne detection system 100 of the present invention can perform precise spectral analysis as a sufficiently decohered signal by simultaneously filtering the reference light 13 signal and the measurement light signal, and then adding a large delay to the reference light 13 signal to give the two optical signals different delays. For example, the self-heterodyne detection system 100 of the present invention may include a light source 10, a programmable filter 20, a photodetector 30, and an electrical spectrum analyzer 40.

[0034] The light source 10 may include an optical frequency comb light source. The light 11 generated by the light source 10 may have a frequency comb spectrum 17. The frequency comb spectrum 17 may include a wavelength comb spectrum or a comb wavelength, but the present invention is not limited thereto. The frequency comb spectrum 17 may have a center wavelength of 1550 nm. The light source 10 may include an optical frequency comb for evaluating frequency stability. The light source 10 may be a light source in which two or more modes exist and have different frequency components from each other. For example, the light source 10 may include an electro-optic optical frequency comb, a micro-comb, or a mode-locked laser.

[0035] The programmable filter 20 can be installed adjacent to the light source 10. The programmable filter 20 can simultaneously filter the reference light 13 and the measurement light 15 of the light 11 to generate a decoherence signal. The programmable filter 20 can use the light source 10 of the optical frequency comb light source to determine the beating frequency signal 19 according to the repetition rate of the optical frequency comb, and stably measure broadband laser linewidths from narrow to wide linewidths over a long period of time.

[0036] The photodetector 30 can be placed between the programmable filter 20 and the electrical spectrum analyzer 40. The photodetector 30 can detect light 11. For example, the photodetector 30 may include a photodiode.

[0037] The electrical spectrum analyzer 40 can be connected to the photodetector 30. The electrical spectrum analyzer 40 can analyze the photodetection signal to analyze the frequency and wavelength components of the light 11.

[0038] Therefore, the self-heterodyne detection system 100 of the present invention can stably and over a long period of time measure a broadband laser linewidth using the light source 10 of an optical frequency comb light source.

[0039] Figure 3 shows an example of a self-heterodyne detection system 100 according to the concept of the present invention. Figure 4 shows the frequency comb spectra 17, first peak wavelength 21, second peak wavelength 23, and beating frequency signal 19 of the light 11, reference light 13, and measurement light 15 from Figure 3.

[0040] Referring to Figures 3 and 4, the self-heterodyne detection system 100 of the present invention may further include an interferometer 50.

[0041] The interferometer 50 can be installed between the light source 10 and the photodetector 30. The interferometer 50 can transmit and interfere with light 11. For example, the interferometer 50 may include a Mach-Zehnder interferometer. The interferometer 50 can split light 11 having a frequency comb spectrum 17 into a reference light 13 and a measurement light 15, and interfere the reference light 13 and the measurement light 15 to generate a beating frequency signal 19 of light 11. The reference light 13 and the measurement light 15 may each have a first peak wavelength 21 and a second peak wavelength 23. The first peak wavelength 21 and the second peak wavelength 23 may be different from each other. In one example, the interferometer 50 may include an input coupler 52, an output coupler 54, and a branch waveguide 56. The input coupler 52 may be connected to the light source 10. The input coupler 52 can split the light 11 into approximately 1:1 portions and provide them to the branch waveguide 56. The output coupler 54 can be connected to the photodetector 30. The output coupler 54 can cause interference in the light 11 within the branch waveguide 56. The branch waveguide 56 can be provided between the input coupler 52 and the output coupler 54. The branch waveguide 56 can be branched at the input coupler 52 and connected to the output coupler 54. In one example, the branch waveguide 56 may include a first branch waveguide 55 and a second branch waveguide 57. The first branch waveguide 55 and the second branch waveguide 57 may be parallel to each other.

[0042] The programmable filter 20 can be connected to the first branch waveguide 55 and the second branch waveguide 57, respectively. For example, the programmable filter 20 may include a first programmable filter 22 and a second programmable filter 24. The first programmable filter 22 can be connected in series with the first branch waveguide 55. The first programmable filter 22 can select a first peak wavelength 21 or a first peak frequency of the reference light 13 in the first branch waveguide 55. The second programmable filter 24 can be connected in series with the second branch waveguide 57. The second programmable filter 24 can select a second peak wavelength 23 or a second peak frequency of the measurement light 15 in the second branch waveguide 57. The first programmable filter 22 and the second programmable filter 24 can increase the spectral measurement reliability of the beating frequency signal 19 by appropriately setting the degree of delay according to the linewidth of the light 11 of the optical frequency comb. The first programmable filter 22 and the second programmable filter 24 can precisely adjust the size of each wavelength component according to the attenuation level of the light 11. Furthermore, the first programmable filter 22 and the second programmable filter 24 can adjust the degree of delay through a phase control function and a pig-tailed structure. For example, each of the first programmable filter 22 and the second programmable filter 24 may include a programmable pulse shaper.

[0043] The polarization tuner 60 can be connected to the second branch waveguide 57 between the second programmable filter 24 and the output coupler 54. The polarization tuner 60 can adjust the polarization of the measurement light 15 in the second branch waveguide 57. The measurement light 15 and the reference light 13 can be interfered with at the output coupler 54 to generate a beating frequency signal 19.

[0044] The light source 10, photodetector 30, and electrical spectrum analyzer 40 can be configured in the same manner as shown in Figure 2.

[0045] Figure 5 shows an example of a self-heterodyne detection system 100 based on the concept of the present invention.

[0046] Referring to Figure 5, each of the first programmable filter 22 and the second programmable filter 24 can include an optical bandpass filter. The first programmable filter 22 and the second programmable filter 24 of the optical bandpass filter can select the first peak wavelength 21 and the second peak wavelength 23 of the reference light 13 and the measurement light 15, respectively.

[0047] The light source 10, photodetector 30, electrical spectrum analyzer 40, interferometer 50, and polarization tuner 60 can be configured in the same manner as shown in Figure 3.

[0048] Figure 6 shows an example of a self-heterodyne detection system 100 based on the concept of the present invention.

[0049] Referring to Figure 6, the self-heterodyne detection system 100 of the present invention may further include a first nonlinear crystal plate 70 and a second nonlinear crystal plate 80.

[0050] The first nonlinear crystal plate 70 can be provided between the light source 10 and the input coupler 52. The first nonlinear crystal plate 70 can increase the bandwidth of the light 11. The first nonlinear crystal plate 70 may include BBO (Beta Barium Borate), PPKTP (Periodically Poled Potassium Titanyl Phosphate), and PPLN (Periodically Poled Lithium Niobate). Alternatively, the first nonlinear crystal plate 70 may include inorganic materials such as silicon (Si), silicon nitride (SiN), aluminum gallium arsenide (AlGaAs), or silicon carbide (SiC), but the present invention is not limited thereto.

[0051] The second nonlinear crystal plate 80 can be provided between the programmable filter 20 and the output coupler 54. One of the second nonlinear crystal plates 80 can be provided in the first branch waveguide 55 between the first programmable filter 22 and the output coupler 54. The other of the second nonlinear crystal plates 80 can be provided in the second branch waveguide 57 between the second programmable filter 24 and the output coupler 54. Each of the second nonlinear crystal plates 80 may have a thickness thinner than the thickness of the first nonlinear crystal plate 70. The second nonlinear crystal plates 80 may have the same thickness as each other. The second nonlinear crystal plates 80 can increase the bandwidth of the reference light 13 and the measurement light 15 of the light 11. The second nonlinear crystal plate 80 may have the same material as the first nonlinear crystal plate 70. For example, the second nonlinear crystal plate 80 may include BBO (Beta Barium Borate), PPKTP (Periodically Poled Potassium Titanyl Phosphate), and PPLN (Periodically Poled Lithium Niobate). Alternatively, the second nonlinear crystal plate 80 may include inorganic materials such as silicon (Si), silicon nitride (SiN), aluminum gallium arsenide (AlGaAs), or silicon carbide (SiC), but the present invention is not limited thereto.

[0052] The light source 10, photodetector 30, electrical spectrum analyzer 40, interferometer 50, and polarization tuner 60 can be configured in the same manner as in Figure 5.

[0053] Figure 7 shows an example of a self-heterodyne detection system 100 based on the concept of the present invention.

[0054] Referring to Figure 7, the programmable filter 20 of the self-heterodyne detection system 100 of the present invention may further include a third programmable filter 26.

[0055] The third programmable filter 26 can be provided between the output coupler 54 and the photodetector 30. The third programmable filter 26 may include a pulse shaper. The third programmable filter 26 can remove noise from the second nonlinear crystal plate 80.

[0056] The light source 10, photodetector 30, electrical spectrum analyzer 40, interferometer 50, polarization tuner 60, first programmable filter 22, and second programmable filter 24 can be configured in the same manner as in Figure 6.

[0057] While embodiments of the present invention have been described above with reference to the attached drawings, those with ordinary skill in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without altering its technical idea or essential features. Therefore, the embodiments described above should be understood to be illustrative and not limiting in all respects. [Explanation of Symbols]

[0058] 10 light source 20 Programmable Filters 30 Photodetectors 40. Electrospectrometry analyzer 50 Interferometer 60 Polarization adjuster 100 Self-Heterodyne Detection Systems

Claims

1. A frequency comb light source that generates light, A photodetector for detecting the aforementioned light, An electrical spectrum analyzer connected to the photodetector, which uses the detection signal from the photodetector to analyze the frequency and wavelength of the light, An interferometer including an input coupler provided between the frequency comb light source and the photodetector to receive the light, a branch waveguide branched by the input coupler, and an output coupler connected to the branch waveguide, A programmable filter provided in the branch waveguide for selecting the peak wavelength of the light, A self-heterodyne detection system including...

2. Each of the aforementioned programmable filters includes a pulse shaper or an optical bandpass filter. The self-heterodyne detection system according to claim 1.

3. The aforementioned branch waveguide is First branch waveguide and A second branch waveguide parallel to the first branch waveguide, A self-heterodyne detection system according to claim 1, comprising:

4. The aforementioned programmable filter is A first programmable filter connected to the first branch waveguide, A second programmable filter connected to the second branch waveguide, A self-heterodyne detection system according to claim 3, including the above.

5. Polarization tuner connected to the second branch waveguide between the second programmable filter and the output coupler The self-heterodyne detection system according to claim 4, further comprising:

6. A frequency comb light source that generates light, A photodetector for detecting the aforementioned light, An electrical spectrum analyzer connected to the photodetector, which uses the detection signal from the photodetector to analyze the frequency and wavelength of the light, An interferometer including an input coupler provided between the frequency comb light source and the photodetector to receive the light, a first branch waveguide and a second branch waveguide branched by the input coupler, and an output coupler connected to the first branch waveguide and the second branch waveguide, A first programmable filter and a second programmable filter are provided in the first branch waveguide and the second branch waveguide for selecting the peak wavelength of the light, A first nonlinear crystal plate is provided between the frequency comb light source and the input coupler, A self-heterodyne detection system including...

7. The second nonlinear crystal plate between each of the first programmable filter and the second programmable filter and the output coupler. The self-heterodyne detection system according to claim 6, further comprising:

8. The first nonlinear crystal plate and the second nonlinear crystal plate include BBO (Beta Barium Borate), PPKTP (Periodically Poled Potassium Titanyl Phosphate), and PPLN (Periodically Poled Lithium Niobate), The self-heterodyne detection system according to claim 7.

9. The first nonlinear crystal plate and the second nonlinear crystal plate include silicon (Si), silicon nitride (SiN), aluminum gallium arcenide (AlGaAs), or silicon carbide (SiC). The self-heterodyne detection system according to claim 7.

10. A third programmable filter provided between the output coupler and the photodetector. The self-heterodyne detection system according to claim 6, further comprising:

Images