JP4413688B2 - Millimeter wave light source - Google Patents

Description

  The present invention relates to a technique for forming a millimeter-wave light source used for frequency-variable low phase noise millimeter-wave electromagnetic wave generation.

  Conventionally, in the field of radio astronomy and imaging, the use of millimeter waves in a region exceeding 100 GHz has been attracting attention, and accordingly, methods and devices for generating millimeter waves have attracted attention. In particular, a variable frequency and low noise generator that covers a wide frequency range is essential for astronomical observation and analysis.

  Conventionally, the generation of electromagnetic waves has been performed by an all-electric method. However, when the frequency becomes near 100 GHz, the generation of electromagnetic waves is difficult by the all-electric method. Further, since the electric circuit used in the millimeter wave band transmitter and multiplier uses a resonant circuit, the frequency variable region is limited.

  Therefore, a method of generating an electromagnetic wave by generating an optical signal (optical millimeter wave signal) whose intensity is modulated at a frequency in the millimeter wave region as an optical signal and photoelectrically converting the optical millimeter wave signal has been studied.

  As a simple method, as shown in FIG. 7, after the polarizations of the outputs of the fixed wavelength light source 100 and the variable wavelength light source 102 are combined by the two polarization controllers 101 and 101 arranged respectively, the optical coupler 103 is used. Combine at. By doing so, it is possible to generate an optical millimeter-wave signal having a variable frequency. However, since it is difficult to synchronize the two lasers, the phase noise is large and the frequency drift is also large.

  On the other hand, multiple line spectra are generated from the same light source such as an optical comb generator, and two line spectra at a desired frequency interval are selected using an optical filter such as AWG (Arrayed Waveguide Greating). Later, the method of combining by combining polarized waves is attracting attention as a method for generating millimeter waves with relatively small phase noise.

  However, in the past, as shown in FIG. 7, the optical fiber was connected between the AWG and the optical coupler, so in order to change the interval between the two line spectra, the fiber was replaced corresponding to the desired frequency interval. Yes.

  Further, when the optical fiber is connected between the AWG and the optical coupler, when the optical fiber expands and contracts due to a temperature change, the optical path length difference between the two optical signals is not constant. As a result, the phase difference between the two optical signals to be combined is not constant, and as a result, the phase of the millimeter wave signal obtained by photoelectric conversion varies according to the expansion and contraction of the optical fiber, and phase noise at 10 kHz or less It is getting bigger.

The wavelength of the optical signal used in long-distance optical communication is around 1550 nm. That is, the phase of the millimeter wave signal generated by the expansion and contraction of the 390 nm fiber corresponding to ¼ of the wavelength changes by 90 degrees, but it is difficult to suppress the expansion and contraction range of the optical fiber length to 1 μm or less. Thus, development of a stable and variable frequency millimeter-wave light source with low noise even at 10 kHz or less is expected.
T. Yamamoto, and S. Kawanishi, "Generation of low-noise optical frequency comb and optical beat signal using phase modulator," in Tech. Dig. JK workshop on microwave and millimeter-wave photonics 2004, pp. 15-19, 2004 .

However, a conventional millimeter wave light source generates a plurality of line spectra from the same light source such as an optical comb generator for generating a millimeter wave signal, selects two line spectra with a desired frequency interval using AWG, When using a method that combines waves to combine, it is difficult to change the interval between two line spectra,
Further, as a result of expansion and contraction of the optical fiber between the optical filter and the optical coupler, the phase noise at 10 kHz or less has increased.

  In view of such problems, the present invention makes it possible to obtain an optical signal composed of two line spectra having a desired frequency interval by changing the input channel of the input signal or the center frequency of the input signal, and An object of the present invention is to provide a millimeter-wave light source with a low phase noise that can make the optical path length difference between two line spectra constant.

The present invention according to claim 1 is composed of an optical comb generator for generating a plurality of line spectra having a constant frequency interval, an arrayed waveguide grating having a plurality of output channels, and a plurality of optical couplers. In the millimeter wave light source, the output channel spacing of the arrayed waveguide grating is the same as the line spectrum spacing of the optical comb generator, and the two output channels of the arrayed waveguide grating with different output channel spacings are Connected to the input of each of the optical couplers, the arrayed waveguide grating further includes a plurality of input channels, and is output from the optical coupler by changing the input channels for inputting the plurality of line spectra. The gist is that the frequency interval between two combined line spectra can be changed.

According to a second aspect of the present invention, in the first aspect, the arrayed waveguide grating and the plurality of optical couplers are formed on the same planar lightwave circuit and connected to each other by a polarization maintaining optical waveguide. In the same plane lightwave circuit, the optical path lengths through which two line spectra combined by the optical coupler pass are equal.

In the present invention as set forth in claim 1 and claim 2 , in the light source composed of an optical comb generator, an arrayed waveguide grating, and an optical coupler for generating a plurality of line spectra having a constant frequency interval, an arrayed waveguide is provided. As a result of the two output channels of the arrayed waveguide grating having the same channel spacing of the grating and the line spectrum of the optical comb generator being different and having different channel spacings being connected to the input of the optical coupler, by varying puff Rukoto input channel, and the gist that outputs an optical signal obtained by multiplexing only two line spectrum of having the desired frequency interval among the plurality of line spectra.

  Furthermore, since the arrayed waveguide grating and the optical coupler are formed on the same horizontal lightwave circuit and both are connected by the optical waveguide, the main purpose is to eliminate variations in the optical path length due to temperature changes and the like. .

  According to the present invention, it is possible to obtain an optical signal composed of two line spectra having a desired frequency interval by changing the input channel of the input signal or the center frequency of the input signal, and two line spectra. Therefore, it is possible to provide a millimeter wave light source with low phase noise.

  Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

First, the 1st Embodiment of this invention is shown. FIG. 1 shows a millimeter wave light source 1 according to a first embodiment of the present invention. A plurality of line spectra 10 generated from the optical comb generator 2 at a frequency interval of f ₀ are input to an AWG (Arrayed Waveguide Greating) 3 via an AWG input channel 8 and demultiplexed. The demultiplexed line spectrum 10 is output from the AWG output channel 7.

  Two AWG output channels 7 of the AWG 3 are selected so that the outputs are input to the optical couplers 4, 5, 6. The AWGs corresponding to the optical couplers 4, 5, 6 are provided. The channel intervals of the output channels 7 are all set differently.

As a result, an optical signal in which two line spectra having different frequency intervals are combined is output from each of the optical couplers 4, 5, and 6, and two line spectra having a desired frequency interval are selected by selecting an output port. It is possible to obtain an optical signal consisting of For example, in FIG. 1, the optical signal output from the optical coupler 4 is a line spectrum 11 and is generated at a frequency interval of three times f ₀ (3 * f ₀ in the figure). Similarly, a line spectrum 12 generated at a frequency interval of twice f ₀ is output from the optical coupler 5 (2 * f ₀ in the figure), and generated from the optical coupler 6 at a frequency interval of 1 time f _0. The line spectrum 13 is output (f ₀ in the figure).

  However, in this method, since the AWG output channel 7 of the AWG 3 corresponding to the line spectrum 10 output from the optical comb generator 2 is distributed to each of the couplers 4, 5, and 6, two line spectra obtained from the output from the AWG 3 are obtained. The maximum value of the frequency interval is less than 1/2 of the maximum frequency interval between the line spectra 10 output from the optical comb generator 2.

  Next, a second embodiment of the present invention will be described.

  FIG. 2 shows a millimeter wave light source according to the second embodiment of the present invention. In the second embodiment of the present invention, the AWG 20 is provided with a plurality of AWG input channels 25. The AWG input channel 25 includes four optical signal input units Ch_A, Ch_B, Ch_C, and Ch_D in FIG.

  In the AWG 20, when an optical signal having the same frequency is input to a certain input channel, it is output from an output channel corresponding to a position symmetrical to the central channel of the AWG 20. That is, by changing the AWG input channel 25 for inputting the optical signal from the same optical comb generator 2, the AWG output channel 26 for outputting the optical signal changes.

Since the frequency interval between the two AWG output channels connected to the optical couplers 21, 22, 23, and 24 is changed according to the position of the AWG output channel 26, the AWG input channel 25 for inputting the optical comb signal is changed. An optical signal composed of two line spectra having a desired frequency interval can be obtained. For example, in FIG. 2, the optical signal output from the optical coupler 21 is a line spectrum 16 and is generated at a frequency interval of four times f ₀ (4 * f ₀ in the figure). Similarly, (3 * f 0 in the _figure) line spectrum 17 generated in the frequency interval is output three times f ₀ from the optical coupler _22, the optical coupler 23 is generated at a frequency interval of twice f ₀ is a line spectrum 18 which is the output (2 * f 0 in the _figure), the line spectrum 19 generated by a frequency interval of 1 × f ₀ is output from the optical coupler 24 (f ₀ in the _figure).

For example, in the AWG input channel 25, when an optical comb signal is input to Ch_A, a signal obtained by combining two line spectra having a frequency difference f ₀ is output from Ch_H, and from Ch_E when input to Ch_D. A signal obtained by combining two line spectra having a frequency difference of 4 * f ₀ is output. If this method is used, it is possible to generate an optical signal obtained by cutting out two line spectra at the maximum frequency interval of the optical signal output from the optical comb generator 2.

  Next, a third embodiment of the present invention will be described.

  FIG. 3 shows a millimeter wave light source according to the third embodiment of the present invention. In the third embodiment, an optical comb generator 2 in which the center frequency of the optical signal is variable is used. In the AWG 30, when the frequency of the line spectrum 39 input to the AWG input channel 40 is changed, the channel from which the optical signal is output among the plurality of output channels of the AWG output channel 27 is switched according to the change in frequency. This is because the two output ports connected to the optical couplers 31, 32, 33, and 34 are provided so that the frequency intervals differ depending on the positions of the plurality of channels of the AWG output channel 27. By changing the center frequency of the line spectrum 39 of the optical signal output from the optical comb generator 2, it is possible to obtain an optical signal composed of two line spectra at a desired frequency interval.

For example, in FIG. 3, the optical signal output from the optical coupler 31 is a line spectrum 35 and is generated at a frequency interval of f ₀ that is four times (4 * f ₀ in the figure). Similarly, (3 * f 0 in the _figure) line spectrum 36 generated by a frequency spacing of 3 times f ₀ from the optical coupler 32 is _output, generated at a frequency spacing of two times f ₀ from the optical coupler 33 is output line spectrum 37 which is (2 * f 0 in the _figure), the line spectrum 38 generated by a frequency interval of 1 × f ₀ is output from the optical coupler 34 (f ₀ in the _figure).

  Next, a fourth embodiment of the present invention will be described.

  The configuration shown in FIG. 4 is the same as the configuration of the millimeter wave light source in the second embodiment of the present invention already described, and the AWG 43 and the optical couplers 46, 47, 48, 49 are on the same PLC (horizontal plane light wave circuit) 41. It is characterized in that it is formed. The AWG 43 and the optical couplers 46, 47, 48 and 49 are connected to each other by the optical waveguide 42. By using the polarization-maintaining optical waveguide 42 in the PLC 41, a polarization controller for aligning polarization before multiplexing is unnecessary.

  In addition, the optical path lengths through which the two cut out line spectra pass are designed to be equal. As a result, the temperature change of the PLC 41 occurs, and even if the PLC 41 expands and contracts, the optical path length difference through which the two-line spectrum passes becomes 0, and the resulting phase fluctuation of the millimeter wave signal is suppressed.

In such a millimeter-wave light source according to a fourth embodiment of the arrangement, with respect to a line spectrum 54 input to the PLC41, the optical signal output from the optical coupler 46 is a line spectrum 50, and the four times the frequency of f ₀ It occurs at intervals (4 * f ₀ in the figure). Similarly, a line spectrum 51 generated at a frequency interval of three times f ₀ is output from the optical coupler 47 (3 * f ₀ in the figure), and generated from the optical coupler 48 at a frequency interval of twice f _0. is output to a line spectrum 52 is (2 * f 0 in the _figure), the line spectrum 53 generated by a frequency interval of 1 × f ₀ is output from the optical coupler 49 (f ₀ in the _figure).

  FIG. 5 shows a light source realized by connecting the AWG 43 and one of the optical couplers 46, 47, 48, and 49 with an optical fiber as compared with the light source using the present technology according to the fourth embodiment. FIG. 60 shows a phase noise measurement diagram 60 of the generated 120 GHz millimeter wave signal. It can be seen that phase noise of 10 kHz or less is significantly reduced by the present technology in comparison between the present technology 61 and the optical fiber use 62.

Next, a fifth embodiment of the present invention will be described. FIG. 6 uses the optical comb generator 65 capable of changing the interval of the line spectrum 67 of the optical signal from the optical comb generator 65 (f ₀ + Δf) in the second embodiment already described. . Since each channel of the AWG 66 has a constant bandwidth, a line spectrum having an arbitrary frequency interval can be obtained by changing the line spectrum interval so that the line spectrum is included in the bandwidth.

In the millimeter wave light source according to the fifth embodiment having such a configuration, the optical signal output from the optical coupler 72 becomes the line spectrum 68 with respect to the line spectrum 67 input to the AWG input channel 76, which is four times ( occur at a frequency interval of _{f 0 + Δf) (4 *} (f 0 + Δf in the figure)). Similarly, a line spectrum 69 generated at a frequency interval of 3 times (f ₀ + Δf) is output from the optical coupler 73 (3 * (f ₀ + Δf) in the figure), and 2 times (( f ₀ + Δf) line spectrum 70 generated in the frequency interval is output (2 * in FIG. _{(f 0} + _Δf)), line spectrum generated by the frequency spacing of 1 times from the optical coupler 75 _{(f 0} + _Δf) 71 is output ((f ₀ + Δf) in the figure).

  In the first to fifth embodiments of the present invention described above, after extracting an optical signal having two line spectra separated by a desired frequency, the respective line spectra of the two types of extracted optical signals are extracted. By taking the difference frequency, a millimeter wave having a desired frequency can be generated. In this case, after the two line spectra are combined by the AWG, the combined optical signal is input to a photoelectric conversion element such as a photodiode, whereby a millimeter wave signal having a frequency corresponding to the frequency difference between the two modes is obtained. It may be generated.

  Moreover, according to the 1st-5th embodiment which concerns on this invention, the following effects are acquired.

(1) Since the AWG and the optical coupler are provided on the same PLC and connected by an optical waveguide, the optical path length difference through which two line spectra cut out by the AWG pass is always constant. Thus, the phase noise of the millimeter wave signal obtained is reduced.

(2) By connecting two AWG output channels with different channel intervals to an optical coupler, the frequency of the input channel and the input optical signal is changed, thereby generating an optical signal composed of two line spectra having a desired frequency difference. It becomes possible.

The block diagram for demonstrating the millimeter wave light source which concerns on the 1st Embodiment of this invention is shown. The block diagram for demonstrating the millimeter wave light source which concerns on the 2nd Embodiment of this invention is shown. The block diagram for demonstrating the millimeter wave light source which concerns on the 3rd Embodiment of this invention is shown. The block diagram for demonstrating the millimeter wave light source which concerns on the 4th Embodiment of this invention is shown. The measurement figure for demonstrating the result of the noise measurement by the millimeter wave light source which concerns on the 4th Embodiment of this invention is shown. The block diagram for demonstrating the millimeter wave light source which concerns on the 5th Embodiment of this invention is shown. The schematic block diagram for demonstrating the structure of the light source by a prior art is shown.

Explanation of symbols

1 Millimeter wave light source 2 Optical comb generator 3 AWG
4, 5, 6 Optical coupler 7 AWG output channel 8 AWG input channel 10 Line spectrum (f ₀ )
11-line spectrum (3 * f ₀ )
12-line spectrum (2 * f ₀ )
13-line spectrum (f ₀ )
41 PLC

Claims (2)

In a millimeter-wave light source composed of an optical comb generator that generates a plurality of line spectra at a constant frequency interval, an arrayed waveguide grating having a plurality of output channels, and a plurality of optical couplers,
The output channel spacing of the arrayed waveguide grating is the same as the line spectrum spacing of the optical comb generator, and the two output channels of the arrayed waveguide grating with different output channel spacing are each of the optical couplers. Connected to the input ,
The arrayed waveguide grating further includes a plurality of input channels, and a frequency interval between two combined line spectra output from the optical coupler by changing the input channels for inputting the plurality of line spectra. Millimeter wave light source characterized by being able to change . The arrayed waveguide grating and the plurality of optical couplers are:
Formed on the same planar lightwave circuit and connected to each other by polarization maintaining optical waveguides,
2. The millimeter wave light source according to claim 1, wherein optical path lengths through which two line spectra combined by the optical coupler pass are equal on the same plane light wave circuit.

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