JP3711031B2 - High frequency signal generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-frequency signal generator that generates a high-frequency signal in a range from a microwave to a submillimeter wave.
[0002]
[Prior art]
As a conventional high-frequency signal generator, a device using ultra-wideband coherent white light output from a coherent white light source is known.
[0003]
FIG. 6 shows a configuration example of a coherent white light source. In the figure, the coherent white light source is composed of an excitation pulse light source 21 that outputs an excitation light pulse having a center frequency ν ₀ and a repetition frequency f ₀ [Hz], and a nonlinear optical medium 22 having a predetermined dispersion slope and dispersion. The If necessary, a band removal filter 23 for removing the excitation light pulse may be provided on the output side of the nonlinear optical medium 22.
[0004]
When an excitation light pulse having a repetition frequency f ₀ [Hz] output from the excitation pulse light source 21 is input to the nonlinear optical medium 22, coherent white light with a longitudinal mode interval f ₀ (Hz) is generated in an ultra wide band. In the case where an optical fiber is used as the nonlinear optical medium 22, coherent white light having a spectral width over a wavelength band of 200 nm or more can be generated. This is called a super continuum (SC) light source (reference: Fujii, edited by Yamabayashi, ultra high-speed network technology, future network technology series 5, Telecommunications Association, pp.266-267, (2000)).
[0005]
FIG. 7 shows a configuration example of a conventional high-frequency signal generator. In the figure, the coherent white light source 11 has the configuration shown in FIG. The coherent white light 31 having the center frequency ν ₀ , the longitudinal mode interval f ₀ [Hz], and the repetition frequency f ₀ [Hz] output from the coherent white light source 11 is input to the Fabry-Perot filter 33 of the optical filter group 32. . The period (free spectrum range (FSR)) of the Fabry-Perot filter 33 is set to just nf ₀ [Hz] (n is a natural number), and the longitudinal mode interval of the output is nf ₀ [Hz].
[0006]
The output of the Fabry-Perot filter 33 is input to the arrayed waveguide grating filter (AWG) 34, an optical frequency _{ν 1, ν 2, ...,} ν m plurality of optical frequency components are cut out around the each different output Demultiplexed to the port. At this time, the repetition frequency of the short optical pulse train 35 of each output port of the AWG 34 is nf ₀ [Hz] at any output port (optical frequency), and the pulse width is Gaussian type due to the transmission band Δν of the AWG 34. In the case of 0.44 / Δν and sech ² type, it is expressed as 0.315 / Δν. Note that the repetition frequency of the short optical pulse train 35 can be freely selected by an integer multiple of f ₀ by the FSR of the Fabry-Perot filter 33, and the pulse width can also be arbitrarily selected according to the characteristics of the AWG 34.
[0007]
If the output light pulse train 35 generated by the above configuration is received by the light receiving element 36 and converted into an electric signal, an electric pulse having a repetition frequency f ₀ can be generated. Further, if a band pass filter is provided at the output of the light receiving element 36 and the harmonic component nf ₀ [Hz] of the repetition frequency f ₀ is extracted, a sine wave of nf ₀ [Hz] can be generated.
[0008]
[Problems to be solved by the invention]
By the way, the light receiving element has a rating of input light power, and when input power exceeding the rating is input, the output is saturated and a desired high frequency component is lowered.
[0009]
On the other hand, the spectrum of the optical pulse input to the light receiving element 36 of the conventional high-frequency signal generator has a large number of bright line spectral components at intervals of f ₀ , and the desired high-frequency component is only one of them. Absent. Therefore, in the configuration in which the light pulse is input to the light receiving element 36 and a desired high frequency component is extracted from the output electric signal, not only a small part of the energy of the light pulse is used but also the energy of other unnecessary bright line spectral components. The light receiving element 36 is saturated, and it is difficult to sufficiently obtain an output of a desired high frequency component.
[0010]
An object of the present invention is to provide a high-frequency signal generator capable of solving a problem such as saturation of a light receiving element due to an unnecessary optical spectrum and efficiently generating a high-frequency signal with a simple configuration.
[0011]
[Means for Solving the Problems]
The high-frequency signal generation device of the present invention receives a coherent white light source that outputs a coherent white light having a center frequency ν ₀ and a longitudinal mode interval f ₀ [Hz], and a plurality of coherent white lights that are arranged at a longitudinal mode interval f ₀ . From the emission line spectrum of the two, the frequency (ν ₀ + n ₁ f ₀ ) [Hz] and (ν ₀ + n ₂ f ₀ ) [Hz] (n ₁ and n ₂ are integers and n ₁ > n ₂ ) An optical filter that outputs an emission line spectrum, an optical multiplexer that combines the two emission line spectra output from the optical filter, and an output light of the optical multiplexer are input, and a difference frequency (n ₁ −n ₂ ) a light receiving element that converts the output into a high-frequency electrical signal of f ₀ [Hz] and outputs it.
[0012]
In this way, by extracting two emission line spectra from the plurality of emission line spectra in the coherent white light with an optical filter, combining them and inputting them to the light receiving element, the difference frequency between the two emission line spectra is obtained. The high-frequency electrical signal can be generated.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 shows a first embodiment of the high-frequency signal generator of the present invention. In the figure, the high-frequency signal generator of the present embodiment receives a coherent white light source 11 that outputs coherent white light having a center frequency ν ₀ and a longitudinal mode interval f ₀ [Hz], and a coherent white light, and a longitudinal mode interval f. An optical filter 12 that outputs two emission line spectra from among a plurality of emission line spectra arranged at ₀ , an optical multiplexer 13 that combines the two emission line spectra output from the optical filter 12, and an optical multiplexer 13 Is provided with a light receiving element 14 that converts the output light into an electric signal and an electric signal output port 15.
[0014]
The coherent white light source 11 has the configuration shown in FIG. Moreover, you may provide the optical amplifiers 16, 17, and 18 in the output stage of the coherent white light source 11, and the output stage of the optical filter 12 as needed.
[0015]
Here, the two bright line spectra selected by the optical filter 12 are represented by frequencies (ν ₀ + n ₁ f ₀ ) [Hz] and (ν ₀ + n ₂ f ₀ ) [Hz] (n ₁ and n ₂ are integers and n ₁ > N ₂ ), a high-frequency electrical signal having a difference frequency (n ₁ −n ₂ ) f ₀ [Hz] between the two emission line spectra is output to the output port 15.
[0016]
In the configuration of the present embodiment, excitation pulse light is generated in a frequency region in which an existing electric oscillator with a frequency f ₀ [Hz] can be used with the excitation pulse light source 21 of the coherent white light source 11 shown in FIG. Then, the excitation pulse light is input to the nonlinear optical medium 22 to output coherent white light having a broadened optical spectrum. From this expanded light spectrum (coherent white light), two bright line spectra having a difference frequency corresponding to a high frequency that is difficult to be generated by a normal electric circuit are cut out, combined, and received by the light receiving circuit 14 Thus, a high-frequency signal having the difference frequency can be generated. As described above, since only the bright line spectrum necessary for generating the high-frequency signal is used in the expanded light spectrum, saturation of the light receiving circuit 14 can be suppressed.
[0017]
(Second Embodiment)
FIG. 2 shows a second embodiment of the high-frequency signal generator of the present invention. In the figure, the feature of this embodiment is that an arrayed waveguide grating filter (AWG) is used as the optical filter 12 in the first embodiment, and the emission line spectrum of coherent white light is extracted from each different output port. To.
[0018]
FIG. 2 (a) shows the optical spectrum of coherent white light. The coherent white light has bright line spectra arranged at a longitudinal mode interval f ₀ [Hz] with the center frequency ν ₀ as the center.
[0019]
FIG. 2B shows the transmission spectrum characteristics of the output port n ₁ of the optical filter (AWG) 12. The transmission center frequency is (ν ₀ + n ₁ f ₀ ) [Hz]. FIG. 2C shows the transmission spectrum characteristic of the output port n ₂ of the optical filter (AWG) 12. The transmission center frequency is (ν ₀ + n ₂ f ₀ ) [Hz]. The output ports n ₁ and n ₂ of the optical filter (AWG) 12 have a transmission band B for extracting one of the emission line spectra. Here, emission line spectra separated by 3f ₀ are extracted. As a result, a high-frequency electric signal having a frequency of 3 f ₀ [Hz] is output to the output port 15.
[0020]
The AWG has periodicity because it uses optical interference in its operation principle. That is, the transmission spectrum characteristics shown in FIGS. 2B and 2C have the transmission characteristics of the transmission band B for each period called a free spectrum range (FSR). As desirable characteristics of the optical filter (AWG) 12 in the present embodiment,
(1) The transmission band B is sufficiently small and the adjacent emission line spectrum can be sufficiently suppressed.
(2) It is sufficiently large with respect to the frequency (n ₁ −n ₂ ) f ₀ [Hz] of the high-frequency electrical signal output by the FSR,
(3) Low loss,
It is. Currently, an AWG that satisfies these conditions has been published in the literature (K. Okamoto et al., “Fabrication of 128-channel arrayed-waveguide grating multiplexer with 25 GHz channel spacing”, Electron. Lett., Vol. 32, pp. 1474-1476. , 1996) has a filter band B = 25 GHz, FSR = 3.2 THz, loss 3.5 to 6 dB, and can be sufficiently designed from microwave to submillimeter wave (10 GHz to 1000 GHz). ing.
[0021]
In the configuration of the present embodiment, the output light power from each output port of the optical filter (AWG) 12 is (coherent white light power / number of bright line spectra in FSR). The number of bright line spectra in the FSR is 128 in the above-mentioned document, and the output light power from each output port is 0.1 mW or less when the coherent white light power is 10 mW.
[0022]
Here, in order to increase the output light power, an optical amplifier (erbium-doped optical fiber amplifier) 16 is connected to the output of the coherent white light source 11. Further, the optical amplifiers 17 and 18 may be connected to each output port of the optical filter 12. However, when the optical amplifiers 17 and 18 are used, spontaneous emission light noise output from the optical amplifier causes saturation when incident on the light receiving element 14, so that an emission band line filter is used in front of the light receiving element 14. It is desirable to remove spontaneous emission light noise generated in the light spectrum other than the components.
[0023]
The configuration shown in FIG. 2 corresponds to the difference frequency between the bright line spectra of the two output ports of the optical filter (AWG) 12 and the frequency of the high-frequency electric signal to be output. The combination of the output ports is changed. Thus, the frequency of the high-frequency electrical signal can be arbitrarily switched. Therefore, as shown in FIG. 3, by extracting two sets of bright line spectra in parallel from different output ports of the optical filter 12, it is possible to simultaneously output a plurality of high-frequency electric signals having different frequencies. Note that the example shown in FIG. 3 is a configuration in which two sets of emission line spectra are extracted, and includes two sets of optical amplifiers 17 and 18, an optical multiplexer 13, and a light receiving element 14. It is also possible to extract the emission line spectrum. In that case, a configuration may be adopted in which one emission line spectrum is shared.
[0024]
In addition, as shown in FIG. 4, a high-frequency electrical signal can be obtained by inserting an optical space switch 19 between the optical filter 12 and the optical multiplexer 13 and switching the output port of the optical filter 12 connected to the optical multiplexer 13. Can be switched arbitrarily.
[0025]
Further, as shown in FIG. 5, two or more sets of bright line spectra are selectively extracted from the output port of the optical space switch 19 to simultaneously output a plurality of high-frequency electric signals having different frequencies, It can be switched arbitrarily according to the setting.
[0026]
Moreover, the operational stability can be improved by making all the optical components (11 to 19) shown in FIGS.
[0027]
【The invention's effect】
As described above, the high-frequency signal generation device of the present invention combines two light line spectra out of the line spectrums constituting the coherent white light output from the coherent white light source, and receives the light. It is possible to generate a high-frequency electric signal in a region extending from a microwave to a submillimeter wave corresponding to a relative difference in frequency. As a result, problems such as saturation of the light receiving element due to an unnecessary light spectrum can be solved, and a high-frequency electric signal can be efficiently generated with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of a high-frequency signal generator of the present invention.
FIG. 2 is a block diagram showing a second embodiment of the high-frequency signal generator of the present invention.
FIG. 3 is a block diagram showing a third embodiment of the high-frequency signal generator of the present invention.
FIG. 4 is a block diagram showing a fourth embodiment of the high-frequency signal generator of the present invention.
FIG. 5 is a block diagram showing a fifth embodiment of the high-frequency signal generator of the present invention.
FIG. 6 is a block diagram illustrating a configuration example of a coherent white light source.
FIG. 7 is a block diagram showing a configuration example of a conventional high-frequency signal generator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Coherent white light source 12 Optical filter 13 Optical multiplexer 14 Light receiving element 15 Output port 16, 17, 18 Optical amplifier 19 Optical space switch 21 Excitation pulse light source 22 Nonlinear optical medium 23 Band removal filter 31 Coherent white light 32 Optical filter group 33 Fabry-Perot filter 34 arrayed waveguide grating filter (AWG)
35 Short optical pulse train

Claims (3)

A coherent white light source that outputs coherent white light having a center frequency ν ₀ and a longitudinal mode interval of f ₀ [Hz];
The coherent white light is input, and a frequency (ν ₀ + n ₁ f ₀ ) [Hz] and (ν ₀ + n ₂ f ₀ ) [Hz] (n) are selected from a plurality of emission line spectra arranged at the longitudinal mode interval f _{0. 1} and n ₂ are integers and an optical filter that outputs two emission line spectra of n ₁ > n ₂ ),
An optical multiplexer that multiplexes two emission line spectra output from the optical filter, and an output light of the optical multiplexer, and a difference frequency (n ₁ −n ₂ ) f ₀ between the two emission line spectra. A light-receiving element that converts and outputs a high-frequency electrical signal of [Hz],
The optical filter has a transmission band characteristic that sufficiently suppresses the adjacent bright line spectrum for each of the plurality of output ports, and has a free spectrum range (FSR) of (n ₁ −n ₂ ) f ₀ [Hz]. A high-frequency signal generator characterized by using a sufficiently large arrayed waveguide grating filter (hereinafter referred to as “AWG”) to extract the two emission line spectra from its two output ports . In the high frequency signal generator of Claim 1 ,
A plurality of sets of the two emission line spectra are extracted from the AWG, and each of the two emission line spectra is combined by a plurality of optical multiplexers and received by the corresponding light receiving elements, and each of the plurality of light receiving elements has a different frequency difference. A high-frequency signal generator characterized by having a configuration for outputting a high-frequency electrical signal. In the high frequency signal generator according to claim 1 or 2,
An optical space switch for selecting two predetermined output ports of the AWG connected to the optical multiplexer is provided between the AWG and the optical multiplexer, and the high-frequency electrical signal is selected according to the selection of the optical space switch. The high frequency signal generator characterized by having the structure which switches the frequency of.

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