JP4928779B2 - Light source for millimeter wave generation - Google Patents

Description

  The present invention relates to a technique for generating an optical millimeter-wave signal used for generating a millimeter wave.

  In recent years, in the field of radio celestial observation and imaging, a technique for generating a millimeter wave in a region exceeding 100 GHz has attracted attention. In particular, a millimeter-wave generator with low noise and a variable frequency that covers a wide frequency range is essential for radio astronomical observation equipment.

  However, the conventional all-electric method makes it difficult to generate an electromagnetic wave having a frequency exceeding 100 GHz. In addition, since the electric circuit used in the millimeter wave band transmitter and multiplier uses a resonant circuit, the variable region is limited.

  Therefore, a technique for 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 and photoelectrically converting the optical millimeter wave signal has been studied.

  As a method for generating an optical millimeter wave signal, as shown in FIG. 7, the outputs of the fixed wavelength light source 71 and the variable wavelength light source 72 are polarized by the polarization controllers 73 and 74 and multiplexed by the optical coupler 75. However, since it is difficult to synchronize the two lasers, the phase noise is large and the frequency drift is also large.

  Further, as means for generating a coherent optical millimeter-wave signal, one using a laser resonator such as a mode-locked laser is known, but the variable frequency range of these lasers is small.

  As a stable optical millimeter-wave light source having a large variable region, a light source using an optical heterodyne method using sideband formation by an optical modulator and optical demultiplexing / combining as shown in FIG. 8 is known.

  The light source shown in FIG. 8 includes an optical modulator 1, a single mode laser 2, a synthesizer 3, a DC bias power supply 4, a first optical coupler 11, first and second optical bandpass filters 21, 22 and a second light. A coupler 12 is included. The optical modulator 1 modulates the optical signal output from the single mode laser 2 with a high-frequency signal having a frequency fh (1/2 of the desired millimeter-wave frequency f) generated in the synthesizer 3, thereby generating an optical carrier signal. An optical signal including fc and sideband signals fc−fh and fc + fh having a frequency interval fh is output. This optical signal is demultiplexed into two by the first optical coupler 11 and input to the first and second optical bandpass filters 21 and 22 to extract two sideband signals. By combining the extracted two sideband signals by the second optical coupler 12, an optical millimeter-wave signal modulated at a desired frequency f can be obtained.

  The frequency stability of the optical millimeter wave signal generated by the light source shown in FIG. 8 is almost the same as that of the synthesizer 3 used for modulation of the single mode laser beam. Moreover, it is possible to change the frequency of the generated optical millimeter-wave signal by changing the frequency of the high-frequency signal used for modulation.

  Normally, in this method, in order to increase the strength of the sideband signal, the voltage of the DC bias power supply 4 connected to the optical modulator 1 is set to suppress the optical carrier signal fc, as indicated by a point A in FIG. Carrier suppression modulation is used. FIG. 9 shows the static characteristics of the optical modulator 1, where the horizontal axis represents the DC bias voltage to be applied and the vertical axis represents the light transmittance.

  However, since the static characteristics of the optical modulator 1 change depending on the temperature change and the usage time, the set bias voltage deviates from the optimum value when used for a long time, and the intensity of the sideband signal is weakened. There is a problem that the S / N ratio of the optical millimeter wave signal is lowered.

  In order to prevent such deviation of the bias point, an auto bias control function that always provides an optimum bias voltage is required. FIG. 10 is a block diagram showing a configuration of an apparatus having an auto bias control function when the optical modulator 101 is used for data signal modulation in optical communication. In data signal modulation, if the bias voltage deviates from the optimum value, the degree of modulation of the optical signal decreases and distortion of the signal waveform at the optical signal stage occurs. Therefore, in order to obtain error-free transmission at the receiver, a larger light reception is required. Power is needed. In order to maximize the modulation degree of the optical signal, it is necessary to control the bias voltage so that the light transmittance becomes an intermediate point indicated by a point B in FIG.

The auto-bias control function shown in FIG. 10 inputs a modulation signal of about 10 kHz separately from the data modulation signal to the optical modulator 101, demultiplexes a part of the output of the optical modulator 101, and monitors the photodiode 105. Thus, the deviation of the bias point is prevented by controlling the DC voltage source 104 so that the 10 kHz signal component is always maximized by the feedback circuit 106. A technique described in Patent Document 1 is known as a technique for controlling the operating point of an optical modulator.
JP 2005-91517 A

A light source for generating millimeter waves according to the present invention comprises laser output means for outputting a single mode laser light, high frequency signal generating means for generating a high frequency signal having a frequency half the desired millimeter wave frequency, and the single mode laser light. Optical modulation means for outputting an optical signal including an optical carrier signal and first and second sideband signals by modulating with the high frequency signal, and the optical modulation means for adjusting the intensity of the optical carrier signal A DC bias power source connected; a demultiplexing unit that demultiplexes the output of the optical modulation unit; and a plurality of input channels for inputting the optical signals demultiplexed by the demultiplexing unit. said arrayed waveguide grating having a plurality of output channels for outputting sideband signal and the optical carrier signal separately, first output from the arrayed waveguide grating, It includes a multiplexing means for multiplexing the second side band signal, and a control means for the intensity of the optical carrier signal output from the arrayed waveguide grating to control the DC bias power supply so as to minimize, and The demultiplexing means, the arrayed waveguide diffraction grating, and the multiplexing means are formed in the same planar lightwave circuit without crossing the optical waveguide .

  The present invention has been made in view of the above, and an object of the present invention is to automatically control the bias voltage of an optical modulator in a millimeter-wave generation light source using a carrier suppression modulation method, thereby stabilizing light. It is to generate a millimeter wave signal.

  The light source for generating a millimeter wave according to the present invention includes a laser output means for outputting a single mode laser light, a high frequency signal generating means for generating a high frequency signal having a frequency half the desired millimeter wave frequency, and a single mode laser light having a high frequency Optical modulation means for outputting an optical signal including an optical carrier signal and a sideband signal by modulating with the signal, a DC bias power source connected to the optical modulation means for adjusting the intensity of the optical carrier signal, and an optical signal The first and second extraction means for extracting the sideband signal from the signal, the third extraction means for extracting the optical carrier signal from the optical signal, and the sideband signal output from the first and second extraction means are combined. And a control means for controlling the DC bias power supply so that the intensity of the optical carrier signal output from the third extraction means is minimized. To.

  In the present invention, an optical modulator modulates a single mode laser beam with a high-frequency signal to generate an optical signal including a sandband signal, extracts the sideband signal, and combines the optical signals. A wave signal can be generated. In addition, the optical carrier signal is extracted from the optical signal output from the optical modulator, and the DC bias power source connected to the optical modulator is controlled so that the intensity of the optical carrier signal is minimized. An optical millimeter-wave signal can be generated.

  According to the present invention, in a millimeter wave generating light source using the carrier suppression modulation method, it is possible to automatically control the bias voltage of the optical modulator and generate a stable optical millimeter wave signal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration of a millimeter wave generating light source according to the present embodiment. The millimeter-wave generating light source shown in FIG. 8 is the same as that shown in FIG. 8 and the feedback circuit 6 for controlling the DC bias power supply 4, and the other configurations and operations are the same as those shown in FIG. 8.

  As described with reference to FIG. 8, an optical millimeter-wave signal is generated, the optical signal output from the optical modulator 1 is demultiplexed by the first optical coupler 11, and the optical signal is output by the third optical bandpass filter 23. The carrier signal fc is extracted, and the intensity of the optical carrier signal fc is converted into a current amount by the monitoring photodiode 5. The feedback circuit 6 controls the DC bias power supply 4 so that the converted current amount is always minimized. Thereby, the intensity of the optical carrier signal fc included in the optical signal output from the optical modulator 1 can always be minimized.

  Therefore, according to the present embodiment, the optical modulator 1 modulates the single-mode laser light with a high-frequency signal having the frequency fh (1/2 of the desired frequency f), so that the optical carrier signal fc and the sideband signal fc are obtained. Since an optical signal including −fh and fc + fh is output, the sideband signals fc−fh and fc + fh are extracted from the optical signal and combined to obtain an optical millimeter-wave signal having a desired frequency f.

  Further, the third optical bandpass filter 23 extracts the optical carrier signal fc from the optical signal modulated in the optical modulator 1, and the DC bias power source 4 so that the intensity of the optical carrier signal fc is minimized. Since the optimum bias voltage for carrying out carrier suppression modulation can be maintained even if the static characteristics of the optical modulator 1 change due to temperature changes or changes with time, the optical power is automatically controlled. A wave signal can be generated.

[Second Embodiment]
FIG. 2 is a block diagram showing the configuration of the millimeter wave generating light source in the present embodiment. The millimeter-wave generating light source shown in the figure includes a third optical coupler 13, a monitoring photodiode 5, and a feedback circuit 6 in addition to the one shown in FIG. The operation is the same as that shown in FIG.

  As described with reference to FIG. 8, an optical millimeter-wave signal is generated, and the second optical beam is generated by the third optical coupler disposed between the second optical bandpass filter 22 and the second optical coupler 12. The sideband signal fc + fh extracted by the bandpass filter 22 is demultiplexed, and the intensity of the sideband signal fc + fh is converted into a current amount by the monitoring photodiode 5. The feedback circuit 6 controls the DC bias power supply 4 so that the converted current amount always becomes the maximum. Thereby, the intensity | strength of the sideband signals fc-fh and fc + fh contained in the optical signal output from the optical modulator 1 can always be maximized.

  Therefore, according to the present embodiment, the feedback circuit 6 automatically controls the DC bias power supply 4 so that the intensity of the extracted sideband signal fc + fh is always maximized. Even if the static characteristics of the optical modulator 1 change, it is possible to maintain an optimum bias voltage for performing carrier suppression modulation, and it is possible to generate a stable optical millimeter-wave signal.

  In the present embodiment, the bias voltage is controlled so that the intensity of the sideband signal fc + fh extracted by the second optical bandpass filter 22 is maximized, but the third optical coupler is connected to the first optical coupler. A bias voltage is controlled between the band pass filter 21 and the second optical coupler 12 so that the intensity of the side band signal fc-fh extracted by the first optical band pass filter 21 is maximized. Also good.

[Third Embodiment]
FIG. 3 is a block diagram showing the configuration of the millimeter wave generating light source according to the present embodiment. The millimeter wave generating light source shown in the figure is different from that shown in FIG. 1 in that the first optical coupler 11 and the first, second and third optical bandpass filters 21, 22, and 23 are arrayed waveguides. It is replaced with a diffraction grating 7 (AWG: Arrayed Waveguide Grating).

  The light input from the input waveguide of the arrayed waveguide grating 7 reaches a different output waveguide for each wavelength due to the phase difference caused by the difference in length of the propagating arrayed waveguide, and is demultiplexed. Is output. Therefore, when the optical signal output from the optical modulator 1 is input to the arrayed waveguide grating 7, the optical carrier signal fc and the sideband signals fc−fh and fc + fh having different wavelengths are demultiplexed by the arrayed waveguide grating 7. 8 and 1, the demultiplexed sideband signals fc−fh and fc + fh are combined to generate an optical millimeter wave signal, and the optical carrier signal fc The DC bias power supply 4 can be controlled so as to be minimized.

  The output channel spacing of the arrayed waveguide grating 7 is preferably equal to the frequency fh of the high-frequency signal used for modulating the optical signal, but even if it is not equal to the frequency fh, the optical carrier signal fc and the sideband signal fc−fh, What is necessary is that each of fc + fh is demultiplexed.

  Therefore, according to the present embodiment, the first optical coupler 11 and the first, second and third optical bandpass filters 21, 22, 23 are configured by the arrayed waveguide diffraction grating 7. The number of parts required for control can be reduced.

  The first optical coupler 11 and the first and second optical bandpass filters 21 and 22 may be replaced with the arrayed waveguide diffraction grating 7 in the millimeter wave generating light source shown in FIG.

[Fourth Embodiment]
FIG. 4 is a block diagram showing the configuration of the millimeter wave generating light source in the present embodiment. The millimeter wave generating light source shown in FIG. 3 is one in which an arrayed waveguide diffraction grating 7 and a second optical coupler 12 are formed in a planar lightwave circuit (PLC) among those shown in FIG. .

  The planar lightwave circuit 8 forms an optical circuit on a silicon or quartz substrate and realizes various functions such as optical signal multiplexing / demultiplexing. When the arrayed waveguide diffraction grating 7 and the second optical coupler 12 are connected with an optical fiber as shown in FIG. 3, the optical path length difference between the sideband signals fc−fh and fc + fh deviated due to temperature change or the like varies. Since the phase difference between the sideband signals fc−fh and fc + fh varies, the phase of the generated optical millimeter-wave signal varies and phase noise increases. By forming the arrayed waveguide diffraction grating 7 and the second optical coupler 12 in the same planar lightwave circuit 8, both sideband signals fc−fh and fc + fh pass even if the planar lightwave circuit 8 expands and contracts due to a temperature change. Since the optical path length difference is 0, the phase variation of the generated optical millimeter wave signal can be suppressed.

  Therefore, according to the present embodiment, by forming the arrayed waveguide diffraction grating 7 and the second optical coupler 12 in the same planar lightwave circuit 8, even if the optical path length changes due to temperature change, both sidebands Since the optical path length difference through which the signals fc−fh and fc + fh pass can be made zero, fluctuations in the phase of the generated optical millimeter wave signal can be suppressed.

[Fifth Embodiment]
FIG. 5 is a block diagram showing a configuration of a millimeter wave generating light source according to the present embodiment. The millimeter wave generating light source shown in the figure includes a fourth optical coupler 14 that demultiplexes the optical signal output from the optical modulator 1 with respect to that shown in FIG. A plurality of input channels are provided.

  In the example shown in FIG. 4, the optical waveguide that outputs the optical carrier signal fc needs to intersect one of the optical waveguides that output the sideband signals fc−fh and fc + fh. The crossing of the optical waveguides on the planar lightwave circuit 8 requires a large area and has disadvantages such as an increase in crosstalk between channels. The arrayed waveguide grating 7 is provided with two input channels. From the optical signal input to one input channel, the output of the sideband signals fc−fh and fc + fh is selected, and the optical signal input to the other input channel is selected. By selecting the output of the optical carrier signal fc, the optical signals output from the arrayed waveguide grating 7 do not need to intersect as shown in FIG.

  Therefore, according to the present embodiment, the optical signal output from the optical modulator 1 is demultiplexed and separately input to a plurality of input channels provided in the arrayed waveguide diffraction grating 7, whereby one input channel Since the output of the sideband signals fc−fh and fc + fh can be selected from the optical signal input to, and the output of the optical carrier signal fc can be selected from the optical signal input to the other input channel. There is no need to cross the optical waveguides formed in the planar lightwave circuit 8.

[Sixth Embodiment]
FIG. 6 is a block diagram showing a configuration of a millimeter wave generating light source according to the present embodiment. The millimeter wave generating light source shown in the figure is the one in which the fourth optical coupler is formed in the planar lightwave circuit 8 among those shown in FIG.

  Therefore, according to the present embodiment, the fourth optical coupler is also formed in the same planar lightwave circuit 8, so that the number of parts necessary for auto bias control can be reduced.

  In any of the embodiments, the millimeter wave generating light source is composed of all components that maintain polarization, but when all or some of the components that do not retain polarization are used, Immediately before the optical coupler for combining the sideband signals and outputting the optical millimeter wave signal, it is necessary to align the polarization of the sideband signal by the polarization controller.

  In any of the embodiments, the sideband signals fc−fh and fc + fh separated from the optical carrier signal fc are extracted to generate the optical millimeter-wave signal. The sideband signal of 2 × N × fh (N is a natural number) is extracted and combined to generate an optical millimeter-wave signal with a frequency of 2 × N × fh. You may let them.

It is a block diagram which shows the structure of the light source for millimeter wave generation in 1st Embodiment. It is a block diagram which shows the structure of the light source for millimeter wave generation in 2nd Embodiment. It is a block diagram which shows the structure of the light source for millimeter wave generation in 3rd Embodiment. It is a block diagram which shows the structure of the light source for millimeter wave generation in 4th Embodiment. It is a block diagram which shows the structure of the light source for millimeter wave generation in 5th Embodiment. It is a block diagram which shows the structure of the light source for millimeter wave generation in 6th Embodiment. It is a block diagram which shows the structure of the conventional light source for millimeter wave generation. It is a block diagram which shows the structure of another conventional millimeter wave generation light source. It is a figure which shows the light transmittance with respect to the bias voltage of an optical modulator. It is a block diagram which shows the structure of the apparatus which has the auto bias control function for a data signal modulation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical modulator 2 ... Single mode laser 3 ... Synthesizer 4 ... DC bias power supply 5 ... Photodiode for monitoring 6 ... Feedback circuit 7 ... Array waveguide diffraction grating 8 ... Planar light wave circuit 11, 12, 13, 14 ... Optical coupler 21, 22, 23 ... Optical bandpass filter

Claims (1)

Laser output means for outputting a single mode laser beam;
High-frequency signal generating means for generating a high-frequency signal having a frequency half the desired millimeter-wave frequency;
Optical modulation means for outputting an optical signal including an optical carrier signal and first and second sideband signals by modulating the single mode laser light with the high-frequency signal;
A DC bias power supply connected to the optical modulation means for adjusting the intensity of the optical carrier signal;
Demultiplexing means for demultiplexing the output of the light modulation means;
The arrayed waveguide having a plurality of input channels for inputting the optical signals demultiplexed by the demultiplexing means, and a plurality of output channels for separately outputting the first and second sideband signals and the optical carrier signal. A diffraction grating,
A multiplexing means for multiplexing the first and second sideband signals output from the arrayed waveguide diffraction grating ;
Control means for controlling the DC bias power supply so that the intensity of the optical carrier signal output from the arrayed waveguide grating is minimized ,
A millimeter-wave generating light source , wherein the branching means, the arrayed waveguide diffraction grating, and the multiplexing means are formed in the same planar lightwave circuit without crossing the optical waveguide .

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