JPS62259035A - Lorentz type spectrum oscillator - Google Patents

Abstract

PURPOSE:To take a measurement with high efficiency and high accuracy by adjusting the output frequency and amplitude of a low-frequency drift voltage generator. CONSTITUTION:The output of a white noise source 1 is level-adjusted by the 1st variable attenuator 2 and then inputted to the 1st adder 5. The output of a low-frequency oscillator 3 which uses the low-frequency drift voltage generator is level-adjusted by the 2nd variable attenuator 4 and then inputted to an adder 5, which performs amplitude addition to the white noise. The white noise on which the low-frequency drift component is superposed is amplified 6 and then inputted to a voltage-controlled oscillator (VCO) 7. A Lorentz type spectrum which has a frequency drift appears at the output of the VCO 7. This spectrum width is settable to an optional value by adjusting the quantity of attenuation of the attenuator 2. Further, the speed and size of the frequency drift are adjustable to optional values by adjusting the oscillation frequency of each oscillator 3 and the quantity of attenuation of the attenuator 4. Thus, a measurement is taken with high efficiency and high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a laser beam spectrum simulation device used in the development and evaluation of coherent optical communication devices.

(Prior art) Coherent optical communication systems using optical heterodyne and homodyne detection have the advantage of being capable of high-density multiplex communication and long-distance communication compared to direct detection systems that use only the intensity of light. There is. In the development of receivers used in coherent optical communications, it is often necessary to consider the effects of the spectrum spread and frequency drift of laser light. Conventionally, when trying to conduct an evaluation experiment to determine how much the receiver, especially the demodulation circuit, is affected by spectrum broadening and frequency drift, two laser beams are actually combined and heterodyne detection or homodyne detection is performed. However, a method has been adopted in which the beat obtained by this is used as demodulation. (Emura et al. “External light feedback type DBRLD
Study of PSK optical heterodyne differential synchronous detection method using optical heterodyne differential synchronous detection method', 1960 National Conference of the Institute of Electronics and Communication Engineers, 2648) However, this evaluation method uses multiple light sources, so it is troublesome to assemble the optical system. However, it has the disadvantage that only the spectral width specific to the light source can be obtained.It also has the disadvantage of being inferior in terms of accuracy and efficiency.

Therefore, if there is an oscillator that oscillates in the beat frequency band and can adjust the spectrum spread and frequency drift amount, it becomes possible to evaluate the demodulation circuit efficiently and with high accuracy. However, until now there has been no oscillator with such a function.

(Problems to be Solved by the Invention) The present invention aims to improve the efficiency and accuracy of evaluation experiments for coherent optical communication receivers by providing a new oscillator that can adjust spectrum broadening and frequency drift, which were not available in the past. It is something.

(Means for Solving the Problem) A Lorentzian spectrum oscillator according to the present invention includes a white noise source having an output power adjustment function, a low frequency drift voltage generator having an output frequency and output voltage adjustment function,
An adder for adding the amplitudes of the two output signals of the white noise source and the low frequency drift voltage generator, and a voltage controlled oscillator (VCO) that uses the output signal of this adder as an input signal for controlling the oscillation frequency. It is configured. Among these, the output of the white noise source is the thermal noise generated by the resistor amplified by a high gain amplifier, and its amplitude has a Gaussian distribution.

Generally, when frequency deviation is Gaussian distributed in FM modulation, it is known that if the modulation band is set sufficiently large compared to the time resolution of the observation system, the spectrum of the modulated wave becomes Lorentzian. (Yuyo and other 6 statistical physics)
PP227-235 Iwanami Shoten) The present invention focuses on this principle and sets the band of the white noise source and the modulation band of the VCo sufficiently wide to make the output signal spectrum of the vCO Lorentzian. The spectral width is set to an arbitrary value by adjusting the output signal of the source.

Furthermore, using the low frequency drift voltage generator, vCO
It is now possible to give a frequency drift to the output. By adjusting the output frequency and amplitude of the low frequency drift voltage generator, the speed and magnitude of frequency drift (frequency deviation) can be set arbitrarily.

(Example) FIG. 1 shows a first example of the present invention. The output of a white noise source 1 using a high gain amplifier is level-adjusted by a first variable attenuator 2 and then input to a first adder 5 .

Further, the output of the low frequency oscillator 3 used as a low frequency drift voltage generator is level-adjusted by the second variable attenuator 4, and then input to the first adder 5, where the amplitude is added to white noise. The white noise on which the low frequency drift component is superimposed is amplified by the amplifier 6 and then input to the VCO 7 . A Lorentzian spectrum with frequency drift appears in the output of the VCO 7. This spectral width can be set to any value by adjusting the amount of attenuation of the first variable attenuator 2. Further, the speed and magnitude of the frequency drift can be adjusted to arbitrary values by adjusting the third oscillation frequency of the low frequency oscillator and the attenuation amount of the second variable attenuator 4, respectively.

FIG. 2 shows the measured values of the spectrum obtained with the system of the first example. The measurement conditions are as follows.

In this measurement, since the purpose was to observe the spectral shape, the low frequency oscillator 3 was not used, and the output of the white noise source 1 was input directly to the VCO 7.

The observed results shown in Figure 2 are in good agreement with the theoretical value of the Lorentzian spectrum (solid line).

FIG. 3 shows a second embodiment of the invention. The second embodiment is obtained by removing the amplifier 6 from the system of the first embodiment. Although this embodiment has a narrower spectrum width range than the first embodiment, it has the advantage of a simpler configuration.

Therefore, it can be said that this system is effective when conducting evaluation experiments for relatively narrow spectral widths.

(Effects of the Invention) As described in detail above, by using the apparatus according to the present invention, a Lorentzian spectrum having an arbitrary spectral width and frequency drift can be electrically generated. This eliminates the need for the optical system conventionally used to evaluate demodulation circuits for coherent optical communications, making it possible to perform highly efficient and highly accurate measurements.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG. 2 is a diagram showing a first embodiment of the present invention.
Figure 3 is a diagram showing the measured values of the spectra of Examples.
It is a figure showing an example of. In the figure 1. White noise source 2. First variable attenuator 3, low frequency oscillator 4. Second variable attenuator 5, first adder 6. Amplifier 7. It is a VCO. 1: White noise source 2: First variable attenuator 6: Amplifier 3: Low frequency oscillator 7: VCO 4: Second variable attenuator 5: First adder Fig. 1 Fig. 3

Claims (1)

[Claims] A white noise source with an output power adjustment function, a low frequency drift voltage generator with an output frequency and output voltage adjustment function, and for adding the amplitudes of the two output signals of the white noise source and the low frequency drift voltage generator. 1. A Lorentzian spectrum oscillator comprising: an adder; and a voltage-controlled oscillator that uses the output signal of the adder as an input signal for controlling the oscillation frequency.