JPS62279732A - Heterodyne detection method by amplification degree modulation of avalanche photodiode - Google Patents

Abstract

PURPOSE:To reduce the number of parts, to simplify a circuit and to enable a high sensitivity of the heterodyne detection of an optical high-frequency signal by modulating the amplification degree of an avalanche photodiode by means of using the signal of a local oscillator. CONSTITUTION:A high-frequency signal from a local oscillator 20 of the frequency(fr) is placed upon a direct current power source 10 connected to an avalanche photodiode 40 by a coupler 30. Therefore the amplification degree of the diode 40 is modulated and the signal of a difference frequency fd=¦fs-fr¦ which is between the optical high frequency signal of the frequency (fs) and the frequency (fr) is generated inside the diode 40. The signal of the difference frequency (fd) is imputted in a measuring instrument 60 through a filter 50. Thus the circuit can be simplified by eliminating the need for the electric circuit element such as a mixer, etc. and moreover a slight optical high-frequency signal can be detected by raising the utilization efficiency of the signal.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention is used in fields that use optical high-speed signals, such as optical communication and optical application measurement. This paper relates to a heterogain detection method using amplification modulation of an avalanche photodiode.

[Conventional technology]

Avalanche photodiodes are used when performing heterodyne detection using optical high-frequency signals.

After converting the optical high-frequency signal into an electrical signal using a high-speed photodetector such as a pin photodiode.

Frequency mixing is performed with the signal from the local oscillator in an electric circuit element such as a frequency mixer.

A common method is to extract a signal with a difference frequency.

When using the above conventional technology, the frequency band that can be detected by the photodetector 9 frequency mixer is limited, and it is required to efficiently transmit high frequency signals from the photodetector to the mixer. However, since the output impedance of photodetectors is generally high, the matching with low-impedance transmission systems and measuring instruments is poor (unless special measures are taken, the efficiency of signal utilization is low). For the purpose of improving the strength ratio.

Multi-stage amplifiers and mixers may also be used.

Handling high frequency electrical signals is complicated.

[Problem that the invention seeks to solve]

The present invention is for performing heterodyne detection of an original high frequency signal with higher sensitivity using a simpler method than in the prior art.

[Means for solving problems]

The present invention detects a signal of a difference frequency with high sensitivity by passing a high-frequency current having a slightly different frequency from the above-mentioned high-frequency signal, superimposing it on a DC bias current, to an avalanche photodiode receiving the original high-frequency signal. The present invention relates to a heterodyne detection method using amplification modulation of an avalanche photodiode, which is characterized by the following.

In photodetectors that convert original high-frequency signals into electrical signals,
By simultaneously performing frequency mixing and converting into a difference frequency signal, it is possible to perform hetero gain detection without depending on the performance of electric circuit elements such as mixers. Furthermore, according to this method, since the signal is converted into a low frequency signal inside the photodetector, handling is easier than when extracting a high frequency signal. Moreover, in a photodetector with an amplification effect,
By modulating the bias power supply, it is possible to modulate its amplification degree. An avalanche photodiode is a photodetector that has sensitivity over a wide band up to several GHz and has an amplification effect. By passing a high frequency current through the avalanche photodiode so as to be superimposed on the DC bias current, high frequency modulation of the degree of amplification becomes possible.

Figure 1 shows its outline. The avalanche photodiode 40 is generally used with the DC power supply 10 connected, but in the present invention, a high frequency signal from the local oscillator 20 with a frequency fr is connected to the coupler 30 in order to modulate the amplification degree. Superimpose it on this. As a result, the amplification degree of the avalanche photodiode 40 is modulated, and the difference frequency between the original high frequency signal of frequency fs, fd 1fs-frl
is generated inside the avalanche photodiode 40.

It can be observed through the filter 50. The frequency fs is generally about 100 MHz to 2 GHz, and in order to directly extract it, it is necessary to transmit it at low impedance, so the matching with the AC impedance of the avalanche photodiode is poor, so special measures have to be taken. Otherwise, the efficiency of signal use will be low. However, it is easy to lower the difference frequency, and the low frequency signal can be input directly to the high input impedance measuring instrument 60 without taking into account the impedance of the transmission system. The utilization efficiency of the signal that is later transmitted and measured is extremely high in the present invention (compared to the conventional method in which a high frequency signal is extracted and then a difference frequency signal is generated using a 9-frequency mixer, etc.).

It is possible to obtain a voltage signal several times to ten times as large.

〔Example〕

FIG. 2 shows an example of a specific circuit. The DC power supply 10 is
It is connected to the coupler 30 inside the case via a protective resistor (1-100Ω) and a feedthrough capacitor (100-1000pF).

The high frequency signal from the local oscillator 20 is connected via a coaxial connector to a coupler 30 inside the case, where it is superimposed with the DC signal.Transformer 31.Capacitor 3
2. Coil 33.34. The combination of Schottky barrier diodes 35 corresponds to coupler 30 in FIG. The transformer 31 protects the two oscillators 20 from DC voltage, converts the high frequency signal oscillating with an output impedance of 50Ω to a high impedance, and improves the modulation efficiency of the amplification degree in the avalanche photodiode 40. The coupling capacitor 32 is.

A high frequency signal from the transformer 31 is transmitted to the avalanche odd diode 40.

The capacitance of the avalanche photodiode 40 is selected to be large enough to block the difference frequency signal generated inside the avalanche photodiode 40. The high frequency signal is from several hundred MHz to 2 GHz, and the difference frequency signal is IMH2.
If it is below, approximately 20 pF to 100 pF is appropriate. The coils 33 and 34 are for blocking alternating current components. 33 is a coil of about 0.1-1 μF which has the function of blocking high frequency signals, and 34 is a coil of about 0.1-1 μF.

1. To block difference frequency signals. - It is a coil of about 10mH. In the above system, the DC signal and the high frequency signal are superimposed, and the protective Schottky barrier diode 35
The avalanche photodiode 40 is reached through the avalanche photodiode 40, and its amplification degree is modulated. When an optical high frequency signal of frequency fs is incident on this, a difference frequency signal is generated inside the avalanche photodiode 40. The frequency fd of the difference frequency signal is
When sufficiently low compared to fs and fr, the coil 51
(0,1-1 μH).

After passing through a filter 50 constituted by a coupling capacitor 52 (0.01-1 μF), the signal is taken out of the case via a coaxial connector and observed by a measuring device 60. The coil 51 is used to block high frequency signals, and the capacitor 52 is used to block DC signals. On the other hand, the high frequency signal is detected using a 50Ω resistor 71 and can be observed with a measuring device 72 via a coaxial connector.

As an application example of the above heterodyne detection method.

The high-resolution rangefinder is shown in Figure 3. In a rangefinder that uses light wave modulation, by increasing the modulation frequency, the distance measurement scale becomes finer, making it possible to measure with higher resolution.

A coupler 8 connects signals from a DC power supply 81 and a high frequency oscillator 82.
3 to drive the semiconductor laser 84 with a high frequency modulation signal of frequency fs. The optical high frequency signal emitted from the semiconductor laser 84 travels back and forth between the nine reflecting mirrors 90 and is detected by the avalanche seven photodiodes 40. Here, by measuring the phase difference between the signal from the high frequency oscillator 82 and the signal from the avalanche photodiode 40, the distance to the first reflecting mirror 90 can be determined. However, it is generally difficult to directly measure the phase of a high frequency signal, and the phase difference is measured after converting the high frequency signal into a low frequency signal using two local oscillators 20. At this time, the signal from the high frequency oscillator 82 is.

The frequency f from the local oscillator 20 by the frequency mixer 85
The signal from the run chef odd diode 40 is converted into a low frequency signal of frequency fd by frequency mixing with the signal of r.

Do not use elements such as frequency mixers (.

By modulating the amplification degree of the avalanche photodiode 40, heterodyne detection can be performed inside the avalanche photodiode 40. The heterodyne-detected difference frequency signal is detected by a phase difference measuring device 61 via a filter 50, and the phase difference φ with the signal from the two-frequency mixer 85 is determined here.

At this time, what is the distance from the reflecting mirror?

L=(N+φ/2π)・C/(2・fs)+d.

Although N is an unknown integer, it can be easily determined by measuring φ using several fs. C is light-speed dust, and d is a constant constant of the device. As is clear from the above equation, the phase difference φ is measured using the difference frequency signal of frequency fd, but when calculating the distance, the modulation wavelength c/rs calculated from the frequency fs of the optical high frequency signal is used as a scale. fs)) fd, it is possible to perform high-resolution distance measurement using a fine scale using a high-frequency signal while performing measurements in a low-frequency region where high sensitivity can be easily obtained.

〔Effect of the invention〕

For heterodyne detection of optical high frequency signals.

In the conventional method, a high-speed photodetector converts the signal into a high-frequency electrical signal, and then uses a two-frequency mixer or the like to perform frequency mixing with signals from two local oscillators to obtain a heterodyne signal. According to the method of the present invention, a hetero gain signal is obtained as the output of the avalanche photodiode by modulating the amplification degree of the avalanche photodiode, which is one of the high-speed photodetectors, using a signal from one local oscillator. .

This eliminates the need for electric circuit elements such as mixers, which eliminates the hassle of transmitting high-frequency signals.

Not only is this removed, but the strength of the hetero gain signal is also improved. Therefore, it not only contributes to cost reduction by reducing the number of parts and simplifying the circuit, but also enables detection of weaker original high frequency signals, making it possible to detect weaker signals such as the rangefinder shown in the above embodiment. It is effective in measurements targeting

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an apparatus for carrying out the second invention.
The figure shows an example of a specific electronic circuit for carrying out the present invention. Also, Figure 3 1. FIG. 1 is a configuration diagram of a range finder as a specific application example of the present invention. 10 DC power supply 20 Local oscillator 30 Coupler 31 Transformer 32 Coupling capacitor 33 Coil 34 Coil 35 Schottky barrier diode 40 Avalanche photodiode 50 Filter 51 Coil 52 Capacitor 60 Measuring device 61 Phase difference measuring device 71 Resistor 72 High frequency signal measuring device 81 DC Power supply 82 High frequency oscillator 83 Coupler semiconductor laser 85 Frequency mixer (G) Reflector Designated agent Figure 1

Claims (1)

[Claims] It is characterized by detecting a signal at a difference frequency with high sensitivity by passing a high-frequency current with a slightly different frequency from the above-mentioned high-frequency signal to an avalanche photodiode receiving an optical high-frequency signal, superimposed on a DC bias current. A heterodyne detection method using amplification modulation of an avalanche photodiode.