JPH01147436A - Autocorrelation type heterodyne optical communication system - Google Patents

Abstract

PURPOSE:To omit a local oscillation light source and to build a large-capacity light transmission system at a low cost by passing one light signal through optical routes of different distances and again synthesizing the same so as to interference the light signals with each other. CONSTITUTION:The light signal subjected to the modulation to alternately switch the basic wavelength of the light and the signal deviated by a certain specific micro- wavelength from the basic wavelength in the light signal in the same manner as heretofore is transmitted on a signal transmission side and a light interference device having the distance spacing shown as follows are placed on a signal reception side. Namely, the optical route acting as the light interference device is constituted of an optical path a1, optical paths a2, a3, optical paths b1-b3, translucent mirrors m1, m4, reflecting mirrors m2, m3 and a photodetector APD consisting of an avalanche photodiode. The delay distance (d) of the optical path is so determined as to satisfy d=(b1+b3)=(basic wavelength of light)X(n+0.5) (n is a positive integer). The signal having the same envelope as the source signal on the signal transmission side is thereby obtd. with the photodetector APD and the need for the local oscillation light source is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical transmission system, and particularly to a heterodyne optical communication system.

Blank space below [Prior art] Conventionally, this type of heterodyne optical communication system detects an output signal obtained by interfering with an input optical signal on the receiving side and a local oscillation light source generated on the receiving side. The source signal was obtained from KotoK.

[Problem that the invention seeks to solve]

The fundamental wavelength of the local oscillation light source mentioned above deviates from the fundamental wavelength generated on the transmitting side by a certain value, but this deviation must be kept constant with extremely high precision on the transmitting and receiving sides. It won't happen. but.

Manufacturing a radar diode for heterodyne communication with such characteristics requires special processing technology compared to ordinary radar diodes, making it unsuitable for mass production and requiring high manufacturing costs. It had become.

[Means for solving problems]

The autocorrelation heterodyne optical communication system according to the present invention uses a conventional heterodyne laser diode on the transmitting side to alternately switch between the fundamental wavelength of light and a signal shifted by a certain minute wavelength from the fundamental wavelength. Transmit the modulated signal.

On the other hand, on the receiving side (the fundamental wavelength of the radar diode)
It is characterized by having an optical interference device and a normal photodetector having an interval of X(n+0.5) (where n is a positive integer).

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings.

First, from the transmitting side, the data string of the source signal, which is the signal to be transmitted, is 5(t)2, and a kind of difference signal Δ5(t) is created from this data string. , is obtained from the following formula.

Δ5(t). 1 = (Δ5(t)., +5(t).,) 1st digit ■Here, the subscript Ol is S is 0. or 1.

The voltage M(t) applied to the oscillation frequency control terminal of the radar diode for heterodyne.

machine 0 = bias voltage 10k·Δ5(t). 1
■Determine. Here, the bias voltage is the reference voltage for the Raded diode to transmit at the fundamental frequency f0.

The constant is an incremental voltage for obtaining a frequency change Δf that is optimal for performing optical heterodyne detection.

By doing as above, Δ5(t). When 1 is O, the optical frequency is f. , Δ5(t). When 1 is 1, (fo
The source signal is modulated into an optical signal, specifically as shown in FIG. 2.

Next, in the receiving section, the first
Create the optical path shown in the figure (this is an example). In FIG. 1, al is the optical path of the input signal.

ml is the light input from optical path a1 to optical path a2 and optical path b1.
The semi-transmissive mirror m4 is a semi-transmissive mirror that transmits the light coming from the optical path a2 as it is to the optical path a3, and reflects the light coming from the optical path b3 to the optical path a3. Also, m2 and m3
is a normal reflector, and APD is a photodetector using an avalanche 7 photodiode.

The delay distance d of the optical path is for the example shown in FIG.

(b1+bs) However, if the optical path configuration is different, it is necessary to add water each time. The optical path delay distance d is.

d”=(bt +b3)=(fundamental wavelength of light)
n+0.5) ■However, n is determined to satisfy a positive integer.

When Equation 0 is satisfied, if the optical frequency after a certain point in time (speed of light) The power is almost O, and the photodetector APD no longer detects light.

On the other hand, if the optical frequency after (speed of light) Xd time from a certain point differs by Δf, the light synthesized by the semi-transmissive mirror m4 will be in the form of overlapping waves of f and (f + Δf). In the device APD, light having a width of Δf is detected.

From the relationship between this and equations (1) and (2), the source signal 5(t) on the transmitting side of the photodetector APD. A signal with the same envelope as 1 will be obtained. Here, the local oscillation light source that was conventionally required is no longer necessary. A concrete example of the operation on the receiving side is shown in Part 3.
As shown in the figure. The waveform created in the above example is used as the optical input waveform. The waveform of the photodetector APD is 5(t
). 1 has been reproduced.

〔Effect of the invention〕

As explained above, the present invention enables local oscillation with a highly accurate oscillation frequency, which is conventionally required, by passing one optical signal through optical paths of different distances, recombining it, and causing interference. A low-cost, high-capacity optical transmission system in which the light source can be omitted and the source signal can be detected even if the frequency stability of the transmitting side changes to some extent due to interference between the optical signal and itself. can be constructed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of an optical path on the receiving side to which the present invention is applied, and FIGS. 2 and 3 are time charts of signals that do not provide a detailed explanation of the present invention. In the figure, 2m□ 1m4 is a semi-transmissive mirror tm2+”3 is a reflective mirror,
APD is a photodetector.

Claims (1)

[Claims] 1. In the heterodyne optical communication system, the transmitting side transmits and receives an optical signal that is modulated by alternating the fundamental wavelength of light and a signal shifted by a certain minute wavelength from that fundamental wavelength. Fundamental wavelength x (n+0.5) on the side
An autocorrelation type heterodyne optical communication system that detects light without using a local oscillation light source by placing an optical interferometer with a distance interval of (n is a positive integer).