JPS6346022A - Optical multiplex transmission system - Google Patents

Abstract

PURPOSE:To make it unnecessary to use a special control terminal, and to demultiplex the number of multiplex optical signals by constituting the titled system so that an average transmission power between the multiplex optical signals is changed and transmitted by a transmission side, and a DC component of the optical signal which is detected by an output becomes maximum by using a specific optical demultiplexer by a reception side. CONSTITUTION:A transmitting means 1 contains means Mo1-Mo4 for setting each average transmission power of plural optical signals to prescribed different values, and a receiving means 2 contains an optical demultiplexer DEMUX to which plural pieces of optical directional couplers C1, C2 in which two pieces of optical waveguides L1, L3 have been connected to inputs and outputs, respectively, have been connected in a cascade shape. A demultiplexing optical frequency interval of the optical demultiplexer DEMUX and and input optical frequency interval are made to coincide in advance by setting a value of an optical path length difference to a prescribed value at the time of manufacture, and by a control means CONTIO, a relative effective length of two pieces of optical waveguides L1, L2 is controlled so that a DC component of an output of the optical demultiplexer DEMUX becomes maximum, by which an absolute value of the demultiplexing optical frequency can be made to coincide with the input optical frequency. In this way, by manufacturing on one plane optical waveguide, the number of multiplex optical signals can be increased.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical multiplex transmission system, and in particular to an optical multiplex transmission system that increases the number of multiplexed channels by multiplexing and transmitting optical signals with narrow frequency intervals of Gl (z order). The present invention relates to a de-DM (frequency division) type optical multiplexing transmission system that enables this.

[Conventional technology]

The conventionally known optical FDM transmission system does not have a means to vary the average transmission power for each channel on the transmitting side, and uses an optical demultiplexer with the configuration described below on the receiving side. Ta.

FIG. 4 is a block diagram showing an example of a conventional optical demultiplexer for optical FDM transmission, which has a basic structure of a Matsuhatsu Ender interferometer. In Figure 4, C1 and C2 are 3
dB optical directional coupler, L1 to 1.6 are optical waveguides, M is an optical length adjustment section, D is a photodetector, and C0NT is a control circuit. Here, the optical waveguides L3 and L4 are different in length. The optical directional couplers C1 and C2 divide the input optical signal into 1=1 and output it. For example, in the case of the optical directional coupler C1, the optical signal input to the optical waveguide L1 is divided into two parts. The optical signal input to the optical waveguide L2 is input to the optical waveguide L3 and L4, and the optical signal input to the optical waveguide L3 is input to the optical waveguide L3 and L4.
The optical signal entering the optical directional coupler CI from the optical waveguide L1
and L2, the optical signal entering the optical directionality detector CI from the optical waveguide L4 is output to the optical waveguides L1 and L2 at a ratio of 1:1, respectively.

At this time, the phases of the divided optical signals are shifted by 90 degrees from each other.

When an optical signal is input to the optical waveguide L1 in the configuration shown in FIG. 4, the input optical signal is divided into two by the optical directional coupler C1, and then combined again by the optical directional coupler C2. At this time, the optical signal passing through the optical waveguide L3 and the optical signal passing through the optical waveguide L4 interfere with each other according to their phase difference (propagation delay phase difference). The phase difference depends on the optical length difference between the optical waveguides L3 and L4. For example, when the phase difference is such that the optical signals combined into the optical waveguide L5 strengthen each other, the optical signals combined into the optical waveguide L6 weaken each other. .

Therefore, depending on this phase difference, the optical signal is outputted to the optical waveguide L5 or to the optical waveguide L6.

Expressing this in equations, the i3 transient characteristic T (1-5) from the optical waveguide L1 to the optical waveguide L5 and the transmission characteristic T (1-6) from the optical waveguide L1 to the optical waveguide L6 are as follows. become.

'(1-5) -5in2(δ) T(1-6) = cos2(δ) Here, n is the refractive index of the optical waveguide, and ΔL is the optical waveguide L3 and 1
, 4, C is the speed of light in vacuum, f is the optical frequency, and δ represents the propagation delay phase difference. The propagation delay phase difference δ depends on the optical frequency f.

Figure 5 shows the transmission characteristics T (1-5) and T (1-6
) is plotted as a function of optical frequency f.

By utilizing this optical frequency dependence of the transmission characteristic, for example, the optical signals of optical frequencies f1 and f2 shown in FIG. 5 can be separated into optical waveguides L5 and L6, respectively. In other words, it functions as an optical demultiplexer with the basic structure of a Matsuhatsu Enda interferometer.

The absolute value and frequency interval of each optical frequency to be demultiplexed is determined by the difference in optical path length between the optical waveguides L3 and L4. f to the frequency interval is expressed as 2 n・ΔL, for example, n=1.5 (refractive index of glass), Δf
=10GHz, then ΔL=10. It becomes hn. This frequency interval can be set with sufficient accuracy based on the difference in optical path length when manufacturing the optical waveguide.

On the other hand, when the input optical frequency f is the peak of the transmission characteristic shown in FIG.
However, since the optical frequency f is a large value of about 200 THz, even if the refractive index n or the optical path length difference ΔL is slightly shifted, n π ・ ΔL is Since it deviates from mπ, it is difficult to satisfy this condition simply by setting the optical path length difference ΔL during manufacturing.

Even if this condition is temporarily satisfied, the demultiplexed optical frequency becomes temporally unstable due to fluctuations in the optical path length difference ΔL due to external disturbances such as temperature fluctuations. Therefore, as a method of matching the demultiplexed optical frequency to the human-powered optical frequency, the method described below has been conventionally considered (see Japanese Patent Laid-Open Nos. 61-80109).

Photodetector D, optical length adjustment section M and control circuit C in Fig. 4
0NT is a component for controlling the demultiplexed optical frequency. Furthermore, with this configuration, a portion of the optical signal that has passed is reflected at one end of the optical waveguide L5.

The reflection at one end of the optical waveguide L5 may be natural reflection due to a cleavage of the optical waveguide, or a reflective coating may be applied if necessary. The optical length adjustment section M changes the refractive index of the optical waveguide by an external signal. For example, in the case of a dielectric waveguide, the refractive index is changed by applying an electric field, and in the case of a glass optical waveguide, the optical length is adjusted by changing the refractive index by applying heat. It has become.

Now, when optical signals of optical frequencies f and f2 are input to the optical waveguide L1, if the input optical frequency and the transmission center frequency of the optical demultiplexer match, the optical signal of the optical frequency f1 is transmitted to the optical waveguide L5. , the optical signal of optical frequency f2 is output to the leading wavepath L6 (or vice versa). At this time, the optical waveguide L
The partially reflected optical signal of optical frequency f, (or r2) at 5 returns to the optical waveguide L1 along the original path, and nothing is output to the optical waveguide L2. On the other hand, when the frequencies do not match, the optical frequency f1 input to the optical waveguide L1
The optical signal is divided into optical waveguides L5 and L6 and outputted, and the optical signal reflected by optical waveguide L5 is further outputted to optical waveguide L5.
2 and output to Ll. In other words, the optical waveguide L2 receives an optical output corresponding to the frequency shift. Therefore, the optical signal power outputted from the optical waveguide L2 is detected by a photodetector, and the control circuit C0 is configured to minimize this power.
By applying a signal to the optical length adjustment section M using the NT, the input optical frequency and the demultiplexed optical frequency can be matched.

The operating principle of the optical demultiplexer described hereinabove was for the case of demultiplexing a two-wave multiplexed optical signal. To separate two or more waves of optical signals, the periodicity of this optical demultiplexer is utilized. For example, to demultiplex a four-wave multiplexed optical signal, three optical demultiplexers with different demultiplexing frequency intervals are arranged in a cascade as shown in FIG. In FIG. 6, (optical waveguides L1 to L6, optical directional couplers 01 to C2, optical length adjustment section M1, control circuit C0NT1 and photodetector DI) constitute the first stage optical demultiplexer, (optical waveguide L5 , L7~Lll, optical directional coupler 03
~C4, optical length adjustment unit M2, control circuit C0NT2 and photodetector D2) and (optical waveguide L6, L12~L1)
6. The optical directional couplers 05 to C6, the optical length adjustment section M3, the control circuit C0NT3, and the photodetector D3) each constitute a second-stage demultiplexer. Here, the optical path length difference between the optical waveguides L8 and L9 and the optical waveguide L13 and Ll4 is set to 1/2 of the optical path length difference between the optical waveguides L3 and L4, and the photodetectors D1 to D3
If a control signal is applied to the optical length adjustment units M1 to M3 so that the optical signal power received by the optical demultiplexer is minimized, each optical demultiplexer has the transmission characteristics shown in FIGS. 7(a) to (dl). Figure (al) and Figure 7 (C1 respectively show the demultiplexing characteristics from the optical waveguide L1 to L5 and from the optical waveguide L1 to L6 in the first stage optical demultiplexer; (bl and (di) indicate the demultiplexing characteristics of the second-stage optical demultiplexer.

Therefore, the optical frequencies f, , f2, f3 with constant frequency intervals
When the optical signals of f4 and Then, the optical frequency f is obtained from the group of optical frequencies r1 and f3, respectively.
1 and f3, and a group of optical frequencies f2 and f4 can be split into optical frequencies f2 and f4. When multiplexed optical signals of four or more waves are to be demultiplexed, they may be combined in a cascade in the optical demultiplexer in the same manner.

The above are conventionally considered optical demultiplexers for optical FDM transmission and their demultiplexing frequency control methods.

[Problem that the invention seeks to solve]

However, this conventional example has two problems. One is that, as shown in FIG. 4, the input optical signal is reflected by the optical waveguide L5, resulting in a transmission loss of the optical demultiplexer. If the reflectance is lowered in an attempt to improve this, the intensity of the optical signal detected by the control photodetector decreases, making control difficult.

The second problem is actual production. The above-mentioned optical demultiplexer requires a control optical waveguide in addition to the input/output waveguide necessary for demultiplexing the original optical signal. Because there are limits to the dimensions of the optical waveguide substrate and the bending radius of the optical waveguide that can actually be manufactured, the need for an extra optical waveguide means that an optical demultiplexer with increased multiplexing can be placed on the same plane optical waveguide. This poses difficulties when attempting to fabricate them.

For example, a configuration example of a planar optical waveguide optical demultiplexer for four waves can be considered as shown in FIG. Kokote L1~1.16
, M1 to M3, and C1 to C6 correspond to the symbols in FIG. In this configuration example, it is not possible to take out the reflected optical signals to the leading waveguides I and 7 to the outside, and it is not possible to control the demultiplexed optical frequency. In conventional examples that require optical waveguides other than the originally required optical waveguides, there is a problem in that it is difficult to increase the number of multiplexed optical demultiplexers by fabricating multi-stage optical demultiplexers on the same plane waveguide.

The purpose of the present invention is to solve the above problems.
An object of the present invention is to provide an optical multiplex transmission system that makes it possible to demultiplex multiplexed optical signals without using special control terminals on the receiving side.

[Means for solving problems]

The present invention provides optical multiplex transmission including a transmitting means for multiplexing and transmitting a plurality of optical signals of different optical frequencies, and a receiving means for receiving the multiplexed optical signal from the transmitting means and separating it into the plurality of optical signals. In the method, the transmitting means includes means for setting the average transmission power of each of the plurality of optical signals to a predetermined different value, and the receiving means includes two optical waveguides connected to input and output, respectively. The optical demultiplexer includes a plurality of optical directional couplers connected in a cascade, and this optical demultiplexer detects the relative effective length of the two optical waveguides using the output of the optical demultiplexer. The present invention is characterized in that a control means 110 is provided for controlling the DC component of the optical signal to be maximized.

[For production]

In the optical demultiplexer having the basic structure of the Matsuhatsu Ender interferometer shown in FIG. When υ is manually input, the output power obtained by removing the modulation component and extracting only the DC component is the average sending 1ε power a and a2, the optical frequency f1, the frequency interval Δf between the optical frequencies f1 and f2, and the optical path length. It is given by a formula including the difference ΔL.

Therefore, the splitting optical frequency interval of the optical demultiplexer and the input optical frequency interval f are made to match in advance by setting the value of the optical path length difference ΔL to a predetermined value at the time of manufacture, and the control means By controlling the relative effective lengths of the two optical waveguides so that the DC component of the output of the demultiplexer is maximized, the absolute value of the demultiplexed optical frequency can be made equal to the human-powered optical frequency r. can.

That is, there is no need to take out the control terminals as in the conventional method, and it becomes possible to fabricate a large number of optical demultiplexers on one planar optical waveguide and increase the number of multiplexed optical signals.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. Here, O31 to 034 are optical oscillators, MO1 to MO4 are optical modulators, MUX is an optical multiplexer, DEMUX is an optical demultiplexer,
R1-R4 are optical receivers. Optical oscillator O3I~O3
4. The transmitter 1 is connected to the optical modulators MO1 to MO4 and the optical multiplexer MUX, and the optical demultiplexer DEMUX and the receiver R1
~R4 constitute the receiving section 2. With this configuration, in the transmitter 1, signals are added to the optical outputs of the optical oscillators 031 to O34 by the optical modulators MO1 to MO4 and transmitted. At this time, the output level of each of the optical oscillators 031 to 034 is set to be different depending on the optical frequency. Figures 2 and 3 show the optical demultiplexer 1 of the receiving section 2)
FIG. 2 is a detailed diagram of E M jJ The configuration of the optical demultiplexer and its operating principle are basically the same as those described in the conventional example, but it differs from the conventional example in that the demultiplexed optical frequency is controlled without using a special control waveguide terminal. . In the following, it will be shown that the demultiplexed optical frequency can be controlled with this configuration.

First, we will discuss the case of two-wave multiplexing. In Figure 2, Ll
-L6 is an optical waveguide, C1 and C2 are 3 dB optical directional couplers, DIO is a photodetector, MIO is an optical length adjustment unit and C
0NTIO is a control circuit. The photodetector DIO is not specially equipped for controlling the frequency of the demultiplexed light, but is for receiving the transmitted optical signal, and controls the frequency of the demultiplexed light using this output. When the modulation component is removed and only the DC component is extracted from the optical signal received by the photodetector DIO, the output power P is: P-at cos2 (K-f +) + az cos
2(K-f,)-a 1cos"(K-f I)+a
7 cos” (K-f, +K・Δf)−−−−−−+
11 = n π · ΔL / c Δf = f2 - f.

It can be expressed as However, al and a2 are the average transmission powers of optical signals of optical frequencies f1 and f2, respectively, n is the effective refractive index of the optical waveguide, ΔL is the optical path length difference between optical waveguides L3 and L4, C is the speed of light in vacuum, and Δf is the input optical frequency interval. In equation (1), the first term on the right side represents the transmission of the optical signal with the optical frequency f1, and the second term represents the transmission of the optical signal with the optical frequency f2. The splitting optical frequency interval of the optical demultiplexer is the input optical frequency interval Δ
The condition that matches f is K・Δf−π/2 (rn: integer)---(2)
Also, the condition that the absolute value of the demultiplexed optical frequency matches the input optical frequency is K−f, −mπ −−−−−−(3)
It is. The condition of equation (2) is, for example, effective refractive index n=1.
5, the optical path length difference ΔL- for Δf=10GHz
It becomes 10.2 mm. This can be satisfied by setting the optical path length difference ΔL when manufacturing the optical waveguide.

On the other hand, in order to satisfy the condition of formula (3), the optical length adjustment section M10
It is necessary to perform control using Now, assuming that the conditions of formula (2) are satisfied by the settings at the time of optical waveguide fabrication, formula (1) is as follows: P = a, C082(K・f +) + 32si
n”(K, f 2) = (a + − a z) cos2(
K-f +) + a 2 (41. Here, for example, if a is set as >32 in the transmitter 1,
The output power P becomes maximum when -f,=mπ. Therefore, the control circuit C0NT is set so that the DC component of the optical signal η detected by the photodetector DIO is maximized.
l0cIf you add a signal to the optical length adjustment unit MIO,
-f and -mπ are always satisfied, and the input optical frequency and demultiplexed optical frequency can be matched.

In this way, by varying the average transmission power of the input optical signal for each optical frequency, it is possible to control the demultiplexed optical frequency. According to this, there is no need to use the optical waveguide L2 for control as in the conventional example shown in FIG.

Next, the case of four-wave multiplexing will be explained. In Fig. 3, L1 to L6 are optical waveguides, 01 to C6 are 3 dB optical directional couplers, Mll to M13 are optical length adjustment units, Dll and D12 are photodetectors, CON Tll to C0NT13
is the control circuit. Fig. 3 shows a configuration in which three optical demultiplexers shown in Fig. 2 are combined in a cascade configuration (optical waveguide L1
~L6, optical directional coupler 01~C2, optical length adjustment unit Ml
1 and control circuit CON Tl1), the first stage optical demultiplexer is connected to (optical waveguides L5, L7 to Lll, optical directional coupler 0
3 to C4, optical length adjustment section M12 and control circuit C0NT
12) and (optical waveguides L6, L12 to L16, optical directional couplers 05 to C6, optical length adjustment section M13 and control circuit C0NT13) each constitute a second stage optical demultiplexer. In this configuration, the optical frequencies f1 and f are sent to the leading waveguide L1.
When the optical signals of 2, f3 and f are input, the output power pH is the DC component of the optical signal detected by the photodetector Dll, and the output is the DC component of the optical signal detected by the photodetector DI2. Power P12 is P11=a, 5in
2(K+・f+)cos2(Kz−f+)+a
, 5in2(K+・f 2)cos2(Kz・f
2)+a 3sin”(K+・f:1)CO32
(K 2.f 3)+a a 5in2(K +・f
4) CO3” (K2・f 4) PI3- a + c
os2(K+・f+)cos”(K3・f+)+
a 2cos”(K +-f z)cos”(K3・f
2) + a, cos”(K+・f 3) cos”(
K3・f:+)+a, cos2(K+-f4
)cos2(K3-f4)K,=nπ・Δ
It can be expressed as L 1 / c Kz = nn - ΔL 2 / c K3 = n π · ΔL 3 / c. Here, a1 to a4 are the average transmission powers of optical signals with optical frequencies f1 to r4, ΔLl is the optical path length difference between optical waveguides L, 3 and 1.4, and ΔL2 is the optical path length between optical waveguides L8 and L9. difference,
ΔL 3 is the difference in optical path length between the optical waveguides L13 and I,14. In the right-hand side of equation (5) and (6), the first term, second term, third term, and fourth term are respectively optical frequencies f, , f2, f
3 and f, represent the transmission of optical signals. The condition that the input optical frequency interval Δf and the demultiplexed optical frequency interval match is as follows, and this can be satisfied when manufacturing the optical waveguide. Assuming that the condition of equation (7) is satisfied, (5)
Equation and equation (6) are as follows: P11= a 15inJK1・f +)cos”(K
z・f +)+ a 2cos”(K+・f +)co
s”(K2- f, + π/4)+a 3sin2(
K +・f +) sin2 (K z・f +) + a
a cos2 (K+・f +) sin2 (Kz, f +
+TC/ 4)P 12= a + 5inJK+・
' z) sin2 (K3・f 2 + yr/ 4) +
a z con2(K+・f2)CO3”(K
3・f J123sin2(K+・f2)cos”(K
3・fg+π/4)+a a cos2(K I-f
2) sin2(K3-fg)-=~(9). The conditions for matching the demultiplexed optical frequencies are, for example, an optical signal of optical frequency f is sent to the optical waveguide LIO, an optical signal of optical frequency f2 is sent to the optical waveguide L16, an optical signal of optical frequency f3 is sent to the optical waveguide Lll, and an optical signal of optical frequency f4 is sent to the optical waveguide L16. The optical signal of
When outputting to 5, K+'f+=(m++1/2)
π〜−−(101K 2− f , = m 2n
−−−−−−αDK, ・f2=m3π
---1---θ. However, m
, , m2 and m3 are integers. Since K1- and 3 can be finely adjusted by the optical length adjustment units Mll to M13, if appropriate signals can be applied to the optical length adjustment units Mll to M13, the conditions of formulas 00)2 to 02 can be satisfied. is possible.

It will be shown below that if a certain relationship holds between the average transmission powers a1 to a4, a control signal can be given to the optical length adjustment units Mll to M13 so as to satisfy the conditions of formulas 00)2 to 0.

For simplicity, if K, -f, -O1 are written as 2.f and -O2 is written as 3.f2-O3, equation (8) can be rewritten as follows.

P 11 = 1/2 ・sin”(O1)・((a
, -a 3) cos(2・θz)+(O2O4)s
in(2・O2)+(a,+a3 ax aa))+
1/24a z a a) cos(2・O2)
+az/2+3・a,/2 −−−−−030
Looking at the output power pH as a function of 01 from equation 3, if the value in brackets on the right side is []〉0, then θ+ = (m
It can be seen that the output power pH is maximum when ++1/2). Therefore, if the value in [ ] is 0, then if a signal is applied to the optical length adjustment unit M11 so that the output power-pH is maximized,
The condition of formula C101 is always satisfied.

Given a certain relationship between the average transmission powers a1 to a4,
It will be shown below that [ ] is always 0 and that the condition of formula 001 can be realized. If we rewrite the inside [], (]=(a,-a,,)cos(2,θz)”(a++
a3)-(a 4- a z) sin(2・O2)-(
az+an) ---------It becomes a circle. Here, it is assumed that al>aa, O4>O2.

J, (1Yu2 right side>-(at-aa)+(at+33)
(O4O2) (ax + a4) = 2- < a 3-a a) -----
-O5. From equation (b), it can be seen that if aa>O4, the value in [ ] is always positive. That is, a , > a 3 > a 4 > a 2 −
--- If +IQ is set, it will always be []>0, and the condition of equation 00) can be satisfied by applying a signal to the optical length adjustment unit Mll so as to maximize the output power pH.

00) When the condition of the formula is satisfied, the output power -p
H is Pll-(at aa) CO32(Kz-f+)+
23-------Responsibility m. Assuming that the condition of the O0 formula is satisfied, K2
・The output power pH is maximum when f,=m2π. Therefore, CIQ
With the input optical signal power set to satisfy the condition of the formula, if a signal is applied to the optical length adjustment units Mll and M12 so that the output power pH becomes maximum, first, the signal to the optical length adjustment unit Mll becomes 00. ) is satisfied, and then the condition of αD2 is satisfied.

On the other hand, if equation (9) satisfies the conditions of equation 00), then PI3-(az a4) cos''(K3・f z)
+a4---m. Assuming that the condition of equation (2) is satisfied, K
The output power P12 becomes maximum when 2°f2−m3π. Therefore, if a signal is applied to the optical length adjustment section M13 so as to maximize the output power P12 while a control signal is being applied to the optical length adjustment section Mll, the condition of Equation 13 is always satisfied.

The feature of the present invention is that in FIG.
4 and an optical demultiplexer DEMUX consisting of the optical demultiplexer shown in FIG. The reason is that the control is configured so that the DC component of the current is maximized.

In other words, the conventional technology includes: +a) A means for changing the average transmission power of each frequency of a multiplexed optical signal on the transmitting side; (1)) A special control terminal on the optical demultiplexer on the receiving side. The difference is that it does not use .

〔Effect of the invention〕

As explained below, the present invention transmits by changing the average transmission power between multiplexed optical signals on the transmitting side, and
Using an optical demultiplexer configured as shown in the figure or Fig. 3,
By configuring the control means so that the DC component of the optical signal detected at the output is maximized, the multiplexed optical frequency and the transmission frequency of the optical demultiplexer can be matched. Therefore, there is no need to use special control terminals in the optical demultiplexer, so compared to the conventional example, a large number of optical demultiplexers can be fabricated in one planar optical waveguide, and the number of multiplexed optical signals can be increased. effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a block diagram showing an embodiment of the optical demultiplexer shown in FIG. 1. FIG. 3 is a block diagram showing another embodiment of the optical demultiplexer shown in FIG. 1. FIG. 4 is a block diagram showing an example of a conventional optical demultiplexer. Figure 5 shows its transmission characteristics. FIG. 6 is a block diagram showing another example of a conventional optical demultiplexer. Figure 7 shows its transmission characteristics. FIG. 8 is an explanatory diagram showing the actual structure of a conventional optical demultiplexer. DESCRIPTION OF SYMBOLS 1... Transmission part, 2... Receiving part, 01-C6... Optical directional coupler, C0NT,, C0NTl - C0NT3
, C0NTIO to C0NT13...control circuit, DXD
I~D3, DIO~DI2...photodetector, DEMUX
... Optical demultiplexer, f1 to f4... Optical frequency, L1 to L
16... Optical guide 9 wave path, M, Ml to M3, MIO to M13... Optical length adjustment section, MOI to MO4... Optical modulator, MUX... Optical multiplexer, O81 to O34... Optical oscillator, R1-R4・
...Optical receiver.

Claims (1)

[Claims] (1) Optical multiplex transmission system including a transmitting means for multiplexing and transmitting a plurality of optical signals of different optical frequencies, and a receiving means for receiving the multiplexed optical signal from the transmitting means and separating it into the plurality of optical signals. In the above, the transmitting means includes means for setting the average transmission power of each of the plurality of optical signals to predetermined different values, and the receiving means includes an optical waveguide having two optical waveguides connected to input and output, respectively. The optical demultiplexer includes a plurality of directional couplers connected in a cascade, and the relative effective length of the two optical waveguides is detected by the output of the optical demultiplexer. An optical multiplex transmission system characterized by the addition of a control means for controlling the DC component of an optical signal to a maximum.