JPH05167560A - Frequency multiple optical modulating system - Google Patents

Abstract

PURPOSE:To realize the frequency multiple optical modulating system capable of receiving high quality picture without distortion or attenuation due to a mixing device. CONSTITUTION:More than two brightness modulators 1 are connected in series. A brightness modulator 1 performs the only optical modulation through carrier electric signals modulated by one signal, drives the other brightness modulator with the carrier electric signal with the carrier frequency changed, obtaining a brightness modulation signal with its frequency multiplied by applying the modulated light signal to the brightness modulator. Thus, no amplifier is required behind the mixing device because of no distortion and attenuation by the mixing device, resulting in simplifying the circuitry and decreasing the production cost. In addition, the high quality picture can be received with no deterioration and distortion of signals due to the back flow of electric signals to the other electric signal source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The frequency multiplexing optical modulation system of the present invention is used for optical transmission of an optical CATV system, for example.

[0002]

2. Description of the Related Art Signals to be sent are S ₁ (t), S ₂
(T), S ₃ (t), ...
Let the electric signals (carrier electric signals) obtained by modulating the carrier waves of ₁ , f ₂ , f ₃ ... Be e ₁ , e ₂ , e ₃ ... It is expressed as follows. e ₁ = A ₁ (1 + m ₁ S ₁ (t)) · cos 2πf ₁ t e ₂ = A ₂ (1 + m ₂ S ₂ (t)) · cos 2πf ₂ t A ₁ , A ₂ ; a constant m indicating the magnitude of amplitude ₁ , m ₂ ; Degree of modulation In FM modulation, it is expressed as follows. e ₁ = A ₁ cos (2π (f ₁ + S ₁ (t)) t) e ₂ = A ₂ cos (2π (f ₂ + S ₂ (t)) t)

As shown in FIG. 4, the frequency-multiplexed optical modulation system in the conventional optical CATV system is a plurality of carrier electrical signals e ₁ , e ₂ , e ₃ of different frequencies modulated by different signals.
.. is mixed by the mixer A as an electric signal as shown in FIG.
The mixed signal E = e ₁ + e ₂ + e ₃ ... Is amplified by the amplifier B and then input to the optical intensity modulator D to output the optical signal H of FIG. 5A emitted from the LD light source. The brightness was modulated as shown in FIG.

[0004]

The conventional frequency multiplexing optical modulation system shown in FIG. 4 has the following problems. ． Since the electric carrier signals e ₁ + e ₂ + e ₃ ... Are mixed as they are in the mixer A, the electric carrier signal is distorted by the distortion of the mixer A itself. ． Carrier electrical signals of other frequencies e ₁ + e ₂ + e ₃ ...
May flow back to the signal source of another frequency via the mixer A, and the backflow also deteriorates the electric carrier signal and causes distortion. ． Since the mixer A attenuates, it is necessary to insert the amplifier B after the mixer A for amplification, and the amplifier B also causes distortion. Further, since this amplifier A amplifies signals of many frequencies, it must be capable of constant amplification over a very wide frequency range, which is technically difficult to realize. ． Optical CATV due to distortion due to various causes as described above
The quality of the image received at the terminal of the system deteriorates. ． Since the mixer and the amplifier are designed in advance considering the channels for optical transmission, it is not possible to easily increase the channels as needed.

It is an object of the present invention to realize a frequency-multiplexed optical modulation system capable of receiving a high quality image in a terminal of an optical CATV system without the above distortion and attenuation.

[0006]

In the frequency-multiplexed optical modulation system of the present invention, two or more optical intensity modulators 1 are connected in series as shown in FIG. 1, and one optical intensity modulator 1 modulates with one signal. Only the optical modulation is performed by the generated carrier electric signals e ₁ , e ₂ , e ₃ ... And carrier frequencies f ₁ , f ₂ , f _3.
... drives another light intensity modulator 1 at a carrier electrical signal _{e 1, e 2, e 3} ··· with different, passing an optical signal modulated in earlier in the light intensity modulator 1 Is used to obtain a frequency-multiplexed light intensity modulation signal.

[0007]

[Action] In the frequency-multiplexed optical modulation method of the present invention, without mixing the carrier electrical signal _{e 1, e 2, e 3} ··· , the individual carrier electrical signal _{e 1, e 2, e 3} ··· Since the light intensity modulators 1 connected in series are individually driven, it is not necessary to provide the mixer A and the amplifier B as shown in FIG. Moreover, the frequency-multiplexed optical intensity modulation signal can be easily obtained by sequentially passing the previously modulated optical signal through the optical intensity modulators connected in series. Also, other carrier electric signals do not flow back to other electric signal sources.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 showing an embodiment of the frequency multiplexing optical modulation system of the present invention, LD is a light source, is a light intensity modulator,
₁ , e ₂ , e ₃ ... Are carrier electrical signals. The carrier electric signals e ₁ , e ₂ , e ₃ ...
_The frequency f at ₁ (t), S ₂ (t), S ₃ (t) ...
It is an electric signal obtained by modulating carrier waves of ₁ , f ₂ , f ₃ ... The optical intensity modulator 1 uses the carrier electric signal e
₁ , e ₂ , e _3, ... Are prepared and connected in series.

In the present invention, each of the light intensity modulators 1 is driven by the individual carrier electric signals e ₁ , e ₂ , e ₃ ... ₁ is subjected to optical intensity modulation, and the optical signals (optical signals previously subjected to optical intensity modulation) a ₂ , a ₃ ... , Obtain a frequency-multiplexed light intensity modulation signal.

By the way, the optical signal at point A in FIG. 1 is shown in FIG.
The direct current as shown in (a) is modulated by the optical brightness modulator 1 in the first stage and the optical signal at point B in FIG.
(B)}, and then sequentially modulated in the light intensity modulator 1 in the subsequent stage to obtain the C point in FIG.
2C, and the optical signal at point E in FIG.
(D) and FIG. 2 (e) are multiplexed.

In the frequency-multiplexed optical modulation system of the present invention, FIG.
If there is an interaction between the light intensity modulators 1 connected in series as shown in, the light intensity modulator 1 as shown in FIG.
The optical isolator 2 may be inserted between the stages.

If the light level is lowered, an optical amplifier (a device for amplifying light as it is) 3 may be inserted between appropriate stages of the optical intensity modulator 1 as shown in FIG.

[0013]

The frequency multiplexing optical modulation system of the present invention has the following effects. ． Since there is no need to use a mixer, there is no distortion or attenuation due to the mixer. Also, since there is no attenuation in the mixer,
It is not necessary to provide the amplifier B after the mixer A as in the above.
Therefore, the circuit configuration is simplified and the cost is reduced. ． The optical intensity modulator 1 is used to transmit carrier electrical signals e ₁ , e ₂ , e ₃
Since there are as many as ...
₁ , e ₂ , e ₃ ... Are completely electrically insulated, and other carrier electric signals do not flow back to other electric signal sources, and there is no concern about signal deterioration or distortion due to backflow. . ． Due to the above effects, the image quality of the image received at the terminal of the optical CATV system does not deteriorate. ． The number of channels can be easily increased by preparing an optical intensity modulator for only the required channels. Furthermore, it is possible to deal with high frequencies relatively easily. ． Even when the modulation degree is changed for each of the electric carrier signals e ₁ , e ₂ , e _3, ..., It can be easily changed because the frequency band of each signal is narrow.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of a frequency multiplexing optical modulation system of the present invention.

2A to 2E are waveform explanatory diagrams at points A to Z in the frequency multiplexing optical modulation system of FIG.

FIG. 3 is an explanatory diagram showing another embodiment of the frequency multiplexing optical modulation method of the present invention.

FIG. 4 is an explanatory diagram showing an example of a conventional frequency multiplexing optical modulation method.

5A and 5B are waveform explanatory diagrams in the frequency-multiplexed optical modulation system of FIG.

[Explanation of symbols]

1 is a light intensity modulator, e ₁ , e ₂ , e ₃ ... are carrier electrical signals S ₁ (t), S ₂ (t), S ₃ (t) ...

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location H04B 10/06 H04N 7/22 8943-5C // H04N 7/16 Z 8838-5C

Claims (1)

[Claims] 1. Two or more light intensity modulators 1 are connected in series,
In one optical brightness modulator 1, only optical modulation is performed by the carrier electric signal modulated by one signal, and another optical brightness modulator is driven by the carrier electric signal whose carrier frequency is changed. A frequency-multiplexed optical modulation system characterized in that a frequency-multiplexed optical intensity modulation signal is obtained by passing an optical signal that has been modulated before that.