JP2008054202A - Optical transmitter - Google Patents

Optical transmitter Download PDF

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JP2008054202A
JP2008054202A JP2006230695A JP2006230695A JP2008054202A JP 2008054202 A JP2008054202 A JP 2008054202A JP 2006230695 A JP2006230695 A JP 2006230695A JP 2006230695 A JP2006230695 A JP 2006230695A JP 2008054202 A JP2008054202 A JP 2008054202A
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signal
frequency
modulation
signals
light
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Yoshihiro Hashimoto
義浩 橋本
Tokuichi Miyazaki
徳一 宮崎
Toshio Sakane
敏夫 坂根
Masahide Miyaji
正英 宮地
Junichi Ota
順一 太田
Toshiyuki Miyamoto
敏行 宮本
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Sumitomo Osaka Cement Co Ltd
Sumitomo Electric Industries Ltd
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Sumitomo Osaka Cement Co Ltd
Sumitomo Electric Industries Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration of a DU ratio caused by the matter that modulation components of different orders of each tone signal exist in close vicinity, when phase modulation is performed using two tone signals. <P>SOLUTION: Signals of frequencies f<SB>1</SB>and f<SB>2</SB>(=n×f<SB>1</SB>or =f<SB>1</SB>/n) are generated by a phase modulation signal generator 30, and phase modulation by these signals and intensity modulation of a CATV signal are applied to an optical signal and are transmitted. To control the relation between frequencies f<SB>1</SB>and f<SB>2</SB>, a multiplier or divider is used for the generator 30, or feedback control using a PLL circuit is applied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、光送信機に係り、特にＣＡＴＶ伝送システムに適した光送信機に関する。   The present invention relates to an optical transmitter, and more particularly to an optical transmitter suitable for a CATV transmission system.

光ＣＡＴＶ（Cable Television）システムは、光ファイバを使ってテレビの映像・音声信号をケーブル伝送するシステムであり、例えば約１１０ＣＨに及ぶＡＭ信号／ＱＡＭ信号（ＡＭ；Amplitude Modulation、ＱＡＭ；Quadrature Amplitude Modulation）を７０〜７７０ＭＨｚの周波数帯を利用し副搬送波多重して伝送する。
同システムでは、光変調デバイスや光検波器等の非線形応答に起因する非線形歪、マルチチャネル変調に起因する相互変調歪が発生する。これらの歪成分は、雑音帯域内に生成されると映像にビート雑音を生じさせ、映像品質を劣化させる原因となる。このため、出来るだけ歪成分は低減する必要がある。
従来、２次歪（ＣＳＯ；Composite Second Order beat）と３次歪（ＣＴＢ；Composite Triple Beat）の発生メカニズムと発生する周波数、歪電力等については理論的に解明されており、歪の補正・低減方法も提案されている（例えば、非特許文献１、２参照）。なお、ＣＳＯは２次高調波成分と２次相互変調歪の和、ＣＴＢは３次高調波成分と３次相互変調歪の和でそれぞれ定義される歪成分を表す。 An optical CATV (Cable Television) system is a system for cable transmission of video / audio signals of television using optical fiber, for example, AM signal / QAM signal (AM: Amplitude Modulation, QAM: Quadrature Amplitude Modulation) covering about 110 CH. Is transmitted by subcarrier multiplexing using a frequency band of 70 to 770 MHz.
In this system, non-linear distortion caused by non-linear response such as an optical modulation device or an optical detector, and inter-modulation distortion caused by multi-channel modulation are generated. When these distortion components are generated within the noise band, they generate beat noise in the video and cause video quality to deteriorate. For this reason, it is necessary to reduce the distortion component as much as possible.
Conventionally, the second-order distortion (CSO; Composite Second Order beat) and third-order distortion (CTB: Composite Triple Beat) generation mechanism, generated frequency, distortion power, etc. have been theoretically clarified, and distortion correction and reduction. A method has also been proposed (see, for example, Non-Patent Documents 1 and 2). CSO represents a sum of the second harmonic component and the second order intermodulation distortion, and CTB represents a distortion component defined by the sum of the third harmonic component and the third order intermodulation distortion.

一方、光ＣＡＴＶシステムでは、光ファイバ増幅器を用いて伝送信号のパワーを増大させることにより、伝送距離を伸ばし、あるいは各家庭への分配数を増やすことが可能である。しかし、高いピーク電力を持つ光信号をファイバへ入力すると、誘導ブリリュアン散乱（ＳＢＳ；Stimulated Brillouin Scattering）が生じ、伝送品質を劣化させる問題がある。
そこで、ＳＢＳの発生を回避する対策として、通常、位相変調によって光キャリアの電力を複数の周波数帯へ拡散させ、１つの光キャリア当たりのピーク電力を下げる方法がとられる。その一方式に、キャリア電力の拡散を十分効果的にするためトーン信号（位相変調に用いる信号）による位相変調の変調度を深くし、その上で周波数の異なる２つのトーン信号を利用する方式が提案されている。
より具体的には、第１トーン信号として、隣り合う次数のデータ変調成分が重ならないよう、データ変調周波数（７７０ＭＨｚ）の２倍より大きい周波数であるｆ１＝２ＧＨｚ程度の信号が選ばれる。また、第２トーン信号としては、第１トーン信号による位相変調で生じる２次高調波成分（４ＧＨｚ帯）との干渉を避けるため、ｆ１のほぼ３倍となる周波数ｆ２＝６ＧＨｚ程度の信号が選ばれる。
James C. Daly他、Fiber Optic Intermodulation Distortion、“IEEE Transactions on Communications”、１９８２年８月、Vol.Com-30、No.8 Yang-Han Lee他、The Impact of Laser Phase Noise on the Coherent Subcarrier Multiplexing System、“Journal of Lightwave Technology”、１９９１年３月、Vol.9、No.3 On the other hand, in an optical CATV system, it is possible to increase the transmission distance or increase the number of distribution to each home by increasing the power of the transmission signal using an optical fiber amplifier. However, when an optical signal having a high peak power is input to the fiber, stimulated Brillouin scattering (SBS) occurs and transmission quality is deteriorated.
Therefore, as a countermeasure for avoiding the occurrence of SBS, generally, a method of spreading the power of the optical carrier to a plurality of frequency bands by phase modulation and reducing the peak power per optical carrier is taken. One of the methods is to deepen the degree of phase modulation by tone signals (signals used for phase modulation) in order to make carrier power diffusion sufficiently effective, and then use two tone signals with different frequencies. Proposed.
More specifically, a signal of about f 1 = 2 GHz, which is a frequency greater than twice the data modulation frequency (770 MHz), is selected as the first tone signal so that adjacent data modulation components of the next order do not overlap. Further, as the second tone signal, a signal having a frequency f 2 = 6 GHz which is approximately three times f 1 in order to avoid interference with the second harmonic component (4 GHz band) generated by the phase modulation by the first tone signal. Is selected.
James C. Daly et al., Fiber Optic Intermodulation Distortion, “IEEE Transactions on Communications”, August 1982, Vol.Com-30, No.8 Yang-Han Lee et al., The Impact of Laser Phase Noise on the Coherent Subcarrier Multiplexing System, “Journal of Lightwave Technology”, March 1991, Vol. 9, No. 3

ところが、こうした２トーン信号を用いた位相変調方式では、実験の結果、受信信号に含まれる所要波と不要波の比であるＤＵ比が劣化し、伝送後の映像品質に悪影響を及ぼすことが判明した。特に、伝送経路中に光学的な反射点、例えば光ファイバと各伝送機器間の接続部やファイバ途中のスプライス部などが多く存在し、これらの場所において大きな反射を生じる光ＣＡＴＶシステムでは、伝送光と反射光との干渉によって寄生強度変調が起こり、２乗検波後の信号にこの寄生強度変調による強度変化も検波されてしまう。このときに従来の送信機では、周波数ｆ１とｆ２の関係は厳密に制御されていなかったために、周波数ｆ１の３次高調波成分と周波数ｆ２の１次成分との差周波に相当する成分が寄生強度として現れ、信号波を妨害していることが判明した。また、反射の起きない系（例えば専用線で構築した従来システム等）では、寄生強度変調が発生しないため上記の問題は顕在化していなかったことも判明した。 However, in the phase modulation method using such a two-tone signal, as a result of experiments, it has been found that the DU ratio, which is the ratio between the required wave and the unnecessary wave included in the received signal, deteriorates and adversely affects the video quality after transmission. did. In particular, in an optical CATV system in which there are many optical reflection points in the transmission path, such as a connection between an optical fiber and each transmission device and a splice in the middle of the fiber, and a large reflection occurs at these locations, Parasitic intensity modulation occurs due to interference between the reflected light and the reflected light, and the intensity change due to the parasitic intensity modulation is also detected in the signal after the square detection. In a conventional transmitter in this case, because the relationship of the frequency f 1 and f 2 are that were not strictly controlled, corresponds to the difference frequency between the third harmonic component of the frequency f 1 and frequency f 2 of the first-order component It was found that the component that appears was appearing as parasitic strength and disturbed the signal wave. It has also been found that the above-mentioned problem has not been realized in a system in which reflection does not occur (for example, a conventional system constructed with a dedicated line) because parasitic intensity modulation does not occur.

本発明は上記の点に鑑みてなされたものであり、その目的は、２つのトーン信号を用いて位相変調をする場合に、各トーン信号の異なる次数の変調成分が近接して存在することで生じるＤＵ比の劣化を抑制することが可能な光送信機を提供することにある。   The present invention has been made in view of the above points. The object of the present invention is that, when phase modulation is performed using two tone signals, modulation components of different orders of the respective tone signals are present close to each other. An object of the present invention is to provide an optical transmitter capable of suppressing the deterioration of the DU ratio.

本発明は上記の課題を解決するためになされたものであり、請求項１に記載の発明は、光を発生させて変調手段に供給する光源と、供給された光を変調する前記変調手段と、を備え、前記変調手段は、光を所定の周波数で位相変調して高次成分を生成する位相変調手段と、伝送するデータで光を強度変調する強度変調手段と、から構成され、前記変調手段によって変調された光信号を伝送路へ送出する光送信機であって、前記位相変調手段は、一方の周波数が他方の周波数のｎ倍（ｎは整数）となる周波数関係が満たされるよう２つの信号を制御する制御手段と、前記制御手段を利用して周波数が制御された少なくとも２つの信号を生成する信号生成手段と、を有し、前記生成された少なくとも２つの信号により光を位相変調することを特徴とする光送信機である。   The present invention has been made to solve the above problems, and the invention according to claim 1 includes a light source that generates light and supplies the light to the modulation means, and the modulation means that modulates the supplied light. The modulation means comprises phase modulation means for phase-modulating light at a predetermined frequency to generate higher-order components, and intensity modulation means for intensity-modulating light with data to be transmitted, and the modulation An optical transmitter for transmitting an optical signal modulated by the means to the transmission line, wherein the phase modulation means is configured to satisfy a frequency relationship in which one frequency is n times (n is an integer) the other frequency. Control means for controlling two signals, and signal generation means for generating at least two signals whose frequencies are controlled by using the control means, and phase-modulating light by the generated at least two signals Features to do An optical transmitter.

また、請求項２に記載の発明は、請求項１に記載の光送信機において、前記制御手段は、入力される信号の周波数をｎ倍に変換する逓倍器から成り、前記信号生成手段は、１つの基準信号を生成するとともに、該基準信号を前記制御手段に入力して前記周波数関係を満足する信号を生成することを特徴とする。   According to a second aspect of the present invention, in the optical transmitter according to the first aspect, the control unit includes a multiplier that converts the frequency of the input signal to n times, and the signal generation unit includes: One reference signal is generated, and the reference signal is input to the control means to generate a signal that satisfies the frequency relationship.

また、請求項３に記載の発明は、請求項１に記載の光送信機において、前記制御手段は、入力される信号の周波数を１／ｎ倍に変換する分周器から成り、前記信号生成手段は、１つの基準信号を生成するとともに、該基準信号を前記制御手段に入力して前記周波数関係を満足する信号を生成することを特徴とする。   According to a third aspect of the present invention, in the optical transmitter according to the first aspect, the control means comprises a frequency divider that converts the frequency of the input signal to 1 / n times, and the signal generation The means generates one reference signal and inputs the reference signal to the control means to generate a signal satisfying the frequency relationship.

また、請求項４に記載の発明は、請求項１に記載の光送信機において、前記信号生成手段は、互いに周波数の異なる信号を発生する少なくとも２つの信号源から成り、前記制御手段は、前記信号源からの各出力信号に基づいてそれぞれの信号源に対して周波数のフィードバック制御を行うことを特徴とする。   According to a fourth aspect of the present invention, in the optical transmitter according to the first aspect, the signal generating means includes at least two signal sources that generate signals having different frequencies, and the control means Frequency feedback control is performed on each signal source based on each output signal from the signal source.

本発明によれば、一方の周波数が他方の周波数のｎ倍となるように位相変調信号の周波数が制御されるので、各トーン信号の変調成分が完全に重なり、ＤＵ比の劣化が抑制される。   According to the present invention, since the frequency of the phase modulation signal is controlled so that one frequency is n times the other frequency, the modulation components of the tone signals are completely overlapped, and the deterioration of the DU ratio is suppressed. .

以下、図面を参照しながら本発明の実施形態について詳しく説明する。
図１は、本発明の一実施形態による光送信機の構成図である。光送信機１は、レーザダイオード（ＬＤ）１０と、変調器２０と、位相変調信号生成部３０と、ＣＡＴＶ信号生成部４０とを有している。レーザダイオード１０と変調器２０は光学的に接続され、２つの信号生成部３０、４０と変調器２０とは電気的に接続されている。レーザダイオード１０から出力される光信号は、変調器２０において位相変調とＣＡＴＶ信号による変調が施されて、光ファイバ伝送路（図示せず）へと送出される。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram of an optical transmitter according to an embodiment of the present invention. The optical transmitter 1 includes a laser diode (LD) 10, a modulator 20, a phase modulation signal generation unit 30, and a CATV signal generation unit 40. The laser diode 10 and the modulator 20 are optically connected, and the two signal generators 30 and 40 and the modulator 20 are electrically connected. The optical signal output from the laser diode 10 is subjected to phase modulation and modulation by the CATV signal in the modulator 20 and sent to an optical fiber transmission line (not shown).

レーザダイオード１０は、シングルモード発振によって単一周波数の光信号を発生させて、変調器２０へ供給する。この周波数をｆ０とする。
変調器２０は、位相変調部２１と強度変調部２２を有しており、位相変調部２１側がレーザダイオード１０に接続される。また、位相変調部２１は位相変調信号生成部３０に、強度変調部２２はＣＡＴＶ信号生成部４０に、それぞれ繋がっている。各変調部２１、２２は、電気光学効果を有するＬＮ（ＬｉＮｂＯ３）基板上に光導波路と電極を形成したものである。この光導波路に各電極から電界を印加することで、伝搬する光信号に位相変化が与えられる。 The laser diode 10 generates an optical signal having a single frequency by single mode oscillation and supplies the optical signal to the modulator 20. This frequency is f 0.
The modulator 20 includes a phase modulation unit 21 and an intensity modulation unit 22, and the phase modulation unit 21 side is connected to the laser diode 10. The phase modulation unit 21 is connected to the phase modulation signal generation unit 30, and the intensity modulation unit 22 is connected to the CATV signal generation unit 40. Each of the modulators 21 and 22 is formed by forming an optical waveguide and an electrode on an LN (LiNbO 3 ) substrate having an electro-optic effect. By applying an electric field from each electrode to this optical waveguide, a phase change is given to the propagating optical signal.

位相変調信号生成部３０は、周波数ｆ１の第１トーン信号と周波数ｆ２＝ｎ・ｆ１＋Δｆ（ただし、ｎは整数）の第２トーン信号の２つの電気信号を生成して位相変調部２１へ供給する。ここではｆ１＝２ＧＨｚ、ｎ＝３とする。なお、Δｆは後述する周波数制御によってΔｆ＝０が実現されるが、説明のため明示的に表記している。位相変調部２１を伝搬する光は、この第１および第２トーン信号でその位相を変調される。 The phase modulation signal generation unit 30 generates two electrical signals of a first tone signal having a frequency f 1 and a second tone signal having a frequency f 2 = n · f 1 + Δf (where n is an integer) to generate a phase modulation unit. To 21. Here, f 1 = 2 GHz and n = 3. Note that Δf = 0 is realized by frequency control, which will be described later, but is explicitly shown for the sake of explanation. The phase of the light propagating through the phase modulator 21 is modulated by the first and second tone signals.

ＣＡＴＶ信号生成部４０は、ＣＡＴＶの伝送データを強度変調部２２へ供給する。強度変調部２２の光導波路は、マッハツェンダー（ＭＺ）干渉系を構成している。その各アームを伝搬する光の位相を、上記伝送データで変調する。変調後の伝搬光が合波（干渉）され、強度変調された光信号が出力される。   The CATV signal generation unit 40 supplies the CATV transmission data to the intensity modulation unit 22. The optical waveguide of the intensity modulator 22 constitutes a Mach-Zehnder (MZ) interference system. The phase of light propagating through each arm is modulated with the transmission data. The modulated propagation light is combined (interfered), and an intensity-modulated optical signal is output.

図２は、本光送信機１から送信される信号の周波数スペクトルを示した図である。レーザダイオード１０の出力光が変調器２０へ入力され、位相変調部２１で周波数ｆ１とｆ２で位相変調を受けた後、強度変調部２２でＣＡＴＶ信号による強度変調を受けて伝送路へ出力されると、その光信号のスペクトルは同図（ａ）に示すようなものとなる。 FIG. 2 is a diagram illustrating a frequency spectrum of a signal transmitted from the optical transmitter 1. The output light of the laser diode 10 is input to the modulator 20, subjected to phase modulation at the frequencies f 1 and f 2 by the phase modulation unit 21, and then subjected to intensity modulation by the CATV signal at the intensity modulation unit 22 and output to the transmission line. Then, the spectrum of the optical signal is as shown in FIG.

図２（ａ）において、変調器２０へ入力された周波数ｆ０のメインキャリア光に加えて、位相変調部２１での位相変調によって、変調周波数ｆ１とｆ２に対応する複数のサブキャリア光（高調波成分）が現れる。すなわち、周波数ｆ１（＝２ＧＨｚ）の変調信号からは、周波数ｆ０±２ＧＨｚ、ｆ０±４ＧＨｚ、ｆ０±６ＧＨｚにそれぞれ１次、２次、３次のサブキャリア光が生成され、周波数ｆ２（＝６ＧＨｚ＋Δｆ）の変調信号からは、周波数ｆ０±６ＧＨｚ±Δｆに１次のサブキャリア光が生成される。なお、より高次の成分は省略する。さらに、これらのキャリア光のサブバンドに、ＣＡＴＶ信号によるブロードな変調スペクトルが現れる。 In FIG. 2A, in addition to the main carrier light having the frequency f 0 input to the modulator 20, a plurality of subcarrier lights corresponding to the modulation frequencies f 1 and f 2 are obtained by the phase modulation in the phase modulation unit 21. (Harmonic component) appears. That is, from the modulation signal of frequency f 1 (= 2 GHz), primary, secondary, and third-order subcarrier lights are generated at frequencies f 0 ± 2 GHz, f 0 ± 4 GHz, and f 0 ± 6 GHz, respectively. From the modulation signal of 2 (= 6 GHz + Δf), primary subcarrier light is generated at the frequency f 0 ± 6 GHz ± Δf. Note that higher order components are omitted. Furthermore, a broad modulation spectrum due to the CATV signal appears in the subbands of these carrier lights.

上記のスペクトルを有した光信号は、受信側でフォトダイオードによって２乗検波されて電気信号に変換される。２乗検波では、各サブキャリアスペクトル自身の積を加算した出力信号が得られる。反射がない伝送路の場合には、異なるサブキャリア積成分は、±成分の存在（例えばｆ０＋２ＧＨｚとｆ０−２ＧＨｚ）によりキャンセルされ余計な周波数成分を発生しない。反射がある伝送路の場合には、サブキャリアの位相関係が異なった光信号が加算されるため、図２（ｂ）の検波後スペクトルにおいて、各サブキャリアの差周波数に相当する信号成分が新たに寄生強度信号として発生してしまう。 The optical signal having the above spectrum is square-detected by a photodiode on the receiving side and converted into an electric signal. In square detection, an output signal is obtained by adding the products of the subcarrier spectra themselves. In the case of a transmission line without reflection, different subcarrier product components are canceled due to the presence of ± components (for example, f 0 +2 GHz and f 0 -2 GHz), and no extra frequency component is generated. In the case of a transmission line with reflection, since optical signals having different subcarrier phase relationships are added, a signal component corresponding to the difference frequency of each subcarrier is newly added in the post-detection spectrum of FIG. Is generated as a parasitic intensity signal.

Δｆがゼロでない場合には、周波数６ＧＨｚと６ＧＨｚ＋Δｆの差周波数であるΔｆの信号成分が現れ、これがＣＡＴＶ信号を妨害する不要波となる。一方、Δｆがゼロの場合には、発生する差周波数成分はＣＡＴＶ信号の帯域外となるため問題とならない。   When Δf is not zero, a signal component of Δf, which is the difference frequency between 6 GHz and 6 GHz + Δf, appears and becomes an unnecessary wave that interferes with the CATV signal. On the other hand, when Δf is zero, the generated difference frequency component is out of the band of the CATV signal, which is not a problem.

図２（ｃ）は光検波後のＣＡＴＶ信号のスペクトルの一部を拡大して示しており、所定の周波数間隔で並んだ各ＣＨ信号（所要波）に加えて、±Δｆ離れた周波数に上記不要波が生じている。受信機内において所望のあるＣＨ信号をチューニングして切り出す際、この不要波も同時に切り取られて映像品質を劣化させる。   FIG. 2C shows an enlarged part of the spectrum of the CATV signal after photodetection. In addition to the CH signals (required waves) arranged at a predetermined frequency interval, the above-mentioned frequency is separated by ± Δf. Unnecessary waves are generated. When a desired CH signal is tuned and cut out in the receiver, the unnecessary wave is also cut out at the same time to deteriorate the video quality.

図３は、位相変調信号生成部３０の構成図である。位相変調信号生成部３０は、信号源３１と、逓倍器３２と、合成器３３とから構成される。
信号源３１は、周波数ｆ１の第１トーン信号を発生させて、それを逓倍器３２と合成器３３に入力する。逓倍器３２は、入力された信号周波数をｎ倍にして出力する既存のデジタル回路である。合成器３３には、信号源３１からの第１トーン信号と逓倍器３２からの周波数ｆ２＝ｎ・ｆ１の第２トーン信号が入力され、これらが合成されて出力される。 FIG. 3 is a configuration diagram of the phase modulation signal generation unit 30. The phase modulation signal generation unit 30 includes a signal source 31, a multiplier 32, and a combiner 33.
The signal source 31 generates a first tone signal having a frequency f 1 and inputs it to the multiplier 32 and the synthesizer 33. The multiplier 32 is an existing digital circuit that outputs an input signal frequency multiplied by n. The synthesizer 33 receives the first tone signal from the signal source 31 and the second tone signal having the frequency f 2 = n · f 1 from the multiplier 32, and synthesizes and outputs them.

上記構成の位相変調信号生成部３０から出力される２つの信号は、一方の周波数が他方の周波数の厳密にｎ倍となる。すなわちΔｆ＝０である。
したがって、図２において不要波は発生しなくなる。 The two signals output from the phase modulation signal generation unit 30 having the above-described configuration have one frequency strictly n times that of the other frequency. That is, Δf = 0.
Therefore, unnecessary waves are not generated in FIG.

図４は、位相変調信号生成部３０の他の例の構成図であり、逓倍器３２に代えて分周器３４を用いたものである。分周器３４は、入力された信号周波数を１／ｎ倍にして出力する既存のデジタル回路である。この構成では、信号源３１からの周波数ｆ１の信号と分周器３４からの周波数ｆ２＝ｆ１／ｎの信号が得られ、Δｆ＝０が実現される。 FIG. 4 is a configuration diagram of another example of the phase modulation signal generation unit 30, in which a frequency divider 34 is used in place of the multiplier 32. The frequency divider 34 is an existing digital circuit that outputs an input signal frequency multiplied by 1 / n. In this configuration, a signal of frequency f 1 from the signal source 31 and a signal of frequency f 2 = f 1 / n from the frequency divider 34 are obtained, and Δf = 0 is realized.

図５は、位相変調信号生成部３０のさらに他の例の構成図である。この構成では、２つの信号源３５、３６と、ＰＬＬ回路３７と、合成器３３とが用いられる。
信号源３５と３６は、それぞれ周波数ｆ１とｆ２のトーン信号を発生している。この２つの信号は、ＰＬＬ回路３７へ入力される。ＰＬＬ回路３７は、入力信号の位相差を検出してその結果を信号源３５にフィードバックする。信号源３５は、ＰＬＬ回路３７からのフィードバック制御を受けて、出力信号の周波数がｆ１＝ｆ２／ｎとなるように制御される。このように制御された周波数ｆ１とｆ２の２つのトーン信号が、合成器３３で合成され出力される。 FIG. 5 is a configuration diagram of still another example of the phase modulation signal generation unit 30. In this configuration, two signal sources 35 and 36, a PLL circuit 37, and a synthesizer 33 are used.
Signal sources 35 and 36 generate tone signals of frequencies f1 and f2, respectively. These two signals are input to the PLL circuit 37. The PLL circuit 37 detects the phase difference of the input signal and feeds back the result to the signal source 35. The signal source 35 receives feedback control from the PLL circuit 37 and is controlled so that the frequency of the output signal is f 1 = f 2 / n. The two tone signals of the frequencies f 1 and f 2 controlled in this way are synthesized by the synthesizer 33 and output.

このように、本実施形態によれば、位相変調信号生成部３０で周波数ｆ１とｆ２（＝ｎ・ｆ１または＝ｆ１／ｎ）の信号を生成して、この信号による位相変調とＣＡＴＶ信号による強度変調を光信号に施して送信する。ｆ１とｆ２の周波数関係を制御するため、位相変調信号生成部３０には、逓倍器３２若しくは分周器３４を利用し、またはＰＬＬ回路３７を使ったフィードバック制御を適用する。これにより、ｆ１とｆ２のそれぞれによる変調成分の異なる次数間に周波数のずれが生じなくなり、検波後の不要波が消え、その結果ＤＵ比が向上して映像品質の劣化を抑えることが出来る。 As described above, according to the present embodiment, the phase modulation signal generation unit 30 generates signals of the frequencies f 1 and f 2 (= n · f 1 or = f 1 / n), and the phase modulation by this signal is performed. The optical signal is intensity-modulated by the CATV signal and transmitted. In order to control the frequency relationship between f 1 and f 2 , feedback control using the multiplier 32 or the frequency divider 34 or the PLL circuit 37 is applied to the phase modulation signal generation unit 30. As a result, no frequency shift occurs between the different orders of the modulation components due to f 1 and f 2 , unnecessary waves after detection disappear, and as a result, the DU ratio is improved and deterioration of video quality can be suppressed. .

以上、図面を参照してこの発明の一実施形態について詳しく説明してきたが、具体的な構成は上述のものに限られることはなく、この発明の要旨を逸脱しない範囲内において様々な設計変更等をすることが可能である。
例えば、変調器２０はＬＮ基板上に構成したものに限定されず、周知の種々の変調器に本発明を適用することが可能である。
また、位相変調信号生成部３０で生成した２つの信号ｆ１とｆ２のうち、一方をレーザダイオード１０に入力して直接変調を行う構成にすることもできる。
また、伝送するデータはＣＡＴＶ信号以外であってもよい。
また、位相変調の変調信号は２つより多くすることもできる。 As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to
For example, the modulator 20 is not limited to the one configured on the LN substrate, and the present invention can be applied to various known modulators.
Alternatively, one of the two signals f 1 and f 2 generated by the phase modulation signal generation unit 30 may be input to the laser diode 10 and directly modulated.
The data to be transmitted may be other than the CATV signal.
Also, the number of phase modulation signals can be more than two.

本発明の一実施形態による光送信機の構成図である。It is a block diagram of the optical transmitter by one Embodiment of this invention. 光送信機から送信される信号の周波数スペクトルを示した図である。It is the figure which showed the frequency spectrum of the signal transmitted from an optical transmitter. 位相変調信号生成部の構成図である。It is a block diagram of a phase modulation signal generation part. 他の位相変調信号生成部の構成図である。It is a block diagram of another phase modulation signal generation part. さらに他の位相変調信号生成部の構成図である。It is a block diagram of another phase modulation signal generation unit.

符号の説明Explanation of symbols

１…光送信機 １０…レーザダイオード ２０…変調器 ２１…位相変調部 ２２…強度変調部 ３０…位相変調信号生成部 ３１…信号源 ３２…逓倍器 ３３…合成器 ３４…分周器 ３５、３６…信号源 ３７…ＰＬＬ回路 ４０…ＣＡＴＶ信号生成部

DESCRIPTION OF SYMBOLS 1 ... Optical transmitter 10 ... Laser diode 20 ... Modulator 21 ... Phase modulation part 22 ... Intensity modulation part 30 ... Phase modulation signal generation part 31 ... Signal source 32 ... Multiplier 33 ... Synthesizer 34 ... Divider 35, 36 ... Signal source 37 ... PLL circuit 40 ... CATV signal generator

Claims (4)

光を発生させて変調手段に供給する光源と、供給された光を変調する前記変調手段と、を備え、前記変調手段は、光を所定の周波数で位相変調して高次成分を生成する位相変調手段と、伝送するデータで光を強度変調する強度変調手段と、から構成され、前記変調手段によって変調された光信号を伝送路へ送出する光送信機であって、
前記位相変調手段は、
一方の周波数が他方の周波数のｎ倍（ｎは整数）となる周波数関係が満たされるよう２つの信号を制御する制御手段と、
前記制御手段を利用して周波数が制御された少なくとも２つの信号を生成する信号生成手段と、
を有し、前記生成された少なくとも２つの信号により光を位相変調する
ことを特徴とする光送信機。 A light source that generates light and supplies the modulated light to the modulation means; and the modulation means that modulates the supplied light, wherein the modulation means phase-modulates the light at a predetermined frequency to generate a higher-order component. An optical transmitter configured to include a modulation unit and an intensity modulation unit that modulates the intensity of light with data to be transmitted, and that transmits an optical signal modulated by the modulation unit to a transmission line,
The phase modulation means includes
Control means for controlling the two signals so as to satisfy a frequency relationship in which one frequency is n times the other frequency (n is an integer);
Signal generating means for generating at least two signals whose frequencies are controlled using the control means;
And optically phase-modulating light with the generated at least two signals. 前記制御手段は、
入力される信号の周波数をｎ倍に変換する逓倍器から成り、
前記信号生成手段は、
１つの基準信号を生成するとともに、該基準信号を前記制御手段に入力して前記周波数関係を満足する信号を生成する
ことを特徴とする請求項１に記載の光送信機。 The control means includes
It consists of a multiplier that converts the frequency of the input signal to n times,
The signal generating means includes
The optical transmitter according to claim 1, wherein one reference signal is generated, and the reference signal is input to the control unit to generate a signal that satisfies the frequency relationship. 前記制御手段は、
入力される信号の周波数を１／ｎ倍に変換する分周器から成り、
前記信号生成手段は、
１つの基準信号を生成するとともに、該基準信号を前記制御手段に入力して前記周波数関係を満足する信号を生成する
ことを特徴とする請求項１に記載の光送信機。 The control means includes
It consists of a frequency divider that converts the frequency of the input signal to 1 / n times,
The signal generating means includes
The optical transmitter according to claim 1, wherein one reference signal is generated, and the reference signal is input to the control unit to generate a signal that satisfies the frequency relationship. 前記信号生成手段は、
互いに周波数の異なる信号を発生する少なくとも２つの信号源から成り、
前記制御手段は、
前記信号源からの各出力信号に基づいてそれぞれの信号源に対して周波数のフィードバック制御を行う
ことを特徴とする請求項１に記載の光送信機。

The signal generating means includes
Consisting of at least two signal sources that generate signals of different frequencies,
The control means includes
The optical transmitter according to claim 1, wherein frequency feedback control is performed on each signal source based on each output signal from the signal source.

JP2006230695A 2006-08-28 2006-08-28 Optical transmitter Pending JP2008054202A (en)

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JPH08265211A (en) * 1995-03-22 1996-10-11 Sony Corp Integrated circuit and transmitter-receiver
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