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JP4980319B2 - Optical transmitter - Google Patents

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JP4980319B2
JP4980319B2 JP2008229825A JP2008229825A JP4980319B2 JP 4980319 B2 JP4980319 B2 JP 4980319B2 JP 2008229825 A JP2008229825 A JP 2008229825A JP 2008229825 A JP2008229825 A JP 2008229825A JP 4980319 B2 JP4980319 B2 JP 4980319B2
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modulation signal
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JP2010068027A (en
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岩月　　勝美
俊二 木村
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Nippon Telegraph and Telephone Corp
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Description

本発明は、光ファイバでＲＦ（無線周波数）変調信号を伝送するための光送信器に関する。   The present invention relates to an optical transmitter for transmitting an RF (radio frequency) modulated signal through an optical fiber.

図１は、従来の光送信器の第１の構成例を示す。
図において、本構成の光送信器は、ＯＦＤＭ（Orthogonal Frequency Division Multiplexing) 等のベースバンド多重信号でＲＦ搬送波を変調したＲＦ変調信号により光変調器を駆動し、光キャリア（ＣＷ光）を変調するＳＣＭ（サブキャリア変調）方式を実現するものである。すなわち、乗算器１１はベースバンド多重信号とＲＦ搬送波を乗算し、フィルタ１２は乗算器１１から出力されるＲＦ変調信号の片側帯波を切り出し、増幅器１３はＲＦ変調信号の片側帯波を増幅してＬＮ変調器１４に入力し、ＬＮ変調器１４は光キャリア（ＣＷ光）をＲＦ変調信号で光強度変調して変調光を出力する。なお、ＬＮ変調器１４は、電気光学効果をもつニオブ酸リチウム(LN:LiNbO3) の結晶を用いた光変調器である。 FIG. 1 shows a first configuration example of a conventional optical transmitter.
In the figure, the optical transmitter of this configuration drives the optical modulator with an RF modulation signal obtained by modulating an RF carrier with a baseband multiplexed signal such as OFDM (Orthogonal Frequency Division Multiplexing) and modulates the optical carrier (CW light). An SCM (subcarrier modulation) system is realized. That is, the multiplier 11 multiplies the baseband multiplexed signal and the RF carrier, the filter 12 cuts out one sideband of the RF modulation signal output from the multiplier 11, and the amplifier 13 amplifies the one sideband of the RF modulation signal. The LN modulator 14 outputs the modulated light by modulating the optical intensity of the optical carrier (CW light) with the RF modulation signal. The LN modulator 14 is an optical modulator using a lithium niobate (LN: LiNbO 3 ) crystal having an electro-optic effect.

ＬＮ変調器１４の変調特性は、入力電圧に対して光出力が正弦波的に変化するため、変調光には図１の変調光スペクトルに示すようにＲＦ変調信号の３次歪み成分が現れる。このため、ＬＮ変調器１４の変調特性の線形部分を利用して３次歪み成分を低減するように、ＲＦ変調信号の電圧が調整される。しかし、ＬＮ変調器１４の変調特性の線形部分は狭いため、光キャリア成分に対するＲＦ変調成分が小さくなり、ＣＮＲまたはＳＮＲを大きく設定することが困難であった。   The modulation characteristic of the LN modulator 14 is that the optical output changes sinusoidally with respect to the input voltage, and therefore, the third-order distortion component of the RF modulation signal appears in the modulated light as shown in the modulated light spectrum of FIG. For this reason, the voltage of the RF modulation signal is adjusted so as to reduce the third-order distortion component using the linear portion of the modulation characteristic of the LN modulator 14. However, since the linear part of the modulation characteristic of the LN modulator 14 is narrow, the RF modulation component with respect to the optical carrier component becomes small, and it is difficult to set a large CNR or SNR.

図２は、従来の光送信器の第２の構成例を示す。
図において、本構成の光送信器は、レーザダイオード（ＬＤ）１５の直接変調を用いて、ＲＦ変調信号を光キャリアに重畳する構成である。ＲＦ変調信号は、図１と同様の乗算器１１、フィルタ１２、増幅器１３を用いて生成され、バイアスＴ１６でバイアス電圧を付加してＬＤ１５を駆動する。ＬＤ１５のＩ−Ｌ特性（注入電流対光出力特性）は、概ね直線性を有しているが、ＬＤの閾値以下のＲＦ変調電流に対しては歪み（クリッピングノイズ）を生じることになる（非特許文献１）。 FIG. 2 shows a second configuration example of a conventional optical transmitter.
In the figure, the optical transmitter of this configuration is configured to superimpose an RF modulation signal on an optical carrier using direct modulation of a laser diode (LD) 15. The RF modulation signal is generated using a multiplier 11, a filter 12, and an amplifier 13 similar to those in FIG. 1, and a bias voltage is added at a bias T16 to drive the LD 15. The IL characteristic (injection current vs. optical output characteristic) of the LD 15 is almost linear, but distortion (clipping noise) is generated for an RF modulation current below the LD threshold (non-clipping noise). Patent Document 1).

図３は、従来の光送信器の第３の構成例を示す。
図において、本構成の光送信器は、図２の構成においてクリッピングノイズを低減するために、フィルタ１２と増幅器１３との間にＦＭ−ＡＭ一括変調器１７を配置し、時間的に変化するＲＦ変調信号（ＡＭ信号）をＦＭ信号に変換する。このＦＭ−ＡＭ一括変調方式により、振幅変化を周波数変化に置き換え、閾値以下のＲＦ変調電流変化が生じないようにしている（非特許文献２）。受信器では、ＦＭ復調器により、もとのＲＦ変調信号に変換する。
A.A.M.SALEH,"FUNDAMENTAL LIMIT ON NUMBER OF CHANNELS IN SUBCARRIER-MULTIPLEXED LIGHTWAVE CATV SYSTEM", ELECTRONICS LETTERS 8th June 1989, Vol.25, No.12, pp.776-777 R.Omoto et al.,"Dynamic range improvement technique for fiber-optic microcell radio system", GLOCOM, pp.260-265, 1993 FIG. 3 shows a third configuration example of a conventional optical transmitter.
In the figure, the optical transmitter of this configuration has an FM-AM batch modulator 17 disposed between the filter 12 and the amplifier 13 in order to reduce clipping noise in the configuration of FIG. The modulation signal (AM signal) is converted into an FM signal. With this FM-AM batch modulation method, the amplitude change is replaced with a frequency change so that an RF modulation current change below a threshold value does not occur (Non-Patent Document 2). In the receiver, it is converted into the original RF modulation signal by the FM demodulator.
AAMSALEH, "FUNDAMENTAL LIMIT ON NUMBER OF CHANNELS IN SUBCARRIER-MULTIPLEXED LIGHTWAVE CATV SYSTEM", ELECTRONICS LETTERS 8th June 1989, Vol.25, No.12, pp.776-777 R. Omoto et al., “Dynamic range improvement technique for fiber-optic microcell radio system”, GLOCOM, pp. 260-265, 1993

ＲＦ変調信号を光キャリアに重畳するＳＣＭ方式を実現する上で、従来技術の構成では３次歪みやクリッピングノイズの問題があった。すなわち、３次歪みにより良好なＣＮＲまたはＳＮＲを得ることが困難であった。また、クリッピングノイズの問題はＦＭ−ＡＭ一括変調方式が考案されているが、広帯域なＲＦ変調信号に対応するＦＭ−ＡＭ一括変調器を実現することが困難であった。   In realizing the SCM method in which the RF modulation signal is superimposed on the optical carrier, the configuration of the prior art has problems of third-order distortion and clipping noise. That is, it is difficult to obtain a good CNR or SNR due to third-order distortion. Further, although the FM-AM batch modulation system has been devised as a problem of clipping noise, it has been difficult to realize an FM-AM batch modulator corresponding to a broadband RF modulation signal.

本発明は、ＳＣＭ方式における３次歪みによるＣＮＲまたはＳＮＲの劣化を回避し、ＦＭ−ＡＭ一括変調方式を用いずにクリッピングノイズを低減することができる光送信器を提供することを目的とする。   An object of the present invention is to provide an optical transmitter capable of avoiding CNR or SNR degradation due to third-order distortion in the SCM scheme and reducing clipping noise without using the FM-AM batch modulation scheme.

第１の発明の光送信器は、ベースバンド多重信号とＲＦ搬送波を乗算し、ＲＦ変調信号を出力する乗算器と、入力電圧対出力電圧が対数特性を有し、ＲＦ変調信号を入力し、対数的に変換したＲＦ変調信号を出力する対数増幅器と、対数的に変換されたＲＦ変調信号で光キャリアを変調し、乗算器から出力されるＲＦ変調信号の振幅に比例した光強度変化を示す変調光を出力する電界吸収型変調器とを備える。   An optical transmitter according to a first aspect of the present invention is a multiplier that multiplies a baseband multiplexed signal and an RF carrier and outputs an RF modulated signal; an input voltage versus an output voltage has logarithmic characteristics; A logarithmic amplifier that outputs a logarithmically converted RF modulation signal and an optical carrier modulated with the logarithmically converted RF modulation signal, and showing a change in light intensity proportional to the amplitude of the RF modulation signal output from the multiplier An electroabsorption modulator that outputs modulated light.

第２の発明の光送信器は、入力電圧対出力電圧が対数特性を有し、ベースバンド多重信号を入力し、対数的に変換されたベースバンド多重信号を出力する第１の対数増幅器と、入力電圧対出力電圧が対数特性を有し、ＲＦ搬送波を入力し、対数的に変換されたＲＦ搬送波を出力する第２の対数増幅器と、対数的に変換されたベースバンド多重信号と対数的に変換されたＲＦ搬送波を加算し、対数的に変換されたＲＦ変調信号を出力する加算器と、加算器から出力される対数的に変換されたＲＦ変調信号で光キャリアを変調し、対数的に変換する前のＲＦ変調信号の振幅に比例した光強度変化を示す変調光を出力する電界吸収型変調器とを備える。   The optical transmitter of the second invention has a first logarithmic amplifier that has a logarithmic characteristic of input voltage to output voltage, inputs a baseband multiplexed signal, and outputs a logarithmically converted baseband multiplexed signal; A second logarithmic amplifier having a logarithmic characteristic of input voltage vs. output voltage, receiving an RF carrier and outputting a logarithmically transformed RF carrier; and logarithmically transformed baseband multiplexed signal logarithmically An adder that adds the converted RF carrier wave and outputs a logarithmically converted RF modulated signal; and an optical carrier that is logarithmically modulated by the logarithmically converted RF modulated signal output from the adder; An electroabsorption modulator that outputs modulated light indicating a change in light intensity proportional to the amplitude of the RF modulated signal before conversion.

本発明の光送信器は、光変調器を駆動するＲＦ変調信号を増幅する増幅器として入力電圧対出力電圧が対数特性を有する対数増幅器を用い、電界吸収型変調器の変調特性の非線形性を補正することにより、変調光はＲＦ変調信号の振幅電圧に比例して変化することになり、３次歪みを低減することができる。これにより、変調光の３次歪みによるＣＳＲやＳＮＲの劣化を改善することができる。   The optical transmitter of the present invention uses a logarithmic amplifier having a logarithmic characteristic of input voltage versus output voltage as an amplifier that amplifies an RF modulation signal that drives the optical modulator, and corrects the nonlinearity of the modulation characteristic of the electroabsorption modulator. As a result, the modulated light changes in proportion to the amplitude voltage of the RF modulation signal, and third-order distortion can be reduced. Thereby, degradation of CSR and SNR due to third-order distortion of modulated light can be improved.

（第１の実施形態）
図４は、本発明の光送信器の第１の実施形態を示す。
図において、乗算器１１はベースバンド多重信号とＲＦ搬送波を乗算し、フィルタ１２は乗算器１１から出力されるＲＦ変調信号の片側帯波およびＲＦ搬送波成分を切り出し、本発明の特徴とする対数増幅器２１に入力する。対数増幅器２１は、入力電圧対出力電圧が対数特性を有し、ＲＦ変調信号の片側帯波を増幅して電界吸収型（ＥＡ：Electro-Absorption）変調器２２に入力し、ＥＡ変調器２２は光キャリア（ＣＷ光）をＲＦ変調信号で光強度変調して変調光を出力する。なお、フィルタ１２は省いてもよい。 (First embodiment)
FIG. 4 shows a first embodiment of the optical transmitter of the present invention.
In the figure, a multiplier 11 multiplies a baseband multiplex signal and an RF carrier, and a filter 12 cuts out one sideband and an RF carrier component of the RF modulation signal output from the multiplier 11, and a logarithmic amplifier that is a feature of the present invention. 21. The logarithmic amplifier 21 has a logarithmic characteristic of input voltage versus output voltage, amplifies a single sideband of an RF modulation signal, and inputs the amplified signal to an electro-absorption (EA) modulator 22. The EA modulator 22 The optical carrier (CW light) is modulated with the RF modulation signal to output the modulated light. Note that the filter 12 may be omitted.

本実施形態の光送信器は、ＲＦ変調信号を対数増幅器２１で増幅することにより、ＲＦ変調信号の振幅電圧Ｖinを対数的に変換し、その出力電圧Ｖは、
Ｖ＝Ａ・logＶin
となる。ここで、Ａは定数（対数アンプゲイン）である。 The optical transmitter of this embodiment amplifies the RF modulation signal by the logarithmic amplifier 21 to logarithmically convert the amplitude voltage Vin of the RF modulation signal, and the output voltage V is
V = A ・ logVin
It becomes. Here, A is a constant (logarithmic amplifier gain).

ＥＡ変調器２２の変調特性は、ＲＦ変調信号の入力電圧Ｖ、変調光出力Ｐopt としたときに
Ｐopt ＝Ｐ0 exp[−(Ｖ／Ｖ0)]
となる。ここで、Ｐ0 、Ｖ0 は定数である。ＥＡ変調器２２の入力電圧Ｖは、対数増幅器２１でＲＦ変調信号の振幅電圧Ｖinを対数的に変換したものであるので、Ａを調整することで得られる変調光出力Ｐopt はＲＦ変調信号の振幅電圧Ｖinに比例して変化することになり、３次歪みを低減することができる。 The modulation characteristic of the EA modulator 22 is Popt = P 0 exp [− (V / V 0 )] when the input voltage V of the RF modulation signal and the modulated light output Popt are used.
It becomes. Here, P 0 and V 0 are constants. Since the input voltage V of the EA modulator 22 is obtained by logarithmically converting the amplitude voltage Vin of the RF modulation signal by the logarithmic amplifier 21, the modulated light output Popt obtained by adjusting A is the amplitude of the RF modulation signal. Since it changes in proportion to the voltage Vin, the third-order distortion can be reduced.

なお、対数増幅器は、一般に演算増幅器（オペアンプ）のフィードバック素子として非線形性をもつバイポーラトランジスタを用い、入出力電圧間に対数の関係をもたせたものである。その用途には、ＲＦ信号の強度を対数変換し、平滑化したエンベロープを出力するものがあり、パワーメータやスペクトルアナライザの表示回路に利用されている。本発明の光送信器で用いる対数増幅器２１は、出力がエンベロープにならないくらい従来の対数増幅器を高速化したものを用いる必要がある。そのためには、例えばＳi 系ＣＭＯＳなどで設計される演算増幅器をＩn Ｐなどの化合物半導体で実現するなど、高速回路設計技術を用いて実現することができる。   A logarithmic amplifier generally uses a bipolar transistor having nonlinearity as a feedback element of an operational amplifier (op amp), and has a logarithmic relationship between input and output voltages. One of its uses is to logarithmically transform the intensity of an RF signal and output a smoothed envelope, which is used for a display circuit of a power meter or a spectrum analyzer. As the logarithmic amplifier 21 used in the optical transmitter of the present invention, it is necessary to use a logarithmic amplifier having a conventional logarithmic amplifier speeded up so that the output does not become an envelope. For that purpose, it can be realized by using a high-speed circuit design technique, for example, an operational amplifier designed with Si-based CMOS or the like is realized with a compound semiconductor such as InP.

（第２の実施形態）
図５は、本発明の光送信器の第２の実施形態を示す。
本実施形態の光送信器では、ベースバンド多重信号およびＲＦ搬送波をそれぞれ対数増幅器２３，２４で増幅し、それぞれ対数的に変換されたベースバンド多重信号およびＲＦ搬送波を生成する。加算器２５はこの対数的に変換されたベースバンド多重信号とＲＦ搬送波を加算してＲＦ変調信号を生成し、フィルタ１２でそのＲＦ変調信号の片側帯波およびＲＦ搬送波成分を切り出すことにより、第１の実施形態の乗算器１１、フィルタ１２および対数増幅器２１を介して出力される対数的に変換されたＲＦ変調信号と同等のものを生成してＥＡ変調器２２に入力する。なお、フィルタ１２は省いてもよい。 (Second Embodiment)
FIG. 5 shows a second embodiment of the optical transmitter of the present invention.
In the optical transmitter of this embodiment, the baseband multiplexed signal and the RF carrier are amplified by logarithmic amplifiers 23 and 24, respectively, and the baseband multiplexed signal and the RF carrier that are logarithmically converted are generated. The adder 25 adds the logarithmically converted baseband multiplexed signal and the RF carrier to generate an RF modulated signal, and the filter 12 cuts out one sideband wave and the RF carrier component of the RF modulated signal. An equivalent of the logarithmically converted RF modulation signal output via the multiplier 11, the filter 12, and the logarithmic amplifier 21 of the first embodiment is generated and input to the EA modulator 22. Note that the filter 12 may be omitted.

対数的に変換されたＲＦ変調信号とＥＡ変調器２２の変調特性の関係は第１の実施形態と同様であり、ＲＦ変調信号の振幅電圧Ｖinに比例して変化する３次歪みの小さい変調光を出力することができる。   The relationship between the logarithmically converted RF modulation signal and the modulation characteristic of the EA modulator 22 is the same as that of the first embodiment, and modulated light with small third-order distortion that changes in proportion to the amplitude voltage Vin of the RF modulation signal. Can be output.

なお、第１の実施形態はベースバンド多重信号とＲＦ搬送波を乗算したものを対数変換しており、本実施形態は対数変換したベースバンド多重信号とＲＦ搬送波を加算しており、ベースバンド多重信号をＢ、ＲＦ搬送波をＲとすると、両者は
log(Ｂ×Ｒ)= logＢ＋logＲ
の関係により等価である。 The first embodiment performs logarithmic conversion of a product of a baseband multiplexed signal and an RF carrier. In the present embodiment, the baseband multiplexed signal and the RF carrier that have been logarithmically converted are added, and the baseband multiplexed signal is added. Is B and RF carrier is R,
log (B × R) = logB + logR
It is equivalent due to the relationship.

（第３の実施形態）
図６は、本発明の光送信器の第３の実施形態を示す。
本実施形態の光送信器は、周波数が互いに異なる複数のＲＦ搬送波にベースバンド信号が重畳された複数のＲＦ変調信号１〜Ｎがあり、それらを加算器２６で加算して多重ＲＦ変調信号を生成し、さらに対数増幅器２７を介して対数的に変換された多重ＲＦ変調信号を生成してＥＡ変調器２２に入力する。 (Third embodiment)
FIG. 6 shows a third embodiment of the optical transmitter of the present invention.
The optical transmitter of this embodiment has a plurality of RF modulation signals 1 to N in which baseband signals are superimposed on a plurality of RF carriers having different frequencies, and adds them by an adder 26 to generate a multiplexed RF modulation signal. Then, a multiple RF modulation signal that is logarithmically converted via the logarithmic amplifier 27 is generated and input to the EA modulator 22.

対数的に変換された多重ＲＦ変調信号とＥＡ変調器２２の変調特性の関係は第１の実施形態と同様であり、対数的に変換する前の多重ＲＦ変調信号の振幅電圧に比例して変化する３次歪みの小さい変調光を出力することができる。   The relationship between the logarithmically converted multiplex RF modulation signal and the modulation characteristic of the EA modulator 22 is the same as in the first embodiment, and changes in proportion to the amplitude voltage of the multiplex RF modulation signal before logarithmically conversion. Thus, modulated light with a small third-order distortion can be output.

（第４の実施形態）
図７は、本発明の光送信器の第４の実施形態を示す。
本実施形態の光送信器は、周波数が互いに異なる複数のＲＦ搬送波にベースバンド信号が重畳された複数のＲＦ変調信号１〜Ｎがあり、それぞれ対数増幅器２８−１〜２８−Ｎを介して対数的に変換されたＲＦ変調信号を生成し、それらを加算器２６で加算して多重ＲＦ変調信号を生成してＥＡ変調器２２に入力する。 (Fourth embodiment)
FIG. 7 shows a fourth embodiment of the optical transmitter of the present invention.
The optical transmitter according to the present embodiment includes a plurality of RF modulation signals 1 to N in which baseband signals are superimposed on a plurality of RF carriers having different frequencies, and logarithms via logarithmic amplifiers 28-1 to 28 -N, respectively. The modulated RF modulation signals are generated and added by an adder 26 to generate a multiple RF modulation signal and input to the EA modulator 22.

対数的に変換された多重ＲＦ変調信号とＥＡ変調器２２の変調特性の関係は第１の実施形態と同様であり、対数的に変換する前の多重ＲＦ変調信号の振幅電圧に比例して変化する３次歪みの小さい変調光を出力することができる。   The relationship between the logarithmically converted multiplex RF modulation signal and the modulation characteristic of the EA modulator 22 is the same as in the first embodiment, and changes in proportion to the amplitude voltage of the multiplex RF modulation signal before logarithmically conversion. Thus, modulated light with a small third-order distortion can be output.

なお、本実施形態の対数増幅器２８は、第３の実施形態の対数増幅器２７に比べて狭帯域のものでよい。   Note that the logarithmic amplifier 28 of the present embodiment may be narrower than the logarithmic amplifier 27 of the third embodiment.

従来の光送信器の第１の構成例を示図。The figure which shows the 1st structural example of the conventional optical transmitter. 従来の光送信器の第２の構成例を示図。The figure which shows the 2nd structural example of the conventional optical transmitter. 従来の光送信器の第３の構成例を示図。The figure which shows the 3rd structural example of the conventional optical transmitter. 本発明の光送信器の第１の実施形態を示す図。The figure which shows 1st Embodiment of the optical transmitter of this invention. 本発明の光送信器の第２の実施形態を示す図。The figure which shows 2nd Embodiment of the optical transmitter of this invention. 本発明の光送信器の第３の実施形態を示す図。The figure which shows 3rd Embodiment of the optical transmitter of this invention. 本発明の光送信器の第４の実施形態を示す図。The figure which shows 4th Embodiment of the optical transmitter of this invention.

符号の説明Explanation of symbols

１１ 乗算器
１２ フィルタ
１３ 増幅器
１４ ＬＮ変調器
１５ レーザダイオード（ＬＤ）
１６ バイアスＴ
１７ ＦＭ−ＡＭ一括変調器
２１，２３，２４，２７，２８ 対数増幅器
２２ 電界吸収型（ＥＡ）変調器
２５，２６ 加算器 11 Multiplier 12 Filter 13 Amplifier 14 LN Modulator 15 Laser Diode (LD)
16 Bias T
17 FM-AM collective modulator 21, 23, 24, 27, 28 Logarithmic amplifier 22 Electroabsorption (EA) modulator 25, 26 Adder

Claims (2)

ベースバンド多重信号とＲＦ搬送波を乗算し、ＲＦ変調信号を出力する乗算器と、
入力電圧対出力電圧が対数特性を有し、前記ＲＦ変調信号を入力し、対数的に変換したＲＦ変調信号を出力する対数増幅器と、
前記対数的に変換されたＲＦ変調信号で光キャリアを変調し、前記乗算器から出力される前記ＲＦ変調信号の振幅に比例した光強度変化を示す変調光を出力する電界吸収型変調器と
を備えたことを特徴とする光送信器。 A multiplier that multiplies the baseband multiplexed signal and the RF carrier, and outputs an RF modulated signal;
A logarithmic amplifier in which an input voltage versus an output voltage has logarithmic characteristics, inputs the RF modulation signal, and outputs a logarithmically converted RF modulation signal;
An electroabsorption modulator that modulates an optical carrier with the logarithmically converted RF modulation signal, and outputs modulated light indicating a change in light intensity proportional to the amplitude of the RF modulation signal output from the multiplier; An optical transmitter comprising: 入力電圧対出力電圧が対数特性を有し、ベースバンド多重信号を入力し、対数的に変換されたベースバンド多重信号を出力する第１の対数増幅器と、
入力電圧対出力電圧が対数特性を有し、ＲＦ搬送波を入力し、対数的に変換されたＲＦ搬送波を出力する第２の対数増幅器と、
前記対数的に変換されたベースバンド多重信号と前記対数的に変換されたＲＦ搬送波を加算し、対数的に変換されたＲＦ変調信号を出力する加算器と、
前記加算器から出力される前記対数的に変換されたＲＦ変調信号で光キャリアを変調し、対数的に変換する前のＲＦ変調信号の振幅に比例した光強度変化を示す変調光を出力する電界吸収型変調器と
を備えたことを特徴とする光送信器。 A first logarithmic amplifier that has a logarithmic characteristic of input voltage versus output voltage, inputs a baseband multiplexed signal, and outputs a logarithmically converted baseband multiplexed signal;
A second logarithmic amplifier, wherein the input voltage vs. output voltage has a logarithmic characteristic, inputs an RF carrier, and outputs a logarithmically transformed RF carrier;
An adder that adds the logarithmically converted baseband multiplexed signal and the logarithmically converted RF carrier, and outputs a logarithmically converted RF modulated signal;
An electric field that modulates an optical carrier with the logarithmically converted RF modulation signal output from the adder, and outputs modulated light indicating a light intensity change proportional to the amplitude of the RF modulation signal before logarithmically conversion. An optical transmitter comprising: an absorption modulator.
JP2008229825A 2008-09-08 2008-09-08 Optical transmitter Expired - Fee Related JP4980319B2 (en)

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US5060310A (en) * 1989-08-10 1991-10-22 Tektronix, Inc. Apparatus and method for reduction of intermodulation distortion in an optical fiber network
JP2797824B2 (en) * 1992-02-20 1998-09-17 日本電気株式会社 Subcarrier multiplexing optical transmission device and I / O card used therefor
JPH0884114A (en) * 1994-09-13 1996-03-26 Mitsubishi Cable Ind Ltd Signal transmitting equipment
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