JP5300923B2 - Spectroscopic system and control method thereof - Google Patents

Spectroscopic system and control method thereof Download PDF

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JP5300923B2
JP5300923B2 JP2011135495A JP2011135495A JP5300923B2 JP 5300923 B2 JP5300923 B2 JP 5300923B2 JP 2011135495 A JP2011135495 A JP 2011135495A JP 2011135495 A JP2011135495 A JP 2011135495A JP 5300923 B2 JP5300923 B2 JP 5300923B2
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直文 清水
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a spectroscopic system in which a signal received without reflection and a signal received after reflection are separated from each other. <P>SOLUTION: In each signal intensity detection circuit (a narrow band filter 118, a wave detector 119, an AD converter 120), a component of each predetermined frequency is separated and extracted from the signal from a receiving mixer 115. Moreover, the wavelength of light from a wavelength variable laser beam source 101 changes the wavelength of the light from the wavelength variable laser beam source 103 so that a period when the wavelength becomes equal to each of a plurality of wavelength becomes discrete during a certain period. <P>COPYRIGHT: (C)2013,JPO&amp;INPIT

Description

本発明は、分光システムおよびその制御方法に関するものである。   The present invention relates to a spectroscopic system and a control method thereof.

従来、ミリ波やテラヘルツ波である電磁波の透過スペクトルまたは反射スペクトルを測定する分光システムとして、例えば図５に示すような装置がある（非特許文献１参照）。   Conventionally, as a spectroscopic system for measuring a transmission spectrum or a reflection spectrum of an electromagnetic wave such as a millimeter wave or a terahertz wave, there is an apparatus as shown in FIG. 5, for example (see Non-Patent Document 1).

このシステムでは、２台の波長可変光源２１、２２から発生する波長λ１（周波数＝Ｃ／λ１、ｃ：光速）、λ２（周波数＝ｃ／λ２）の光を合波分波器２３で一旦合波後、２つに分波させ、その一方を送信部２４、他方を受信部２５に導入する。 In this system, light having wavelengths λ 1 (frequency = C / λ 1 , c: speed of light) and λ 2 (frequency = c / λ 2 ) generated from two wavelength variable light sources 21, 22 are multiplexed and demultiplexed 23. After multiplexing, the signal is split into two, and one of them is introduced into the transmitter 24 and the other into the receiver 25.

図６は、送信部２４に導入される光信号のスペクトルを示す図である。波長の異なる２つの光が合波されたことにより、その周波数差の唸りが生じている。送信部２４は光伝導スイッチと電磁波放射用アンテナで構成されており、波長の異なる２つの光信号が入力されると、唸り周波数ｃ（１／λ１―１／λ２）に対応する電磁波（ミリ波やテラヘルツ波）を発する。送信部２４で発生したミリ波やテラヘルツ波は、この例では、被測定物Ｓを透過し、受信部２５に導入される。 FIG. 6 is a diagram illustrating a spectrum of an optical signal introduced into the transmission unit 24. As a result of the combination of two lights having different wavelengths, the difference in frequency is generated. The transmission unit 24 includes a photoconductive switch and an electromagnetic wave radiation antenna. When two optical signals having different wavelengths are input, an electromagnetic wave ((1 / λ 1 −1 / λ 2 ) corresponding to the turning frequency c (1 / λ 1 −λ 2 ) is transmitted. Emits millimeter waves and terahertz waves. In this example, the millimeter wave and the terahertz wave generated by the transmission unit 24 are transmitted through the device under test S and introduced into the reception unit 25.

受信部２５は光伝導スイッチと電磁波受信用アンテナで形成されており、図６で示される光信号が入射された状態で、電磁波受信用アンテナにミリ波やテラヘルツ波の電磁波が到来すると、その強度に比例した光電流が流れる。波長可変光源２１、２２の波長を掃引した時に、受信部２５で検出される光電流強度の変化は、受信部２５に到来するミリ波やテラヘルツ波の各周波数における電磁波の強度を表す。これは被測定物Ｓに対するミリ波・テラヘルツ波電磁波の透過または反射スペクトルである。この例では、合波分波器２３で波長λ１、λ２の波長を波長計２６、２７で測定し、波長可変光源２１、２２の掃引時の波長精度を高めている。   The receiving unit 25 is formed of a photoconductive switch and an electromagnetic wave receiving antenna, and when an electromagnetic wave of millimeter wave or terahertz wave arrives at the electromagnetic wave receiving antenna with the optical signal shown in FIG. A photocurrent proportional to the current flows. When the wavelengths of the wavelength tunable light sources 21 and 22 are swept, the change in the photocurrent intensity detected by the receiving unit 25 represents the intensity of the electromagnetic wave at each frequency of the millimeter wave and the terahertz wave arriving at the receiving unit 25. This is a transmission or reflection spectrum of a millimeter wave / terahertz wave electromagnetic wave to the object S to be measured. In this example, the wavelength demultiplexer 23 measures the wavelengths λ1 and λ2 with the wavelength meters 26 and 27, and the wavelength accuracy during the sweeping of the wavelength variable light sources 21 and 22 is improved.

“Tunable CW Terahertz source with High-Precision Frequency Control,”A. J. Deninger, T. Goubel, D. Schoenherr, A. Roggenbuck, F. Kison, and P. Meissner, The Joint 33nd International Conference on Infrared and Millimeter Waves and 16th International Conference on Terahertz Electronics, T4B3.1418.“Tunable CW Terahertz source with High-Precision Frequency Control,” AJ Deninger, T. Goubel, D. Schoenherr, A. Roggenbuck, F. Kison, and P. Meissner, The Joint 33nd International Conference on Infrared and Millimeter Waves and 16th International Conference on Terahertz Electronics, T4B3.1418.

図５に示すような装置においては、電磁波の多重反射が問題となることがある。例えば、被測定物Ｓで反射した一部の電磁波は、送信部２４に戻り、そこで再び反射され、もう一度被測定物Ｓに向かう。また、被測定物Ｓを透過して受信部２５に到達した電磁波の一部は、受信部２５で反射され、被測定物Ｓに戻り、そこで再び反射され、もう一度受信部２５に向かう。いずれの場合にしても、光伝導スイッチで電気信号に変換される電磁波は、単純に送信部２４から発せられ受信部２５に直接到達した信号だけではなく、被測定物Ｓと送信部２４を何回か往復した信号、受信部２５と被測定物Ｓを何回か往復した信号、などの重ね合わせである。この場合、反射物の間隔が電磁波の波長の1／2の整数倍のとき、受信部２５に到達する電磁波の強度が強くなるという効果が生じるため、本来測定されるべき、被測定物Ｓに対する電磁波の透過特性が正確に測定できなくなってしまう。   In the apparatus as shown in FIG. 5, multiple reflection of electromagnetic waves may be a problem. For example, a part of the electromagnetic waves reflected by the object to be measured S returns to the transmission unit 24, where it is reflected again and travels toward the object to be measured S again. Further, a part of the electromagnetic wave that has passed through the device under test S and reached the receiving unit 25 is reflected by the receiving unit 25, returns to the device under test S, is reflected again there, and travels toward the receiving unit 25 again. In any case, the electromagnetic wave converted into the electrical signal by the photoconductive switch is not only the signal that is simply emitted from the transmission unit 24 and directly reaches the reception unit 25, but also what the measured object S and the transmission unit 24 are. It is a superposition of a signal that has been reciprocated several times, a signal that has been reciprocated several times between the receiving unit 25 and the measured object S, and the like. In this case, when the distance between the reflecting objects is an integral multiple of 1/2 of the wavelength of the electromagnetic wave, the effect of increasing the intensity of the electromagnetic wave reaching the receiving unit 25 is generated. Electromagnetic transmission characteristics cannot be measured accurately.

本発明は、上記の課題に鑑みてなされたものであり、その目的とするところは、反射しないで受信される信号と反射してから受信される信号を分離できる分光システムおよびその制御方法を提供することにある。   The present invention has been made in view of the above problems, and an object thereof is to provide a spectroscopic system capable of separating a signal received without reflection and a signal received after reflection and a control method thereof There is to do.

上記の課題を解決するために、第１の本発明は、第１の波長可変レーザ光源と、第２の波長可変レーザ光源と、波長固定レーザ光源と、前記第１の波長可変レーザ光源からの光と前記波長固定レーザ光源からの光を合波することにより得られる光ビート信号を電磁波に変換する第１のフォトミキサと、前記第１の波長可変レーザ光源からの光と前記第２の波長可変レーザ光源からの光を合波することにより得られる光ビート信号を電磁波に変換する第２のフォトミキサと、前記第１のフォトミキサからの電磁波を照射された被測定物を経た電磁波と前記第２のフォトミキサからの電磁波とを混合する手段と、前記混合された電磁波から前記波長固定レーザ光源からの光の周波数と前記第２の波長可変レーザ光源からの光の周波数の差に等しい周波数を有する電磁波である中間周波信号を抽出する受信用ミキサと、前記第１の波長可変レーザ光源からの光の波長が一定の期間において前記第２の波長可変レーザ光源からの光の波長を、該波長が予め定められた複数の波長のそれぞれに等しくなる期間が離散的になるように、変化させる手段と、前記第２の波長可変レーザ光源からの光の波長の離散的な変化に伴い前記中間周波信号が有することとなる複数の周波数について当該中間周波信号から当該各周波数の成分を分離して抽出する手段と、を備えることを特徴とする分光システムをもって解決手段とする。   In order to solve the above-described problems, the first aspect of the present invention provides a first wavelength tunable laser light source, a second wavelength tunable laser light source, a wavelength fixed laser light source, and the first wavelength tunable laser light source. A first photomixer that converts an optical beat signal obtained by combining light and light from the wavelength-fixed laser light source into electromagnetic waves, light from the first wavelength-tunable laser light source, and the second wavelength A second photomixer that converts an optical beat signal obtained by combining light from a variable laser light source into an electromagnetic wave; an electromagnetic wave that has passed through a measurement object irradiated with the electromagnetic wave from the first photomixer; Means for mixing the electromagnetic wave from the second photomixer, and the difference between the frequency of the light from the fixed wavelength laser light source and the frequency of the light from the second tunable laser light source from the mixed electromagnetic wave A receiving mixer that extracts an intermediate frequency signal that is an electromagnetic wave having a wave number; and a wavelength of light from the second tunable laser light source in a period in which the wavelength of light from the first tunable laser light source is constant, In accordance with discrete changes in the wavelength of light from the second wavelength tunable laser light source, the means for changing the wavelength so that the period in which the wavelength is equal to each of a plurality of predetermined wavelengths becomes discrete And a means for separating and extracting the components of each frequency from the intermediate frequency signal for a plurality of frequencies that the intermediate frequency signal has.

例えば、前記第２の波長可変レーザ光源からの光の波長を変化させる手段は、前記複数の波長のそれぞれに対応する周波数に等しくなる期間が離散的になるように変化する周波数を有する参照信号を出力する参照信号発生器と、前記波長固定レーザ光源からの光と前記第２の波長可変レーザ光源からの光を合波することにより得られる光ビート信号を電磁波に変換する手段と、前記参照信号の周波数と当該電磁波の周波数との差を検出し当該差がなくなるように前記第２の波長可変レーザ光源を制御する手段とを備える。   For example, the means for changing the wavelength of the light from the second wavelength tunable laser light source may be configured to generate a reference signal having a frequency that changes so that a period equal to a frequency corresponding to each of the plurality of wavelengths becomes discrete. A reference signal generator for outputting, means for converting an optical beat signal obtained by combining light from the fixed wavelength laser light source and light from the second wavelength variable laser light source into electromagnetic waves, and the reference signal And a means for controlling the second tunable laser light source so as to eliminate the difference between the frequency of the electromagnetic wave and the frequency of the electromagnetic wave.

第２の本発明は、第１の本発明に係る分光システムの制御方法であって、前記第１の波長可変レーザ光源からの光の波長が一定の期間において前記第２の波長可変レーザ光源からの光の波長を、該波長が前記複数の波長のそれぞれに等しくなる期間が離散的になるように、変化させることを特徴とする分光システムの制御方法をもって解決手段とする。   A second aspect of the present invention is a method for controlling a spectroscopic system according to the first aspect of the present invention, wherein the wavelength of light from the first wavelength tunable laser light source is from the second wavelength tunable laser light source in a fixed period. The spectral system control method is characterized in that the wavelength of the light is changed so that the period during which the wavelength is equal to each of the plurality of wavelengths is discrete.

第３の本発明は、第１の本発明に係る分光システムの制御方法であって、前記第１のフォトミキサからの電磁波が前記受信用ミキサに到達するまでの到達時間の２倍の周期で前記第１の波長可変レーザ光源からの光の前記一定の波長の値を切り替えることを特徴とする分光システムの制御方法をもって解決手段とする。   A third aspect of the present invention is a method of controlling a spectroscopic system according to the first aspect of the present invention, wherein the electromagnetic wave from the first photomixer has a period twice as long as the arrival time until the electromagnetic wave reaches the reception mixer. The solution is provided by a spectroscopic system control method that switches the value of the constant wavelength of light from the first tunable laser light source.

本発明によれば、反射しないで受信される信号と反射してから受信される信号を分離することができる。   According to the present invention, it is possible to separate a signal received without reflection and a signal received after reflection.

図１は、本実施の形態に係る分光システムの構成を示すブロック図である。FIG. 1 is a block diagram showing the configuration of the spectroscopic system according to the present embodiment. 図２（ａ）は、波長可変レーザ光源１０１の波長の変化を示す図、図２（ｂ）は、参照信号発生器１０８からの参照信号の周波数の変化を示す図、図２（ｃ）は、波長可変レーザ光源１０３の波長の変化を示す図、図２（ｄ）は、受信用ミキサ１１５に到達する電磁波の周波数の変化を示す図である。2A is a diagram showing a change in the wavelength of the tunable laser light source 101, FIG. 2B is a diagram showing a change in the frequency of the reference signal from the reference signal generator 108, and FIG. FIG. 2D is a diagram showing a change in the wavelength of the wavelength tunable laser light source 103, and FIG. 2D is a diagram showing a change in the frequency of the electromagnetic wave reaching the reception mixer 115. 図３（ａ）は、受信用ミキサ１１５に到達する電磁波の周波数の変化を示す図、図３（ｂ）は、受信用ミキサ１１５から出力される中間周波信号の周波数の変化を示す図である。FIG. 3A is a diagram showing a change in the frequency of the electromagnetic wave reaching the reception mixer 115, and FIG. 3B is a diagram showing a change in the frequency of the intermediate frequency signal output from the reception mixer 115. . 各狭帯域フィルタ１１８の透過特性を示す図である。It is a figure which shows the transmission characteristic of each narrow-band filter 118. FIG. 従来の分光システムの構成を示すブロック図である。It is a block diagram which shows the structure of the conventional spectroscopy system. 送信部２４に導入される光信号のスペクトルを示す図である。It is a figure which shows the spectrum of the optical signal introduced into the transmission part.

以下、本発明の実施の形態について図面を参照して説明する。   Hereinafter, embodiments of the present invention will be described with reference to the drawings.

図１は、本実施の形態に係る分光システムの構成を示すブロック図である
分光システムは、ミリ波やテラヘルツ波の電磁波の透過スペクトルを測定するものである。 FIG. 1 is a block diagram showing a configuration of a spectroscopic system according to the present embodiment. The spectroscopic system measures a transmission spectrum of millimeter wave or terahertz wave electromagnetic waves.

図中１０１は波長掃引可能な波長可変レーザ光源、１０２は波長固定レーザ光源、１０３は波長可変レーザ光源１０１と波長固定レーザ光源１０２とは別の波長で発振している発振波長の微調整が可能な波長可変レーザ光源、１０４は波長可変レーザ光源１０１からの光と波長固定レーザ光源１０２の光の合波、波長可変レーザ光源１０１からの光と波長可変レーザ光源１０３からの光の合波、波長固定レーザ光源１０２と波長可変レーザ光源１０３からの光の合波を行う光合分波回路、１０５は波長可変レーザ光源１０１からの光と波長固定レーザ光源１０２からの光の合波により得られる光ビート信号をビート周波数に一致する周波数を有する電磁波に変換して放射するためのフォトミキサ、１０６は波長可変レーザ光源１０１からの光と波長可変レーザ光源１０３からの光の合波により得られる光ビート信号をビート周波数に一致する周波数を有する電磁波に変換して放射するためのフォトミキサ、１０７は波長固定レーザ光源１０２と波長可変レーザ光源１０３からの光の合波により得られる光ビート信号をビート周波数に一致する電気信号に変換するためのフォトダイオード、１０８は波長可変レーザ光源１０３の発振波長を微調整するための参照信号を与えるための参照信号発生器、１０９はフォトダイオード１０７からの電気信号と参照信号発生器１０８からの参照信号を混合するためのミキサ、１１０はフォトダイオード１０７と参照信号発生器１０８からの参照信号の周波数差を検出し、波長可変レーザ光源１０３の発振波長を微調整するための制御信号を出力するための周波数差検出回路、１１１はフォトミキサ１０５から放射される、被測定物の特性評価に用いる電磁波を平行ビームにコリメートするためのコリメート鏡、１１２は被測定物（透過特性が評価される物質）、１１３はフォトミキサ１０６から放射される電磁波（この電磁波は、ヘテロダイン受信器を励起する局部発振信号として用いられる）を平行ビームにコリメートするためのコリメート鏡、１１４は被測定物１１２の特性評価に用いる電磁波とヘテロダイン受信器を励起する局部発振信号として用いられる電磁波を混合するためのハーフミラー、１１５は被測定物１１２を透過してきた電磁波の強度を測定するための受信用ミキサ、１１６は被測定物１１２の特性評価に用いる電磁波とヘテロダイン受信器を励起する局部発振信号として用いられる電磁波を受信用ミキサ１１５に導入するためのコリメート鏡、１１７は受信用ミキサ１１５により中間周波信号に変換された信号の強度を増幅するための受信用増幅器、１１８は狭帯域フィルタ（各狭帯域フィルタの透過特性は互いに異なっている）、１１９は検波器、１２０はＡＤ（アナログディジタル）変換器、１２１は制御装置である。   In the figure, 101 is a wavelength tunable laser light source capable of sweeping, 102 is a wavelength fixed laser light source, 103 is an oscillation wavelength oscillating at a wavelength different from that of the wavelength tunable laser light source 101 and the wavelength fixed laser light source 102. A wavelength tunable laser light source 104 is a combination of light from the wavelength tunable laser light source 101 and light from the wavelength tunable laser light source 102, light from the wavelength tunable laser light source 101 and light from the wavelength tunable laser light source 103, wavelength An optical multiplexing / demultiplexing circuit 105 that combines light from the fixed laser light source 102 and the wavelength tunable laser light source 103, and 105 is an optical beat obtained by combining light from the wavelength variable laser light source 101 and light from the wavelength fixed laser light source 102. A photomixer for converting a signal into an electromagnetic wave having a frequency matching the beat frequency and emitting the electromagnetic wave, 106 is a light from the wavelength tunable laser light source 101 A photomixer for converting an optical beat signal obtained by combining light from the wavelength tunable laser light source 103 into an electromagnetic wave having a frequency matching the beat frequency and emitting the electromagnetic wave, 107 is a wavelength fixed laser light source 102 and a wavelength tunable laser light source A photodiode 108 for converting an optical beat signal obtained by combining light from 103 into an electric signal that matches the beat frequency, and 108 for providing a reference signal for finely adjusting the oscillation wavelength of the tunable laser light source 103 Reference signal generator 109, 109 is a mixer for mixing the electrical signal from the photodiode 107 and the reference signal from the reference signal generator 108, and 110 is the frequency difference between the reference signal from the photodiode 107 and the reference signal generator 108. And outputs a control signal for finely adjusting the oscillation wavelength of the tunable laser light source 103 A frequency difference detection circuit 111 for collimating the electromagnetic wave radiated from the photomixer 105 for collimating the electromagnetic wave used for the characteristic evaluation of the object to be measured into a parallel beam, 112 for the object to be measured (the transmission characteristic is evaluated) Material), 113 is a collimating mirror for collimating an electromagnetic wave radiated from the photomixer 106 (this electromagnetic wave is used as a local oscillation signal for exciting the heterodyne receiver) into a parallel beam, and 114 is a characteristic of the object 112 to be measured. A half mirror for mixing the electromagnetic wave used for evaluation and the electromagnetic wave used as a local oscillation signal for exciting the heterodyne receiver, 115 is a receiving mixer for measuring the intensity of the electromagnetic wave transmitted through the DUT 112, and 116 is Local oscillation signal for exciting electromagnetic wave and heterodyne receiver used for characteristic evaluation of device under test 112 A collimating mirror for introducing an electromagnetic wave used as a signal into the receiving mixer 115, 117 a receiving amplifier for amplifying the intensity of the signal converted into an intermediate frequency signal by the receiving mixer 115, and 118 a narrowband filter ( The transmission characteristics of the narrow-band filters are different from each other.) 119 is a detector, 120 is an AD (analog-digital) converter, and 121 is a control device.

狭帯域フィルタ１１８、検波器１１９、ＡＤ変換器１２０を囲む点線は、このブロックがそれぞれ異なる周波数をもつ信号の強度を測定するための信号強度検出回路であることを示している。   Dotted lines surrounding the narrow band filter 118, the detector 119, and the AD converter 120 indicate that this block is a signal intensity detection circuit for measuring the intensity of signals having different frequencies.

波長固定レーザ光源１０２、波長可変レーザ光源１０３には、例えば、半導体単一モードレーザが用いられる。   For example, a semiconductor single mode laser is used for the fixed wavelength laser light source 102 and the variable wavelength laser light source 103.

フォトミキサ１０５からは、波長可変レーザ光源１０１からの光の周波数と波長固定レーザ光源１０２からの光の周波数の差に等しい周波数を有する電磁波が出力される。   The photomixer 105 outputs an electromagnetic wave having a frequency equal to the difference between the frequency of light from the wavelength tunable laser light source 101 and the frequency of light from the fixed wavelength laser light source 102.

フォトミキサ１０６からは、波長可変レーザ光源１０１からの光の周波数と波長可変レーザ光源１０３からの光の周波数の差に等しい周波数を有する電磁波が出力される。   The photomixer 106 outputs an electromagnetic wave having a frequency equal to the difference between the frequency of the light from the wavelength tunable laser light source 101 and the frequency of the light from the wavelength tunable laser light source 103.

（分光システムの動作）
波長可変レーザ光源１０１、波長可変レーザ光源１０３は当初は、消光状態であり、一方、波長固定レーザ光源１０２は発光しており、その光の波長はλＦＬＳ１に固定されている。波長λＦＬＳ１は、例えば、１．５４７９３４０μｍである。 (Spectroscopic system operation)
The wavelength tunable laser light source 101 and the wavelength tunable laser light source 103 are initially in a quenching state, while the wavelength fixed laser light source 102 emits light, and the wavelength of the light is fixed at λ FLS1 . The wavelength λ FLS1 is, for example, 1.5479340 μm.

この状態で、制御装置１２１は、波長可変レーザ光源１０１に制御信号を送信し、図２（ａ）に示すように、波長可変レーザ光源１０１からの光の波長を時間的に変化させる。   In this state, the control device 121 transmits a control signal to the wavelength tunable laser light source 101, and temporally changes the wavelength of the light from the wavelength tunable laser light source 101 as shown in FIG.

波長可変レーザ光源１０１は、例えば、外部共振器型のレーザを用い、この場合、外部共振器を構成しているミラーや回折格子をモーターなどにより回転や移動させることにより、波長可変レーザ光源１０１からの光の波長を高速で掃引させることができる。また、波長可変レーザ光源１０１は、外部共振器を用いるため、光の波長を広範囲で掃引させることができる。   The wavelength tunable laser light source 101 uses, for example, an external resonator type laser. In this case, by rotating or moving a mirror or a diffraction grating constituting the external resonator by a motor or the like, The wavelength of light can be swept at high speed. Further, since the wavelength tunable laser light source 101 uses an external resonator, the wavelength of light can be swept over a wide range.

波長λＴＬＳ １、λＴＬＳ ２、λＴＬＳ ３は、例えば、それぞれ１．５５０００００μｍ、１．５５０００８０μｍ、１．５５００１６０μｍである。 The wavelengths λ TLS 1 , λ TLS 2 , and λ TLS 3 are, for example, 1.5500,000 μm, 1.5500080 μm, and 1.5500160 μm, respectively.

波長可変レーザ光源１０１は、波長λＴＬＳ １でΔｔだけ発光したあと、Δｔだけ消光し、次にλＴＬＳ ２でΔｔだけ発光し、Δｔだけ消光する、というパターンを繰り返しながら波長が掃引される。Δｔは、フォトミキサ１０５から放射された電磁波が受信用ミキサ１１５に到達するまでの時間の長さである。つまり、制御装置１２１は、波長可変レーザ光源１０１からの光の波長の値をΔｔの２倍の周期で切り替える。 The wavelength tunable laser light source 101 emits light by Δt at the wavelength λ TLS 1 , then extinguishes by Δt, then emits light by Δt at λ TLS 2 , and extinguishes only by Δt, and the wavelength is swept while repeating the pattern. Δt is the length of time until the electromagnetic wave radiated from the photomixer 105 reaches the receiving mixer 115. That is, the control device 121 switches the value of the wavelength of the light from the wavelength tunable laser light source 101 at a cycle that is twice as long as Δt.

また、制御装置１２１は、参照信号発生器１０８に制御信号を送信し、図２（ｂ）に示すように、参照信号の周波数を変化させる。   Further, the control device 121 transmits a control signal to the reference signal generator 108, and changes the frequency of the reference signal as shown in FIG.

参照信号の周波数は、１つのパターンを有し、これをΔｔの時間が経過するごとに繰り返す。また、１つのパターンの中において、参照信号の周波数は、周波数ｆ１、ｆ２、ｆ３、ｆ４のそれぞれに等しくなる期間が離散的になるように変化する。参照信号の周波数は、例えば、ステップ状に変化する。周波数ｆ１、ｆ２、ｆ３、ｆ４は、例えば、それぞれ１５０ＭＨｚ、３００ＭＨｚ、４５０ＭＨｚ、６００ＭＨｚである。 The frequency of the reference signal has one pattern, which is repeated every time Δt elapses. Further, in one pattern, the frequency of the reference signal changes so that periods equal to the frequencies f 1 , f 2 , f 3 , and f 4 become discrete. The frequency of the reference signal changes stepwise, for example. The frequencies f 1 , f 2 , f 3 , and f 4 are, for example, 150 MHz, 300 MHz, 450 MHz, and 600 MHz, respectively.

このような参照信号が出力されると、波長可変レーザ光源１０３からの光の波長は、図２（ｃ）に示すように時間的に変化する。波長λＦＬＳ２ １、λＦＬＳ２ ２、λＦＬＳ２ ３、λＦＬＳ２ ４は、例えば、それぞれ１．５４７９３２８μｍ、１．５４７９３１６μｍ、１．５４７９３０４μｍ、１．５４７９２９２μｍである。 When such a reference signal is output, the wavelength of the light from the wavelength tunable laser light source 103 changes with time as shown in FIG. The wavelengths λ FLS2 1 , λ FLS2 2 , λ FLS2 3 , and λ FLS2 4 are, for example, 1.5479328 μm, 1.5479316 μm, 1.5479304 μm, and 1.5479292 μm, respectively.

つまり、フォトダイオード１０７は、波長固定レーザ光源１０２からの光の周波数と波長可変レーザ光源１０３からの光の周波数の差に等しい周波数を有する電磁波を出力し、そして、ミキサ１０９は、フォトダイオード１０７からの電磁波の周波数と参照信号の周波数の差に等しい周波数を有する信号を出力し、周波数差検出回路１１０は、この信号の周波数がゼロになるように、波長可変レーザ光源１０３を制御するからである。   That is, the photodiode 107 outputs an electromagnetic wave having a frequency equal to the difference between the frequency of the light from the fixed wavelength laser light source 102 and the frequency of the light from the wavelength tunable laser light source 103, and the mixer 109 is output from the photodiode 107. This is because a signal having a frequency equal to the difference between the frequency of the electromagnetic wave and the frequency of the reference signal is output, and the frequency difference detection circuit 110 controls the wavelength tunable laser light source 103 so that the frequency of this signal becomes zero. .

この制御において、周波数差検出回路１１０は、例えば、波長可変レーザ光源１０３の注入電流量やデバイスの温度を変える。   In this control, the frequency difference detection circuit 110 changes, for example, the injection current amount of the wavelength tunable laser light source 103 and the device temperature.

なお、波長固定レーザ光源１０２からの光の周波数と、波長可変レーザ光源１０３からの光の周波数を高い精度（１０桁かそれ以上）で測定し、これら周波数の差が、参照信号の周波数に代わる目標値に一致するように、波長可変レーザ光源１０３を制御してもよい。この場合、フォトダイオード１０７、参照信号発生器１０８、ミキサ１０９、周波数差検出回路１１０は不要である。   The frequency of the light from the fixed wavelength laser light source 102 and the frequency of the light from the wavelength tunable laser light source 103 are measured with high accuracy (10 digits or more), and the difference between these frequencies replaces the frequency of the reference signal. The tunable laser light source 103 may be controlled so as to match the target value. In this case, the photodiode 107, the reference signal generator 108, the mixer 109, and the frequency difference detection circuit 110 are unnecessary.

波長可変レーザ光源１０３からの光の波長が、図２（ｃ）に示すように変化した場合、受信用ミキサ１１５では、図２（ｄ）に示すように、波長可変レーザ光源１０１の点灯からΔｔだけ遅れて周波数ｃ（１／λＴＬＳ １―１／λＦＬＳ１）の電磁波が到達し、更に波長可変レーザ光源１０１の点灯から３Δｔだけ遅れて周波数ｃ（１／λＴＬＳ ２―１／λＦＬＳ１）の電磁波が到達し、波長可変レーザ光源１０１の点灯から５Δｔだけ遅れて周波数ｃ（１／λＴＬＳ ３―１／λＦＬＳ１）の電磁波が到達する、というパターンを繰り返しながら受信する電磁波の周波数が変化していく。ｃは光速である。 When the wavelength of the light from the wavelength tunable laser light source 103 changes as shown in FIG. 2C, the receiving mixer 115 causes Δt from turning on the wavelength tunable laser light source 101 as shown in FIG. An electromagnetic wave having a frequency c (1 / λ TLS 1 −1 / λ FLS1 ) arrives after a delay, and further a frequency c (1 / λ TLS 2 −1 / λ FLS1 ) is delayed by 3Δt from the lighting of the wavelength tunable laser light source 101. The frequency of the received electromagnetic wave changes while repeating the pattern that the electromagnetic wave of the frequency c (1 / λ TLS 3 −1 / λ FLS1 ) arrives at a delay of 5 Δt from the lighting of the wavelength tunable laser light source 101. I will do it. c is the speed of light.

ここで、図３（ａ）のように受信用ミキサ１１５に到着した周波数ｃ（１／λＴＬＳ １―１／λＦＬＳ１）の電磁波について考えると、受信用ミキサ１１５に到着し始めた時の信号は、最短コースを通って受信用ミキサ１１５に到着していることになるから、信号としては、直接波であるといえる。また、それよりも時間的に遅れた信号については、反射などして、長い経路を通ってきた信号と、フォトミキサ１０５から遅れて出てきた信号の重ね合わせとなるから、直接波と間接波の重ね合わせと考えられる。 Here, considering the electromagnetic wave having the frequency c (1 / λ TLS 1 −1 / λ FLS1 ) arriving at the receiving mixer 115 as shown in FIG. 3A, the signal when it starts to arrive at the receiving mixer 115 Since the signal arrives at the receiving mixer 115 through the shortest course, it can be said that the signal is a direct wave. In addition, a signal delayed in time is reflected and overlapped with a signal that has passed through a long path and a signal that has been delayed from the photomixer 105. It is thought that it is a superposition of.

つまり、電磁波の多重反射があった場合、直接受信された電磁波に比べて、反射波は、長い経路を伝播することになる。そのため反射波（間接波）は、直接波よりも時間的に遅れて受信用ミキサ１１５に到達することになる。   That is, when there are multiple reflections of electromagnetic waves, the reflected waves propagate along a longer path than directly received electromagnetic waves. Therefore, the reflected wave (indirect wave) reaches the receiving mixer 115 with a time delay from the direct wave.

前述のように、本実施の形態では、参照信号発生器１０８からの参照信号の周波数をΔｔのなかでｆ１、ｆ２、ｆ３、ｆ４と変化させ、これにより波長可変レーザ光源１０３のからの光の波長をλＦＬＳ２ １、λＦＬＳ２ ２、λＦＬＳ２ ３、λＦＬＳ２ ４と変化させる。 As described above, in the present embodiment, the frequency of the reference signal from the reference signal generator 108 is changed to f 1 , f 2 , f 3 , and f 4 in Δt, thereby the wavelength variable laser light source 103. The wavelength of the light from is changed to λ FLS2 1 , λ FLS2 2 , λ FLS2 3 , and λ FLS2 4 .

すると、図３（ｂ）のように受信用ミキサ１１５から出力される中間周波信号の周波数は、ｃ（１／λＦＬＳ１―１／λＦＬＳ２ １）、ｃ（１／λＦＬＳ１―１／λＦＬＳ２ ２）、ｃ（１／λＦＬＳ１―１／λＦＬＳ２ ３）、ｃ（１／λＦＬＳ１―１／λＦＬＳ２ ４）と時々刻々変化することになる。 Then, the frequency of the intermediate frequency signal output from the receiving mixer 115 as shown in FIG. 3 (b), c (1 / λ FLS1 -1 / λ FLS2 1), c (1 / λ FLS1 -1 / λ FLS2 2), c (1 / λ FLS1 -1 / λ FLS2 3), and it will momentarily change c (1 / λ FLS1 -1 / λ FLS2 4).

各狭帯域フィルタ１１８は、図４に示すように、それぞれ周波数ｃ（１／λＦＬＳ１―１／λＦＬＳ２ １）、ｃ（１／λＦＬＳ１―１／λＦＬＳ２ ２）、ｃ（１／λＦＬＳ１―１／λＦＬＳ２ ３）、ｃ（１／λＦＬＳ１―１／λＦＬＳ２ ４）を中心とした透過帯域を有するように予め設定される。 Each narrowband filter 118, as shown in FIG. 4, each frequency c (1 / λ FLS1 -1 / λ FLS2 1), c (1 / λ FLS1 -1 / λ FLS2 2), c (1 / λ FLS1 -1 / λ FLS2 3), is set in advance so as to have a transmission band centered on c (1 / λ FLS1 -1 / λ FLS2 4).

よって、中間周波信号の周波数ｃ（１／λＦＬＳ１―１／λＦＬＳ２ １）の成分は、その周波数を含む透過帯域を有する信号強度検出回路でのみで検出される。中間周波信号の周波数ｃ（１／λＦＬＳ１―１／λＦＬＳ２ ２）の成分は、その周波数を含む透過帯域を有する信号強度検出回路でのみで検出される。中間周波信号の周波数ｃ（１／λＦＬＳ１―１／λＦＬＳ２ ３）の成分は、その周波数を含む透過帯域を有する信号強度検出回路でのみで検出される。中間周波信号の周波数ｃ（１／λＦＬＳ１―１／λＦＬＳ２ ４）の成分は、その周波数を含む透過帯域を有する信号強度検出回路でのみで検出される。つまり、受信用ミキサ１１５に到達する信号の強度を到達時刻別に測定できる。 Thus, the components of the intermediate frequency signal frequency c (1 / λ FLS1 -1 / λ FLS2 1) is detected only in the signal strength detection circuit having a transmission band including this frequency. Component of the intermediate frequency signal frequency c (1 / λ FLS1 -1 / λ FLS2 2) is detected only in the signal strength detection circuit having a transmission band including this frequency. Component of the intermediate frequency signal frequency c (1 / λ FLS1 -1 / λ FLS2 3) is detected only in the signal strength detection circuit having a transmission band including this frequency. Component of the intermediate frequency signal frequency c (1 / λ FLS1 -1 / λ FLS2 4) is detected only in the signal strength detection circuit having a transmission band including this frequency. That is, the intensity of the signal reaching the reception mixer 115 can be measured for each arrival time.

各ＡＤ変換器１２０は、各検波器１１９の出力をディジタルのデータに変換する。制御装置１２１は、データをそのデータが出力された時間のデータとして記録する。これにより、受信用ミキサ１１５で受信された信号を４つの信号に分離でき、つまり、受信された信号を周波数ｃ（１／λＦＬＳ１―１／λＦＬＳ２ １）をもつ直接波のみからなる信号、と、その他の信号（直接波と間接波が混在した信号）に分離できる。 Each AD converter 120 converts the output of each detector 119 into digital data. The control device 121 records the data as data at the time when the data was output. Thus, the signal received by the receiving mixer 115 can be separated into four signals, i.e., signals consisting of only the direct wave having the received signal frequency c (1 / λ FLS1 -1 / λ FLS2 1), And other signals (signals in which direct waves and indirect waves are mixed).

仮に、このような受信用ミキサ１１５で受信した電磁波を到来時間別に検出する機能がない場合、遅れてくる反射波を切る分けることができない。しかし、本実施の形態では、波長λＦＬＳ２の変化に対応するように、複数ある信号強度検出回路のうち、アクティブなのはいつも一つで、それが時々刻々と変化する、そのため、直接波より遅れて受信用ミキサ１１５に到達する反射波を切り分けることが可能になる。つまりは、反射波の影響を受けない、言い換えれば、多重反射の影響を受けない被測定物に対するミリ波・テラヘルツ波電磁波の透過または反射スペクトルを測定する分光システムが実現できる。 If there is no function for detecting the electromagnetic wave received by the receiving mixer 115 according to the arrival time, the reflected wave that is delayed cannot be separated. However, in the present embodiment, one of the plurality of signal intensity detection circuits is always active so as to correspond to the change of the wavelength λ FLS2 , and it changes from moment to moment, so that it lags behind the direct wave. It is possible to separate the reflected waves that reach the reception mixer 115. That is, it is possible to realize a spectroscopic system that measures the transmission or reflection spectrum of a millimeter wave / terahertz wave electromagnetic wave with respect to an object to be measured that is not affected by reflected waves, that is, not affected by multiple reflections.

制御装置１２１にて記録されるデータは、フォトミキサ１０５からの電磁波が被測定物１１２を透過して、多重反射せずに受信用ミキサ１１５で直接検出される電磁波の強度の周波数依存を表す関数である。この関数は、本実施の形態に係る分光システム自体の持つ周波数特性と、被測定物１１２が持つ電磁波の透過特性の積である。   The data recorded by the control device 121 is a function representing the frequency dependence of the intensity of the electromagnetic wave that is directly detected by the receiving mixer 115 without the multiple reflection of the electromagnetic wave from the photomixer 105 that passes through the DUT 112. It is. This function is the product of the frequency characteristic of the spectroscopic system itself according to the present embodiment and the electromagnetic wave transmission characteristic of the DUT 112.

また、被測定物１１２を設置しない状態で、制御装置１２１にて記録されるデータは、分光システム自体の持つ周波数特性を表す。したがって、予め、被測定物１１２を設置しないで測定しておいたデータで、被測定物１１２を設置した状態で測定したデータを除することで、被測定物１１２が持つ電磁波の透過特性を示すデータを得ることができる。   Further, data recorded by the control device 121 in a state where the device under test 112 is not installed represents the frequency characteristics of the spectroscopic system itself. Therefore, by removing the data measured in a state where the device under test 112 is installed from the data measured without installing the device under test 112 in advance, the transmission characteristics of the electromagnetic wave possessed by the device under test 112 are shown. Data can be obtained.

なお、本実施の形態では、時間により離散的に変化する周波数ごとの透過特性を有する信号強度検出回路を複数用いたが、周波数の変化にあわせて透過特性を離散的に変化させることが可能な同一の信号強度検出回路を用いてもよい。   In this embodiment, a plurality of signal intensity detection circuits having transmission characteristics for each frequency that changes discretely with time are used. However, the transmission characteristics can be changed discretely according to changes in frequency. The same signal strength detection circuit may be used.

また、本実施の形態では、４つの周波数ｆ１〜ｆ４を用いたが、周波数の数は、２以上であれば、任意である。よって、信号強度検出回路も周波数の数に応じて設ければよい。   In the present embodiment, four frequencies f1 to f4 are used, but the number of frequencies is arbitrary as long as it is two or more. Therefore, the signal intensity detection circuit may be provided according to the number of frequencies.

また、本実施の形態では、被測定物１１２の透過特性を求めるのに分光システムを用いたが、これを被測定物１１２の反射特性を求めるのに用いてもよい。   In the present embodiment, the spectroscopic system is used to obtain the transmission characteristic of the object to be measured 112, but this may be used to obtain the reflection characteristic of the object to be measured 112.

１０１、１０３…波長可変レーザ光源
１０２…波長固定レーザ光源
１０４…光合分波回路
１０５、１０６…フォトミキサ
１０７…フォトダイオード
１０８…参照信号発生器
１０９…ミキサ
１１０…周波数差検出回路
１１１、１１３、１１６…コリメート鏡
１１２…被測定物
１１４…ハーフミラー
１１５…受信用ミキサ
１１７…受信用増幅器
１１８…狭帯域フィルタ
１１９…検波器
１２０…ＡＤ変換器
１２１…制御装置 DESCRIPTION OF SYMBOLS 101, 103 ... Variable wavelength laser light source 102 ... Fixed wavelength laser light source 104 ... Optical multiplexing / demultiplexing circuit 105, 106 ... Photo mixer 107 ... Photo diode 108 ... Reference signal generator 109 ... Mixer 110 ... Frequency difference detection circuit 111, 113, 116 DESCRIPTION OF SYMBOLS ... Collimating mirror 112 ... Object to be measured 114 ... Half mirror 115 ... Receiving mixer 117 ... Receiving amplifier 118 ... Narrow band filter 119 ... Detector 120 ... AD converter 121 ... Control device

Claims (4)

第１の波長可変レーザ光源と、
第２の波長可変レーザ光源と、
波長固定レーザ光源と、
前記第１の波長可変レーザ光源からの光と前記波長固定レーザ光源からの光を合波することにより得られる光ビート信号を電磁波に変換する第１のフォトミキサと、
前記第１の波長可変レーザ光源からの光と前記第２の波長可変レーザ光源からの光を合波することにより得られる光ビート信号を電磁波に変換する第２のフォトミキサと、
前記第１のフォトミキサからの電磁波を照射された被測定物を経た電磁波と前記第２のフォトミキサからの電磁波とを混合する手段と、
前記混合された電磁波から前記波長固定レーザ光源からの光の周波数と前記第２の波長可変レーザ光源からの光の周波数の差に等しい周波数を有する電磁波である中間周波信号を抽出する受信用ミキサと、
前記第１の波長可変レーザ光源からの光の波長が一定の期間において前記第２の波長可変レーザ光源からの光の波長を、該波長が予め定められた複数の波長のそれぞれに等しくなる期間が離散的になるように、変化させる手段と、
前記第２の波長可変レーザ光源からの光の波長の離散的な変化に伴い前記中間周波信号が有することとなる複数の周波数について当該中間周波信号から当該各周波数の成分を分離して抽出する手段と、
を備えることを特徴とする分光システム。 A first tunable laser light source;
A second tunable laser light source;
A wavelength-fixed laser light source;
A first photomixer that converts an optical beat signal obtained by combining light from the first wavelength-tunable laser light source and light from the wavelength-fixed laser light source into electromagnetic waves;
A second photomixer that converts an optical beat signal obtained by combining light from the first tunable laser light source and light from the second tunable laser light source into electromagnetic waves;
Means for mixing the electromagnetic wave passed through the measurement object irradiated with the electromagnetic wave from the first photomixer and the electromagnetic wave from the second photomixer;
A receiving mixer for extracting, from the mixed electromagnetic wave, an intermediate frequency signal that is an electromagnetic wave having a frequency equal to a difference between the frequency of light from the wavelength-fixed laser light source and the frequency of light from the second tunable laser light source; ,
A period in which the wavelength of the light from the second tunable laser light source is equal to each of a plurality of predetermined wavelengths in a period in which the wavelength of the light from the first tunable laser light source is constant. Means for changing to be discrete,
Means for separating and extracting components of each frequency from the intermediate frequency signal for a plurality of frequencies that the intermediate frequency signal has in association with discrete changes in the wavelength of light from the second wavelength tunable laser light source When,
A spectroscopic system comprising: 前記第２の波長可変レーザ光源からの光の波長を変化させる手段は、
前記複数の波長のそれぞれに対応する周波数に等しくなる期間が離散的になるように変化する周波数を有する参照信号を出力する参照信号発生器と、
前記波長固定レーザ光源からの光と前記第２の波長可変レーザ光源からの光を合波することにより得られる光ビート信号を電磁波に変換する手段と、
前記参照信号の周波数と当該電磁波の周波数との差を検出し当該差がなくなるように前記第２の波長可変レーザ光源を制御する手段と
を備えることを特徴とする請求項１記載の分光システム。 The means for changing the wavelength of the light from the second tunable laser light source,
A reference signal generator that outputs a reference signal having a frequency that varies such that a period equal to a frequency corresponding to each of the plurality of wavelengths is discrete;
Means for converting an optical beat signal obtained by combining light from the wavelength-fixed laser light source and light from the second wavelength-tunable laser light source into electromagnetic waves;
The spectroscopic system according to claim 1, further comprising: means for detecting a difference between the frequency of the reference signal and the frequency of the electromagnetic wave and controlling the second wavelength tunable laser light source so that the difference is eliminated. 請求項１記載の分光システムの制御方法であって、
前記第１の波長可変レーザ光源からの光の波長が一定の期間において前記第２の波長可変レーザ光源からの光の波長を、該波長が前記複数の波長のそれぞれに等しくなる期間が離散的になるように、変化させることを特徴とする分光システムの制御方法。 A method for controlling a spectroscopic system according to claim 1, comprising:
The wavelength of the light from the second wavelength tunable laser light source is discretely divided into the period when the wavelength of the light from the first wavelength tunable laser light source is equal to each of the plurality of wavelengths. A method for controlling a spectroscopic system, characterized by being changed. 請求項１記載の分光システムの制御方法であって、
前記第１のフォトミキサからの電磁波が前記受信用ミキサに到達するまでの到達時間の２倍の周期で前記第１の波長可変レーザ光源からの光の前記一定の波長の値を切り替えることを特徴とする分光システムの制御方法。 A method for controlling a spectroscopic system according to claim 1, comprising:
The value of the constant wavelength of the light from the first tunable laser light source is switched at a period twice as long as the arrival time until the electromagnetic wave from the first photomixer reaches the receiving mixer. A control method for a spectroscopic system.
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