JP5069712B2 - Optical heterodyne spectrum analyzer - Google Patents

Description

  The present invention relates to a heterodyne type optical heterodyne spectrum analyzer that measures a spectrum of light to be measured. In particular, the present invention relates to a technique for measuring an optical spectrum by reducing light intensity noise when heterodyne reception of measured light by local light.

  The heterodyne type optical spectrum analyzer has the following configuration. For example, one input receives light to be measured and the other input is a local light that can be swept (variable), and is combined to output combined light that is 180 degrees out of phase with each other. To do. One of the two combined lights having different phases is input to one light receiving diode of the two diodes connected in series, and the other combined light is input to the other light receiving diode. The signal extracted from the connection point of the two diodes is a difference signal of the heterodyne signals output from the two diodes, but the two combined beams are added because the phases of the two combined lights differ from each other by 180 degrees. . However, the intensity noise that each light source has is subtracted from each other. Then, the power of the added heterodyne signal is measured as the power of the light to be measured (Patent Document 1).

JP-A-7-55579

  The above-described technique does not necessarily directly couple the output of the optimum light-receiving diode to reduce intensity noise. That is, subtraction (reduction) between light intensity noises is not always performed under optimum conditions. Specifically, in the first route of the “coupler one output-light emitting diode coupling” and the “coupler other output—the other light emitting diode coupling”, the coupler loss or the light emitting diode The optical / electrical conversion characteristics and their wavelength dependence do not always match. The difference in the characteristics between the first route and the second route becomes a difference when the two routes are combined. Even in the result of the combination, the light intensity noise of these differences may not be subtracted and may remain as it is.

  An object of the present invention is to reduce light intensity noise by adopting a configuration in which a heterodyne signal can be extracted with two routes using a coupler, and the two routes can be combined under appropriate conditions by changing the gain of at least one route. An optical heterodyne spectrum analyzer for measuring the spectrum is provided. Also provided is an optical heterodyne spectrum analyzer that reduces the overall gain fluctuation caused by varying one of the gains.

In order to achieve the above object, the invention according to claim 1 is directed to a variable wavelength light source (2) that outputs light having a variable wavelength over a predetermined wavelength range, a light to be measured, and the variable wavelength light source. A coupler (3) that individually receives and combines the light and outputs a first combined light and a second combined light having phases different from each other by approximately 180 degrees, and receives the first combined light and the first combined light. A first light-receiving unit (4a) for converting it into an electrical signal, a second light-receiving unit (4b) for receiving the second combined light and converting it into a second electrical signal, the first electrical signal and the An optical heterodyne spectrum analyzer that measures a spectrum of light under measurement based on a heterodyne signal that is a difference between a second electrical signal and the wavelength of the light, wherein the first electrical signal and the second electrical signal A differential amplifier (6) for taking the difference and outputting the heterodyne signal; Provided between the position where the coupler is combined and the output point of the differential amplifier, the magnitude of the first electrical signal and / or the magnitude of the second electrical signal can be individually varied to A gain variable unit (5) to be input to the differential amplifier, and the gain variable unit to reduce the noise in advance at a plurality of different wavelength points in the predetermined wavelength range with respect to the wavelength of light output from the variable wavelength light source. Is stored in correspondence with each wavelength, and then the spectrum of the light to be measured is measured by varying the wavelength of the light, corresponding to the wavelength. And a gain control unit (12) for controlling the variable gain unit based on the first control value.

  According to a second aspect of the present invention, in the first aspect of the present invention, the variable gain section is provided between the first light receiving means and the differential amplifier, or between the second light receiving means and the differential amplifier. Between or both.

Invention of Claim 3 has the gain adjustment part (9) which adjusts the magnitude | size of the said heterodyne signal in the invention of Claim 1 or 2 after the said output point of the said differential amplifier, The gain control unit pre-corresponds to the wavelength and the first control value, the magnitude of the heterodyne signal after the differential amplifier accompanying the gain variable by the gain variable unit based on the first control value When the second control value for adjusting the fluctuation of the light is stored and then the spectrum of the light to be measured is measured by varying the wavelength of the light, the wavelength is adjusted with respect to the gain adjusting unit. The second control value corresponding to the above is adjusted.

The invention described in claim 4 is a variable wavelength light source (2) for outputting light whose wavelength is varied over a predetermined wavelength range, and the light to be measured and light from the variable wavelength light source are individually received and combined. And a coupler (3) for outputting a first combined light and a second combined light having phases different from each other by approximately 180 degrees, and a first electric signal that receives the first combined light and converts it into a first electric signal. A light receiving unit (4a), a second light receiving unit (4b) that receives the second combined light and converts it into a second electric signal, and a difference between the first electric signal and the second electric signal. An optical heterodyne spectrum analyzer for measuring a spectrum of light to be measured based on a certain heterodyne signal and the wavelength of the light, and taking the difference between the first electrical signal and the second electrical signal to obtain the heterodyne signal. From the differential amplifier (6) for output and the position where the coupler is combined A variable gain provided between the output points of the differential amplifiers and allowing the magnitude of the first electric signal and / or the magnitude of the second electric signal to be individually varied and input to the differential amplifier. When the gain of the unit (5) and the gain variable unit is set to a predetermined gain, after the output of the differential amplifier, the wavelength of the measured light is obtained and detuned by a predetermined wavelength width from the wavelength of the measured light A noise measurement unit (16) including a noise wavelength detection unit (16b) for obtaining a measured wavelength and a noise detection unit (16c) for detecting power at the detuned wavelength, and then a detection result of the noise detection unit The gain control section (12) for controlling the predetermined gain of the variable gain section is provided so that the gain is reduced.

The invention according to claim 5 has the gain adjustment section (9) for adjusting the magnitude of the heterodyne signal after the output point of the differential amplifier in the invention according to claim 4 ,
The noise measurement unit measures a variation in magnitude in the wavelength of the light under measurement before and after the gain control unit controls the gain variable unit, and the gain control unit In addition, the gain adjusting unit is controlled so as to reduce the variation in the size of the measured light.

  According to the configuration of the present invention, when a heterodyne signal is extracted by two routes using a coupler, it can be synthesized after adjusting at least one gain, so that noise (light intensity noise, hereinafter referred to as “noise”) Can be measured. In addition, since the gain can be adjusted in accordance with the change in wavelength, noise can be reduced even if the wavelength of the light to be measured changes. Furthermore, since the means for correcting the fluctuation of the power of the optical spectrum of the light to be measured due to the change of the one gain in order to reduce noise is provided, more accurate optical spectrum measurement can be performed.

It is a figure which shows the function structure of 1st Embodiment. It is a figure which shows the relationship between a signal and noise when gain control and gain adjustment are performed in 1st, 2nd embodiment. It is a figure which shows the data content of a gain data storage part. It is a figure which shows the function structure of 2nd Embodiment. It is a figure which shows the example of one operation | movement flow of the gain control and gain adjustment of 2nd Embodiment.

  In order to reduce noise, an embodiment in which control is performed based on data empirically measured in advance will be described as a first embodiment, and an embodiment in which an optical spectrum is controlled in real time during measurement will be described as a second embodiment. .

[First Embodiment]
In FIG. 1, a variable wavelength light source 2 is a light source that outputs variable light. That is, the light source can be swept in wavelength. Specifically, it is possible to use a semiconductor laser light source that uses an externally provided resonator whose resonator length is variable and outputs light having a wavelength resonated with the resonator length. Generally, any light source that sweeps the wavelength may be used, but here, by changing the wavelength using the micro-electromechanical structure described in Japanese Unexamined Patent Application Publication No. 2007-220864 or Japanese Unexamined Patent Application Publication No. 2008-107096 ( This is referred to as a “MEMS scanner.” A MEMS (Micro Electro Mechanical Systems) will be described as a light source that outputs swept light having a swept wavelength.

The wavelength λ output from the variable wavelength light source 2 using the MEMS scanner in such a gazette is the oscillation wavelength when the MEMS scanner is stationary is λs, the wavelength sweep width ± W, the sweep frequency f, and the time from the start of the sweep. If a term in which the wavelength changes is expressed by a function Λ (so-called wavelength sweep characteristic), it can be expressed by the following equation.
λ = λs + Λ (t)
= Λs + Wsin (2πft).
Examples of numerical values are as follows.
-W to + W: 1534 nm to 1568 nm
λs: 1551 nm
Predetermined wavelength interval: 5 nm
f: 10 kHz or less

  The coupler 3 combines the light to be measured from the light source 1 to be measured and the light from the variable wavelength light source 2 (hereinafter, the output light from the variable wavelength light source 2 is referred to as “local light”) and combines the light. The combined light is output as two combined lights whose phases are approximately 180 degrees different from each other, and one of them is input to the first light receiving unit 4a. Similarly, the other combined light is input to the second light receiving unit 4b.

  The first light receiving unit 4a outputs an electric signal (first electric signal) having a frequency of a difference between the measured light of the combined light and the local light when input, and outputs the output as a differential amplifier 6 To one of the input terminals. Similarly, the second light receiving unit 4 b outputs a second electric signal whose phase is approximately 180 degrees different from that of the first electric signal, and outputs the second electric signal to the other of the differential amplifier 6 via the gain variable unit 5. To the input terminal.

  The differential amplifier 6 amplifies an electrical signal having a difference between the magnitude of the first electrical signal and the magnitude of the second electrical signal received at the two input terminals, and outputs the amplified signal as a heterodyne signal. The magnitude of the heterodyne signal itself is that the first electric signal and the second electric signal are opposite in phase. It will be. On the other hand, the intensity of the combined light of the local light and the measured light that appears in each of the first electric signal (the output of the first light receiving unit 4a) and the second electric signal (the output of the second light receiving unit 4b). Light intensity fluctuations caused by noise are canceled out by the differential amplifier 6 because the phases are mutually in phase. Therefore, the light intensity noise is reduced as the heterodyne signal output from the differential amplifier 6.

  The optimum condition for reducing noise in the heterodyne signal is based on the paths of the two combined lights output from the coupler 3, that is, the branching point of the combined light in the coupler 3, the first light receiving unit 4a, and the differential amplifier 6. Gain difference between the first path to the calculation point and the branching point of the combined light in the coupler 3—the second light receiving unit 4b—the variable gain unit 5—the second path to the calculation point by the differential amplifier 6. There is no. However, in practice, the first or second light receiving units 4a and 4b are different from the optimum conditions because the photoelectric conversion characteristics (conversion gain) are different.

  The gain variable section 5 is for reducing the noise of the heterodyne signal by eliminating the gain difference between the first path and the second path. The gain variable unit 5 may be in the first path or the second path. Further, an optical element or circuit (for example, an optical variable amplifier or an optical variable attenuator) whose gain is variable may be inserted between the first and second light receiving portions 4a and 4b from the coupling position of the coupler 3. However, an electrical element or a circuit (variable amplifier, variable attenuator) having a variable gain may be provided between the first or second light receiving unit 4a, 4b and the position where the difference calculation of the differential amplifier 6 is performed. good. As an electrical circuit, the differential amplifier 6 can vary the gain of the amplifier on the input terminal side that receives the first electrical signal and the gain of the amplifier on the input terminal side that receives the second electrical signal separately. As long as it is a simple circuit, the gain variable unit 5 may be used as one or both amplifiers.

  The gain data storage unit 13 sets a control value N (N1, N2,..., Nk,..., Nm) that minimizes noise when controlling the gain variable unit 5 for each wavelength (or sweep time). Correspondingly) (see FIG. 3). A method for obtaining the control value N will be described later.

  Regarding the control by the gain control unit 12, there are two cases: (a) managing and controlling the relationship between the sweep time and the sweep wavelength in a calibrated form; and (b) managing and controlling the sweep time mainly. It can be explained in an aspect.

(A) When the sweep time and the sweep wavelength are calibrated in association with each other using an etalon or the like as described in the above patent document, or when sweeping while measuring the wavelength by the wavelength measuring means, or MEMS This is an example in which a light source that performs a known sweep with a linear relationship between sweep time and wavelength is used instead of a scanner.

  The measurement control unit 11 applies the wavelength of the local light to the variable wavelength light source 2 in the range from the wavelength λ1 to λm during a predetermined time T (if the repetition frequency f of the sweep is 1 period of time T is 1 / 2f or less at maximum). Give instructions to sweep. For example, when the variable wavelength light source 2 outputs the wavelength λk of the local light, the gain control unit 12 reads the control value Nk corresponding to the wavelength λk from the gain data storage unit 13 to thereby change the gain variable unit. 5 to control the gain. This is repeated from the wavelength λ1 to the wavelength λm within the time T of the sweep time. FIG. 2A shows spectrum data before the gain is varied by the gain variable section 5, and FIG. 2B shows spectrum data after noise reduction by the gain variable by the gain variable section 5. 2B is lower than that of FIG. 2A at the bottom of the light to be measured having the wavelength λk, for example, near the wavelength λk + Δλ.

  Although the control has been described digitally, the gain control unit 12 may convert the control value N of the digital data read from the gain data storage unit 13 into analog data and send it to the gain variable unit 5 for control. In this case, for example, for the control value N between the wavelength λk and the wavelength λk + 1 (1 ≦ k ≦ m), a value obtained by connecting the control value Nk of the wavelength λk and the control value Nk + 1 of the wavelength λk + 1 (that is, with an envelope) A concatenated value) or a control value approximated by the method of least squares may be used.

(B) When the sweep time is mainly managed and controlled In particular, in the case of the wavelength sweep by the MEMS scanner, the wavelength change Λ (t) (wavelength sweep characteristic) changes in a sine wave shape with respect to time. In other words, if the sweep times are t1, t2,..., Tm (<sweep cycle T / 2 or less), the sweep wavelength λ is λs + Λ (t1) = λ1, λs + Λ (t2) = λ2,. , Λs + Λ (tk) = λk,..., Λs + Λ (tm) = λm. At this time, after calibrating the relationship between t1, t2,..., Tm and the actually oscillated wavelengths λ1, λ2,. It can also be managed by wavelength. On the other hand, the wavelength sweep is performed in time, and the wavelength changes with the lapse of time of the sweep, and the noise distribution and power change. Therefore, management by the sweep time is straightforward.

  Therefore, instead of the wavelength performed in (a) above, a control value N that minimizes noise is obtained in advance and stored at time positions corresponding to the sweep times t1, t2,..., Tm. .., Tm corresponding to the sweep time elapsed t1, t2,..., Tm at the actual sweep, and the gain variable section 5 is controlled. During this control, it is executed regardless of what the wavelength is. Also, the sweep time t is entered instead of the wavelength λ in FIG.

  The above (a) and (b) are effectively the same, depending on whether they are managed by wavelength or by time. The following explanation will be made in the form managed by the calibrated wavelength in the same manner as (a) (because the spectrum indicated by wavelength and power is ultimately measured regardless of the sweep time) .) However, in the implementation in the following description, although explanation is omitted, except for the spectrum output by the data processing unit 10 and the spectrum displayed by the display control unit 14a on the display unit 14c, it is managed by the sweep time as in (b). Can be used. Both are within the scope of the present invention.

  However, in obtaining the control values N and P, which will be described later, it may be unavoidable to obtain them at the wavelength λ. In that case, the control value can be acquired at the wavelength λ and associated with the sweep time t corresponding to the wavelength λ, and thereafter managed by time. In particular, if the repetition frequency f of the sweep is as fast as 10 kH, managing by time is easier to deal with in terms of speed.

  The filter unit 7 is for passing only the heterodyne signal in a desired band to be observed and removing other signals outside the band. The power conversion unit 17 converts the power (power) of the heterodyne signal received from the filter unit 7 into a desired power unit and outputs it. For example, it is converted into a logarithm so that it can be read in dB. The A / D converter 8 converts the power of the analog heterodyne signal into digital data.

  Since the gain adjustment unit 9 also varies the magnitude (gain) of the heterodyne signal at the output of the differential amplifier 6 due to the variable gain by the gain variable unit 5, in order to correct the variation accordingly. It is means of. FIG. 2B shows spectrum data after noise reduction by variable gain by the variable gain unit 5. FIG. 2B shows an example in which the power of the heterodyne signal is reduced by Δp due to the gain variable by the gain variable section 5. Therefore, as shown in FIG. 2C, the gain adjusting unit 9 corrects and reduces the power fluctuation Δp. In FIG. 1, the gain adjustment unit 9 is corrected with digital data, but the actual heterodyne signal size (or power level) between the output of the differential amplifier 6 and the A / D conversion unit 8 is used. ) And a variable attenuator may be used.

  Further, the gain fluctuation is not limited to the gain fluctuation caused by the variable gain of the gain variable section 5, but the wavelength-to-amplitude characteristic of the variable wavelength light source 2, the coupler, etc., and the frequency band amplitude characteristic of the heterodyne signal of the differential amplifier 6 ( These totals are also dependent on the gain fluctuation (measurement error factor of power) of the measurement system itself. Therefore, the gain adjusting unit 9 can also correct the gain variation due to the variable gain of the gain variable unit 5 and the gain variation of the measurement system itself.

  In the gain data storage unit 13, when the gain adjusting unit 9 is controlled, control values P (P1, P2,..., Pk for flattening the gain characteristics with respect to the wavelengths λ1, λ2,. ,..., Pm) are stored in advance. The gain controller 12 reads the control values P (P1, P2,..., Pk,..., Pm) corresponding to the wavelengths λ1, λ2,. Thus, the gain is adjusted by sending it to the gain adjusting unit 9 to have a flat characteristic.

  The data processing unit 10 receives digital data (power data) of the power of the heterodyne signal received from the gain adjustment unit 9 and receives the wavelengths λ1, λ2,..., Λk,. By obtaining the power corresponding to λm, that is, the spectrum of the light to be measured is obtained.

  The display control unit 14a of the user interface 14 displays a spectrum image on coordinates on the display unit 14c with the wavelengths λ1, λ2,..., Λk,. Display (see FIGS. 2A, 2B, and 2C).

[Method for Obtaining Control Values N and P in Gain Data Storage Unit 13 in the First Embodiment]
The gain variable unit 5 and the gain adjustment unit 9 operate in (1) calibration mode and (2) optical spectrum measurement mode by the gain control unit 12, the measurement control unit 11, the gain data storage unit 13, and the M data generation unit 15. . Among these, (1) the calibration mode is an operation mode for obtaining a control value in the gain data storage unit 13 performed on the manufacturer or service side before shipment. (2) The optical spectrum measurement mode is an operation that is actually measured by the user, and is an operation that is performed using the control value of the gain data storage unit 13 acquired in the calibration mode of (1). The optical spectrum measurement mode is described in the description of the above configuration. Hereinafter, the description will mainly focus on (1) the calibration mode. Note that (1) the calibration mode and (2) the optical spectrum measurement mode may be switched by an instruction from the operation unit 14b so that both can be performed on the user side.

(1) Calibration Mode At this time, the switch S1 in FIG. 1 is turned on on the “Cal” side in response to a “calibration” instruction from the operation unit 14b. The variable wavelength light source 2 will be described using a MEMS scanner. Therefore, the measurement control unit 11 manages the time from the timing when the variable wavelength light source 2 is instructed to start sweeping, and manages the wavelength by the wavelength change λ = λs + Λ (t) with respect to time.

[A Acquisition of control value N]
(A-1) A wavelength measurement range that can be measured by the variable wavelength light source 2 (that is, the same or narrower than the sweep wavelength range ± W of the variable wavelength light source 2), for example, wavelengths λ1, λ2 in λs−W to λs + W ,..., Λk,..., Λm are prepared.
(A-2) The wavelength of the light to be measured from the light source 1 to be measured is set to λk, the measurement control unit 11 sweeps the variable wavelength light source 2, and the display unit 14c displays the optical spectrum. In this case, the gain controller 12 gives a constant control value P to the gain adjuster 9 regardless of the wavelength of the light to be measured and the wavelength of the variable wavelength light source 2.

  (A-3) In this state, the operator detunes the noise of the bottom of the optical spectrum of the wavelength λk of the display unit 14c (for example, Δλ with respect to the wavelength of the optical spectrum of the measured light in FIG. 2A). The data is input from the operation unit 14b while observing the power at the wavelength point. The input data is sent as a control value Nk by the M data generation unit 15 to the gain variable unit 5 via the gain control unit 12 to control the gain variable unit 5. When the operator determines that the noise is minimized as a result of changing the input data using the operation unit 14b, the operator presses the enter key. When the confirmation key is pressed, the control value Nk output from the M data generation unit 15 is stored in the gain data storage unit 13.

  (A-4) By changing the wavelength λ k of the light to be measured from λ1 to λm (k = 1 to m), the same operation as the above (a-2) and (a-3) is repeated, and the wavelength λ1 The control values N (N1, N2,..., Nk,..., Nm) corresponding to λm are obtained and stored in the gain data storage unit 13.

[B Acquisition of Control Value P]
Here, the gain adjusting unit 9 corrects the gain variation due to the variable gain of the gain variable unit 5 and the gain variation of the measurement system itself, and acquires a control value P corresponding to the correction.
(B-1) Similarly to the above (a-1), the light source 1 to be measured that outputs the light to be measured having the wavelengths λ1, λ2,..., Λk,. , Wavelengths λ 1, λ 2,..., Λk,..., Λm, the power of the measured light is calibrated to the correct calibration value Ls (power), and those that match within the error range are prepared.

  (B-2) The wavelength of the light to be measured from the light source 1 to be measured is set to λk. The gain variable section 5 is controlled by the control value Nk corresponding to the wavelength λk acquired and stored in [Acquisition of a control value N]. And the measurement control part 11 sweeps the variable wavelength light source 2, and the display part 14c displays the optical spectrum.

  (B-3) In this state, the operator variably inputs data using the operation unit 14b so that the power value on the vertical axis of the optical spectrum of the wavelength λk of the display unit 14c matches the calibration value Ls. To do. The input data is sent as a control value P by the M data generation unit 15 to the gain adjustment unit 9 via the gain control unit 12 and controls the gain adjustment unit 9. The operator changes the input data using the operation unit 14b, and presses the confirmation key when the power of the optical spectrum of the wavelength λk actually measured by the data processing unit 10 matches the calibration value Ls. When there is an instruction from the confirmation key, the control value Pk output from the M data generation unit 15 is stored in the gain data storage unit 13.

  (B-4) By changing the wavelength of the light to be measured from λ1 to λm (k = 1 to m), the same operations as in (B-2) and (b-3) are repeated, and the wavelengths λ1 to λm , Pk,..., Pm are acquired and stored in the gain data storage unit 13.

  The acquisition method and order of the control value N and the control value P are not limited to the above. For example, the control value P and the control value N can be acquired in the same manner as described above in the order of the control value P and the control value N, and the control value N and the control value P are acquired for each same wavelength by using the measured light source 1 calibrated from the beginning. There are also methods.

(2) Optical Spectrum Measurement Mode Since this measurement has been described during the description of the above configuration, it will be briefly described here.
In this mode, the switch “S1” is turned on on the “Mes” side in response to a “measurement” instruction from the operation unit 14b.

  (2-1) Connect light to be measured from an unknown light source to be measured 1. The measurement control unit 11 performs measurement by sweeping the wavelength λ of the local light of the variable wavelength light source 2. At this time, information on the wavelengths λ1 to λm corresponding to the sweep time is sent to the gain controller 12. The gain control unit 12 accesses the gain data storage unit 13, reads the control value N corresponding to the wavelengths λ1 to λm, controls the gain variable unit 5 with the control value N, reduces noise, and reduces the wavelengths λ1 to λ1. The control value P corresponding to λm is read out, and the gain adjusting unit 9 is controlled by the control value P, thereby reducing the power fluctuation error with respect to the wavelength.

  (2-2) The display unit 14c displays the optical spectrum of the light to be measured with less noise and more accurate power.

[Second Embodiment]
This embodiment is an embodiment in which noise is reduced in real time during measurement of light to be measured. This will be described with reference to FIGS.

  FIG. 4 is a diagram for explaining the functional configuration of the second embodiment. The difference from FIG. 1 is that the M data generation unit 15 in FIG. 1 receives the control value N in response to an instruction from the operation unit 14b by the operator. In FIG. 4, the noise measurement unit 16 receives the measurement data of the optical spectrum actually measured by the data processing unit 10, and generates the control value N using this measurement data. Is.

  Each component will be described in the order of the operation flow of FIG. Step S1 is a stage prepared in advance before measurement, and Steps S2 to Step 5 are executed in real time in the actual measurement stage. Among them, the processes in Step S2 to Step 4 are repeated for a plurality of sweeps. Step 5 is processed within one sweep time and repeated for each sweep.

  Step S1: The power is calibrated in advance to obtain the control value P. In this calibration, the switch S2 in FIG. 4 is set to be turned on to the CalA side (normally, it is CalB before the start of measurement, and the measurement control unit 11 is switched to CalA by an instruction from the operation unit 14b. The gain control unit 12 calibrates the control value N of the gain variable unit 5 by setting it to a constant value Nt regardless of the wavelength λ. The calibration with the control value Nt of the gain variable unit 5 made constant is different from the description in (b-2) in “b Acquisition of control value P”, and the M data generation unit 15 receives data from the operation unit 14b. There is a difference in processing based on the power value measured by the data processing unit 10 instead of processing, but other processing can be calibrated by the same processing. That is, when the light to be measured having wavelengths λ1, λ2,..., Λk,..., Λm and whose optical power is the correct calibration value Ls is input, the M data generation unit 15 is a control of the gain adjusting unit 9 when the optical power values of the wavelengths λ1, λ2,..., Λk,..., Λm actually measured by the data processing unit 10 become the same as the calibration value Ls. Values P (P1, P2,..., Pk,..., Pm) are acquired and stored in the gain data storage unit 13 corresponding to each wavelength.

  Step S2: The switch S2 is connected to the CalB side (in a normal state before the start of measurement, the measurement is possible and the measurement control unit 11 is connected). Then, upon receiving the unknown light to be measured, the wavelength λ of the variable wavelength light source 2 is actually swept, the control values P1, P2,..., Pk,. Measurement is performed while the control value Nt of the unit 5 remains constant, and the data processing unit 10 obtains the optical spectrum. The control value Nt is initially stored in the calibration gain data storage unit 16d. The noise wavelength detection unit 16b of the noise measurement unit 16 then obtains the peak power of the light to be measured from the spectrum data obtained by the data processing unit 10 (data indicating the spectrum image on the coordinate where the horizontal axis is wavelength and the vertical axis is power). Lx is obtained, and the wavelength λx at the peak power Lx is obtained. Further, a noise wavelength (λx + Δλ) detuned from the wavelength λx of the light to be measured by + Δλ (or −Δλ) is obtained, and a control value Px at the wavelength λx is obtained. Then, the peak power Lx and the wavelength λx are stored in the calibration gain data storage unit 16d. Δλ is the same power as the noise as it is detuned from the peak wavelength λx of the light to be measured, but is the difference between the wavelength at that time and the wavelength λx and is determined empirically beforehand. Is remembered.

  Step S3: The noise detection unit 16c refers to the spectrum data in the data processing unit 10 and detects the noise power at the noise wavelength (λx + Δλ).

  The control data generation unit 16 a sends a variable value as the control value N to the gain control unit 12 to control the gain variable unit 5. The control data generation unit 16a variably controls the control value N, while referring to the noise power detected by the noise detection unit 16c, the control value Nxo when the noise power is minimized, and the wavelength λx at that time A peak power value Lxx at is obtained. Further, the control value Nxo is stored in the gain data storage unit 13 separately from the control value Nt.

  Step S4: When the gain control unit 12 sets and measures the control value Nxo in the gain variable unit 5, the control data generation unit 16a sends the control value Px to the gain control unit 12 to control the gain adjustment unit 9. Then, the control data generation unit 16a refers to the peak power detected by the noise wavelength detection unit 16b, and when the value becomes the previously stored value Lx, that is, from the value Lxx to the value Lx. The control value Pxo when changed is obtained, and the gain data storage unit 13 is made to update the control value Px to the control value Pxo when the wavelength is λx.

  When the necessary data (control values N and P) are obtained in the gain data storage unit 13, the noise measurement unit 16 switches the switch S <b> 2 to “Mes” directly or via the measurement control unit 11.

  Step S5: The gain control unit 12 refers to the gain data storage unit 13, sets the control value of the gain variable unit 5 to the control value Nxo regardless of the sweep wavelength, and sweeps the control value P of the gain adjustment unit 9 The measurement is performed by controlling P1, P2,..., Pxo,. The display control unit 14a receives the data of the optical spectrum of the light to be measured, which is the measurement result, from the data processing unit 10 and displays the data on the display unit 14c. In this case, since the control value Nxo is constant, it is optimal for noise reduction when measuring the light to be measured having the wavelength λx, but not necessarily optimal for other wavelength components. It may not be. In that case, the same operation as described above is performed for the wavelength component. That is, if the peak power of the power when measuring the measured light is at two wavelengths, the control values Nxo1 and Nxo2 and the control values Pxo1 and Pxo2 may be obtained for each.

  When the measurement conditions such as the object of the light to be measured change, the process starts again from step S2. Alternatively, steps S2 to S5 are always repeated as one measurement cycle, and the display at steps 2 to 4 may be configured to maintain and display the result of step S5 measured before that.

  As described above, the light to be measured is improved in noise, and accurate power is measured. If the purpose is to improve only the noise, it is not necessary to calibrate the power and acquire the control value P. The control value P can be kept constant or the gain adjusting unit 9 can be removed and short-circuited. It ’s fine.

  In the above description of FIG. 2, the gain control unit 12, the gain data storage unit 13, and the noise measurement unit 16 have been described as separate blocks, but these may be configured together. The gain controller 12 may perform the operation of the control data generator 16a.

  The measurement control unit 11, the gain control unit 12, the data processing unit 10, and the gain adjustment unit 9 (in the case of correction) are configured by a memory that stores a program that describes the functional operation and a CPU that executes the program. can do.

DESCRIPTION OF SYMBOLS 1 Light source to be measured, 2 Variable wavelength light source, 3 Coupler, 4a 1st light-receiving part,
4b 2nd light-receiving part, 5 gain variable part, 6 differential amplifier, 7 filter part,
8 A / D converter, 9 Gain adjuster, 10 Data processor,
11 measurement control unit, 12 gain control unit, 13 gain data storage unit,
14 user interface, 14a display control unit, 14b operation unit,
14c display unit, 15 M data generation unit, 16 noise measurement unit,
16a control data generation unit, 16b noise wavelength detection unit,
16c noise detection unit, 16d calibration gain data storage unit,
17 power converter,
S1 switch, S2 switch

Claims (5)

A variable wavelength light source (2) that outputs light having a variable wavelength over a predetermined wavelength range, and the light to be measured and the light from the variable wavelength light source are individually received and combined to have a phase that is approximately 180 degrees different from each other. A coupler (3) that outputs the first combined light and the second combined light, a first light receiving unit (4a) that receives the first combined light and converts it into a first electric signal, A second light receiving section (4b) that receives the combined light of two and converts it into a second electric signal, a heterodyne signal that is a difference between the first electric signal and the second electric signal, and a wavelength of the light. An optical heterodyne spectrum analyzer that measures the spectrum of the light to be measured,
A differential amplifier (6) that outputs the heterodyne signal by taking a difference between the first electric signal and the second electric signal, and from a position where the coupler is combined to an output point of the differential amplifier A gain variable section (5) provided between the first electric signal and the second electric signal, or both of them individually and input to the differential amplifier;
The first control value when the gain variable unit is controlled in advance so that the noise is reduced so that the wavelength of light output from the variable wavelength light source is reduced at a plurality of different wavelength points in the predetermined wavelength range is set to each wavelength. When the spectrum of the light to be measured is then measured by varying the wavelength of the light, the gain variable section is based on the first control value corresponding to the wavelength. An optical heterodyne spectrum analyzer comprising: a gain control unit (12) for controlling   The variable gain section is provided between the first light receiving means and the differential amplifier, or between the second light receiving means and the differential amplifier, or both of them. The optical heterodyne spectrum analyzer according to 1. After the output point of the differential amplifier, a gain adjustment unit (9) for adjusting the magnitude of the heterodyne signal is provided, and the gain control unit corresponds to the wavelength and the first control value in advance. And storing a second control value for adjusting a variation in the magnitude of the heterodyne signal after the differential amplifier due to the variable gain by the gain variable unit based on the first control value, when said measured spectrum of the light to be measured by varying the wavelength of the light, according to claim 1, relative to the gain adjustment unit, characterized in that to adjust the second control value corresponding to the wavelength Or the optical heterodyne spectrum analyzer of 2. A variable wavelength light source (2) that outputs light having a variable wavelength over a predetermined wavelength range, and the light to be measured and the light from the variable wavelength light source are individually received and combined to have a phase that is approximately 180 degrees different from each other. A coupler (3) that outputs the first combined light and the second combined light, a first light receiving unit (4a) that receives the first combined light and converts it into a first electric signal, A second light receiving section (4b) that receives the combined light of two and converts it into a second electric signal, a heterodyne signal that is a difference between the first electric signal and the second electric signal, and a wavelength of the light. An optical heterodyne spectrum analyzer that measures the spectrum of the light to be measured,
A differential amplifier (6) that outputs the heterodyne signal by taking a difference between the first electric signal and the second electric signal, and from a position where the coupler is combined to an output point of the differential amplifier A gain variable section (5) provided between the first electric signal and the second electric signal, or both of them individually and input to the differential amplifier;
When the gain of the variable gain section is set to a predetermined gain, a noise wavelength for determining the wavelength of the measured light after the output of the differential amplifier and determining a wavelength detuned by a predetermined wavelength width from the wavelength of the measured light A noise measurement unit (16) including a detection unit (16b) and a noise detection unit (16c) for detecting power at the detuned wavelength, and then the detection result of the noise detection unit is reduced An optical heterodyne spectrum analyzer comprising a gain control unit (12) for controlling the predetermined gain of the gain variable unit . After the output point of the differential amplifier, the gain adjustment unit (9) for adjusting the magnitude of the heterodyne signal,
The noise measurement unit measures a variation in magnitude in the wavelength of the light under measurement before and after the gain control unit controls the gain variable unit, and the gain control unit 5. The optical heterodyne spectrum analyzer according to claim 4 , wherein the gain adjusting unit is controlled so that a variation in the size of the measured light is reduced.

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