JP5807222B2 - Optical spectrum measuring device - Google Patents

Description

  The present invention relates to an optical spectrum measuring apparatus using frequency comb light, and more particularly to an optical spectrum measuring apparatus capable of sweeping in a wide frequency range with high resolution.

Conventionally, an apparatus having a configuration shown in FIG. 7 is known as an optical spectrum measuring apparatus using frequency comb light (see Patent Document 1).
In the optical spectrum measuring apparatus 8, the optical comb light source 81 generates an optical frequency comb having a comb interval of 10 GHz in a range of 4 THz, for example.

The wavelength tunable filter 82 receives an optical frequency comb and passes one component light among the component lights constituting the optical frequency comb.
The SSB light modulator 83 receives the component light from the wavelength tunable filter 82 and irradiates the sample 85 with a signal swept in frequency (for example, about several kHz to 1 MHz) with a predetermined sweep width (10 GHz). The light receiver 84 receives the transmitted light from the sample 85.

The control device (not shown) changes and controls the pass characteristic of the wavelength tunable filter 82 by the control signal, controls the sweep signal applied to the SSB modulator 83, analyzes the signal detected by the light receiver 84 as a spectrum, The analysis result is output to a display or the like.
In the optical spectrum measurement device 8 of FIG. 7, as shown in FIG. 8A, the measurement range is set to 4 THz, and the comb interval is approximately 10 GHz. The tunable filter 82 extracts (cuts out) one comb component (Fn in FIG. 8B) from the optical frequency comb. According to this optical spectrum measurement device 8, the measurement range is greatly expanded.

  Then, as shown in FIG. 8C, continuous sweeping is performed by the SSB modulation device 83, and finally a measurement accuracy of 100 kHz or less is realized.

JP2007-212427

However, in the optical spectrum measuring apparatus 8 shown in FIG. 7, the SSB modulator 83 has to adjust the applied voltage again when the wavelength changes greatly. For this reason, it is not suitable for measuring a large wavelength range at a time.
Further, in the optical spectrum measuring apparatus 8 shown in FIG. 7, the wavelength tunable filter 82 has to cut out only one comb, but it is not easy to produce such a filter at low cost.

  An object of the present invention is to provide an optical spectrum measuring apparatus that has been proposed to solve the above-described problems and that can sweep in a wide frequency range.

The gist of the present invention is [1] to [4].
[1]
In an optical spectrum measurement device comprising a frequency comb light source, a comb light density reducer, a sweeping modulator, a beat generator, and a light receiver, and a sample is set on the incident light side of the beat generator,
The comb light density reducer includes a plurality of low-density frequency comb light (typically for each N), each of which is selected for each predetermined number of frequency comb light elements constituting the frequency comb light generated by the frequency comb light source. N selected low density frequency comb lights, where N is an integer of 2 or more, and one of the distributed low density frequency comb lights is sequentially selected and emitted.
The sweeping modulator is incident on the low-density frequency comb light from the comb light density reducer, performs a sweep for each of the frequency comb optical elements constituting the low-density frequency comb light,
The beat generator generates a beat by adding a reference light of a specific frequency to a low density frequency comb light emitted from the reference modulator formed by sweeping each frequency comb optical element,
The light receiver detects light emitted from the beat generator;
An optical spectrum measuring apparatus characterized by that.

[2]
The comb light density reducer is composed of one or more pairs of an interleaver and an optical switch,
The interleaver distributes the frequency comb light generated by the frequency comb light source to a plurality of low density frequency comb lights selected for each predetermined number, and emits the light.
The optical switch sequentially selects and emits one of the plurality of low density frequency comb lights emitted from an interleaver;
[1] The optical spectrum measuring apparatus according to [1].

[3]
The optical spectrum measuring apparatus according to [1] or [2], wherein an optical phase modulator is used as the sweeping modulator.

[4]
The receiver is
A photoelectric converter that receives the emitted light of the beat generator and converts it into an electrical signal;
A low-pass filter that passes low-frequency components of the photoelectric converter;
The optical spectrum measuring apparatus according to any one of [1] to [3], including:

  According to the optical spectrum measuring apparatus of the present invention, processing is performed by reducing the density of high-frequency frequency comb light by an interleaver, and thus sweeping in a wide frequency range is possible. In addition, since a wavelength tunable filter is not used, a spectrum in a wide frequency range can be measured at a time.

Further, by using an optical phase modulator as the sweeping modulator, adjustment can be made simple or unnecessary, and high-resolution and low-loss frequency sweeping can be performed.
Thereby, a stable measurement result can be obtained.

  Furthermore, in a configuration including a plurality of sweeping modulators, beat generators, and light receivers as a unit, multipath measurement for a single sample or simultaneous measurement of a plurality of samples can be performed.

FIG. 1 is an explanatory view showing an embodiment of an optical spectrum measuring apparatus of the present invention. (A) is a figure which shows the frequency comb light in case of N = 2, (B), (C) is a figure which shows a low density frequency comb light. (A) is a figure which shows the specific structure of a beat generator, (B) is a figure which shows the specific structure of a light receiver. An optical spectrum in which the comb optical density reducer is composed of one interleaver and one optical switch, and selects two comb optical elements generated by the frequency comb light source every two to generate two low density frequency comb lights It is a figure which shows a measuring device. An optical spectrum in which the comb optical density reducer is composed of two interleavers and two optical switchers, and selects four comb optical elements generated by the frequency comb light source to generate two low density frequency comb lights. It is a figure which shows a measuring device. (A) is a figure which shows the comb light density reducer comprised from the comb light density reduction module, (B) shows the frequency arrangement | positioning relationship of a frequency comb light, an intermediate density frequency comb light, and a low density frequency comb light. FIG. It is explanatory drawing of the optical spectrum measuring device using the conventional frequency comb light. (A) is a diagram showing frequency comb light, (B) is a diagram showing a state in which one comb component is cut out from the optical frequency comb, and (C) is a diagram showing a continuous comb component by the SSB modulator. It is a figure which shows a mode that a sweep is performed.

FIG. 1 is an explanatory view showing an embodiment of an optical spectrum measuring apparatus of the present invention.
In FIG. 1, an optical spectrum measuring apparatus 1 includes a frequency comb light source 11, a comb light density reducer 12, a sweeping modulator 13, a beat generator 14, a light receiver 15, a control device 16, and a display output. The device 17 is connected in this order, and a sample 18 is set on the incident light side of the beat generator 14.

The frequency comb light source 11 generates the frequency comb light L1 and outputs the comb light L1 to the comb light density reducer 12.
The comb light density reducer 12 is operated by a control signal SW from the control device 16, and a plurality of low-density frequency comb light (frequency comb light elements constituting the frequency comb light L1 are selected for each predetermined number). Typically, N low density frequency comb lights selected for each N (where N is an integer equal to or greater than 2), and one of the distributed low density frequency comb lights is sequentially selected and emitted. To do.

  In FIG. 1, the emitted light of the comb light density reducer 12 is indicated by L2. The comb light density reducer 12 can be composed of an interleaver and an optical switch as will be described later with reference to FIGS.

If N low-density frequency comb lights are C ₁ , C ₂ ,..., C _N , they can be expressed as follows.
C ₁ : {X ₀ , X ₀ ± N, X ₀ ± 2N, ...},
C ₂ : {X ₀ ± 1, X ₀ ± (N + 1), X ₀ ± (2N + 1), ...},
C ₃ : {X ₀ ± 2, X ₀ ± (N + 2), X ₀ ± (2N + 2), ...},
...
C _N : {X ₀ ± (N−1), X ₀ ± (N + (N−1)), X ₀ ± (2N + (N−1)),.

Here, the numbers in the curly braces are the numbers when the frequency comb optical elements are assigned consecutive numbers including negative, and X ₀ is an arbitrary number assigned to the frequency comb optical elements constituting the frequency comb light. is there.

FIG. 2A shows the frequency comb light L1 when N = 2, and FIGS. 2B and 2C show the low density frequency comb lights C ₁ and C ₂ . 2A to 2C, X ₀ = 0.

The sweeping modulator 13 is operated by a control signal SWP from the control device 16, and is emitted from the comb light density reducer 12 (any _{one of} the low-density frequency comb lights C ₁ , C ₂ ,..., C _N ). Or the frequency comb light element constituting the low density frequency comb light is swept. By using an optical phase modulator as the sweeping modulator 13, a higher-resolution frequency sweep can be performed.

  The beat generator 14 operates in response to a control signal TW from the control device 16 and refers to a specific frequency in the low density frequency comb light L3 emitted from the sweeping modulator 13 in which each frequency comb optical element is swept. Light Lref is added to generate a beat.

  The beat generator 14 can be composed of a reference light source 141 and a multiplexer 142 as shown in FIG. The multiplexer 142 combines the low density frequency comb light L3 and the reference light Lref generated by the reference light source 141, and outputs the combined light as L4.

  The light receiver 15 detects the emitted light L4 from the beat generator 14. As shown in FIG. 3B, the light receiver 15 can be composed of a photoelectric converter 151, a low-pass filter 152, and a beat detector 153. The photoelectric converter 151 receives the emitted light L4 from the beat generator 14 and converts it into a beat electric signal A1, the low-pass filter 152 generates a signal A2 from which the higher-order beat electric signal is removed, and the beat detector 153 The voltage value or the like of the low-order beat signal A2 is detected and converted into information that can be processed by digital processing or the like.

The control device 16 analyzes the signal detected by the light receiver 15 as a spectrum, and sends a control signal to the comb light density reducer 12, the sweeping modulator 13, and the beat generator 14 as described above.
The display output device 17 displays the analysis by the control device 16 on a display or outputs it to a printer.

FIG. 4 is an explanatory view showing a specific embodiment of the optical spectrum measuring apparatus of the present invention.
The optical spectrum measuring apparatus 1 in FIG. 4 includes a frequency comb light source 11, a comb light density reducer 12, a sweeping modulator 13, a beat generator 14, a light receiver 15, a control device 16, and a display output. The device 17 is connected in this order, and a sample 18 is set on the incident light side of the beat generator 14.

The frequency comb light source 11 generates the frequency comb light L1 and outputs the comb light L1 to the comb light density reducer 12. In the comb light density reducer 12, the interleaver 121 receives the frequency comb light L1 from the frequency comb light source 11, and generates low-density frequency comb lights C ₁ and C ₂ . The optical switch 122 selects either C ₁ or C _{2 according} to the control signal (switch signal SW) from the control signal 16 and sends it to the sweeping modulator 13.

Sweeping for modulator 13, emitted light L2 of the optical switching device 122 (low-density frequency comb light C ₁ or C ₂₎ is incident, based on the control signal from the control signal 16 (sweep signal SWP), C ₁ or C Sweep is performed for each of the frequency comb optical elements constituting ₂ .

  As described above, the beat generator 14 adds the reference light Lref having a specific frequency given by the control signal (detection signal TW) to the swept low-density frequency comb light L3 from the reference modulator 13 to generate a beat. Is transmitted to the light receiver 15, and the light receiver 15 detects the emitted light L 4 of the beat generator 14.

  The control device 16 analyzes the signal detected by the light receiver 15 as a spectrum, and the display output device 17 displays the analysis on a display or outputs it to a printer.

  FIG. 5 is an explanatory view showing an optical spectrum measuring apparatus 1 in which comb light density reducers are configured in two stages. The comb light density reducer 12 is composed of comb light density reduction modules 12A and 12B.

In the comb light density reducer 12A, the interleaver 121A receives the frequency comb light L1 from the frequency comb light source 11, and generates low-density frequency comb lights _C01 and _C02 . The optical switch 122A selects either C ₀₁ or C _{02 according} to the control signal (switch signal SW1) from the control signal 16, and sends it to the comb light density reducer 12B.

The interleaver 12B generates the low density frequency comb light C ₁ and C ₃ when the low density frequency comb light C ₀₁ is input, and the low density frequency when the low density frequency comb light C ₀₂ is input. Comb lights C ₂ and C ₄ are generated. Then, the optical switch 122B receives _one of the low density frequency comb lights C ₁ and C ₃ when the low density frequency comb light C ₀₁ is input by the control signal (switch signal SW2) from the control signal 16. When the low density frequency comb light C ₀₂ is being input, one of the low density frequency comb lights C ₂ and C ₄ is sent to the sweeping modulator 13. FIG. 6 shows a frequency arrangement relationship among the frequency comb light L1, the intermediate density frequency comb lights C ₀₁ and C _02, and the low density frequency comb lights C ₁ , C ₂ , C ₃ , and C ₄ .

The sweeping modulator 13 receives the output light L2 (low-density frequency comb light C ₁ , C ₂ , C ₃ , C ₄ ) of the comb light density reducer 12, and receives a control signal (sweep signal SWP) from the control signal 16. ) Based on the frequency comb optical elements constituting C ₁ , C ₂ , C ₃ , and C ₄ .

  The beat generator 14 generates a beat by adding the reference light Lref having a specific frequency given by the control signal (detection signal TW) to the swept low density frequency comb light L3 from the sweeping modulator 13, and receives the light. 15, the light receiver 15 detects the emitted light L <b> 4 of the beat generator 14.

  The control device 16 analyzes the signal detected by the light receiver 15 as a spectrum, and the display output device 17 displays the analysis on a display or outputs it to a printer.

  The optical spectrum measuring apparatus of the present invention can be applied in a wide range of fields such as detection of gas components, detection of crystal structure analysis, and detection of fluid velocity.

DESCRIPTION OF SYMBOLS 1 Optical spectrum measuring device 11 Frequency comb light source 12 Comb light density reducer 12A, 12B Comb light density reduction module 13 Sweep modulator 14 Beat generator 15 Light receiver 16 Control device 17 Display output device 18 Sample 121, 121A, 121B Inter Lever 122, 122A, 122B Optical switch 141 Light source for reference 142 Multiplexer 151 Photoelectric converter 152 Low pass filter

Claims (1)

The beat generator comprises: a frequency comb light source; a comb light density reducer composed of a first stage and a second stage comb light density reduction module; a sweeping modulator; a beat generator; In an optical spectrum measurement device in which a sample is set on the incident light side of
Each of the comb light density reduction modules is composed of an interleaver and an optical switch,
The interleaver comb optical density reduction module of the first stage, the frequency comb light elements constituting the frequency comb light the frequency comb source generates for two low density frequency comb light selected 2 Tsugoto respectively And the optical switch of the first stage comb light density reduction module sends one of the two low density frequency comb lights to the second stage comb light density reduction module;
The interleaver of the second-stage comb light density reduction module has two frequency comb optical elements constituting low-density frequency comb light from the optical switch of the first-stage comb light density reduction module , respectively. allocated to two low density frequency comb light selected every said optical switching device of the second stage comb optical density-reducing module is allocated by the interleaver of the second stage comb optical density-reducing module One of the two low-density frequency comb lights is emitted to the sweeping modulator,
The sweeping modulator is incident on the low-density frequency comb light from the comb light density reducer, performs a sweep for each of the frequency comb optical elements constituting the low-density frequency comb light,
The beat generator generates a beat by adding a reference light of a specific frequency to a low density frequency comb light emitted from the reference modulator formed by sweeping each frequency comb optical element,
The light receiver detects light emitted from the beat generator;
An optical spectrum measuring apparatus characterized by that.