CN1387027A - System and method for detecting light spectrum by waveguide holographic raster - Google Patents

Abstract

A system and a method for detecting optical spectrum with holographic waveguide raster are disclosed. Said method includes applying reflection film on one end of strip waveguide as splitter, converting the optical spectrum to be detected to niterference pattern able to be detected by CCD array near the waveguide, sending the detected interference frings to computer, and fast Fourier transform to obtain the wavelength. Its advantages are high resolution and wide range of spectrum.

Description

A kind of system and method that utilizes the waveguide holographic raster detecting light spectrum

The present invention relates to a kind of system and method for detecting light spectrum, particularly a kind of system and method that utilizes the waveguide holographic raster detecting light spectrum.

In the research of current with following Fibre Optical Sensor, optical fiber communication, spectral analysis, laser mode locking technology etc. and the application, usually need light signal spectrum (or optical wavelength) is done to detect in real time and analysis.In common optical spectrum detecting method, the spectral resolution of prismatic decomposition spectrographic detection is low; Grating beam splitting spectrographic detection complex structure, cost height, volume are big, particularly require under spectral range is big, resolution the is high situation all the more so; Tuning method Fabry-Perot-type cavity interferometric method detecting light spectrum method (U.S. Newport company produces this series products) resolution height, but detectable wavelength coverage is very narrow, costs an arm and a leg; The people such as Mark.Froggat in Virginia, The United States NASA Langley research centre in 1999 have proposed a kind of Fourier transform spectrometer of full optical fiber.Its basic thought is as beam splitter with Bragg fiber grating, forward and backward transmission coupling output direction of light has certain relation with optical fiber grating structural parameter and wavelength near the grating, by near the interference fringe the measurement grating covering, reach the purpose of measure spectrum through the Fourier spectral analysis.That this fiber grating spectrometer has is simple in structure, cost is low, volume is little, the spectral resolution advantages of higher, and shortcoming is that to measure wavelength coverage little.

The purpose of this invention is to provide a kind of system and method that utilizes the waveguide holographic raster detecting light spectrum, design a kind of spectral resolution height, the wavelength detection wide ranges, the waveguide holographic raster light-dividing device of structure dexterity, in conjunction with the linear array ccd detector, and utilize computing machine to obtain spectrum to be measured by Fourier inversion, fully overcome the deficiencies in the prior art.

Realization of the present invention: be further described below in conjunction with accompanying drawing.

Accompanying drawing 1, waveguide optical grating Fourier trasform spectroscopy detection principle figure.

Accompanying drawing 2, waveguide junction composition.

Write holographic grating embodiment 1 synoptic diagram in accompanying drawing 3, the waveguide.

Write holographic grating embodiment 2 synoptic diagram in accompanying drawing 4, the waveguide.

As shown in Figure 1, matrix (8) top that is manufactured with waveguide bar (3) is provided with and computer (7) The Linear CCD Detector that is connected (6), the front end of the waveguide bar (3) on the matrix (8) is provided with autohemagglutination Focus lens (2) and optical fiber (1) or be provided with rutile prism and optical fiber (1) in the front upper end of waveguide bar (3), Be provided with reflectance coating (5) in the rear end of waveguide bar (3). Fiber waveguide is to have the crystal of photorefractive effect Upper titanium diffusion or the ion of adopting of (or other has the material of real time record holographic grating) matrix (8) The slab waveguide (3) that exchange (or other method) is made. Utilize the two-beam interference can be in this waveguide (3) In real time record holographic grating (4) or wipe holographic grating (4) with single beam. This waveguide holographic optical Grid are made beam splitter. The left end of waveguide is by optical fiber (1), GRIN Lens (2) or the waveguide left side The top will be detected spectrum by rutile prism and be coupled in the waveguide (3). The right-hand member of waveguide (3) Be coated with high reflection film (5). Be detected light and propagate along wave guide direction, reverse behind reflectance coating (5) Forward and backward transmission coupling output direction of light is tied with waveguide optical grating near the transmission, holographic grating (4) Structure parameter and wavelength have certain functional relation, i.e. sin α=n_eff-λ/Λ, (α is that coupling output light is with the angle perpendicular to the grating vector direction, n_effBe the effective refractive index of waveguide medium, λ is the ripple of input light Long, Λ is the grating cycle). Transmission coupling output light forms interference fringe, its intensity near grating Be distributed as

, (γ is contrast of fringes). Fringe period with α is about namely relevant with wavelength X. It is neighbouring available so just spectrum to be measured to be converted to waveguide optical grating (4) The interference pattern that Linear CCD Detector (6) detects. Survey by Linear CCD Detector (6) Measure these interference fringes, spectrum is provided by the Fourier transformation that survey striped light intensity deducts the direct current composition $I\left(\mathrm{\λ}\right)=\left|\underset{-\∞}{\overset{\∞}{\∫}}\right[I\left(z\right)-I_0\left]\exp \left({\mathrm{iK}}_{z}Z\right)\mathrm{dz}\right|,$ As calculated machine fast Fourier (Fourier) inverse transformation and light Analysis of spectrum reaches the purpose of measure spectrum. For the grating of some cycles Λ in the waveguide (3), protecting Under the condition of card certainty of measurement, device has certain wavelength measurement scope, in order to expand wavelength measurement Scope, erasable original grating writes the grating of different cycles again, changes detectable wave band Wavelengths centered reaches the spread spectrum investigative range. As shown in Figure 2, fiber waveguide matrix (8) material Material adopts has the crystal of photorefractive effect (such as lithium niobate LiNbO₃) or other to have real time record complete The material of breath grating. The slab waveguide that adopts titanium (Ti) diffusion or ion-exchange or other method to make (3). One end of waveguide (3) is coated with the deielectric-coating (5) of high reflectance.

Writing holographic grating (4) in waveguide (3) can implement with biplane light wave and relevant apparatus.

Embodiment 1, as shown in Figure 3, implementing device that holographic grating (4) writes can be in waveguide (3) with rotation stationary shaft (13) be that fulcrum can be adjusted laser instrument (12) side lower part of launching beam direction spectroscope (11) and two catoptrons (9,10) are set.Implementation method is be that fulcrum can be adjusted laser instrument (12) the institute emitted light beams of launching beam direction with rotation stationary shaft (13), restraint the planar light beam that forms an angle by the beam split of spectroscope (11) and the reflection formed two of two catoptrons (9,10), the optical waveguide (3) on the matrix (8) is implemented holographic grating (4) write.

Embodiment 2, as shown in Figure 4, the device that writes also can be that laser instrument (12) side lower part is provided with beam expanding lens (16), collimation lens (15) and places right-angle prism (14) on the optical waveguide (3).Implementation method is be that fulcrum can be adjusted laser instrument (12) the institute emitted light beams of launching beam direction with rotation stationary shaft (13), by beam expanding lens (16), collimation lens (15) and the planar light beam that places formed two bundles of right-angle prism (14) on the optical waveguide (3) to form an angle, the optical waveguide (3) on the matrix (8) is implemented holographic grating (4) write.Two light beams produce the period profile of interfering and forming light intensity in waveguide (3), distribute because the photorefractive effect of material produces corresponding refractive index cycle in waveguide (3), form holographic phase grating (4).The change in grating cycle can realize by the incident angle that change is incided on the optical splitter.

Advantage of the present invention and good effect: this detecting light spectrum new method has the resolution ratio height, the spectrum branch The rate of distinguishing reaches more than the 0.04nm easily; But the photometry spectral limit is wide, says this spectrographic detection side on the principle The spectral region of method very easily covers infrared to ultraviolet; Draw detection light by the computer Fourier inversion The spectrum result, precision height, reliability are strong; Light-dividing device structure dexterity.

Claims (8)

1, a kind of method of utilizing the waveguide holographic raster detecting light spectrum, it is characterized in that: utilize an end to be coated with the photorefractive crystal slab waveguide (3) of reflectance coating (5) as light-dividing device, convert spectrum to be measured to interference pattern that near the available linear array ccd detector (6) of waveguide optical grating (4) detects, place near the line array CCD detector (6) of waveguide (3) upper surface that the interference fringe information that detects is delivered to computing machine (7), try to achieve spectral wavelength to be measured with the relation of fast Fourier (Fourier) inverse transformation and waveguide holographic raster (4) structural parameters and incident wavelength.

2, the new method of utilizing the waveguide holographic raster detecting light spectrum according to claim 1 is characterized in that: the main executive routine of computing machine is $I\left(\mathrm{\λ}\right)=|\underset{-\∞}{\overset{\∞}{\∫}}\mathrm{\γ}\cos 4\mathrm{\πz}(n_{\mathrm{eff}}-\mathrm{\λ}/\mathrm{\Λ})/\mathrm{\λexp}\left({\mathrm{iK}}_{z}Z\right)\mathrm{dz}|$ Computing formula.

3, the method for utilizing the waveguide holographic raster detecting light spectrum according to claim 1, it is characterized in that: the holographic grating in the waveguide (4) can be wiped in real time and write according to desired spectral resolution and spectral wavelength scope to be measured, utilize two-beam interference can be in waveguide (3) real time record holographic grating (4), utilize single beam to wipe holographic grating (4).

4, a kind of system that utilizes the waveguide holographic raster detecting light spectrum, it is characterized in that: matrix (8) top that is manufactured with waveguide bar (3) is provided with the line array CCD detector (6) that is connected with computing machine (7), the front end of the waveguide bar (3) on the matrix (8) is provided with GRIN Lens (2) and optical fiber (1) or is provided with rutile prism and optical fiber (1) in the preceding upper end of waveguide bar (3), is provided with reflectance coating (5) in the rear end of waveguide bar (3).

5, the system that utilizes the waveguide holographic raster detecting light spectrum according to claim 4 is characterized in that: optical waveguide is to go up the slab waveguide (3) that adopts titanium diffusion or ion-exchange or other method to make at the crystal with photorefractive effect or other matrix of materials (8) with real time record holographic grating.

6, the system that utilizes the waveguide holographic raster detecting light spectrum according to claim 4, it is characterized in that: implementing device that holographic grating (4) writes mainly be in waveguide (3) with rotation stationary shaft (13) be that fulcrum can be adjusted laser instrument (12) side lower part of launching beam direction and is provided with spectroscope (11) and two catoptrons (9,10), or laser instrument (12) side lower part is provided with beam expanding lens (16), collimation lens (15) and places right-angle prism (14) on the optical waveguide (3).

7, the method for utilizing the waveguide holographic raster detecting light spectrum according to claim 3, it is characterized in that: with rotation stationary shaft (13) is laser instrument (12) the institute emitted light beams that fulcrum can be adjusted the emission beam direction, restraint the planar light beam that forms an angle by the beam split of spectroscope (11) and the reflection formed two of two catoptrons (9,10), the optical waveguide (3) on the matrix (8) is implemented holographic grating (4) write.

8, the method for utilizing the waveguide holographic raster detecting light spectrum according to claim 3, it is characterized in that: with rotation stationary shaft (13) is laser instrument (12) the institute emitted light beams that fulcrum can be adjusted the emission beam direction, by beam expanding lens (16), collimation lens (15) and the planar light beam that places formed two bundles of right-angle prism (14) on the optical waveguide (3) to form an angle, the optical waveguide (3) on the matrix (8) is implemented holographic grating (4) write.

Images