CN100371742C - CWDM filter with four channels - Google Patents

Abstract

The invention relates to a multi-channel CWDM optical filter, which comprises a substrate and N stacked structures, wherein N is an odd number not less than 2, and each stacked structure comprises a Fabry-Perot resonant cavity structure and a coupling layer from the substrate side. Wherein, the [ (N +1)/2-1 ] th]The coupling layer and the [ (N +1)/2+1 ] th layer of the stacked structure]The coupling layers of the stacked structure are all (2n +1) L, n is a positive integer, and L represents lambda₀Low refractive index film layer of/4, lambda₀Representing the center wavelength of the channels. Meanwhile, each Fabry-Perot resonant cavity structure is sequentially H (LH) from the substrate side^akL(HL)^aH, a is a positive integer, k is an integer of not less than 2, L represents lambda₀A film layer of low refractive index,/4, H represents lambda₀High refractive index film layer of/4, lambda₀Representing the center wavelength of the channels.

Description

CWDM filter with four channels

technical field

The present invention relates to an optical filter, especially a CWDM optical filter suitable for a coarse wavelength division multiplexing system (CWDM; Coarse Wavelength Division Multip1ex) and having four channels at the same time.

Background technique

Optical filter, or optical filter (optical filter) is a wavelength selective device, which has important applications in optical fiber communication systems and optical sensor systems. Optical filters are divided into two types: passive and active. Passive optical filters are based on prisms, diffraction gratings, and spectral (frequency) filters; active optical filters are passive devices and tunable detectors. Combined, each detector is tuned to a specific frequency.

Among the passive optical filters, there is an interference film filter, which uses high and low refractive index materials to be deposited on substrates made of glass and other materials with a pre-designed thickness (usually λ/4) to meet the requirements. wavelength response characteristics. Generally, the dielectric film interference filter is made of overlapping high-refractive index and low-refractive-index films with a thickness of λ/4. The phase of the light reflected in the high-refractive index layer will not shift, while the low-refractive index The phase of light reflected within the layer is shifted by 180°. Due to the difference in light travel (a multiple of 2*λ/4), the successive reflected light overlaps and recombines in the front, resulting in a high-intensity reflected beam in a narrow wavelength range, while the output wavelength outside this wavelength range will suddenly decrease. Such filters can be used as high-pass filters, low-pass filters or highly reflective layers. Moreover, because its optical properties depend on the reflection and transmission properties of the optical film, its optical film is generally coated with a band-pass filter, low pass filter or high pass filter Or band reject filter.

Figure 2 shows a four-channel CWDM optical filter in the prior art. The overall film structure of this four-channel CWDM filter is: N ₀ /L(HLH)4L(HLH)L(HLH)2L(HLH)L(HLHLH)2L(HLHLH)L(HLH)4L(HLH)L (HLHLH)2L(HLHLH)L(HLH)4L(HLH)L(HLHLH)2L(HLHLH)L(HLH)4L(HLH)L(HLHLH)2L(HLHLH)L(HLH)4L(HLH)L(HLHLH )2L(HLHLH)L(HLH)4L(HLH)L(HLHLH)2L(HLHLH)L(HLH)2L(HLH)L(HLH)4L(HLH)/ _NS ; where, _NS represents the substrate refractive index 1.658 , N ₀ means air, L means λ ₀ /4 low refractive index film layer, H means λ ₀ /4 high refractive index film layer, λ ₀ means the center wavelength of these channels. As shown in FIG. 2 , the 67th and 87th layers from the left are both coupling layers, and are respectively low-refractive-index film layers with a film thickness of one quarter of the central wavelength.

Please refer to Figure 3 for the corresponding spectral characteristic diagram. In the four-channel CWDM optical filter of the prior art, since the film thicknesses of the coupling layers of the 67th layer and the 87th layer are only set to one quarter of one central wavelength. However, the light transmittance of the noise in the two passbands of the CWDM optical filter at 1500-1505nm and 1575-1580nm is relatively large, thus generating large interference ripples (ripple), which reduces the light transmittance. In a general design, the so-called optimization will be performed on the last two layers of the overall film structure with a film thickness other than a quarter of the central wavelength. However, stacking film thicknesses other than a quarter of the central wavelength is a more complicated process.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, provide a kind of CWDM optical filter that is suitable for coarse wavelength division multiplexing system (CWDM; coarse wavelength division multiplex), has four channels at the same time, it can reduce the cost of CWDM assembly. overall loss.

The technical gist of the present invention is to provide a multi-channel CWDM optical filter, including a substrate and N stacked structures, wherein N is an odd number not less than 2, and each stacked structure includes a Fabry-Perot resonance from the substrate side cavity structure with a coupling layer.

Each stack structure includes a first film stack, a space layer, a second film stack and a coupling layer from the substrate side; and relative to the space layer, the first film stack and the second film stack are arranged symmetrically. Among them, the space layer is kL, k is a positive integer greater than or equal to 2, preferably a positive even number, L represents a low refractive index film layer of λ ₀ /4, and λ ₀ represents the center wavelength of these channels.

Moreover, the coupling layer of the [(N+1)/2-1]th stack structure and the coupling layer of the [(N+1)/2+1] stacked structure are both (2n+1)L, n is positive Integer, L represents the low refractive index coating layer of λ ₀ /4, λ ₀ represents the center wavelength of these channels.

Each Fabry-Perot cavity structure is sequentially H(LH) ^a kL(HL) ^a H from the substrate side, and a is a positive integer, k is an integer not less than 2, and L represents λ ₀ /4 The low-refractive-index film layer, H represents the high-refractive-index film layer of λ ₀ /4, and λ ₀ represents the central wavelength of these channels. Wherein, the first membrane stack is H(LH) ^a , and the second membrane stack is (HL) ^a H .

The coupling layer of the other stacked structures is L, and L represents the low refractive index film layer of λ ₀ /4, and λ ₀ represents the center wavelength of these channels.

When the multi-channel CWDM optical filter of the present invention provides four channels of 1510nm, 1530nm, 1550nm and 1570nm, the Fabry-Perot cavity structure from the substrate side is HLH4LHLH, HLH2LHLH, H(LH) ² 2L(HL ) ² H, HLH4LHLH, H(LH) ² 2L(HL) ² H, HLH4LHLH, H(LH) ² 2L(HL) ² H, HLH4LHLH, H(LH) ² 2L(HL) ² H, HLH4LHLH, H( LH) ² 2L(HL) ² H, HLH4LHLH, H(LH) ² 2L(HL) ^2H , HLH2LHLH, HLH4LHLH.

The central wavelength λ ₀ of the multi-channel CWDM optical filter of the present invention is 1540nm. In addition, the coupling layers from the substrate side are L, L, L, L, L, L, 3L, L, 3L, L, L, L, L, L, L in order.

The film layer design technique of the CWDM optical filter with four optical channels of the present invention is: adopted the low-refractive index coupling layer (couplinglayer) of 1/4 center wavelength of odd multiples, to reduce the ripple (couplinglayer) that passband produces Ripple), thereby increasing the light transmittance of the entire filter, thereby reducing the overall loss on the CWDM after assembly.

Description of drawings

Fig. 1 is the film structure schematic diagram of the CWDM optical filter with four channels of the present invention;

Fig. 2 is a schematic diagram of the relationship between the overall film structure and the corresponding light transmittance of a prior art CWDM optical filter;

Fig. 3 is the spectral characteristic diagram corresponding to Fig. 2;

Fig. 4 is a schematic diagram of the relationship between the overall film structure and the corresponding light transmittance of the CWDM optical filter with four channels of the present invention; and

Fig. 5 is a spectrum characteristic diagram of the CWDM optical filter of the present invention.

Detailed ways

The CWDM (coarse wavelength division multiplex) filter 1 with four channels of the present invention will be further described in detail in conjunction with the accompanying drawings of the description.

As shown in FIG. 1 , the CWDM optical filter 1 with four channels of the present invention includes a substrate 10 and N stacked structures 40 ; wherein N is an odd number not less than 2. Each stack structure includes a first film stack 21 , a spacer layer 25 , a second film stack 22 and a coupling layer 30 from the substrate side. Therefore, the first membrane stack 21 , the space layer 25 and the second membrane stack 22 constitute a Fabry-Perot cavity structure 20 . Moreover, relative to the space layer 25 , the first membrane stack 21 and the second membrane stack 22 are arranged symmetrically. Wherein, the spatial layer 25 is kL, and k is a positive integer greater than or equal to 2, preferably a positive even number.

Referring to FIG. 1 and FIG. 4, the coupling layer 30' of the [(N+1)/2-1] stacked structure 40' and the coupling layer 30" of the [(N+1)/2+1] stacked structure 40" Both are (2n+1)L, n is a positive integer, L represents the low refractive index film layer of λ ₀ /4, and λ ₀ represents the center wavelength of these channels. The coupling layer 30 of the rest of the stacked structure is L, L represents a low-refractive-index film layer of λ ₀ /4, and λ ₀ represents the center wavelength of these channels.

Each Fabry-Perot cavity structure is sequentially H(LH) ^a kL(HL) ^a H from the substrate 10 side, and a is a positive integer, k is an integer not less than 2, and L represents λ ₀ /4 The low refractive index film layer, H represents the high refractive index film layer of λ ₀ /4, and λ ₀ represents the center wavelength of each channel of the present invention. Wherein, the first membrane stack can be expressed as H(LH) ^a , and the second membrane stack can be expressed as (HL) ^a H .

When the multi-channel CWDM optical filter 1 of the present invention provides four channels of 1510nm, 1530nm, 1550nm and 1570nm, the structure of the Fabry-Perot cavity from one side of the substrate 10 can be expressed as HLH4LHLH, HLH2LHLH, H(LH ) ² 2L(HL) ² H, HLH4LHLH, H(LH) ² 2L(HL) ² H, HLH4LHLH, H(LH) ² 2L(HL) ² H, HLH4LHLH, H(LH) ² 2L(HL) ² H , HLH4LHLH, H(LH) ² 2L(HL) ² H, HLH4LHLH, H(LH) ² 2L(HL) ² H, HLH2LHLH, HLH4LHLH.

The central wavelength λ ₀ of the multi-channel CWDM optical filter of the present invention is 1540nm. In addition, the coupling layers from the substrate side are L, L, L, L, L, L, 3L, L, 3L, L, L, L, L, L, L in order.

The CWDM optical filter 1 of the present invention is formed by stacking a plurality of (can be 15) Fabry-Perot resonant cavity film stacks 20 with a film thickness of 1/4 of the central wavelength, and has four wavelengths of 1510nm, 1530nm, 1550nm and 1570nm at the same time. optical channel. The central wavelength of the CWDM optical filter of the present invention is located at the central point λ ₀ of the four optical channels, which is 1540nm; and the thickness of all film layers is a quarter of the central wavelength λ ₀ .

Wherein, each space layer 25 adopts the film layer of 1/4 central wavelength λ ₀ film thickness; Composition, and the coupling layer 30 of the Fabry-Perot resonator film stack 20 adopts a low refractive index film layer that is an odd multiple of a quarter of the central wavelength.

The coupling layers 30 respectively located on the 67th and 87th layers can be (2n+1) times a quarter of the central wavelength _λ0 film thickness of the low-refractive index film layer. In the present invention, it is preferable to use a low-refractive-index film layer with a film thickness three times the quarter of the central wavelength.

The surface polishing diameter of the glass substrate 10 of the present invention is 90mm, the thickness is 10mm; the peak transmittance is greater than 90%; the band pass is 1502nm-1578nm. The aforementioned low-refractive index film layer can be made of silicon oxide, while the high-refractive index film layer is made of tantalum oxide, and the substrate is composed of silicon oxide, barium, lithium, sodium and other elements. Wherein, the refractive index of the low refractive index film layer is 1.44, and the refractive index of the high refractive index film layer is 2.1-2.5.

As shown in Figure 4 is a specific embodiment of the present invention. In this figure, counting from the left is the first film layer of the present invention, its 67th layer and 87th layer are also coupling layers, and are respectively three times the low refractive index film layer of the center wavelength film thickness . Fig. 5 is the spectral characteristic diagram corresponding to this embodiment, as can be seen from Fig. 5, in this embodiment, the noise ripples in the two band passbands of 1500-1505nm and 1575-1580nm have been eliminated, so that the optical filter 1 The overall light transmittance is improved.

In summary, a key technical point of the present invention is that the coupling layer 30 connecting the Fabry-Perot resonant cavity film stack and the Fabry-Perot resonant cavity film stack adopts an odd multiple of quarters. The film thickness of one of the central wavelengths is used to reduce the ripple generated by the passband, thereby improving the overall light transmittance of the optical filter 1 . In this way, the whole design does not use a film thickness other than a quarter wavelength at all, which simplifies the corresponding production process and reduces the corresponding production cost.

The film layer design technique of the CWDM optical filter 1 with four optical channels of the present invention is to adopt a low refractive index coupling layer (coupling layer) of an odd multiple of 1/4 central wavelength to reduce the passband generated Ripple, thereby increasing the light transmittance of the entire filter, thereby reducing the overall loss on the CWDM after assembly.

Claims (20)

1. A multi-channel CWDM optical filter comprises a substrate and N stacked structures, wherein N is an odd number not less than 2, each stacked structure comprises a Fabry-Perot resonant cavity structure and a coupling layer from the substrate side, and the optical filter is characterized in that:

the [ (N +1)/2-1 ] th]The coupling layer and the [ (N +1)/2+1 ] th layer of the stacked structure]The coupling layers of the stacked structure are all (2n +1) L, n is a positive integer, and L represents lambda₀Low refractive index film layer of/4, lambda₀Representing the center wavelength of its channel.

2. The multi-channel CWDM filter of claim 1, wherein: each Fabry-Perot cavity structure is sequentially H (LH) from the substrate side^akL(HL)^aH, a is a positive integer, k is an integer of not less than 2, L represents lambda₀A film layer of low refractive index,/4, H represents lambda₀High refractive index film layer of/4, lambda₀Representing the center wavelength of its channel.

3. The multi-channel CWDM filter of claim 2, wherein: the coupling layer of the remaining stacked structure is L, L represents lambda₀Low refractive index film layer of/4, lambda₀Representing the center wavelength of its channel.

4. The multi-channel CWDM filter of claim 2, wherein k is an even number not less than 2.

5. The multi-channel CWDM filter of claim 2, wherein: when four channels of 1510nm, 1530nm, 1550nm and 1570nm are provided, the Fabry-Perot resonator structure from the substrate side is HLH4LHLH, HLH2LHLH, H (LH)²2L(HL)²H、HLH4LHLH、H(LH)²2L(HL)²H、HLH4LHLH、H(LH)²2L(HL)²H、HLH4LHLH、H(LH)²2L(HL)²H、HLH4LHLH、H(LH)²2L(HL)²H、HLH4LHLH、H(LH)²2L(HL)²H. HLH2LHLH, HLH4LHLH, and lambda₀Is 1540 nm.

6. The multi-channel CWDM filter of claim 5, wherein: the coupling layers from the substrate side are L, L, L, L, L, L, 3L, L, 3L, L, L, L, L, L, L in this order.

7. A multi-channel CWDM filter comprises a substrate and N stacked structures, wherein N is an odd number not less than 2, each stacked structure comprises a first film stack, a spacer layer, a second film stack and a coupling layer from the substrate side, characterized in that:

the [ (N +1)/2-1 ] th]The coupling layer and the [ (N +1)/2+1 ] th layer of the stacked structure]The coupling layers of the stacked structure are all (2n +1) L, n is a positive integer, and L represents lambda₀Low refractive index film layer of/4, lambda₀Representing the center wavelength of its channel.

8. The multi-channel CWDM filter of claim 7, wherein the first film stack and the second film stack are symmetrically disposed with respect to the spatial layer.

9. The multi-channel CWDM filter of claim 8, wherein the first film stack is H (LH)^aAnd the second film stack is (HL)^aH, wherein a is a positive integer and L represents lambda₀A film layer of low refractive index,/4, H represents lambda₀High refractive index film layer of/4, lambda₀Representing the center wavelength of its channel.

10. The multi-channel CWDM filter of claim 9, wherein the spatial layer is kL and k is a positive integer greater than or equal to 2.

11. The multi-channel CWDM filter of claim 10, wherein k is a positive even number.

12. The multi-channel CWDM filter of claim 7, wherein: the coupling layer of the remaining stacked structure is L, L represents lambda₀Low refractive index film layer of/4, lambda₀Representing the center wavelength of the channels.

13. The multi-channel CWDM filter of claim 11, wherein: when four channels of 1510nm, 1530nm, 1550nm and 1570nm are provided, each stack structure from the substrate side is [ HLH, 4L, HLH, L]、[HLH、2L、HLH、L]、[H(LH)²、2L、(HL)²H、L]、[HLH、4L、HLH、L]、[H(LH)²、2L、(HL)²H、L]、[HLH、4L、HLH、L]、[H(LH)²、2L、(HL)²H、3L]、[HLH、4L、HLH、L]、[H(LH)²、2L、(HL)²H、3L]、[HLH、4L、HLH、L]、[H(LH)²、2L、(HL)²H、L]、[HLH、4L、HLH、L]、[H(LH)²、2L、(HL)²H、L]、[HLH、2L、HLH、L]、[HLH、4L、HLH、L]And λ₀Is 1540 nm.

14. A four-channel CWDM filter, the four channels are 1510nm, 1530nm, 1550nm and 1570nm, it includes the base plate and odd number stack structure, each stack structure includes a first membrane stack, a space layer, a second membrane stack and a coupling layer from the base plate side, its characterized in that:

the [ (N +1)/2-1 ] th]The coupling layer and the [ (N +1)/2+1 ] th layer of the stacked structure]The coupling layers of the stacked structure are all (2n +1) L, n is a positive integer, L represents λ₀Low refractive index film layer of/4, lambda₀Representing the center wavelength of the four channels at 1540 nm.

15. The four-channel CWDM filter of claim 14, wherein the first film stack and the second film stack are symmetrically disposed with respect to the spatial layer.

16. The four-channel CWDM filter of claim 15, wherein the first film stack is h (lh)^aAnd the second film stack is (HL)^aH, wherein a is a positive integer and L represents lambda₀A film layer of low refractive index,/4, H represents lambda₀High refractive index film layer of/4, lambda₀Representing the center wavelength of its channel, 1540 nm.

17. The four-channel CWDM filter of claim 16, wherein the spatial layer is kL and k is a positive integer greater than or equal to 2.

18. The four-channel CWDM filter of claim 17, wherein k is a positive even number.

19. The four channel CWDM filter of claim 14A light sheet, wherein: the coupling layer of the remaining stacked structure is L, L represents lambda₀Low refractive index film layer of/4, lambda₀Representing the center wavelength of its channel, 1540 nm.

20. The four-channel CWDM filter of claim 18, wherein: each stacked structure from the substrate side is [ HLH, 4L, HLH, L]、[HLH、2L、HLH、L]、[H(LH)²、2L、(HL)²H、L]、[HLH、4L、HLH、L]、[H(LH)²、2L、(HL)²H、L]、[HLH、4L、HLH、L]、[H(LH)²、2L、(HL)²H、3L]、[HLH、4L、HLH、L]、[H(LH)²、2L、(HL)²H、3L]、[HLH、4L、HLH、L]、[H(LH)²、2L、(HL)²H、L]、[HLH、4L、HLH、L]、[H(LH)²、2L、(HL)²H、L]、[HLH、2L、HLH、L]、[HLH、4L、HLH、L]。

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