CN1288464C - Bulk optical interferometer - Google Patents

Abstract

The present invention relates to an optical cross multiplexer based on a Mach-Zehnder interferometer, which can be used as an optical channel in wavelength division multiplexing (WDM) and dense wavelength division multiplexing (DWDM) optical networks cross multiplexer. The optical channel interleaver/deinterleaver mixes sets of WDM and DWDM channels for transmission over the network and/or separates WDM and DWDM signals into sets of channels with channel spacing that is more favorable for future demultiplexing. The interleaved multiplexer according to this invention uses a ring resonator in each of its arms as a phase shifter, thereby providing wide passband and stopband for the flat-head wavelength response.

Description

BULK optical interferometer

Cross-references to related patent applications

This is the first application of the present invention.

technical field

The invention relates to an optical interferometer, in particular to a Mach-Zehnder (Mach-Zehnder) interferometer (MZI)-based, used as a wavelength channel interleaver (interleaver) / de-interleaver (de-interleaver) -interleaver) bulk optical interferometer.

Background technique

As an interface between devices suitable for signals with the first wavelength channel spacing and devices suitable for signals with the second wavelength channel spacing, the optical cross multiplexer has become a A popular tool. In the past, 200GHz channel spacing was the common spacing, but as the need for increased bandwidth grew, 100GHz channel spacing became a standard. In the next generation of communication networks, channel spacing of 50GHz or even 25GHz will become common. However, conventional demultiplexing filters, such as color separation filters, do not have the ability to separate such closely spaced channels without significant channel crosstalk without complex and costly modifications. Therefore, optical crossbar multiplexers are used to separate closely spaced channels into two sets of channels that are twice as far apart. This process continues until the channels are separated enough to allow traditional multiplexing to be effective.

Interleaves come in various forms, such as: birefringent crystal interleavers, which are described in U.S. Patent No. 6,301,046, issued October 9, 2001, which was issued by Cochon. Works by Kuochou Tai et al.; Another example is the integrated lattice cross multiplexer disclosed in the No. 5,596,661 patent published by Charles Henry (Charles Henry) on January 21, 1997; U.S. Patent No. 6,304,689 by Benjamin Dingel et al., published October 16, 2001, and by Reza Paiam, published June 2001 US Patent No. 6,252,716 on the 26th, and the Michelson G-T (Michelson Gires-Tournois) Interferometer (MGTI ). An interleaved multiplexer based on polarization using a split-mirror ring resonator was invented by Gan Zhou et al., which was published as US Patent No. 6,243,200 on June 5, 2001.

An object of the present invention is to overcome the deficiencies of the prior art and provide a simple bulk optical cross multiplexer, which has the advantages of less quantity, low manufacturing cost and reliable and stable performance. part.

Contents of the invention

Therefore, the present invention relates to an optical cross multiplexer comprising:

a first input port for emitting an input beam;

a first beam splitter for splitting the input beam into first and second sub-beams passing through the first and second optical paths, respectively;

A first ring resonator located on the first optical path, the resonator includes at least two surfaces that are substantially total reflection and a first partial reflection surface, the first partial reflection surface injects a part of the first sub-beam into the first ring resonator, and reflecting off the remaining first sub-beams such that light from the first ring resonator mixes with the remaining first sub-beams to form a first remixed sub-beam;

A second ring resonator located on the second optical path, the resonator includes at least two surfaces that are basically total reflection and a second partial reflection surface, the second partial reflection surface injects a part of the second sub-beam into the second ring resonator, and reflecting off the remaining second sub-beams so that the light from the second ring resonator mixes with the remaining second sub-beams to form a second remixed sub-beam;

a second beam splitter for receiving the first and second remixed beamlets, thereby causing interference of the first and second remixed beamlets, and producing first and second output beams;

a first output port for outputting a first output beam; and

A second output port for outputting a second output beam.

Another aspect of the invention relates to a Mach-Zehnder interferometer comprising:

a beam splitter for splitting the input beam into first and second sub-beams and directing the first and second sub-beams along first and second interference arms of the interferometer, respectively;

a first ring resonator within a first interference arm of the interferometer having a first resonance delay affecting the phase response of the first sub-beam;

a second ring resonator within a second interference arm of the interferometer having a second resonance delay affecting the phase response of the second sub-beam;

A beam combiner for interfering the first and second sub-beams to form first and second output beams.

Description of drawings

The invention will be described in detail with reference to the accompanying drawings showing preferred embodiments, in which:

Figure 1 is a schematic diagram of one embodiment of an interferometer according to the invention;

Figure 2 is a schematic diagram of another embodiment of an interferometer according to the invention;

Figures 3a and 3b illustrate alternative examples of ring resonators that may be used in the embodiments of Figures 1 and 2;

Fig. 4 is a schematic diagram of the transmission spectra of two groups of channels in an optical cross multiplexer according to an embodiment of the present invention;

5 is a schematic diagram of the transmission spectra of two groups of channels in an optical cross multiplexer according to another embodiment of the present invention;

FIG. 6 is a graph about the relationship between the phase difference and the wavelength of a group of channels in an optical crossbar multiplexer according to an embodiment of the present invention,

Detailed ways

The interleaver 10 according to the invention is based on a Mach-Zehnder interferometer (MII), into which beams can be injected or exited through one or more of the four ports 11 , 12 , 13 and 14 . Each port includes a collimating/focusing lens 16 optically coupled to a ferrule 17 surrounding one end of a fiber optic waveguide 18 . In our discussion, for the sake of convenience and brevity, we assume that light is launched into the crossbar 10 through the first port 11 and output through the second and third ports 12, 13, respectively. However, those skilled in the art understand that there are other feasible combinations, including: input through the second and/or third ports 12 and 13 respectively, and output through the first and/or fourth ports 11 and 14 respectively.

A typical input beam 20 is a Dense Wavelength Division Multiplexed (DWDM) signal comprising many wavelength channels, the beam 20 is launched through the first port 11 and split by a beam splitter in the form of a first beam splitting coating 23a into The first sub-beam 21 and the second sub-beam 22, wherein the split coating 23a is coated on a part of one side of the first glass (or other transparent object) substrate. The first beam splitting coating 23a preferably splits the input beam 20 into two, that is, the reflectivity ranges from 42% to 50%, and the ideal reflectivity is 50%. The first sub-beam 21 passes through the first substrate 24 until it intersects a first partially reflective surface 26 placed on the opposite side of the first substrate 24 . The reflectivity of the first partially reflective surface 26 is preferably between 42% and 50%. Part of the first sub-beam 21 passes through a first ring resonator 27 comprising a mirror 31 and a further mirror 32 . After passing through the delay distance of the first resonant cavity, the light exits the first ring resonant cavity 27 and mixes with the light reflected from the first partial reflection film layer 26 to form a first remixed sub-beam 33 . The first remixed sub-beam 33 is directed directly into the first substrate 24 .

The second sub-beam 22 is reflected by the first beam-splitting coating 23a while passing through the second glass (or other transparent object) substrate 34 so as to meet the second partially reflective surface. The reflectivity of the second partially reflective surface 36 is preferably between 2.4% and 5.2%. Part of the second sub-beam 22 passes through a second ring resonator 37 comprising a first mirror 41 and a second mirror 42 . The light after the second circular delay distance exits the second circular resonator 37, and is mixed with the light reflected by the second part of the reflective surface 36, and is sent to the first substrate 24, thus forming the second remixed sub-beam 38. The second remixed sub-beam 38 interferes with the first remixed sub-beam 33 on the second beam splitting layer 23b to form part of the light, that is, the first output beam output from the second port 12 and the remaining light, that is, the third The second output beam output from port 13. The reflectivity range of the second light beam splitting layer 23b is also preferably between 43% and 50%, and the ideal reflectivity is 50%. To simplify production, the first and second beam splitting coatings 23a and 23b may have the same reflectivity of 50% and be applied simultaneously.

The optical path from the first split coating 23a to the first partially reflective surface 26 and back to the second split coating 23b is called the first optical path of the Mach-Zehnder interferometer. The optical path from the first split coating 23a to the second partially reflective surface 36 and back to the second split coating 23b is called the second optical path of the Mach-Zehnder interferometer. In order to cause interference, the lengths of the first optical path and the second optical path are different. This length difference is called an optical path length difference. When used as a cross multiplexer, it is preferable that the optical path with a partially reflective surface, that is, the second optical path, is shorter than the other optical paths, and the reflectivity of the partially reflective surface is low, and the ratio between the first optical path and the second optical path The difference in length is half the delay distance of the first resonator, assuming that the delay distances of the first and second resonators are equal. When used as a crossbar multiplexer, one set of wavelength channels, such as even-numbered International Telecommunication Union (ITU) channels, is output by port 12, and another set of wavelength channels, such as odd-numbered ITU channels, is output by port 13.

Figure 2 is a schematic diagram of an embodiment according to the invention in which a minimal amount of substrate material is used. The new first and second substrates 124 and 134 are much thinner than their counterparts 24 and 34 in FIG. 1, respectively. Therefore, a third substrate 144 is required to support the first partially reflective coating 26 . The substrate 124 can also be divided into two separate substrates, each having one of the beam splitting layers 23a and 23b.

3a and 3b are illustrations of another two ring resonators instead of the first and second ring resonators 27 and 37 . The ring resonator 137 ( FIG. 3 a ) comprises a second substrate 34 , a second partially reflective coating 36 and three reflective surfaces 141 , 142 , 143 . Those skilled in the art understand that any number of reflective surfaces may be used. FIG. 3b shows the second ring resonator 37 with a wedge-shaped tab 150 . The adjustment plate 150 whose refractive index is different from that of air can be used to adjust the optical path distance of one of the ring resonators in a small range to properly match the two ring resonators. Fine adjustment of the wedge 150 creates more or less light beams passing through itself, thereby lengthening or shortening the optical path length of the ring resonator.

Figures 4 and 5 illustrate the theoretical transmission spectral response of an interleaver according to the present invention. Solid lines represent even ITU wavelength channels, while dashed lines represent odd ITU wavelength channels. The bandwidth of the passband with -0.5dB loss occupies more than 85% of the free spectral range (FSR) of the interleaver, and the bandwidth of the cutoff band with -25dB loss exceeds 75% of the FSR of the interleaver. The difference in the two response curves is due to the different reflectivities of the first and second partially reflective surfaces 26 and 36 . In order to obtain the graph shown in Figure 4, the reflectivity of the first and second beam-splitting coatings 23a and 23b should be 50% and 48.3%, respectively, while the reflectivity of the first and second partially reflective coatings 26 and 36 The rates were 44.8% and 3.4%, respectively. In order to obtain the graph shown in Figure 5, the reflectivity of the first and second beam splitting coatings 23a and 23b should be 50%, while the reflectivity of the first and second partially reflective coatings 26 and 36 are respectively 42.2% and 3.3%.

The graph shown in FIG. 6 illustrates the phase difference of the odd ITU wavelength channels of the interleaver according to the present invention. On continuous wavelength channels equivalent to the FSR of an optical crossbar multiplexer, the phase difference alternates between 0 and ±π. The horizontal curve segment with 0 phase difference in the figure represents the constructive interference part, that is, the flattop passband, while the horizontal curve segment with ±π phase difference represents the destructive interference part, that is, the intercept band.

The device according to this invention can also be used to deinterleave two sets of complementary wavelength channels. Each of the two input beams includes a set of complementary wavelength channels therein, and the two beams are respectively input into the second and third ports 12 and 13 (or the first and fourth ports 11 and 14), and are Introduced into a beam splitter where the two beams interfere and are split into two sub-beams. Each sub-beam reaches one of the ring resonators 27 or 37, and forms two remixed sub-beams, which are mixed again in the beam splitter and sent from the first or fourth port 11 or 14 output (or output from the second or third port 12 or 13).

Claims (15)

1. optical interdferometer device comprises:

Be used for launching the first input end mouth of input beam;

Be used for input beam is divided into respectively first beam splitter through first and second beamlet of first and second light paths;

Be positioned at first toroidal resonator of first light path, this resonator comprises at least two surface and the first's reflectings surface that belong to total reflection substantially, first's reflecting surface is injected first toroidal resonator with the part of first beamlet, and remaining first beamlet is reflected away, like this, the light that postpones through first resonance from first toroidal resonator mixes with remaining first beamlet, and formation first is the blend sub light beam again;

Be positioned at second toroidal resonator of second light path, this resonator comprises at least two surface and the second portion reflectings surface that belong to total reflection substantially, the second portion reflecting surface is injected second toroidal resonator with second a beamlet part, and remaining second beamlet is reflected away, like this, the light that postpones through second resonance from second toroidal resonator mixes with remaining second beamlet, and formation second is the blend sub light beam again;

Second beam splitter is used for receiving the first and second blend sub light beams again, thereby causes first and second interference of blend sub light beam again, and produces first and second output beams;

Be used for exporting first output port of first output beam; And

Be used for exporting second output port of second output beam.

2. device according to claim 1, wherein first beam splitter comprises that lip-deep first light beam of the substrate that is coated in substantial transparent cuts apart coating, this reflectivity range of cutting apart coating is between 43% to 50%.

3. device according to claim 2, wherein second beam splitter comprises that being coated in lip-deep second of substrate of cutting apart the adjacent substantial transparent of coating with first light beam cuts apart coating, this reflectivity range of cutting apart coating is between 43% to 50%.

4. device according to claim 3, wherein first's reflectance coating is painted on another surface of substrate of substantial transparent.

5. device according to claim 1, wherein first optical path length is meant from first beam splitter and returns the distance of second beam splitter to first toroidal resonator; Second optical path length is meant from first beam splitter and returns the distance of second beam splitter to second toroidal resonator; Wherein first resonance postpones to postpone to equate with second resonance; First optical path length has more half the distance that is equivalent to that first resonance postpones than second optical path length.

6. device according to claim 5, wherein the reflectivity of first's reflectance coating is between 42% to 50%.

7. device according to claim 6, wherein the reflectivity of second portion reflectance coating is between 2.4% to 5.2%.

8. device according to claim 1, wherein first toroidal resonator also comprises the adjustment sheet that is used for regulating optical path length.

9. device according to claim 7, wherein input beam comprises a plurality of wavelength division multiplexed channels; First output beam comprises first group of channel of described a plurality of channels, and second output beam comprises second group of channel of described a plurality of channels.

10. device according to claim 9, wherein first group of channel comprises one or more odd number ITU channels; Second group of channel comprises one or more even number ITU channels.

11. a Mach-Zehnder interferometer comprises:

Beam splitter is used for a branch of input beam is separated into first and second beamlets, and interferes arm and second to interfere directed first and second beamlets of arm along first of interferometer respectively;

Be positioned at first toroidal resonator that interferometer first is interfered arm, had the first resonance delay of the phase response that influences first beamlet;

Be positioned at second toroidal resonator that interferometer second is interfered arm, had the second resonance delay of the phase response that influences second beamlet;

Be used for interfering first and second beamlets to form the light beam mixer of first and second output beams.

12. device according to claim 11, wherein first toroidal resonator also comprises the adjustment sheet that is used for regulating optical path length.

13. device according to claim 11, wherein first resonance postpones to postpone to equate basically with second resonance, and first length of interfering arm has more than the length of the second interference arm and is equivalent to first half the distance of delay that resonates.

14. device according to claim 13, wherein input beam comprises a plurality of wavelength division multiplexed channels, and first output beam comprises first group of channel of described a plurality of channels, and second output beam comprises second group of channel of described a plurality of channels.

15. device according to claim 13, wherein first group of channel comprises one or more odd number ITU channels, and second group of channel comprises one or more even number ITU channels.

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