JP5510073B2 - Narrow band reflection filter and light modulator - Google Patents

Description

  The present invention relates to a narrow band reflection filter and an optical modulation device.

  In recent years, a modulator using a ring resonator (ring resonator type modulator) has been studied in order to reduce the size and drive voltage of a modulator for optical communication. A ring resonator type modulator has a structure in which a ring-shaped waveguide (ring waveguide) is coupled to a bus waveguide, and an electrode for modulating the refractive index of the waveguide is provided around the ring waveguide. Is formed.

  In a ring resonator type modulator, continuous light input from one end of a bus waveguide is intensity-modulated according to the voltage applied to the ring waveguide, and is output as modulated light from the other end. is there. In such a ring resonator type modulator, the resonance wavelength of the ring resonator changes depending on the ambient temperature, and the semiconductor laser or the like serving as a continuous light source also resonates depending on the ambient temperature. Wavelength changes. For this reason, an optical semiconductor device having a configuration in which a light source such as a semiconductor laser and a ring resonator are mounted on the same chip is disclosed.

  Moreover, as a wavelength tunable filter, a filter using a ring resonator, which splits light incident from an external element into two ports is disclosed.

JP 2010-27664 A International Publication No. 07/029647 Pamphlet

  As an optical element using such a ring resonator, a 4-port ring resonator type narrow band filter as shown in FIG. 1A and a 2-port ring resonator as shown in FIG. There is a mold all-pass filter. The 4-port ring resonator type narrowband filter shown in FIG. 1A is a filter corresponding to the resonance wavelength of the ring resonator 211, and the ring resonator 211 is close to the two waveguides 212 and 213. Has been placed. For this reason, four input / output units 212a, 212b, 213a, and 213b are provided. In addition, the two-port ring resonator type all-pass filter shown in FIG. 1B allows light of the wavelength of the waveguide to pass through the entire region, and the ring resonator 221 is close to one waveguide 222. Has been placed. For this reason, it has two input-output parts 222a and 222b. Note that the 2-port ring resonator type all-pass filter shown in FIG. 1B does not have a function of extracting a specific wavelength by itself.

  Incidentally, a waveguide made of silicon or the like used in silicon photonics or the like has a large refractive index difference from the periphery of the waveguide. Therefore, a manufacturing error in manufacturing the ring resonator and the waveguide greatly affects the characteristics of the optical element using the ring resonator. For this reason, when a 4-port ring resonator type narrowband filter and a 2-port ring resonator type all-pass filter are mixed with an optical element, the resonance wavelength is matched because both structures are different. It was difficult to do. In addition, in the 4-port ring resonator type narrowband filter, the ring resonator 211 needs to be disposed close to the two waveguides 212 and 213, and thus is more susceptible to manufacturing errors.

  Therefore, there is a need for a narrow band reflection filter and an optical modulation device that are not easily affected by manufacturing errors and that can be used stably even when environmental conditions and the like change.

According to one aspect of the present embodiment, a first coupler having two input / output ports on each of a first side and a second side for branching and coupling light, and a first coupler for branching and coupling light. A second coupler having two input / output ports on each of the first and second sides, a first coupler for branching and coupling light, and a third coupler having two input / output ports on the second side, respectively The one input / output port on the second side of the first coupler and the one input / output port on the first side of the second coupler are connected by a first waveguide. The other input / output port on the second side of the first coupler and the one input / output port on the first side of the third coupler are connected by a second waveguide. The two input / output ports on the second side of the second coupler are connected by a third waveguide, and the third coupler Two output ports of the second side of the plug is connected by a fourth waveguide, the third of the waveguide cavity to 180 ° shifts the phase of light of a predetermined resonant wavelength close to is disposed, said fourth waveguide be those not disposed proximate the cavity to 180 ° shifting the phase of light of a predetermined resonant wavelength, said first coupler Of the light incident on the first coupler from one input / output port on the first side, the light having the predetermined resonance wavelength whose phase is shifted by 180 ° in the third waveguide is The light emitted from one input / output port on the first side of one coupler, and the first coupler makes the incident light from the input / output port on the first side or the second side 1: 1. Branches equally, the second coupler and the third coupler. La is characterized in that the do not evenly splits the light incident from the first side or output ports of said second side.

  According to the disclosed reflection filter and light modulation device, it is less susceptible to manufacturing errors and less susceptible to temperature changes and the like, and thus can be used stably even when environmental conditions and the like change.

Explanatory diagram of ring resonator Structure diagram of narrowband reflection filter in the first embodiment Manufacturing process figure which shows the manufacturing method of the narrow-band reflective filter in 1st Embodiment Explanatory drawing of the waveguide and ring resonator in 1st Embodiment Structure diagram of light modulation device in first embodiment Structure diagram of light modulation device in second embodiment

  Modes for carrying out the invention will be described below.

[First Embodiment]
As a first embodiment, a narrow band reflection filter and an optical modulation device will be described. In the present embodiment, in a ring resonator or the like, a predetermined resonance wavelength (resonance point) is based on a phenomenon in which the phase is shifted by 180 °, and is formed by an optical coupler, a ring resonator, and the like and a waveguide. A narrow band reflection filter and a light modulation device having the reflection filter.

  The narrowband reflection filter in the present embodiment will be described based on FIG. The narrow-band reflection filter in the present embodiment includes a first coupler 20, a second coupler 30, a third coupler 40, a ring resonator 50, and a waveguide connecting them on the same chip (substrate) 1. Have. This narrow-band reflection filter is connected to an SOA (Semiconductor Optical Amplifier) 10 serving as a light source, and FIG. 2 shows an example in which the SOA 10 is provided on the chip 1.

  The SOA 10 is a reflective SOA, and includes a total reflection mirror 11 on one side, and is connected to the waveguide 12 on the other side where the total reflection mirror 11 is not provided.

  The first coupler 20 is a 2 × 2 coupler that branches and couples incident light 1: 1, and has ports 21 and 22 on one side (first side), and the other side (second side). I / O ports 23 and 24 are provided on the other side. The second coupler 30 is, for example, a 2 × 2 coupler that branches and couples incident light at 45:55, has input / output ports 31 and 32 on one side (first side), and the other side. Input / output ports 33 and 34 are provided on the (second side). The third coupler 40 is, for example, a 2 × 2 coupler that branches and couples incident light at 45:55, has input / output ports 41 and 42 on one side (first side), and the other side. Input / output ports 43 and 44 are provided on the (second side). It should be noted that the second coupler 30 and the third coupler 40 may have ratios other than those described above as long as the coupling ratio is slightly deviated from 1: 1, so that the ratio is optimal depending on the application and usage conditions. Is formed. The first coupler 20, the second coupler 30, and the third coupler 40 may be any optical coupler, and may be an MMI (Multi-Mode Interference) coupler or a structure having a waveguide close to each other. Is formed.

  One input / output port 21 of the first coupler 20 is connected to the waveguide 12, and light from the SOA 10 enters the first coupler 20 from the input / output port 21 via the waveguide 12. The light incident on the first coupler 20 from the input / output port 21 is branched in the first coupler 20, and the light incident on the waveguide 25 via the input / output port 23 and the waveguide 26 via the input / output port 24. It is divided into the light incident on.

The light incident on the waveguide 25 enters the second coupler 30 from the input / output port 31 on one side (first side) of the second coupler 30. In the second coupler 30, the other input / output ports 33 and 34 are connected to one waveguide 35. That is, one end of the waveguide 35 is connected to the input / output port 33, and the other end of the waveguide 35 is connected to the input / output port 34. Therefore, the light incident on the second coupler 30 from the input / output port 31 is branched in the second coupler 30, emitted from the input / output ports 33 and 34, and enters the waveguide 35. A ring resonator 50 is provided close to the waveguide 35, and the phase of the light having the resonance wavelength λ ₀ in the ring resonator 50 is shifted 180 ° (inverted 180 °) by the ring resonator 50. On the other hand, the phase of light having a wavelength other than the resonance wavelength λ ₀ is not shifted by the ring resonator 50. Thereafter, the light in the waveguide 35 enters the input / output ports 33 and 34 again, is coupled and branched in the second coupler 30, and is emitted from the input / output ports 31 and 32. At this time, the light extracted from the output port 32 to the waveguide 36 is affected by interference, so that the amount of light corresponds to the difference in the coupling ratio of the second coupler 30. On the other hand, the light emitted from the input / output port 31 enters the input / output port 23 of the first coupler 20 via the waveguide 25.

Further, the light incident on the waveguide 26 enters the third coupler 40 from the input / output port 41 on one side (first side) of the third coupler 40. In the third coupler 40, the other input / output ports 43 and 44 are connected to one waveguide 45. That is, one end of the waveguide 45 is connected to the input / output port 43, and the other end of the waveguide 45 is connected to the input / output port 44. Therefore, the light incident on the third coupler 40 from the input / output port 41 is branched in the third coupler 40, emitted from the input / output ports 43 and 44, and enters the waveguide 45. Since the ring resonator is not provided close to the waveguide 45, the phase does not shift. I.e., not the phase is 180 ° shifted in the optical wavelength lambda _0. Thereafter, the light in the waveguide 45 enters the input / output ports 43 and 44 again, is coupled and branched in the third coupler 40, and is emitted from the input / output ports 41 and 42. At this time, the light extracted from the input / output port 42 to the waveguide 46 is affected by interference, so that the amount of light corresponds to the difference in coupling ratio of the third coupler 40. On the other hand, the light emitted from the input / output port 41 enters the input / output port 24 of the first coupler 20 through the waveguide 26.

Of the light incident on the first coupler 20, the light having the wavelength λ ₀ , which is the resonance wavelength in the ring resonator 50, has a phase between the light incident from the input / output port 23 and the light incident from the input / output port 24. The phase is shifted by 180 °. For this reason, light is emitted from the input / output port 21 that first enters the first coupler 20 due to interference in the first coupler 20, and then enters the SOA 10 via the waveguide 12. Since the opposite side of the SOA10 total reflection mirror 11 is provided, the total reflection mirror 11 and the resonator by the narrow band reflection filter as described above is formed, in SOA10, light of the wavelength lambda ₀ is lasing. The narrow-band filter in the present embodiment, as functions as a mirror for light of a wavelength lambda _0.

On the other hand, among the light incident on the first coupler 20, the light having a wavelength other than the wavelength λ ₀ has the same phase as the light incident from the input / output port 23 and the light incident from the input / output port 24. Therefore, the light is emitted from the input / output port 22 different from the input / output port 21 that first enters the first coupler 20 due to interference in the first coupler 20. Therefore, since it does not return to the SOA 10, it does not enter the SOA 10 again.

  As described above, the narrow-band reflection filter in the present embodiment is formed by the first coupler 20, the second coupler 30, the third coupler 40, the ring resonator 50, and the waveguide connecting them, and is specified. It is possible to reflect only the light of the wavelength. Therefore, as described above, a laser is formed by combining this narrow-band reflection filter and the reflective SOA 10. Note that the narrowband reflection filter in the present embodiment does not need to be provided on the same chip 1 as the SOA 10, but by providing the SOA 10 and the narrowband reflection filter on the same chip 1, the temperature change can be further improved. It can be less susceptible.

(Production method)
Next, the manufacturing method of the narrow-band reflection filter in this Embodiment is demonstrated based on FIG.

First, an SOI (Silicon on Insulator) substrate 60 as shown in FIG. In this SOI substrate 60, a BOX layer 62 in which SiO ₂ having a thickness of about 3 μm is formed on a silicon (Si) substrate 61, and a silicon layer 63 having a thickness of about 250 nm are further formed.

  Next, as shown in FIG. 3B, a waveguide 70 is formed in the silicon layer 63. The waveguide 70 is an optical waveguide serving as a waveguide for light having a predetermined wavelength. The width A of the waveguide 70 is about 480 nm, and the height B is about 200 nm. Specifically, the waveguide 70 is formed by applying a photoresist on the silicon layer 63 and performing exposure and development with an exposure apparatus to form a resist pattern (not shown) in the region where the waveguide 70 is formed. Form. Thereafter, using this resist pattern as a mask, the silicon layer 63 in a region where the resist pattern is not formed is removed by dry etching such as RIE (Reactive Ion Etching). This dry etching by RIE or the like is performed until the thickness C of the silicon layer 63 in the region where the resist pattern is not formed becomes about 50 nm. Thereafter, by removing the resist pattern, a waveguide 70 having a rib structure having the rib region 71 is formed. At this time, in the waveguide 70, the distance D between the closest portions of the waveguide 35 connected to the input / output ports 33 and 34 of the second waveguide 30 and the waveguide of the ring resonator 50 is And about 150 nm.

Next, as illustrated in FIG. 3C, an interlayer insulating film 64 is formed on the waveguide 70 and the rib region 71. The interlayer insulating film 64 is formed by depositing a film made of SiO ₂ with a thickness of 1 μm by CVD (Chemical Vapor Deposition) or the like.

  The waveguide 70 formed in this way is a waveguide for the waveguides 12, 25, 26, 35, 36, 45, and 46 and the ring resonator 50 shown in FIG. Note that the first coupler 20, the second coupler 30, and the third coupler 40 can also be formed by the same method as the waveguide 70 described above when they are formed by waveguides. It becomes.

  The ring resonator 50 in the present embodiment may have a shape close to a perfect circle, or may have an elliptical shape or a racetrack shape. For example, the ring resonator 50 having the structure shown in FIG. 4 has a shape in which a linear portion having a radius of about 2.5 μm and a curved portion having a radius of curvature of about 7.2 μm are combined. At this time, the ring resonator 50 and the waveguide 35 are disposed closest to each other in the linear portion of the ring resonator 50, and the interval between the adjacent portions is about 150 nm.

Further, the resonator part in which the ring resonator 50 is formed may be a resonator having any structure as long as the phase of the light having the wavelength λ ₀ can be shifted by 180 °. Further, it may be a disk-type resonator having a structure having no opening at the center.

(Light modulation device)
Next, the light modulation device in the present embodiment will be described with reference to FIG. This light modulation device is a light modulation device having the above-described narrow-band reflection filter. On the same chip (substrate) 2, the above-described narrow-band reflection filter, the first modulator 80 connected to the waveguide 36, and the waveguide are connected. A second modulator 90 connected to the waveguide 46 is included. The first modulator 80 and the second modulator 90 have the same structure and are Mach-Zehnder (MZ) type modulators.

  Specifically, the first modulator 80 includes a coupler 81, waveguides 82 and 83 branched by the coupler 81, and a coupler 84 connected to the waveguides 82 and 83. A ring resonator group 85 is provided adjacent to the waveguide 82, and a ring resonator group 86 is provided adjacent to the waveguide 83. The ring resonator groups 85 and 86 serve as phase shifters. The ring resonator group 85 is formed by ring resonators 85a, 85b, and 85c, and the ring resonator group 86 includes ring resonators 86a, 86b, and 86c. Thereby, the phase of light can be efficiently shifted at the resonance wavelength.

  Similarly, the second modulator 90 includes a coupler 91, waveguides 92 and 93 branched by the coupler 91, and a coupler 94 connected to the waveguides 92 and 93. A ring resonator group 95 is provided adjacent to the waveguide 92, and a ring resonator group 96 is provided adjacent to the waveguide 93. The ring resonator groups 95 and 96 serve as phase shifters. The ring resonator group 95 is formed by ring resonators 95a, 95b, and 95c, and the ring resonator group 96 includes ring resonators 96a, 96b, and 96c. Thereby, the phase of light can be efficiently shifted at the resonance wavelength. In FIG. 5, as an example, a case where a ring resonator group is formed by three ring resonators each is shown.

  In addition, since the first modulator 80 and the second modulator 90 are formed of a waveguide, a coupler, and a ring resonator, they can be simultaneously manufactured by the same method as the narrow-band reflection filter in the present embodiment. Is possible. In the present embodiment, the light modulation device having the first modulator 80 and the second modulator 90, that is, the light modulation device having two modulators has been described. However, the light modulation device having three or more modulators is provided. It may be a light modulation device.

  In the light modulation device of the present embodiment, all ring resonators are formed on the same chip, and the ring resonators 95a, 96a, 50 are all formed in the same shape, and each waveguide The distance from is also formed at substantially the same interval. In this way, by forming all ring resonators with the same shape, etc., errors during manufacturing can be minimized, and there are factors that change optical characteristics such as temperature changes. In this case, it is possible to realize a stable operation as much as possible. Similarly to the case shown in FIG. 2, by arranging the SOA 10 on the chip 2, it is possible to further improve the response to the temperature change.

[Second Embodiment]
Next, a second embodiment will be described. The light modulation device in the present embodiment has a structure having the narrow band reflection filter in the first embodiment, and is a light modulation device having one MZ type modulator.

  The light modulation device in the present embodiment will be described with reference to FIG. The light modulation device in the present embodiment includes a coupler (fourth coupler) 110 in which the narrowband reflection filter, the waveguides 36 and 46 in the first embodiment are connected, and a ring on the same chip (substrate) 101. A resonator group 121 and a ring resonator group 122 are provided. The ring resonator group 121 is disposed in the vicinity of the waveguide 36, and the ring resonator group 122 is disposed in the vicinity of the waveguide 46. The ring resonator groups 121 and 122 serve as phase shifters. The ring resonator group 121 is formed by ring resonators 121a, 121b, and 121c, and the ring resonator group 122 includes ring resonators 122a, 122b, 122c and 122d. As a result, the phase can be efficiently shifted at the resonance wavelength. In the present application, the waveguide 36 may be referred to as a fifth waveguide, and the waveguide 46 may be referred to as a sixth waveguide. The waveguide 36 and the waveguide 46 may be one of the couplers (fourth couplers) 110. Is connected to one input / output port 111 and the other input / output port 112 on the side (first side).

  In the present embodiment, the ring resonator group 121 is formed by three ring resonators 121a, 121b, and 121c. However, the ring resonator group 122 includes four ring resonators 122a, 122b, 122c and 122d. This is because the light from the waveguide 36 is light modulated by the ring resonator 50, so that the light passing through the waveguide 36 and the light passing through the waveguide 46 have the same number in order to further improve the stability of characteristics and the like. This is to be modulated by the ring resonator. The light modulation device in the present embodiment has a structure having one MZ modulator, but the number of couplers can be reduced by one compared to the light modulation device in the first embodiment. it can.

  Although the embodiment has been described in detail above, it is not limited to the specific embodiment, and various modifications and changes can be made within the scope described in the claims.

In addition to the above description, the following additional notes are disclosed.
(Appendix 1)
A first coupler having two input / output ports each on a first side and a second side for branching and coupling light;
A second coupler having two input / output ports each on a first side and a second side for branching and coupling light;
A third coupler having two input / output ports each on a first side and a second side for branching and coupling light;
One input / output port on the second side of the first coupler and one input / output port on the first side of the second coupler are connected by a first waveguide. The other input / output port on the second side of the first coupler and the one input / output port on the first side of the third coupler are connected by a second waveguide,
The two input / output ports on the second side of the second coupler are connected by a third waveguide, and the two input / output ports on the second side of the third coupler are the fourth input / output ports. Connected by waveguides,
A resonator that shifts a predetermined wavelength by 180 ° is disposed close to the third waveguide, and a resonator that shifts a predetermined wavelength by 180 ° is disposed close to the fourth waveguide. A narrow-band reflection filter characterized by not being made.
(Appendix 2)
The narrowband reflection filter according to appendix 1, wherein the resonator is a ring resonator or a disk resonator.
(Appendix 3)
A reflective SOA is connected to one input / output port on the first side of the first coupler on a surface opposite to a surface on which a mirror is formed in the reflective SOA. The narrowband reflection filter according to Supplementary Note 1 or 2, which is characterized by the following.
(Appendix 4)
The first coupler, the second coupler, the third coupler, and the resonator are formed on the same substrate as the SOA, according to any one of appendices 1 to 3, Narrow band reflection filter.
(Appendix 5)
The first coupler branches the light incident from the input / output port on the first side or the second side evenly in a ratio of 1: 1, and includes the second coupler and the third coupler. The narrowband reflection filter according to any one of appendices 1 to 4, wherein the coupler does not equally split light incident from the input / output port on the first side or the second side.
(Appendix 6)
The narrowband reflective filter according to appendix 5,
A first optical module connected via a waveguide to the other input / output port on the first side of the second coupler;
A second optical module connected via a waveguide to the other input / output port on the first side of the third coupler;
An optical modulation device comprising:
(Appendix 7)
The optical modulator according to appendix 6, wherein the first optical module and the second optical module are Mach-Zehnder type modulators.
(Appendix 8)
The optical modulator according to appendix 6 or 7, wherein a plurality of the third coupler and the second optical module or a plurality of the second coupler and the first optical module are provided.
(Appendix 9)
The narrowband reflective filter according to appendix 5,
A fifth waveguide connected to the other input / output port on the first side of the second coupler;
A sixth waveguide connected to the other input / output port on the first side of the third coupler;
A resonator provided proximate to the fifth waveguide;
A resonator provided proximate to the sixth waveguide;
A fourth coupler in which the fifth waveguide and one input / output port on the first side are connected, and a fourth coupler in which the sixth waveguide and the other input / output port on the first side are connected; ,
An optical modulation device comprising:
(Appendix 10)
There are a plurality of resonators provided close to the sixth waveguide, and they are closer to the sixth waveguide than the number of resonators provided close to the fifth waveguide. The light modulation device according to appendix 9, wherein the number of resonators provided is one larger.

1 Chip (substrate)
10 SOA
DESCRIPTION OF SYMBOLS 11 Total reflection mirror 12 Waveguide 20 1st coupler 21, 22, 23, 24 Input / output port 25 Waveguide (1st waveguide)
26 Waveguide (second waveguide)
30 Second coupler 31, 32, 33, 34 Input / output port 35 Waveguide (third waveguide)
36 Waveguide 40 Third coupler 41, 42, 43, 44 Input / output port 45 Waveguide (fourth waveguide)
46 Waveguide 50 Ring resonator

Claims (4)

A first coupler having two input / output ports each on a first side and a second side for branching and coupling light;
A second coupler having two input / output ports each on a first side and a second side for branching and coupling light;
A third coupler having two input / output ports each on a first side and a second side for branching and coupling light;
One input / output port on the second side of the first coupler and one input / output port on the first side of the second coupler are connected by a first waveguide. The other input / output port on the second side of the first coupler and the one input / output port on the first side of the third coupler are connected by a second waveguide,
The two input / output ports on the second side of the second coupler are connected by a third waveguide, and the two input / output ports on the second side of the third coupler are the fourth input / output ports. Connected by waveguides,
Wherein the third waveguide are arranged close to each resonator to 180 ° shifting the phase of light of a predetermined resonant wavelength, said fourth predetermined phase of the light resonance wavelength in the waveguide 180 ° the resonators to be shifted are not placed close together ,
Of the light incident on the first coupler from one input / output port on the first side of the first coupler, the phase of the light is shifted by 180 ° in the third waveguide. Light of a wavelength is emitted from one input / output port on the first side of the first coupler;
The first coupler branches the light incident from the input / output port on the first side or the second side evenly in a ratio of 1: 1, and includes the second coupler and the third coupler. The narrow band reflection filter according to claim 1, wherein the coupler does not evenly split the light incident from the input / output port on the first side or the second side .   The narrow band reflection filter according to claim 1, wherein the resonator is a ring resonator or a disk resonator. The narrow-band reflection filter according to claim 1 or 2 ,
A first optical module connected via a waveguide to the other input / output port on the first side of the second coupler;
A second optical module connected via a waveguide to the other input / output port on the first side of the third coupler;
It has a first light module is a one which shifts the phase of light of the predetermined resonance wavelength, the second optical module der Rukoto which shifts the phase of light of the predetermined resonance wavelength A light modulation device characterized by the above. The narrow-band reflection filter according to claim 1 or 2 ,
A fifth waveguide connected to the other input / output port on the first side of the second coupler;
A sixth waveguide connected to the other input / output port on the first side of the third coupler;
A resonator provided proximate to the fifth waveguide;
A resonator provided proximate to the sixth waveguide;
A fourth coupler in which the fifth waveguide and one input / output port on the first side are connected, and a fourth coupler in which the sixth waveguide and the other input / output port on the first side are connected; ,
An optical modulation device comprising:

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