JP5902633B2 - Mach-Zehnder multiplexing / demultiplexing filter - Google Patents

Description

  The present invention relates to a Mach-Zehnder multiplexing / demultiplexing filter having a function of multiplexing / demultiplexing light of a plurality of wavelengths used for optical communication, and it is easy to design and adjust a delay amount set in a delay circuit of a Mach-Zehnder interferometer. It has been devised to be able to.

  In recent years, not only long-distance transmission but also the opticalization of LAN is progressing so as to support high-speed transmission of a LAN (Local Area Network). The 100Gbps Ethernet (registered trademark) specification has already been formulated, and optical signals of 4 waves (4 different wavelengths) are transmitted as 100GBASE-LR4 and 100GBASE-ER4, respectively, transmitting 10km and 40km using single mode optical fiber. Is used to achieve 25 Gbps x 4 = 100 Gbps data transmission by transmitting approximately 25 Gbps at each wavelength.

As described above, in light of the opticalization aiming at increasing the capacity of the LAN, in a transmission system of a system that transmits four-wave optical signals using a single optical fiber, 4 A DFB (distributed feedback) laser and modulator are integrated (see Non-Patent Document 1).
The light source shown in Non-Patent Document 1 has a configuration in which four lasers that output four standard-wave lights are integrated on one chip, and each of the bulk components is connected to form a light source for four waves. This is expected to reduce power consumption because it can be made smaller and the number of temperature control mechanisms can be reduced.

  However, in the configuration of Non-Patent Document 1, a 4 × 1 MMI coupler (a multimode interference coupler with four inputs and one output) is used as a four-wave multiplexer. When the 4 × 1 MMI coupler is used as a 4-wave multiplexer, there is a 6 dB loss as a principle loss. That is, in principle, only 25% of the output can be extracted outside, so much light is wasted.

  Therefore, attempts have been made to replace the multiplexing filter (multiplexer) with a low-loss filter. Arrayed waveguide gratings (AWG: arrayed waveguide gratings) and etched planar concave gratings (PCGs) are known as multiplexing filters used in such places, but AWGs and PCGs are four-wave MUXs (Multiplexers). : Mixer) The size of the filter becomes large.

  Therefore, a combination filter (Mach-Zehnder multiplexing / demultiplexing filter) using a Mach-Zehnder interferometer including a delay circuit is conceivable. When combining four light beams, a multiplexing filter can be realized with two first-stage Mach-Zehnder interferometers and one second-stage Mach-Zehnder interferometer (see FIG. 6 described later). There is an advantage that the size can be reduced as compared with AWG and PCGs.

T. Fujisawa et al, “1.3-μm 4 × 25-Gb / s Monolithically Integrated Light Source for Metro Area 100-Gb / s Ethernet”, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 23, NO. 6, MARCH 15, 2011 K. Watanabe et al., "Trimming of InP-based Mach-Zehnder interferometer by filling side cladding of high-mesa waveguide with resin", Electronics letters, VOL. 47, NO. 22, 2011

  There are two problems that arise when combining Mach-Zehnder interferometers in multiple stages to form a multiplexing filter.

One problem is absolute wavelength. The FSR (Free Spectral Range) is hardly deviated from the design due to the manufacturing error, but the absolute wavelength greatly varies depending on the manufacturing error.
For this, a mechanism for adjusting by some method after manufacture may be provided. For example, as shown in Non-Patent Document 2, there is a method of adjusting a side surface of a semiconductor high mesa waveguide by filling a resin.

When combining four light beams, at least two Mach-Zehnder interferometers in the first stage are required (Note that the MMI coupler and Y-branch splitter are used in the second stage, even if they are not Mach-Zehnder interferometers. can do).
In this case, the delay amount set for the first Mach-Zehnder interferometer at the first stage and the delay amount set for the second Mach-Zehnder interferometer at the first stage are finely adjusted so that a phase difference of 90 ° is obtained. That is, the first and second Mach-Zehnder interferometers so that the phase difference between the light output from the first Mach-Zehnder interferometer and the light output from the second Mach-Zehnder interferometer is 90 °. It is necessary to finely adjust the delay amount set to. This fine adjustment is another problem.

  Here, the operation of the Mach-Zehnder interferometer filter will be described. The numerical values and materials shown below are examples, and other numerical values and materials may be used.

Here, a waveguide has a high mesa structure with InGaAsP formed on an InP semiconductor substrate as a core, and λ1 = 1295.5 nm, λ2 = 1300.0 nm, λ3 = 1304.5 nm, λ4 = 1309 nm in a wavelength (λ) 1.3 μm band. A multiplexing filter that combines the four light beams will be described.
In this specification, λ (λ1, λ2, λ3, λ4) is used to indicate different light and also indicate the wavelength of each light. For example, λ1 indicates one light and also indicates that the wavelength of this light is λ1.

FIG. 4 is a diagram showing one Mach-Zehnder interferometer 1. The Mach-Zehnder interferometer 1 includes a pair of (upper and lower) arm waveguides that connect two input waveguides 2a and 2b, two 3dB couplers 3a and 3b, and 3dB coupler 3a and 3dB coupler 3b. 4a and 4b and two output waveguides 5a and 5b. The arm waveguides 4a and 4b are formed with delay circuits for adding a phase difference to the light passing through the both waveguides. The delay circuit, and is formed by the difference between the length of the upper arm waveguide 4 a length and a lower arm waveguide 4 b.

  Now, assuming that the effective refractive index of the arm waveguides 4a and 4b forming the delay circuit is 3.243 (ignoring chromatic dispersion characteristics), the amount of delay (the length of the upper arm waveguide 4a and the lower arm waveguide 4b Length difference) ΔL1 is assumed to be 28.056 μm.

When white light (broad light) is input from the input waveguide 2a, the spectrum of the light that appears in the output waveguides 5a and 5b is obtained by calculation as shown in FIG.
The output 1 from the output waveguide 5a is indicated by a solid line, and the output 2 from the output waveguide 5b is indicated by a dotted line. The output 1 is ON, that is, the light passes through at a wavelength of 1.309 μm of λ4, and has a characteristic of being blocked in the vicinity of λ2 = 1.300 μm. At output 2, they are inverted.
In this case, the case where white light is input from the input waveguide 2a has been described. However, light λ2 having a wavelength of 1.300 μm is input from the input waveguide 2a and light λ4 having a wavelength of 1.309 μm is input from the input waveguide 2b due to reciprocity of the light. It can be seen that both light λ2 and λ4 are combined and output to the output 1 from the output waveguide 5a.

  When trying to multiplex the light of λ1 and λ3, it is necessary to give the delay circuit a phase difference of 90 ° with respect to the characteristic of FIG. 5A as the delay amount. If calculated as 27.959 μm, the light of λ1 and λ3 can be multiplexed this time, and the characteristic of FIG. 5B is obtained.

  In order to further multiplex the combination of light of λ1 and λ3 with the combination of light of λ2 and λ4, the delay amount ΔL is a value ΔL3 = 56.112 μm, which is twice the delay amount ΔL1 when the previous combination of λ2 and λ4 is combined. When set, characteristics as shown in FIG. 5C are obtained.

Therefore, as in the Mach-Zehnder multiplexing / demultiplexing filter shown in FIG. 6, the delay amount is ΔL2 with the first Mach-Zehnder interferometer 1A of the first stage of the 2-input 2-output in which the delay amount is ΔL1. The second Mach-Zehnder interferometers 1B in the first stage of the 2-input 2-outputs are arranged, and the outputs of the first and second Mach-Zehnder interferometers 1A, 1B are respectively 2-input 2 with a delay amount ΔL3. By adopting a configuration in which the output is input to the third Mach-Zehnder interferometer 1C at the second stage, it is possible to multiplex four lights of λ1, λ2, λ3, and λ4 into one waveguide. .
In FIG. 6, in indicates an input port, out indicates an output port, and mo indicates a monitor port.

  As described above, the first Mach-Zehnder interferometer 1A in the first stage and the second Mach-Zehnder interferometer 1B in the first stage are very similar in the configuration in which the delay amount ΔL is slightly different. A shifted relationship with a phase difference of 90 ° is required.

  However, it is very difficult to actually make this. First, the design is complicated because the delay amount ΔL must be changed slightly. Also in manufacturing, it is very difficult to reproduce the delicate delay amount ΔL added in the design. Even if the two Mach-Zehnder interferometers 1A and 1B in the first stage have a phase relationship of 90 °, if the absolute wavelength does not match, trimming will be performed by some method, but each is different. Therefore, there is a problem that the 90 ° phase shift is broken again.

This delay amount depends on the refractive index of the material composing the waveguide, but in the case of a circuit using a semiconductor, it is only about 100 nm (if the wavelength is 1.3 μm in a vacuum, it is 1 / 3, and a phase difference of 90 °, that is, a quarter wavelength, which is about 100 nm). The difference in the delay amount is only about several hundred nm, and the actual lengths of the upper arm and the lower arm necessary for generating the delay amount are actually longer. Nevertheless, the two first-stage Mach-Zehnder interferometers 1A and 1B must be designed with a slight difference of 0.1 μm due to design differences, and must be manufactured with good yield.

  In addition, since the delay amounts of the first and second Mach-Zehnder interferometers 1A and 1B in the first stage are different, when the temperature of the outside air where the element is placed changes, the absolute wavelength also shifts. There arises a problem that the interval between the transmission wavelengths indicated by the Zender interferometers 1A and 1B is also relatively shifted. That is, when a Mach-Zehnder interferometer with a slightly changed delay is used for the first-stage multiplexer, the temperature characteristics of the first-stage Mach-Zehnder interferometer 1A and the first-stage second Mach-Zehnder interferometer 1B are the same. Different between.

  Furthermore, even if the absolute wavelength is adjusted after manufacturing by some method, the delay amount itself is different between the first Mach-Zehnder interferometer 1A in the first stage and the second Mach-Zehnder interferometer 1B in the first stage. Different. In this way, different adjustment amounts are required, and there is a problem that adjustment takes time.

  In view of the above prior art, the present invention is designed and adjusted for the delay amount set in order to set the phase difference between the first and second Mach-Zehnder interferometers of the first stage in the Mach-Zehnder multiplexing / demultiplexing filter to 90 °. It is an object of the present invention to provide a Mach-Zehnder multiplexing / demultiplexing filter that can be easily performed.

The configuration of the present invention that solves the above problems includes a first Mach including a first coupler, a second coupler, and a pair of arm waveguides that connect the first coupler and the second coupler. A Zender interferometer,
A second Mach-Zehnder interferometer comprising a third coupler, a fourth coupler, and a pair of arm waveguides connecting the third coupler and the fourth coupler;
A multiplexer / demultiplexer connected to the second coupler and the fourth coupler;
In a Mach-Zehnder multiplexing / demultiplexing filter that combines and demultiplexes light of four different wavelengths
The delay amount of the delay circuit formed by the arm waveguide of the first Mach-Zehnder interferometer is the same as the delay amount of the delay circuit formed by the arm waveguide of the second Mach-Zehnder interferometer,
The first coupler, the second coupler, and the third coupler are two-input two-output couplers, and the fourth coupler is a two-input one-output coupler. .

  In the configuration of the invention, the multiplexer / demultiplexer is any one of a Mach-Zehnder interferometer, an MMI coupler, and a Y-branch splitter.

  Further, in the configuration of the present invention, each of the first coupler, the second coupler, and the third coupler is any one of an MMI coupler and a directional coupler, and the fourth coupler is: It is one of an MMI coupler and a Y-branch splitter.

In the configuration of the present invention, the fourth coupler is an MMI coupler, and a monitoring waveguide is provided at the end of the body of the fourth coupler adjacent to the output waveguide of the MMI coupler. It is characterized by being.

In the present invention, in the Mach-Zehnder multiplexing / demultiplexing filter constituted by the first-stage first and second Mach-Zehnder interferometers and the second-stage multiplexing / demultiplexing filter, Although the delay amount of the Mach-Zehnder interferometer is the same, by devising the coupler type of the first and second Mach-Zehnder interferometers, the phase difference between the first and second Mach-Zehnder interferometers is 90 °. I have to.
As described above, since the delay amounts of the first and second Mach-Zehnder interferometers are the same, fine adjustment of the design of the delay circuit becomes unnecessary, and the delay amount can be easily designed and adjusted. Further, when trimming, the same amount of trimming may be performed on the first and second Mach-Zehnder interferometers, and the trimming can be easily performed. Furthermore, the temperature characteristics of the first and second Mach-Zehnder interferometers are also equal.

The block diagram which shows the light source provided with the Mach-Zehnder multiplexing / demultiplexing filter which concerns on Example 1 of this invention. The block diagram which expands and shows the Mach-Zehnder multiplexing / demultiplexing filter used in Example 1. FIG. The block diagram which shows the light source provided with the Mach-Zehnder multiplexing / demultiplexing filter which concerns on Example 2 of this invention. The block diagram which shows one Mach-Zehnder interferometer. The characteristic view which shows the output characteristic of a Mach-Zehnder interferometer. The block diagram which shows the conventional Mach-Zehnder multiplexing / demultiplexing filter.

  Hereinafter, a Mach-Zehnder multiplexing / demultiplexing filter according to the present invention will be described in detail based on examples.

[Example 1]
FIG. 1 is a configuration diagram illustrating a monolithic integrated light source 10 for 100 GbE including a Mach-Zehnder multiplexing / demultiplexing filter 100 according to a first embodiment of the present invention.
The light source 10 includes a semiconductor laser section (Laser diode section: LD section) 200, an electroabsorption modulator section (Electroabsorption modulator section: EAM section) 300, a photodiode section (PhotoDiode section: PD section) 400, and a multi-stage It consists of a Mach-Zehnder multiplexing / demultiplexing filter 100 using a Mach-Zehnder interferometer.
The Mach-Zehnder multiplexing / demultiplexing filter 100 has a function of multiplexing and demultiplexing light. However, as shown in FIG. 100 functions as a multiplexer.

The Mach-Zehnder multiplexing / demultiplexing filter 100 includes two first-stage Mach-Zehnder interferometers 110 and 120 and a second-stage Mach-Zehnder interferometer (multiplexing / demultiplexing device) 130.
The LD unit 200 is configured by four semiconductor lasers LD1, LD2, LD3, and LD4 that generate four light beams, for example, λ1 = 1295.5 nm, λ2 = 1300.0 nm, λ3 = 1304.5 nm, and λ4 = 1309 nm.
The EAM unit 300 includes four electroabsorption modulators EAM1, EAM2, EAM3, and EAM4.
The PD unit 400 includes four photodiodes PD1, PD2, PD3, and PD4.

The lights λ1, λ2, λ3, and λ4 output from the semiconductor lasers LD1, LD2, LD3, and LD4 are modulated by the electroabsorption modulators EAM1, EAM2, EAM3, and EAM4, and then the Mach-Zehnder multiplexing / demultiplexing filter 100. And is combined by passing through the Mach-Zehnder multiplexing / demultiplexing filter 100 as will be described later.
Lights λ1, λ2, λ3, and λ4 output from the semiconductor lasers LD1, LD2, LD3, and LD4 are detected by the photodiodes PD1, PD2, PD3, and PD4.

The LD unit 200 is formed by forming an n-InP clad, an InAlGaAs barrier, an LD multiple quantum well active layer composed of an InAlGaAs quantum well, and a p-InP clad on an n-type InP substrate.
The EAM unit 300 is formed by forming an n-InP clad, an InGaAsP guide layer, an InAlGaAs barrier, an EAM multiple quantum well active layer composed of an InAlGaAs quantum well, and a p-InP clad on an n-type InP substrate.
The core layer and upper and lower cladding layers of the passive part (Mach-Zehnder multiplexing / demultiplexing filter) 100 have the same configuration as that of the EAM part 300, but there is no upper electrode for insulation.

  Here, the active layer of the LD unit 200 uses a multiple quantum well structure such that the band gap wavelength is 1.3 μm, and the active layer of the EAM unit 300 has a band gap wavelength of the well layer that is detuned from the LD unit 200. Is used such that the wavelength between the first quantization levels is 1.23 μm for a given strain so that the thickness becomes 70 nm at room temperature.

  For the passive part (Mach-Zehnder multiplexing / demultiplexing filter) 100, the core layer is InGaAsP with a band gap wavelength of 1.15 μm, and the lower cladding is n-InP. The composition of the barrier material is assumed to lattice match with the substrate, but there is no problem even if strain is introduced into the barrier layer for the purpose of strain compensation. The composition ratio of the semiconductor mixed crystal is specified by the strain amount, the well width, and the wavelength between the first quantization levels. However, the composition ratio is not an important matter in the present invention and will not be specifically described here.

Next, a method for manufacturing the light source 10 in which the modulators according to this embodiment are integrated will be described.
First, a lower clad and an active part of the LD part 200 are grown on an n-type InP substrate. The portions other than the necessary portion of the LD portion 200 are etched by wet etching, and the core layer of the active portion and the passive portion (Mach-Zehnder multiplexing / demultiplexing filter) 100 of the EAM portion 300 is regrown by butt joint.

  Furthermore, the core part of the passive part (Mach-Zehnder multiplexing / demultiplexing filter) 100 is cut by etching except the necessary parts of the LD part 200, the EAM part 300, and the passive part (Mach-Zehnder multiplexing / demultiplexing filter) 100. The butt joint regrowth.

  After forming a diffraction grating in the LD section 200, a p-InP upper clad is grown by 2 μm, and further a p-InGaAs contact layer is grown, so that the semiconductor laser section 200, the electroabsorption modulator section 300, the Mach-Zehnder A wafer for forming the multiplexing / demultiplexing filter 100 is completed.

  Here, if the multi-stage Mach-Zehnder multiplexing / demultiplexing filter 100 is formed as it is, the upper clad is p-InP, so that the loss of light is large and the emitted light power is reduced. Therefore, here, the upper clad of the passive part (Mach-Zehnder multiplexing / demultiplexing filter) 100 is further etched away from this state, and non-doped InP is regrown by butt joint.

  In the completed wafer, the LD unit 200, the EAM unit 300, the passive unit (Mach-Zehnder multiplexing / demultiplexing filter) 100, and the PD unit 400 are subjected to a ridge waveguide forming process, and the passive unit (Mach-Zehnder multiplexing / demultiplexing filter) ) 100 is subjected to a high mesa waveguide forming process and an electrode forming process, and after cleaving, a non-reflective coating is applied to the front and rear end faces of the chip, thereby completing the light source 10 as an element.

FIG. 2 is an enlarged configuration diagram of only the Mach-Zehnder multiplexing / demultiplexing filter 100 which is a passive portion in the present invention.
The Mach-Zehnder multiplexing / demultiplexing filter 100 has the same delay amount as ΔL1 (= 28.056 μm), compared with the first stage Mach-Zehnder interferometer 110 having a delay amount of ΔL1 (= 28.056 μm). The second stage Mach-Zehnder interferometer 120 and the second stage Mach-Zehnder interferometer 130 whose delay amount is ΔL3 (= ΔL1 × 2 = 56.112 μm).
The second-stage Mach-Zehnder interferometer 130 is connected to the first-stage first and second Mach-Zehnder interferometers 110, 120 and is output from the first and second Mach-Zehnder interferometers 110, 120. Are combined.

  As described above, it is one feature of the present invention that the delay amounts of the first and second Mach-Zehnder interferometers 110 and 120 in the first stage are set to the same delay amount ΔL1.

The first stage Mach-Zehnder interferometer 110 includes two input waveguides 112a and 112b, a 2 × 2 MMI type first coupler 113a, a 2 × 2 MMI type second coupler 113b, It consists of a pair of arm waveguides 114a and 114b connecting the coupler 113a and the second coupler 113b, and two output waveguides 115a and 115b.
The length of the arm waveguide 114a is different from the length of the arm waveguide 114b so as to form a delay circuit having a delay amount ΔL1.

The output waveguide 115 a is connected to the input side of the second stage Mach-Zehnder interferometer 130. That is, the Mach-Zehnder interferometer 130 is connected to the second coupler 113b of the Mach-Zehnder interferometer 110 through the output waveguide 115a.
The output waveguide 115b extends as a waveguide to the end of the chip and serves as a monitoring port mo. Through this monitoring port, the characteristics of the first Mach-Zehnder interferometer 110 in the first stage can be evaluated.

The second stage Mach-Zehnder interferometer 120 includes two input waveguides 122a and 122b, a 2 × 2 MMI-type third coupler 123a, a 2 × 1 MMI-type fourth coupler 123b, It comprises a pair of arm waveguides 124a, 124b connecting the coupler 123a and the fourth coupler 123b, and one output waveguide 125a.
The length of the arm waveguide 124a is different from the length of the arm waveguide 124b so as to form a delay circuit having a delay amount ΔL1.

  The output waveguide 125 a is connected to the input side of the second stage Mach-Zehnder interferometer 130. That is, the Mach-Zehnder interferometer 130 is connected to the fourth coupler 123b of the Mach-Zehnder interferometer 120 through the output waveguide 125a.

  Thus, in the first Mach-Zehnder interferometer 110 in the first stage, the second coupler 113b is a 2 × 2 MMI type coupler, whereas in the second Mach-Zehnder interferometer 120 in the first stage, It is another feature of the present invention that the fourth coupler 123b is not a 2 × 2 MMI type coupler but a 2 × 1 MMI type coupler.

  When a 90 ° phase difference is provided between the first Mach-Zehnder interferometer at the first stage and the second Mach-Zehnder interferometer at the first stage, as described above, the first and second Mach-Zehnders are conventionally used. The amount of delay of the Zender interferometer was adjusted.

On the other hand, in the configuration of this embodiment,
(Α) Although the delay amounts of the first and second Mach-Zehnder interferometers 110 and 120 in the first stage are also ΔL1,
(Β) The second coupler 113b of the first Mach-Zehnder interferometer 110 is a 2 × 2 MMI type coupler, whereas the fourth coupler 123b of the second Mach-Zehnder interferometer 120 is 2 × 2 It is a 2 × 1 MMI type coupler, not a 2MMI type coupler.

By adopting the above configurations (α) and (β), the phase difference between the first and second Mach-Zehnder interferometers 110 and 120 in the first stage is set to 90 °. That is, the phase difference between the light output from the first Mach-Zehnder interferometer 110 and the light output from the second Mach-Zehnder interferometer 120 is set to 90 °.
This is configured by paying attention to the fact that the phase difference differs by 90 ° between when light passes through a 2 × 2 MMI type coupler and when light passes through a 2 × 1 MMI type coupler. That is, it is configured by paying attention to the fact that the amount of delay of light generated when light passes through a 2 × 1 MMI type coupler is π / 2 as a phase amount.

The second-stage Mach-Zehnder interferometer (multiplexer / demultiplexer) 130 includes two input waveguides 132a and 132b, a second coupler 133a of 2 × 2 MMI type, and a sixth coupler of 2 × 2 MMI type. 133b, a pair of arm waveguides 134a and 134b connecting the fifth coupler 133a and the sixth coupler 133b, and two output waveguides 135a and 135b.
The length of the arm waveguide 134a is different from the length of the arm waveguide 134b so as to form a delay circuit having a delay amount ΔL3.

  The output waveguide 135a extends as a waveguide to the end of the chip and serves as a monitoring port mo. Through this monitoring port, the characteristics of the second stage Mach-Zehnder interferometer 130 can be evaluated. The output waveguide 135b extends as a waveguide to the end of the chip and serves as an output port out.

In the Mach-Zehnder multiplexing / demultiplexing filter 100 configured as described above, the light λ2 and λ4 input to the first Mach-Zehnder interferometer 110 at the first stage are combined by passing through the Mach-Zehnder interferometer 110. And input to the second stage Mach-Zehnder interferometer 130.
Lights λ1 and λ3 input to the second stage Mach-Zehnder interferometer 120 are combined by passing through the Mach-Zehnder interferometer 120 and input to the second stage Mach-Zehnder interferometer 130.

The combined light λ2, λ4 that passes through the first Mach-Zehnder interferometer 110 at the first stage and is input to the Mach-Zehnder interferometer 130 at the second stage, and the second Mach-Zehnder interferometer 120 at the first stage. The phase difference between the combined lights λ1 and λ3 that pass through and input to the second stage Mach-Zehnder interferometer 130 is 90 °.
Therefore, the light λ2, λ4 and the light λ1, λ3 input to the second-stage Mach-Zehnder interferometer 130 are combined by passing through the second-stage Mach-Zehnder interferometer 130, and the output waveguide 135b and It is output via the output port out. That is, four light beams λ2, λ4, λ1, and λ3 are combined and output.

  In order to make the phase difference between the first and second Mach-Zehnder interferometers 110 and 120 in the first stage 90 °, the advantage obtained by adopting the configuration shown in the above (α) and (β) is It is as follows.

When a phase difference of only 90 ° is given between the first and second Mach-Zehnder interferometers 110 and 120, it is not necessary to adjust the delay amount of each Mach-Zehnder interferometer 110 and 120, and the same design may be used. Also, it can be designed very efficiently.
Compared to the case where the delay amount is adjusted and the phase difference between the first and second Mach-Zehnder interferometers is adjusted as before, adjusting the phase difference with the coupler is more resistant to manufacturing errors. Even if the accuracy is somewhat coarse, the phase relationship of 90 ° can be maintained.

  When the Mach-Zehnder multiplexing / demultiplexing filter 100 is used as a laser beam MUX (multiplexer) as in this embodiment, the laser oscillation wavelength and the transmission wavelength of the Mach-Zehnder multiplexing / demultiplexing filter 100 are manufactured. May vary depending on error. However, the first and second Mach-Zehnder interferometers 110 and 120 are adjacent to the same substrate and have the same delay amount. That is, even if the transmission wavelengths of the first and second Mach-Zehnder interferometers 110 and 120 are different from the wavelengths, the amounts of these two deviations are almost equal.

  In this case, the characteristics of the Mach-Zehnder interferometers 110 and 120 are adjusted by some method so that the transmission wavelength and the laser oscillation wavelength coincide with each other. 120 may be applied.

  On the other hand, in the case where the conventional 90 ° phase difference is formed by the delay amount, the 90 ° phase relationship itself may be shifted, so that the respective adjustment amounts may be different. However, in the configuration of the present embodiment, since the same adjustment amount is sufficient, the adjustment time can be shortened.

  Also, here, the single arm side of the first and second Mach-Zehnder interferometers 110 and 120 is shown as a straight line, but if the delay amount of ΔL1 can be set, the two arm waveguides are curved. It is the same even if configured.

Here, the fourth coupler 123b of the second Mach-Zehnder interferometer 120 in the first stage is a 2 × 1 MMI type coupler, but the second coupler 113b of the first Mach-Zehnder interferometer 110 in the first stage is 2 Even when a × 1 MMI type coupler is used and the fourth coupler 123b of the second Mach-Zehnder interferometer 120 in the first stage is a 2 × 2 MMI type coupler, the same operation as that shown in FIGS. Needless to say, the effect can be realized.
That is, in the example of FIG. 1, the Mach-Zehnder interferometer 110 is the first Mach-Zehnder interferometer, and the Mach-Zehnder interferometer 120 is the second Mach-Zehnder interferometer, but the Mach-Zehnder interferometer 110 is the second Mach-Zehnder interferometer. The interferometer and the Mach-Zehnder interferometer 120 may be the first Mach-Zehnder interferometer.

  In the above embodiment, one of the second coupler 113b of the first Mach-Zehnder interferometer 110 at the first stage and the fourth coupler 123b of the second Mach-Zehnder interferometer 120 at the first stage is 2 × 2 MMI. However, the two-input one-output (2 × 1) type coupler is not limited to the MMI type coupler. For example, a Y-branch type 2 × 1 coupler (Y-branch splitter) having a phase difference of 90 ° when passing through the coupler can be adopted for one 2 × 2 MMI type coupler.

  In the above embodiment, the first coupler 113a, the second coupler 113b, and the third coupler 123a are 2 × 2 MMI type couplers. However, these couplers 113a, 113b, and 123a are in the direction of two inputs and two outputs. It can also be composed of a sex coupler.

[Example 2]
FIG. 3 is a block diagram showing a monolithic integrated light source 10A for 100 GbE equipped with a Mach-Zehnder multiplexing / demultiplexing filter 100A according to Embodiment 2 of the present invention.
In the second embodiment, a monitoring waveguide 126 adjacent to the output waveguide 125a is formed at the end of the body of the 2 × 1 MMI type fourth coupler 123b of the second Mach-Zehnder interferometer 120 in the first stage. ing. The monitoring waveguide 126 extends to the end of the chip and forms a monitor port MO for monitoring the characteristics of the second Mach-Zehnder interferometer 120.
The structure of the other parts is the same as that of the light source 10 shown in FIGS.

  When a 2 × 1 MMI type coupler is used as the fourth coupler 123b, it is preferable to install a monitor port MO for monitoring the characteristics of the second Mach-Zehnder interferometer 120.

The monitor port MO when a 2 × 1 MMI type coupler is used will be described.
A typical 2 × 1 MMI type coupler has a configuration in which a wide multimode waveguide serving as an MMI body is connected to two input waveguides, and one output waveguide is connected to an output.
By appropriately selecting the width and length of the MMI body portion, the light input in phase from the two inputs is condensed on the exit waveguide. At this time, if a phase difference occurs, the light is not condensed at the center.

Therefore, as a method of extracting the light that is not collected to the outside, it is possible to obtain another monitor output by connecting another monitor waveguide 126 beside the output waveguide 125a.
In this case, since the main (original output) and the inverted output (quenching is performed at the wavelength transmitted by the main) can be obtained, information such as the main transmission wavelength can be obtained.

  Note that the light output through the monitoring waveguide 126 is about 3 dB lower than the light output from the port of the 2 × 2 MMI coupler, but can be monitored. In particular, when the monitoring waveguide 126 is disposed immediately after the LD section 200, it is possible to monitor sufficiently even if the light intensity drops by about 3 dB.

  Without this monitor port MO, only the output light transmitted through the first stage Mach-Zehnder interferometer 110 and the output light transmitted through the second stage Mach-Zehnder interferometer 130 can be obtained. When trimming the second Mach-Zehnder interferometer 120, information on how much adjustment should be made cannot be obtained.

  In the second embodiment, since the monitor port MO is formed by the monitoring waveguide 126 adjacent to the output waveguide 125a at the end of the body of the fourth coupler 123b, the characteristics of the second Mach-Zehnder interferometer 120 are monitored. The amount of adjustment when trimming the second Mach-Zehnder interferometer 120 can be grasped.

Example 3
In the first embodiment shown in FIGS. 1 and 2 and the second embodiment shown in FIG. 3, the Mach-Zehnder interferometer 130 is used as the second-stage multiplexer / demultiplexer. Instead of MMI couplers or Y-branch splitters can be used.

The Mach-Zehnder multiplexing / demultiplexing filter of the present invention is used not only as a multiplexer that multiplexes a plurality of light beams output from a laser, but also as a demultiplexer that multiplexes a plurality of waves of light. Can do.
For example, in the example of FIG. 2, when the combined four light beams λ1, λ2, λ3, and λ4 are input from the output waveguide 135b, the light beams λ1, λ2, λ3, and λ4 are demultiplexed to generate the light λ1. Are output from the input waveguide 122b, the light λ2 is output from the input waveguide 112a, the light λ3 is output from the input waveguide 122a, and the light λ4 is output from the input waveguide 112b.

1, 1A, 1B, 1C Mach-Zehnder interferometer 2a, 2b Input waveguide 3a, 3b Coupler 4a, 4b Arm waveguide 5a, 5b Output waveguide 10, 10A Light source 100, 100A Mach-Zehnder multiplexing / demultiplexing filter 110, 120 First-stage Mach-Zehnder interferometer 130 Second-stage Mach-Zehnder interferometer 112a, 112b, 122a, 122b, 132a, 132b Input waveguide 113a, 113b, 123a, 123b, 133a, 133b Coupler 114a, 114b, 124a, 124b , 134a, 134b Arm waveguide 115a, 115b, 125a, 135a, 135b Output waveguide 126 Waveguide for monitoring

Claims (4)

A first Mach-Zehnder interferometer comprising a first coupler, a second coupler, and a pair of arm waveguides connecting the first coupler and the second coupler;
A second Mach-Zehnder interferometer comprising a third coupler, a fourth coupler, and a pair of arm waveguides connecting the third coupler and the fourth coupler;
A multiplexer / demultiplexer connected to the second coupler and the fourth coupler;
In a Mach-Zehnder multiplexing / demultiplexing filter that combines and demultiplexes light of four different wavelengths
The delay amount of the delay circuit formed by the arm waveguide of the first Mach-Zehnder interferometer is the same as the delay amount of the delay circuit formed by the arm waveguide of the second Mach-Zehnder interferometer,
The first coupler, the second coupler, and the third coupler are two-input two-output couplers, and the fourth coupler is a two-input one-output coupler. Mach-Zehnder multiplexing / demultiplexing filter.   2. The Mach-Zehnder multiplexer / demultiplexer filter according to claim 1, wherein the multiplexer / demultiplexer is any one of a Mach-Zehnder interferometer, an MMI coupler, or a Y-branch splitter.   Each of the first coupler, the second coupler, and the third coupler is either an MMI coupler or a directional coupler, and the fourth coupler is an MMI coupler or a Y-branch splitter. The Mach-Zehnder multiplexing / demultiplexing filter according to claim 1 or 2, wherein the Mach-Zehnder multiplexing / demultiplexing filter is any one. The fourth coupler is an MMI coupler, and a monitoring waveguide is provided at an end of a body portion of the fourth coupler adjacent to an output waveguide of the MMI coupler. The Mach-Zehnder multiplexing / demultiplexing filter according to claim 1 or 2.

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