JP2006235657A - Optical demultiplexer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical demultiplexer whose device can be made small-sized and which will not depend on the polarized state of the optical signal. <P>SOLUTION: Each of a plurality of drop elements has a control light input port to which a control light is inputted, a signal light input port to which a signal light is inputted, and a drop signal output port from which the signal light is outputted, in synchronism with the input of the control light. A signal waveguide makes a time-division multiplexed signal light branch and inputs a plurality of branched signal lights to signal light input ports of the drop elements. A control waveguide makes one control light branch and make a plurality of branched control lights reach the corresponding drop elements, while making them delayed gradually by respective fixed interval of times. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical demultiplexer, and more particularly to an optical demultiplexer that is simple to configure and control.

  In recent years, wavelength division multiplexing (WDM) optical communication schemes have been developed as large-capacity optical communication schemes. Optical time division multiplexing (OTDM) optical communication schemes aimed at large-capacity communications and time wavelength division multiplexing (TWDM) optical communications Methods have been proposed and research on these methods is ongoing.

  The WDM optical communication system is a system for increasing signal density by wavelength multiplexing of signal light. Time division methods such as the OTDM optical communication method and the TWDM optical communication method are methods for increasing signal density by dividing signal light of the same wavelength by time and assigning it to a number of channels.

  The response speed of the electric signal is limited by the movement time of carriers in the semiconductor element, and is slower than the response speed of light. For example, the speed limit of electrical signals is currently considered to be about 40 Gbit / s. In order to process an OTDM signal exceeding this speed, it is necessary to divide the optical signal by high-speed optical signal processing and reduce it to a bit rate that allows electrical processing (demux).

  In light of this background, recently, optical elements (optical demultiplexers) that demultiplex optical signals without converting them into electrical signals have been studied. Conventionally, non-linear loop mirror (NOLM) type, Mach-Zehnder type, polarization separation type and other optical demultiplexers have been proposed.

FIG. 15A shows a schematic diagram of a NOLM type optical demultiplexer. The optical signal sig ₁ reaches the branch point 102 of the optical fiber loop 101 via the input-side optical fiber 100. The optical signal sig ₁ is branched at a branch point 102 into an optical signal sig ₂ that travels counterclockwise in the loop 101 and an optical signal sig ₃ that travels clockwise. The optical signal sig ₁ is a signal in which four channels from channel # 1 to channel # 4 are time-division multiplexed.

A non-linear waveguide 103 is inserted at a position asymmetric with respect to the branch point 102 in the optical loop 101. The optical signal sig ₂ traveling in the counterclockwise direction reaches the nonlinear waveguide 103 earlier than the optical signal sig ₃ traveling in the clockwise direction. Immediately after the channel # ₂ of the optical signal sig ₂ passes through the nonlinear waveguide 103, the control light pulse con is input into the nonlinear waveguide 103. When the control light pulse con is input, the refractive index of the nonlinear waveguide 103 changes, and the phases of the light of the channels # 3 and # 4 of the optical signal sig ₂ are shifted by π. In FIG. 15, the pulse whose phase is shifted by π is hatched.

Since the optical signal sig ₃ arrives at the nonlinear waveguide 103 later than the optical signal sig ₂ , when the control light pulse con is input to the nonlinear waveguide 103, only the channel # 1 has the nonlinear waveguide. Not passing. For this reason, the phase of the light of the channels # 2 to # 4 of the optical signal sig ₃ is shifted by π.

When the optical signals sig ₂ and sig ₃ return to the branch point 102, channels # 1, # 3, and # 4 having the same phase among the two channels travel in the input side optical fiber 100, and the phase shift Channel # 2 that travels in the output side optical fiber 105. In this way, only one channel signal can be separated from the time-division multiplexed optical signal sig ₁ .

  In the NOLM type optical demultiplexer, the time required for the optical signal to pass through the optical loop 101 limits the signal speed that can be processed. In addition, since an optical fiber loop is used, it is difficult to reduce the size of the apparatus.

FIG. 15B shows a schematic diagram of a Mach-Zehnder optical demultiplexer. Non-linear waveguides 121 and 122 are inserted into the two arms of the Mach-Zehnder interferometer 120, respectively. The optical signal sig ₁₀ is branched into optical signals sig ₁₁ and sig ₁₂ , which are introduced into the nonlinear waveguides 121 and 122, respectively. The control light pulse con is input to the nonlinear waveguides 121 and 122 at different timings.

In the non-linear waveguide 121, the control light pulse con is input immediately after the pulse of the channel # 1 passes, and in the non-linear waveguide 122, the control light pulse con is immediately after the pulse of the channel # 2 passes. Entered. The phase of the light of the channels # 2 to # 4 of the optical signal sig ₁₁ that has passed through the nonlinear waveguide 121 is shifted by π, and the light of the channels # 3 and # 4 of the optical signal sig ₁₂ that has passed through the nonlinear waveguide 122 Is shifted by π.

By combining the optical signals sig ₁₁ and sig _{12, the} signals of the channels # 1, # 3 and # 4 are introduced into the output optical fiber 125, and the signal of the channel # 2 is introduced into the other output optical fiber 126. be introduced.

  In the Mach-Zehnder optical demultiplexer, a non-linear waveguide is inserted and two arms arranged in parallel to each other are required. For this reason, an apparatus will become large.

FIG. 15C shows a schematic diagram of a polarization separation type optical demultiplexer. The optical signal sig ₂₀ enters the birefringent crystal 130. The birefringent crystal 130 delays the TM mode light by one pulse with respect to the TE mode light. The optical signal sig ₂₁ and the control light pulse con that have passed through the birefringent crystal 130 are input to the nonlinear waveguide 131. Immediately after the TE mode channel # 2 pulse passes through the nonlinear waveguide 131, the control light pulse con is input to the nonlinear waveguide 131.

The phase of the light of the pulses of the TE mode channels # 3 and # 4 of the optical signal sig ₂₂ that has passed through the nonlinear waveguide 131 is delayed by π, and the phase of the light of the pulses of the TM mode channels # 2 to # 4 is Delayed by π. The optical signal sig ₂₂ that has passed through the non-linear waveguide 131 is input to the birefringent crystal 132. The birefringent crystal 132 delays the TE mode light by one pulse with respect to the TM mode light. Thus, in the optical signal sig ₂₃ that has passed through the birefringent crystal 132, each pulse of the TM mode coincides with the position of the pulse of the corresponding channel of the TE mode.

In the optical signal sig ₂₃ , the phases of the TM mode pulses of the channels # 1, # 3, and # 4 and the TE mode pulses are in phase, but the pulses of both modes of the channel # 2 have a phase difference. By inputting the optical signal sig ₂₃ to the polarizer 133, only the pulse of channel # 2 can be separated.

  As described above, in the polarization separation type optical demultiplexer, the intensity of the TM mode and the TE mode of the input optical signal is required to be approximately equal. However, in general, the polarization state of an optical signal propagating through an optical fiber is not constant. For this reason, the polarization separation type optical demultiplexer is not suitable for practical use.

  As described above, any of the conventional optical demultiplexers has problems such as an increase in the size of the apparatus and dependence on the polarization state of an optical signal.

  An object of the present invention is to provide an optical demultiplexer that can be downsized and does not depend on the polarization state of an optical signal.

According to one aspect of the invention,
A plurality of drop elements, each of which has a control light input port to which control light is input, a signal light input port to which signal light is input, and a signal light that is output in synchronization with the input of the control light A drop element having a drop signal output port,
A signal waveguide for branching the time-division multiplexed signal light, and inputting the branched signal lights to the signal light input ports of the drop elements, respectively;
There is provided an optical demultiplexer having a control waveguide for branching one control light and gradually delaying each of the plurality of branched control lights to the corresponding drop element by a certain time.

According to another aspect of the invention,
N drop elements (N is an integer of 2 or more), each of the drop elements being a control light input port to which control light is input, a signal light input port to which signal light is input, and a control light A drop element having a drop signal output port from which signal light is output in synchronization with the input;
A signal waveguide that is time-division multiplexed to a multiplicity of N and that has N channels of signal light input to each signal light input port of the drop element;
And a control waveguide for branching one control light into N and inputting the branched i-th (i is an integer between 1 and N) control light to the control light input port of the i-th drop element. The signal waveguide and the control waveguide are connected to the control light and the signal so that the control light input to the i-th drop element is synchronized with the i-th channel of the signal light input to the i-th drop element. An optical demultiplexer is provided that delays one of the lights relative to the other.

According to yet another aspect of the invention,
N drop elements from the first stage to the Nth stage (N is an integer of 2 or more), each of the drop elements is a control light input port to which control light is input, and signal light is input Signal light input port, a drop signal output port from which signal light is output in synchronization with the input of control light, and a through signal that outputs signal light at least during a period in which no signal light is output to the drop signal output port A drop element having an output port;
A first optical waveguide for inputting the time-division multiplexed signal light to the signal light input port of the first-stage drop element;
A second optical waveguide connecting the through signal output port of each drop element to the signal light input port of the next-stage drop element;
There is provided an optical demultiplexer having a control waveguide for branching one control light and causing each of the plurality of branched control lights to reach the corresponding drop element by gradually delaying the control light by a certain time as it goes downstream. The

  Since the control waveguide gradually delays the control light by a certain time to reach the drop element, an optical demultiplexer that does not need to generate a pulse of control light for each time-division multiplexed channel is realized. The drop element can be composed of a combination of multimode interferometers. Therefore, it is possible to perform demaxing without depending on the polarization state of the signal light, and it is possible to reduce the size of the optical demultiplexer.

  With reference to FIGS. 1 and 2, the configuration and operating principle of the optical switch according to the first embodiment of the present invention will be described.

  FIG. 1A is a plan view of an optical switch according to the first embodiment. The optical switch according to the first embodiment includes a first stage multimode interferometer (MMI) 1, a second stage multimode interferometer (MMI) 2, and nonlinear optical waveguides 3 and 4. The MMIs 1 and 2 have a waveguide laminated structure in which a core layer with a relative dielectric constant of 3.25 is sandwiched between clad layers with a relative dielectric constant of 3.18, and the core layers in the direction perpendicular to the light incident direction. The width (length of one side in the vertical direction in FIG. 1) W1 is 15 μm, and the length (length of one side in the horizontal direction in FIG. 1) L1 of the core layer in the direction parallel to the incident direction of light is 320 μm. In FIG. 1, the light is reduced in the incident direction. InGaAs can be used as the material of the core layer, and InP can be used as the material of the cladding layer. These materials can be formed on the substrate by metal organic chemical vapor deposition (MOCVD). Waveguides and multimode interferometers are also formed by combining lithography and buried growth used in semiconductor processes.

  The nonlinear optical waveguides 3 and 4 are constituted by semiconductor optical amplifiers (SOA). The width (length of one side in the vertical direction in FIG. 1) W2 of the SOA is 2.5 μm, and the length (length of one side in the horizontal direction in FIG. 1) is 140 μm. In order to perform sufficient phase modulation of light passing therethrough, the simulation result described below does not change even if the length is increased to 140 μm or more. The nonlinear waveguides 3 and 4 change the refractive index of the waveguide by being excited optically or electrically. The MMIs 1 and 2 and the nonlinear waveguides 3 and 4 are formed on a single semiconductor substrate.

  The first-stage MMI has one input port 1A, a first output port 1B, and a second output port 1C. The second-stage MMI2 has a first input port 2A, a second input port 2B, a first output port 2C, and a second output port 2D. The nonlinear waveguide 3 connects the first output port 1B of the first stage MMI1 to the first input port 2A of the second stage MMI2, and the nonlinear waveguide 4 connects to the first stage MMI1. The second output port 1C is connected to the second input port 2B of the second stage MMI2.

  The first-stage MMI1 and the second-stage MMI2 have a line-symmetric shape with respect to the first virtual straight line C1 that connects the centers of the nonlinear waveguides 3 and 4. The waveguide structure including the first-stage MMI1, the second-stage MMI2, and the non-linear waveguides 3 and 4 has a line-symmetric shape with respect to the second virtual straight line C2 parallel to the light incident direction. The input port 1A of the first stage MMI1 and the first output port 2C of the second stage MMI2 are arranged at point-symmetrical positions with respect to the intersection of the first virtual line C1 and the second virtual line C2. ing. The first output port 2C and the second output port 2D of the second-stage MMI 2 are arranged at line target positions with respect to the second virtual straight line.

  As shown in FIG. 1A, in a state where the non-linear waveguides 3 and 4 are not changed in refractive index, the signal light input from the input port 1A of the first-stage MMI 1 is non-linear waveguide 3 And 4 and output from the first output port 2C of the second stage MMI2.

  As shown in FIG. 1B, the nonlinear waveguide 3 is in a state where the refractive index is changed by being excited with light or electrically. The non-linear waveguide 3 whose refractive index has changed is hatched. The symmetry of the optical circuit is lost, and signal light is also output from the second output port 2D. The state in which no signal light is output from the second output port 2D of the second-stage MMI 2 corresponds to the off state, and the state in which the signal light is output corresponds to the on state.

  By causing the refractive index change to occur intermittently, it is possible to shift from the off state to the on state.

  FIG. 2 shows the result of optical path simulation using the beam propagation method for the optical switch shown in FIG. 2A, 2B, and 2C show a state in which the refractive index of both the nonlinear waveguides 3 and 4 is not changed, a state in which the refractive index of the nonlinear waveguide 4 is changed, and The state where the refractive index of the nonlinear waveguide 3 is changed is shown. In FIG. 2, a portion having a high light intensity is shown in white.

  As shown in FIG. 2A, in the state where the refractive indexes of the nonlinear waveguides 3 and 4 are not changed, the incident light passes through the two nonlinear waveguides 3 and 4, and the second stage It can be confirmed that the signal is output from the first output port 2C of the MMI 2 and not output from the second output port 2D. As shown in FIGS. 2B and 2C, when the refractive index of one of the nonlinear waveguides 3 and 4 is changed, the first output port 2C and the second output of the second-stage MMI 2 are used. It can be confirmed that signal light is output from both of the mouths 2D.

  In the state where the refractive indexes of the two nonlinear waveguides 3 and 4 are not changed, the signal light is not substantially output from the second output port 2D of the second-stage MMI 2, so RZ (Return to Zero) ) A switch is realized. This is an optical switch having excellent characteristics from a practical viewpoint.

  Next, an optical switch according to a second embodiment of the present invention will be described with reference to FIGS.

  FIG. 3 is a plan view of an optical switch according to the second embodiment. Similar to the optical switch according to the first embodiment, the optical switch according to the second embodiment includes a first stage MMI 11, a second stage MMI 12, and nonlinear waveguides 13 and 14. The connection relationship of each component is the same as that of the optical switch of the first embodiment, and the shape and size of each component are different.

  The width W3 and length L3 of the core layer of the first-stage MMI 11 are 15 μm and 130 μm, respectively. The width W4 and the length L4 of the core layer of the second stage MMI 12 are 15 μm and 80 μm, respectively. The symmetry is broken with respect to the third virtual straight line C3 passing through the intermediate point in the longitudinal direction of the nonlinear waveguides 13 and 14. Symmetry is maintained with respect to the fourth virtual straight line C4 parallel to the light incident direction. The input port 11A of the first stage MMI 11 is arranged on the fourth virtual straight line C4.

  FIG. 4 shows the result of optical path simulation using the beam propagation method for the optical switch shown in FIG. FIG. 4A shows a state where the refractive indexes of both the nonlinear waveguides 13 and 14 are not changed, and FIG. 4B shows a state where the refractive index of the nonlinear waveguide 13 is changed. . In FIG. 4, a portion having a high light intensity is shown in white.

  As shown in FIG. 4A, in the state where the refractive indexes of the nonlinear waveguides 13 and 14 are not changed, the incident light passes through the two nonlinear waveguides 13 and 14, and the second stage It can be confirmed that the two outputs 12C and 12D of the MMI 12 are almost equally output. This is because the optical switch is line symmetric with respect to the fourth virtual straight line C4.

  As shown in FIG. 4B, in the state where the refractive index of the nonlinear waveguide 13 is changed, the intensity of light output from the first output port 12C of the second-stage MMI 12 is weakened, and the second It can be confirmed that the intensity of the light output from the output port 12D is increased. Thus, switching can be performed by changing the intensity of the output light. However, unlike the case of the first embodiment, the RZ switch is not realized.

  Next, the configuration and operation of the optical switch according to the third embodiment of the present invention will be described with reference to FIGS.

  In the optical switches according to the first and second embodiments, the MMI has a two-stage configuration. However, in the third embodiment, the MMI includes one MMI 21 and two nonlinear waveguides 22 and 23. . The width W5 and the length L5 of the core layer of the NNI 21 are 15 μm and 320 μm, respectively. The MMI 21 has one input port 21A, a first output port 21B, and a second output port 21C.

  Nonlinear waveguides 22 and 23 are connected to the first output port 21B and the second output port 21C, respectively.

  FIG. 6 shows the result of optical path simulation using the beam propagation method for the optical switch shown in FIG. 6A shows a state where the refractive indexes of both the nonlinear waveguides 22 and 23 are not changed, and FIG. 6B shows a state where the refractive index of the nonlinear waveguide 22 is changed. . In FIG. 6, a portion having a high light intensity is shown in white.

  As shown in FIG. 6A, in the state where the refractive indexes of the nonlinear waveguides 22 and 23 are not changed, the incident light propagates almost evenly to the two nonlinear waveguides 22 and 23. I can confirm that.

  As shown in FIG. 6B, in a state where the refractive index of the nonlinear waveguide 22 is changed, the intensity of light emitted from the second output port 21C is increased, and the light is emitted from the first output port 21B. It can be confirmed that the intensity of the light to be weakened. Thus, switching can be performed by changing the intensity of the output light. However, as in the case of the second embodiment, the RZ switch is not realized.

  Next, specific methods for changing the refractive index of the nonlinear waveguide according to the first to third embodiments will be described.

  FIG. 7 shows a schematic perspective view of a semiconductor amplifier (SOA) constituting the nonlinear waveguide. An active layer 200 having a gain for optical amplification is sandwiched between a p-type semiconductor layer 201 and an n-type semiconductor layer 202. The active layer 200 is composed of a semiconductor layer formed of a semiconductor material having a smaller band gap than the semiconductor layers 201 and 202 on both sides, or a quantum well layer. The active layer 200 is made of InGaAsP, for example, and the semiconductor layers 201 and 202 on both sides are made of InP.

  When a forward bias is applied to the active layer 200, the carrier distribution in the active layer 200 is in an inverted distribution state, and the refractive index of the active layer 200 changes. When the optical signal 203 enters the active layer 200 from one end face of the active layer 200, the optical signal undergoes phase modulation and is emitted from the opposite end face.

  In this way, the refractive index can be changed by applying an electrical signal to the nonlinear waveguide made of SOA.

  In FIG. 7, the method of electrically changing the refractive index of the nonlinear waveguide has been described. In this method, the response speed of the optical switch is limited by the processing speed of the electrical signal. In order to perform switching at higher speed, it is preferable to change the refractive index of the nonlinear waveguide by an optical signal. Hereinafter, a method for causing a refractive index change by an optical signal will be described.

  FIG. 8 shows a schematic cross-sectional view of the optical switch used in the first embodiment shown in FIG. A pair of reflecting mirrors 31 and 32 are arranged with their reflecting surfaces facing each other so as to sandwich the non-linear waveguide 3. On the first stage MMI1, a control light waveguide 33 is arranged in parallel to the substrate surface. A reflecting mirror 30 that reflects the emitted control light con toward the substrate side is disposed at the emission end of the control light waveguide 33.

  The pair of reflecting mirrors 31 and 32 can be composed of a dielectric or semiconductor multilayer film, for example. The oblique reflecting mirror 30 can be formed by etching the end face of the waveguide obliquely.

  The control light con emitted from the control light waveguide 33 is reflected toward the substrate (non-linear waveguide) by the reflecting mirror 30 disposed obliquely with respect to the substrate surface. The control light con reflected by the reflecting mirror 30 is repeatedly reflected by the pair of reflecting mirrors 31 and 32. At this time, the control light con excites the nonlinear waveguide 3 and changes its refractive index.

  With reference to FIG. 9, the configuration and operation of an optical switch according to a fourth embodiment of the present invention will be described.

  FIG. 9A shows a plan view of an optical switch according to the fourth embodiment. The optical switch according to the fourth embodiment includes an MMI 40 for introducing control light, a waveguide, in addition to the first-stage MMI1, the second-stage MMI2, and the nonlinear waveguides 3 and 4 according to the first embodiment shown in FIG. The waveguide 41 and 42 are included. In the first embodiment, the case where only one input port 1A is provided in the first stage MMI1 is shown. However, in the fourth embodiment, the first straight line MMI1 is symmetrical with the incident light 1A with respect to the virtual straight line C2. Another input port 1D is provided at the position.

  The control light introducing MMI 40 has a first input port 40A, a second input port 40B, a first output port 40C, and a second output port 40D. The waveguide 41 connects the first output port 40C of the control light introducing MMI 40 and the first input port 1A of the first-stage MMI1. Further, the signal light sig is combined with the control light propagating in the waveguide 41 and input to the first input port 1A of the first stage MMI1. The wavelength of the signal light sig is, for example, 1.55 μm, and the wavelength of the control light is shorter than the wavelength of the signal light, for example, 1.3 μm or 1.48 μm.

  As shown in FIG. 9B, when the control light pulse con is incident from the second input port 40B of the control light introducing MMI 40, the control light con pulse passes through the waveguides 41 and 42, and is nonlinearly guided. Input to the waveguide 3. As a result, the nonlinear waveguide 3 is excited and its refractive index changes. Since this is the same as the state shown in FIG. 2C, the signal light sig is output almost equally from the first output port 2C and the second output port 2D of the second-stage MMI2. The

  As shown in FIG. 9C, when the control light pulse con is incident from the first input port 40A of the control light introducing MMI 40, the control light pulse con reaches the nonlinear waveguide 4. As a result, the nonlinear waveguide 4 is excited and its refractive index changes.

FIG. 10 shows the time variation of the refractive index of the nonlinear waveguides 3 and 4. Curves n ₃ and n ₄ indicate the refractive indices of the nonlinear waveguides 3 and 4, respectively. At time t _1, as shown in FIG. 9 (B), it is input to control light pulse con, the refractive index of the nonlinear waveguide 3 is changed. The refractive index returns to the original refractive index with a fixed time constant. In time t _2, the as shown in FIG. 9 (C), it is entered the control light pulse con, the refractive index of the nonlinear waveguide 4 varies. At this time, the refractive index n ₄ of the non-linear waveguide 4, so as to be substantially equal to the refractive index n ₃ of the non-linear waveguide 3, the non-linear waveguide 3 and 4 are designed in the time.

As shown in FIG. 9C, when both the refractive indexes of the nonlinear waveguides 3 and 4 change, the symmetry of the optical circuit is ensured, and the second stage as in the case of FIG. 9A. The signal light sig is output only from the first output port 2C of the MMI 2, and the signal light sig is not output from the second output port 2D. Thus, between times _{t 1} and _{t 2,} the signal light sig is outputted from the second output port 2D of the second stage MMI2, the time _{t 2} later, the second output port 2D, the signal light sig is not output.

As shown in FIG. 10, at time _{t 3,} the incident control light pulse from the second input port 40B of the control light introducing MMI40, at time _{t 4,} and enters the control light pulse from the first input port 40A . Thus, between times t ₃ and t _4, it can be emitted signal light sig from the second output port 2D.

By periodically repeating the above operation, the signal light sig can be output from the second output port 2D only during a desired period. The control at times t ₁ and t ₃ in FIG. 10 is called push control, and the control at times t ₂ and t ₄ is called pull control. The optical switch according to the fourth embodiment can perform push-pull control.

  By filtering the light output from the output port with a wavelength filter, it is possible to cut out the control light and extract only the signal light. Thereby, the S / N ratio of the signal light can be improved.

  Next, the configuration and operation of an optical switch according to a fifth embodiment of the present invention will be described with reference to FIG.

  FIG. 11A is a plan view of an optical switch according to the fifth embodiment. Hereinafter, differences from the optical switch according to the fourth embodiment shown in FIG. 9A will be described.

  In the fourth embodiment, the signal light sig and the control light pulse con are combined in the waveguide 41, but in the fifth embodiment, the signal light sig and the control light pulse con are Are combined.

  The signal light sig is input to the first input port 50A of the multiplexing MMI 50. The control light pulse con output from the first output port 40C of the control light introducing MMI 40 is input to the second input port 50B of the multiplexing MMI 50. The signal light sig output from the output port of the multiplexing MMI 50 and the control light pulse con are input to the first input port 1A of the first stage MMI1.

  A control light branching MMI 60 is disposed in front of the control light introducing MMI 40. The control light branching MMI has an input port 60A, a first output port 60C, and a second output port 60D. The first output port 60C is connected to the first input port 40A of the control light introducing MMI 40 via the waveguide 62, and the second output port 60D is connected to the control light introducing MMI 40 via the waveguide 61. It is connected to the second input port 40B. The waveguide 62 is longer than the waveguide 61. That is, the waveguide 62 constitutes a delay circuit.

A control light pulse con is input from the input port 60A of the control light branching MMI 60. The control light pulse con is output almost uniformly to the first output port 60C and the second output port 60D. The control light pulse con ₁ passing through the waveguide 62 reaches the control light introduction MMI 40 with a delay from the control light pulse con ₂ passing through the waveguide 61. This delay time corresponds to the delay from the time t ₁ shown in FIG 10 to t _2. For this reason, push-pull control can be performed only by inputting one control light pulse con.

  FIG. 11B shows a block diagram of an optical switch 70 in which the internal optical circuit of the optical switch in FIG. 11A is a black box. The optical switch 70 has a control light input port 70C to which the control light pulse con is input, a signal light input port 70S to which the signal light sig is input, and two output ports 70T and 70D. The control light input port 70C corresponds to the input port 60A of the control light branching MMI 60 in FIG. 11A, and the control light input port 70C corresponds to the input port 50A of the multiplexing MMI 50 in FIG. . The output ports 70T and 70D correspond to the output ports 2C and 2D of the second-stage MMI2 in FIG. 11A, respectively.

  When the control light pulse con is input from the control light input port 70C, the signal light sig is output from the output port 70D for a certain period. Therefore, the output port 70D is referred to as a drop signal output port. The other output port 70T is referred to as a through signal output port. In this specification, the optical switch 70 is referred to as a drop element.

  FIG. 12 is a schematic plan view of an optical demultiplexer according to the sixth embodiment. The optical demultiplexer according to the sixth embodiment includes four drop elements 70 (1) to 70 (4), four photoelectric conversion elements 75 (1) to 75 (4), a signal optical waveguide 72, and a control optical waveguide 71. It is comprised including. Each of the drop elements 70 (1) to 70 (4) is the same as the drop element 70 according to the fifth embodiment shown in FIG.

  A signal light sig that is time-division multiplexed to a multiplicity of 4 and includes pulses of channels # 1 to # 4 is branched into four signal lights by a signal optical waveguide 72. The branched signal light sig is input to the signal light input ports of the drop elements 70 (1) to 70 (4), respectively.

The control light pulse con is branched into _four control light pulses con _{1 to} con 4 by the control light waveguide 71. The branched control light pulses con _{1 to} con ₄ are input to the control light input ports of the drop elements 70 (1) to 70 (4), respectively. The four control light pulses con ₁ to con ₄ reach the corresponding drop elements 70 (1) to 70 (4) with a gradual delay by a certain time. More specifically, the control light pulse con _i reaches the drop element 70 (i) at the time when the pulse of the channel #i of the signal light sig reaches the drop element 70 (i). Thereby, push control is performed. Also, the pull control is completed before the pulse of channel # (i + 1) arrives.

  For this reason, only the pulse of channel #i is output from the drop signal output port of the drop element 70 (i). In this way, time-division multiplexed signal light sig can be separated and a signal for each channel can be obtained. For example, four signal lights of 40 Gb / s can be obtained from signal light of 160 Gb / s. The signal light of channel #i is input to the photoelectric conversion element 75 (i) and converted into an electrical signal.

  FIG. 13 is a schematic plan view of an optical demultiplexer according to the seventh embodiment of the present invention. In the sixth embodiment, four drop elements are connected in parallel. In the seventh embodiment, four drop elements 70 (1) to 70 (4) are connected in cascade. That is, the through signal output port of the drop element 70 (i) is connected to the signal light input port of the next-stage drop element 70 (i + 1). The photoelectric conversion elements 75 (1) to 75 (4) are connected to the drop signal output ports of the drop elements 70 (1) to 70 (4), respectively.

The signal light sig that has been time-division multiplexed at a multiplicity of 4 is input to the signal light input port of the first-stage drop element 70 (1). The control light pulse con is branched into _four control light pulses con _{1 to} con ₄ . The branched control light pulses con _{1 to} con ₄ are respectively input to the control light input ports of the drop elements 70 (1) to 70 (4).

The control optical waveguide 80 controls the control light pulse so that the control light pulse con _i reaches the drop element 70 (i) at the time when the pulse of the channel #i of the signal light sig reaches the drop element 70 (i). con _{1 to} con ₄ are delayed by a predetermined time. When the control light pulse con _i reaches the drop element 70 (i), pull control is performed by the drop element 70 (i). Also, push control is completed before the pulse of channel # (i + 1) arrives.

  For this reason, only the pulse of channel #i is output from the drop signal output port of the drop element 70 (i). In this way, time-division multiplexed signal light sig can be separated and a signal for each channel can be obtained. The signal light of channel #i is input to the photoelectric conversion element 75 (i) and converted into an electrical signal.

  In the sixth and seventh embodiments, the case where the signal light of multiplicity 4 is separated has been described. Generally, when the signal light of multiplicity N is separated, parallel connection or cascade connection is performed. The number of drop elements may be N.

  In the sixth and seventh embodiments, one control light pulse is branched, and each of the plurality of branched control lights is allowed to reach the corresponding drop element gradually delayed by a certain time. . For this reason, it is not necessary to generate a control light pulse for each time-division multiplexed channel.

  Next, the effects of both embodiments will be described while comparing the sixth embodiment and the seventh embodiment.

  In the sixth embodiment, since the signal light sig is divided into four equal parts, the intensity of the signal light sig input to each drop element 70 (i) is about ¼ of the intensity of the original signal light sig. . In contrast, in the seventh embodiment, since one signal light sig passes through the four drop elements 70 (1) to 70 (4) in order, there is almost no decrease in signal intensity. For this reason, in the seventh embodiment, the intensity of the signal light of each separated channel can be kept high.

  In the seventh embodiment, the signal purity decreases every time the signal light sig passes through the drop element 70 (i). Specifically, the signal waveform is broken, noise is mixed, or jitter is generated. On the other hand, in the sixth embodiment, the signal purity hardly deteriorates.

  In the sixth embodiment, the control optical waveguide 71 and the signal optical waveguide 72 intersect. For this reason, attention must be paid to the waveguide design.

  Next, the configuration and operation of an optical switch according to an eighth embodiment of the present invention will be described with reference to FIG. In the first to seventh embodiments, the first-stage MMI and the second-stage MMI are connected by two non-linear waveguides, but the number of waveguides may be three or more. At this time, at least one waveguide needs to be a non-linear waveguide. In the eighth embodiment, there are four waveguides connecting the first-stage MMI and the second-stage MMI.

  FIG. 14A is a schematic plan view of an optical switch according to the eighth embodiment. The first-stage MMI 91 and the second-stage MMI 92 are connected to each other through four waveguides 93, 94, 95, and 96. The first-stage MMI 91 has a first input port 91A and a second input port 91B, and the second-stage MMI 92 has a first output port 92A and a second output port 92B.

  The first-stage MMI 91, the second-stage MMI 92, and the waveguides 93 to 96 are line-symmetric with respect to a virtual straight line C2 parallel to the light incident direction. Waveguides 94 and 95 are arranged at symmetrical positions. Waveguides 93 and 96 are disposed outside the waveguides 94 and 95. The waveguides 94 and 95 are non-linear waveguides, and the waveguides 93 and 96 are ordinary waveguides.

  The width W6 of the first stage MMI 91 and the second stage MMI 92 is 12 μm, and the length L6 is 345 μm. A length L7 of the waveguides 93 to 96 is 100 μm, a width W7 of the waveguides 93 and 96 is 1.5 μm, and a width W8 of the waveguides 94 and 95 is 1.0 μm. The two input ports 91A and 91B are arranged at both ends of the input side edge of the first stage MMI 91, and the two output ports 92A and 92B are arranged at both ends of the output side edge of the second stage MMI 92. Yes.

  FIGS. 14B and 14C show the results of optical path simulation using the beam propagation method. FIG. 14B shows a state in which the refractive indexes of the nonlinear waveguides 94 and 95 are not changed, and FIG. 14C shows a state in which the refractive indexes of the nonlinear waveguides 94 and 95 are changed. The refractive index of the core part of the first stage MMI 91, the second stage MMI 92, and the waveguides 93 and 96 is 3.25, and the refractive index of the surrounding clad part is 3.18. The refractive index of the core portions of the waveguides 94 and 95 is 3.25 in the state of FIG. 14B and 3.18 in the state of FIG. The closed curve shown in the figure is an isolight intensity curve.

  As shown in FIG. 14B, when the refractive indexes of the non-linear waveguides 94 and 95 are not changed, the signal light input from the second input port 91B of the first-stage MMI 91 is 4 It is confirmed that the light passes through the two waveguides 93 to 96 and is output from the second output port 92B of the second-stage MMI 92. No signal light is output from the first output port 92A.

  As shown in FIG. 14C, in the state where the refractive indexes of the non-linear waveguides 94 and 95 are changed, the signal light input from the second input port 91B is received by the two waveguides 93 and 96 at both ends. And is output from the two output ports 92A and 92B of the second-stage MMI 92. The intensity of the signal light output from the first output port 92A is stronger than the intensity of the signal light output from the second output port 92B.

  As can be seen from the simulation results shown in FIGS. 14B and 14C, the optical switch according to the eighth embodiment uses the second output port 92B of the second-stage MMI 92 as the through signal output port, and the first switch The output port 92A can be used as a drop element having a drop signal output port.

  In the optical switches and optical demultiplexers according to the first to eighth embodiments, a plurality of optical elements can be formed monolithically on a single semiconductor substrate. For this reason, it is possible to reduce the size of the apparatus. Note that the monolithic structure is not necessarily required, and an optical fiber or an optical crystal can be used as the waveguide.

  Further, since the operations of the optical switches and the optical demultiplexers according to the first to eighth embodiments do not depend on the polarization state of the signal light, the signal light output from the optical fiber can be processed.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

  The invention described in the following supplementary notes is derived from the above embodiments.

(Supplementary note 1) a first multi-mode interferometer having a first input port to which signal light is input and at least two output ports;
Propagating light output from the first output port connected to each of the one or more first output ports selected from the plurality of output ports, and changing the refractive index by an external trigger signal A resulting first optical waveguide;
A second optical waveguide connected to each of one or more second output ports selected from the plurality of output ports and propagating light output from the second output port;
An optical switch comprising trigger means for supplying a trigger signal for changing a refractive index of the first optical waveguide to the first optical waveguide.

  (Supplementary note 2) The optical switch according to supplementary note 1, wherein the first optical waveguide includes a semiconductor optical amplifier.

  (Additional remark 3) Furthermore, it has at least 2 input port and a 1st output port, and several input ports are the output end of the said 1st optical waveguide, and the output end of the said 2nd optical waveguide, respectively. The optical switch according to appendix 1 or 2, further comprising a second multi-mode interferometer connected to the switch.

  (Supplementary Note 4) In the second multimode interferometer, the refractive index of the first optical waveguide is changed, and one phase of the signal light propagating through the first optical waveguide and the second optical waveguide is changed. 4. The optical switch according to appendix 3, wherein when the signal is delayed from the other phase, the intensity of the signal light output from the first output port of the second multimode interferometer is changed.

  (Supplementary note 5) The optical switch according to supplementary note 3 or 4, wherein the second multi-mode interferometer has a second output port in addition to the first output port.

  (Supplementary Note 6) In the second multimode interferometer, the refractive index of the first optical waveguide is changed, and one phase of the signal light propagating through the first optical waveguide and the second optical waveguide is changed. The optical switch according to appendix 5, wherein when the signal is delayed from the other phase, the intensity of the signal light output from the first output port and the second output port of the second multimode interferometer is changed.

  (Supplementary Note 7) The second multimode interferometer is configured so that the first multimode interferometer relates to a virtual straight line connecting a center point of the first optical waveguide and a center point of the second optical waveguide. The optical switch according to any one of appendices 3 to 6, wherein the optical switch has a line-symmetric shape.

(Appendix 8) The trigger means is
A pair of reflecting mirrors facing each other with the first optical waveguide interposed therebetween and configured to multiplexly reflect the control light;
8. The optical switch according to any one of appendices 1 to 7, further comprising control light introducing means for introducing control light into the pair of reflecting mirrors so as to be multiple-reflected by the reflecting mirrors.

(Supplementary note 9) The first multimode interferometer has a second input port in addition to the first input port,
The trigger means is
A third multi-mode interferometer having a first input port to which control light is input, a first output port and a second output port;
A third optical waveguide for inputting light output from the second output port of the third multimode interferometer to the second input port of the first multimode interferometer;
A multiplexing optical element configured to multiplex light output from the first output port of the third multimode interferometer with signal light and input the light to the first input port of the first multimode interferometer; The optical switch according to any one of appendices 1 to 7, including:

  (Supplementary Note 10) The multiplexing optical element includes a first input port connected to a first output port of the third multimode interferometer, a second input port to which signal light is input, Light input from the first input port and the second input port is multiplexed and output from the output port, and the output port is connected to the first input port of the first multimode interferometer The optical switch according to appendix 9, including a fourth multimode interferometer.

  (Additional remark 11) The optical switch of Additional remark 9 or 10 whose said 2nd optical waveguide is a nonlinear waveguide which produces a refractive index change with the intensity | strength of the input light.

  (Supplementary Note 12) The third multimode interferometer has a second input port in addition to the first input port, and control light is input from the first input port of the third multimode interferometer. Then, when the control light is output from the first output port of the first multimode interferometer and the control light is input from the second input port of the third multimode interferometer, the control light is output. The optical switch according to appendix 11, wherein light is output from a second output port of the first multimode interferometer.

  (Additional remark 13) The said trigger means further branches the control light input from the input port, and mutually sends a timing to the first input port and the second input port of the third multimode interferometer. Item 13. The optical switch according to appendix 12, including a branch delay optical element that is shifted and input.

(Supplementary Note 14) The branch delay optical element includes:
An input port to which control light is input, a fifth multi-mode interferometer that outputs control light input from the input port from the first output port and the second output port;
A fourth optical waveguide connecting the first output port of the fifth multimode interferometer and the first input port of the third multimode interferometer;
A fifth output of the fifth multimode interferometer is connected to a second input of the third multimode interferometer, and the fifth optical waveguide is different in length from the fourth optical waveguide. 14. The optical switch according to appendix 13, which has a waveguide.

(Supplementary Note 15) A plurality of drop elements, each of which is synchronized with a control light input port to which control light is input, a signal light input port to which signal light is input, and control light input. A drop element having a drop signal output port from which signal light is output;
A signal waveguide for branching the time-division multiplexed signal light, and inputting the branched signal lights to the signal light input ports of the drop elements, respectively;
An optical demultiplexer having a control waveguide for branching one control light and causing each of the plurality of branched control lights to reach the corresponding drop element gradually delayed by a certain time.

(Supplementary Note 16) N drop elements (N is an integer of 2 or more), each of the drop elements includes a control light input port to which control light is input, a signal light input port to which signal light is input, And a drop element having a drop signal output port from which signal light is output in synchronization with the input of the control light,
A signal waveguide that is time-division multiplexed to a multiplicity of N and that has N channels of signal light input to each signal light input port of the drop element;
And a control waveguide for branching one control light into N and inputting the branched i-th (i is an integer between 1 and N) control light to the control light input port of the i-th drop element. The signal waveguide and the control waveguide are connected to the control light and the signal so that the control light input to the i-th drop element is synchronized with the i-th channel of the signal light input to the i-th drop element. An optical demultiplexer that delays one of the lights relative to the other.

(Supplementary Note 17) N drop elements (N is an integer of 2 or more) from the first stage to the Nth stage, and each of the drop elements has a control light input port to which control light is input, A signal light input port for receiving signal light, a drop signal output port for outputting signal light in synchronization with the input of control light, and signal light at least during a period when no signal light is output to the drop signal output port A drop element having a through signal output port to output;
A first optical waveguide for inputting the time-division multiplexed signal light to the signal light input port of the first-stage drop element;
A second optical waveguide connecting the through signal output port of each drop element to the signal light input port of the next-stage drop element;
An optical demultiplexer comprising: a control waveguide for branching one control light and causing each of the plurality of branched control lights to reach the corresponding drop element by gradually delaying the control light by a fixed time as it goes downstream.

(Supplementary note 18) The signal light is a signal in which N channels are time-division multiplexed,
The control waveguide transmits the control light input to the i-th drop element (i is an integer of 1 to N) and the i-th channel of the signal light input to the i-th drop element. Item 18. The optical demultiplexer according to item 17, which is synchronized with the optical demultiplexer.

  (Supplementary note 19) The optical demultiplexer according to any one of supplementary notes 15 to 18, wherein the drop element includes the optical switch according to supplementary notes 9 to 14.

  (Additional remark 20) Furthermore, the optical demultiplexer in any one of Additional remark 15 thru | or 19 which has a converter which converts the signal light output from each drop signal output port of the said drop element into an electrical signal.

1 is a schematic plan view of an optical switch according to a first embodiment of the present invention. It is a figure which shows the result of having simulated the mode of the propagation of the signal light of the optical switch by a 1st Example. It is a schematic plan view of the optical switch by the 2nd Example of this invention. It is a figure which shows the result of having simulated the mode of the propagation of the signal light of the optical switch by a 2nd Example. It is a schematic plan view of the optical switch by the 3rd Example of this invention. It is a figure which shows the simulation result of the mode of the propagation of the signal light of the optical switch by a 3rd Example. It is a perspective view of the nonlinear waveguide (semiconductor optical amplifier) used for the optical switch by an Example. It is the schematic which shows the optical system for introduce | transducing excitation light into the nonlinear waveguide used for the optical switch by an Example. It is a schematic plan view of the optical switch by the 4th Example of this invention. It is a graph which shows the time fluctuation of the refractive index of the two nonlinear waveguides of the optical switch by the 4th example. It is the schematic plan view and block diagram of the optical switch by the 5th Example of this invention. It is the schematic of the optical demultiplexer by the 6th Example of this invention. It is the schematic of the optical demultiplexer by the 7th Example of this invention. It is a figure which shows the schematic plan view of the optical switch by the 8th Example of this invention, and the simulation result of the mode of propagation of signal light. It is the schematic of the conventional optical demultiplexer.

Explanation of symbols

1, 11, 91 1st stage MMI
2, 12, 92 Second stage MMI
3, 4, 13, 14, 22, 23, 94, 95 Non-linear waveguide 21 MMI
30, 31, 32 Reflector 33 Control optical waveguide 40 Control light introducing MMI
41, 42, 61, 62, 93, 96 Waveguide 50 MMI for multiplexing
60 MMI for control light branching
70 Optical switches 71 and 80 Control optical waveguides 72 and 81 Signal optical waveguide 200 Active layer 201 p-type semiconductor layer 202 n-type semiconductor layer 203 Optical signal

Claims (4)

A plurality of drop elements, each of which has a control light input port to which control light is input, a signal light input port to which signal light is input, and a signal light that is output in synchronization with the input of the control light A drop element having a drop signal output port,
A signal waveguide for branching the time-division multiplexed signal light, and inputting the branched signal lights to the signal light input ports of the drop elements, respectively;
An optical demultiplexer having a control waveguide for branching one control light and causing each of the plurality of branched control lights to reach the corresponding drop element gradually delayed by a certain time. N drop elements (N is an integer of 2 or more), each of the drop elements being a control light input port to which control light is input, a signal light input port to which signal light is input, and a control light A drop element having a drop signal output port from which signal light is output in synchronization with the input;
A signal waveguide that is time-division multiplexed to a multiplicity of N and that has N channels of signal light input to each signal light input port of the drop element;
And a control waveguide for branching one control light into N and inputting the branched i-th (i is an integer between 1 and N) control light to the control light input port of the i-th drop element. The signal waveguide and the control waveguide are connected to the control light and the signal so that the control light input to the i-th drop element is synchronized with the i-th channel of the signal light input to the i-th drop element. An optical demultiplexer that delays one of the lights relative to the other. N drop elements from the first stage to the Nth stage (N is an integer of 2 or more), each of the drop elements is a control light input port to which control light is input, and signal light is input Signal light input port, a drop signal output port from which signal light is output in synchronization with the input of control light, and a through signal that outputs signal light at least during a period in which no signal light is output to the drop signal output port A drop element having an output port;
A first optical waveguide for inputting the time-division multiplexed signal light to the signal light input port of the first-stage drop element;
A second optical waveguide connecting the through signal output port of each drop element to the signal light input port of the next-stage drop element;
An optical demultiplexer comprising: a control waveguide for branching one control light and causing each of the plurality of branched control lights to reach the corresponding drop element by gradually delaying the control light by a fixed time as it goes downstream. The signal light is a signal in which N channels are time-division multiplexed,
The control waveguide transmits the control light input to the i-th drop element (i is an integer of 1 to N) and the i-th channel of the signal light input to the i-th drop element. The optical demultiplexer according to claim 3, which is synchronized with the optical demultiplexer.

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