JP2009128644A - Light signal processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflection type light signal processor provided with a monitor function. <P>SOLUTION: This light signal processor includes a spectral diffraction element 51 for dispersing an incident light signal into a plurality of light signals having different wavelengths, to be emitted at emission angles in response to the wavelengths, a convergence lens 52 for converging the light signal dispersed in each wavelength by the spectral diffraction element, a signal processing element 53 for modulating each of the light signals converged by the convergence lens, a mirror 100 for reflecting one part to change an optical path, and for transmitting one part of the residual, as to each light signal modulated by the signal processing element, and one or a plurality of photodiodes 101 for monitoring an intensity of each light signal transmitted through the mirror. The light signal processor is compactified and integrated by this manner, since branch elements such as photocouplers of the number corresponding to the wavelengths are not required to be provided further in the reflection type light signal processor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical signal processing device. More specifically, the present invention relates to a reflection type optical signal processing apparatus having a monitor function.

  As the speed and capacity of optical communication networks have increased, there has been an increasing need for optical signal processing apparatuses such as those represented by processing of wavelength division multiplexing (WDM) transmission signals. For example, there is a demand for a function of switching the path of multiplexed optical signals between nodes. An optical signal processing apparatus has been increased in speed by performing path conversion without changing the optical-electrical conversion.

  On the other hand, from the viewpoint of miniaturization and integration of an optical signal processing device, research and development of a waveguide type optical circuit (PLC: Planar Lightwave Circuit) is in progress. In a PLC, for example, a core made of quartz glass is formed on a silicon substrate, and various functions are integrated on one chip, thereby realizing an optical functional device with low loss and high reliability. Furthermore, a complex optical signal processing component (apparatus) that combines a plurality of PLC chips and other optical functional components has also appeared.

  For example, Patent Document 1 discloses an optical signal processing device in which a waveguide type optical circuit (PLC) including AWG or the like and a spatial modulation element such as a liquid crystal element are combined. More specifically, a wavelength blocker including a PLC and a collimating lens arranged symmetrically with respect to the liquid crystal element, a wavelength equalizer, a dispersion compensator, and the like are being studied. In these optical signal processing devices, optical signal processing is performed independently for each wavelength for a plurality of optical signals having different wavelengths.

  FIG. 5 is a conceptual diagram illustrating an example of an optical signal processing apparatus. In this optical signal processing apparatus, an optical signal is input / output via the spectroscopic element 51. The spectroscopic element 51 demultiplexes a plurality of optical signals having different wavelengths at an emission angle θ corresponding to the wavelengths. The demultiplexed optical signal is emitted toward the condenser lens 52. The optical signal condensed by the condensing lens 52 is condensed on each condensing point at a predetermined position of the signal processing element 53 having a function of intensity modulation, phase modulation or deflection corresponding to the emission angle θ. . That is, it should be noted that the optical signal is collected at different positions of the signal processing element depending on the wavelength of the input optical signal. The signal processing element 53 is, for example, a liquid crystal element composed of a plurality of element elements (pixels). By controlling the transmittance of each element, the optical signal of each wavelength is subjected to intensity modulation and the like, and a predetermined signal processing function is realized. The optical signal subjected to the signal processing is reflected by the mirror 54 to reverse the traveling direction. The optical signal further passes through the condenser lens 52 and is multiplexed again in the spectroscopic element 51. As is generally well known, the spectroscopic element 51 can also multiplex optical signals according to the traveling direction. The combined optical signal of each wavelength is output again as output light to the outside of the optical signal processing device.

  In FIG. 5, the spectroscopic element 51 is conceptually shown and may be any element that can demultiplex and multiplex according to the wavelength of the optical signal. For example, the spectroscopic elements include a grating, a prism, and an arrayed waveguide grating (AWG). The signal processing element only needs to be capable of modulating the intensity or phase of the optical signal, or the intensity and phase, or capable of deflecting the traveling direction of the optical signal. For example, the signal processing element includes a liquid crystal element, a MEMS (Micro Electro Mechanical Systems) mirror, and a nonlinear crystal.

  The optical signal processing device shown in FIG. 5 is configured to perform both demultiplexing and multiplexing of an optical signal by one spectroscopic element by folding the optical signal using a mirror (in this specification, this The configuration is called a reflective type.) An apparatus that performs optical signal processing such as a wavelength block is not limited to this configuration.

  In addition, optical signal processing devices such as wavelength blockers, wavelength equalizers, and dispersion compensators that input multiple optical signals with different wavelengths and perform optical signal processing independently for each wavelength monitor the intensity of the optical signal for each wavelength. By doing so, parameters such as optical signal power are acquired and used for signal processing. Therefore, a part of the optical signal that is input to or output from the optical signal processing device is branched inside or outside of the optical signal processing device using a branching element such as an optical coupler, and is further divided into wavelength components. A mechanism for demultiplexing optical signals having different wavelengths using a wave element and monitoring the optical signals of the respective wavelengths is required.

Japanese Patent Laid-Open No. 2002-250828 (FIGS. 20, 29D, etc.)

  From the viewpoint of miniaturization and integration of the optical signal processing device, the mechanism for monitoring each optical signal of each wavelength is small and is provided inside the optical signal processing device and has a simplified configuration. Is desirable.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a reflection type optical signal processing apparatus having a monitor function.

  In order to achieve such an object, an optical signal processing device according to the present invention includes a spectroscopic unit that splits an incident optical signal into a plurality of optical signals having different wavelengths and emits them at an emission angle according to the wavelength, Condensing means for condensing each of the optical signals separated by wavelength by the spectroscopic means, signal processing means for modulating each of the optical signals collected by the condensing means, and modulation by the signal processing means A reflection-type optical signal processing apparatus including a mirror that reflects each of the optical signals and changes an optical path, wherein the mirror reflects a part of each of the optical signals modulated by the signal processing means And further includes one or a plurality of photodiodes for monitoring the intensity of the optical signal transmitted through the mirror.

  In one embodiment, an arrayed waveguide grating is used as the spectroscopic means. In addition, a dielectric multilayer mirror in which films having different refractive indexes are stacked is used as a mirror. Further, a second lens array for condensing the optical signal transmitted through the mirror onto the photodiode can be provided between the mirror and the photodiode.

  As described above, according to the present invention, the mirror essentially provided in the reflection type optical signal processing apparatus is configured to reflect a part of the optical signal and transmit the remaining part. The optical signal transmitted through the mirror is received directly or indirectly by the photodiode provided behind the mirror, so that the number of optical couplers or the like corresponding to the number of wavelengths is reflected in the reflective optical signal processing device. There is no need to further provide a branch element, and a miniaturized and integrated optical signal processing apparatus can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a conceptual diagram showing an example of an optical signal processing apparatus according to an embodiment of the present invention. The optical signal processing apparatus according to the present embodiment splits an incident optical signal into a plurality of optical signals having different wavelengths and splits the optical signal for each wavelength by the spectral element 51 that emits the optical signal at an emission angle corresponding to the wavelength. A condensing lens 52 for condensing each optical signal, a signal processing element 53 for modulating each of the optical signals collected by the condensing lens 52, and each of the optical signals modulated by the signal processing element 53 , A mirror 100 that reflects part of the light and changes the optical path and transmits the remaining part, and a plurality of photodiodes 101-1 and 101-2 for monitoring the intensity of the optical signal transmitted through the mirror 100, 101-3.

  The spectroscopic element 51 can be configured using, for example, a grating, a prism, an arrayed waveguide diffraction grating (AWG), or the like.

  The signal processing element 53 only needs to be capable of modulating the intensity or phase of the optical signal, or the intensity and phase, or capable of deflecting the traveling direction of the optical signal (in this specification, the intensity or phase of the optical signal, or Modulating intensity and phase and deflecting the traveling direction of an optical signal is called modulation.) The signal processing element can be configured using, for example, a liquid crystal element, a MEMS (Micro Electro Mechanical Systems) mirror, a nonlinear crystal, or the like.

  The mirror 100 can be configured using, for example, a dielectric multilayer mirror in which films having different refractive indexes are stacked.

  The optical signal processing apparatus according to the present embodiment may further include a second lens array 102 (FIG. 2B) that focuses the optical signal transmitted through the mirror 100 on the light receiving surface of the photodiode 101. . The second lens can be configured using a convex lens.

In the optical signal processing apparatus of this embodiment, optical signals are input / output via the spectroscopic element 51. The spectroscopic element 51 demultiplexes a plurality of optical signals having different wavelengths at an emission angle θ corresponding to the wavelengths. In FIG. 1, the wavelengths of the demultiplexed optical signals are shown as λ ₁ , λ ₂ , and λ ₃ (λ ₁ <λ ₂ <λ ₃ ), respectively. The demultiplexed optical signals are emitted toward the condenser lens 52, respectively.

  Each optical signal collected by the condensing lens 52 is collected at each condensing point at a predetermined position of the signal processing element 53 having a function of modulating intensity modulation, phase modulation, or deflection in accordance with the emission angle θ. Lighted. That is, the optical signal is condensed at different positions of the signal processing element according to the wavelength of the input optical signal. The signal processing element 53 is, for example, a liquid crystal element composed of a plurality of element elements (pixels). By controlling the transmittance and the like of each element element, the optical signal of each wavelength is modulated such as intensity modulation, and a predetermined signal processing function is realized. A part of the optical signal subjected to the signal processing is reflected by the mirror 100 to reverse the traveling direction. The optical signal reflected by the mirror 100 further passes through the condenser lens 52 and is multiplexed again by the spectroscopic element 51. The combined optical signal of each wavelength is output again as output light to the outside of the optical signal processing device.

On the other hand, the optical signal of each wavelength transmitted through the mirror 100 is received by the photodiode 101. FIG. 1 shows that optical signals having wavelengths λ ₁ , λ ₂ , and λ ₃ are received by the photodiodes 101-1, 101-2, and 101-3, respectively.

FIG. 2 is a diagram showing a state in which a part of the optical signal subjected to signal processing by the signal processing element 53 passes through the mirror 100 and is directly received by the photodiode 101, and FIG. 2 is a diagram illustrating a state in which an optical signal transmitted through the light beam is collected by a convex lens 102 and received by a photodiode 101. FIG. FIG. 2 shows an example in which the signal processing element 53 is configured using a liquid crystal element as shown in FIG. The optical signals having wavelengths λ ₁ , λ ₂ , and λ ₃ are condensed by the condenser lens 52 onto the pixel element elements (pixels) 506-1, 506-2, and 506-3 of the liquid crystal element, respectively, and are subjected to signal processing. .

  FIG. 4 is a diagram showing a schematic configuration of a liquid crystal optical variable attenuator (liquid crystal VOA) 500 that can be used as the signal processing element 53. 4A is an enlarged side view of the pixel portion of the liquid crystal VOA 500, and FIG. 4B is an enlarged front view of the liquid crystal VOA 500. FIG. The liquid crystal VOA 500 has a structure in which a liquid crystal element 550 is sandwiched between two polarizing elements 502. The liquid crystal element 550 has a structure in which the liquid crystal 510 is sandwiched between two glass substrates 504 on which an ITO (Indium Tin Oxide) electrode 506 and an alignment film 508 are formed.

  As described above, a place where each optical signal dispersed by the spectroscopic element 51 such as an arrayed waveguide diffraction grating (AWG) is collected corresponds to a place of each pixel 506 of the ITO electrode in FIG. 4B.

  In the liquid crystal VOA 500 of this embodiment, the liquid crystal element 550 is a twisted nematic liquid crystal element, and the liquid crystal element 550 is sandwiched between the front and rear by a polarizer 502 that transmits only polarized light in the horizontal direction. The liquid crystal VOA 500 applies a desired voltage to the ITO electrode 506 of the transparent conductive film when horizontally polarized light is incident on each pixel, so that the polarization plane of the optical signal is 0 to 90 degrees on the vertical plane with respect to the optical axis. Can rotate up to. Since the polarizer 502 is also provided on the output side, it acts as a variable optical attenuator. That is, the optical signal is subjected to signal processing by being subjected to intensity modulation in the liquid crystal VOA 500.

  Incidentally, in recent years, the transmission speed of an optical signal in an optical communication system has been increased to, for example, 40 Gbps, and it is desirable that the signal processing element can transmit the optical signal in as wide a band as possible. In the example of the liquid crystal VOA 500 shown in FIG. 4, it is required to increase the size of each ITO electrode pixel 506 to reduce the gap between the ITO electrode pixels 506.

  Further, it is desirable to increase the light receiving surface of each photodiode 101 so that the power of the optical signal can be monitored more efficiently.

  However, when the light receiving surface of each photodiode 101 is enlarged, there is a problem that the photodiode receives the crosstalk light of the adjacent channel and a monitoring error occurs. There are two causes for this.

  The first factor is due to the fact that the mirror 100 has a Gaussian beam waist in the structure shown in FIG. 1, and therefore the light beam after passing through the mirror tends to spread. Actually, for the convenience of mounting the photodiode 101, the mirror 100 and the photodiode 101 are provided with a gap on the order of 100 μm, for example, so that the spread light enters the photodiode for monitoring the intensity of the optical signal of the adjacent channel. there's a possibility that.

  The second factor is due to the actual mounting of the photodiode 101. In other words, in the actual mounting, using a photodiode array in which the light receiving portions of a plurality of photodiodes 101-1, 101-2,... Are manufactured on a single chip is advantageous because a large number of photodiodes can be mounted at a time. is there. However, the light scattered in the photodiode chip may be input to the photodiode for monitoring the intensity of the optical signal in the adjacent channel.

  Such crosstalk tends to increase by increasing the light receiving surface of each photodiode 101 as shown in FIG.

  Therefore, as shown in FIG. 2 (b), the light receiving surface of the photodiode 101 is arranged by further arranging a convex lens 102 for condensing each optical signal transmitted through the mirror 100 onto the light receiving surface of each photodiode 101. Without increasing the size, crosstalk can be prevented and monitoring with reduced monitoring error can be performed.

  FIG. 3 is a table for explaining crosstalk monitored by the photodiode 101. The values shown in the table of FIG. 3 are as follows. In FIG. 2, the pitch (distance between the centers) between the pixels 506 is 250 μm, the gap between the pixels 506 is 10 μm, the diameter of each photodiode (PD) 101 and the lens. It is evaluated as a value obtained by measuring crosstalk using the presence or absence of 102 as a parameter.

  As shown in FIG. 3, by using a photodiode having a small diameter together with the lens 102, it is possible to provide a reflection type optical signal processing apparatus having a monitoring function that prevents crosstalk.

  In FIG. 2, a photodiode 101 in which a plurality of single (individual) photodiodes are mounted may be used, or a photodiode in which multiple arrays of photodiodes are integrated as one chip. In FIG. 2, the lens 102 may be a combination of a plurality of single (individual) lenses or a multi-array microlens array. Further, the type is not particularly limited as long as the lens has a function of condensing light so as to achieve the above-described object.

  From the viewpoint of improving reliability, such a photodiode may be enclosed in a hermetically sealed package. In this case, the window material on the front surface of the package is a mirror shown in FIGS. 2 (a) and 2 (b). 100 may also be used. There are advantages that the number of members is reduced and mounting becomes easy.

  In the present embodiment, an example of a form that is reflected by a mirror and returned to the same optical path as shown in FIG. 1 is described. However, this patent is not limited to that form as long as it has the same advantage. . For example, an optical signal may be incident on the mirror in a direction perpendicular to the paper surface of FIG. 1 with a slight deviation from vertical, and the input port and the output port may be separated vertically in the paper surface vertical direction.

It is a figure for demonstrating schematic structure of the optical signal processing apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating the effect | action in the optical signal processing apparatus which concerns on one Embodiment of this invention, (a) is a figure which shows the case where the optical signal which permeate | transmitted the mirror is directly received by a photodiode, (b) ) Is a diagram illustrating a case where an optical signal transmitted through a mirror is collected by a convex lens and received by a photodiode. It is a table | surface for demonstrating the crosstalk monitored with the photodiode of the optical signal processing apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating schematic structure of the liquid crystal optical variable attenuator (liquid crystal VOA) used for the optical signal processing apparatus which concerns on one Embodiment of this invention, (a) is a side view, (b) is a front view. . It is a figure for demonstrating schematic structure of the conventional optical signal processing apparatus.

Explanation of symbols

51 Spectral Element 52 Lens 53 Signal Processing Element 54,100 Mirror 101 Photodiode 102 Lens 500 Liquid Crystal VOA
506 Electrode (pixel)

Claims (4)

A spectroscopic unit that splits an incident optical signal into a plurality of optical signals having different wavelengths and emits the optical signal at an emission angle corresponding to the wavelength;
Condensing means for condensing the optical signals spectrally separated for each wavelength by the spectroscopic means;
In an optical signal processing device comprising signal processing means for modulating each of the optical signals collected by the light collecting means,
For each of the optical signals modulated by the signal processing means, a mirror that reflects part of the optical signal to change the optical path and transmits the remaining part of the optical signal;
An optical signal processing apparatus comprising: one or a plurality of photodiodes for monitoring the intensity of an optical signal transmitted through the mirror.   The optical signal processing apparatus according to claim 1, wherein the spectroscopic means is an arrayed waveguide diffraction grating.   The optical signal processing apparatus according to claim 1, wherein the mirror is a dielectric multilayer mirror in which films having different refractive indexes are stacked.   2. The optical signal processing according to claim 1, further comprising an array of second lenses for condensing the optical signal transmitted through the mirror onto the photodiode, between the mirror and the photodiode. apparatus.

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