JP2012004982A - Optical signal processing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical signal processing apparatus for an optical signal to which multivalue phase modulation is performed, without using an AD converter.SOLUTION: An optical signal processing apparatus has an optical input port 1, and four-stage optical phase receiving means cascade-connected to the optical input port 1. Optical phase receiving means 5a of a first stage has optical tap means 2a, and optical phase determination means 4a connected to an output of the tap optically. The optical tap means 2a divides an optical signal into a tap output and a main output. Optical phase receiving means 5b of a second stage has optical frequency doubler means 3a, optical tap means 2b connected to the output of the optical frequency doubler means 3a optically, and optical phase determination means 4b connected to the output of the tap optically. Optical phase receiving means 5c of a third stage is similar to the second stage. Optical phase receiving means 5d of a fourth stage as the last stage has optical frequency doubler means 3c, and optical phase determination means 4d connected to the output of the optical frequency doubler means 3c optically. Each optical frequency doubler means doubles an optical frequency and an optical phase.

Description

  The present invention relates to an optical signal processing apparatus, and more particularly to an optical signal processing apparatus for determining the phase of a multilevel phase-modulated optical signal.

  In order to further increase the capacity of optical communication systems, transmission formats with high spectrum utilization efficiency are being actively studied. Such transmission formats include PSK (Phase Shift Keying) that gives information to the phase of light, ASK (Amplitude Shift Keying) that gives information to the amplitude of light, or QAM that gives information to both the phase and amplitude. (Quadrature Amplitude Modulation). Among them, DPSK (Differential Phase Shift Keying) and DQPSK (Differential Quadrature Phase Shift Keying), which modulate the phase in a differential manner, have already been put into practical use, and QPSK (Quadrature Shading) that does not use differential is also in progress. It is in. Furthermore, (D) 8PSK, 16QAM, etc. with high spectrum utilization efficiency are being actively studied.

  In demodulating DPSK, which is binary phase modulation, or DQPSK, which is quaternary phase modulation, a binary signal can be directly extracted using DLI (Delay Line Interferometer). However, in order to demodulate a further multilevel optical signal such as D8PSK, it has been conventionally necessary to use an analog-to-digital converter (ADC) in addition to DLI. FIG. 1 shows the configuration of a conventional optical signal processing device for demodulating a D8PSK optical signal (see Non-Patent Document 1).

  The conventional optical signal processing apparatus includes an input optical port 101, a 1 × 3 optical coupler 102, delay interferometers 103a and 103b, balance detectors 104a and 104b, a detector 105, electric amplifiers 106a and 106b, and 106 c, analog-digital converters 107 a, 107 b and 107 c, and a digital signal processor 108. With this configuration, light amplitude and differential phase information is acquired by the balance detectors 104a and 104b, light intensity information is acquired by the detector 105, and these data are digitally converted by the analog-to-digital converters 107a, 107b, and 107c. A multi-value optical signal is demodulated by converting it into data and processing it by the digital signal processor 108.

  FIG. 2 shows a second example of a conventional optical signal processing apparatus. Optical input ports 101a and 101b, polarization multiplexed optical hybrid 109, balance detectors 104a, 104b, 104c and 104d, electric amplifiers 106a, 106b, 106c and 106d, analog-digital converters 107a, 107b, 107c and 107d and a digital signal processor 108. Here, the polarization multiplexed optical hybrid 109 includes polarization separators 110a and 110b and 90 ° C. optical hybrids 111a and 111b. With such a configuration, signal light is input to the optical input port 101a, local light is input to the optical input port 101b, and light changes, amplitude, and phase information are received by the balance detectors 104a, 104b, 104c, and 104d. Is obtained and processed by the digital signal processor 108 to demodulate the multi-value optical signal.

N. Kikuchi, K. Mandai, K. Sekine, S. Sasaki, ‘‘ Incoherent 32-level optical multilevel signaling technologies ’’, J. Lightwave Circuit, vol. 26, no. 1, pp. 150-157, 2008.

  A conventional optical signal processing apparatus needs to use a high-speed ADC. However, it is difficult to increase the number of bits with a high-speed ADC. In addition, since a high-speed ADC consumes a large amount of power, there is a problem of increasing the power consumption of the entire optical signal processing apparatus. Since this power consumption is generated by a small ADC chip, there is also a problem that heat management of the optical signal processing apparatus is difficult. there were.

  The present invention has been made in view of such problems, and the object thereof is to provide an optical signal processing device for an optical signal subjected to multilevel phase modulation without using an ADC, while suppressing power consumption. An object of the present invention is to realize a high-speed and high-resolution optical signal processing apparatus.

  In order to achieve such an object, according to the first aspect of the present invention, an optical input port is connected in cascade from the first stage to the Nth stage (N is an integer of 2 or more) in this order. An optical signal processing apparatus comprising N stages of optical phase receiving means, wherein the first stage of optical phase receiving means branches the optical signal input to the input optical port into a tap output and a main output. Optical tap means and a first optical phase discriminating means optically connected to the tap output of the first optical tap means, the i-th optical phase receiving means (i from 2 to (N− 1) is an integer up to 1), and when N = 2, it is an empty set.) Is the optical frequency and optical phase, respectively, optically connected to the main output of the (i-1) th optical tap means. Tap the outputs of the (i-1) th optical frequency multiplier and the (i-1) th optical frequency multiplier. And an i-th optical tap means branching to the main output, and an i-th optical phase determining means optically connected to the tap output of the i-th optical tap means, and an N-th optical phase receiving means (N−1) th optical frequency multiplication means for multiplying the optical frequency and optical phase optically connected to the main output of the (N−1) th optical tap means, respectively, And an Nth optical phase discrimination means optically connected to the output of the optical frequency multiplication means.

  According to a second aspect of the present invention, in the first aspect, at least one of the first to (N-1) th optical frequency multipliers is an optical nonlinear waveguide. M order harmonic generation (M is an integer greater than or equal to 2) is used, and each optical phase discrimination means in the same stage as the at least one optical frequency multiplication means is a light for discriminating the phase with a resolution of 2π / M. It is a phase discrimination means.

  According to a third aspect of the present invention, in the first or second aspect, at least one of the first to (N-1) th optical frequency multipliers is an optical nonlinear waveguide. Pump light having an optical frequency different from that of the optical signal incident on the non-linear waveguide of the at least one optical frequency multiplying means, which uses M-th harmonic generation by a waveguide (M is an integer of 2 or more). And a filter that removes the optical frequency component of the incident optical signal and the optical frequency component of the pump light from the optical signal that has undergone the difference frequency generation in the nonlinear waveguide, It is characterized by converting the optical frequency.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the optical phase discrimination means is a Mach-Zehnder interferometer and a balance detector optically connected to the output of the Mach-Zehnder interferometer. It is characterized by providing.

  According to a fifth aspect of the present invention, in any one of the first to third aspects, the optical phase discrimination means is optically connected to the 90-degree optical hybrid circuit and the output of the 90-degree optical hybrid circuit. It is characterized by being a balanced detector.

  According to a sixth aspect of the present invention, in the third aspect, the at least one optical frequency multiplying means is an optical frequency doubling means using second harmonic generation by the optical nonlinear waveguide. It is characterized by.

  According to a seventh aspect of the present invention, in any one of the second to sixth aspects, the optical nonlinear waveguide is an optical waveguide provided on a periodically poled lithium niobate. And

  Further, an eighth aspect of the present invention is the wavelength multiplexer according to any one of the first to seventh aspects, wherein the optical frequency multiplication means has at least two input ports and at least one output port, An optical nonlinear waveguide optically connected to the output port of the wavelength multiplexer, and a wavelength component having at least one input port and at least one output port optically connected to the output of the optical nonlinear waveguide And a waver.

  According to a ninth aspect of the present invention, in any one of the first to seventh aspects, the optical frequency multiplier includes a wavelength multiplexer having at least two input ports and at least one output port, A 1-input 2-output polarization separator optically connected to an output port of the wavelength multiplexer; a first polarization conversion element optically connected to one output of the polarization separator; Two optical nonlinear waveguides optically connected to the other output of the polarization separator and the output of the first polarization conversion element, respectively, and one output of the two optical nonlinear waveguides 2 input 1 output optically connected to the second polarization conversion element optically connected, the other output of the two optical nonlinear waveguides, and the output of the second polarization conversion element, respectively. A polarization combiner and at least one optically connected to the output of the polarization combiner And a wavelength demultiplexer having at least three output ports.

  According to the present invention, it is possible to provide a simple and low power consumption optical signal processing apparatus by connecting optical frequency multiplication means for multiplying optical frequency and optical phase in cascade.

It is a figure showing the conventional optical signal processing apparatus. It is a figure showing the 2nd example of the conventional optical signal processing apparatus. It is a figure showing the structure of the optical signal processing apparatus which concerns on 1st Embodiment. It is a figure showing the 1st implementation example of the optical frequency doubling means of 1st Embodiment. It is a figure showing the 2nd implementation example of the optical frequency doubling means of 1st Embodiment. It is a figure showing the 3rd implementation example of the optical frequency doubling means of 1st Embodiment. It is a figure showing the implementation example of the optical phase discrimination | determination means of 1st Embodiment. It is a figure showing the structure of the optical signal processing apparatus which concerns on 2nd Embodiment. It is a figure showing the implementation example of the optical frequency quadruple means of 2nd Embodiment. It is a figure showing the 1st implementation example of the phase discrimination means of 2nd Embodiment. It is a figure showing the 2nd implementation example of the phase discrimination means of 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 3 shows the configuration of the optical signal processing apparatus according to the first embodiment. The optical signal processing apparatus according to the first embodiment includes an optical input port 1 and four stages of optical phase receiving means 5a, 5b, 5c and 5d connected in cascade to the optical input port 1. The first-stage optical phase receiving means 5a includes an optical tap means 2a having a main output and a tap output, and an optical phase determination means 4a optically connected to the tap output of the optical tap means 2a. The optical tap means 2a branches the optical signal into its tap output and main output. The second-stage optical phase receiving means 5b includes an optical frequency doubling means 3a, an optical tap means 2b having a main output and a tap output optically connected to the output of the optical frequency doubling means 3a, and an optical tap. Optical phase discriminating means 4b optically connected to the tap output of the means 2b. The third-stage optical phase receiving means 5c includes an optical frequency doubling means 3b, an optical tap means 2c optically connected to the output of the optical frequency doubling means 3b and having a main output and a tap output, and an optical tap. It comprises optical phase discrimination means 4c optically connected to the tap output of means 2c. The final-stage fourth-stage optical phase receiving means 5d includes an optical frequency doubling means 3c and an optical phase discrimination means 4d optically connected to the output of the optical frequency doubling means 3c.

  Here, the optical tap means 2a, 2b, and 2c can be realized using an optical fiber coupler, a waveguide coupler, or the like. The optical tap means 2a, 2b and 2c have a smaller branching ratio within the range allowed by the light receiving sensitivity of the optical phase discriminating means 4a, 4b and 4c, particularly as the optical frequency doubling means 3a, 3b and 3c. Considering the case of using

  In the first embodiment of the present invention, the number of stages of the optical phase receiving means is four. However, the present invention is not limited to this example, and the number of stages may be 2, 3, 3, 5, or more. I do not care. When N is generalized as an integer of 2 or more, the i-th optical phase receiving means (i is an integer from 2 to (N−1), and an empty set when N = 2) is the ( The output of the (i-1) th optical frequency doubling means optically connected to the main output of the i-1) optical tap means, and the output of the (i-1) th optical frequency doubling means is the tap output. I-th optical tap means branched to the main output, and i-th optical phase discrimination means optically connected to the tap output of the i-th optical tap means. The N-th optical phase receiving means at the final stage includes (N-1) th optical frequency doubling means optically connected to the main output of the (N-1) th optical tap means, N-th optical phase discrimination means optically connected to the output of the (N-1) optical frequency doubling means.

  In this embodiment, the optical frequency doubling means for doubling the optical frequency and the optical phase will be described as an example. However, as described in the second embodiment, the optical frequency and the optical phase are quadrupled. Optical frequency multiplying means for multiplying may be used.

  Next, specific examples of optical frequency doubling means and optical phase discrimination means in the optical signal processing apparatus of the first embodiment and the operation principle thereof will be described, and then the entire optical signal processing apparatus of the first embodiment. The principle of operation will be described.

First Implementation Example of Optical Frequency Doubler Means FIG. 4 shows an implementation example of the optical frequency doubler means of the optical signal processing apparatus according to the first embodiment. The optical frequency doubling means of FIG. 4 includes an optical input port 6, an optical waveguide 8 provided on a periodically poled lithium niobate 7 optically connected to the optical input port 6, An optical filter 9 optically connected to the output and an optical output port 10 optically connected to the output of the optical filter 9 are provided.

Next, the operation of an implementation example of the optical frequency doubling means of the optical signal processing device according to the first embodiment shown in FIG. 4 will be described. Assuming that the optical frequency of the input optical signal is f ₀ , second harmonic generation (SHG: Second Harmonic Generation) is caused by the second-order optical nonlinear effect in the optical waveguide 8 provided on the periodically poled lithium niobate 7. As a result, a component of the optical frequency 2f ₀ is generated. By removing the component of the optical frequency f _{0 by} the optical filter 9, only the component of the optical frequency 2f ₀ is extracted. Here, the optical electric field E _s of the input optical signal is defined as A _s as a real constant, and φ _s (t) as the optical phase changing with time.

The output optical electric field E _o of the optical frequency doubler means that A _o is a real constant.

As is apparent from the equation, not only the optical frequency but also the optical phase term is doubled.

Here, in the realization example of the optical frequency doubling means of the first embodiment described above, it is assumed that the lithium niobate 7 which is periodically poled in order to double the optical frequency is used. This is because second harmonics can be generated. However, the present invention is not limited to this example. Of course, an optical nonlinear material such as a polymer or an optical fiber may be used. When an optical waveguide is formed of an optical nonlinear material, this is called a “nonlinear waveguide” in this specification.
Further, the configuration of the optical waveguide 8 can be formed by diffusion or a ridge waveguide.

Second Implementation Example of Optical Frequency Doubler Means FIG. 5 shows a second implementation example of the optical frequency doubler means of the optical signal processing apparatus according to the first embodiment. Optical frequency doubling means of Figure 5 includes an optical input port 6, a pump light source 11 of the optical frequency f _p, and the silica-based arrayed waveguide grating filter 12a optically connected to an optical input port 6, the array Optical waveguide 8 provided on periodically poled lithium niobate 7 optically connected to the output of waveguide grating filter 12a, and silica-based arrayed waveguide grating filter optically connected to the output of optical waveguide 8 12b and an optical output port 10 optically connected to the output of the arrayed waveguide grating filter 12b. Here, the quartz-based arrayed waveguide grating filter 12a, the lithium niobate 7, and the quartz-based arrayed waveguide grating filter 12b are directly connected to each other.

Next, the operation of the second implementation example of the optical frequency doubling means of the optical signal processing device according to the first embodiment shown in FIG. 5 will be described. If the optical frequency of the input optical signal is f ₀ and the optical frequency of the pump light is f _p (which is different from the optical frequency f ₀ ), the optical waveguide provided on the periodically poled lithium niobate 7. the second-order optical nonlinear effect in the 8 second harmonic: and (SHG second harmonic generation), components of the optical frequency 2f ₀ -f _p is generated by subsequent difference frequency generation thereto. Therefore, only the component of the optical frequency 2f ₀ -f _p is extracted by removing the components of the components and the optical frequency f _p of the optical frequency f ₀ in the array waveguide grating filter 12b. The output of the optical frequency doubling means at this time is

And given. Also at this time, the optical phase term is doubled as in the first implementation example shown in FIG. On the other hand the light frequency is converted to 2f ₀ -f _p.

In general, in the optical communication, a wavelength of 1.55 micron band is often used. However, in the second implementation example of the optical frequency doubling means shown in FIG. 5, the optical frequency f ₀ of the optical signal and the light of the pump light are used. by the frequency f _p and each 1.55 micron band, since the wavelength of 1.55 micron band at the output of the optical frequency doubling means is obtained, optical communication components of a general purpose there is an advantage that it can be used.

  Here, as for the lithium niobate 8, another optical nonlinear material can be used as in the first implementation example of FIG.

  Further, in the second implementation example of the optical frequency doubling means in FIG. 5, silica-based arrayed waveguide grating filters 12a and 12b are used as optical filters and are joined to lithium niobate. This is because it has excellent transmission / cutoff characteristics and can provide a small optical frequency double output. However, the present invention is not limited to this example, and a lattice type optical waveguide filter, a transversal type optical waveguide filter, or a multilayer film may be used instead of the arrayed waveguide grating filter. A filter may be used. Of course, an optical filter such as an arrayed waveguide grating and lithium niobate may be connected by an optical fiber instead of being directly joined.

FIG. 6 shows a third example of realization of the optical frequency doubling means of the optical signal processing apparatus according to the first embodiment. Optical frequency doubling means of Figure 6 includes an optical input optical port 6, a pump light source 11 of the optical frequency f _p, and the silica-based arrayed waveguide grating filter 12a optically connected to an optical input port 6, A Mach-Zehnder waveguide polarization multiplexer / demultiplexer 13a optically connected to the output of the arrayed waveguide grating filter 12a, and a polyimide half wavelength inclined at 45 degrees provided at one output of the polarization multiplexer / demultiplexer 13a Optical waveguides 8a and 8b provided on the periodically poled lithium niobate 7 optically connected to the two outputs of the polarization conversion element 14a and the polarization multiplexing / demultiplexing element 13a, respectively; Polarization conversion element 14b by a polyimide half-wave plate inclined at 45 degrees provided on one of the outputs of 8b, and a Mach-Zehnder waveguide polarization optically connected to the respective outputs of optical waveguides 8a and 8b. The multiplexing / demultiplexing element 13b, the silica-based arrayed waveguide grating filter 12b optically connected to the output of the polarization multiplexing / demultiplexing element 13b, and the optical output optically connected to the output of the arrayed waveguide grating filter 12b Port 10. Here, the silica-based arrayed waveguide grating filter 12a, the polarization multiplexing / demultiplexing element 13a, and the polarization converting element 14a are formed on a single substrate. The wave element 13b and the polarization conversion element 14b are formed on a separate substrate. These substrates and lithium niobate 7 are directly connected to each other.

In the third implementation example of the optical frequency doubling means shown in FIG. 6, when the optical frequency of the input optical signal is f ₀ and the optical frequency of the pump light is f _p , as in the implementation example 2 in FIG. In the optical waveguide 8 provided on the periodically poled lithium niobate 7, the second harmonic (SHG) is generated by the second-order optical nonlinear effect, and the optical frequency 2f _{0 is} generated by the subsequent difference frequency generation. component of the -f _p occurs. Therefore, only the component of the optical frequency 2f ₀ -f _p is extracted by removing the components of the components and the optical frequency f _p of the optical frequency f ₀ in the array waveguide grating filter 12b. The output of the optical frequency doubling means at this time is

And given. Also at this time, the optical phase term is doubled as in the first implementation example shown in FIG. On the other hand the light frequency is 2f ₀ -f _p.

  In addition, in the third realization example of the optical frequency doubling means shown in FIG. 6, since the polarization diversity structure is formed by the polarization multiplexing / demultiplexing element 13 and the polarization converting element 14, There is an advantage that the optical phase can be doubled regardless of the polarization state of the optical signal input to the port 6.

  Here, in the third realization example of the optical frequency doubling means in FIG. 6, it is assumed that a Mach-Zehnder type polarization multiplexing / demultiplexing element using a silica-based optical waveguide is used as the polarization multiplexing / demultiplexing element 13 and the polarization converting element 14 is used. The polyimide half-wave plate is used because this combination makes it possible to realize a polarization multiplexing / demultiplexing element and a polarization converting element with excellent integration. However, the present invention is not limited to this example. A polarizing prism made of calcite or a polarizing prism made of a photonic crystal may be used.

  In FIG. 6, the arrayed waveguide grating filter 12a has been described as an example, but an equivalent function can be achieved as long as the wavelength multiplexer has at least two input ports and at least one output port. Similarly, the arrayed waveguide grating filter 12b has been described as an example. However, if the wavelength demultiplexer has at least one input port and at least one output port optically connected to the output of the waveguide 8, A similar function can be performed.

  Further, although the Mach-Zehnder type polarization multiplexing / demultiplexing element 13a has been described as an example, the same function can be used as long as it is a 1-input 2-output polarization separator optically connected to the output port of the wavelength multiplexer. Can be fulfilled. Similarly, the Mach-Zehnder waveguide polarization multiplexing / demultiplexing element 13b has been described as an example. Of the two optical nonlinear waveguides, the output of which the polarization conversion element 14b is not provided, and the polarization conversion A 2-input 1-output polarization combiner that is optically connected to the output of the element 14b can perform the same function.

Implementation Example of Optical Phase Discriminating Unit Next, an implementation example of the optical phase discrimination unit of the optical signal processing device according to the first embodiment of the present invention will be described. The optical phase discrimination means shown in FIG. 7 includes an optical input port 15, a delay interferometer 16 that is a waveguide type Mach-Zehnder interferometer optically connected to the optical input port 15, and a delay interferometer 16. The balance detector 17 optically connected to the two outputs, the electrical amplifier 18 electrically connected to the output of the balance detector, and the electrical output port electrically connected to the output of the electrical amplifier 18 With. Here, the delay amount D of the delay interferometer 16 is set to substantially coincide with the bit interval T of the optical signal, and each arm of the delay interferometer 16 is provided with a heater as a phase adjusting means.

Here, with regard to the delay amount D and the bit interval T, optimal reception can be performed by setting D = T in an ideal line state. However, for example, when the band of the line is limited, it is non-ideal. When there is a factor, it is known that the influence of the non-ideal factor can be suppressed by making the delay amount D shorter than the bit interval T, for example, D = 0.7T.
At this time, by adjusting the phase adjusting means, it is possible to set so that the output is -1 when the phase difference between adjacent bits of the optical signal is 0.5π, and the output is 1 when the phase difference is 1.5π.

Description of Operation of Optical Signal Processing Apparatus According to First Embodiment Next, the operation of the optical signal processing apparatus according to the first embodiment of the present invention shown in FIG. 3 will be described with reference to Table 1. The optical frequency doubling means shown in FIG. 6 is used as the optical frequency doubling means, and the optical phase determining means shown in FIG. 7 is used as the optical phase determining means. However, the reason why the optical frequency doubling means shown in FIG. 6 is used as the optical frequency doubling means is that this configuration has small polarization dependence and can use optical components in a general-purpose optical communication wavelength band. This is because the signal processing apparatus can be provided, but the present invention is not limited to this example. Even if the optical frequency doubling means shown in FIG. 4 is used, the optical frequency doubling means shown in FIG. Of course, it does not matter.

By adjusting the phase adjusting means of the optical phase discriminating means shown in FIG. 7 with the optical signal processing device shown in FIG. 3, the outputs I1 to I4 from the first stage to the fourth stage are as follows: Can be set to
I1 = cos [(φ + π / 16) + π / 2]
I2 = cos [2 (φ + π / 16) + π / 2]
I3 = cos [4 (φ + π / 16) + π / 2]
I4 = cos [8 (φ + π / 16) + π / 2]
Here, φ is the phase difference between adjacent bits.

  Table 1 shows the output at each stage. Further, if the positive output is assigned as “1” and the negative output is assigned as “0” in Table 1, a 4-bit binary output can be obtained as shown in Table 1. As apparent from Table 1, this binary output is a value obtained by analog-digital conversion of the phase of the input optical signal. As described above, by using the optical signal processing apparatus according to the first embodiment of the present invention, the phase of the input optical signal can be converted from analog to digital at the optical stage. The number of stages of analog-digital conversion can be increased by increasing the number of optical phase receiving means 5.

(Second Embodiment)
FIG. 8 shows a configuration of an optical signal processing device according to the second embodiment of the present invention. The optical signal processing apparatus according to the second embodiment includes an optical input port 1 and two-stage optical phase receiving means 23 a and 23 b connected in cascade to the optical input port 1. The first-stage optical phase receiving unit 23a includes an optical tap unit 2a and an optical phase determination unit 22a optically connected to the tap output of the optical tap unit 2a. The second-stage optical phase receiving means 23b in the final stage includes an optical frequency quadruple means 21a, an optical tap means 2b optically connected to the output of the optical frequency quadruple means 21a, and a tap output of the optical tap means 2b. And optical phase discriminating means 22b optically connected.

  Here, as in the first embodiment, the optical tap means 2a and 2b can be realized by using an optical fiber coupler, a waveguide coupler, or the like. Further, the branching ratio of the optical tap means 2a and 2b is preferably made smaller in the range allowed by the light receiving sensitivity of the optical phase discriminating means 24a and 24b, especially when an optical nonlinear material is used as the optical frequency quadruple means 21a. What is preferable is the same as in the first embodiment.

  Furthermore, in the second embodiment of the present invention, in the second stage optical phase receiving means, an optical tap means 2b is provided at the output of the optical frequency quadruple means 21a, and the optical frequency quadruple means 21a is provided via this. The optical phase discrimination means 22b is assumed to be optically connected. However, the present invention is not limited to this example. Even if the optical phase discriminating means 22b is optically connected directly to the output of the optical frequency quadruple means 21a except for the optical tap means 2b, Of course.

  In the second embodiment, the number of stages of the optical phase receiving means is 2. However, the present invention is not limited to this example, and the number of stages may be 3, 4, 5, or more. .

  Next, an implementation example of the optical frequency doubling means 21a and the optical phase discrimination means 22a and 22b and the operation principle thereof in the optical signal processing apparatus of the second embodiment will be described, and then the optical signal processing apparatus of the second embodiment. The overall operation principle will be described.

Realization Example of Optical Frequency Quadruple Means FIG. 9 shows an implementation example of the optical frequency quadruple means of the optical signal processing apparatus according to the second embodiment of the present invention. 9 includes an optical input port 6, an optical waveguide 8a provided on a periodically poled lithium niobate 7a optically connected to the optical input port 6, and an optical waveguide 8a. An optical filter 9a optically connected to the output, an optical waveguide 8b provided on the periodically poled lithium niobate 7b optically connected to the optical filter 9a, and an optical connection to the output of the optical waveguide 8b And the optical output port 10 optically connected to the output of the optical filter 9b. In this way, the optical frequency quadrupling means can be realized by connecting the optical frequency doubling means shown in FIG. 4 in cascade.

  In FIG. 9, the optical frequency doubling means shown in FIG. 4 is connected in cascade. However, the present invention is not limited to this example, and the optical frequency doubling means shown in FIG. 5 is connected in cascade. Alternatively, the optical frequency doubling means shown in FIG. 6 may be connected in cascade, or any one of the optical frequency doubling means shown in FIGS. 4 to 6 may be connected to any one of the optical frequencies shown in FIGS. Of course, it does not matter if it is cascaded with the double means.

First Implementation Example of Optical Phase Discriminating Unit FIG. 10 shows a first implementation example of the optical phase discrimination unit of the optical signal processing apparatus according to the second embodiment of the present invention. The optical phase discriminating means in FIG. 10 is optically connected to the optical input port 15, the optical coupler 24 that roughly divides the optical signal input to the optical input port 15, and the output of the optical coupler 24. Delay interferometers 16a and 16b, balance detectors 18a and 18b optically connected to respective outputs of the delay interferometers 16a and 16b, and electrically connected to outputs of the balance detectors 18a and 18b. Electrical amplifiers 19a and 19b and electrical output ports 20a and 20b electrically connected to the outputs of the electrical amplifiers 19a and 19b are provided. The delay interferometers 16a and 16b include phase shifters 17a, 17b, 17c and 17d for adjusting the interferometer phases, respectively. Further, the delay amounts of the delay interferometers 16a and 16b are set so as to substantially match the bit interval T of the optical signal.

  By adjusting the phase shifters 17a, 17b, 17c, and 17d with this configuration, it is possible to extract the sine component and the cosine component of the phase difference between adjacent bits from the electrical output ports 20a and 20b, respectively, and the phase is 2π / It is possible to discriminate with a resolution of 4.

Second Implementation Example of Optical Phase Discriminating Unit FIG. 11 shows a second implementation example of the optical phase discrimination unit of the optical signal processing apparatus according to the second embodiment of the present invention. The optical phase discrimination means in FIG. 11 causes the local light source 25, the optical input ports 15a and 15b, the optical signal input to the optical input port 15a and the local light input to the optical input port 15b to interfere with each other. 90-degree optical hybrid circuit 26, balance detectors 18a and 18b optically connected to the output of 90-degree optical hybrid circuit 26, and electric amplifier 19a optically connected to the outputs of balance detectors 18a and 18b 19b, and an electrical output port 20 electrically connected to the outputs of the electrical amplifiers 19a and 19b. With such a configuration, it is possible to extract the sine component and the cosine component of the phase between the signal bits from the electrical output ports 20a and 20b, respectively.

Operation of optical signal processing device according to second embodiment Next, the operation of the optical signal processing device according to the second embodiment of the present invention shown in FIG. 8 will be described with reference to Table 2. The optical frequency quadruple means shown in FIG. 6 is used as the optical frequency quadruple means, and the optical phase discrimination means shown in FIG. 10 is used as the optical phase discrimination means. However, the present invention is not limited to this example. Of course, the optical phase discrimination means shown in FIG. 11 may be used.

Now, with the optical signal processing device shown in FIG. 8, the outputs I1 to I2 from the first stage to the second stage are adjusted as follows by adjusting the phase adjustment means of the optical phase discrimination means shown in FIG. Can be set to
I1a = cos [(φ + π / 16) + π / 2]
I1b = cos [(φ + π / 16) -π]
I2a = cos [4 (φ + π / 16) + π / 2]
I2b = cos [4 (φ + π / 16) -π]
Here, φ is the phase difference between adjacent bits.

  Table 2 shows the output of each stage at this time. Further, if the positive output is assigned to “1” and the negative output is assigned to “0” in Table 2, a 4-bit binary output can be obtained as shown in Table 2. As apparent from Table 2, this binary output is also a value obtained by analog-digital conversion of the phase of the input optical signal. As described above, by using the optical signal processing apparatus according to the second embodiment of the present invention, the phase of the input optical signal can be converted from analog to digital at the optical stage. The number of stages of analog-digital conversion can be increased by increasing the number of optical phase receiving means.

  In this way, the optical frequency quadruple means for quadrupling the optical frequency as shown in FIG. 6 is used, and the phase discrimination means for discriminating the phase shown in FIG. 10 with a resolution of 2π / 4 is used as the optical phase discrimination means. Thus, the phase of the input optical signal can be converted from analog to digital. When M is generalized as an integer of 2 or more, the phase of the input optical signal can be converted from analog to digital by using the optical frequency M multiplication means and the phase discrimination means for discriminating the phase with a resolution of 2π / M. .

DESCRIPTION OF SYMBOLS 1 Optical input port 2 Optical tap means 3 Optical frequency doubling means 4 Optical phase discriminating means 5 Optical phase receiving means 6 Optical input port 7 Periodically poled lithium niobate 8 Optical waveguide 9 Optical filter 10 Optical output port 11 Pump Light source 12 Array waveguide grating filter 13 Polarization multiplexer / demultiplexer 14 Polarization converter 15 Optical input port 16 Delay interferometer 17 Phase shifter 18 Balance detector 19 Electrical amplifier 20 Electrical output port 21 Optical frequency quadrature means 22 Optical phase discriminating means 23 Optical phase receiving means 24 Optical coupler 25 Local light source 26 90 degree optical hybrid

Claims (9)

An optical input port;
An optical signal processing apparatus comprising N-stage optical phase receiving means connected in cascade from the first stage to the N-th stage (N is an integer of 2 or more),
The first-stage optical phase receiving means is configured to optically input a first optical tap means for branching an optical signal input to the input optical port into a tap output and a main output, and a tap output of the first optical tap means. First optical phase discrimination means connected to each other,
The i-th optical phase receiving means (i is an integer from 2 to (N-1), and an empty set when N = 2) is the main output of the (i-1) -th optical tap means. And (i-1) optical frequency multiplying means optically connected to the optical frequency, and the outputs of the (i-1) optical frequency multiplying means are tap output and main output. An i-th optical tap means for branching into i, and an i-th optical phase discrimination means optically connected to a tap output of the i-th optical tap means,
The Nth stage optical phase receiving means is an (N-1) th optical frequency multiplying means for multiplying the optical frequency and optical phase optically connected to the main output of the (N-1) th optical tap means, respectively. And an Nth optical phase discrimination means optically connected to the output of the (N-1) th optical frequency multiplication means. At least one of the first to (N-1) optical frequency multipliers uses M-th harmonic generation (M is an integer of 2 or more) by an optical nonlinear waveguide. And
2. The optical signal processing device according to claim 1, wherein each optical phase determination unit in the same stage as the at least one optical frequency multiplication unit is an optical phase determination unit that determines a phase with a resolution of 2π / M. . At least one of the first to (N-1) optical frequency multipliers uses M-th harmonic generation (M is an integer of 2 or more) by an optical nonlinear waveguide. And
From the pump light source that enters pump light having an optical frequency different from that of the incident optical signal into the nonlinear waveguide of the at least one optical frequency multiplying unit, and from the optical signal that has undergone difference frequency generation in the nonlinear waveguide, The optical signal processing apparatus according to claim 1, further comprising: a filter that removes a component of the optical frequency of the optical signal and the optical frequency of the pump light, thereby converting the optical frequency.   4. The optical signal processing apparatus according to claim 1, wherein the optical phase discrimination means includes a Mach-Zehnder interferometer and a balance detector optically connected to an output of the Mach-Zehnder interferometer. .   4. The light according to claim 1, wherein the optical phase discrimination means is a 90-degree optical hybrid circuit and a balance detector optically connected to an output of the 90-degree optical hybrid circuit. Signal processing device.   4. The optical signal processing apparatus according to claim 3, wherein the at least one optical frequency multiplying unit is an optical frequency doubling unit that uses second harmonic generation by the optical nonlinear waveguide.   7. The optical signal processing apparatus according to claim 2, wherein the optical nonlinear waveguide is an optical waveguide provided on a periodically poled lithium niobate. The optical frequency multiplication means is
A wavelength multiplexer having at least two input ports and at least one output port;
An optical nonlinear waveguide optically connected to an output port of the wavelength multiplexer;
8. A wavelength demultiplexer having at least one input port and at least one output port optically connected to the output of the optical nonlinear waveguide. Optical signal processing device. The optical frequency multiplication means is
A wavelength multiplexer having at least two input ports and at least one output port;
A 1-input 2-output polarization separator optically connected to the output port of the wavelength multiplexer;
A first polarization conversion element optically connected to one output of the polarization separator;
Two optical nonlinear waveguides optically connected to the other output of the polarization separator and the output of the first polarization conversion element,
A second polarization conversion element optically connected to one output of the two optical nonlinear waveguides;
A two-input one-output polarization combiner optically connected to the other output of the two optical nonlinear waveguides and the output of the second polarization conversion element;
8. A wavelength demultiplexer having at least one input port and at least three output ports optically connected to the output of the polarization combiner. Optical signal processing device.

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