JP2008177997A - Optical phase modulation evaluating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical phase modulation evaluating apparatus capable of more accurately evaluating a modulation state of an optical phase modulation signal than the prior art. <P>SOLUTION: An optical phase modulation evaluation module 10 is equipped with a bit retarder 15 which gives an optical path length corresponding to one-bit delay of a symbol rate on optical paths of third light 103 and fifth light 105, and an optical phase difference setter 16 which gives delay of a predetermined optical phase, other than zero, to at least one of ninth light 109 and tenth light 110. The optical phase difference setter 16 is equipped with a translucent plate 16a provided on an optical path of the ninth light 109 and a translucent plate 16b provided on an optical path of the tenth light 110. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical phase modulation evaluation apparatus that evaluates an optical phase modulation signal in which an optical carrier wave in a coherent optical communication system is phase-modulated by a data signal.

  Conventionally, as an optical phase modulation evaluation apparatus for evaluating an optical phase modulation signal in which an optical carrier wave is phase-modulated by a data signal at a predetermined symbol rate, optical phase detection of the optical phase modulation signal is performed by one bit delay interferometer. One that evaluates the phase modulation characteristics of an optical phase modulation signal is known (see, for example, Patent Document 1).

  A conventional optical phase modulation evaluation apparatus 1 shown in Patent Document 1 is shown in FIG. As shown in FIG. 13, the optical phase modulation evaluation apparatus 1 includes a bit delay interferometer 2, a PD (light receiver) 3, and a signal processing unit 4.

  The optical phase modulation signal that is the light to be measured by the optical phase modulation evaluation apparatus 1 is generated by phase-modulating the optical carrier wave with the data signal, and is input to the bit delay interferometer 2 as an optical phase detector. . The bit delay interferometer 2 is composed of a Mach-Zehnder interferometer using an optical waveguide. The optical phase modulation signal input from the port 2a is separated from the light passing through the arm 2c and the arm 2d (bit delay) in the demultiplexing unit 2b. The light passing through the arm 2c and the light passing through the arm 2d are combined and interfered by the combining unit 2e. Thereby, the change in the phase of the optical phase modulation signal is converted into the change in the optical intensity, and two optical intensity modulation signals whose phases are different from each other by 180 ° (π) are output from the two ports 2g and 2h, respectively. The bit delay unit 2f has an optical path length of the arm 2d corresponding to the delay amount so that the delay amount (delay time difference) between the two arms becomes a delay amount (time) corresponding to one bit of the symbol rate. Is longer than the optical path length of the arm 2c.

The PD 3 photoelectrically converts the light intensity modulation signal output from the port 2g of the bit delay interferometer 2 and outputs an electrical signal. The signal processing unit 4 demodulates the data signal from the electrical signal output from the PD 3. Therefore, the optical phase modulation evaluation apparatus 1 can evaluate the optical phase modulation signal by performing error rate measurement and waveform observation using the demodulated signal output from the signal processing unit 4.
JP-A-6-21891

However, such a conventional optical phase modulation evaluation apparatus cannot measure the relative phase difference between optical phase modulation signals (hereinafter referred to as “relative bit phase difference” as appropriate). There was a problem that the modulation state of the signal could not be accurately evaluated. Hereinafter, the reason will be described using mathematical expressions. The phase difference between relative bits is represented by Δφ _mod .

First, the electric field intensity of the optical phase modulation signal that is phase-modulated with the phase difference Δφ _mod between the relative bits and is input to the port 2a of the bit delay interferometer 2 is expressed by equation (1).

E = E ₀ · exp {j (ωt + Δφ _mod )} (1)
Next, the optical phase modulation signal is demultiplexed into light passing through the arm 2c and light passing through the arm 2d in the demultiplexing unit 2b, and when each is input to the multiplexing unit 2e, the light that has passed through the arm 2c. And the electric field intensities E _a and E _{b and the} light intensities P _a and P _b of the light passing through the arm 2d are expressed by the equations (2) to (5), respectively.

E _a = A _a · exp {j (ωt + φ _a )} (2)
E _b = A _b · exp {j (ωt + φ _b )} (3)
P _a = | E _a · E _a ^* | (4)
P _b = | E _b · E _b ^* | (5)
Here, phi _a light phase, phi _b of the arm 2c shows an optical phase of the arm 2d. E _a ^* represents _a conjugate complex number of E _a , and E _b ^* represents a conjugate complex number of E _b . In the equations (2) and (3), the relative inter-bit phase difference Δφ _mod in the equation (1) is omitted for easy understanding.

  The light intensity P of the combined light in the combining unit 2e is expressed as in equation (6) using the above equations (2) and (3).

P = (E _a + E _b ) · (E _a ^* + E _b ^* )
= A _a ² + A _b ² + 2 · A _a · A _b · cos (φ _a −φ _b ) (6)
Then, when the electric field strength is A _a = A _b = 1/2 and the relative inter-bit phase difference Δφ _mod is taken into consideration, the light intensity P of the combined light (interference light) is expressed by the following equation (7). Further, when the optical phase difference (φ _a −φ _b ) between the arm 2c and the arm 2d (referred to as appropriate between two arms) is represented by φ, the equations (7) to (8) are obtained.

P = 0.5 + 0.5 cos (Δφ _mod + φ _a −φ _b ) (7)
P = 0.5 + 0.5 cos (Δφ _mod + φ) (8)
Furthermore, it is equal to the optical phase phi _b of the optical phase phi _a of the arm 2d of the arm _{2c (φ a = φ b)} , i.e., when the optical phase difference phi = 0 between the two arms, the light intensity P of the combined beam is It is given by equation (9).

P = 0.5 + 0.5 cos (Δφ _mod ) (9)
Incidentally, the light intensity P represented by the equation (9) is the light intensity of the light intensity modulation signal output from the port 2g or the port 2h. Thus, (9) When expressed by equation (10) the light intensity P as an optical intensity modulated signal P ₁ output from the port 2g of the formula, from the port 2h, as represented by equation (11) In addition, a light intensity modulation signal P ₂ having a phase difference of 180 ° (π) is output.

P ₁ = 0.5 + 0.5 cos (Δφ _mod ) (10)
P ₂ = 0.5−0.5 cos (Δφ _mod ) (11)
As a result, when the light intensity modulation signal P ₁ represented by the equation (10) is input to the PD 3 and subjected to photoelectric conversion, and thereafter the offset power is canceled, the light intensity I _α given by the equation (12) is obtained. The electric signal is output to the signal processing unit 4.

I _α ∝0.5 cos (Δφ _mod ) (12)
Therefore, the signal processing unit 4 obtains in advance the relationship between the relative inter-bit phase difference Δφ _mod and the light intensity I _α based on the above equation (12), so that the relative inter-bit phase difference is obtained from the light intensity I _α. Although it seems that Δφ _mod can be measured, as shown in FIG. 14, two relative bit phase differences Δφ _mod correspond to one light intensity I _α , and one of them cannot be specified. . That is, the conventional optical phase modulation evaluation apparatus 1 cannot measure the relative inter-bit phase difference Δφ _mod, and thus has a problem that the modulation state of the optical phase modulation signal cannot be accurately evaluated.

  The present invention has been made to solve the conventional problems, and an object of the present invention is to provide an optical phase modulation evaluation apparatus that can more accurately evaluate the modulation state of an optical phase modulation signal than in the prior art.

  An optical phase modulation evaluation apparatus according to claim 1 of the present invention includes an optical input unit (11) for inputting an optical phase modulation signal (a) in which an optical carrier wave is phase-modulated by a data signal at a predetermined symbol rate, and an input An optical branching unit (12) for branching the optical phase modulation signal (a) thus obtained into a first light (101) and a second light (102); A demultiplexer that demultiplexes light (103) and fourth light (104) and demultiplexes the second light (102) into fifth light (105) and sixth light (106). (13a) and the third light (103) is reflected and output as the seventh light (107), and the fifth light (105) is reflected and output as the eighth light (108). The first corner mirror (14a) and the fourth light (104) are reflected as ninth light (109). And the second corner mirror (14b) that reflects and outputs the sixth light (106) as the tenth light (110), the seventh light (107), and the ninth light (109). ) To convert the phase change of the optical phase modulation signal (a) into a change in light intensity, and the first and second light intensity conversion signals (111, 111) having an optical phase difference of π from each other. 112) and the eighth light (108) and the tenth light (110) are combined to convert the phase change of the optical phase modulation signal (a) into a light intensity change. And a multiplexer (13b) for outputting third and fourth light intensity conversion signals (113, 114) having an optical phase difference of π from each other, and the first corner mirror (14a) from the duplexer (13a). ) To reach the multiplexer (13b) One bit of the symbol rate on the optical path and on the optical path of two lights from the duplexer (13a) to the multiplexer (13b) via the second corner mirror (14b) A bit delay unit (15) for providing a corresponding delay, an optical path of two lights from the demultiplexer (13a) through the first corner mirror (14a) to the multiplexer (13b), and A predetermined optical phase is applied to at least one of the two lights on one of the two light paths from the duplexer (13a) through the second corner mirror (14b) to the multiplexer (13b). Optical phase difference setting means (16) for providing a delay of the first and second light receiving sections for receiving and converting at least one of the first and second light intensity conversion signals (111, 112) into an electrical signal (120) and the first And a second light receiving unit (130) that receives and converts at least one of the fourth light intensity conversion signals (113, 114) into an electrical signal, and the first and second light receiving units (120). , 130) and a signal processing unit (140) for analyzing the optical phase modulation signal (a) based on the output signal.

  With this configuration, the optical phase modulation evaluation apparatus according to claim 1 of the present invention includes two optical interferometers, and a phase difference between one optical interferometer and a phase difference between the other optical interferometers. Since the difference is set to a predetermined value, the phase difference between the relative bits can be specified separately from the conventional one. Therefore, the optical phase modulation evaluation apparatus of the present invention can evaluate the modulation state of the optical phase modulation signal more accurately than before.

  An optical phase modulation evaluation apparatus according to claim 2 of the present invention includes an optical input unit (11) for inputting an optical phase modulation signal (a) in which an optical carrier wave is phase-modulated by a data signal at a predetermined symbol rate. An optical branching unit (12) for branching the input optical phase modulation signal (a) into a first light (101) and a second light (102), and the first light (101) The third light (103) and the fourth light (104) are demultiplexed, and the second light (102) is demultiplexed into the fifth light (105) and the sixth light (106). The waver (13a) and the third light (103) are reflected and output as seventh light (107), and the fifth light (105) is reflected and reflected as eighth light (108). The first corner mirror (14a) for outputting and the ninth light (109) reflecting the fourth light (104) And the second corner mirror (14b) that reflects and outputs the sixth light (106) as the tenth light (110), and the seventh light (107) and the ninth light. (109) are combined to convert the phase change of the optical phase modulation signal (a) into a change in light intensity, and the first and second light intensity conversion signals (π) having an optical phase difference of π from each other ( 111, 112) and combining the eighth light (108) and the tenth light (110) to change the phase of the optical phase modulation signal (a) into a change in light intensity. A multiplexer (13b) for converting and outputting third and fourth light intensity conversion signals (113, 114) having an optical phase difference of π from each other; the first corner mirror (14a); and the second corner At least one of the mirrors (14b) is a predetermined one A corner mirror moving means (51) for applying a delay corresponding to one bit of the symbol rate, and the multiplexer (13a) through the first corner mirror (14a) and the multiplexer (13a). 13b) and two optical paths of light from the duplexer (13a) to the multiplexer (13b) via the second corner mirror (14b). An optical phase difference setting means (16) for giving a delay of a predetermined optical phase to at least one of the two lights, and at least one of the first and second light intensity conversion signals (111, 112) A first light receiving unit (120) that receives and converts it into an electrical signal; and a second light receiving unit that receives at least one of the third and fourth light intensity conversion signals (113, 114) and converts it into an electrical signal. Light receiving part (1 0) and a signal processing unit (140) for analyzing the optical phase modulation signal (a) based on the output signals of the first and second light receiving units (120, 130). ing.

With this configuration, the optical phase modulation evaluation apparatus according to claim 2 of the present invention includes two optical interferometers, and a phase difference in one optical interferometer and a phase difference in the other optical interferometer. Since the difference is set to a predetermined value, the phase difference between the relative bits can be specified separately from the conventional one. Therefore, the optical phase modulation evaluation apparatus of the present invention can evaluate the modulation state of the optical phase modulation signal more accurately than before.

  Furthermore, the optical phase modulation evaluation apparatus according to claim 3 of the present invention includes a multiplexer / demultiplexer (13) in which the duplexer (13a) and the multiplexer (13b) are integrated. have.

  With this configuration, the optical phase modulation evaluation apparatus according to claim 3 of the present invention can be simplified in structure as compared with the one using the duplexer and the multiplexer.

  Furthermore, in the optical phase modulation evaluation apparatus according to claim 4 of the present invention, the optical branching section (12) includes an optical coupler (12c).

  With this configuration, the optical phase modulation evaluation apparatus according to claim 4 of the present invention can branch the input optical phase modulation signal into the first light and the second light by the optical coupler.

  Furthermore, in the optical phase modulation evaluation apparatus according to claim 5 of the present invention, the optical phase difference setting means (16) includes the optical phase delay amount given to the ninth light (109) and the tenth light. The difference from the optical phase delay amount given to (110) is set to π / 2.

  With this configuration, the optical phase modulation evaluation apparatus according to claim 5 of the present invention can most easily identify the phase difference between the relative bits, so that the modulation state of the optical phase modulation signal can be evaluated more accurately than before. can do.

  Furthermore, in the optical phase modulation evaluation apparatus according to claim 6 of the present invention, the bit delay unit (15) selects and switches one of a plurality of optical path lengths predetermined according to the symbol rate. have.

  With this configuration, the optical phase modulation evaluation apparatus according to claim 6 of the present invention can accurately evaluate optical phase modulation signals of different symbol rates with a single apparatus.

  Further, in the optical phase modulation evaluation apparatus according to claim 7 of the present invention, the bit delay unit (15) is a parallel plate made of a transparent material having a thickness that gives a delay amount corresponding to one bit of the symbol rate. A plurality of the parallel plates (21a, 21b) each having a thickness corresponding to each of the plurality of symbol rates can be set, and a delay amount corresponding to the symbol rate can be set by switching between the parallel plates (21a, 21b). It has a configuration.

  With this configuration, the optical phase modulation evaluation apparatus according to claim 7 of the present invention can easily give a delay amount corresponding to a different symbol rate.

Furthermore, in the optical phase modulation evaluation apparatus according to claim 8 of the present invention, the bit delay unit (15) includes a first parallel plate (23a ₁ , 23b ₁ ) and a second parallel plate (23a ₂ , 23b). ₂ ) is a pair of parallel plates (23a, 23b) of two transparent materials arranged in a square shape, and the pair of parallel plates (thicknesses corresponding to each of the symbol rates) ( 23a, 23b), and a pair of parallel plates (23a, 23b) can be switched to set a delay amount corresponding to the symbol rate.

  With this configuration, in the optical phase modulation evaluation apparatus according to claim 8 of the present invention, the bit delay unit switches the optical path length in accordance with the symbol rate by switching a pair of two parallel plates made of a transparent material. be able to.

  Furthermore, in the optical phase modulation evaluation apparatus according to claim 9 of the present invention, the bit delay unit (15) is a pair of wedge-shaped transmission bodies (24a, 24b) in which the transmission surfaces face each other. And it has the structure which can set the said delay amount corresponding to each of several said symbol rates by moving at least any one of this transmission body (24a, 24b), adjusting an optical path length.

  With this configuration, the optical phase modulation evaluation apparatus according to claim 9 of the present invention includes a plurality of bit delay units that adjust the optical path length by moving at least one of the pair of wedge-shaped transmission bodies. The delay amount corresponding to each of the symbol rates can be set.

  Furthermore, in the optical phase modulation evaluation apparatus according to claim 10 of the present invention, the optical phase difference setting means (16) is a parallel plate (16a, 16b) made of a transparent material, and the parallel plate (16a, 16b) can be set to an arbitrary delay amount by changing the incident angle of light to the parallel plates (16a, 16b) by rotating.

  With this configuration, the optical phase modulation evaluation apparatus according to claim 10 of the present invention sets the optical phase delay amount according to the change in the wavelength of the optical phase modulation signal, or the optical path length associated with a temperature change or the like. When setting the delay amount of the optical phase due to fluctuation, a small delay amount can be set accurately, so that the modulation state of the optical phase modulation signal can be evaluated more accurately than before.

  Furthermore, in the optical phase modulation evaluation apparatus according to an eleventh aspect of the present invention, the optical phase difference setting means (16) includes two parallel plates (16e, 16f) made of a transparent material arranged in a C shape. ), And at least one of the two parallel plates (16e, 16f) is rotated to change the incident angle of the light to the parallel plates (16e, 16f). It has a configuration that can be set.

  With this configuration, the optical phase modulation evaluation apparatus according to claim 11 of the present invention can suppress the beam shift of the transmitted light of the optical phase difference setting unit.

  Furthermore, in the optical phase modulation evaluation apparatus according to claim 12 of the present invention, the signal processing unit (140) is a signal processing unit for evaluating a modulation phase of the optical phase modulation signal (a), and the demultiplexing The second corner mirror (14b) from the duplexer (13a) on the optical path of the two lights from the filter (13a) via the first corner mirror (14a) to the multiplexer (13b) An optical phase adjusting means (31) for delaying the optical phase in any of the two optical paths to the multiplexer (13b) via the optical phase, and varying the optical phase delay amount to The initial phase (φ) of the relative bit phase difference calculated by the signal processing unit (140) is adjustable.

  With this configuration, the optical phase modulation evaluation apparatus according to the twelfth aspect of the present invention can arbitrarily set the initial phase (φ) for the light to be measured having different wavelengths.

  Furthermore, in the optical phase modulation evaluation apparatus according to claim 13 of the present invention, the signal processing unit (140) is a signal processing unit for evaluating a modulation phase of the optical phase modulation signal (a), and the multiplexing An optical path length adjusting means (41) for adjusting an optical path length on an optical path between the optical device (13b) and at least one of the first and second light receiving units (120, 130), The first and second light receiving units (120, 130) have a configuration in which the phase of the electric signal converted can be adjusted.

  With this configuration, in the optical phase modulation evaluation apparatus according to the thirteenth aspect of the present invention, the optical path length adjusting unit adjusts the optical path length so that the first light receiving unit and the second light receiving unit respectively convert the electric light. The phase of the signal can be adjusted to a phase difference of 180 ° (π).

  The present invention can provide an optical phase modulation evaluation apparatus having an effect that the modulation state of an optical phase modulation signal can be evaluated more accurately than before.

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

(First embodiment)
First, the configuration of the optical phase modulation evaluation apparatus according to the first embodiment of the present invention will be described. First, the configuration of the optical phase modulation evaluation module provided in the optical phase modulation evaluation apparatus will be described.

  As shown in FIG. 1, an optical phase modulation evaluation module 10 includes an optical input unit 11 that inputs an optical phase modulation signal a, an optical branching unit 12 that branches the input optical phase modulation signal a into two lights, A multiplexer / demultiplexer 13 that demultiplexes one incident light into transmitted light and reflected light and multiplexes and outputs the two incident lights, and reflects / multiplexes the light from the multiplexer / demultiplexer 13. A first corner mirror 14a and a second corner mirror 14b that are output to 13, a bit delay unit 15 that provides an optical path length corresponding to a 1-bit delay of the symbol rate, and an optical phase difference setting unit 16 that sets an optical phase difference The phase control means 17 for instructing the optical phase difference setting value 16 to the optical phase difference setting device 16 and the first to fourth lights that receive the light from the multiplexer / demultiplexer 13 and output the light to the optical fibers 19a to 19d, respectively. Output units 18a to 18d.

  Here, the optical phase modulation evaluation module 10 includes two Mach-Zehnder interferometers.

  First, the first Mach-Zehnder interferometer reaches the first optical output unit 18a from the optical input unit 11 via the optical branching unit 12, the multiplexer / demultiplexer 13, the first corner mirror 14a, and the multiplexer / demultiplexer 13. An optical path (hereinafter referred to as “11th optical path”) and a second optical output unit from the optical input unit 11 via the optical branching unit 12, the multiplexer / demultiplexer 13, the second corner mirror 14b, and the multiplexer / demultiplexer 13. 18b (hereinafter referred to as “the twelfth optical path”).

  Next, the second Mach-Zehnder interferometer passes from the optical input unit 11 to the third optical output unit 18c via the optical branching unit 12, the multiplexer / demultiplexer 13, the first corner mirror 14a, and the multiplexer / demultiplexer 13. And the fourth optical output from the optical input unit 11 through the optical branching unit 12, the multiplexer / demultiplexer 13, the second corner mirror 14b, and the multiplexer / demultiplexer 13. And an optical path to the portion 18d (hereinafter referred to as “the twenty-second optical path”).

  The optical input unit 11 includes a lens that collimates input light, and receives an optical phase modulation signal a whose optical carrier wave is phase-modulated at a predetermined symbol rate by a data signal. Specifically, the optical input unit 11 receives an optical phase-modulated signal that is phase-modulated into a phase-modulated signal such as DPSK (Differential Phase Shift Keying) or DQPSK (Differential Quadrature Phase Shift Keying) with a symbol rate of 20 Gbps or 40 Gbps. ing. The above-described phase modulation method and symbol rate are examples, and the optical phase modulation signal a input to the optical input unit 11 is not limited to these.

  The optical branching unit 12 includes, for example, a plurality of mirrors 12 a and a beam splitter 12 b as shown in the figure, and branches the light input by the optical input unit 11 into the first light 101 and the second light 102. It has become.

  The multiplexer / demultiplexer 13 is composed of, for example, a non-polarizing beam splitter, and demultiplexes one incident light into transmitted light and reflected light, and multiplexes and outputs two incident lights.

  Specifically, the multiplexer / demultiplexer 13 transmits the first light 101 from the optical branching unit 12 and outputs it as the third light 103, and reflects the first light 101 from the optical branching unit 12. Thus, the light is output as the fourth light 104. Further, the multiplexer / demultiplexer 13 transmits the second light 102 from the optical branching unit 12 and outputs it as the fifth light 105, and reflects the second light 102 from the optical branching unit 12 to reflect the second light 102. 6 light 106 is output.

  Further, the multiplexer / demultiplexer 13 multiplexes and interferes with the two sets of input light, thereby converting the change in the optical phase into the change in the optical intensity, and two lights having an optical phase difference of π from each other. An intensity conversion signal is output.

  Specifically, the multiplexer / demultiplexer 13 combines the seventh light 107 and the ninth light 109 to convert a change in the phase of the optical phase modulation signal a into a change in light intensity, thereby mutually π The first optical intensity conversion signal 111 and the second optical intensity conversion signal 112 having the optical phase difference of 2 are output, and the optical phase modulation signal is obtained by combining the eighth light 108 and the tenth light 110. A phase change of a is converted into a change of light intensity, and a third light intensity conversion signal 113 and a fourth light intensity conversion signal 114 having an optical phase difference of π are output.

  For example, as shown in FIG. 2, the multiplexer / demultiplexer 13 may be divided into a demultiplexer 13a and a multiplexer 13b using two non-polarizing beam splitters.

  The bit delay unit 15 includes a translucent plate, for example, a quartz glass plate, which transmits the third light 103 and the fifth light 105 and has the same refractive index and is parallel, and includes the third light 103 and the fifth light. An optical path length corresponding to a 1-bit delay of the symbol rate is given on the 105 optical paths.

  Here, when the delay time t [s] corresponding to one bit of the symbol rate, the refractive index of the translucent plate is represented by n, and the speed of light in vacuum is represented by c, the third light 103 and the fifth light 105 The thickness d of the translucent plate in the traveling direction is expressed by equation (13).

d = c * t / (n-1) (13)
In the equation (13), the delay time t [s] corresponding to 1 bit is t = 1 / SR [when the symbol rate of the optical phase modulation signal a input to the optical input unit 11 is represented by SR [bps]. s], t = 25 [ps] when the symbol rate SR = 40 [Gbps], and t = 50 [ps] when the symbol rate SR = 20 [Gbps]. Therefore, when the refractive index of the transmissive plate is 1.5 and the symbol rate SR = 40 [Gbps], the thickness d of the transmissive plate is 15 [mm]. When the symbol rate SR is 20 [Gbps], the thickness d of the translucent plate is 30 [mm].

  As described above, the bit delay unit 15 gives an optical path difference corresponding to 1 bit between the two optical paths of the first and second Mach-Zehnder interferometers according to the symbol rate of the optical phase modulation signal a. Can be done.

  By the way, the bit delay unit 15 is not limited to the above-described configuration, and may be configured as shown in FIG. 3, for example. The bit delay unit 15 shown in FIG. 3 includes two translucent plates 15a and 15b in which the incident surface and the exit surface of the third light 103 and the fifth light 105 are parallel and have the same refractive index. Yes. The translucent plates 15a and 15b are configured so that the incident angle at the translucent plate 15a and the emission angle at the translucent plate 15b are equal to each of the third light 103 and the fifth light 105. It is tilted symmetrically in a letter shape.

  In addition, the bit delay device 15 can also be comprised only by the translucent board 15a or 15b, for example. For example, when only the translucent plate 15 a is used, the translucent plate 15 a refracts the third light 103 and the fifth light 105, so that the third light 103 and the fifth light 105 are illustrated as illustrated. A phenomenon (hereinafter referred to as “beam shift”) occurs between the incident optical axis and the outgoing optical axis. This beam shift is not a problem in practice because the beam itself has a certain width, but it is possible to further eliminate the influence of the beam shift by providing it symmetrically inclined in a C shape as shown in the figure. This is preferable. Further, in the configuration of the bit delay unit 15 shown in FIG. 3, unlike the case where the incident angles of the third light 103 and the fifth light 105 are set at approximately 0 °, the return light from the incident surface is transmitted. This is preferable because it can be suppressed.

  Returning to FIG. 1, the description of the configuration of the optical phase modulation evaluation module 10 will be continued.

  The first corner mirror 14a is configured by combining two mirrors at a predetermined angle as shown in the figure, and outputs reflected light in a direction opposite to the traveling direction of the incident light through an optical path different from the incident light. Yes. Specifically, the first corner mirror 14a reflects the third light 103 and the fifth light 105 that have passed through the bit delay device 15 to form the seventh light 107 and the eighth light 108, respectively. It outputs to the waver 13.

  The second corner mirror 14b has the same configuration as that of the first corner mirror 14a, and reflects the fourth light 104 and the sixth light 106 from the multiplexer / demultiplexer 13, respectively. The light 110 is output to the optical phase difference setting unit 16.

The optical phase difference setting device 16 includes a translucent plate 16a provided on the optical path of the ninth light 109 and a translucent plate 16b provided on the optical path of the tenth light 110, and is phase-controlled. Follow the instructions of the means 17, the phase difference between the 11th optical path and the second 12 optical path and ([Delta] [phi _1), the phase difference between the first 21 optical path and the second 22 optical path difference between _{(Δφ 2) (Δφ 1 -Δφ} 2) π The optical phase difference is set to / 2. The translucent plates 16a and 16b respectively include a translucent plate, for example, a quartz glass plate, which transmits the ninth light 109 and the tenth light 110 and has the same refractive index and is parallel. In addition, each thickness of the translucent board 16a and 16b may be the same, and may mutually differ. Alternatively, the optical phase difference setting unit 16 may be configured by only one of the translucent plates 16a and 16b, and the optical phase difference (Δφ ₁ −Δφ ₂ ) may be set to π / 2. The optical phase difference setting unit 16 corresponds to the optical phase difference setting means of the present invention.

  It should be noted that the delay amount of the bit delay unit 15 taking into account the delay amount generated by the optical phase difference setting unit 16 can be set, that is, the difference between the two optical paths of the Mach-Zehnder interferometer is a delay corresponding to one bit of the symbol rate. .

  The translucent plate 16a is configured to make the ninth light 109 incident at a constant incident angle. On the other hand, the translucent plate 16b can be rotated in the direction of the arrow shown, and the optical path length of the tenth light 110 can be changed.

  The optical phase difference setting device 16 is not limited to the above-described configuration, and may be configured as shown in FIG. The optical phase difference setting unit 16 shown in FIG. 4 includes translucent plates 16 c and 16 d provided on the optical path of the ninth light 109 and a translucency provided on the optical path of the tenth light 110. Plates 16e and 16f and holding plates 16g and 16h for holding translucent plates 16e and 16f, respectively, are provided.

  The translucent plates 16c and 16d are symmetrically inclined with respect to the ninth light 109 so that the incident angle on the translucent plate 16c and the emission angle on the translucent plate 16d are equal. It has been.

  The translucent plates 16e and 16f are provided so as to be symmetrically inclined in a C shape so that the incident angle of the translucent plate 16e and the emission angle of the translucent plate 16f are equal to the tenth light 110. It has been. In addition, the translucent plates 16e and 16f are configured so that at least one of the holding plates 16g and 16h that respectively hold the tenth plate with respect to the optical phase of the ninth light 109 is rotated in the A direction or the B direction in the drawing. The optical phase of the light 110 can be set.

  With this configuration, the optical phase difference setting unit 16 shown in FIG. 4 connects the translucent plate 16c and the translucent plate 16d, and the translucent plate 16e and the translucent plate 16f with a predetermined angle. In this case, it is preferable to symmetrically incline the C shape so that the influence of beam shift can be eliminated. Further, this configuration is preferable because the return light from the incident surface can be suppressed, unlike the case where the incident angles of the ninth light 109 and the tenth light 110 are substantially 0 °.

  Returning to FIG. 1 again, the description of the configuration of the optical phase modulation evaluation module 10 will be continued.

  Each of the first to fourth light output units 18a to 18d includes a lens, and the light intensity conversion signals 111 to 114 are condensed on the optical fibers 19a to 19d, respectively.

  The first light output unit 18a receives the first light intensity conversion signal 111 and outputs it to the optical fiber 19a. The second light output unit 18b receives the second light intensity conversion signal 112 and outputs it to the optical fiber 19b. The third light output unit 18c receives the third light intensity conversion signal 113 and outputs it to the optical fiber 19c. The fourth light output unit 18d receives the fourth light intensity conversion signal 114 and outputs it to the optical fiber 19d.

  Next, the configuration of an optical phase modulation evaluation apparatus provided with the above-described optical phase modulation evaluation module 10 will be described.

  As shown in FIG. 5, the optical phase modulation evaluation apparatus 100 according to the present embodiment includes an optical phase modulation evaluation module 10, balanced receivers 120 and 130, a signal processing unit 140, and a display unit 150. . Four optical fibers 19 a to 19 d are connected between the optical phase modulation evaluation module 10 and the balanced receivers 120 and 130.

  The balanced receiver 120 receives light intensity conversion signals from the optical phase modulation evaluation module 10 and photoelectrically converts them (hereinafter referred to as “PD”) 121 and 122, and electric signals (PDs 121 and 122 photoelectrically converted) (Hereinafter referred to as “photoelectric conversion signal”).

  The PD 121 receives the first light intensity conversion signal 111 from the first light output unit 18a (see FIG. 1) of the optical phase modulation evaluation module 10 via the optical fiber 19a, performs photoelectric conversion, and subtracts the photoelectric conversion signal. Is output to the device 123. The PD 122 receives the second light intensity conversion signal 112 from the second light output unit 18b (see FIG. 1) of the optical phase modulation evaluation module 10 through the optical fiber 19b, performs photoelectric conversion, and subtracts the photoelectric conversion signal. Is output to the device 123.

  The subtractor 123 outputs a difference between the photoelectric conversion signal output from the PD 121 and the photoelectric conversion signal output from the PD 122.

  With the above configuration, the balanced receiver 120 receives the light intensity conversion signal from the optical fibers 19 a and 19 b, that is, the light intensity conversion signal from the first Mach-Zehnder interferometer, and outputs it to the signal processing unit 140. It is like that.

  The balanced receiver 130 includes PDs 131 and 132 that receive and photoelectrically convert the light intensity conversion signal from the optical phase modulation evaluation module 10, and a subtractor 133 that performs subtraction of the photoelectric conversion signal photoelectrically converted by the PD 131 and 132. ing.

  The PD 131 inputs the third light intensity conversion signal 113 from the third light output unit 18c (see FIG. 1) of the optical phase modulation evaluation module 10 through the optical fiber 19c, performs photoelectric conversion, and subtracts the photoelectric conversion signal. Is output to the device 133. The PD 132 receives the fourth light intensity conversion signal 114 from the fourth light output unit 18d (see FIG. 1) of the optical phase modulation evaluation module 10 via the optical fiber 19d, performs photoelectric conversion, and subtracts the photoelectric conversion signal. Is output to the device 133.

  The subtracter 133 outputs a difference between the photoelectric conversion signal output from the PD 131 and the photoelectric conversion signal output from the PD 132.

  With the above configuration, the balanced receiver 130 receives the balanced light intensity conversion signals from the optical fibers 19c and 19d, that is, the light intensity conversion signal from the second Mach-Zehnder interferometer, and outputs the received signal to the signal processing unit 140. It is like that.

The signal processing unit 140 calculates the relative inter-bit phase difference Δφ _mod due to the phase modulation of the optical phase modulation signal a input to the optical phase modulation evaluation module 10 based on the output signals of the balanced receivers 120 and 130, and Relative bit phase difference histograms, constellations, relative bit phase difference versus time graphs, and the like are obtained.

That is, although not shown, the signal processing unit 140 previously measured and stored the relationship between the output signals output from the balanced receivers 120 and 130 and the phase difference Δφ _mod between the relative bits of the optical phase modulation signal a. A phase difference table, phase difference calculating means for calculating a relative inter-bit phase difference Δφ _mod of the output signals output from the balanced receivers 120 and 130 based on data stored in the phase difference table, and calculated relative bits And a means for calculating a relative inter-bit phase difference histogram, a constellation, a relative inter-bit phase difference versus time graph, and the like based on the inter-phase difference Δφ _mod .

  The display unit 150 includes a liquid crystal display, for example, and displays a relative inter-bit phase difference histogram calculated by the signal processing unit 140, a constellation, a relative inter-bit phase difference versus time graph, and the like.

  Next, the operation of the optical phase modulation evaluation apparatus 100 in the present embodiment will be described.

  First, the operation of the optical phase modulation evaluation module 10 will be described with reference to FIG.

  First, the optical input unit 11 receives the optical phase modulation signal a and outputs it to the optical branching unit 12.

  Next, the optical branching unit 12 branches the light input by the optical input unit 11 into the first light 101 and the second light 102 and outputs the branched light to the multiplexer / demultiplexer 13.

  Further, the multiplexer / demultiplexer 13 demultiplexes the input first light 101 into the third light 103 and the fourth light 104, and outputs the third light 103 to the bit delay device 15. 4 light 104 is output to the second corner mirror 14b. The multiplexer / demultiplexer 13 demultiplexes the input second light 102 into the fifth light 105 and the sixth light 106, and outputs the fifth light 105 to the bit delay unit 15. 6 light 106 is output to the second corner mirror 14b.

  Subsequently, the second corner mirror 14 b reflects the input fourth light 104 and outputs it as the ninth light 109 to the translucent plate 16 a of the optical phase difference setting device 16, and the ninth light 109. Is transmitted through the translucent plate 16 a and input to the multiplexer / demultiplexer 13. The second corner mirror 14b reflects the input sixth light 106 and outputs it as tenth light 110 to the light transmitting plate 16b of the optical phase difference setting device 16, and the tenth light 110 is The light is transmitted through the translucent plate 16 b and input to the multiplexer / demultiplexer 13. Here, the tenth light 110 input to the translucent plate 16b is delayed by the translucent plate 16b so that the twenty-second optical path has a predetermined phase difference with respect to the twelfth optical path. Is output to the device 13.

  On the other hand, the third light 103 and the fifth light 105 input to the bit delay unit 15 are delayed by a delay time corresponding to one bit of the symbol rate by the bit delay unit 15, respectively, and the first corner mirror 14a. Is input.

  Next, the first corner mirror 14 a reflects the third light 103 delayed by the bit delay device 15 and outputs it to the multiplexer / demultiplexer 13 as the seventh light 107. The first corner mirror 14 a reflects the fifth light 105 delayed by the bit delay device 15 and outputs it to the multiplexer / demultiplexer 13 as the eighth light 108.

  Subsequently, the multiplexer / demultiplexer 13 multiplexes and interferes with the eighth light 108 and the tenth light 110 to convert the phase change into the light intensity change, and has an optical phase difference of π from each other. The first light intensity conversion signal 111 and the second light intensity conversion signal 112 are output. Further, the multiplexer / demultiplexer 13 combines the seventh light 107 and the ninth light 109 to interfere with each other, thereby converting the phase change into the light intensity change and having an optical phase difference of π from each other. The third light intensity conversion signal 113 and the fourth light intensity conversion signal 114 are output.

  Then, the first light output unit 18a receives the first light intensity conversion signal 111 and outputs it to the optical fiber 19a. The second light output unit 18b receives the second light intensity conversion signal 112 and outputs it to the optical fiber 19b. The third light output unit 18c receives the third light intensity conversion signal 113 and outputs it to the optical fiber 19c. The fourth light output unit 18d receives the fourth light intensity conversion signal 114 and outputs it to the optical fiber 19d.

  Next, the subsequent operation of the optical phase modulation evaluation module 10 will be described with reference to FIG.

  First, in the balanced receiver 120, the PD 121 receives the first light intensity conversion signal 111 from the first light output unit 18a (see FIG. 1) via the optical fiber 19a, performs photoelectric conversion, and converts the photoelectric conversion signal into the photoelectric conversion signal. Output to the subtractor 123.

  Similarly, the PD 122 receives the second light intensity conversion signal 112 from the second light output unit 18b (see FIG. 1) via the optical fiber 19b, performs photoelectric conversion, and outputs the photoelectric conversion signal to the subtractor 123. To do.

  Next, the subtractor 123 outputs the difference between the photoelectric conversion signal output from the PD 121 and the photoelectric conversion signal output from the PD 122 to the signal processing unit 140.

Here, the first light intensity conversion signal 111 and the second light intensity conversion signal 112 are defined as P ₁ and P ₂ based on the same conditions as described in the section “Problems to be Solved by the Invention”, respectively. When expressed by mathematical formulas, P ₁ and P ₂ are represented by formulas (10) and (11) (repost).

P ₁ = 0.5 + 0.5 cos (Δφ _mod ) (10)
P ₂ = 0.5−0.5 cos (Δφ _mod ) (11)
Therefore, the output signal P output from the subtractor 123 is expressed by the equation (14), the offset power is canceled, and the light intensity is doubled. As a result, the light intensity I _α corresponding to the output signal P output from the subtractor 123 is expressed by equation (15).

P = P ₁ −P ₂ = cos (Δφ _mod ) (14)
I _α ∝cos (Δφ _mod ) (15)
Next, in the balanced receiver 130, the PD 131 receives the third light intensity conversion signal 113 from the third light output unit 18c (see FIG. 1) via the optical fiber 19c, performs photoelectric conversion, and performs photoelectric conversion. Is output to the subtracter 133.

  Similarly, the PD 132 receives the fourth light intensity conversion signal 114 from the fourth light output unit 18d (see FIG. 1) via the optical fiber 19d, performs photoelectric conversion, and outputs the photoelectric conversion signal to the subtracter 133. To do.

  Next, the subtracter 133 outputs the difference between the photoelectric conversion signal output from the PD 131 and the photoelectric conversion signal output from the PD 132 to the signal processing unit 140.

Here, the third light intensity conversion signal 113 and the fourth light intensity conversion signal 114 are set as P ₁ and P ₂ based on the same conditions as described in the section “Problems to be Solved by the Invention”, respectively. In terms of mathematical expression, since the optical phase difference setting device 16 (see FIG. 1) is provided, P ₁ and P ₂ are represented by the expressions (16) and (17).

P ₁ = 0.5 + 0.5 cos (Δφ _mod + π / 2) (16)
P ₂ = 0.5−0.5 cos (Δφ _mod + π / 2) (17)
Therefore, the output signal P output from the subtracter 133 is expressed by the equation (18), and the offset power is canceled and the light intensity is doubled. As a result, the light intensity _Iβ corresponding to the output signal P output from the subtracter 133 is expressed by equation (19).

P = P ₁ −P ₂ = cos (Δφ _mod + π / 2) (18)
I _β ∝cos (Δφ _mod + π / 2) (19)
The light intensity I _β expressed by the equation (19) has a relationship as shown in FIG. 6 with respect to the light intensity I _α expressed by the equation (15). That is, the light intensity I _beta, becomes phase than the light intensity I _alpha is delayed by π / 2 (90 °).

Subsequently, the signal processing unit 140 measures and stores in advance the relationship between the output signals output from the balanced receivers 120 and 130 and the relative inter-bit phase difference Δφ _mod of the optical phase modulation signal a (not shown). ), The relative inter-bit phase difference Δφ _mod is calculated based on the output signals output from the balanced receivers 120 and 130, respectively. Further, the signal processing unit 140 obtains a relative inter-bit phase difference histogram, a constellation, a relative inter-bit phase difference versus time graph, and the like based on the calculated relative inter-bit phase difference Δφ _mod , and displays these data on the display unit 150. Output to.

Here, as described above, since there is a phase difference of π / 2 between the phase of the light intensity I _{α and} the phase of the light intensity I _β , the signal processing unit 140 determines that the light intensity I _α and I _β are Based on this, the relative inter-bit phase difference Δφ _mod can be specified (see FIG. 6).

  Finally, the display unit 150 displays a relative bit phase difference histogram calculated by the signal processing unit 140, a constellation, a relative bit phase difference versus time graph, and the like.

  As described above, according to the optical phase modulation evaluation module 10 in the present embodiment, the bit delay unit 15 receives the symbols of the input optical phase modulation signal a for the third light 103 and the fifth light 105. The optical phase difference setting unit 16 delays by one bit of the rate, and sets the optical phase difference between the ninth light 109 and the tenth light 110 to a predetermined optical phase difference excluding zero. Therefore, unlike conventional ones, two optical interferometers are configured with one module, and signals with optical phase differences of 0 and π / 2 can be output at the same time. Can be set. Therefore, the optical phase modulation evaluation module 10 in the present embodiment can evaluate the modulation state of the optical phase modulation signal a more accurately than in the past.

  Moreover, according to the optical phase modulation evaluation apparatus 100 in the present embodiment, the optical phase modulation evaluation module 10 that can measure the relative phase difference between the optical phase modulation signals a is provided. A relative inter-bit phase difference histogram, a constellation, a relative inter-bit phase difference versus time graph, and the like can be calculated based on the relative inter-bit phase difference of the phase modulation signal a. The optical phase modulation signal a can be evaluated more accurately.

  In the above-described embodiment, the configuration in which the optical branching unit 12 includes the plurality of mirrors 12a has been described as an example. However, the present invention is not limited to this, and for example, as illustrated in FIG. The same effect can be obtained when the optical branching unit 12 includes the optical coupler 12c.

  In the above-described embodiment, the bit delay unit 15 is provided on the optical paths of the third light 103 and the fifth light 105, and the optical phase difference is set on the optical paths of the ninth light 109 and the tenth light 110. The configuration provided with the vessel 16 has been described as an example, but the present invention is not limited to this.

  Specifically, the bit delay unit 15 includes, on the optical path of the fourth light 104 and the sixth light 106, the seventh light 107 and the fifth light 105, in addition to the optical paths of the third light 103 and the fifth light 105. It can be configured to be provided either on the optical path of the eighth light 108 or on the optical path of the ninth light 109 or the tenth light 110.

  On the other hand, the optical phase difference setting unit 16 includes the fourth light 104 and the sixth light on the optical paths of the third light 103 and the fifth light 105 in addition to the optical paths of the ninth light 109 and the tenth light 110. The light 106 can be provided either on the optical path of the light 106 or on the optical path of the seventh light 107 or the eighth light 108.

(Second Embodiment)
Next, a second embodiment of the optical phase modulation evaluation apparatus according to the present invention will be described.

  As shown in FIG. 8, the optical phase modulation evaluation module 20 included in the optical phase modulation evaluation apparatus in the present embodiment is a bit delay unit 15 of the optical phase modulation evaluation module 10 (see FIG. 1) in the first embodiment. Is changed to a bit delay device 21 and a delay amount setting means 22 is added. Therefore, the same components as those of the optical phase modulation evaluation module 10 are denoted by the same reference numerals, and redundant description is omitted.

Bit delay unit 21 has a thickness and the transparent plate 21a of _{d 1} in the traveling direction of the third light 103 and a fifth light 105, a thickness and a translucent plate 21b of _{d 2} . Although not shown, the bit delay unit 21 is held by a parallel holding unit that can move in the direction of the arrow shown in the figure, and an optical path length corresponding to a one-bit delay of the symbol rate is switched according to the symbol rate. It is like that.

  The delay amount setting means 22 receives the symbol rate designation signal and outputs a signal indicating an instruction to switch the light-transmitting plates 21a and 21b to the bit delay unit 21.

The translucent plates 21a and 21b are made of, for example, a quartz glass plate. The translucent plate 21a has a refractive index of 1.5 and a thickness d ₁ = 30 [mm], for example, and delays the optical phase modulation signal a having a symbol rate SR = 20 [Gbps] by one bit. ing. The translucent plate 21b has a refractive index of 1.5 and a thickness d ₂ = 15 [mm], for example, and delays the optical phase modulation signal a having a symbol rate SR = 40 [Gbps] by one bit. ing.

  Note that the configuration of the bit delay device 21 is not limited to that shown in FIG. 8, and may be as shown in FIG. 9, for example.

First, the bit delay unit 23 shown in FIG. 9A has two light-transmitting plates 23a ₁ and 23b ₁ and 23a ₂ and 23b ₂ which are different in thickness and are made of parallel plates of the same material. For the third light 103 and the fifth light 105 so that the incident angles of the light-transmitting plates 23a ₁ and 23b ₁ and the emission angles of the light-transmitting plates 23a ₂ and 23b ₂ are equal. The plates 23a ₁ and 23b ₁ and 23a ₂ and 23b ₂ are arranged so as to be symmetrically inclined in a letter C shape. Here, the 23a side where the translucent plate is thick is for symbol rate SR = 20 [Gbps], and the 23b side where the translucent plate is thin is for symbol rate SR = 40 [Gbps]. . With this configuration, the bit delay unit 23 shown in FIG. 9A can switch the optical path length in accordance with the symbol rate by translating the bit delay unit 23 in the direction of the illustrated arrow.

  Next, the bit delay unit 24 shown in FIG. 9B includes two transmission bodies 24a whose cross sections parallel to the traveling directions of the third light 103 and the fifth light 105 are triangular (wedge-shaped). 24b. The transmissive body 24a is fixed to a holding portion (not shown), and the transmissive body 24b can move in the direction of the arrow shown. With this configuration, the bit delay unit 24 shown in FIG. 9B can switch the optical path length according to the symbol rate by moving the transmissive body 24b in the direction of the arrow shown.

  The two transmission bodies 24a and 24b may be configured to be movable. In FIG. 9B, the incident angle and the emission angle of the third light 103 and the fifth light 105 are substantially 0 °, but the transmission bodies 24a and 24b are inclined to The incident angle and the emission angle of the light 103 and the fifth light 105 may be set to predetermined angles. This configuration is preferable because reflection at the incident surface can be suppressed.

  As described above, according to the optical phase modulation evaluation module 20 in the present embodiment, the bit delay unit 21 is a translucent plate having different thicknesses in the traveling direction of the third light 103 and the fifth light 105. Since the configuration includes 21a and 21b, an optical path length corresponding to a one-bit delay of the symbol rate can be switched and provided according to the symbol rate.

  In addition, although the example in the case of a symbol rate of 20 [Gbps] and 40 [Gbps] has been described, the present invention is not limited to this. For example, by configuring the bit delay unit 21 with three parallel plates having different thicknesses, it is possible to cope with three symbol rates.

(Third embodiment)
Next, a third embodiment of the optical phase modulation evaluation apparatus according to the present invention will be described.

  As shown in FIG. 10, the optical phase modulation evaluation module 30 included in the optical phase modulation evaluation apparatus according to the present embodiment includes a phase adjustment delay in addition to the optical phase modulation evaluation module 10 (see FIG. 1) according to the first embodiment. A device 31 is added. Therefore, the same components as those of the optical phase modulation evaluation module 10 are denoted by the same reference numerals, and redundant description is omitted.

  The phase adjusting delay unit 31 includes a translucent plate such as a quartz glass plate that transmits the seventh light 107 and the eighth light 108 and has the same refractive index and is parallel. The phase adjusting delay unit 31 can be rotated in the direction of the arrow shown in the figure, and gives a predetermined optical path length on the optical paths of the seventh light 107 and the eighth light 108. The phase adjusting delay unit 31 corresponds to the optical phase difference adjusting means of the present invention.

Therefore, the optical path lengths of the seventh light 107 and the eighth light 108 change by rotating the phase adjusting delay unit 31 in the direction of the arrow shown in the figure, and as a result, the first to fourth light output units 18a. The light intensity with respect to the relative inter-bit phase difference Δφ _mod of the light intensity conversion signals output from ˜18d varies. By adjusting the delay amount of the phase adjusting delay unit 31, the initial phase (φ) of the relative inter-bit phase difference calculated based on the light intensity of the light intensity conversion signal can be adjusted.

  Note that the configuration of the phase adjusting delay unit 31 is not limited to that shown in FIG. 10. For example, similarly to the translucent plates 16 e and 16 f of the optical phase difference setting unit 16 described in FIG. 4. Two rotatable light-transmitting plates are provided, and the incident angle on one light-transmitting plate is equal to the emission angle on the other light-transmitting plate with respect to the seventh light 107 and the eighth light 108. It can also be set as the structure which inclines symmetrically to a square shape so that it may become.

  Since the optical phase modulation evaluation module 30 is configured as described above, the optical phase modulation evaluation module 30 is used in place of the optical phase modulation evaluation module 10 shown in FIG. By monitoring the photoelectric conversion signals output by the respective 132, the optical phase of the light intensity conversion signals input to the balanced receivers 120 and 130 can be easily adjusted.

As described above, according to the optical phase modulation evaluation module 30 in the present embodiment, the phase adjusting delay unit 31 transmits the seventh light 107 and the eighth light 108 and is rotatable. Therefore, by changing the optical path lengths of the seventh light 107 and the eighth light 108, the phases of the light intensity conversion signals output from the first to fourth light output units 18a to 18d are changed. It is possible to shift and add an offset phase to the relative inter-bit phase difference Δφ _mod .

  In the above-described embodiment, the configuration in which the phase adjusting delay unit 31 is provided on the optical paths of the seventh light 107 and the eighth light 108 has been described, but the present invention is not limited to this. On the optical path of the two lights from the multiplexer / demultiplexer 13 via the first corner mirror 14a to the multiplexer / demultiplexer 13 and from the multiplexer / demultiplexer 13 to the multiplexer / demultiplexer 13 via the second corner mirror 14b. It is possible to adopt a configuration in which the phase adjusting delay unit 31 is provided on either of the two optical paths.

(Fourth embodiment)
Next, a fourth embodiment of the optical phase modulation evaluation apparatus according to the present invention will be described.

  As shown in FIG. 11, the optical phase modulation evaluation module 40 included in the optical phase modulation evaluation apparatus according to the present embodiment includes a phase adjuster 41 in addition to the optical phase modulation evaluation module 10 (see FIG. 1) according to the first embodiment. Is added. Therefore, the same components as those of the optical phase modulation evaluation module 10 are denoted by the same reference numerals, and redundant description is omitted.

  The phase adjuster 41 adjusts the phase of the photoelectric conversion signal in the balanced receivers 120 and 130 (see FIG. 5), and is provided on the optical path of the second light intensity conversion signal 112 as shown in FIG. The mirror 41a, the corner mirror 41b, and the mirror 41c, and the mirror 41d, the corner mirror 41e, and the mirror 41f provided on the optical path of the fourth light intensity conversion signal 114 are provided. The corner mirrors 41b and 41e are separately held by holding means (not shown) and can move independently of each other in the direction of the arrow in the figure. Here, the phase adjuster 41 corresponds to the optical path length adjusting means of the present invention.

  With this configuration, the phase adjuster 41 can independently change the optical path length of the second light intensity conversion signal 112 and the optical path length of the fourth light intensity conversion signal 114.

  In FIG. 11, the initial position of the corner mirror 41b is the optical path length (111, 18a, 19a) from the multiplexer / demultiplexer 13 to the PD 121 (see FIG. 5) and the multiplexer / demultiplexer 13 to the PD 122 (see FIG. 5). It is preferable that the optical path length (112, 18b, 19b) up to () is approximately equal. The initial position of the corner mirror 41e is the optical path length (113, 18c, 19c) from the multiplexer / demultiplexer 13 to the PD 131 (see FIG. 5) and the optical path from the multiplexer / demultiplexer 13 to the PD 132 (see FIG. 5). It is preferable to set the length (114, 18d, 19d) at a substantially equal position.

  Since the optical phase modulation evaluation module 40 is configured as described above, the balanced receivers 120 and 130 can be obtained by using the optical phase modulation evaluation module 40 instead of the optical phase modulation evaluation module 10 shown in FIG. The phase of the photoelectric conversion signal at can be adjusted to a phase difference of 180 ° (π).

  Therefore, for example, even when the optical fibers 19a and 19b shown in FIG. 5 are slightly different in length from each other, the phase of the photoelectric conversion signals of the PDs 121 and 122 is shifted from the desired value. By adjusting the device 41, it can be matched with the desired value.

  As described above, according to the optical phase modulation evaluation module 40 in the present embodiment, the phase adjuster 41 determines the optical path length of the second light intensity conversion signal 112 and the optical path length of the fourth light intensity conversion signal 114. Since the configurations are changed independently of each other, the phases of the photoelectric conversion signals in the balanced receivers 120 and 130 can be adjusted.

  In the above-described embodiment, the configuration in which the phase adjuster 41 is provided on the optical path of the second light intensity conversion signal 112 and the fourth light intensity conversion signal 114 has been described, but the present invention is limited to this. Instead, the same effect can be obtained by providing the phase adjuster 41 on the optical path between the multiplexer / demultiplexer 13 and at least one of the balanced receivers 120 and 130.

  In addition, the configuration of the phase adjuster 41 is not limited to that shown in FIG. 11. For example, the light is transmitted through the optical paths of the second light intensity conversion signal 112 and the fourth light intensity conversion signal 114, respectively. An optical plate can be provided, and the two light-transmitting plates can be separately rotated to change the optical path length.

(Fifth embodiment)
Next, a fifth embodiment of the optical phase modulation evaluation apparatus according to the present invention will be described.

  As shown in FIG. 12, the optical phase modulation evaluation module 50 provided in the optical phase modulation evaluation apparatus according to the present embodiment changes a part of the optical phase modulation evaluation module 20 (see FIG. 8) according to the second embodiment. The bit delay unit 21 is abolished and a corner mirror moving means 51 is added. Therefore, the same components as those of the optical phase modulation evaluation module 20 are denoted by the same reference numerals, and redundant description is omitted.

  In the present embodiment, the delay amount setting means 22 receives a symbol rate designation signal and outputs a signal for giving an optical path length corresponding to a 1-bit delay of the symbol rate to the corner mirror moving means 51. ing.

  Based on the delay amount setting signal output from the delay amount setting unit 22, the corner mirror moving unit 51 gives the first corner mirror 14a an optical path length corresponding to a 1-bit delay of the symbol rate in the direction of the arrow in the figure. It is designed to move. The first corner mirror 14a is held by a holder (not shown) and moves in the direction of the arrow in the figure.

  As described above, according to the optical phase modulation evaluation module 50 in the present embodiment, the corner mirror moving unit 51 sets the optical path length corresponding to the 1-bit delay of the symbol rate by moving the first corner mirror 14a. Therefore, the bit delay amount can be adjusted corresponding to a plurality of symbol rates.

  In the above-described embodiment, the configuration in which the corner mirror moving unit 51 moves the first corner mirror 14a has been described. However, the present invention is not limited to this, and the first corner mirror 14a and the second corner mirror 14a are moved. A similar effect can be obtained by a configuration in which at least one of the mirrors 14b is moved so as to give an optical path length corresponding to a one-bit delay of the symbol rate.

  In addition, the optical phase modulation evaluation module 50 according to the present embodiment is combined with the bit delay unit 15 (see FIG. 1), the bit delay unit 21 (see FIG. 8), etc. An optical path length corresponding to the delay can be provided.

  As described above, the optical phase modulation evaluation apparatus according to the present invention has an effect that the modulation state of the optical phase modulation signal can be evaluated more accurately than before, and the optical carrier wave in the coherent optical communication system is the data signal. It is useful as an optical phase modulation evaluation apparatus that evaluates an optical phase modulation signal phase-modulated by the above.

The block diagram which shows the structure in 1st Embodiment of the optical phase modulation evaluation module which concerns on this invention The figure which shows the structural example which divided | segmented the multiplexer / demultiplexer into the splitter and the multiplexer in 1st Embodiment of the optical phase modulation evaluation module which concerns on this invention The figure which shows the other structural example of a bit delay device in 1st Embodiment of the optical phase modulation evaluation module which concerns on this invention. The figure which shows the other structural example of an optical phase difference setting device in 1st Embodiment of the optical phase modulation evaluation module which concerns on this invention. 1 is a block diagram showing a configuration of an optical phase modulation evaluation apparatus including an optical phase modulation evaluation module according to the present invention. The figure which shows the phase relationship of optical intensity I _alpha and I _beta in 1st Embodiment of the optical phase modulation evaluation module which concerns on this invention The block diagram which shows the other structural example of the optical branching part in 1st Embodiment of the optical phase modulation evaluation module which concerns on this invention The block diagram which shows the structure in 2nd Embodiment of the optical phase modulation evaluation module which concerns on this invention The figure which shows the other structural example of a bit delay device in 2nd Embodiment of the optical phase modulation evaluation module which concerns on this invention. The block diagram which shows the structure in 3rd Embodiment of the optical phase modulation evaluation module which concerns on this invention The block diagram which shows the structure in 4th Embodiment of the optical phase modulation evaluation module which concerns on this invention The block diagram which shows the structure in 5th Embodiment of the optical phase modulation evaluation module which concerns on this invention Block diagram showing the configuration of a conventional optical phase modulation evaluation module The figure which shows the phase of optical intensity I _alpha in the conventional optical phase modulation evaluation apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical phase modulation evaluation module 11 Optical input part 12 Optical branch part 12a Multiple mirror 12b Beam splitter 12c Optical coupler 13 Multiplexer 13a Demultiplexer 13b Multiplexer 14a First corner mirror 14b Second corner mirror 15 Bit delay 15a, 15b Translucent plate 16 Optical phase difference setting device (optical phase difference setting means)
16a to 16f Translucent plate 16g, 16h Holding plate 17 Phase control means 18a First light output unit 18b Second light output unit 18c Third light output unit 18d Fourth light output unit 19a to 19d Optical fiber 20 Optical phase modulation evaluation module 21 bit delay units 21a, 21b translucent plate 22 delay amount setting means 23 bit delay units 23a (23a ₁ , 23a ₂ ), 23b (23b ₁ , 23b ₂ ) translucent plate 24 (24a, 24b) Transmitter 30 Optical phase modulation evaluation module 31 Phase adjustment delay device (optical phase adjustment means)
40 optical phase modulation evaluation module 41 phase adjuster (optical path length adjusting means)
41a, 41c, 41d, 41f Mirror 41b, 41e Corner mirror 50 Optical phase modulation evaluation module 51 Corner mirror moving means 100 Optical phase modulation evaluation device 101 First light 102 Second light 103 Third light 104 Fourth light 105 5th light 106 6th light 107 7th light 108 8th light 109 9th light 110 10th light 111 1st light intensity conversion signal 112 2nd light intensity conversion signal 113 3rd Light intensity conversion signal 114 Fourth light intensity conversion signal 120, 130 Balanced receiver 121, 122, 131, 132 PD
123, 133 Subtractor 140 Signal processing unit 150 Display unit

Claims (13)

An optical input unit (11) for inputting an optical phase modulation signal (a) in which an optical carrier wave is phase-modulated by a data signal at a predetermined symbol rate, and the inputted optical phase modulation signal (a) is converted into a first light ( 101) and the second light (102), and the first light (101) is split into the third light (103) and the fourth light (104). And a demultiplexer (13a) for demultiplexing the second light (102) into a fifth light (105) and a sixth light (106), and reflecting the third light (103). A first corner mirror (14a) that outputs the seventh light (107) and reflects the fifth light (105) and outputs it as the eighth light (108); and the fourth light (104). ) And output as the ninth light (109) and reflect the sixth light (106). By combining the second corner mirror (14b) output as the tenth light (110), the seventh light (107) and the ninth light (109), the optical phase modulation signal (a ) Is converted into a change in light intensity to output first and second light intensity conversion signals (111, 112) having an optical phase difference of π, and the eighth light (108). By combining the tenth light (110) with the tenth light (110), the phase change of the optical phase modulation signal (a) is converted into a change in light intensity, and the third and fourth optical phase differences having a π optical phase difference from each other are obtained. A multiplexer (13b) that outputs a light intensity conversion signal (113, 114), and 2 from the duplexer (13a) to the multiplexer (13b) via the first corner mirror (14a). On the optical path of two lights and from the duplexer (13a) A bit delay unit (15) for providing a delay corresponding to one bit of the symbol rate in one of two optical paths to the multiplexer (13b) via the mirror (14b); On the optical path of two lights from the waver (13a) to the multiplexer (13b) via the first corner mirror (14a) and from the duplexer (13a) to the second corner mirror (14b) An optical phase difference setting means (16) that gives a delay of a predetermined optical phase to at least one of the two lights on any one of the two light paths reaching the multiplexer (13b) via A first light receiving unit (120) that receives and converts at least one of the first and second light intensity conversion signals (111, 112) into an electric signal; and the third and fourth light intensities. Conversion signal (113, 114 A second light receiving unit (130) that receives at least one of the optical signals and converts it into an electrical signal, and the optical phase modulation signal based on the output signals of the first and second light receiving units (120, 130). An optical phase modulation evaluation apparatus comprising a signal processing unit (140) for analyzing (a). An optical input unit (11) for inputting an optical phase modulation signal (a) in which an optical carrier wave is phase-modulated by a data signal at a predetermined symbol rate, and the inputted optical phase modulation signal (a) is converted into a first light ( 101) and the second light (102), and the first light (101) is split into the third light (103) and the fourth light (104). And a demultiplexer (13a) for demultiplexing the second light (102) into a fifth light (105) and a sixth light (106), and reflecting the third light (103). A first corner mirror (14a) that outputs the seventh light (107) and reflects the fifth light (105) and outputs it as the eighth light (108); and the fourth light (104). ) And output as the ninth light (109) and reflect the sixth light (106). By combining the second corner mirror (14b) output as the tenth light (110), the seventh light (107) and the ninth light (109), the optical phase modulation signal (a ) Is converted into a change in light intensity to output first and second light intensity conversion signals (111, 112) having an optical phase difference of π, and the eighth light (108). By combining the tenth light (110) with the tenth light (110), the phase change of the optical phase modulation signal (a) is converted into a change in light intensity, and the third and fourth optical phase differences having a π optical phase difference from each other are obtained. A multiplexer (13b) that outputs a light intensity conversion signal (113, 114) and at least one of the first corner mirror (14a) and the second corner mirror (14b) are moved in a predetermined direction to generate the symbol. Corresponds to 1 bit of rate A corner mirror moving means (51) for providing an extension; and on the optical path of the two lights from the duplexer (13a) to the multiplexer (13b) via the first corner mirror (14a) At least one of the two lights on the optical path of the two lights from the waver (13a) to the multiplexer (13b) via the second corner mirror (14b) has a predetermined optical phase. An optical phase difference setting means (16) for providing a delay, and a first light receiving section (for receiving at least one of the first and second light intensity conversion signals (111, 112) and converting it into an electrical signal ( 120), a second light receiving unit (130) that receives and converts at least one of the third and fourth light intensity conversion signals (113, 114) into an electrical signal, and the first and Second light receiving part (120, 13 ) Signal processing unit (140 analyzing the optical phase modulation signal (a) based on the output signal of) the optical phase modulation evaluating apparatus characterized by comprising a. The optical phase modulation evaluation apparatus according to claim 1 or 2, further comprising a multiplexer / demultiplexer (13) in which the duplexer (13a) and the multiplexer (13b) are integrated. The optical phase modulation evaluation apparatus according to any one of claims 1 to 3, wherein the optical branching section (12) includes an optical coupler (12c). The optical phase difference setting means (16) sets the difference between the optical phase delay amount applied to the ninth light (109) and the optical phase delay amount applied to the tenth light (110) to π / 2. The optical phase modulation evaluation apparatus according to claim 1, wherein the optical phase modulation evaluation apparatus is set. The optical phase modulation evaluation apparatus according to claim 1, wherein the bit delay unit (15) selects and switches one of a plurality of optical path lengths determined in advance according to the symbol rate. The bit delay unit (15) is a parallel plate (21a, 21b) of a transparent material having a thickness that gives a delay amount corresponding to one bit of the symbol rate, and corresponds to each of the plurality of symbol rates. 7. The optical phase modulation evaluation apparatus according to claim 6, wherein a plurality of the parallel plates (21a, 21b) having a predetermined thickness are provided, and a delay amount corresponding to the symbol rate can be set by switching between them. The bit delay unit (15) is made of two transparent materials in which a first parallel plate (23a ₁ , 23b ₁ ) and a second parallel plate (23a ₂ , 23b ₂ ) are arranged in a C shape. A pair of parallel plates (23a, 23b) having a plurality of parallel plate pairs (23a, 23b) each having a thickness corresponding to each of the plurality of symbol rates, the parallel plate pairs (23a, 23b). The optical phase modulation evaluation apparatus according to claim 6, wherein a delay amount corresponding to the symbol rate can be set by switching. The bit delay unit (15) is a pair of wedge-shaped transmission bodies (24a, 24b) arranged so that the transmission surfaces face each other, and at least one of the transmission bodies (24a, 24b) The optical phase modulation evaluation apparatus according to claim 1, wherein the delay amount corresponding to each of the plurality of symbol rates can be set by moving and adjusting an optical path length. The optical phase difference setting means (16) is a parallel plate (16a, 16b) made of a transparent material, and rotates the parallel plate (16a, 16b) to transmit light to the parallel plate (16a, 16b). The optical phase modulation evaluation apparatus according to any one of claims 1 to 9, wherein an arbitrary delay amount can be set by changing an incident angle. The optical phase difference setting means (16) is a pair of two parallel plates (16e, 16f) made of a transparent material arranged in a letter C shape, and the two parallel plates (16e, 16f) Any one of claims 1 to 9 can be set to an arbitrary delay amount by changing the incident angle of the light to the parallel plate (16e, 16f) by rotating at least one of them. The optical phase modulation evaluation apparatus described. The signal processing unit (140) is a signal processing unit that evaluates the modulation phase of the optical phase modulation signal (a), and passes through the first corner mirror (14a) from the duplexer (13a). On the optical path of two lights reaching the multiplexer (13b) and on the optical path of two lights reaching the multiplexer (13b) from the duplexer (13a) via the second corner mirror (14b) And an optical phase adjusting means (31) for giving a delay of the optical phase, and by varying the delay amount of the optical phase, the initial phase of the phase difference between the relative bits calculated by the signal processing unit (140) ( The optical phase modulation evaluation apparatus according to any one of claims 1 to 11, wherein φ) is adjustable. The signal processing unit (140) is a signal processing unit that evaluates a modulation phase of the optical phase modulation signal (a), and includes the multiplexer (13b) and the first and second light receiving units (120, 120). 130), an optical path length adjusting means (41) for adjusting an optical path length on an optical path between at least one of the light receiving sections, and the first and second light receiving sections (120, 130) converted respectively. 12. The optical phase modulation evaluation apparatus according to claim 1, wherein the phase of the electric signal is adjustable.

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