JP2009246578A - Optical transmission device, and optical test device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission device which controls the phase difference of an optical signal passed through a data modulation section to a predetermined phase difference without causing a deterioration in a phase-modulated optical signal, and to provide an optical test device having the device. <P>SOLUTION: The optical transmission device 1 includes a π/2 phase shift section 22 which gives a phase difference of π/2 between branched optical signals L11 and L12, modulators 23a and 23b which modulate the optical signals L11 and L12 respectively using data signals D1 and D2 input from outside, an RZ modulator 30 which performs RZ intensity modulation on the combined optical signals L11 and L12, and a phase adjusting circuit 48 which adjusts the phase difference between the optical signals L11 and L12 given by the π/2 phase shift section 22 to π/2 using a signal obtained by multiplying a signal obtained by multiplying the data signals D1 and D2 by each other, by a photodetection signal R1 output from a photodiode 43. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical transmission apparatus that transmits a phase-modulated optical signal and an optical test apparatus including the apparatus.

  In recent years, research and development have been actively conducted to realize large capacity and long distance of optical transmission systems. In particular, DPSK (Differential Phase Shift Keying) and DQPSK (Differential Quadrature Phase Shift Keying) are used to increase the maximum transmission speed of optical transmission systems from 10 Gbps (bit per second) to 40 Gbps. The practical application of an optical transmission system using a phase modulation method such as shift modulation is expected.

In Patent Document 1 below, a pair of arms that form a data modulation unit that divides and modulates light from a light source, and a predetermined phase difference (for example, π / 2) with respect to an optical signal that passes through each of these arms. A phase shift unit for providing a signal, and combining the optical signal transmitted through the data modulation unit and transmitting it as a phase modulated optical signal. The phase shift unit is controlled based on at least one of the power maximum value, power minimum value, and phase of the low-frequency signal included in the phase-modulated optical signal obtained by superimposing and combining the optical signals on which the low-frequency signal is superimposed. Techniques to do this are disclosed.
JP 2007-43638 A

  By the way, in the technique disclosed in Patent Document 1 described above, in order to control the phase shift unit, a low frequency signal is superimposed on the optical signal that passes through each of the pair of arms forming the data modulation unit. A phase-modulated optical signal is obtained by combining optical signals on which frequency signals are superimposed. However, since the phase of the phase-modulated optical signal transmitted from the optical transmission device is changed by superimposing the low-frequency signal, there is a problem that the phase-modulated signal is deteriorated.

  The present invention has been made in view of the above circumstances, and an optical transmitter capable of controlling a phase difference of an optical signal via a data modulation unit to a predetermined phase difference without causing deterioration of the phase-modulated optical signal, And it aims at providing an optical test apparatus provided with the said apparatus.

In order to solve the above-described problems, the optical transmission apparatus of the present invention is configured so that the first and second optical signals (L11, L12) obtained by branching input light have a predetermined phase difference. Modulator (20) for controlling the phase of at least one of the two optical signals and modulating the first and second optical signals in accordance with the first and second data signals (D1, D2) input from the outside. In the optical transmission device (1) that outputs a phase-modulated optical signal (L1) obtained by combining the first and second optical signals via the modulation unit, the first data signal and the second data signal A first calculation unit (44) that multiplies, a light receiving unit (43) that receives the phase-modulated optical signal, an output signal of the first calculation unit, and a light reception signal (R1) output from the light receiving unit. A second arithmetic unit (45) for multiplying, and an output signal of the second arithmetic unit First controlled by the modulating unit it has, is characterized in that it comprises a phase adjustment unit (48) for adjusting the phase difference between the second optical signal.
According to the present invention, the first and second data signals input from the outside are multiplied by the first calculation unit, and the output signal of the first calculation unit and the light reception signal output from the light receiving unit are the second calculation unit. The phase adjustment unit adjusts the phase difference between the first and second optical signals using the output signal of the second calculation unit.
The optical transmission device of the present invention further includes an averaging processing unit (46) that averages the output signal of the second arithmetic unit, and the phase adjusting unit is averaged by the averaging processing unit. A phase difference between the first and second optical signals is adjusted using a signal.
Moreover, the optical transmission apparatus of the present invention includes a first low-pass filter (51) for reducing the frequency of the output signal of the first arithmetic unit, and a second low-pass filter for reducing the frequency of the light reception signal output from the light receiving unit. (52), wherein the second arithmetic unit multiplies the signal that has passed through the first and second low-pass filters.
The optical transmission apparatus of the present invention includes a third low-pass filter (61a) for reducing the frequency of the first data signal, a fourth low-pass filter (61b) for reducing the frequency of the second data signal, and the light reception. And a fifth low-pass filter (62) for reducing the frequency of the received light signal output from the unit, wherein the first arithmetic unit multiplies the signal that has passed through the third and fourth low-pass filters, The second operation unit multiplies the output signal of the first operation unit by the signal that has passed through the fifth low-pass filter.
Further, in the optical transmission device of the invention, the phase adjustment unit uses the signal averaged by the averaging processing unit and the signal obtained by averaging the light reception signal output from the light reception unit. Calculating the absolute value of the amount of deviation of the phase difference between the first and second optical signals from the target phase difference and adjusting the phase difference between the first and second optical signals using the absolute value. It is a feature.
The optical test apparatus of the present invention is the optical test apparatus for testing an optical receiver that receives a phase-modulated optical signal, and transmits the phase-modulated optical signal received by the optical receiver. An optical transmitter is provided.

  According to the present invention, the first calculation unit multiplies the first and second data signals input from the outside, and the second calculation unit outputs the output signal of the first calculation unit and the light reception signal output from the light receiving unit. The phase adjustment unit adjusts the phase difference between the first and second optical signals using the output signal of the second calculation unit. For this reason, it is not necessary to superimpose the low frequency signal used for adjusting the phase difference between the first and second optical signals on the phase-modulated optical signal as in the prior art. Therefore, there is an effect that the phase difference of the optical signal passing through the data modulation unit can be controlled to a predetermined phase difference without causing deterioration of the phase modulation optical signal.

  Hereinafter, an optical transmission apparatus and an optical test apparatus according to embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing a main configuration of the optical transmission apparatus according to the first embodiment of the present invention. As shown in FIG. 1, the optical transmission device 1 of the present embodiment includes a light source 10, a modulation unit 20, an RZ modulator 30, amplifiers 41a and 41b, drivers 42a and 42b, a photodiode 43 (light receiving unit), and a mixer 44 (first unit). 1 calculation unit), a mixer 45 (second calculation unit), averaging processing units 46 and 47, and a phase adjustment circuit 48 (phase adjustment unit), and a data signal D1 (first data signal) input from the outside ) And the data signal D2 (second data signal) to generate and transmit a phase-modulated optical signal L1. It is assumed that the optical transmission device 1 of this embodiment transmits a phase-modulated optical signal L1 modulated by the DQPSK method.

  The light source 10 is, for example, a laser diode (LD) and emits continuous light (CW light: Continuous Wave). The modulation unit 20 includes a Mach-Zehnder modulator having a pair of an I arm 21a and a Q arm 21b, and the continuous light from the light source 10 is converted into an optical signal L11 (first optical signal) and the Q arm 21b via the I arm 21a. The optical signal L12 (second optical signal) is branched into two, and modulation is performed on each of the optical signals L11 and L12 according to the data signals D1 and D2 inputted from the outside, and then they are combined ( And phase-modulated optical signal is generated. In the example shown in FIG. 1, the I arm 21a is provided with a modulator 23a, and the Q arm 21b is provided with a π / 2 phase shift unit 22 and a modulator 23b. The π / 2 phase shift unit 22 may be provided not on the Q arm 21b but on the I arm 21a.

  The π / 2 phase shift unit 22 gives a phase difference of π / 2 between the optical signal L11 via the I arm 21a and the optical signal L12 via the Q arm 21b. The π / 2 phase shift unit 22 includes, for example, a pair of electrodes arranged so as to sandwich an optical waveguide through which the optical signal L12 propagates, and a predetermined voltage (DC bias) is applied to the pair of electrodes. Thus, a phase difference of π / 2 is given between the optical signals L11 and L12. The phase difference can be finely adjusted by finely adjusting the voltage applied to the pair of electrodes included in the π / 2 phase shift unit 22.

  The modulator 23a phase-modulates the optical signal L11 via the I arm 21a in accordance with the drive signal output from the driver 42a. The modulator 23a includes, for example, a pair of modulation electrodes arranged so as to sandwich the optical waveguide through which the optical signal L11 propagates, and one electrode provided in the vicinity of the optical waveguide. Is applied to the pair of modulation electrodes, the optical signal L11 via the I arm 21a is phase-modulated, and a predetermined voltage (DC bias) is applied to the electrodes to adjust the operating point.

  The modulator 23b phase-modulates the optical signal L12 via the Q arm 21b in accordance with the drive signal output from the driver 42b. Similarly to the modulator 23b, the modulator 23a also includes, for example, a pair of modulation electrodes arranged so as to sandwich the optical waveguide through which the optical signal L12 propagates, and one electrode provided close to the optical waveguide. In this configuration, the drive signal from the driver 42b is applied to the pair of modulation electrodes, whereby the optical signal L12 via the Q arm 21b is phase-modulated, and the operation is performed by applying a predetermined voltage (DC bias) to the electrodes. The point is adjusted.

  The RZ modulator 30 further performs RZ intensity modulation on the phase-modulated optical signal generated by the modulation unit 20, and is unnecessary when the optical signals L1 and L2 are modulated by the modulators 23a and 23b of the modulation unit 20. A phase-modulated optical signal L1 from which various signal components are removed is generated. The RZ modulator 30 is, for example, a Mach-Zehnder modulator having a modulation electrode and an electrode on one arm, and an RZ signal S1 input from the outside is applied to the modulation electrode of the RZ modulator 30, thereby modulating the modulation unit. The phase modulated optical signal generated at 20 is RZ intensity modulated. Further, the operating point of the RZ modulator 30 is adjusted by applying a predetermined voltage (DC bias) to the electrodes.

  The amplifiers 41a and 41b amplify the data signals D1 and D2 input from the outside with a predetermined amplification factor, respectively. The frequency of the data signals D1 and D2 is about 20 GHz. The drivers 42a and 42b receive the data signals D1 and D2 amplified by the amplifiers 41a and 41b, respectively, and output drive signals corresponding to the data signals D1 and D2 to the modulators 23a and 23b, respectively. . The photodiode (PD) 43 receives a part of the phase modulation optical signal generated by the modulation unit 20 and outputs a light reception signal R1 indicating the intensity thereof. The frequency of the light reception signal R1 is about 20 GHz. Instead of the photodiode 43, a photodiode 43 ′ that receives a part of the phase-modulated optical signal L1 output from the RZ modulator 30 may be used.

  The mixer 44 multiplies the data signal D1 amplified by the amplifier 41a and the data signal D2 amplified by the amplifier 41b. The mixer 45 multiplies the output signal of the mixer 44 and the light reception signal R1 output from the photodiode PD. The averaging processor 46 performs an averaging process on the output signal of the mixer 45, and the averaging processor 47 performs an averaging process on the light reception signal R1 output from the photodiode PD. The phase adjustment circuit 48 uses the signals output from the averaging processing units 46 and 47, and the absolute value of the deviation amount from the target phase difference of the phase difference between the optical signals L11 and L12 in the modulation unit 20 (deviation amount itself). And the phase difference is adjusted using the absolute value of the deviation. Specifically, the phase adjustment circuit 48 adjusts the phase difference between the optical signals L11 and L12 to be “π / 2”.

  The optical transmission apparatus 1 having the above configuration multiplies a signal obtained by multiplying the data signals D1 and D2 input from the outside by the mixer 44 and the reception signal R1 output from the photodiode 43 by the mixer 45. The phase difference between the optical signals L11 and L12 in the modulator 20 is adjusted to be “π / 2”. Hereinafter, the principle will be described.

  First, the light reception signal R1 output from the photodiode 43 will be described. FIG. 2 is a diagram illustrating an example of a waveform of the light reception signal R1 output from the photodiode 43. FIG. 2A illustrates a case where the phase difference between the optical signals L11 and L12 is 90 degrees (π / 2). It is a figure which shows the example of the waveform of light reception signal R1, (b) is a figure which shows the example of the waveform of light reception signal R1 in case the phase difference between optical signal L11 and L12 is 110 degree | times.

  When the phase difference between the optical signals L11 and L12 is the target phase difference (90 degrees (π / 2)), the received light signal R1 is the maximum amplitude of the normalized amplitude as shown in FIG. Is substantially “1”, and a waveform in which a trough portion V1 with a small amplitude appears is shown in some places. On the other hand, when the phase difference between the optical signals L11 and L12 is 110 degrees and deviates from the target phase difference (90 degrees (π / 2)), as shown in FIG. The waveform itself is the same as the light receiving signal R1 shown in FIG. 2A, but the first waveform W1 having a maximum amplitude of approximately “1.2” and the second waveform having a maximum amplitude of approximately “0.8”. W2 appears.

但し、上記（１）式中の変数は以下の通りである。
Ｉ（ｔ）：データ信号Ｄ１の値（１，−１）
Ｑ（ｔ）：データ信号Ｄ２の値（１，−１）
θ：光信号Ｌ１，Ｌ２間の位相差
θ_０：全体の位相回転 If the phase modulated optical signal L1 modulated by the DQPSK method is y (t), the phase modulated optical signal L1 can be expressed by the following equation (1) on the complex plane.

However, the variables in the above equation (1) are as follows.
I (t): Value of data signal D1 (1, -1)
Q (t): Value of data signal D2 (1, -1)
θ: phase difference between optical signals L1 and L2 θ ₀ : overall phase rotation

但し、上記（２）式中のｋは、フォトダイオード４３の感度等に依存する定数である。 When the light reception signal R1 output from the photodiode 43 is PO, the light reception signal R1 obtained by receiving the phase-modulated optical signal L1 expressed by the above equation (1) by the photodiode 43 is expressed by the following equation (2). Is done.

However, k in the above equation (2) is a constant depending on the sensitivity of the photodiode 43 and the like.

The first waveform W1 shown in FIG. 2B is a waveform obtained when PO, which is the light reception signal R1 output from the photodiode 43, is maximized. The maximum value PO _max of the light reception signal R1 is equal to the value I (t) of the data signal D1, that is, the value I (t) of the data signal D1 and the data signal D2 when the signs of the values I (t) and Q (t) of the data signal D2 match. It is obtained when the values Q (t) of D2 are both “1” or both are “−1”, and are expressed by the following equation (3).

On the other hand, the second waveform W2 shown in FIG. 2B is a waveform obtained when PO, which is the light reception signal R1 output from the photodiode 43, is minimized. The minimum value PO _min of the light receiving signal R1 is the case where the sign of the value I (t) of the data signal D1 and the value Q (t) of the data signal D2 are different, that is, the value I (t) of the data signal D1 and the data signal D2 Is obtained when the value Q (t) is (1, −1) or (−1, 1), and is expressed by the following equation (4).

このため、上記（５）式で示される受光信号Ｒ１の最大値ＰＯ_ｍａｘと最小値ＰＯ_ｍｉｎとの差分を用いてπ／２位相シフト部２２を調整すれば光信号Ｌ１１，Ｌ１２間の位相差を目標位相差にすることができると考えられる。 When the difference between the above equations (3) and (4) is obtained, the following equation (5) is obtained, and it can be seen that a value corresponding to the phase difference between the optical signals L1 and L2 is obtained.

Therefore, if the π / 2 phase shift unit 22 is adjusted using the difference between the maximum value PO _max and the minimum value PO _min of the received light signal R1 expressed by the above equation (5), the phase difference between the optical signals L11 and L12. Is considered to be the target phase difference.

The difference (PO _max −PO _min ) between the maximum value and the minimum value of the light reception signal R1 shown in the above equation (5) is the signal obtained by multiplying the data signals D1 and D2 and the light reception signal R1 output from the photodiode 43. Is obtained by calculating a time average of a signal obtained by multiplying (the output signal of the mixer 45). Hereinafter, the principle will be described.

ここで、データ信号Ｄ１，Ｄ２が、それぞれ値「１」，「−１」を同数だけ取るとすると、ミキサ４５の出力信号ＶＯの平均値ＡＶＯは以下の（７）式で表される。

The output signal VO of the mixer 45 is expressed by the following formula (6) using the formula (2) described above.

Here, if the data signals D1 and D2 take the same number of values “1” and “−1”, respectively, the average value AVO of the output signal VO of the mixer 45 is expressed by the following equation (7).

Referring to the equation (7), the average value AVO of the output signal of the mixer 45 is a value corresponding to the phase difference θ between the optical signals L1 and L2, and has the same form as the equation (5). For this reason, the difference (PO _max −PO _min ) between the maximum value and the minimum value of the light reception signal R1 shown in the above equation (5) is the signal obtained by multiplying the data signals D1 and D2 and the light reception output from the photodiode 43. It can be seen that it is obtained by calculating the time average of the signal obtained by multiplying the signal R1 (the output signal of the mixer 45).

  FIG. 3 is a simulation result showing the relationship between the phase difference between the optical signals L1 and L2 in the modulation unit 20 and the signal output from the averaging processing unit 46. Referring to FIG. 3, the signal output from the averaging processing unit 46 is 90 degrees (π / 2) where the phase difference between the optical signals L1 and L2 is the target phase difference, as shown in the above equation (7). Or it turns out that it becomes zero at -90 degree | times (-(pi) / 2). The inclination direction (tangential inclination) of the signal output from the averaging processing unit 46 is set to -90 degrees (-90 degrees) when the target phase difference between the optical signals L1 and L2 is set to 90 degrees (π / 2). Since this is opposite to the case of setting to π / 2), care must be taken when adjusting the π / 2 phase shifter 22.

  Here, only with the signal output from the averaging processing unit 46, the absolute value of the deviation amount of the phase difference between the optical signals L1 and L2 in the modulation unit 20 from the target phase difference is not known. For this reason, there are cases where the phase adjustment circuit 48 cannot set an appropriate control constant for controlling the π / 2 phase shift unit 22. In the present embodiment, a modulation unit is obtained by normalizing a signal output from the averaging processing unit 46 using a signal obtained by averaging the received light signal R1 output from the photodiode 43 by the averaging processing unit 47. The absolute value of the deviation amount of the phase difference between the optical signals L1 and L2 at 20 from the target phase difference is obtained.

従って、平均化処理部４６，４７から出力される信号の比は以下の（９）式で表される。

The average value APO (the signal output from the averaging processing unit 47) of the light reception signal R1 output from the photodiode 43 is expressed by the following equation (8).

Therefore, the ratio of the signals output from the averaging processing units 46 and 47 is expressed by the following equation (9).

位相調整回路４８は、上記（１０）式から目標位相差からのずれ量の絶対値Δθを算出し、この絶対値Δθを用いてπ／２位相シフト部２２を制御することにより、光信号Ｌ１，Ｌ２間の位相差を調整する。 Here, when the target phase difference between the optical signals L1 and L2 is set to 90 degrees (π / 2), and the absolute value of the deviation amount from this target phase difference is Δθ, the absolute value Δθ of the deviation amount is 10)

The phase adjustment circuit 48 calculates the absolute value Δθ of the deviation amount from the target phase difference from the above equation (10), and controls the π / 2 phase shift unit 22 by using this absolute value Δθ, whereby the optical signal L1. , L2 is adjusted.

  FIG. 4 is a simulation result showing the relationship between the deviation amount of the phase difference between the optical signals L1 and L2 from the target phase difference and the absolute value of the deviation amount calculated by the phase adjustment circuit 48. As shown in FIG. 4, the absolute value of the shift amount calculated by the phase adjustment circuit 48 is substantially equal to the phase difference between the optical signals L1 and L2 in the modulation unit 20, and the graph showing these relationships is a straight line passing through the origin. You can see that

  Next, the operation of the optical transmission apparatus 1 according to the present embodiment will be described. When continuous light from the light source 10 enters the modulation unit 20, for example, it is branched into an optical signal L11 via the I arm 21a and an optical signal L12 via the Q arm 21b at an intensity ratio of 1: 1. The optical signal L11 branched to the I arm 21a is modulated by the modulator 23a according to the data signal D1 input from the outside. On the other hand, the optical signal L12 branched to the Q arm 21b is first changed in phase by π / 2 in the π / 2 phase shift unit 22, and a phase difference of π / 2 is given to the optical signal L11. Next, the modulator 23b receives modulation according to the data signal D2 input from the outside.

  Thereafter, the optical signals L11 and L12 modulated by the modulators 23a and 23b are combined (combined), and the modulation unit 20 outputs a phase-modulated optical signal in which the optical signals L11 and L12 are combined. This phase-modulated optical signal is subjected to RZ intensity modulation according to the RZ signal S1 incident on the RZ modulator 30 and input from the outside. Thereby, the RZ modulator 30 transmits the phase-modulated optical signal L1 from which unnecessary signal components generated when the optical signals L1 and L2 are modulated by the modulators 23a and 23b are removed. A part of the phase-modulated optical signal output from the modulation unit 20 is received by the photodiode 43, and the received light signal R 1 is output from the photodiode 43.

  With the above operation, the data signals D1 and D2 (data signals D1 and D2 amplified by the amplifiers 41a and 41b) input from the outside are multiplied by the mixer 44, and then output from the output signal of the mixer 44 and the photodiode 43. The received light signal R1 is multiplied by the mixer 45. Then, the averaging processor 46 performs an averaging process on the output signal of the mixer 45, and a signal indicating the average value of the output signal of the mixer 45 is input from the averaging processor 46 to the phase adjustment circuit 48. The averaging processing unit 47 performs an averaging process on the light reception signal R1 output from the photodiode 43, and a signal indicating the average value of the light reception signal R1 is input from the averaging processing unit 47 to the phase adjustment circuit 48. .

  The phase adjustment circuit 48 uses the signals output from the averaging processing units 46 and 47, and the absolute value of the deviation amount from the target phase difference of the phase difference between the optical signals L11 and L12 in the modulation unit 20 (deviation amount itself). Is calculated. Specifically, the absolute value Δθ of the deviation amount is obtained by substituting the signals output from the averaging processing units 46 and 47 into the above-described equation (10). Then, the phase adjustment circuit 48 controls the π / 2 phase shift unit 22 using the absolute value Δθ of the deviation amount, so that the phase difference between the optical signals L11 and L12 in the modulation unit 20 becomes the target phase (90 degrees ( π / 2)).

  As described above, the optical transmission device 1 of the present embodiment uses a signal obtained by multiplying the signal obtained by multiplying the data signals D1 and D2 input from the outside and the light reception signal R1 output from the photodiode 43. The phase difference between the optical signals L11 and L12 in the modulation unit 20 is adjusted to be “π / 2”. For this reason, unlike the prior art, there is no need to superimpose a low-frequency signal on the phase-modulated optical signal L1 in order to adjust the π / 2 phase shift unit 22. Therefore, in this embodiment, the phase difference between the optical signals L11 and L12 via the modulation unit 20 can be controlled to a predetermined phase difference without causing deterioration of the phase-modulated optical signal L1. Here, since the adjustment of the phase difference between the optical signals L11 and L12 via the modulation unit 20 is performed based on the absolute value of the deviation amount from the target phase difference (deviation amount itself), the target phase difference can be quickly achieved. It is possible to adjust.

[Second Embodiment]
FIG. 5 is a block diagram showing a main configuration of the optical transmission apparatus according to the second embodiment of the present invention. As shown in FIG. 5, the optical transmission device 2 of the present embodiment is obtained by adding a low-pass filter (LPF) 51 (first low-pass filter) and a low-pass filter 52 (second low-pass filter) to the optical transmission device 1 shown in FIG. 1. It is a configuration. The low-pass filter 51 reduces the frequency of the output signal of the mixer 44 whose frequency is about 20 GHz to several hundred MHz. Similarly, the low pass filter 52 reduces the frequency of the received light signal R1 having a frequency of about 20 GHz to several hundred MHz.

  The reason why the low-pass filters 51 and 52 are provided to reduce the frequency of the output signal and the received light signal R1 of the mixer 44 is that the mixer 45 can easily perform multiplication without complicating the circuit configuration of the mixer 45. Here, when the low-pass filters 51 and 52 are provided, the signal level of the output signal of the mixer 44 and the light reception signal R1 is lowered. Therefore, the phase adjustment circuit 48 needs to correct the decrease in the signal level.

  Also in the optical transmitter 2 described above, the light in the modulation unit 20 is obtained using a signal obtained by multiplying a signal obtained by multiplying data signals D1 and D2 input from the outside and a light reception signal R1 output from the photodiode 43. The phase difference between the signals L11 and L12 is adjusted to be “π / 2”. For this reason, also in this embodiment, the phase difference between the optical signals L11 and L12 via the modulation unit 20 can be controlled to a predetermined phase difference without causing deterioration of the phase-modulated optical signal L1. Also in this embodiment, since the phase difference between the optical signals L11 and L12 is adjusted based on the absolute value of the deviation amount from the target phase difference (deviation amount itself), the target phase difference is adjusted in a short time. It is possible. Furthermore, in this embodiment, since the circuit configuration of the mixer 45 can be simplified, the cost can be reduced.

[Third Embodiment]
FIG. 6 is a block diagram showing a main configuration of an optical transmission apparatus according to the third embodiment of the present invention. As illustrated in FIG. 6, the optical transmission device 3 of the present embodiment is similar to the optical transmission device 1 illustrated in FIG. 1 in that a low-pass filter (LPF) 61 a (third low-pass filter), a low-pass filter 61 b (fourth low-pass filter), and a low-pass filter. 62 (fifth low-pass filter) and capacitors 63 and 64 are added.

  The low-pass filters 61a and 61b reduce the frequency of the data signals D1 and D2 having a frequency of about 20 GHz to several hundred MHz, respectively. Similarly, the low pass filter 62 reduces the frequency of the received light signal R1 having a frequency of about 20 GHz to several hundred MHz. These low-pass filters 61a, 61b, and 62 are provided to easily perform multiplication in each of the mixers 44 and 45 without complicating the circuit configuration of the mixers 44 and 45.

  The capacitor 63 removes the DC component of the signal input from the mixer 44 to the mixer 45, and the capacitor 64 removes the DC component of the signal input from the low pass filter 62 to the mixer 45. By providing the capacitors 63 and 64, for example, when the value “1” of the data signal D1 is different from the number of values “−1”, the value “1” of the data signal D2 is different from the number of values “−1”. , And the influence of offset that occurs when the number of “H (high)” level and “L (low)” level of the received light signal is different.

  In the optical transmitter 3 described above, as in the second embodiment, the phase difference between the optical signals L11 and L12 via the modulation unit 20 is controlled to a predetermined phase difference without causing deterioration of the phase modulated optical signal L1. be able to. Also in this embodiment, it is possible to adjust the target phase difference in a short time. Furthermore, in this embodiment, since the circuit configuration of the mixers 63 and 64 can be simplified, the cost can be reduced.

  The optical transmitter according to the embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and can be freely changed within the scope of the present invention. For example, the same capacitors as the capacitors 63 and 64 included in the optical transmission device 3 of the third embodiment can be applied to the optical transmission devices 1 and 2 of the first and second embodiments. In the first to third embodiments, the configuration in which the π / 2 phase shift unit 22 and the modulator 23b are separately provided in the Q arm 21b has been described as an example. However, the π / 2 phase shift is described. The present invention can also be applied to a configuration in which only the modulator having both the function of the unit 22 and the function of the modulator 23b is provided in the Q arm 21b.

  The optical transmitter of the present invention can also be provided in an optical test apparatus that tests an optical receiver that receives a phase-modulated optical signal. By providing the optical transmission device of the present invention in an optical test device, it is possible to test the optical reception device with high accuracy using a phase-modulated optical signal in which no deterioration such as a phase change has occurred.

It is a block diagram which shows the principal part structure of the optical transmitter by 1st Embodiment of this invention. It is a figure which shows an example of the waveform of the light reception signal R1 output from the photodiode 43. FIG. It is a simulation result which shows the relationship between the phase difference between the optical signals L1 and L2 in the modulation | alteration part 20, and the signal output from the averaging process part 46. FIG. 10 is a simulation result showing a relationship between a deviation amount of a phase difference between optical signals L1 and L2 from a target phase difference and an absolute value of a deviation amount calculated by the phase adjustment circuit 48. It is a block diagram which shows the principal part structure of the optical transmitter by 2nd Embodiment of this invention. It is a block diagram which shows the principal part structure of the optical transmitter by 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical transmitter 20 Modulator 43 Photodiode 44, 45 Mixer 46 Averaging processing part 48 Phase adjustment circuit 51, 52 Low pass filter 61a, 61b Low pass filter 62 Low pass filter D1, D2 Data signal L1 Phase modulation optical signal L11, L12 Light Signal R1 Light reception signal

Claims (6)

While controlling the phase of at least one of the first and second optical signals so that the first and second optical signals obtained by branching the input light have a predetermined phase difference, An optical transmission that includes a modulation unit that modulates the first and second optical signals in accordance with a second data signal, and that outputs a phase-modulated optical signal obtained by combining the first and second optical signals via the modulation unit. In the device
A first arithmetic unit that multiplies the first data signal and the second data signal;
A light receiving unit for receiving the phase-modulated optical signal;
A second calculation unit that multiplies the output signal of the first calculation unit by the light reception signal output from the light receiving unit;
An optical transmission apparatus comprising: a phase adjustment unit that adjusts a phase difference between the first and second optical signals controlled by the modulation unit using an output signal of the second calculation unit. An averaging processing unit for averaging the output signal of the second arithmetic unit;
The optical transmission device according to claim 1, wherein the phase adjustment unit adjusts a phase difference between the first and second optical signals using a signal averaged by the averaging processing unit. A first low-pass filter for reducing the frequency of the output signal of the first arithmetic unit;
A second low-pass filter that reduces the frequency of the light-receiving signal output from the light-receiving unit,
The optical transmission device according to claim 2, wherein the second calculation unit multiplies the signal that has passed through the first and second low-pass filters. A third low-pass filter for reducing the frequency of the first data signal;
A fourth low-pass filter for reducing the frequency of the second data signal;
A fifth low-pass filter that reduces the frequency of the light-receiving signal output from the light-receiving unit,
The first arithmetic unit multiplies the signal through the third and fourth low-pass filters,
The optical transmission device according to claim 2, wherein the second calculation unit multiplies the output signal of the first calculation unit by a signal that has passed through the fifth low-pass filter.   The phase adjustment unit uses the signal averaged by the averaging processing unit and a signal obtained by averaging the light reception signal output from the light reception unit, and the first and second optical signals of the modulation unit. 3. The optical transmission according to claim 2, wherein an absolute value of a deviation amount of the phase difference from the target phase difference is calculated, and the phase difference between the first and second optical signals is adjusted using the absolute value. apparatus. In an optical test apparatus for testing an optical receiver that receives a phase-modulated optical signal,
An optical test apparatus comprising: the optical transmission apparatus according to claim 1, which transmits the phase-modulated optical signal received by the optical reception apparatus.

Images