JP3397699B2 - Time division type wavelength monitor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time division type wavelength monitoring device for monitoring each wavelength of wavelength multiplexed light and the light intensity of each wavelength.

[0002]

2. Description of the Related Art FIG. 10 shows a configuration example of a conventional wavelength monitoring circuit. In the figure, the wavelength-division multiplexed light (wavelength λ1
.About..lamda..sub.n) and the reference wavelength light output from the reference light source whose absolute frequency is stabilized to the absorption line of the atom or molecule are input to predetermined input ports of the arrayed waveguide diffraction grating 11, respectively. The temperature of the arrayed waveguide diffraction grating 11 depends on the thermistor 1.
It is detected by 2 and input to the temperature control circuit 13, and is controlled to a predetermined temperature by the Peltier element 14. Photodetectors 15 are connected to the output ports # 1 to # n + 2 of the arrayed-waveguide diffraction grating 11, respectively, and the wavelength monitoring output is obtained by the arithmetic means (logarithmic amplifier) 16 in the subsequent stage. The wavelength monitoring output (error signal) for the reference wavelength light is
The temperature is fed back to the temperature control circuit 13 via the negative feedback loop.

FIG. 11 shows the transmission characteristics of the arrayed waveguide diffraction grating 11. In the arrayed waveguide diffraction grating 11, the transmission characteristic of the output port shows a demultiplexing characteristic like a Gaussian function with respect to the input from one input port. Also, the transmission center wavelength interval of each output port is the wavelength multiplexed light (wavelengths λ1 to λn)
Is set to 1/2 of the wavelength interval of.

FIG. 12 shows the transmission characteristics of two adjacent output ports of the arrayed waveguide diffraction grating 11. The transmission center frequency interval is Δν _sp , the transmission width (full width at half maximum) is Δν, and FIG. 12 shows the case where the normalized transmission width (Δν / Δν _sp ) is 0.6. The horizontal axis is the normalized frequency normalized by the transmission center frequency interval, and the vertical axis is the transmittance.

The transmission characteristics of the arrayed waveguide diffraction grating 11 are
The figure shows the crosstalk overlaid on the ideal Gaussian shape due to manufacturing errors and in-plane refractive index distribution.
The approximate function of the transmission characteristic is H ₁ (ν / Δν _sp ) = η ₁ [XT + exp {-4ln2 (ν / Δν _sp
+0.5) ² / (Δν ₁ / Δν _sp ) ² }] H ₂ (ν / Δν _sp ) = η ₂ [XT + exp {-4ln2 (ν / Δν _sp
−0.5) ² / (Δν ₂ / Δν _sp ) ² }]. Note that η ₁ and η ₂ are transmission efficiencies, and XT is crosstalk. In FIG. 12, XT = −30 dB.

The photodetectors 15 shown in FIG. 10 are used in pairs, detect the light intensities extracted at two adjacent output ports of the arrayed waveguide diffraction grating 11, and calculate means 16
Compare with. The ratio H ₂ (ν / Δν _sp ) / H ₁ (ν / Δν _sp ) of the adjacent port outputs is uniquely given to the normalized frequency, and is shown in FIG. 13 (1).
A wavelength discrimination characteristic as shown in is obtained. Here, the normalized transmission width (Δν / Δν _sp ) is set to 0.6, the crosstalk XT is set to −25 dB, and the normalized frequency (1/2 of the normalized frequency in FIG. 12) normalized at the wavelength multiplexing interval is plotted on the horizontal axis. , A wavelength discrimination characteristic without crosstalk is shown by a broken line, a wavelength discrimination characteristic with one wavelength input is shown by a one-dot chain line, and a wavelength discrimination characteristic with 32 wavelength inputs is shown by a solid line.

Further, in the calculating means 16, the transmittance H is calculated from the optical frequency ν obtained by taking the ratio of the outputs of the adjacent ports.
Calculate (ν / Δν _sp ). On the other hand, from the relationship of the individual port output ηH (ν / Δν _sp ) Pin to the input wavelength light intensity Pin, η is measured and stored in advance to obtain Pin.
Can be calculated. With such a function, a wavelength monitoring output and a light intensity monitoring output can be obtained.

[0008]

In the configuration of the conventional wavelength monitoring circuit, as shown in FIG. 13 (1), when the transmission characteristic of the arrayed waveguide diffraction grating 11 used as the wavelength monitoring section is ideally a Gaussian shape. The wavelength discrimination characteristic is a straight line (dashed line), but the deviation from the ideal straight line becomes larger (solid line) due to an increase in the number of wavelength multiplexes.

FIG. 13B shows the error amount of the wavelength discrimination characteristic when 32 wavelengths are input with respect to the wavelength discrimination characteristic when one wavelength is input.
This wavelength discrimination error amount is equivalent to the error amount when the wavelength discrimination characteristic at the time of inputting one wavelength is held as correction data in the wavelength monitoring circuit and correction is performed. Here, 100
It can be seen that a measurement error of about 12 GHz at maximum occurs within the wavelength discrimination range when converted to the case of the wavelength equidistant arrangement of GHz (the slope of the straight line of the wavelength discrimination characteristic in the Gaussian shape is 1.5 GHz / dB).

As described above, when the number of multiplexed wavelengths increases, the crosstalk of the arrayed-waveguide diffraction grating 11 (including the crosstalk when a photodiode array is used as a photodetector) causes a large wavelength measurement error. Becomes

It is an object of the present invention to provide a compact and highly reliable time division type wavelength monitoring device which can measure each wavelength of wavelength multiplexed light with high accuracy even when the number of wavelength division multiplexing increases. .

[0012]

According to another aspect of the present invention, there is provided a time-division type wavelength monitoring device, wherein a wavelength-division multiplexed light is demultiplexed, an arbitrary wavelength is selected by an optical gate switch, and an arrayed waveguide diffraction grating and a wavelength discriminating means. Is input to a wavelength monitoring circuit that performs cross wavelength discrimination. As a result, each wavelength of the wavelength multiplexed light is measured individually, so that crosstalk can be reduced and a wavelength measurement error can be reduced with respect to a change in the number of wavelength multiplexed lights.

According to another aspect of the present invention, there is provided a time division type wavelength monitoring device, wherein a reference wavelength light stabilized with high accuracy is input to a wavelength monitoring circuit,
This is a configuration in which the error amount obtained by wavelength discrimination of the reference wavelength light is negatively fed back. As a result, it is possible to improve the accuracy of the wavelength monitoring circuit.

According to a third aspect of the present invention, there is provided a time-division type wavelength monitoring device, wherein an arrayed-waveguide diffraction grating is used as an optical demultiplexer for demultiplexing wavelength multiplexed light. In the time division type wavelength monitoring device of the fourth aspect, the optical demultiplexer and the two arrayed waveguide diffraction gratings used for wavelength monitoring are formed on the same substrate.

In the time division type wavelength monitoring device of the fifth aspect, the two arrayed waveguide diffraction gratings used for the optical demultiplexer and the wavelength monitoring are constituted by one arrayed waveguide diffraction grating.
According to a sixth aspect of the present invention, in the time division type wavelength monitoring device, a 1 × 2 optical switch is used as an optical gate switch, and one of the outputs is input to the wavelength monitoring circuit.

According to a seventh aspect of the present invention, there is provided a time-division type wavelength monitoring device, in which a photodetector is connected to the other output of the 1 × 2 optical switch used as an optical gate switch to measure the light intensity.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment: Claim 1,
2, 3) FIG. 1 shows a first embodiment of the time division type wavelength monitoring device of the present invention.

In the figure, wavelength-multiplexed light obtained by multiplexing a plurality of wavelength lights λ1 to λn is input to a predetermined input port of an arrayed-waveguide diffraction grating 21 used as an optical demultiplexer, and a predetermined wavelength corresponding to the input port. Each wavelength light is demultiplexed and output to the output port of. Here, output port # 1
It is assumed that the wavelength lights .lamda.1 to .lamda.n are demultiplexed into .about. # N. The demultiplexed wavelength lights are input to a plurality of optical gate switches 22 that are individually turned on / off. Each optical gate switch 22 is on / off controlled by a switch control circuit 23 so that only one wavelength light to be monitored is output.

The output of each optical gate switch 22 and each input port # 1 to # 1 of the arrayed waveguide diffraction grating 11 for wavelength monitoring.
#N are respectively connected. Arrayed waveguide diffraction grating 11
Has a plurality of output ports whose transmission center wavelength interval is set to the wavelength interval of the wavelength division multiplexed light, and each optical gate switch 22
From each of the wavelengths individually input to the corresponding input ports from the two adjacent predetermined output ports #j, # j +
Output to 1.

Further, the reference wavelength light λref whose absolute frequency is stabilized in the absorption line of an atom or a molecule is input to a predetermined input port #m of the arrayed waveguide diffraction grating 11, and two predetermined adjacent output ports. It is output to #k and # k + 1.

The temperature of the arrayed waveguide diffraction grating 11 is detected by the thermistor 12 and input to the temperature control circuit 13, and is controlled to a predetermined temperature by the Peltier element 14. Output ports #j, # j + 1, # of the arrayed waveguide diffraction grating 11
The photodetector 15 is connected to k and # k + 1,
The wavelength monitoring output is obtained from the calculating means (for example, logarithmic amplifier) 16 in the subsequent stage. The wavelength monitoring output (error signal) for the reference wavelength light λ ref is fed back to the temperature control circuit 13 via the negative feedback loop to control the crossover frequency of the transmission characteristics of the adjacent output ports to a constant value.

Array waveguide diffraction gratings 21 and 1 shown above
FIG. 2 shows the state of the multiplexing / demultiplexing of the light of each wavelength in No. 1. Although the arrayed waveguide diffraction grating 11 functions as an optical demultiplexer in the conventional configuration shown in FIG. 10, here, each wavelength light input from a different input port is output port #j,
It functions as an optical multiplexer that outputs to # j + 1. However, since each wavelength light is individually input via the optical gate switch 22, each wavelength light is output as output ports #j, # j + 1.
Will be output individually.

FIG. 3A shows the transmission characteristics of an arrayed waveguide diffraction grating (optical demultiplexer AWG) 21 used as an optical demultiplexer. FIG. 3B shows the output level of the optical gate switch 22 (the input level of each input port of the arrayed waveguide diffraction grating (wavelength monitoring AWG) 11 for wavelength monitoring). Here, the optical gate switch 22 to which the wavelength light λi is input
Is turned on and the optical gate switch 22 to which light of another wavelength is input is turned off. This output level difference is
It is based on the extinction ratio of the optical gate switch 22. Other than the wavelength light λi is a crosstalk component.

FIG. 3 (3) shows the transmission characteristics of the wavelength monitoring AWG 11. In particular, the transmission characteristics of the output ports #j and # j + 1 as seen from the input port #i are shown by thick lines. The wavelength monitoring AWG 11 is set in advance so that the wavelength light λi to be monitored becomes the intersection of the transmission characteristics of the output ports #j and # j + 1.

FIG. 3 (4) shows the outputs of the output ports #j and # j + 1 of the wavelength monitoring AWG 11. The level difference between the wavelength light λi to be monitored and the other wavelength light is determined by the optical gate switch 22.
Is based on the crosstalk between the extinction ratio and the transmission characteristics of the wavelength monitoring AWG 11.

FIG. 4 (1) shows the wavelength discrimination characteristic in the first embodiment. Here, the arrayed waveguide diffraction grating 1
The normalized transmission width (Δν / Δν _sp ) of 1, 21 is 0.6, the crosstalk XT is -25 dB, the extinction ratio of the optical gate switch 22 is 35 dB, and the wavelength discrimination characteristic without crosstalk is indicated by a broken line and one wavelength input. The wavelength discrimination characteristic is shown by a one-dot chain line, and the wavelength discrimination characteristic when 32 wavelengths are input is shown by a solid line. The dashed line and the solid line almost overlap.

FIG. 4B shows the error amount of the wavelength discrimination characteristic when 32 wavelengths are input with respect to the wavelength discrimination characteristic when one wavelength is input.
It is two orders of magnitude smaller than the error amount in the conventional configuration of FIG. 13 (2), and it can be seen that the variation of the wavelength discrimination characteristic is extremely small with respect to the variation of the input wavelength multiplex number. For example, in the wavelength discrimination range (± 0.25), the conventional configuration is ± 8
While a wavelength discriminating error of dB occurs, this embodiment has an extremely small value of ± 0.03 dB. Further, in the configuration of the present embodiment, it is possible to measure up to the normalized frequency range ± 0.5 as the wavelength discrimination range.

Here, in order to perform highly accurate wavelength measurement, instead of calculating the error amount based on the linear approximation when there is no crosstalk, correction is performed based on the wavelength discrimination specific data at one wavelength input. The correction curve described above may be applied. Further, in order to obtain the correction curve, it is possible to use a wavelength swept light source or the like, capture the output of the wavelength monitoring circuit as data while sweeping the wavelength, and hold it in the circuit. For example, when the above correction is used, the wavelength measurement error of the present embodiment is ± 0.03 dB, and the slope of the straight line of the wavelength discrimination characteristic of Gaussian shape is 1.5 for 100 GHz evenly-spaced wavelength multiplexed light.
If the frequency is GHz / dB, the wavelength error is about 0.05 GHz.

(Second Embodiment: Claims 1, 2, 3,
6, 7) FIG. 5 shows a second embodiment of the time division type wavelength monitoring device of the present invention. The feature of this embodiment is that a 1 × 2 optical switch 24 is used as the optical gate switch 22, one output of which is connected to each input port of the arrayed waveguide diffraction grating 11 and the other output is connected to a photodetector 25. There is a place to do it. The switch control circuit 23 connects the output of one 1 × 2 optical switch 24 to the input port of the arrayed waveguide diffraction grating 11 and the output of another 1 × 2 optical switch 24 to the photodetector 25 for monitoring. The light intensity of the wavelength light other than the target wavelength is measured. Other configurations are similar to those of the first embodiment.

When knowing the relative intensity of light intensity,
This is possible by measuring the amount of fluctuation of the photodetector output from the initial value. If absolute strength is required,
This is possible by measuring the output of each photodetector with respect to the wavelength and holding it in the circuit while sweeping the wavelength tunable light source having a known light intensity.

(Third Embodiment: Claims 1, 2, 3)
5, 6, 7) FIG. 6 shows a third embodiment of the time division type wavelength monitoring device of the present invention. The feature of this embodiment lies in that the arrayed waveguide diffraction grating (21) used as an optical demultiplexer and the arrayed waveguide diffraction grating (11) for wavelength monitoring are configured by one arrayed waveguide diffraction grating 31. . Other configurations are similar to those of the second embodiment.

The arrayed waveguide diffraction grating 31 can have a port arrangement as shown in FIG. 7 depending on the design. Input port # 0
The wavelength-multiplexed light is input from the above, and the wavelength lights λ1 to λn are demultiplexed and output to the output ports # 1 to #n. Further, the wavelength lights λ1 to λn are individually input from the input ports # n + 1 to # 2n and output from the output ports #j and # j + 1. The transmission characteristics of the arrayed waveguide diffraction grating 41 are shown in FIG.

FIG. 8 (1) shows the transmission characteristics seen from the input port # 0. For example, when the wavelength multiplexed light (λ1 to λ10) is input from the input port # 0, the wavelength lights λ1 to λ10 are demultiplexed and output to the output ports # 1 to # 10, respectively.

FIGS. 8 (2) and 8 (3) show output ports #j and # j +.
1 shows the transmission characteristics. This characteristic is the same even when the input / output ports are reversed. For example, with respect to the input from the input port # 17, the wavelength λ1 is designed to be in the middle of the transmission center wavelengths of the output ports #j and # j + 1. here,
When the output port # 1 and the input port # 17 are connected via a 1 × 2 optical switch and the wavelength light λ1 is input from the input port # 17, the transmission characteristics shown in thick lines in FIGS. 8 (2) and 8 (3). Wavelength discrimination is performed by using.

(Fourth Embodiment: Claims 1, 2, 3)
4, 6, 7) FIG. 9 shows a fourth embodiment of the time division type wavelength monitoring device of the present invention. The feature of this embodiment lies in that an arrayed waveguide diffraction grating 21 used as an optical demultiplexer and an arrayed waveguide diffraction grating 11 for wavelength monitoring are independently configured on one PLC substrate 41. Other configurations are similar to those of the third embodiment.

[0036]

As described above, since the time division type wavelength monitoring apparatus according to the first aspect is configured to perform wavelength discrimination individually for each wavelength light of the wavelength division multiplexed light, even when the number of wavelength division multiplexing increases. Minimize the effects of crosstalk components,
The measurement wavelength error can be made extremely small. That is, it is possible to make the change in the wavelength discrimination characteristic due to the change in the number of wavelengths extremely small. In addition, the wavelength discrimination measurement range can be expanded to about twice that of the conventional configuration.

In the time division type wavelength monitoring device of the second aspect, by using the arrayed waveguide diffraction grating stabilized for the wavelength of the reference wavelength light for wavelength monitoring, stable wavelength discrimination is performed for a long period of time. be able to.

In the time division type wavelength monitoring device according to the third to fifth aspects, the miniaturization and the high reliability can be achieved by using the optical demultiplexer and the two arrayed waveguide diffraction gratings for wavelength monitoring. .

In the time division type wavelength monitoring device of the sixth and seventh aspects, by using the 1 × 2 optical switch as the optical gate switch, it is possible to measure the light intensity of the wavelength light other than the wavelength monitoring.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a time division type wavelength monitoring device of the present invention.

FIG. 2 is a diagram showing a state of multiplexing and demultiplexing light of each wavelength in arrayed waveguide diffraction gratings 21 and 11.

FIG. 3 is a diagram for explaining the operation of the first embodiment.

FIG. 4 is a diagram showing a wavelength discrimination characteristic of the first embodiment.

FIG. 5 is a block diagram showing a second embodiment of the time division type wavelength monitoring device of the present invention.

FIG. 6 is a block diagram showing a third embodiment of the time division type wavelength monitoring device of the present invention.

FIG. 7 is a diagram showing an example of port arrangement of an arrayed waveguide diffraction grating 31.

FIG. 8 is a diagram showing transmission characteristics of the arrayed waveguide diffraction grating 31.

FIG. 9 is a block diagram showing a fourth embodiment of the time division type wavelength monitoring device of the present invention.

FIG. 10 is a block diagram showing a configuration example of a conventional wavelength monitoring circuit.

FIG. 11 is a diagram showing transmission characteristics of the arrayed waveguide diffraction grating 11.

FIG. 12 is a diagram showing transmission characteristics of two adjacent output ports of the arrayed waveguide diffraction grating 11.

FIG. 13 is a diagram showing wavelength discrimination characteristics of a conventional configuration.

[Explanation of symbols]

11,21,31 Arrayed waveguide diffraction grating 12 Thermistor 13 Temperature control circuit 14 Peltier element 15 Photodetector 16 computing means 22 Optical gate switch 23 Switch control circuit 24 1 × 2 optical switch 25 photo detector 41 PLC board

Continuation of the front page (56) Reference JP-A-11-38265 (JP, A) JP-A-10-32363 (JP, A) JP-A-9-252283 (JP, A) JP-A-8-251105 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01M 11/00-11/08 H04B 9/00 H04B 17/00-17/02

Claims (7)

(57) [Claims] 1. An optical demultiplexer for inputting wavelength-division-multiplexed light in which a plurality of wavelengths of light are multiplexed and demultiplexing into each wavelength light, and an input of each wavelength light demultiplexed by the optical demultiplexer, respectively. A plurality of optical gate switches that individually transmit or block, a switch control circuit that sets the plurality of optical gate switches to a transmission state one by one, and individually outputs the light of each wavelength; and a plurality of optical gate switches. A plurality of corresponding input ports and a plurality of output ports whose transmission center wavelength interval is set to the wavelength interval of the wavelength-division multiplexed light, each of which is individually input to the corresponding input port from each of the optical gate switches. A first arrayed-waveguide diffraction grating that outputs wavelength light to two predetermined adjacent output ports, and the transmitted light of two predetermined adjacent output ports of the first arrayed waveguide diffraction grating is converted into an electrical signal. do it Of taking the ratio, time, characterized in that a wavelength discrimination means for performing a wavelength discrimination of the selected wavelength light by the switch control circuit split type wavelength monitoring device. 2. The time-division type wavelength monitoring device according to claim 1, wherein the reference wavelength light whose absolute frequency is stabilized in the absorption line of an atom or a molecule is input to the first arrayed waveguide diffraction grating, and the reference wavelength thereof is input. Take the ratio of the output of the adjacent port where the light is output,
A time division type wavelength monitoring device comprising means for controlling a crossover frequency of transmission characteristics of adjacent output ports of the first arrayed waveguide diffraction grating to a constant value according to the ratio. 3. The time division type wavelength monitoring device according to claim 1, wherein the optical demultiplexer includes a second arrayed waveguide diffraction grating that demultiplexes each wavelength light into a predetermined output port and outputs the demultiplexed light. A time division type wavelength monitoring device characterized by being used. 4. The time division type wavelength monitoring device according to claim 3 , wherein the first arrayed waveguide diffraction grating and the second arrayed waveguide diffraction grating are formed on the same substrate. Type wavelength monitoring device. 5. The time division type wavelength monitoring device according to claim 3 , wherein the first arrayed waveguide diffraction grating and the second arrayed waveguide diffraction grating are constituted by one arrayed waveguide diffraction grating. A time division type wavelength monitoring device. 6. The time division type wavelength monitoring device according to claim 1, wherein the optical gate switch is a 1-input 2-output optical switch,
A time-division type wavelength monitoring device, wherein one output is connected to each input port of the first arrayed waveguide diffraction grating. 7. The time division type wavelength monitoring device according to claim 6, wherein a photodetector is connected to the other output of the 1-input 2-output optical switch to detect the light intensity of each wavelength light. A time division type wavelength monitoring device characterized by: