JP2003057702A - Optical frequency sweeper, wavelength packet generator, wavelength packet communication network, and phase change measuring method for optical frequency sweeper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate frequency sweep light having a wide band width with simple control in an optical frequency sweeper using an optical modulator utilizing electrooptic effects as an optical frequency shifter, to provide a wavelength packet generator which uses the optical frequency sweeper to generate a wavelength packet, and to provide a wavelength packet communication network using the wavelength packet generator. SOLUTION: The optical frequency sweeper is provided with the optical modulator utilizing electrooptic effects instead of an optical frequency shifter utilizing acoustooptic effects, and the optical path length of an optical resonator is adjusted to adjust phase change ϕC of a modulation signal per round in the optical resonator, and thus the optical frequency sweeper is so set that matching of the phase of a modulation side-band in lower orders of the optical modulator may not occur.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical frequency sweeping device for sweeping the frequency of an optical pulse with high accuracy and stability.

Further, the present invention uses the optical frequency sweeping device of the present invention as a light source, and a wavelength for generating an optical packet in which optical pulses having different wavelengths are modulated with a transmission signal (referred to as "wavelength packet" in this specification). The present invention relates to a packet generator.

Further, the present invention relates to a wavelength packet communication network in which a center node is provided with the wavelength packet generator of the present invention and the wavelength of a wavelength packet is routed as route information or address information.

The present invention further relates to a phase change measuring method for the optical frequency sweeping device of the present invention.

[0005]

2. Description of the Related Art FIG. 9 shows a configuration example of a conventional optical frequency sweeping device (reference document: Japanese Patent Laid-Open No. 6-110102).

In the figure, continuous light output from a master laser 11 is pulsed by an optical pulse modulator 12 and input to an optical ring resonator 14 via an optical coupler 13. The optical ring resonator 14 is output from the optical coupler 13, the optical delay line 15, the optical amplifier 16, the optical frequency shifter 17 having the frequency shift width Δf, the optical switch 18, and the optical amplifier 16 which are the input / output means of light. Emitted light noise (ASE
Optical bandpass filter (BP) for removing noise
F) 19 is included in the optical path. The optical pulse modulator 12 and the optical switch 18 are synchronously controlled by the synchronization control circuit 20.

The loss in the optical ring resonator 14 is caused by the optical amplifier 1
Since the optical pulse is compensated by 6, the optical pulse input from the optical coupler 13 into the optical ring resonator 14 can circulate in it a number of times. This optical pulse is Δf by the optical frequency shifter 17 every time the optical ring resonator 14 is rotated once.
Undergo a frequency shift of. As a result, the output port of the optical coupler 13 outputs a train of optical pulses having different frequencies by Δf. The synchronization control circuit 20 includes the optical pulse modulator 1
2 and the optical switch 18 are periodically driven,
The optical pulse train whose frequency is swept in the step of f is periodically output.

The frequency shift width of the optical frequency shifter 17 is determined by the RF frequency of the oscillator that drives the optical frequency shifter. Since the RF frequency fluctuation of this oscillator is generally sufficiently smaller than the optical frequency fluctuation of the master laser 11, each output pulse from this optical frequency sweeping device has an optical frequency reference with the same frequency accuracy as the master laser 11. Is available as.

Therefore, using this optical frequency sweeping device,
For example, an optical frequency synthesizer that generates continuous light whose frequency is controlled with high precision, a light source for a wavelength division multiplexing optical communication network, and measurement of loss wavelength dependence and dispersion characteristics of WDM elements, which contribute to the sophistication of optical communication networks. Applications are possible.

[0010]

In the conventional optical frequency sweeping device, an AOS (Acousto-optic frequency shifter) utilizing the acousto-optic effect was used as the optical frequency shifter 17. While AOS has the advantage of operating as an ideal optical frequency shifter that does not generate frequency components other than the primary shift (frequency shift at the same interval as the drive frequency) component,
Due to the characteristics of acousto-optic effect, the maximum frequency shift width is 1 GHz
It was about. Therefore, in order to expand the optical frequency sweep width, the number of rounds of the optical pulse must be increased.
However, the number of turns (optical frequency sweep width) is limited by the transmission bandwidth of the optical bandpass filter 19 arranged in the optical ring resonator 14. On the other hand, if the transmission band width of the optical bandpass filter 19 is expanded, the degree of accumulation of ASE noise increases with each round of the optical pulse, making it difficult to sweep the optical frequency in a wide band.

Therefore, a configuration is known in which a narrow band frequency variable optical bandpass filter having a variable transmission center frequency is used instead of the optical bandpass filter 19 having a fixed transmission center frequency (Japanese Patent Laid-Open No. 6-110103). Issue). The ASE noise is effectively removed by performing synchronous control to shift the transmission center frequency of the variable frequency optical bandpass filter in accordance with the frequency shift of the optical pulse that circulates in the optical ring resonator. This allows
The number of rounds of the optical pulse is increased, and broadband optical frequency sweeping is possible. However, there is a problem that the synchronous control system for controlling this variable frequency optical bandpass filter becomes complicated.

By the way, as the optical frequency shifter 17,
It is considered to use an optical modulator that utilizes an electro-optical effect having a wider modulation band than the acousto-optical effect of OS. An example of the configuration of an optical modulator utilizing this electro-optical effect is shown in FIGS.

FIG. 10 shows a configuration of a 4-branch Mach-Zehnder type optical modulator (hereinafter referred to as "4MZ modulator") including four phase modulators. Modulations having different phases by π / 2 are applied to the four phase modulators. The electric field component is E _in exp
When the monochromatic light represented by (iωt) is input, the output electric field is E _out = E _in exp (iωt) [J ₁ (δ) exp (iω _m t) exp (iφ) −J ₃ (δ) exp ( −3iω _m t) exp (−3iφ) + J ₅ (δ) exp (5iω _m t) exp (5iφ) −J ₇ (δ) exp (−7iω _m t) exp (−7iφ) +…]… (1) Is expressed as Here, ω is an optical carrier angular frequency, ω _m is a modulation signal angular frequency, δ is a modulation index, φ is a modulation signal initial phase, and J _k is a kth-order Bessel function. The initial phase of the optical carrier is set to 0.

FIG. 11 shows the configuration of a two-branch Mach-Zehnder type optical modulator (hereinafter referred to as "2MZ modulator") including two phase modulators. Square wave modulations having different π / 2 phases are applied to the two phase modulators. The electric field component is E _in
When monochromatic light represented by exp (iωt) is input, its output electric field is also E _out = E _in exp (iωt) [(2 / π) exp (iω _m t) exp (iφ) − (2 / 3π) exp (−3iω _m t) exp (−3iφ) + (2 / 5π) exp (5iω _m t) exp (5iφ) − (2 / 7π) exp (−7iω _m t) exp (−7iφ) +… ]… (2)

As described above, when the 4MZ modulator or the 2MZ modulator is used, the modulation sidebands other than the first-order modulation sidebands are significantly suppressed, so that they can approximately function as an optical frequency shifter. Therefore, by using these optical modulators as the optical frequency shifter of the optical frequency sweeping device of FIG. 9, it can be expected to increase the frequency shift for each round of the optical pulse to several tens GHz.

However, when a 4MZ modulator or a 2MZ modulator is used, an optical pulse is generated depending on conditions such as the amount of phase change of the modulation frequency per revolution time of the optical resonator and the dispersion value of the optical path of the optical resonator. There is a problem that the frequency spectrum of is spread. This means that a linear optical frequency sweep cannot be performed by repeating the frequency shift of f _m = ω _m / 2π.

A description will be given below using the results of computer simulation. Although it is assumed here that a 4MZ modulator is used, as can be seen from equations (1) and (2), a 4MZ modulator is used.
Since the output frequency components of the modulator and the 2MZ modulator are the same and only the amplitudes are different, the tendency of the result is the same even if the use of the 2MZ modulator is assumed.

The output electric field of the optical modulator to which the light whose electric field component is E _in exp (iωt) is input and which is driven at the angular frequency ω _m is
It is generally expressed by the following equation.

[0019]

[Equation 1]

This optical modulator is arranged in an optical frequency sweeping device, and the electric field spectrum of a circulating optical pulse is represented by a vertical vector of N elements. Each element of the vector represents a modulation sideband with an interval of ω _m , and is arranged so that the optical frequency decreases from top to bottom. In the 4MZ modulator, since the primary modulation sideband becomes the dominant output component, the frequency of the dominant sideband in the output of the optical modulator arranged in the optical frequency sweeping device should be shifted by ω _m for each revolution. Corresponding to, the reference point of the spectrum is to be shifted by ω _m for each revolution. At this time, the modulation characteristic of the modulator with respect to the light pulse which makes one round can be expressed by the following N × N matrix having M ₁ as a diagonal element.

[0021]

[Equation 2]

For a 4MZ modulator, n = 4x + 1 (x =
The element M _n for 0, ± 1, ± 2, ...) is represented by M _n = J _n (δ) exp (inφ) (5). Other coefficients are 0. Here, φ is the modulation signal phase with respect to the reference phase, and δ is the modulation index.

The calculation model is shown in FIG. The input optical pulse is modulated by the 4MZ modulator every time it circulates in the optical ring resonator, and a modulated sideband is generated. Neglecting the phase velocity dispersion of the optical path in the optical ring resonator, the phase of all modulation sidebands seen by an observer moving at the speed c / n leading the light pulse is stationary.
The phase of the input optical pulse and the modulation signal at the 0th round is set to 0
And the reference point of the optical phase. The vector representing the electric field spectrum of the optical pulse is converted by the matrix M for each circulation. The modulation signal phase is ω _m τ per revolution with respect to the reference phase
_C change, and the change is added every lap. Therefore, if φ _C = ω _m τ _C is set, the elements of the matrix M in the kth round are φ → kφ _C in the equation (5). The optical amplifier amplifies so that the total power of each term of the electric field vector becomes 1. The influence of ASE noise output from the optical amplifier is ignored.

Using the above model, the powers of the primary and high-order modulation sidebands with respect to the number of turns of the optical pulse were calculated with φ _C = 0 as a parameter. N in equation (4) is
33. In the electric field vector of the input light pulse, the central element was 1, and the other elements were 0. The modulation index was 1.8. The calculation result is shown in FIG.

In FIG. 13, the horizontal axis represents the number of turns of the optical pulse, and the vertical axis represents the relative power of each modulation sideband with respect to the total optical pulse power. Already -3 after 6 laps of light pulse
The next sideband becomes dominant, and the higher the sideband (on the side of the minus sign) becomes dominant as the circuit goes around. This makes a linear sweep of the optical frequency impossible.

From the above calculation results, when the optical modulator utilizing the electro-optical effect is used as the optical frequency shifter, depending on the value of the parameter such as the phase change amount of the modulation signal per one turn of the optical resonator, It can be seen that there is a problem that the frequency spectrum of the optical pulse spreads and linear sweeping of the optical frequency becomes impossible.

The present invention is an optical frequency sweeping device using an optical modulator utilizing the electro-optical effect as an optical frequency shifter, which is capable of generating frequency sweeping light having a large bandwidth with simple control. The purpose is to provide a device.

Further, it is an object of the present invention to provide a wavelength packet generator that generates a wavelength packet using the optical frequency sweeping device and a wavelength packet communication network using the wavelength packet generator.

Furthermore, in the optical frequency sweeping device of the present invention, there is provided a phase change measuring method used for strictly adjusting the value of the phase change φ _C of the modulation signal per one revolution time of the optical resonator by the variable optical delay line. The purpose is to do.

[0030]

An optical frequency sweeping device of the present invention is disclosed in JP-A-6-110102 or JP-A-6-110102.
An optical modulator using an electro-optical effect is provided in place of the optical frequency shifter of the optical frequency sweep device described in Japanese Patent No. 110103, and the optical resonator 1 is adjusted by adjusting the optical path length of the optical resonator.
The phase change φ _C of the modulation signal per cycle is adjusted so that the phases of the low-order modulation sidebands of the optical modulator are not matched (claim 1).

Here, the angular frequency of the modulation signal for driving the optical modulator is ω _m , and the time for the optical pulse to make one round in the optical resonator is τ.
_{When C} , the value of φ _C = ω _m τ _C is 2nπ, ± nπ /
It is set so as to be different from both 2 and ± nπ / 4 (n is an arbitrary integer) (claim 2). A variable optical delay line may be provided as a means for adjusting the optical path length of the optical resonator (claim 3).

This optical modulator uses a 4-branch Mach-Zehnder type optical modulator including four phase modulators, and applies a modulation whose phase is different by π / 2 to each of the four phase modulators (claim 4). ). A two-branch Mach-Zehnder type optical modulator including two phase modulators may be used, and square wave modulations having different π / 2 phases may be applied to the two phase modulators (claim 5).

Further, a phase velocity dispersion adjusting means for setting the phase velocity dispersion of the optical path to a predetermined value may be provided on the optical path of the optical resonator (claim 6). Furthermore, on the optical path of the optical resonator,
A phase velocity dispersion slope adjusting means for setting the phase velocity dispersion slope of the optical path to a predetermined value may be provided (claim 7).

The wavelength packet generator of the present invention modulates the optical pulse output from the optical frequency sweeping device according to any one of claims 1 to 7 and the optical output means of the optical frequency sweeping device with a transmission signal, An optical modulator for generating a wavelength packet having a different wavelength for each packet (claim 8).

Further, there may be provided optical modulation means for modulating the optical pulse output from the optical pulse modulation means with a transmission signal and inputting it to the optical resonator from the optical input means (claim 9). Alternatively, the first optical modulation means for modulating the optical pulse output from the optical output means of the optical frequency sweeping device with the transmission signal, and the optical pulse output from the optical pulse modulation means with the transmission signal, and the optical input means. From the optical resonator to the optical resonator, the first optical modulator is used to place different transmission signals on each wavelength packet within one sweep cycle, and the wavelength within one sweep cycle is used. When the same transmission signal is put on the packet, the first or second optical modulator may be used (claim 10).

The wavelength packet communication network of the present invention is connected to the wavelength packet generator according to any one of claims 8 to 10 through an optical fiber and is output from the wavelength packet generator. A wavelength branching unit that branches wavelength packets of different wavelengths corresponding to the wavelengths, and a plurality of optical receiving devices that respectively receive the wavelength packets of the respective wavelengths branched by the wavelength branching unit (claim 11).

The measuring method for measuring the phase change φ _C of the modulation signal with the optical frequency sweeping device of the present invention is as follows: applying a sinusoidal intensity modulation to the continuous light input in the preceding stage of the optical pulse modulating means,
The output light output from the optical input / output means of the optical resonator is received and converted into an electric signal, the frequency spectrum of the electric signal is analyzed, and the frequency of the intensity modulation component of the output light of the optical resonator is measured. A sine wave intensity modulation signal applied by the intensity modulator is measured for a phase change that occurs each time the optical resonator makes one revolution (claim 12).

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment of Optical Frequency Sweeping Device: Claims 1 to 5> FIG. 1 shows a first embodiment of the optical frequency sweeping device of the present invention. In the figure, continuous light output from the master laser 11 is pulsed by an optical pulse modulator 12 and input to an optical ring resonator 14 via an optical coupler 13. The optical ring resonator 14 includes an optical coupler 13, which is a light input / output unit, an optical delay line 15 having a fixed delay amount, an optical amplifier 16, and an optical modulator (4MZ modulation) that uses an electro-optical effect as an optical frequency shifter. Bowl, 2MZ
Modulator) 25, optical switch 18, optical bandpass filter (BPF) 19, and variable optical delay line 2 with variable delay amount.
6 is included in the optical path. The optical pulse modulator 12 and the optical switch 18 are synchronously controlled by the synchronization control circuit 20. The optical delay line 15 and the variable optical delay line 26 may be integrated, or the length of the optical delay line 15 may be physically adjusted without using the variable optical delay line 26.

The feature of this embodiment is that an optical modulator 25 utilizing the electro-optical effect is used instead of the conventional optical frequency shifter 17 shown in FIG. 7, and a variable optical delay line 26 is provided in the optical ring resonator 14. I have just inserted. The variable optical delay line 26 changes one round time of the optical ring resonator 14.
As a result, the phase change φ _C of the modulation signal per one round time of the optical ring resonator is adjusted so that the primary modulation sideband is always dominant. For example, when an erbium-doped optical fiber amplifier is used as the optical amplifier 16, the amplification band is usually about 4 THz. Therefore, when the modulation frequency is 10 GHz, the primary modulation sideband component is dominant over a maximum of about 400 turns. All you have to do is

The concept of adjusting φ _C by the variable optical delay line 26 is as follows. With 4MZ modulator as an optical modulator 25, since the modulation sideband at 4Omega _m intervals by the formula (5) is _{generated, 4xφ C = 4xω m τ C} = 2nπ between the primary modulation sidebands ... The phase of the modulation sideband of the 4x + 1 order that satisfies the relationship of (6) is matched, and the modulation sideband grows. Where x
Is an integer other than 0, and n is an integer. Also, φ _C = 2nπ
If, the phases of all modulation sidebands are matched.

Therefore, if the time τ _C required for the optical pulse to make one round in the optical ring resonator 14 is adjusted so that the low-order modulation sidebands other than the first order do not satisfy the condition of the equation (6), the phase matching is achieved. It does not occur, and it is expected that the primary modulation sideband with the highest modulation efficiency will always be dominant. If the number of turns is about 400, the modulation efficiency is relatively high-third order, +
If the 5th-order, -7th-order, and + 9th-order modulation sidebands are not phase-matched, the 1st-order modulation sideband can always be dominant. From equation (6), -3rd order, + 5th order, -7th order,
In order that the + 9th-order modulation sidebands are not phase-matched, φ _C ≠ 2nπ (condition that the phases of all the modulation sidebands are not matched) φ _C ≠ ± nπ / 2 (-3rd-order + 5th-order modulation sidebands) The condition that φ does not match the phase) φ _C ≠ ± nπ / 4 (the condition that the phases of the -7th and + 9th order modulation sidebands do not match) must be satisfied.

As an example, FIG. 2 shows the results when φ _C = π / 5 using the model shown in FIG. At this time, it can be seen that the −3rd-order modulation sideband is suppressed to about −15 dB at the maximum with respect to the 1st-order modulation sideband. Moreover, it can be seen that the linear modulation of the optical frequency can be realized after the first modulation sideband becomes dominant even after 400 cycles.

<Second Embodiment of Optical Frequency Sweeping Device: Claims 6 and 7> In the calculation of the first embodiment of the optical frequency sweeping device, it is assumed that the phase velocity dispersion of the optical path of the optical ring resonator 14 is zero. is doing. However, if there is phase velocity dispersion,
The phase relationship of each modulation sideband changes depending on the phase velocity dispersion. Therefore, even if φ _C is appropriately adjusted by the variable optical delay line 26, it may be difficult to linearly sweep the optical frequency.

In the configuration of the second embodiment of the optical frequency sweeping device of the present invention shown in FIG. 3, the phase velocity dispersion compensator 27 is inserted in the optical path of the optical ring resonator 14 to make the phase velocity dispersion of the optical path zero. The above problem can be solved by adjusting to.

If the phase velocity dispersion of the optical path of the optical ring resonator 14 does not have wavelength dependency (there is a phase velocity dispersion slope), a phase velocity dispersion slope compensator may be inserted.

<Third Embodiment of Optical Frequency Sweeping Device: Claims 6 and 7> In the second embodiment of the optical frequency sweeping device, the phase velocity dispersion of the optical path of the optical ring resonator 14 is made zero. , To prevent the phase relationship of each modulation sideband from changing due to the phase velocity dispersion, but on the contrary, to provide an appropriate phase velocity dispersion, an appropriate phase difference for each modulation sideband of the circulating optical pulse. By giving
It is also possible to prevent low-order modulation sidebands other than the first-order from satisfying equation (6).

The third embodiment of the optical frequency sweeping device of the present invention is a dispersion device having a predetermined phase velocity dispersion, instead of the phase velocity dispersion compensator 27 in the configuration of the second embodiment shown in FIG. insert.

<Fourth Embodiment of Optical Frequency Sweeping Device> In the optical frequency sweeping device of each of the above-mentioned embodiments, the optical bandpass filter 19 having a fixed transmission center frequency is replaced with a narrow transmission center frequency variable. A band frequency variable optical bandpass filter (variable BPF) may be used. The synchronization control circuit 20 effectively removes ASE noise by performing synchronization control that shifts the transmission center frequency of the frequency variable optical bandpass filter in accordance with the frequency shift of the optical pulse that circulates in the optical ring resonator 14. can do. As a result, the number of rounds of the optical pulse is increased, and it becomes possible to sweep the optical frequency in a wide band.

Although the optical ring resonator 14 is used in each of the above-described embodiments, the optical frequency sweeping device can be similarly configured by using, for example, a Fabry-Perot resonator.

<First Embodiment of Wavelength Packet Generator: Claim 8> FIG. 4 shows a first embodiment of the wavelength packet generator of the present invention. In the figure, the wavelength packet generator of the present embodiment comprises the optical frequency sweeping device 10 and the transmission signal applying optical modulator 31. Here, the optical frequency sweeping device 10 of the first embodiment shown in FIG. 1 is shown, but other embodiments may be used.

The transmission signal applying optical modulator 31 is connected to the subsequent stage of the output port of the optical coupler 13. The transmission signal applying optical modulator 31 modulates the frequency-swept optical pulse train with a transmission signal to convert it into a wavelength packet train and sends it out. Here, it is possible to modulate the wavelength packets of different frequencies within one sweep cycle with the corresponding transmission signals, or it is possible to modulate all the wavelength packets within one sweep cycle with the same transmission signal. The latter is used in a later-described wavelength packet communication network for broadcast transmission of the same transmission signal (content) to a plurality of remote nodes.

<Second Embodiment of Wavelength Packet Generator: Claim 9> FIG. 5 shows a second embodiment of the wavelength packet generator of the present invention. In the figure, in the wavelength packet generator of the present embodiment, the transmission signal applying optical modulator 31 of the first embodiment is arranged in front of the input port of the optical coupler 13 of the optical ring resonator 14. That is, the optical pulse output from the optical pulse modulator 12 is modulated by the transmission signal in the transmission signal applying optical modulator 32 and input to the optical ring resonator 14 to generate a frequency-shifted wavelength packet. Wavelength packets having the same signal within one sweep period are output to the output port of the optical coupler 13. The present embodiment is different from the configuration of the first embodiment in that
It is easy to put the same transmission signal on wavelength packets within one sweep period.

<Third Embodiment of Wavelength Packet Generator: Claim 10> FIG. 6 shows a third embodiment of the wavelength packet generator of the present invention. In the figure, in addition to the optical modulator 31 of the first embodiment, the wavelength packet generation device of the present embodiment is provided in the preceding stage of the input port of the optical coupler 13 of the optical ring resonator 14 shown in the second embodiment. Light modulator 3
2 are arranged.

In this embodiment, when a different transmission signal is placed on each wavelength packet within one sweep cycle, the transmission signal applying optical modulator 31 is used to send the same transmission signal on each wavelength packet within one sweep cycle. In case of making it possible, the optical modulator 3 for applying the transmission signal
2 can be used properly.

<Embodiment of Wavelength Packet Communication Network: Claim 11> FIG. 7 shows an embodiment of a wavelength packet communication network of the present invention. The wavelength packet communication network of the present embodiment is characterized in that the wavelength packet generation device 30 of the present invention is arranged in the center node 41.

In the figure, the center node 41 and a plurality of remote nodes 42 are connected via an optical fiber 43 and a wavelength router 44. The wavelength packet generator 30 arranged in the center node 41 sequentially outputs wavelength packets having wavelengths corresponding to the destination remote node, and sends them to the optical fiber 43 as a wavelength packet string.
This wavelength packet sequence reaches the wavelength router 44 via the optical fiber 43, is distributed to different ports corresponding to the respective wavelengths, and reaches the corresponding remote nodes 42.
For example, assuming that the wavelengths assigned to the remote nodes 42a to 42d are λa to λd, by setting the wavelength of the wavelength packet addressed to the remote node 42a to λa, the wavelength router 43 automatically performs routing by wavelength,
The wavelength packet of wavelength λa is transmitted to the remote node 42a.

Here, in the wavelength packet generator 30, the optical modulator 31 arranged at the subsequent stage of the output port of the optical coupler 13 of the optical ring resonator 14 of the optical frequency sweeping device 10.
In this case, "individual communication" is realized when different transmission signals are placed on each wavelength packet within one sweep cycle. Also,
By using the optical modulator 32 arranged before the input port of the optical coupler 13 of the optical ring resonator 14 or the optical modulator 31 arranged after the output port of the optical coupler 13, wavelength packets within one sweep period When the same transmission signal is placed, "broadcast type communication" is realized.

<Measurement Method of Phase Change φ _C of Modulated Signal per Revolution of Optical Resonator: Claim 12> In the optical frequency sweeping device of the present invention (wavelength packet generator using the same, wavelength packet communication network) , The variable optical delay line 25 causes the phase change φ _C of the modulation signal per revolution time of the optical resonator.
It is important to strictly adjust the value of. For that purpose, φ _C must be measured with high accuracy.

For example, OTDR (Optical Time Domain)
Φ _C can be obtained by measuring the distance of the optical path of the optical resonator using Reflectometry or the like. But,
For example, if the modulation frequency is 10 GHz and the refractive index of the optical path is 1.5, the distance required for the phase of the modulation signal to rotate by 2π is about 2 cm. Therefore, φ _C can be accurately measured using the distance measurement information by OTDR. Is difficult.

FIG. 8 shows a structural example of a measurement system for accurately obtaining φ _C. The present measurement system, in addition to the configuration of the optical frequency sweep device 10 described above, receives an optical intensity modulator 51 that applies sinusoidal intensity modulation to the output light of the master laser 11, and an output optical pulse train of the optical coupler 13. A photodetector 52 for converting into an electric signal and an electric signal frequency analyzer 53 for analyzing the frequency spectrum of the electric signal output from the photodetector 52 are added.

The modulated signal is not applied to the optical modulator 25 used as the optical frequency shifter, but a signal of the same frequency is applied to the optical intensity modulator 51. By applying only an appropriate bias signal to the optical modulator 25, the optical pulse is set to pass through without modulation. The continuous light to which the intensity modulation of the angular frequency ω _m is applied by the optical intensity modulator 51 is pulsed by the optical pulse modulator 12 and input to the optical ring resonator 14. In the optical ring resonator 14, the optical pulse circulates while maintaining the intensity modulation pattern of ω _m . As a result, in the intensity modulation pattern of the obtained light output, a phase “jump” occurs at the joint portion of the light pulse.

Here, when this light output is photoelectrically converted by the photodetector 52, an electric signal I _d (t) of the following equation is obtained.

[0063]

[Equation 3]

Here, d (t) is a delta function. formula
The second term of the phase portion of (7) indicates that the phase of the electric signal I _d (t) causes “jump” by ω _m τ _C (= φ _C ) every time τ _C. If φ _C = 2nπ + β (n = 0, 1, 2, ...), the intensity modulation frequency of the electric signal I _d (t) is from f _m to β.
/ (2πτ _C ) shift. Therefore, by measuring the shift of the intensity modulation frequency of I _d (t) from f _{m with} the electric signal frequency analyzer 53, the value of φ _C (or β) can be accurately measured.

[0065]

As described above, the optical frequency sweep device of the present invention can generate an optical frequency sweep pulse having a large bandwidth with simple control.

Further, the wavelength packet generator using the optical frequency sweeping device of the present invention can stably generate a wavelength packet whose wavelength is controlled with high precision by simple control.

Further, in the wavelength packet communication network using the wavelength packet generator of the present invention, stable wavelength packet routing becomes possible.

Further, according to the phase change measuring method of the present invention, it is possible to accurately obtain the value of the phase change φ _C of the modulation signal per one round time of the optical resonator set in the variable optical delay line of the optical frequency sweeping device. .

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an optical frequency sweeping device of the present invention.

FIG. 2 is a diagram showing the result of computer simulation when φ _C = π / 5 in the first embodiment.

FIG. 3 is a block diagram showing a second embodiment of the optical frequency sweeping device of the present invention.

FIG. 4 is a block diagram showing a first embodiment of a wavelength packet generator of the present invention.

FIG. 5 is a block diagram showing a second embodiment of a wavelength packet generator of the present invention.

FIG. 6 is a block diagram showing a third embodiment of the wavelength packet generation device of the present invention.

FIG. 7 is a block diagram showing an embodiment of a wavelength packet communication network of the present invention.

FIG. 8 is a diagram showing a configuration example of a measurement system for accurately obtaining φ _C.

FIG. 9 is a block diagram showing a configuration example of a conventional optical frequency sweep device.

FIG. 10 is a diagram showing a configuration of a 4-branch Mach-Zehnder type optical modulator (4MZ modulator).

FIG. 11 is a diagram showing a configuration of a two-branch Mach-Zehnder type optical modulator (2MZ modulator).

FIG. 12 is a diagram showing a computer simulation model.

FIG. 13 is a diagram showing a result of computer simulation when φ _C = 0.

[Explanation of symbols]

10 Optical frequency sweeper 11 master laser 12 Optical pulse modulator 13 Optical coupler 14 Optical ring resonator 15 Optical delay line 16 Optical amplifier 17 Optical frequency shifter 18 optical switch 19 Optical bandpass filter (BPF) 20 Synchronous control device 25 Optical modulator using electro-optic effect 26 Variable optical delay line 27 Phase velocity dispersion compensator 30 wavelength packet generator 31, 32 Optical modulator for applying transmission signal 41 Center node 42 remote node 43 optical fiber 44 wavelength router 51 Light intensity modulator 52 Photodetector 53 Electric signal frequency analyzer

Continued front page    F term (reference) 2G086 CC03 EE12                 2K002 AA02 AB12 BA06 DA07 DA08                       HA05                 5F072 HH05 HH07 JJ20 SS06 YY17                 5K002 AA02 BA06 DA02 DA05 FA01

Claims (12)

[Claims] 1. An optical pulse modulating means for converting continuous light inputted from the outside into an optical pulse, an optical frequency shifter for giving a predetermined frequency shift to the propagation light of the optical path on the optical path, an optical amplifier, and an optical switch. An optical resonator having a means for removing spontaneous emission optical noise generated in an optical amplifier, an optical delay line, and an optical input for inputting the optical pulse output from the optical pulse modulating means to the optical resonator. Means, a synchronization control means for synchronously controlling a modulation signal for the optical pulse modulation means and an opening / closing signal for the optical switch, and an optical output means for taking out the frequency-swept optical pulse around the optical resonator to the outside. An optical frequency sweeping device comprising: an optical modulator using an electro-optical effect instead of the optical frequency shifter; and further adjusting an optical path length of the optical resonator to provide an optical resonator 1
An optical frequency sweeping device, characterized in that the phase change φ _C of the modulation signal per cycle is adjusted so that the phases of the low-order modulation sidebands of the optical modulator do not match. 2. The optical frequency sweeping device according to claim 1, wherein an angular frequency of a modulation signal for driving the optical modulator is ω _m , and a time for the optical pulse to make a round in the optical resonator is τ _C. Then, the value of φ _C = ω _m τ _C is 2nπ, ± nπ / 2, ± n
An optical frequency sweeping device, which is set to be different from any of π / 4 (n is an arbitrary integer). 3. The optical frequency sweeping device according to claim 1 or 2, further comprising a variable optical delay line as means for adjusting the optical path length of the optical resonator. 4. The optical frequency sweeping device according to claim 1, wherein the optical modulator uses a 4-branch Mach-Zehnder type optical modulator including four phase modulators. An optical frequency sweeping device, characterized in that it is configured to apply a modulation whose phase is different by π / 2 each. 5. The optical frequency sweeping device according to claim 1, wherein the optical modulator uses a two-branch Mach-Zehnder type optical modulator including two phase modulators. To π / 2
An optical frequency sweeping device, characterized in that it is configured to apply square wave modulation having different phases. 6. The optical frequency sweeping device according to claim 1, further comprising a phase velocity dispersion adjusting unit on the optical path of the optical resonator for setting a phase velocity dispersion of the optical path to a predetermined value. An optical frequency sweeping device characterized in that 7. The optical frequency sweeping device according to claim 6, further comprising a phase velocity dispersion slope adjusting unit on the optical path of the optical resonator for setting a phase velocity dispersion slope of the optical path to a predetermined value. Optical frequency sweeping device. 8. The optical frequency sweeping device according to claim 1, wherein the optical pulse output from the optical output means of the optical frequency sweeping device is modulated with a transmission signal, and the wavelength is different for each packet. A wavelength packet generator comprising: an optical modulator that generates a wavelength packet. 9. The optical frequency sweeping device according to claim 1, wherein the optical pulse output from the optical pulse modulating means is modulated with a transmission signal, and the optical input means transfers the optical pulse to the optical resonator. A wavelength packet generator comprising: an optical modulator for inputting; and a wavelength packet having a different wavelength for each packet from the optical output means. 10. The optical frequency sweeping device according to claim 1, and a first optical modulator that modulates the optical pulse output from the optical output device of the optical frequency sweeping device with a transmission signal. A second optical modulator that modulates an optical pulse output from the optical pulse modulator with a transmission signal and inputs the optical pulse from the optical input unit to the optical resonator. The first optical modulation means is used when different transmission signals are loaded, and the first or second optical modulation means is used when the same transmission signal is loaded on wavelength packets within one sweep period. A wavelength packet generator characterized in that it is configured to output wavelength packets having different wavelengths for each. 11. The wavelength packet generation device according to claim 8, and wavelengths of different wavelengths output from the wavelength packet generation device, which are connected to the wavelength packet generation device via an optical fiber. A wavelength packet communication network comprising: a wavelength branching unit for branching a packet corresponding to a wavelength; and a plurality of optical receiving devices for respectively receiving wavelength packets of respective wavelengths branched by the wavelength branching unit. 12. A measuring method for measuring a phase change φ _C of a modulation signal by the optical frequency sweeping device according to claim 1, wherein sinusoidal intensity modulation is applied to continuous light input in the preceding stage of the optical pulse modulating means. Then, the output light output from the optical input / output unit of the optical resonator is received and converted into an electric signal, the frequency spectrum of the electric signal is analyzed, and the frequency of the intensity modulation component of the output light of the optical resonator is analyzed. And measuring the phase change that the sinusoidal intensity-modulated signal applied by the optical intensity modulator undergoes each time the optical resonator makes one revolution. .