JP2001086070A - Optical cdma inverse spread demodulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical CDMA inverse spread demodulator, capable of reducing unnecessary side lobe components of a decoded optical pulse and reducing the output level of non-decoded optical pulse. SOLUTION: Frequency components are timewisely changed according to the optical intensity of decoded signal light by connecting a means 13 to chirp signal light frequency and an optical filter 14 with the trailing stage of an inverse spread demodulator 12 which performs inverse spread demodulation of an optical CDMA signal spread and demodulated by a spread demodulator which performs spread demodulation of a signal in an optical area, and only frequency components corresponding to the main peak pulse of the demodulated signal light are extracted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CDMA (Code Div) for performing spread modulation and despread demodulation of a signal in an optical domain.
The present invention relates to a demodulator in a multiple-access multiple access system.

[0002]

2. Description of the Related Art In the optical CDMA system, random access and self-routing operation can be systematically realized by codes without using elements such as optical switches. Therefore, application to optical LAN and optical switching is being studied.

FIG. 1 shows an example of a conventional optical CDMA system. In the figure, 1-1, 1-2, 1-3,... -3,... Are spread modulators for performing signal spread modulation in the optical domain, 3 is a star coupler, 4-1 to 4-2, 4-3,. It is a spread demodulator.

Short light pulse light sources 1-1, 1-2, 1-3,
.. Represents a plurality of spread modulators 2-1, 2-2, 2-3,.
And a plurality of spread modulators 2-1 and 2-1.
2-2, 2-3,... And a plurality of despread demodulators 4-1.
Are connected to the star coupler 3 so as to face each other with the star coupler 3 interposed therebetween.

Each of the spread modulators 2-1, 2-2, 2-3,...
... is a lattice type optical circuit in which J asymmetric Mach-Zehnder interferometers (J is an integer of 1 or more, J = 2 in this figure) having optical path length differences ΔL, 2ΔL,. Also, each of the despread demodulators 4-1 4-2, 4-
3,... Indicate optical path length differences of JΔL and (J−1) Δ, respectively.
L,... ΔL (J is an integer of 1 or more; in this drawing, J =
It is composed of a lattice type optical circuit in which the asymmetric Mach-Zehnder interferometer of 2) is cascaded.

Here, the spread modulator 2-2 and the despread demodulator are used.
The coupling ratio of the directional couplers 5a to 5f constituting the device 4-2 is
0.5, and the repetition frequency f (Hz) (f ≦ c /
(2 ^JnΔL), c is the speed of light, and n is short of the refractive index of the waveguide)
When an optical pulse enters the spread modulator 2-2, 1 / f
2 during the (sec) time frame^JOptical pulse trains
A period Δt (= nΔL / c)) is newly generated and a code sequence
Is configured. This code sequence constitutes the spread modulator 2-2
Phase information of the phase shifters 6a and 6b. This
Is input to the despread demodulator 4-2.
In the case, each light pulse is 2^JSeparated into light pulses
Thereafter, coherent electric field components are added.

When the setting of the phase shifters 6c and 6d constituting the despread demodulator 4-2 satisfies the decoding conditions for the phase shifters 6a and 6b, the optical power is concentrated at the center of the pulse and decoding is performed. However, if the setting is different from the decoding condition, the incident coded pulse is further spread in time and decoding is not performed.

FIG. 2 shows an input / output optical pulse train in the system of FIG. 1. FIG. 2 (a) shows an incident optical pulse train, and FIG. 2 (b) shows a generated code sequence after passing through a spread modulator when J = 2. FIG. 3C shows the output light pulse train after passing through the despreading demodulator satisfying the decoding condition, and FIG. 2D shows the output light pulse train after passing through the despreading demodulator not satisfying the decoding condition. . In this figure, for simplicity, the influence of one pulse of the incident light pulse train is shown.

[0009]

The conventional system described above has a disadvantage that even when the decoding conditions are satisfied, a side lobe component is generated around the decoded optical pulse, and the S / N ratio on the receiving side is deteriorated. there were. Further, when the decoding condition is not satisfied, an optical pulse train (non-decoded optical pulse) which is further temporally spread occurs, and there is a disadvantage that the S / N ratio of a desired decoded signal is deteriorated. This is a CD
This shows that the auto-correlation characteristic and the cross-correlation characteristic of the MA spread modulator and despread demodulator deviate from ideal states.

SUMMARY OF THE INVENTION The present invention has been made in view of the above prior art, and is an optical CDMA inverse multiplexing apparatus capable of reducing unnecessary side lobe components of a decoded light pulse and reducing the output level of a non-decoded light pulse. It is an object to provide a spread demodulator.

[0011]

In order to solve the above-mentioned problems, an optical CDMA despreading demodulator according to the present invention includes a despreading demodulator for despreading and demodulating an optical CDMA signal spread-modulated in an optical domain. Means for chirping the signal light frequency;
The optical filter and the optical filter are connected in this order (claim 1).

Since the frequency component of the signal light that has passed through the means for chirping the signal light frequency changes with time according to the light intensity, only the frequency component corresponding to the main peak pulse of the decoded signal light is extracted by the optical filter. By
The unnecessary side lobe component of the decoded light pulse can be reduced, and the output level of the non-decoded light pulse can be reduced.

Means for chirping the signal light frequency include self-phase modulation (SPM: Se) of an optical pulse in an optical fiber (claim 2) and a semiconductor laser amplifier (claim 3).
(IfPhase Modulation) effect and the like can be used. Alternatively, the signal light frequency can be chirped by performing phase modulation in synchronization with the signal light (claim 4).

As the optical filter, an arrayed waveguide grating (claim 5), a lattice type optical circuit (claim 6), a transversal type optical circuit (claim 7) and the like can be used. Since these optical filters can change the center frequency and the pass bandwidth, they can support various carrier frequency signals, bit rates, and light intensity pulses.

[0015]

FIG. 3 shows a first embodiment of an optical CDMA despreading demodulator according to the present invention, here an embodiment corresponding to claim 1. In the drawing, reference numeral 11 denotes an optical input. Part 1
Reference numeral 2 denotes a despread demodulator for performing despread demodulation of a signal in the optical domain;
3 is a means for chirping the signal light frequency, 14 is an optical filter for extracting only a frequency component corresponding to the main peak pulse of the decoded signal light, 15 is an optical output unit, and 16 and 17 are optical coupling units.

The optical chirp means 13 is connected to the subsequent stage of the despread demodulator 12 via an optical coupling section 16, and the optical chirp means 13 is further connected to an optical filter 14 via an optical coupling section 17. The optical pulse input from the input unit 11 and despread and demodulated by the despreading demodulator 12 is subjected to optical chirp by the optical chirp unit 13 and further output from the optical output unit 15 via the optical filter 14.

FIG. 4 shows an optical CDMA system using the optical CDMA despread demodulator of FIG.
.., 21-2, 21-3,...
-1, 22-2, 22-3,... Are spread modulators for performing spread modulation of signals in the optical domain, 23 is a star coupler, 24-
The optical CDM shown in FIG.
A despread demodulator.

Short light pulse light sources 21-1, 21-2, 21
-3,... Indicate a plurality of spread modulators 22-1, 22-2, 2
., And a plurality of spread modulators 22-1, 22-2, 22-3,... And a plurality of optical CDMA despread demodulators 24-1, 24-2. 24-3,
Are connected to the star coupler 23 so as to face each other with the star coupler 23 interposed therebetween.

FIG. 5 shows the spread modulators 22-1 and 22 shown in FIG.
, 22-3,..., And FIG.
DMA despread demodulators 24-1, 24-2, 24-3,...
Are examples of the configuration of the despread demodulator part (despread demodulator 12 in FIG. 3).

In FIG. 5, the optical path length differences are ΔL and 2Δ, respectively.
L two asymmetric Mach-Zehnder interferometers are connected in cascade. Generally, the optical path length differences are ΔL, 2ΔL, 4ΔL,
...... 2 ^K ΔL ^(K is an integer of 1 or more) it is possible to configure the cascading asymmetrical Mach-Zehnder interferometer.
In FIG. 6, the configuration of FIG. 5 is opposed (the input unit and the output unit are interchanged).

5 and 6, 25a to 25p denote waveguides (25a, 25b, 25i, and 25j denote input waveguides,
25g, 25h, 25o, 25p are output waveguides), 26
a to 26f are directional couplers, and 27a to 27d are phase shifters.

Examples of the directional coupler include a configuration in which two waveguides are brought close to each other, a configuration in which a symmetric Mach-Zehnder interferometer or a symmetric Mach-Zehnder interferometer is cascaded in multiple stages, a multimode interference (MMI) coupler, and the like. Conceivable. Further, as the phase shifter, for example, when a glass waveguide is used, a heater for inducing a refractive index change by a thermo-optic effect is used, and when a ferroelectric waveguide is used, a refractive index change is induced by an electro-optic effect. And the like for the purpose.

FIG. 7 shows an input / output optical pulse train in the optical CDMA system shown in FIG. 4 using the spread modulators shown in FIGS. 5 and 6, and a despread demodulator. FIG. A generated code sequence (an optical pulse train input from the input waveguide 25a and output to the output waveguide 25g), FIG.
Are φa = φb = π, φc = φ in the phase shifters of FIGS.
An outgoing light pulse train (a light pulse train input from the input waveguide 25i and output to the output waveguide 25o) when a phase of d = 0 is given (when the decoding condition is satisfied), and FIG. Φa = φb = π, φc for phase shifters 5 and 6
= Π, φd = 0 (when the decoding condition is not satisfied), the outgoing light pulse train shown in FIG. 3D, the outgoing light pulse train shown in FIG. 2B passing through the optical chirp means and the optical filter FIG. 11E shows an emission light pulse train after the light emission pulse train shown in FIG. 10C has passed through the optical chirp means and the optical filter (note that φa, φb, φc and φd represent the phase shift values of the phase shifters 27a, 27b, 27c, and 27d, respectively.) In this figure, for simplicity, the influence of one pulse of the incident light pulse train is shown.

FIG. 8 shows the spread modulators 22-1 and 22 shown in FIG.
, 22-3,... And optical CDMA despread demodulator 24
This shows another example of the configuration of the despread demodulator portion of -1, 24-2, 24-3,..., In which the spread modulator and the despread demodulator portion have the same shape.

In FIG. 8, a 1 × 4 optical splitter and a 4 × 1 optical multiplexer are connected via four waveguides having optical path length differences ΔL, 2ΔL, and 3ΔL. In FIG. 8, 31a-3
1 f is a waveguide, 32 is a 1 × 4 optical splitter, 33 a to 33
d is a phase shifter, and 34 is a 4 × 1 optical multiplexer.

Examples of the configuration of the optical splitter and the optical multiplexer include:
A configuration in which a star coupler, an MMI coupler, and a 2 × 2 directional coupler are cascaded in multiple stages, a configuration in which Y branch waveguides are cascaded in multiple stages, and the like are conceivable. When an optical pulse train is incident with this configuration, spread modulation and despread demodulation of the optical pulse train are performed by a combination of the delay time difference of the waveguide and the set value of the phase shifter, as in the configurations of FIGS. Done.

FIG. 9 shows the spread modulators 22-1 and 22-2 in FIG.
, 22-3,... And optical CDMA despread demodulator 24
-1, 24-2, 24-3,... Show still another configuration example of the despreading demodulator portion, in which the spreading modulator and the despreading demodulator portion have the same shape. .

FIG. 9 shows an arrayed waveguide grating pair configuration in which the input / output portions of two arrayed waveguide gratings are connected using a plurality of waveguides. In FIG. 9, 41a-41
f is a waveguide, 42a and 42b are arrayed waveguide gratings, 43
a to 43d are slab waveguides of an arrayed waveguide grating;
a, 44b are arrayed waveguides of an arrayed waveguide grating, 45a
45d is a phase shifter.

In the diffusion modulator having the above-described configuration, the incident light from the waveguide 41a is divided into the waveguides 41b to 41b for each frequency component.
The phase shifters 45a to 45d divide and emit the light,
After being subjected to a phase shift in (1) and (2), they are multiplexed in the waveguide 41f.
The multiplexed signal is obtained by the despread demodulator having the above-described configuration.
Demultiplexed again for each corresponding frequency component, after phase shift,
Are multiplexed. The decoding and non-decoding of the optical pulse train in the frequency domain are performed by combining the set values of the phase shifts in the phase shifters 45a to 45d.

However, when the spread modulator and the despread demodulator shown in FIG. 8 or FIG. 9 are used,
Ideal decoding and non-decoding are not performed as in the case of the configurations of FIGS.

Therefore, as shown in FIG. 3, means for chirping the signal light frequency is arranged at the subsequent stage of the despread demodulator,
By arranging an optical filter in the subsequent stage, which does not pass a side lobe component having a low power level or a frequency component covered by the non-decoded signal light, but passes only a frequency component covered by the decoded main peak pulse, The lobe component and the non-decoded signal light component can be removed, and the S / N ratio can be improved.

FIG. 10 shows a second embodiment of the optical CDMA despreading demodulator according to the present invention, here, an embodiment corresponding to claim 2, in which the same components as those in FIG. 3 are the same. It is represented by a sign. That is, 11 is an optical input unit, 12 is a despread demodulator, 14 is an optical filter, 15 is an optical output unit,
Reference numeral 17 denotes an optical coupling unit, and reference numeral 51 denotes an optical fiber.

Here, as a means for chirping the signal light frequency, the self-phase modulation effect of the light pulse in the optical fiber 51 is used.

Assuming that the envelope function of the light pulse is E and the refractive index inherent to glass is n (f) (f is the optical frequency), the effective refractive index of the optical fiber is n (f, | E | ² ) = cβ / (2πf) = n (f) + n ₂ | E | ² (1) Here, β is a propagation constant, and n ₂ is an optical Kerr constant.

The phase Φ of light is expressed as follows: Φ = 2πft−βz (2) Here, t is time, and z is coordinates in the traveling direction of light.

Since the instantaneous angular frequency is represented by the time derivative of the phase, the instantaneous frequency is f (t) = (1 / 2π) (dΦ / dt) = f− (fn ₂ / c) z (d | E | ² / dt) (3)

At the leading edge of the light pulse, d | E | ² / dt>
0, since d | E | ² / dt <0 at the trailing edge of the light pulse, chirping occurs in which the optical frequency becomes higher toward the trailing edge of the light pulse according to equation (3).

FIG. 11 shows how the optical frequency of an optical pulse changes due to the self-phase modulation effect in the optical fiber. FIG. 11A shows the optical pulse waveform, and FIG. 11B shows the optical frequency change. Are respectively shown.

As can be seen from equation (3), when the light pulse intensity is small, the frequency change becomes small. It is assumed that the frequency change due to the side lobe component or the non-decoded signal light component falls within the range of f ₁ ≦ Δf ≦ f ₂ (4). Since the frequency change due to the main peak pulse exceeds the range of Expression (4), the range of Expression (4) is not passed, and the optical filter 14 is set to pass the range other than Expression (4). The lobe component and the non-decoded signal light component can be removed, and the S / N ratio can be improved.

FIG. 12 shows a third embodiment of the optical CDMA despreading demodulator according to the present invention, here, an embodiment corresponding to claim 3, in which the same components as in FIG. 3 are the same. It is represented by a sign. That is, 11 is an optical input unit, 12 is a despread demodulator, 14 is an optical filter, 15 is an optical output unit,
Reference numeral 17 denotes an optical coupling unit, and reference numeral 52 denotes a semiconductor laser amplifier.

Here, a semiconductor laser amplifier 52 is used as means for chirping the signal light frequency. In the semiconductor laser amplifier, the same frequency shift as that in the example shown in FIG. 11 occurs. Therefore, by appropriately setting the optical filter 14, the side lobe component and the non-decoded signal light component are removed, and the S / N ratio is improved. Can be done.

The advantage of the configuration example of FIG. 12 is that unlike the configuration example of FIG. 10, there is no need to use a long optical fiber, so that all the elements are integrated on the same substrate using the hybrid integration technology. What is possible is:

FIG. 13 shows a fourth embodiment of the optical CDMA despreading demodulator according to the present invention, in which the fourth embodiment corresponds to claim 4. In the drawing, the same components as those in FIG. 3 are the same. It is represented by a sign. That is, 11 is an optical input unit, 12 is a despread demodulator, 14 is an optical filter, 15 is an optical output unit,
Reference numeral 17 denotes an optical coupling unit, and 53 denotes a phase modulator.

Here, a phase modulator 53 is used as a means for chirping the signal light frequency. A phase modulator using a ferroelectric waveguide (for example, LiNbO ₃ ) can be considered.

The phase modulator 53 is driven using an electric signal synchronized with the signal light. Since the instantaneous angular frequency component is represented by the time derivative of the phase as shown in Expression (3), the optical frequency of the signal light also changes with time. Although the side lobe component and the optical frequency change component of the non-decoded signal light are not localized as in the equation (4) due to the self-phase modulation effect, the light which transmits only the optical frequency of the main peak pulse portion is transmitted. By inserting a filter, side lobe components and non-decoded signal light components can be reduced, and the S / N ratio can be improved.

In the configuration example shown in FIG. 13, all the elements can be integrated on the same substrate by using the hybrid integration technique.

FIG. 14 shows a fifth embodiment of the optical CDMA despreading demodulator according to the present invention. In this embodiment, an embodiment corresponding to claim 5 is shown, wherein 61a to 61i are waveguides,
62 is a despread demodulator, 63 is means for chirping the signal light frequency, 64a and 64b are directional couplers, 65 is a phase shifter, 66 is an arrayed waveguide grating, and 67a and 67b are slab waveguides of an arrayed waveguide grating. , 68 are array waveguides of the array waveguide grating.

The following conditions are required for an optical filter for extracting a desired frequency component of the signal light chirped by the means for chirping the signal light frequency. That is,
In order to support various signal light carrier frequencies, a center frequency variable filter is required. Also, considering that the signal light intensity and the bit rate take various values, the main peak pulse, the side lobe, and the bandwidth of the non-decoded signal light component may change. A passband variable filter is also required.

In FIG. 14, the signal light from the waveguide 61c is distributed to the waveguide 61g or 61h by adjusting the phase shifter 65 of the next-stage symmetric Mach-Zehnder interferometer (optical switch). Waveguide 61g
Filter characteristic between -61i, compared with the filter characteristic between the waveguides 61h-61i, the center frequency is increased by f _sp (channel frequency interval of the arrayed waveguide grating). Therefore, a tunable filter can be configured.

FIG. 14 shows an example of the configuration of a wavelength tunable filter for two wavelengths. However, by cascading optical switches in multiple stages and combining them with an arrayed waveguide grating,
A wavelength tunable filter of M wavelengths (M is an integer of 2 or more) can be configured.

The input / output waveguide 6 of the arrayed waveguide grating
By changing the opening of the connection portion with the slab waveguide of 1g to 61i, it is possible to obtain a filter characteristic in which the center frequency is constant and the pass bandwidth is variable (for example, K.K.
Okamoto et al. , “Fabricati
on of Variable Bandwidth F
ilters Using Arrayed-Wave
guide Gratings ", Electroni
cs Letters, vol. 31, no. 18, A
ugust 1995, pp. 139-157. 1592-1593), and an optical filter characteristic whose center frequency is variable and whose pass bandwidth is variable can be realized by combining with a switch.

FIG. 15 shows a sixth embodiment of the optical CDMA despreading demodulator according to the present invention, here, an embodiment corresponding to claim 6, in which 71a to 71p are waveguides,
72 is a despread demodulator, 73 is means for chirping the signal light frequency, 74a to 74f are directional couplers, 75a to 7
5e is a phase shifter.

In FIG. 15, waveguides 71c and 71d
Hereinafter, in the lattice type optical circuit including the five-stage asymmetric Mach-Zehnder interferometer (right side in the drawing), the coupling between the directional couplers 74a to 74f is a characteristic between the waveguide 71c or 71d and the waveguide 71o or 71p. By changing the ratio and the phase shift values of the phase shifters 75a to 75e, an optical filter characteristic with a variable pass bandwidth can be realized.

FIG. 16 shows an example of calculation of characteristics when an asymmetric Mach-Zehnder interferometer of FSR = 70 GHz is cascaded in 12 stages. 6.9 to 25.8 G for 3 dB bandwidth
It can be seen that a variable width of Hz can be achieved.

Since the center frequency can be changed by changing the phase shift values of the phase shifters 75a to 75e, the optical CDMA inverse filter having the center frequency variable and the pass band width variable optical filter in the configuration of FIG. A spread demodulator can be realized.

FIG. 17 shows a seventh embodiment of the optical CDMA despreading demodulator according to the present invention, here, an embodiment corresponding to claim 7, wherein 81a to 81t denote waveguides,
82 is a despread demodulator, 83 is means for chirping the signal light frequency, 84a to 84h are directional couplers, 85a to 8
5h is a phase shifter and 86 is a multiplexer.

Examples of the configuration of the multiplexer 86 include a configuration in which a star coupler, an MMI coupler, and a 2 × 2 directional coupler are cascaded in multiple stages, a configuration in which Y branch waveguides are cascaded in multiple stages, and the like. .

In FIG. 17, waveguides 81c and 81d
Thereafter (right side in the drawing) eight directional couplers (tap)
In the transversal type optical circuit composed of the optical waveguide and the multiplexer, as a characteristic between the waveguides 81c and 81t, the coupling ratio of the directional couplers 84a to 84h and the phase shift value of the phase shifters 85a to 85h are changed. And an optical filter having a variable center frequency and a variable pass band width (for example, E. Pawlowski, K. Takiguchi).
i et al. , "Variable Bandwi
dth and Tunable Center Fr
equipmentFilter Using Trans
versal-Form Programmable
Optical Filter ", Electroni
csLetters, vol. 32, no. 2, Jan
uary 1996, pp. 139-143. 113-114)
With the configuration of FIG. 17, it is possible to realize an optical CDMA despread demodulator including an optical filter whose center frequency is variable and whose pass bandwidth is variable.

The optical coupler, the waveguide section and the like of the optical CDMA despreading demodulator according to the embodiment of the present invention used a silica glass waveguide. The hybrid integration of the silica glass waveguide and the semiconductor laser amplifier is performed by a PLC (P
(lanar Lightwave Circuit) platform.

That is, after the terrace region 92 was formed on the Si substrate 91 by anisotropic etching, the SiO ₂ lower cladding layer 93 was formed by a flame deposition method so as to completely fill the terrace region 92.

Next, planarization polishing was performed to form a height reference plane when the semiconductor laser amplifier was mounted, exposing the surface of the Si terrace. Subsequently, in order to make the height of the core of the waveguide coincide with the height of the active layer of the semiconductor laser amplifier, SiO 2 is used.
_{(2) A} height adjusting layer 94 and a SiO ₂ core layer 95 doped with GeO ₂ as a dopant were deposited. Subsequently, a core portion was formed by etching the core layer using a circuit configuration pattern as shown in FIG. 12 and the like, and then an SiO ₂ upper cladding layer 96 was deposited to complete the fabrication of the waveguide portion.

Next, the upper cladding layer and the height adjusting layer in the portion where the semiconductor laser amplifier mounting portion and the electric wiring portion were to be formed were etched to expose the Si terrace surface. Finally, an insulating SiO ₂ film (not shown) is formed on the surface of the Si terrace, and an Au electric wiring 97 and an AuSn solder pattern 98 are formed thereon, thereby forming a semiconductor laser amplifier 99 (active layer 99).
a).

As a phase shifter using the thermo-optic effect, a thin film heater and electric wiring (both not shown) were deposited on a predetermined waveguide.

It is clear that the waveguide portion of the optical CDMA despreading demodulator of the present invention is not limited to a glass waveguide but can be realized using a ferroelectric waveguide, a semiconductor waveguide, a polymer waveguide, an optical fiber, or the like. is there. It is also clear that this can be realized by using a hybrid integrated configuration in which several types of waveguides are combined.

[0065]

As described above, according to the present invention,
By arranging the means for chirping the signal light frequency and the optical filter on the receiving side, it becomes possible to reduce unnecessary side lobe components of the decoded light signal pulse and to reduce the output level of the non-decoded light signal pulse.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of a conventional optical CDMA system.

FIG. 2 is a diagram showing an input / output optical pulse train in the optical CDMA system of FIG. 1;

FIG. 3 is a configuration diagram showing a first embodiment of an optical CDMA despread demodulator according to the present invention;

FIG. 4 is an optical CD using the optical CDMA despread demodulator of FIG.
Configuration diagram showing MA system

FIG. 5 is a diagram showing a configuration example of a spread modulator in FIG. 4;

FIG. 6 is a diagram showing a configuration example of a despread demodulator part (despread demodulator in FIG. 3) of the optical CDMA despread demodulator in FIG. 4;

FIG. 7 is a diagram showing an input / output optical pulse train in the optical CDMA system of FIG. 4;

8 is a diagram showing another configuration example of the despread demodulator part of the spread modulator and the optical CDMA despread demodulator in FIG.

9 is a diagram showing still another configuration example of the despreading demodulator portion of the spreading modulator and the optical CDMA despreading demodulator in FIG.

FIG. 10 is a configuration diagram showing a second embodiment of the optical CDMA despread demodulator according to the present invention;

FIG. 11 is a diagram showing an optical frequency change due to a self-phase modulation effect of an optical pulse in an optical fiber.

FIG. 12 is a configuration diagram illustrating a third embodiment of the optical CDMA despread demodulator according to the present invention;

FIG. 13 is a configuration diagram showing a fourth embodiment of the optical CDMA despread demodulator according to the present invention;

FIG. 14 is a configuration diagram showing a fifth embodiment of the optical CDMA despread demodulator according to the present invention;

FIG. 15 is a configuration diagram showing a sixth embodiment of the optical CDMA despread demodulator according to the present invention;

FIG. 16 is a diagram illustrating a calculation example of a variable pass band width characteristic of a lattice type optical filter.

FIG. 17 is a configuration diagram showing a seventh embodiment of the optical CDMA despread demodulator according to the present invention;

FIG. 18 is a sectional view of an embodiment of a PLC hybrid integrated circuit configuration.

[Explanation of symbols]

1-1, 1-2, 1-3,..., 21-1, 21-2,
21-3,...: Short light pulse light source, 2-1, 2-2, 2
-3, ..., 22-1, 22-2, 22-3, ...: spread modulator, 3, 23: star coupler, 4-1, 4-2,
4-3,..., 12, 62, 72, 82: despread demodulators, 5a to 5f, 26a to 26f, 64a, 64b, 7
4a to 74f, 84a to 84h: directional coupler, 6a to
6f, 27a-27d, 33a-33d, 45a-45
d, 65, 75a to 75e, 85a to 85h: phase shifter, 11: optical input unit, 13, 63, 73, 83: means for chirping signal light frequency, 14: optical filter, 1
5: Optical output unit, 16, 17: Optical coupling unit, 24-1, 24
−2, 24-3,...: Optical CDMA despread demodulator, 25
a to 25p, 31a to 31f, 41a to 41f, 61a
To 61i, 71a to 71p, 81a to 81t: waveguide,
32: 1 × 4 optical splitter, 34: 4 × 1 optical multiplexer, 4
2a, 42b, 66: arrayed waveguide grating, 43a to 43
d, 67a, 67b: slab waveguide of arrayed waveguide grating, 44a, 44b, 68: arrayed waveguide of arrayed waveguide grating, 51: optical fiber, 52: semiconductor laser amplifier, 53: phase modulator, 86: composite Wave device, 91: Si substrate, 92: Terrace region, 93: Lower cladding layer, 94:
Height adjustment layer, 95: core layer, 96: upper cladding layer, 9
7: electrical wiring, 98: solder pattern, 99: semiconductor laser amplifier, 99a: active layer of semiconductor laser amplifier.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/02 10/18 H04J 13/00 (72) Inventor Takashi Saida 2-3-3 Otemachi, Chiyoda-ku, Tokyo No. 1 Inside Nippon Telegraph and Telephone Corporation (72) Inventor Manabu Oguma 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term within Nippon Telegraph and Telephone Corporation (reference) 2K002 AA02 AB12 CA13 CA15 DA10 DA11 HA18 5K002 AA04 CA02 CA12 CA14 DA12 5K022 EE02 EE32

Claims (7)

[Claims] A despread demodulator for despreading and demodulating an optical CDMA signal spread-modulated by a spread modulator for performing spread modulation of a signal in an optical domain, wherein a signal light frequency is chirped at a stage subsequent to the despread demodulator. Means and an optical filter are connected in this order. 2. The optical fiber according to claim 1, wherein the means for chirping the signal light frequency is an optical fiber.
DMA despread demodulator. 3. An optical CDMA despreading demodulator according to claim 1, wherein said means for chirping said signal light frequency is a semiconductor laser amplifier. 4. The optical C according to claim 1, wherein the means for chirping the signal light frequency is a phase modulator.
DMA despread demodulator. 5. The optical filter, comprising: an input waveguide, a waveguide array, an output waveguide, a first fan-shaped slab waveguide connecting the input waveguide and the waveguide array, An array waveguide grating comprising a second fan-shaped slab waveguide for connecting the waveguide array and the output waveguide, wherein the length of the waveguide array is sequentially increased by a predetermined waveguide length. 2. The optical CD according to claim 1, wherein:
MA despread demodulator. 6. The optical filter according to claim 1, wherein the optical filter is a lattice type optical circuit in which one stage of an asymmetric Mach-Zehnder interferometer or N stages (N is an integer of 2 or more) of asymmetric Mach-Zehnder interferometers are cascaded. The optical CD according to claim 1.
MA despread demodulator. 7. The I directional coupler, wherein the optical filter couples the first one waveguide and I (I is an integer of 2 or more) waveguides at I different positions. And a second waveguide, wherein the I waveguides are combined with the first waveguide, and then combined into a second waveguide by a multiplexer. 2. The optical CDMA despreading demodulator according to claim 1, wherein the optical CDMA despreading demodulator is a transversal type optical circuit.