JPH09127561A - Optical time-division multiplexing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make gentle the band characteristics of a band-pass filter which passes time-division multiplex signal light. SOLUTION: A pulse train light generation part 100 generates pulse train light of 1st wavelength λ1 (0.7749μm) with a frequency of 100GHz. A modulator 110 modulates the signal light at a bit rate of 6.3Gbit/s of 2nd wavelength 22 (1.53μm) and outputs modulated light of a 1st and a 2nd channel. A 1st multiplexer 130 superposes the modulated light of the 1st channel on the pulse train light and a dummy phase matching element 210 generates multiplex signal light of the 1st channel of 3rd wavelength λ2 (1.57μm). A demultiplexer 140 removes the modulated light from the output from the 1st multiplexer 130 and the resulting light is supplied to a 2nd multiplexer 150. The 2nd multiplexer 150 superposes the modulated light of the 2nd channel on the pulse train light from the 1st multiplexer 130 and the dummy phase matching element 210 generates multiplex signal light of the 2nd channel of the 3rd wavelength λ3 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical time division multiplexer that time-division multiplexes optical signals of a plurality of channels.
The present invention relates to an optical time division multiplexing device suitable for use in an optical transmission system such as an optical switching system or an optical LAN.

[0002]

2. Description of the Related Art In recent years, ultrahigh-speed, ultra-large-capacity optical communication technology has been researched and put into practical use because of the need for large-capacity communication such as high-speed data communication and image transmission. For example, in an optical switching system of a public communication network, an optical signal with a bit rate near 10 Gbit / s from each route is multiplexed into an optical signal with a bit rate near 100 Gbit / s without performing optical-electrical conversion. There is a need for an all-optical time-division multiplex device.

An example of such an all-optical time division multiplexer of the order of 100 Gbit / s is, for example, Electronics Letters, Vol. 30, No. 20, pp. 1697.
~ 1698, (1994), an optical time division multiplexer using wavelength conversion by four-wave mixing has been proposed.

This optical time division multiplexer generates light having a _first wavelength λ ₁ , for example, a wavelength of 1.547 μm, by using an erbium-doped fiber laser (EDFL), for example.
This is combined by a planar type multiplexer, etc., and a predetermined frequency at the same timing as the time slot of the time division multiplexed signal of the desired bit rate, for example, 100G
The pulse train light of Hz is generated. On the other hand, the optical signals of the respective channels which are time-division-multiplexed are modulated by a modulator using an erbium-doped fiber laser or the like at a second bit length λ _2, for example, a wavelength of 1.537 μm and a predetermined bit rate, for example Each is modulated into Gbit / s modulated light.

The modulated signal light is superimposed on a predetermined position of the pulse train light of 100 GHz for each channel, and the first wavelength λ ₁ of the modulated light and the second wavelength of the pulse train light is superposed.
Wavelength λ ₂ is converted into light having a _third wavelength λ ₃ by four-wave mixing using the third-order optical nonlinear effect, and time division multiplexed light having a bit rate of 100 Gbit / s is formed. For example, the modulated light of the first channel is combined with the pulse train light by the combiner and input to the four-wave mixing fiber. As is well known, in a four-wave mixing fiber, when light of a plurality of wavelengths propagates through a medium such as a fiber, light of a plurality of wavelengths is generated by optical nonlinear interaction. For example, in this case 1.
Light with wavelengths of 1.557 μm and 1.527 μm is obtained from the pulse train light of 547 μm and the modulated light of 1.537 μm.

The output of the first four-wave mixing fiber has the wavelength-demultiplexer remove the 1.537 μm modulated light of the first channel, and the third wavelength is output at a predetermined position of the pulse train light of 100 GHz having the first wavelength. The multiplexed signal of the wavelength is output while mounted. Similarly to the above, the modulated light of the second channel from the modulator is delayed by a predetermined time and multiplexed on the output. In other words, 10 times the multiplexed signal of the first channel is superimposed.
The modulated light of the second channel is multiplexed with different pulses of the pulse train light of 0 GHz, and a multiplexed signal of the third wavelength is obtained by the four-wave mixing fiber as in the case of the first channel. These are cascaded in a plurality of stages to obtain a time division multiplexed signal in which the optical signals of the respective channels are multiplexed on the time axis. When the light in each channel is multiplexed, the output of the final stage is passed through an optical bandpass filter (OBPF) that allows only the light of the third wavelength of 1.557 μm to pass through 100 Gbi.
Time division multiplexing with a bit rate of t / s was realized.

As described above, according to the above-mentioned document,
Generate pulse train light of desired frequency of 100GHz,
By combining this and modulated light obtained by respectively modulating the signal lights of a plurality of channels by four-wave mixing using the third-order optical nonlinear effect, it is possible to achieve 10
We were able to obtain time-division multiplexed signal light with a desired bit rate of 0 Gbit / s.

[0008]

However, in the above-mentioned conventional technique, since the third-order nonlinear four-wave mixing is used, the wavelength λ ₁ of the pulse train light and the wavelength λ of the modulated light are used.
_It is necessary to make ₂ and the wavelength very close to each other, and the wavelength of the generated time-division multiplexed signal light is also the wavelength λ ₃ close to them, so as a bandpass filter to pass this, an extremely narrow band There was a problem that a filter had to be used. For example, in the above example,
To obtain light with a wavelength of 1.557 μm as a time division multiplexed signal, pulse train light with a wavelength of 1.547 μm and 1.537 μm
Modulated light was needed. Since each of these has a wavelength interval of 10 nm, an excellent narrow band filter that divides these into bands has been required. Further, in the case of four-wave mixing, since other mixing components are also generated at the same time, there is a problem that it is not easy to extract the time division multiplexed signal light. Furthermore, when a fiber line is used as the four-wave mixing element, its length is usually several tens of kilometers, which causes a problem that the device becomes large.

The present invention solves the above-mentioned problems, alleviates the requirement for a band-pass filter, and can obtain a time division multiplexed signal of an accurate wavelength without mixing other wavelengths with a small device. An object is to provide a time division multiplexer.

[0010]

In order to solve the above-mentioned problems, an optical time division multiplexer according to the present invention allocates optical signals of a plurality of channels to predetermined time slots and multiplexes them on a time axis. In the demultiplexing / multiplexing device, pulse train light generating means for generating pulse train light having a predetermined frequency in response to a time interval of a time slot, the pulse train light sequentially generating pulse light having a first wavelength as pulse train light. Second generating means for modulating the optical signal of each channel at a predetermined bit rate
Modulated light output means for respectively outputting the modulated light of the wavelength of,
Multiplexing means for sequentially allocating modulated light to predetermined positions of the pulse train light for each channel to form time division multiplexed signal light, and output from the output of wavelengths other than the time division multiplexed signal light are connected to the multiplexing means. And a bandpass filter that passes only time-division multiplexed signal light by band limiting the light and the multiplexing means includes pulse train light from the pulse train light generating means and modulated light of a predetermined channel from the modulated light output means. And a difference frequency for generating a difference frequency component between the combined pulse train light of the first wavelength and the modulated light of the second wavelength to generate light of the third wavelength. The component generating means corrects the phase mismatch due to the difference in the propagation constants of the lights having different wavelengths, and at the same time, generates the difference frequency components as the time-division multiplexed signal light of the third wavelength by the quasi phase matching. Frequency component Characterized in that it comprises a forming unit.

In this case, the difference frequency component generating means is a quasi-phase matching element in which the substrate of the secondary optical nonlinear medium is provided with a grating at a predetermined cycle and an optical waveguide is formed in a direction orthogonal to the grating. It is characterized by being.

Further, it is advantageous that the quasi-phase matching element contains niobium lithium oxide as a substrate of the second-order nonlinear medium. The quasi-phase matching element may include lithium thallate as a substrate of the second-order optical nonlinear medium. The quasi phase matching element may include potassium titanate phosphate as a substrate of the second-order optical nonlinear medium. Similarly, the quasi-phase matching element may include a gallium arsenide-based semiconductor material as the secondary optical nonlinear medium. further,
The quasi-phase matching element may include an indium phosphide-based semiconductor material as the second-order optical nonlinear medium.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of an optical time division multiplexer according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an embodiment of an optical time division multiplexer according to the present invention. The optical time division multiplexing apparatus according to the present embodiment uses 100 GHz pulse train light of a _first wavelength λ ₁ forming a predetermined time slot of a time division multiplexed signal and a plurality of channels of signal light at predetermined bit rates. Modulated second
Is an all-optical type time division multiplexer that forms the time division multiplexed signal light of the third wavelength λ ₃ from the modulated light of the wavelength λ ₂ of. In particular, in the present embodiment, when the time division multiplexed signal light of the third wavelength λ ₃ is obtained, the quasi-phase matching element formed by the secondary optical nonlinear element having the periodic structure is 1st wavelength λ ₁ and 2nd wavelength λ
A difference frequency component of ₂ (1 / λ ₃ = 1 / λ ₁ -1 / λ ₂ ) is generated and a time division multiplexed signal of the third wavelength λ ₃ is output. In addition, in the present embodiment, for ease of description, a case where signal light of two channels is time-division multiplexed will be described as an example.

More specifically, as shown in FIG. 1, the optical time division multiplexer according to this embodiment has a pulse train light generator 100.
A modulator 110, a delay element 120, a first multiplexer (MUX1) 130, a demultiplexer 140, a second multiplexer (MUX2) 150, and a bandpass filter 160.
The output of the pulse train generation unit 100 and the first output of the modulator 110 are connected to the multiplexer 130 of the first multiplexer, and the signal light of the first channel is multiplexed into the pulse train light,
The output of the first multiplexer 130 and the second output of the modulator 110 via the delay element 120 are connected to the multiplexer 150 of FIG. 1 via the demultiplexer 140 to multiplex the signal light of the second channel. Then, the band-pass filter 160 is connected to the output of the second multiplexer 150, and the time division multiplexed signal light of the desired bit rate in which the two channels are multiplexed is obtained. Of course, circuits similar to the multiplexers 130 and 150 may be connected in multiple stages to time-division multiplex the signal lights of a plurality of channels.

Explaining the details of each section, the pulse train light generating section 100 determines the timing at the same interval as the time slot of the time division multiplexed signal of a desired bit rate, for example,
This is a pulse source that generates repetitive pulses of 100 GHz, and in this embodiment is a light generation circuit that outputs pulse train light of a _first wavelength λ _{1 that} is extremely shorter than the wavelength λ ₃ of the target time division multiplexed signal.

In other words, in the present embodiment, as will be described later, the quasi-phase matching element using the quadratic nonlinear effect produces the difference frequency component of the wavelengths λ ₁ and λ ₂ of the two lights. .
A laser oscillator that generates a pulse train light having a wavelength less than half of the signal light of wavelength λ _{3 in} the 5 μm band, for example, 0.7749 μm is effectively applied in this embodiment. For example, a semiconductor laser using a semiconductor material such as gallium arsenide (GaAs) is effectively used as an oscillator that oscillates light having a wavelength of 0.7749 μm.

Planar type multiplexers are connected in series to this, and pulsed light of a frequency of several GHz oscillated by a laser is repeated by the multiplexer to obtain 0.7749
A pulsed light with a single wavelength of μm is generated as a pulse train light of 100 GHz which is the bit rate of the time division multiplexed signal.

In this case, the semiconductor laser is applied, but of course, a fiber laser or the like added with a predetermined medium may be used. The generated pulse train light of 100 GHz is sequentially supplied to the first multiplexer 130, and the modulated light of the first channel from the modulator 110 is sequentially superposed on it.

The modulator 110 generates modulated light having a _second wavelength λ ₂ , for example, 1.53 μm, which is obtained by modulating the signal light of a plurality of channels at a predetermined bit rate, for example, a bit rate of 6.3 Gbit / s. The first multiplexer
A signal source for sequentially supplying 130 and the second multiplexer 150.

In the modulator 110 of this embodiment, for example, an erbium-doped fiber laser (EDFL) is effectively applied, and a high output pumping light is given in response to an input signal light, whereby 1.53 μm to 1.55 μm. Is a laser modulator that outputs modulated light of a single wavelength. In this case, the fiber laser is applied, but a semiconductor laser may be applied similarly to the pulse train light generator 100. As for the generated modulated light, the modulated light of the first channel is the first multiplexer 13
0, and the modulated light of the second channel is supplied to the second multiplexer 150 via the delay circuit 120.

The multiplexers 130 and 150 are the pulse sources 100.
From the light of the first wavelength λ _{1 and} the light of the second wavelength λ ₂ by combining the pulse light at the predetermined position with the modulated light from the modulator 110. Third
Is a multiplexing circuit for generating light of wavelength λ ₃ and obtaining time-division multiplexed signal light. Multiplexers 120 and 130 of this embodiment
Is an optical multiplexer 200 and a quasi-phase matching element as shown in FIG.
Including 210 and.

An optical coupler such as a semi-transmissive mirror is applied to the optical multiplexer 200, and as shown in FIG. 1, pulse train light of wavelength λ ₁ goes straight, and at the same time, modulated light of wavelength λ ₂ from the lower side of the paper surface. Wavelengths λ ₁ and λ ₂
Is a coupler that wavelength-multiplexes the light of. Combined light λ _1,
λ ₂ is supplied to the quasi phase matching element 210.

The quasi-phase matching element 210 corrects the phase mismatch due to the propagation constants of the light of _two different wavelengths λ ₁ and λ ₂ , and at the same time, the difference frequency component (1 / λ of those wavelengths λ ₁ and λ ₂ ). ₁ -1 / λ ₂ =
This is a difference frequency component generation element that forms and outputs 1 / λ ₃ ).
As shown in FIG. 2, the quasi phase matching element 210 of the present embodiment has
A domain inversion grating 310 is formed near the surface of a substrate 300 of niobium lithium oxide (LiNbO ₃ ) by thermal diffusion of titanium (Ti) at a predetermined period Λ, and an optical waveguide 320 by a proton exchange method is formed in a direction orthogonal to this. It is a second-order optical nonlinear element having a periodic refractive index distribution structure in which is formed. This second-order optical nonlinear element has a wavelength λ ₁ input to the optical waveguide 320,
When the light of λ ₂ travels through the optical waveguide 320, the light of the difference frequency component λ ₃ is generated by receiving the second-order nonlinear optical effect.
The grating period Λ so that its component is maximized.
Are formed. In this embodiment, the quasi phase matching element 210
As a non-linear material to obtain the same effect, as a non-linear material to obtain the same effect, for example, tantalum lithium oxide (LiTaO ₃ ) or an inorganic material such as potassium titanate phosphate (KTP), or gallium arsenide (GaAs) or A semiconductor material such as indium phosphide (InP) may be applied. Light of wavelengths λ _1, λ _{2, and} λ ₃ from the quasi-phase matching element 210 is a demultiplexer.
It is supplied to the second multiplexer 150 or the bandpass filter 160 via 140.

Like the multiplexer 200, the demultiplexer 140 is formed of a semi-transmissive mirror or the like, reflects the modulated light of 1.53 μm to the other, and the remaining pulse train light and the formed time division multiplex light. It is an output circuit that transmits signal light. This duplexer 140
Is a modulated light demultiplexing circuit that is connected to the outputs of the multiplexers when three or more stages of multiplexers are used and sequentially removes the modulated light after forming the multiplexed signal in the preceding stage. The bandpass filter 160 is a filter that passes the time-division signal light of the third wavelength λ ₃ from the second multiplexer 150, and its pass band is 1.53 in this embodiment.
It suffices to have a band characteristic of about 40 nm that separates the μm modulated light and the 1.57 μm multiplexed signal light.

Next, the operation of the optical time division multiplexer according to this embodiment will be described. First, the pulse train generation unit 100 oscillates 100 GHz pulse train light in sequence. In this case, in this embodiment, the pulse train light is formed by pulse light having a _first wavelength λ ₁ of 0.7749 μm, which is much shorter than the modulated light. The generated pulse train light is supplied to the first multiplex 130, passes through this, and is sequentially supplied to the second multiplexer 150. In this state, the pulse train light that has passed through the second multiplexer 150 is blocked by the bandpass filter 160, and the output from this device cannot be obtained.

In this state, when the signal light of the first channel and the signal light of the second channel are respectively supplied to the modulator 110, the modulator 110 converts the signal light of each channel into a modulation speed of 6.3. 1.53 μm at Gbit / s
And outputs the modulated light having the second wavelength λ ₂ . As for the modulated light output from each of the modulators 110, the modulated light of the first channel is directly supplied to the first multiplexer 130 without delay, and the modulated light of the second channel is delayed by the delay element 12.
It is supplied to the second multiplexer 150 via 0 via a delay time of a predetermined time.

The modulated light supplied to the first multiplexer 130 is sequentially combined with the pulse light at a predetermined position of the pulse train light supplied from the pulse train light generator 100 by the multiplexer 200. , To the quasi phase matching element 210. A first wavelength lambda ₁ of the pulse train light supplied to the quasi-phase matching element 210, the modulated light of the first channel of the second wavelength lambda _2, when sequentially propagating along the optical waveguide 320, The wavelength of the difference frequency component (1 / λ ₁ -1 / λ ₂ = 1 / λ ₃ ) is generated by the second-order optical nonlinear effect of the substrate 300 of niobium lithium oxide. In this case, the third wavelength λ ₃ is 1.57
It has a wavelength of μm. Moreover, the generated third wavelength λ ₃
Is sequentially phase-matched by the grating 310, and is output as an effective value together with the first wavelength λ ₁ and the second wavelength λ ₂ .

The light of the _three wavelengths λ _1, λ ₂ and λ ₃ output from the first multiplexer 130 is output to the second by the demultiplexer 140.
It is reflected modulated light and the other wavelength lambda _2, the multiplexed signal light formed pulse train light second multiplexer
Supplied to 150. In the second multiplexer 150, these wavelengths λ ₁ and λ ₃ are sequentially supplied to the bandpass filter 160 with little influence. As a result, the time-division multiplexed signal light of the first channel is superimposed on the predetermined position of the pulse train light.

After that, when the signal light of the first channel is input to the modulator 110, it is modulated to the second wavelength λ ₂ and supplied to the first multiplexer 130, and the predetermined position of the pulse train light is supplied. That is, the third wavelength λ is superposed on the position of the predetermined time slot by the quasi phase matching element 210.
_It is generated in ₃ and output together with the pulse train light.
The generated multiplexed light of the first channel is sequentially supplied to the bandpass filter 160 together with the pulse train light.

On the other hand, the delayed modulated light of the second channel is a pulse at a predetermined position different from the pulse on which the signal light of the first channel is superimposed on the pulse train light passing through the first multiplexer 130. A quasi-phase matching element of the second multiplexer 150 after being multiplexed with the light by the multiplexer 200.
Supplied to 210. As a result, similar to the modulated light of the first channel, the difference frequency component with the pulse train light of the first wavelength λ ₁ is quasi-phase matched, and the three wavelengths λ ₁ , λ ₂ ,
λ ₃ is output from the second multiplexer 150. After that, when the signal light of the second channel is input to the modulator 110, it is modulated in the same manner as the signal light of the first channel,
It is supplied to the second multiplexer 150 via the delay element 120 and is superimposed on a predetermined position of the pulse train light to generate the third signal.
Of wavelength λ ₃ and are sequentially output to the bandpass filter 160.

In the bandpass filter 160 which receives the pulse train light on which the time division multiplexed signal lights of the first and second channels are superposed, only the generated multiplexed signal light of the third wavelength λ ₃ is passed, The wavelength λ ₁ of the pulse train light and the wavelength λ _{2 of the} modulated light are blocked. This allows the bandpass filter
From 160, only the signal light of the third wavelength λ ₃ of each of the first channel and the second channel is output as the signal light which is time division multiplexed at the bit rate of 100 Gbit / s.

As described above, according to the optical time division multiplexer of the present embodiment, the pulse train light of the _first wavelength λ ₁ and the modulated light of the second wavelength λ ₂ are multiplexed to the third wavelength λ ₃ . Since the signal forming element uses the quasi-phase matching difference frequency generating element, the wavelength intervals of the respective wavelengths λ ₁ , λ ₂ , λ ₃ can be widened. As a result, the band characteristic of the band filter that passes the time division multiplexed signal can be made gentle. That is, in the present embodiment, since a second-order nonlinear element in which a periodic refractive index distribution structure is formed on the substrate 300 made of niobium lithium oxide can form a multiple signal by utilizing the second-order nonlinear effect, it is theoretically possible. At 1 / λ ₃ = 1 / λ ₁ -1 / λ
_All you need to do is satisfy the relationship of ₂ . As a result, the train light of the first wavelength λ ₁ can be set to 0.7749 μm, which is about half the wavelength of the second wavelength λ ₂ and the third wavelength λ ₃ , as in the above-described embodiment. In addition, the second wavelength λ ₂
By adjusting the wavelength λ ₁ of the pulse train light appropriately, the third wavelength λ ₃ can be set to a wavelength interval of 40 nm or more of 1.53 μm and 1.57 μm. As a result, the separation of the light of wavelength λ ₂ at the output of the first multiplexer 130 and the extraction of the light of wavelength λ ₁ at the bandpass filter 160 can be carried out relatively easily, and in particular the requirements for the bandpass filter 160. Is considerably eased. Also usually dozens
2 without using a four-wave mixing fiber with a length of km
Quasi-Phase Matching Element 210 (Normally several cm long)
Since, is used, a small device can be realized.

In the above embodiment, the demultiplexer 140 for removing the modulated light is provided between the first multiplexer 130 and the second multiplexer 150, respectively.
However, in the present invention, they may be included in the multiplexers 130 and 150. In this case, the invention can also be applied to a case where three or more channels are time-division multiplexed by connecting multiple multiplexers in cascade.

[0034]

As described above, according to the optical time division multiplexing apparatus of the present invention, the pulse train light of the first wavelength that forms the timing of the time slot of the desired time division multiplexing signal and the signal light of a plurality of channels. When the time-division multiplexed signal light of the third wavelength is obtained from the modulated light of the second wavelength which is modulated at a predetermined bit rate, the pulse train light of the first wavelength and the modulated light of the second wavelength are obtained. While compensating for the phase mismatch due to the difference in the propagation constants of the light of different wavelengths,
Since the difference frequency component generating means by quasi-phase matching for generating the difference frequency components as the time division multiplexed signal light of the third wavelength is used, at least the pulse train light of the first wavelength and the formed third train. It is possible to set a wide wavelength interval between the wavelength and the time division multiplexed signal light. Therefore, it is possible to make the band characteristic of the bandpass filter which passes the time division multiplexed signal of the third wavelength from the output of the final stage of the multiplexing means including these wavelengths relatively gentle, and to obtain from the output. The excellent effect that the time-division-multiplexed signal that is generated can be an accurate signal light without noise is exhibited.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an optical time division multiplexer according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a quasi phase matching element applied to the embodiment of FIG.

[Explanation of symbols]

 100 Pulse train light generator 110 Modulator 130,150 Multiplexer 160 Bandpass filter 200 Combiner 210 Quasi-phase matching-difference frequency generator 300 Second-order nonlinear element 310 Grating 320 Optical waveguide

Claims (7)

[Claims] 1. An optical time division multiplexing apparatus for allocating optical signals of a plurality of channels to predetermined time slots and multiplexing them on a time axis, wherein the apparatus has a predetermined frequency in response to a time interval of the time slots. Pulse train light generating means for generating the pulse train light, and pulse train light generating means for sequentially generating the pulse light of the first wavelength as the pulse train light, and the optical signal of each channel at a predetermined bit rate. Modulated light output means for outputting the modulated light of the second wavelength, which has been modulated by, respectively, and the modulated light is sequentially assigned to predetermined positions of the pulse train light for each channel to form time division multiplexed signal light. A multiplexing means and a time division multiplexed signal which is connected to the multiplexing means and band-limits light of a wavelength other than the time division multiplexed signal light from the output of the multiplexing means. And a multiplexing means for sequentially multiplexing the pulse train light from the pulse train light generating means and the modulated light of a predetermined channel from the modulated light output means. And difference frequency component generation means for generating a difference frequency component of the combined pulse train light of the first wavelength and modulated light of the second wavelength to generate light of the third wavelength. And a difference frequency component generation means by quasi phase matching that corrects the phase mismatch due to the difference in the propagation constants of lights of different wavelengths and generates the difference frequency components as time division multiplexed signal light of the third wavelength. An optical time division multiplexing device characterized by the above. 2. The optical time division multiplexing apparatus according to claim 1, wherein the difference frequency generation means applies a grating to a substrate of the second-order optical nonlinear medium at a predetermined cycle and is orthogonal to the grating. An optical time division multiplexing device, which is a quasi-phase matching element in which an optical waveguide is formed in a direction. 3. The optical time division multiplexer according to claim 2, wherein the quasi phase matching element contains niobium lithium oxide as a substrate of a second-order nonlinear medium. 4. The optical time division multiplexer according to claim 2, wherein the quasi phase matching element includes lithium thallate as a substrate of a second-order optical nonlinear medium. 5. The optical time division multiplexer according to claim 2, wherein the quasi phase matching element includes potassium titanate phosphate as a substrate of the second-order optical nonlinear medium. 6. The optical time division multiplexer according to claim 2, wherein the quasi phase matching element includes a gallium arsenide semiconductor material as a second-order optical nonlinear medium. 7. The optical time division multiplexer according to claim 2, wherein the quasi phase matching element includes an indium phosphide-based semiconductor material as a second-order optical nonlinear medium.