JPH05102927A - Generating method for optical data pulse train - Google Patents

Abstract

PURPOSE:To provide an optical data pulse train generating method which can generate the optical data pulse trains at a super-high speed and with no limitation by an electrical modulation speed. CONSTITUTION:An optical pulse 6 passes through a beam splitter 1 and is divided into plural diffracted beams by a diffraction grating 2. Then the diffracted beams are turned into the one-dimensional perallel beams by a collimator lens 3 and then made incident on a space modulator 4. The modulator 4 is divided into plural segments according to the number of information bits. Then only the transmitted beams reach a reflector 5 among those beams that are transmitted (bit 1) or cut off (bit 0) by the modulator 4. These transmitted beams are reflected on a stepped reflecting surface end the optical path difference, i.e., the time delay is caused between the beams at a fixed interval. Then these beams are condensed on the same optical path by a collimator lens 3 via the modulator 4. These condenced beams have the time delays at the fixed intervals end therefore a time series pulse train 7 is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical data pulse train generating method for generating an optical pulse train having data of an arbitrary number of bits from one optical pulse by an optical method.
This can be applied to, for example, generation of an optical data pulse train used for real-time writing of an ultrafast photon echo memory.

[0002]

2. Description of the Related Art Conventionally, an optical data pulse train used for writing in a photon echo memory is CW (continuous w) by an acousto-optic (AO) modulator or an electro-optic (EO) modulator.
ave) by providing the appropriate intensity modulation to the laser, or by extracting the appropriate pulse from the mode-locked laser pulse train with an AO or EO modulator.

A method is also known in which two independent pulse lasers are used and the interval between the pulses of both lasers is changed to write data bit by bit. It is difficult to write data in real time in writing to the ultra-high speed photon echo memory in the picosecond region, so the optical path difference between the reference light pulse and the write pulse is changed bit by bit, and data writing is repeated for a desired number of bits. The method has been adopted. An example thereof is shown in FIG.

As shown in FIG. 5, a light pulse emitted from a laser (not shown) is split by a beam splitter 51 into a reference light 52 and a writing light 53. The writing light 53 is transmitted (for example, bit 1) or blocked (for example, bit 0) by the shutter 54. A time delay plate 55 is placed on the optical path of the writing light 53, and the writing light 53 enters the photon echo memory medium 56 with a certain time delay with respect to the reference light 52. This stores 1-bit data. Subsequently, the thickness of the time delay plate 55 is increased by an amount corresponding to the data pulse interval,
Writing is performed in the same manner as the first bit by the next optical pulse. By repeating this operation a desired number of times, data having a desired number of bits can be transferred to the photon echo memory medium 56.
Can be written on.

[0005]

However, the method of intensity-modulating the output light of the CW laser by the modulator of AO or EO and the method of extracting the pulse from the pulse train of the mode-locked laser depend on the frequency driving the modulator. Due to limitations, it is difficult to generate sub-nanosecond data pulse trains.

The method of writing by changing the optical path difference between the reference light pulse and the write pulse for each bit (FIG. 5) is not real-time writing, and is not suitable for practical use of an ultrahigh-speed photon echo memory. ..

Therefore, an object of the present invention is to provide an optical data pulse train generation method for generating an optical data pulse train at an ultrahigh speed (for example, in the picosecond range) without being limited by the electrical modulation speed.

[0008]

The gist of the present invention for achieving the above object is to spatially spread or distribute one optical pulse, and add spatial data to the distributed light by a spatial light modulator or the like, An optical data pulse train generating method is characterized in that an optical data pulse train is generated by providing a time delay on the optical path corresponding to each bit, condensing and returning to the same optical path.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first for generating an optical data pulse train.
It is a block diagram of the optical system of an Example. In the figure, 1 is a beam splitter, 2 is a diffraction grating, 3 is a collimator lens, 4 is a spatial modulator, 5 is a reflecting mirror having a stepwise reflecting surface, 6 is a base optical pulse, and 7 is generated light. It is a data pulse train. As shown in the figure, one light pulse 6 passes through the beam splitter 1 and is divided by the diffraction grating 2 into a plurality of diffracted light beams. At this time, it is preferable to use a hologram so that the intensity of each diffracted light beam becomes uniform. Each diffracted light flux is made into a one-dimensional parallel light flux by the collimator lens 3 and is incident on the spatial modulator 4. Spatial modulator 4
Are divided into a plurality of segments corresponding to the respective incident light beams, and each segment represents 1-bit spatial data.
The number of segments corresponds to the number of information bits.
In FIG. 1, a 7-bit spatial data string "1011001"
Is represented.

Transmitted (bit 1) by the spatial modulator 4.
Alternatively, only the transmitted light flux of the blocked (bit 0) light flux reaches the reflecting mirror 5. Due to the stepwise reflecting surface of the reflecting mirror 5, an optical path difference at a constant interval, that is, a time delay occurs between the respective light beams. The transmitted light flux reflected by the reflecting mirror 5 passes through the spatial modulator 4 and is condensed by the collimator lens 3 on the same optical path. At this time, since each of the condensed light beams has a time delay of a constant interval, a pulse train 7 is generated which is spatially condensed but has a time delay at a certain interval. To do. Through the above process, an optical data pulse train can be generated from one optical pulse.

As the spatial modulator 4, any device capable of controlling the transmittance such as a pinhole array, a liquid crystal shutter array, an AO or EO modulator, etc. can be adopted, and it is desirable that it be rewritten for each data set. ..

Further, in the present embodiment, the data given to each light beam is described as a bit signal represented by a binary number, but in addition to this, each segment of the spatial modulator 4 produces an image for each light beam. Information may be added to the time series of the image data.

Here, although the reflecting mirror 5 having the stepwise reflecting surface is used in this embodiment, other forms may be used. Two cases are shown in FIGS. 2 and 3.

In FIG. 2, reference numeral 21 is a transparent medium in which the refractive index n is changed and distributed stepwise, and 22 is a plane reflecting mirror. In this reflective optical system, when each light beam passes through the transparent medium 21, the optical path difference Δl is caused because the refractive index is different at each place.
= Resulting 2d the _{(n m + 1 -nm m)} .

In FIG. 3, reference numeral 31 is a transparent medium whose thickness changes stepwise at regular intervals, and 32 is a plane reflecting mirror. In this reflection optical system, when each light flux passes through the transparent medium 21, the optical path difference Δ is caused because the thickness of each transmission position is different.
l = results in a _{2n (d m + 1 -d m} ).

Next, a second embodiment of the present invention will be described. In the first embodiment, the basic light pulse is divided into a plurality of light fluxes by the diffraction grating, but in the present embodiment, the basic light pulse is a spatially expanded sheet beam.

FIG. 4 is a block diagram of an optical system for generating an optical data pulse train. In FIG. 4, 41 is a beam splitter, 42 is an optical system for expanding into a one-dimensional sheet beam, 43 is a spatial modulator, 44 is a blazed grating, 4
Reference numeral 5 is a base optical pulse, and 46 is a generated optical data pulse train.

As shown in the figure, the optical pulse 45 passes through the beam splitter 41, is expanded into a sheet beam by the optical system 42, and then enters the spatial modulator 43.
The spatial modulator 43 has a segment corresponding to an arbitrary number of bits and represents spatial data. The incident sheet beam can transmit the segment representing the transmissive state (bit 1) but not the segment representing the blocking state (bit 0). The transmitted light flux is blazed grating 44.
Is reflected in the opposite direction by the same optical path as at the time of incidence. At this time, the respective transmitted light fluxes have a certain time delay due to the difference in optical path length. Then, the respective light beams are transmitted to the spatial modulator 4
After passing 3, the optical system 42 collects the light on the same optical path.
At this time, since each of the collected light fluxes is time-delayed at a constant interval, a pulse train 46, which is spatially focused but has a time-delayed delay, is generated.

The pulse interval is determined by the segment interval of the spatial modulator 43 and the blazed angle of the blazed grating 44. Further, since the spatially expanded sheet beam is used, the number of bits of the optical data pulse train 46 to be generated is
It is determined by the number of segments of the spatial modulator 43.

Furthermore, when the individual pulse intensity of the optical data pulse train 46 becomes significantly weaker than that of the original optical pulse 45, a regenerative optical amplifier is provided for amplification.

[0022]

As described above in detail, according to the present invention, the optical pulse group is provided with a relative optical path difference by the action of the spatial modulator and the optical time delay, and the light is condensed with the time delay. Since a time-series optical data pulse train is generated, it is possible to generate an ultrahigh-speed optical data train that depends only on the pulse width of the original optical pulse and the optical time delay without using a high-speed electrical modulation means. it can.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of another form of a catoptric system for realizing time delay of an optical pulse.

FIG. 3 is an explanatory diagram of still another form of a catoptric system for realizing a time delay of an optical pulse.

FIG. 4 is a configuration diagram of a second embodiment.

FIG. 5 is an explanatory diagram of a conventional optical data pulse generation method.

[Explanation of symbols]

 1,41 Beam splitter 2 Diffraction grating 3 Collimator lens 4,43 Spatial modulator 5 Reflector 6,45 Optical pulse 7,46 Optical data pulse train 21,31 Transparent medium 22,32 Planar reflector 42 Optical for expanding to sheet beam System 44 Blazed lattice

Claims (7)

[Claims] 1. An optical pulse is spatially distributed, spatial bit signal information is given to each part of the distributed light, a relative optical path difference is given to each part and a time delay is given, and then the light is condensed. An optical data pulse train generating method characterized by generating an optical data pulse train as a time-series bit signal. 2. An optical pulse group is spread over a spatially dispersed optical pulse group, spatial bit signal information is added to the optical pulse group, and then the optical pulse group is provided with a relative optical path difference and time delay is performed. The optical data pulse train generating method according to claim 1, wherein the optical data pulse train is generated by condensing light. 3. The optical data pulse train generating method according to claim 2, wherein one of a diffraction grating and a hologram is used to spread the one optical pulse into a spatially dispersed optical pulse group. 4. The optical data pulse train generation method according to claim 1, wherein a spatial light modulator is used to add spatial bit signal information to each part of the distributed light. 5. The optical data pulse train generating method according to claim 4, wherein the spatial light modulator has a function of controlling transmittance. 6. The optical data pulse train generating method according to claim 5, wherein the spatial light modulator is one of a liquid crystal shutter array, an acousto-optic modulator, and an electro-optic modulator. 7. The optical data pulse train generating method according to claim 1, wherein an optical system for spatially expanding one optical pulse to form a one-dimensional sheet beam is used.