JP3083111B2 - Optical data pulse train generation method - Google Patents

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 an arbitrary number of bits of data 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 in an ultra-high-speed photon echo memory.

[0002]

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

There is also known a method of writing data one bit at a time by using two independent pulse lasers and changing the interval between the pulses of both lasers. Since it is difficult to write data in real time in the ultra-high speed photon echo memory in the picosecond region, the writing of data is repeated by a desired number of bits by changing the optical path difference between the reference light pulse and the writing pulse for each bit. The method has been adopted. An example is shown in FIG.

As shown in FIG. 5, a light pulse emitted from a laser (not shown) is split into a reference light 52 and a writing light 53 by a beam splitter 51. 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. Thus, 1-bit data is stored. Subsequently, the thickness of the time delay plate 55 is increased by an amount corresponding to the data pulse interval,
Writing is performed by the next light pulse in the same manner as in the first bit. By repeating this operation a desired number of times, data of a desired number of bits can be stored in the photon echo memory medium 56.
Can be written to.

[0005]

However, the method of modulating the intensity of the output light of a CW laser by an AO or EO modulator and the method of extracting a pulse from a pulse train of a mode-locked laser depend on the frequency at which the modulator is driven. Due to the 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 writing pulse for each bit (FIG. 5) is not real-time writing, and is not suitable for practical use of an ultra-high-speed photon echo memory. .

It is therefore an object of the present invention to provide an optical data pulse train generation method for generating an optical data pulse train at an extremely high speed (for example, in a picosecond region) without being limited by an electric modulation speed.

[0008]

The gist of the present invention to achieve the above object is to spread or distribute one light pulse spatially, and to apply spatial data to the distributed light by a spatial light modulator or the like. An optical data pulse train generation method is characterized in that a time delay is provided on an optical path corresponding to each bit, and an optical data pulse train is generated by condensing light and returning it 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 example for generating an optical data pulse train.
It is a lineblock diagram of an 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 step-like reflecting surface, 6 is a base light pulse, and 7 is generated light. It is a data pulse train. As shown, one light pulse 6 passes through the beam splitter 1 and is split 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 beam is converted into a one-dimensional parallel light beam by the collimator lens 3 and is incident on the spatial modulator 4. Spatial modulator 4
Is divided into a plurality of segments corresponding to each incident light beam, and each segment represents 1-bit spatial data.
Note that the number of segments corresponds to the number of information bits.
In FIG. 1, a 7-bit spatial data string "1011001"
Is represented.

Transmission (bit 1) by the spatial modulator 4
Alternatively, only the transmitted light beam among the light beams blocked (bit 0) reaches the reflecting mirror 5. Due to the stepped reflecting surface of the reflecting mirror 5, a light path difference at a fixed interval, that is, a time delay occurs between the respective light beams. The transmitted light beam reflected by the reflecting mirror 5 is condensed on the same optical path by the collimator lens 3 via the spatial modulator 4. At this time, since each of the condensed light beams has a time delay at a fixed interval, a pulse train 7 having a time delay at a certain interval is generated although it is spatially condensed. I do. Through the above process, an optical data pulse train can be generated from one optical pulse.

As the spatial modulator 4, any device that can control the transmittance, such as a pinhole array, a liquid crystal shutter array, an AO or EO modulator, can be used, and it is preferable that the spatial modulator 4 be rewritten for each data set. .

Furthermore, in this embodiment, the data to be given to each light beam is described as a bit signal represented by a binary number. Information may be added to form a time series of image data.

Here, in this embodiment, the reflecting mirror 5 having the step-like reflecting surface is used, but another form may be used. Two examples are shown in FIGS.

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

In FIG. 3, reference numeral 31 denotes a transparent medium whose thickness changes stepwise at regular intervals, and 32 denotes a plane reflecting mirror. In this reflection optical system, when each light flux passes through the transparent medium 21, the thickness of each transmission position is different, so that the optical path difference Δ
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 base optical pulse is divided into a plurality of light beams by the diffraction grating. However, the present embodiment is characterized in that the base optical pulse is formed into 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, reference numeral 41 denotes a beam splitter; 42, an optical system for expanding a one-dimensional sheet beam; 43, a spatial modulator; 44, a blazed grating;
Reference numeral 5 denotes a base optical pulse, and reference numeral 46 denotes a generated optical data pulse train.

As shown in the figure, the light pulse 45 is transmitted through the beam splitter 41 and spread into a sheet beam by the optical system 42 before being incident on 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 transmission state (bit 1), but cannot transmit the segment representing the blocking state (bit 0). The transmitted light flux is blazed grating 44
Is reflected in the opposite direction on the same optical path as that at the time of incidence. At this time, each transmitted light beam has a certain time delay due to a difference in optical path length. Each light beam is transmitted to the spatial modulator 4.
After passing through 3, the light is converged on the same optical path by the optical system 42.
At this time, since each of the collected light beams has a time delay at a constant interval, a pulse train 46 having a delay at a constant interval is generated although it is spatially collected.

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 a spatially spread sheet beam is used, the number of bits of the generated optical data pulse train 46 is
It is determined by the number of segments of the spatial modulator 43.

Further, when the individual pulse intensities of the optical data pulse train 46 are significantly weaker than those of the original optical pulse 45, a reproduction optical amplifier is provided and amplified.

[0022]

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

[Brief description of the drawings]

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

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

FIG. 3 is an explanatory diagram of a reflection optical system of still another embodiment 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]

 Reference Signs List 1,41 beam splitter 2 diffraction grating 3 collimator lens 4,43 spatial modulator 5 reflecting mirror 6,45 light pulse 7,46 light data pulse train 21,31 transparent medium 22,32 plane reflecting mirror 42 optics for spreading to sheet beam System 44 blazed grating

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-1-272237 (JP, A) JP-A-1-138542 (JP, A) JP-A-2-199885 (JP, A) JP-A-1- 232844 (JP, A) JP-A-1-155797 (JP, A) JP-A-60-90443 (JP, A) JP-B-41-6972 (JP, B1) JP-T-5-505078 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H04J 14/08 H04B 10/00 G02B 27/09

Claims (7)

(57) [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, a time delay is given, and then the light is collected. An optical data pulse train as a time-series bit signal. 2. An optical pulse group is spread into a spatially dispersed optical pulse group, and spatial bit signal information is added to the optical pulse group. 2. The optical data pulse train generating method according to claim 1, wherein the light is condensed. 3. The optical data pulse train generation method according to claim 2, wherein one of a diffraction grating and a hologram is used to spread said one optical pulse into a spatially dispersed optical pulse group. 4. The optical data pulse train generating method according to claim 1, wherein a spatial light modulator is used to give spatial bit signal information to each part of the distributed light. 5. An optical data pulse train generating method according to claim 4, wherein said spatial light modulator has a function of controlling transmittance. 6. The optical data pulse train generating method according to claim 5, wherein said 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 is used in which one optical pulse is spatially spread to form a one-dimensional sheet beam.