JPH03141031A - Optical recording medium and its reader - Google Patents

Abstract

PURPOSE:To record more information by a small space by recording different information in accordance with the depth size of a pit, and to read out the information by the phase variation quantity of a first and a second optical beat signals whose frequencies are little different. CONSTITUTION:Depth dn of pit 32 of a disk 24 is set to 255 steps and informa tion of 8 bits/byte is recorded by one pit. Accordingly, by the same size, the recording capacity comes to eight folds. In a reader, the phase of a measuring signal SM whose intensity is varied by the interference of a measuring beam LMa and LMb different in frequency is varied in accordance with a variation of optical path length of the measuring beam LMa irradiating alternately the bottom face 34 of the pit 32 and the upper face 36 of track 30 as the disk 24 rotates, therefore, when information (n) corresponding to the depth dn of the pit is read out, based on the phase variation quantity of the signal SM, read-out can be executed at a high speed and with high accuracy, noise of vibration, etc., in the depth direction is offset and the read-out accuracy is satisfactorily obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical recording medium and a reading device thereof, and particularly relates to an optical recording medium and a reading device having a large recording capacity per unit area and a fast reading speed. .

2. Description of the Related Art Predetermined information is recorded by providing a large number of pits on a predetermined track, and the reflected light of the light irradiated along the track changes depending on the focus. Optical recording media from which information can be read have been widely used in recent years. Examples include optical video discs, digital audio discs, and optical cards. Conventionally, information is recorded on such optical recording media depending on the presence or absence of pits and the length of the pits. For example, 8 bits are used to record 1 byte of information, or 8 bits are used to record 1 byte of information. The length of the pit was set in 256 steps so that information for each minute could be recorded. In addition, the reading device that reads the recording from the recording medium irradiates light along the track and receives the reflected light, and based on the change in the light intensity of the reflected light due to the presence or absence of pits, the reading device detects the presence or absence of pits and the bits. It was designed to detect length.

Problems to be Solved by the Invention In such recording media, it is strongly desired to be able to record more information in a small space, and the above-mentioned optical recording media are no exception to this. Also, regarding the reading speed of the information,
There is a strong desire to speed up the process.

Against this background, the present invention was made with the object of increasing the recording capacity per unit area and making it possible to read the recording at high speed.

Means for Solving the Problems In order to achieve the above object, the present invention provides a method in which predetermined information is recorded by providing a large number of pits on a predetermined track, and irradiation is performed along the track. An optical recording medium in which the information is read based on the reflected light of the pit changing depending on the pit, the depth of the pit being changed in multiple stages, and different information being read depending on the depth. It is characterized by being recorded.

Further, a reading device suitably used for reading information recorded on such an optical recording medium is (a) moved relative to the optical recording medium along the track, thereby reading the information recorded on the optical recording medium; Irradiation of irradiating the upper surface of the side part of the pit with a first light, and irradiating the part of the track where the pit is formed with a second light having a slightly different frequency from the first light. means and (b
) a photoelectric conversion element that outputs a beat signal on which the reflected lights of the first and second lights are incident together and whose signal intensity changes due to the interference of the reflected lights; (d) phase detection means for detecting the amount of phase change of the beat signal as the optical path difference between the first and second lights is changed; and an extraction means for extracting the corresponding information.

Functions and Effects of the First Invention In the above-mentioned optical recording medium, different information is recorded depending on the depth dimension of the pit, so the optical recording medium can be made smaller if the recording capacity is the same. , the recording capacity of an optical recording medium of the same size can be increased. In addition, as a large amount of information is recorded in one pit, the time required to detect the difference in the depth dimension of the pit, which changes in multiple stages, becomes shorter than the time required to detect the presence or absence of a pit. If they are the same, the read time will be shortened by the reduction in the number of bits,
The amount of information read per unit time increases.

Incidentally, if the depth of the pits is divided into, for example, 255 levels, 8 bits of information can be recorded in 1 pit, compared to conventional optical recording media that record 1 bit of information depending on the presence or absence of pits. Therefore, if the density of pits is the same, the recording capacity will be eight times as large, and if the time to detect the difference in pit depth is approximately the same as the time to detect the presence or absence of pits, then the reading time will be 1 /8.

Functions and Effects of the Second Invention Furthermore, in the reading device, the irradiation means irradiates the top surface of the track and the portion where the pits are formed on the optical recording medium with first and second lights having different frequencies. When the reflected light of the above light is made incident on the charging conversion element, a beat signal whose signal intensity changes due to the interference of the reflected light is output. Since the irradiation means is moved relative to the optical recording medium along the track, the second light is alternately irradiated onto the bottom surface of the pit and the top surface of the track as the irradiation means moves relative to the optical recording medium along the track. The optical path difference between the first and second lights is changed according to the depth dimension, and the phase of the beat signal is also changed accordingly. Then, the amount of phase change of this beat signal is detected by the phase detection means, and information corresponding to the depth dimension of the pit is extracted by the extraction means based on the amount of phase change. Note that the top surfaces of the tracks to which the first and second lights are irradiated do not necessarily have to be the same, and there may be a certain level difference between them.

In this way, the reading device of the present invention extracts information corresponding to the depth dimension of the pit using so-called heterogain interference, and therefore, the reading device of the present invention extracts information corresponding to the depth dimension of the pit using so-called heterogain interference. The information recorded on the device can be read out with high precision and speed. In particular, the first light is irradiated onto the top surface of the track, and information corresponding to the depth dimension of the pit is extracted with the top surface of the track as a reference. Noise caused by relative vibration in the horizontal direction is canceled out, resulting in higher detection accuracy.

By using such a reading device and the optical recording medium, the object of the present invention, which is to increase the recording capacity per unit area and to be able to read the recording at high speed, can be effectively achieved. be done.

Note that such a reading device is merely an example of a device suitably used for reading information recorded on the optical recording medium of the present invention, and is capable of detecting differences in the depth dimensions of pits that change in multiple stages. It is also possible to use a reading device.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

In FIG. 1, 10a and 10b are current-controlled semiconductor lasers with frequencies F, , f
, are linearly polarized laser beams that are slightly different from each other, −, L
emits b. The semiconductor lasers 10a and 10b are provided parallel to the X-axis and two axes that are parallel to the paper surface of FIG. 1 and perpendicular to each other, and the polarization planes (
The planes of vibration of the electric field Peltor) are arranged parallel to the plane of the paper.

One laser beam L1 is made into parallel light by a collimating lens 12 provided on the X-axis, and then a non-polarizing beam splitter (hereinafter referred to as
NPBS) 14, and the reference beam Ll
1m and measurement beam L. divided into The reference beam Ll1m transmitted through the NPBSl4 is made incident on the optical sensor 16, such as a photodiode, provided on the X-axis, while
Measurement beam L reflected by NPBSl4. is a polarizing beam splitter (hereinafter referred to as PBS) whose incident surface is placed on the z-axis and is parallel to the plane of the paper.18. ．． 1/4 wavelength plate 20,
The light passes through the condenser lens 22 and is irradiated onto a disk-shaped optical disk 24 as an optical recording medium, is reflected by the optical disk 24, and is incident on the PBS 18 through the condenser lens 22 and the quarter-wave plate 20. . At this time, the measurement beam LMa that has passed through the 174-wavelength plate 20 twice in a round trip is turned into linearly polarized light whose plane of polarization is rotated by 90 degrees compared to the forward path, and is reflected by the PBS 18 and sent to an optical sensor such as a photodiode. 26.

Further, the other laser beam Lb is made into parallel light by a collimating lens 28 provided on the z-axis, and then the NP
The beam is made incident on BS l 4 and is divided into a reference beam Llk and a measurement beam LN&. Reference beam L reflected by NPBSl4. is incident on the optical sensor 16, while the measurement beam LHh transmitted through the NPBSl 4 is
B318. 1/4 wavelength plate 20. and condenser lens 22
The light is irradiated onto the optical disk 24 through the optical disk 24, is reflected by the optical disk 24, and is incident on the PBS 1 B via the condenser lens 22 and the quarter-wave plate 20. This measurement beam L. Also, the measurement beam L. as well as 174
By passing through the wave plate 20 twice, the plane of polarization is rotated by 90'', so that it is reflected by the PBS 18 and incident on the optical sensor 26.

The optical disk 24 is rotated by a rotation drive device (not shown) about a rotation axis S that is parallel to the X-axis and orthogonal to the X-axis. A large number of concentric tracks 3
0 is set, and a large number of pits 32 are formed along the track 30. This pit 32 has a depth dimension d.

is changed in 255 steps with equal steps, and the depth dimension d
7, different information n is recorded respectively. FIG. 2 shows an enlarged view of this pit 32, and the central pit 32 has the deepest depth dimension d22. This is the case where the rightmost pit 32 has the third depth dimension d. Therefore, from the depth dimension d where the pit 32 is not formed, to the depth dimension d21. A total of 256 pieces of information, that is, 8 bits of information n (which usually represents 1 byte of information)
=0 to 255) will be recorded by one pit 32.

Here, each of the optical elements is fixed to a machine frame (not shown),
By rotating the optical disk 24 about the rotation axis S, the measurement beam L HatLNi is irradiated along the track 30 . Furthermore, by moving each optical element together with the machine frame in the X-axis direction, the measurement beam "H1+LHb" is irradiated onto another track 30.

The tracking of the measurement beam L 1411 + LMk is performed so that the X-axis is located between the region where the pit 32 is present and the pit 3 in the X-axis direction, that is, in the radial direction of the optical disc 24.
The measurement beam LMs is controlled to be located at the boundary with the region where the pit 32 does not exist, and the measurement beam LMs is focused on the region where the pit 32 is present. The light is focused on a portion where no pit 32 exists. That is, the semiconductor laser 10a is displaced from the X-axis in the X-axis direction by Δ2, and the semiconductor laser 10b is displaced by ΔX from the X-axis in the X-axis direction. Measurement beam L. (Laser light Lb) will be explained specifically. As shown in FIG. 3, the focal length of the collimating lens 28 is f
t, the focal length of the condenser lens 22 is ft, and the measurement beam L.

When the deviation dimension between the irradiation position and the two axes is defined as X, the displacement amount ΔX is obtained by the following equation (1). Therefore, for example, ft”20m, f!=2m, xb=0.4
When n is assumed, ΔX is 4 nm. Note that if the focal length of the collimating lens 12 is 20°, the displacement amount Δ2 of the semiconductor laser 10a is also set to 4#m, so that the irradiation position of the measurement beam LHs is 0°4 from the two axes.
#11 will be shifted.

Δx=XbX(f+/fi ---(1) And, for example, if the diameter of each pit 32 of the optical disc 24 is 0.8
Accordingly, if the interval between the pits 32 in the radial direction of the optical disk 24 is 0.8 us, the measurement beams L, 4. is irradiated to the center of the area where the pit 32 exists in the radial direction of the optical disc 24, and the measurement beam Lsb
is irradiated to the center of the area where there is no. As a result, the measurement beam L. As the optical disk 24 rotates, the measurement beam LHh is alternately irradiated onto the bottom surface 34 of the pit 32 and the top surface of the track 30, in this embodiment the top surface 36 of the optical disk 24, according to the spacing between the pits 32 on the track 30. is always irradiated onto the upper surface 36 regardless of the rotation of the optical disk 240.

In this embodiment, the measurement beam LMb corresponds to the first light, and is the measurement beam L. , corresponds to the second light.

Further, the semiconductor lasers 10a, 10b, collimating lenses 12, 28, NPBS 14, PBS 18.1/
The irradiation means 38 includes the four-wavelength plate 20, the condenser lens 22, a frame to which they are fixed, a drive device for moving the frame in the X-axis direction, and the like.

On the other hand, the semiconductor lasers 10a and 10b are Δ2. When displaced by ΔX, the laser beam is made into parallel light by the collimating lens 12.28,
The optical axis of L is the X axis.

Tilt with respect to the X axis. This inclination angle θ is determined by the displacement amount Δ2. When ΔX is 4#ll, it is expressed by the following equation (2). Then, when the laser beams L- and Lb are tilted in this manner, the reference beam Ll1m and the beam incident on the optical sensor 16.26. .

Measurement beam L. Andri. are combined with their leading axes intersecting each other, but the crossing angle is 2θ=
0.4 mrad and their reference beam L. and Ll b + measurement beam LMa and ri. are made to interfere with each other.

θ-4n/20mm (rad)=0.2 (sra
d) ...(2) The above measurement beam L. optical sensor 26
The complex amplitude U at the top. , is the optical path length from the semiconductor laser 10a to the optical sensor 26, +2d, the amplitude of the electric field Peltor is Ea, and the initial phase is φ, the laser beam.

(Measurement beam L.) 2π/λ, where the wavelength is λ3.

=, it is expressed by the following equation (3). Furthermore, the complex amplitude uNk of the measurement beam LH& on the optical sensor 26 is
The distance from the semiconductor laser tob to the optical sensor 26! .

, the amplitude of the electric field Peltor is Eb, the initial phase is φ1, the wavelength of the laser beam Lb (measurement beam L xb) is λb, and 2
When π/λ,=, it is expressed by the following equation (4). The change component IN of the light intensity on the optical sensor 26 is the measurement beam L or the beam intensity. The light intensity due to interference with
a+umb l”, k.

i,,,kb ・l M b + φ1. Since φ1 is constant, it is expressed by the following equation (5). Therefore, the optical sensor 26 outputs a measurement signal SM whose signal intensity changes according to the change component let. In this embodiment, the optical sensor 26 corresponds to a photoelectric conversion element, and the measurement signal SM is Corresponds to a beat signal.

uHs=Ea eXP t [km' 1mm +
2 km ” da-2πf, t+φ1]...
(3) uHb=Eb eXP t Ckh' 1. b
21t fht+φ1]...(4) In "CoS(2km' da 2flE(fa
fb) to tenφ. □t] ...(5) Also, the complex amplitude u1m of the reference beam Lla on the optical sensor I6 is determined by the optical path length from the semiconductor laser lOa to the optical sensor 16 as j! o, it is expressed by the following equation (6), where the complex amplitude u*b of the reference beam Llk on the optical sensor 16 is the distance from the semiconductor laser 10b to the optical sensor 16!
. Then, it is expressed by the following equation (7), and the change component III of the light intensity on the optical sensor 16 is expressed by the following equation (8). Therefore, the optical sensor 16 outputs the reference signal SR whose signal strength changes according to the change component Im.

uma=Ea eXP t'(km' ll*
2 N f at+φ, ]...(6) u*b=Eb eXp t Ckb・l*b 2x
rbt+φ,]...(7) 1m ” cos (2z(fs fb)t+φco
*slL)...(8) Here, change component 1. That is, the measurement signal SM is such that the bottom surface 34 of the pit 32 and the top surface 36 of the track 30 are alternately irradiated with the measurement beam LNm, and the measurement beam L is irradiated by 2d depending on the depth dimension d of the pit 32. By changing the optical path difference with the change component! In other words, the phase is changed with respect to the reference signal SR, and this phase change amount ΔΦ is expressed by the following equation (9) as is clear from the above equations (5) and (8). By detecting the amount of phase change ΔΦ between the signals SM and SR, information n corresponding to the depth dimension d and % of the pit 32 is detected.

ΔΦ=2, d7−4πd, /λ, (9) The phase detection means 40 shown in FIG.
are respectively supplied to comparator circuits 42 and 44, shaped into rectangular waves, and then supplied to counter circuits 46 and 48. The counter circuits 46 and 48 count the wave numbers of the measurement signal SM and the reference signal SR, which have been shaped into rectangular waves, at predetermined intervals, for example, every 1 msec, and output them to the latch circuits 50 and 52. , the count value is the latch circuit 50
．． 52 and then subtracted by a subtracter 54. Then, the subtraction (1:N) is temporarily stored in the latch circuit 56. The subtraction value N is such that one phase 2π of the phase change amount ΔΦ is taken as one unit.

Further, the rectangular measurement signal SM and reference signal SR output from the comparator circuits 42 and 44 are transmitted to the crystal oscillator 58.
AN together with the pulse signal SP of frequency fc output from
The signal is supplied to the D circuit 60.

The measurement signal SM is supplied to the AND circuit 60 via the NOT circuit 62, and the number of pulses P of the pulse signal SP'' that has passed through the AND circuit 60 is counted by the counter circuit 64 at a predetermined timing. It is temporarily stored in the latch circuit 66.

FIG. 5 is a time chart showing an example of the measurement signal SM' inverted by the NOT circuit 62, the reference signal SR, and the pulse signal SP° passed through the AND circuit 60.

The number of pulses P is 1 phase 2 of the phase change amount ΔΦ.
This corresponds to the part smaller than π, and if the frequencies of the measurement signal SM are r, (-r, -fb), then the decimal part M smaller than 2π of the amount of phase change ΔΦ is expressed by the following equation.

Further, using the M and the subtraction value N, the phase change amount ΔΦ is expressed by the following equation 01). Note that the frequency f
c is set to a value sufficiently larger than the frequency f.

M=PX Cfs/fc) ...0ω
ΔΦ=2π(N+M)...01) The subtraction value N and the number of pulses P are each read into the extraction means 70 via the data bus line 68. The retrieving means 70 includes a CPU 72, a RAM 74, and a ROM 76, and utilizes the temporary storage function of the RAM 74 while
Signal processing is performed according to a program stored in advance in M76, and information n corresponding to the depth dimensions d and l of bit 32 is extracted from the subtraction value N and the number of pulses P. Specifically,
For example, the level difference (d, -d,) of the depth dimension d7 of the pit 32.

) is set to 1/8 of the wavelength λ of the laser beam, then
The depth dimension d7 is expressed by the following equation (21) using the information n, while the following equation surface is derived from the above equations (9) and 00, so the information n is ultimately determined according to the following equation (b). That is, calculate the decimal part M from the pulse number P according to the above formula, and add the decimal part M and the subtraction value N to obtain 4.
All you have to do is double it.

cL -n ・λ1/8...021d7-λ-(N
+M)/2 ・ ・ ・Side n-4 (N0M
) ・ ・ ・04) Then, the optical disk 24 is driven to rotate around the rotation axis S, and the irradiation position of the measurement beam L□*LHb is on one track 3.
By being moved along 0, its track 3
Information n corresponding to the depth dimension d7 of the bit 32 formed as 0 is sequentially read out. Further, the irradiation means 38
By moving in the axial direction, that is, in the radial direction of the optical disc 24, the irradiation position of the measurement beam LMan LHb is sequentially changed to another track 30, thereby reading the information recorded on the entire surface of the optical disc 24.

Here, in the optical disc 24 of this embodiment, the depth dimension d7 of the pit 32 is divided into 255 levels, and one bit 32
Because 1 byte of information (8 bits worth of information) is recorded using the 4-byte method, compared to the conventional method of recording information based on no pits or length, it is possible to record information using the same recording capacity. If so, the size (area) of the optical disk 24 is 1
On the other hand, if the optical disc 24 is of the same size, its recording capacity will be eight times as large. Furthermore, since one byte of information n is read from the depth dimension d7 of one pit 32, if the time to read that information n is approximately the same as the time to detect the presence or absence of a bit, the reading per unit time is This increases the amount of information by eight times, making high-speed processing possible.

Further, the reading device of this embodiment that reads the information recorded on the optical disk 24 has a measurement beam L having a different frequency.
The phase of the measurement signal SM whose signal intensity changes due to the interference between Mm and LHb is determined by the optical path length of the measurement beam LMa that is alternately irradiated onto the bottom surface 34 of the pit 32 and the top surface 36 of the track 30 as the optical disk 24 rotates. Since the information n corresponding to the depth dimension dn of the bit 32 is read based on the amount of phase change ΔΦ of the measurement signal SM from where it is changed according to the change, the information n corresponding to the depth dimension dn of the bit 32 is read. Information can be read with high precision and high speed. As a result, the optical disc 24, on which 1 byte of information n is recorded at high density according to the depth dimension d of the bit 32, can effectively perform its functions, and high-speed processing of information reading is realized. be.

In particular, the measurement beam L mentioned above. is constantly irradiated onto the upper surface 36 of the track 30 regardless of the rotation of the optical disk 24, and detects the amount of phase change ΔΦ of the measurement signal SM that changes according to the depth dimension d7 of the bit 32 with the upper surface 36 as a reference, and determines the depth. Since the information n corresponding to the dimension d7 is taken out, noise caused by relative vibrations between the optical disc 24 and the irradiation means 38 in the bit depth direction, that is, in the two-axis directions, is canceled out, and the depth dimension The amount of phase change ΔΦ corresponding to d7 is detected with high accuracy, and the accuracy of reading information n is accordingly improved.

In addition, in this embodiment, the reference beams Llla+Llllk separated from the laser beams L, L, are interfered with each other to extract the reference signal SR, and the reference signal SR and the measurement signal S are
Since the phase change amount ΔΦ of the measurement signal SM is detected by comparing the phase change amount ΔΦ with improves.

Next, another embodiment of the present invention will be described. In the following embodiments, parts substantially common to those in the above embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 6 shows an example in which a two-frequency orthogonal laser 80 is used in place of the semiconductor lasers 10a and 10b.The two-frequency orthogonal laser 80 is arranged on the Z axis, and has slightly different frequencies and polarization planes. Two types of linearly polarized light L that are orthogonal to each other
A laser beam (LP + Ls) containing P and P is emitted. The laser beam (LP + Ls) is
4, a portion of the light is reflected by the polarizer 82, and the linearly polarized light L is incident on the optical sensor 16.
A reference signal SR whose signal strength changes due to interference between P and L3 is output. In addition, the laser beam (LP + Ls) that has passed through the NPBS l4 is separated by the Wollaston prism '84 into linearly polarized beams L2 and L3 according to its polarization plane, and its traveling direction is centered on the two axes and the X axis. The light beams are tilted in opposite directions, and are irradiated onto the optical disk 24 by the condenser lenses 22, respectively.

The irradiation positions of the linearly polarized light LP and the linearly polarized light LP on the optical disc 24 are spaced apart from each other by about 0.8 tna in the X-axis direction, that is, in the radial direction of the optical disc 24, and the linearly polarized light LP is irradiated onto a portion where the bit 32 is not present. On the other hand, linearly polarized light is irradiated onto the portion where the bit 32 is formed. The linearly polarized light reflected by the optical disk 24 and the condensing lens 22. It passes through the Wollaston prism 82 and its leading axes are aligned, and N
After being reflected by the PB 314, the light passes through the polarizer 86 and is made incident on the optical sensor 26. As a result, the optical sensor 26 outputs a measurement signal SM whose signal intensity changes due to the linearly polarized light reflected by the optical disk 24 and the interference of L3.

The measurement signal SM is such that as the optical disc 24 rotates, the irradiation position of the linearly polarized light Ls on the optical disc 24 is alternately changed between the bottom surface 34 of the bit 32 and the top surface 36 of the track 30, and the optical path length is depth dimension d,
By changing the optical path difference from the linearly polarized light LP in accordance with the change in the optical path length, the phase is changed in accordance with the change in the optical path difference. Therefore, information n corresponding to the depth dimension d7 of the bit 32 is extracted by detecting the phase change amount ΔΦ of the measurement signal SM, for example, by the phase detection means 40 or the like.

This embodiment also provides the same effects as the first embodiment.

In this embodiment, the two-frequency orthogonal laser 80, NP
BS14. Wollaston prism 84° condensing lens 2.
The irradiation means 88 is composed of linearly polarized light LP,
L3 is the first. This corresponds to the second light.

Although the embodiments of the present invention have been described above in detail based on the drawings, the present invention can also be implemented in other embodiments.

For example, in the embodiment described above, the depth dimension d of the bit 32 is 2.
It is divided into 55 stages, and one byte of information is recorded in one bit 32, but the depth dimension d7 is set to 1.
The depth can be changed by recording 1 nibble (4 bits) of information in 5 steps, making 1 byte of information with 2 bits, or increasing the number of steps in the depth dimension d7 to (2'-1) or more. The number of stages of the length d can be set as appropriate.

Further, in the embodiment described above, the upper surface 36 of the optical disk 24 and the upper surface of the track 30 are made to coincide with each other, but it is also possible to form grooves or the like on the upper surface of the optical disk 24 to provide tracks.

Further, in the embodiment described above, the optical disk 24 has been described in which a large number of tracks 30 are arranged concentrically, but the present invention can be similarly applied to a rectangular optical card or the like in which a large number of tracks 30 are arranged in parallel to each other.

Further, the reading device of the above embodiment emits laser light.

Although the reference signal SR is extracted by dividing L, y (Lp+Ls) by NPBSl 4, it is also possible to extract this reference signal SR electrically from the oscillation frequency signal of a laser or the like.

Further, in the above embodiment, when extracting information n, bit 32
Although the case has been described in which the level difference in the depth dimension d7 is set to λ, /8, it goes without saying that this level difference can be changed as appropriate.

Although other examples are not provided, the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a cross section of a main part of an optical disc according to an embodiment of the present invention and an optical configuration of an irradiation means in a reading device for the optical disc. FIG. 2 is an enlarged sectional view of the optical disc of FIG. 1. FIG. 3 is a diagram illustrating the deviation of the laser and the irradiation position from the optical axis in the irradiation means of FIG. 1. FIG. 4 is a block diagram illustrating the signal processing section of the reading device in the embodiment of FIG. 1. FIG. 5 is a time chart showing an example of the signals SM", SR, and SP" in FIG. FIG. 6 is a diagram illustrating a main part of another embodiment of the present invention, and corresponds to FIG. 1. Figure 1 - 24: Optical disk (optical recording medium) 26, optical sensor (charge conversion element) 30 Nidrak 32: Bit 36: Top surface 38.88: Irradiation means 40, phase detection means 70: Ejection means, 1h, LP: First light LNa*LS: Second light SM: Measurement signal (beat signal)

Claims (2)

[Claims] (1) Predetermined information is recorded by providing a large number of pits on a predetermined track, and
An optical recording medium in which the information is read based on the reflected light of the light irradiated along the track being changed by the pit, the depth of the pit being changed in multiple stages, and the depth An optical recording medium characterized in that different information is recorded depending on the information. (2) A reading device for reading information recorded on the optical recording medium according to claim (1), wherein the reading device reads information recorded on the optical recording medium according to claim (1), wherein the reading device is configured to read information recorded on the optical recording medium according to claim (1), by being moved relative to the optical recording medium along the track. Irradiation of irradiating a first light onto the upper surface and a side part of the pit, and irradiating a portion of the track where the pit is formed with a second light having a slightly different frequency from the first light. means, the reflected lights of the first and second lights are incident together;
a photoelectric conversion element that outputs a beat signal whose signal intensity changes due to interference of the reflected light; and a photoelectric conversion element that outputs a beat signal whose signal intensity changes due to interference of the reflected light; and the beat as the optical path difference between the first and second lights is changed according to the depth dimension of the pit A reading device comprising: a phase detection means for detecting the amount of phase change of a signal; and an extraction means for taking out information corresponding to the depth dimension of the pit based on the amount of phase change.