JP2656847B2 - Information playback device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an information reproducing apparatus for reproducing information recorded on an optical information recording medium by using a multiple interference effect.

[Prior Art] In recent years, there has been remarkable progress in the development of optical information recording media called optical memories such as optical disks, optical cards, and optical tapes, and recording / reproducing devices using the same. Such a recording / reproducing apparatus has an advantage that the cost per bit is lower than that of a magnetic disk or the like and that a high transfer rate can be obtained because the optical memory has the feature of high density recording. Therefore, research and development have been actively conducted to further increase the density of optical memories.

In order to increase the density of the optical memory, for example, miniaturization of the minimum bit size, multi-level recording of information, multiplex recording of information, and the like have been proposed, and various methods have been proposed. Among them, with regard to the conventionally known multi-valued technology, most of the proposals use a continuous reflectance change of a dye medium or a phase change medium. These proposals basically correspond to binary information up to now, and have high contrast 2
It further subdivides the intermediate values of the two different reflectance levels. For this reason, in principle, the SNR is sacrificed, and the multi-value is obtained, which causes deterioration of the error rate.

In the method using the change in reflectance, the simplest is:
Assuming that the substrate has a complex refractive index N ₁ and the medium has a complex refractive index N ₂ , the reflectance R is represented by the following equation.

Here, n _m (m = 1,2) is a refractive index, and K _m (m = 1,2) is an attenuation coefficient, and N _m = n _m −iK _m . For example, in the case of TeO _x system of a phase change medium, when an amorphous state, N ₂ = 3.5-0.8i, because in the crystalline state is N ₂ = 3.9-1.3i, changes in reflectance and N ₁ = 1.6 [Delta] R Is as small as 6%. Further, this ΔR is subdivided, and the change of ΔR with respect to the light energy required for recording is nonlinear, so that equalization is difficult, and
It is not easy to control the light energy required for recording.

On the other hand, it is not intended to be multi-valued,
As a technique to increase the SNR, as shown in JP-B-63-26463, a metal mirror with high reflectivity is provided on the back surface of the medium, and due to the multiple interference effect of the thin film, the difference in reflectivity between the two states is expanded. Methods for improving contrast have been proposed. Japanese Patent Publication No. 63-26463 proposes an increase in reflectance change due to a change in absorption coefficient. However, this method eliminates the above-described problems of multileveling, nonlinearity, and difficulty in controlling light energy. It cannot be solved. Rather, when trying to apply to multi-leveling, it is highly possible that the nonlinearity of the change in reflectance increases by combining the change in the absorption spectrum and the multiple interference effect. In other words, just because the difference between the two reflectances corresponding to such binary values is increased, the contrast is improved, and the SNR as binary data can be improved, characteristics suitable for multi-valued data are always obtained. Do not mean.

In a digital memory, when the number of multilevel levels at the medium level is L, the number M of information recording bits when binary data is recorded is represented by the following equation.

M = log ₂ L For example, in the above-described multi-level conversion based on the change in reflectivity, even if 8-level multi-level (L = 8) is realized in the medium, the recordable information amount is 3 bits (M = 3). Is only tripled. Considering signal processing of devices such as computers that receive data from digital memory and processing systems such as modulation and demodulation in the memory, the effect of multi-level conversion will be remarkable because 8-bit multi-level conversion is likely. , 256 as a medium
It is necessary to secure multi-levels.

When multi-leveling is performed using the reflectance with respect to such light intensity, 256 levels of multi-leveling are performed even if ideally, even if the reflectance from 0 to 100% changes linearly and equally. This is a change of 0.390% per level, and it is understood that practical application is extremely difficult in view of the medium production technology, the light source intensity stabilization technology, the detection technology, and the like.

In addition, the same photochemical hole burning (hereinafter referred to as PH) using the optical absorption spectrum as in JP-B-63-26463.
B) A multiplex recording method utilizing the effect has also been proposed. In this multiplex recording method, multi-value recording should be possible in principle by multiplex recording. However, at present, the PHB method has just finished the principle confirmation experiment at cryogenic temperatures, and it is technically difficult to stably realize a medium having many narrow-band absorption spectra at room temperature. Further, when performing a series of basic operations as a memory such as recording, reproducing, and erasing of information, the light source needs to have a sufficiently narrow spectrum width than each narrow absorption spectrum width. At present, there are many other issues to be solved besides the instability of the medium itself, such as the necessity of simultaneously sweeping the wavelength and the need to control the absolute value of the wavelength.

[Problems to be Solved by the Invention] As described above, many problems remain as the conventional multi-valued technology, particularly problems such as low SNR and low multi-valued degree. was there. In addition, although proposals have been made to increase the degree of multi-leveling, it is the fact that many issues remain.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an information reproducing apparatus which can realize a high SNR and a high multi-level degree and can reproduce information with high reliability. .

[Means for Solving the Problems] In order to achieve the above object, a first and a second reflective layer arranged in parallel to each other at a predetermined interval so that light reflected by each of them causes multiple interference, An optical information recording medium comprising a medium layer in which information is recorded as a change in the refractive index of the medium is irradiated with a reproducing light beam having a variable wavelength, and the light reflected or transmitted from the medium is provided between the reflective layers. In a device for discriminating recorded information by detecting a wavelength causing multiple interference from light, a wavelength dispersion element for dispersing the wavelength of reflected light or transmitted light from the medium is provided, and the wavelength dispersion element is opposed to the dispersion direction of the dispersion element. Then, an information reproducing apparatus is provided, wherein an array sensor for detecting a spectrum of light dispersed by the dispersive element and detecting a wavelength corresponding to recorded information is provided.

Examples Hereinafter, examples of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the information reproducing apparatus of the present invention.

In FIG. 1, reference numeral 1 denotes a recording medium for recording multi-valued information by utilizing the optical large interference effect. The specific configuration of the recording medium 1 will be described later in detail. Reference numeral 2 denotes a semiconductor laser which is a first light source for information recording, and reference numeral 3 denotes a collimator lens which makes the laser light of the semiconductor laser 2 parallel. 4 is a semiconductor laser which is a second light source for information reproduction,
Reference numeral 5 denotes a collimator lens that converts the laser light of the semiconductor laser 4 into parallel light. 6 and 7 are beam splitters,
Reference numeral 8 denotes a pickup lens, 9 denotes a dispersion prism, 10 denotes a sensor lens, and 39 denotes a one-dimensional CCD. The dispersion prism 9 is for dispersing the light reflected from the recording medium, and is one-dimensional CCD3.
Reference numeral 9 is disposed so as to face the dispersion direction.

The light converted into parallel light by each collimator lens 3, 5 is
The beams are combined by the beam splitter 6. The medium 1 is driven by a motor (not shown), and is configured to scan the medium with a light beam emitted from the light source.

The recording semiconductor laser 2 is a laser having a relatively high output, and is driven by a recording laser drive circuit 31. Terminal
From 30, a word represented by a binary signal of many bits (for example, 8 bits) is sequentially input. The input word is converted into a corresponding signal level in the modulation circuit 32 according to a predetermined table. For example, if one word is composed of 8 bits, there are 256 words, and a recording signal modulated to 256 levels corresponding to each word is output from the modulation circuit. This recording signal is input to the recording laser drive circuit 31, and the semiconductor laser 2 emits a recording light beam having an intensity corresponding to the signal level.

The recording light beam is collimated by the collimator lens 3, passes through the beam splitters 6 and 7, and is imaged as a minute spot on the medium layer of the medium 1 by the pickup lens 8. The medium layer is heated by the irradiation of the recording light beam, and a signal is recorded as a series of minute recording regions having a changed refractive index. Here, each minute recording area shows a refractive index corresponding to the intensity of the irradiated light beam. That is, one word is recorded in one recording area. The output of the signal from the modulation circuit 32 is performed at a constant period based on the clock signal output from the clock signal generation circuit 33. Therefore, a minute recording area is formed on the recording medium 1 at a constant pitch in the light beam scanning direction.

On the other hand, a relatively low-output laser is used as the semiconductor laser 4 for reproduction. The semiconductor laser 4 is driven by a reproduction laser drive circuit 34. The reproduction laser drive circuit 34 sweeps the wavelength of the reproduction light beam emitted from the semiconductor laser 4 at a constant period in synchronization with the clock signal input from the clock signal generation circuit 33. Such a wavelength sweep can be performed, for example, by using a normal DH laser and changing the amount of current injected into the laser. If a tandem electrode type wavelength variable semiconductor laser proposed in Japanese Patent Application Laid-Open No. 63-32985 or the like is used, a wider range and higher speed sweeping can be performed. The clock signal generation circuit 33 synchronizes the clock signal with the minute recording area on the medium, for example, by detecting a synchronization mark previously recorded on the medium. Then, based on the clock signal, the semiconductor laser 4 is controlled to perform at least one wavelength sweep in the minute recording area.

The light beam for reproduction emitted from the semiconductor laser 4 is reflected by the beam splitter 6, passes through the beam splitter 7, and
An image is formed as a minute spot on the medium layer of the medium 1 by the pickup lens 8. The light reflected by the medium 1 and modulated according to the recorded information is separated by a beam splitter 7 from incident light from a laser. And the dispersion prism 9
, And condensed by the sensor lens 10 to produce a one-dimensional CCD3
Received at 9.

The output of the one-dimensional CCD 39 is input to the peak detection circuit 35,
Here, the peak of the detection signal is detected. Then, based on the clock signal input from the clock signal generation circuit 33, the clock circuit 36 counts the time from the start of the sweep of the wavelength of the reproduction light beam to the detection of the peak. As described later, the present invention converts information recorded as a change in the refractive index of the medium layer of the medium 1 into a change in the wavelength at which interference occurs using the optical multiple interference effect, and detects the change. . In the apparatus shown in FIG. 1, since the wavelength is swept at a constant rate, the above-described change in the wavelength appears as the time from the start of the sweep. Therefore, the information reproducing circuit 37
From the time measured at 36, the information recorded on the medium 1 is reproduced and output from the terminal 38. In the present embodiment, by configuring the light receiving system with a spectroscope system, even if there is a fluctuation in the wavelength sweep waveform, the wavelength is spatially separated and separated, so that occurrence of jitter is prevented as described later. Things.

The recording light beam and the reproducing light beam are not shown, but the focus position of the light spot is three-dimensionally controlled by auto-focusing and auto-tracking control. In both of the above-mentioned semiconductor lasers, it is also possible to convert the optical output having an elliptical distribution into a light having a shape close to a perfect circular distribution by a beam shaping prism or the like, if necessary.

Next, a specific configuration of the recording medium 1 will be described. Second
FIG. 1 shows a cross-sectional structure of the recording medium 1.

The recording medium 1 is a medium having a double-sided structure in which recording and reproduction can be performed on both sides. 11a and 11b are transparent polycarbonate substrates, on each of which a reflective layer and a medium layer are alternately formed. First, first reflective layers 12a and 12b are formed on substrates 11a and 11b, respectively, and medium layers 13a and 13b whose refractive indexes change by heat are formed on the surfaces thereof. Further, second reflective layers 14a and 14b are formed on each of the medium layers 13a and 13b, and these are adhered by the adhesive layer 15. Each layer is formed in parallel with each other at a predetermined interval, and causes multiple interference as described later.

As the medium layers 13a and 13b, TeO _x , InSeTlCo, GeTeS _b Tl, G
Inorganic media such as eTeSe and organic media such as anthraquinone dielectrics, dioxazine compounds and triphenodithiazine compounds are suitable. Further, the multilayer reflective layers 12a, 12b
The layers 14a and 14b are formed by alternately stacking layers having a high refractive index and layers having a low refractive index with an optical path length corresponding to / 4 of the wavelength. The material of each reflective layer is SiO ₂ , S
A dielectric such as i ₃ N ₄ , MgF ₄ , Al ₂ O ₃ is used. In order to produce such a recording medium 1, first, the substrates 11a and 11b on both sides are formed.
A first reflective layer, a medium layer, and a second reflective layer are sequentially formed thereon by a sputtering method or a coating method. Then, the substrates 11a and 11b are bonded with an adhesive (adhesive layer 15) with the second reflective layers facing each other, thereby completing a recording medium for double-sided recording.

Further, in the recording medium 1 of the present embodiment, a so-called Fabry-Perot etalon is realized by the configuration of the medium layer sandwiched between the first reflection layer and the second reflection layer. That is, as described later, the incident light is repeatedly reflected between the two reflection layers, and a multiple interference effect occurs. The present invention performs multi-level recording of information by effectively utilizing the multiple interference effect.

The recording medium 1 is irradiated with a laser beam focused on a minute spot by a pickup lens in the same manner as a normal optical head, and information is reproduced from the reflected light from the etalon section. For simplicity of explanation, the two reflective layers 12a, both sides of the 14a in the air, assuming that R both reflectance, reflectance R _E from the etalon is expressed by equation (1).

Here, F corresponds to the so-called finesse, and represents the sharpness of the interference fringes, and is obtained by equation (2).

Ψ is a phase difference represented by the following equation (3).

Here, n _M is the refractive index of the medium layer 13a, and λ is the wavelength of light.

Here, when representing the reflectivity R _E as a function of the phase difference [psi, third
As shown in the figure. In FIG. 3, m is an integer and
Where Expression (4) is satisfied, sharp and dark interference fringes appear.

Ψ = 2πm (4) The change in the phase difference Ψ is generally represented by (5) from equation (3).

This new multi-level recording method uses multi-level information,
The change in the refractive index Δn _M is recorded as a phase difference change Δ 差 on the medium. Then, in the reproduction, by sweeping the wavelength of light, a wavelength corresponding to Δλ that gives a phase difference that just cancels the phase difference ΔΨ caused by Δn _M ,
Condition (4) is restored. That is, when the wavelength is swept over time, sharp interference fringes appear at a wavelength that matches the phase difference corresponding to the value of the recorded information, and a pulse corresponding to FIG. 3 is obtained as a time waveform. The position Δt of this pulse on the time axis gives multi-value information. Refractive index,
The correspondence between wavelength and time is as follows when the wavelength sweep is linear.
It is expressed by equation (6).

To perform the recording, a change ΔΨ in the phase difference represented by the equation (5) is given by controlling Δn _M generated by heating by the laser. In the reproduction, light having a wavelength change that cancels the phase difference change is incident, and a sharp dark fringe is detected. That is, when the wavelength is swept as described above and a pulse appearing in the reflected light intensity of the medium is detected, the wavelength at that time is a wavelength corresponding to the phase difference.

However, if the wavelength sweep at the time of reproduction fluctuates, that is, if the wavelength sweep waveform is unstable, the second equality of the equation (6) does not hold, and the time of the detected pulse is accurately multi-valued. Will no longer respond. The sawtooth wave is optimal for the wavelength sweep waveform to satisfy the expression (6). However, the variation in the slope, the variation in each peak wavelength, the non-linearity of the slope, and the like become the jitter of the reproduced signal, and the error rate decreases. It will deteriorate. In order to solve this problem, for example, precise wavelength control may be performed. However, it is difficult to employ the optical head because the circuit configuration of a wavelength detection system and a control system is complicated and large. In the present invention, the first
As described in the figure, the light receiving system is composed of a dispersing prism 9 and a one-dimensional CC.
By using D39 or the like, it is possible to easily solve the problem of the jitter of the reproduced signal.

The specific operation of the embodiment shown in FIG. 1 will be described with reference to FIG. FIG. 2A is a diagram showing an arrangement state of minute recording areas (hereinafter, referred to as cells) in the track direction of the recording medium 1. In this example, cell Ci, (i = 1,2
..) Are arranged in a line in the track direction, and are arranged spatially or temporally at the same pitch. The cell referred to here corresponds to a pit in a compact disk and a domain in a magneto-optical disk, and is fundamentally different from the conventional inter-mark recording or mark length recording. That is, multi-valued information can be recorded at a unique position, and the interval and length of each cell are independent of the information to be recorded.

FIG. 4 (b) shows a wavelength sweep waveform of the reproducing semiconductor laser 4, wherein the horizontal axis represents time and the vertical axis represents wavelength. In the figure,
In contrast to the ideal sweep waveform 18 shown by the broken line, the waveform sweep waveform 17
Indicates a waveform having fluctuations such as a change in inclination, a non-linear undulation, and a parallel shift. Wavelength sweep waveform 17
Is used, but this is the simplest sweep wave, and the relationship between time and wavelength is linear.
This is because the wavelength density per unit time becomes constant, and when the light is dispersed by a spectroscope, a nearly uniform distribution becomes possible.
The effective sweep range of the wavelength is λ ₁ ≦ λ ≦ λ _2, and some margin is taken without using the longest wavelength and the vicinity of the maximum value.

FIG. 4 (c) shows the time change of the reflected light intensity from the recording medium 1 when the cell of FIG. 4 (a) is read with the wavelength sweep waveforms 17 and 18 of FIG. 4 (b). The axis is time and the vertical axis is reflected light intensity. In the figure, reference numeral 19 denotes the intensity of reflected light when read with the wavelength sweep waveform 17, and reference numeral 20 denotes the intensity of reflected light when read with the ideal sweep waveform 18. Such a change in reflected light intensity is pulse-like and occurs at a wavelength that cancels the recorded phase difference ΔΨ (t = t _i ). This pulse corresponds to the interference fringes shown in FIG. In this case, cells C ₃ , C
_4, when reading of C _5, when the wavelength varies as the wavelength-sweeping waveform 17 occurs, the time of appearance of the optical pulses t ₃ ', t _4', as shown as t ₅ ', deviates from the original appears Time Become a jitter.

FIG. 4D is a diagram showing an example of driving of the one-dimensional CCD 39. The exposure time texp is made shorter than the scanning time for one cell Ci to reduce crosstalk between cells.
FIG. 4E shows the output waveform 22 of the one-dimensional CCD 39.
The horizontal axis is time, and the vertical axis is voltage. Here, the light incident on the dispersing prism 9 has different angles at which the light undergoes dispersion depending on the wavelength at each time. If the angle is f and the focal length of the θ (λ) sensor lens 10 is f, an image forming plane, that is, one-dimensional CCD3
The position x on 9 is represented by x = fθ (λ) (7) Angle change Δθ (λ) due to wavelength change Δλ
Is small, it can be considered that Δθ (λ) ∝Δλ, so that Δx∝fΔλ (8), and the light spot scans on the one-dimensional CCD 39 as the wavelength is swept. This scanning is repeated for each cell Ci shown in FIG. Scanning by the reproducing spot of the cell C _i on the recording medium 1 is a relative movement of the mechanical medium and the light spot (optical axis), the scanning of the light spot on the 1-dimensional CCD39 is performed purity optically. Therefore, in principle, there is no crosstalk between both scans, and it does not cause jitter.

More specifically, since the wavelength and the spatial position on the one-dimensional CCD 39, that is, the number of bits of the array sensor of the one-dimensional CCD 39, are uniquely fixed by the relationship of the equations (7) and (8), the sweep waveform
Even if the time position of the interference fringe pulse of the reflected light intensity 19 fluctuates due to a wavelength fluctuation such as 17, the wavelength position on the one-dimensional CCD 39 does not fluctuate.
The output of the CCD 39 does not fluctuate, and a signal free of jitter is obtained. FIG. 4 (f) is a pulse waveform representing the position of the wavelength corresponding to the interference fringe from the output of the one-dimensional CCD 39 of FIG. 4 (e).
23, and the width of each pulse represents the multilevel information of each cell.

Next, another embodiment of the present invention will be described. In the above-described embodiment, the wavelength at which the interference fringe is generated is detected by sweeping the wavelength of the light source.In this embodiment, without performing the wavelength sweep, a reproduction light source having a spectrum width corresponding to the swept wavelength is used. Used. Therefore, since no wavelength sweep is required,
In this embodiment, the configuration of the device can be simplified. As the reproducing light source, an LED (light emitting diode) or a white light source is used instead of the reproducing semiconductor laser 4 shown in FIG. However, in order to obtain a desired spectral width, it is necessary that the light source has a sufficiently large spectral width. Even if a band-pass filter that transmits a desired spectrum is disposed between the light source and the beam splitter 6, Good. In this configuration, the light source does not need to modulate any wavelength, and may be driven by DC. When such a light source for reproduction is used, the reflected light from the recording medium 1 is dispersed by the dispersing prism 9 as in the above-described embodiment, and the spectrum is expanded on the one-dimensional CCD 39 by the sensor lens 10.

FIG. 5 is a time chart showing the information reproducing operation of this embodiment. FIG. 5A shows a spectrum 24 of the light source. The horizontal axis represents time, and the vertical axis represents light intensity. FIG. 5B shows an example of the output waveform 25 of the one-dimensional CCD 39, in which the horizontal axis represents time,
The vertical axis is the voltage. By adjusting the arrangement of the dispersing prism 9 and the one-dimensional CCD 39, a necessary wavelength range λ ₁ ≦ λ ≦ λ ₂
The other light is not incident on the one-dimensional CCD 39. The same applies to the above embodiment, but the number of elements of the one-dimensional CCD 39 should be at least 256 bits for 256 levels in accordance with the degree of multi-level. In this case, if spatial sampling is performed at one wavelength, that is, one level Nbit with a margin, the accuracy can be further improved. However, a resolution exceeding the resolution determined by the dispersion prism 9 and the sensor lens 10 cannot be obtained. In this way, the output waveform 25 has a one-dimensional CCD 39
The selected spectral distribution appears within the exposure time texp. Since the interference fringe shown in FIG. 3 exists at a wavelength for canceling the recorded phase difference, a pulse corresponding to the interference fringe is generated. FIG. 5 (c) shows a pulse waveform 26 representing the position of the wavelength corresponding to the interference fringe obtained from the output waveform of FIG. 5 (b). Indicates multi-valued information. Therefore, multi-valued information can be reproduced by measuring the pulse width.

In this embodiment, the light spot on the medium becomes large because the spatial coherence and the temporal coherence of the light source are usually worse than those in the above embodiment. Therefore, the spatial resolution may be reduced and the visibility of interference fringes may be degraded. However, since it is not necessary to sweep the wavelength of the light source, the configuration of the apparatus can be greatly simplified.

In the above embodiment, the dispersion optical system is exemplified by the dispersion prism, the sensor lens, and the one-dimensional CCD, but is not limited to this. For example, a grating may be used instead of the dispersing prism, and in that case, a phase type grating or a reflection type grating may be used so as to improve a certain order of diffraction efficiency. In addition, by providing the dispersing prism itself with imaging performance, the device can be simplified and downsized, and a concave grating, a grating lens, a hologram, or the like can be employed. Although a one-dimensional CCD has been described as an example of the sensor, the present invention is not limited to this. For example, an array of divided photodiodes or a two-dimensional sensor array may be used. Although the recording medium is of a reflection type in the embodiment, it may be of a transmission type.

[Effects of the Invention] As described above, according to the present invention, the reflected light from the recording medium is dispersed by the wavelength dispersion element, and the dispersed light is received by the array-shaped sensor. There is an effect that information can be reproduced without being affected by fluctuations. That is, the wavelength of the light beam for reproduction fluctuates and is unstable,
Even if there is a fluctuation such as a non-linear undulation or a parallel shift, the wavelength on the array-like sensor does not change, and a signal without jitter can be obtained. Therefore, there is an effect that not only a high SNR and a high multi-level degree can be obtained, but also information can be reproduced with high reliability irrespective of the fluctuation of the wavelength of the reproduction light beam.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an information reproducing apparatus according to the present invention, FIG. 2 is a sectional view showing a recording medium used in the present invention, and FIG. 3 is a characteristic showing an optical multiple interference effect of the recording medium. FIG. 4 is a time chart showing the information reproducing operation of the embodiment, and FIG. 5 is a time chart showing the information reproducing operation of another embodiment. 1: Recording medium 2: Semiconductor laser for recording 3, 5: Collimator lens 4: Semiconductor laser for reproduction 6, 7: Beam splitter 8: Pickup lens 9: Dispersion prism, 10: Sensor lens 11a, 11b: Substrate, 12a , 12b: first reflection layer 13a, 13b: medium layer, 14a, 14b: second reflection layer 15: adhesive layer 31: recording laser drive circuit 32: modulation circuit 33: clock signal generation circuit 34: reproduction laser drive circuit 35: Peak detection circuit 36: Clock circuit, 37: Information reproduction circuit 39: One-dimensional CCD

(72) Inventor Eiji Yamaguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Susumu Matsumura 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (1)

(57) [Claims] 1. A first and a second reflective layer arranged in parallel with each other at a predetermined interval so that light reflected by each of them causes multiple interference. Irradiating an optical information recording medium comprising a medium layer on which information is recorded as a change in rate with a reproducing light beam whose wavelength changes, and detecting a wavelength causing multiple interference from reflected light or transmitted light from the medium. In an apparatus for determining recorded information, a wavelength dispersion element for dispersing the wavelength of reflected light or transmitted light from the medium is provided, and the light dispersed by the dispersion element is opposed to the dispersion direction of the dispersion element. An information reproducing apparatus, comprising an array sensor for detecting a spectrum and detecting a wavelength corresponding to recorded information.