FR2494476A1 - DEVICE FOR RECORDING INFORMATION ON AN OPTICALLY EXPLORABLE DISK-SHAPED INFORMATION CARRIER - Google Patents

Abstract

INFORMATION CARRIER 1 FOR THE STORAGE OF OPTICALLY DETECTABLE INFORMATION, IN WHICH A PERIODIC TRACK MODULATION HAS BEEN ESTABLISHED, THE PERIOD CORRESPONDING TO A FREQUENCY WITH THE POWER SPECTRUM OF THE NUMERICALLY CODED INFORMATION TO BE RECORDED AT LEAST A ZERO POINT TO GENERATE, DURING RECORDING AND / OR READING, A BIT FREQUENCY SYNCHRONIZATION SIGNAL, AND THIS MODULATION PRESENTING FROM TRACK TO TRACK, IN THE RADIAL DIRECTION, A SHIFT PHASE IN ORDER TO DETECT AN ACCIDENTAL PASSAGE OF A TRACK ON A NEARBY TRACK. APPLICATION: RECORDING AND / OR DIGITAL READING DEVICES.

Description

"Device for recording information on a carrier

  of information in disc form explorable by

optical channel ".

  The invention relates to a device for recording

  information about a carrier of information 1

  a disk-like substrate 5 with a layer 6.

  radiation-sensitive information with regions

  information 9 rows in a configuration of pistons

your spirals or concentric.

  A carrier of information of the type described in the pre-

  ambule, as well as a device for the registration of in-

  training on such a carrier and / or reading the information

  such a carrier are known from the French patent application No. 2,420,182 filed by the applicant,

  said useful information regions alternating with

  synchronization information that contains the

  draws from the following useful information region. When using such a carrier of information, the generation of the synchronization information is complicated and sometimes

  little trustworthy. During the reading of the informa-

  it is possible but complicated to generate a synchronization signal from the recorded useful signal and

  information signals recorded in the regions of

  synchronization training. When registering information

  tion in the ad hoc regions, the generation of

  synchronization data is even more complicated, since in this case it is only possible to use the information recorded in the synchronization information regions, whereas it is then possible to use a generator a synchronization signal which, during the reading of the information of the synchronization information regions, is made to operate in synchronism,

  with a phase locked loop, with the

  training recorded in the syn-

  nization. In addition to the complication mentioned above

  This has the further disadvantage that at the beginning of each synchronization information region, the operation of said phase-locked loop must again take place in synchronism and that the synchronous pace with the movement of the information carrier for recording useful information in the regions ad

  hoc is not reliable; it follows that each region of in-

  useful training is not taken advantage of until its

  given that it is necessary to reserve

  pace to compensate for the effects of speed fluctuations

  information carrier and the registrar

  information as a result of the variation in

  operating frequency of the information signal generator

  mation. That is why it is recommended in the said application

  to provide for additional regions of information

  synchronization in said useful information regions, which, while reducing the problems in question, does not eliminate them however and means a reduction in the bearer information storage capacity. In the case of carriers of information in which synchronization information regions are not used between the useful information regions, which for example is the case of carriers of information used for the recording of signaling signals. coded digital audio frequency, the generation of synchronization signals is even more

complicated.

  In the French patent application No. 81 00 148 of January 1981 also filed by the applicant, it was proposed as a solution to this problem to provide the wearer

  prior to periodic track modulation.

  to simplify the generation of the sync signal.

  nization. This earlier patent application was incorpo-

  in the present application as figures 1-13 with descrip-

  tion. In the device? of the kind described in the preamble there is yet another problem that plays a role. When recording digital information, the reliability of the recorded information must be very high. For this purpose

  several methods have already been proposed to correct

  information signal. An annoying defect, which annihilates all the measures taken to increase this reliability, occurs if during the recording, the laser beam accidentally deviates from the track by "scratching" the already inscribed information. If this occurs, this recording stripe will extend over the information contained in the neighboring sectors under the effect of the inertia of a radial tracking system applied (see for this purpose the United States patent of America NI 4,223,187); what

  causes damage to a large amount of information

  contained in the same information region; even from

  these methods of correction do not make it possible to

to this situation.

  A possible solution to this problem is to

  the signal from the radial tracking system and, if this is

  gnal exceeds set limits, stop recording

  and to re-enter information in another region of information

  mation. In this respect, it should be noted that the unjustified judgment of

  registration gives rise to regions of

  reinstated and that the unjustified failure of the

  registration leads to poor reliability of information

  recorded. In this respect, the above method of monitoring

  this of the radial tracking signal is not entirely

  satisfactory that it derives its information from a

  signal spectrum whose frequency is relatively low and is therefore quite sensitive to

  non-fatal disturbances, such as variations in

  efficient reflection of the disk and local defects of the disk, disturbances often giving rise, it is true, to

  a defect in pursuit, which is not, however,

  sez big to deflect the beam to another track

  so that there is a stop of the recording process

  really, a decision which, basically, would not be necessary.

  Now, the object of the invention is to provide a device

  which, while belonging to the kind mentioned in the preamble

  bule, is not affected by the said disadvantages

his job.

  The device according to the invention is remarkable in that, for the reading of a recording wearer

  in which the information regions 9 present a

  a periodic track whose period corresponds to a frequency whose power spectrum of the digitally encoded information to be recorded or recorded has at least substantially zero point to generate when

  recording and / or reading a signal of syn-

  bit rate timing for synchronization of

  digitally coded information, whereas this modula-

  periodical track was established in the runway.

  that points of this track modulation, at one

  mutually equal, extend from one track to the other along a line A deviating from the radial direction B, so that in a radial direction, the modulation of each track, depending on the angle tangential of the disk-shaped information carrier, is always out of phase with respect to the modulation of the contiguous track in this radial direction, and that in the other radial direction, it is always out of phase with respect to the modulation of the contiguous track in the other radial direction, it comprises firstly a band filter 28, 29 passing to filter in this detected radiation a signal whose frequency is determined by the period of the periodic track modulation and which, as

  synchronization signal, is supplied to the recording circuit.

  to synchronize the useful information signal to be recorded in an invariable phase ratio with the periodic track modulation, so that the information

  to be recorded is recorded in an internal phase relationship

  variable with said periodic track modulation and

  apart from a phase comparison circuit 29, 75 for monitoring the momentary phase of said filtered signal in

  the goal of generating a stop signal of the recording process.

  when the phase differs to a predetermined extent

  of a phase signal varying monotonically

  born. The invention is based on the idea that, in the system recommended by said prior patent application, system in which it is possible to previously elaborate on the carrier of information a frequency which is in synchronism with the bit frequency of the information signal useful for

  to record and who, both during the reading of informa-

  that during the recording of information is de-

  tectable without significant interference with said information signal.

  useful and without loss of storage capacity of

  so that a reliable and synchronous synchronization signal is always available, it is possible by monitoring the phase rate of the periodic track modulation, to generate a signal indicating whether the

  recording beam deviates to an inad-

  said track, since in this case there is detection of

  phase shift of the adjacent runway. This method is less sensitive to low frequency disturbances due to

  that it borrows its information from a high-frequency signal

  accordingly. A preferred embodiment of this device may have the particularity that the phase comparison circuit is interposed in a phase-locked loop,

  this phase comparison circuit receiving said signal fil-

  as well as the signal emitted by an oscillator which is

  sent by the output signal of this phase comparison circuit through a bandwidth filter, the signal

  the output of this phase comparison circuit being

to a window detector.

  This device provided with optical means serving

  ter on the useful information regions a light beam modulated with the information to be recorded as well as to orient an auxiliary beam on the regions of useful information

  located behind the modulated beam for the purpose of reading

  formed by the modulated light beam, may have the additional feature that the auxiliary light source for reading the periodic track modulation may be used for generating the synchronization signal for synchronizing the information recording effected by means of the light beam, as well as for the application of the signal to the circuit

reason of phase.

  The following description, with reference to the accompanying drawings,

  all given as an example, will make clear how

the invention can be realized.

  FIGS. 1a-1c illustrate a possible embodiment of an information carrier with regard to which it is possible to apply the principle according to the invention, FIG. 1a being a plan view of said carrier, FIG. 1b showing on a larger scale part of a track 4 of said carrier, and Figure lc finally representing on an even larger scale a synchronization information region of the track portion shown in Figure lb.

  Figure 2 shows a small portion of the following section

  the plane II-II 'in figure la.

  Figures 3a to 3d are schematic sections long

  of a portion of the track 4, Figure 3a showing this section in the case of a prefabricated disc without information and responding to a known technique, the figure

  3b showing the same section as Figure 3a after the inscription

  tion information in information area 9, the figure

  3c showing such a cut in the case of a prefabricated disk

  qué non equipped with information and responding to the invention and finally figure 3d showing the same section as Figure 3c after

  the registration of digital information.

  Figure 3e shows schematically the signal obtained during the reading of the information of the section of the track

  4 shown in section in Figure 3d.

  Figure 3f is a schematic plan view of a

  section of track 4 after the nu-

  in a way other than that illustrated in the figures

3b and 3d.

  Figure 4 shows the power spectra

  to three digital information signal modulations.

  Figure 5 illustrates the modulations in question.

  Figure 6 shows schematically a provision of

  for the manufacture of an information carrier according to

  FIG. 3c, schematically a device for the insertion of

  information in the bearer in question, and in c a device for reading information from an information carrier.

  Figure 7 illustrates several examples of a modula-

  periodic track according to the invention.

  Figure 8 shows in principle a part of

  reading a device for reading a digital signal

  that of a carrier of information according to the invention and / or

  for recording a digital signal on such a por-

  whereas in B, the figure 8 shows the spectrum of

  frequency of the signal detected by the detector 27 of FIG.

re 8a.

  FIG. 9 shows at a device corresponding to FIG. 8a and also suitable for generating a radial tracking signal, while in b, FIG. 9 shows the frequency spectrum of the signal detected by FIG.

detector 27.

  FIG. 10 illustrates a variant of the response device

in figure 9a.

  FIG. 11 shows a device according to FIG. 9a, designed for a radially modulated information carrier having substantially the same period as the periodic track modulation, whereas in b, said FIG. 11 shows the spectrum of signal frequency detected by the

detector 27 of FIG.

  FIG. 12 represents a device designed for a carrier with information of radial track modulation having

  the same period as the periodic track modulation.

  FIG. 13 represents a part of a device for recording an information signal on an information carrier according to the invention for obtaining a synchronization signal during the recording by

  the use of an auxiliary laser beam.

  Figure 14 shows the periodic track modulation

  that according to Figure 7 and modified according to the invention.

  FIG. 15 shows an information carrier provided with

  a periodic track modulation according to Figure 14.

  FIG. 16 shows a device for recording

  information about a carrier of information

  a periodic track modulation according to the invention.

  Figures 17 and 18 show some diagrams for illustrating the operation of the device according to

Figure 16. -

  Figure 1 illustrates in a, b and c a mode of

  possible carrier of information that can be applied to

  quer the principle according to the invention; FIG. 1a is a plan view of said carrier, FIG. 1b shows on a larger scale part of a track 4 of said carrier, and the FIG.

  lc finally shows on a larger scale a region of

  synchronizing formation of said track portion. The

  information carrier 1 is provided with a spiral track 4.

  This is subdivided into a large number of sectors 7, for example 128 sectors per carrier revolution. Each sector 7 has a useful information region 9 serving

  to the recording of a useful digital coded information-

  as well as a synchronization information region 8.

  To ensure that the digital information is recorded in an exactly defined track, the track 4 acts as a servopist. For this purpose, the information regions 9 of the sectors 7 have a structure of amplitude as shown in FIG. 2. This FIG. 2 shows a small portion of the section along the plane II-II of FIG. several adjacent sections of track, including information regions, the servopist 4. The direction of the servopists 4 is perpendicular to the plane of the drawing. These servopists 4, in particular the information regions 9, are developed in the form of a groove in the substrate 5. As a result, for the digital information inscription on the carrier, it is possible to precisely coincide with the

  servopist 4 a radiation beam oriented on the door

  in other words to adjust the spot position of said beam in the radial direction with a servo system that takes advantage of the light reflected by the wearer. Measurement

  of the radial position of the radiation spot on the por-

  may correspond to the measurement practiced in the

  which are also provided for in the case of

  optical training provided with a video signal, and as described inter alia in the publication "I.E.E.E. Transactions on

  consumer electronics "page 307, published in November 1976.

  To enable the recording of digital information

  that the information carrier body is provided with a layer of material 6. which, being exposed to adequate radiation,

  undergoes a change that can be detected optically.

  In fact, it would be sufficient for only the information sections 9 of the sectors to be provided with such a layer. From the technical point of view of manufacture, however, it is simpler to provide such a layer with the entire surface of the information carrier. Said layer 6 may be a thin metal layer, for example in tellurium. Under the influence of laser radiation of sufficient intensity, this metal layer can be locally melted, so that locally said layer 6 acquires another reflection coefficient and that in the case where a beam of reading radiation process

  reading information from a runway equipped with informa-

  In this way, there is a modulation of

  reflected beam, this modulation

  corresponding to the recorded information.

  The layer 6 may also be formed by two layers of material chemically reacting to the influence of incident radiation, an aluminum layer for example being developed on an iron layer. At the point where such a beam of energy-rich radiation strikes the plate, it forms

  the substance Fe A16 which reflects light in a medio manner.

  cre. The same effect occurs in the case of a layer in

  bismuth developed on a tellurium layer, an opportunity for

  what is the substance Bi 2Te3- It is also possible to

  to use a single layer of tellurium.

  Because using the servopist shaped like

  a groove in the substrate 5, the beam spot of

  The registration procedure coincides precisely with this servo, particularly when exploring a region.

  information, the digital information that modulates the

  The inscription radiation level is precisely entered in the information region coinciding with this track.

  On reading the above, we see that the por-

  of information intended for the person using them and in which information is not yet recorded in the bearer's useful information regions, include a throat structure in these information regions to

  inside the sectors. In addition, such a carrier of information

  in each sector, a region of information

  synchronization 8 made in the form of optical detectable relief structure. FIG. 1b shows on a larger scale part of a track 4, this part making it possible to observe the succession of several useful information regions 9 and information regions.

  8. In this case, the synchronization regions

  8 form a relief structure, consisting of a

  succession of troughs alternating with intermediate regions

  diaries. The depth of the valleys in this structure of the synchronization information region is greater than the depth of the servopist in the information region

  9. According to general optical rules, this depth

  Hollow valence is chosen, depending on the shape of these hollows in the selected reading system, so as to give rise to the optimum reading of the information represented by the structure. If we start from a reading system in which the radiation beam reflected by the information carrier is detected by a single photodetector, the depth can be chosen equal to? '/ 4, the reference t

  indicating the wavelength of the beam of radiation

  Lisa. When in this case the depth of the servopist in the information region 9 is chosen to be equal to> / 8 or less, this servopist hardly influences the amount of

  light that detects the detector.

  To indicate in more detail the conception of the

  In the same way, in order to simplify this figure, the information layer 6 has not yet been drawn again and again to such a synchronization information region in FIG. been represented. Such synchronization information region 8 has two parts, namely an indication part 10 and an address part 11. In

  this part of address 11, we have stored all the information

  necessary to control the registration process.

  When writing digital information, it is converted into a series of bits arranged in correspondence to words. This part of the address contains information about the distribution of the words, so that during the registration is defined the positioning of the bit words and that during the reading is performed the proper decoding of these words. In addition, said address portion 11 contains

  information about the track number of the circumference

  related track. Following a technique of modula-

  suitable for the recording medium, this information is in the form of a structure

  in relief. Because of this, the carrier of information

  already has, in addition to the servopist practiced as a groove in the information regions 9, also all the information which is indispensable for the positioning of the information as a series of bits arranged in words in these information regions, it is possible to impose less stringent requirements on the registration and reading device used by the person. Since in addition this completely elaborated information is in the form of a relief structure in the information carrier, the latter is suitable for mass production for which it is possible to take advantage of the usual molding techniques.

  Figure 3 shows in Aa d schematically and in a sequence

  Servomotor 4, a part of a tele servopist 4

  in the region of informatlon of the establishment 8 and one of the rules of the in-

  useful training 9; FIG. 3a shows such a section in the case of a prefabricated non-information disc answering a known technique, FIG. 3b showing said section after the digital information entry 14 in the information region 9, FIG. 3c showing such a section in the case of a prefabricated disk not provided

  information in which it is prepared, in accordance with the

  vention, synchronization information, while Figure 3d finally shows the section according to Figure 3c after the information entry 14 in the useful information region 9. Figure 3e schematically illustrates the signal obtained during the reading the information section of the track 4, shown in section in Figure 3b while Figure 3d is a schematic plan view of a section of the track 4 after the registration of digital information in a way other than that illustrated in Figures 3b and

3d.

  The prefabricated disk is provided with useservogorge (servo

  track) 4 made in a substrate 5 for example using a laser beam. By modulating the intensity of the laser beam, it is then possible to enter in the synchronization region 8 information formed by a raised structure comprising "wells". Then, the assembly and, to facilitate the operation , also the part of the wearer

  1 outside the gorges (tracks) 4, can

  to be coated with the reflective information layer 6. In this prefabricated carrier, the inscription in the region

  useful information 9 can take place because, for example,

  using a laser beam, "holes" 14 are

  practiced in the reflective information layer 6.

  Such carrier provided with information is illustrated in Figure 3b. When registering the information, ie when

  the development of the holes 14, as well as during the reading

  re of this information for example using a laser beam, it is important that the recording or reproduction of the information is synchronized using a signal ad

  on which the synchronization information regions

  8 may contain information. In order to

  have a suitable synchronization signal

  broken during the registration of information in the region 9 and therefore also during the reading of the information they contain, the servopist 4 is, in accordance with

  the invention, provided with a structure which gives rise to a

  of the light reflected by the carrier of information

while following the servopist 4 during the read-

  ture or registration of information.

  However, the structure thus developed must not disturb the reading of the information. That this belongs to the possibilities is explained with reference to FIGS. 4 and 5, FIG. 4 showing the power spectra of three possible modulations of binary information signal and FIG. 5 diagrammatically illustrating the modulations in question. In FIG. 5, there is illustrated at a modulation generally known as "biphase" modulation. On this occasion, the digital signal presented is converted into a binary signal which, in the case where said digital signal has the logic level "one" is positive during the time interval T / 2 but negative during the time interval subscribed. -

  At T / 2, the reference T indicates the bit duration of the digital signal presented. A presented digital signal having the logical zero level exactly provides the binary signal

  opposite, that is to say a signal which is negative during the

  time T / 2 and positive during the subsequent time interval T / 2. This modulation technique provides

  a binary signal whose frequency spectrum of distribution

  energy corresponds to curve a in Figure 4.

  In this case, the frequency fo corresponds to 1 / T.

  Figure 5 illustrates in b a known modulation known as "Miller modulation". The binary signal generated by practicing this modulation involves a change

  halfway between a logic level "one" of the digital signal

  presented and near the junction of two logical levels

  consecutives "zero". The frequency spectrum of the binary signal obtained using this modulation technique

  corresponds to the curve b in FIG.

  Finally, FIG. 5 illustrates in c a modulation known under the name of "quadriphase modulation" according to which the series of bits presented of the digital signal is firstly subdivided into consecutive groups of two bits (called dibits). From each group of two bits with duration 2T,

  it is deduced a binary signal whose appearance in a first

  first time interval T corresponds to that of the two original bits, whereas the pace is reversed in the subsequent time interval T. The possible bit combinations 11, 00, 01 and 10 are therefore converted into combinations of bits 1100, 0011, 0110 and 1001. The binary signal obtained using this modulation technique offers a frequency spectrum as shown by the curve

in Figure 4.

  Looking at Figure 4, we can see

  easily that these modulation techniques have as parti-

  commonality that the resulting binary signal does not have strong components at relatively

  low, for example frequencies below 0.2 fo.

  This particularity is especially interesting when

  use of a carrier of optical information and recording and playback systems used in combination with such a carrier. As already mentioned above, we use

  in the case of this kind of systems, both a servo

  ge to precisely focus the spot on the

  information carrier, that a servo setting that adjusts the posi-

  the spot and makes it coincide precisely with the information track. Since the adjustment signals required for these servo-adjustments are derived from a beam of radiation reflected by the information carrier and also modulated by the relief structure of the synchronization information region, it is very

  important that the frequency spectrum of the binary signal

  shopped in the address part does not include any form

  your components in the frequency band used for

  the adjustment signals. Figure 4 shows that the ban-

  Frequencies below about 0.2 are well suited for this kind of control signals. The adjustment signals for said servosystems may, for example, extend to a maximum frequency of 15 kHz. If, for example, the frequency f 0 = 500 kHz is chosen, it can be seen from FIG. 5 that the binary signals a, b, or c do not have a frequency of 15 kHz. at a lower frequency, than

  very low amplitude components.

  Figure 4 also shows that

  the frequency 2 fo and when using the method of mo-

  Quadruple zero-point modulation occurs in the spectrum also at the fo frequency. It is therefore possible

  to provide the information bearer with a structure of information

  frequency synchronization without having to worry about interference with the information signal. Zero points at frequency 2 fo also occur when

  practice other modulation methods.

  When using quad-phase modulation as well as some other modulations, the frequency fo is appropriate

  very well for this purpose, this frequency corresponding to the frequency

  quence of bit 1 / T, so that this modulation quadriphase '

  becomes very attractive. Also in the case of modula-

  In some cases, it is possible to develop a structure with a frequency fo, given that at i6

  this frequency fo, the components of the spectrum are relative-

  weak. Moreover, it is theoretically possible to

  to the structure a modulation which corresponds to a frequency

  more than 2%, which however is not generally

  not practical in practice. Indeed, with regard to

  a maximum information density on the wearer, the dimensions

  tions of the wells 13 and 14 and which, for a determined rotational speed of the disc 1, correspond to n at a duration of bit 1/2 T, will be chosen as close

  as much as possible of the resolving power of the recording system

  used, so that a surface structure corresponding to frequencies greater than 2

  hardly detectable. Using special modulation techniques

  In addition, it is possible to obtain zero points in the power spectra at frequencies other than

  the frequency fo or the frequency 2 fo, for example the frequency

  quence 1/2 fo. Moreover, reference is made here to the previously unpublished patent application filed by the same Applicant under No. 8,006,165 and advocating a

  improved modulation technique.

  Figure 3c is a section of an information carrier

  according to the invention, which section corresponds to the section se-

  3a and o the surface of said carrier is provided with a relief structure at height at least at the location

  runway 4. A possibility to achieve such a structure

  ture is the modulation of laser radiation using -

  which is the formation of the synchronization information region 8 and the groove 4 of the useful information region 9. In the example considered, this is achieved in the synchronization region 8 only between the wells 13 due to limit-the intensity of the radiation of the laser beam. In principle, however, also the substance of

  well may be provided with a relief structure.

  As can be seen in FIG. 3d, it is possible, in the case of the disk according to the invention, also to register

  information about making holes 14 in the

  reflective che 9 which covers the relief structure.

  Figure 3 shows by way of example the appearance of a

  obtained during the exploration of a relief structure

  according to Figure 3d. This signal has minima

  right of the wells or holes 13 and 14, as well as an amplitude modulation which corresponds to the modulation structure

  (d in FIG. 3c) and having the frequency fo on the maximum

  my. The background with modulation structure of the holes 14

  barely at the signal, given that as a consequence of

  the distance of the reflective layer 6, this reflective background

  scarcely shines light. In this regard, it should be noted that it is also possible for example to develop on a reflective substrate 5 a non-reflective layer 6, locally remote. Therefore, the frequency demodulation fo will be read exactly as needed at the locations of the holes 14 o

  DA non-reflective layer is far away.

  In FIGS. 3a to 3d, the wells 13 and the recesses 14 are drawn as holes and wells in one piece, and therefore in the case where it concerns more than a single bit, recesses and holes form a oblong groove whose length corresponds to several bits that succeed one another. However, it is also possible to develop each bit as wells or separate holes. Figure 3f illustrates this and

  shows a track 4 whose structure of modulation of information

  synchronization is indicated by hatching

  different. In the synchronization information area

  8, wells 13 are in this case elaborated for example on the maxima and minima of the structure, and are coated

  also of the reflective layer 6, which is symbolic

  The information holes 14 can be formed in the useful information region 8 in the reflective layer 6 on the information holes 8.

  maxima and minima of the synchronization information structure

  tion. As a variant, it is possible, as shown in the useful information region 9, in FIG. 3f, to develop holes 14 'on the zero points of the information structure. The location of the wells and holes 13, 14 is in this respect non-essential since the phase relationship with the information structure is invariable and known. Also

  the shape of the information structure is not important.

  Thus instead of the crenellated form shown in Figure 3, the structure can very well have a sinusoidal shape which is perfectly possible during the fabrication using a modulated laser beam . The only

  important point is that the information structure of syn-

  chronization has a suitably de-

  tectable at frequency fo or 2 fo, and does not have any

  your components in the spectrum of the information signal

  useful digital technology that is registered or to be registered, which is generally

  the case when the information structure d has a fundamental frequency fo or 2 fo having only high order harmonics, the first harmonic following tart

  then 2 fo or 4 fo which, as shown in Figure 4, is

  kills outside the relevant part of the spectrum of

useful training.

  To illustrate the embodiment of the structures according to FIG. 3, FIG. 6 diagrammatically represents a device for the manufacture of an information carrier according to FIG. 3c, b a device for the registration of information in the carrier according to FIG. FIG. 3c, and finally in c a device for reading the information of a

such carrier provided with information.

  In the device according to FIG. 6a, the

  The beam 16 emitted by a laser 15 is projected onto the rotary disc 1, for example through an intensity modulator 57, a mirror 17 and a focusing optical system 18, to form on the disc the groove (track). spiral -30 4 (Figure 1). The operation of the laser 15 is controlled

  by a circuit 20 to give rise to a pulsating radiation

  the laser 15 to make the wells 13 (FIG. 3)

  in the synchronization information region 8.-The function

  modulator 57 is controlled by a source 19 at frequency fo (or 2 fo) to realize in the groove 4 a

  synchronization information modulation structure.

  As a variant, it is also possible to modulate the radiation, even emitted by the laser 15. The disk 1 is

  set in motion by a motor 21 whose speed is

  mandated by a servo setting including for example a gen-

  tachometer 22, a reference source for

  24 and a servo amplifier 23.

  Useful information regions 8 on the correct location in the track 4, and possibly to realize the fo modulation in a correct tangential distribution on the disk, the control circuit 20 and possibly the source 19 at frequency fo can be coupled to said servo-adjustment . In addition, the circuit 20 is controlled by the source 19 in order to ensure a correct phase relationship between the synchronization wells 13 and the synchronization modulation structure. After this process, disk 1 can be

provided with layer 6.

  FIG. 6b schematically represents a device for providing the prefabricated disk 6 with information while

  simultaneously reading the information modulation structure

  synchronization. The device in question comprises the rotary disc 1 and. a laser 15 whose beam 16 is projected onto this disk 1 through a semipermeable mirror 17 and a focusing optical system 18. With the aid of a cell 27, which is for example a photodiode, a reflected beam 30 is measured and converted into an electrical signal in which the bandpass filter 28 then isolates the frequency component fo (or 2 fo) from the synchronization modulation structure elaborated especially in the track 4. Optionally, this signal can still be provided a phase locked loop 29 which improves the quality of the filtering, accentuates the constancy of the signal

  synchronization and compensates for possible signal

  short periods. Exit 31 then makes available

  the synchronization signal. The useful information can be written by pulse modulating the laser beam 16, by placing a modulator directly in the beam or, as shown in FIG. 6b, by virtue of

  modulate the very radiation of the laser 15 by means of a cir-

  firing 25, whose information is supplied through an input 26 and which is synchronized with the signal available on the output 31. In the reflected beam 60, it is read, through the photosensitive member 27 and a reading circuit 30,

  information of the synchronization sections, this information

  The operation of this read circuit 30 can also be synchronized.

  using the signal available on output 31. This

  training can be used to also synchronize the operation of the circuit 25 as well as to search on

  the disc the exact position. This information is used

  also in a servo-adjustment which is not shown in FIG. 6b and which serves to bring the optical system 18 and the mirror 17 into the correct radial position to enter the information in the desired section of the track 4 as well as

  to adjust the drive of the disc 1, which on the

  Figure 6b is symbolized by the dashed line 62.

  In addition, the device may be provided with a track tracking circuit 33 which deduces a signal tracking signal from the detector 27 to maintain the beam 16 oriented on the track 4 by controlling the angle formed by the mirror 17 relative to the beam 16, which in FIG. 6b is symbolized by the dashed line 61. Such a tracking circuit is described for example in FIG.

  U.S. Patent No. 4,223,187.

  FIG. 6c represents a device for reading the information of a disk 1, provided with information, said device being in practice also combined with the device according to FIG. 6b. As previously, the device comprises a laser 15 whose beam 16 is projected onto the disk 1 through the mirror 17 and the optical system 18. The reflected beam 60 is detected by a photodiode 27 and the electrical signal obtained in this way is brought to pass through a band filter 28 pass-through fo and a phase-locked loop 29 tuned to the frequency fo, so that the output 31 provides the timing signal fo (or 2 fo). With the aid of the reading circuit 33, we decode

  out of the electrical signal provided by photodiode 17 the

  training recorded in the disc, so that one

  34 of the reading circuit 33 provides information to the

  digital information as well as the information contained

  synchronization information regions 8. Synchronization

  The operation of this read circuit 33 is performed with the signal available on the output 31. Moreover,

  with the help of a tracking circuit 33, it is possible to

  from the beam detected by the photodiode 27 a tracking signal for the purpose of controlling the mirror 27 so that the beam 16 correctly follows the track 4. The motor 21 setting the disk in motion can be

  incorporated into a servo setting which, for example, carries a genera-

  tachometer 22, a reference source 24 and a servoamplifier 23 to adjust the speed of rotation,

  said servo-adjustment being able to be coupled to the reading circuit

  30. In addition, the device comprises a mechanism 35 for radially moving the optical system 17 with the mirror 17 and the detector 27, this system being indicated by 36 in FIG. 6c, so that, at choice, the reading of a part

  of the disk can take place under the control of

  training provided at an input 37 of the mechanism 35, likewise

  that by the information which, at the exit 32 of the circuit of

  30, is obtained from the information regions of

synchronization.

  The synchronization information structure that is developed or developed in runway 4 may affect

  many shapes. Figure 7 illustrates in this respect several

  some examples. FIG. 7a schematically shows a track 4 in which the synchronization information is produced in the form of pitch variation (depth) indicated symbolically by interrupted hatching,

  information being developed for example using a

  laser intensity control of the registering laser intensity

  the information in lane 4; for its part, Figure 7b shows

  Track 4 in which the synchronization information is produced as a variation of the width of the

  Track 4, for example by modulating the focus

  laser beam, in which purpose for example the objective 18 (Figure 6a) is adjustable with the device 51 (Figure 6a); it is also possible to combine a variation of width and a variation of depth, which

  In practice, this will often be the case in the presence of

  dimming of beam intensity or focus

  of laser. Figure 7c shows track 4 in which the

  synchronization training is developed in the form of

  radiating the position of runway 4, aim in the

  what for example the angle that forms the mirror 17 (Figure 6c)

  relative to the beam 16 can be modulated with the aid of

  positive 58. In addition, all the variations specified below

  have a length of period Lo equal to Lo =, the reference

  V indicates the tangential velocity of the disk 1 to said location while the reference f indicates the frequency of the

  desired synchronization signal, this frequency f corresponds to

  laying at a zero point in the frequency spectrum of the useful information to be recorded, for example the frequency

  fo in case of quadriphase modulation (Figures 4c and 5c).

  One of the possibilities for obtaining a signal of

  tracking is to impose an oscillation (vobula-

  radially to the groove track, for example by

  adequate control of the mirror 17 (Figure 6a); that is

  to impose on the track a radial displacement varying for example sinusoldally, this displacement on the disk having

  a wavelength which, when reproducing information,

  of this carrier at his normal speed, gives rise to a

  light intensity variation by the detector 27 (FIG.

  6), the frequency of this variation in light intensity

  outside the spectrum of useful information and being, for example, lower than the frequency

  0.2 fo (FIG. 4), as described, for example, in said patent

  United States of America N04 223 187.

  For example by synchronous detection, it is possible

  to deduce from this signal component a measure of the

  the center of the detector in relation to the center of the track 4. Such a radial oscillation can be combined

  with a synchronization information modulation structure

  tion, for example with the modulation structure shown in Figure 7a, such a combination being illustrated in Figure 7d. A particular combination is obtained when on the disk the oscillation acquires a wavelength which is equal to that of the synchronization information modulation structure with a phase relationship

  invariable, which makes synchronous detection superfluous.

  Figure 7e illustrates such a structure, and on this

  FIG. 7, a depth modulation structure (indi-

  alternatively shaded regions and not) in lane 4 is combined with a displaced radial position variation of 900 (i.e., one quarter of the period of this structure) relative to the structure. depth modulation, this position variation can be generated with the device according to Figure 6a by modulating the angle between the mirror 17 and the beam 16 with the aid of the device 58. When furthermore the modulation structure of depth is chosen so

  the "shallow" parts of this modulation

  together with the surface of the disk-shaped information carrier 1, there remains in the radial direction of the servo-motor 4 still a succession of asymmetric wells between which

  tangential distances equal to that

  Lo. Figure 7f illustrates an example of such a pis-

you.

  Figure 8a illustrates the principle of the reading part

  of a device for recording information

  useful information in a carrier of information consistent with the

  the reproduction and reproduction of this information

  holds this carrier, Figure 8b showing the frequency spectrum

  the signal I detected by the detector 27. The

  The signal provided by the detector 27 has the spectrum shown in FIG. 8b, in this case the spectrum of a quad-phase modulated signal Sd and a synchronization signal. Sc. This signal Sc is isolated by means of a bandwidth filter 28 which is preferably followed by a phase-locked loop 29. Said signal Sc can be taken from the output 31. The digital signal Sd, namely the signal recorded in the synchronization information region 8 and being, at the heart of the information reading, the signal

  registered in the synchronization information system 8 and that recorded

  in the infonDation rUt utie Ba and d Stcted using a = int of the-

  3), the function is synchronized by the signal Sc. The useful read signal of the mite appears on the output 32. In the case of the signal detonator 27, it is still possible to deduce a radial tracking signal. During the recording of information in useful information regions 9, the circuit 30 detects only the information recorded in the synchronization regions 8, this information then being supplied, together with the signal Sc, to the circuit 25 for the purpose of

  modulate the beam of a recording laser 15.

  Using a low frequency radial oscillation to obtain a radial tracking signal, the device according to FIG. 9a can be used, FIG. 9b showing the frequency spectrum of the signal detected by the

  27. When reading information from a pis-

  4 to radial oscillation, a photodetector 27 can be successfully used which, along a tangential line,

  is divided into two parts a and b. An amplifier of difference

  40 or equivalent means provides the difference

-

  between the signals detected by the parts a and b, while a sum amplifier 41 or an equivalent means

provides the sum of these signals.

  As before, the frequency spectrum (FIG. 9b) comprises the quad-phase modulated signal Sd, lesigal

  of synchronization Sc and the low frequency signal Sw provo-

  by the track oscillation. In the sum signal, this oscillation manifests itself as an amplitude modulation for which the signal Sc acts as a carrier, which in Figure 9b is indicated as the sidebands Sc-W and Sc + W, the amplitude of these lateral bands being equal to zero when the detector 27 exactly follows the center 45 of

  track 4. The filtering of this sum signal in the

  28 provides the signal Sc and, provided that the frequency band of this filter is not too narrow, also said sidebands. The output signal of said filter 28 is supplied to the phase locked loop 29, and an output 31 of this loop 29 becomes the seat of the signal Sc. Said output signal of said filter 28 is supplied together with the signal Sc , also to a demodulator

  synchronized 42. This then provides the modulation Sw.

  From the difference signal of the amplifier 40, with the bandwidth filter 38 and the phase-locked loop 29, the radial oscillation frequency is recovered which, together with the output signal of the demodulator 42, is supplied to a receiver. The output 44 of this detector 43 then becomes the seat of the modulation of the oscillation signal Sw which can be used as a radial tracking signal and represents the spacing relative to the center of the track 4, represented by the mixed lines 45 in Figure 9a. This radial tracking signal can then control the mirror 17, which is symbolically shown by

Figures 6b and 6c.

  From the sum signal available on the output of the amplifier 41, it is recovered then, of the same

  in the device according to Figure 8a, the information

  Track 4. With regard to the registration of

  information, it is possible to take similar measures to those shown for the device according to Figure 8a, which is also the case for

according to Figures 10, 11a and 12.

  FIG. 10 illustrates, with respect to the device according to FIG. 9, a variant allowing a better isolation (filtering) of the signal. In the case envisaged, the detector 27 is divided both along a tangential line and along a radial line, so that four quadrants a, b, c, and d are formed; quadrants a and b on the one hand and c and d

  on the other hand lying on both sides of the line

  while the quadrants have other parts and more

  part are on both sides of the radial line.

  An amplifier 41 or equivalent means determines the sum of the signals generated by the quadrants a, b, c and d, so that the amplifier in question is mainly sensitive to variations in the intensity of the beam reflected by the track 4, therefore sensitive to the useful signal Sd, while an amplifier

  indicator 421 defines the difference between the signals of the quadrants a, b and c, d located on either side of the line

  tangentially, so that this amplifier 42 is parti-

  particularly sensitive to variations of track 4 in di-

  radial rection, therefore to the signal Sw; finally, an amplifier 46 defines the difference between the signals of the quadrants a, c on the one hand and b, d, on the other hand, located on either side of the radial line, so that this amplifier 46 is particularly sensitive to variations of the track in

  tangential direction, therefore to the synchronization signal Sc.

  As in the case of the device according to FIG. 9a, the synchronization signal Sc is recovered in the output signal of the amplifier 46 by means of a band filter.

  28 and a loop 29 phase locked, tan-

  say that with filter 38 and lock loop 39

  phase is recovered the frequency of the oscillation signal

Sw.

The output signal of the filter 28, which signal comprises the oscillation signal Sw as amplitude modulation of the signal Sc, is detected in synchronism with the signal Sc by means of a synchronized detector 42, and provides the signal Sw which, as variation of amplitude, comprises the spacing of the detector 27 with respect to the center 45 of the track 4. This

  signal Sw is detected in synchronism with the output signal.

  of the phase-locked loop 39, i.e. with the oscillation frequencies, using a synchronized detector 43, so that a radial tracking signal

  appears at exit 44. The useful signal is extracted from

  the output signal of the amplifier 41 using the

  reading 30 synchronized by the signal Sc.

  The operation of the devices according to FIGS. 9a and 10 can, with regard to obtaining the signal of

  radial continuation, be explained mathematically as follows.

  The signal I detected by the detector 27 is a synchronization information modulation product of the oscillation modulation and the radial tracking error, which

  (apart from the useful signal) is expressed by the relation

  I = Ar sin (wt) sin (wt) where Ar is a function of the tracking error, ww is the pulse of the oscillation signal Swi Wc is the pulse of the synchronization signal Sc, while t indicates the weather. Synchronous detection with the Sc signal

  provides the term Ar sin (wwt) while the syn-

  subsequent wave with oscillation frequency WW provides the signal Ar. The division of the detector 27 performed only along a radial line to increase the sensitivity

  synchronization signal Sc, can be applied

  analogous for the device according to Figure 8a.

  Figure lla shows a reading part of a

  of useful information contained in it

  a track 4 incorporating a modular structure

  synchronization information and imposed an

  for obtaining a radial tracking signal, the frequency of the oscillation signal Sw being approximately equal to the frequency of the signal Sc. On its side, FIG. 11b shows the frequency spectrum in which the reference Sd represents the useful signal while the reference Sc-w represents the term with a frequency equal to the difference between the frequencies of the signals Sc and Sw, this difference being for example equal to 30 kHz, and said term occurring because the photodiode 27 receives the product of modulation

  oscillation and modulation of synchro-

  nization. Therefore, this term is located in the lower part

  frequency spectrum and is hardly disturbed by the information

  digitalisation. The amplitude of this term constitutes the radial tracking signal. In the case where the generator 45 of the track is followed correctly, the amplitude is equal to zero. There then remains oscillation on the one hand a term with the double of the frequencies of difference, a term which

  is not used, and secondly the oscillation frequency

itself.

  Like the device according to Figure 10, the arrangement

  the subject in question comprises an amplifier 41 in front of

  denote the sum of the signals supplied by the quadrants a, b, c and d of the photodiode 27, the sum signal from which, with the aid of a bandpass filter 48, the term with the said difference frequency is isolated . With the aid of the synchronized detector 43 which receives this difference frequency, this

  term is demodulated, while eventually, through

  low-pass filter 49, the tracking signal ra-

diale appears on exit 44.

  The obtaining of the synchronization signal Sc takes place in the same way as in the case of the device according to the figure, namely because, with the aid of the amplifier 46, the difference between the signals of the two radial quadrants is determined. a, c, and b, d of the photodiode 27, this difference being supplied to the phase-locked loop 29 after filtering by means of the band filter 28. In the same way as in the device according to FIG. the oscillation signal Sw is obtained by taking, with the aid of the amplifier 421, the difference between the signals supplied by the two axial quadrants a, b on the one hand and c, d on the other hand the photodiode 27, and provide this difference to a loop 39 phase locked through a filter

band 38.

  The difference frequency supplied to the detector 43 of the read circuit is obtained by providing a synchronized detector 42 with the synchronization signal Sc obtained in this manner and the oscillation signal Sw, after which the

  signal obtained having said difference frequency is

  nor to the detector 43 through the band filter 47.

  With the aid of the reading circuit 30, the functioning of which

  is synchronized by the signal Sc it is possible to

  get the useful signal that the output signal contains

of the amplifier 41.

  When the frequency of the signal Sw is chosen equal

  at the signal frequency Sc, we clearly see on the

  gure llb that the frequency difference term is directly

  the tracking signal which identifies with a

  DC current. In this case, this tracking signal of

  you can be obtained without synchronous detection.

  A phase difference between the two track modulations is indispensable, since in the case where the two modulations are in phase, it is possible to distinguish only one modulation. An optimal phase difference is found to be equal to 900. Such a structure is illustrated in FIGS. 7e and 7d and the exploration of this structure is possible using the simple circuit according to FIG.

figure 12.

  In the case of the device according to FIG. 12, the photo-

  diode 27 is divided into two radial halves a and b for the optimal detection of the synchronization signal Sc which appears at the output 31 of defining the difference

  between the signals provided by the two halves a, b of

  said difference in the band filter 48, and

  provide it to the phase locked loop 29. Through the

  3 tring the output signal of the amplifier 46 using a

  low-pass filter 49, it appears on a direct output 44

  the radial tracking signal. The digital signal is recovered from the difference signal by means of the read circuit 30 whose operation is synchronized by the signal Sc. As an alternative, it is also possible to

  obtain the wanted signal and the low-level tracking signal.

  frequency from the sum of the signals provided by the

  two detector halves (photodiode).

  Regarding the tracking motion

  when recording useful signals, it is possible to

  to complete the devices according to FIGS. 8a to 12 by a device which modulates a laser beam 16 and whose operation is synchronized by the signal Sc and

  by the signal read in the synchronization information

  tion, as explained with reference to Figure 6b.

  In what precedes, we always left from one

  detector 27 which detects the reflected beam 16 (Figure 6).

  Especially in the presence of high bit rates, it may be disadvantageous to recover during registration

  useful information in the information regions, -

  which, compared to the reading of information,

  takes place with a relative laser beam of radiation-

  intense - the beam timing information

  each time reflected between two impulses of inscription.

  Since, in order to be able to detect the useful signal

  In this case, the device according to FIG. 13, in which the track 4, with respect to the detector 27 moves in the direction of the arrow 63, can be used in this type of case. is explored by a beam 16a recording information and by a tracking beam 16b, these two beams being obtained for example by means of a dividing element

  beam 68, mirrors 17a and 17b and optical systems

  18a and 18b. To modulate the beam 16a, it is possible to

  a modulator in beam 16a. This device

  It carries a photodiode 27 which, for the purpose of reading useful signals and tracking signals, may otherwise fully correspond to the devices according to any of Figs. 8a, 9a, 10, 11a, and 12a. In addition, the device comprises a photodiode 50 for detecting the reflection of the tracking beam 16b which, at a certain

  distance behind the beam 16a, is projected on the track.

  During the reading process as well as during the reading

  information from the synchronization information regions

  8 the fact that the signal detected by the photodiode 27 is supplied to the phase-locked loop 29 through an amplifier, which in order not to complicate the

  figure in question was not shown (for example,

  plifier 46 in Fig. la), and the band filter (e.g. filter 28 in Fig. 11a), gives rise to

  obtaining the synchronization signal Sc. Moreover, in particular

  during registration, one obtains similarly

  from the signal detected by the photodiode 50

  said synchronization signal through a not shown band filter and a phase locked loop 501, which signal is however delayed with respect to the signal

  synchronization obtained through photodiode 27. Through

  to a delay device 51, the output signal is supplied to an output 31. In a phase comparator 52, the phase of the delayed synchronization signal is compared

  to that of the synchronization signal obtained by the photo-

  diode 27, while through the switch 53, said disc

  positive delay 51 is set so that the delayed signal through the delay device 51 and obtained by the photodiode 50 is in phase with the signal obtained by the photodiode 51. During the reading of information of

  in the ad hoc regions 9, the said switching

  53 is closed and the delay device is set so that the synchronization signal of the photodiode

  , delayed by this device 51, is in phase with the

  synchronization signal obtained by photodiode 27. During the registration of useful information in the ad hoc regions

  9, said switch 53 is open, and the sync signal

  is obtained, through photodiode 50, from

  of the reflected auxiliary beam 16b, and delayed by the

  positive 51 of a delay adjusted during the reading of

  information of the synchronization information regions 8.

  The switch 53 is served by the synchronization information signals that the read circuit 30 has read in

region 9.

  It will be noted here that the recording of information

  by the use of unitary wells (which means that

  training is recorded with distinct variations

  tectables in the surface structure of the information carrier

  as shown in Figure 3f) gives rise to a composition

  2of frequency in the spectrum (Figure 4) of the signal being explored. This should not be a disadvantage for the use of a synchronization information modulation structure, since this modulation, in the case where the frequency thereof is equal to 2 f, can be put to good use. during the registration of the information, while in the case where, during the registration, is maintained

  a correct phase relationship with the synchronization signal

  tion, said modulation coincides during the reading with the component 2 fo as a consequence of the use of unitary wells. By practicing quadriphase modulation (figures

  4c and 5c) of the clock signal at frequency equal to fo, la-

  said component with frequency 2 fo is not in said case

embarrassing.

  During recording, as a result of all kinds of disturbances, such as local defects of the disc 1 or shocks, the laser beam 16 sometimes enters information in a given sector 9 (FIG. 16). ) of a track, deviates from the track and crosses a nearby track by superimposing information in the

  sector concerned, while this sector is already

  training or still needs to be filled with information. Although the radial tracking mechanism is able to bring the beam back onto the runway, this situation is untimely because, apart from the incomplete registration in the area to be initially filled with infowmation, the sector (s) must be considered. (s) as being also

  Lost (s). This situation should be avoided. If the

  the water is moving off a track, the recording process must be

  the recording is stopped so that no neighboring tracks

  is damaged. In this case, the sector 9 where the

  was in progress at that time, is considered lost

  and the information will have to be re-entered in a new section.

  9. A reliable method for detecting an over-tracking defect in good time can be followed if the disc 1 described with reference to FIGS. 14 and 15 is used. This disc comprises preformed tracks 4, in which provided synchronization information as described in

  Figures 1 to 13. However, the modulation of syn-

  chroring is planned so that points of equal phase extend along a line A, in a direction that deviates from the radial direction B. As a result, the phase of the structure of

  synchronization contained in track 44 has a different

  positive phase compared to the structure of syn-

  chronization contained in track 4 ', as well as a difference

  negative phase compared to that contained in the

track 4 ".

  When the beam 16 deviates from the track 4, there occurs in the synchronization signal explored, in the direction, a positive or negative phase shift with respect to the monotonic phase variation occurring during the tracking of the track 4 This phase shift is detectable and one can deduce from its amplitude a signal which indicates a

  inadmissible runway error and which makes it possible to stop

  cessation of registration. It is possible to deduce from the polarity of the phase shift of the information on the direction of the - track tracking defect, information which could be used to bring the beam 16 back in time on the track 4, so that the recording process can be resumed

in the following sector 9.

  In FIG. 4, a phase difference L 34 of 900 between the synchronization modulations of the successive tracks has always been used. This is the optimal phase ratio; in fact, a phase difference of 0 0 or 3600 does not give a faulty signal, whereas the information on the direction is lost for a phase difference of 1800. The disk according to FIGS. 14 and 15 has the advantage that during playback, the influence of crosstalk is reduced by

the phase shift.

  Fig. 16 shows an embodiment of a device for recording information on a disk

  according to figures 14 and 15. For the principle of

  reference is made to the description in Figures 1 to 13,

  and FIGS. 6b and 12, in which corresponding references have been used. As opposed to the device

  according to FIG. 12, it is assumed that the tracks 4, 4 ', 4 "

  feel a low-frequency sweep, as described for example with reference to figures 9 and 10. So is it

  necessary to adapt in correspondence the device 33 ser-

  to deduce the radial tracking signal. In addition, with respect to FIG. 6b, the recording modulator 25 is provided with an input 70. A signal applied to this input is

  stop the registration process.

  In the device according to FIG.

  phase lock 29 is provided with a synchro-demodulator

  which, as for the phase, compares the synchronization signal

  generated by the filter 28 to the signal emitted by a voltage controlled oscillator 72, which oscillator is controlled by the output signal of the demodulator 71, a signal obtained through the low-pass filter 73. The output signal of the oscillator 72 forms the synchronization signal Sc which is output at the output 31. The output signal of the demodulator 71 is a measure of the momentary phase difference between

  the output signal of the oscillator 72 and the signal

  from disk 1 and obtained through filter 28.

  If in track 4, as shown in FIG. 17a, a useful information track T is inscribed in a sector

  determined 9 between the synchronization regions 8 (see

  1), a monotonic synchronization signal is obtained

  Sc. In this case, the output signal of the modulator 71 (re-

  shown in Figure 17b) is approximately equal to zero. If, for any reason whatsoever, the useful information track T deviates from lane 4 while heading towards lane 4 ', the

  the output signal of the demodulator 71 will increase in order to

  In these conditions, the recording process must be stopped before the track T comes to be on the neighboring track 4 '. it

  is revealed by the amplitude of the output signal of the demodula-

  71. In the same way, the useful information track T can deviate in the other direction, which, like the

  shown in Figure 17b, gives rise to a negative output signal

  the demodulator 71. The demodulator is followed by a de-

  window sensor 75, which is connected through a filter

  low pass 74 and detects whether the output signal of the demodulator

  71 exceeds predetermined limits + Sd or -Sd

  (Figure 17b), and then generates at exit 76 a signal (fi

  17c) which stops the registration process at

  through the input 70 of the recording modulator 25.

  The low-pass filter 74 serves to make the system

  sensitive to disturbing pulses etc., and where appropriate, it can be combined with a low-pass filter 73, which is indicated by the dashed line 77 in Fig. 16. When the information track T deviates in runway 4, the tracking signal also has a greater positive or negative value than during undisturbed track tracking. It is possible

  to detect this by means of a detector

  be 78, and combine its output signal with the output signal of the window sensor 75 in a combined arrangement 78, which is represented by dashed lines in FIG. 16. Where appropriate, this dual protection is desirable to increase the operational safety of the

  system. In principle, the protection provided by

  of the tracking signal is less suitable than the protection provided by the phase difference signal at the output of the demodulator 71 because, as shown in FIG. 18, the tracking signal receives its information from a low frequency portion C of the spectrum, and

  said phase difference signal receives its informa-

  of a high-frequency part E of the spectrum, while disturbances such as variations in the reflection of the disk and small surface defects of the disk r which

  would not give rise to a change of track as

  shown in Figure 17a occur, too,

  in a low frequency part D of the spectrum.

Claims (3)

  1.- Device for recording information on an information carrier (1) comprising a disk-shaped substrate (5) with a layer (6) of sensitive information   radiation and provided with information regions (9)   in a configuration of spiral tracks or   centric, device provided with a light source (15),   an optical system (17, 18) for orienting a light beam.   the information regions (9) of said information carrier, a recording circuit (25) for modulating the light beam according to the digital signal to be recorded, and an optical system with a detector (27) to detect the radiation (60) that the   information carrier has reflected or been missed,   rised in that, for the reading of a record carrier,   in which. the information regions (9) present   a periodic track modulation whose period corresponds to   weight at a frequency whose power spectrum of   digitally coded training to be recorded or recorded has at least substantially a zero point for generating during recording and / or playback a signal   of synchronization at bit rate for the synchronization   of the digitally encoded information, whereas this periodic track modulation has been established in the track so that points of this track modulation at a mutually equal phase extend from one track to the other along the track. a line (A) deviating from the radial direction (B),   in a radial sense, the modulation of each piston   depending on the tangential angle of the information carrier   disc, is always out of phase with respect to the modulation of the contiguous track in this   radial direction, and that in the other radial direction, it is always   days out of phase with respect to the modulation of the contiguous track in the other radial direction, it comprises on the one hand a passing band filter (28, 29) for filtering in the other direction.   this radiation detects a signal whose frequency is de-   terminated by period of periodic track modulation   and which, as a synchronization signal, is supplied to the cir-   recording process (25) to synchronize the signal of   useful training to record in an internal phase report   variable with the periodic track modulation, so that the information to be recorded is recorded in a   phase relationship that is invariable with said modulation of   periodically, and on the other hand a phase comparison circuit (29, 75) for monitoring the momentary phase   said filtered signal in order to generate a signal of   ret of the recording process when the phase differs in a predetermined measure from that of a phase signal monotonically varying.   2.- Device according to claim 1, characterized in   the phase comparison circuit (29) is interposed   in a phase locked loop, said phase comparison circuit receiving said filtered signal as well as the signal emitted by an oscillator (72) which is controlled by the output signal of this phase comparison circuit through a filter of bandwidth, the output signal of this phase comparison circuit being applied to a window detector (75).   3.- Device according to one of claims I1 and 2, mu-   or optical means (17, 18) for orienting on the useful information regions (9) of the light beam (16a) modulated with the information to be recorded and for orienting an auxiliary beam (16b) on the regions of useful information (9) located behind the modulated beam in order to read the information recorded by the light beam   modulated, characterized in that the auxiliary light beam   an area (16b) for reading the periodic track mulling can be used for generating the   synchronization used to synchronize the registration of in-   training carried out by means of the other light beam,   as well as for the application of the signal to the circuit of phase reason (29).