JPS58189848A - Fiber type optical head - Google Patents

Abstract

PURPOSE:To obtain an optical head which is small-sized, lightweight and low- cost and has high performance, by butting the propagation axes of the light of a polarized optical fiber and the 1st fiber-shaped polarizer so as to be aligned with each other and crossing the propagation axis of the 2nd fiber-shaped polarizer at right angles to a single polarized optical fiber and the propagation axis of the light of the 1st fiber-shaped polarizer. CONSTITUTION:The fiber polarizer 9 is polished to 45 deg. inclination with respect to the propagation axis of light in one end. A single polarized optical fiber 8 satisfies the specific equation in length. In the fiber polarizers 9, 10, the direction of the electric field vector having the least light absorbing loss is denoted by the x axis (low loss axis). The polarizer 9 and the fiber 8 are butted so that the low loss axis of the polarizer 9 and the main axis of the optical fiber 8 have a 45 deg. angle and the propagation axis of the polarizer 9 and that of the optical fiber 8 are aligned with each other, the optical propagation axis of the polarizer 10, the fiber 8 and the optical propagation axis of the polarizer 9 are orthogonal to each other, and the low loss axes of the polarizers 9, 10 are intersected at right angles with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a compact and high performance optical head fM for optical video discs.

Optical disk memory is capable of high tMlf and large capacity recording, and its recording and playback speed is X) Mblt/s・C
Since it can travel at the speed of light (T), it is attracting attention as a future large-capacity memory.

The original disk was recorded and reproduced in a non-contact manner using a laser beam focused on a spot of about 1 μm in diameter, and a conventional optical helad was constructed as shown in FIG. 1st
In the figure, 74 is a disk, λ is a mirror, 3 is a polarizing beam splitter, L is a filter, S is a photodetector, and 6 is a lens. Laser light is beam splinter, l'jlli
The reflected light then enters the surface of the disc l, and the intensity or phase of the reflected light is modulated depending on the presence or absence of information on the disc l. A portion of the inverse IJ light is guided to a photodetector j by a beam splinter 3r, where information on the disk l is read. As can be seen from FIG. 1, the conventional optical head requires a polarizing beam splitter 3 and a large number of lenses 6, so it has the drawbacks of being difficult to align optical axes and being susceptible to vibrations and the like. In addition, parts such as the polarizing beam splinter 3 are expensive.

There was also the drawback of receiving it.

The purpose of the present invention is to eliminate the drawbacks χ of the conventional D.
By appropriately using a single-polarized optical fiber and a fiber-type polarizer Y, it is possible to provide a compact, lightweight, inexpensive, and high-performance optical head.

In order to achieve this object, the present invention includes a first seventh eyeper-type polarizer that receives light from a light source, a first fiber-type polarizer that guides the light from the second fiber-type polarizer to an optical disk, and a second fiber-type polarizer that receives light from the source disk. a single polarization ft fiber that receives the light;
A second fiber type polarizer is provided to guide light from the single polarized optical fiber to a photodetector, and the first and second fiber type polarizers are coated with a metal film, and the gold layer is coated with a metal film.
When the direction of the electric field vector with the smallest absorption loss due to the 4ys is set as the low loss axis, the end face of the first fiber polarizer on the single-IJ four-wave fiber side
7 With respect to the original propagation axis of the Aipah-type polarizer, the inclination of ℃ 0 is taken, and the propagation constants of the two orthogonal fundamental modes of the single polarization optical fiber are Yβ1 and β3, and m1 is an integer. , the length l of the single polarization optical fiber is 7-(m
+-)π/1β]-β11 Satisfying the above condition, the first fiber polarizer and the single-polarized optical fiber are connected so that the low-loss axis and the main axis of the single-polarized optical fiber are referenced. S has no angle fY, and the above period -
The original propagation axes of the fiber-type polarizer and the polarized optical fiber are aligned so that the propagation axes of the light of the second fiber-type polarizer are aligned. The fiber-type polarizer is arranged in such a way that it is perpendicular to the light propagation axis, and the low-loss axes of the first and second fiber-type polarizers are perpendicular to each other.

Hereinafter, the present invention will be described in detail based on the drawings.

Fig. 2 1 The actual product m@i% of the present invention, where 7
1 optical disk, t is single polarization optical fiber, 9 and/or
θ is a fiber polarizer, // is a laser, /2 is a photodetector, and /3 is a lens.

The light from the laser//f) is the original fiber from the fiber Cedar polarizer de! The reflected light I from the optical disk 7 passes through the lenses 13 and jt, the fiber tY:, and is emitted from the fiber polarizer /σ to the photodetector /2 VC.

The cross-sectional structure of a single source fiber r is as shown in FIG. 3, for example, where /- is the core, lj is the stress applying part,
/6 beam 57 domo (T, Ho5aka at
ml.

@Low-1oss single polariza
tion fibers with asymmet-
ric strmin blrefr%ng@nee
”, Electron, Lett,, vol.
.

/7. no, lj, p,! 10. /911
reference).

The cross section 1w structure of the fiber-type polarizer 9 and /θ is, for example, as shown in Figure 3, where 17 is the core, /I is the gland, and /9 is a metal film such as gold or aluminum (as described by Hosaka et al. "Method for manufacturing fiber polarizer", patent application 1973
(See No. 6-20 route).

In the single polarization optical fiber ffl'n shown in Fig. 3, ξ
The propagation constant β1 of the mode polarized in the DA direction and the propagation constant β2 of the mode polarized in the DA direction are determined by the boron oxide (
JOs) varies depending on the molar concentration If. For example, B,
When the concentration of ox is /I moj, (p+ −It
)/to=t, +Jx to-' (1). Here, % = π7/λ, where λ is the wavelength of light in vacuum. Direct IN! polarized in the direction of reference j0 with respect to the principal axis (ζ or η axis) VC of such a single polarization optical fiber l! @When light Y enters, the electric field component of the output light is B5 x a cow (ωt-βll)
(2-IJEη = a ao hatake (ω is one βx
I) (2-2)
becomes. where l is the amplitude, ω is the angular frequency, and l is the length of the single polarization fiber. The fiber length l is 1-(m+-
) f/lβl−βil (5) (m: integer) When E7=±a sin (ω is one β!l)
(4) becomes. In other words, in this case, (mξ)0(Bη) = a (5), and the emitted light becomes circularly polarized light. As is clear from the above, K
, it can be seen that the fiber length performs the same as a single polarization optical fiber 1% wave plate whose fiber length satisfies equation (3).

Next, in the 7-eyeper type @ photon 9 or 1 photon lO shown in Figure 1, there is almost no loss of light polarized in the X-axis direction, but
The light source polarized in the y-axis direction suffers a large loss due to absorption by the metal film 19. When using kl-OsY as metal 1%/9, extinction ratio is 17 dB with fiber length 1.
, insertion loss 0.3 dB/Cm (both λ=1.l
Ifim) was obtained.

As shown in FIG. 5, when linearly polarized light is incident in the 4H direction with respect to the main axis of a single-polarized optical fiber l that acts as a 3A wave plate, the output light becomes circularly polarized as described above. However, the reflected light of this light is again converted into a single polarized wave': I
At the point t, -y Aiba vCa ``5'' and % W Ofj, linearly polarized light in the direction orthogonal to the 1 ryo 1 yuan direct stock @ party is obtained. However, in FIG. 5, 26 is a reflection plate,
Black arrows and white arrows represent incident light and reflected light, respectively.

Next, the polarization state of light in the embodiment of the optical head shown in the second figure is shown in FIG. In FIG. 6, one end surface of the fiber-shaped photon section is polished to an angle of 1150 with respect to the light propagation axis. It is assumed that the single polarization optical fiber I satisfies the acidity (5)2. In the fiber polarizers 9 and 10, the direction of the electric field vector with the smallest light absorption loss is defined as the X axis (low loss axis). Fiber-type polarizer 9 and single-polarized optical fiber t and ge, the low-loss axis of the polarizer d and the main axis of the optical fiber t have no angle t, and the propagation axis of the polarizer t and the main axis of the optical fiber t are The optical propagation axis of the 7-eyeper type polarizer/θ is orthogonal to the optical propagation axis of the optical fiber t and the polarizer 90,
Moreover, the low loss axes of 1ji, 9 and io are designed to be perpendicular to each other.

In the above configuration, the laser//Y is appropriately adjusted #Ii so that the source of the linearly polarized light from the laser l/ is parallel to the X axis. As a result, the laser light enters the VC single-polarization optical fiber l as shown by the black arrow without undergoing attenuation. Since the length of the single polarization fiber t is x5c@ which satisfies equation (6), the light emitted from the original fiber l becomes α circularly polarized, and in this state, the video disc 7
incident on . Depending on the presence or absence of information on the video disk 7, the reflected light whose phase has changed enters the single polarization optical fiber IVC again, and the above-mentioned process VCz = 0.
At the 0 point, the polarization direction of the reflected light becomes linearly polarized light in a direction orthogonal to the original direction, as shown by the white arrow.

This reflected light (reflected at one end surface of the fiber-type polarizer dj0 and incident on the second 7-eyeper type polarizer lθ).

Here, it is assumed that l[il of the fiber polarizer lθ is parallel to the polarization direction of the reflected light indicated by the white arrow. Therefore, the reflected light from the video disk 7 reaches the photodetector /2 without being attenuated in the fiber polarizer /θ.

Here, the percentage of reflected light from the video disc 7, that is, the unnecessary reflected light other than the signal light will be explained.

This unnecessary reflected light is incident on the fiber polarizer q from the laser /l, and is transmitted through the single polarization fiber l at the point z-O.
jt, which is reflected at the end face of and returns to the laser //@ (this is assumed to be unnecessary light l), and light which is reflected again at the plane l' of the fiber polarizer 9 and enters the fiber polarizer 10. (Let this be unnecessary light ■) is rh7w, s'? 170 to
- a single polarization 7 fiber reflected by the video disc 7;
Of the Z light (white arrow l''l) that passes through and returns, it enters the 7-eye polarizer and returns to the laser l/side.

Among the unnecessary lights of the above J-rays, non-gP! Since the light is polarized in the y-axis direction (direction of maximum absorption loss) of both fiber-type polarizers and lo, it receives a large attenuation in the fiber-type polarizer, so the stability of the laser It is possible to eliminate the adverse effects on the performance or the signal NfIa sound ratio. Also, let us consider the unnecessary light l, and calculate the incident light l
o Since it is double-sided, there is almost no problem. However, if this level of weak unnecessary reflected light becomes a problem, the FC can be reduced by coating the end face Y of the single polarization fiber t at %5xOK with anti-reflection coating. Since the generation of I can be suppressed and the amount of unnecessary light can be removed by fiber-type photons lθ, a high-performance optical head Y without unnecessary reflected light can be constructed.

As is clear from the above explanation, 1. According to the present invention, it is possible to create a lightweight, inexpensive, and high-performance optical head Y without using expensive optical components such as a polarizing beam splinter.
Furthermore, the optical fiber has n1 flexibility, and has the great advantage that the entire optical head can be made extremely compact.

[Brief explanation of drawings]

Fig. 1 & Fig. 1. An example of a conventional optical hand.
Fig. 2 4 A diagram showing an actual example of the optical head of the present invention, Fig. 3 and the reference drawings show the single polarized light 7 fibers and fiber type polarized light that supports the optical head shown in Fig. 2. Perspective view,
FIG. 5 is a perspective view showing the polarized light S in a polarizing fiber equivalent to an H wavelength plate, and FIG. 1 is an enlarged view of the embodiment shown in FIG. FIG. l...video disc, co...mirror,!・・・
Polarized beam splinter, da laser! ...Photodetector. 6.-Lens% 7...Video disc. l...Single end wave fiber% 9,10...Fiber type polarizer. //...Laser, /l...Light detection! l
. /J lens, /4t...core. 1, V・Okai・1 Yoto, /6・・Kura7doi/7・・v T, ttnee・−kufund, /Q−・7Metal film 6 〃・−・! 5! ,
, firing plate. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Scope of Claims] A first fiber polarizer that receives the light of Ll i#fl- and others, and a first fiber polarizer that guides the light from the I-7 Aiper polarizer to the Y optical disk (reflected light from the optical disk). Light receiving song
A polarized light beam 7 and a second fiber polarizer for guiding the light from the single polarized light beam 7 to a photodetector; VC,@
The single-wave light 7 fiber side surface of the first fiber-type polarizer is 4 with respect to the light propagation axis of the first fiber-type polarizer.
1s, and the propagation constants of the two orthogonal fundamental modes of the single polarization optical fiber are '/+ β. and when m is an integer, the length j of the single polarization optical fiber is 1 = (tn+-1-)t/l Itoβ! 1. Satisfying the snow condition, @Abut-th fiber Cedar polarization. Single-polarized optical fiber with single-polarized optical fiber, front with low-loss axis @
The main axis of the monopolarized optical fiber is at an angle aS, and the optical propagation axes of the fiber polarizer and the single-wave optical fiber are aligned.
The propagation axis of the first and second fiber type @photons is
The polarized optical fiber and the first fiber-type polarized light are perpendicular to the propagation axis of the light, and the low-loss axes of the first fiber-type polarizer and the first fiber-type polarizer are arranged so that they intersect with each other. Kaoru Features and T) Puiper-shaped optical head.