Collimating optical system for semiconductor lasers

 

(57) Abstract:

Collimating optical system includes sequentially located along the beams of the semiconductor lasers, lenses, and prisms. Ribs refractive dihedral angles of the prisms are oriented parallel to the planes of semiconductor junctions. Ribs refractive dihedral angles of the first and second prisms are located on different sides of the laser beam. The parameters characterizing the properties of the optical system and the material of the prisms, are related by a mathematical ratio. Ensures the constancy of the spatial position of the output collimated beam when exposed to low and high ambient temperatures. 1 Il.

The invention relates to a collimating optical systems with refractive elements and can be used in optical systems locations, optical communication, management, and Supervisory devices.

Known collimating optical system containing sequentially arranged along the first rays negative optical component, the first group of prisms, a positive optical component, the second group of prisms and the second negative optical companysm is selected within 10-40oand the orientation angle of the prisms with respect to the optical axis associated with the refractive angle ratio = (2-3) [1].

As follows from the description, the most effective is the use of the specified optical system for callmerobbie emission of semiconductor lasers. This eliminates the need in the first optical component.

The disadvantage of this optical system in the case of its application to semiconductor lasers is the angular offset of the output collimated beam when exposed to low and high temperature, due to the inconvenience of operation and deterioration of the guidance accuracy of the output beam. Cause angular displacement of the output beam when exposed to low and high temperature is, first, the temperature change of the emission wavelength of a semiconductor laser and dispersion of the material of the prisms, secondly, the temperature change of the refractive index of the prisms.

The closest to the technical nature of the claimed optical system is a collimating optical system for a semiconductor laser containing sequentially located along the ray lens and prisms, ribs prelomlyayutsya within 25-40oangular magnification G of the group of prisms is selected from the following equation:

< / BR>
where the angles of divergence of the semiconductor laser 0.5 in planes parallel and perpendicular to the plane of semiconductor transition, respectively, the front focal plane of the lens is shifted relative to the subject plane at distanceodefined by a relation

< / BR>
where the size of the body of the glow of a semiconductor laser in planes parallel and perpendicular to the plane of semiconductor transition, respectively, and the longitudinal spherical aberration (u) of the lens is selected from the following equation

(u) = -2/3o(u/)2,

where u is the aperture angle of the lens [2].

As follows from the description, collimating optical system can be used to obtain a collimated beam from the multiple semiconductor lasers. Thus instead of a single lens is used several lenses mounted opposite the semiconductor lasers, and the angular magnification G of the group of prisms is selected from the following equation:

< / BR>
where the angles of divergence of the radiation of semiconductor lasers in planes parallel to the s lasers [2].

The disadvantage of this optical system when using it for one or several semiconductor lasers is the angular offset of the output collimated beam when exposed to low and high temperature, due to the inconvenience of operation and deterioration of the guidance accuracy of the output beam. Cause angular displacement of the output beam when exposed to low and high temperatures are, first, the temperature change of the emission wavelength of a semiconductor laser and dispersion of the material of the prisms, secondly, the temperature change of the refractive index of the prisms.

An object of the invention is to provide for continuity in the spatial position of the output collimated beam when exposed to low and high temperature environment.

The technical result is achieved by the collimating optical system for semiconductor lasers containing sequentially located along the rays with lenses that are installed opposite to the semiconductor lasers, and a group of prisms, refracting ribs dihedral angles which are oriented parallel to the planes of semiconductors is tion of the laser beam, when this is done the following relationship:

< / BR>
< / BR>
i/ni- ratio dependence of the angular deviation of the rays from the refractive index of the i-th prism

nithe dispersion of the material of the i-th prism

/t - temperature coefficient of the emission wavelength of a semiconductor laser,

ni/t - temperature coefficient of the refractive index of the i-th prism

Githe angular magnification of the i-th prism

m is the number of prisms,

- wavelength semiconductor lasers,

- the angular divergence of the semiconductor laser according to the level of 0.5 in the plane perpendicular to semiconductor transition,

f is the focal length of the lenses.

The constancy of the spatial position of the collimated output beam when exposed to low and high temperatures is ensured by the fact that the action of the first prism is compensated by the action of the second and subsequent prisms.

The drawing shows a collimating optical system for semiconductor lasers, the cross-section in a plane perpendicular to the plane of the semiconductor transitions.

Collimating optical system sod the prism 3-6. The edges of the dihedral angles formed by refracting faces of the prisms are oriented parallel to the planes of semiconductor transitions of semiconductor lasers 1. Thus, edges refractive dihedral angles of the prisms 3 and 4 are located on opposite sides relative to the laser beam.

In the coordinate system shown in the drawing, the plane of the semiconductor transitions are oriented parallel to the YZ plane, the optical axis of the lens is oriented parallel to the Z-axis, and the edges refractive dihedral angles of the prisms is parallel to the y-axis.

Input face of all prisms are installed perpendicular to the incident beam, and the deflection angle of the ray in the prism 3 are equal in magnitude and opposite in sign to the angle of deviation of the ray in the prism 4, and the angle of deflection of the ray in the prism 5 are equal in magnitude and opposite in sign to the angle of deviation of the ray in the prism 6.

The angular dispersion of the prism 3 is less than the angular dispersion of the prism 4-6. To this end, the prism 3 is made of glass with low dispersion and prisms 4-6 - glass with a large variance.

Collimating optical system works in the following way. Highly divergent light beam from each of the semiconductor LAZ z-axis. In the XZ-plane, all these beams are combined into a single beam, which passes through the group of prisms. Prism transforms the light beam, reducing its transverse size and increasing its angular divergence. As a result, the output of the collimating optical system is formed by the light beam with the required geometrical parameters.

For example, if you want to form a collimated light beam, close to axisymmetric, then the design parameters of the collimating optical system should be chosen in accordance with [2].

When the temperature of the environment is the angular deflection of the light beam on each of the prisms. The reason for this are, firstly, the temperature change of the emission wavelength of a semiconductor laser and dispersion of the material of the prisms, secondly, the temperature change of the refractive index of the prisms.

Since the angular displacement caused by changes in ambient temperature are small, the angular deflection of the light beam in the whole group of prisms is determined by the sum of the angular displacements at each of the prisms, taken with regard to sign and multiplied by the angular magnification of all followed by prisms.

Specified the output angles of the first and second prisms are located on different sides relative to the light beam. Indeed, as the angular magnification of the prism is greater than one, then the terms corresponding to the first and second prisms are largest in absolute value, as well as ribs refractive dihedral angles of these prisms are located on different sides relative to the light beam, these terms have opposite signs and can be mutually compensated. Components corresponding to the third and subsequent prisms, considerably less than that specified, so the location of these prisms is not essential for mutual compensation of all prisms.

There is almost no need to provide full mutual compensation of all prisms. It is sufficient if the angular offset of the output collimated beam corresponding to the maximum possible temperature change, will not exceed the absolute value of 1/4 angular divergence of the beam is 0.5.

Thus, due to incomplete mutual compensation of all prisms ensures the constancy of the spatial position of the output collimated beam when exposed to low and high temperature environment.

Let us introduce the notation:

d/dt is the angular change of the first deflection of the beams at the i-th prism when the temperature changes by 1oC,

Githe angular magnification of the i-th prism

m is the number of prisms,

t is the maximum change in ambient temperature,

- the angular divergence of the collimated output beam 0.5;

- wavelength semiconductor laser,

- the angular divergence of the semiconductor laser according to the level of 0.5 in the plane perpendicular to semiconductor transition,

f is the focal length of the lens.

The change of the angular deviation is considered positive if it is directed in a clockwise direction, and negative if it is directed counterclockwise.

The condition of constancy of the spatial position of the output collimated beam when exposed to low and high temperature environment is determined by the ratio:

< / BR>
In the plane perpendicular to the semiconductor junction, the semiconductor laser emits only a single transverse mode, so the light beam in this plane is the Gaussian beam. The angular divergence of the collimated output beam of 0.5 is defined by the following relation (see, for example [3]):

< / BR>
A typical value of the maximum is wearing (2), you can get

< / BR>
In the collimating optical system shown in the drawing, the number of prisms m = 4, and the relation (3) can be represented in the form

< / BR>
The change of the angular deviation of rays on each lens depends on the refractive index of the prism, which, in turn, depends on the wavelength of the semiconductor laser and the ambient temperature. The change of the angular deviation of the ray on the i-th prism when the temperature changes by 1oC is defined by the following ratio:

< / BR>
where nithe dispersion of the material of the i-th prism, defined as the change in the refractive index with the change of the wavelength by 1 nm,

/t - temperature coefficient of the emission wavelength of a semiconductor laser, defined as the change in wavelength in nm when the temperature changes by 1oC.

ni/t - temperature coefficient of the refractive index of the i-th prism, defined as the change in the refractive index when the temperature changes by 1oC.

Consider the specific example collimating optical system for ten semiconductor lasers of the type SDL-2360, whose wavelength = 830 nm, the corners of Rasheeda, 8o30othe size of the body of the glow in the planes parallel and perpendicular to the plane of the semiconductor junction, 1001 μm, the temperature coefficient of wavelength /t = 0.3 nm/deg. [4].

We assume that in the collimating optical system shown in Fig. 1, the entrance face of the prism is set perpendicular to the incident rays, the refractive angles of the prisms are made the same and equal to = 33omoreover , the prism 3 is made of glass STC and prism 4-6 - glass TF. The refractive index of these glasses are approximately equal, but the glass STC has a much smaller variance than the glass TF. Note that the condition of equality of the transverse dimensions of the light beam at the output collimating optical system [2].

The angular divergence of the collimated output beam of 0.5 is found from the relations (2) and is = 10 angular minutes.

The change of the angular deviation of the rays in the collimating optical system while changing the ambient temperature on the 1oC is the ratio of (4) and (5). Using constants glass, are specified in [5], obtain

d/dt = 0.008 mrad/deg. The expression in the right-hand side of (4) is equal to 0.02 mrad/deg, i.e. sooo angular deflection of beams = 0.9 angular minutes that is almost insignificant. Note that if all prisms were made of glass TF, the corresponding values would be d/dt = 0.1 mrad/deg = 12 minutes of arc, which in many cases is invalid.

Thus in the proposed collimating optical system ensures the constancy of the spatial position of the output collimated beam when exposed to low and high temperature environment, which allows its use in optical systems locations, optical communication, management and Supervisory devices operating in the field.

List of used sources

1. USSR author's certificate N 1624392, G 02 B 27/30, 30.01.91.

2. RF patent N 2107743, G 02 B 27/30, 10.01.98.

3. Pakhomov, I. I., Tsibulya A. B. design of optical systems of laser devices. - M.: Radio and communication, 1986, S. 6.

4. Laser diode product catalog. Spectra Diode Labs. - 1993.

5. Optical glass. Album - catalogue of the USSR - GDR. In/On Mashpriborintorg, 1984.

Collimating optical system for semiconductor lasers containing sequentially located along the rays with lenses that are installed opposite to the semiconductor lasers, and a group of prisms, the Dov, characterized in that the ribs refractive dihedral angles of the first and second prisms are located on different sides of the laser beam, it performs the following relationship:

< / BR>
< / BR>
i/ni- ratio dependence of the angular deviation of the rays from the refractive index of the i-th prism;

nithe dispersion of the material of the i-th prism;

/t - temperature coefficient of the emission wavelength of a semiconductor laser;

ni/t temperature coefficient of the refractive index of the i-th prism;

Githe angular magnification of the i-th prism;

m is the number of prisms;

- wavelength semiconductor laser;

- the angular divergence of the semiconductor laser according to the level of 0.5 in the plane perpendicular to semiconductor transition;

f is the focal length of the lens.

 

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