ISO 11807-1:2001 統合光学—用語, 語彙—パート1：基本的な用語と記号 | ページ 5

3.1.1

integrated optics

planar optical radiation-waveguide structures, manufactured either in or on a substrate, including the optical components necessary for the input and output coupling of optical radiation

Note 1 to entry: In this context the term “planar” will be taken to include small deviations from planarity such as are incurred with, for example, Luneberg lenses. By use of a suitable substrate material, it is possible to integrate both opto-electronic and purely optical functions on the same substrate. The simplest case is electrodes, which can be used for controlling the properties of a waveguide. It is, however, possible to fabricate lasers and detectors using compound semiconductor materials.

Note 2 to entry: It is envisaged that integrated optical components will be combined with other microtechnologies, such as microelectronics and micromechanics, to make more complex systems. However, such systems are beyond the scope of this part of ISO 11807, which will be concerned only with the integrated optical component and its immediate interfaces (see IEC 60050-731/06-43).

3.2.1

waveguide

transmission line designed to guide optical power consisting of structures which guide optical radiation on the basis of a higher refractive index in the core and a lower index of refraction in the surrounding material

Note 1 to entry: Waveguide structure is defined in 3.5.

3.2.1.1

slab waveguide

planar waveguide

waveguide which confines the optical radiation only perpendicular to the substrate ( x -direction)

3.2.1.2

strip waveguide

channel waveguide

waveguide which confines the element radiation in a two-dimensional cross-sectional area perpendicular to the substrate surface along a one-dimensional path

3.2.2

mode

eigenfunction of Maxwell's equations, representing an electromagnetic field in a certain space domain and belonging to a family of independent solutions defined by specific boundary conditions

Note 1 to entry: Each mode is defined according to its order in the vertical and horizontal directions and its polarization, the latter being separated into TE- and TM-modes. The mode order is given by indexing TE _ij and TM _ij , where the first index i defines the horizontal order and the second one j the vertical order.

3.3.1

guided mode

electromagnetic wave whose electric field decays monotonically in the transverse direction everywhere external to the core and which does not lose radiant power

Note 1 to entry: The modes are ordered with the following notations: TE _ij and TM _ij , where TE and TM represent respectively the y - and x- direction of polarization, and i and j define the mode indices along x and y respectively.

3.3.1.1

single-mode waveguide

waveguide which guides only one mode order

Note 1 to entry: The waveguide mode may consist of two orthogonal states of polarization.

3.3.1.2

multi-mode waveguide

waveguide which supports more than one guided mode

3.3.1.3

TE-mode

transverse electromagnetic wave, where the main component of the electric field vector is parallel to the substrate surface

Note 1 to entry: Strictly speaking, in strip waveguides, hybrid modes having the non-zero component of the electric and magnetic field in the direction of propagation do exist. Pure TE- and TM-waves are only found in waveguides with a corresponding geometry — for example in slab waveguides. For integrated optical waveguides in planar substrates, it is natural to define the polarization state relative to the substrate surface. Because the terms TE and TM are used and well understood in general language in the context of planar waveguides, they are also applied in the same sense to strip waveguides.

3.3.1.4

TM-mode

transverse electromagnetic wave where the main component of the magnetic field vector is parallel to the substrate surface

3.3.1.5

cutoff wavelength

wavelength in vacuo above which a given mode cannot exist in the waveguide

Note 1 to entry: Due to the generally short length of integrated optical waveguides, the measured value largely depends on the waveguide structure. Therefore special waveguide structures have to be fabricated to measure the cutoff wavelength. The measurement methods known for optical fibres cannot be applied to integrated optical waveguides.

Note 2 to entry: In fibre optics, the term cutoff wavelength is used to describe the cutoff wavelength of the second-order mode. The reason is that the fundamental mode of a symmetrical dielectric waveguide has no cutoff and the cutoff wavelength of the second order mode determines the single mode condition.

3.3.2

leaky mode

mode having an evanescent field in the transverse direction external to the core for a finite distance but with an oscillating field in the transverse direction everywhere beyond that distance

Note 1 to entry: A leaky mode is attenuated due to radiation losses along the waveguide.

3.3.3

radiation mode

mode which transfers power in the transverse direction everywhere external to the core

3.3.4

evanescent field

time varying electromagnetic field in an integrated optical waveguide whose field amplitude decays very rapidly and monotonically in the transverse direction outside the core, but without an accompanying phase shift

3.3.5

waveguide cutoff

transition of a guided mode at which the propagation changes from being guided to being leaky or radiative

3.3.6

effective refractive index

equivalent refractive index

n_eff

ratio of the speed of light in vacuo to the phase velocity of the guided mode

Note 1 to entry: The effective or equivalent refractive index is determined by the waveguide dimensions and the refractive index profile of the waveguide, including the medium bordering the core of the waveguide and the wavelength. Each mode capable of propagation is characterized by its individual effective or equivalent refractive index.

3.4.1

refractive index profile

refractive index n ( x , y ) across a cross section of the waveguide as a function of position

3.4.2

step index profile

refractive index profile which is characterized by an almost constant refractive index within the waveguide core and a sharp drop in refractive index at the border between the core and the substrate and superstrate

Note 1 to entry: The width of the transition is small in comparison with the wavelength.

3.4.3

graded index profile

refractive index profile whose width of the transition is large in comparison with the wavelength

3.4.4

relative refractive index difference

∆n

3.4.5

acceptance angle

θ

Note 1 to entry: The horizontal and vertical acceptance angle of a non-circular symmetrical waveguide can be different.

Note 2 to entry: The acceptance angle is, according to IEC 60050-731/03-84, defined as half the angle of the coupled radiation bundle. In contrast, the divergence angle of laser radiation is defined as the full angle (see ISO 11145).

3.4.6

numerical aperture

na_m

sine of the vertex half-angle of the largest cone of guided optical radiation which can enter or leave the waveguide multiplied by refractive index of the medium in which the vertex of the cone is located

Note 1 to entry: See notes to 3.4.5.

3.4.7

numerical aperture

na_s

Note 1 to entry: See 3.4.12.

3.4.8

launch angle

angle between the direction of maximum intensity of the input radiation and the optical axis of the waveguide

3.4.9

normalized frequency

Note 1 to entry: The normalized frequency allows a simple estimation of the cutoff wavelength; V_x and V_y are also called the V -numbers of the integrated optical waveguide.

3.4.10

near-field pattern

distribution of the optical power density along a perpendicular cross section at or very close to the exit face of the waveguide

Note 1 to entry: Due to the close distance to the exit face, diffraction is negligible and therefore the near-field pattern also is assumed to represent the distribution of the power density inside the waveguide. The full width at which this distribution is reduced to half the maximum value is called the full width of half maximum FWHM (of the mode).

Note 2 to entry: In most cases, an integrated optical waveguide has an asymmetrical refractive index profile in the vertical direction, in contrast to a fibre. Therefore, the near-field distribution is symmetrical in the horizontal ( y ) direction and asymmetrical in the vertical ( x ) direction.

3.4.11

near-field centre

position of the maximum of the near-field distribution

3.4.12

spot size

w_{x 1}, w_{x 2}, w_{y 1}, w_{y 2}

distances between the near-field centre of the fundamental mode and the point where the Gaussian intensity profile approximated from the actual profile falls to 1/e² of the maximum value at the centre in either side of x - and y -direction

3.4.13

mode field width

the sum of w_{x 1} and w_{x 2} in x -direction respectively the sum of w_{y 1} and w_{y 2} in y -direction

3.4.14

near-field asymmetry

A_{x , y}

3.4.15

far-field pattern

radiation pattern which describes the relative distribution of the optical power density as a function of angle at the position where the radiation pattern does not vary with the distance from the waveguide end face

Note 1 to entry: For integrated optical waveguides, the far-field distribution is influenced by the shape and position of the edge surface relative to the near field centre.

3.5.1

core

central region of an integrated optical waveguide, in which the radiation power is mainly confined

3.5.2

cladding

material surrounding the waveguide core

Note 1 to entry: In contrast to optical fibres for integrated optical waveguides, the cladding often consists of more than one material. Normally, it is necessary to distinguish between lower cladding and upper cladding due to the planar fabrication process of integrated optical waveguides.

3.5.3

substrate

carrier onto or within which the integrated optical waveguide is fabricated

3.5.4

superstrate

medium or layer structure with which the integrated optical waveguide is covered

Note 1 to entry: An electrode, for example, should not be designated as a superstrate. Although it covers the waveguide, it would not influence the optical properties of the waveguide due to an optically insulating layer of sufficient thickness.

3.6.1

wavelength dispersion

dependence of the phase velocities or the effective or equivalent refractive indices of the modes of a waveguide on the wavelength

Note 1 to entry: The wavelength dispersion is influenced by the material composition, the geometry of the waveguide, the polarization and the order of the guided mode.

Note 2 to entry: In optical fibres, the wavelength dispersion is defined as the dependence of group velocities of the modes on the wavelength.

Note 3 to entry: The term dispersion is used for describing the wavelength dependence of some physical properties. In all sections of this subclause, when properties having a wavelength dependence are described, the wavelength under consideration is to be stated.

3.6.1.1

material dispersion

dependence of the refractive index of the material on the wavelength

3.6.1.2

waveguide dispersion

dependence of the effective or equivalent refractive index of a particular mode on the dimensions of the waveguide, its refractive index profile and the wavelength, when refractive indices are assumed to be independent of wavelength

3.6.2

mode dispersion

difference in phase velocity of modes of different order at the same wavelength

Note 1 to entry: For optical fibres the term modal dispersion is used, because this effect influences the propagation of optical signals in a negative sense. Here, in integrated optics, the mode dispersion may provide the optical functionality of a device.

3.6.3

waveguide birefringence

B

3.7.1

transfer matrix

matrix which describes the transfer characteristic of an integrated optical element with N + M ports

Note 1 to entry: The input waveguides are numbered beginning with 1 to N and the output waveguides beginning from N +1 to N + M as shown in Figure 2. The matrix element α_ij , corresponds to the loss by coupling radiation into waveguide j (launch port) and emitting radiation from waveguide i (measurement port). The diagonal elements for example refer to the return loss of the waveguides.

3.7.2

attenuation

loss

diminution of time average in radiation power in integrated optical devices

Note 1 to entry: For integrated optical elements, the power loss is related to two cross-sectional areas of the corresponding waveguide.

Note 2 to entry: Generally, for integrated optical devices, the input and output configuration which is used to measure the attenuation has to be specified. If the device is assembled with optical fibres, the power is launched into one fibre and the output power is measured at another fibre.

3.7.3

waveguide loss

α_w

Note 1 to entry: Waveguide loss is expressed in decibels.

3.7.4

waveguide loss coefficient

α

Note 1 to entry: Waveguide loss coefficient is expressed in decibels per metre.

3.7.5

insertion loss

α_I

Note 1 to entry: Insertion loss is expressed in decibels.

3.7.6

directivity

near-end cross talk

α_D

Note 1 to entry: Directivity or near-end cross talk is expressed in decibels.

3.7.7

coupling loss

α_c

Note 1 to entry: Coupling loss is expressed in decibels.

3.7.8

cross talk

far-end cross talk

α_F

Note 1 to entry: Cross talk, or far-end cross talk, is expressed in decibels.

3.7.9

return loss

α_R

Note 1 to entry: Return loss is expressed in decibels.

3.7.10

excess loss

α_E

Note 1 to entry: Excess loss is expressed in decibels.

3.7.11

deviation of uniformity

α_u

Note 1 to entry: Deviation of uniformity is expressed in decibels.

3.7.12

deviation of polarization dependent loss

α_PDL

Note 1 to entry: Deviation of polarization dependent loss is expressed in decibels.